Sample records for ablative heat shield

  1. Ablative heat shield design for space shuttle

    NASA Technical Reports Server (NTRS)

    Seiferth, R. W.

    1973-01-01

    Ablator heat shield configuration optimization studies were conducted for the orbiter. Ablator and reusable surface insulation (RSI) trajectories for design studies were shaped to take advantage of the low conductance of ceramic RSI and high temperature capability of ablators. Comparative weights were established for the RSI system and for direct bond and mechanically attached ablator systems. Ablator system costs were determined for fabrication, installation and refurbishment. Cost penalties were assigned for payload weight penalties, if any. The direct bond ablator is lowest in weight and cost. A mechanically attached ablator using a magnesium subpanel is highly competitive for both weight and cost.

  2. Visualization of Capsule Reentry Vehicle Heat Shield Ablation Using Naphthalene PLIF

    NASA Technical Reports Server (NTRS)

    Combs, Christopher S.; Clemens, Noel T.; Danehy, Paul M.

    2014-01-01

    The Orion Multi-Purpose Crew Vehicle (MPCV) will use an ablative heat shield and improved understanding of the ablation process would be beneficial for design purposes. Given that ablation is a multi-physics process involving heat and mass transfer, codes aiming to predict heat shield ablation are in need of experimental data pertaining to the turbulent transport of ablation products for validation. At The University of Texas at Austin, a technique is being developed that uses planar laser-induced fluorescence (PLIF) of a low-temperature sublimating ablator (naphthalene) to visualize the transport of ablation products in a supersonic flow. Since ablation at reentry temperatures can be difficult to recreate in a laboratory setting it is desirable to create a limited physics problem and simulate the ablation process at relatively low temperature conditions using naphthalene. A scaled Orion MPCV model with a solid naphthalene heat shield has been tested in a Mach 5 wind tunnel at various angles of attack in the current work. PLIF imaging reveals the distribution of the ablation products as they are transported into the heat-shield boundary layer and over the capsule shoulders into the separated shear layer and backshell recirculation region. Visualizations of the capsule shear layer using both naphthalene PLIF and Schlieren imaging compared favorably. High concentrations of naphthalene in the capsule separated flow region, intermittent turbulent structures on the heat shield surface, and interesting details of the capsule shear layer structure were observed using the naphthalene PLIF technique. The capsule shear layer was also shown to generally appear to be more turbulent at lower angles of attack. Furthermore, the PLIF signal increased steadily over the course of a run indicating that during a wind tunnel run the model heated up and the rate of naphthalene ablation increased. The shear layer showed increasing signs of turbulence over the course of a wind tunnel run

  3. Naphthalene Planar Laser-Induced Fluorescence Imaging of Orion Multi-Purpose Crew Vehicle Heat Shield Ablation Products

    NASA Astrophysics Data System (ADS)

    Combs, Christopher S.; Clemens, Noel T.; Danehy, Paul M.

    2013-11-01

    The Orion Multi-Purpose Crew Vehicle (MPCV) calls for an ablative heat shield. In order to better design this heat shield and others that will undergo planetary entry, an improved understanding of the ablation process is required. Given that ablation is a multi-physics process involving heat and mass transfer, codes aiming to predict heat shield ablation are in need of experimental data pertaining to the turbulent transport of ablation products for validation. At The University of Texas at Austin, a technique is being developed that uses planar laser-induced fluorescence (PLIF) of a low-temperature sublimating ablator (naphthalene) to visualize the transport of ablation products in a supersonic flow. Since ablation at reentry temperatures can be difficult to recreate in a laboratory setting it is desirable to create a limited physics problem and simulate the ablation process at relatively low temperature conditions using naphthalene. A scaled Orion MPCV model with a solid naphthalene heat shield has been tested in a Mach 5 wind tunnel at various angles of attack in the current work. PLIF images have shown high concentrations of scalar in the capsule wake region, intermittent turbulent structures on the heat shield surface, and interesting details of the capsule shear layer structure. This work was supported by a NASA Office of the Chief Technologist's Space Technology Research Fellowship (NNX11AN55H).

  4. Study of low-cost fabrication of ablative heat shields

    NASA Technical Reports Server (NTRS)

    Norwood, L. B.

    1972-01-01

    The major objectives were accomplished in three tasks: (1) modification of the ablative material composition for ease of fabrication as well as thermal and mechanical performance; (2) scaled-up, simplified, manufacturing techniques which resulted in cost reductions; and (3) the identification of a significant design problem caused by the differential pressure buildup imposed on mechanically attached ablative heat shield panels during launch.

  5. Development of Naphthalene PLIF for Visualizing Ablation Products From a Space Capsule Heat Shield

    NASA Technical Reports Server (NTRS)

    Combs, C. S.; Clemens, N. T.; Danehy, P. M.

    2014-01-01

    The Orion Multi-Purpose Crew Vehicle (MPCV) will use an ablative heat shield. To better design this heat shield and others that will undergo planetary entry, an improved understanding of the ablation process would be beneficial. Here, a technique developed at The University of Texas at Austin that uses planar laser-induced fluorescence (PLIF) of a low-temperature sublimating ablator (naphthalene) to enable visualization of the ablation products in a hypersonic flow is applied. Although high-temperature ablation is difficult and expensive to recreate in a laboratory environment, low-temperature sublimation creates a limited physics problem that can be used to explore ablation-product transport in a hypersonic flow-field. In the current work, a subscale capsule reentry vehicle model with a solid naphthalene heat shield has been tested in a Mach 5 wind tunnel. The PLIF technique provides images of the spatial distribution of sublimated naphthalene in the heat-shield boundary layer, separated shear layer, and backshell recirculation region. Visualizations of the capsule shear layer using both naphthalene PLIF and Schlieren imaging compared favorably. PLIF images have shown high concentrations of naphthalene in the capsule separated flow region, intermittent turbulent structures on the heat shield surface, and interesting details of the capsule shear layer structure. It was shown that, in general, the capsule shear layer appears to be more unsteady at lower angels of attack. The PLIF images demonstrated that during a wind tunnel run, as the model heated up, the rate of naphthalene ablation increased, since the PLIF signal increased steadily over the course of a run. Additionally, the shear layer became increasingly unsteady over the course of a wind tunnel run, likely because of increased surface roughness but also possibly because of the increased blowing. Regions with a relatively low concentration of naphthalene were also identified in the capsule backshell

  6. Investigation of low-cost fabrication of ablative heat shields

    NASA Technical Reports Server (NTRS)

    Massions, V. P.; Mach, R. W.

    1973-01-01

    The fabrication, testing, and evaluation of materials and techniques employed in the fabrication of ablative heat shield panels are described. Results of this effort show projected reductions in labor man-hours for dielectric curing of panels when compared to panels molded in a steam-heated press. In addition, panels were fabricated with more than one density within the cross-section. These dual-density panels show significant weight and cost reduction potentials.

  7. Study of critical defects in ablative heat shield systems for the space shuttle

    NASA Technical Reports Server (NTRS)

    Miller, C. C.; Rummel, W. D.

    1974-01-01

    Experimental results are presented for a program conducted to determine the effects of fabrication-induced defects on the performance of an ablative heat shield material. Exposures representing a variety of space shuttle orbiter mission environments-humidity acoustics, hot vacuum and cold vacuum-culuminating in entry heating and transonic acoustics, were simulated on large panels containing intentional defects. Nondestructive methods for detecting the defects, were investigated. The baseline materials were two honeycomb-reinforced low density, silicone ablators, MG-36 and SS-41. Principal manufacturing-induced defects displaying a critical potential included: off-curing of the ablator, extreme low density, undercut (or crushed) honeycomb reinforcements, and poor wet-coating of honeycomb.

  8. Low cost fabrication of ablative heat shields

    NASA Technical Reports Server (NTRS)

    Cecka, A. M.; Schofield, W. C.

    1972-01-01

    A material and process study was performed using subscale panels in an attempt to reduce the cost of fabricating ablative heat shield panels. Although no improvements were made in the material formulation, a significant improvement was obtained in the processing methods compared to those employed in the previous work. The principal feature of the new method is the press filling and curing of the ablation material in a single step with the bonding and curing of the face sheet. This method was chosen to replace the hand troweling and autoclave curing procedure used previously. Double-curvature panels of the same size as the flat panels were fabricated to investigate fabrication problems. It was determined that the same materials and processes used for flat panels can be used to produce the curved panels. A design with severe curvatures consisting of radii of 24 x 48 inches was employed for evaluation. Ten low-density and ten high-density panels were fabricated. With the exception of difficulties related to short run non-optimum tooling, excellent panel filling and density uniformity were obtained.

  9. Remote Recession Sensing of Ablative Heat Shield Materials

    NASA Technical Reports Server (NTRS)

    Winter, Michael W.; Stackpoole, Margaret; Nawaz, Anuscheh; Gonzales, Gregory Lewis; Ho, Thanh

    2014-01-01

    Material recession and charring are two major processes determining the performance of ablative heat shield materials. Even in ground testing, the characterization of these two mechanisms relies on measurements of material thickness before and after testing, thus providing only information integrated over the test time. For recession measurements, optical methods such as imaging the sample surface during testing are under investigation but require high alignment and instrument effort, therefore being not established as a standard measurement method. For char depth measurements, the most common method so far consists in investigation of sectioned samples after testing or in the case of Stardust where core extractions were performed to determine char information. In flight, no reliable recession measurements are available, except total recession after recovering the heat shield on ground. Developments of mechanical recession sensors have been started but require substantial on board instrumentation adding mass and complexity. In this work, preliminary experiments to evaluate the feasibility of remote sensing of material recession and possibly char depth through optically observing the emission signatures of seeding materials in the post shock plasma is investigated. It is shown that this method can provide time resolved recession measurements without the necessity of accurate alignment procedures of the optical set-up and without any instrumentation on board of a spacecraft. Furthermore, recession data can be obtained without recovering flight hardware which would be a huge benefit for inexpensive heat shield material testing on board of small re-entry probes, e.g. on new micro-satellite re-entry probes as a possible future application of Cubesats or RBR

  10. An Analysis of Ablation-Shield Requirements for Manned Reentry Vehicles

    NASA Technical Reports Server (NTRS)

    Roberts, Leonard

    1960-01-01

    The problem of sublimation of material and accumulation of heat in an ablation shield is analyzed and the results are applied to the reentry of manned vehicles into the earth's atmosphere. The parameters which control the amount of sublimation and the temperature distribution within the ablation shield are determined and presented in a manner useful for engineering calculation. It is shown that the total mass loss from the shield during reentry and the insulation requirements may be given very simply in terms of the maximum deceleration of the vehicle or the total reentry time.

  11. Major uncertainties influencing entry probe heat shield design

    NASA Technical Reports Server (NTRS)

    Congdon, W.

    1974-01-01

    Factors influencing the design of an outer planet probe heat shield are discussed. Major factors included are: uncertainties in composition and scale height of the planet atmospheres; the augmentation/attenuation of entry heating by ablation products requires more computer study and testing; carbon heat shields, especially carbon phenolic, possessing improved resistance to spallation need developing; and white silica reflecting heat shields with improved resistance to bulk vitrification need further developing.

  12. Retro Rocket Motor Self-Penetrating Scheme for Heat Shield Exhaust Ports

    NASA Technical Reports Server (NTRS)

    Marrese-Reading, Colleen; St.Vaughn, Josh; Zell, Peter; Hamm, Ken; Corliss, Jim; Gayle, Steve; Pain, Rob; Rooney, Dan; Ramos, Amadi; Lewis, Doug; hide

    2009-01-01

    A preliminary scheme was developed for base-mounted solid-propellant retro rocket motors to self-penetrate the Orion Crew Module heat shield for configurations with the heat shield retained during landings on Earth. In this system the motors propel impactors into structural push plates, which in turn push through the heat shield ablator material. The push plates are sized such that the remaining port in the ablator material is large enough to provide adequate flow area for the motor exhaust plume. The push plate thickness is sized to assure structural integrity behind the ablative thermal protection material. The concept feasibility was demonstrated and the performance was characterized using a gas gun to launch representative impactors into heat shield targets with push plates. The tests were conducted using targets equipped with Fiberform(R) and PICA as the heat shield ablator material layer. The PICA penetration event times were estimated to be under 30 ms from the start of motor ignition. The mass of the system (not including motors) was estimated to be less than 2.3 kg (5 lbs) per motor. The configuration and demonstrations are discussed.

  13. Thermal Protection System (Heat Shield) Development - Advanced Development Project

    NASA Technical Reports Server (NTRS)

    Kowal, T. John

    2010-01-01

    The Orion Thermal Protection System (TPS) ADP was a 3 1/2 year effort to develop ablative TPS materials for the Orion crew capsule. The ADP was motivated by the lack of available ablative TPS's. The TPS ADP pursued a competitive phased development strategy with succeeding rounds of development, testing and down selections. The Project raised the technology readiness level (TRL) of 8 different TPS materials from 5 different commercial vendors, eventual down selecting to a single material system for the Orion heat shield. In addition to providing a heat shield material and design for Orion on time and on budget, the Project accomplished the following: 1) Re-invigorated TPS industry & re-established a NASA competency to respond to future TPS needs; 2) Identified a potentially catastrophic problem with the planned MSL heat shield, and provided a viable, high TRL alternate heat shield design option; and 3) Transferred mature heat shield material and design options to the commercial space industry, including TPS technology information for the SpaceX Dragon capsule.

  14. Orion Heat Shield Testing

    NASA Image and Video Library

    2015-05-26

    THE ORION HEAT SHIELD, WHICH WAS AT NASA’S MARSHALL SPACE FLIGHT CENTER FROM MARCH-MAY 2015 FOR ENGINEERING AND ANALYSIS, IS READIED FOR DEPARTURE AT THE END OF ITS STAY. THE HEAT SHIELD’S ABLATED SURFACE MATERIAL WAS REMOVED AT MARSHALL FOR ANALYSIS, USING THE CENTER’S STATE-OF-THE-ART SEVEN-AXIS MILLING MACHINE. IT NEXT WILL GO TO NASA’S LANGLEY RESEARCH CENTER FOR WATER-IMPACT TESTING. NASA’S JOHNSON SPACE CENTER LEADS THE ORION PROGRAM FOR NASA.

  15. Orion Heat Shield Testing

    NASA Image and Video Library

    2015-05-28

    THE ORION HEAT SHIELD, WHICH WAS AT NASA’S MARSHALL SPACE FLIGHT CENTER FROM MARCH-MAY 2015 FOR ENGINEERING AND ANALYSIS, IS READIED FOR DEPARTURE AT THE END OF ITS STAY. THE HEAT SHIELD’S ABLATED SURFACE MATERIAL WAS REMOVED AT MARSHALL FOR ANALYSIS, USING THE CENTER’S STATE-OF-THE-ART SEVEN-AXIS MILLING MACHINE. IT NEXT WILL GO TO NASA’S LANGLEY RESEARCH CENTER FOR WATER-IMPACT TESTING. NASA’S JOHNSON SPACE CENTER LEADS THE ORION PROGRAM FOR NASA.

  16. Low-cost fabrication and direct bond installation of flat, single-curvature and compound-curvature ablative heat shield panels

    NASA Technical Reports Server (NTRS)

    Norwood, L. B.

    1972-01-01

    Procedures for low cost fabrication and direct bond installation of flat, single curved, and compound curvature ablative heat shields on a DC-3 aircraft are discussed. The panel sizes and attachment locations are identified. In addition to the bonding of the four contoured panels, two flat panels were bonded to the nearly flat, lower surface of the center wing section. The detailed requirements and objectives of the investigation are described.

  17. X-Ray Computed Tomography Inspection of the Stardust Heat Shield

    NASA Technical Reports Server (NTRS)

    McNamara, Karen M.; Schneberk, Daniel J.; Empey, Daniel M.; Koshti, Ajay; Pugel, D. Elizabeth; Cozmuta, Ioana; Stackpoole, Mairead; Ruffino, Norman P.; Pompa, Eddie C.; Oliveras, Ovidio; hide

    2010-01-01

    The "Stardust" heat shield, composed of a PICA (Phenolic Impregnated Carbon Ablator) Thermal Protection System (TPS), bonded to a composite aeroshell, contains important features which chronicle its time in space as well as re-entry. To guide the further study of the Stardust heat shield, NASA reviewed a number of techniques for inspection of the article. The goals of the inspection were: 1) to establish the material characteristics of the shield and shield components, 2) record the dimensions of shield components and assembly as compared with the pre-flight condition, 3) provide flight infonnation for validation and verification of the FIAT ablation code and PICA material property model and 4) through the evaluation of the shield material provide input to future missions which employ similar materials. Industrial X-Ray Computed Tomography (CT) is a 3D inspection technology which can provide infonnation on material integrity, material properties (density) and dimensional measurements of the heat shield components. Computed tomographic volumetric inspections can generate a dimensionally correct, quantitatively accurate volume of the shield assembly. Because of the capabilities offered by X-ray CT, NASA chose to use this method to evaluate the Stardust heat shield. Personnel at NASA Johnson Space Center (JSC) and Lawrence Livermore National Labs (LLNL) recently performed a full scan of the Stardust heat shield using a newly installed X-ray CT system at JSC. This paper briefly discusses the technology used and then presents the following results: 1. CT scans derived dimensions and their comparisons with as-built dimensions anchored with data obtained from samples cut from the heat shield; 2. Measured density variation, char layer thickness, recession and bond line (the adhesive layer between the PICA and the aeroshell) integrity; 3. FIAT predicted recession, density and char layer profiles as well as bondline temperatures Finally suggestions are made as to future uses

  18. Orion Heat Shield Foam Blocks Prefitting

    NASA Image and Video Library

    2016-10-24

    Tile blocks have been prefitted around the heat shield for the Orion crew module inside the Neil Armstrong Operations and Checkout Building high bay at NASA's Kennedy Space Center in Florida. The heat shield is one of the most critical elements of Orion and protects it and the future astronauts inside from searing temperatures experienced during reentry through Earth's atmosphere when they return home. For Exploration Mission-1, the top layer of Orion's heat shield that is primarily responsible for helping the crew module endure reentry heat will be composed of approximately 180 blocks, which are made of an ablative material called Avcoat designed to wear away as it heats up. Orion is being prepared for its flight on the agency's Space Launch System for Exploration Mission-1 in late 2018. Orion is the exploration spacecraft designed to carry astronauts to destinations not yet explored by humans, including an asteroid and NASA's Journey to Mars. It will have emergency abort capability, sustain the crew during space travel and provide safe re-entry from deep space return velocities.

  19. High purity silica reflective heat shield development

    NASA Technical Reports Server (NTRS)

    Nachtscheim, P. R.; Blome, J. C.

    1976-01-01

    A hyperpure vitreous silica material is being developed for use as a reflective and ablative heat shield for planetary entry. Various purity grades and forms of raw materials were evaluated along with various processing methods. Slip casting of high purity grain was selected as the best processing method, resulting in a highly reflective material in the wavelength bands of interest (the visible and ultraviolet regions). The selected material was characterized with respect to optical, mechanical and physical properties using a limited number of specimens. The process has been scaled up to produce a one-half scale heat shield (18 in. dia.) (45.72 cm) for a Jupiter entry vehicle. This work is now being extended to improve the structural safety factor of the heat shield by making hyperpure silica material tougher through the addition of silica fibers.

  20. Finite-Rate Ablation Boundary Conditions for Carbon-Phenolic Heat-Shield

    NASA Technical Reports Server (NTRS)

    Chen, Y.-K.; Milos, Frank S.

    2003-01-01

    A formulation of finite-rate ablation surface boundary conditions, including oxidation, nitridation, and sublimation of carbonaceous material with pyrolysis gas injection, has been developed based on surface species mass conservation. These surface boundary conditions are discretized and integrated with a Navier-Stokes solver. This numerical procedure can predict aerothermal heating, chemical species concentration, and carbonaceous material ablation rate over the heatshield surface of re-entry space vehicles. In this study, the gas-gas and gas-surface interactions are established for air flow over a carbon-phenolic heatshield. Two finite-rate gas-surface interaction models are considered in the present study. The first model is based on the work of Park, and the second model includes the kinetics suggested by Zhluktov and Abe. Nineteen gas phase chemical reactions and four gas-surface interactions are considered in the present model. There is a total of fourteen gas phase chemical species, including five species for air and nine species for ablation products. Three test cases are studied in this paper. The first case is a graphite test model in the arc-jet stream; the second is a light weight Phenolic Impregnated Carbon Ablator at the Stardust re-entry peak heating conditions, and the third is a fully dense carbon-phenolic heatshield at the peak heating point of a proposed Mars Sample Return Earth Entry Vehicle. Predictions based on both finite-rate gas- surface interaction models are compared with those obtained using B' tables, which were created based on the chemical equilibrium assumption. Stagnation point convective heat fluxes predicted using Park's finite-rate model are far below those obtained from chemical equilibrium B' tables and Zhluktov's model. Recession predictions from Zhluktov's model are generally lower than those obtained from Park's model and chemical equilibrium B' tables. The effect of species mass diffusion on predicted ablation rate is also

  1. Coupled Ablation, Heat Conduction, Pyrolysis, Shape Change and Spallation of the Galileo Probe

    NASA Technical Reports Server (NTRS)

    Milos, Frank S.; Chen, Y.-K.; Rasky, Daniel J. (Technical Monitor)

    1995-01-01

    The Galileo probe enters the atmosphere of Jupiter in December 1995. This paper presents numerical methodology and detailed results of our final pre-impact calculations for the heat shield response. The calculations are performed using a highly modified version of a viscous shock layer code with massive radiation coupled with a surface thermochemical ablation and spallation model and with the transient in-depth thermal response of the charring and ablating heat shield. The flowfield is quasi-steady along the trajectory, but the heat shield thermal response is dynamic. Each surface node of the VSL grid is coupled with a one-dimensional thermal response calculation. The thermal solver includes heat conduction, pyrolysis, and grid movement owing to surface recession. Initial conditions for the heat shield temperature and density were obtained from the high altitude rarefied-flow calculations of Haas and Milos. Galileo probe surface temperature, shape, mass flux, and element flux are all determined as functions of time along the trajectory with spallation varied parametrically. The calculations also estimate the in-depth density and temperature profiles for the heat shield. All this information is required to determine the time-dependent vehicle mass and drag coefficient which are necessary inputs for the atmospheric reconstruction experiment on board the probe.

  2. Orion Heat Shield Manufacturing Producibility Improvements for the EM-1 Flight Test Program

    NASA Technical Reports Server (NTRS)

    Koenig, William J.; Stewart, Michael; Harris, Richard F.

    2018-01-01

    This paper describes how the ORION program is incorporating improvements in the heat shield design and manufacturing processes reducing programmatic risk and ensuring crew safety in support of NASA's Exploration missions. The approach for the EFT-1 heat shield utilized a low risk Apollo heritage design and manufacturing process using an Avcoat TPS ablator with a honeycomb substrate to provide a one piece heat shield to meet the mission re-entry heating environments. The EM-1 mission will have additional flight systems installed to fly to the moon and return to Earth. Heat shield design and producibility improvements have been incorporated in the EM-1 vehicle to meet deep space mission requirements. The design continues to use the Avcoat material, but in a block configuration to enable improvements in consistant and repeatable application processes using tile bonding experience developed on the Space Shuttle Transportation System Program.

  3. Heat Shield Paves the Way for Commercial Space

    NASA Technical Reports Server (NTRS)

    2014-01-01

    The Phenolic-Impregnated Carbon Ablator (PICA) heat shield, a lightweight material designed to withstand high temperatures, was used for the Stardust’s reentry into Earth’s atmosphere. Hawthorne, California-based SpaceX later worked with the inventors at Ames Research Center to outfit PICA on its Dragon capsule, which is now delivering cargo to and from the International Space Station through NASA’s Commercial Resupply Services contracts program.

  4. Heat Shield in Pieces

    NASA Technical Reports Server (NTRS)

    2005-01-01

    This image from NASA's Mars Exploration Rover Opportunity shows the remains of the rover's heat shield, broken into two key pieces, the main piece on the left side and a broken-off flank piece near the middle of the image. The heat shield impact site is identified by the circle of red dust on the right side of the picture. In this view, Opportunity is approximately 20 meters (66 feet) away from the heat shield, which protected it while hurtling through the martian atmosphere.

    In the far left of the image, a meteorite called 'Heat Shield Rock,' sits nearby, The Sun is reflecting off the silver-colored underside of the internal thermal blankets of the heat shield.

    The rover spent 36 sols investigating how the severe heating during entry through the atmosphere affected the heat shield. The most obvious is the fact that the heat shield inverted upon impact.

    This is an approximately true-color rendering of the scene acquired around 1:22 p.m. local solar time on Opportunity sol 324 (Dec. 21, 2004) in an image mosaic using panoramic filters at wavelengths of 750, 530, and 430 nanometers.

  5. Optical ablation/temperature gage (COTA)

    NASA Astrophysics Data System (ADS)

    Cassaing, J.; Balageas, D.

    ONERA has ground and flight tested for heat-shield recession a novel technique, different from current radiation and acoustic measurement methods. It uses a combined ablation/temperature gage that views the radiation optically from a cavity embedded within the heat shield. Flight measurements, both of temperature and of passage of the ablation front, are compared with data generated by a predictive numerical code. The ablation and heat diffusion into the instrumented ablator can be simulated numerically to evaluate accurately the errors due to the presence of the gage. This technology was established in 1978 and finally adopted after ground tests in arc heater facilities. After four years of flight evaluations, it is possible to evaluate and criticize the sensor reliability.

  6. Orion Heat Shield Move

    NASA Image and Video Library

    2017-10-23

    Technicians move the Orion heat shield for Exploration Mission-1 toward the thermal chamber in the Neil Armstrong Operations and Checkout Building high bay at NASA's Kennedy Space Center in Florida. Protective pads are being attached to the heat shield surface. The heat shield will undergo a thermal cycle test to verify acceptable workmanship and material quality. The test also serves to verify the heat shield's thermal protection systems have been manufactured and assembled correctly. The Orion spacecraft will launch atop NASA's Space Launch System rocket on its first uncrewed integrated flight.

  7. Computational Fluid Dynamic Solutions of Optimized Heat Shields Designed for Earth Entry

    DTIC Science & Technology

    2010-01-01

    domain ρ = Density (kg/m3) σ = Stefan Boltzmann constant τ = Shear stress tensor τT−V = T-V relaxation time τe−V = e-V relaxation time xi φ = Sweep angle...Vehicle DES = Differential evolutionary Scheme DOR = Design Optimization Tools DPLR = Data Parallel Line Relaxation GSLR = Gauss- Seidel Line... Stefan - Boltzmann constant. This model provides accurate heating predictions, especially for the non-ablating heat-shields explored in this work. Various

  8. Orion Heat Shield

    NASA Image and Video Library

    2015-05-06

    ENGINEERS FROM AMES RESEARCH CENTER AND MARSHALL SPACE FLIGHT CENTER REMOVE AVCOAT SEGMENTS FROM THE SURFACE OF THE ORION HEAT SHIELD, THE PROTECTIVE SHELL DESIGNED TO HELP THE NEXT GENERATION CREW MODULE WITHSTAND THE HEAT OF ATMOSPHERIC REENTRY. THE HEAT SHIELD FLEW TO SPACE DURING THE EFT-1 FULL SCALL FLIGHT TEST OF ORION IN DECEMBER 2014

  9. Ames Research Center Shear Tests of SLA-561V Heat Shield Material for Mars-Pathfinder

    NASA Technical Reports Server (NTRS)

    Tauber, Michael; Tran, Huy; Henline, William; Cartledge, Alan; Hui, Frank; Tran, Duoc; Zimmerman, Norm

    1996-01-01

    This report describes the results of arc-jet testing at Ames Research Center on behalf of Jet Propulsion Laboratory (JPL) for the development of the Mars-Pathfinder heat shield. The current test series evaluated the performance of the ablating SLA-561V heat shield material under shear conditions. In addition, the effectiveness of several methods of repairing damage to the heat shield were evaluated. A total of 26 tests were performed in March 1994 in the 2 in. X 9 in. arc-heated turbulent Duct Facility, including runs to calibrate the facility to obtain the desired shear stress conditions. A total of eleven models were tested. Three different conditions of shear and heating were used. The non-ablating surface shear stresses and the corresponding, approximate, non-ablating surface heating rates were as follows: Condition 1, 170 N/m(exp 2) and 22 W/cm(exp 2); Condition 2, 240 N/m(exp 2) and 40 W/cm(exp 2); Condition 3, 390 N/m(exp 2) and 51 W/cm(exp 2). The peak shear stress encountered in flight is represented approximately by Condition 1; however, the heating rate was much less than the peak flight value. The peak heating rate that was available in the facility (at Condition 3) was about 30 percent less than the maximum value encountered during flight. Seven standard ablation models were tested, of which three models were instrumented with thermocouples to obtain in-depth temperature profiles and temperature contours. An additional four models contained a variety of repair plugs, gaps, and seams. These models were used to evaluated different repair materials and techniques, and the effect of gaps and construction seams. Mass loss and surface recession measurements were made on all models. The models were visually inspected and photographed before and after each test. The SLA-561 V performed well; even at test Condition 3, the char remained intact. Most of the resins used for repairs and gap fillers performed poorly. However, repair plugs made of SLA-561V performed

  10. Transport properties associated with carbon-phenolic ablators

    NASA Technical Reports Server (NTRS)

    Biolsi, L.

    1982-01-01

    Entry vehicle heat shields designed for entry into the atmosphere of the outer planets are usually made of carbonaceous material such as carbon-phenolic ablator. Ablative injection of this material is an important mechanism for reducing the heat at the surface of the entry vehicle. Conductive transport properties in the shock layer are important for some entry conditions. The kinetic theory of gases has been used to calculate the transport properties for 17 gaseous species obtained from the ablation of carbon-phenolic heat shields. Results are presented for the pure species and for the gas mixture.

  11. Research and application of surface heat treatment for multipulse laser ablation of materials

    NASA Astrophysics Data System (ADS)

    Cai, Song; Chen, Genyu; Zhou, Cong

    2015-11-01

    This study analysed a laser ablation platform and built heat transfer equations for multipulse laser ablation of materials. The equations include three parts: laser emission after the material melt and gasification; end of laser emission after the material melts and there is the presence of a super-hot layer and solid-phase heat transfer changes during material ablation. For each of the three parts, the effects of evaporation, plasma shielding and energy accumulation under the pulse interval were considered. The equations are reasonable, and all the required parameters are only related to the laser parameters and material properties, allowing the model to have a certain versatility and practicability. The model was applied for numerical simulation of the heat transfer characteristics in the multipulse laser ablation of bronze and diamond. Next, experiments were conducted to analyse the topography of a bronze-bonded diamond grinding wheel after multipulse laser ablation. The theoretical analysis and experimental results showed that multipulse laser can merge the truing and dressing on a bronze-bonded diamond grinding wheel. This study provides theoretical guidance for optimising the process parameters in the laser ablation of a bronze-bonded diamond grinding wheel. A comparative analysis showed that the numerical solution to the model is in good agreement with the experimental data, thus verifying the correctness and feasibility of the heat transfer model.

  12. Study of the ablative effects on tektites: Atmosphere entry of a swarm of tektites. [shielding by hypersonic wake

    NASA Technical Reports Server (NTRS)

    Sepri, P.; Chen, K. K.

    1977-01-01

    The large variety of ablation markings observed on recovered tektites lead to the previously proposed swarm wake model which states that the lead peripheral tektites bore the blunt of aerodynamic heating upon entry, and that the bulk of tektites in the wake enjoyed partial shielding at the expense of the leaders. Further considerations are presented in support of this model. Quantitative assessments indicate that wake shielding might indeed have provided for substantially less heating than would have been experienced by a tektite entering an undisturbed atmosphere along a similar trajectory. For the case of strong wake shielding it is even possible that the surface temperature of a falling tektite had barely reached its melting point. In the distribution of tektites, there is a size band (near R = 0.5 cm) which is least susceptible to melting.

  13. Exploratory Environmental Tests of Several Heat Shields

    NASA Technical Reports Server (NTRS)

    Goodman, George P.; Betts, John, Jr.

    1961-01-01

    Exploratory tests have been conducted with several conceptual radiative heat shields of composite construction. Measured transient temperature distributions were obtained for a graphite heat shield without insulation and with three types of insulating materials, and for a metal multipost heat shield, at surface temperatures of approximately 2,000 F and 1,450 F, respectively, by use of a radiant-heat facility. The graphite configurations suffered loss of surface material under repeated irradiation. Temperature distribution calculated for the metal heat shield by a numerical procedure was in good agreement with measured data. Environmental survival tests of the graphite heat shield without insulation, an insulated multipost heat shield, and a stainless-steel-tile heat shield were made at temperatures of 2,000 F and dynamic pressures of approximately 6,000 lb/sq ft, provided by an ethylene-heated jet operating at a Mach number of 2.0 and sea-level conditions. The graphite heat shield survived the simulated aerodynamic heating and pressure loading. A problem area exists in the design and materials for heat-resistant fasteners between the graphite shield and the base structure. The insulated multipost heat shield was found to be superior to the stainless-steel-tile heat shield in retarding heat flow. Over-lapped face-plate joints and surface smoothness of the insulated multi- post heat shield were not adversely affected by the test environment. The graphite heat shield without insulation survived tests made in the acoustic environment of a large air jet. This acoustic environment is random in frequency and has an overall noise level of 160 decibels.

  14. Orion Heat Shield

    NASA Image and Video Library

    2015-05-06

    OVERSEEING ORION HEAT SHIELD WORK IN MARSHALL'S SEVEN-AXIS MILLING AND MACHINING FACILITY ARE, FROM LEFT, JOHN KOWAL, MANAGER OF ORION'S THERMAL PROTECTION SYSTEM AT JOHNSON SPACE CENTER; NICHOLAS CROWLEY, AN AMES ENGINEERING TECHNICIAN; AND ROB KORNIENKO, AMES ENGINEERING BRANCH CHIEF. THE HEAT SHIELD FLEW TO SPACE DURING THE EFT-1 FULL SCALE FLIGHT TEST OF ORION IN DECEMBER, 2014

  15. Orion Heat Shield Move

    NASA Image and Video Library

    2017-10-23

    Lockheed Martin engineers and technicians prepare the Orion heat shield for Exploration Mission-1 for its move to the thermal chamber in the Neil Armstrong Operations and Checkout Building high bay at NASA's Kennedy Space Center in Florida. The heat shield will undergo a thermal cycle test to verify acceptable workmanship and material quality. The test serves to verify the heat shield's thermal protection systems have been manufactured and assembled correctly. The Orion spacecraft will launch atop NASA's Space Launch System rocket on its first uncrewed integrated flight.

  16. Heat Shield's Main Piece

    NASA Technical Reports Server (NTRS)

    2005-01-01

    NASA's Mars Exploration Rover Opportunity caught this view of the main piece of the spacecraft's heat shield during the rover's 328th martian day, or sol (Dec. 25, 2004). A separation spring can be seen on the ground to the lower left side of the heat shield.

  17. Parasitic heat loss reduction in AMTEC cells by heat shield optimization

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Borkowski, C.A.; Svedberg, R.C.; Hendricks, T.J.

    1997-12-31

    Alkali metal thermal to electric conversion (AMTEC) cell performance can be increased by the proper design of thermal radiative shielding internal to the AMTEC cell. These heat shields essentially lower the radiative heat transfer between the heat input zone of the cell and the heat rejection zone of the cell. In addition to lowering the radiative heat transfer between the heat input and heat rejection surfaces of the cell, the shields raise the AMTEC cell performance by increasing the temperature of the beta alumina solid electrolyte (BASE). This increase in temperature of the BASE tube allows the evaporator temperature tomore » be increased without sodium condensing within the BASE tubes. Experimental testing and theoretical analysis have been performed to compare the relative merits of two candidate heat shield packages: (1) chevron, and (2) cylindrical heat shields. These two heat shield packages were compared to each other and a baseline cell which had no heat shields installed. For the two heat shield packages, the reduction in total heat transfer is between 17--27% for the heat input surface temperature varying from 700 C, 750 C, and 800 C with the heat rejection surface temperature kept at 300 C.« less

  18. Ablative shielding for hypervelocity projectiles

    NASA Technical Reports Server (NTRS)

    Rucker, Michelle A. (Inventor)

    1993-01-01

    A hypervelocity projectile shield which includes a hollow semi-flexible housing fabricated from a plastic like, or otherwise transparent membrane which is filled with a fluid (gas or liquid) is presented. The housing has a inlet valve, similar to that on a tire or basketball, to introduce an ablating fluid into the housing. The housing is attached by a Velcro mount or double-sided adhesive tape to the outside surface of a structure to be protected. The housings are arrayed in a side-by-side relationship for complete coverage of the surface to be protected. In use, when a hypervelocity projectile penetrates the outer wall of a housing it is broken up and then the projectile is ablated as it travels through the fluid, much like a meteorite 'burns up' as it enters the earth's atmosphere, and the housing is deflated. The deflated housing can be easily spotted for replacement, even from a distance. Replacement is then accomplished by simply pulling a deflated housing off the structure and installing a new housing.

  19. Crumpled Heat Shield

    NASA Technical Reports Server (NTRS)

    2008-01-01

    The Phoenix Mars Lander's Surface Stereo Imager took this image of the spacecraft's crumpled heat shield on Sept. 16, 2008, the 111th Martian day of the mission.

    The 2-1/2 meter (about 8-1/2 feet) heat shield landed southeast of Phoenix, about halfway between the spacecraft and its backshell/parachute. The backshell/parachute touched ground 300 meters (1,000 ft) to the south of the lander.

    The dark area to the right of the heat shield is the 'bounce mark' it made on impact with the Red Planet. This image is the highest-resolution image that will likely be taken by the lander, and is part of the 1,500-image 'Happily Ever After' panorama.

    The Phoenix mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is led by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.

  20. Ablation article and method

    NASA Technical Reports Server (NTRS)

    Erickson, W. D.; Sullivan, E. M. (Inventor)

    1973-01-01

    An ablation article, such as a conical heat shield, having an ablating surface is provided with at least one discrete area of at least one seed material, such as aluminum. When subjected to ablation conditions, the seed material is ablated. Radiation emanating from the ablated seed material is detected to analyze ablation effects without disturbing the ablation surface. By providing different seed materials having different radiation characteristics, the ablating effects on various areas of the ablating surface can be analyzed under any prevailing ablation conditions. The ablating article can be provided with means for detecting the radiation characteristics of the ablated seed material to provide a self-contained analysis unit.

  1. Curiosity Heat Shield in Detail

    NASA Image and Video Library

    2012-08-08

    This color full-resolution image showing the heat shield of NASA Curiosity rover was obtained during descent to the surface of Mars. This image shows the inside surface of the heat shield, with its protective multi-layered insulation.

  2. X-ray Micro-Tomography of Ablative Heat Shield Materials

    NASA Technical Reports Server (NTRS)

    Panerai, Francesco; Ferguson, Joseph; Borner, Arnaud; Mansour, Nagi N.; Barnard, Harold S.; MacDowell, Alastair A.; Parkinson, Dilworth Y.

    2016-01-01

    X-ray micro-tomography is a non-destructive characterization technique that allows imaging of materials structures with voxel sizes in the micrometer range. This level of resolution makes the technique very attractive for imaging porous ablators used in hypersonic entry systems. Besides providing a high fidelity description of the material architecture, micro-tomography enables computations of bulk material properties and simulations of micro-scale phenomena. This presentation provides an overview of a collaborative effort between NASA Ames Research Center and Lawrence Berkeley National Laboratory, aimed at developing micro-tomography experiments and simulations for porous ablative materials. Measurements are carried using x-rays from the Advanced Light Source at Berkeley Lab on different classes of ablative materials used in NASA entry systems. Challenges, strengths and limitations of the technique for imaging materials such as lightweight carbon-phenolic systems and woven textiles are discussed. Computational tools developed to perform numerical simulations based on micro-tomography are described. These enable computations of material properties such as permeability, thermal and radiative conductivity, tortuosity and other parameters that are used in ablator response models. Finally, we present the design of environmental cells that enable imaging materials under simulated operational conditions, such as high temperature, mechanical loads and oxidizing atmospheres.Keywords: Micro-tomography, Porous media, Ablation

  3. Extraterrestrial Regolith Derived Atmospheric Entry Heat Shields

    NASA Technical Reports Server (NTRS)

    Hogue, Michael D.; Mueller, Robert P.; Sibille, Laurent; Hintze, Paul E.; Rasky, Daniel J.

    2016-01-01

    High-mass planetary surface access is one of NASAs technical challenges involving entry, descent and landing (EDL). During the entry and descent phase, frictional interaction with the planetary atmosphere causes a heat build-up to occur on the spacecraft, which will rapidly destroy it if a heat shield is not used. However, the heat shield incurs a mass penalty because it must be launched from Earth with the spacecraft, thus consuming a lot of precious propellant. This NASA Innovative Advanced Concept (NIAC) project investigated an approach to provide heat shield protection to spacecraft after launch and prior to each EDL thus potentially realizing significant launch mass savings. Heat shields fabricated in situ can provide a thermal-protection system for spacecraft that routinely enter a planetary atmosphere. By fabricating the heat shield with space resources from materials available on moons and asteroids, it is possible to avoid launching the heat-shield mass from Earth. Regolith has extremely good insulating properties and the silicates it contains can be used in the fabrication and molding of thermal-protection materials. In this paper, we will describe three types of in situ fabrication methods for heat shields and the testing performed to determine feasibility of this approach.

  4. Heat flow from the West African Shield

    NASA Astrophysics Data System (ADS)

    Brigaud, Frédéric; Lucazeau, Francis; Ly, Saidou; Sauvage, Jean François

    1985-09-01

    The heat flow over Precambrian shields is generally lower than over other continental provinces. Previous observations at 9 sites of the West African shield have shown that heat flow ranges from 20 mW m -2 in Niger to 38-42 mW m -2 in Liberia, Ghana and Nigeria. Since some of these values are lower than expected for Precambrian shields, it is important to find out whether or not they are representative of the entire shield before trying to derive its thermal structure. In this paper, we present new heat flow determinations from seven sites of the West African shield. These indicate that the surface heat flow is comparable with that of other Precambrian shields in the world.

  5. ADEPT Heat Shield Testing

    NASA Image and Video Library

    2015-10-16

    NASA is developing the next generation of heat shield to enable astronauts to go to Mars and other deep space destinations. Called the Adaptive Deployable Entry and Placement Technology or ADEPT, the heat shield is mechanically deployable and uses a flexible woven carbon fabric as its skin. Recently, engineers successfully completed a series of tests in the Ames Arc Jet facility. Other tests conducted in wind tunnels at Ames demonstrated that the ADEPT materials and system perform well under planetary re-entry conditions.

  6. The SRB heat shield: Aeroelastic stability during reentry

    NASA Technical Reports Server (NTRS)

    Ventres, C. S.; Dowell, E. H.

    1977-01-01

    Wind tunnel tests of a 3% scale model of the aft portion of the SRB equipped with partially scaled heat shields were conducted for the purpose of measuring fluctuating pressure levels in the aft skirt region. During these tests, the heat shields were observed to oscillate violently, the oscillations in some instances causing the heat shields to fail. High speed films taken during the tests reveal a regular pattern of waves in the fabric starting near the flow stagnation point and progressing around both sides of the annulus. The amplitude of the waves was too great, and their pattern too regular, for them to be attributed to the fluctuating pressure levels measured during the tests. The cause of the oscillations observed in the model heat shields, and whether or not similar oscillations will occur in the full scale SRB heat shield during reentry were investigated. Suggestions for modifying the heat shield so as to avoid the oscillations are provided, and recommendations are made for a program of vibration and wind tunnel tests of reduced-scale aeroelastic models of the heat shield.

  7. Preparing Mars Science Laboratory Heat Shield

    NASA Image and Video Library

    2011-05-13

    Technicians at Lockheed Martin Space Systems, Denver, prepare the heat shield for NASA Mars Science Laboratory. With a diameter of 4.5 meters nearly 15 feet, this heat shield is the largest ever built for a planetary mission.

  8. Fiber-optic temperature profiling for thermal protection system heat shields

    NASA Astrophysics Data System (ADS)

    Black, Richard J.; Costa, Joannes M.; Zarnescu, Livia; Hackney, Drew A.; Moslehi, Behzad; Peters, Kara J.

    2016-11-01

    To achieve better designs for spacecraft heat shields for missions requiring atmospheric aero-capture or entry/reentry, reliable thermal protection system (TPS) sensors are needed. Such sensors will provide both risk reduction and heat-shield mass minimization, which will facilitate more missions and enable increased payloads and returns. This paper discusses TPS thermal measurements provided by a temperature monitoring system involving lightweight, electromagnetic interference-immune, high-temperature resistant fiber Bragg grating (FBG) sensors with a thermal mass near that of TPS materials together with fast FBG sensor interrogation. Such fiber-optic sensing technology is highly sensitive and accurate, as well as suitable for high-volume production. Multiple sensing FBGs can be fabricated as arrays on a single fiber for simplified design and reduced cost. Experimental results are provided to demonstrate the temperature monitoring system using multisensor FBG arrays embedded in a small-size super-light ablator (SLA) coupon which was thermally loaded to temperatures in the vicinity of the SLA charring temperature. In addition, a high-temperature FBG array was fabricated and tested for 1000°C operation, and the temperature dependence considered over the full range (cryogenic to high temperature) for which silica fiber FBGs have been subjected.

  9. Flexible Ablators: Applications and Arcjet Testing

    NASA Technical Reports Server (NTRS)

    Arnold, James O.; Venkatapathy, Ethiraj; Beck, Robin A S.; Mcguire, Kathy; Prabhu, Dinesh K.; Gorbunov, Sergey

    2011-01-01

    Flexible ablators were conceived in 2009 to meet the technology pull for large, human Mars Exploration Class, 23 m diameter hypersonic inflatable aerodynamic decelerators. As described elsewhere, they have been recently undergoing initial technical readiness (TRL) advancement by NASA. The performance limits of flexible ablators in terms of maximum heat rates, pressure and shear remain to be defined. Further, it is hoped that this emerging technology will vastly expand the capability of future NASA missions involving atmospheric entry systems. This paper considers four topics of relevance to flexible ablators: (1) Their potential applications to near/far term human and robotic missions (2) Brief consideration of the balance between heat shield diameter, flexible ablator performance limits, entry vehicle controllability and aft-body shear layer impingement of interest to designers of very large entry vehicles, (3) The approach for developing bonding processes of flexible ablators for use on rigid entry bodies and (4) Design of large arcjet test articles that will enable the testing of flexible ablators in flight-like, combined environments (heat flux, pressure, shear and structural tensile loading). Based on a review of thermal protection system performance requirements for future entry vehicles, it is concluded that flexible ablators have broad applications to conventional, rigid entry body systems and are enabling to large deployable (both inflatable and mechanical) heat shields. Because of the game-changing nature of flexible ablators, it appears that NASA's Office of the Chief Technologist (OCT) will fund a focused, 3-year TRL advancement of the new materials capable of performance in heat fluxes in the range of 200-600 W/sq. cm. This support will enable the manufacture and use of the large-scale arcjet test designs that will be a key element of this OCT funded activity.

  10. Mars Exploration Rover Heat Shield Recontact Analysis

    NASA Technical Reports Server (NTRS)

    Raiszadeh, Behzad; Desai, Prasun N.; Michelltree, Robert

    2011-01-01

    The twin Mars Exploration Rover missions landed successfully on Mars surface in January of 2004. Both missions used a parachute system to slow the rover s descent rate from supersonic to subsonic speeds. Shortly after parachute deployment, the heat shield, which protected the rover during the hypersonic entry phase of the mission, was jettisoned using push-off springs. Mission designers were concerned about the heat shield recontacting the lander after separation, so a separation analysis was conducted to quantify risks. This analysis was used to choose a proper heat shield ballast mass to ensure successful separation with low probability of recontact. This paper presents the details of such an analysis, its assumptions, and the results. During both landings, the radar was able to lock on to the heat shield, measuring its distance, as it descended away from the lander. This data is presented and is used to validate the heat shield separation/recontact analysis.

  11. Fused silica reflecting heat shields for outer planet entry probes

    NASA Technical Reports Server (NTRS)

    Congdon, W. M.; Peterson, D. L.

    1975-01-01

    The development of slip-cast fused silica is discussed as a heat shield designed to meet the needs of outer-planet entry probes. The distinguishing feature of silica is its ability to reflect the radiation imposed by planetary-entry environments. This reflectivity is particularly sensitive to degradation by the presence of trace amounts of contaminants introduced by the starting materials or by processing. The microstructure of a silica configuration also significantly influences the reflectivity and other thermomechanical properties. The processing techniques attendant on controlling microstructure while maintaining purity are discussed. The selection of a starting material of essential purity precludes the use of purified natural quartz and requires the use of synthetic fused silica. The silica is characterized in a limited combined heating test environment. The surface mass loss is controlled by liquid runoff from a relatively low-temperature melt layer; the reflectance is basically maintained and the material achieves a surprisingly high heat of ablation.

  12. Heat shield characterization: Outer planet atmospheric entry probe

    NASA Technical Reports Server (NTRS)

    Mezines, S. A.; Rusert, E. L.; Disser, E. F.

    1976-01-01

    A full scale carbon phenolic heat shield was fabricated for the Outer Planet Probe in order to demonstrate the feasibility of molding large carbon phenolic parts with a new fabrication processing method (multistep). The sphere-cone heat shield was molded as an integral unit with the nose cap plies configured into a double inverse chevron shape to achieve the desired ply orientation. The fabrication activity was successful and the feasibility of the multistep processing technology was established. Delaminations or unbonded plies were visible on the heat shield and resulted from excessive loss of resin and lack of sufficient pressure applied on the part during the curing cycle. A comprehensive heat shield characterization test program was conducted, including: nondestructive tests with the full scale heat shield and thermal and mechanical property tests with small test specimen.

  13. Enabling a Better Aft Heat Shield Solution for Future Mars Science Laboratory Class Vehicles

    NASA Technical Reports Server (NTRS)

    McGuire, Mary K.; Covington, Melmoth A.; Goldstein, Howard E.; Arnold, James O.; Beck, Robin

    2013-01-01

    System studies are described that compare masses and estimated manufacturing costs of options for the as-flown Mars Science Laboratory (MSL) aft body Thermal Light Weight Ablator (SLA) 561-V and its thickness was not optimized using the standard TPS Sizer Tool widely used for heat shield design. Use of the TPS sizing tool suggests that optimization of the SLA thickness could reduce the aft heat shield mass by 40 percent. Analysis of the predicted aft-shell aerothermodynamics suggests that the bulk of MSL class entry vehicle heat shields could incorporate Advanced Flexible Reusable Surface Insulation (AFRSI). AFRSI has a wellestablished record of relatively inexpensive manufacturing and flight certification based on its use on the lee side of the Space Shuttle. Runs with the TPS Sizer show that the AFRSI solution would be 60 percent lighter than the as-flown SLA. The issue of Reaction Control System (RCS) heating on the aft shell could be addressed by locally impregnating the AFRSI with silicone to enhance its robustness to short bursts ofheating. Stagnation point arcjet testing has shown that silicone impregnated AFRSI performs well at heat rates of 115 W/cm2 and 0.1 atmospheres for a duration of 40 seconds, far beyond conditions that are expected for MSL class vehicles. The paper concludes with a discussion of manufacturing processes for AFRSI, impregnation approaches and relative cost comparisons to the SLA solution.

  14. Ames Research Center Mars/Pathfinder Heat Shield Design Verification ARC-JET Test

    NASA Technical Reports Server (NTRS)

    Tran, Huy K.; Hui, Frank; Wercinski, Paul; Cartledge, Alan; Tauber, Mike; Tran, Duoc T.; Chen, Y. K.; Arnold, James O. (Technical Monitor)

    1995-01-01

    Design verification tests were performed on samples representing the aerobrake of the Mars/Pathfinder vehicle. The test specimens consisted of the SLA-561V ablator bonded to the honeycomb structure. The primary objective was to evaluate the ablation materials performance and to measure temperatures within the ablator, at the structural bondline and at the back sheet of the honeycomb structure. Other objectives were to evaluate the effect of ablative repair plug material treatment and voids in the heat shield. A total of 29 models were provided for testing in the Ames 60MW arc-jet facility. Of these, 23 models were flat-faced and six remaining models were curved edge ones, intended to simulate the conditions on the curved rim of the forebody where the maximum shear occurred. Eight sets of test conditions were used. The stagnation point heating rates varied from 47 to 240 W/cm2 and the stagnation pressures from 0.15 to 0.27 atm. (The maximum flight values are 132 W/cm2 and 0.25 atm) The majority of these runs were made at a nominal stagnation pressure of 0.25 atm. Two higher pressure runs were made to check the current (denser) ablation material for spallation, or other forms of thermal stress failure. Over 60% of the flatfaced models yielded good thermocouple data and all produced useful surface recession information. Of the five curved-edge models that were tested, only one gave good data; the remaining ones experienced model-holder failure. The test results can be summarized by noting that no failure of the ablative material was observed on any model. Also, the bondline temperature design limit of 250 C was never reached within an equivalent flight time despite a stagnation point heat load that exceeded the maximum flight value by up to 130%. At heating rates of over 200W/cm2 and stagnation pressures of 0.25 atm, or greater, the average surface recessions exceeded 0.5 cm on some models. The surface roughness increased dramatically at pressures above 0.25 atm and

  15. Large Heat Shield for Mars Science Laboratory

    NASA Image and Video Library

    2009-07-10

    This image shows NASA Mars Science Laboratory heat shield, and a spacecraft worker at Lockheed Martin Space Systems, Denver. It is the largest heat shield ever built for descending through the atmosphere of any planet.

  16. Experimental assessment of the performance of ablative heat shield materials from plasma wind tunnel testing

    NASA Astrophysics Data System (ADS)

    Löhle, S.; Hermann, T.; Zander, F.

    2018-06-01

    A method for assessing the performance of typical heat shield materials is presented in this paper. Three different material samples, the DLR material Zuram, the Airbus material Asterm and the carbon preform Calcarb were tested in the IRS plasma wind tunnel PWK1 at the same nominal condition. State of the art diagnostic tools, i.e., surface temperature with pyrometry and thermography and boundary layer optical emission spectroscopy were completed by photogrammetric surface recession measurements. These data allow the assessment of the net heat flux for each material. The analysis shows that the three materials each have a different effect on heat flux mitigation with ASTERM showing the largest reduction in surface heat flux. The effect of pyrolysis and blowing is clearly observed and the heat flux reduction can be determined from an energy balance.

  17. Multiplate Radiation Shields: Investigating Radiational Heating Errors

    NASA Astrophysics Data System (ADS)

    Richardson, Scott James

    1995-01-01

    Multiplate radiation shield errors are examined using the following techniques: (1) analytic heat transfer analysis, (2) optical ray tracing, (3) numerical fluid flow modeling, (4) laboratory testing, (5) wind tunnel testing, and (6) field testing. Guidelines for reducing radiational heating errors are given that are based on knowledge of the temperature sensor to be used, with the shield being chosen to match the sensor design. Small, reflective sensors that are exposed directly to the air stream (not inside a filter as is the case for many temperature and relative humidity probes) should be housed in a shield that provides ample mechanical and rain protection while impeding the air flow as little as possible; protection from radiation sources is of secondary importance. If a sensor does not meet the above criteria (i.e., is large or absorbing), then a standard Gill shield performs reasonably well. A new class of shields, called part-time aspirated multiplate radiation shields, are introduced. This type of shield consists of a multiplate design usually operated in a passive manner but equipped with a fan-forced aspiration capability to be used when necessary (e.g., low wind speed). The fans used here are 12 V DC that can be operated with a small dedicated solar panel. This feature allows the fan to operate when global solar radiation is high, which is when the largest radiational heating errors usually occur. A prototype shield was constructed and field tested and an example is given in which radiational heating errors were reduced from 2 ^circC to 1.2 ^circC. The fan was run continuously to investigate night-time low wind speed errors and the prototype shield reduced errors from 1.6 ^ circC to 0.3 ^circC. Part-time aspirated shields are an inexpensive alternative to fully aspirated shields and represent a good compromise between cost, power consumption, reliability (because they should be no worse than a standard multiplate shield if the fan fails), and accuracy

  18. Influence of the shielding effect on the formation of a micro-texture on the cermet with nanosecond pulsed laser ablation.

    PubMed

    Yuan, Jiandong; Liang, Liang; Jiang, Lelun; Liu, Xin

    2018-04-01

    The degree of laser pulse overlapping in a laser scanning path has a significant impact on the ablation regime in the laser machining of a micro-texture. In this Letter, a nanosecond pulsed laser is used to prepare the micro-scaled groove on WC-8Co cermet under different scanning speeds. It is observed that as the scanning speed increases, the ablated trace morphology in the first scanning pass transits from a succession of intermittent deep dimples to the consecutive overlapped shallow pits. The test result also indicates that ablated trace morphology with respect to the low scanning speed stems from a plume shielding effect. Moreover, the ablation regime considering the shielding effect in micro-groove formation process is clarified. The critical scanning speed that can circumvent the shielding effect is also summarized with respect to different laser powers.

  19. Experimental assessment of the performance of ablative heat shield materials from plasma wind tunnel testing

    NASA Astrophysics Data System (ADS)

    Löhle, S.; Hermann, T.; Zander, F.

    2017-12-01

    A method for assessing the performance of typical heat shield materials is presented in this paper. Three different material samples, the DLR material uc(Zuram), the Airbus material uc(Asterm) and the carbon preform uc(Calcarb) were tested in the IRS plasma wind tunnel PWK1 at the same nominal condition. State of the art diagnostic tools, i.e., surface temperature with pyrometry and thermography and boundary layer optical emission spectroscopy were completed by photogrammetric surface recession measurements. These data allow the assessment of the net heat flux for each material. The analysis shows that the three materials each have a different effect on heat flux mitigation with ASTERM showing the largest reduction in surface heat flux. The effect of pyrolysis and blowing is clearly observed and the heat flux reduction can be determined from an energy balance.

  20. High purity silica reflecting heat shield development

    NASA Technical Reports Server (NTRS)

    Congdon, W.

    1974-01-01

    A reflecting heat shield composed of fused silica in which the scattering results from the refractive index mismatch between silica particles and the voids introduced during the fabrication process is developed. Major considerations and conclusions of the development are: the best material to use is Type A, which is capable of ultra-high-purity and which does not show the 0.243 micrometer absorption band; the reflection efficiency of fused silica is decreased at higher temperatures due to the bathochromic shift of the ultraviolet cut-off; for a given silica material, over the wavelength region and particle sizes tested, the monodisperse particle size configurations produce higher reflectances than continuous particle size configurations; and the smaller monodisperse particle size configurations give higher reflectance than the larger ones. A reflecting silica configuration that is an efficient reflector of shock layer radiation at high ablation temperatures is achieved by tailoring the matrix for optimum scattering and using an ultra-high-purity material.

  1. Orion Heat Shield

    NASA Image and Video Library

    2015-03-09

    THE ORION HEAT SHIELD THAT SUCCESSFULLY SURVIVED A HIGH-VELOCITY REENTRY DURING ITS DEC. 5 FLIGHT TEST, IS CONTINUING ITS JOURNEY, NOW AT MARSHALL. IT ARRIVED ON MONDAY, MARCH 9 AND WILL BE INSTALLED IN THE BUILDING 4705 7-AXIS MILLING AND MACHINING CENTER.

  2. Single laser based pump-probe technique to study plasma shielding during nanosecond laser ablation of copper thin films

    NASA Astrophysics Data System (ADS)

    Nammi, Srinagalakshmi; Vasa, Nilesh J.; Gurusamy, Balaganesan; Mathur, Anil C.

    2017-09-01

    A plasma shielding phenomenon and its influence on micromachining is studied experimentally and theoretically for laser wavelengths of 355 nm, 532 nm and 1064 nm. A time resolved pump-probe technique is proposed and demonstrated by splitting a single nanosecond Nd3+:YAG laser into an ablation laser (pump laser) and a probe laser to understand the influence of plasma shielding on laser ablation of copper (Cu) clad on polyimide thin films. The proposed nanosecond pump-probe technique allows simultaneous measurement of the absorption characteristics of plasma produced during Cu film ablation by the pump laser. Experimental measurements of the probe intensity distinctly show that the absorption by the ablated plume increases with increase in the pump intensity, as a result of plasma shielding. Theoretical estimation of the intensity of the transmitted pump beam based on the thermo-temporal modeling is in qualitative agreement with the pump-probe based experimental measurements. The theoretical estimate of the depth attained for a single pulse with high pump intensity value on a Cu thin film is limited by the plasma shielding of the incident laser beam, similar to that observed experimentally. Further, the depth of micro-channels produced shows a similar trend for all three wavelengths, however, the channel depth achieved is lesser at the wavelength of 1064 nm.

  3. Flow-dependent vascular heat transfer during microwave thermal ablation.

    PubMed

    Chiang, Jason; Hynes, Kieran; Brace, Christopher L

    2012-01-01

    Microwave tumor ablation is an attractive option for thermal ablation because of its inherent benefits over radiofrequency ablation (RFA) in the treatment of solid tumors such as hepatocellular carcinoma (HCC). Microwave energy heats tissue to higher temperatures and at a faster rate than RFA, creating larger, more homogenous ablation zones. In this study, we investigate microwave heating near large vasculature using coupled fluid-flow and thermal analysis. Low-flow conditions are predicted to be more likely to cause cytotoxic heating and, therefore, vessel thrombosis and endothelial damage of downstream tissues. Such conditions may be more prevalent in patient with severe cirrhosis or compromised blood flow. High-flow conditions create the more familiar heat-sink effect that can protect perivascular tissues from the intended thermal damage. These results may help guide placement and use of microwave ablation technologies in future studies.

  4. Numerical Modeling of Ablation Heat Transfer

    NASA Technical Reports Server (NTRS)

    Ewing, Mark E.; Laker, Travis S.; Walker, David T.

    2013-01-01

    A unique numerical method has been developed for solving one-dimensional ablation heat transfer problems. This paper provides a comprehensive description of the method, along with detailed derivations of the governing equations. This methodology supports solutions for traditional ablation modeling including such effects as heat transfer, material decomposition, pyrolysis gas permeation and heat exchange, and thermochemical surface erosion. The numerical scheme utilizes a control-volume approach with a variable grid to account for surface movement. This method directly supports implementation of nontraditional models such as material swelling and mechanical erosion, extending capabilities for modeling complex ablation phenomena. Verifications of the numerical implementation are provided using analytical solutions, code comparisons, and the method of manufactured solutions. These verifications are used to demonstrate solution accuracy and proper error convergence rates. A simple demonstration of a mechanical erosion (spallation) model is also provided to illustrate the unique capabilities of the method.

  5. Biggest-Ever Heat Shield Prepared for Mars Spacecraft

    NASA Image and Video Library

    2011-05-13

    The heat shield for NASA Mars Science Laboratory is the largest ever built for a planetary mission. This image shows the heat shield being prepared at Lockheed Martin Space Systems, Denver, in April 2011.

  6. The kinetics of reaction of the by-products of ablative materials at high temperatures and the rate of heat transfer between hot surfaces and reactive gases

    NASA Technical Reports Server (NTRS)

    Spokes, G. N.; Beadle, P. C.; Gac, N. A.; Golden, D. M.; King, K. D.; Benson, S. W.

    1971-01-01

    Research has been conducted by means of laboratory experiments to enhance understanding of the fundamental mechanisms of heterogeneous and homogeneous chemical reactions taking place during ablative processes that accompany the reentry or manned space vehicles into planetary atmospheres. Fundamental mechanisms of those chemical reactions believed to be important in the thermal degradation of ablative plastic heat shield materials, and the gases evolved, are described.

  7. Investigation of low-cost ablative heat shield fabrication for space shuttles

    NASA Technical Reports Server (NTRS)

    Chandler, H. H.

    1972-01-01

    Improvements in the processes and design to reduce the manufacturing costs for low density ablative panels for the space shuttle are discussed. The areas that were studied included methods of loading honeycomb core, alternative reinforcement concepts, and the use of reusable subpanels. A review of previous studies on the fabrication of low-cost ablative panels and on permissible defects that do not affect thermal performance was conducted. Considerable differences in the quoted prices for ablative panels, even though the various contractors had reported similar fabrication times were discovered. How these cost differences arise from different estimating criteria and which estimating assumptions and other costs must be included in order to arrive at a realistic price are discussed.

  8. Carbon Nanotube-Enhanced Carbon-Phenenolic Ablator Material

    NASA Technical Reports Server (NTRS)

    Kikolaev, P.; Stackpoole, M.; Fan, W.; Cruden, B. A.; Waid, M.; Moloney, P.; Arepalli, S.; Arnold, J.; Partridge, H.; Yowell, L.

    2006-01-01

    This viewgraph presentation reviews the use of PICA (phenolic impregnated carbon ablator) as the selected material for heat shielding for future earth return vehicles. It briefly reviews the manufacturing of PICA and the advantages for the use of heat shielding, and then explains the reason for using Carbon Nanotubes to improve strength of phenolic resin that binds carbon fibers together. It reviews the work being done to create a carbon nanotube enhanced PICA. Also shown are various micrographic images of the various PICA materials.

  9. Heat-shield for Extreme Entry Environment Technology (HEEET) Development Status

    NASA Technical Reports Server (NTRS)

    Venkatapathy, Ethiraj; Ellerby, Don; Gage, Peter

    2016-01-01

    The Heat shield for Extreme Entry Environment Technology (HEEET) Project is a NASA STMD and SMD co-funded effort. The goal is to develop and mission infuse a new ablative Thermal Protection System that can withstand extreme entry. It is targeted to support NASA's high priority missions, as defined in the latest decadal survey, to destinations such as Venus and Saturn in-situ robotic science missions. Entry into these planetary atmospheres results in extreme heating. The entry peak heat-flux and associated pressure are estimated to be between one and two orders of magnitude higher than those experienced by Mars Science Laboratory or Lunar return missions. In the recent New Frontiers community announcement NASA has indicated that it is considering providing an increase to the PI managed mission cost (PIMMC) for investigations utilizing the Heat Shield for Extreme Entry Environment Technology (HEEET) and in addition, NASA is considering limiting the risk assessment to only their accommodation on the spacecraft and the mission environment. The HEEET ablative TPS utilizes 3D weaving technology to manufacture a dual layer material architecture. The 3-D weaving allows for flat panels to be woven. The dual layer consists of a top layer designed to withstand the extreme external environment while the inner or insulating layer by design, is designed to achieve low thermal conductivity, and it keeps the heat from conducting towards the structure underneath. Both arc jet testing combined with material properties have been used to develop thermal response models that allows for comparison of performance with heritage carbon phenolic. A 50% mass efficiency is achieved by the dual layer construct compared to carbon phenolic for a broad range of missions both to Saturn and Venus. The 3-D woven flat preforms are molded to achieve the shape as they are compliant and then resin infusion with curing forms a rigid panels. These panels are then bonded on to the aeroshell structure. Gaps

  10. Trajectory-based heating analysis for the European Space Agency/Rosetta Earth Return Vehicle

    NASA Technical Reports Server (NTRS)

    Henline, William D.; Tauber, Michael E.

    1994-01-01

    A coupled, trajectory-based flowfield and material thermal-response analysis is presented for the European Space Agency proposed Rosetta comet nucleus sample return vehicle. The probe returns to earth along a hyperbolic trajectory with an entry velocity of 16.5 km/s and requires an ablative heat shield on the forebody. Combined radiative and convective ablating flowfield analyses were performed for the significant heating portion of the shallow ballistic entry trajectory. Both quasisteady ablation and fully transient analyses were performed for a heat shield composed of carbon-phenolic ablative material. Quasisteady analysis was performed using the two-dimensional axisymmetric codes RASLE and BLIMPK. Transient computational results were obtained from the one-dimensional ablation/conduction code CMA. Results are presented for heating, temperature, and ablation rate distributions over the probe forebody for various trajectory points. Comparison of transient and quasisteady results indicates that, for the heating pulse encountered by this probe, the quasisteady approach is conservative from the standpoint of predicted surface recession.

  11. Decoupled Method for Reconstruction of Surface Conditions From Internal Temperatures On Ablative Materials With Uncertain Recession Model

    NASA Technical Reports Server (NTRS)

    Oliver, A. Brandon

    2017-01-01

    Obtaining measurements of flight environments on ablative heat shields is both critical for spacecraft development and extremely challenging due to the harsh heating environment and surface recession. Thermocouples installed several millimeters below the surface are commonly used to measure the heat shield temperature response, but an ill-posed inverse heat conduction problem must be solved to reconstruct the surface heating environment from these measurements. Ablation can contribute substantially to the measurement response making solutions to the inverse problem strongly dependent on the recession model, which is often poorly characterized. To enable efficient surface reconstruction for recession model sensitivity analysis, a method for decoupling the surface recession evaluation from the inverse heat conduction problem is presented. The decoupled method is shown to provide reconstructions of equivalent accuracy to the traditional coupled method but with substantially reduced computational effort. These methods are applied to reconstruct the environments on the Mars Science Laboratory heat shield using diffusion limit and kinetically limited recession models.

  12. Performance of a Light-Weight Ablative Thermal Protection Material for the Stardust Mission Sample Return Capsule

    NASA Technical Reports Server (NTRS)

    Covington, M. A.

    2005-01-01

    New tests and analyses are reported that were carried out to resolve testing uncertainties in the original development and qualification of a lightweight ablative material used for the Stardust spacecraft forebody heat shield. These additional arcjet tests and analyses confirmed the ablative and thermal performance of low density Phenolic Impregnated Carbon Ablator (PICA) material used for the Stardust design. Testing was done under conditions that simulate the peak convective heating conditions (1200 W/cm2 and 0.5 atm) expected during Earth entry of the Stardust Sample Return Capsule. Test data and predictions from an ablative material response computer code for the in-depth temperatures were compared to guide iterative adjustment of material thermophysical properties used in the code so that the measured and predicted temperatures agreed. The PICA recession rates and maximum internal temperatures were satisfactorily predicted by the computer code with the revised properties. Predicted recession rates were also in acceptable agreement with measured rates for heating conditions 37% greater than the nominal peak heating rate of 1200 W/sq cm. The measured in-depth temperature response data show consistent temperature rise deviations that may be caused by an undocumented endothermic process within the PICA material that is not accurately modeled by the computer code. Predictions of the Stardust heat shield performance based on the present evaluation provide evidence that the maximum adhesive bondline temperature will be much lower than the maximum allowable of 250 C and an earlier design prediction. The re-evaluation also suggests that even with a 25 percent increase in peak heating rates, the total recession of the heat shield would be a small fraction of the as-designed thickness. These results give confidence in the Stardust heat shield design and confirm the potential of PICA material for use in new planetary probe and sample return applications.

  13. Preliminary Development of a Multifunctional Hot Structure Heat Shield

    NASA Technical Reports Server (NTRS)

    Walker, Sandra P.; Daryabeigi, Kamran; Samareh, Jamshid A.; Armand, Sasan C.; Perino, Scott V

    2014-01-01

    Development of a Multifunctional Hot Structure Heat Shield concept has initiated with the goal to provide advanced technology with significant benefits compared to the current state of the art heat shield technology. The concept is unique in integrating the function of the thermal protection system with the primary load carrying structural component. An advanced carbon-carbon material system has been evaluated for the load carrying structure, which will be utilized on the outer surface of the heat shield, and thus will operate as a hot structure exposed to the severe aerodynamic heating associated with planetary entry. Flexible, highly efficient blanket insulation has been sized for use underneath the hot structure to maintain desired internal temperatures. The approach was to develop a preliminary design to demonstrate feasibility of the concept. The preliminary results indicate that the concept has the potential to save both mass and volume with significantly less recession compared to traditional heat shield designs, and thus provide potential to enable new planetary missions.

  14. The Influence of Ablation on Radiative Heating for Earth Entry

    NASA Technical Reports Server (NTRS)

    Johnston, Christopher O.; Gnoffo, Peter A.; Sutton, Kenneth

    2008-01-01

    Using the coupled ablation and radiation capability recently included in the LAURA flowfield solver, this paper investigates the influence of ablation on the shock-layer radiative heating for Earth entry. The extension of the HARA radiation model, which provides the radiation predictions in LAURA, to treat a gas consisting of the elements C, H, O, and N is discussed. It is shown that the absorption coefficient of air is increased with the introduction of the C and H elements. A simplified shock layer model is studied to show the impact of temperature, as well as the abundance of C and H, on the net absorption or emission from an ablation contaminated boundary layer. It is found that the ablation species reduce the radiative flux in the vacuum ultraviolet, through increased absorption, for all temperatures. However, in the infrared region of the spectrum, the ablation species increase the radiative flux, through strong emission, for temperatures above 3,000 K. Thus, depending on the temperature and abundance of ablation species, the contaminated boundary layer may either provide a net increase or decrease in the radiative flux reaching the wall. To assess the validity of the coupled ablation and radiation LAURA analysis, a previously analyzed Mars-return case (15.24 km/s), which contains significant ablation and radiation coupling, is studied. Exceptional agreement with previous viscous shock-layer results is obtained. A 40% decrease in the radiative flux is predicted for ablation rates equal to 20% of the free-stream mass flux. The Apollo 4 peak-heating case (10.24 km/s) is also studied. For ablation rates up to 3.4% of the free-stream mass flux, the radiative heating is reduced by up to 19%, while the convective heating is reduced by up to 87%. Good agreement with the Apollo 4 radiometer data is obtained by considering absorption in the radiometer cavity. For both the Mars return and the Apollo 4 cases, coupled radiation alone is found to reduce the radiative

  15. Magnetic resonance-guided shielding of prefocal acoustic obstacles in focused ultrasound therapy: application to intercostal ablation in liver.

    PubMed

    Salomir, Rares; Petrusca, Lorena; Auboiroux, Vincent; Muller, Arnaud; Vargas, Maria-Isabel; Morel, Denis R; Goget, Thomas; Breguet, Romain; Terraz, Sylvain; Hopple, Jerry; Montet, Xavier; Becker, Christoph D; Viallon, Magalie

    2013-06-01

    The treatment of liver cancer is a major public health issue because the liver is a frequent site for both primary and secondary tumors. Rib heating represents a major obstacle for the application of extracorporeal focused ultrasound to liver ablation. Magnetic resonance (MR)-guided external shielding of acoustic obstacles (eg, the ribs) was investigated here to avoid unwanted prefocal energy deposition in the pathway of the focused ultrasound beam. Ex vivo and in vivo (7 female sheep) experiments were performed in this study. Magnetic resonance-guided high-intensity focused ultrasound (MRgHIFU) was performed using a randomized 256-element phased-array transducer (f∼1 MHz) and a 3-T whole-body clinical MR scanner. A physical mask was inserted in the prefocal beam pathway, external to the body, to block the energy normally targeted on the ribs. The effectiveness of the reflecting material was investigated by characterizing the efficacy of high-intensity focused ultrasound beam reflection and scattering on its surface using Schlieren interferometry. Before high-intensity focused ultrasound sonication, the alignment of the protectors with the conical projections of the ribs was required and achieved in multiple steps using the embedded graphical tools of the MR scanner. Multiplanar near real-time MR thermometry (proton resonance frequency shift method) enabled the simultaneous visualization of the local temperature increase at the focal point and around the exposed ribs. The beam defocusing due to the shielding was evaluated from the MR acoustic radiation force impulse imaging data. Both MR thermometry (performed with hard absorber positioned behind a full-aperture blocking shield) and Schlieren interferometry indicated a very good energy barrier of the shielding material. The specific temperature contrast between rib surface (spatial average) and focus, calculated at the end point of the MRgHIFU sonication, with protectors vs no protectors, indicated an important

  16. High temperature ablation of kaolinite layered silicate/phenolic resin/asbestos cloth nanocomposite.

    PubMed

    Bahramian, Ahmad Reza; Kokabi, Mehrdad; Famili, Mohammad Hossein Navid; Beheshty, Mohammad Hossein

    2008-01-15

    The successful return of re-entry space vehicle, which is subjected to severe aerodynamic heating, is largely accompanied by some provisions to reduce the heat transfer to the structure. Heat shield is the best protection means which undergoes physical, chemical, and mostly endothermal transformations. The objective of this work is to investigate the ablating, charring, and thermal degradation behaviour of heat shield resol-type phenolic resin/kaolinite/asbestos cloth nanocomposite by oxyacetylene flame test with an external heat flux of 8 x 10(9)W/m(2) and 3000 K hot gas temperature and thermal analyzer techniques. Kinetic parameters of thermal degradation and temperature distribution at the back surface of the nanocomposite heat shield were determined and compared with that of composite counterpart.

  17. Carbon phenolic heat shields for Jupiter/Saturn/Uranus entry probes

    NASA Technical Reports Server (NTRS)

    Mezines, S.

    1974-01-01

    Carbon phenolic heat shield technology is reviewed. Heat shield results from the outer planetary probe mission studies are summarized along with results of plasma jet testing of carbon phenolic conducted in a ten megawatt facility. Missile flight data is applied to planetary entry conditions. A carbon phenolic heat shield material is utilized and tailored to accommodate each of the probe missions. An integral heat shield approach is selected over in order to eliminate a high temperature interface problem and permit direct bonding of the carbon phenolic to the structural honeycomb sandwich. The sandwich is filled with a very fine powder to minimize degradation of its insulation properties by the high conductive hydrogen/helium gases during the long atmospheric descent phase.

  18. (NESC) NASA Engineering and Safety Center Orion Heat Shield Carr

    NASA Image and Video Library

    2014-04-29

    (NESC) NASA Engineering and Safety Center Orion Heat Shield Carrier Structure: Titanium Orthogrid heat shield sub-component dynamic test article : person in the photo Jim Jeans (Background: Mike Kirsch, James Ainsworth)

  19. Non-Intrusive Sensor for In-Situ Measurement of Recession Rate of Ablative and Eroding Materials

    NASA Technical Reports Server (NTRS)

    Papadopoulos, George (Inventor); Tiliakos, Nicholas (Inventor); Thomson, Clint (Inventor); Benel, Gabriel (Inventor)

    2014-01-01

    A non-intrusive sensor for in-situ measurement of recession rate of heat shield ablatives. An ultrasonic wave source is carried in the housing. A microphone is also carried in the housing, for collecting the reflected ultrasonic waves from an interface surface of the ablative material. A time phasing control circuit is also included for time-phasing the ultrasonic wave source so that the waves reflected from the interface surface of the ablative material focus on the microphone, to maximize the acoustic pressure detected by the microphone and to mitigate acoustic velocity variation effects through the material through a de-coupling process that involves a software algorithm. A software circuit for computing the location off of which the ultrasonic waves scattered to focus back at the microphone is also included, so that the recession rate of the heat shield ablative may be monitored in real-time through the scan-focus approach.

  20. Impact of the retained heat shield concept on science instruments

    NASA Technical Reports Server (NTRS)

    Kessler, W. C.

    1974-01-01

    Associated interface problems between the mass spectrometer and the actual probe design are considered along with the problem of producing a clean sample to the gas detection instrument. Of particular interest is the penetration of the heat shield by the mass spectrometer sampling tube, because it must be demonstrated that the sampling tube can penetrate the heat shield and that the mass spectrometer can be supplied with a contaminant-free gas sample, free of contaminants from out-gassing of the heat shield.

  1. Orion EFT-1 Heat Shield Move from LASF to VAB Highbay 2

    NASA Image and Video Library

    2017-04-26

    The Orion heat shield from Exploration Flight Test-1, secured on a transporter, arrives at the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida. The heat shield was moved from the Launch Abort System Facility. The heat shield is being transferred from the Orion Program to the Ground Systems Development and Operations Program, Landing and Recovery Operations. In the VAB, the heat shield will be integrated with the Orion ground test article and used for future underway recovery testing.

  2. Orion EFT-1 Heat Shield Move from LASF to VAB Highbay 2

    NASA Image and Video Library

    2017-04-26

    The Orion heat shield from Exploration Flight Test-1 has arrived in High Bay 2 in the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida. The heat shield was moved from the Launch Abort System Facility. The heat shield is being transferred from the Orion Program to the Ground Systems Development and Operations Program, Landing and Recovery Operations. In the VAB, the heat shield will be integrated with the Orion ground test article and used for future underway recovery testing.

  3. Thermal, Radiation and Impact Protective Shields (TRIPS) for Robotic and Human Space Exploration Missions

    NASA Technical Reports Server (NTRS)

    Loomis, M. P.; Arnold, J. L.

    2005-01-01

    New concepts for protective shields for NASA s Crew Exploration Vehicles (CEVs) and planetary probes offer improved mission safety and affordability. Hazards include radiation from cosmic rays and solar particle events, hypervelocity impacts from orbital debris/ micrometeorites, and the extreme heating environment experienced during entry into planetary atmospheres. The traditional approach for the design of protection systems for these hazards has been to create single-function shields, i.e. ablative and blanket-based heat shields for thermal protection systems (TPS), polymer or other low-molecular-weight materials for radiation shields, and multilayer, Whipple-type shields for protection from hypervelocity impacts. This paper introduces an approach for the development of a single, multifunctional protective shield, employing nanotechnology- based materials, to serve simultaneously as a TPS, an impact shield and as the first line of defense against radiation. The approach is first to choose low molecular weight ablative TPS materials, (existing and planned for development) and add functionalized carbon nanotubes. Together they provide both thermal and radiation (TR) shielding. Next, impact protection (IP) is furnished through a tough skin, consisting of hard, ceramic outer layers (to fracture the impactor) and sublayers of tough, nanostructured fabrics to contain the debris cloud from the impactor before it can penetrate the spacecraft s interior.

  4. Orion EFT-1 Heat Shield Move from LASF to VAB Highbay 2

    NASA Image and Video Library

    2017-04-26

    A flatbed truck carrying the Orion heat shield from Exploration Flight Test-1, backs into High Bay 2 in the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida. The heat shield was moved from the Launch Abort System Facility. The heat shield is being transferred from the Orion Program to the Ground Systems Development and Operations Program, Landing and Recovery Operations. In the VAB, the heat shield will be integrated with the Orion ground test article and used for future underway recovery testing.

  5. Orion EFT-1 Heat Shield Move from LASF to VAB Highbay 2

    NASA Image and Video Library

    2017-04-26

    A flatbed truck carrying the Orion heat shield from Exploration Flight Test-1, prepares to back into High Bay 2 in the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida. The heat shield was moved from the Launch Abort System Facility. The heat shield is being transferred from the Orion Program to the Ground Systems Development and Operations Program, Landing and Recovery Operations. In the VAB, the heat shield will be integrated with the Orion ground test article and used for future underway recovery testing.

  6. Evaluation of dispersion strengthened nickel-base alloy heat shields for space shuttle application

    NASA Technical Reports Server (NTRS)

    Johnson, R., Jr.; Killpatrick, D. H.

    1975-01-01

    The design, fabrication, and testing of a full-size, full-scale TD Ni-20Cr heat shield test array in simulated mission environments is described along with the design and fabrication of two additional full-size, full-scale test arrays to be tested in flowing gas test facilities at the NASA Langley Research Center. Cost and reusability evaluations of TD Ni-20Cr heat shield systems are presented, and weight estimates of a TD Ni-20Cr heat shield system for use on a shuttle orbiter vehicle are made. Safe-line expectancy of a TD Ni-20Cr heat shield system is assessed. Non-destructive test techniques are evaluated to determine their effectiveness in quality assurance checks of TD Ni-20Cr components such as heat shields, heat shield supports, close-out panels, formed cover strips, and edge seals. Results of tests on a braze reinforced full-scale, subsize panel are included. Results show only minor structural degradation in the main TD Ni-20Cr heat shields of the test array during simulated mission test cycles.

  7. Design and Laboratory Validation of a Capacitive Sensor for Measuring the Recession of Thin-Layered Ablator

    NASA Technical Reports Server (NTRS)

    Noffz, Gregory K.; Bowman, Michael P.

    1996-01-01

    Flight vehicles are typically instrumented with subsurface thermocouples to estimate heat transfer at the surface using inverse analysis procedures. If the vehicle has an ablating heat shield, however, temperature time histories from subsurface thermocouples no longer provide enough information to estimate heat flux at the surface. In this situation, the geometry changes and thermal energy leaves the surface in the form of ablation products. The ablation rate is required to estimate heat transfer to the surface. A new concept for a capacitive sensor has been developed to measure ablator depth using the ablator's dielectric effect on a capacitor's fringe region. Relying on the capacitor's fringe region enables the gage to be flush mounted in the vehicle's permanent structure and not intrude into the ablative heat shield applied over the gage. This sensor's design allows nonintrusive measurement of the thickness of dielectric materials, in particular, the recession rates of low-temperature ablators applied in thin (0.020 to 0.060 in. (0.05 to 0.15 mm)) layers. Twenty capacitive gages with 13 different sensing element geometries were designed, fabricated, and tested. A two-dimensional finite-element analysis was performed on several candidate geometries. Calibration procedures using ablator-simulating shims are described. A one-to-one correspondence between system output and dielectric material thickness was observed out to a thickness of 0.055 in. (1.4 mm) for a material with a permittivity about three times that of air or vacuum. A novel method of monitoring the change in sensor capacitance was developed. This technical memorandum suggests further improvements in gage design and fabrication techniques.

  8. Family System of Advanced Charring Ablators for Planetary Exploration Missions

    NASA Technical Reports Server (NTRS)

    Congdon, William M.; Curry, Donald M.

    2005-01-01

    Advanced Ablators Program Objectives: 1) Flight-ready(TRL-6) ablative heat shields for deep-space missions; 2) Diversity of selection from family-system approach; 3) Minimum weight systems with high reliability; 4) Optimized formulations and processing; 5) Fully characterized properties; and 6) Low-cost manufacturing. Definition and integration of candidate lightweight structures. Test and analysis database to support flight-vehicle engineering. Results from production scale-up studies and production-cost analyses.

  9. Ablation dynamics - from absorption to heat accumulation/ultra-fast laser matter interaction

    NASA Astrophysics Data System (ADS)

    Kramer, Thorsten; Remund, Stefan; Jäggi, Beat; Schmid, Marc; Neuenschwander, Beat

    2018-05-01

    Ultra-short laser radiation is used in manifold industrial applications today. Although state-of-the-art laser sources are providing an average power of 10-100 W with repetition rates of up to several megahertz, most applications do not benefit from it. On the one hand, the processing speed is limited to some hundred millimeters per second by the dynamics of mechanical axes or galvanometric scanners. On the other hand, high repetition rates require consideration of new physical effects such as heat accumulation and shielding that might reduce the process efficiency. For ablation processes, process efficiency can be expressed by the specific removal rate, ablated volume per time, and average power. The analysis of the specific removal rate for different laser parameters, like average power, repetition rate or pulse duration, and process parameters, like scanning speed or material, can be used to find the best operation point for microprocessing applications. Analytical models and molecular dynamics simulations based on the so-called two-temperature model reveal the causes for the appearance of limiting physical effects. The findings of models and simulations can be used to take advantage and optimize processing strategies.

  10. Boeing CST-100 Starliner Base Heat Shield Installation

    NASA Image and Video Library

    2018-03-15

    On March 15, the base heat shield for Boeing’s CST-100 Starliner was freshly installed on the bottom of Spacecraft 1 in the High Bay of the Commercial Crew and Cargo Processing Facility at Kennedy Space Center. This is the spacecraft that will fly during the Pad Abort Test. The next step involves installation of the back shells and forward heat shield, and then the crew module will be mated to the service module for a fit check. Finally, the vehicle will head out to White Sands Missile Range in New Mexico for testing.

  11. Orion EFT-1 Heat Shield Offload from Truck onto Foam Pads (Dunna

    NASA Image and Video Library

    2017-04-27

    The Orion heat shield from Exploration Flight Test-1 has arrived in High Bay 2 of the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida. The heat shield is being transferred from the Orion Program to the Ground Systems Development and Operations Program, Landing and Recovery Operations. In the VAB, the heat shield will be integrated with the Orion ground test article and used for future underway recovery testing.

  12. Orion EFT-1 Heat Shield Offload from Truck onto Foam Pads (Dunna

    NASA Image and Video Library

    2017-04-27

    Inside High Bay 2 in the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida, the Orion heat shield from Exploration Flight Test-1 is secured on foam blocks. The heat shield is being transferred from the Orion Program to the Ground Systems Development and Operations Program, Landing and Recovery Operations. In the VAB, the heat shield will be integrated with the Orion ground test article and used for future underway recovery testing.

  13. Heat shield manifold system for a midframe case of a gas turbine engine

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Mayer, Clinton A.; Eng, Jesse; Schopf, Cheryl A.

    A heat shield manifold system for an inner casing between a compressor and turbine assembly is disclosed. The heat shield manifold system protects the outer case from high temperature compressor discharge air, thereby enabling the outer case extending between a compressor and a turbine assembly to be formed from less expensive materials than otherwise would be required. In addition, the heat shield manifold system may be configured such that compressor bleed air is passed from the compressor into the heat shield manifold system without passing through a conventional flange to flange joint that is susceptible to leakage.

  14. Gamma heating in reflector heat shield of gas core reactor

    NASA Technical Reports Server (NTRS)

    Lofthouse, J. H.; Kunze, J. F.; Young, T. E.; Young, R. C.

    1972-01-01

    Heating rate measurements made in a mock-up of a BeO heat shield for a gas core nuclear rocket engine yields results nominally a factor of two greater than calculated by two different methods. The disparity is thought to be caused by errors in neutron capture cross sections and gamma spectra from the low cross-section elements, D, O, and Be.

  15. Compression Pad Cavity Heating Augmentation on Orion Heat Shield

    NASA Technical Reports Server (NTRS)

    Hollis, Brian R.

    2011-01-01

    An experimental study has been conducted to assess the effects of compression pad cavities on the aeroheating environment of the Project Orion Crew Exploration Vehicle heat shield. Testing was conducted in Mach 6 and 10 perfect-gas wind tunnels to obtain heating measurements in and around the compression pads cavities using global phosphor thermography. Data were obtained over a wide range of Reynolds numbers that produced laminar, transitional, and turbulent flow within and downstream of the cavities. The effects of cavity dimensions on boundary-layer transition and heating augmentation levels were studied. Correlations were developed for transition onset and for the average cavity-heating augmentation.

  16. Orion EFT-1 Heat Shield Offload from Truck onto Foam Pads (Dunna

    NASA Image and Video Library

    2017-04-27

    Inside High Bay 2 in the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida, workers help prepare the Orion heat shield from Exploration Flight Test-1 for unloading off its transporter. The heat shield is being transferred from the Orion Program to the Ground Systems Development and Operations Program, Landing and Recovery Operations. In the VAB, the heat shield will be integrated with the Orion ground test article and used for future underway recovery testing.

  17. Orion EFT-1 Heat Shield Offload from Truck onto Foam Pads (Dunna

    NASA Image and Video Library

    2017-04-27

    Inside High Bay 2 in the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida, a worker helps prepare the Orion heat shield from Exploration Flight Test-1 for unloading off its transporter. The heat shield is being transferred from the Orion Program to the Ground Systems Development and Operations Program, Landing and Recovery Operations. In the VAB, the heat shield will be integrated with the Orion ground test article and used for future underway recovery testing.

  18. Orion EFT-1 Heat Shield Move from LASF to VAB Highbay 2

    NASA Image and Video Library

    2017-04-26

    The Orion heat shield from Exploration Flight Test-1, secured on a transporter, departs the Launch Abort System Facility at NASA's Kennedy Space Center in Florida, for its move to the Vehicle Assembly Building (VAB). The heat shield is being transferred from the Orion Program to the Ground Systems Development and Operations Program, Landing and Recovery Operations. In the VAB, the heat shield will be integrated with the Orion ground test article and used for future underway recovery testing.

  19. Orion EFT-1 Heat Shield Move from LASF to VAB Highbay 2

    NASA Image and Video Library

    2017-04-26

    Inside the Launch Abort System Facility at NASA's Kennedy Space Center in Florida, the Orion heat shield from Exploration Flight Test-1 is being prepared for its move to the Vehicle Assembly Building (VAB). The heat shield is being transferred from the Orion Program to the Ground Systems Development and Operations Program, Landing and Recovery Operations. In the VAB, the heat shield will be integrated with the Orion ground test article and used for future underway recovery testing.

  20. Heat flow from the Liberian Precambrian Shield

    NASA Astrophysics Data System (ADS)

    Sass, J. H.; Behrendt, J. C.

    1980-06-01

    Uncorrected heat flow in iron formation rocks from three areas within the Liberian part of the West African Shield ranges from 50 to more than 80 mW m-2. When corrections are applied for topography and refraction, the range of heat flow is narrowed to between 38 and 42 mW m-2. In comparison with heat flows from other parts of the West African Craton, these values are consistent with preliminary results from Ghana (42±8 mW m-2) and Nigeria (38±2 mW m-2) but are somewhat higher than values from Niger (20 mW m-2) and neighboring Sierra Leone (26 mW m-2). The Liberian values are significantly lower than the heat flow offshore in the equatorial Atlantic Ocean (58±8 m W m-2), suggesting large lateral temperature gradients within the lithosphere near the coast. Values of heat production from outcrops of crystalline basement rocks near the holes are between 2 and 2.3 /μW m-3. A heat-flow/heat-production relation cannot be established because of the small range of values; however, assuming a `characteristic depth' of 8 km (similar to the North American Craton) the reduced heat flow of from 20 to 25 mW m-2 is consistent with that from other Precambrian shields.

  1. Orion EFT-1 Heat Shield Offload from Truck onto Foam Pads (Dunna

    NASA Image and Video Library

    2017-04-27

    Inside High Bay 2 in the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida, a worker monitors the progress as a crane lowers the Orion heat shield from Exploration Flight Test-1 onto foam blocks. The heat shield is being transferred from the Orion Program to the Ground Systems Development and Operations Program, Landing and Recovery Operations. In the VAB, the heat shield will be integrated with the Orion ground test article and used for future underway recovery testing.

  2. Orion EFT-1 Heat Shield Offload from Truck onto Foam Pads (Dunna

    NASA Image and Video Library

    2017-04-27

    Inside High Bay 2 in the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida, workers monitor the progress as a crane lowers the Orion heat shield from Exploration Flight Test-1 onto foam blocks. The heat shield is being transferred from the Orion Program to the Ground Systems Development and Operations Program, Landing and Recovery Operations. In the VAB, the heat shield will be integrated with the Orion ground test article and used for future underway recovery testing.

  3. Orion EFT-1 Heat Shield Offload from Truck onto Foam Pads (Dunna

    NASA Image and Video Library

    2017-04-27

    Inside High Bay 2 in the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida, a crane is attached to the Orion heat shield from Exploration Flight Test-1 for unloading off its transporter. The heat shield is being transferred from the Orion Program to the Ground Systems Development and Operations Program, Landing and Recovery Operations. In the VAB, the heat shield will be integrated with the Orion ground test article and used for future underway recovery testing.

  4. Orion EFT-1 Heat Shield Move from LASF to VAB Highbay 2

    NASA Image and Video Library

    2017-04-26

    Inside the Launch Abort System Facility at NASA's Kennedy Space Center in Florida, the Orion heat shield from Exploration Flight Test-1 is secured on a transporter and ready for its move to the Vehicle Assembly Building (VAB). The heat shield is being transferred from the Orion Program to the Ground Systems Development and Operations Program, Landing and Recovery Operations. In the VAB, the heat shield will be integrated with the Orion ground test article and used for future underway recovery testing.

  5. Orion EFT-1 Heat Shield Move from LASF to VAB Highbay 2

    NASA Image and Video Library

    2017-04-26

    Inside the Launch Abort System Facility at NASA's Kennedy Space Center in Florida, the Orion heat shield from Exploration Flight Test-1 is being loaded onto a transporter for its move to the Vehicle Assembly Building (VAB). The heat shield is being transferred from the Orion Program to the Ground Systems Development and Operations Program, Landing and Recovery Operations. In the VAB, the heat shield will be integrated with the Orion ground test article and used for future underway recovery testing.

  6. Orion EFT-1 Heat Shield Move from LASF to VAB Highbay 2

    NASA Image and Video Library

    2017-04-26

    Inside the Launch Abort System Facility at NASA's Kennedy Space Center in Florida, a crane lowers the Orion heat shield from Exploration Flight Test-1 onto a transporter for its move to the Vehicle Assembly Building (VAB). The heat shield is being transferred from the Orion Program to the Ground Systems Development and Operations Program, Landing and Recovery Operations. In the VAB, the heat shield will be integrated with the Orion ground test article and used for future underway recovery testing.

  7. Numerical method of carbon-based material ablation effects on aero-heating for half-sphere

    NASA Astrophysics Data System (ADS)

    Wang, Jiang-Feng; Li, Jia-Wei; Zhao, Fa-Ming; Fan, Xiao-Feng

    2018-05-01

    A numerical method of aerodynamic heating with material thermal ablation effects for hypersonic half-sphere is presented. A surface material ablation model is provided to analyze the ablation effects on aero-thermal properties and structural heat conduction for thermal protection system (TPS) of hypersonic vehicles. To demonstrate its capability, applications for thermal analysis of hypersonic vehicles using carbonaceous ceramic ablators are performed and discussed. The numerical results show the high efficiency and validation of the method developed in thermal characteristics analysis of hypersonic aerodynamic heating.

  8. Regolith-Derived Heat Shield for Planetary Body Entry and Descent System with In-Situ Fabrication

    NASA Technical Reports Server (NTRS)

    Hogue, Michael D.; Mueller, Robert P.; Sibille, Laurent; Hintze, Paul E.; Rasky, Daniel J.

    2012-01-01

    High-mass planetary surface access is one of NASA's Grand Challenges involving entry, descent, and landing (EDL). Heat shields fabricated in-situ can provide a thermal protection system for spacecraft that routinely enter a planetary atmosphere. Fabricating the heat shield from extraterrestrial regolith will avoid the costs of launching the heat shield mass from Earth. This project will investigate three methods to fabricate heat shield using extraterrestrial regolith.

  9. Orion EFT-1 Heat Shield Offload from Truck onto Foam Pads (Dunna

    NASA Image and Video Library

    2017-04-27

    Inside High Bay 2 in the Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center in Florida, a crane lifts the Orion heat shield from Exploration Flight Test-1 up off its transporter. It will be lowered onto foam blocks. The heat shield is being transferred from the Orion Program to the Ground Systems Development and Operations Program, Landing and Recovery Operations. In the VAB, the heat shield will be integrated with the Orion ground test article and used for future underway recovery testing.

  10. On thermal stress failure of the SNAP-19A RTG heat shield

    NASA Technical Reports Server (NTRS)

    Pitts, W. C.; Anderson, L. A.

    1974-01-01

    Results of a study on thermal stress problems in an amorphous graphite heat shield that is part of the launch-abort protect system for the SNAP-19A radio-isotope thermoelectric generators (RTG) that will be used on the Viking Mars Lander are presended. The first result is from a thermal stress analysis of a full-scale RTG heat source that failed to survive a suborbital entry flight test, possibly due to thermal stress failure. It was calculated that the maximum stress in the heat shield was only 50 percent of the ultimate strength of the material. To provide information on the stress failure criterion used for this calculation, some heat shield specimens were fractured under abort entry conditions in a plasma arc facility. It was found that in regions free of stress concentrations the POCO graphite heat shield material did fracture when the local stress reached the ultimate uniaxial stress of the material.

  11. Regolith-Derived Heat Shield for Planetary Body Entry and Descent System with In-Situ Fabrication

    NASA Technical Reports Server (NTRS)

    Hogue, Michael D.; Mueller, Robert P.; Sibille, Laurent; Hintze, Paul E.; Rasky, Daniel J.

    2012-01-01

    High-mass planetary surface access is one of NASA's Grand Challenges involving entry, descent, and landing (EDL). Heat shields fabricated in-situ can provide a thermal protection system for spacecraft that routinely enter a planetary atmosphere. Fabricating the heat shield from extraterrestrial regolith will avoid the costs of launching the heat shield mass from Earth. This project investigated three methods to fabricate heat shield using extraterrestrial regolith and performed preliminary work on mission architectures.

  12. An Approximate Ablative Thermal Protection System Sizing Tool for Entry System Design

    NASA Technical Reports Server (NTRS)

    Dec, John A.; Braun, Robert D.

    2005-01-01

    A computer tool to perform entry vehicle ablative thermal protection systems sizing has been developed. Two options for calculating the thermal response are incorporated into the tool. One, an industry-standard, high-fidelity ablation and thermal response program was integrated into the tool, making use of simulated trajectory data to calculate its boundary conditions at the ablating surface. Second, an approximate method that uses heat of ablation data to estimate heat shield recession during entry has been coupled to a one-dimensional finite-difference calculation that calculates the in-depth thermal response. The in-depth solution accounts for material decomposition, but does not account for pyrolysis gas energy absorption through the material. Engineering correlations are used to estimate stagnation point convective and radiative heating as a function of time. The sizing tool calculates recovery enthalpy, wall enthalpy, surface pressure, and heat transfer coefficient. Verification of this tool is performed by comparison to past thermal protection system sizings for the Mars Pathfinder and Stardust entry systems and calculations are performed for an Apollo capsule entering the atmosphere at lunar and Mars return speeds.

  13. An Approximate Ablative Thermal Protection System Sizing Tool for Entry System Design

    NASA Technical Reports Server (NTRS)

    Dec, John A.; Braun, Robert D.

    2006-01-01

    A computer tool to perform entry vehicle ablative thermal protection systems sizing has been developed. Two options for calculating the thermal response are incorporated into the tool. One, an industry-standard, high-fidelity ablation and thermal response program was integrated into the tool, making use of simulated trajectory data to calculate its boundary conditions at the ablating surface. Second, an approximate method that uses heat of ablation data to estimate heat shield recession during entry has been coupled to a one-dimensional finite-difference calculation that calculates the in-depth thermal response. The in-depth solution accounts for material decomposition, but does not account for pyrolysis gas energy absorption through the material. Engineering correlations are used to estimate stagnation point convective and radiative heating as a function of time. The sizing tool calculates recovery enthalpy, wall enthalpy, surface pressure, and heat transfer coefficient. Verification of this tool is performed by comparison to past thermal protection system sizings for the Mars Pathfinder and Stardust entry systems and calculations are performed for an Apollo capsule entering the atmosphere at lunar and Mars return speeds.

  14. Heat flow from the Liberian precambrian shield

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Sass, J.H.; Behrendt, J.C.

    1980-06-10

    Uncorrected heat flow in iron formation rocks from three areas within the Liberian part of the West African Shield ranges from 50 to more than 80 mW m/sup -2/. When corrections are applied for topography and refraction, the range of heat flow is narrowed to between 38 and 42 mW m/sup -2/. In comparison with heat flows from other parts of the West African Craton, these values are consistent with preliminary results from Ghana (42 +- 8 mW m/sup -2/) and Nigeria (38 +- 2 mW /sup -2/) but are somewhat higher than values from Niger (20 mW m/sup -2/)more » and neighboring Sierra Leone (26 mW m/sup -2/). The Liberian values are significantly lower than the heat flow offshore in the equatorial Atlantic Ocean (58 +- 8 mW m/sup -2/), suggesting large lateral temperature gradients within the lithosphere near the coast. Values of heat production from outcrops of crystalline basement rocks near the holes are between 2 and 2.3 ..mu..W m/sup -3/. A heat-flow/heat-production relation cannot be established because of the small range of values; however, assuming a 'characteristic depth' of 8 km (similar to the North American Craton) the reduced heat flow of from 20 to 25 mW m/sup -2/ is consistent with that from other Precambrian shields.« less

  15. Effect of nonparallel placement of in-circle bipolar radiofrequency ablation probes on volume of tissue ablated with heat sink.

    PubMed

    Pillai, Krishna; Al-Alem, Ihssan; Akhter, Javed; Chua, Terence C; Shehata, Mena; Morris, David L

    2015-06-01

    Percutaneous bipolar radiofrequency ablation (RFA) is a minimally invasive technique for treating liver tumors. It is not always possible to insert the bipolar probes parallel to each other on either side of tumor, since it restricts maneuverability away from vital structures or ablate certain tumor shape. Therefore, we investigated how nonparallel placement of probes affected ablation. Bipolar RFA in parallel and in divergent positions were submerged in tissue model (800 mL egg white) at 37°C and ablated. Temperature probes, T1 and T2 were placed 8.00 mm below the tip of the probes, T3 in between the probe coil elements and T4 and T5 at water inlet and outlet, respectively. Both models with heat sink (+HS) and without (-HS) were investigated. The mean ablated tissue volume, mass, density and height increased linearly with unit angle increase for -HS model. With +HS, a smaller increase in mean volume and mass, a slightly greater increase in mean density but a reduction in height of tissue was seen. The mean ablation time and duration of maximum temperature with +HS was slightly larger, compared with -HS, while -HS ablated at a slightly higher temperature. The heat sink present was minimal for probes in parallel position compared to nonparallel positions. Divergence from parallel insertion of bipolar RFA probes increased the mean volume, mass, and density of tissue ablated. However, the presence of large heat sinks may limit the application of this technique, when tumors border on larger vessels. © The Author(s) 2014.

  16. Pressure Venting Tests of Phenolic Impregnated Carbon Ablator (PICA)

    NASA Technical Reports Server (NTRS)

    Blosser, Max L.; Knutson, Jeffrey R.

    2015-01-01

    A series of tests was devised to investigate the pressure venting behavior of one of the candidate ablators for the Orion capsule heat shield. Three different specimens of phenolic impregnated carbon ablator (PICA) were instrumented with internal pressure taps and subjected to rapid pressure changes from near vacuum to one atmosphere and simulated Orion ascent pressure histories. The specimens vented rapidly to ambient pressure and sustained no detectable damage during testing. Peak pressure differences through the thickness of a 3-inch-thick specimen were less than 1 psi during a simulated ascent pressure history.

  17. Woven Thermal Protection System Based Heat-shield for Extreme Entry Environments Technology (HEEET)

    NASA Technical Reports Server (NTRS)

    Ellerby, Donald; Venkatapathy, Ethiraj; Stackpoole, Margaret; Chinnapongse, Ronald; Munk, Michelle; Dillman, Robert; Feldman, Jay; Prabhu, Dinesh; Beerman, Adam

    2013-01-01

    NASA's future robotic missions utilizing an entry system into Venus and the outer planets, namely, Saturn, Uranus, Neptune, result in extremely high entry conditions that exceed the capabilities of state of the art low to mid density ablators such as PICA or Avcoat. Therefore mission planners typically assume the use of a fully dense carbon phenolic heat shield similar to what was flown on Pioneer Venus and Galileo. Carbon phenolic is a robust TPS material however its high density and relatively high thermal conductivity constrain mission planners to steep entries, with high heat fluxes and pressures and short entry durations, in order for CP to be feasible from a mass perspective. The high entry conditions pose challenges for certification in existing ground based test facilities and the longer-term sustainability of CP will continue to pose challenges. In 2012 the Game Changing Development Program (GCDP) in NASA's Space Technology Mission Directorate funded NASA ARC to investigate the feasibility of a Woven Thermal Protection System (WTPS) to meet the needs of NASA's most challenging entry missions. This project was highly successful demonstrating that a Woven TPS solution compares favorably to CP in performance in simulated reentry environments and provides the opportunity to manufacture graded materials that should result in overall reduced mass solutions and enable a much broader set of missions than does CP. Building off the success of the WTPS project GCDP has funded a follow on project to further mature and scale up the WTPS concept for insertion into future NASA robotic missions. The matured WTPS will address the CP concerns associated with ground based test limitations and sustainability. This presentation will briefly discuss results from the WTPS Project and the plans for WTPS maturation into a heat-shield for extreme entry environment.

  18. Woven Thermal Protection System Based Heat-shield for Extreme Entry Environments Technology (HEEET)

    NASA Technical Reports Server (NTRS)

    Chinnapongse, Ronald; Ellerbe, Donald; Stackpoole, Maragaret; Venkatapathy, Ethiraj; Beerman, Adam; Feldman, Jay; Peterson Keith; Prabhu, Dinesh; Dillman, Robert; Munk, Michelle

    2013-01-01

    NASA's future robotic missions utilizing an entry system into Venus and the outer planets, namely, Saturn, Uranus, Neptune, result in extremely severe entry conditions that exceed the capabilities of state of the art low to mid density ablators such as PICA or Avcoat. Therefore mission planners typically assume the use of a fully dense carbon phenolic heat shield similar to what was flown on Pioneer Venus and Galileo. Carbon phenolic (CP) is a robust TPS material however its high density and relatively high thermal conductivity constrain mission planners to steep entries, with high heat fluxes and pressures and short entry durations, in order for CP to be feasible from a mass perspective. The high entry conditions pose challenges for certification in existing ground based test facilities and the longer-­-term sustainability of CP will continue to pose challenges. In 2012 the Game Changing Development Program (GCDP) in NASA's Space Technology Mission Directorate funded NASA ARC to investigate the feasibility of a Woven Thermal Protection System (WTPS) to meet the needs of NASA's most challenging entry missions. This project was highly successful demonstrating that a Woven TPS solution compares favorably to CP in performance in simulated reentry environments and provides the opportunity to manufacture graded materials that should result in overall reduced mass solutions and enable a much broader set of missions than does CP. Building off the success of the WTPS project GCDP has funded a follow on project to further mature and scale up the WTPS concept for insertion into future NASA robotic missions. The matured WTPS will address the CP concerns associated with ground based test limitations and sustainability. This presentation will briefly discuss results from the WTPS Project and the plans for WTPS maturation into a heat-­-shield for extreme entry environment.

  19. Simulated Reentry Heating by Torching

    NASA Technical Reports Server (NTRS)

    Harvey, Gale A.

    2008-01-01

    The two first order reentry heating parameters are peak heating flux (W/cm2) and peak heat load (kJ/cm2). Peak heating flux (and deceleration, gs) is higher for a ballistic reentry and peak heat load is higher for a lifting reentry. Manned vehicle reentries are generally lifting reentries at nominal 1-5 gs so that personnel will not be crushed by high deceleration force. A few off-nominal manned reentries have experienced 8 or more gs with corresponding high heating flux (but below nominal heat load). The Shuttle Orbiter reentries provide about an order of magnitude difference in peak heating flux at mid-bottom (TPS tiles, approximately 6 W/cm2 or 5 BTU/ft2- sec) and leading edge (RCC, approximately 60 W/cm2 or 50 BTU/ft2- sec). Orion lunar return and Mars sample lander are of the same order of magnitude as orbiter leading edge peak heat loads. Flight temperature measurements are available for some orbiter TPS tile and RCC locations. Return-to-Flight on-orbit tile-repair-candidate-material-heating performance was evaluated by matching propane torch heating of candidate-materials temperatures at several depths to orbiter TPS tile flight-temperatures. Char and ash characteristics, heat expansion, and temperature histories at several depths of the cure-in-place ablator were some of the TPS repair material performance characteristics measured. The final char surface was above the initial surface for the primary candidate (silicone based) material, in contrast to a receded surface for the Apollo-type ablative heat shield material. Candidate TPS materials for Orion CEV (LEO and lunar return), and for Mars sample lander are now being evaluated. Torching of a candidate ablator material, PICA, was performed to match the ablation experienced by the STARDUST PICA heat shield. Torching showed that the carbon fiberform skeleton in a sample of PICA was inhomogeneous in that sample, and allowed measurements (of the clumps and voids) of the inhomogeneity. Additional reentry

  20. Laser ablation under different electron heat conduction models in inertial confinement fusion

    NASA Astrophysics Data System (ADS)

    Li, Shuanggui; Ren, Guoli; Huo, Wen Yi

    2018-06-01

    In this paper, we study the influence of three different electron heat conduction models on the laser ablation of gold plane target. Different from previous studies, we concentrate on the plasma conditions, the conversion efficiency from laser into soft x rays and the scaling relation of mass ablation, which are relevant to hohlraum physics study in indirect drive inertial confinement fusion. We find that the simulated electron temperature in corona region is sensitive to the electron heat conduction models. For different electron heat conduction models, there are obvious differences in magnitude and spatial profile of electron temperature. For the flux limit model, the calculated conversion efficiency is sensitive to flux limiters. In the laser ablation of gold, most of the laser energies are converted into x rays. So the scaling relation of mass ablation rate is quite different from that of low Z materials.

  1. Isotherm Sensor Calibration Program for Mars Science Laboratory Heat Shield Flight Data Analysis

    NASA Technical Reports Server (NTRS)

    Santos, Jose A.; Oishi, Tomo; Martinez, Ed R.

    2011-01-01

    Seven instrumented sensor plugs were installed on the Mars Science Laboratory heat shield in December 2008 as part of the Mars Science Laboratory Entry, Descent, and Landing Instrumentation (MEDLI) project. These sensor plugs contain four in-depth thermocouples and one Hollow aErothermal Ablation and Temperature (HEAT) sensor. The HEAT sensor follows the time progression of a 700 C isotherm through the thickness of a thermal protection system (TPS) material. The data can be used to infer char depth and, when analyzed in conjunction with the thermocouple data, the thermal gradient through the TPS material can also be determined. However, the uncertainty on the isotherm value is not well defined. To address this uncertainty, a team at NASA Ames Research Center is carrying out a HEAT sensor calibration test program. The scope of this test program is described, and initial results from experiments conducted in the laboratory to study the isotherm temperature of the HEAT sensor are presented. Data from the laboratory tests indicate an isotherm temperature of 720 C 60 C. An overview of near term arc jet testing is also given, including preliminary data from 30.48cm 30.48cm PICA panels instrumented with two MEDLI sensor plugs and tested in the NASA Ames Panel Test Facility. Forward work includes analysis of the arc jet test data, including an evaluation of the isotherm value based on the instant in time when it reaches a thermocouple depth.

  2. Development of lightweight ceramic ablators and arc-jet test results

    NASA Technical Reports Server (NTRS)

    Tran, Huy K.

    1994-01-01

    Lightweight ceramic ablators (LCA's) were recently developed at Ames to investigate the use of low density fibrous substrates and organic resins as high temperature, high strength ablative heat shields. Unlike the traditional ablators, LCA's use porous ceramic/carbon fiber matrices as substrates for structural support, and polymeric resins as fillers. Several substrates and resins were selected for the initial studies, and the best performing candidates were further characterized. Three arcjet tests were conducted to determine the LCA's thermal performance and ablation characteristics in a high enthalpy, hypersonic flow environment. Mass loss and recession measurements were obtained for each sample at post test, and the recession rates were determined from high speed motion films. Surface temperatures were also obtained from optical pyrometers.

  3. Experimental Evaluation of the Heat Sink Effect in Hepatic Microwave Ablation.

    PubMed

    Ringe, Kristina I; Lutat, Carolin; Rieder, Christian; Schenk, Andrea; Wacker, Frank; Raatschen, Hans-Juergen

    2015-01-01

    To demonstrate and quantify the heat sink effect in hepatic microwave ablation (MWA) in a standardized ex vivo model, and to analyze the influence of vessel distance and blood flow on lesion volume and shape. 108 ex vivo MWA procedures were performed in freshly harvested pig livers. Antennas were inserted parallel to non-perfused and perfused (700,1400 ml/min) glass tubes (diameter 5mm) at different distances (10, 15, 20mm). Ablation zones (radius, area) were analyzed and compared (Kruskal-Wallis Test, Dunn's multiple comparison Test). Temperature changes adjacent to the tubes were measured throughout the ablation cycle. Maximum temperature decreased significantly with increasing flow and distance (p<0.05). Compared to non-perfused tubes, ablation zones were significantly deformed by perfused tubes within 15 mm distance to the antenna (p<0.05). At a flow rate of 700 ml/min ablation zone radius was reduced to 37.2% and 80.1% at 10 and 15 mm tube distance, respectively; ablation zone area was reduced to 50.5% and 89.7%, respectively. Significant changes of ablation zones were demonstrated in a pig liver model. Considerable heat sink effect was observed within a diameter of 15 mm around simulated vessels, dependent on flow rate. This has to be taken into account when ablating liver lesions close to vessels.

  4. Experimental Evaluation of the Heat Sink Effect in Hepatic Microwave Ablation

    PubMed Central

    Ringe, Kristina I.; Lutat, Carolin; Rieder, Christian; Schenk, Andrea; Wacker, Frank; Raatschen, Hans-Juergen

    2015-01-01

    Purpose To demonstrate and quantify the heat sink effect in hepatic microwave ablation (MWA) in a standardized ex vivo model, and to analyze the influence of vessel distance and blood flow on lesion volume and shape. Materials and Methods 108 ex vivo MWA procedures were performed in freshly harvested pig livers. Antennas were inserted parallel to non-perfused and perfused (700,1400 ml/min) glass tubes (diameter 5mm) at different distances (10, 15, 20mm). Ablation zones (radius, area) were analyzed and compared (Kruskal-Wallis Test, Dunn’s multiple comparison Test). Temperature changes adjacent to the tubes were measured throughout the ablation cycle. Results Maximum temperature decreased significantly with increasing flow and distance (p<0.05). Compared to non-perfused tubes, ablation zones were significantly deformed by perfused tubes within 15mm distance to the antenna (p<0.05). At a flow rate of 700ml/min ablation zone radius was reduced to 37.2% and 80.1% at 10 and 15mm tube distance, respectively; ablation zone area was reduced to 50.5% and 89.7%, respectively. Conclusion Significant changes of ablation zones were demonstrated in a pig liver model. Considerable heat sink effect was observed within a diameter of 15mm around simulated vessels, dependent on flow rate. This has to be taken into account when ablating liver lesions close to vessels. PMID:26222431

  5. A comparison of direct heating during radiofrequency and microwave ablation in ex vivo liver

    PubMed Central

    Andreano, Anita; Brace, Christopher L

    2012-01-01

    Purpose To determine the magnitude and spatial distribution of temperature elevations when using 480 kHz RF and 2.45 GHz microwave energy in ex vivo liver models. Materials and Methods A total of sixty heating cycles (20 s at 90 W) were performed in normal, RF ablated and microwave ablated liver tissues (n=10 RF and n=10 microwave in each tissue type). Heating cycles were performed using a 480 kHz generator and 3 cm cooled-tip electrode (RF) or a 2.45 GHz generator and 14-gauge monopole (microwave) and designed to isolate direct heating from each energy type. Tissue temperatures were measured using fiberoptic thermosensors 5, 10 and 15 mm radially from the ablation applicator at the depth of maximal heating. Power delivered, sensor location, heating rates and maximal temperatures were compared using mixed effects regression models. Results No significant differences were noted in mean power delivered or thermosensor locations between RF and microwave heating groups (P>0.05). Microwaves produced significantly more rapid heating than RF at 5, 10 and 15mm in normal tissue (3.0 vs. 0.73, 0.85 vs. 0.21 and 0.17 vs. 0.09 °C/s; P<.05); and at 5 and 10mm in ablated tissues (2.3 ± 1.4 vs. 0.7 ± 0.3, 0.5 ± 0.3 vs. 0.2 ± 0.0 C/s, P<.05). The radial depth of heating was approximately 5mm greater for microwaves than RF. Conclusions Direct heating obtained with 2.45 GHz microwave energy using a single needle-like applicator is faster and covers a larger volume of tissue than 480 kHz RF energy. Keywords: microwave ablation, direct heating, thermal ablation PMID:22572764

  6. Laser heating and ablation at high repetition rate in thermal confinement regime

    NASA Astrophysics Data System (ADS)

    Brygo, François; Semerok, A.; Oltra, R.; Weulersse, J.-M.; Fomichev, S.

    2006-09-01

    Laser heating and ablation of materials with low absorption and thermal conductivity (paint and cement) were under experimental and theoretical investigations. The experiments were made with a high repetition rate Q-switched Nd:YAG laser (10 kHz, 90 ns pulse duration and λ = 532 nm). High repetition rate laser heating resulted in pulse per pulse heat accumulation. A theoretical model of laser heating was developed and demonstrated a good agreement between the experimental temperatures measured with the infrared pyrometer and the calculated ones. With the fixed wavelength and laser pulse duration, the ablation threshold fluence of paint was found to depend on the repetition rate and the number of applied pulses. With a high repetition rate, the threshold fluence decreased significantly when the number of applied pulses was increasing. The experimentally obtained thresholds were well described by the developed theoretical model. Some specific features of paint heating and ablation with high repetition rate lasers are discussed.

  7. Diminished tektite ablation in the wake of a swarm

    NASA Technical Reports Server (NTRS)

    Sepri, P.; Chen, K. K.; Okeefe, J. A.

    1981-01-01

    Observations of ablation markings on tektite surfaces reveal that a large variation in aerodynamic heating must have occurred among the members of a swarm during atmospheric entry. In a few cases, the existence of jagged features indicates that these tektite surfaces may have barely reached the melting temperature. Such an observation seems to be incompatible with the necessarily large heating rates suffered by other tektites which exhibit the ring wave melt flow. A reconciliation is proposed in the form of a wake shielding model which is a natural consequence of swarm entry. Calculations indicate that the observed ablation variations are actually possible for swarm entry at greater than escape velocity. This aerodynamic conclusion provides support for the arguments favoring extraterrestrial origin of tektites.

  8. Boeing CST-100 Heat Shield Testing

    NASA Image and Video Library

    2017-05-31

    A heat shield is used during separation test activities with Boeing's Starliner structural test article. The test article is undergoing rigorous qualification testing at the company's Huntington Beach Facility in California. Boeing’s CST-100 Starliner will launch on the Atlas V rocket to the International Space Station as part of NASA’s Commercial Crew Program.

  9. Heat sink phenomenon of bipolar and monopolar radiofrequency ablation observed using polypropylene tubes for vessel simulation.

    PubMed

    Al-Alem, Ihssan; Pillai, Krishna; Akhter, Javed; Chua, Terence C; Morris, David L

    2014-06-01

    Radiofrequency ablation (RFA) is widely used for treating liver tumors; recurrence is common owing to proximity to blood vessels possibly due to the heat sink effect. We seek to investigate this phenomenon using unipolar and bipolar RFA on an egg white tumor tissue model and an animal liver model. Temperature profiles during ablation (with and without vessel simulation) were studied, using both bipolar and unipolar RFA probes by 4 strategically placed temperature leads to monitor temperature profile during ablation. The volume of ablated tissue was also measured. The volume ablated during vessel simulation confirmed the impact of the heat sink phenomenon. The heat sink effect of unipolar RFA was greater compared with bipolar RFA (ratio of volume affected 2:1) in both tissue and liver models. The volume ablated using unipolar RFA was less than the bipolar RFA (ratio of volume ablated = 1:4). Unipolar RFA achieved higher ablation temperatures (122°C vs 98°C). Unipolar RFA resulted in tissue damage beyond the vessel, which was not observed using bipolar RFA. Bipolar RFA ablates a larger tumor volume compared with unipolar RFA, with a single ablation. The impact of heat sink phenomenon in tumor ablation is less so with bipolar than unipolar RFA with sparing of adjacent vessel damage. © The Author(s) 2013.

  10. Regolith Derived Heat Shield for Planetary Body Entry and Descent System with In Situ Fabrication

    NASA Technical Reports Server (NTRS)

    Hogue, Michael D.; Meuller, Robert P.; Sibille, Laurent; Hintze, Paul E.; Rasky, Daniel J.

    2012-01-01

    This NIAC project investigated an innovative approach to provide heat shield protection to spacecraft after launch and prior to each EDL thus potentially realizing significant launch mass savings. Heat shields fabricated in situ can provide a thermal-protection system for spacecraft that routinely enter a planetary atmosphere. By fabricating the heat shield with space resources from materials available on moons and asteroids, it is possible to avoid launching the heat-shield mass from Earth. Regolith has extremely good insulating properties and the silicates it contains can be used in the fabrication and molding of thermal-protection materials. Such in situ developed heat shields have been suggested before by Lewis. Prior research efforts have shown that regolith properties can be compatible with very-high temperature resistance. Our project team is highly experienced in regolith processing and thermal protection systems (TPS). Routine access to space and return from any planetary surface requires dealing with heat loads experienced by the spacecraft during reentry. Our team addresses some of the key issues with the EDL of human-scale missions through a highly innovative investigation of heat shields that can be fabricated in space by using local resources on asteroids and moons. Most space missions are one-way trips, dedicated to placing an asset in space for economical or scientific gain. However, for human missions, a very-reliable heat-shield system is necessary to protect the crew from the intense heat experienced at very high entry velocities of approximately 11 km/s at approximately Mach 33 (Apollo). For a human mission to Mars, the return problem is even more difficult, with predicted velocities of up to 14 km/s, at approximately Mach 42 at the Earth-atmosphere entry. In addition to human return, it is very likely that future space-travel architecture will include returning cargo to the Earth, either for scientific purposes or for commercial reasons

  11. Regolith Derived Heat Shield for Planetary Body Entry and Descent System with In Situ Fabrication

    NASA Technical Reports Server (NTRS)

    Hogue, Michael D.; Mueller, Robert P.; Sibille, Laurent; Hintze, Paul E.; Rasky, Daniel J.

    2013-01-01

    This NIAC project investigated an innovative approach to provide heat shield protection to spacecraft after launch and prior to each EDL thus potentially realizing significant launch mass savings. Heat shields fabricated in situ can provide a thermal-protection system for spacecraft that routinely enter a planetary atmosphere. By fabricating the heat shield with space resources from materials available on moons and asteroids, it is possible to avoid launching the heat-shield mass from Earth. Regolith has extremely good insulating properties and the silicates it contains can be used in the fabrication and molding of thermal-protection materials. Such in situ developed heat shields have been suggested before by Lewis. Prior research efforts have shown that regolith properties can be compatible with very-high temperature resistance. Our project team is highly experienced in regolith processing and thermal protection systems (TPS). Routine access to space and return from any planetary surface requires dealing with heat loads experienced by the spacecraft during reentry. Our team addresses some of the key issues with the EDL of human-scale missions through a highly innovative investigation of heat shields that can be fabricated in space by using local resources on asteroids and moons. Most space missions are one-way trips, dedicated to placing an asset in space for economical or scientific gain. However, for human missions, a very-reliable heat-shield system is necessary to protect the crew from the intense heat experienced at very high entry velocities of approximately 11 km/s at approximately Mach 33 (Apollo). For a human mission to Mars, the return problem is even more difficult, with predicted velocities of up to 14 km/s, at approximately Mach 42 at the Earth-atmosphere entry. In addition to human return, it is very likely that future space-travel architecture will include returning cargo to the Earth, either for scientific purposes or for commercial reasons

  12. Evaluation of the energy transfer in the char zone during ablation. Part 2: In-depth response of ablative composites, volume 1. Ph.D. Thesis, 1975. Final Report

    NASA Technical Reports Server (NTRS)

    Pike, R. W.; Delvalle, E. G.

    1974-01-01

    The decomposition of ablative composites is described along with the transport phenomena of pyrolysis gases which result from the decomposition of these plastics as they flow through the porous char of char-forming ablators. The pyrolysis products are those formed by the thermal degradation of nylon-phenolic resin and silicone elastomer composites. Emphasis is placed on the nature and extent of chemical reactions of the pyrolysis products and the char, along with the energy absorbed by the combined pyrolysis and char zone. Chemical reactions with thermodynamically consistent kinetic data are determined in order to develop a realistic analysis for predicting the thermal performance of ablative heat shields.

  13. Potassium titanyl phosphate laser tissue ablation: development and experimental validation of a new numerical model.

    PubMed

    Elkhalil, Hossam; Akkin, Taner; Pearce, John; Bischof, John

    2012-10-01

    The photoselective vaporization of prostate (PVP) green light (532 nm) laser is increasingly being used as an alternative to the transurethral resection of prostate (TURP) for treatment of benign prostatic hyperplasia (BPH) in older patients and those who are poor surgical candidates. In order to achieve the goals of increased tissue removal volume (i.e., "ablation" in the engineering sense) and reduced collateral thermal damage during the PVP green light treatment, a two dimensional computational model for laser tissue ablation based on available parameters in the literature has been developed and compared to experiments. The model is based on the control volume finite difference and the enthalpy method with a mechanistically defined energy necessary to ablate (i.e., physically remove) a volume of tissue (i.e., energy of ablation E(ab)). The model was able to capture the general trends experimentally observed in terms of ablation and coagulation areas, their ratio (therapeutic index (TI)), and the ablation rate (AR) (mm(3)/s). The model and experiment were in good agreement at a smaller working distance (WD) (distance from the tissue in mm) and a larger scanning speed (SS) (laser scan speed in mm/s). However, the model and experiment deviated somewhat with a larger WD and a smaller SS; this is most likely due to optical shielding and heat diffusion in the laser scanning direction, which are neglected in the model. This model is a useful first step in the mechanistic prediction of PVP based BPH laser tissue ablation. Future modeling efforts should focus on optical shielding, heat diffusion in the laser scanning direction (i.e., including 3D effects), convective heat losses at the tissue boundary, and the dynamic optical, thermal, and coagulation properties of BPH tissue.

  14. Ablation-cooled material removal with ultrafast bursts of pulses

    NASA Astrophysics Data System (ADS)

    Kerse, Can; Kalaycıoğlu, Hamit; Elahi, Parviz; Çetin, Barbaros; Kesim, Denizhan K.; Akçaalan, Önder; Yavaş, Seydi; Aşık, Mehmet D.; Öktem, Bülent; Hoogland, Heinar; Holzwarth, Ronald; Ilday, Fatih Ömer

    2016-09-01

    The use of femtosecond laser pulses allows precise and thermal-damage-free removal of material (ablation) with wide-ranging scientific, medical and industrial applications. However, its potential is limited by the low speeds at which material can be removed and the complexity of the associated laser technology. The complexity of the laser design arises from the need to overcome the high pulse energy threshold for efficient ablation. However, the use of more powerful lasers to increase the ablation rate results in unwanted effects such as shielding, saturation and collateral damage from heat accumulation at higher laser powers. Here we circumvent this limitation by exploiting ablation cooling, in analogy to a technique routinely used in aerospace engineering. We apply ultrafast successions (bursts) of laser pulses to ablate the target material before the residual heat deposited by previous pulses diffuses away from the processing region. Proof-of-principle experiments on various substrates demonstrate that extremely high repetition rates, which make ablation cooling possible, reduce the laser pulse energies needed for ablation and increase the efficiency of the removal process by an order of magnitude over previously used laser parameters. We also demonstrate the removal of brain tissue at two cubic millimetres per minute and dentine at three cubic millimetres per minute without any thermal damage to the bulk.

  15. Ablation-cooled material removal with ultrafast bursts of pulses.

    PubMed

    Kerse, Can; Kalaycıoğlu, Hamit; Elahi, Parviz; Çetin, Barbaros; Kesim, Denizhan K; Akçaalan, Önder; Yavaş, Seydi; Aşık, Mehmet D; Öktem, Bülent; Hoogland, Heinar; Holzwarth, Ronald; Ilday, Fatih Ömer

    2016-09-01

    The use of femtosecond laser pulses allows precise and thermal-damage-free removal of material (ablation) with wide-ranging scientific, medical and industrial applications. However, its potential is limited by the low speeds at which material can be removed and the complexity of the associated laser technology. The complexity of the laser design arises from the need to overcome the high pulse energy threshold for efficient ablation. However, the use of more powerful lasers to increase the ablation rate results in unwanted effects such as shielding, saturation and collateral damage from heat accumulation at higher laser powers. Here we circumvent this limitation by exploiting ablation cooling, in analogy to a technique routinely used in aerospace engineering. We apply ultrafast successions (bursts) of laser pulses to ablate the target material before the residual heat deposited by previous pulses diffuses away from the processing region. Proof-of-principle experiments on various substrates demonstrate that extremely high repetition rates, which make ablation cooling possible, reduce the laser pulse energies needed for ablation and increase the efficiency of the removal process by an order of magnitude over previously used laser parameters. We also demonstrate the removal of brain tissue at two cubic millimetres per minute and dentine at three cubic millimetres per minute without any thermal damage to the bulk.

  16. Supplemental heating of deposition tooling shields

    DOEpatents

    Ohlhausen, James A.; Peebles, Diane E.; Hunter, John A.; Eckelmeyer, Kenneth H.

    2000-01-01

    A method of reducing particle generation from the thin coating deposited on the internal surfaces of a deposition chamber which undergoes temperature variation greater than 100.degree. C. comprising maintaining the temperature variation of the internal surfaces low enough during the process cycle to keep thermal expansion stresses between the coating and the surfaces under 500 MPa. For titanium nitride deposited on stainless steel, this means keeping temperature variations under approximately 70.degree. C. in a chamber that may be heated to over 350.degree. C. during a typical processing operation. Preferably, a supplemental heater is mounted behind the upper shield and controlled by a temperature sensitive element which provides feedback control based on the temperature of the upper shield.

  17. A Reliability Comparison of Classical and Stochastic Thickness Margin Approaches to Address Material Property Uncertainties for the Orion Heat Shield

    NASA Technical Reports Server (NTRS)

    Sepka, Steven A.; McGuire, Mary Kathleen; Vander Kam, Jeremy C.

    2018-01-01

    The Orion Thermal Protection System (TPS) margin process uses a root-sum-square approach with branches addressing trajectory, aerothermodynamics, and material response uncertainties in ablator thickness design. The material response branch applies a bondline temperature reduction between the Avcoat ablator and EA9394 adhesive by 60 C (108 F) from its peak allowed value of 260 C (500 F). This process is known as the Bond Line Temperature Material Margin (BTMM) and is intended to cover material property and performance uncertainties. The value of 60 C (108 F) is a constant, applied at any spacecraft body location and for any trajectory. By varying only material properties in a random (monte carlo) manner, the perl-based script mcCHAR is used to investigate the confidence interval provided by the BTMM. In particular, this study will look at various locations on the Orion heat shield forebody for a guided and an abort (ballistic) trajectory.

  18. A Reliability Comparison of Classical and Stochastic Thickness Margin Approaches to Address Material Property Uncertainties for the Orion Heat Shield

    NASA Technical Reports Server (NTRS)

    Sepka, Steve; Vander Kam, Jeremy; McGuire, Kathy

    2018-01-01

    The Orion Thermal Protection System (TPS) margin process uses a root-sum-square approach with branches addressing trajectory, aerothermodynamics, and material response uncertainties in ablator thickness design. The material response branch applies a bond line temperature reduction between the Avcoat ablator and EA9394 adhesive by 60 C (108 F) from its peak allowed value of 260 C (500 F). This process is known as the Bond Line Temperature Material Margin (BTMM) and is intended to cover material property and performance uncertainties. The value of 60 C (108 F) is a constant, applied at any spacecraft body location and for any trajectory. By varying only material properties in a random (monte carlo) manner, the perl-based script mcCHAR is used to investigate the confidence interval provided by the BTMM. In particular, this study will look at various locations on the Orion heat shield forebody for a guided and an abort (ballistic) trajectory.

  19. Wall ablation of heated compound-materials into non-equilibrium discharge plasmas

    NASA Astrophysics Data System (ADS)

    Wang, Weizong; Kong, Linghan; Geng, Jinyue; Wei, Fuzhi; Xia, Guangqing

    2017-02-01

    The discharge properties of the plasma bulk flow near the surface of heated compound-materials strongly affects the kinetic layer parameters modeled and manifested in the Knudsen layer. This paper extends the widely used two-layer kinetic ablation model to the ablation controlled non-equilibrium discharge due to the fact that the local thermodynamic equilibrium (LTE) approximation is often violated as a result of the interaction between the plasma and solid walls. Modifications to the governing set of equations, to account for this effect, are derived and presented by assuming that the temperature of the electrons deviates from that of the heavy particles. The ablation characteristics of one typical material, polytetrafluoroethylene (PTFE) are calculated with this improved model. The internal degrees of freedom as well as the average particle mass and specific heat ratio of the polyatomic vapor, which strongly depends on the temperature, pressure and plasma non-equilibrium degree and plays a crucial role in the accurate determination of the ablation behavior by this model, are also taken into account. Our assessment showed the significance of including such modifications related to the non-equilibrium effect in the study of vaporization of heated compound materials in ablation controlled arcs. Additionally, a two-temperature magneto-hydrodynamic (MHD) model accounting for the thermal non-equilibrium occurring near the wall surface is developed and applied into an ablation-dominated discharge for an electro-thermal chemical launch device. Special attention is paid to the interaction between the non-equilibrium plasma and the solid propellant surface. Both the mass exchange process caused by the wall ablation and plasma species deposition as well as the associated momentum and energy exchange processes are taken into account. A detailed comparison of the results of the non-equilibrium model with those of an equilibrium model is presented. The non-equilibrium results

  20. Mars Science Laboratory Heat Shield Integration for Flight

    NASA Image and Video Library

    2011-11-10

    During final stacking of NASA Mars Science Laboratory spacecraft, the heat shield is positioned for integration with the rest of the spacecraft in this photograph from inside the Payload Hazardous Servicing Facility at NASA Kennedy Space Center, Fla.

  1. High-purity silica reflecting heat shield development

    NASA Technical Reports Server (NTRS)

    Congdon, W. M.

    1974-01-01

    A high-purity, fused-silica reflecting heat shield for the thermal protection of outer-planet probes was developed. Factors that strongly influence the performance of a silica heat shield were studied. Silica-bonded silica configurations, each prepared by a different technique, were investigated and rated according to its relative merits. Slip-casting was selected as the preferred fabrication method because it produced good reflectivity and good strength, and is relatively easy to scale up for a full-size outer-planet probe. The slips were cast using a variety of different particle sizes: continuous particle-size slips; monodisperse particle-size slips; and blends of monodisperse particle-size slips were studied. In general, smaller particles gave the highest reflectance. The monodisperse slips as well as the blend slips gave a higher reflectance than the continuous particle-size slips. An upgraded and fused natural quartz was used to study the effects of microstructure on reflectance and as the baseline to ascertain the increase in reflectance obtained from using a higher-purity synthetic material.

  2. Composite Structures Materials Testing for the Orion Crew Vehicle Heat Shield

    NASA Technical Reports Server (NTRS)

    Khemani, Farah N.

    2011-01-01

    As research is being performed for the new heat shield for the Orion capsule, National Aeronautics and Space Administration (NASA) is developing the first composite heat shield. As an intern of the Structures Branch in the Engineering Directorate (ES 2), my main task was to set up a test plan to determine the material properties of the honeycomb that will be used on the Orion Crew Module heat shield to verify that the composite is suitable for the capsule. Before conducting composite shell tests, which are performed to simulate the crush performance of the heat shield on the capsule, it is necessary to determine the compression and shear properties of the composite used on the shell. During this internship, I was responsible for developing a test plan, designing parts for the test fixtures as well as getting them fabricated for the honeycomb shear and compression testing. This involved work in Pro/Engineer as well as coordinating with Fab Express, the Building 9 Composite Shop and the Structures Test Laboratory (STL). The research and work executed for this project will be used for composite sandwich panel testing in the future as well. As a part of the Structures Branch, my main focus was to research composite structures. This involves system engineering and integration (SE&I) integration, manufacturing, and preliminary testing. The procedures for these projects that were executed during this internship included design work, conducting tests and performing analysis.

  3. Photogrammetric Measurement of Recession Rates of Low Temperature Ablators Subjected to High Speed Flow

    DTIC Science & Technology

    2011-06-01

    recession rate prediction of carbon based, camphor and dry ice at hypersonic velocities...paradichlorobenzene, naphthalene, camphor , and ammonium chloride (Kohlman & Richardson, 1969). Except for dry ice, these materials require stagnation temperatures... Camphor , for example, sublimates at ~170C. With the reestablished interest in expendable ablative heat shields, these past experiences have

  4. Computational Modeling of Ablation on an Irradiated Target

    NASA Astrophysics Data System (ADS)

    Mehmedagic, Igbal; Thangam, Siva

    2017-11-01

    Computational modeling of pulsed nanosecond laser interaction with an irradiated metallic target is presented. The model formulation involves ablation of the metallic target irradiated by pulsed high intensity laser at normal atmospheric conditions. Computational findings based on effective representation and prediction of the heat transfer, melting and vaporization of the targeting material as well as plume formation and expansion are presented along with its relevance for the development of protective shields. In this context, the available results for a representative irradiation from 1064 nm laser pulse is used to analyze various ablation mechanisms, variable thermo-physical and optical properties, plume expansion and surface geometry. Funded in part by U. S. Army ARDEC, Picatinny Arsenal, NJ.

  5. Aerothermodynamic optimization of Earth entry blunt body heat shields for Lunar and Mars return

    NASA Astrophysics Data System (ADS)

    Johnson, Joshua E.

    A differential evolutionary algorithm has been executed to optimize the hypersonic aerodynamic and stagnation-point heat transfer performance of Earth entry heat shields for Lunar and Mars return manned missions with entry velocities of 11 and 12.5 km/s respectively. The aerothermodynamic performance of heat shield geometries with lift-to-drag ratios up to 1.0 is studied. Each considered heat shield geometry is composed of an axial profile tailored to fit a base cross section. Axial profiles consist of spherical segments, spherically blunted cones, and power laws. Heat shield cross sections include oblate and prolate ellipses, rounded-edge parallelograms, and blendings of the two. Aerothermodynamic models are based on modified Newtonian impact theory with semi-empirical correlations for convection and radiation. Multi-objective function optimization is performed to determine optimal trade-offs between performance parameters. Objective functions consist of minimizing heat load and heat flux and maximizing down range and cross range. Results indicate that skipping trajectories allow for vehicles with L/D = 0.3, 0.5, and 1.0 at lunar return flight conditions to produce maximum cross ranges of 950, 1500, and 3000 km respectively before Qs,tot increases dramatically. Maximum cross range increases by ˜20% with an increase in entry velocity from 11 to 12.5 km/s. Optimal configurations for all three lift-to-drag ratios produce down ranges up to approximately 26,000 km for both lunar and Mars return. Assuming a 10,000 kg mass and L/D = 0.27, the current Orion configuration is projected to experience a heat load of approximately 68 kJ/cm2 for Mars return flight conditions. For both L/D = 0.3 and 0.5, a 30% increase in entry vehicle mass from 10,000 kg produces a 20-30% increase in Qs,tot. For a given L/D, highly-eccentric heat shields do not produce greater cross range or down range. With a 5 g deceleration limit and L/D = 0.3, a highly oblate cross section with an

  6. Experimental Investigation on the Specific Heat of Carbonized Phenolic Resin-Based Ablative Materials

    NASA Astrophysics Data System (ADS)

    Zhao, Te; Ye, Hong; Zhang, Lisong; Cai, Qilin

    2017-10-01

    As typical phenolic resin-based ablative materials, the high silica/phenolic and carbon/phenolic composites are widely used in aerospace field. The specific heat of the carbonized ablators after ablation is an important thermophysical parameter in the process of heat transfer, but it is rarely reported. In this investigation, the carbonized samples of the high silica/phenolic and carbon/phenolic were obtained through carbonization experiments, and the specific heat of the carbonized samples was determined by a 3D DSC from 150 °C to 970 °C. Structural and compositional characterizations were performed to determine the mass fractions of the fiber and the carbonized product of phenolic which are the two constituents of the carbonized samples, while the specific heat of each constituent was also measured by 3D DSC. The masses of the carbonized samples were reduced when heated to a high temperature in the specific heat measurements, due to the thermal degradation of the carbonized product of phenolic resin in the carbonized samples. The raw experimental specific heat of the two carbonized samples and the carbonized product of phenolic resin was modified according to the quality changes of the carbonized samples presented by TGA results. Based on the mass fraction and the specific heat of each constituent, a weighted average method was adopted to obtain the calculated results of the carbonized samples. Due to the unconsolidated property of the fiber samples which impacts the reliability of the DSC measurement, there is a certain deviation between the experimental and calculated results of the carbonized samples. Considering the similarity of composition and structure, the data of quartz glass and graphite were used to substitute the specific heat of the high silica fiber and carbon fiber, respectively, resulting in better agreements with the experimental ones. Furthermore, the accurate specific heat of the high silica fiber and carbon fiber bundles was obtained by

  7. Evaluation of dispersion strengthened nickel-base alloy heat shields for space shuttle application

    NASA Technical Reports Server (NTRS)

    Johnson, R., Jr.; Killpatrick, D. H.

    1973-01-01

    The work reported constitutes the first phase of a two-phase program. Vehicle environments having critical effects on the thermal protection system are defined; TD Ni-20Cr material characteristics are reviewed and compared with TD Ni-20Cr produced in previous development efforts; cyclic load, temperature, and pressure effects on TD Ni-20Cr sheet material are investigated; the effects of braze reinforcement in improving the efficiency of spotwelded, diffusion-bonded, or seam-welded joints are evaluated through tests of simple lap-shear joint samples; parametric studies of metallic radiative thermal protection systems are reported; and the design, instrumentation, and testing of full-scale subsize heat shield panels are described. Tests of full-scale subsize panels included simulated meteoroid impact tests; simulated entry flight aerodynamic heating in an arc-heated plasma stream; programmed differential pressure loads and temperatures simulating mission conditions; and acoustic tests simulating sound levels experienced by heat shields during about boost flight. Test results are described, and the performances of two heat shield designs are compared and evaluated.

  8. Optical Property Enhancement and Durability Evaluation of Heat Receiver Aperture Shield Materials

    NASA Technical Reports Server (NTRS)

    deGroh, Kim K.; Jaworske, Donald A.; Smith, Daniela C.

    1998-01-01

    Under the Solar Dynamic Flight Demonstration (SDFD) program, NASA Lewis Research Center worked with AlliedSignal Aerospace, the heat receiver contractor, on the development, characterization and durability testing of refractory metals to obtain appropriate optical and thermal properties for the SDFD heat receiver aperture shield. Molybdenum and tungsten foils were grit-blasted using silicon carbide or alumina grit under various grit-blasting conditions for optical property enhancement. Black rhenium coated tungsten foil was also evaluated. Tungsten, black rhenium-coated tungsten, and grit-blasted tungsten screens of various mesh sizes were placed over the pristine and grit-blasted foils for optical property characterization. Grit-blasting was found to be effective in decreasing the specular reflectance and the absorptance/emittance ratio of the refractory foils. The placement of a screen further enhanced these optical properties, with a grit-blasted screen over a grit-blasted foil producing the best results. Based on the optical property enhancement results, samples were tested for atomic oxygen and vacuum heat treatment durability. Grit-blasted (Al2O3 grit) 2 mil tungsten foil was chosen for the exterior layer of the SDFD heat receiver aperture shield. A 0.007 in. wire diameter, 20 x 20 mesh tungsten screen was chosen to cover the tungsten foil. Based on these test results, a heat receiver aperture shield test unit has been built with the screen covered grit-blast tungsten foil exterior layers. The aperture shield was tested and verified the thermal and structural durability of the outer foil layers during an off-pointing period.

  9. Ablative overlays for Space Shuttle leading edge ascent heat protection

    NASA Technical Reports Server (NTRS)

    Strauss, E. L.

    1975-01-01

    Ablative overlays were evaluated via a plasma-arc simulation of the ascent pulse on the leading edge of the Space Shuttle Orbiter. Overlay concepts included corkboard, polyisocyanurate foam, low-density Teflon, epoxy, and subliming salts. Their densities ranged from 4.9 to 81 lb per cu ft, and the thicknesses varied from 0.107 to 0.330 in. Swept-leading-edge models were fabricated from 30-lb per cu ft silicone-based ablators. The overlays were bonded to maintain the surface temperature of the base ablator below 500 F during ascent. Foams provided minimum-weight overlays, and subliming salts provided minimum-thickness overlays. Teflon left the most uniform surface after ascent heating.

  10. High purity silica reflective heat shield development

    NASA Technical Reports Server (NTRS)

    Blome, J. C.; Drennan, D. N.; Schmitt, R. J.

    1974-01-01

    Measurements were made of reflectance in the vacuum ultraviolet down to 0.15 micron. Scattering coefficients (S) and absorption coefficients (K) were also measured. These coefficients express the optical properties and are used directly in a thermodynamic analysis for sizing a heat shield. The effect of the thin silica melt layer formed during entry was also studied from the standpoint of trapped radiant energy.

  11. Radiofrequency Thermal Ablation Heat Energy Transfer in an Ex-Vivo Model.

    PubMed

    Thakur, Shivani; Lavito, Sandi; Grobner, Elizabeth; Grobner, Mark

    2017-12-01

    Little work has been done to consider the temperature changes and energy transfer that occur in the tissue outside the vein with ultrasound-guided vein ablation therapy. In this experiment, a Ex-Vivo model of the human calf was used to analyze heat transfer and energy degradation in tissue surrounding the vein during endovascular radiofrequency ablation (RFA). A clinical vein ablation protocol was used to determine the tissue temperature distribution in 10 per cent agar gel. Heat energy from the radiofrequency catheter was measured for 140 seconds at fixed points by four thermometer probes placed equidistant radially at 0.0025, 0.005, and 0.01 m away from the RFA catheter. The temperature rose 1.5°C at 0.0025 m, 0.6°C at 0.005 m, and 0.0°C at 0.01 m from the RFA catheter. There was a clinically insignificant heat transfer at the distances evaluated, 1.4 ± 0.2 J/s at 0.0025 m, 0.7 ± 0.3 J/s at 0.0050 m, and 0.3 ± 0.0 J/s at 0.01 m. Heat degradation occurred rapidly: 4.5 ± 0.5 J (at 0.0025 m), 4.0 ± 1.6 J (at 0.0050 m), and 3.9 ± 3.6 J (at 0.01 m). Tumescent anesthesia injected one centimeter around the vein would act as a heat sink to absorb the energy transferred outside the vein to minimize tissue and nerve damage and will help phlebologists strategize options for minimizing damage.

  12. Noninvasive Assessment of Tissue Heating During Cardiac Radiofrequency Ablation Using MRI Thermography

    PubMed Central

    Kolandaivelu, Aravindan; Zviman, Menekhem M.; Castro, Valeria; Lardo, Albert C.; Berger, Ronald D.; Halperin, Henry R.

    2010-01-01

    Background Failure to achieve properly localized, permanent tissue destruction is a common cause of arrhythmia recurrence after cardiac ablation. Current methods of assessing lesion size and location during cardiac radiofrequency ablation are unreliable or not suited for repeated assessment during the procedure. MRI thermography could be used to delineate permanent ablation lesions because tissue heating above 50°C is the cause of permanent tissue destruction during radiofrequency ablation. However, image artifacts caused by cardiac motion, the ablation electrode, and radiofrequency ablation currently pose a challenge to MRI thermography in the heart. In the current study, we sought to demonstrate the feasibility of MRI thermography during cardiac ablation. Methods and Results An MRI-compatible electrophysiology catheter and filtered radiofrequency ablation system was used to perform ablation in the left ventricle of 6 mongrel dogs in a 1.5-T MRI system. Fast gradient-echo imaging was performed before and during radiofrequency ablation, and thermography images were derived from the preheating and postheating images. Lesion extent by thermography was within 20% of the gross pathology lesion. Conclusions MR thermography appears to be a promising technique for monitoring lesion formation and may allow for more accurate placement and titration of ablation, possibly reducing arrhythmia recurrences. PMID:20657028

  13. SPACECRAFT (S/C)-012 - COMMAND MODULE (CM) - HEAT SHIELD INSTALLATION

    NASA Image and Video Library

    1966-04-18

    S66-41851 (1966) --- High angle view of Spacecraft 012 Command Module, looking toward -Z axis, during preparation for installation of the crew compartment heat shield, showing mechanics working on aft bay.

  14. Heat flow, heat production, and crustal temperatures in the Archaean Bundelkhand craton, north-central India: Implications for thermal regime beneath the Indian shield

    NASA Astrophysics Data System (ADS)

    Podugu, Nagaraju; Ray, Labani; Singh, S. P.; Roy, Sukanta

    2017-07-01

    Heat flow and heat production data sets constrain the crustal thermal structure in the 2.5-3.5 Ga Bundelkhand craton, the oldest cratonic core in northern Indian shield, for the first time and allow comparisons with the southern Indian shield. Temperature measurements carried out in 10 boreholes at five sites in the craton, combined with systematic thermal conductivity measurements on major rock types, yield low heat flow in the range of 32-41 mW m-2, which is distinct from the generally high heat flow reported from other parts of the northern Indian shield. Radioelemental measurements on 243 samples of drill cores and outcrops reveal both large variability and high average heat production for the Neo-Archaean to Palaeo-Proterozoic granites (4.0 ± 2.1 (SD) μW m-3) relative to the Meso-Archaean tonalite-trondhjemite-granodiorite (TTG) gneisses (2.0 ± 1.0 (SD) μW m-3). On the basis of new heat flow and heat production data sets combined with available geological and geophysical information, a set of steady state, heat flow-crustal heat production models representative of varying crustal scenarios in the craton are envisaged. Mantle heat flow and Moho temperatures are found to be in the range of 12-22 mW m-2 and 290-420°C, respectively, not much different from those reported for the similar age Dharwar craton in southern India. This study reveals similar mantle thermal regimes across the northern and southern parts of the Indian shield, in spite of varying surface heat flow regimes, implying that much of the intraprovince and interprovince variations in the Indian shield are explained by variations in upper crustal heat production.

  15. Heat Shield Construction for NASA InSight Mission

    NASA Image and Video Library

    2015-05-27

    In this February 2015 scene from a clean room at Lockheed Martin Space Systems, Denver, specialists are building the heat shield to protect NASA's InSight spacecraft when it is speeding through the Martian atmosphere. Note: After thorough examination, NASA managers have decided to suspend the planned March 2016 launch of the Interior Exploration using Seismic Investigations Geodesy and Heat Transport (InSight) mission. The decision follows unsuccessful attempts to repair a leak in a section of the prime instrument in the science payload. http://photojournal.jpl.nasa.gov/catalog/PIA19404

  16. Heat Shield for Extreme Entry Environment Technology (HEEET)

    NASA Technical Reports Server (NTRS)

    Venkatapathy, Ethiraj

    2017-01-01

    The Heat Shield for Extreme Entry Environment Technology (HEEET) project seeks to mature a game changing Woven Thermal Protection System (TPS) technology to enable in situ robotic science missions recommended by the NASA Research Council Planetary Science Decadal Survey committee. Recommended science missions include Venus probes and landers; Saturn and Uranus probes; and high-speed sample return missions.

  17. Heat sink effect on tumor ablation characteristics as observed in monopolar radiofrequency, bipolar radiofrequency, and microwave, using ex vivo calf liver model.

    PubMed

    Pillai, Krishna; Akhter, Javid; Chua, Terence C; Shehata, Mena; Alzahrani, Nayef; Al-Alem, Issan; Morris, David L

    2015-03-01

    Thermal ablation of liver tumors near large blood vessels is affected by the cooling effect of blood flow, leading to incomplete ablation. Hence, we conducted a comparative investigation of heat sink effect in monopolar (MP) and bipolar (BP) radiofrequency ablation (RFA), and microwave (MW) ablation devices.With a perfused calf liver, the ablative performances (volume, mass, density, dimensions), with and without heat sink, were measured. Heat sink was present when the ablative tip of the probes were 8.0 mm close to a major hepatic vein and absent when >30 mm away. Temperatures (T1 and T2) on either side of the hepatic vein near the tip of the probes, heating probe temperature (T3), outlet perfusate temperature (T4), and ablation time were monitored.With or without heat sink, BP radiofrequency ablated a larger volume and mass, compared with MP RFA or MW ablation, with latter device producing the highest density of tissue ablated. MW ablation produced an ellipsoidal shape while radiofrequency devices produced spheres.Percentage heat sink effect in Bipolar radiofrequency : Mono-polar radiofrequency : Microwave was (Volume) 33:41:22; (mass) 23:56:34; (density) 9.0:26:18; and (relative elipscity) 5.8:12.9:1.3, indicating that BP and MW devices were less affected.Percentage heat sink effect on time (minutes) to reach maximum temperature (W) = 13.28:9.2:29.8; time at maximum temperature (X) is 87:66:16.66; temperature difference (Y) between the thermal probes (T3) and the temperature (T1 + T2)/2 on either side of the hepatic vessel was 100:87:20; and temperature difference between the (T1 + T2)/2 and temperature of outlet circulating solution (T4), Z was 20.33:30.23:37.5.MW and BP radiofrequencies were less affected by heat sink while MP RFA was the most affected. With a single ablation, BP radiofrequency ablated a larger volume and mass regardless of heat sink.

  18. Heat Sink Effect on Tumor Ablation Characteristics as Observed in Monopolar Radiofrequency, Bipolar Radiofrequency, and Microwave, Using Ex Vivo Calf Liver Model

    PubMed Central

    Pillai, Krishna; Akhter, Javid; Chua, Terence C.; Shehata, Mena; Alzahrani, Nayef; Al-Alem, Issan; Morris, David L.

    2015-01-01

    Abstract Thermal ablation of liver tumors near large blood vessels is affected by the cooling effect of blood flow, leading to incomplete ablation. Hence, we conducted a comparative investigation of heat sink effect in monopolar (MP) and bipolar (BP) radiofrequency ablation (RFA), and microwave (MW) ablation devices. With a perfused calf liver, the ablative performances (volume, mass, density, dimensions), with and without heat sink, were measured. Heat sink was present when the ablative tip of the probes were 8.0 mm close to a major hepatic vein and absent when >30 mm away. Temperatures (T1 and T2) on either side of the hepatic vein near the tip of the probes, heating probe temperature (T3), outlet perfusate temperature (T4), and ablation time were monitored. With or without heat sink, BP radiofrequency ablated a larger volume and mass, compared with MP RFA or MW ablation, with latter device producing the highest density of tissue ablated. MW ablation produced an ellipsoidal shape while radiofrequency devices produced spheres. Percentage heat sink effect in Bipolar radiofrequency : Mono-polar radiofrequency : Microwave was (Volume) 33:41:22; (mass) 23:56:34; (density) 9.0:26:18; and (relative elipscity) 5.8:12.9:1.3, indicating that BP and MW devices were less affected. Percentage heat sink effect on time (minutes) to reach maximum temperature (W) = 13.28:9.2:29.8; time at maximum temperature (X) is 87:66:16.66; temperature difference (Y) between the thermal probes (T3) and the temperature (T1 + T2)/2 on either side of the hepatic vessel was 100:87:20; and temperature difference between the (T1 + T2)/2 and temperature of outlet circulating solution (T4), Z was 20.33:30.23:37.5. MW and BP radiofrequencies were less affected by heat sink while MP RFA was the most affected. With a single ablation, BP radiofrequency ablated a larger volume and mass regardless of heat sink. PMID:25738477

  19. Aft Engine shop worker removes a heat shield on Columbia's main engines

    NASA Technical Reports Server (NTRS)

    2002-01-01

    KENNEDY SPACE CENTER, FLA. - Doug Buford, with the Aft Engine shop, works at removing a heat shield on Columbia, in the Orbiter Processing Facility. After small cracks were discovered on the LH2 Main Propulsion System (MPS) flow liners in two other orbiters, program managers decided to move forward with inspections on Columbia before clearing it for flight on STS-107. After removal of the heat shields, the three main engines will be removed. Inspections of the flow liners will follow. The July 19 launch of Columbia on STS-107 has been delayed a few weeks

  20. Aft Engine shop worker removes a heat shield on Columbia's main engines

    NASA Technical Reports Server (NTRS)

    2002-01-01

    KENNEDY SPACE CENTER, FLA. -- Doug Buford, with the Aft Engine shop, works at removing a heat shield on Columbia, in the Orbiter Processing Facility. After small cracks were discovered on the LH2 Main Propulsion System (MPS) flow liners in two other orbiters, program managers decided to move forward with inspections on Columbia before clearing it for flight on STS-107. After removal of the heat shields, the three main engines will be removed. Inspections of the flow liners will follow. The July 19 launch of Columbia on STS-107 has been delayed a few weeks

  1. Aft Engine shop worker removes a heat shield on Columbia's main engines

    NASA Technical Reports Server (NTRS)

    2002-01-01

    KENNEDY SPACE CENTER, FLA. -- Doug Buford (top), with the Aft Engine shop, along with another worker, removes a heat shield on one of Columbia's engines. After small cracks were discovered on the LH2 Main Propulsion System (MPS) flow liners in two other orbiters, program managers decided to move forward with inspections on Columbia before clearing it for flight on STS-107. After removal of the heat shields, the three main engines will be removed. Inspections of the flow liners will follow. The July 19 launch of Columbia on STS-107 has been delayed a few weeks

  2. Regolith-Derived Heat Shield for Planetary Body Entry and Descent System with In Situ Fabrication

    NASA Technical Reports Server (NTRS)

    Hogue, Michael D.; Mueller, Robert P.; Rasky, Daniel J.; Hintze, Paul E.; Sibille, Laurent

    2011-01-01

    In this paper we will discuss a new mass-efficient and innovative way of protecting high-mass spacecraft during planetary Entry, Descent & Landing (EDL). Heat shields fabricated in situ can provide a thermal-protection system (TPS) for spacecraft that routinely enter a planetary atmosphere. By fabricating the heat shield with space resources from regolith materials available on moons and asteroids, it is possible to avoid launching the heat-shield mass from Earth. Three regolith processing and manufacturing methods will be discussed: 1) oxygen & metal extraction ISRU processes produce glassy melts enriched in alumina and titania, processed to obtain variable density, high melting point and heat-resistance; 2) compression and sintering of the regolith yield low density materials; 3) in-situ derived high-temperature polymers are created to bind regolith particles together, with a lower energy budget.

  3. Heating Augmentation Due to Compression Pad Cavities on the Project Orion CEV Heat Shield

    NASA Technical Reports Server (NTRS)

    Hollis, Brian R.

    2009-01-01

    An experimental study has been conducted to assess the effects of compression pad cavities on the aeroheating environment of the Project Orion CEV heat-shield. Testing was conducted in Mach 6 and Mach 10 perfect-gas wind tunnels to obtain heating measurements in and around the compression pads cavities using global phosphor thermography. Data were obtained over a wide range of Reynolds numbers that produced laminar, transitional, and turbulent flow within and downstream of the cavities. The effects of cavity dimensions on boundary-layer transition and heating augmentation levels were studied. Correlations were developed for transition onset and for the average cavity-heating augmentation.

  4. Experimental investigation of the dynamics of pellet ablation on the Texas Experimental Tokamak

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Durst, R.D.

    1988-01-01

    Rapid fluctuations in the ablation of hydrogen pellets in the Texas Experimental Tokamak were studied using fast photographic techniques. It is proposed that the fluctuations are a type of relaxation oscillation driven by the motion of the particle across the magnetic field. This is shown to be consistent with a time-dependent model of plasma shielding due to Kaufmann et al. A technique to include this effect in calculations of pellet ablation is discussed. Spatially resolved measurements of the temperature and density in the pellet-ablation cloud were obtained by line-to-continuum ratios and Stark broadening, respectively. Typical parameters in the pellet-ablation cloudmore » are 5-6 eV and 1.0-1.5 {times} 10{sup 17} cm{sup {minus}3}. The flow along the magnetic field is found to be isobaric. The heating of the expanding ablatant is strongly asymmetric, being stronger on the side facing the electron-drift direction. This may be due to suprathermal electrons.« less

  5. 3D Multifunctional Ablative Thermal Protection System

    NASA Technical Reports Server (NTRS)

    Feldman, Jay; Venkatapathy, Ethiraj; Wilkinson, Curt; Mercer, Ken

    2015-01-01

    NASA is developing the Orion spacecraft to carry astronauts farther into the solar system than ever before, with human exploration of Mars as its ultimate goal. One of the technologies required to enable this advanced, Apollo-shaped capsule is a 3-dimensional quartz fiber composite for the vehicle's compression pad. During its mission, the compression pad serves first as a structural component and later as an ablative heat shield, partially consumed on Earth re-entry. This presentation will summarize the development of a new 3D quartz cyanate ester composite material, 3-Dimensional Multifunctional Ablative Thermal Protection System (3D-MAT), designed to meet the mission requirements for the Orion compression pad. Manufacturing development, aerothermal (arc-jet) testing, structural performance, and the overall status of material development for the 2018 EM-1 flight test will be discussed.

  6. Residual heat deposition in dental enamel during IR laser ablation at 2.79, 2.94, 9.6, and 10.6 microm.

    PubMed

    Fried, D; Ragadio, J; Champion, A

    2001-01-01

    The principal factor limiting the rate of laser ablation of dental hard tissue is the risk of excessive heat accumulation in the tooth. Excessive heat deposition or accumulation may result in unacceptable damage to the pulp. The objective of this study was to measure the residual heat deposition during the laser ablation of dental enamel at those IR laser wavelengths well suited for the removal of dental caries. Optimal laser ablation systems minimize the residual heat deposition in the tooth by efficiently transferring the deposited laser energy to kinetic and internal energy of ejected tissue components. The residual heat deposition in dental enamel was measured at laser wavelengths of 2.79, 2.94, 9.6, and 10.6 microm and pulse widths of 150 nsec -150 microsec using bovine block "calorimeters." Water droplets were applied to the surface before ablation with 150 microsec Er:YAG laser pulses to determine the influence of an optically thick water layer on reducing heat deposition. The residual heat was at a minimum for fluences well above the ablation threshold where measured values ranged from 25-70% depending on pulse duration and wavelength for the systems investigated. The lowest values of the residual heat were measured for short (< 20 micros) CO(2) laser pulses at 9.6 microm and for Q-switched erbium laser pulses at 2.79 and 2.94 microm. Droplets of water applied to the surface before ablation significantly reduced the residual heat deposition during ablation with 150 microsec Er:YAG laser pulses. Residual heat deposition can be markedly reduced by using CO(2) laser pulses of less than 20 microsec duration and shorter Q-switched Er:YAG and Er:YSGG laser pulses for enamel ablation. Copyright 2001 Wiley-Liss, Inc.

  7. Implicit Coupling Approach for Simulation of Charring Carbon Ablators

    NASA Technical Reports Server (NTRS)

    Chen, Yih-Kanq; Gokcen, Tahir

    2013-01-01

    This study demonstrates that coupling of a material thermal response code and a flow solver with nonequilibrium gas/surface interaction for simulation of charring carbon ablators can be performed using an implicit approach. The material thermal response code used in this study is the three-dimensional version of Fully Implicit Ablation and Thermal response program, which predicts charring material thermal response and shape change on hypersonic space vehicles. The flow code solves the reacting Navier-Stokes equations using Data Parallel Line Relaxation method. Coupling between the material response and flow codes is performed by solving the surface mass balance in flow solver and the surface energy balance in material response code. Thus, the material surface recession is predicted in flow code, and the surface temperature and pyrolysis gas injection rate are computed in material response code. It is demonstrated that the time-lagged explicit approach is sufficient for simulations at low surface heating conditions, in which the surface ablation rate is not a strong function of the surface temperature. At elevated surface heating conditions, the implicit approach has to be taken, because the carbon ablation rate becomes a stiff function of the surface temperature, and thus the explicit approach appears to be inappropriate resulting in severe numerical oscillations of predicted surface temperature. Implicit coupling for simulation of arc-jet models is performed, and the predictions are compared with measured data. Implicit coupling for trajectory based simulation of Stardust fore-body heat shield is also conducted. The predicted stagnation point total recession is compared with that predicted using the chemical equilibrium surface assumption

  8. Heating Augmentation in Laminar Flow Due to Heat-Shield Cavities on the Project Orion CEV

    NASA Technical Reports Server (NTRS)

    Hollis, Brian R.

    2008-01-01

    An experimental study has been conducted to assess the effects of compression pad cavities on the aeroheating environment of the Project Orion CEV heat-shield at laminar conditions. Testing was conducted in Mach 6 and Mach 10 perfect-gas wind tunnels to obtain heating measurements on and around the compression pads using global phosphor thermography. Consistent trends in heating augmentation levels were observed in the data and correlations of average and maximum heating at the cavities were formulated in terms of the local boundary-layer parameters and cavity dimensions. Additional heating data from prior testing of Genesis and Mars Science Laboratory models were also examined to extend the parametric range of cavity heating correlations.

  9. Regolith-Derived Heat Shield for Planetary Body Entry and Descent System with In Situ Fabrication

    NASA Technical Reports Server (NTRS)

    Hogue, Michael D.; Mueller, Robert P.; Rasky, Daniel; Hintze, Paul; Sibille, Laurent

    2012-01-01

    In this paper we will discuss a new mass-efficient and innovative way of protecting high-mass spacecraft during planetary Entry, Descent & Landing (EDL). Heat shields fabricated in situ can provide a thermal-protection system (TPS) for spacecraft that routinely enter a planetary atmosphere. By fabricating the heat shield with space resources from regolith materials available on moons and asteroids, it is possible to avoid launching the heat-shield mass from Earth. Two regolith processing and manufacturing methods will be discussed: 1) Compression and sintering of the regolith to yield low density materials; 2) Formulations of a High-temperature silicone RTV (Room Temperature Vulcanizing) compound are used to bind regolith particles together. The overall positive results of torch flame impingement tests and plasma arc jet testing on the resulting samples will also be discussed.

  10. Ablation enhancement of silicon by ultrashort double-pulse laser ablation

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zhao, Xin; Shin, Yung C.

    In this study, the ultrashort double-pulse ablation of silicon is investigated. An atomistic simulation model is developed to analyze the underlying physics. It is revealed that the double-pulse ablation could significantly increase the ablation rate of silicon, compared with the single pulse ablation with the same total pulse energy, which is totally different from the case of metals. In the long pulse delay range (over 1 ps), the enhancement is caused by the metallic transition of melted silicon with the corresponding absorption efficiency. At ultrashort pulse delay (below 1 ps), the enhancement is due to the electron excitation by the first pulse.more » The enhancement only occurs at low and moderate laser fluence. The ablation is suppressed at high fluence due to the strong plasma shielding effect.« less

  11. Thermal fatigue tests of a radiative heat shield panel for a hypersonic transport

    NASA Technical Reports Server (NTRS)

    Webb, Granville L.; Clark, Ronald K.; Sharpe, Ellsworth L.

    1985-01-01

    A pair of corrugation stiffened, beaded skin Rene 41 heat shield panels were exposed to 20,000 thermal cycles between room temperature and 1450 F to evaluate the thermal fatigue response of Rene 41 metallic heat shields for hypersonic cruise aircraft applications. At the conclusion of the tests, the panels retained substantial structural integrity; however, there were cracks and excessive wear in the vicinity of fastener holes and there was an 80-percent loss in ductility of the skin. Shrinkage of the panel which caused the cracks and wear must be considered in design of panels for Thermal Protection Systems (TPS) applications.

  12. Phoenix Spacecraft Heat Shield Deployment Test

    NASA Image and Video Library

    2007-05-16

    In the Payload Hazardous Servicing Facility, workers monitor the Phoenix spacecraft during a heat shield deployment test, with a firing of ordnance associated with the separation device. Phoenix will land in icy soils near the north polar permanent ice cap of Mars and explore the history of the water in these soils and any associated rocks, while monitoring polar climate. Landing is planned in May 2008 on arctic ground where a mission currently in orbit, Mars Odyssey, has detected high concentrations of ice just beneath the top layer of soil. Launch of Phoenix aboard a Delta II rocket is targeted for Aug. 3 from Cape Canaveral Air Force Station in Florida.

  13. Carbon Nanotube-enhanced Carbon-phenolic Ablator Material

    NASA Technical Reports Server (NTRS)

    Nikolaev, P.; Stackpoole, M.; Fan, W.; Cruden, B.; Waid, M.; Maloney, P.; Arepalli, S.; Arnold, J.; Partridge, H.; Yowell, L.

    2006-01-01

    Phenolic impregnated carbon ablator (PICA) is a thermal protection system (TPS) material developed at NASA Ames Research Center in the mid-90 s for Discovery missions. It was used on the Stardust return capsule heat shield which successfully executed the highest speed Earth entry to date on January 15, 2006. PICA is a porous fibrous carbon insulation infiltrated with phenolic resin, and is an excellent ablator that is effective for heating rates up to 1000 W/sq cm. It is one of several candidate TPS materials for the next generation of crewed spacecraft for Lunar and Mars missions. We will describe an ongoing research effort at NASA to improve mechanical properties of the phenolic matrix with carbon nanotubes. The aim is two-fold: to increase overall TPS strength during reentry and to improve Micrometeoroid/Orbital Debris (MMOD) protection in space. The former requires at least a good dispersion of nanotubes in phenolic, while the latter also requires covalent bonding between them to couple and transfer impact energy effectively from matrix to nanotubes. We will discuss the required chemical functionalization of nanotubes, processing issues and test results.

  14. Heat generation caused by ablation of dental hard tissues with an ultrashort pulse laser (USPL) system.

    PubMed

    Braun, Andreas; Krillke, Raphael Franz; Frentzen, Matthias; Bourauel, Christoph; Stark, Helmut; Schelle, Florian

    2015-02-01

    Heat generation during the removal of dental hard tissues may lead to a temperature increase and cause painful sensations or damage dental tissues. The aim of this study was to assess heat generation in dental hard tissues following laser ablation using an ultrashort pulse laser (USPL) system. A total of 85 specimens of dental hard tissues were used, comprising 45 specimens of human dentine evaluating a thickness of 1, 2, and 3 mm (15 samples each) and 40 specimens of human enamel with a thickness of 1 and 2 mm (20 samples each). Ablation was performed with an Nd:YVO4 laser at 1,064 nm, a pulse duration of 9 ps, and a repetition rate of 500 kHz with an average output power of 6 W. Specimens were irradiated for 0.8 s. Employing a scanner system, rectangular cavities of 1-mm edge length were generated. A temperature sensor was placed at the back of the specimens, recording the temperature during the ablation process. All measurements were made employing a heat-conductive paste without any additional cooling or spray. Heat generation during laser ablation depended on the dental hard tissue (enamel or dentine) and the thickness of the respective tissue (p < 0.05). Highest temperature increase could be observed in the 1-mm thickness group for enamel. Evaluating the 1-mm group for dentine, a significantly lower temperature increase could be measured (p < 0.05) with lowest values in the 3-mm group (p < 0.05). A time delay for temperature increase during the ablation process depending on the material thickness was observed for both hard tissues (p < 0.05). Employing the USPL system to remove dental hard tissues, heat generation has to be considered. Especially during laser ablation next to pulpal tissues, painful sensations and potential thermal injury of pulp tissue might occur.

  15. Heat Shield Cavity Parametric Experimental Aeroheating for a Proposed Mars Smart Lander Aeroshell

    NASA Technical Reports Server (NTRS)

    Liechty, Derek S.; Hollis, Brian R.

    2002-01-01

    The proposed Mars Smart Lander is to be attached through its aeroshell to the main spacecraft bus, thereby producing cavities in the heat shield. To study the effects these cavities will have on the heating levels experienced by the heat shield, an experimental aeroheating investigation was performed at the NASA Langley Research Center in the 20-Inch Mach 6 Air Tunnel. The effects of Reynolds number, angle-of-attack, and cavity size and location on aero-heating levels and distributions were determined and are presented. To aid the discussion on the effects of the cavities, laminar, thin-layer Navier-Stokes flow field solutions were post-processed to calculate relevant boundary layer properties such as boundary layer height and momentum thickness, edge Mach number, and streamwise pressure gradient. It was found that the effect of the cavities varies with angle-of-attack, freestream Reynolds number, and cavity size and location. The presence of a cavity raised the downstream heating rates by as much as 325% as a result of boundary layer transition.

  16. Orion EFT-1 Heat Shield move from LASF to VAB for Ground Test Article Integration

    NASA Image and Video Library

    2017-04-26

    The heat shield for Exploration Flight Test-1 is transferred from the Orion Program to the Ground Systems Development and Operations Program, Landing and Recovery Operations to be integrated with the Ground Test Article to be utilized for future Underway Recovery Testing. After transport from the Launch Abort System Facility (LASF) to the Vehicle Assembly Building (VAB), the heat shield is lifted off of the transport truck and placed onto foam pads (dunnage) for inspection in Highbay 2 of the VAB.

  17. Phoenix Spacecraft Heat Shield Deployment Test

    NASA Image and Video Library

    2007-05-16

    In the Payload Hazardous Servicing Facility, a worker monitors the Phoenix spacecraft during a heat shield deployment test, with a firing of ordnance associated with the separation device. Phoenix will land in icy soils near the north polar permanent ice cap of Mars and explore the history of the water in these soils and any associated rocks, while monitoring polar climate. Landing is planned in May 2008 on arctic ground where a mission currently in orbit, Mars Odyssey, has detected high concentrations of ice just beneath the top layer of soil. Launch of Phoenix aboard a Delta II rocket is targeted for Aug. 3 from Cape Canaveral Air Force Station in Florida.

  18. Heat-Irrigate Effect' of Radiofrequency Ablation on Relevant Regional Hepatocyte in Living Swine Liver-Initial Study on Pathology.

    PubMed

    Jiang, Kai; Chen, Jiye; Liu, Yang; Liu, Jiang; Liu, Aijun; Dong, Jiahong; Huang, Zhiqiang

    2015-05-01

    Radiofrequency ablation (RFA) is one of the effective methods for HCC treatment. However, because of the "heat-sink effect" (HSE), it is very difficult to achieve a complete ablation in intrahepatic tumors. This study establishes the animal model of RFA on living swine liver and observes the 'heat-irrigate effect' on relevant regional hepatocytes. Three liver segments of 6 Guangxi Bama mini-pigs were selected to be ablated closed to segmental outflow vessel under surveillance of sonography for 6 min, and pathological changes of relevant downstream region were observed. We observed an elliptic shape of ablated area with diameter of 2.2 ± 1.1 cm on gross liver. Thermal damage was seen in downstream regional of relevant portal vein under microscope. However, adjacent area around the vessel was remained intact. In conclusion, the 'heat-irrigate effect' in RFA could cause thermal damage along the downstream region of relevant portal vein and this influence decreased gradually toward the surface.

  19. Development of Low Density Flexible Carbon Phenolic Ablators

    NASA Technical Reports Server (NTRS)

    Stackpole, Mairead; Thornton, Jeremy; Fan, Wendy; Agrawal, Parul; Doxtad, Evan; Gasch, Matt

    2011-01-01

    Phenolic Impregnated Carbon Ablator (PICA) was the enabling TPS material for the Stardust mission where it was used as a single piece heatshield. PICA has the advantages of low density (0.27g/cm3) coupled with efficient ablative capability at high heat fluxes. Under the Orion program, PICA was also shown to be capable of both ISS and lunar return missions however some unresolved issues remain for its application in a tiled configuration for the Orion-specific design. In particular, the problem of developing an appropriate gap filler resulted in the Orion program selecting AVCOAT as the primary heatshield material over PICA. We are currently looking at alternative architectures to yield flexible and more conformal carbon phenolic materials with comparable densities to PICA that will address some of the design issues faced in the application of a tiled PICA heat shield. These new materials are viable TPS candidates for upcoming NASA missions and as material candidates for private sector Commercial Orbital Transportation Services (COTS). This presentation will discuss flexible alternatives to PICA and include preliminary mechanical and thermal properties as well as arc jet and LHMEL screening test results.

  20. Heat Stress-Induced PI3K/mTORC2-Dependent AKT Signaling Is a Central Mediator of Hepatocellular Carcinoma Survival to Thermal Ablation Induced Heat Stress

    PubMed Central

    Thompson, Scott M.; Callstrom, Matthew R.; Jondal, Danielle E.; Butters, Kim A.; Knudsen, Bruce E.; Anderson, Jill L.; Lien, Karen R.; Sutor, Shari L.; Lee, Ju-Seog; Thorgeirsson, Snorri S.; Grande, Joseph P.; Roberts, Lewis R.; Woodrum, David A.

    2016-01-01

    Thermal ablative therapies are important treatment options in the multidisciplinary care of patients with hepatocellular carcinoma (HCC), but lesions larger than 2–3 cm are plagued with high local recurrence rates and overall survival of these patients remains poor. Currently no adjuvant therapies exist to prevent local HCC recurrence in patients undergoing thermal ablation. The molecular mechanisms mediating HCC resistance to thermal ablation induced heat stress and local recurrence remain unclear. Here we demonstrate that the HCC cells with a poor prognostic hepatic stem cell subtype (Subtype HS) are more resistant to heat stress than HCC cells with a better prognostic hepatocyte subtype (Subtype HC). Moreover, sublethal heat stress rapidly induces phosphoinositide 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) dependent-protein kinase B (AKT) survival signaling in HCC cells in vitro and at the tumor ablation margin in vivo. Conversely, inhibition of PI3K/mTOR complex 2 (mTORC2)-dependent AKT phosphorylation or direct inhibition of AKT function both enhance HCC cell killing and decrease HCC cell survival to sublethal heat stress in both poor and better prognostic HCC subtypes while mTOR complex 1 (mTORC1)-inhibition has no impact. Finally, we showed that AKT isoforms 1, 2 and 3 are differentially upregulated in primary human HCCs and that overexpression of AKT correlates with worse tumor biology and pathologic features (AKT3) and prognosis (AKT1). Together these findings define a novel molecular mechanism whereby heat stress induces PI3K/mTORC2-dependent AKT survival signaling in HCC cells and provide a mechanistic rationale for adjuvant AKT inhibition in combination with thermal ablation as a strategy to enhance HCC cell killing and prevent local recurrence, particularly at the ablation margin. PMID:27611696

  1. Thermal protection for hypervelocity flight in earth's atmosphere by use of radiation backscattering ablating materials

    NASA Technical Reports Server (NTRS)

    Howe, John T.; Yang, Lily

    1991-01-01

    A heat-shield-material response code predicting the transient performance of a material subject to the combined convective and radiative heating associated with the hypervelocity flight is developed. The code is dynamically interactive to the heating from a transient flow field, including the effects of material ablation on flow field behavior. It accomodates finite time variable material thickness, internal material phase change, wavelength-dependent radiative properties, and temperature-dependent thermal, physical, and radiative properties. The equations of radiative transfer are solved with the material and are coupled to the transfer energy equation containing the radiative flux divergence in addition to the usual energy terms.

  2. Development, fabrication and test of a high purity silica heat shield

    NASA Technical Reports Server (NTRS)

    Rusert, E. L.; Drennan, D. N.; Biggs, M. S.

    1978-01-01

    A highly reflective hyperpure ( 25 ppm ion impurities) slip cast fused silica heat shield material developed for planetary entry probes was successfully scaled up. Process development activities for slip casting large parts included green strength improvements, casting slip preparation, aggregate casting, strength, reflectance, and subscale fabrication. Successful fabrication of a one-half scale Saturn probe (shape and size) heat shield was accomplished while maintaining the silica high purity and reflectance through the scale-up process. However, stress analysis of this original aggregate slip cast material indicated a small margin of safety (MS. = +4%) using a factor of safety of 1.25. An alternate hyperpure material formulation to increase the strength and toughness for a greater safety margin was evaluated. The alternate material incorporates short hyperpure silica fibers into the casting slip. The best formulation evaluated has a 50% by weight fiber addition resulting in an 80% increase in flexural strength and a 170% increase in toughness over the original aggregate slip cast materials with comparable reflectance.

  3. Modeling of Heat Transfer and Ablation of Refractory Material Due to Rocket Plume Impingement

    NASA Technical Reports Server (NTRS)

    Harris, Michael F.; Vu, Bruce T.

    2012-01-01

    CR Tech's Thermal Desktop-SINDA/FLUINT software was used in the thermal analysis of a flame deflector design for Launch Complex 39B at Kennedy Space Center, Florida. The analysis of the flame deflector takes into account heat transfer due to plume impingement from expected vehicles to be launched at KSC. The heat flux from the plume was computed using computational fluid dynamics provided by Ames Research Center in Moffet Field, California. The results from the CFD solutions were mapped onto a 3-D Thermal Desktop model of the flame deflector using the boundary condition mapping capabilities in Thermal Desktop. The ablation subroutine in SINDA/FLUINT was then used to model the ablation of the refractory material.

  4. Study of the ablative effects on tektites. [wake shielding during atmospheric entry

    NASA Technical Reports Server (NTRS)

    Sepri, P.; Chen, K. K.

    1976-01-01

    Equations are presented which provide approximate parameters describing surface heating and tektite deceleration during atmosphere passage. Numerical estimates of these parameters using typical initial and ambient conditions support the conclusion that the commonly assumed trajectories would not have produced some of the observed surface markings. It is suggested that tektites did not enter the atmosphere singly but rather in a swarm dense enough to afford wake shielding according to a shock envelope model which is proposed. A further aerodynamic mechanism is described which is compatible with hemispherical pits occurring on tektite surfaces.

  5. Non-linear dual-phase-lag model for analyzing heat transfer phenomena in living tissues during thermal ablation.

    PubMed

    Kumar, P; Kumar, Dinesh; Rai, K N

    2016-08-01

    In this article, a non-linear dual-phase-lag (DPL) bio-heat transfer model based on temperature dependent metabolic heat generation rate is derived to analyze the heat transfer phenomena in living tissues during thermal ablation treatment. The numerical solution of the present non-linear problem has been done by finite element Runge-Kutta (4,5) method which combines the essence of Runge-Kutta (4,5) method together with finite difference scheme. Our study demonstrates that at the thermal ablation position temperature predicted by non-linear and linear DPL models show significant differences. A comparison has been made among non-linear DPL, thermal wave and Pennes model and it has been found that non-linear DPL and thermal wave bio-heat model show almost same nature whereas non-linear Pennes model shows significantly different temperature profile at the initial stage of thermal ablation treatment. The effect of Fourier number and Vernotte number (relaxation Fourier number) on temperature profile in presence and absence of externally applied heat source has been studied in detail and it has been observed that the presence of externally applied heat source term highly affects the efficiency of thermal treatment method. Copyright © 2016 Elsevier Ltd. All rights reserved.

  6. Effects of heat transfer and energy absorption in the ablation of biological tissues by pulsetrain-burst (>100 MHz) ultrafast laser processing

    NASA Astrophysics Data System (ADS)

    Forrester, Paul; Bol, Kieran; Lilge, Lothar; Marjoribanks, Robin

    2006-09-01

    Energy absorption and heat transfer are important factors for regulating the effects of ablation of biological tissues. Heat transfer to surrounding material may be desirable when ablating hard tissue, such as teeth or bone, since melting can produce helpful material modifications. However, when ablating soft tissue it is important to minimize heat transfer to avoid damage to healthy tissue - for example, in eye refractive surgery (e.g., Lasik), nanosecond pulses produce gross absorption and heating in tissue, leading to shockwaves, which kill and thin the non-replicating epithelial cells on the inside of the cornea; ultrafast pulses are recognized to reduce this effect. Using a laser system that delivers 1ps pulses in 10μs pulsetrains at 133MHz we have studied a range of heat- and energy-transfer effects on hard and soft tissue. We describe the ablation of tooth dentin and enamel under various conditions to determine the ablation rate and chemical changes that occur. Furthermore, we characterize the impact of pulsetrain-burst treatment of collagen-based tissue to determine more efficient methods of energy transfer to soft tissues. By studying the optical science of laser tissue interaction we hope to be able to make qualitative improvements to medical treatments using lasers.

  7. Metal-wool heat shields for space shuttle. [design, fabrication, and attachment to structure

    NASA Technical Reports Server (NTRS)

    Miller, R. C.; Clure, J. L.

    1974-01-01

    The packaging of metal wool for reusable thermal heat shields applied to aerodynamic and other surfaces for the space shuttle was analyzed and designed, and samples were fabricated and experimentally studied. Parametric trends were prepared for selected configurations. An all-metal thermally efficient, reliable, reusable and producible heat shield system was designed and structurally tested for use on spacecraft aerodynamic surfaces where temperatures do not exceed 810 K. Stainless steel sheet, primarily for structure and secondarily in the transverse plane for thermal expansion, was shown to accommodate thermal expansion in all directions when restrained at the edges and heated to 1360 K. Aerodynamic loads of 0.35 x 1000,000 newtons/sq meter, and higher, may be easily accepted by structures of this design. Seven all-metal thermal protection specimens, 12.7 cm square and 2.5 cm thick were fabricated and are being experimentally evaluated at simulated shuttle entry conditions in an arc jet facility.

  8. Heat Shielding Characteristics and Thermostructural Performance of a Superalloy Honeycomb Sandwich Thermal Protection System (TPS)

    NASA Technical Reports Server (NTRS)

    Ko, William L.

    2004-01-01

    Heat-transfer, thermal bending, and mechanical buckling analyses have been performed on a superalloy "honeycomb" thermal protection system (TPS) for future hypersonic flight vehicles. The studies focus on the effect of honeycomb cell geometry on the TPS heat-shielding performance, honeycomb cell wall buckling characteristics, and the effect of boundary conditions on the TPS thermal bending behavior. The results of the study show that the heat-shielding performance of a TPS panel is very sensitive to change in honeycomb core depth, but insensitive to change in honeycomb cell cross-sectional shape. The thermal deformations and thermal stresses in the TPS panel are found to be very sensitive to the edge support conditions. Slight corrugation of the honeycomb cell walls can greatly increase their buckling strength.

  9. Evaluation of coated columbium alloy heat shields for space shuttle thermal protection system application. Volume 2, phase 2: Subsize heat shield and small size TPS evaluation

    NASA Technical Reports Server (NTRS)

    Black, W. E.

    1973-01-01

    Initially a trade study was conducted of seven heat shield configurations. These were evaluated for structural reliability, fabricability, weight, inspectability, and refurbishability. Two concepts, a tee-stiffened and an open corrugation, were selected as offering the most potential for system success. Fourteen subsize heat shields of a full scale section were fabricated from C-129Y and Cb-752 and silicide coated with R-512E. These subsize panels were subjected to a simulated flight profile representing temperature, local surface pressures, and applied pressure differential loads. All corrugated panels of both alloys sustained 100 cycles without structural or coating failure. All Cb-752/R-512E panels performed well with one panel being successfully repaired after 66 cycles and completing 100 cycles. As a result of this evaluating the Cb-752/R-512E system was selected for hardware application during the subsequent phases. In addition, the tee-stiffened configuration was selected for further development and application in Phase III. This selection was based on an overall assessment of relative weight, cost, and structural performance of the tee-stiffened and open corrugation TPS.

  10. Numerical calculation of the parameters of the efflux from a helium dewar used for cooling of heat shields in a satellite

    NASA Technical Reports Server (NTRS)

    Brendley, K.; Chato, J. C.

    1982-01-01

    The parameters of the efflux from a helium dewar in space were numerically calculated. The flow was modeled as a one dimensional compressible ideal gas with variable properties. The primary boundary conditions are flow with friction and flow with heat transfer and friction. Two PASCAL programs were developed to calculate the efflux parameters: EFFLUZD and EFFLUXM. EFFLUXD calculates the minimum mass flow for the given shield temperatures and shield heat inputs. It then calculates the pipe lengths, diameter, and fluid parameters which satisfy all boundary conditions. Since the diameter returned by EFFLUXD is only rarely of nominal size, EFFLUXM calculates the mass flow and shield heat exchange for given pipe lengths, diameter, and shield temperatures.

  11. Validation of PICA Ablation and Thermal-Response Model at Low Heat Flux

    NASA Technical Reports Server (NTRS)

    Milos, Frank S.; Chen, Yih-Kanq

    2009-01-01

    Phenolic Impregnated Carbon Ablator (PICA) was the forebody heatshield material on the Stardust sample-return capsule and is also a primary candidate material for the Mars Science Lander (MSL), the Orion Crew Module, and the SpaceX Dragon vehicle. As part of the heatshield qualification for Orion, physical and thermal properties of virgin and charred PICA were measured, and an ablation and thermal response model was developed. We validated the model by comparing it with recession and temperature data from stagnation arcjet tests conducted over a wide range of stagnation heat flux of 107 to 1102 W/sq cm. The effect of orthotropic thermal conductivity was evident in the thermal response of the arcjet models. In general, model predictions compared well with the data; however, the uncertainty of the recession prediction was greatest for heat fluxes below 200 W/sq cm. More recent MSL testing focused on the low heat flux regime of 45 to 250 W/sq cm. The new results confirm the recession uncertainty, especially for pressures below 6 kPa. In this work we focus on improving the model predictions for MSL and Orion tests below 250 W/sq cm.

  12. Experimental determination of ablation vapor species from carbon phenolic heat-shield materials

    NASA Technical Reports Server (NTRS)

    Lincoln, K. A.

    1981-01-01

    The relative concentrations of vapors produced from carbon phenolic composites under thermal loadings approximating those expected at peak heating during vehicle entry into the atmospheres of the outer planets have been determined. The technique of vaporizing the surface of bulk samples by laser irradiation while measuring in situ the vapor species by mass spectrometry is described. Results show that vapor composition varies with irradiance level and with depth of heating (or extent of pyrolysis). Attempts are made to compare these experimental results with the theoretical predictions from computer codes.

  13. Thermal Testing of Ablators in the NASA Johnson Space Center Radiant Heat Test Facility

    NASA Technical Reports Server (NTRS)

    Del Papa, Steven; Milhoan, Jim; Remark, Brian; Suess, Leonard

    2016-01-01

    A spacecraft's thermal protection system (TPS) is required to survive the harsh environment experienced during reentry. Accurate thermal modeling of the TPS is required to since uncertainties in the thermal response result in higher design margins and an increase in mass. The Radiant Heat Test Facility (RHTF) located at the NASA Johnson Space Center (JSC) replicates the reentry temperatures and pressures on system level full scale TPS test models for the validation of thermal math models. Reusable TPS, i.e. tile or reinforced carbon-carbon (RCC), have been the primary materials tested in the past. However, current capsule designs for MPCV and commercial programs have required the use of an ablator TPS. The RHTF has successfully completed a pathfinder program on avcoat ablator material to demonstrate the feasibility of ablator testing. The test results and corresponding ablation analysis results are presented in this paper.

  14. The characterization of neural tissue ablation rate and corresponding heat affected zone of a 2 micron Tm3+ doped fiber laser(Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Marques, Andrew J.; Jivraj, Jamil; Reyes, Robnier; Ramjist, Joel; Gu, Xijia J.; Yang, Victor X. D.

    2017-02-01

    Tissue removal using electrocautery is standard practice in neurosurgery since tissue can be cut and cauterized simultaneously. Thermally mediated tissue ablation using lasers can potentially possess the same benefits but with increased precision. However, given the critical nature of the spine, brain, and nerves, the effects of direct photo-thermal interaction on neural tissue needs to be known, yielding not only high precision of tissue removal but also increased control of peripheral heat damage. The proposed use of lasers as a neurosurgical tool requires that a common ground is found between ablation rates and resulting peripheral heat damage. Most surgical laser systems rely on the conversion of light energy into heat resulting in both desirable and undesirable thermal damage to the targeted tissue. Classifying the distribution of thermal energy in neural tissue, and thus characterizing the extent of undesirable thermal damage, can prove to be exceptionally challenging considering its highly inhomogenous composition when compared to other tissues such as muscle and bone. Here we present the characterization of neural tissue ablation rate and heat affected zone of a 1.94 micron thulium doped fiber laser for neural tissue ablation. In-Vivo ablation of porcine cerebral cortex is performed. Ablation volumes are studied in association with laser parameters. Histological samples are taken and examined to characterize the extent of peripheral heat damage.

  15. Infra-red and vibration tests of hybrid ablative/ceramic matrix technological breadboards for earth re-entry thermal protection systems

    NASA Astrophysics Data System (ADS)

    Barcena, Jorge; Garmendia, Iñaki; Triantou, Kostoula; Mergia, Konstatina; Perez, Beatriz; Florez, Sonia; Pinaud, Gregory; Bouilly, Jean-Marc; Fischer, Wolfgang P. P.

    2017-05-01

    A new thermal protection system for atmospheric earth re-entry is proposed. This concept combines the advantages of both reusable and ablative materials to establish a new hybrid concept with advanced capabilities. The solution consists of the design and the integration of a dual shield resulting on the overlapping of an external thin ablative layer with a Ceramic Matrix Composite (CMC) thermo-structural core. This low density ablative material covers the relatively small heat peak encountered during re-entry the CMC is not able to bear. On the other hand the big advantage of the CMC based TPS is of great benefit which can deal with the high integral heat for the bigger time period of the re-entry. To verify the solution a whole testing plan is envisaged, which as part of it includes thermal shock test by infra-red heating (heating flux up to 1 MW/m2) and vibration test under launcher conditions (Volna and Ariane 5). Sub-scale tile samples (100×100 mm2) representative of the whole system (dual ablator/ceramic layers, insulation, stand-offs) are specifically designed, assembled and tested (including the integration of thermocouples). Both the thermal and the vibration test are analysed numerically by simulation tools using Finite Element Models. The experimental results are in good agreement with the expected calculated parameters and moreover the solution is qualified according to the specified requirements.

  16. Characterization of Pancreatic Cancer Cell Thermal Response to Heat Ablation or Cryoablation.

    PubMed

    Baumann, Kenneth W; Baust, John M; Snyder, Kristi K; Baust, John G; Van Buskirk, Robert G

    2017-08-01

    One of the most lethal carcinomas is pancreatic cancer. As standard treatment using chemotherapy and radiation has shown limited success, thermal regimens (cryotherapy or heat ablation) are emerging as viable alternatives. Although promising, our understanding of pancreatic cancer response to thermal ablation remains limited. In this study, we investigated the thermal responses of 2 pancreatic cancer cell lines in an effort to identify the minimum lethal temperature needed for complete cell death to provide guidance for in vivo applications. PANC-1 and BxPC-3 were frozen (-10°C to -25°C) or heated (45°C-50°C) in single and repeated exposure regimes. Posttreatment survival and recovery were analyzed using alamarBlue assay over a 7-day interval. Modes of cell death were assessed using fluorescence microscopy (calcein acetoxymethyl ester/propidium iodide) and flow cytometry (YO-PRO-1/propidium iodide). Freezing to -10°C resulted in minimal cell death. Exposure to -15°C had a mild impact on PANC-1 survival (93%), whereas BxPC-3 was more severely damaged (33%). Exposure to -20°C caused a significant reduction in viability (PANC-1 = 23%; BxPC-3 = 2%) whereas -25°C yielded complete death. Double freezing exposure was more effective than single exposure. Repeat exposure to -15°C resulted in complete death of BxPC-3, whereas -20°C severely impacted PANC-1 (7%). Heating to 45°C resulted in minimum cell death. Exposure to 48°C yielded a slight increase in cell loss (PANC-1 = 85%; BxPC-3 = 98%). Exposure to 50°C caused a significant decline (PANC-1 = 70%; BxPC-3 = 9%) with continued deterioration to 0%. Double heating to 45°C resulted in similar effects observed in single exposures, whereas repeated 48°C resulted in significant increases in cell death (PANC-1 = 68%; BxPC-3 = 29%). In conclusion, we observed that pancreatic cancer cells were completely destroyed at temperatures <-25°C or >50°C using single thermal exposures. Repeated exposures resulted in

  17. Analysis of internal ablation for the thermal control of aerospace vehicles

    NASA Technical Reports Server (NTRS)

    Camberos, Jose A.; Roberts, Leonard

    1989-01-01

    A new method of thermal protection for transatmospheric vehicles is introduced. The method involves the combination of radiation, ablation and transpiration cooling. By placing an ablating material behind a fixed-shape, porous outer shield, the effectiveness of transpiration cooling is made possible while retaining the simplicity of a passive mechanism. A simplified one-dimensional approach is used to derive the governing equations. Reduction of these equations to non-dimensional form yields two parameters which characterize the thermal protection effectiveness of the shield and ablator combination for a given trajectory. The non-dimensional equations are solved numerically for a sample trajectory corresponding to glide re-entry. Four typical ablators are tested and compared with results obtained by using the thermal properties of water. For the present level of analysis, the numerical computations adequately support the analytical model.

  18. Microwave liver ablation: influence of hepatic vein size on heat-sink effect in a porcine model.

    PubMed

    Yu, Nam C; Raman, Steven S; Kim, Young Jun; Lassman, Charles; Chang, Xinlian; Lu, David S K

    2008-07-01

    To determine influence of hepatic vein size on perfusion-mediated attenuation in adjacent microwave thermal ablation. With approval of the institutional animal research committee, seven Yorkshire pigs underwent percutaneous (n = 2) or open (n = 5) microwave liver ablation under general anesthesia. In each, multiple ultrasound-guided, nonoverlapping thermal lesions were created within 1 cm of hepatic veins in a 5-10-minute ablation at 45 W. After euthanasia, the liver was harvested and sectioned at 0.5-cm intervals and the degree of perivascular coagulation attenuation was graded on histopathologic analysis. Correlation between venous size (small, < or =3 mm; medium, 3-6 mm; and large, >6 mm) and attenuation grade was performed with use of the Spearman rank test. In 63 of 103 sections (61%)--29 of 37 (78%) small, 27 of 48 (56%) medium, and seven of 18 (39%) large veins--the thermal injury extended to the vein wall around the entire circumference of the coagulation front without distortion of the ablation margin. In 40 of 103 sections (38.9%), varying degrees of concave distortion of perivenous ablation margins were noted, with significant correlation between vein size and heat-sink extent (P < .01). However, thermal injury extended to the vascular wall in all sections without complete circumferential sparing of liver tissue. Around two thrombosed veins, thermal lesions encased the vessels, producing paradoxically convex ablation margins. Although the heat-sink effect was significantly dependent on hepatic vein size, the majority of pathologic sections exhibited no or minimal effect. Further study is required to assess clinical implications.

  19. Interstitial ultrasound ablation of tumors within or adjacent to bone: Contributions of preferential heating at the bone surface

    NASA Astrophysics Data System (ADS)

    Scott, Serena J.; Prakash, Punit; Salgaonkar, Vasant; Jones, Peter D.; Cam, Richard N.; Han, Misung; Rieke, Viola; Burdette, E. Clif; Diederich, Chris J.

    2013-02-01

    Preferential heating of bone due to high ultrasound attenuation may enhance thermal ablation performed with cathetercooled interstitial ultrasound applicators in or near bone. At the same time, thermally and acoustically insulating cortical bone may protect sensitive structures nearby. 3D acoustic and biothermal transient finite element models were developed to simulate temperature and thermal dose distributions during catheter-cooled interstitial ultrasound ablation near bone. Experiments in ex vivo tissues and tissue-mimicking phantoms were performed to validate the models and to quantify the temperature profiles and ablated volumes for various distances between the interstitial applicator and the bone surface. 3D patient-specific models selected to bracket the range of clinical usage were developed to investigate what types of tumors could be treated, applicator configurations, insertion paths, safety margins, and other parameters. Experiments show that preferential heating at the bone surface decreases treatment times compared to when bone is absent and that all tissue between an applicator and bone can be ablated when they are up to 2 cm apart. Simulations indicate that a 5-7 mm safety margin of normal bone is needed to protect (thermal dose < 6 CEM43°C and T < 45°C) sensitive structures behind ablated bone. In 3D patient-specific simulations, tumors 1.0-3.8 cm (L) and 1.3-3.0 cm (D) near or within bone were ablated (thermal dose > 240 CEM43°C) within 10 min without damaging the nearby spinal cord, lungs, esophagus, trachea, or major vasculature. Preferential absorption of ultrasound by bone may provide improved localization, faster treatment times, and larger treatment zones in tumors in and near bone compared to other heating modalities.

  20. Galileo Probe forebody thermal protection

    NASA Technical Reports Server (NTRS)

    Green, M. J.; Davy, W. C.

    1981-01-01

    Material response solutions for the forebody heat shield on the candidate 310-kg Galileo Probe are presented. A charring material ablation analysis predicts thermochemical surface recession, insulation thickness, and total required heat shield mass. Benchmark shock layer solutions provide the imposed entry heating environments on the ablating surface. Heat shield sizing results are given for a nominal entry into modeled nominal and cool-heavy Jovian atmospheres, and for two heat-shield property models. The nominally designed heat shield requires a mass of at least 126 kg and would require an additional 13 kg to survive entry into the less probable cool-heavy atmosphere. The material-property model with a 30% surface reflectance reduces these mass requirements by as much as 16%.

  1. Vapor Grown Carbon Fiber/Phenolic Matrix Composites for Rocket Nozzles and Heat Shields

    NASA Technical Reports Server (NTRS)

    Patton, R. D.; Pittman, C. U., Jr.; Wang, L.; Day, A.; Hill, J. R.

    2001-01-01

    The ablation and mechanical and thermal properties of vapor grown carbon fiber (VGCF)/phenolic resin composites were evaluated to determine the potential of using this material in solid rocket motor nozzles. Composite specimens with varying VGCF loading (30%-50% wt) including one sample with ex-rayon carbon fiber plies were prepared and exposed to a plasma torch for 20 s with a heat flux of 16.5 MW/sq m at approximately 1650 C. Low erosion rates and little char formation were observed, confirming that these materials were promising for rocket motor nozzle materials. When fiber loadings increased, mechanical properties and ablative properties improved. The VGCF composites had low thermal conductivities (approximately 0.56 W/m-C) indicating they were good insulating materials. If a 65% fiber loading in VGCF composite can be achieved, then ablative properties are projected to be comparable to or better than the composite material currently used on the Space Shuttle Reusable Solid Rocket Motor (RSRM).

  2. Modelling of labour productivity loss due to climate change: HEAT-SHIELD

    NASA Astrophysics Data System (ADS)

    Kjellstrom, Tord; Daanen, Hein

    2016-04-01

    Climate change will bring higher heat levels (temperature and humidity combined) to large parts of the world. When these levels reach above thresholds well defined by human physiology, the ability to maintain physical activity levels decrease and labour productivity is reduced. This impact is of particular importance in work situations in areas with long high intensity hot seasons, but also affects cooler areas during heat waves. Our modelling of labour productivity loss includes climate model data of the Inter-Sectoral Impact Model Inter-comparison Project (ISI-MIP), calculations of heat stress indexes during different months, estimations of work capacity loss and its annual impacts in different parts of the world. Different climate models will be compared for the Representative Concentration Pathways (RCPs) and the outcomes of the 2015 Paris Climate Conference (COP21) agreements. The validation includes comparisons of modelling outputs with actual field studies using historical heat data. These modelling approaches are a first stage contribution to the European Commission funded HEAT-SHIELD project.

  3. Experimental performance of an ablative material as an external insulator for a hypersonic research aircraft

    NASA Technical Reports Server (NTRS)

    Puster, R. L.; Chapman, A. J.

    1977-01-01

    An ablative material composed of silica-filled elastomeric silicone was tested to evaluate its thermal and structural performance as an external insulator, or heat shield, for a hypersonic research aircraft. The material was also tested to determine whether it would form a durable char layer when initially heated and thereafter function primarily as an insulator with little further pyrolysis or char removal. Aerothermal tests were representative of nominal Mach 6 cruise conditions of the aircraft, and additional tests were representative of Mach 8 cruise and interference heating conditions. Radiant heating tests were used to simulate the complete nominal Mach 6 surface-temperature history. The silica char that formed during aerothermal tests was not durable. The char experienced a general and preferential surface recession, with the primary mechanism for char removal being erosion. Tests revealed that radiant heating is not a valid technique for simulating aerodynamic heating of the material.

  4. Nonequilibrium Ablation of Phenolic Impregnated Carbon Ablator

    NASA Technical Reports Server (NTRS)

    Milos, Frank S.; Chen, Yih K.; Gokcen, Tahir

    2012-01-01

    In previous work, an equilibrium ablation and thermal response model for Phenolic Impregnated Carbon Ablator was developed. In general, over a wide range of test conditions, model predictions compared well with arcjet data for surface recession, surface temperature, in-depth temperature at multiple thermocouples, and char depth. In this work, additional arcjet tests were conducted at stagnation conditions down to 40 W/sq cm and 1.6 kPa. The new data suggest that nonequilibrium effects become important for ablation predictions at heat flux or pressure below about 80 W/sq cm or 10 kPa, respectively. Modifications to the ablation model to account for nonequilibrium effects are investigated. Predictions of the equilibrium and nonequilibrium models are compared with the arcjet data.

  5. New heat flow measurements in Oman and the thermal state of the Arabian Shield and Platform

    NASA Astrophysics Data System (ADS)

    Rolandone, Frédérique; Lucazeau, Francis; Leroy, Sylvie; Mareschal, Jean-Claude; Jorand, Rachel; Goutorbe, Bruno; Bouquerel, Hélène

    2013-03-01

    The present-day thermal regime of the Arabian plate is affected by the dynamics of the Afar plume and the rifting of the Red Sea and the Gulf of Aden. The Arabian plate is a Precambrian Shield and its thermal regime, before the plume and rifting activities, should be similar to that of other Precambrian Shields with a thick lithosphere. This is consistent with low heat-flow values measured in Saudi Arabia (35-44 mWm- 2), but not with recent measurements in Jordan that show higher heat flow (56-66 mWm- 2). We have conducted measurements in the eastern Arabian plate to obtain 10 new heat-flux values. We also derived 20 heat-flux values from oil exploration wells. Our measurements show that surface heat flux is uniformly low (45 mWm- 2) in the eastern Arabian Shield and is consistent with low crustal heat production (0.7 μWm- 3). A steady-state geotherm for the Arabian platform that intersects the isentropic temperature profile at a depth of 150 km is consistent with the seismic observations. Differences in heat flow between the eastern (60 mWm- 2) and the western (45 mWm- 2) parts of Arabia reflect differences in crustal heat production as well as a higher mantle heat flux in the west. Seismic tomography studies of the mantle beneath Arabia show this east-west contrast. The lithospheric thickness for the Arabian plate is 150 km, and the progressive thinning near the Red Sea is caused by the thermal erosion of the plume. The Afar plume mostly affects the base of the Arabian lithosphere along the Red Sea and the western part of the Gulf of Aden by channeling magmas from the asthenosphere through the rift. The continental domain is not affected by rifting in the Gulf of Aden. The main thermal effect of the Arabian plate is probably the channeling of the Afar plume to the North.

  6. Measuring space radiation shielding effectiveness

    NASA Astrophysics Data System (ADS)

    Bahadori, Amir; Semones, Edward; Ewert, Michael; Broyan, James; Walker, Steven

    2017-09-01

    Passive radiation shielding is one strategy to mitigate the problem of space radiation exposure. While space vehicles are constructed largely of aluminum, polyethylene has been demonstrated to have superior shielding characteristics for both galactic cosmic rays and solar particle events due to the high hydrogen content. A method to calculate the shielding effectiveness of a material relative to reference material from Bragg peak measurements performed using energetic heavy charged particles is described. Using accelerated alpha particles at the National Aeronautics and Space Administration Space Radiation Laboratory at Brookhaven National Laboratory, the method is applied to sample tiles from the Heat Melt Compactor, which were created by melting material from a simulated astronaut waste stream, consisting of materials such as trash and unconsumed food. The shielding effectiveness calculated from measurements of the Heat Melt Compactor sample tiles is about 10% less than the shielding effectiveness of polyethylene. Shielding material produced from the astronaut waste stream in the form of Heat Melt Compactor tiles is therefore found to be an attractive solution for protection against space radiation.

  7. Microwave ablation of the liver: a description of lesion evolution over time and an investigation of the heat sink effect.

    PubMed

    Bhardwaj, N; Dormer, J; Ahmad, F; Strickland, A D; Gravante, G; West, K; Dennison, A R; Lloyd, D M

    2011-12-01

    Microwave ablation has been successfully used to treat unresectable liver tumours for many years. However, despite its widespread use, there seems to be a relative paucity of experimental data regarding lesion evolution and the effects of any surrounding vasculature on ablation morphology. The aim of this study was to investigate the principal pathological changes in the liver following microwave ablation, in particular the heat sink effect. In addition we carefully reviewed the available literature to provide an overview of all relevant pathological studies. Microwave ablation was carried out on male rats at various distances from the hilum. Histological (H&E) and immunocytochemical (caspase 3) analyses of the lesion were performed at various time points; 0, 4, 24, 48  hours, 2 weeks and 1 month. A literature review was carried out using Medline, Embase and the Cochrane database to identify all relevant histological studies. The lesion underwent complete coagulative necrosis and was extremely regular at the ablation edge with no evidence of any influence from surrounding blood vessels at all time points. H&E and caspase 3 results were consistent and microwave caused little collateral damage outside the intended ablation zone. This study suggests that microwave ablation is extremely concise and is minimally affected by the heat sink effect. Comparative investigations with other treatment modalities are required.

  8. Oxidation and emittance of superalloys in heat shield applications

    NASA Technical Reports Server (NTRS)

    Wiedemann, K. E.; Clark, R. K.; Unnam, J.

    1986-01-01

    Recently developed superalloys that form alumina coatings have a high potential for heat shield applications for advanced aerospace vehicles at temperatures above 1095C. Both INCOLOY alloy MA 956 (of the Inco Alloys International, Inc.), an iron-base oxide-dispersion-strengthened alloy, and CABOT alloy No. 214 (of the Cabot Corporation), an alumina-forming nickel-chromium alloy, have good oxidation resistance and good elevated temperature strength. The oxidation resistance of both alloys has been attributed to the formation of a thin alumina layer (alpha-Al2O3) at the surface. Emittance and oxidation data were obtained for simulated Space Shuttle reentry conditions using a hypersonic arc-heated wind tunnel. The surface oxides and substrate alloys were characterized using X-ray diffraction and scanning and transmission electron microscopy with an energy-dispersive X-ray analysis unit. The mass loss and emittance characteristics of the two alloys are discussed.

  9. Minimal vascular flows cause strong heat sink effects in hepatic radiofrequency ablation ex vivo.

    PubMed

    Lehmann, Kai S; Poch, Franz G M; Rieder, Christian; Schenk, Andrea; Stroux, Andrea; Frericks, Bernd B; Gemeinhardt, Ole; Holmer, Christoph; Kreis, Martin E; Ritz, Jörg P; Zurbuchen, Urte

    2016-08-01

    The present paper aims to assess the lower threshold of vascular flow rate on the heat sink effect in bipolar radiofrequency ablation (RFA) ex vivo. Glass tubes (vessels) of 3.4 mm inner diameter were introduced in parallel to bipolar RFA applicators into porcine liver ex vivo. Vessels were perfused with flow rates of 0 to 1,500 ml/min. RFA (30 W power, 15 kJ energy input) was carried out at room temperature and 37°C. Heat sink effects were assessed in RFA cross sections by the decrease in ablation radius, area and by a high-resolution sector planimetry. Flow rates of 1 ml/min already caused a significant cooling effect (P ≤ 0.001). The heat sink effect reached a maximum at 10 ml/min (18.4 mm/s) and remained stable for flow rates up to 1,500 ml/min. Minimal vascular flows of ≥1 ml/min cause a significant heat sink effect in hepatic RFA ex vivo. A lower limit for volumetric flow rate was not found. The maximum of the heat sink effect was reached at a flow rate of 10 ml/min and remained stable for flow rates up to 1,500 ml/min. Hepatic inflow occlusion should be considered in RFA close to hepatic vessels. © 2016 Japanese Society of Hepato-Biliary-Pancreatic Surgery.

  10. Endogenous Heat-Shock Protein Induction with or Without Radiofrequency Ablation or Cryoablation in Patients with Stage IV Melanoma.

    PubMed

    Domingo-Musibay, Evidio; Heun, James M; Nevala, Wendy K; Callstrom, Matthew; Atwell, Thomas; Galanis, Evanthia; Erickson, Lori A; Markovic, Svetomir N

    2017-09-01

    Percutaneous thermal ablation combined with in situ granulocyte-macrophage colony-stimulating factor cytokine therapy was technically feasible and well tolerated.No significant clinical or immunologic responses were seen. Melanoma tumor-derived heat-shock proteins (HSPs) and HSP-peptide complexes can elicit protective antitumor responses. The granulocyte-macrophage colony-stimulating factor (GM-CSF) chemokine can also promote uptake and processing by professional antigen presenting cells (APCs). On this basis, we designed a pilot study of percutaneous thermal ablation as a means to induce heat-shock protein vaccination plus GM-CSF to determine safety and preliminary antitumor activity of this combination. This study was designed to assess overall safety of percutaneous ablation combined with GM-CSF for unresectable, metastatic melanoma including uveal and mucosal types. All patients received heat-shock therapy (42°C for 30 minutes), then received one of three treatments: (a) intralesional GM-CSF (500 mcg standard dose); (b) radiofrequency ablation (RFA) + GM-CSF; or (c) cryoablation plus GM-CSF. The primary endpoint of the study was the induction of endogenous HSP70 and melanoma-specific cytotoxic T lymphocytes (CTL). Nine patients (three per study arm) were enrolled. No dose-limiting toxicity was observed as specified per protocol. All patients developed progressive disease and went on to receive alternative therapy. Median overall survival (OS) was 8.2 months (95% confidence interval [CI] 2-17.2). The study was not powered to detect a difference in clinical outcome among treatment groups. Percutaneous thermal ablation plus GM-CSF was well tolerated, technically feasible, and demonstrated an acceptable adverse event profile comparable to conventional RFA and cryoablation. While HSP70 was induced following therapy, the degree of HSP70 elevation was not associated with clinical outcome or induced CTL responses. While percutaneous thermal ablation plus GM

  11. Continuum approach for aerothermal flow through ablative porous material using discontinuous Galerkin discretization.

    NASA Astrophysics Data System (ADS)

    Schrooyen, Pierre; Chatelain, Philippe; Hillewaert, Koen; Magin, Thierry E.

    2014-11-01

    The atmospheric entry of spacecraft presents several challenges in simulating the aerothermal flow around the heat shield. Predicting an accurate heat-flux is a complex task, especially regarding the interaction between the flow in the free stream and the erosion of the thermal protection material. To capture this interaction, a continuum approach is developed to go progressively from the region fully occupied by fluid to a receding porous medium. The volume averaged Navier-Stokes equations are used to model both phases in the same computational domain considering a single set of conservation laws. The porosity is itself a variable of the computation, allowing to take volumetric ablation into account through adequate source terms. This approach is implemented within a computational tool based on a high-order discontinuous Galerkin discretization. The multi-dimensional tool has already been validated and has proven its efficient parallel implementation. Within this platform, a fully implicit method was developed to simulate multi-phase reacting flows. Numerical results to verify and validate the methodology are considered within this work. Interactions between the flow and the ablated geometry are also presented. Supported by Fund for Research Training in Industry and Agriculture.

  12. Direct measurements of sample heating by a laser-induced air plasma in pre-ablation spark dual-pulse laser-induced breakdown spectroscopy (LIBS).

    PubMed

    Register, Janna; Scaffidi, Jonathan; Angel, S Michael

    2012-08-01

    Direct measurements of temperature changes were made using small thermocouples (TC), placed near a laser-induced air plasma. Temperature changes up to ~500 °C were observed. From the measured temperature changes, estimates were made of the amount of heat absorbed per unit area. This allowed calculations to be made of the surface temperature, as a function of time, of a sample heated by the air plasma that is generated during orthogonal pre-ablation spark dual-pulse (DP) LIBS measurements. In separate experiments, single-pulse (SP) LIBS emission and sample ablation rate measurements were performed on nickel at sample temperatures ranging from room temperature to the maximum surface temperature that was calculated using the TC measurement results (500 °C). A small, but real sample temperature-dependent increase in both SP LIBS emission and the rate of sample ablation was found for nickel samples heated up to 500 °C. Comparison of DP LIBS emission enhancement values for bulk nickel samples at room temperature versus the enhanced SP LIBS emission and sample ablation rates observed as a function of increasing sample temperature suggests that sample heating by the laser-induced air plasma plays only a minor role in DP LIBS emission enhancement.

  13. Fused slurry silicide coatings for columbium alloys reentry heat shields. Volume 1: Evaluation analysis

    NASA Technical Reports Server (NTRS)

    Fitzgerald, B.

    1973-01-01

    The R-512E (Si-20Cr-20Fe) fused slurry silicide coating process was optimized to coat full size (20in x 20in) single face rib and corrugation stiffened panels fabricated from FS-85 columbium alloy for 100 mission space shuttle heat shield applications. Structural life under simulated space shuttle lift-off stresses and reentry conditions demonstrated reuse capability well beyond 100 flights for R-512E coated FS-85 columbium heat shield panels. Demonstrated coating damage tolerance showed no immediate structural failure on exposure. The FS-85 columbium alloy was selected from five candidate alloys (Cb-752, C-129Y, WC-3015, B-66 and FS-85) based on the evaluation tests which have designed to determine: (1) change in material properties due to coating and reuse; (2) alloy tolerance to coating damage; (3) coating emittance characteristics under reuse conditions; and (4) new coating chemistries for improved coating life.

  14. Microscreen radiation shield for thermoelectric generator

    DOEpatents

    Hunt, Thomas K.; Novak, Robert F.; McBride, James R.

    1990-01-01

    The present invention provides a microscreen radiation shield which reduces radiative heat losses in thermoelectric generators such as sodium heat engines without reducing the efficiency of operation of such devices. The radiation shield is adapted to be interposed between a reaction zone and a means for condensing an alkali metal vapor in a thermoelectric generator for converting heat energy directly to electrical energy. The radiation shield acts to reflect infrared radiation emanating from the reaction zone back toward the reaction zone while permitting the passage of the alkali metal vapor to the condensing means. The radiation shield includes a woven wire mesh screen or a metal foil having a plurality of orifices formed therein. The orifices in the foil and the spacing between the wires in the mesh is such that radiant heat is reflected back toward the reaction zone in the interior of the generator, while the much smaller diameter alkali metal atoms such as sodium pass directly through the orifices or along the metal surfaces of the shield and through the orifices with little or no impedance.

  15. A probabilistic sizing tool and Monte Carlo analysis for entry vehicle ablative thermal protection systems

    NASA Astrophysics Data System (ADS)

    Mazzaracchio, Antonio; Marchetti, Mario

    2010-03-01

    Implicit ablation and thermal response software was developed to analyse and size charring ablative thermal protection systems for entry vehicles. A statistical monitor integrated into the tool, which uses the Monte Carlo technique, allows a simulation to run over stochastic series. This performs an uncertainty and sensitivity analysis, which estimates the probability of maintaining the temperature of the underlying material within specified requirements. This approach and the associated software are primarily helpful during the preliminary design phases of spacecraft thermal protection systems. They are proposed as an alternative to traditional approaches, such as the Root-Sum-Square method. The developed tool was verified by comparing the results with those from previous work on thermal protection system probabilistic sizing methodologies, which are based on an industry standard high-fidelity ablation and thermal response program. New case studies were analysed to establish thickness margins on sizing heat shields that are currently proposed for vehicles using rigid aeroshells for future aerocapture missions at Neptune, and identifying the major sources of uncertainty in the material response.

  16. Comparison of heat induced damage at the saphenofemoral junction after ablation with 1,470 nm laser or radiofrequency.

    PubMed

    Ozcinar, Evren; Cakici, Mehmet; Korun, Oktay; Han, Unsal; Kiziltepe, Ugursay

    2017-03-01

    The aim of this study was to evaluate the heat induced damage at the saphenofemoral junction level according to histopathological changes after radiofrequency or 1,470 nm radial tip laser ablation. Varicose vein segments of 6-10 mm in diameter were exposed to radiofrequency (Closure Fast catheter, 7 cm heat segment, one cycle, 15 seconds, 10 Watt, 120 °C) or laser ablation (1,470 nm radial tip, continuous wave, vein diameter: 6 cm/8 cm/10 cm-power: 10 Watt-pullback speed: 2.2 mm/s, 1.7 mm/s, 1.3 mm/s-LEED: 45J/cm, 60J/cm, 75J/cm-EFE 25J/cm 2 , respectively). Approximate 2 cm segments of the vein were left untreated, then histopathological examinations of the untouched segments (5 slices: level 1 - furthest segment, level 2 - nearest segment) for heat induced damage were performed. A total damage scoring system was established, including the presence of endothelial swelling, intimal thickening, cellular vacuolisation in the muscle layer, oedema in the tunica media, and extent of necrosis. At level 1, the furthest segment of the specimen, there was no significant difference between the laser and control group, while the total damage score of the radiofrequency group was significantly higher than the control group (p < 0.01). Radiofrequency group had higher total damage score compared to the laser group at level 1 (p < 0.01), 2 (p < 0.01), and 5 (p < 0.01); while no significant difference was observed at level 3 (p = 0.46) and 4 (p = 0.13). Significant heat induced damage may be seen even if the 2 cm segment of the vessel is left unablated. Radiofrequency ablation seems to cause more histological damage than laser ablation in this ex vivo study. Further in vivo studies are necessary, in order to validate these findings.

  17. Emission Spectroscopic Boundary Layer Investigation during Ablative Material Testing in Plasmatron.

    PubMed

    Helber, Bernd; Chazot, Olivier; Hubin, Annick; Magin, Thierry E

    2016-06-09

    Ablative Thermal Protection Systems (TPS) allowed the first humans to safely return to Earth from the moon and are still considered as the only solution for future high-speed reentry missions. But despite the advancements made since Apollo, heat flux prediction remains an imperfect science and engineers resort to safety factors to determine the TPS thickness. This goes at the expense of embarked payload, hampering, for example, sample return missions. Ground testing in plasma wind-tunnels is currently the only affordable possibility for both material qualification and validation of material response codes. The subsonic 1.2MW Inductively Coupled Plasmatron facility at the von Karman Institute for Fluid Dynamics is able to reproduce a wide range of reentry environments. This protocol describes a procedure for the study of the gas/surface interaction on ablative materials in high enthalpy flows and presents sample results of a non-pyrolyzing, ablating carbon fiber precursor. With this publication, the authors envisage the definition of a standard procedure, facilitating comparison with other laboratories and contributing to ongoing efforts to improve heat shield reliability and reduce design uncertainties. The described core techniques are non-intrusive methods to track the material recession with a high-speed camera along with the chemistry in the reactive boundary layer, probed by emission spectroscopy. Although optical emission spectroscopy is limited to line-of-sight measurements and is further constrained to electronically excited atoms and molecules, its simplicity and broad applicability still make it the technique of choice for analysis of the reactive boundary layer. Recession of the ablating sample further requires that the distance of the measurement location with respect to the surface is known at all times during the experiment. Calibration of the optical system of the applied three spectrometers allowed quantitative comparison. At the fiber scale

  18. Emission Spectroscopic Boundary Layer Investigation during Ablative Material Testing in Plasmatron

    PubMed Central

    Helber, Bernd; Chazot, Olivier; Hubin, Annick; Magin, Thierry E.

    2016-01-01

    Ablative Thermal Protection Systems (TPS) allowed the first humans to safely return to Earth from the moon and are still considered as the only solution for future high-speed reentry missions. But despite the advancements made since Apollo, heat flux prediction remains an imperfect science and engineers resort to safety factors to determine the TPS thickness. This goes at the expense of embarked payload, hampering, for example, sample return missions. Ground testing in plasma wind-tunnels is currently the only affordable possibility for both material qualification and validation of material response codes. The subsonic 1.2MW Inductively Coupled Plasmatron facility at the von Karman Institute for Fluid Dynamics is able to reproduce a wide range of reentry environments. This protocol describes a procedure for the study of the gas/surface interaction on ablative materials in high enthalpy flows and presents sample results of a non-pyrolyzing, ablating carbon fiber precursor. With this publication, the authors envisage the definition of a standard procedure, facilitating comparison with other laboratories and contributing to ongoing efforts to improve heat shield reliability and reduce design uncertainties. The described core techniques are non-intrusive methods to track the material recession with a high-speed camera along with the chemistry in the reactive boundary layer, probed by emission spectroscopy. Although optical emission spectroscopy is limited to line-of-sight measurements and is further constrained to electronically excited atoms and molecules, its simplicity and broad applicability still make it the technique of choice for analysis of the reactive boundary layer. Recession of the ablating sample further requires that the distance of the measurement location with respect to the surface is known at all times during the experiment. Calibration of the optical system of the applied three spectrometers allowed quantitative comparison. At the fiber scale

  19. Protective and Heat Retention Effects of Thermo-sensitive Basement Membrane Extract (Matrigel) in Hepatic Radiofrequency Ablation in an Experimental Animal Study.

    PubMed

    Fu, Jing-Jing; Wang, Song; Yang, Wei; Gong, Wei; Jiang, An-Na; Yan, Kun; Chen, Min-Hua

    2017-07-01

    To evaluate the protective effect of using thermo-sensitive basement membrane extract (Matrigel) for hydrodissection to minimize thermal injury to nearby structures and to evaluate its heat sink effect on the ablation zone in radiofrequency ablation (RFA) of the liver. First, the viscosity profile and heat sink effect of Matrigel were assessed during RFA in vitro and ex vivo. Fresh pig liver tissue was used, and the temperature changes in Matrigel and in 5% dextrose in water (D5W) during RFA were recorded. Then, the size of the ablation zone in the peripheral liver after RFA was measured. Second, in an in vivo study, 45 Sprague-Dawley rats were divided into three groups of 15 rats each (Matrigel, D5W and control). In the experimental groups, artificial ascites with 10 ml of Matrigel or D5W were injected using ultrasound guidance prior to RFA. The frequency of thermal injury to the nearby organs was compared among the three groups, with assessments of several locations: near the diaphragm, the abdominal wall and the gastrointestinal (GI) tract. Finally, the biological degradation of Matrigel by ultrasound was evaluated over 60 days. First, Matrigel produced a greater heat retention (less heat sink) effect than D5W during ex vivo ablation (63 ± 9 vs. 26 ± 6 °C at 1 min on the surface of the liver, P < 0.001). Hepatic ablation zone volume did not differ between the two groups. Second, thermal injury to the nearby structures was found in 14 of 15 cases (93.3%) in the control group, 8 of 15 cases (53.3%) in the D5W group, and 1 of 15 cases (6.7%) in the Matrigel group. Significant differences in the thermal injury rates for nearby structures were detected among the three groups (P < 0.001). The most significant difference in the thermal injury rate was found in locations near the GI tract (P = 0.003). Finally, Matrigel that was injected in vivo was gradually degraded during the following 60 days. Using thermo-sensitive Matrigel as a hydrodissection

  20. All fiber cladding mode stripper with uniform heat distribution and high cladding light loss manufactured by CO2 laser ablation

    NASA Astrophysics Data System (ADS)

    Jebali, M. A.; Basso, E. T.

    2018-02-01

    Cladding mode strippers are primarily used at the end of a fiber laser cavity to remove high-power excess cladding light without inducing core loss and beam quality degradation. Conventional manufacturing methods of cladding mode strippers include acid etching, abrasive blasting or laser ablation. Manufacturing of cladding mode strippers using laser ablation consist of removing parts of the cladding by fused silica ablation with a controlled penetration and shape. We present and characterize an optimized cladding mode stripper design that increases the cladding light loss with a minimal device length and manufacturing time. This design reduces the localized heat generation by improving the heat distribution along the device. We demonstrate a cladding mode stripper written on a 400um fiber with cladding light loss of 20dB, with less than 0.02dB loss in the core and minimal heating of the fiber and coating. The manufacturing process of the designed component is fully automated and takes less than 3 minutes with a very high throughput yield.

  1. The heat-pipe resembling action of boiling bubbles in endovenous laser ablation

    PubMed Central

    van den Bos, Renate R.; van Ruijven, Peter W. M.; Nijsten, Tamar; Neumann, H. A. Martino; van Gemert, Martin J. C.

    2010-01-01

    Endovenous laser ablation (EVLA) produces boiling bubbles emerging from pores within the hot fiber tip and traveling over a distal length of about 20 mm before condensing. This evaporation-condensation mechanism makes the vein act like a heat pipe, where very efficient heat transport maintains a constant temperature, the saturation temperature of 100°C, over the volume where these non-condensing bubbles exist. During EVLA the above-mentioned observations indicate that a venous cylindrical volume with a length of about 20 mm is kept at 100°C. Pullback velocities of a few mm/s then cause at least the upper part of the treated vein wall to remain close to 100°C for a time sufficient to cause irreversible injury. In conclusion, we propose that the mechanism of action of boiling bubbles during EVLA is an efficient heat-pipe resembling way of heating of the vein wall. PMID:20644976

  2. Modelling ultrafast laser ablation

    NASA Astrophysics Data System (ADS)

    Rethfeld, Baerbel; Ivanov, Dmitriy S.; E Garcia, Martin; Anisimov, Sergei I.

    2017-05-01

    This review is devoted to the study of ultrafast laser ablation of solids and liquids. The ablation of condensed matter under exposure to subpicosecond laser pulses has a number of peculiar properties which distinguish this process from ablation induced by nanosecond and longer laser pulses. The process of ultrafast ablation includes light absorption by electrons in the skin layer, energy transfer from the skin layer to target interior by nonlinear electronic heat conduction, relaxation of the electron and ion temperatures, ultrafast melting, hydrodynamic expansion of heated matter accompanied by the formation of metastable states and subsequent formation of breaks in condensed matter. In case of ultrashort laser excitation, these processes are temporally separated and can thus be studied separately. As for energy absorption, we consider peculiarities of the case of metal irradiation in contrast to dielectrics and semiconductors. We discuss the energy dissipation processes of electronic thermal wave and lattice heating. Different types of phase transitions after ultrashort laser pulse irradiation as melting, vaporization or transitions to warm dense matter are discussed. Also nonthermal phase transitions, directly caused by the electronic excitation before considerable lattice heating, are considered. The final material removal occurs from the physical point of view as expansion of heated matter; here we discuss approaches of hydrodynamics, as well as molecular dynamic simulations directly following the atomic movements. Hybrid approaches tracing the dynamics of excited electrons, energy dissipation and structural dynamics in a combined simulation are reviewed as well.

  3. Gravity Scaling of a Power Reactor Water Shield

    NASA Technical Reports Server (NTRS)

    Reid, Robert S.; Pearson, J. Boise

    2008-01-01

    Water based reactor shielding is being considered as an affordable option for use on initial lunar surface power systems. Heat dissipation in the shield from nuclear sources must be rejected by an auxiliary thermal hydraulic cooling system. The mechanism for transferring heat through the shield is natural convection between the core surface and an array of thermosyphon radiator elements. Natural convection in a 100 kWt lunar surface reactor shield design has been previously evaluated at lower power levels (Pearson, 2007). The current baseline assumes that 5.5 kW are dissipated in the water shield, the preponderance on the core surface, but with some volumetric heating in the naturally circulating water as well. This power is rejected by a radiator located above the shield with a surface temperature of 370 K. A similarity analysis on a water-based reactor shield is presented examining the effect of gravity on free convection between a radiation shield inner vessel and a radiation shield outer vessel boundaries. Two approaches established similarity: 1) direct scaling of Rayleigh number equates gravity-surface heat flux products, 2) temperature difference between the wall and thermal boundary layer held constant on Earth and the Moon. Nussult number for natural convection (laminar and turbulent) is assumed of form Nu = CRa(sup n). These combined results estimate similarity conditions under Earth and Lunar gravities. The influence of reduced gravity on the performance of thermosyphon heat pipes is also examined.

  4. High power microwave ablation of normal swine lung: impact of duration of energy delivery on adverse event and heat sink effects.

    PubMed

    Kodama, Hiroshi; Ueshima, Eisuke; Gao, Song; Monette, Sebastien; Paluch, Lee-Ronn; Howk, Kreg; Erinjeri, Joseph P; Solomon, Stephen B; Srimathveeravalli, Govindarajan

    2018-04-18

    The purpose of this study is to assess the impact of duration of energy delivery on adverse events (AEs) and heat sink effects during high power microwave ablation (MWA) of normal swine lung. High power (100 W) MWA was performed with short (2 min, 18 ablations) or long (10 min, nine ablations) duration of energy delivery in unilateral lung of swine (n = 10). CT imaging was done prior to sacrifice at 2 or 28 d post-treatment, with additional imaging at 7 and 14 d for the latter cohort. Ablation zones were assessed with CT imaging and histopathology analysis. Differences in AEs and ablation characteristics between groups were compared with Fisher's exact test and Student's t-test, respectively. There were no significant differences in formation of air-filled needle tract, cavitation, and pneumonia (p > 0.5) between the treatment groups. Intra-procedural pneumothorax requiring chest tube placement occurred in three animals. Substantial (>20%, p = 0.01) intra-procedural ablation zone distortion was observed in both groups. The presence of large airways or blood vessels did not result in heat sink effect within the ablation zones and was not indicative of reduced ablation size. Increased energy delivery yielded larger (8.9 ± 3.1 cm 3 vs. 3.4 ± 1.7 cm 3 , p < 0.001) spherical ablations (sphericity: 0.70 ± 0.10 vs. 0.56 ± 0.13, p = 0.01). High power MWA of normal lung with longer duration of energy delivery can create larger spherical ablations, without significant differences in post-procedure AEs when compared with shorter energy delivery time.

  5. Novel Hybrid Ablative/Ceramic Heatshield for Earth Atmospheric Re-Entry

    NASA Astrophysics Data System (ADS)

    Barcena, J.; Florez, S.; Perez, B.; Pinaud, G.; Bouilly, J.-M.; Fischer, W. P. P.; de Montburn, A.; Descomps, M.; Zuber, C.; Rotaermel, W.; Hald, H.; Pereira, C.; Mergia, K.; Triantou, K.; Marinou, A.; Vekinis, G.; Ionescu, G.; Ban, C.; Stefan, A.; Leroy, V.; Bernard, D.; Massuti, B.; Herdrich, G.

    2014-06-01

    Original approaches based on ablative materials and novel TPS solutions are required for space applications, where resistance to extreme oxidative environments and high temperatures are required. For future space exploration the demands for the thermal shield go beyond the current state-of-the-art. Therefore, the development of new thermal protection materials and systems at a reasonable mass budget is absolutely essential to ensure European non-dependence on corresponding restricted technologies. The three year long FP7 project HYDRA aims at the development of a novel thermal protection system through the integration of a low density ablative outer-shield on top of an advanced thermo-structural ceramic composite layer and will provide an innovative technology solution consistent with the capabilities of European technologies and material providers. This paper summarizes the current status of the scientific activities carried out after two years of progress in terms of design, integration and verification of a robust and lightweight thermal shield solution for atmospheric earth re-entry.

  6. Novel tumor-ablation device for liver tumors utilizing heat energy generated under an alternating magnetic field.

    PubMed

    Sato, Koichi; Watanabe, Yuji; Horiuchi, Atsushi; Yukumi, Shungo; Doi, Takashi; Yoshida, Motohira; Yamamoto, Yuji; Maehara, Tsunehiro; Naohara, Takashi; Kawachi, Kanji

    2008-07-01

    We have developed a novel tumor-ablation device for liver tumors utilizing heat energy induced by magnesium ferrite (MgFe(2)O(4)) particles under an alternating magnetic field (AMF) produced by electric currents. This novel device can repeatedly heat liver tumors at lower temperature than usual heating devices, such as radiofrequency ablation therapy, with slight infliction of pain. This study assesses its heating effect on rat liver tumors as local therapy. The small needle was manufactured from MgFe(2)O(4) particles by sintering at 1100 degrees C. After a MgFe(2)O(4) needle was inserted into liver tumors comprising of dRLh-84 cells, the tumors were heated for 30 min under an AMF. We examined cellular activity by using nicotinamide adenine dinucleotide (NADH) diaphorase staining and terminal deoxynucleotidyl transferase-mediated digoxigenin-dUTP nick-end labeling (TUNEL) staining, and evaluated the effect of suppressing tumor growth by sequentially comparing the tumor diameter with that of the control group. The mean temperature of the heated tumors was 60.2 +/- 1.8 degrees C. The tumor cells were constricted, and chromatin of nuclei had shrunk immediately after heating. The heat-injury area that contained the tumors was negative for NADH diaphorase activity. After 3 days, the tumor cells in the heat-injury area became positive for TUNEL staining, which detects cell death. At 7 days, the mean tumor diameters were significantly smaller in the heating group than in the control group (6.15 +/- 0.47 mm vs 16.89 +/- 2.69 mm; P < 0.05). This device, utilizing heat energy induced by ferromagnetic metal under an AMF, appears useful as local thermotherapy for human liver cancer.

  7. New methods to detect particle velocity and mass flux in arc-heated ablation/erosion facilities

    NASA Technical Reports Server (NTRS)

    Brayton, D. B.; Bomar, B. W.; Seibel, B. L.; Elrod, P. D.

    1980-01-01

    Arc-heated flow facilities with injected particles are used to simulate the erosive and ablative/erosive environments encountered by spacecraft re-entry through fog, clouds, thermo-nuclear explosions, etc. Two newly developed particle diagnostic techniques used to calibrate these facilities are discussed. One technique measures particle velocity and is based on the detection of thermal radiation and/or chemiluminescence from the hot seed particles in a model ablation/erosion facility. The second technique measures a local particle rate, which is proportional to local particle mass flux, in a dust erosion facility by photodetecting and counting the interruptions of a focused laser beam by individual particles.

  8. Optimation of cooled shields in insulations

    NASA Technical Reports Server (NTRS)

    Chato, J. C.; Khodadadi, J. M.; Seyed-Yagoobi, J.

    1984-01-01

    A method to optimize the location, temperature, and heat dissipation rate of each cooled shield inside an insulation layer was developed. The method is based on the minimization of the entropy production rate which is proportional to the heat leak across the insulation. It is shown that the maximum number of shields to be used in most practical applications is three. However, cooled shields are useful only at low values of the overall, cold wall to hot wall absolute temperature ratio. The performance of the insulation system is relatively insensitive to deviations from the optimum values of the temperature and location of the cooling shields. Design curves for rapid estimates of the locations and temperatures of cooling shields in various types of insulations, and an equation for calculating the cooling loads for the shields are presented.

  9. Laser ablation based fuel ignition

    DOEpatents

    Early, J.W.; Lester, C.S.

    1998-06-23

    There is provided a method of fuel/oxidizer ignition comprising: (a) application of laser light to a material surface which is absorptive to the laser radiation; (b) heating of the material surface with the laser light to produce a high temperature ablation plume which emanates from the heated surface as an intensely hot cloud of vaporized surface material; and (c) contacting the fuel/oxidizer mixture with the hot ablation cloud at or near the surface of the material in order to heat the fuel to a temperature sufficient to initiate fuel ignition. 3 figs.

  10. Laser ablation based fuel ignition

    DOEpatents

    Early, James W.; Lester, Charles S.

    1998-01-01

    There is provided a method of fuel/oxidizer ignition comprising: (a) application of laser light to a material surface which is absorptive to the laser radiation; (b) heating of the material surface with the laser light to produce a high temperature ablation plume which emanates from the heated surface as an intensely hot cloud of vaporized surface material; and (c) contacting the fuel/oxidizer mixture with the hot ablation cloud at or near the surface of the material in order to heat the fuel to a temperature sufficient to initiate fuel ignition.

  11. Trajectory characteristics and heating of hypervelocity projectiles having large ballistic coefficients

    NASA Technical Reports Server (NTRS)

    Tauber, Michael E.

    1986-01-01

    A simple, approximate equation describing the velocity-density relationship (or velocity-altitude) has been derived from the flight of large ballistic coefficient projectiles launched at high speeds. The calculations obtained by using the approximate equation compared well with results for numerical integrations of the exact equations of motion. The flightpath equation was used to parametrically calculate maximum body decelerations and stagnation pressures for initial velocities from 2 to 6 km/s. Expressions were derived for the stagnation-point convective heating rates and total heat loads. The stagnation-point heating was parametrically calculated for a nonablating wall and an ablating carbon surface. Although the heating rates were very high, the pulse decayed quickly. The total nose-region heat shield weight was conservatively estimated to be only about 1 percent of the body mass.

  12. ANALYSIS OF FACTORS AFFECTING OUTCOME OF ULTRASOUND-GUIDED RADIOFREQUENCY HEAT ABLATION FOR TREATMENT OF PRIMARY HYPERPARATHYROIDISM IN DOGS.

    PubMed

    Bucy, Daniel; Pollard, Rachel; Nelson, Richard

    2017-01-01

    Radiofrequency (RF) parathyroid ablation is a noninvasive treatment for hyperparathyroidism in dogs. There are no published data assessing factors associated with RF parathyroid ablation success or failure in order to guide patient selection and improve outcome. The purpose of this retrospective analytical study was to determine whether imaging findings, biochemical data, or concurrent diseases were associated with RF heat ablation treatment failure. For inclusion in the study, dogs must have had a clinical diagnosis of primary hyperparathyroidism, undergone cervical ultrasound and RF ablation of abnormal parathyroid tissue, and must have had at least 3 months of follow-up information available following the date of ultrasound-guided parathyroid ablation. Dogs were grouped based on those with recurrent or persistent hypercalcemia and those without recurrent or persistent hypercalcemia following therapy. Parathyroid nodule size, thyroid lobe size, nodule location, and presence of concurrent disease were recorded. Recurrence of hypercalcemia occurred in 9/32 dogs that had ablation of abnormal parathyroid tissue (28%) and one patient had persistent hypercalcemia (3%) following parathyroid ablation. Nodule width (P = 0.036), height (P = 0.028), and largest cross-sectional area (P = 0.023) were larger in dogs that had recurrent or persistent hypercalcemia following ablation. Hypothyroidism was more common in dogs with recurrent disease (P = 0.044). Radiofrequency ablation was successful in 22/32 (69%) dogs. Larger parathyroid nodule size and/or concurrent hypothyroidism were associated with treatment failure in dogs that underwent ultrasound-guided RF parathyroid nodule ablation. © 2016 American College of Veterinary Radiology.

  13. Impact of cross-field motion on ablation of high-Z dust in fusion edge plasmas

    DOE PAGES

    Smirnov, R. D.; Krasheninnikov, S. I.

    2017-07-05

    The impact of cross-field motion of high-Z dust grains on their shielding by ablation cloud in edge plasmas of tokamaks is analyzed. The modification of the existing high-Z dust shielding theory is developed, which takes the dust motion effects into account. We show that the cross-field motion can lead to a large factor increase of the dust ablation rate, as compared to the previous model. It is also shown that the motion effects take place when the dust cross-field velocity exceeds a threshold value. We also obtain the dependencies of the dust ablation flux on the dust velocity and ofmore » the threshold velocity on the dust size and the ambient plasma temperature.« less

  14. Impact of cross-field motion on ablation of high-Z dust in fusion edge plasmas

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Smirnov, R. D.; Krasheninnikov, S. I.

    The impact of cross-field motion of high-Z dust grains on their shielding by ablation cloud in edge plasmas of tokamaks is analyzed. The modification of the existing high-Z dust shielding theory is developed, which takes the dust motion effects into account. We show that the cross-field motion can lead to a large factor increase of the dust ablation rate, as compared to the previous model. It is also shown that the motion effects take place when the dust cross-field velocity exceeds a threshold value. We also obtain the dependencies of the dust ablation flux on the dust velocity and ofmore » the threshold velocity on the dust size and the ambient plasma temperature.« less

  15. High-temperature metal purification using a compact, portable rf heating and levitation system on the wake shield

    NASA Technical Reports Server (NTRS)

    Hahs, C. A.

    1990-01-01

    The potential use of a compact, battery-operated rf levitator and heating system to purify high-temperature melting materials in space is described. The wake shield now being fabricated for the Space Vacuum Epitaxy Center will provide an Ultra-high vacuum (10(exp -14) Torr hydrogen, 10(exp -14) Torr helium, 10(exp -30) Torr oxygen). The use of the wake shield to purify Nb, Ti, W, Ir, and other metals to a purity level not achievable on earth is described.

  16. Correlations for Boundary-Layer Transition on Mars Science Laboratory Entry Vehicle Due to Heat-Shield Cavities

    NASA Technical Reports Server (NTRS)

    Hollis, Brian R.; Liechty, Derek S.

    2008-01-01

    The influence of cavities (for attachment bolts) on the heat-shield of the proposed Mars Science Laboratory entry vehicle has been investigated experimentally and computationally in order to develop a criterion for assessing whether the boundary layer becomes turbulent downstream of the cavity. Wind tunnel tests were conducted on the 70-deg sphere-cone vehicle geometry with various cavity sizes and locations in order to assess their influence on convective heating and boundary layer transition. Heat-transfer coefficients and boundary-layer states (laminar, transitional, or turbulent) were determined using global phosphor thermography.

  17. Shield system

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Finch, D.R.; Chandler, J.R.; Church, J.P.

    1979-01-01

    The SHIELD system is a powerful new computational tool for calculation of isotopic inventory, radiation sources, decay heat, and shielding assessment in part of the nuclear fuel cycle. The integrated approach used in this system permitss the communication and management of large fields of numbers efficiently thus permitting the user to address the technical rather than computer aspects of a problem. Emphasis on graphical outputs permits large fields of resulting numbers to be efficiently displayed.

  18. A Simplified Approach for the Rapid Generation of Transient Heat-Shield Environments

    NASA Technical Reports Server (NTRS)

    Wurster, Kathryn E.; Zoby, E. Vincent; Mills, Janelle C.; Kamhawi, Hilmi

    2007-01-01

    A simplified approach has been developed whereby transient entry heating environments are reliably predicted based upon a limited set of benchmark radiative and convective solutions. Heating, pressure and shear-stress levels, non-dimensionalized by an appropriate parameter at each benchmark condition are applied throughout the entry profile. This approach was shown to be valid based on the observation that the fully catalytic, laminar distributions examined were relatively insensitive to altitude as well as velocity throughout the regime of significant heating. In order to establish a best prediction by which to judge the results that can be obtained using a very limited benchmark set, predictions based on a series of benchmark cases along a trajectory are used. Solutions which rely only on the limited benchmark set, ideally in the neighborhood of peak heating, are compared against the resultant transient heating rates and total heat loads from the best prediction. Predictions based on using two or fewer benchmark cases at or near the trajectory peak heating condition, yielded results to within 5-10 percent of the best predictions. Thus, the method provides transient heating environments over the heat-shield face with sufficient resolution and accuracy for thermal protection system design and also offers a significant capability to perform rapid trade studies such as the effect of different trajectories, atmospheres, or trim angle of attack, on convective and radiative heating rates and loads, pressure, and shear-stress levels.

  19. [Efficacy of using rivaroxaban for treatment of heat-induced thrombosis after endovenous laser ablation].

    PubMed

    Fokin, A A; Borsuk, D A; Kazachkov, E L

    The study was aimed at assessing efficacy of using rivaroxaban for treatment of endothermal heat-induced thrombosis (EHIT) after endovenous laser ablation (EVLA) of saphenous veins. Our prospective study included a total of 1,326 patients subjected to 1,514 EVLAs. In 1,091 (72.1%) cases the great saphenous vein (GSV) was ablated, in 124 (8.2%) cases the anterior accessory vein (AAV) was treated and in 299 (19.7%) cases the small saphenous vein (SSV) was treated. Heat-induced thrombosis developed in 21 (1.4%) cases: in 19 cases in the basin of the great saphenous vein and in 2 cases in the anterior accessory saphenous vein. No heat-induced thromboses in the basin of the small saphenous vein were observed. In 9 (0.6%) cases there was class 1 EHIT (according to the Kabnick classification), class 2 EHIT was noted in 10 (0.7%) cases and class 3 EHIT was observed in 2 (0.1%) cases. All patients with EHIT were given rivaroxaban: patients with class 1 EHIT received it at a single daily dose of 20 mg, patients with class 2 and 3 EHIT - at a dose of 15 mg twice daily. In one (4.8%) case the drug had to be discontinued on day two due to the development of dyspeptic events. All patients were found to have complete regression of the heat-induced thrombus within 6-25 days. No cases of clinical manifestations of pulmonary artery thromboembolism were observed. A conclusion was drawn that in clinical practice EHIT is an important and insufficiently studied problem. Rivaroxaban may be used as an oral agent for treatment of heat-induced thromboses after EVLA. Further studies are required to examine its efficacy and safety profile.

  20. A Fast Code for Jupiter Atmospheric Entry Analysis

    NASA Technical Reports Server (NTRS)

    Yauber, Michael E.; Wercinski, Paul; Yang, Lily; Chen, Yih-Kanq

    1999-01-01

    A fast code was developed to calculate the forebody heating environment and heat shielding that is required for Jupiter atmospheric entry probes. A carbon phenolic heat shield material was assumed and, since computational efficiency was a major goal, analytic expressions were used, primarily, to calculate the heating, ablation and the required insulation. The code was verified by comparison with flight measurements from the Galileo probe's entry. The calculation required 3.5 sec of CPU time on a work station, or three to four orders of magnitude less than for previous Jovian entry heat shields. The computed surface recessions from ablation were compared with the flight values at six body stations. The average, absolute, predicted difference in the recession was 13.7% too high. The forebody's mass loss was overpredicted by 5.3% and the heat shield mass was calculated to be 15% less than the probe's actual heat shield. However, the calculated heat shield mass did not include contingencies for the various uncertainties that must be considered in the design of probes. Therefore, the agreement with the Galileo probe's values was satisfactory in view of the code's fast running time and the methods' approximations.

  1. Coatings for aircraft gas turbine engines and space shuttle heat shields: A review of Lewis Research Center programs

    NASA Technical Reports Server (NTRS)

    Grisaffe, S. J.; Merutka, J. P.

    1972-01-01

    The status of several coating programs is reviewed. These include efforts on protecting aircraft gas turbine engine materials from oxidation/corrosion and on protecting refractory metal reentry heat shields from oxidation.

  2. Laser-launched flyer plate and confined laser ablation for shock wave loading: validation and applications.

    PubMed

    Paisley, Dennis L; Luo, Sheng-Nian; Greenfield, Scott R; Koskelo, Aaron C

    2008-02-01

    We present validation and some applications of two laser-driven shock wave loading techniques: laser-launched flyer plate and confined laser ablation. We characterize the flyer plate during flight and the dynamically loaded target with temporally and spatially resolved diagnostics. With transient imaging displacement interferometry, we demonstrate that the planarity (bow and tilt) of the loading induced by a spatially shaped laser pulse is within 2-7 mrad (with an average of 4+/-1 mrad), similar to that in conventional techniques including gas gun loading. Plasma heating of target is negligible, in particular, when a plasma shield is adopted. For flyer plate loading, supported shock waves can be achieved. Temporal shaping of the drive pulse in confined laser ablation allows for flexible loading, e.g., quasi-isentropic, Taylor-wave, and off-Hugoniot loading. These techniques can be utilized to investigate such dynamic responses of materials as Hugoniot elastic limit, plasticity, spall, shock roughness, equation of state, phase transition, and metallurgical characteristics of shock-recovered samples.

  3. A Fast Code for Jupiter Atmospheric Entry

    NASA Technical Reports Server (NTRS)

    Tauber, Michael E.; Wercinski, Paul; Yang, Lily; Chen, Yih-Kanq; Arnold, James (Technical Monitor)

    1998-01-01

    A fast code was developed to calculate the forebody heating environment and heat shielding that is required for Jupiter atmospheric entry probes. A carbon phenolic heat shield material was assumed and, since computational efficiency was a major goal, analytic expressions were used, primarily, to calculate the heating, ablation and the required insulation. The code was verified by comparison with flight measurements from the Galileo probe's entry; the calculation required 3.5 sec of CPU time on a work station. The computed surface recessions from ablation were compared with the flight values at six body stations. The average, absolute, predicted difference in the recession was 12.5% too high. The forebody's mass loss was overpredicted by 5.5% and the heat shield mass was calculated to be 15% less than the probe's actual heat shield. However, the calculated heat shield mass did not include contingencies for the various uncertainties that must be considered in the design of probes. Therefore, the agreement with the Galileo probe's values was considered satisfactory, especially in view of the code's fast running time and the methods' approximations.

  4. THERMAL PROPERTIES AND HEATING AND COOLING DURABILITY OF REACTOR SHIELDING CONCRETE (in Japanese)

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Hosoi, J.; Chujo, K.; Saji, K.

    1959-01-01

    A study was made of the thermal properties of various concretes made of domestic raw materials for radiation shields of a power reactor and of a high- flux research reactor. The results of measurements of thermal expansion coefficient, specific heat, thermal diffusivity, thermal conductivity, cyclical heating, and cooling durability are described. Relationships between thermal properties and durability are discussed and several photographs of the concretes are given. It is shown that the heating and cooling durability of such a concrete which has a large thermal expansion coefficient or a considerable difference between the thermal expansion of coarse aggregate and themore » one of cement mortar part or aggregates of lower strength is very poor. The decreasing rates of bending strength and dynamical modulus of elasticity and the residual elongation of the concrete tested show interesting relations with the modified thermal stress resistance factor containing a ratio of bending strength and thermal expansion coefficient. The thermal stress resistance factor seems to depend on the conditions of heat transfer on the surface and on heat release in the concrete. (auth)« less

  5. Lightweight Shield Against Space Debris

    NASA Technical Reports Server (NTRS)

    Redmon, John W., Jr.; Lawson, Bobby E.; Miller, Andre E.; Cobb, W. E.

    1992-01-01

    Report presents concept for lightweight, deployable shield protecting orbiting spacecraft against meteoroids and debris, and functions as barrier to conductive and radiative losses of heat. Shield made in four segments providing 360 degree coverage of cylindrical space-station module.

  6. Post-Flight Evaluation of PICA and PICA-X - Comparisons of the Stardust SRC and Space-X Dragon 1 Forebody Heatshield Materials

    NASA Technical Reports Server (NTRS)

    Stackpoole, M.; Kao, D.; Qu, V.; Gonzales, G.

    2013-01-01

    Phenolic Impregnated Carbon Ablator (PICA) was developed at NASA Ames Research Center. As a thermal protection material, PICA has the advantages of being able to withstand high heat fluxes with a relatively low density. This ablative material was used as the forebody heat shield material for the Stardust sample return capsule, which re-entered the Earths atmosphere in 2006. Based on PICA, SpaceX developed a variant, PICA-X, and used it as the heat shield material for its Dragon spacecraft, which successfully orbited the Earth and re-entered the atmosphere during the COTS Demo Flight 1 in 2010. Post-flight analysis was previously performed on the Stardust PICA heat shield material. Similarly, a near-stagnation core was obtained from the post-flight Dragon 1 heat shield, which was retrieved from the Pacific Ocean. Materials testing and analyses were performed on the core to evaluate its ablation performance and post-flight properties. Comparisons between PICA and PICA-X are made where applicable. Stardust and Dragon offer rare opportunities to evaluate materials post-flight - this data is beneficial in understanding material performance and also improves modeling capabilities.

  7. Effects of material composition on the ablation performance of low density elastomeric ablators

    NASA Technical Reports Server (NTRS)

    Tompkins, S. S.; Kabana, W. P.

    1973-01-01

    The ablation performance of materials composed of various concentrations of nylon, hollow silica spheres, hollow phenolic spheres, and four elastomeric resins was determined. Both blunt-body and flat-panel specimens were used, the cold-wall heating-rate ranges being 0.11 to 0.8 MW/sq m, respectively. The corresponding surface pressure ranges for these tests were 0.017 to 0.037 atmosphere and 0.004 to 0.005 atmosphere. Some of the results show that (1) the addition of nylon significantly improved the ablation performance, but the nylon was not compatible with one resin system; (2) panel and blunt-body specimen data do not show the same effect of phenolic sphere content on ablation effectiveness; and (3) there appears to be an optimum concentration of hollow silica spheres for good ablation performance. The composition of an efficient, nonproprietary ablator for lifting body application is identified and the ablation performance of this ablator is compared with the performance of three commercially available materials.

  8. Investigation the effect of outdoor air infiltration on the heat-shielding characteristics the outer walls of high-rise buildings

    NASA Astrophysics Data System (ADS)

    Vytchikov, Yu. S.; Kostuganov, A. B.; Saparev, M. E.; Belyakov, I. G.

    2018-03-01

    The presented article considers the influence of infiltrated outdoor air on the heat-shielding characteristics of the exterior walls of modern residential and public buildings. A review of the sources devoted to this problem confirmed its relevance at the present time, especially for high-rise buildings. The authors of the article analyzed the effect of longitudinal and transverse air infiltration on the heat-shielding characteristics of the outer wall of a 25-story building that was built in Samara. The results showed a significant reduction of the reduced resistance to the heat transfer of the outer wall when air is infiltrated through it. There are the results of full-scale examination of external walls to confirm the calculated data. Based on the results of the study carried out by the authors of the article, general recommendations on the internal finishing of the outer walls of high-rise buildings are given.

  9. Microwave ablation at 10.0 GHz achieves comparable ablation zones to 1.9 GHz in ex vivo bovine liver.

    PubMed

    Luyen, Hung; Gao, Fuqiang; Hagness, Susan C; Behdad, Nader

    2014-06-01

    We demonstrate the feasibility of using high-frequency microwaves for tissue ablation by comparing the performance of a 10 GHz microwave ablation system with that of a 1.9 GHz system. Two sets of floating sleeve dipole antennas operating at these frequencies were designed and fabricated for use in ex vivo experiments with bovine livers. Combined electromagnetic and transient thermal simulations were conducted to analyze the performance of these antennas. Subsequently, a total of 16 ablation experiments (eight at 1.9 GHz and eight at 10.0 GHz) were conducted at a power level of 42 W for either 5 or 10 min. In all cases, the 1.9 and 10 GHz experiments resulted in comparable ablation zone dimensions. Temperature monitoring probes revealed faster heating rates in the immediate vicinity of the 10.0 GHz antenna compared to the 1.9 GHz antenna, along with a slightly delayed onset of heating farther from the 10 GHz antenna, suggesting that heat conduction plays a greater role at higher microwave frequencies in achieving a comparably sized ablation zone. The results obtained from these experiments agree very well with the combined electromagnetic/thermal simulation results. These simulations and experiments show that using lower frequency microwaves does not offer any significant advantages, in terms of the achievable ablation zones, over using higher frequency microwaves. Indeed, it is demonstrated that high-frequency microwave antennas may be used to create reasonably large ablation zones. Higher frequencies offer the advantage of smaller antenna size, which is expected to lead to less invasive interstitial devices and may possibly lead to the development of more compact multielement arrays with heating properties not available from single-element antennas.

  10. Radiofrequency ablation during continuous saline infusion can extend ablation margins

    PubMed Central

    Ishikawa, Toru; Kubota, Tomoyuki; Horigome, Ryoko; Kimura, Naruhiro; Honda, Hiroki; Iwanaga, Akito; Seki, Keiichi; Honma, Terasu; Yoshida, Toshiaki

    2013-01-01

    AIM: To determine whether fluid injection during radiofrequency ablation (RFA) can increase the coagulation area. METHODS: Bovine liver (1-2 kg) was placed on an aluminum tray with a return electrode affixed to the base, and the liver was punctured by an expandable electrode. During RFA, 5% glucose; 50% glucose; or saline fluid was infused continuously at a rate of 1.0 mL/min through the infusion line connected to the infusion port. The area and volume of the thermocoagulated region of bovine liver were determined after RFA. The Joule heat generated was determined from the temporal change in output during the RFA experiment. RESULTS: No liquid infusion was 17.3 ± 1.6 mL, similar to the volume of a 3-cm diameter sphere (14.1 mL). Mean thermocoagulated volume was significantly larger with continuous infusion of saline (29.3 ± 3.3 mL) than with 5% glucose (21.4 ± 2.2 mL), 50% glucose (16.5 ± 0.9 mL) or no liquid infusion (17.3 ± 1.6 mL). The ablated volume for RFA with saline was approximately 1.7-times greater than for RFA with no liquid infusion, representing a significant difference between these two conditions. Total Joule heat generated during RFA was highest with saline, and lowest with 50% glucose. CONCLUSION: RFA with continuous saline infusion achieves a large ablation zone, and may help inhibit local recurrence by obtaining sufficient ablation margins. RFA during continuous saline infusion can extend ablation margins, and may be prevent local recurrence. PMID:23483097

  11. Integrated Solar Concentrator and Shielded Radiator

    NASA Technical Reports Server (NTRS)

    Clark, David Larry

    2010-01-01

    A shielded radiator is integrated within a solar concentrator for applications that require protection from high ambient temperatures with little convective heat transfer. This innovation uses a reflective surface to deflect ambient thermal radiation, shielding the radiator. The interior of the shield is also reflective to provide a view factor to deep space. A key feature of the shield is the parabolic shape that focuses incoming solar radiation to a line above the radiator along the length of the trough. This keeps the solar energy from adding to the radiator load. By placing solar cells along this focal line, the concentration of solar energy reduces the number and mass of required cells. By shielding the radiator, the effective reject temperature is much lower, allowing lower radiator temperatures. This is particularly important for lower-temperature processes, like habitat heat rejection and fuel cell operations where a high radiator temperature is not feasible. Adding the solar cells in the focal line uses the concentrating effect of the shield to advantage to accomplish two processes with a single device. This shield can be a deployable, lightweight Mylar structure for compact transport.

  12. Characterization of Candidate Materials for Remote Recession Measurements of Ablative Heat Shield Materials

    NASA Technical Reports Server (NTRS)

    Butler, Bradley D.; Winter, Michael; Panerai, Francesco; Martin, Alexandre; Bailey, Sean C. C.; Stackpoole, Margaret; Danehy, Paul M.; Splinter, Scott

    2016-01-01

    A method of remotely measuring surface recession of a material sample in a plasma flow through emission spectroscopy of the post shock layer was characterized through experiments in the NASA Langley HYMETS arc jet facility. Different methods for delivering the seed products into the Phenolic Impregnated Carbon Ablator (PICA) material samples were investigated. Three samples were produced by seeding the PICA material with combinations of Al, Si, HfO2, VB2, Al2O3, SiO2, TiC, HfC, NaCl, and MgCl2 through infusing seed materials into a core of PICA, or through encapsulating seed material in an epoxy disk, mechanically bonding the disk to a PICA sample. The PICA samples seeded with the candidate tracers were then tested at surface temperatures near 2400 K under low pressure air plasma. The emission of Al, Ti, V, Na, and Mg in the post-shock layer was observed in the UV with a high resolution imaging spectrometer viewing the whole stagnation line from the side, and from UV to NIR with a fiber-coupled miniaturized spectrometer observing the sample surface in the wavelength range from 200 nm to 1,100 nm from the front through a collimator. Al, Na, and Mg were found to be emitting in the post-shock spectra even before the recession reached the seeding depth - therefore possibly characterizing the pyrolysis process rather than the recession itself. The appearance of Ti and V emission in the spectra was well correlated with the actual recession which was monitored through a video of the front surface of the sample. The applicability of a seed material as an indicator for recession appears to be related to the melting temperature of the seed material. Future parametric studies will be carried out in low power plasma facilities at the University of Kentucky.

  13. Miniaturization of Microwave Ablation Antennas

    NASA Astrophysics Data System (ADS)

    Luyen, Hung

    Microwave ablation (MWA) is a promising minimally invasive technique for the treatment of various types of cancers as well as non-oncological diseases. In MWA, an interstitial antenna is typically used to deliver microwave energy to the diseased tissue and heat it up to lethal temperature levels that induce cell death. The desired characteristics of the interstitial antenna include a narrow diameter to minimize invasiveness of the treatment, a low input reflection coefficient at the operating frequency, and a localized heating zone. Most interstitial MWA antennas are fed by coaxial cables and designed for operation at either 915 MHz or 2.45 GHz. Coax-fed MWA antennas are commonly equipped with coaxial baluns to achieve localized heating. However, the conventional implementation of coaxial baluns increases the overall diameters of the antennas and therefore make them more invasive. It is highly desirable to develop less invasive antennas with shorter active lengths and smaller diameters for MWA applications. In this work, we demonstrate the feasibility of using higher frequency microwaves for tissue ablation and present several techniques for decreasing diameters of MWA antennas. First, we investigated MWA at higher frequencies by conducting numerical and experimental studies to compare ablation performance at 10 GHz and 1.9 GHz. Simulation and ex vivo ablation experiment results demonstrate comparable ablation zone dimensions achieved at these two frequencies. Operating at higher frequencies enables interstitial antennas with shorter active lengths. This can be combined with smaller-diameter antenna designs to create less invasive applicators or allow integration of multiple radiating elements on a single applicator to have better control and customization of the heating patterns. Additionally, we present three different coax-fed antenna designs and a non-coaxial-based balanced antenna that have smaller-diameter configurations than conventional coax-fed balun

  14. X-Ray Micro-Tomography Applied to Nasa's Materials Research: Heat Shields, Parachutes and Asteroids

    NASA Technical Reports Server (NTRS)

    Panerai, Francesco; Borner, Arnaud; Ferguson, Joseph C.; Mansour, Nagi N.; Stern, Eric C.; Barnard, Harold S.; Macdowell, Alastair A.; Parkinson, Dilworth Y.

    2017-01-01

    X-ray micro-tomography is used to support the research on materials carried out at NASA Ames Research Center. The technique is applied to a variety of applications, including the ability to characterize heat shield materials for planetary entry, to study the Earth- impacting asteroids, and to improve broadcloths of spacecraft parachutes. From micro-tomography images, relevant morphological and transport properties are determined and validated against experimental data.

  15. CFD Analysis of Hypersonic Flowfields With Surface Thermochemistry and Ablation

    NASA Technical Reports Server (NTRS)

    Henline, W. D.

    1997-01-01

    In the past forty years much progress has been made in computational methods applied to the solution of problems in spacecraft hypervelocity flow and heat transfer. Although the basic thermochemical and physical modeling techniques have changed little in this time, several orders of magnitude increase in the speed of numerically solving the Navier-Stokes and associated energy equations have been achieved. The extent to which this computational power can be applied to the design of spacecraft heat shields is dependent on the proper coupling of the external flow equations to the boundary conditions and governing equations representing the thermal protection system in-depth conduction, pyrolysis and surface ablation phenomena. A discussion of the techniques used to do this in past problems as well as the current state-of-art is provided. Specific examples, including past missions such as Galileo, together with the more recent case studies of ESA/Rosetta Sample Comet Return, Mars Pathfinder and X-33 will be discussed. Modeling assumptions, design approach and computational methods and results are presented.

  16. A Novel Combination of Thermal Ablation and Heat-Inducible Gene therapy for Breast Cancer Treatment

    DTIC Science & Technology

    2009-04-01

    intensity focused ultrasound ( HIFU ) has been developed as an emerging non-invasive strategy for cancer treatment by thermal ablation of tumor tissue. The...Leenders, G., et al., Histopathological changes associated with high intensity focused ultrasound ( HIFU ) treatment for localised adenocarcinoma of...invasive strategy for cancer therapy [1, 2]. Through HIFU exposure, acoustic energy is focused into a deep-sited tumor volume and converted into heat

  17. Testing of Advanced Conformal Ablative TPS

    NASA Technical Reports Server (NTRS)

    Gasch, Matthew; Agrawal, Parul; Beck, Robin

    2013-01-01

    In support of the CA250 project, this paper details the results of a test campaign that was conducted at the Ames Arcjet Facility, wherein several novel low density thermal protection (TPS) materials were evaluated in an entry like environment. The motivation for these tests was to investigate whether novel conformal ablative TPS materials can perform under high heat flux and shear environment as a viable alternative to rigid ablators like PICA or Avcoat for missions like MSL and beyond. A conformable TPS over a rigid aeroshell has the potential to solve a number of challenges faced by traditional rigid TPS materials (such as tiled Phenolic Impregnated Carbon Ablator (PICA) system on MSL, and honeycomb-based Avcoat on the Orion Multi Purpose Crew Vehicle (MPCV)). The compliant (high strain to failure) nature of the conformable ablative materials will allow better integration of the TPS with the underlying aeroshell structure and enable monolithic-like configuration and larger segments to be used in fabrication.A novel SPRITE1 architecture, developed by the researchers at NASA Ames was used for arcjet testing. This small probe like configuration with 450 spherecone, enabled us to test the materials in a combination of high heat flux, pressure and shear environment. The heat flux near the nose were in the range of 500-1000 W/sq cm whereas in the flank section of the test article the magnitudes were about 50 of the nose, 250-500W/sq cm range. There were two candidate conformable materials under consideration for this test series. Both test materials are low density (0.28 g/cu cm) similar to Phenolic Impregnated Carbon Ablator (PICA) or Silicone Impregnated Refractory Ceramic Ablator (SIRCA) and are comprised of: A flexible carbon substrate (Carbon felt) infiltrated with an ablative resin system: phenolic (Conformal-PICA) or silicone (Conformal-SICA). The test demonstrated a successful performance of both the conformable ablators for heat flux conditions between 50

  18. Development of fused slurry silicide coatings for tantalum reentry heat shields

    NASA Technical Reports Server (NTRS)

    Warnock, R. V.; Stetson, A. R.

    1972-01-01

    A fused slurry silicide coating was developed to provide atmospheric reentry protection for the 90Ta-lOW alloy. Overlaying the silicide with a highly refractory glass greatly improved total lifetime and reliability of the coating system. Low pressure, slow cycle lifetimes in excess of 100 cycles were consistently recorded for 1700 K - 13 and 1300 N/sq m test conditions. A minimum of 25 cycles was obtained for 1810 K - 1300 N/sq m conditions. About 50 simulated reentry cycles (variable temperature, pressure, and stress) were endured by coated 1-inch miniature heat shield panels when exposed to a maximum of 1700 K and either internal or external pressure conditions.

  19. The impact of frequency on the performance of microwave ablation.

    PubMed

    Sawicki, James F; Shea, Jacob D; Behdad, Nader; Hagness, Susan C

    2017-02-01

    The use of higher frequencies in percutaneous microwave ablation (MWA) may offer compelling interstitial antenna design advantages over the 915 MHz and 2.45 GHz frequencies typically employed in current systems. To evaluate the impact of higher frequencies on ablation performance, we conducted a comprehensive computational and experimental study of microwave absorption and tissue heating as a function of frequency. We performed electromagnetic and thermal simulations of MWA in ex vivo and in vivo porcine muscle at discrete frequencies in the 1.9-26 GHz range. Ex vivo ablation experiments were performed in the 1.9-18 GHz range. We tracked the size of the ablation zone across frequency for constant input power and ablation duration. Further, we conducted simulations to investigate antenna feed line heating as a function of frequency, input power, and cable diameter. As the frequency was increased from 1.9 to 26 GHz the resulting ablation zone dimensions decreased in the longitudinal direction while remaining relatively constant in the radial direction; thus at higher frequencies the overall ablation zone was more spherical. However, cable heating at higher frequencies became more problematic for smaller diameter cables at constant input power. Comparably sized ablation zones are achievable well above 1.9 GHz, despite increasingly localised power absorption. Specific absorption rate alone does not accurately predict ablation performance, particularly at higher frequencies where thermal diffusion plays an important role. Cable heating due to ohmic losses at higher frequencies may be controlled through judicious choices of input power and cable diameter.

  20. Effect of parameters on picosecond laser ablation of Cr12MoV cold work mold steel

    NASA Astrophysics Data System (ADS)

    Wu, Baoye; Liu, Peng; Zhang, Fei; Duan, Jun; Wang, Xizhao; Zeng, Xiaoyan

    2018-01-01

    Cr12MoV cold work mold steel, which is a difficult-to-machining material, is widely used in the mold and dye industry. A picosecond pulse Nd:YVO4 laser at 1064 nm was used to conduct the study. Effects of operation parameters (i.e., laser fluence, scanning speed, hatched space and number of scans) were studied on ablation depth and quality of Cr12MoV at the repetition rate of 20 MHz. The experimental results reveal that all the four parameters affect the ablation depth significantly. While the surface roughness depends mainly on laser fluence or scanning speed and secondarily on hatched space or number of scans. For laser fluence and scanning speed, three distinct surface morphologies were observed experiencing transition from flat (Ra < 1.40 μm) to bumpy (Ra = 1.40 - 2.40 μm) eventually to rough (Ra > 2.40 μm). However, for hatched space and number of scan, there is a small bumpy and rough zone or even no rough zone. Mechanisms including heat accumulation, plasma shielding and combustion reaction effects are proposed based on the ablation depth and processing morphology. By appropriate management of the laser fluence and scanning speed, high ablation depth with low surface roughness can be obtained at small hatched space and high number of scans.

  1. Numerical analysis of Hall effect on the performance of magnetohydrodynamic heat shield system based on nonequilibrium Hall parameter model

    NASA Astrophysics Data System (ADS)

    Li, Kai; Liu, Jun; Liu, Weiqiang

    2017-01-01

    Magnetohydrodynamic (MHD) heat shield system, a novel thermal protection technique in the hypersonic field, has been paid much attention in recent years. In the real flight condition, not only the Lorentz force but also the Hall electric field is induced by the interaction between ionized air post shock and magnetic field. In order to analyze the action mechanisms of the Hall effect, numerical methods of coupling thermochemical nonequilibrium flow field with externally applied magnetic field as well as the induced electric field are constructed and validated. Based on the nonequilibrium model of Hall parameter, numerical simulations of the MHD heat shield system is conducted under two different magnetic induction strengths (B0=0.2 T, 0.5 T) on a reentry capsule forebody. Results show that, the Hall effect is the same under the two magnetic induction strengths when the wall is assumed to be conductive. For this case, with the Hall effect taken into account, the Lorentz force counter stream diminishes a lot and the circumferential component dominates, resulting that the heat flux and shock-off distance approach the case without MHD control. However, for the insulating wall, the Hall effect acts in different ways under these two magnetic induction strengths. For this case, with the Hall effect taken into account, the performance of MHD heat shield system approaches the case neglecting the Hall effect when B0 equals 0.2 T. Such performance becomes worse when B0 equals 0.5 T and the aerothermal environment on the capsule shoulder is even worse than the case without MHD control.

  2. ABLATIVE COMPOSITES FOR LIFTING REENTRY THERMAL PROTECTION.

    DTIC Science & Technology

    MECHANICAL PROPERTIES, THERMAL CONDUCTIVITY, ABLATION, DENSITY, TABLES(DATA), SPECIFIC HEAT, THERMOGRAVIMETRIC ANALYSIS, CORROSION RESISTANCE, COLORIMETRY , HEAT RESISTANT MATERIALS, ATMOSPHERE ENTRY.

  3. Effect of laser absorption on picosecond laser ablation of Cr12MoV mold steel, 9Cr18 stainless steel and H13A cemented carbide

    NASA Astrophysics Data System (ADS)

    Wu, Baoye; Liu, Peng; Wang, Xizhao; Zhang, Fei; Deng, Leimin; Duan, Jun; Zeng, Xiaoyan

    2018-05-01

    Due to excellent properties, Cr12MoV mold steel, 9Cr18 stainless steel and H13A cemented carbide are widely used in industry. In this paper, the effect of absorption of laser light on ablation efficiency and roughness have been studied using a picosecond pulse Nd:YVO4 laser. The experimental results reveal that laser wavelength, original surface roughness and chemical composition play an important role in controlling ablation efficiency and roughness. Firstly, higher ablation efficiency with lower surface roughness is achieved on the ablation of 9Cr18 at 532, comparing with 1064 nm. Secondly, the ablation efficiency increases while the Ra of the ablated region decreases with the decrease of original surface roughness on ablation of Cr12MoV mold steel at 532 nm. Thirdly, the ablation efficiency of H13A cemented carbide is much higher than 9Cr18 stainless steel and Cr12MoV mold steel at 1064 nm. Scanning electron microscopy images reveals the formation of pores on the surface of 9Cr18 stainless steel and Cr12MoV mold steel at 532 nm while no pores are formed at 1064 nm. As to H13A cemented carbide, worm-like structure is formed at 1064 nm. The synergetic effects of the heat accumulation, plasma shielding and ablation threshold on laser ablation efficiency and machining quality were analyzed and discussed systematically in this paper.

  4. Evaluation of coated columbium alloy heat shields for space shuttle thermal protection system application. Volume 3, phase 3: Full size TPS evaluation

    NASA Technical Reports Server (NTRS)

    Baer, J. W.; Black, W. E.

    1974-01-01

    The thermal protection system (TPS), designed for incorporation with space shuttle orbiter systems, consists of one primary heat shield thermally and structurally isolated from the test fixture by eight peripheral guard panels, all encompassing an area of approximately 12 sq ft. TPS components include tee-stiffened Cb 752/R-512E heat shields, bi-metallic support posts, panel retainers, and high temperature insulation blankets. The vehicle primary structure was simulated by a titanium skin, frames, and stiffeners. Test procedures, manufacturing processes, and methods of analysis are fully documented. For Vol. 1, see N72-30948; for Vol. 2, see N74-15660.

  5. Percutaneous radiofrequency ablation for hepatic tumors abutting the diaphragm: clinical assessment of the heat-sink effect of artificial ascites.

    PubMed

    Nam, Sang Yu; Rhim, Hyunchul; Kang, Tae Wook; Lee, Min Woo; Kim, Young-Sun; Choi, Dongil; Lee, Won Jae; Park, Yulri; Chang, Ilsoo; Lim, Hyo K

    2010-02-01

    This study was designed to assess whether artificial ascites has a heat-sink effect on the ablation zone for percutaneous radiofrequency ablation (RFA) of hepatic tumors abutting the diaphragm. We retrospectively assessed 28 patients who underwent percutaneous RFA for the treatment of a single nodular hepatic tumor that abutted the diaphragm from July 2000 to December 2006. All patients underwent ultrasound-guided RFA using internally cooled electrodes. A single ablation for 12 minutes was applied using 3-cm active-tip electrodes. We divided patients into two groups on the basis of whether artificial ascites was introduced before RFA: Group A consisted of patients who received artificial ascites with a mean of 760 mL of a 5% dextrose in water solution (n = 15) and group B consisted of patients who did not receive artificial ascites (n = 13). The volume of the ablation zone was measured on CT images obtained immediately after the ablation procedure, and imaging findings were compared for both groups using the Student's t test. We also compared the local tumor progression rate between both groups using the chi-square test (mean follow-up, 37.4 months). There was no significant difference between the two patient groups with regard to age, sex, Child-Pugh class, or tumor location (p > 0.05). The tumors were significantly smaller in group A patients (mean +/- SD, 1.6 +/- 0.5 cm) than in group B patients (2.1 +/- 0.7 cm) (p = 0.019). The mean volume of the RFA zone was 31.6 +/- 11.9 cm(3) in group A patients and 30.9 +/- 11.0 cm(3) in group B patients. There was no significant difference between the groups in the ablation volume (p = 0.871). Local tumor progression was noted in four patients (26.7%) in group A and in three patients (23.1%) in group B. There was no significant difference in the local tumor progression rate between the two groups (p = 0.83). Artificial ascites did not show a heat-sink effect on the volume of the ablation zone after percutaneous RFA for the

  6. Modeling and Validation of Microwave Ablations with Internal Vaporization

    PubMed Central

    Chiang, Jason; Birla, Sohan; Bedoya, Mariajose; Jones, David; Subbiah, Jeyam; Brace, Christopher L.

    2014-01-01

    Numerical simulation is increasingly being utilized for computer-aided design of treatment devices, analysis of ablation growth, and clinical treatment planning. Simulation models to date have incorporated electromagnetic wave propagation and heat conduction, but not other relevant physics such as water vaporization and mass transfer. Such physical changes are particularly noteworthy during the intense heat generation associated with microwave heating. In this work, a numerical model was created that integrates microwave heating with water vapor generation and transport by using porous media assumptions in the tissue domain. The heating physics of the water vapor model was validated through temperature measurements taken at locations 5, 10 and 20 mm away from the heating zone of the microwave antenna in homogenized ex vivo bovine liver setup. Cross-sectional area of water vapor transport was validated through intra-procedural computed tomography (CT) during microwave ablations in homogenized ex vivo bovine liver. Iso-density contours from CT images were compared to vapor concentration contours from the numerical model at intermittent time points using the Jaccard Index. In general, there was an improving correlation in ablation size dimensions as the ablation procedure proceeded, with a Jaccard Index of 0.27, 0.49, 0.61, 0.67 and 0.69 at 1, 2, 3, 4, and 5 minutes. This study demonstrates the feasibility and validity of incorporating water vapor concentration into thermal ablation simulations and validating such models experimentally. PMID:25330481

  7. Experimental Studies of the Aerothermal Characteristics of the Project Orion CEV heat Shield in High Speed Transitional and Turbulent Flows

    NASA Technical Reports Server (NTRS)

    Wadhams, T.P.; MacLean, M.; Holden, M.S.; Cassady, A.M.

    2009-01-01

    An experimental program has been completed by CUBRC exploring laminar, transitional, and turbulent flows over a 7.0% scale model of the Project ORION CEV geometry. This program was executed primarily to answer questions concerning the increase in heat transfer on the windward, or "hot shoulder" of the CEV heat shield from laminar to turbulent flow. To answer these questions CUBRC constructed and instrumented a 14.0 inch diameter Project ORION CEV model and ran a range of Reynolds numbers based on diameter from 1.0 to over 40 million at a Mach number of 8.0. These Reynolds numbers were selected to cover laminar to turbulent heating data on the "hot shoulder". Data obtained during these runs will be used to guide design decisions as they apply to heat shield thickness and extent. Several experiments at higher enthalpies were achieved to obtain data for code validation with real gas effects and transition. CUBRC also performed computation studies of these experiments to aid in the data reduction process and study turbulence modeling.

  8. Shrinkable sleeve eliminates shielding gap in RF cable

    NASA Technical Reports Server (NTRS)

    1965-01-01

    RF shielding gap between an RF cable and a multipin connector is eliminated by a sleeve assembly installed between the connector and the terminated portion of the shielding. The assembly is enclosed in a heat-shrinkable plastic sleeve which completes the continuous RF shield.

  9. KENNEDY SPACE CENTER, FLA. - United Space Alliance employees Jeremy Schwarz (left) and Chris Keeling install new tiles on the heat shield of main engine 1 for the orbiter Discovery. A heat shield is a protective layer on a spacecraft designed to protect it from the high temperatures, usually those that result from aerobraking during reentry into the Earth’s atmosphere.

    NASA Image and Video Library

    2003-09-23

    KENNEDY SPACE CENTER, FLA. - United Space Alliance employees Jeremy Schwarz (left) and Chris Keeling install new tiles on the heat shield of main engine 1 for the orbiter Discovery. A heat shield is a protective layer on a spacecraft designed to protect it from the high temperatures, usually those that result from aerobraking during reentry into the Earth’s atmosphere.

  10. The heat shield for the Mars Polar Lander is attached

    NASA Technical Reports Server (NTRS)

    1998-01-01

    In the Spacecraft Assembly and Encapsulation Facility-2 (SAEF-2), workers lower the heat shield onto the Mars Polar Lander. Scheduled to be launched on Jan. 3, 1999, the lander is a solar- powered spacecraft designed to touch down on the Martian surface near the northern-most boundary of the south pole in order to study the water cycle there. The lander also will help scientists learn more about climate change and current resources on Mars, studying such things as frost, dust, water vapor and condensates in the Martian atmosphere. It is the second spacecraft to be launched in a pair of Mars '98 missions. The first is the Mars Climate Orbiter, which is due to be launched aboard a Delta II rocket from Launch Complex 17A on Dec. 11, 1998.

  11. SPECIAL ISSUE DEVOTED TO THE 25th ANNIVERSARY OF THE A.M. PROKHOROV GENERAL PHYSICS INSTITUTE: High-speed ablation of ultradeep channels by a phase-conjugate dynamically controlled passively Q-switched Nd:YAG laser

    NASA Astrophysics Data System (ADS)

    Basiev, T. T.; Garnov, S. V.; Klimentov, S. M.; Pivovarov, P. A.; Gavrilov, A. V.; Smetanin, S. N.; Solokhin, S. A.; Fedin, A. V.

    2007-10-01

    Parameters of high-speed ablation of ultradeep channels by controlled pulse trains from a single-mode phase-conjugate dynamic cavity Nd:YAG laser emitting 20-200-ns, 70-250-mJ pulses at a pulse repetition rate in a train of 40-250 kHz are studied. The optimal parameters of ablation are found, for which a long-lived region of a hot rarefied gas was maintained in the ultradeep channel, which suppressed the shielding action of the surface plasma. The control of the lasing process during ablation optimises not only the heating and plasma formation, but also the removal of the processed material in the pause between laser pulses. Adaptive regulation of lasing parameters during ablation made it possible to obtain ultradeep channels of length 8-27 mm and diameters 80-300 μm of the input and output holes in metals (aluminium, steel and Inconel 718 nickel superalloy) and ultrahard ceramics (Al2O3, AlN, SiC).

  12. Enhanced Radiofrequency Ablation With Magnetically Directed Metallic Nanoparticles.

    PubMed

    Nguyen, Duy T; Tzou, Wendy S; Zheng, Lijun; Barham, Waseem; Schuller, Joseph L; Shillinglaw, Benjamin; Quaife, Robert A; Sauer, William H

    2016-05-01

    Remote heating of metal located near a radiofrequency ablation source has been previously demonstrated. Therefore, ablation of cardiac tissue treated with metallic nanoparticles may improve local radiofrequency heating and lead to larger ablation lesions. We sought to evaluate the effect of magnetic nanoparticles on tissue sensitivity to radiofrequency energy. Ablation was performed using an ablation catheter positioned with 10 g of force over prepared ex vivo specimens. Tissue temperatures were measured and lesion volumes were acquired. An in vivo porcine thigh model was used to study systemically delivered magnetically guided iron oxide (FeO) nanoparticles during radiofrequency application. Magnetic resonance imaging and histological staining of ablated tissue were subsequently performed as a part of ablation lesion analysis. Ablation of ex vivo myocardial tissue treated with metallic nanoparticles resulted in significantly larger lesions with greater impedance changes and evidence of increased thermal conductivity within the tissue. Magnet-guided localization of FeO nanoparticles within porcine thigh preps was demonstrated by magnetic resonance imaging and iron staining. Irrigated ablation in the regions with greater FeO, after FeO infusion and magnetic guidance, created larger lesions without a greater incidence of steam pops. Metal nanoparticle infiltration resulted in significantly larger ablation lesions with altered electric and thermal conductivity. In vivo magnetic guidance of FeO nanoparticles allowed for facilitated radiofrequency ablation without direct infiltration into the targeted tissue. Further research is needed to assess the clinical applicability of this ablation strategy using metallic nanoparticles for the treatment of cardiac arrhythmias. © 2016 American Heart Association, Inc.

  13. Microscreen radiation shield for thermoelectric generator

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Hunt, T.K.; Novak, R.F.; McBride, J.R.

    1990-08-14

    This patent describes a radiation shield adapted to be interposed between a reaction zone and a means for condensing an alkali metal vapor in a thermoelectric generator for converting heat energy directly to electrical energy. The radiation shield comprises woven wire mesh screen, the spacing between the wires forming the mesh screen being such that the radiation shield reflects thermal radiation while permitting the passage of alkali metal vapor therethrough.

  14. Composite Aerogel Multifoil Protective Shielding

    NASA Technical Reports Server (NTRS)

    Jones, Steven M.

    2013-01-01

    New technologies are needed to survive the temperatures, radiation, and hypervelocity particles that exploration spacecraft encounter. Multilayer insulations (MLIs) have been used on many spacecraft as thermal insulation. Other materials and composites have been used as micrometeorite shielding or radiation shielding. However, no material composite has been developed and employed as a combined thermal insulation, micrometeorite, and radiation shielding. By replacing the scrims that have been used to separate the foil layers in MLIs with various aerogels, and by using a variety of different metal foils, the overall protective performance of MLIs can be greatly expanded to act as thermal insulation, radiation shielding, and hypervelocity particle shielding. Aerogels are highly porous, low-density solids that are produced by the gelation of metal alkoxides and supercritical drying. Aerogels have been flown in NASA missions as a hypervelocity particle capture medium (Stardust) and as thermal insulation (2003 MER). Composite aerogel multifoil protective shielding would be used to provide thermal insulation, while also shielding spacecraft or components from radiation and hypervelocity particle impacts. Multiple layers of foil separated by aerogel would act as a thermal barrier by preventing the transport of heat energy through the composite. The silica aerogel would act as a convective and conductive thermal barrier, while the titania powder and metal foils would absorb and reflect the radiative heat. It would also capture small hypervelocity particles, such as micrometeorites, since it would be a stuffed, multi-shock Whipple shield. The metal foil layers would slow and break up the impacting particles, while the aerogel layers would convert the kinetic energy of the particles to thermal and mechanical energy and stop the particles.

  15. Thermocouple shield

    DOEpatents

    Ripley, Edward B [Knoxville, TN

    2009-11-24

    A thermocouple shield for use in radio frequency fields. In some embodiments the shield includes an electrically conductive tube that houses a standard thermocouple having a thermocouple junction. The electrically conductive tube protects the thermocouple from damage by an RF (including microwave) field and mitigates erroneous temperature readings due to the microwave or RF field. The thermocouple may be surrounded by a ceramic sheath to further protect the thermocouple. The ceramic sheath is generally formed from a material that is transparent to the wavelength of the microwave or RF energy. The microwave transparency property precludes heating of the ceramic sheath due to microwave coupling, which could affect the accuracy of temperature measurements. The ceramic sheath material is typically an electrically insulating material. The electrically insulative properties of the ceramic sheath help avert electrical arcing, which could damage the thermocouple junction. The electrically conductive tube is generally disposed around the thermocouple junction and disposed around at least a portion of the ceramic sheath. The concepts of the thermocouple shield may be incorporated into an integrated shielded thermocouple assembly.

  16. Actively driven thermal radiation shield

    DOEpatents

    Madden, Norman W.; Cork, Christopher P.; Becker, John A.; Knapp, David A.

    2002-01-01

    A thermal radiation shield for cooled portable gamma-ray spectrometers. The thermal radiation shield is located intermediate the vacuum enclosure and detector enclosure, is actively driven, and is useful in reducing the heat load to mechanical cooler and additionally extends the lifetime of the mechanical cooler. The thermal shield is electrically-powered and is particularly useful for portable solid-state gamma-ray detectors or spectrometers that dramatically reduces the cooling power requirements. For example, the operating shield at 260K (40K below room temperature) will decrease the thermal radiation load to the detector by 50%, which makes possible portable battery operation for a mechanically cooled Ge spectrometer.

  17. Phoenix Mars Lander Spacecraft Heat Shield Installation

    NASA Image and Video Library

    2007-05-11

    In the Payload Hazardous Servicing Facility, technicians complete the installation of the heat shield on the Phoenix Mars Lander spacecraft. The Phoenix mission is the first project in NASA's first openly competed program of Mars Scout missions. Phoenix will land in icy soils near the north polar permanent ice cap of Mars and explore the history of the water in these soils and any associated rocks, while monitoring polar climate. Landing is planned in May 2008 on arctic ground where a mission currently in orbit, Mars Odyssey, has detected high concentrations of ice just beneath the top layer of soil. It will serve as NASA's first exploration of a potential modern habitat on Mars and open the door to a renewed search for carbon-bearing compounds, last attempted with NASA's Viking missions in the 1970s. A stereo color camera and a weather station will study the surrounding environment while the other instruments check excavated soil samples for water, organic chemicals and conditions that could indicate whether the site was ever hospitable to life. Microscopes can reveal features as small as one one-thousandth the width of a human hair. Launch of Phoenix aboard a Delta II rocket is targeted for Aug. 3 from Cape Canaveral Air Force Station in Florida.

  18. Phoenix Mars Lander Spacecraft Heat Shield Installation

    NASA Image and Video Library

    2007-05-11

    In the Payload Hazardous Servicing Facility, technicians prepare to install the heat shield on the Phoenix Mars Lander spacecraft. The Phoenix mission is the first project in NASA's first openly competed program of Mars Scout missions. Phoenix will land in icy soils near the north polar permanent ice cap of Mars and explore the history of the water in these soils and any associated rocks, while monitoring polar climate. Landing is planned in May 2008 on arctic ground where a mission currently in orbit, Mars Odyssey, has detected high concentrations of ice just beneath the top layer of soil. It will serve as NASA's first exploration of a potential modern habitat on Mars and open the door to a renewed search for carbon-bearing compounds, last attempted with NASA's Viking missions in the 1970s. A stereo color camera and a weather station will study the surrounding environment while the other instruments check excavated soil samples for water, organic chemicals and conditions that could indicate whether the site was ever hospitable to life. Microscopes can reveal features as small as one one-thousandth the width of a human hair. Launch of Phoenix aboard a Delta II rocket is targeted for Aug. 3 from Cape Canaveral Air Force Station in Florida.

  19. Phoenix Mars Lander Spacecraft Heat Shield Installation

    NASA Image and Video Library

    2007-05-11

    In the Payload Hazardous Servicing Facility, the heat shield for the Phoenix Mars Lander is moved into position for installation on the spacecraft. The Phoenix mission is the first project in NASA's first openly competed program of Mars Scout missions. Phoenix will land in icy soils near the north polar permanent ice cap of Mars and explore the history of the water in these soils and any associated rocks, while monitoring polar climate. Landing is planned in May 2008 on arctic ground where a mission currently in orbit, Mars Odyssey, has detected high concentrations of ice just beneath the top layer of soil. It will serve as NASA's first exploration of a potential modern habitat on Mars and open the door to a renewed search for carbon-bearing compounds, last attempted with NASA's Viking missions in the 1970s. A stereo color camera and a weather station will study the surrounding environment while the other instruments check excavated soil samples for water, organic chemicals and conditions that could indicate whether the site was ever hospitable to life. Microscopes can reveal features as small as one one-thousandth the width of a human hair. Launch of Phoenix aboard a Delta II rocket is targeted for Aug. 3 from Cape Canaveral Air Force Station in Florida.

  20. Phoenix Mars Lander Spacecraft Heat Shield Installation

    NASA Image and Video Library

    2007-05-11

    In the Payload Hazardous Servicing Facility, technicians install the heat shield on the Phoenix Mars Lander spacecraft. The Phoenix mission is the first project in NASA's first openly competed program of Mars Scout missions. Phoenix will land in icy soils near the north polar permanent ice cap of Mars and explore the history of the water in these soils and any associated rocks, while monitoring polar climate. Landing is planned in May 2008 on arctic ground where a mission currently in orbit, Mars Odyssey, has detected high concentrations of ice just beneath the top layer of soil. It will serve as NASA's first exploration of a potential modern habitat on Mars and open the door to a renewed search for carbon-bearing compounds, last attempted with NASA's Viking missions in the 1970s. A stereo color camera and a weather station will study the surrounding environment while the other instruments check excavated soil samples for water, organic chemicals and conditions that could indicate whether the site was ever hospitable to life. Microscopes can reveal features as small as one one-thousandth the width of a human hair. Launch of Phoenix aboard a Delta II rocket is targeted for Aug. 3 from Cape Canaveral Air Force Station in Florida.

  1. Nanosecond laser-metal ablation at different ambient conditions

    NASA Astrophysics Data System (ADS)

    Elsied, Ahmed M.; Dieffenbach, Payson C.; Diwakar, Prasoon K.; Hassanein, Ahmed

    2018-05-01

    Ablation of metals under different ambient conditions and laser fluences, was investigated through series of experiments. A 1064 nm, 6 ns Nd:YAG laser was used to ablate 1 mm thick metal targets with laser energy ranging from 2 mJ to 300 mJ. The experiments were designed to study the effect of material properties, laser fluence, ambient gas, and ambient pressure on laser-metal ablation. The first experiment was conducted under vacuum to study the effect of laser fluence and material properties on metal ablation, using a wide range of laser fluences (2 J/cm2 up to 300 J/cm2) and two different targets, Al and W. The second experiment was conducted at atmospheric pressure using two different ambient gases air and argon, to understand the effect of ambient gas on laser-metal ablation process. The third experiment was conducted at two different pressures (10 Torr and 760 Torr) using the same ambient gas to investigate the effect of ambient pressure on laser-metal ablation. To compare the different ablation processes, the amount of mass ablated, ablation depth, crater profile and melt formation were measured using White Light Profilometer (WLP). The experimental results show that at low laser fluence: the ablated mass, ablation depth, and height of molten layer follow a logarithmic function of the incident laser fluence. While, at high laser fluence they follow a linear function. This dependence on laser fluence was found to be independent on ambient conditions and irradiated material. The effect of ambient pressure was more pronounced than the effect of ambient gas type. Plasma shielding effect was found to be very pronounced in the presence of ambient gas and led to significant reduction in the total mass ablation.

  2. Resin-Impregnated Carbon Ablator: A New Ablative Material for Hyperbolic Entry Speeds

    NASA Technical Reports Server (NTRS)

    Esper, Jaime; Lengowski, Michael

    2012-01-01

    Ablative materials are required to protect a space vehicle from the extreme temperatures encountered during the most demanding (hyperbolic) atmospheric entry velocities, either for probes launched toward other celestial bodies, or coming back to Earth from deep space missions. To that effect, the resin-impregnated carbon ablator (RICA) is a high-temperature carbon/phenolic ablative thermal protection system (TPS) material designed to use modern and commercially viable components in its manufacture. Heritage carbon/phenolic ablators intended for this use rely on materials that are no longer in production (i.e., Galileo, Pioneer Venus); hence the development of alternatives such as RICA is necessary for future NASA planetary entry and Earth re-entry missions. RICA s capabilities were initially measured in air for Earth re-entry applications, where it was exposed to a heat flux of 14 MW/sq m for 22 seconds. Methane tests were also carried out for potential application in Saturn s moon Titan, with a nominal heat flux of 1.4 MW/sq m for up to 478 seconds. Three slightly different material formulations were manufactured and subsequently tested at the Plasma Wind Tunnel of the University of Stuttgart in Germany (PWK1) in the summer and fall of 2010. The TPS integrity was well preserved in most cases, and results show great promise.

  3. 2015 Summer Series - Jeremy Vander Kam - Burn to Shine: Experiences and Lessons from the Orion Heat Shield

    NASA Image and Video Library

    2015-06-25

    NASA's mission to push the limits of human exploration to beyond low earth orbit and to Mars will take humans farther than ever before. Achieving these goals requires collaborations and development of new technology. NASA Ames' expertise in re-entry technology is helping develop the architecture to achieve these goals. The Orion Heat Shield is an example of the materials and technology development needed to sustain heating rates far greater than missions returning from the International Space Station. Jeremy Vander Kam describes details working with this engineering and scientific marvel.

  4. Aeroshell for Mars Science Laboratory

    NASA Technical Reports Server (NTRS)

    2008-01-01

    This image from July 2008 shows the aeroshell for NASA's Mars Science Laboratory while it was being worked on by spacecraft technicians at Lockheed Martin Space Systems Company near Denver.

    This hardware was delivered in early fall of 2008 to NASA's Jet Propulsion Laboratory, Pasadena, Calif., where the Mars Science Laboratory spacecraft is being assembled and tested.

    The aeroshell encapsulates the mission's rover and descent stage during the journey from Earth to Mars and shields them from the intense heat of friction with that upper atmosphere during the initial portion of descent.

    The aeroshell has two main parts: the backshell, which is on top in this image and during the descent, and the heat shield, on the bottom. The heat shield in this image is an engineering unit for testing. The heat shield to be used in flight will be substituted later. The heat shield has a diameter of about 15 feet. For comparison, the heat shields for NASA's Mars Exploraton Rovers Spirit and Opportunity were 8.5 feet and the heat shields for the Apollo capsules that protected astronauts returning to Earth from the moon were just under 13 feet.

    In addition to protecting the Mars Science Laboratory rover, the backshell provides structural support for the descent stage's parachute and sky crane, a system that will lower the rover to a soft landing on the surface of Mars. The backshell for the Mars Science Laboratory is made of an aluminum honeycomb structure sandwiched between graphite-epoxy face sheets. It is covered with a thermal protection system composed of a cork/silicone super light ablator material that originated with the Viking landers of the 1970s. This ablator material has been used on the heat shields of all NASA Mars landers in the past, but this mission is the first Mars mission using it on the backshell.

    The heat shield for Mars Science Laboratory's flight will use tiles made of phenolic impregnated carbon ablator. The engineering unit in

  5. Radiation shielding materials and containers incorporating same

    DOEpatents

    Mirsky, Steven M.; Krill, Stephen J.; Murray, Alexander P.

    2005-11-01

    An improved radiation shielding material and storage systems for radioactive materials incorporating the same. The PYRolytic Uranium Compound ("PYRUC") shielding material is preferably formed by heat and/or pressure treatment of a precursor material comprising microspheres of a uranium compound, such as uranium dioxide or uranium carbide, and a suitable binder. The PYRUC shielding material provides improved radiation shielding, thermal characteristic, cost and ease of use in comparison with other shielding materials. The shielding material can be used to form containment systems, container vessels, shielding structures, and containment storage areas, all of which can be used to house radioactive waste. The preferred shielding system is in the form of a container for storage, transportation, and disposal of radioactive waste. In addition, improved methods for preparing uranium dioxide and uranium carbide microspheres for use in the radiation shielding materials are also provided.

  6. Radiation Shielding Materials and Containers Incorporating Same

    DOEpatents

    Mirsky, Steven M.; Krill, Stephen J.; and Murray, Alexander P.

    2005-11-01

    An improved radiation shielding material and storage systems for radioactive materials incorporating the same. The PYRolytic Uranium Compound (''PYRUC'') shielding material is preferably formed by heat and/or pressure treatment of a precursor material comprising microspheres of a uranium compound, such as uranium dioxide or uranium carbide, and a suitable binder. The PYRUC shielding material provides improved radiation shielding, thermal characteristic, cost and ease of use in comparison with other shielding materials. The shielding material can be used to form containment systems, container vessels, shielding structures, and containment storage areas, all of which can be used to house radioactive waste. The preferred shielding system is in the form of a container for storage, transportation, and disposal of radioactive waste. In addition, improved methods for preparing uranium dioxide and uranium carbide microspheres for use in the radiation shielding materials are also provided.

  7. Advanced Carbon Fabric/Phenolics for Thermal Protection Applications.

    DTIC Science & Technology

    1982-02-01

    structural properties are lower than rayon-based carbon fabriL analogues, they appear to be adequate for most ablative heat- shielding applications...34Development of Ablative Nozzles. Part II Ablative Nozzle Concept, Scaling Law , and Test Results," IAS Mtg. on Large Rockets, Sacramento, CA., Oct. 30

  8. Non-coaxial-based microwave ablation antennas for creating symmetric and asymmetric coagulation zones

    NASA Astrophysics Data System (ADS)

    Mohtashami, Yahya; Luyen, Hung; Hagness, Susan C.; Behdad, Nader

    2018-06-01

    We present an investigation of a new class of microwave ablation (MWA) antennas capable of producing axially symmetric or asymmetric heating patterns. The antenna design is based on a dipole fed by a balanced parallel-wire transmission line. The angle and direction of the deployed dipole arms are used to control the heating pattern. We analyzed the specific absorption rate and temperature profiles using electromagnetic and thermal simulations. Two prototypes were fabricated and tested in ex vivo ablation experiments: one was designed to produce symmetric heating patterns and the other was designed to generate asymmetric heating patterns. Both fabricated prototypes exhibited good impedance matching and produced localized coagulation zones as predicted by the simulations. The prototype operating in porcine muscle created an ˜10 cm3 symmetric ablation zone after 10 min of ablation with a power level of 18 W. The prototype operating in egg white created an ˜4 cm3 asymmetric ablation zone with a directionality ratio of 40% after 5 min of ablation with a power level of 25 W. The proposed MWA antenna design shows promise for minimally invasive treatment of tumors in various clinical scenarios where, depending on the situation, a symmetric or an asymmetric heating pattern may be needed.

  9. High-speed scanning ablation of dental hard tissues with a λ=9.3-μm CO2 laser: heat accumulation and peripheral thermal damage

    NASA Astrophysics Data System (ADS)

    Nguyen, Daniel; Staninec, Michal; Lee, Chulsung; Fried, Daniel

    2010-02-01

    A mechanically scanned CO2 laser operated at high laser pulse repetition rates can be used to rapidly and precisely remove dental decay. This study aims to determine whether these laser systems can safely ablate enamel and dentin without excessive heat accumulation and peripheral thermal damage. Peripheral thermal damage can adversely impact the mechanical strength of the irradiated tissue, particularly for dentin, and reduce the adhesion characteristics of the modified surfaces. Samples were derived from noncarious extracted molars. Pulpal temperatures were recorded using microthermocouples situated at the pulp chamber roof of samples (n=12), which were occlusally ablated using a rapid-scanning, water-cooled 300 Hz CO2 laser over a two minute time course. The mechanical strength of facially ablated dentin (n=10) was determined via four-point bend test and compared to control samples (n=10) prepared with 320 grit wet sand paper to simulate conventional preparations. Composite-to-enamel bond strength was measured via single-plane shear test for ablated/non-etched (n=10) and ablated/acid-etched (n=8) samples and compared to control samples (n=9) prepared by 320 grit wet sanding. Thermocouple measurements indicated that the temperature remained below ambient temperature at 19.0°C (s.d.=0.9) if water-cooling was used. There was no discoloration of either dentin and enamel, the treated surfaces were uniformly ablated and there were no cracks observable on the laser treated surfaces. Fourpoint bend tests yielded mean mechanical strengths of 18.2 N (s.d.=4.6) for ablated dentin and 18.1 N (s.d.=2.7) for control (p>0.05). Shear tests yielded mean bond strengths of 31.2 MPa (s.d.=2.5, p<0.01) for ablated/acid-etched samples, 5.2 MPa (s.d.=2.4, p<0.001) for ablated/non-etched samples, and 37.0 MPa (s.d.=3.6) for control. The results indicate that a rapid-scanning 300 Hz CO2 laser can effectively ablate dentin and enamel without excessive heat accumulation and with minimal

  10. Numerical study of double-pulse laser ablation of Al

    NASA Astrophysics Data System (ADS)

    Förster, G. D.; Lewis, Laurent J.

    2018-06-01

    The effect of double laser pulses (DPs) on the ablation process in solids is studied using a hybrid two-temperature model combining a continuum description of the conduction band electrons with a classical molecular dynamics (MD) approach for the ions. The study is concerned with double pulses with delays in the range of 0-50 ps and absorbed laser fluences of 0.5, 1.0, and 1.5 J/m 2 [i.e., 1-3 times the ablation threshold for single-pulse ablation (SP)], taking Al as a generic example of simple metals. A detailed analysis, including the assessment of thermodynamic pathways and cavitation rates, leads to a comprehensive picture of the mechanisms active during the different stages of the ablation process initiated by DPs. This study provides an explanation for several phenomena observed in DP ablation experiments. In particular, with respect to SP ablation, crater depths are reduced, which can be explained by the compensation of the rarefaction wave from the first laser pulse with the compression wave from the second pulse, or, at higher fluences and larger delays, by the fact that the target surface is shielded with matter ablated by the first laser pulse. Also, we discuss how smoother surface structures obtained using DPs may be related to features found in the simulations—viz., reduced mechanical strain and peak lattice temperatures. Finally, vaporization appears to be enhanced in DP ablation, which may improve the resolution of emission spectra.

  11. The heat shield for the Mars Polar Lander is attached

    NASA Technical Reports Server (NTRS)

    1998-01-01

    In the Spacecraft Assembly and Encapsulation Facility-2 (SAEF-2), workers get ready to lift the heat shield for the Mars Polar Lander off the workstand before attaching it to the lander. Scheduled to be launched on Jan. 3, 1999, the lander is a solar- powered spacecraft designed to touch down on the Martian surface near the northern-most boundary of the south pole in order to study the water cycle there. The lander also will help scientists learn more about climate change and current resources on Mars, studying such things as frost, dust, water vapor and condensates in the Martian atmosphere. It is the second spacecraft to be launched in a pair of Mars '98 missions. The first is the Mars Climate Orbiter, which is due to be launched aboard a Delta II rocket from Launch Complex 17A on Dec. 11, 1998.

  12. Preliminary Analysis of a Water Shield for a Surface Power Reactor

    NASA Technical Reports Server (NTRS)

    Pearson, J. Boise

    2006-01-01

    A water based shielding system is being investigated for use on initial lunar surface power systems. The use of water may lower overall cost (as compared to development cost for other materials) and simplify operations in the setup and handling. The thermal hydraulic performance of the shield is of significant interest. The mechanism for transferring heat through the shield is natural convection. A simple 1-D thermal model indicates the necessity of natural convection to maintain acceptable temperatures and pressures in the water shield. CFD analysis is done to quantify the natural convection in the shield, and predicts sufficient natural convection to transfer heat through the shield with small temperature gradients. A test program will he designed to experimentally verify the thermal hydraulic performance of the shield, and to anchor the CFD models to experimental results.

  13. An analytical and experimental evaluation of shadow shields and their support members

    NASA Technical Reports Server (NTRS)

    Stochl, R. J.; Boyle, R. J.

    1972-01-01

    Experimental tests were performed on a model shadow shield thermal protection system to examine the effect of certain configuration variables. The experimental results were used to verify the ability of an analytical program to predict the shadow shield performance including the shield-support interaction. In general, the analysis (assuming diffuse surfaces) agreed well with the experimental support temperature profiles. The agreement for the shield profiles was not as good. The results demonstrated: (1) shadow shields can be effective in reducing the heat transfer into cryogenic propellant tanks, and (2) the conductive heat transfer through supports can be reduced by selective surface coatings.

  14. Multi-Dimensional, Non-Pyrolyzing Ablation Test Problems

    NASA Technical Reports Server (NTRS)

    Risch, Tim; Kostyk, Chris

    2016-01-01

    Non-pyrolyzingcarbonaceous materials represent a class of candidate material for hypersonic vehicle components providing both structural and thermal protection system capabilities. Two problems relevant to this technology are presented. The first considers the one-dimensional ablation of a carbon material subject to convective heating. The second considers two-dimensional conduction in a rectangular block subject to radiative heating. Surface thermochemistry for both problems includes finite-rate surface kinetics at low temperatures, diffusion limited ablation at intermediate temperatures, and vaporization at high temperatures. The first problem requires the solution of both the steady-state thermal profile with respect to the ablating surface and the transient thermal history for a one-dimensional ablating planar slab with temperature-dependent material properties. The slab front face is convectively heated and also reradiates to a room temperature environment. The back face is adiabatic. The steady-state temperature profile and steady-state mass loss rate should be predicted. Time-dependent front and back face temperature, surface recession and recession rate along with the final temperature profile should be predicted for the time-dependent solution. The second problem requires the solution for the transient temperature history for an ablating, two-dimensional rectangular solid with anisotropic, temperature-dependent thermal properties. The front face is radiatively heated, convectively cooled, and also reradiates to a room temperature environment. The back face and sidewalls are adiabatic. The solution should include the following 9 items: final surface recession profile, time-dependent temperature history of both the front face and back face at both the centerline and sidewall, as well as the time-dependent surface recession and recession rate on the front face at both the centerline and sidewall. The results of the problems from all submitters will be

  15. Heat flow, seismic cut-off depth and thermal modeling of the Fennoscandian Shield

    NASA Astrophysics Data System (ADS)

    Veikkolainen, Toni; Kukkonen, Ilmo T.; Tiira, Timo

    2017-12-01

    Being far from plate boundaries but covered with seismograph networks, the Fennoscandian Shield features an ideal test laboratory for studies of intraplate seismicity. For this purpose, this study applies 4190 earthquake events from years 2000-2015 with magnitudes ranging from 0.10 to 5.22 in Finnish and Swedish national catalogues. In addition, 223 heat flow determinations from both countries and their immediate vicinity were used to analyse the potential correlation of earthquake focal depths and the spatially interpolated heat flow field. Separate subset analyses were performed for five areas of notable seismic activity: the southern Gulf of Bothnia coast of Sweden (area 1), the northern Gulf of Bothnia coast of Sweden (area 2), the Swedish Norrbotten and western Finnish Lapland (area 3), the Kuusamo region of Finland (area 4) and the southernmost Sweden (area 5). In total, our subsets incorporated 3619 earthquake events. No obvious relation of heat flow and focal depth exists, implying that variations of heat flow are primarily caused by shallow lying heat producing units instead of deeper sources. This allows for construction of generic geotherms for the range of representative palaeoclimatically corrected (steady-state) surface heat flow values (40-60 mW m-2). The 1-D geotherms constructed for a three-layer crust and lithospheric upper mantle are based on mantle heat flow constrained with the aid of mantle xenolith thermobarometry (9-15 mW m-2), upper crustal heat production values (3.3-1.1 μWm-3) and the brittle-ductile transition temperature (350 °C) assigned to the cut-off depth of seismicity (28 ± 4 km). For the middle and lower crust heat production values of 0.6 and 0.2 μWm-3 were assigned, respectively. The models suggest a Moho temperature range of 460-500 °C.

  16. KENNEDY SPACE CENTER, FLA. - United Space Alliance employees (from left) Daryl Burke, Jay Beason and Tom Summers check new tiles installed on the heat shield of main engine 1 for the orbiter Discovery. A heat shield is a protective layer on a spacecraft designed to protect it from the high temperatures, usually those that result from aerobraking during reentry into the Earth’s atmosphere.

    NASA Image and Video Library

    2003-09-23

    KENNEDY SPACE CENTER, FLA. - United Space Alliance employees (from left) Daryl Burke, Jay Beason and Tom Summers check new tiles installed on the heat shield of main engine 1 for the orbiter Discovery. A heat shield is a protective layer on a spacecraft designed to protect it from the high temperatures, usually those that result from aerobraking during reentry into the Earth’s atmosphere.

  17. Moldable cork ablation material

    NASA Technical Reports Server (NTRS)

    1977-01-01

    A successful thermal ablative material was manufactured. Moldable cork sheets were tested for density, tensile strength, tensile elongation, thermal conductivity, compression set, and specific heat. A moldable cork sheet, therefore, was established as a realistic product.

  18. Shield Design for Lunar Surface Applications

    NASA Astrophysics Data System (ADS)

    Johnson, Gregory A.

    2006-01-01

    A shielding concept for lunar surface applications of nuclear power is presented herein. The reactor, primary shield, reactor equipment and power generation module are placed in a cavity in the lunar surface. Support structure and heat rejection radiator panels are on the surface, outside the cavity. The reactor power of 1,320 kWt was sized to deliver 50 kWe from a thermoelectric power conversion subsystem. The dose rate on the surface is less than 0.6 mRem/hr at 100 meters from the reactor. Unoptimized shield mass is 1,020 kg which is much lighter than a comparable 4π shield weighing in at 17,000 kg.

  19. Reentry Thermal Analysis of a Generic Crew Exploration Vehicle Structure

    NASA Technical Reports Server (NTRS)

    Ko, William L.; Gong, Leslie; Quinn, Robert D.

    2007-01-01

    Comparative studies were performed on the heat-shielding characteristics of honeycomb-core sandwich panels fabricated with different materials for possible use as wall panels for the proposed crew exploration vehicle. Graphite/epoxy sandwich panel was found to outperform aluminum sandwich panel under the same geometry due to superior heat-shielding qualities and lower material density. Also, representative reentry heat-transfer analysis was performed on the windward wall structures of a generic crew exploration vehicle. The Apollo low Earth orbit reentry trajectory was used to calculate the reentry heating rates. The generic crew exploration vehicle has a graphite/epoxy composite honeycomb sandwich exterior wall and an aluminum honeycomb sandwich interior wall, and is protected with the Apollo thermal protection system ablative material. In the thermal analysis computer program used, the TPS ablation effect was not yet included; however, the results from the nonablation heat-transfer analyses were used to develop a "virtual ablation" method to estimate the ablation heat loads and the thermal protection system recession thicknesses. Depending on the severity of the heating-rate time history, the virtual ablation period was found to last for 87 to 107 seconds and the ablation heat load was estimated to be in the range of 86 to 88 percent of the total heat load for the ablation time period. The thermal protection system recession thickness was estimated to be in the range of 0.08 to 0.11 inches. For the crew exploration vehicle zero-tilt and 18-degree-tilt stagnation points, thermal protection system thicknesses of h = {0.717, 0.733} inches were found to be adequate to keep the substructural composite sandwich temperature below the limit of 300 F.

  20. NASA Ames Helps Re-enter the Dragon (Centerpiece for TWAN and Web)

    NASA Image and Video Library

    2012-05-14

    When the SpaceX Dragon spacecraft returns to Earth after its mission to the International Space Station, it will depend on a heat shield material called PICA-X to protect it during reentry. The heat shield material, called Phenolic Impregnated Carbon Ablator or PICA-X, was developed in partnership with NASA Ames Research Center.

  1. Focused US system for MR imaging-guided tumor ablation.

    PubMed

    Cline, H E; Hynynen, K; Watkins, R D; Adams, W J; Schenck, J F; Ettinger, R H; Freund, W R; Vetro, J P; Jolesz, F A

    1995-03-01

    To measure the performance characteristics of a focused ultrasound (US) system for magnetic resonance (MR) imaging-guided tumor ablation. The authors constructed a focused US system for MR imaging-guided tumor ablation. The location of the heated region and thermal dose were monitored with temperature-sensitive MR images obtained in phantoms and rabbit skeletal muscle after application of each sonic pulse. The region heated by the focused ultrasound beam was within 1 mm of that observed on temperature-sensitive fast gradient-echo MR images of in vivo rabbit skeletal muscle. Analysis of heat flow and the rate of coagulation necrosis provided an estimate of the size of the ablated region that was in agreement with experimental findings. MR imaging provides target definition and control for thermal therapy in regions of variable perfusion or in tissues that are not well characterized.

  2. Evaluation of dispersion strengthened nickel-base alloy heat shields for space shuttle application

    NASA Technical Reports Server (NTRS)

    Johnson, R., Jr.; Killpatrick, D. H.

    1976-01-01

    The results obtained in a program to evaluate dispersion-strengthened nickel-base alloys for use in a metallic radiative thermal protection system operating at surface temperatures to 1477 K for the space shuttle were presented. Vehicle environments having critical effects on the thermal protection system are defined; TD Ni-20Cr characteristics of material used in the current study are compared with previous results; cyclic load, temperature, and pressure effects on sheet material residual strength are investigated; the effects of braze reinforcement in improving the efficiency of spotwelded joints are evaluated; parametric studies of metallic radiative thermal protection systems are reported; and the design, instrumentation, and testing of full scale subsize heat shield panels in two configurations are described. Initial tests of full scale subsize panels included simulated meteoroid impact tests, simulated entry flight aerodynamic heating, programmed differential pressure loads and temperatures simulating mission conditions, and acoustic tests simulating sound levels experienced during boost flight.

  3. Ultrafast dynamics of hard tissue ablation using fs-lasers.

    PubMed

    Domke, Matthias; Wick, Sebastian; Laible, Maike; Rapp, Stephan; Huber, Heinz P; Sroka, Ronald

    2018-05-29

    Several studies on hard tissue laser ablation demonstrated that ultrafast lasers enable precise material removal without thermal side effects. Although the principle ablation mechanisms have been thoroughly investigated, there are still open questions regarding the influence of material properties on transient dynamics. In this investigation, we applied pump-probe microscopy to record ablation dynamics of biomaterials with different tensile strengths (dentin, chicken bone, gallstone, kidney stones) at delay times between 1 ps and 10 μs. Transient reflectivity changes, pressure and shock wave velocities, and elastic constants were determined. The result revealed that absorption and excitation show the typical well-known transient behaviour of dielectric materials. We observed for all samples a photomechanical laser ablation process, where ultrafast expansion of the excited volume generates pressure waves leading to fragmentation around the excited region. Additionally, we identified tensile-strength-related differences in the size of ablated craters and ejected particles. The elastic constants derived were in agreement with literature values. In conclusion, pressure-wave-assisted material removal seems to be a general mechanism for hard tissue ablation with ultrafast lasers. This photomechanical process increases ablation efficiency and removes heated material, thus ultrafast laser ablation is of interest for clinical application where heating of the tissue must be avoided. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

  4. Computer modeling of the combined effects of perfusion, electrical conductivity, and thermal conductivity on tissue heating patterns in radiofrequency tumor ablation.

    PubMed

    Ahmed, Muneeb; Liu, Zhengjun; Humphries, Stanley; Goldberg, S Nahum

    2008-11-01

    To use an established computer simulation model of radiofrequency (RF) ablation to characterize the combined effects of varying perfusion, and electrical and thermal conductivity on RF heating. Two-compartment computer simulation of RF heating using 2-D and 3-D finite element analysis (ETherm) was performed in three phases (n = 88 matrices, 144 data points each). In each phase, RF application was systematically modeled on a clinically relevant template of application parameters (i.e., varying tumor and surrounding tissue perfusion: 0-5 kg/m(3)-s) for internally cooled 3 cm single and 2.5 cm cluster electrodes for tumor diameters ranging from 2-5 cm, and RF application times (6-20 min). In the first phase, outer thermal conductivity was changed to reflect three common clinical scenarios: soft tissue, fat, and ascites (0.5, 0.23, and 0.7 W/m- degrees C, respectively). In the second phase, electrical conductivity was changed to reflect different tumor electrical conductivities (0.5 and 4.0 S/m, representing soft tissue and adjuvant saline injection, respectively) and background electrical conductivity representing soft tissue, lung, and kidney (0.5, 0.1, and 3.3 S/m, respectively). In the third phase, the best and worst combinations of electrical and thermal conductivity characteristics were modeled in combination. Tissue heating patterns and the time required to heat the entire tumor +/-a 5 mm margin to >50 degrees C were assessed. Increasing background tissue thermal conductivity increases the time required to achieve a 50 degrees C isotherm for all tumor sizes and electrode types, but enabled ablation of a given tumor size at higher tissue perfusions. An inner thermal conductivity equivalent to soft tissue (0.5 W/m- degrees C) surrounded by fat (0.23 W/m- degrees C) permitted the greatest degree of tumor heating in the shortest time, while soft tissue surrounded by ascites (0.7 W/m- degrees C) took longer to achieve the 50 degrees C isotherm, and complete ablation

  5. Effect of heat sink on the recurrence of small malignant hepatic tumors after radiofrequency ablation.

    PubMed

    Lin, Zheng-Yu; Li, Guo-Lin; Chen, Jin; Chen, Zhong-Wu; Chen, Yi-Ping; Lin, Sun-Zhi

    2016-12-01

    The aim of this study was to investigate the effect of heat sink on the recurrence of hepatic malignant tumors <3 cm after percutaneous radiofrequency ablation (RFA). This study included 564 hepatic malignant tumors <3 cm in 381 patients. Preoperative images were used to determine whether these tumors were adjacent to vessels, and the diameter of adjacent vessels was measured. RFA was performed computed tomography (CT), magnetic resonance imaging (MRI) and ultrasound (US) guidance, and postoperative imaging follow-up was then conducted. SPSS software version 17.0 was used for data processing, and the χ2 test was used for comparative analysis. Two-sided P < 0.05 indicated statistical significance. A total of 33 recurrences were found: 15 in the MR group (15/468), 12 in the US group (12/53), and 6 in the CT group (6/43). Of the 101 lesions adjacent to blood vessels larger than 3 mm, 20 showed recurrence: 10 in the MR group (10/77), 7 in the US group (7/17), and 3 in the CT group (3/7). The recurrence rate of perivascular lesions was higher than that of nonperivascular lesions, and the rate in the MR group was lower those in the US and CT groups. The curative effect of MRI-guided RFA is better than those of US- and CT-guided ablation. The heat sink effect is an important factor affecting recurrence of hepatic malignant tumors after RFA.

  6. Does artificial ascites induce the heat-sink phenomenon during percutaneous radiofrequency ablation of the hepatic subcapsular area?: an in vivo experimental study using a rabbit model.

    PubMed

    Kim, Young Sun; Rhim, Hyunchul; Choi, Dongil; Lim, Hyo K

    2009-01-01

    To evaluate the effect of the heat-sink phenomenon induced by artificial ascites on the size of the ablation zone during percutaneous radiofrequency (RF) ablation of the hepatic subcapsular area in an in vivo rabbit model. A total of 21 percutaneous rabbit liver RF ablations were performed with and without artificial ascites (5% dextrose aqueous solution). The rabbits were divided into three groups: a) control group (C, n = 7); b) room temperature ascites group (R, n = 7); and c) warmed ascites group (W, n = 7). The tip of a 1 cm, internally cooled electrode was placed on the subcapsular region of the hepatic dome via ultrasound guidance, and ablation was continued for 6 min. Changes in temperature of the ascites were monitored during the ablation. The size of the ablation zones of the excised livers and immediate complications rates were compared statistically between the groups (Mann-Whitney U test, Kruskal-Wallis test, linear-by-linear association, p = 0.05). One rabbit from the "W" group expired during the procedure. In all groups, the ascites temperatures approached their respective body temperatures as the ablations continued; however, a significant difference in ascites temperature was found between groups "W" and "R" throughout the procedures (39.2+/-0.4 degrees C in group W and 33.4+/-4.3 degrees C in group R at 6 min, p = 0.003). No significant difference was found between the size of the ablation zones (782.4+/-237.3 mL in group C, 1,172.0+/-468.9 mL in group R, and 1,030.6+/-665.1 mL in group W, p = 0.170) for the excised liver specimens. Diaphragmatic injury was identified in three of seven cases (42.9%) upon visual inspection of group "C" rabbits (p = 0.030). Artificial ascites are not likely to cause a significant heat-sink phenomenon in the percutaneous RF ablation of the hepatic subcapsular region.

  7. Laboratory simulations of atmospheric entry of micrometeoroids: ablation of magnesium

    NASA Astrophysics Data System (ADS)

    Bones, David; Gomez Martin, Juan Carlos; Diego Carrillo Sanchez, Juan; Dobson, Alexander; Plane, John

    2017-04-01

    We address the uncertainty in the cosmic dust input into the Earth's atmosphere by simulating the atmospheric entry of micrometeoroids in a custom built chamber, capable of heating particles to 3000 K in 2 s and able to precisely reproduce representative heating profiles. In lieu of interplanetary cosmic dust, we use a range of ground-up recovered meteorites and mineral analogues. We measure the ablation of two metals simultaneously with laser induced fluorescence (LIF). The resulting ablation profiles can be compared with the composition of the remaining, unablated particle, as determined from scanning electron microscopy-energy dispersive x-ray (SEM-EDX) analysis. Building on earlier studies of Na, Fe and Ca, here we present Mg profiles and compare them with results from our chemical ablation model (CABMOD). In general, Mg behaves as predicted, beginning to ablate steadily as one broad ablation peak once temperatures reach 2000 K. In contrast Fe, which should behave similarly to Mg, typically has two ablation peaks due to being present in two distinct phases.

  8. Shielding effects in the laser-generated copper plasma under reduced pressures of He atmosphere

    NASA Astrophysics Data System (ADS)

    Burger, M.; Pantić, D.; Nikolić, Z.; Djeniže, S.

    2016-02-01

    Irradiation of samples was performed with 6 ns, 1064 nm Nd:YAG laser. For an applied irradiance range (108-1010 W/cm2), the ablation process exhibits non-linear dependance. Ablated mass of the sample was directly determined using 100 ng resolution mass comparator after ablation under various pressures of helium. The ablation rates were dictated by plasma formation mechanisms as well as ambient conditions. However, the surrounding atmosphere did not significantly affect the value of threshold irradiance of about 2 ×109 W /cm2 for the onset of ablation mechanism change. This value is additionally verified via spectroscopic information from Cu I lines in the range from 0.4 to 1 μs after the laser pulse. Behaviour of spectral lines was monitored with respect to the laser pulse energy. Plasma diagnostics of axial electron density and excitation temperature distributions was performed under He pressure of 200 Torr. An influence of the possible shielding mechanisms responsible for the plasma absorption is discussed.

  9. Microwave ablation in primary and secondary liver tumours: technical and clinical approaches.

    PubMed

    Meloni, Maria Franca; Chiang, Jason; Laeseke, Paul F; Dietrich, Christoph F; Sannino, Angela; Solbiati, Marco; Nocerino, Elisabetta; Brace, Christopher L; Lee, Fred T

    2017-02-01

    Thermal ablation is increasingly being utilised in the treatment of primary and metastatic liver tumours, both as curative therapy and as a bridge to transplantation. Recent advances in high-powered microwave ablation systems have allowed physicians to realise the theoretical heating advantages of microwave energy compared to other ablation modalities. As a result there is a growing body of literature detailing the effects of microwave energy on tissue heating, as well as its effect on clinical outcomes. This article will discuss the relevant physics, review current clinical outcomes and then describe the current techniques used to optimise patient care when using microwave ablation systems.

  10. Experimental evaluation of joint designs for a space-shuttle orbiter ablative leading edge

    NASA Technical Reports Server (NTRS)

    Tompkins, S. S.; Kabana, W. P.

    1975-01-01

    The thermal performance of two types of ablative leading-edge joints for a space-shuttle orbiter were tested and evaluated. Chordwise joints between ablative leading-edge segments, and spanwise joints between ablative leading-edge segments and reusable surface insulation tiles were exposed to simulated shuttle heating environments. The data show that the thermal performance of models with chordwise joints to be as good as jointless models in simulated ascent-heating and orbital cold-soak environments. The suggestion is made for additional work on the joint seals, and, in particular, on the effects of heat-induced seal-material surface irregularities on the local flow.

  11. Atmospheric pressure arc discharge with ablating graphite anode

    NASA Astrophysics Data System (ADS)

    Nemchinsky, V. A.; Raitses, Y.

    2015-06-01

    The anodic carbon arc discharge is used to produce carbon nanoparticles. Recent experiments with the carbon arc at atmospheric pressure helium demonstrated the enhanced ablation rate for narrow graphite anodes resulting in high deposition rates of carbonaceous products on the copper cathode (Fetterman et al 2008 Carbon 46 1322-6). The proposed model explains these results with interconnected steady-state models of the cathode and the anode processes. When considering cathode functioning, the model predicts circulation of the particles in the near-cathode region: evaporation of the cathode material, ionization of evaporated atoms and molecules in the near-cathode plasma, return of the resulting ions to the cathode, surface recombination of ions and electrons followed again by cathode evaporation etc. In the case of the low anode ablation rate, the ion acceleration in the cathode sheath provides the major cathode heating mechanism. In the case of an intensive anode ablation, an additional cathode heating is due to latent fusion heat of the atomic species evaporated from the anode and depositing at the cathode. Using the experimental arc voltage as the only input discharge parameter, the model allows us to calculate the anode ablation rate. A comparison of the results of calculations with the available experimental data shows reasonable agreement.

  12. Computational Analysis of Arc-Jet Wedge Tests Including Ablation and Shape Change

    NASA Technical Reports Server (NTRS)

    Goekcen, Tahir; Chen, Yih-Kanq; Skokova, Kristina A.; Milos, Frank S.

    2010-01-01

    Coupled fluid-material response analyses of arc-jet wedge ablation tests conducted in a NASA Ames arc-jet facility are considered. These tests were conducted using blunt wedge models placed in a free jet downstream of the 6-inch diameter conical nozzle in the Ames 60-MW Interaction Heating Facility. The fluid analysis includes computational Navier-Stokes simulations of the nonequilibrium flowfield in the facility nozzle and test box as well as the flowfield over the models. The material response analysis includes simulation of two-dimensional surface ablation and internal heat conduction, thermal decomposition, and pyrolysis gas flow. For ablating test articles undergoing shape change, the material response and fluid analyses are coupled in order to calculate the time dependent surface heating and pressure distributions that result from shape change. The ablating material used in these arc-jet tests was Phenolic Impregnated Carbon Ablator. Effects of the test article shape change on fluid and material response simulations are demonstrated, and computational predictions of surface recession, shape change, and in-depth temperatures are compared with the experimental measurements.

  13. Emerging needle ablation technology in urology.

    PubMed

    Leveillee, Raymond J; Pease, Karli; Salas, Nelson

    2014-01-01

    Thermal ablation of urologic tumors in the form of freezing (cryoablation) and heating (radiofrequency ablation) have been utilized successfully to treat and ablate soft tissue tumors for over 15 years. Multiple studies have demonstrated efficacy nearing that of extirpative surgery for certain urologic conditions. There are technical limitations to their speed and safety profile because of the physical limits of thermal diffusion. Recently, there has been a desire to investigate other forms of energy in an effort to circumvent the limitations of cryoblation and radiofrequency ablation. This review will focus on three relatively new energy applications as they pertain to tissue ablation: microwave, irreversible electroporation, and water vapor. High-intensity-focused ultrasound nor interstitial lasers are discussed, as there have been no recently published updates. Needle and probe-based ablative treatments will continue to play an important role. As three-dimensional imaging workstations move from the advanced radiologic interventional suite to the operating room, surgeons will likely still play a pivotal role in the +-application of these probe ablative devices. It is essential that the surgeon understands the fundamentals of these devices in order to optimize their application.

  14. Refractory metal shielding /insulation/ increases operating range of induction furnace

    NASA Technical Reports Server (NTRS)

    Ebihara, B. T.

    1965-01-01

    Thermal radiation shield contains escaping heat from an induction furnace. The shield consists of a sheet of refractory metal foil and a loosely packed mat of refractory metal fibers in a concentric pattern. This shielding technique can be used for high temperature ovens, high temperature fluid lines, and chemical reaction vessels.

  15. Microwave Tissue Ablation: Biophysics, Technology and Applications

    PubMed Central

    2010-01-01

    Microwave ablation is an emerging treatment option for many cancers, cardiac arrhythmias and other medical conditions. During treatment, microwaves are applied directly to tissues to produce rapid temperature elevations sufficient to produce immediate coagulative necrosis. The engineering design criteria for each application differ, with individual consideration for factors such as desired ablation zone size, treatment duration, and procedural invasiveness. Recent technological developments in applicator cooling, power control and system optimization for specific applications promise to increase the utilization of microwave ablation in the future. This article will review the basic biophysics of microwave tissue heating, provide an overview of the design and operation of current equipment, and outline areas for future research for microwave ablation. PMID:21175404

  16. High Tc superconductors as thermal radiation shields

    NASA Astrophysics Data System (ADS)

    Zeller, A. F.

    1990-06-01

    The feasibility of using high-Tc superconductor films as IR-radiation shields for liquid-helium-temperature dewars is investigated. Calculations show that a Ba-Ca-Sr-Cu-O superconductor with Tc of 110 K, combined with a liquid-nitrogen temperature shield with an emissivity of 0.03 should produce an upper limit to the radiative heat transfer of 15 mW/sq m. The reduction of reflectivity depends on the field level and the extent of field penetration into the superconductor film, whose surface also would provide magnetic shielding for low magnetic fields. Such shields, providing both magnetic and thermal radiation shielding would be useful for spaceborne applications where exposure to the degrading effects of moist air would not be a problem.

  17. Ablation and Thermal Response Property Model Validation for Phenolic Impregnated Carbon Ablator

    NASA Technical Reports Server (NTRS)

    Milos, F. S.; Chen, Y.-K.

    2009-01-01

    Phenolic Impregnated Carbon Ablator was the heatshield material for the Stardust probe and is also a candidate heatshield material for the Orion Crew Module. As part of the heatshield qualification for Orion, physical and thermal properties were measured for newly manufactured material, included emissivity, heat capacity, thermal conductivity, elemental composition, and thermal decomposition rates. Based on these properties, an ablation and thermal-response model was developed for temperatures up to 3500 K and pressures up to 100 kPa. The model includes orthotropic and pressure-dependent thermal conductivity. In this work, model validation is accomplished by comparison of predictions with data from many arcjet tests conducted over a range of stagnation heat flux and pressure from 107 Watts per square centimeter at 2.3 kPa to 1100 Watts per square centimeter at 84 kPa. Over the entire range of test conditions, model predictions compare well with measured recession, maximum surface temperatures, and in depth temperatures.

  18. Artificial meteor ablation studies - Iron oxides.

    NASA Technical Reports Server (NTRS)

    Blanchard, M. B.

    1972-01-01

    Artificial meteor ablation was performed on natural minerals composed predominantly of magnetite and hematite by using an arc-heated plasma stream of air. Analysis indicates that most of the ablated debris was composed of two or more minerals. Wustite, a metastable mineral, was found to occur as a common product. The 'magnetite' sample, which was 80% magnetite, 14% hematite, 4% apatite, and 2% quartz, yielded ablated products consisting of more than 12 different minerals. Magnetite occurred in 91% of the specimens examined, hematite in 16%, and wustite in 30%. The 'hematite' sample, which was 96% hematite and 3% quartz, yielded ablated products consisting of more than 13 different minerals. Hematite occurred in 47% of the specimens examined, magnetite in 60%, and wustite in 28%. The more volatile elements (Si, P, and Cl) were depleted by about 50%. This study has shown that artificially created ablation products from iron oxides exhibit unique properties that can be used for identification.

  19. Experimental Investigation of Roughness Effects on Transition Onset and Turbulent Heating Augmentation on a Hemisphere at Mach 6 and Mach 10

    NASA Technical Reports Server (NTRS)

    Hollis, Brian R.

    2017-01-01

    An experimental investigation of the effects of distributed surface roughness on boundary-layer transition and turbulent heating has been conducted. Hypersonic wind tunnel testing was performed using hemispherical models with surface roughness patterns simulating those produced by heat shield ablation. Global aeroheating and transition onset data were obtained using phosphor thermography at Mach 6 and Mach 10 over a range of roughness heights and free stream Reynolds numbers sufficient to produce laminar, transitional and turbulent flow. Upstream movement of the transition onset location and increasing heating augmentation over predicted smooth-wall levels were observed with both increasing roughness heights and increasing free stream Reynolds numbers. The experimental heating data are presented herein, as are comparisons to smooth-wall heat transfer distributions from computational flow-field simulations. The transition onset data are also tabulated, and correlations of these data are presented.

  20. Solar Wind Ablation of Terrestrial Planet Atmospheres

    NASA Technical Reports Server (NTRS)

    Moore, Thomas Earle; Fok, Mei-Ching H.; Delcourt, Dominique C.

    2009-01-01

    Internal plasma sources usually arise in planetary magnetospheres as a product of stellar ablation processes. With the ignition of a new star and the onset of its ultraviolet and stellar wind emissions, much of the volatiles in the stellar system undergo a phase transition from gas to plasma. Condensation and accretion into a disk is replaced by radiation and stellar wind ablation of volatile materials from the system- Planets or smaller bodies that harbor intrinsic magnetic fields develop an apparent shield against direct stellar wind impact, but UV radiation still ionizes their gas phases, and the resulting internal plasmas serve to conduct currents to and from the central body along reconnected magnetic field linkages. Photoionization and thermalization of electrons warms the ionospheric topside, enhancing Jeans' escape of super-thermal particles, with ambipolar diffusion and acceleration. Moreover, observations and simulations of auroral processes at Earth indicate that solar wind energy dissipation is concentrated by the geomagnetic field by a factor of 10-100, enhancing heavy species plasma and gas escape from gravity, and providing more current carrying capacity. Thus internal plasmas enable coupling with the plasma, neutral gas and by extension, the entire body. The stellar wind is locally loaded and slowed to develop the required power. The internal source plasma is accelerated and heated, inflating the magnetosphere as it seeks escape, and is ultimately blown away in the stellar wind. Bodies with little sensible atmosphere may still produce an exosphere of sputtered matter when exposed to direct solar wind impact. Bodies with a magnetosphere and internal sources of plasma interact more strongly with the stellar wind owing to the magnetic linkage between the two created by reconnection.

  1. High temperature metal purification using a compact portable rf heating and levitation system on the wake shield

    NASA Technical Reports Server (NTRS)

    Hahs, C. A.

    1990-01-01

    The Wake Shield Facility (WSF) can provide an ideal vacuum environment for the purification of high temperature metals in space. The Modular Electromagnetic Levitator (MEL), will provide the opportunity to study undercooling of metals in space and allow to determine material properties in space. The battery powered rf levitation and heating system developed for the MEL demonstrated efficiency of 36 percent. This system is being considered to purify metals at temperatures below 3000 C.

  2. Radiofrequency ablation of liver tumors (I): biological background.

    PubMed

    Vanagas, Tomas; Gulbinas, Antanas; Pundzius, Juozas; Barauskas, Giedrius

    2010-01-01

    Majority of patients suffering from liver tumors are not candidates for surgery. Currently, minimal invasive techniques have become available for local destruction of hepatic tumors. Radiofrequency ablation is based on biological response to tissue hyperthermia. The aim of this article is to review available biological data on tissue destruction mechanisms. Experimental evidence shows that tissue injury following thermal ablation occurs in two distinct phases. The initial phase is direct injury, which is determined by energy applied, tumor biology, and tumor microenvironment. The temperature varies along the ablation zone and this is reflected by different morphological changes in affected tissues. The local hyperthermia alters metabolism, exacerbates tissue hypoxia, and increases thermosensitivity. The second phase - indirect injury - is observed after the cessation of heat stimulus. This phase represents a balance of several promoting and inhibiting mechanisms, such as induction of apoptosis, heat shock proteins, Kupffer cell activation, stimulation of the immune response, release of cytokines, and ischemia-reperfusion injury. A deeper understanding of the underlying mechanisms may possibly lead to refinements in radiofrequency ablation technology, resulting in advanced local tumor control and prolonged overall survival.

  3. Thermal protection performance of magnetohydrodynamic heat shield system based on multipolar magnetic field

    NASA Astrophysics Data System (ADS)

    Kai, Li; Jun, Liu; Weiqiang, Liu

    2017-07-01

    In order to cover the shortage of dipole magnetic field in the magnetohydrodynamic(MHD) heat shield system, physical model of a multipolar magnetic field with central and peripheral solenoids is constructed. By employing the governing equations of three dimensional thermochemical nonequilibrium flow with electromagnetic source terms based on the low magneto-Reynolds assumption, the flow control performance of the dipole and multipolar magnetic fields are numerically simulated. To make the results comparable, two groups of cases are designed by first assuming equal stagnation magnetic induction strength and secondly assuming equal ampere-turns. Results show that, the five-magnet system, whose central polar orientation is the same with the peripheral ones, have stronger work capability and better shock control and thermal protection performance. Moreover, the five-solenoid systems are the best when the ampere-turns of the central solenoid are twice and fourth of the peripheral ones under those two circumstances respectively. Compared with the dipole magnetic field, the stagnation non-catalytic heat fluxes are decreased by a factor of 47.5% and 34.0% respectively.

  4. KENNEDY SPACE CENTER, FLA. - While Jay Beason (left), with United Space Alliance, looks on, Jeremy Schwarz (front) and Tom Summers (behind), also with USA, place new tiles on the heat shield of main engine 1 for the orbiter Discovery. A heat shield is a protective layer on a spacecraft designed to protect it from the high temperatures, usually those that result from aerobraking during reentry into the Earth’s atmosphere.

    NASA Image and Video Library

    2003-09-23

    KENNEDY SPACE CENTER, FLA. - While Jay Beason (left), with United Space Alliance, looks on, Jeremy Schwarz (front) and Tom Summers (behind), also with USA, place new tiles on the heat shield of main engine 1 for the orbiter Discovery. A heat shield is a protective layer on a spacecraft designed to protect it from the high temperatures, usually those that result from aerobraking during reentry into the Earth’s atmosphere.

  5. Hobel stripper for shielded and unshielded flat conductor cable

    NASA Technical Reports Server (NTRS)

    Angele, W.

    1971-01-01

    Stripping tool exposes an area of shield for grounding purposes without removing an area of insulation between terminated shield and exposed conductors. Tool does not require heated blade and is capable of removing small portions of material at a time, to any depth.

  6. Fracture in Phenolic Impregnated Carbon Ablator

    NASA Technical Reports Server (NTRS)

    Agrawal, Parul; Chavez-Garcia, Jose F.

    2011-01-01

    The thermal protection materials used for spacecraft heat shields are subjected to various thermal-mechanical loads during an atmospheric entry which can threaten the structural integrity of the system. This paper discusses the development of a novel technique to understand the failure mechanisms inside thermal protection materials. The focus of research is Phenolic Impregnated Carbon Ablator (PICA). It has successfully flown on the Stardust spacecraft and is the TPS material chosen for the Mars Science Laboratory (MSL) and Dragon spacecraft. Although PICA has good thermal properties, structurally, it is a weak material. In order to thoroughly understand failure in PICA, fracture tests were performed on FiberForm* (precursor of PICA), virgin and charred PICA materials. Several samples of these materials were tested to investigate failure mechanisms at a microstructural scale. Stress-strain data were obtained simultaneously to estimate the fracture toughness. It was found that cracks initiated and grew in the FiberForm when a critical stress limit was reached such that the carbon fibers separated from the binder. However, both for virgin and charred PICA, crack initiation and growth occurred in the matrix (phenolic) phase. Both virgin and charred PICA showed greater strength values compared to FiberForm coupons, confirming that the presence of the porous matrix helps in absorbing the fracture energy.

  7. Mathematical study of the effects of different intrahepatic cooling on thermal ablation zones.

    PubMed

    Peng, Tingying; O'Neill, David; Payne, Stephen

    2011-01-01

    Thermal ablation of a tumour in the liver with Radio Frequency energy can be accomplished by using a probe inserted into the tissue under the guidance of medical imaging. The extent of ablation can be significantly affected by heat loss due to the high blood perfusion in the liver, especially when the tumour is located close to large vessels. A mathematical model is thus presented here to investigate the heat sinking effects of large vessels, combining a 3D two-equation coupled bio-heat model and a 1D model of convective heat transport across the blood vessel surface. The model simulation is able to recover the experimentally observed different intrahepatic cooling on thermal ablation zones: hepatic veins showed a focal indentation whereas portal veins showed broad flattening of the ablation zones. Moreover, this study also illustrates that this shape derivation can largely be attributed to the temperature variations between the microvascular branches of portal vein as compared with hepatic vein. In contrast, different amount of surface heat convection on the vessel wall between these two types of veins, however, has a minor effect.

  8. Results of tests on a specimen of the SRB aft skirt heat shield curtain in the MSFC LRLF

    NASA Technical Reports Server (NTRS)

    Dean, W. G.

    1980-01-01

    A full scale segment of the actual Solid Rocket Booster aft skirt heat shield curtain was tested in the Large Radiant Lamp Facility (LRLF) at Marshall Space Flight Center. The curtain was mounted in the horizontal position in the same manner as it is to be mounted on the SRB. A shaker rig was designed and used to provide a motion of the curtain, simulating that to be caused in flight by vehicle acoustics. Thermocouples were used to monitor curtain materials temperatures. Both ascent and reentry heat loads were applied to the test specimen. All aspects of the test setup performed as expected, and the test was declared successful.

  9. Modelling of pulsed electron beam induced graphite ablation: Sublimation versus melting

    NASA Astrophysics Data System (ADS)

    Ali, Muddassir; Henda, Redhouane

    2017-12-01

    Pulsed electron beam ablation (PEBA) has recently emerged as a very promising technique for the deposition of thin films with superior properties. Interaction of the pulsed electron beam with the target material is a complex process, which consists of heating, phase transition, and erosion of a small portion from the target surface. Ablation can be significantly affected by the nature of thermal phenomena taking place at the target surface, with subsequent bearing on the properties, stoichiometry and structure of deposited thin films. A two stage, one-dimensional heat conduction model is presented to describe two different thermal phenomena accounting for interaction of a graphite target with a polyenergetic electron beam. In the first instance, the thermal phenomena are comprised of heating, melting and vaporization of the target surface, while in the second instance the thermal phenomena are described in terms of heating and sublimation of the graphite surface. In this work, the electron beam delivers intense electron pulses of ∼100 ns with energies up to 16 keV and an electric current of ∼400 A to a graphite target. The temperature distribution, surface recession velocity, ablated mass per unit area, and ablation depth for the graphite target are numerically simulated by the finite element method for each case. Based on calculation findings and available experimental data, ablation appears to occur mainly in the regime of melting and vaporization from the surface.

  10. Impact of Coupled Radiation and Ablation on the Aerothermodynamics of Meteor Entries

    NASA Technical Reports Server (NTRS)

    Johnston, Christopher O.; Stern, Eric C.

    2017-01-01

    A high-fidelity approach for simulating the aerothermodynamic environments of meteor entries is developed. Two primary components of this model are coupled radiation and coupled ablation. Coupled radiation accounts for the impact of radiation on the flow field energy equations, while coupled ablation explicitly models the injection of ablation products within the flow field and radiation simulations. For a meteoroid with a velocity of 20 km/s, coupled radiation reduces the stagnation point radiative heating by over 60%. For altitudes below 40 km, the impact of coupled radiation on the flow field structure is shown to be fundamentally different, as a result of the large optical thicknesses, than that seen for reentry vehicles, which do not reach such altitudes at velocities greater than 10 km/s. The impact of coupled ablation (with coupled radiation) is shown to provide at least a 70% reduction in the radiative heating relative to the coupled-radiation-only cases. This large reduction is partially the result of the low ionization energies, relative to air species, of ablation products. The low ionization energies of ablation products, such as Mg and Ca, provide strong photoionization and atomic line absorption in regions of the spectrum that air species do not. MgO and CaO are also shown to provide significant absorption. Turbulence is shown to impact the distribution of ablation products through the shock- layer, which results in up to a 100% increase in the radiative heating downstream of the stagnation point. To create a database of heat transfer coefficients the developed model was applied to a range of cases. This database considered velocities ranging from 14 to 20 km/s, altitudes ranging from 20 to 50 km, and nose radii ranging from 1 to 100 m. The heat transfer coefficients from these simulations are below 0.045 for the range of cases (with turbulence), which is significantly lower than the canonical value of 0.1.

  11. Fiber Bragg grating based temperature profiling in ferromagnetic nanoparticles-enhanced radiofrequency ablation

    NASA Astrophysics Data System (ADS)

    Jelbuldina, Madina; Korobeinyk, Alina V.; Korganbayev, Sanzhar; Inglezakis, Vassilis J.; Tosi, Daniele

    2018-07-01

    In this work, we report the real-time temperature profiling performed with a fiber Bragg grating (FBG) sensing system, applied to a ferromagnetic nanoparticles (NP)-enhanced radiofrequency ablation (RFA) for interventional cancer care. A minimally invasive RFA setup has been prepared and applied ex vivo on a liver phantom; NPs (with concentrations of 5 and 10 mg/mL) have been synthesized and injected within the tissue prior to ablation, in order to facilitate the heat distribution to the peripheral sides of the treated tissue. A network of 15 FBG sensors has been deployed in situ in order to detect the parenchymal temperature distribution and estimate the thermal profiles in real time during the ablation, highlighting the impact of the NPs on the RFA mechanism. The results confirm that NP-enhanced ablation with 5 mg/mL density shows a better heat penetration that a standard RFA achieving an almost double-sized lesion, while a higher density (10 mg/mL) does not improve the heat distribution. Thermal data are reported highlighting both spatial and temporal gradients, evaluating the capability of NPs to deliver sufficient heating to the peripheral sides of the tumor borders.

  12. Heat flow and heat generation in greenstone belts

    NASA Technical Reports Server (NTRS)

    Drury, M. J.

    1986-01-01

    Heat flow has been measured in Precambrian shields in both greenstone belts and crystalline terrains. Values are generally low, reflecting the great age and tectonic stability of the shields; they range typically between 30 and 50 mW/sq m, although extreme values of 18 and 79 mW/sq m have been reported. For large areas of the Earth's surface that are assumed to have been subjected to a common thermotectonic event, plots of heat flow against heat generation appear to be linear, although there may be considerable scatter in the data. The relationship is expressed as: Q = Q sub o + D A sub o in which Q is the observed heat flow, A sub o is the measured heat generation at the surface, Q sub o is the reduced heat flow from the lower crust and mantle, and D, which has the dimension of length, represents a scale depth for the distribution of radiogenic elements. Most authors have not used data from greenstone belts in attempting to define the relationship within shields, considering them unrepresentative and preferring to use data from relatively homogeneous crystalline rocks. A discussion follows.

  13. Boundary Layer Transition over Blunt Hypersonic Vehicles Including Effects of Ablation-Induced Out-Gassing

    NASA Technical Reports Server (NTRS)

    Li, Fei; Choudhari, Meelan; Chang, Chau-Lyan; White, Jeffery

    2011-01-01

    Computations are performed to study the boundary layer instability mechanisms pertaining to hypersonic flow over blunt capsules. For capsules with ablative heat shields, transition may be influenced both by out-gassing associated with surface pyrolysis and the resulting modification of surface geometry including the formation of micro-roughness. To isolate the effects of out-gassing, this paper examines the stability of canonical boundary layer flows over a smooth surface in the presence of gas injection into the boundary layer. For a slender cone, the effects of out-gassing on the predominantly second mode instability are found to be stabilizing. In contrast, for a blunt capsule flow dominated by first mode instability, out-gassing is shown to be destabilizing. Analogous destabilizing effects of outgassing are also noted for both stationary and traveling modes of crossflow instability over a blunt sphere-cone configuration at angle of attack.

  14. Optical feedback-induced light modulation for fiber-based laser ablation.

    PubMed

    Kang, Hyun Wook

    2014-11-01

    Optical fibers have been used as a minimally invasive tool in various medical fields. However, due to excessive heat accumulation, the distal end of a fiber often suffers from severe melting or devitrification, leading to the eventual fiber failure during laser treatment. In order to minimize thermal damage at the fiber tip, an optical feedback sensor was developed and tested ex vivo. Porcine kidney tissue was used to evaluate the feasibility of optical feedback in terms of signal activation, ablation performance, and light transmission. Testing various signal thresholds demonstrated that 3 V was relatively appropriate to trigger the feedback sensor and to prevent the fiber deterioration during kidney tissue ablation. Based upon the development of temporal signal signatures, full contact mode rapidly activated the optical feedback sensor possibly due to heat accumulation. Modulated light delivery induced by optical feedback diminished ablation efficiency by 30% in comparison with no feedback case. However, long-term transmission results validated that laser ablation assisted with optical feedback was able to almost consistently sustain light delivery to the tissue as well as ablation efficiency. Therefore, an optical feedback sensor can be a feasible tool to protect optical fiber tips by minimizing debris contamination and delaying thermal damage process and to ensure more efficient and safer laser-induced tissue ablation.

  15. Advanced Rigid Ablative TPS

    NASA Technical Reports Server (NTRS)

    Gasch, Matthew J.

    2011-01-01

    NASA Exploration Systems Mission Directorate s (ESMD) Entry, Descent, and Landing (EDL) Technology Development Project (TDP) and the NASA Aeronautics Research Mission Directorate s (ARMD) Hypersonics Project are developing new advanced rigid ablators in an effort to substantially increase reliability, decrease mass, and reduce life cycle cost of rigid aeroshell-based entry systems for multiple missions. Advanced Rigid Ablators combine ablation resistant top layers capable of high heat flux entry and enable high-speed EDL with insulating mass-efficient bottom that, insulate the structure and lower the areal weight. These materials may benefit Commercial Orbital Transportation Services (COTS) vendors and may potentially enable new NASA missions for higher velocity returns (e.g. asteroid, Mars). The materials have been thermally tested to 400-450 W/sq cm at the Laser Hardened Materials Evaluation Lab (LHMEL), Hypersonics Materials Evaluation Test System (HyMETS) and in arcjet facilities. Tested materials exhibit much lower backface temperatures and reduced recession over the baseline materials (PICA). Although the EDL project is ending in FY11, NASA in-house development of advanced ablators will continue with a focus on varying resin systems and fiber/resin interactions.

  16. Integrated Thermal Protection Systems and Heat Resistant Structures

    NASA Technical Reports Server (NTRS)

    Pichon, Thierry; Lacoste, Marc; Barreteau, R.; Glass, David E.

    2006-01-01

    In the early stages of NASA's Exploration Initiative, Snecma Propulsion Solide was funded under the Exploration Systems Research & Technology program to develop a CMC heatshield, a deployable decelerator, and an ablative heat shield for reentry vehicles. Due to changes within NASA's Exploration Initiative, this task was cancelled in early FY06. This paper will give an overview of the work that was accomplished prior to cancellation. The Snecma team consisted of MT Aerospace, Germany, and Materials Research & Design (MR&D), NASA Langley, NASA Dryden, and NASA Ames in the United States. An Apollo-type capsule was chosen as the reference vehicle for the work. NASA Langley generated the trajectory and aerothermal loads. Snecma and MT Aerospace began the design of a ceramic aft heatshield (CAS) utilizing C/SiC panels as the capsule heatshield. MR&D led the design of a C/SiC deployable decelerator, NASA Ames led the characterization of several ablators, NASA Dryden led the development of a heath management system and the high temperature structures testing, and NASA Langley led the insulation characterization. Though the task was pre-maturely cancelled, a significant quantity of work was accomplished.

  17. Magnetic Resonance Mediated Radiofrequency Ablation.

    PubMed

    Hue, Yik-Kiong; Guimaraes, Alexander R; Cohen, Ouri; Nevo, Erez; Roth, Abraham; Ackerman, Jerome L

    2018-02-01

    To introduce magnetic resonance mediated radiofrequency ablation (MR-RFA), in which the MRI scanner uniquely serves both diagnostic and therapeutic roles. In MR-RFA scanner-induced RF heating is channeled to the ablation site via a Larmor frequency RF pickup device and needle system, and controlled via the pulse sequence. MR-RFA was evaluated with simulation of electric and magnetic fields to predict the increase in local specific-absorption-rate (SAR). Temperature-time profiles were measured for different configurations of the device in agar phantoms and ex vivo bovine liver in a 1.5 T scanner. Temperature rise in MR-RFA was imaged using the proton resonance frequency method validated with fiber-optic thermometry. MR-RFA was performed on the livers of two healthy live pigs. Simulations indicated a near tenfold increase in SAR at the RFA needle tip. Temperature-time profiles depended significantly on the physical parameters of the device although both configurations tested yielded temperature increases sufficient for ablation. Resected livers from live ablations exhibited clear thermal lesions. MR-RFA holds potential for integrating RF ablation tumor therapy with MRI scanning. MR-RFA may add value to MRI with the addition of a potentially disposable ablation device, while retaining MRI's ability to provide real time procedure guidance and measurement of tissue temperature, perfusion, and coagulation.

  18. Novel Low-Density Ablators Containing Hyperbranched Poly(azomethine)s

    NASA Technical Reports Server (NTRS)

    Tigelaar, Dean

    2011-01-01

    An ablative composite is low-density (0.25 to 0.40 g/cu cm), easy to fabricate, and superior to the current state-of-the-art ablator (phenolic impregnated carbon ablator, PICA) in terms of decomposition temperature, char yield, and mechanical strength. Initial ablative testing with a CO2 laser under high-heat-flux (1,100 W/sq cm) conditions showed these new ablators are over twice as effective as PICA in terms of weight loss, as well as transfer of heat through the specimen. The carbon fiber/poly(azomethine) composites have the same density as PICA, but are 8 to 11 times stronger to irreversible breaking by tensile compression. In addition, polyazomethine char yields by thermogravimetric analysis are 70 to 80 percent at 1,000 C. This char yield is 10 to 20 percent higher than phenolic resins, as well as one of the highest char yields known for any polymer. A high char yield holds the composite together better toward shearing forces on reentry, as well as reradiates high heat fluxes. This innovative composite is stronger than PICA, so multiple pieces can be sealed together without fracture. Researchers have also studied polyazomethines before as linear polymers. Due to poor solubility, these polymers precipitate from the polymerization solvent as a low-molecular-weight (2 to 4 repeat units) powder. The only way found to date to keep linear polyazomethines in solution is by adding solubilizing side groups. However, these groups sacrifice certain polymer properties. These hyperbranched polyazomethines are high molecular weight and fully aromatic.

  19. The Femtosecond Laser Ablation on Ultrafine-Grained Copper

    NASA Astrophysics Data System (ADS)

    Lu, Jianxun; Wu, Xiaoyu; Ruan, Shuangchen; Guo, Dengji; Du, Chenlin; Liang, Xiong; Wu, Zhaozhi

    2018-07-01

    To investigate the effects of femtosecond laser ablation on the surface morphology and microstructure of ultrafine-grained copper, point, single-line scanning, and area scanning ablation of ultrafine-grained and coarse-grained copper were performed at room temperature. The ablation threshold gradually increased and materials processing became more difficult with decreasing grain size. In addition, the ablation depth and width of the channels formed by single-line scanning ablation gradually increased with increasing grain size for the same laser pulse energy. The microhardness of the ablated specimens was also evaluated as a function of laser pulse energy using area scanning ablation. The microhardness difference before and after ablation increased with decreasing grain size for the same laser pulse energy. In addition, the microhardness after ablation gradually decreased with increasing laser pulse energy for the ultrafine-grained specimens. However, for the coarse-grained copper specimens, no clear changes of the microhardness were observed after ablation with varying laser pulse energies. The grain sizes of the ultrafine-grained specimens were also surveyed as a function of laser pulse energy using electron backscattered diffraction (EBSD). The heat generated by laser ablation caused recrystallization and grain growth of the ultrafine-grained copper; moreover, the grain size gradually increased with increasing pulse energy. In contrast, no obvious changes in grain size were observed for the coarse-grained copper specimens with increasing pulse energy.

  20. The Femtosecond Laser Ablation on Ultrafine-Grained Copper

    NASA Astrophysics Data System (ADS)

    Lu, Jianxun; Wu, Xiaoyu; Ruan, Shuangchen; Guo, Dengji; Du, Chenlin; Liang, Xiong; Wu, Zhaozhi

    2018-05-01

    To investigate the effects of femtosecond laser ablation on the surface morphology and microstructure of ultrafine-grained copper, point, single-line scanning, and area scanning ablation of ultrafine-grained and coarse-grained copper were performed at room temperature. The ablation threshold gradually increased and materials processing became more difficult with decreasing grain size. In addition, the ablation depth and width of the channels formed by single-line scanning ablation gradually increased with increasing grain size for the same laser pulse energy. The microhardness of the ablated specimens was also evaluated as a function of laser pulse energy using area scanning ablation. The microhardness difference before and after ablation increased with decreasing grain size for the same laser pulse energy. In addition, the microhardness after ablation gradually decreased with increasing laser pulse energy for the ultrafine-grained specimens. However, for the coarse-grained copper specimens, no clear changes of the microhardness were observed after ablation with varying laser pulse energies. The grain sizes of the ultrafine-grained specimens were also surveyed as a function of laser pulse energy using electron backscattered diffraction (EBSD). The heat generated by laser ablation caused recrystallization and grain growth of the ultrafine-grained copper; moreover, the grain size gradually increased with increasing pulse energy. In contrast, no obvious changes in grain size were observed for the coarse-grained copper specimens with increasing pulse energy.

  1. A direct method for fabricating tongue-shielding stent.

    PubMed

    Wang, R R; Olmsted, L W

    1995-08-01

    During oral cancer radiotherapy, a tongue-shielding radiation stent guides the patient's upper and lower jaws to a repeatable position, attenuates radiation doses, and protects the tongue and structures adjacent to the irradiated field. Conventionally, a tongue-shielding radiation stent is made of heat-cured polymethyl methacrylate resin in which a low-melting Pb-Bi-Sn alloy is embedded as a shielding layer. Its use involves multiple and lengthy clinical and laboratory procedures. An improved polyvinyl siloxane-metal composite shielding system for radioprotection has recently been developed. This two-component, base and catalyst, putty material offers a shielding effect similar to that of the conventional shielding alloys. Its major advantages are that it is simple to use, requires only one clinical appointment, and affords efficient collaboration between dental and medical teams during cancer treatment. This article describes a simplified direct method of fabricating a tongue-shielding stent with the use of a new polyvinylsiloxane-metal composite in conjunction with impression putty material.

  2. Dynamics of excimer laser ablation of thin tungsten films studied by fast photography

    NASA Astrophysics Data System (ADS)

    Toth, Zsolt; Hopp, Bela; Kantor, Zoltan; Ignacz, Ferenc; Szoerenyi, Tamas; Bor, Zsolt

    1994-09-01

    The time evolution of ablation and material transport during ArF excimer laser induced blow off of tungsten films from glass substrates is studied by fast photography using delayed dye laser pulses. The analysis of experimental results combined with heat flow calculations provides evidence that tungsten removal in the solid phase is the dominant mechanism in the 40 - 200 mJ/cm2 fluence domain, while partially inhomogeneous melting is observed between 200 and 800 mJ/cm2. In this fluence range, solid fragments and a halo consisting of molten droplets are observed indicating spatial separation of the two phases. The molten phase advances faster, forming a protective mist in front of the solid piece(s). At yet higher fluences (800 - 1000 mJ/cm2), a well separated solid phase could be recorded under the halo although model calculations suggest full vaporization of the layer. This unexpected phenomenon is explained by the optical shielding effect of the halo.

  3. Ablation Predictions for Carbonaceous Materials Using Two Databases for Species Thermodynamics

    NASA Technical Reports Server (NTRS)

    Milos, F. S.; Chen, Y.-K.

    2013-01-01

    During previous work at NASA Ames Research Center, most ablation predictions were obtained using a species thermodynamics database derived primarily from the JANAF thermochemical tables. However, the chemical equilibrium with applications thermodynamics database, also used by NASA, is considered more up to date. In this work, ablation analyses were performed for carbon and carbon phenolic materials using both sets of species thermodynamics. The ablation predictions are comparable at low and moderate heat fluxes, where the dominant mechanism is carbon oxidation. For high heat fluxes where sublimation is important, the predictions differ, with the chemical equilibrium with applications model predicting a lower ablation rate. The disagreement is greater for carbon phenolic than for carbon, and this difference is attributed to hydrocarbon species that may contribute to the ablation rate. Sample calculations for representative Orion and Stardust environments show significant differences only in the sublimation regime. For Stardust, if the calculations include a nominal environmental uncertainty for aeroheating, then the chemical equilibrium with applications model predicts a range of recession that is consistent with measurements for both heatshield cores.

  4. A study of photothermal laser ablation of various polymers on microsecond time scales.

    PubMed

    Kappes, Ralf S; Schönfeld, Friedhelm; Li, Chen; Golriz, Ali A; Nagel, Matthias; Lippert, Thomas; Butt, Hans-Jürgen; Gutmann, Jochen S

    2014-01-01

    To analyze the photothermal ablation of polymers, we designed a temperature measurement setup based on spectral pyrometry. The setup allows to acquire 2D temperature distributions with 1 μm size and 1 μs time resolution and therefore the determination of the center temperature of a laser heating process. Finite element simulations were used to verify and understand the heat conversion and heat flow in the process. With this setup, the photothermal ablation of polystyrene, poly(α-methylstyrene), a polyimide and a triazene polymer was investigated. The thermal stability, the glass transition temperature Tg and the viscosity above Tg were governing the ablation process. Thermal decomposition for the applied laser pulse of about 10 μs started at temperatures similar to the start of decomposition in thermogravimetry. Furthermore, for polystyrene and poly(α-methylstyrene), both with a Tg in the range between room and decomposition temperature, ablation already occurred at temperatures well below the decomposition temperature, only at 30-40 K above Tg. The mechanism was photomechanical, i.e. a stress due to the thermal expansion of the polymer was responsible for ablation. Low molecular weight polymers showed differences in photomechanical ablation, corresponding to their lower Tg and lower viscosity above the glass transition. However, the difference in ablated volume was only significant at higher temperatures in the temperature regime for thermal decomposition at quasi-equilibrium time scales.

  5. The Mixed Processing Models Development Of Thermal Fracture And Laser Ablation On Glass Substrate

    NASA Astrophysics Data System (ADS)

    Huang, Kuo-Cheng; Wu, Wen-Hong; Tseng, Shih-Feng; Hwang, Chi-Hung

    2011-01-01

    As the industries of cell phone and LCD TV were vigorously flourishing and the manufacturing requirements for LCD glass substrate were getting higher, the thermal fracture cutting technology (TFCT) has progressively become the main technology for LCD glass substrate cutting. Due to using laser as the heat source, the TFCT has many advantages, such as uniform heating, small heat effect zone, and high cutting speed, smooth cutting surface and low residual stress, etc. Moreover, a general laser ablation processing or traditional diamond wheel cutting does not have the last two advantages. The article presents a mixed processing of glass substrate, which consists of TFCT and laser ablation mechanisms, and how to enhance the cutting speed with little ablation laser energy. In this study, a 10W Nd:YAG laser and a 40W CO2 laser are used as the heat source of TFCT and laser ablation processing, respectively. The result indicates that the speed of the mixed processing is more than twice the speed of TFCT. Furthermore, after the mixed processing, the residual stresses in the glass substrates are also smaller.

  6. Interactive Volumetry Of Liver Ablation Zones.

    PubMed

    Egger, Jan; Busse, Harald; Brandmaier, Philipp; Seider, Daniel; Gawlitza, Matthias; Strocka, Steffen; Voglreiter, Philip; Dokter, Mark; Hofmann, Michael; Kainz, Bernhard; Hann, Alexander; Chen, Xiaojun; Alhonnoro, Tuomas; Pollari, Mika; Schmalstieg, Dieter; Moche, Michael

    2015-10-20

    Percutaneous radiofrequency ablation (RFA) is a minimally invasive technique that destroys cancer cells by heat. The heat results from focusing energy in the radiofrequency spectrum through a needle. Amongst others, this can enable the treatment of patients who are not eligible for an open surgery. However, the possibility of recurrent liver cancer due to incomplete ablation of the tumor makes post-interventional monitoring via regular follow-up scans mandatory. These scans have to be carefully inspected for any conspicuousness. Within this study, the RF ablation zones from twelve post-interventional CT acquisitions have been segmented semi-automatically to support the visual inspection. An interactive, graph-based contouring approach, which prefers spherically shaped regions, has been applied. For the quantitative and qualitative analysis of the algorithm's results, manual slice-by-slice segmentations produced by clinical experts have been used as the gold standard (which have also been compared among each other). As evaluation metric for the statistical validation, the Dice Similarity Coefficient (DSC) has been calculated. The results show that the proposed tool provides lesion segmentation with sufficient accuracy much faster than manual segmentation. The visual feedback and interactivity make the proposed tool well suitable for the clinical workflow.

  7. Interactive Volumetry Of Liver Ablation Zones

    NASA Astrophysics Data System (ADS)

    Egger, Jan; Busse, Harald; Brandmaier, Philipp; Seider, Daniel; Gawlitza, Matthias; Strocka, Steffen; Voglreiter, Philip; Dokter, Mark; Hofmann, Michael; Kainz, Bernhard; Hann, Alexander; Chen, Xiaojun; Alhonnoro, Tuomas; Pollari, Mika; Schmalstieg, Dieter; Moche, Michael

    2015-10-01

    Percutaneous radiofrequency ablation (RFA) is a minimally invasive technique that destroys cancer cells by heat. The heat results from focusing energy in the radiofrequency spectrum through a needle. Amongst others, this can enable the treatment of patients who are not eligible for an open surgery. However, the possibility of recurrent liver cancer due to incomplete ablation of the tumor makes post-interventional monitoring via regular follow-up scans mandatory. These scans have to be carefully inspected for any conspicuousness. Within this study, the RF ablation zones from twelve post-interventional CT acquisitions have been segmented semi-automatically to support the visual inspection. An interactive, graph-based contouring approach, which prefers spherically shaped regions, has been applied. For the quantitative and qualitative analysis of the algorithm’s results, manual slice-by-slice segmentations produced by clinical experts have been used as the gold standard (which have also been compared among each other). As evaluation metric for the statistical validation, the Dice Similarity Coefficient (DSC) has been calculated. The results show that the proposed tool provides lesion segmentation with sufficient accuracy much faster than manual segmentation. The visual feedback and interactivity make the proposed tool well suitable for the clinical workflow.

  8. Power converter having improved EMI shielding

    DOEpatents

    Beihoff, Bruce C.; Kehl, Dennis L.; Gettelfinger, Lee A.; Kaishian, Steven C.; Phillips, Mark G.; Radosevich, Lawrence D.

    2006-06-13

    EMI shielding is provided for power electronics circuits and the like via a direct-mount reference plane support and shielding structure. The thermal support may receive one or more power electronic circuits. The support may aid in removing heat from the circuits through fluid circulating through the support. The support forms a shield from both external EMI/RFI and from interference generated by operation of the power electronic circuits. Features may be provided to permit and enhance connection of the circuitry to external circuitry, such as improved terminal configurations. Modular units may be assembled that may be coupled to electronic circuitry via plug-in arrangements or through interface with a backplane or similar mounting and interconnecting structures.

  9. Lithium granule ablation and penetration during ELM pacing experiments at DIII-D

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Lunsford, R.; Bortolon, A.; Roquemore, A. L.

    At DIII-D, lithium granules were radially injected into the plasma at the outer midplane to trigger and pace edge localized modes (ELMs). Granules ranging in size from 300 to 1000 microns were horizontally launched into H-mode discharges with velocities near 100 m/s, and granule to granule injection frequencies less than 500 Hz. While the smaller granules were only successful in triggering ELMs approximately 20% of the time, the larger granules regularly demonstrated ELM triggering efficiencies of greater than 80%. A fast visible camera looking along the axis of injection observed the ablation of the lithium granules. We used the durationmore » of ablation as a benchmark for a neutral gas shielding calculation, and approximated the ablation rate and mass deposition location for the various size granules, using measured edge plasma profiles as inputs. In conclusion, this calculation suggests that the low triggering efficiency of the smaller granules is due to the inability of these granules to traverse the steep edge pressure gradient region and reach the top of the pedestal prior to full ablation.« less

  10. Lithium granule ablation and penetration during ELM pacing experiments at DIII-D

    DOE PAGES

    Lunsford, R.; Bortolon, A.; Roquemore, A. L.; ...

    2016-05-25

    At DIII-D, lithium granules were radially injected into the plasma at the outer midplane to trigger and pace edge localized modes (ELMs). Granules ranging in size from 300 to 1000 microns were horizontally launched into H-mode discharges with velocities near 100 m/s, and granule to granule injection frequencies less than 500 Hz. While the smaller granules were only successful in triggering ELMs approximately 20% of the time, the larger granules regularly demonstrated ELM triggering efficiencies of greater than 80%. A fast visible camera looking along the axis of injection observed the ablation of the lithium granules. We used the durationmore » of ablation as a benchmark for a neutral gas shielding calculation, and approximated the ablation rate and mass deposition location for the various size granules, using measured edge plasma profiles as inputs. In conclusion, this calculation suggests that the low triggering efficiency of the smaller granules is due to the inability of these granules to traverse the steep edge pressure gradient region and reach the top of the pedestal prior to full ablation.« less

  11. 3D photomechanical model of tooth enamel ablation by Er-laser radiation

    NASA Astrophysics Data System (ADS)

    Belikov, Andrey V.; Shatilova, Ksenia V.; Skrypnik, Alexei V.

    2014-02-01

    The three-dimensional (3D) photomechanical model of human tooth enamel ablation is described. It takes into account: the structural peculiarities of enamel, Er-laser beam energy spatial distribution and laser radiation attenuation in the tissue. Dynamics change of enamel coefficient of absorption during ablation is also discussed. We consider the 3D photomechanical model of incomplete removal (modification) of the enamel rods by the pressure of water contained in the enamel pores and heated by laser radiation, and complete removal (ablation) of the enamel rods as result of hydroxyapatite heated by laser radiation and evaporation. Modeling results are in close agreement with the experimental results.

  12. Investigations on laser hard tissue ablation under various environments

    NASA Astrophysics Data System (ADS)

    Kang, H. W.; Oh, J.; Welch, A. J.

    2008-06-01

    The purpose of this study was to investigate the effect of liquid environments upon laser bone ablation. A long-pulsed Er,Cr:YSGG laser was employed to ablate bovine bone tibia at various radiant exposures under dry, wet (using water or perfluorocarbon) and spray environmental conditions. Energy loss by the application of liquid during laser irradiation was evaluated, and ablation performance for all conditions was quantitatively measured by optical coherence tomography (OCT). Microscope images were also used to estimate thermal side effects in tissue after multiple-pulse ablation. Wet using water and spray conditions equally attenuated the 2.79 µm wavelength laser beam. Higher transmission efficiency was obtained utilizing a layer of perfluorocarbon. Dry ablation exhibited severe carbonization due to excessive heat accumulation. Wet condition using water resulted in similar ablation volume to the dry case without carbonization. The perfluorocarbon layer produced the largest ablation volume but some carbonization due to the poor thermal conductivity. Spray induced clean cutting with slightly reduced efficiency. Liquid-assisted ablation provided significant beneficial effects such as augmented material removal and cooling/cleaning effects during laser osteotomy.

  13. Microwave ablation devices for interventional oncology.

    PubMed

    Ward, Robert C; Healey, Terrance T; Dupuy, Damian E

    2013-03-01

    Microwave ablation is one of the several options in the ablation armamentarium for the treatment of malignancy, offering several potential benefits when compared with other ablation, radiation, surgical and medical treatment modalities. The basic microwave system consists of the generator, power distribution system and antennas. Often under image (computed tomography or ultrasound) guidance, a needle-like antenna is inserted percutaneously into the tumor, where local microwave electromagnetic radiation is emitted from the probe's active tip, producing frictional tissue heating, capable of causing cell death by coagulation necrosis. Half of the microwave ablation systems use a 915 MHz generator and the other half use a 2450 MHz generator. To date, there are no completed clinical trials comparing microwave devices head-to-head. Prospective comparisons of microwave technology with other treatment alternatives, as well as head-to-head comparison with each microwave device, is needed if this promising field will garner more widespread support and use in the oncology community.

  14. Thermal performance of 625-kg/cu m elastomeric ablative materials on spherically blunted 0.44-radian cones

    NASA Technical Reports Server (NTRS)

    Champman, A. J.

    1972-01-01

    Spherically blunted 0.44-radian (25 deg) half-angle conical models coated with elastomeric ablative materials were tested in supersonic arc-heated wind tunnels to evaluate performance of the ablators over a range of conditions typical of lifting entry. Four test conditions were combinations of stagnation point-heat transfer rates of 2.3 and 4.5 MW/m2 and stagnation pressures of 20 and 2kN/m2. Afterbody values of heat transfer rate and pressure were 0.05 to 0.20 of stagnation point values. Stagnation enthalpy varied from 4.4 to 25 MJ/kg (1900 to 11000 Btu/lbm) and free-stream Mach number was in a range from 3.5 to 4. Ablative materials retained the spherical nose shape throughout tests at the lower heat transfer level, but receded, assuming a flattened nose shape, during tests at the high heat transfer level. The residue layer that formed on the conical after-body was weak, friable, and extensively cracked. The reference ablative material, which contained phenolic microspheres, generally retained the conical shape on the model afterbody. However, a modified ablator, in which phenolic microspheres were replaced with silica microspheres, deformed and separated from the undegraded material, and thereby produced a very uneven surface. Substrate temperatures and ablator recession were in good agreement with values computed by a numerical analysis.

  15. Aperture Shield Materials Characterized and Selected for Solar Dynamic Space Power System

    NASA Technical Reports Server (NTRS)

    1995-01-01

    The aperture shield in a solar dynamic space power system is necessary to prevent thermal damage to the heat receiver should the concentrated solar radiation be accidentally or intentionally focused outside of the heat receiver aperture opening and onto the aperture shield itself. Characterization of the optical and thermal properties of candidate aperture shield materials was needed to support the joint U.S./Russian solar dynamic space power effort for Mir. The specific objective of testing performed at the NASA Lewis Research Center was to identify a high-temperature material with a low specular reflectance, a low solar absorptance, and a high spectral emittance so that during an off-pointing event, the amount of solar energy reflecting off the aperture shield would be small, the ratio of solar absorptance to spectral emittance would provide the lowest possible equilibrium temperature, and the integrity of the aperture shield would remain intact.

  16. Complex permittivity measurements during high temperature recycling of space shuttle antenna window and dielectric heat shield materials

    NASA Technical Reports Server (NTRS)

    Bassett, H. L.; Bomar, S. H., Jr.

    1973-01-01

    The research performed and the data obtained on candidate space shuttle antenna window and heat shield materials are presented. The measurement technique employs a free-space focused beam microwave bridge for obtaining RF transmission data, and a device which rotates a sample holder which is heated on one side by natural gas-air flames. The surface temperature of each sample is monitored by IR pyrometry; embedded and rear surface thermocouples are also used in obtaining temperature data. The surface of the sample undergoing test is subjected to approximately the same temperature/time profile that occurs at a proposed antenna position on the space shuttle as it re-enters. The samples are cycled through ten of these temperature profiles to determine the recycling effects. Very little change was noted in the materials due to the recycling.

  17. Shielding Development for Nuclear Thermal Propulsion

    NASA Technical Reports Server (NTRS)

    Caffrey, Jarvis A.; Gomez, Carlos F.; Scharber, Luke L.

    2015-01-01

    Radiation shielding analysis and development for the Nuclear Cryogenic Propulsion Stage (NCPS) effort is currently in progress and preliminary results have enabled consideration for critical interfaces in the reactor and propulsion stage systems. Early analyses have highlighted a number of engineering constraints, challenges, and possible mitigating solutions. Performance constraints include permissible crew dose rates (shared with expected cosmic ray dose), radiation heating flux into cryogenic propellant, and material radiation damage in critical components. Design strategies in staging can serve to reduce radiation scatter and enhance the effectiveness of inherent shielding within the spacecraft while minimizing the required mass of shielding in the reactor system. Within the reactor system, shield design is further constrained by the need for active cooling with minimal radiation streaming through flow channels. Material selection and thermal design must maximize the reliability of the shield to survive the extreme environment through a long duration mission with multiple engine restarts. A discussion of these challenges and relevant design strategies are provided for the mitigation of radiation in nuclear thermal propulsion.

  18. Design, fabrication and test of Load Bearing multilayer insulation to support a broad area cooled shield

    NASA Astrophysics Data System (ADS)

    Dye, S. A.; Johnson, W. L.; Plachta, D. W.; Mills, G. L.; Buchanan, L.; Kopelove, A. B.

    2014-11-01

    Improvements in cryogenic propellant storage are needed to achieve reduced or Zero Boil Off of cryopropellants, critical for long duration missions. Techniques for reducing heat leak into cryotanks include using passive multi-layer insulation (MLI) and vapor cooled or actively cooled thermal shields. Large scale shields cannot be supported by tank structural supports without heat leak through the supports. Traditional MLI also cannot support shield structural loads, and separate shield support mechanisms add significant heat leak. Quest Thermal Group and Ball Aerospace, with NASA SBIR support, have developed a novel Load Bearing multi-layer insulation (LBMLI) capable of self-supporting thermal shields and providing high thermal performance. We report on the development of LBMLI, including design, modeling and analysis, structural testing via vibe and acoustic loading, calorimeter thermal testing, and Reduced Boil-Off (RBO) testing on NASA large scale cryotanks. LBMLI uses the strength of discrete polymer spacers to control interlayer spacing and support the external load of an actively cooled shield and external MLI. Structural testing at NASA Marshall was performed to beyond maximum launch profiles without failure. LBMLI coupons were thermally tested on calorimeters, with superior performance to traditional MLI on a per layer basis. Thermal and structural tests were performed with LBMLI supporting an actively cooled shield, and comparisons are made to the performance of traditional MLI and thermal shield supports. LBMLI provided a 51% reduction in heat leak per layer over a previously tested traditional MLI with tank standoffs, a 38% reduction in mass, and was advanced to TRL5. Active thermal control using LBMLI and a broad area cooled shield offers significant advantages in total system heat flux, mass and structural robustness for future Reduced Boil-Off and Zero Boil-Off cryogenic missions with durations over a few weeks.

  19. Interstitial ablation and imaging of soft tissue using miniaturized ultrasound arrays

    NASA Astrophysics Data System (ADS)

    Makin, Inder R. S.; Gallagher, Laura A.; Mast, T. Douglas; Runk, Megan M.; Faidi, Waseem; Barthe, Peter G.; Slayton, Michael H.

    2004-05-01

    A potential alternative to extracorporeal, noninvasive HIFU therapy is minimally invasive, interstitial ultrasound ablation that can be performed laparoscopically or percutaneously. Research in this area at Guided Therapy Systems and Ethicon Endo-Surgery has included development of miniaturized (~3 mm diameter) linear ultrasound arrays capable of high power for bulk tissue ablation as well as broad bandwidth for imaging. An integrated control system allows therapy planning and automated treatment guided by real-time interstitial B-scan imaging. Image quality, challenging because of limited probe dimensions and channel count, is aided by signal processing techniques that improve image definition and contrast. Simulations of ultrasonic heat deposition, bio-heat transfer, and tissue modification provide understanding and guidance for development of treatment strategies. Results from in vitro and in vivo ablation experiments, together with corresponding simulations, will be described. Using methods of rotational scanning, this approach is shown to be capable of clinically relevant ablation rates and volumes.

  20. A study on EMI shielding enhancement behaviors of Ni-plated CFs-reinforced polymer matrix composites by post heat treatment

    NASA Astrophysics Data System (ADS)

    Kim, Kwan-Woo; Han, Woong; Kim, Byoung-Suhk; Kim, Byung-Joo; An, Kay-Hyeok

    2017-09-01

    In order to develop the high quality electromagnetic interference shielding efficiency (EMI-SE) materials, Ni-plated carbon fiber fabrics (Ni-CFFs) were prepared by an electroless method. Effects of post heat-treatment conditions on EMI-SE and electrical conductivity of Ni-CFFs/epoxy composites were also investigated. The morphologies and structural properties of Ni-CFFs were measured by a SEM and a XRD. It was found that all the Ni peaks increased with increasing post-heat treatment temperature, indicating that some impurities were removed and nickel particle sharp crystalline peaks. Also, It was found that the EMI-SE of composites enhanced was increased after post heat-treatment. In the frequency range of electromagnetic wave occurred from appliances (3.0 × 107-6.0 × 108), EMI-SE of post-heat treatment Ni-CFs was increased. This result concludes that the EMI-SE of the composites can be enhanced according to the microstructure of Ni in the Ni-CFFs/epoxy composites.

  1. 3D Material Response Analysis of PICA Pyrolysis Experiments

    NASA Technical Reports Server (NTRS)

    Oliver, Brandon A.

    2017-01-01

    Primarily interested in improving ablation modeling for use in inverse reconstruction of flight environments on ablative heat shields. Ablation model is essentially a component of the heat flux sensor, so model uncertainties lead to measurement uncertainties. Non-equilibrium processes have been known to be significant in low density ablators for a long time, but increased accuracy requirements of the reconstruction process necessitates incorporating this physical effect. Attempting to develop a pyrolysis model for implementation in material response based on the PICA data produced by Bessire and Minton. Pyrolysis gas species molar yields as a function of temperature and heating rate. Several problems encountered while trying to fit Arrhenius models to the data led to further investigation of the experimental setup.

  2. Two-Dimensional Finite Element Ablative Thermal Response Analysis of an Arcjet Stagnation Test

    NASA Technical Reports Server (NTRS)

    Dec, John A.; Laub, Bernard; Braun, Robert D.

    2011-01-01

    The finite element ablation and thermal response (FEAtR, hence forth called FEAR) design and analysis program simulates the one, two, or three-dimensional ablation, internal heat conduction, thermal decomposition, and pyrolysis gas flow of thermal protection system materials. As part of a code validation study, two-dimensional axisymmetric results from FEAR are compared to thermal response data obtained from an arc-jet stagnation test in this paper. The results from FEAR are also compared to the two-dimensional axisymmetric computations from the two-dimensional implicit thermal response and ablation program under the same arcjet conditions. The ablating material being used in this arcjet test is phenolic impregnated carbon ablator with an LI-2200 insulator as backup material. The test is performed at the NASA, Ames Research Center Interaction Heating Facility. Spatially distributed computational fluid dynamics solutions for the flow field around the test article are used for the surface boundary conditions.

  3. Role of a single shield in thermocouple measurements in hot air flow

    NASA Astrophysics Data System (ADS)

    Ma, Hongwei; Shi, Lei; Tian, Yangtao

    2017-12-01

    To investigate the role of a single shield on steady temperature measurement using thermocouples in hot air flow, a methodology for solving convection, conduction, and radiation in one single model is provided. In order to compare with the experimental results, a cylindrical computational domain is established, which is the same size with the hot calibration wind-tunnel. In the computational domain, two kinds of thermocouples, the bare-bead and the single-shielded thermocouples, are simulated respectively. Surface temperature distribution and the temperature measurement bias of the two typical thermocouples are compared. The simulation results indicate that: 1) The existence of the shield reduces bead surface heat flux and changes the direction of wires inner heat conduction in a colder surrounding; 2) The existence of the shield reduces the temperature measurement bias both by improving bead surface temperature and by reducing surface temperature gradient; 3) The shield effectively reduces the effect of the ambient temperature on the temperature measurement bias; 4) The shield effectively reduces the influence of airflow velocity on the temperature measurement bias.

  4. Eddy current heating in magnetic refrigerators

    NASA Technical Reports Server (NTRS)

    Kittel, Peter

    1990-01-01

    Eddy current heating can be a significant source of parasitic heating in low temperature magnetic refrigerators. To study this problem a technique to approximate the heating due to eddy currents has been developed. A formula is presented for estimating the heating within a variety of shapes commonly found in magnetic refrigerators. These shapes include circular, square, and rectangular rods; cylindrical and split cylindrical shells; wire loops; and 'coil foil. One set of components evaluated are different types of thermal radiation shields. This comparison shows that a simple split shield is almost as effective (only 23 percent more heating) as using a shield, with the same axial thermal conductivity, made of 'coil foil'.

  5. Monitoring of tissue ablation using time series of ultrasound RF data.

    PubMed

    Imani, Farhad; Wu, Mark Z; Lasso, Andras; Burdette, Everett C; Daoud, Mohammad; Fitchinger, Gabor; Abolmaesumi, Purang; Mousavi, Parvin

    2011-01-01

    This paper is the first report on the monitoring of tissue ablation using ultrasound RF echo time series. We calcuate frequency and time domain features of time series of RF echoes from stationary tissue and transducer, and correlate them with ablated and non-ablated tissue properties. We combine these features in a nonlinear classification framework and demonstrate up to 99% classification accuracy in distinguishing ablated and non-ablated regions of tissue, in areas as small as 12mm2 in size. We also demonstrate significant improvement of ablated tissue classification using RF time series compared to the conventional approach of using single RF scan lines. The results of this study suggest RF echo time series as a promising approach for monitoring ablation, and capturing the changes in the tissue microstructure as a result of heat-induced necrosis.

  6. Overview of the CHarring Ablator Response (CHAR) Code

    NASA Technical Reports Server (NTRS)

    Amar, Adam J.; Oliver, A. Brandon; Kirk, Benjamin S.; Salazar, Giovanni; Droba, Justin

    2016-01-01

    An overview of the capabilities of the CHarring Ablator Response (CHAR) code is presented. CHAR is a one-, two-, and three-dimensional unstructured continuous Galerkin finite-element heat conduction and ablation solver with both direct and inverse modes. Additionally, CHAR includes a coupled linear thermoelastic solver for determination of internal stresses induced from the temperature field and surface loading. Background on the development process, governing equations, material models, discretization techniques, and numerical methods is provided. Special focus is put on the available boundary conditions including thermochemical ablation and contact interfaces, and example simulations are included. Finally, a discussion of ongoing development efforts is presented.

  7. Overview of the CHarring Ablator Response (CHAR) Code

    NASA Technical Reports Server (NTRS)

    Amar, Adam J.; Oliver, A. Brandon; Kirk, Benjamin S.; Salazar, Giovanni; Droba, Justin

    2016-01-01

    An overview of the capabilities of the CHarring Ablator Response (CHAR) code is presented. CHAR is a one-, two-, and three-dimensional unstructured continuous Galerkin finite-element heat conduction and ablation solver with both direct and inverse modes. Additionally, CHAR includes a coupled linear thermoelastic solver for determination of internal stresses induced from the temperature field and surface loading. Background on the development process, governing equations, material models, discretization techniques, and numerical methods is provided. Special focus is put on the available boundary conditions including thermochemical ablation, surface-to-surface radiation exchange, and flowfield coupling. Finally, a discussion of ongoing development efforts is presented.

  8. Laser Ablation Experiments on the Tamdakht H5 Chondrite

    NASA Technical Reports Server (NTRS)

    White, Susan M.; Stern, Eric

    2017-01-01

    High-powered lasers were used to induce ablation and to form fusion crusts in the lab on Tamdakht H5 chondrites and basalt. These ground tests were undertaken to improve our understanding, and ultimately improve our abilty to model and predict, meteoroid ablation during atmospheric entry. The infrared fiber laser at the LHMEL facilty, operated in the continuous wave (i.e. non-pulsed) mode, provided radiation surface heat flux at levels similar to meteor entry for these tests. Results are presented from the first round of testing on samples of Tamdakht H5 ordinary chondrite which were ex-posed to entry-relevant heating rates between 2 and 10 kWcm2.

  9. Rail gun performance and plasma characteristics due to wall ablation

    NASA Technical Reports Server (NTRS)

    Ray, P. K.

    1986-01-01

    The experiment of Bauer, et al. (1982) is analyzed by considering wall ablation and viscous drag in the plasma. Plasma characteristics are evaluated through a simple fluid-mechanical analysis considering only wall ablation. By equating the energy dissipated in the plasma with the radiation heat loss, the average properties of the plasma are determined as a function of time.

  10. Nonlinear Analysis of Two-phase Circumferential Motion in the Ablation Circumstance

    NASA Astrophysics Data System (ADS)

    Xiao-liang, Xu; Hai-ming, Huang; Zi-mao, Zhang

    2010-05-01

    In aerospace craft reentry and solid rocket propellant nozzle, thermal chemistry ablation is a complex process coupling with convection, heat transfer, mass transfer and chemical reaction. Based on discrete vortex method (DVM), thermal chemical ablation model and particle kinetic model, a computational module dealing with the two-phase circumferential motion in ablation circumstance is designed, the ablation velocity and circumferential field can be thus calculated. The calculated nonlinear time series are analyzed in chaotic identification method: relative chaotic characters such as correlation dimension and the maximum Lyapunov exponent are calculated, fractal dimension of vortex bulbs and particles distributions are also obtained, thus the nonlinear ablation process can be judged as a spatiotemporal chaotic process.

  11. Technique for Configuring an Actively Cooled Thermal Shield in a Flight System

    NASA Technical Reports Server (NTRS)

    Barkfknecht, Peter; Mustafi, Shuvo

    2011-01-01

    Broad area cooling shields are a mass-efficient alternative to conductively cooled thermal radiation shielding. The shield would actively intercept a large portion of incident thermal radiation and transport the heat away using cryogenic helium gas. The design concept consists of a conductive and conformable surface that maximizes heat transfer and formability. Broad Area Cooled (BAC) shields could potentially provide considerable mass savings for spaceflight applications by eliminating the need for a rigid thermal radiation shield for cryogen tanks. The BAC consists of a network of capillary tubes that are thermally connected to a conductive shield material. Chilled helium gas is circulated through the network and transports unwanted heat away from the cryogen tanks. The cryogenic helium gas is pumped and chilled simultaneously using a specialized pulse-tube cryocooler, which further improves the mass efficiency of the system. By reducing the thermal environment temperature from 300 to 100 K, the radiative heat load on a cryogen tank could be reduced by an order of magnitude. For a cryogenic liquid propellant scenario of oxygen and hydrogen, the boiloff of hydrogen would be significantly reduced and completely eliminated for oxygen. A major challenge in implementing this technology on large tanks is that the BAC system must be easily scalable from lab demonstrations to full-scale missions. Also, the BAC shield must be conformable to complex shapes like spheres without losing the ability to maintain constant temperature throughout. The initial design maximizes thermal conductivity between the capillary tube and the conductive radiation shielding by using thin, corrugated aluminum foil with the tube running transverse to the folds. This configuration has the added benefit of enabling the foil to stretch and contract longitudinally. This allows the BAC to conform to the complex curvature of a cryogen tank, which is key to its success. To demonstrate a BAC shield

  12. Interactive Volumetry Of Liver Ablation Zones

    PubMed Central

    Egger, Jan; Busse, Harald; Brandmaier, Philipp; Seider, Daniel; Gawlitza, Matthias; Strocka, Steffen; Voglreiter, Philip; Dokter, Mark; Hofmann, Michael; Kainz, Bernhard; Hann, Alexander; Chen, Xiaojun; Alhonnoro, Tuomas; Pollari, Mika; Schmalstieg, Dieter; Moche, Michael

    2015-01-01

    Percutaneous radiofrequency ablation (RFA) is a minimally invasive technique that destroys cancer cells by heat. The heat results from focusing energy in the radiofrequency spectrum through a needle. Amongst others, this can enable the treatment of patients who are not eligible for an open surgery. However, the possibility of recurrent liver cancer due to incomplete ablation of the tumor makes post-interventional monitoring via regular follow-up scans mandatory. These scans have to be carefully inspected for any conspicuousness. Within this study, the RF ablation zones from twelve post-interventional CT acquisitions have been segmented semi-automatically to support the visual inspection. An interactive, graph-based contouring approach, which prefers spherically shaped regions, has been applied. For the quantitative and qualitative analysis of the algorithm’s results, manual slice-by-slice segmentations produced by clinical experts have been used as the gold standard (which have also been compared among each other). As evaluation metric for the statistical validation, the Dice Similarity Coefficient (DSC) has been calculated. The results show that the proposed tool provides lesion segmentation with sufficient accuracy much faster than manual segmentation. The visual feedback and interactivity make the proposed tool well suitable for the clinical workflow. PMID:26482818

  13. Phenolic Impregnated Carbon Ablators (PICA) as Thermal Protection Systems for Discovery Missions

    NASA Technical Reports Server (NTRS)

    Tran, Huy K.; Johnson, Christine E.; Rasky, Daniel J.; Hui, Frank C. L.; Hsu, Ming-Ta; Chen, Timothy; Chen, Y. K.; Paragas, Daniel; Kobayashi, Loreen

    1997-01-01

    This paper presents the development of the light weight Phenolic Impregnated Carbon Ablators (PICA) and its thermal performance in a simulated heating environment for planetary entry vehicles. The PICA material was developed as a member of the Light Weight Ceramic Ablators (LCA's), and the manufacturing process of this material has since been significantly improved. The density of PICA material ranges from 14 to 20 lbm/ft(exp 3), having uniform resin distribution with and without a densified top surface. The thermal performance of PICA was evaluated in the Ames arc-jet facility at cold wall heat fluxes from 375 to 2,960 BtU/ft(exp 2)-s and surface pressures of 0.1 to 0.43 atm. Heat loads used in these tests varied from 5,500 to 29,600 BtU/ft(exp 2) and are representative of the entry conditions of the proposed Discovery Class Missions. Surface and in-depth temperatures were measured using optical pyrometers and thermocouples. Surface recession was also measured by using a template and a height gage. The ablation characteristics and efficiency of PICA are quantified by using the effective heat of ablation, and the thermal penetration response is evaluated from the thermal soak data. In addition, a comparison of thermal performance of standard and surface densified PICA is also discussed.

  14. Picosecond laser ablation of polyamide electrospun nanofibers

    NASA Astrophysics Data System (ADS)

    Götze, Marco; Krimig, Olaf; Kürbitz, Tobias; Henning, Sven; Heilmann, Andreas; Hillrichs, Georg

    2017-02-01

    Electrospun nanofibers mats have a great potential in tissue engineering and regenerative medicine. Their high porosity and enormous volume to surface ratio stimulate the growth and adhesion of mammalian cells and serve as a stable support structure. These suitable properties can be further optimized by structuring of the nanofibers. Ultrashort pulsed lasers can be used for modifying of the electrospun nanofibers without significant heat exposure. It seems also possible to generate very fine cuts from the fiber mats. In this study, polyamide electrospun nanofibers samples were processed with picosecond UV-laser irradiation (λ = 355 nm, τ = 15 ps). The samples were processed in dry, wet and immersed condition. To optimize cutting and structuring of nanofiber tissue flakes, the influence of different laser parameters on line widths, edge quality, heat-affected zone (HAZ) and the contamination of the fibers by ablated particles (debris) were examined. One additional aim was the minimization of the flake size. It was possible to generate nanofiber flakes in the sub-millimeter range. The quality of the nanofiber flakes could be improved by ablation near the ablation threshold of the material. For cutting under wet conditions shrinking of the flakes has to be taken into account.

  15. MHD heat flux mitigation in hypersonic flow around a blunt body with ablating surface

    NASA Astrophysics Data System (ADS)

    Bityurin, V. A.; Bocharov, A. N.

    2018-07-01

    One of the possible applications of magnetohydrodynamic flow control is considered. Namely, the surface heat flux mitigation by means of magnetohydrodynamic (MHD) interaction in hypersonic flow around a blunt body. The 2D computational model realizes a coupled solution of chemically non-equilibrium ionized airflow in magnetic field. Heat- and mass-transfer due to the ablation of materials from the body surface is taken into account. Two cases of free-stream flow conditions are considered: moderate free-stream velocity (7500 m s‑1) case and high free-stream velocity (11 000 m s‑1) case. It is shown that the first flow case results in moderate ionization in the shock layer, while the second flow case results in high ionization. In the first case, the Hall effect is significant, and effective electrical conductivity in the shock layer is rather low. In the second case, the Hall effect reduces, and effective conductivity is high. Even if the Hall effect is strong, as in the first case, intensive MHD deceleration of the flow behind the shock is provided due to the presence of insulating boundaries, the bow shock front and non-conductive wall of the blunt body. In the second case, high effective conductivity provides a high intensity of MHD flow deceleration. In both cases, a strong effect of MHD interaction on the flow structure is observed. As a consequence, a noticeable reduction of the surface heat flux is revealed for reasonable values of magnetic induction. The new treatment of mechanism for the surface heat flux reduction is proposed, which is different from commonly used one assuming that MHD interaction increases the bow shock stand-off distance, and, consequently results in a decrease of the mean temperature drop across the shock layer. The new effect of ‘saturation of heat flux’ is discussed.

  16. Effects of shielded or unshielded laser and electrohydraulic lithotripsy on rabbit bladder.

    PubMed

    Bhatta, K M; Rosen, D I; Flotte, T J; Dretler, S P; Nishioka, N S

    1990-04-01

    The pulsed dye laser and electrohydraulic lithotriptor (EHL) are both effective devices for fragmenting urinary and biliary calculi. Both fragment stones by producing a plasma-mediated shockwave. Recently, a plasma shield consisting of a hollow spring and a metal end cap has been described for use with the laser and EHL devices in an attempt to minimize tissue damage without adversely affecting stone fragmentation rates. The tissue effects produced by a pulsed dye laser and an EHL device with and without plasma shields were examined and compared using rabbit urinary bladders. If blood was present, the unshielded laser perforated the bladder wall in two pulses. However, in the absence of blood, over 100 pulses were needed for the laser to perforate the bladder. A mean of six pulses were required to perforate the bladder wall with a shielded laser. The unshielded EHL perforated the bladder wall in two pulses, whereas, the shielded EHL required a mean of 35 pulses. Microscopically, areas of exposure revealed hemorrhage and tissue ablation. We conclude that all devices examined can produce significant tissue damage when discharged directly onto bladder epithelium.

  17. An investigation on 800 nm femtosecond laser ablation of K9 glass in air and vacuum

    NASA Astrophysics Data System (ADS)

    Xu, Shi-zhen; Yao, Cai-zhen; Dou, Hong-qiang; Liao, Wei; Li, Xiao-yang; Ding, Ren-jie; Zhang, Li-juan; Liu, Hao; Yuan, Xiao-dong; Zu, Xiao-tao

    2017-06-01

    Ablation rates of K9 glass were studied as a function of femtosecond laser fluences. The central wavelength was 800 nm, and pulse durations of 35 fs and 500 fs in air and vacuum were employed. Ablation thresholds of 0.42 J/cm2 and 2.1 J/cm2 were obtained at 35 fs and 500 fs, respectively, which were independent with the ambient conditions and depend on the incident pulse numbers due to incubation effects. The ablation rate of 35 fs pulse laser increased with the increasing of laser fluence in vacuum, while in air condition, it slowly increased to a plateau at high fluence. The ablation rate of 500 fs pulse laser showed an increase at low fluence and a slow drop of ablation rate was observed at high fluence in air and vacuum, which may due to the strong defocusing effects associated with the non-equilibrium ionization of air, and/or the shielding effects of conduction band electrons (CBEs) produced by multi-photon ionization and impact ionization in K9 glass surface. The typical ablation morphologies, e.g. smooth zone and laser-induced periodic surface structures (LIPSS) were also presented and illustrated.

  18. Local ablative treatments for hepatocellular carcinoma: An updated review

    PubMed Central

    Facciorusso, Antonio; Serviddio, Gaetano; Muscatiello, Nicola

    2016-01-01

    Ablative treatments currently represent the first-line option for the treatment of early stage unresectable hepatocellular carcinoma (HCC). Furthermore, they are effective as bridging/downstaging therapies before orthotopic liver transplantation. Contraindications based on size, number, and location of nodules are quite variable in literature and strictly dependent on local expertise. Among ablative therapies, radiofrequency ablation (RFA) has gained a pivotal role due to its efficacy, with a reported 5-year survival rate of 40%-70%, and safety. Although survival outcomes are similar to percutaneous ethanol injection, the lower local recurrence rate stands for a wider application of RFA in hepato-oncology. Moreover, RFA seems to be even more cost-effective than liver resection for very early HCC (single nodule ≤ 2 cm) and in the presence of two or three nodules ≤ 3 cm. There is increasing evidence that combining RFA to transarterial chemoembolization may increase the therapeutic benefit in larger HCCs without increasing the major complication rate, but more robust prospective data is still needed to validate these pivotal findings. Among other thermal treatments, microwave ablation (MWA) uses high frequency electromagnetic energy to induce tissue death via coagulation necrosis. In comparison to RFA, MWA has several theoretical advantages such as a broader zone of active heating, higher temperatures within the targeted area in a shorter treatment time and the lack of heat-sink effect. The safety concerns raised on the risks of this procedure, due to the broader and less predictable necrosis areas, have been recently overcome. However, whether MWA ability to generate a larger ablation zone will translate into a survival gain remains unknown. Other treatments, such as high-intensity focused ultrasound ablation, laser ablation, and cryoablation, are less investigated but showed promising results in early HCC patients and could be a valuable therapeutic option in

  19. High-speed scanning ablation of dental hard tissues with a λ = 9.3 μm CO2 laser: adhesion, mechanical strength, heat accumulation, and peripheral thermal damage

    PubMed Central

    Nguyen, Daniel; Chang, Kwang; Hedayatollahnajafi, Saba; Staninec, Michal; Chan, Kenneth; Lee, Robert; Fried, Daniel

    2011-01-01

    CO2 lasers can be operated at high laser pulse repetition rates for the rapid and precise removal of dental decay. Excessive heat accumulation and peripheral thermal damage is a concern when using high pulse repetition rates. Peripheral thermal damage can adversely impact the mechanical strength of the irradiated tissue, particularly for dentin, and reduce the adhesion characteristics of the modified surfaces. The interpulpal temperature rise was recorded using microthermocouples situated at the roof of the pulp chamber on teeth that were occlusally ablated using a rapidly-scanned CO2 laser operating at 9.3 μm with a pulse duration of 10 to 15 μs and repetition rate of 300 Hz over a 2 min time course. The adhesion strength of laser treated enamel and dentin surfaces was measured for various laser scanning parameters with and without post-ablation acid etching using the single-plane shear test. The mechanical strength of laser-ablated dentin surfaces were determined via the four-point bend test and compared to control samples prepared with 320 grit wet sand paper to simulate conventional preparations. Thermocouple measurements indicated that the temperature remained below ambient temperature if water-cooling was used. There was no discoloration of either dentin or enamel laser treated surfaces, the surfaces were uniformly ablated, and there were no cracks visible. Four-point bend tests yielded mean mechanical strengths of 18.2 N (s.d. = 4.6) for ablated dentin and 18.1 N (s.d. = 2.7) for control (p > 0.05). Shear tests yielded mean bond strengths approaching 30 MPa for both enamel and dentin under certain irradiation conditions. These values were slightly lower than nonirradiated acid-etched control samples. Additional studies are needed to determine if the slightly lower bond strength than the acid-etched control samples is clinically significant. These measurements demonstrate that enamel and dentin surfaces can be rapidly ablated by CO2 lasers with minimal

  20. High-speed scanning ablation of dental hard tissues with a λ = 9.3 μm CO2 laser: adhesion, mechanical strength, heat accumulation, and peripheral thermal damage

    NASA Astrophysics Data System (ADS)

    Nguyen, Daniel; Chang, Kwang; Hedayatollahnajafi, Saba; Staninec, Michal; Chan, Kenneth; Lee, Robert; Fried, Daniel

    2011-07-01

    CO2 lasers can be operated at high laser pulse repetition rates for the rapid and precise removal of dental decay. Excessive heat accumulation and peripheral thermal damage is a concern when using high pulse repetition rates. Peripheral thermal damage can adversely impact the mechanical strength of the irradiated tissue, particularly for dentin, and reduce the adhesion characteristics of the modified surfaces. The interpulpal temperature rise was recorded using microthermocouples situated at the roof of the pulp chamber on teeth that were occlusally ablated using a rapidly-scanned CO2 laser operating at 9.3 μm with a pulse duration of 10 to 15 μs and repetition rate of 300 Hz over a 2 min time course. The adhesion strength of laser treated enamel and dentin surfaces was measured for various laser scanning parameters with and without post-ablation acid etching using the single-plane shear test. The mechanical strength of laser-ablated dentin surfaces were determined via the four-point bend test and compared to control samples prepared with 320 grit wet sand paper to simulate conventional preparations. Thermocouple measurements indicated that the temperature remained below ambient temperature if water-cooling was used. There was no discoloration of either dentin or enamel laser treated surfaces, the surfaces were uniformly ablated, and there were no cracks visible. Four-point bend tests yielded mean mechanical strengths of 18.2 N (s.d. = 4.6) for ablated dentin and 18.1 N (s.d. = 2.7) for control (p > 0.05). Shear tests yielded mean bond strengths approaching 30 MPa for both enamel and dentin under certain irradiation conditions. These values were slightly lower than nonirradiated acid-etched control samples. Additional studies are needed to determine if the slightly lower bond strength than the acid-etched control samples is clinically significant. These measurements demonstrate that enamel and dentin surfaces can be rapidly ablated by CO2 lasers with minimal

  1. High-speed scanning ablation of dental hard tissues with a λ = 9.3 μm CO2 laser: adhesion, mechanical strength, heat accumulation, and peripheral thermal damage.

    PubMed

    Nguyen, Daniel; Chang, Kwang; Hedayatollahnajafi, Saba; Staninec, Michal; Chan, Kenneth; Lee, Robert; Fried, Daniel

    2011-07-01

    CO(2) lasers can be operated at high laser pulse repetition rates for the rapid and precise removal of dental decay. Excessive heat accumulation and peripheral thermal damage is a concern when using high pulse repetition rates. Peripheral thermal damage can adversely impact the mechanical strength of the irradiated tissue, particularly for dentin, and reduce the adhesion characteristics of the modified surfaces. The interpulpal temperature rise was recorded using microthermocouples situated at the roof of the pulp chamber on teeth that were occlusally ablated using a rapidly-scanned CO(2) laser operating at 9.3 μm with a pulse duration of 10 to 15 μs and repetition rate of 300 Hz over a 2 min time course. The adhesion strength of laser treated enamel and dentin surfaces was measured for various laser scanning parameters with and without post-ablation acid etching using the single-plane shear test. The mechanical strength of laser-ablated dentin surfaces were determined via the four-point bend test and compared to control samples prepared with 320 grit wet sand paper to simulate conventional preparations. Thermocouple measurements indicated that the temperature remained below ambient temperature if water-cooling was used. There was no discoloration of either dentin or enamel laser treated surfaces, the surfaces were uniformly ablated, and there were no cracks visible. Four-point bend tests yielded mean mechanical strengths of 18.2 N (s.d. = 4.6) for ablated dentin and 18.1 N (s.d. = 2.7) for control (p > 0.05). Shear tests yielded mean bond strengths approaching 30 MPa for both enamel and dentin under certain irradiation conditions. These values were slightly lower than nonirradiated acid-etched control samples. Additional studies are needed to determine if the slightly lower bond strength than the acid-etched control samples is clinically significant. These measurements demonstrate that enamel and dentin surfaces can be rapidly ablated by CO(2) lasers with

  2. EXPERIMENTAL EVALUATION OF THE THERMAL PERFORMANCE OF A WATER SHIELD FOR A SURFACE POWER REACTOR

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    REID, ROBERT S.; PEARSON, J. BOSIE; STEWART, ERIC T.

    2007-01-16

    Water based reactor shielding is being investigated for use on initial lunar surface power systems. A water shield may lower overall cost (as compared to development cost for other materials) and simplify operations in the setup and handling. The thermal hydraulic performance of the shield is of significant interest. The mechanism for transferring heat through the shield is natural convection. Natural convection in a 100 kWt lunar surface reactor shield design is evaluated with 2 kW power input to the water in the Water Shield Testbed (WST) at the NASA Marshall Space Flight Center. The experimental data from the WSTmore » is used to validate a CFD model. Performance of the water shield on the lunar surface is then predicted with a CFD model anchored to test data. The experiment had a maximum water temperature of 75 C. The CFD model with 1/6-g predicts a maximum water temperature of 88 C with the same heat load and external boundary conditions. This difference in maximum temperature does not greatly affect the structural design of the shield, and demonstrates that it may be possible to use water for a lunar reactor shield.« less

  3. Analysis of ablation debris from natural and artificial iron meteorites

    NASA Technical Reports Server (NTRS)

    Blanchard, M. B.; Davis, A. S.

    1977-01-01

    Artificial ablation studies were performed on iron and nickel-iron samples using an arc-heated plasma of ionized air. Experiment conditions simulated a meteoroid traveling about 12 km/sec at an altitude of 70 km. The artificially produced fusion crusts and ablation debris show features very similar to natural fusion crusts of the iron meteorites Boguslavka, Norfork, and N'Kandhla and to magnetic spherules recovered from Mn nodules. X-ray diffraction, electron microprobe, optical, and scanning electron microscope analyses reveal that important mineralogical, elemental, and textural changes occur during ablation. Some metal is melted and ablated. The outer margin of the melted rind is oxidized and recrystallizes as a discontinuous crust of magnetite and wustite. Adjacent to the oxidized metallic ablation zone is an unoxidized metallic ablation zone in which structures such as Widmannstatten bands are obliterated as the metal is transformed to unequilibrated alpha 2 nickel-iron. Volatile elements are vaporized and less volatile elements undergo fractionation.

  4. Optimization of the Mu2e Production Solenoid Heat and Radiation Shield

    NASA Astrophysics Data System (ADS)

    Pronskikh, V. S.; Coleman, R.; Glenzinski, D.; Kashikhin, V. V.; Mokhov, N. V.

    2014-03-01

    The Mu2e experiment at Fermilab is designed to study the conversion of a negative muon to electron in the field of a nucleus without emission of neutrinos. Observation of this process would provide unambiguous evidence for physics beyond the Standard Model, and can point to new physics beyond the reach of the LHC. The main parts of the Mu2e apparatus are its superconducting solenoids: Production Solenoid (PS), Transport Solenoid (TS), and Detector Solenoid (DS). Being in the vicinity of the beam, PS magnets are most subjected to the radiation damage. In order for the PS superconducting magnet to operate reliably, the peak neutron flux in the PS coils must be reduced by 3 orders of magnitude by means of sophisticatedly designed massive Heat and Radiation Shield (HRS), optimized for the performance and cost. An issue with radiation damage is related to large residual electrical resistivity degradation in the superconducting coils, especially its Al stabilizer. A detailed MARS15 analysis and optimization of the HRS has been carried out both to satisfy the Mu2e requirements to the radiation quantities (such as displacements per atom, peak temperature and power density in the coils, absorbed dose in the insulation, and dynamic heat load) and cost. Results of MARS15 simulations of these radiation quantities are reported and optimized HRS models are presented; it is shown that design levels satisfy all requirements.

  5. Imaging Features of Radiofrequency Ablation with Heat-Deployed Liposomal Doxorubicin in Hepatic Tumors

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Hong, Cheng William, E-mail: williamhongcheng@gmail.com; Chow, Lucy, E-mail: lucychow282@gmail.com; Turkbey, Evrim B., E-mail: evrimbengi@yahoo.com

    2016-03-15

    IntroductionThe imaging features of unresectable hepatic malignancies in patients who underwent radiofrequency ablation (RFA) in combination with lyso-thermosensitive liposomal doxorubicin (LTLD) were determined.Materials and MethodsA phase I dose escalation study combining RFA with LTLD was performed with peri- and post- procedural CT and MRI. Imaging features were analyzed and measured in terms of ablative zone size and surrounding penumbra size. The dynamic imaging appearance was described qualitatively immediately following the procedure and at 1-month follow-up. The control group receiving liver RFA without LTLD was compared to the study group in terms of imaging features and post-ablative zone size dynamics atmore » follow-up.ResultsPost-treatment scans of hepatic lesions treated with RFA and LTLD have distinctive imaging characteristics when compared to those treated with RFA alone. The addition of LTLD resulted in a regular or smooth enhancing rim on T1W MRI which often correlated with increased attenuation on CT. The LTLD-treated ablation zones were stable or enlarged at follow-up four weeks later in 69 % of study subjects as opposed to conventional RFA where the ablation zone underwent involution compared to imaging acquired immediately after the procedure.ConclusionThe imaging features following RFA with LTLD were different from those after standard RFA and can mimic residual or recurrent tumor. Knowledge of the subtle findings between the two groups can help avoid misinterpretation and proper identification of treatment failure in this setting. Increased size of the LTLD-treated ablation zone after RFA suggests the ongoing drug-induced biological effects.« less

  6. Parametric Study of an Ablative TPS and Hot Structure Heatshield for a Mars Entry Capsule Vehicle

    NASA Technical Reports Server (NTRS)

    Langston, Sarah L.; Lang, Christapher G.; Samareh, Jamshid A.

    2017-01-01

    The National Aeronautics and Space Administration is planning to send humans to Mars. As part of the Evolvable Mars Campaign, different en- try vehicle configurations are being designed and considered for delivering larger payloads than have been previously sent to the surface of Mars. Mass and packing volume are driving factors in the vehicle design, and the thermal protection for planetary entry is an area in which advances in technology can offer potential mass and volume savings. The feasibility and potential benefits of a carbon-carbon hot structure concept for a Mars entry vehicle is explored in this paper. The windward heat shield of a capsule design is assessed for the hot structure concept as well as an ablative thermal protection system (TPS) attached to a honeycomb sandwich structure. Independent thermal and structural analyses are performed to determine the minimum mass design. The analyses are repeated for a range of design parameters, which include the trajectory, vehicle size, and payload. Polynomial response functions are created from the analysis results to study the capsule mass with respect to the design parameters. Results from the polynomial response functions created from the thermal and structural analyses indicate that the mass of the capsule was higher for the hot structure concept as compared to the ablative TPS for the parameter space considered in this study.

  7. Graphite Ablation and Thermal Response Simulation Under Arc-Jet Flow Conditions

    NASA Technical Reports Server (NTRS)

    Chen, Y.-K.; Milos, F. S.; Reda, D. C.; Stewart, D. A.; Venkatapathy, Ethiraj (Technical Monitor)

    2002-01-01

    The Two-dimensional Implicit Thermal Response and Ablation program, TITAN, was developed and integrated with a Navier-Stokes solver, GIANTS, for multidimensional ablation and shape change simulation of thermal protection systems in hypersonic flow environments. The governing equations in both codes are demoralized using the same finite-volume approximation with a general body-fitted coordinate system. Time-dependent solutions are achieved by an implicit time marching technique using Gauess-Siedel line relaxation with alternating sweeps. As the first part of a code validation study, this paper compares TITAN-GIANTS predictions with thermal response and recession data obtained from arc-jet tests recently conducted in the Interaction Heating Facility (IHF) at NASA Ames Research Center. The test models are graphite sphere-cones. Graphite was selected as a test material to minimize the uncertainties from material properties. Recession and thermal response data were obtained from two separate arc-jet test series. The first series was at a heat flux where graphite ablation is mainly due to sublimation, and the second series was at a relatively low heat flux where recession is the result of diffusion-controlled oxidation. Ablation and thermal response solutions for both sets of conditions, as calculated by TITAN-GIANTS, are presented and discussed in detail. Predicted shape change and temperature histories generally agree well with the data obtained from the arc-jet tests.

  8. Alternative High Performance Polymers for Ablative Thermal Protection Systems

    NASA Technical Reports Server (NTRS)

    Boghozian, Tane; Stackpoole, Mairead; Gonzales, Greg

    2015-01-01

    Ablative thermal protection systems are commonly used as protection from the intense heat during re-entry of a space vehicle and have been used successfully on many missions including Stardust and Mars Science Laboratory both of which used PICA - a phenolic based ablator. Historically, phenolic resin has served as the ablative polymer for many TPS systems. However, it has limitations in both processing and properties such as char yield, glass transition temperature and char stability. Therefore alternative high performance polymers are being considered including cyanate ester resin, polyimide, and polybenzoxazine. Thermal and mechanical properties of these resin systems were characterized and compared with phenolic resin.

  9. Vehicle drive module having improved EMI shielding

    DOEpatents

    Beihoff, Bruce C.; Kehl, Dennis L.; Gettelfinger, Lee A.; Kaishian, Steven C.; Phillips, Mark G.; Radosevich, Lawrence D.

    2006-11-28

    EMI shielding in an electric vehicle drive is provided for power electronics circuits and the like via a direct-mount reference plane support and shielding structure. The thermal support may receive one or more power electronic circuits. The support may aid in removing heat from the circuits through fluid circulating through the support. The support forms a shield from both external EMI/RFI and from interference generated by operation of the power electronic circuits. Features may be provided to permit and enhance connection of the circuitry to external circuitry, such as improved terminal configurations. Modular units may be assembled that may be coupled to electronic circuitry via plug-in arrangements or through interface with a backplane or similar mounting and interconnecting structures.

  10. Ablation and radiation coupled viscous hypersonic shock layers, volume 1

    NASA Technical Reports Server (NTRS)

    Engel, C. D.

    1971-01-01

    The results for a stagnation-line analysis of the radiative heating of a phenolic-nylon ablator are presented. The analysis includes flow field coupling with the ablator surface, equilibrium chemistry, a step-function diffusion model and a coupled line and continuum radiation calculation. This report serves as the documentation, i e. users manual and operating instructions for the computer programs listed in the report.

  11. Thermal Ablation Modeling for Silicate Materials

    NASA Technical Reports Server (NTRS)

    Chen, Yih-Kanq

    2016-01-01

    A thermal ablation model for silicates is proposed. The model includes the mass losses through the balance between evaporation and condensation, and through the moving molten layer driven by surface shear force and pressure gradient. This model can be applied in ablation simulations of the meteoroid or glassy Thermal Protection Systems for spacecraft. Time-dependent axi-symmetric computations are performed by coupling the fluid dynamics code, Data-Parallel Line Relaxation program, with the material response code, Two-dimensional Implicit Thermal Ablation simulation program, to predict the mass lost rates and shape change. For model validation, the surface recession of fused amorphous quartz rod is computed, and the recession predictions reasonably agree with available data. The present parametric studies for two groups of meteoroid earth entry conditions indicate that the mass loss through moving molten layer is negligibly small for heat-flux conditions at around 1 MW/cm(exp. 2).

  12. Microwave ablation of hepatocellular carcinoma

    PubMed Central

    Poggi, Guido; Tosoratti, Nevio; Montagna, Benedetta; Picchi, Chiara

    2015-01-01

    Although surgical resection is still the optimal treatment option for early-stage hepatocellular carcinoma (HCC) in patients with well compensated cirrhosis, thermal ablation techniques provide a valid non-surgical treatment alternative, thanks to their minimal invasiveness, excellent tolerability and safety profile, proven efficacy in local disease control, virtually unlimited repeatability and cost-effectiveness. Different energy sources are currently employed in clinics as physical agents for percutaneous or intra-surgical thermal ablation of HCC nodules. Among them, radiofrequency (RF) currents are the most used, while microwave ablations (MWA) are becoming increasingly popular. Starting from the 90s’, RF ablation (RFA) rapidly became the standard of care in ablation, especially in the treatment of small HCC nodules; however, RFA exhibits substantial performance limitations in the treatment of large lesions and/or tumors located near major heat sinks. MWA, first introduced in the Far Eastern clinical practice in the 80s’, showing promising results but also severe limitations in the controllability of the emitted field and in the high amount of power employed for the ablation of large tumors, resulting in a poor coagulative performance and a relatively high complication rate, nowadays shows better results both in terms of treatment controllability and of overall coagulative performance, thanks to the improvement of technology. In this review we provide an extensive and detailed overview of the key physical and technical aspects of MWA and of the currently available systems, and we want to discuss the most relevant published data on MWA treatments of HCC nodules in regard to clinical results and to the type and rate of complications, both in absolute terms and in comparison with RFA. PMID:26557950

  13. Initial development of an ablative leading edge for the space shuttle orbiter

    NASA Technical Reports Server (NTRS)

    Daforno, G.; Rose, L.; Graham, J.; Roy, P.

    1974-01-01

    A state-of-the-art preliminary design for typical wing areas is developed. Seven medium-density ablators (with/without honeycomb, flown on Apollo, Prime, X15A2) are evaluated. The screening tests include: (1) leading-edge models sequentially subjected to ascent heating, cold soak, entry heating, post-entry pressure fluctuations, and touchdown shock, and (2) virgin/charred models subjected to bondline strains. Two honeycomb reinforced 30 pcf elastomeric ablators were selected. Roughness/recession degradation of low speed aerodynamics appears acceptable. The design, including attachments, substructure and joints, is presented.

  14. Gravity Scaling of a Power Reactor Water Shield

    NASA Technical Reports Server (NTRS)

    Reid, Robert S.; Pearson, J. Boise

    2007-01-01

    A similarity analysis on a water-based reactor shield examined the effect of gravity on free convection between a reactor shield inner and outer vessel boundaries. Two approaches established similarity between operation on the Earth and the Moon: 1) direct scaling of Rayleigh number equating gravity-surface heat flux products, 2) temperature difference between the wall and thermal boundary layer held constant. Nusselt number for natural convection (laminar and turbulent) is assumed of form Nu = CRa(sup n).

  15. Photoactive dye-enhanced tissue ablation for endoscopic laser prostatectomy.

    PubMed

    Ahn, Minwoo; Hau, Nguyen Trung; Van Phuc, Nguyen; Oh, Junghwan; Kang, Hyun Wook

    2014-11-01

    Laser light has been widely used as a surgical tool to treat benign prostate hyperplasia (BPH) over 20 years. Recently, application of high laser power up to 200 W was often reported to swiftly remove a large amount of prostatic tissue. The purpose of this study was to validate the feasibility of photoactive dye injection to enhance light absorption and eventually to facilitate tissue vaporization with low laser power. Chicken breast tissue was selected as a target tissue due to minimal optical absorption at the visible wavelength. Four biocompatible photoactive dyes, including amaranth (AR), black dye (BD), hemoglobin powder (HP), and endoscopic marker (EM), were selected and tested in vitro with a customized 532 nm laser system with radiant exposure ranging from 0.9 to 3.9 J/cm(2) . Light absorbance and ablation threshold were measured with UV-Vis spectrometer and Probit analysis, respectively, and compared to feature the function of the injected dyes. Ablation performance with dye-injection was evaluated in light of radiant exposure, dye concentration, and number of injection. Higher light absorption by injected dyes led to lower ablation threshold as well as more efficient tissue removal in the order of AR, BD, HP, and EM. Regardless of the injected dyes, ablation efficiency principally increased with radiant exposure, dye concentration, and number of injection. Among the dyes, AR created the highest ablation rate of 44.2 ± 0.2 µm/pulse due to higher absorbance and lower ablation threshold. High aspect ratios up to 7.1 ± 0.4 entailed saturation behavior in the tissue ablation injected with AR and BD, possibly resulting from plume shielding and increased scattering due to coagulation. Preliminary tests on canine prostate with a hydraulic injection system demonstrated that 80 W with dye injection yielded comparable ablation efficiency to 120 W with no injection, indicating 33% reduced laser power with almost equivalent performance. Due to

  16. Fiber-delivered mid-infrared (6-7) laser ablation of retinal tissue under perfluorodecalin

    NASA Astrophysics Data System (ADS)

    Mackanos, Mark A.; Joos, Karen M.; Jansen, E. Duco

    2003-07-01

    The Er:YAG laser (l=2.94mm) is an effective tool in vitreo-retinal surgery. Pulsed mid-infrared (l=6.45 mm) radiation from the Free Electron Laser has been touted as a potentially superior cutting tool. To date, use of this laser has been limited to applications in an air environment. The goal of this study was: 1) determine feasibility of fiberoptic delivery of 6.45mm using silverhalide fibers (d=700mm); 2) use infrared transparent vitreous substitute (perfluorodecalin) to allow non-contact ablation of the retina at 6.45mm. Fiber damage threshold=7.8J/cm2 (0.54GW/cm2) while transmission loss=0.54dB/m, allowing supra-ablative radiant exposures to the target. FTIR measurements of perfluorodecalin at 6.45mm yielded ma=3mm-1. Pump-probe imaging of ablation of a tissue-phantom through perfluorodecalin showed feasibility of non-contact ablation at l=6.45mm. Ablation of the retinal membranes of enucleated pig eyes was carried out under perfluorodecalin (5 Hz, 1.3 J/cm2). Each eye was cut along its equator to expose the retina. Vitreous was replaced by perfluorodecalin and laser radiation was delivered to the retina via the silverhalide fiber. The eye was rotated (at 2 rpm) using a stepper motor (0.9o/step) to create an ablation circle around the central axis of the retina (50% spot-to-spot overlap). Histological analysis of ablation yield and collateral damage will be presented. We have shown that using l=6.45mm delivered via silver halide fibers through perfluorodecalin allowed non-contact laser ablation. Remote structures are shielded, as the radiant exposure falls below the ablation threshold owing non-negligible absorption of perfluorodecalin at 6.45mm. This may optimize efficacy and safety of laser-based vitreoretinal surgery.

  17. Evaluation of coated columbium alloy heat shields for space shuttle thermal protection system application

    NASA Technical Reports Server (NTRS)

    Black, W. E.

    1977-01-01

    A three-phase program to develop and demonstrate the feasibility of a metallic heat shield suitable for use on Space Shuttle Orbiter class vehicles at operating surface temperatures of up to 1590 K (2400 F) is summarized. An orderly progression of configuration studies, material screening tests, and subscale structural tests was performed. Scale-up feasibility was demonstrated in the final phase when a sizable nine-panel array was fabricated and successfully tested. The full-scale tests included cyclic testing at reduced air pressure to 1590 K (2400 F) and up to 158 dB overall sound pressure level. The selected structural configuration and design techniques succesfully eliminated thermal induced failures. The thermal/structural performance of the system was repeatedly demonstrated. Practical and effective field repair methods for coated columbium alloys were demonstrated. Major uncertainties of accessibility, refurbishability, and durability were eliminated.

  18. Similarities and differences in ablative and non-ablative iron oxide nanoparticle hyperthermia cancer treatment

    NASA Astrophysics Data System (ADS)

    Petryk, Alicia A.; Misra, Adwiteeya; Kastner, Elliot J.; Mazur, Courtney M.; Petryk, James D.; Hoopes, P. Jack

    2015-03-01

    The use of hyperthermia to treat cancer is well studied and has utilized numerous delivery techniques, including microwaves, radio frequency, focused ultrasound, induction heating, infrared radiation, warmed perfusion liquids (combined with chemotherapy), and recently, metallic nanoparticles (NP) activated by near infrared radiation (NIR) and alternating magnetic field (AMF) based platforms. It has been demonstrated by many research groups that ablative temperatures and cytotoxicity can be produced with locally NP-based hyperthermia. Such ablative NP techniques have demonstrated the potential for success. Much attention has also been given to the fact that NP may be administered systemically, resulting in a broader cancer therapy approach, a lower level of tumor NP content and a different type of NP cancer therapy (most likely in the adjuvant setting). To use NP based hyperthermia successfully as a cancer treatment, the technique and its goal must be understood and utilized in the appropriate clinical context. The parameters include, but are not limited to, NP access to the tumor (large vs. small quantity), cancer cell-specific targeting, drug carrying capacity, potential as an ionizing radiation sensitizer, and the material properties (magnetic characteristics, size and charge). In addition to their potential for cytotoxicity, the material properties of the NP must also be optimized for imaging, detection and direction. In this paper we will discuss the differences between, and potential applications for, ablative and non-ablative magnetic nanoparticle hyperthermia.

  19. Parametric Thermal and Flow Analysis of ITER Diagnostic Shield Module

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Khodak, A.; Zhai, Y.; Wang, W.

    As part of the diagnostic port plug assembly, the ITER Diagnostic Shield Module (DSM) is designed to provide mechanical support and the plasma shielding while allowing access to plasma diagnostics. Thermal and hydraulic analysis of the DSM was performed using a conjugate heat transfer approach, in which heat transfer was resolved in both solid and liquid parts, and simultaneously, fluid dynamics analysis was performed only in the liquid part. ITER Diagnostic First Wall (DFW) and cooling tubing were also included in the analysis. This allowed direct modeling of the interface between DSM and DFW, and also direct assessment of themore » coolant flow distribution between the parts of DSM and DFW to ensure DSM design meets the DFW cooling requirements. Design of the DSM included voids filled with Boron Carbide pellets, allowing weight reduction while keeping shielding capability of the DSM. These voids were modeled as a continuous solid with smeared material properties using analytical relation for thermal conductivity. Results of the analysis lead to design modifications improving heat transfer efficiency of the DSM. Furthermore, the effect of design modifications on thermal performance as well as effect of Boron Carbide will be presented.« less

  20. Parametric Thermal and Flow Analysis of ITER Diagnostic Shield Module

    DOE PAGES

    Khodak, A.; Zhai, Y.; Wang, W.; ...

    2017-06-19

    As part of the diagnostic port plug assembly, the ITER Diagnostic Shield Module (DSM) is designed to provide mechanical support and the plasma shielding while allowing access to plasma diagnostics. Thermal and hydraulic analysis of the DSM was performed using a conjugate heat transfer approach, in which heat transfer was resolved in both solid and liquid parts, and simultaneously, fluid dynamics analysis was performed only in the liquid part. ITER Diagnostic First Wall (DFW) and cooling tubing were also included in the analysis. This allowed direct modeling of the interface between DSM and DFW, and also direct assessment of themore » coolant flow distribution between the parts of DSM and DFW to ensure DSM design meets the DFW cooling requirements. Design of the DSM included voids filled with Boron Carbide pellets, allowing weight reduction while keeping shielding capability of the DSM. These voids were modeled as a continuous solid with smeared material properties using analytical relation for thermal conductivity. Results of the analysis lead to design modifications improving heat transfer efficiency of the DSM. Furthermore, the effect of design modifications on thermal performance as well as effect of Boron Carbide will be presented.« less

  1. Temperature monitoring by infrared radiation measurements during ArF excimer laser ablation with cornea

    NASA Astrophysics Data System (ADS)

    Ishihara, Miya; Arai, Tsunenori; Sato, Shunichi; Nakano, Hironori; Obara, Minoru; Kikuchi, Makoto

    1999-06-01

    We measured infrared thermal radiation from porcine cornea during various fluences ArF excimer laser ablations with 1 microsecond(s) rise time. To obtain absolute temperature by means of Stefan-Boltzman law of radiation, we carried out a collection efficiency and detective sensitivity by a pre-experiment using panel heater. We measured the time course of the thermal radiation intensity with various laser fluences. We studied the relation between the peak cornea temperature during the ablation and irradiation fluences. We found the ablation situations, i.e., sub-ablation threshold, normal thermal ablation, and over-heated ablation, may be judged by both of the measured temperature transient waveforms and peak temperature. The boundary fluences corresponding to normal thermal ablation were 90 and 160 mJ/cm2. Our fast remote temperature monitoring during cornea ablation might be useful to control ablation quality/quantity of the cornea ArF laser ablation, that is PRK.

  2. Modeling of beam-target interaction during pulsed electron beam ablation of graphite: Case of melting

    NASA Astrophysics Data System (ADS)

    Ali, Muddassir; Henda, Redhouane

    2017-02-01

    A one-dimensional thermal model based on a two-stage heat conduction equation is employed to investigate the ablation of graphite target during nanosecond pulsed electron beam ablation. This comprehensive model accounts for the complex physical phenomena comprised of target heating, melting and vaporization upon irradiation with a polyenergetic electron beam. Melting and vaporization effects induced during ablation are taken into account by introducing moving phase boundaries. Phase transition induced during ablation is considered through the temperature dependent thermodynamic properties of graphite. The effect of electron beam efficiency, power density, and accelerating voltage on ablation is analyzed. For an electron beam operating at an accelerating voltage of 15 kV and efficiency of 0.6, the model findings show that the target surface temperature can reach up to 7500 K at the end of the pulse. The surface begins to melt within 25 ns from the pulse start. For the same process conditions, the estimated ablation depth and ablated mass per unit area are about 0.60 μm and 1.05 μg/mm2, respectively. Model results indicate that ablation takes place primarily in the regime of normal vaporization from the surface. The results obtained at an accelerating voltage of 15 kV and efficiency factor of 0.6 are satisfactorily in good accordance with available experimental data in the literature.

  3. Experimental application of thermosensitive paramagnetic liposomes for monitoring magnetic resonance imaging guided thermal ablation.

    PubMed

    Frich, Lars; Bjørnerud, Atle; Fossheim, Sigrid; Tillung, Terje; Gladhaug, Ivar

    2004-12-01

    The use of a liposomal paramagnetic agent with a T(1)-relaxivity that increases markedly at temperatures above the phase transition temperature (T(m)) of the liposomal membrane was evaluated during magnetic resonance imaging (MRI) guided hyperthermia ablation. A neodymium-yttrium aluminum garnet (Nd-YAG) laser unit and a radiofrequency ablation system were used for tissue ablation in eight rabbit livers in vivo. One ablation was made in each animal prior to administration of the liposomal agent. Liposomes with a T(m) of 57 degrees C containing gadodiamide (GdDTPA-BMA) were injected iv, and two additional ablations were performed. T(1)-weighted scans were performed in heated tissue, after tissue temperature had normalized, and 15-20 min after normalization of tissue temperature. Increase in signal intensity (DeltaSI) for ablations prior to injection of the agent was 13.0% (SD = 5.7) for the laser group and 9.1% (SD = 7.9) for the radiofrequency group. Signal intensity after administration of the agent unrelated to heating was not statistically significant (DeltaSI = 1.4%, P = 0.35). For ablations made after injection of the agent, a significant increase was found in the laser (DeltaSI = 34.5%, SD = 11.9) and radiofrequency group (DeltaSI = 21.6%, SD = 22.7). The persistent signal enhancement found in areas exposed to a temperature above the threshold temperature above T(m) allows thermal monitoring of MRI guided thermal ablation. (c) 2004 Wiley-Liss, Inc.

  4. Experimental Evaluation of a Water Shield for a Surface Power Reactor

    NASA Technical Reports Server (NTRS)

    Pearson, J. B.; Reid, R.; Sadasivan, P.; Stewart, E.

    2007-01-01

    A water based shielding system is being investigated for use on initial lunar surface power systems. The use of water may lower overall cost (as compared to development cost for other materials) and simplify operations in the setup and handling. The thermal hydraulic performance of the shield is of significant interest. The mechanism for transferring heat through the shield is natural convection. A representative lunar surface reactor design is evaluated at various power levels in the Water Shield Testbed (WST) at the NASA Marshall Space Flight Center. The evaluation compares the experimental data from the WST to CFD models. Performance of a water shield on the lunar surface is predicted by CFD models anchored to test data, and by matching relevant dimensionless parameters.

  5. Advanced Multifunctional MMOD Shield: Radiation Shielding Assessment

    NASA Technical Reports Server (NTRS)

    Rojdev, Kristina; Christiansen, Eric

    2013-01-01

    As NASA is looking to explore further into deep space, multifunctional materials are a necessity for decreasing complexity and mass. One area where multifunctional materials could be extremely beneficial is in the micrometeoroid orbital debris (MMOD) shield. A typical MMOD shield on the International Space Station (ISS) is a stuffed whipple shield consisting of multiple layers. One of those layers is the thermal blanket, or multi-layer insulation (MLI). Increasing the MMOD effectiveness of MLI blankets, while still preserving their thermal capabilities, could allow for a less massive MMOD shield. Thus, a study was conducted to evaluate a concept MLI blanket for an MMOD shield. In conjunction, this MLI blanket and the subsequent MMOD shield was also evaluated for its radiation shielding effectiveness towards protecting crew. The overall MMOD shielding system using the concept MLI blanket proved to only have a marginal increase in the radiation mitigating properties. Therefore, subsequent analysis was performed on various conceptual MMOD shields to determine the combination of materials that may prove superior for radiation mitigating purposes. The following paper outlines the evaluations performed and discusses the results and conclusions of this evaluation for radiation shielding effectiveness.

  6. Shielding of Sensitive Electronic Devices in Magnetic Nanoparticle Hyperthermia Using Arrays of Coils

    NASA Astrophysics Data System (ADS)

    Spirou, S. V.; Tsialios, P.; Loudos, G.

    2015-09-01

    In Magnetic Nanoparticle Hyperthermia (MNH) an externally applied electromagnetic field transfers energy to the magnetic nanoparticles in the body, which in turn convert this energy into heat, thus locally heating the tissue they are located in. This external electromagnetic field is sufficiently strong so as to cause interference and affect sensitive electronic equipment. Standard shielding of magnetic fields involves Faraday cages or coating with high-permeability shielding alloys; however, these techniques cannot be used with optically sensitive devices, such as those employed in Optical Coherence Tomography or radionuclide imaging. In this work we present a method to achieve magnetic shielding using an array of coils. The magnetic field generated by a single coil was calculated using the COMSOL physics simulation toolkit. Software was written in C/C++ to import the single-coil data, and then calculate the positions, number of turns and currents in the shielding coils in order to minimize the magnetic field strength at the desired location. Simulations and calculations have shown that just two shielding coils can reduce the magnetic field by 2-3 orders of magnitude.

  7. Preparation and Ablating Behavior of FGM used in a Heat Flux Rocket Engine

    NASA Astrophysics Data System (ADS)

    He, Xiaodong; Han, Jiecai; Zhang, Xinghong

    2002-01-01

    rocket engine. As a result, TiB2-Cu FGM showed excellent resistant ablating properties. There is only a little loss of the mass after heated for 40 seconds in the wind tunnel. Meanwhile no cracks and breakup appeared in the FGM under the sharp thermal shock condition. Key words: functionally graded materials, combustion synthesis, ablation, thermal shock, thermal stress

  8. Global microwave endometrial ablation for menorrhagia treatment

    NASA Astrophysics Data System (ADS)

    Fallahi, Hojjatollah; Å ebek, Jan; Frattura, Eric; Schenck, Jessica; Prakash, Punit

    2017-02-01

    Thermal ablation is a dominant therapeutic option for minimally invasive treatment of menorrhagia. Compared to other energy modalities for ablation, microwaves offer the advantages of conformal energy delivery to tissue within short times. The objective of endometrial ablation is to destroy the endometrial lining of the uterine cavity, with the clinical goal of achieving reduction in bleeding. Previous efforts have demonstrated clinical use of microwaves for endometrial ablation. A considerable shortcoming of most systems is that they achieve ablation of the target by translating the applicator in a point-to-point fashion. Consequently, treatment outcome may be highly dependent on physician skill. Global endometrial ablation (GEA) not only eliminates this operator dependence and simplifies the procedure but also facilitates shorter and more reliable treatments. The objective of our study was to investigate antenna structures and microwave energy delivery parameters to achieve GEA. Another objective was to investigate a method for automatic and reliable determination of treatment end-point. A 3D-coupled FEM electromagnetic and heat transfer model with temperature and frequency dependent material properties was implemented to characterize microwave GEA. The unique triangular geometry of the uterus where lateral narrow walls extend from the cervix to the fundus forming a wide base and access afforded through an endocervical approach limit the overall diameter of the final device. We investigated microwave antenna designs in a deployed state inside the uterus. The impact of ablation duration on treatment outcome was investigated. Prototype applicators were fabricated and experimentally evaluated in ex vivo tissue to verify the simulation results and demonstrate proof-of-concept.

  9. Thermal ablation of an aluminium film upon absorption of a femtosecond laser pulse

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Bezhanov, S G; Kanavin, A P; Uryupin, S A

    We have found the time dependence of the ablation depth of aluminium irradiated by a femtosecond laser pulse. It is shown to what extent an increase in the radiation energy flux density leads to an increase in the quasi-stationary value of the ablation depth. By reducing the aluminium film thickness down to one hundred nanometres and less, the ablation depth significantly increases. At the same time, the quasi-stationary value of the ablation depth of a thin film is obtained due to the removal of heat from the focal spot region. (interaction of laser radiation with matter. laser plasma)

  10. Fire-Resistant Reinforcement Makes Steel Structures Sturdier

    NASA Technical Reports Server (NTRS)

    2006-01-01

    Built and designed by Avco Corporation, the Apollo heat shield was coated with an ablative material whose purpose was to burn and, thus, dissipate energy. The material charred to form a protective coating which blocked heat penetration beyond the outer surface. Avco Corporation subsequently entered into a contract with Ames Research Center to develop spinoff applications of the heat shield in the arena of fire protection, specifically for the development of fire-retardant paints and foams for aircraft. This experience led to the production of Chartek 59, manufactured by Avco Specialty Materials (a subsidiary of Avco Corporation eventually acquired by Textron, Inc.) and marketed as the world s first intumescent epoxy material. As an intumescent coating, Chartek 59 expanded in volume when exposed to heat or flames and acted as an insulating barrier. It also retained its space-age ablative properties and dissipated heat through burn-off. Further applications were discovered, and the fireproofing formulation found its way into oil refineries, chemical plants, and other industrial facilities working with highly flammable products.

  11. Preliminary Evaluation of Convective Heat Transfer in a Water Shield for a Surface Power Reactor

    NASA Technical Reports Server (NTRS)

    Pearson J. Boise; Reid, Robert S.

    2007-01-01

    As part of the Vision for Space Exploration, the end of the next decade will bring man back to the surface of the moon. A crucial issue for the establishment of human presence on the moon will be the availability of compact power sources. This presence could require greater than 10's of kWt's in follow on years. Nuclear reactors are well suited to meet the needs for power generation on the lunar or Martian surface. Radiation shielding is a key component of any surface power reactor system. Several competing concepts exist for lightweight, safe, robust shielding systems such as a water shield, lithium hydride (LiH), and boron carbide. Water offers several potential advantages, including reduced cost, reduced technical risk, and reduced mass. Water has not typically been considered for space reactor applications because of the need for gravity to fix the location of any vapor that could form radiation streaming paths. The water shield concept relies on the predictions of passive circulation of the shield water by natural convection to adequately cool the shield. This prediction needs to be experimentally evaluated, especially for shields with complex geometries. NASA Marshall Space Flight Center has developed the experience and facilities necessary to do this evaluation in its Early Flight Fission - Test Facility (EFF-TF).

  12. Considerations for theoretical modeling of thermal ablation with catheter-based ultrasonic sources: implications for treatment planning, monitoring and control

    PubMed Central

    Prakash, Punit; Diederich, Chris J.

    2012-01-01

    Purpose To determine the impact of including dynamic changes in tissue physical properties during heating on feedback controlled thermal ablation with catheter-based ultrasound. Additionally, we compared impact several indicators of thermal damage on predicted extents of ablation zones for planning and monitoring ablations with this modality. Methods A 3D model of ultrasound ablation with interstitial and transurethral applicators incorporating temperature based feedback control was used to simulate thermal ablations in prostate and liver tissue. We investigated five coupled models of heat dependent changes in tissue acoustic attenuation/absorption and blood perfusion of varying degrees of complexity.. Dimensions of the ablation zone were computed using temperature, thermal dose, and Arrhenius thermal damage indicators of coagulative necrosis. A comparison of the predictions by each of these models was illustrated on a patient-specific anatomy in the treatment planning setting. Results Models including dynamic changes in blood perfusion and acoustic attenuation as a function of thermal dose/damage predicted near-identical ablation zone volumes (maximum variation < 2.5%). Accounting for dynamic acoustic attenuation appeared to play a critical role in estimating ablation zone size, as models using constant values for acoustic attenuation predicted ablation zone volumes up to 50% larger or 47% smaller in liver and prostate tissue, respectively. Thermal dose (t43 ≥ 240min) and thermal damage (Ω ≥ 4.6) thresholds for coagulative necrosis are in good agreement for all heating durations, temperature thresholds in the range of 54 °C for short (< 5 min) duration ablations and 50 °C for long (15 min) ablations may serve as surrogates for determination of the outer treatment boundary. Conclusions Accounting for dynamic changes in acoustic attenuation/absorption appeared to play a critical role in predicted extents of ablation zones. For typical 5—15 min ablations

  13. Echo decorrelation imaging of ex vivo HIFU and bulk ultrasound ablation using image-treat arrays

    NASA Astrophysics Data System (ADS)

    Fosnight, Tyler R.; Hooi, Fong Ming; Colbert, Sadie B.; Keil, Ryan D.; Barthe, Peter G.; Mast, T. Douglas

    2017-03-01

    In this study, the ability of ultrasound echo decorrelation imaging to map and predict heat-induced cell death was tested using bulk ultrasound thermal ablation, high intensity focused ultrasound (HIFU) thermal ablation, and pulse-echo imaging of ex vivo liver tissue by a custom image-treat array. Tissue was sonicated at 5.0 MHz using either pulses of unfocused ultrasound (N=12) (7.5 s, 50.9-101.8 W/cm2 in situ spatial-peak, temporal-peak intensity) for bulk ablation or focused ultrasound (N=21) (1 s, 284-769 W/cm2 in situ spatial-peak, temporal-peak intensity and focus depth of 10 mm) for HIFU ablation. Echo decorrelation and integrated backscatter (IBS) maps were formed from radiofrequency pulse-echo images captured at 118 frames per second during 5.0 s rest periods, beginning 1.1 s after each sonication pulse. Tissue samples were frozen at -80˚C, sectioned, vitally stained, imaged, and semi-automatically segmented for receiver operating characteristic (ROC) analysis. ROC curves were constructed to assess prediction performance for echo decorrelation and IBS. Logarithmically scaled mean echo decorrelation in non-ablated and ablated tissue regions before and after electronic noise and motion correction were compared. Ablation prediction by echo decorrelation and IBS was significant for both focused and bulk ultrasound ablation. The log10-scaled mean echo decorrelation was significantly greater in regions of ablation for both HIFU and bulk ultrasound ablation. Echo decorrelation due to electronic noise and motion was significantly reduced by correction. These results suggest that ultrasound echo decorrelation imaging is a promising approach for real-time prediction of heat-induced cell death for guidance and monitoring of clinical thermal ablation, including radiofrequency ablation and HIFU.

  14. Double-layer neutron shield design as neutron shielding application

    NASA Astrophysics Data System (ADS)

    Sariyer, Demet; Küçer, Rahmi

    2018-02-01

    The shield design in particle accelerators and other high energy facilities are mainly connected to the high-energy neutrons. The deep penetration of neutrons through massive shield has become a very serious problem. For shielding to be efficient, most of these neutrons should be confined to the shielding volume. If the interior space will become limited, the sufficient thickness of multilayer shield must be used. Concrete and iron are widely used as a multilayer shield material. Two layers shield material was selected to guarantee radiation safety outside of the shield against neutrons generated in the interaction of the different proton energies. One of them was one meter of concrete, the other was iron-contained material (FeB, Fe2B and stainless-steel) to be determined shield thicknesses. FLUKA Monte Carlo code was used for shield design geometry and required neutron dose distributions. The resulting two layered shields are shown better performance than single used concrete, thus the shield design could leave more space in the interior shielded areas.

  15. Heat Transfer in Metal Foam Heat Exchangers at High Temperature

    NASA Astrophysics Data System (ADS)

    Hafeez, Pakeeza

    Heat transfer though open-cell metal foam is experimentally studied for heat exchanger and heat shield applications at high temperatures (˜750°C). Nickel foam sheets with pore densities of 10 and 40 pores per linear inch (PPI), have been used to make the heat exchangers and heat shields by using thermal spray coating to deposit an Inconel skin on a foam core. Heat transfer measurements were performed on a test rig capable of generating hot gas up to 1000°C. The heat exchangers were tested by exposing their outer surface to combustion gases at a temperature of 550°C and 750°C while being cooled by air flowing through them at room temperature at velocities up to 5 m/s. The temperature rise of the air, the surface temperature of the heat exchangers and the air temperature inside the heat exchanger were measured. The volumetric heat transfer coefficient and Nusselt number were calculated for different velocities. The heat transfer performance of the 40PPI sample brazed with the foil is found to be the most efficient. Pressure drop measurements were also performed for 10 and 40PPI metal foam. Thermographic measurements were done on 40PPI foam heat exchangers using a high temperature infrared camera. A high power electric heater was used to produce hot air at 300°C that passed over the foam heat exchanger while the cooling air was blown through it. Heat shields were made by depositing porous skins on metal foam and it was observed that a small amount of coolant leaking through the pores notably reduces the heat transfer from the hot gases. An analytical model was developed based assuming local thermal non-equilibrium that accounts for the temperature difference between solid and fluid phase. The experimental results are found to be in good agreement with the predicted values of the model.

  16. Comparison of remote magnetic navigation ablation and manual ablation of idiopathic ventricular arrhythmia after failed manual ablation.

    PubMed

    Kawamura, Mitsuharu; Scheinman, Melvin M; Tseng, Zian H; Lee, Byron K; Marcus, Gregory M; Badhwar, Nitish

    2017-01-01

    Catheter ablation for idiopathic ventricular arrhythmia (VA) is effective and safe, but efficacy is frequently limited due to an epicardial origin and difficult anatomy. The remote magnetic navigation (RMN) catheter has a flexible catheter design allowing access to difficult anatomy. We describe the efficacy of the RMN for ablation of idiopathic VA after failed manual ablation. Among 235 patients with idiopathic VA referred for catheter ablation, we identified 51 patients who were referred for repeat ablation after a failed manual ablation. We analyzed the clinical characteristics, including the successful ablation site and findings at electrophysiology study, in repeat procedures conducted using RMN as compared with manual ablation. Among these patients, 22 (43 %) underwent repeat ablation with the RMN and 29 (57 %) underwent repeat ablation with a manual ablation. Overall, successful ablation rate was significantly higher using RMN as compared with manual ablation (91 vs. 69 %, P = 0.02). Fluoroscopy time in the RMN was 17 ± 12 min as compared with 43 ± 18 min in the manual ablation (P = 0.009). Successful ablation rate in the posterior right ventricular outflow tract (RVOT) plus posterior-tricuspid annulus was higher with RMN as compared with manual ablation (92 vs. 50 %, P = 0.03). Neither groups exhibited any major complications. The RMN is more effective in selected patients with recurrent idiopathic VA after failed manual ablation and is associated with less fluoroscopy time. The RMN catheters have a flexible design enabling them to access otherwise difficult anatomy including the posterior tricuspid annulus and posterior RVOT.

  17. Assessment of tbe Performance of Ablative Insulators Under Realistic Solid Rocket Motor Operating Conditions (a Doctoral Dissertation)

    NASA Technical Reports Server (NTRS)

    Martin, Heath Thomas

    2013-01-01

    Ablative insulators are used in the interior surfaces of solid rocket motors to prevent the mechanical structure of the rocket from failing due to intense heating by the high-temperature solid-propellant combustion products. The complexity of the ablation process underscores the need for ablative material response data procured from a realistic solid rocket motor environment, where all of the potential contributions to material degradation are present and in their appropriate proportions. For this purpose, the present study examines ablative material behavior in a laboratory-scale solid rocket motor. The test apparatus includes a planar, two-dimensional flow channel in which flat ablative material samples are installed downstream of an aluminized solid propellant grain and imaged via real-time X-ray radiography. In this way, the in-situ transient thermal response of an ablator to all of the thermal, chemical, and mechanical erosion mechanisms present in a solid rocket environment can be observed and recorded. The ablative material is instrumented with multiple micro-thermocouples, so that in-depth temperature histories are known. Both total heat flux and thermal radiation flux gauges have been designed, fabricated, and tested to characterize the thermal environment to which the ablative material samples are exposed. These tests not only allow different ablative materials to be compared in a realistic solid rocket motor environment but also improve the understanding of the mechanisms that influence the erosion behavior of a given ablative material.

  18. The Laser ablation of a metal foam: The role of electron-phonon coupling and electronic heat diffusivity

    NASA Astrophysics Data System (ADS)

    Rosandi, Yudi; Grossi, Joás; Bringa, Eduardo M.; Urbassek, Herbert M.

    2018-01-01

    The incidence of energetic laser pulses on a metal foam may lead to foam ablation. The processes occurring in the foam may differ strongly from those in a bulk metal: The absorption of laser light, energy transfer to the atomic system, heat conduction, and finally, the atomistic processes—such as melting or evaporation—may be different. In addition, novel phenomena take place, such as a reorganization of the ligament network in the foam. We study all these processes in an Au foam of average porosity 79% and an average ligament diameter of 2.5 nm, using molecular dynamics simulation. The coupling of the electronic system to the atomic system is modeled by using the electron-phonon coupling, g, and the electronic heat diffusivity, κe, as model parameters, since their actual values for foams are unknown. We show that the foam coarsens under laser irradiation. While κe governs the homogeneity of the processes, g mainly determines their time scale. The final porosity reached is independent of the value of g.

  19. Automated microwave ablation therapy planning with single and multiple entry points

    NASA Astrophysics Data System (ADS)

    Liu, Sheena X.; Dalal, Sandeep; Kruecker, Jochen

    2012-02-01

    Microwave ablation (MWA) has become a recommended treatment modality for interventional cancer treatment. Compared with radiofrequency ablation (RFA), MWA provides more rapid and larger-volume tissue heating. It allows simultaneous ablation from different entry points and allows users to change the ablation size by controlling the power/time parameters. Ablation planning systems have been proposed in the past, mainly addressing the needs for RFA procedures. Thus a planning system addressing MWA-specific parameters and workflows is highly desirable to help physicians achieve better microwave ablation results. In this paper, we design and implement an automated MWA planning system that provides precise probe locations for complete coverage of tumor and margin. We model the thermal ablation lesion as an ellipsoidal object with three known radii varying with the duration of the ablation and the power supplied to the probe. The search for the best ablation coverage can be seen as an iterative optimization problem. The ablation centers are steered toward the location which minimizes both un-ablated tumor tissue and the collateral damage caused to the healthy tissue. We assess the performance of our algorithm using simulated lesions with known "ground truth" optimal coverage. The Mean Localization Error (MLE) between the computed ablation center in 3D and the ground truth ablation center achieves 1.75mm (Standard deviation of the mean (STD): 0.69mm). The Mean Radial Error (MRE) which is estimated by comparing the computed ablation radii with the ground truth radii reaches 0.64mm (STD: 0.43mm). These preliminary results demonstrate the accuracy and robustness of the described planning algorithm.

  20. Nanoparticle mediated ablation of breast cancer cells using a nanosecond pulsed electric field

    NASA Astrophysics Data System (ADS)

    Burford, Christopher

    In the past, both nanomaterials and various heating modalities have been researched as means for treating cancers. However, many of the current methodologies have the flaws of inconsistent tumor ablation and significant destruction of healthy cells. Based on research performed using constant radiofrequency electric fields and metallic nanoparticles (where cell necrosis is induced by the heating of these nanoparticles) we have developed a modality that simlarly uses functionalized metallic nanoparticles, specific for the T47D breast cancer cell line, and nanosecond pulsed electric fields as the hyperthermic inducer. Using both iron oxide and gold nanoparticles the results of our pilot studies indicated that up to 90% of the cancer cells were ablated given the optimal treatment parameters. These quantities of ablated cells were achieved using a cumulative exposure time 6 orders of magnitude less than most in vitro radiofrequency electric field studies.

  1. Ablation for Atrial Fibrillation

    PubMed Central

    2006-01-01

    . Ablation involves directing an energy source at cardiac tissue. For instance, radiofrequency energy uses heat to burn tissue near the source of the arrhythmia. The purpose is to create a series of scar tissue, so that the aberrant electrical pathways can no longer exist. Because the pulmonary veins are the predominant source of AF initiation, the primary goal of ablation is to isolate the pulmonary veins from the left atria through the creation of a conduction block. There are 2 methods of ablation: catheter ablation and surgical (operative) ablation. Radiofrequency energy is most commonly used for ablation. Catheter ablation involves inserting a catheter through the femoral vein to access the heart and burn abnormal foci of electrical activity by direct contact or by isolating them from the rest of the atrium. The surgical ablation is performed minimally invasively via direct visualization or with the assistance of a special scope for patients with lone AF. Review Strategy In March 2006, the following databases were searched: Cochrane Library International Agency for Health Technology Assessment (first quarter 2006), Cochrane Database of Systematic Reviews (first quarter 2006), Cochrane Central Register of Controlled Trials (first quarter 2006), MEDLINE (1966 to February 2006), MEDLINE In-Process and Other Non-indexed Citations (1966 to March 1, 2006), and EMBASE (1980 to 2006 week 9). The Medical Advisory Secretariat also searched Medscape on the Internet for recent reports on trials that were unpublished but that were presented at international conferences. In addition, the Web site Current Controlled Trials (www.controlled-trials.com) was searched for ongoing trials investigating ablation for atrial fibrillation. Search terms included: radiofrequency ablation, catheter ablation and atrial fibrillation. Summary of Findings Sixteen RCTs were identified that compared ablation methods in patients with AF. Two studies were identified that investigated first-line therapy for

  2. Nonthermal ablation of deep brain targets: A simulation study on a large animal model

    PubMed Central

    Top, Can Barış; White, P. Jason; McDannold, Nathan J.

    2016-01-01

    Purpose: Thermal ablation with transcranial MRI-guided focused ultrasound (FUS) is currently limited to central brain targets because of heating and other beam effects caused by the presence of the skull. Recently, it was shown that it is possible to ablate tissues without depositing thermal energy by driving intravenously administered microbubbles to inertial cavitation using low-duty-cycle burst sonications. A recent study demonstrated that this ablation method could ablate tissue volumes near the skull base in nonhuman primates without thermally damaging the nearby bone. However, blood–brain disruption was observed in the prefocal region, and in some cases, this region contained small areas of tissue damage. The objective of this study was to analyze the experimental model with simulations and to interpret the cause of these effects. Methods: The authors simulated prior experiments where nonthermal ablation was performed in the brain in anesthetized rhesus macaques using a 220 kHz clinical prototype transcranial MRI-guided FUS system. Low-duty-cycle sonications were applied at deep brain targets with the ultrasound contrast agent Definity. For simulations, a 3D pseudospectral finite difference time domain tool was used. The effects of shear mode conversion, focal steering, skull aberrations, nonlinear propagation, and the presence of skull base on the pressure field were investigated using acoustic and elastic wave propagation models. Results: The simulation results were in agreement with the experimental findings in the prefocal region. In the postfocal region, however, side lobes were predicted by the simulations, but no effects were evident in the experiments. The main beam was not affected by the different simulated scenarios except for a shift of about 1 mm in peak position due to skull aberrations. However, the authors observed differences in the volume, amplitude, and distribution of the side lobes. In the experiments, a single element passive

  3. Transport properties for a mixture of the ablation products C, C2, and C3

    NASA Technical Reports Server (NTRS)

    Biolsi, L.; Fenton, J.; Owenson, B.

    1981-01-01

    The ablation of carbon-phenolic heat shields upon entry into the atmosphere of one of the outer planets leads to the injection of large amounts of C, C2, and C3 into the shock layer. These species must be included in the calculation of transport properties in the shock layer. The kinetic theory of gases has been used to obtain accurate results for the transport properties of monatomic carbon. The Hulburt-Hirschelder potential, the most accurate general purpose atom-atom potential for states with an attractive minimum, was used to represent such states and repulsive states were represented by fitting quantum mechanical potential energy curves with the exponential repulsive potential. These results were orientation averaged according to the peripheral force model to obtain transport collision integrals for the C-C2 and C2-C2 interaction. Results for C3 were obtained by ignoring the presence of the central carbon atom. The thermal conductivity, viscosity, and diffusion coefficients for pure C, C2, and C3, and for mixtures of these gases, were then calculated from 1000 K - 25,000 K.

  4. Vapor shielding models and the energy absorbed by divertor targets during transient events

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Skovorodin, D. I., E-mail: dskovorodin@gmail.com; Arakcheev, A. S.; Pshenov, A. A.

    2016-02-15

    The erosion of divertor targets caused by high heat fluxes during transients is a serious threat to ITER operation, as it is going to be the main factor determining the divertor lifetime. Under the influence of extreme heat fluxes, the surface temperature of plasma facing components can reach some certain threshold, leading to an onset of intense material evaporation. The latter results in formation of cold dense vapor and secondary plasma cloud. This layer effectively absorbs the energy of the incident plasma flow, turning it into its own kinetic and internal energy and radiating it. This so called vapor shieldingmore » is a phenomenon that may help mitigating the erosion during transient events. In particular, the vapor shielding results in saturation of energy (per unit surface area) accumulated by the target during single pulse of heat load at some level E{sub max}. Matching this value is one of the possible tests to verify complicated numerical codes, developed to calculate the erosion rate during abnormal events in tokamaks. The paper presents three very different models of vapor shielding, demonstrating that E{sub max} depends strongly on the heat pulse duration, thermodynamic properties, and evaporation energy of the irradiated target material. While its dependence on the other shielding details such as radiation capabilities of material and dynamics of the vapor cloud is logarithmically weak. The reason for this is a strong (exponential) dependence of the target material evaporation rate, and therefore the “strength” of vapor shield on the target surface temperature. As a result, the influence of the vapor shielding phenomena details, such as radiation transport in the vapor cloud and evaporated material dynamics, on the E{sub max} is virtually completely masked by the strong dependence of the evaporation rate on the target surface temperature. However, the very same details define the amount of evaporated particles, needed to provide an effective

  5. Graphite and ablative material response to CO2 laser, carbon-arc, and xenon-arc radiation

    NASA Technical Reports Server (NTRS)

    Brewer, W. D.

    1976-01-01

    The behavior was investigated of graphite and several charring ablators in a variety of high-radiative heat-flux environments. A commercial-grade graphite and nine state-of-the-art charring ablators were subjected to various radiative environments produced by a CO2 laser and a carbon arc. Graphite was also tested in xenon-arc radiation. Heat-flux levels ranged from 10 to 47 MW/sq m. Tests were conducted in air, nitrogen, helium, and a CO2-N2 mixture which simulated the Venus atmosphere. The experimental results were compared with theoretical results obtained with a one-dimensional charring-ablator analysis and a two-dimensional subliming-ablator analysis. Neither the graphite nor the charring ablators showed significant differences in appearance or microstructure after testing in the different radiative environments. The performance of phenolic nylon and graphite was predicted satisfactorily with existing analyses and published material property data. Good agreement between experimental and analytical results was obtained by using sublimation parameters from a chemical nonequilibrium analysis of graphite sublimation. Some charring ablators performed reasonably well and could withstand radiative fluxes of the level encountered in certain planetary entries. Other materials showed excessive surface recession and/or large amounts of cracking and spalling, and appear to be unsuitable for severe radiative environments.

  6. Response Modeling of Lightweight Charring Ablators and Thermal Radiation Testing Results

    NASA Technical Reports Server (NTRS)

    Congdon, William M.; Curry, Donald M.; Rarick, Douglas A.; Collins, Timothy J.

    2003-01-01

    Under NASA's In-Space Propulsion/Aerocapture Program, ARA conducted arc-jet and thermal-radiation ablation test series in 2003 for advanced development, characterization, and response modeling of SRAM-20, SRAM-17, SRAM-14, and PhenCarb-20 ablators. Testing was focused on the future Titan Explorer mission. Convective heating rates (CW) were as high as 153 W/sq cm in the IHF and radiation rates were 100 W/sq cm in the Solar Tower Facility. The ablators showed good performance in the radiation environment without spallation, which was initially a concern, but they also showed higher in-depth temperatures when compared to analytical predictions based on arc-jet thermal-ablation response models. More testing in 2003 is planned in both of these facility to generate a sufficient data base for Titan TPS engineering.

  7. Progress Towards providing Heat-Shield for Extreme Entry Environment Technology (HEEET) for Venus and other New Froniters Missions

    NASA Technical Reports Server (NTRS)

    Venkatapathy, Ethiraj; Ellerby, Don; Gage, Peter

    2017-01-01

    Heat-shield for Extreme Entry Environment Technology (HEEET) has been in development since 2014 with the goal of enabling missions to Venus, Saturn and other high-speed sample return missions. It is offered as a new technology and incentivized for mission use in the New Frontiers 4 AO by NASA. The current plans are to mature the technology to TRL 6 by FY18. The HEEET Team has been working closely with multiple NF-4 proposals to Venus, Saturn and has been supporting recent Ice-Giants mission studies. This presentation will provide progress made to date and the plans for development in FY18.

  8. Producibility of fibrous refractory composite insulation, FRCI 40-20. [for reusable heat shielding

    NASA Technical Reports Server (NTRS)

    Strauss, E. L.; Johnson, C. W.; Graese, R. W.; Campbell, R. L.

    1983-01-01

    Fibrous Refractory Composite Insulation (FRCI) is a NASA-developed, second generation, reusable heat-shield material that comprises a mixture of aluminoborosilicate fibers, silica fibers, and silicon carbide. Under NASA contract, a program was conducted to demonstrate the capability for manufacturing FRCI 40-20 billets. A detailed fabrication procedure was written and validated by testing specimens from the first two billets. The material conformed to NASA requirements for density, tensile strength, modulus of rupture, thermal expansion, cristobalite content, and uniformity. Twenty-four billets were prepared to provide 20 deliverable articles. Production billets were checked for density, modulus of rupture, cristobalite content, and uniformity. Billet density ranged from 309.48 to 332.22 kg/cu m (19.32 to 20.74 lb/cu ft) and modulus of rupture from 4690 to 10,140 kPa (680 to 1470 psi). Cristobalite content was less than 1 percent. A Weibull analysis of modulus-of-rupture data indicated a 1.5 percent probability for failure below the specified strength of 4480 kPa (650 psi).

  9. Flight and ground tests of a very low density elastomeric ablative material

    NASA Technical Reports Server (NTRS)

    Olsen, G. C.; Chapman, A. J., III

    1972-01-01

    A very low density ablative material, a silicone-phenolic composite, was flight tested on a recoverable spacecraft launched by a Pacemaker vehicle system; and, in addition, it was tested in an arc heated wind tunnel at three conditions which encompassed most of the reentry heating conditions of the flight tests. The material was composed, by weight, of 71 percent phenolic spheres, 22.8 percent silicone resin, 2.2 percent catalyst, and 4 percent silica fibers. The tests were conducted to evaluate the ablator performance in both arc tunnel and flight tests and to determine the predictability of the albator performance by using computed results from an existing one-dimensional numerical analysis. The flight tested ablator experienced only moderate surface recession and retained a smooth surface except for isolated areas where the char was completely removed, probably following reentry and prior to or during recovery. Analytical results show good agreement between arc tunnel and flight test results. The thermophysical properties used in the analysis are tabulated.

  10. The thermal and mechanical properties of a low density elastomeric ablation material

    NASA Technical Reports Server (NTRS)

    Engelke, W. T.; Robertson, R. W.; Bush, A. L.; Pears, C. D.

    1973-01-01

    Thermal and mechanical properties data were obtained for a low density elastomeric resin based ablation material with phenolic-glass honeycomb reinforcement. Data were obtained for the material in the charred and uncharred state. Ablation material specimens were charred in a laboratory furnace at temperatures in the range from 600 K to 1700 K to obtain char specimens representative of the ablation char layer formed during reentry. These specimens were then used to obtain effective thermal conductivity, heat capacity, porosity, and permeability data at the char formation temperature. This provided a boxing of the data which enables the prediction of the transient response of the material during ablation. Limited comparisons were made between the furnace charred specimens and specimens which had been exposed to simulated reentry conditions.

  11. Fracture in Phenolic Impregnated Carbon Ablator

    NASA Technical Reports Server (NTRS)

    Agrawal, Parul; Chavez-Garcia, Jose F.

    2011-01-01

    The thermal protection materials used for spacecraft heat shields are subjected to various thermal-mechanical loads during an atmospheric reentry which can threaten the structural integrity of the system. This paper discusses the development of a novel technique to understand the failure mechanisms inside the thermal protection material, Phenolic Impregnated Carbon Ablator (PICA). PICA has successfully flown on the Stardust spacecraft and was the TPS material chosen for the Mars Science Laboratory (MSL), that will fly in 2011. Although PICA has good thermal properties, structurally, it is a weak material. To thoroughly understand failure in PICA, experiments were performed using FiberForm(Registered TradeMark) (precursor of PICA), virgin and furnace-charred PICA. Several small samples were tested inside an electron microscope to investigate the failure mechanisms. Micrographs were obtained before and after the failure in order to study crack initiation and growth. Videos were obtained to capture failure mechanisms in real time. Stress-strain data was obtained simultaneously for all the samples with the help of a data acquisition system, integrated to the mechanical stages. It was found that cracks initiated and grew in the FiberForm when a critical stress limit was reached such that the carbon fibers separated from the binder. However, both for virgin and charred PICA, crack initiation and growth occurred in the matrix (phenolic) phase. Both virgin and charred PICA showed greater strength values compared to FiberForm coupons, confirming that the presence of the porous matrix helps in absorbing the fracture energy.

  12. Diagnostic evaluations of a beam-shielded 8-cm mercury ion thruster

    NASA Technical Reports Server (NTRS)

    Nakanishi, S.

    1978-01-01

    An engineering model thruster fitted with a remotely actuated graphite fiber polyimide composite beam shield was tested in a 3- by 6.5-meter vacuum facility for in-situ assessment of beam shield effects on thruster performance. Accelerator drain current neutralizer floating potential and ion beam floating potential increased slightly when the shield was moved into position. A target exposed to the low density regions of the ion beam was used to map the boundaries of energetic fringe ions capable of sputtering. The particle efflux was evaluated by measurement of film deposits on cold, heated, bare, and enclosed glass slides.

  13. Stagnation-Point Shielding by Melting and Vaporization

    NASA Technical Reports Server (NTRS)

    Roberts, Leonard

    1959-01-01

    An approximate theoretical analysis was made of the shielding mechanism whereby the rate of heat transfer to the forward stagnation point of blunt bodies is reduced by melting and evaporation. General qualitative results are given and a numerical example, the melting and evaporation of ice, is presented and discussed in detail.

  14. Shields-1, A SmallSat Radiation Shielding Technology Demonstration

    NASA Technical Reports Server (NTRS)

    Thomsen, D. Laurence, III; Kim, Wousik; Cutler, James W.

    2015-01-01

    The NASA Langley Research Center Shields CubeSat initiative is to develop a configurable platform that would allow lower cost access to Space for materials durability experiments, and to foster a pathway for both emerging and commercial-off-the-shelf (COTS) radiation shielding technologies to gain spaceflight heritage in a relevant environment. The Shields-1 will be Langleys' first CubeSat platform to carry out this mission. Radiation shielding tests on Shields-1 are planned for the expected severe radiation environment in a geotransfer orbit (GTO), where advertised commercial rideshare opportunities and CubeSat missions exist, such as Exploration Mission 1 (EM-1). To meet this objective, atomic number (Z) graded radiation shields (Zshields) have been developed. The Z-shield properties have been estimated, using the Space Environment Information System (SPENVIS) radiation shielding computational modeling, to have 30% increased shielding effectiveness of electrons, at half the thickness of a corresponding single layer of aluminum. The Shields-1 research payload will be made with the Z-graded radiation shields of varying thicknesses to create dose-depth curves to be compared with baseline materials. Additionally, Shields-1 demonstrates an engineered Z-grade radiation shielding vault protecting the systems' electronic boards. The radiation shielding materials' performances will be characterized using total ionizing dose sensors. Completion of these experiments is expected to raise the technology readiness levels (TRLs) of the tested atomic number (Z) graded materials. The most significant contribution of the Z-shields for the SmallSat community will be that it enables cost effective shielding for small satellite systems, with significant volume constraints, while increasing the operational lifetime of ionizing radiation sensitive components. These results are anticipated to increase the development of CubeSat hardware design for increased mission lifetimes, and enable

  15. Monitoring of thermal dose during ablation therapy using quantum dot-mediated fluorescence thermometry.

    PubMed

    Bensalah, Karim; Tuncel, Altug; Hanson, Willard; Stern, Joshua; Han, Bumsoo; Cadeddu, Jeffrey

    2010-12-01

    The objective of this study was to demonstrate the feasibility of quantum dot (QD)-mediated fluorescence thermometry to monitor thermal dose in an in-vitro thermal ablation zone generated by laser-heated gold nanoshells (LGNS). Hyperthermic cell death of human prostate cancer cell line (PC-3) was determined after various heating settings and correlated to the thermal conditions using an Arrhenius model prior to LGNS ablation. PC-3 cells with gold nanoshells (GNS) and QDs were exposed to a near-infrared laser and QD excitation light. When the cells were heated by GNS, local temperature was measured using the temperature-dependent fluorescence intensity of QDs. Using the predetermined Arrhenius model, the thermal dose (i.e., cell death of PC-3 cells) by LGNS was estimated with local temperatures measured with QD-mediated thermometry. The estimated thermal dose was confirmed with calcein-acetoxy-methylester viability assay. For PC-3 cell line, the activation energy and frequency factor of the Arrhenius model were 86.78 kcal/mol and 6.35 × 10(55) Hz, respectively. During LGNS ablation of PC-3 cells, QD-mediated temperature measurement showed that the temperature of the laser spot increased rapidly to ∼58 °C ± 4 °C. The estimated thermal dose showed that cell death reached to ∼90% in 120 seconds. The death cell zone observed after staining corresponded to a peak area of the temperature profile generated after analysis of the QD fluorescence intensity. This study shows that the QD fluorescence thermometry can accurately monitor the PC-3 cell death by LGNS ablation. This approach holds promises for a better monitoring of thermal ablation procedures in clinical practice.

  16. Modelling and Optimization of Four-Segment Shielding Coils of Current Transformers

    PubMed Central

    Gao, Yucheng; Zhao, Wei; Wang, Qing; Qu, Kaifeng; Li, He; Shao, Haiming; Huang, Songling

    2017-01-01

    Applying shielding coils is a practical way to protect current transformers (CTs) for large-capacity generators from the intensive magnetic interference produced by adjacent bus-bars. The aim of this study is to build a simple analytical model for the shielding coils, from which the optimization of the shielding coils can be calculated effectively. Based on an existing stray flux model, a new analytical model for the leakage flux of partial coils is presented, and finite element method-based simulations are carried out to develop empirical equations for the core-pickup factors of the models. Using the flux models, a model of the common four-segment shielding coils is derived. Furthermore, a theoretical analysis is carried out on the optimal performance of the four-segment shielding coils in a typical six-bus-bars scenario. It turns out that the “all parallel” shielding coils with a 45° starting position have the best shielding performance, whereas the “separated loop” shielding coils with a 0° starting position feature the lowest heating value. Physical experiments were performed, which verified all the models and the conclusions proposed in the paper. In addition, for shielding coils with other than the four-segment configuration, the analysis process will generally be the same. PMID:28587137

  17. Modelling and Optimization of Four-Segment Shielding Coils of Current Transformers.

    PubMed

    Gao, Yucheng; Zhao, Wei; Wang, Qing; Qu, Kaifeng; Li, He; Shao, Haiming; Huang, Songling

    2017-05-26

    Applying shielding coils is a practical way to protect current transformers (CTs) for large-capacity generators from the intensive magnetic interference produced by adjacent bus-bars. The aim of this study is to build a simple analytical model for the shielding coils, from which the optimization of the shielding coils can be calculated effectively. Based on an existing stray flux model, a new analytical model for the leakage flux of partial coils is presented, and finite element method-based simulations are carried out to develop empirical equations for the core-pickup factors of the models. Using the flux models, a model of the common four-segment shielding coils is derived. Furthermore, a theoretical analysis is carried out on the optimal performance of the four-segment shielding coils in a typical six-bus-bars scenario. It turns out that the "all parallel" shielding coils with a 45° starting position have the best shielding performance, whereas the "separated loop" shielding coils with a 0° starting position feature the lowest heating value. Physical experiments were performed, which verified all the models and the conclusions proposed in the paper. In addition, for shielding coils with other than the four-segment configuration, the analysis process will generally be the same.

  18. Measurement of the transient shielding effectiveness of shielding cabinets

    NASA Astrophysics Data System (ADS)

    Herlemann, H.; Koch, M.

    2008-05-01

    Recently, new definitions of shielding effectiveness (SE) for high-frequency and transient electromagnetic fields were introduced by Klinkenbusch (2005). Analytical results were shown for closed as well as for non closed cylindrical shields. In the present work, the shielding performance of different shielding cabinets is investigated by means of numerical simulations and measurements inside a fully anechoic chamber and a GTEM-cell. For the GTEM-cell-measurements, a downscaled model of the shielding cabinet is used. For the simulations, the numerical tools CONCEPT II and COMSOL MULTIPHYSICS were available. The numerical results agree well with the measurements. They can be used to interpret the behaviour of the shielding effectiveness of enclosures as function of frequency. From the measurement of the electric and magnetic fields with and without the enclosure in place, the electric and magnetic shielding effectiveness as well as the transient shielding effectiveness of the enclosure are calculated. The transient SE of four different shielding cabinets is determined and discussed.

  19. Replacement of Ablators with Phase-Change Material for Thermal Protection of STS Elements

    NASA Technical Reports Server (NTRS)

    Kaul, Raj K.; Stuckey, Irvin; Munafo, Paul M. (Technical Monitor)

    2002-01-01

    As part of the research and development program to develop new Thermal Protection System (TPS) materials for aerospace applications at NASA's Marshall Space Flight Center (MSFC), an experimental study was conducted on a new concept for a non-ablative TPS material. Potential loss of TPS material and ablation by-products from the External Tank (ET) or Solid Rocket Booster (SRB) during Shuttle flight with the related Orbiter tile damage necessitates development of a non-ablative thermal protection system. The new Thermal Management Coating (TMC) consists of phase-change material encapsulated in micro spheres and a two-part resin system to adhere the coating to the structure material. The TMC uses a phase-change material to dissipate the heat produced during supersonic flight rather than an ablative material. This new material absorbs energy as it goes through a phase change during the heating portion of the flight profile and then the energy is slowly released as the phase-change material cools and returns to its solid state inside the micro spheres. The coating was subjected to different test conditions simulating design flight environments at the NASA/MSFC Improved Hot Gas Facility (IHGF) to study its performance.

  20. Shielded regeneration heating element for a particulate filter

    DOEpatents

    Gonze, Eugene V [Pinckney, MI; Ament, Frank [Troy, MI

    2011-01-04

    An exhaust system includes a particulate filter (PF) that is disposed downstream from an engine. The PF filters particulates within an exhaust from the engine. A heating element heats particulate matter in the PF. A catalyst substrate or a flow converter is disposed upstream from said heating element. The catalyst substrate oxidizes the exhaust prior to reception by the heating element. The flow converter converts turbulent exhaust flow to laminar exhaust flow prior to reception by the heating element.

  1. Development of Low Density, Flexible Carbon Phenolic Ablators

    NASA Technical Reports Server (NTRS)

    Stackpoole, Mairead; Thornton, Jeremy; Fan, Wendy; Covington, Alan; Doxtad, Evan; Beck, Robin; Gasch, Matt; Arnold, Jim

    2012-01-01

    Phenolic Impregnated Carbon Ablator (PICA) was the enabling TPS material for the Stardust mission where it was used as a single piece heatshield. PICA has the advantages of low density (approximately 0.27 grams per cubic centimeter) coupled with efficient ablative capability at high heat fluxes. Due to its brittle nature and low strain to failure recent efforts at NASA ARC have focused on alternative architectures to yield flexible and more conformal carbon phenolic materials with comparable densities to PICA. This presentation will discuss flexible alternatives to PICA and include preliminary mechanical and thermal properties as well as recent arc jet and LHMEL screening test results.

  2. Tissue shrinkage in microwave ablation of liver: an ex vivo predictive model.

    PubMed

    Amabile, Claudio; Farina, Laura; Lopresto, Vanni; Pinto, Rosanna; Cassarino, Simone; Tosoratti, Nevio; Goldberg, S Nahum; Cavagnaro, Marta

    2017-02-01

    The aim of this study was to develop a predictive model of the shrinkage of liver tissues in microwave ablation. Thirty-seven cuboid specimens of ex vivo bovine liver of size ranging from 2 cm to 8 cm were heated exploiting different techniques: 1) using a microwave oven (2.45 GHz) operated at 420 W, 500 W and 700 W for 8 to 20 min, achieving complete carbonisation of the specimens, 2) using a radiofrequency ablation apparatus (450 kHz) operated at 70 W for a time ranging from 6 to 7.5 min obtaining white coagulation of the specimens, and 3) using a microwave (2.45 GHz) ablation apparatus operated at 60 W for 10 min. Measurements of specimen dimensions, carbonised and coagulated regions were performed using a ruler with an accuracy of 1 mm. Based on the results of the first two experiments a predictive model for the contraction of liver tissue from microwave ablation was constructed and compared to the result of the third experiment. For carbonised tissue, a linear contraction of 31 ± 6% was obtained independently of the heating source, power and operation time. Radiofrequency experiments determined that the average percentage linear contraction of white coagulated tissue was 12 ± 5%. The average accuracy of our model was determined to be 3 mm (5%). The proposed model allows the prediction of the shrinkage of liver tissues upon microwave ablation given the extension of the carbonised and coagulated zones. This may be useful in helping to predict whether sufficient tissue volume is ablated in clinical practice.

  3. Demonstration of the range over which the Langley Research Center digital computer charring ablation program (CHAP) can be used with confidence: Comparisons of CHAP predictions and test data for three ablation materials

    NASA Technical Reports Server (NTRS)

    Moyer, C. B.; Green, K. A.

    1972-01-01

    Comparisons of ablation calculations with the charring ablation computer code and ablation test data are presented over a wide range of environmental conditions in air for three materials: low-density nylon phenolic, Avcoat 5026-39HC/G, and a filled silicon elastomer. Heat fluxes considered range from over 500 Btu/sq ft-sec to less than 50 Btu/sq ft-sec. Pressures range from 0.5 atm to .004 atm. Enthalpies range from about 2000 Btu/lb to 18000 Btu/lb. Predictions of recession, pyrolysis penetration, and thermocouple responses are considered. Recession predictions for nylon phenolic are good as steady state is approached, but strongly transient cases are underpredicted. Pyrolysis penetrations and thermocouple responses are very well predicted. Recession amounts for Avcoat and silicone elastomer are less well predicted, although high heat flux cases near steady state are fairly satisfactory. Pyrolysis penetrations and thermocouple responses are very well predicted.

  4. Radiofrequency ablation of hepatocellular carcinoma: pros and cons.

    PubMed

    Rhim, Hyunchul; Lim, Hyo K

    2010-09-01

    Among locoregional treatments for hepatocellular carcinoma (HCC), radiofrequency ablation (RFA) has been accepted as the most popular alternative to curative transplantation or resection, and it shows an excellent local tumor control rate and acceptable morbidity. The benefits of RFA have been universally validated by the practice guidelines of international societies of hepatology. The main advantages of RFA include 1) it is minimally invasive with acceptable morbidity, 2) it enables excellent local tumor control, 3) it has promising long-term survival, and 4) it is a multimodal approach. Based on these pros, RFA will play an important role in managing the patient with early HCC (smaller than 3 cm with fewer than four tumors). The main limitations of current RFA technology in hepatic ablation include 1) limitation of ablation volume, 2) technically infeasible in some tumors due to conspicuity and dangerous location, and 3) the heat-sink effect. Many technical approaches have been introduced to overcome those limitations, including a novel guiding modality, use of artificial fluid or air, and combined treatment strategies. RFA will continue to play a role as a representative ablative modality in the management of HCC, even in the era of targeted agents.

  5. Radiofrequency Ablation of Hepatocellular Carcinoma: Pros and Cons

    PubMed Central

    Lim, Hyo K.

    2010-01-01

    Among locoregional treatments for hepatocellular carcinoma (HCC), radiofrequency ablation (RFA) has been accepted as the most popular alternative to curative transplantation or resection, and it shows an excellent local tumor control rate and acceptable morbidity. The benefits of RFA have been universally validated by the practice guidelines of international societies of hepatology. The main advantages of RFA include 1) it is minimally invasive with acceptable morbidity, 2) it enables excellent local tumor control, 3) it has promising long-term survival, and 4) it is a multimodal approach. Based on these pros, RFA will play an important role in managing the patient with early HCC (smaller than 3 cm with fewer than four tumors). The main limitations of current RFA technology in hepatic ablation include 1) limitation of ablation volume, 2) technically infeasible in some tumors due to conspicuity and dangerous location, and 3) the heat-sink effect. Many technical approaches have been introduced to overcome those limitations, including a novel guiding modality, use of artificial fluid or air, and combined treatment strategies. RFA will continue to play a role as a representative ablative modality in the management of HCC, even in the era of targeted agents. PMID:21103289

  6. Corium shield

    DOEpatents

    McDonald, Douglas B.; Buchholz, Carol E.

    1994-01-01

    A shield for restricting molten corium from flowing into a water sump disposed in a floor of a containment vessel includes upper and lower walls which extend vertically upwardly and downwardly from the floor for laterally bounding the sump. The upper wall includes a plurality of laterally spaced apart flow channels extending horizontally therethrough, with each channel having a bottom disposed coextensively with the floor for channeling water therefrom into the sump. Each channel has a height and a length predeterminedly selected for allowing heat from the molten corium to dissipate through the upper and lower walls as it flows therethrough for solidifying the molten corium therein to prevent accumulation thereof in the sump.

  7. Use of a radio frequency shield during 1.5 and 3.0 Tesla magnetic resonance imaging: experimental evaluation.

    PubMed

    Favazza, Christopher P; King, Deirdre M; Edmonson, Heidi A; Felmlee, Joel P; Rossman, Phillip J; Hangiandreou, Nicholas J; Watson, Robert E; Gorny, Krzysztof R

    2014-01-01

    Radiofrequency (RF) shields have been recently developed for the purpose of shielding portions of the patient's body during magnetic resonance imaging (MRI) examinations. We present an experimental evaluation of a commercially available RF shield in the MRI environment. All tests were performed on 1.5 T and 3.0 T clinical MRI scanners. The tests were repeated with and without the RF shield present in the bore, for comparison. Effects of the shield, placed within the scanner bore, on the RF fields generated by the scanner were measured directly using tuned pick-up coils. Attenuation, by as much as 35 dB, of RF field power was found inside the RF shield. These results were supported by temperature measurements of metallic leads placed inside the shield, in which no measurable RF heating was found. In addition, there was a small, simultaneous detectable increase (∼1 dB) of RF power just outside the edges of the shield. For these particular scanners, the autocalibrated RF power levels were reduced for scan locations prescribed just outside the edges of the shield, which corresponded with estimations based on the pick-up coil measurements. Additionally, no significant heating during MRI scanning was observed on the shield surface. The impact of the RF shield on the RF fields inside the magnet bore is likely to be dependent on the particular model of the RF shield or the MRI scanner. These results suggest that the RF shield could be a valuable tool for clinical MRI practices.

  8. Use of a radio frequency shield during 1.5 and 3.0 Tesla magnetic resonance imaging: experimental evaluation

    PubMed Central

    Favazza, Christopher P; King, Deirdre M; Edmonson, Heidi A; Felmlee, Joel P; Rossman, Phillip J; Hangiandreou, Nicholas J; Watson, Robert E; Gorny, Krzysztof R

    2014-01-01

    Radiofrequency (RF) shields have been recently developed for the purpose of shielding portions of the patient’s body during magnetic resonance imaging (MRI) examinations. We present an experimental evaluation of a commercially available RF shield in the MRI environment. All tests were performed on 1.5 T and 3.0 T clinical MRI scanners. The tests were repeated with and without the RF shield present in the bore, for comparison. Effects of the shield, placed within the scanner bore, on the RF fields generated by the scanner were measured directly using tuned pick-up coils. Attenuation, by as much as 35 dB, of RF field power was found inside the RF shield. These results were supported by temperature measurements of metallic leads placed inside the shield, in which no measurable RF heating was found. In addition, there was a small, simultaneous detectable increase (∼1 dB) of RF power just outside the edges of the shield. For these particular scanners, the autocalibrated RF power levels were reduced for scan locations prescribed just outside the edges of the shield, which corresponded with estimations based on the pick-up coil measurements. Additionally, no significant heating during MRI scanning was observed on the shield surface. The impact of the RF shield on the RF fields inside the magnet bore is likely to be dependent on the particular model of the RF shield or the MRI scanner. These results suggest that the RF shield could be a valuable tool for clinical MRI practices. PMID:25378957

  9. Ion separation effects in mixed-species ablators for inertial-confinement-fusion implosions

    NASA Astrophysics Data System (ADS)

    Amendt, Peter; Bellei, Claudio; Ross, J. Steven; Salmonson, Jay

    2015-02-01

    Recent efforts to demonstrate significant self-heating of the fuel and eventual ignition at the National Ignition Facility make use of plastic (CH) ablators [O. A. Hurricane et al., Phys. Plasmas 21, 056314 (2014), 10.1063/1.4874330]. Mainline simulation techniques for modeling CH capsule implosions treat the ablator as an average-atom fluid and neglect potential species separation phenomena. The mass-ablation process for a mixture is shown to lead to the potential for species separation, parasitic energy loss according to thermodynamic arguments, and reduced rocket efficiency. A generalized plasma barometric formula for a multispecies concentration gradient that includes collisionality and steady flows in spherical geometry is presented. A model based on plasma expansion into a vacuum is used to interpret reported experimental evidence for ablator species separation in an inertial-confinement-fusion target [J. S. Ross et al., Rev. Sci. Instrum. 83, 10E323 (2012)]. The possibility of "runaway" hydrogen ions in the thermoelectric field of the ablation front is conjectured.

  10. Ion separation effects in mixed-species ablators for inertial-confinement-fusion implosions.

    PubMed

    Amendt, Peter; Bellei, Claudio; Ross, J Steven; Salmonson, Jay

    2015-02-01

    Recent efforts to demonstrate significant self-heating of the fuel and eventual ignition at the National Ignition Facility make use of plastic (CH) ablators [O. A. Hurricane et al., Phys. Plasmas 21, 056314 (2014)]. Mainline simulation techniques for modeling CH capsule implosions treat the ablator as an average-atom fluid and neglect potential species separation phenomena. The mass-ablation process for a mixture is shown to lead to the potential for species separation, parasitic energy loss according to thermodynamic arguments, and reduced rocket efficiency. A generalized plasma barometric formula for a multispecies concentration gradient that includes collisionality and steady flows in spherical geometry is presented. A model based on plasma expansion into a vacuum is used to interpret reported experimental evidence for ablator species separation in an inertial-confinement-fusion target [J. S. Ross et al., Rev. Sci. Instrum. 83, 10E323 (2012)]. The possibility of "runaway" hydrogen ions in the thermoelectric field of the ablation front is conjectured.

  11. 193 nm ArF laser ablation and patterning of chitosan thin films

    NASA Astrophysics Data System (ADS)

    Aesa, A. A.; Walton, C. D.

    2018-06-01

    This paper reports laser ablation studies on spin-coated biopolymer chitosan films, β-l,4-1inked 2-amino-2-deoxy- d-glucopyranose. Chitosan has been irradiated using an ArF laser emitting at 193 nm. An ablation threshold of F T = 85±8 mJ cm-2 has been determined from etch rate measurements. Laser-ablated chitosan is characterised using white light interferometry, scanning electron microscopy, and thermo-gravimetric analysis. Laser ablation of chitosan is discussed in terms of thermal and photoacoustic mechanisms. Heat transfer is simulated to assist in the understanding of laser-irradiated chitosan using a finite-element method and the software package COMSOL Multi-Physics™. As a demonstrator, a micro-array of square structures in the form of a crossed grating has been fabricated by laser ablation using a mask projection scanning method. The initial investigations show no evidence of thermal damage occurring to the adjacent chitosan when operating at a moderately low laser fluence of 110 mJ cm-2.

  12. Radiative properties of advanced spacecraft heat shield materials

    NASA Technical Reports Server (NTRS)

    Cunnington, G. R.; Funai, A. I.; Mcnab, T. K.

    1983-01-01

    Experimental results are presented to show the effects of simulated reentry exposure by convective heating and by radiant heating on spectral and total emittance of statically oxidized Inconel 617 and Haynes HS188 superalloys to 1260 K and a silicide coatea (R512E) columbium 752 alloy to 1590 K. Convective heating exposures were conducted in a supersonic arc plasma wind tunnel using a wedge-shaped specimen configuration. Radiant tests were conducted at a pressure of .003 atmospheres of dry air at a flow velocity of several meters per second. Convective heating specimens were subjected to 8, 20, and 38 15-min heating cycles, and radiant heating specimens were tested for 10, 20, 50, and 100 30-min heating cycles. Changes in radiative properties are explained in terms of changes in composition resulting from simulated reentry tests. The methods used to evaluate morphological, compositional and crystallographic changes include: Auger electron spectroscopy; scanning electron microscopy; X-ray diffraction analysis; and electron microprobe analysis.

  13. Model-based feasibility assessment and evaluation of prostate hyperthermia with a commercial MR-guided endorectal HIFU ablation array

    PubMed Central

    Salgaonkar, Vasant A.; Prakash, Punit; Rieke, Viola; Ozhinsky, Eugene; Plata, Juan; Kurhanewicz, John; Hsu, I-C. (Joe); Diederich, Chris J.

    2014-01-01

    Purpose: Feasibility of targeted and volumetric hyperthermia (40–45 °C) delivery to the prostate with a commercial MR-guided endorectal ultrasound phased array system, designed specifically for thermal ablation and approved for ablation trials (ExAblate 2100, Insightec Ltd.), was assessed through computer simulations and tissue-equivalent phantom experiments with the intention of fast clinical translation for targeted hyperthermia in conjunction with radiotherapy and chemotherapy. Methods: The simulations included a 3D finite element method based biothermal model, and acoustic field calculations for the ExAblate ERUS phased array (2.3 MHz, 2.3 × 4.0 cm2, ∼1000 channels) using the rectangular radiator method. Array beamforming strategies were investigated to deliver protracted, continuous-wave hyperthermia to focal prostate cancer targets identified from representative patient cases. Constraints on power densities, sonication durations and switching speeds imposed by ExAblate hardware and software were incorporated in the models. Preliminary experiments included beamformed sonications in tissue mimicking phantoms under MR temperature monitoring at 3 T (GE Discovery MR750W). Results: Acoustic intensities considered during simulation were limited to ensure mild hyperthermia (Tmax < 45 °C) and fail-safe operation of the ExAblate array (spatial and time averaged acoustic intensity ISATA < 3.4 W/cm2). Tissue volumes with therapeutic temperature levels (T > 41 °C) were estimated. Numerical simulations indicated that T > 41 °C was calculated in 13–23 cm3 volumes for sonications with planar or diverging beam patterns at 0.9–1.2 W/cm2, in 4.5–5.8 cm3 volumes for simultaneous multipoint focus beam patterns at ∼0.7 W/cm2, and in ∼6.0 cm3 for curvilinear (cylindrical) beam patterns at 0.75 W/cm2. Focused heating patterns may be practical for treating focal disease in a single posterior quadrant of the prostate and diffused heating patterns may be

  14. Vaporization characteristics of carbon heat shields under radiative heating.

    NASA Technical Reports Server (NTRS)

    Davy, W. C.; Bar-Nun, A.

    1972-01-01

    Study of the vaporization characteristics of samples of ATJ graphite, a material that has been considered for use on a Jovian probe. These samples were subjected to radiative heating loads of approximately 2 kW/sq cm in argon atmospheres of pressures from 0.00046 to 1 atm. Surface temperatures, mass loss rates, and spatially resolved emission spectral data were recorded. These data are analyzed to determine carbon vapor pressure as a function of temperature and are compared with current models for the vapor pressure of carbon. The effects of finite vaporization (i.e., nonequilibrium) rates are considered and compared with experiment. Estimates of the heat of vaporization from an energy balance are also presented.

  15. A Proposed Method for Upper Eyelid and Infrabrow Tightening Using a Transcutaneous Temperature Controlled Radiofrequency Device With Opaque Plastic Eye Shields.

    PubMed

    Key, Douglas J; Boudreaux, Lauren

    2016-11-01

    Laxity of the eyelid and periorbital area, a common manifestation of aging, is usually addressed via blepharoplasty and/ or fat transfer. Given the trend toward safer, less invasive treatments preferred by those patients reticent to undergo more invasive procedures, viable alternatives have been sought. Transcutaneous temperature controlled radiofrequency (TTCRF) integrates non- invasive super cial RF treatment with automatic temperature feedback control of energy deposition, as a stimulator of overall collagen remodeling; however, the globe of the eye is particularly sensitive to RF energy. The purpose of the study was to propose a method by which TTCRF and other non-ablative modalities could be used to treat eyelid and infrabrow laxity, with autoclavable opaque black haptic scleral contact lenses protecting the globe of the eye. Subjects (n=40, 36 women and 4 men, age range, 33-72) with mild to moderate laxity of the eyelid and infrabrow were treated with TTCRF using black plastic eye shields (Oculoplastik, Montreal, Quebec, Canada) to protect the globe of the eye from heat and RF energy. With the shields in place subjects were treated with the 10 mm small monopolar emitter of the ThermiSmooth device (Thermi, Irving, Tex.), using small circular looping motions to safely elevate the temperature of target tissue to the therapeutically rel- evant range for approximately 6 minutes; tissue temperature was measured in real time using the device's forward-looking infrared imaging. No major adverse events were recorded. Treatment was safe and tolerable for all subjects. The use of autoclavable opaque black plastic eye shields provides a safe method of treating the upper eye lid and infrabrow using TTCRF. J Drugs Dermatol. 2016;15(11):1302-1305..

  16. Prediction of Ablation Rates from Solid Surfaces Exposed to High Temperature Gas Flow

    NASA Technical Reports Server (NTRS)

    Akyuzlu, Kazim M.; Coote, David

    2013-01-01

    A mathematical model and a solution algorithm is developed to study the physics of high temperature heat transfer and material ablation and identify the problems associated with the flow of hydrogen gas at very high temperatures and velocities through pipes and various components of Nuclear Thermal Rocket (NTR) motors. Ablation and melting can be experienced when the inner solid surface of the cooling channels and the diverging-converging nozzle of a Nuclear Thermal Rocket (NTR) motor is exposed to hydrogen gas flow at temperatures around 2500 degrees Kelvin and pressures around 3.4 MPa. In the experiments conducted on typical NTR motors developed in 1960s, degradation of the cooling channel material (cracking in the nuclear fuel element cladding) and in some instances melting of the core was observed. This paper presents the results of a preliminary study based on two types of physics based mathematical models that were developed to simulate the thermal-hydrodynamic conditions that lead to ablation of the solid surface of a stainless steel pipe exposed to high temperature hydrogen gas near sonic velocities. One of the proposed models is one-dimensional and assumes the gas flow to be unsteady, compressible and viscous. An in-house computer code was developed to solve the conservations equations of this model using a second-order accurate finite-difference technique. The second model assumes the flow to be three-dimensional, unsteady, compressible and viscous. A commercial CFD code (Fluent) was used to solve the later model equations. Both models assume the thermodynamic and transport properties of the hydrogen gas to be temperature dependent. In the solution algorithm developed for this study, the unsteady temperature of the pipe is determined from the heat equation for the solid. The solid-gas interface temperature is determined from an energy balance at the interface which includes heat transfer from or to the interface by conduction, convection, radiation, and

  17. Ablation Behavior of Plasma-Sprayed La1-xSrxTiO3+δ Coating Irradiated by High-Intensity Continuous Laser.

    PubMed

    Zhu, Jinpeng; Ma, Zhuang; Gao, Yinjun; Gao, Lihong; Pervak, Vladimir; Wang, Lijun; Wei, Chenghua; Wang, Fuchi

    2017-10-11

    Laser protection for optical components, particularly those in high-power laser systems, has been a major concern. La 1-x Sr x TiO 3+δ with its good optical and thermal properties can be potentially applied as a high-temperature optical protective coating or high-reflectivity material for optical components. However, the high-power laser ablation behavior of plasma-sprayed La 1-x Sr x TiO 3+δ (x = 0.1) coatings has rarely been investigated. Thus, in this study, laser irradiation experiments were performed to study the effect of high-intensity continuous laser on the ablation behavior of the La 1-x Sr x TiO 3+δ coating. The results show that the La 1-x Sr x TiO 3+δ coating undergoes three ablation stages during laser irradiation: coating oxidation, formation and growth of new structures (columnar and dendritic crystals), and mechanical failure. A finite-element simulation was also conducted to explore the mechanism of the ablation damage to the La 1-x Sr x TiO 3+δ coating and provided a good understanding of the ablation behavior. The apparent ablation characteristics are attributed to the different temperature gradients determined by the reflectivity and thermal diffusivity of the La 1-x Sr x TiO 3+δ coating material, which are critical factors for improving the antilaser ablation property. Now, the stainless steel substrate deposited by it can effectively work as a protective shield layer against ablation by laser irradiation.

  18. Nanobubble Ultrasound Contrast Agents for Enhanced Delivery of Thermal Sensitizer to Tumors Undergoing Radiofrequency Ablation

    PubMed Central

    Perera, Reshani H.; Solorio, Luis; Wu, Hanping; Gangolli, Mihika; Silverman, Eric; Hernandez, Christopher; Peiris, Pubudu M.; Broome, Ann-Marie

    2013-01-01

    Purpose Pluronic has been shown to sensitize various tumor cell lines to chemotherapy and hyperthermia by altering the membrane fluidity, depleting ATP, and modulating the heat shock protein 70 expression. In our prior work, Pluronic was also used to formulate nanosized ultrasound contrast agents. In the current study we evaluate the use of these contrast agents as vehicles for image-guided delivery of Pluronic to improve outcomes of tumor radiofrequency (RF) ablation. Methods Lipid-shelled Pluronic nanobubbles were prepared and examined for size distribution, zeta potential, stability, biodistribution, accumulation of nanobubbles in the tumor, and treatment efficacy. LS174-T xenograft tumor-bearing mice were used to evaluate tumor growth suppression and measure treatment efficacy after RF ablation. Results The average diameter of Pluronic bubbles was 230 nm, and initial bubble echogenicity was 16 dB. In vitro, cells exposed to Pluronic nanobubbles exhibited low cytotoxicity in the absence of ultrasound, even if heat (43°C) was applied. When the cells were exposed to Pluronic nanobubbles, heat, and ultrasound; viability was significantly reduced. In vivo, tumors treated with ultrasound-modulated nanobubbles prior to RF ablation showed a significant reduction in growth compared to the RF alone (P<0.05). Conclusion Lipid and Pluronic-shelled, echogenic nanobubbles combined with ultrasound modulation can serve as an effective theranostic method for sensitization of tumors to RF ablation. PMID:23943542

  19. Nanobubble ultrasound contrast agents for enhanced delivery of thermal sensitizer to tumors undergoing radiofrequency ablation.

    PubMed

    Perera, Reshani H; Solorio, Luis; Wu, Hanping; Gangolli, Mihika; Silverman, Eric; Hernandez, Christopher; Peiris, Pubudu M; Broome, Ann-Marie; Exner, Agata A

    2014-06-01

    Pluronic has been shown to sensitize various tumor cell lines to chemotherapy and hyperthermia by altering the membrane fluidity, depleting ATP, and modulating the heat shock protein 70 expression. In our prior work, Pluronic was also used to formulate nanosized ultrasound contrast agents. In the current study we evaluate the use of these contrast agents as vehicles for image-guided delivery of Pluronic to improve outcomes of tumor radiofrequency (RF) ablation. Lipid-shelled Pluronic nanobubbles were prepared and examined for size distribution, zeta potential, stability, biodistribution, accumulation of nanobubbles in the tumor, and treatment efficacy. LS174-T xenograft tumor-bearing mice were used to evaluate tumor growth suppression and measure treatment efficacy after RF ablation. The average diameter of Pluronic bubbles was 230 nm, and initial bubble echogenicity was 16 dB. In vitro, cells exposed to Pluronic nanobubbles exhibited low cytotoxicity in the absence of ultrasound, even if heat (43 ºC) was applied. When the cells were exposed to Pluronic nanobubbles, heat, and ultrasound; viability was significantly reduced. In vivo, tumors treated with ultrasound-modulated nanobubbles prior to RF ablation showed a significant reduction in growth compared to the RF alone (P<0.05). Lipid and Pluronic-shelled, echogenic nanobubbles combined with ultrasound modulation can serve as an effective theranostic method for sensitization of tumors to RF ablation.

  20. Upgrade of the LHC magnet interconnections thermal shielding

    NASA Astrophysics Data System (ADS)

    Musso, Andrea; Barlow, Graeme; Bastard, Alain; Charrondiere, Maryline; Chrul, Anna; Damianoglou, Dimitrios; Deferne, Guy; Dib, Gaëlle; Duret, Max; Guinchard, Michael; Prin, Hervé; Strychalski, Michał; Craen, Arnaud Vande; Villiger, Gilles; Wright, Loren

    2014-01-01

    The about 1700 interconnections (ICs) between the Large Hadron Collider (LHC) superconducting magnets include thermal shielding at 50-75 K, providing continuity to the thermal shielding of the magnet cryostats to reduce the overall radiation heat loads to the 1.9 K helium bath of the magnets. The IC shield, made of aluminum, is conduction-cooled via a welded bridge to the thermal shield of the adjacent magnets which is actively cooled. TIG welding of these bridges made in the LHC tunnel at installation of the magnets induced a considerable risk of fire hazard due to the proximity of the multi-layer insulation of the magnet shields. A fire incident occurred in one of the machine sectors during machine installation, but fortunately with limited consequences thanks to prompt intervention of the operators. LHC is now undergoing a 2 years technical stop during which all magnet's ICs will have to be opened to consolidate the magnet electrical connections. The IC thermal shields will therefore have to be removed and re-installed after the work is completed. In order to eliminate the risk of fire hazard when re-welding, it has been decided to review the design of the IC shields, by replacing the welded bridges with a mechanical clamping which also preserves its thermal function. An additional advantage of this new solution is the ease in dismantling for maintenance, and eliminating weld-grinding operations at removal needing radioprotection measures because of material activation after long-term operation of the LHC. This paper describes the new design of the IC shields and in particular the theoretical and experimental validation of its thermal performance. Furthermore a status report of the on-going upgrade work in the LHC is given.

  1. Concurrent application of charge using a novel circuit prevents heat-related coagulum formation during radiofrequency ablation.

    PubMed

    Lim, Bernard; Venkatachalam, Kalpathi L; Jahangir, Arshad; Johnson, Susan B; Asirvatham, Samuel J

    2008-08-01

    Thromboembolism resulting from coagulum formation on the catheter and electrode surfaces is a serious complication with radiofrequency ablation procedures for heart rhythm disorders. Why coagulum occurs despite therapeutic heparinization is unclear. In this report, we demonstrate a novel approach to minimize coagulum formation based on the electromolecular characteristics of fibrinogen. Atomic force microscopy was used to establish that fibrinogen deposited on surfaces underwent conformational changes that resulted in spontaneous clot formation. We then immersed ablation catheters that were uncharged, negatively, or positively charged in heparinized blood for 30 minutes and noted the extent of clot formation. In separate experiments, ablation catheters were sutured to the ventricle of an excised porcine heart immersed in whole, heparinized blood and radiofrequency ablation performed for 5 minutes with and without charge delivered to the catheter tips. Electron microscopy of the catheter tips showed surface coverage of fibrin clot of the catheter to be 33.8% for negatively charged catheters, compared with 84.7% (P = 0.01) in noncharged catheters. There was no significant difference in surface coverage of fibrin clot between positively charged catheters (93.8%) and noncharged catheters (84.7%, P = ns). In contrast, the thickness of surface clot coverage for positively charged catheters was 87.5%, compared with 28.45% (P= 0.03) for noncharged catheters and 11.25% (P = 0.03) for negatively charged catheters, compared with noncharged catheters. We describe a novel method of placing negative charge on electrodes during ablation that reduced coagulum formation. This may decrease thromboembolism-related complications with radiofrequency ablation procedures.

  2. Changes in optical properties during heating of ex vivo liver tissues

    NASA Astrophysics Data System (ADS)

    Nagarajan, Vivek Krishna; Gogineni, Venkateshwara R.; White, Sarah B.; Yu, Bing

    2017-02-01

    Thermal ablation is the use of heat to induce cell death through coagulative necrosis. Ideally, complete ablation of tumor cells with no damage to surrounding critical structures such as blood vessels, nerves or even organs is desired. Ablation monitoring techniques are often employed to ensure optimal tumor ablation. In thermal tissue ablation, tissue damage is known to be dependent on the temperature and time of exposure. Aptly, current methods for monitoring ablation rely profoundly on local tissue temperature and duration of heating to predict the degree of tissue damage. However, such methods do not take into account the microstructural and physiological changes in tissues as a result of thermocoagulation. Light propagation within biological tissues is known to be dependent on the tissue microstructure and physiology. During tissue denaturation, changes in tissue structure alter light propagations in tissue which could be used to directly assess the extent of thermal tissue damage. We report the use of a spectroscopic system for monitoring the tissue optical properties during heating of ex vivo liver tissues. We observed that during tissue denaturation, continuous changes in wavelength-averaged μa(λ) and μ's(λ) followed a sigmoidal trend and are correlated with damage predicted by Arrhenius model.

  3. High-Flux, High-Temperature Thermal Vacuum Qualification Testing of a Solar Receiver Aperture Shield

    NASA Technical Reports Server (NTRS)

    Kerslake, Thomas W.; Mason, Lee S.; Strumpf, Hal J.

    1997-01-01

    As part of the International Space Station (ISS) Phase 1 program, NASA Lewis Research Center (LERC) and the Russian Space Agency (RSA) teamed together to design, build and flight test the world's first orbital Solar Dynamic Power System (SDPS) on the Russian space station Mir. The Solar Dynamic Flight Demonstration (SDFD) program was to operate a nominal 2 kWe SDPS on Mir for a period up to 1-year starting in late 1997. Unfortunately, the SDFD mission was demanifested from the ISS phase 1 shuttle program in early 1996. However, substantial flight hardware and prototypical flight hardware was built including a heat receiver and aperture shield. The aperture shield comprises the front face of the cylindrical cavity heat receiver and is located at the focal plane of the solar concentrator. It is constructed of a stainless steel plate with a 1-m outside diameter, a 0.24-m inside diameter and covered with high-temperature, refractory metal Multi-Foil Insulation (MFI). The aperture shield must minimize heat loss from the receiver cavity, provide a stiff, high strength structure to accommodate shuttle launch loads and protect receiver structures from highly concentrated solar fluxes during concentrator off-pointing events. To satisfy Mir operational safety protocols, the aperture shield was required to accommodate direct impingement of the intensely concentrated solar image for a 1-hour period. To verify thermal-structural durability under the anticipated high-flux, high-temperature loading, an aperture shield test article was constructed and underwent a series of two tests in a large thermal vacuum chamber configured with a reflective, point-focus solar concentrator and a solar simulator. The test article was positioned near the focal plane and exposed to concentrated solar flux for a period of 1-hour. In the first test, a near equilibrium temperature of 1862 K was attained in the center of the shield hot spot. In the second test, with increased incident flux, a near

  4. Artificial meteor ablation studies: Olivine

    NASA Technical Reports Server (NTRS)

    Blanchard, M. B.; Cunningham, G. G.

    1973-01-01

    Artificial meteor ablation was performed on a Mg-rich olivine sample using an arc-heated plasma of ionized air. Experimental conditions simulated a meteor traveling about 12 km/sec at an altitude of 70 km. The mineral content of the original olivine sample was 98% olivine (including traces of olivine alteration products) and 2% chromite. Forsterite content of the original olivine was Fo-89. After ablation, the forsterite content had increased to Fo-94 in the recrystallized olivine. In addition, lamella-like intergrowths of magnetite were prevalent constituents. Wherever magnetite occurred, there was an increase in Mg and a corresponding decrease in Fe for the recrystallized olivine. The Allende fusion crust consisted of a recrystallized olivine, which was more Mg-rich and Fe-deficient than the original meteorite's olivine, and abundant magnetite grains. Although troilite and pentlandite were the common opaque mineral constituents in this meteorite, magnetite was the principal opaque mineral found in the fusion crust.

  5. The effects of Magnetic Resonance Imaging-guided High-Intensity Focused Ultrasound ablation on human cadaver breast tissue.

    PubMed

    Merckel, Laura G; Deckers, Roel; Baron, Paul; Bleys, Ronald L A W; van Diest, Paul J; Moonen, Chrit T W; Mali, Willem P Th M; van den Bosch, Maurice A A J; Bartels, Lambertus W

    2013-10-05

    Magnetic Resonance Imaging-guided High-Intensity Focused Ultrasound (MR-HIFU) is a promising technique for non-invasive breast tumor ablation. The purpose of this study was to investigate the effects of HIFU ablation and thermal exposure on ex vivo human breast tissue. HIFU ablations were performed in three unembalmed cadaveric breast specimens using a clinical MR-HIFU system. Sonications were performed in fibroglandular and adipose tissue. During HIFU ablation, time-resolved anatomical MR images were acquired to monitor macroscopic tissue changes. Furthermore, the breast tissue temperature was measured using a thermocouple to investigate heating and cooling under HIFU exposure. After HIFU ablation, breast tissue samples were excised and prepared for histopathological analysis. In addition, thermal exposure experiments were performed to distinguish between different levels of thermal damage using immunohistochemical staining. Irreversible macroscopic deformations up to 3.7 mm were observed upon HIFU ablation both in fibroglandular and in adipose tissue. No relationship was found between the sonication power or the maximum tissue temperature and the size of the deformations. Temperature measurements after HIFU ablation showed a slow decline in breast tissue temperature. Histopathological analysis of sonicated regions demonstrated ablated tissue and morphologically complete cell death. After thermal exposure, samples exposed to three different temperatures could readily be distinguished. In conclusion, the irreversible macroscopic tissue deformations in ex vivo human breast tissue observed during HIFU ablation suggest that it might be relevant to monitor tissue deformations during MR-HIFU treatments. Furthermore, the slow decrease in breast tissue temperature after HIFU ablation increases the risk of heat accumulation between successive sonications. Since cell death was inflicted after already 5 minutes at 75°C, MR-HIFU may find a place in non-invasive treatment of

  6. Ablative performance of uncoated silicone-modified and shuttle baseline reinforced carbon composites

    NASA Technical Reports Server (NTRS)

    Dicus, D. L.; Hopko, R. N.; Brown, R. D.

    1976-01-01

    The relative ablative performance of uncoated silicone-modified reinforced carbon composite (RCC) and uncoated shuttle baseline RCC substrates was investigated. The test specimens were 13 plies (5.3 to 5.8 millimeters) thick and had a 25-millimeter-diameter test face. Prior to arc tunnel testing, all specimens were subjected to a heat treatment simulating the RCC coating process. During arc tunnel testing, the specimens were exposed to cold wall heating rates of 178 to 529 kilowatts/sq m and stagnation pressures ranging from 0.015 to 0.046 atmosphere at Mach 4.6 in air, with and without preheating in nitrogen. The results show that the ablative performance of uncoated silicone-modified RCC substrates is significantly superior to that of uncoated shuttle baseline RCC substrates over the range of heating conditions used. These results indicate that the silicone-modified RCC substrate would yield a substantially greater safety margin in the event of complete coating loss on the shuttle orbiter.

  7. Optimization by means of an analytical heat transfer model of a thermal insulation for CSP applications based on radiative shields

    NASA Astrophysics Data System (ADS)

    Gaetano, A.; Roncolato, J.; Montorfano, D.; Barbato, M. C.; Ambrosetti, G.; Pedretti, A.

    2016-05-01

    The employment of new gaseous heat transfer fluids as air or CO2, which are cheaper and environmentally friendly, is drawing more and more attention within the field of Concentrated Solar Power applications. However, despite the advantages, their use requires receivers with a larger heat transfer area and flow cross section with a consequent greater volume of thermal insulation. Solid thermal insulations currently used present high thermal inertia which is energetically penalizing during the daily transient phases faced by the main plant components (e.g. receivers). With the aim of overcoming this drawback a thermal insulation based on radiative shields is presented in this study. Starting from an initial layout comprising a solid thermal insulation layer, the geometry was optimized avoiding the use of the solid insulation keeping performance and fulfilling the geometrical constraints. An analytical Matlab model was implemented to assess the system thermal behavior in terms of heat loss taking into account conductive, convective and radiative contributions. Accurate 2D Computational Fluid Dynamics (CFD) simulations were run to validate the Matlab model which was then used to select the most promising among three new different designs.

  8. Characterization of Material Response During Arc-Jet Testing with Optical Methods Status and Perspectives

    NASA Technical Reports Server (NTRS)

    Winter, Michael

    2012-01-01

    The characterization of ablation and recession of heat shield materials during arc jet testing is an important step towards understanding the governing processes during these tests and therefore for a successful extrapolation of ground test data to flight. The behavior of ablative heat shield materials in a ground-based arc jet facility is usually monitored through measurement of temperature distributions (across the surface and in-depth), and through measurement of the final surface recession. These measurements are then used to calibrate/validate materials thermal response codes, which have mathematical models with reasonably good fidelity to the physics and chemistry of ablation, and codes thus calibrated are used for predicting material behavior in flight environments. However, these thermal measurements only indirectly characterize the pyrolysis processes within an ablative material pyrolysis is the main effect during ablation. Quantification of pyrolysis chemistry would therefore provide more definitive and useful data for validation of the material response codes. Information of the chemical products of ablation, to various levels of detail, can be obtained using optical methods. Suitable optical methods to measure the shape and composition of these layers (with emphasis on the blowing layer) during arc jet testing are: 1) optical emission spectroscopy (OES) 2) filtered imaging 3) laser induced fluorescence (LIF) and 4) absorption spectroscopy. Several attempts have been made to optically measure the material response of ablative materials during arc-jet testing. Most recently, NH and OH have been identified in the boundary layer of a PICA ablator. These species are suitable candidates for a detection through PLIF which would enable a spatially-resolved characterization of the blowing layer in terms of both its shape and composition. The recent emission spectroscopy data will be presented and future experiments for a qualitative and quantitative

  9. Teflon probing for the flow characterization of arc-heated wind tunnel facilities

    NASA Astrophysics Data System (ADS)

    Gulli, Stefano; Ground, Cody; Crisanti, Matthew; Maddalena, Luca

    2014-02-01

    The experimental flow characterization of the arc-heated wind tunnel of the University of Texas at Arlington is investigated in this work using ablative Teflon probes in combination with total pressure measurements. A parallel analytical work, focused on the dimensional analysis of the ablation process, has been conducted with the purpose of improving existing semi-empirical correlations for the heat blockage due to the mass injection inside the boundary layer. A control volume analysis at the receding surface of the specimens is used to calculate the wall heat transfer for a non-ablating probe by including the blockage effect. The new correlations, obtained for the convective blockage, show an improvement of the correlation coefficient of 110 % with respect to those available in literature, once a new blowing parameter containing the stagnation pressure is introduced. A correlation developed by NASA during the Round-Robin program, which relates the Teflon mass loss rate to the total pressure and cold-wall heat flux measured experimentally, is also used to predict the wall heat transfer referred to the ablation temperature of Teflon. For both approaches, a simplified stagnation point convective heat transfer equation allows the average stagnation enthalpy to be calculated. Several locations downstream of the nozzle exit have been surveyed, and selected points of the facility's performance map have been used for the experimental campaign. The results show that both approaches provide similar results in terms of stagnation heat flux and enthalpy prediction with uncertainties comparable to those provided by standard intrusive heat flux probes ( δ q max < 25 %). The analysis of the Teflon's ablated surface does not reveal significant flow non-uniformities, and a 1.14 heat flux enhancement factor due to the shock-shock interaction is detectable at x = 3.5 in. from the nozzle exit plane. The results show the use of ablative probes for the flow characterization of arc

  10. Chemical nonequilibrium Navier-Stokes solutions for hypersonic flow over an ablating graphite nosetip

    NASA Technical Reports Server (NTRS)

    Chen, Y. K.; Henline, W. D.

    1993-01-01

    The general boundary conditions including mass and energy balances of chemically equilibrated or nonequilibrated gas adjacent to ablating surfaces have been derived. A computer procedure based on these conditions was developed and interfaced with the Navier-Stokes solver for predictions of the flow field, surface temperature, and surface ablation rates over re-entry space vehicles with ablating Thermal Protection Systems (TPS). The Navier-Stokes solver with general surface thermochemistry boundary conditions can predict more realistic solutions and provide useful information for the design of TPS. A test case with a proposed hypersonic test vehicle configuration and associated free stream conditions was developed. Solutions with various surface boundary conditions were obtained, and the effect of nonequilibrium gas as well as surface chemistry on surface heating and ablation rate were examined. The solutions of the GASP code with complete ablating surface conditions were compared with those of the ASC code. The direction of future work is also discussed.

  11. Performance of solar shields. [Skylab 1 micrometeoroid shield difficulties

    NASA Technical Reports Server (NTRS)

    Schwinghamer, R. J.

    1974-01-01

    The loss of the micrometeoroid shield from the Orbital Workshop section of Skylab 1 about 63 seconds after lift-off, was the catalyst for a prodigious effort to develop a substitute for the passive portion of the thermal control system. An intensive effort is described in which numerous potential thermal shield materials were assessed, and during which period ten specific shield designs were developed and carried through various stages of development and test. Thermal shield materials data are discussed, including optical, strength, fatigue, outgassing, tackiness, ultraviolet radiation, and material memory properties. Specifically addressed are thermal shield materials selection criteria and the design, development, and test requirements associated with the successful development of Skylab thermal shields, and specifically the two thermal shields subsequently deployed over the exposed gold foil skin of the Orbital Workshop. Also considered are the general performance and thermal improvements provided by both the parasol design deployed by the Skylab 1 crew, and the sail design deployed by the Skylab 2 crew.

  12. NASA Testing the Webb Telescope's MIRI Thermal Shield

    NASA Image and Video Library

    2017-12-08

    NASA engineer Acey Herrera recently checked out copper test wires inside the thermal shield of the Mid-Infrared Instrument, known as MIRI, that will fly aboard NASA's James Webb Space Telescope. The shield is designed to protect the vital MIRI instrument from excess heat. At the time of the photo, the thermal shield was about to go through rigorous environmental testing to ensure it can perform properly in the extreme cold temperatures that it will encounter in space. Herrera is working in a thermal vacuum chamber at NASA's Goddard Space Flight Center in Greenbelt, Md. As the MIRI shield lead, Herrera along with a thermal engineer and cryo-engineer verify that the shield is ready for testing. On the Webb telescope, the pioneering camera and spectrometer that comprise the MIRI instrument sit inside the Integrated Science Instrument Module flight structure, that holds Webb's four instruments and their electronic systems during launch and operations. Read more: 1.usa.gov/15I0wrS Credit: NASA/Chris Gunn NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

  13. Mechanism analysis of Magnetohydrodynamic heat shield system and optimization of externally applied magnetic field

    NASA Astrophysics Data System (ADS)

    Li, Kai; Liu, Jun; Liu, Weiqiang

    2017-04-01

    As a novel thermal protection technique for hypersonic vehicles, Magnetohydrodynamic (MHD) heat shield system has been proved to be of great intrinsic value in the hypersonic field. In order to analyze the thermal protection mechanisms of such a system, a physical model is constructed for analyzing the effect of the Lorentz force components in the counter and normal directions. With a series of numerical simulations, the dominating Lorentz force components are analyzed for the MHD heat flux mitigation in different regions of a typical reentry vehicle. Then, a novel magnetic field with variable included angle between magnetic induction line and streamline is designed, which significantly improves the performance of MHD thermal protection in the stagnation and shoulder areas. After that, the relationships between MHD shock control and MHD thermal protection are investigated, based on which the magnetic field above is secondarily optimized obtaining better performances of both shock control and thermal protection. Results show that the MHD thermal protection is mainly determined by the Lorentz force's effect on the boundary layer. From the stagnation to the shoulder region, the flow deceleration effect of the counter-flow component is weakened while the flow deflection effect of the normal component is enhanced. Moreover, there is no obviously positive correlation between the MHD shock control and thermal protection. But once a good Lorentz force's effect on the boundary layer is guaranteed, the thermal protection performance can be further improved with an enlarged shock stand-off distance by strengthening the counter-flow Lorentz force right after shock.

  14. Self-generated clouds of micron-sized particles as a promising way of a Solar Probe shielding from intense thermal radiation of the Sun

    NASA Astrophysics Data System (ADS)

    Dombrovsky, Leonid A.; Reviznikov, Dmitry L.; Kryukov, Alexei P.; Levashov, Vladimir Yu

    2017-10-01

    An effect of shielding of an intense solar radiation towards a solar probe with the use of micron-sized SiC particles generated during ablation of a composite thermal protection material is estimated on a basis of numerical solution to a combined radiative and heat transfer problem. The radiative properties of particles are calculated using the Mie theory, and the spectral two-flux model is employed in radiative transfer calculations for non-uniform particle clouds. A computational model for generation and evolution of the cloud is based on a conjugated heat transfer problem taking into account heating and thermal destruction of the matrix of thermal protection material and sublimation of SiC particles in the generated cloud. The effect of light pressure, which is especially important for small particles, is also taken into account. The computational data for mass loss due to the particle cloud sublimation showed the low value about 1 kg/m2 per hour at the distance between the vehicle and the Sun surface of about four radii of the Sun. This indicates that embedding of silicon carbide or other particles into a thermal protection layer and the resulting generation of a particle cloud can be considered as a promising way to improve the possibilities of space missions due to a significant decrease in the vehicle working distance from the solar photosphere.

  15. Magnetic Shielding of an Adiabatic Demagnetization Refrigerator for TES Microcalorimeter Operation

    NASA Astrophysics Data System (ADS)

    Hishi, U.; Fujimoto, R.; Kunihisa, T.; Takakura, S.; Mitsude, T.; Kamiya, K.; Kotake, M.; Hoshino, A.; Shinozaki, K.

    2014-09-01

    We are developing a compact adiabatic demagnetization refrigerator (ADR) dedicated for TES X-ray microcalorimeter operation. Ferric ammonium alum (FAA) was grown in a stainless-steel container in our laboratory. This salt pill was mounted together with a superconducting magnet and a conventional mechanical heat-switch in a dedicated helium cryostat. Using this system, we achieved mK and a hold time of h below 100 mK. Initially, we used a 3 mm thick silicon steel shield around the ADR magnet and a Nb/Cryoperm double shield around the detector. However, this silicon steel shield allowed a mT field at the detector position when a full field (3 T) was applied, and caused the Nb shield around the detector to trap a magnetic field. The observed transition curve of a TES was broad ( mK) compared to mK obtained in a dilution refrigerator. By increasing the shield thickness to 12 mm, transition width was improved to mK, which suggests that the shields work as expected. When we operated a TES microcalorimeter, energy resolution was eV (FWHM) at 5.9 keV.

  16. Lightning Strike Ablation Damage Influence Factors Analysis of Carbon Fiber/Epoxy Composite Based on Coupled Electrical-Thermal Simulation

    NASA Astrophysics Data System (ADS)

    Yin, J. J.; Chang, F.; Li, S. L.; Yao, X. L.; Sun, J. R.; Xiao, Y.

    2017-10-01

    According to the mathematical analysis model constructed on the basis of energy-balance relationship in lightning strike, and accompany with the simplified calculation strategy of composite resin pyrolysis degree dependent electrical conductivity, an effective three dimensional thermal-electrical coupling analysis finite element model of composite laminate suffered from lightning current was established based on ABAQUS, to elucidate the effects of lighting current waveform parameters and thermal/electrical properties of composite laminate on the extent of ablation damage. Simulated predictions agree well with the composite lightning strike directed effect experimental data, illustrating the potential accuracy of the constructed model. The analytical results revealed that extent of composite lightning strike ablation damage can be characterized by action integral validly, there exist remarkable power function relationships between action integral and visual damage area, projected damage area, maximum damage depth and damage volume of ablation damage, and enhancing the electrical conductivity and specific heat of composite, ablation damage will be descended obviously, power function relationships also exist between electrical conductivity, specific heat and ablation damage, however, the impact of thermal conductivity on the extent of ablation damage is not notable. The conclusions obtained provide some guidance for composite anti-lightning strike structure-function integration design.

  17. Thermo-Chemical Phenomena Simulation for Ablation

    DTIC Science & Technology

    2011-02-21

    DATES COVERED (1/01/08-30/11/10) 4. TITLE AND SUBTITLE Thermo- Chemical Phenomena Simulation for Ablation 5a. CONTRACT NUMBER...First, a physic based chemical kinetic model for high-temperature gas is developed and verified by comparing with data from the RAM-C-II probe and the...found to be negligible and the energy exchange is dominated by the chemical process for conductive-convective heat transfer. A simplified and more

  18. Laser-induced thermal ablation of cancerous cell organelles.

    PubMed

    Letfullin, Renat R; Szatkowski, Scott A

    2017-07-01

    By exploiting the physical changes experienced by cancerous organelles, we investigate the feasibility of destroying cancerous cells by single and multipulse modes of laser heating. Our procedure consists of two primary steps: determining the normal and cancerous organelles optical properties and simulating the heating of all of the major organelles in the cell to find the treatment modes for the laser ablation of cancerous organelles without harming healthy cells. Our simulations show that the cancerous nucleus can be selectively heated to damaging temperatures, making this nucleus a feasible therapeutic particle and removing the need for nanoparticle injection. Because of the removal of this extra step, the procedure we propose is simpler and safer for the patient.

  19. Microscopic Scale Simulation of the Ablation of Fibrous Materials

    NASA Technical Reports Server (NTRS)

    Lachaud, Jean Romain; Mansour, Nagi N.

    2010-01-01

    Ablation by oxidation of carbon-fiber preforms impregnated in carbonized phenolic matrix is modeled at microscopic scale. Direct numerical simulations show that the carbonized phenolic matrix ablates in volume leaving the carbon fibers exposed. This is due to the fact that the reactivity of carbonized phenolic is higher than the reactivity of carbon fibers. After the matrix is depleted, the fibers ablate showing progressive reduction of their diameter. The overall material recession occurs when the fibers are consumed. Two materials with the same carbon-fiber preform, density and chemical composition, but with different matrix distributions are studied. These studies show that at moderate temperatures (< 1000 K) the microstructure of the material influences its recession rate; a fact that is not captured by current models that are based on chemical composition only. Surprisingly, the response of these impregnated-fiber materials is weakly dependent on the microstructure at very high temperatures (e.g., Stardust peak heating conditions: 3360K).

  20. Comparative study on laser tissue ablation between PV and HPS lasers

    NASA Astrophysics Data System (ADS)

    Kang, Hyun Wook; Jebens, David; Mitchell, Gerald; Koullick, Ed

    2008-02-01

    Laser therapy for obstructive benign prostatic hyperplasia (BPH) has gained broad adoption due to effective tissue removal, immediate hemostasis, and minor complications. The aim of this study is to quantitatively compare ablation characteristics of PV (Photoselective Vaporization) and the newly introduced HPS (High Performance System) 532 nm lasers. Bovine prostatic tissues were ablated in vitro, using a custom-made scanning system. Laser-induced volume produced by two lasers was quantified as a function of applied power, fiber working distance (WD), and treatment speed. Given the same power of 80 W and speed of 4 mm/s, HPS created up to 50 % higher tissue ablation volume than PV did. PV induced a rapid decrease of ablation volume when WD increased from 0.5 mm to 3 mm while HPS yielded almost constant tissue removal up to 3 mm for both 80 W and 120 W. As the treatment speed increased, both lasers reached saturation in tissue ablation volume. Lastly, both PV and HPS lasers exhibited approximately 1 mm thick heat affected zone (HAZ) in this study although HPS created twice deeper ablation channels with a depth of up to 4 mm. Due to a smaller beam size and a higher output power, HPS maximized tissue ablation rate with minimal thermal effects to the adjacent tissue. Furthermore, more collimated beam characteristics provides more spatial flexibility and may even help to decrease the rate of fiber degradation associated with thermal damage from debris reattachment to the tip.

  1. Shielding Gas and Heat Input Effects on the Mechanical and Metallurgical Characterization of Gas Metal Arc Welding of Super Martensitic Stainless Steel (12Cr5Ni2Mo) Joints

    NASA Astrophysics Data System (ADS)

    Prabakaran, T.; Prabhakar, M.; Sathiya, P.

    This paper deals with the effects of shielding gas mixtures (100% CO2, 100% Ar and 80 % Ar + 20% CO2) and heat input (3.00, 3.65 and 4.33kJ/mm) on the mechanical and metallurgical characteristics of AISI 410S (American Iron and Steel Institute) super martensitic stainless steel (SMSS) by gas metal arc welding (GMAW) process. AISI 410S SMSS with 1.2mm diameter of a 410 filler wire was used in this study. A detailed microstructural analysis of the weld region as well as the mechanical properties (impact, microhardness and tensile tests at room temperature and 800∘C) was carried out. The tensile and impact fracture surfaces were further analyzed through scanning electron microscope (SEM). 100% Ar shielded welds have a higher amount of δ ferrite content and due to this fact the tensile strength of the joints is superior to the other two shielded welds.

  2. Tissue healing response following hyperthermic vapor ablation in the porcine longissimus muscle

    NASA Astrophysics Data System (ADS)

    Grantham, John T.; Grisez, Brian T.; Famoso, Justin; Hoey, Michael; Dixon, Chris; Coad, James E.

    2015-03-01

    As the use of hyperthermic ablation technologies has increased, so too has the need to understand their effects on tissue and their healing responses. This study was designed to characterize tissue injury and healing following hyperthermic vapor ablation in the in vivo porcine longissimus muscle model. The individual ablations were performed using the NxThera Vapor Delivery System (NxThera Inc., Minneapolis, MN). To assess the vapor ablation's evolution, the swine were euthanized post-treatment on Day 0, Day 3, Day 7, Day 14, Day 28, Day 45 and Day 90. Triphenyltetrazolium chloride viability staining (TTC staining) was used to macroscopically assess the extent of each vapor ablation within the tissue. The ablation associated healing responses were then histologically evaluated for acute inflammation, chronic inflammation, foreign body reaction and fibrosis. Two zones of tissue injury were initially identified in the ablations: 1) a central zone of complete coagulative necrosis and 2) an outer "transition zone" of viable and non-viable cells. The ablations initially increased in size from Day 0 to Day 7 and then progressively decreased in size though Day 45. The initial Day 3 healing changes originated in the transition zone with minimal acute and chronic inflammation. As time progressed, granulation tissue began to form by Day 7 and peaked around Day 14. Collagen formation, deposition and remodeling began in the adjacent healthy tissue by Day 28, replaced the ablation site by Day 45 and reorganized by Day 90. In conclusion, this vapor ablation technology provided a non-desiccating form of hyperthermic ablation that resulted in coagulative necrosis without a central thermally/heat-fixed tissue component, followed a classical wound healing pathway, and healed with minimal associated inflammation.

  3. Plasma Heating: An Advanced Technology

    NASA Technical Reports Server (NTRS)

    1994-01-01

    The Mercury and Apollo spacecraft shields were designed to protect astronauts from high friction temperatures (well over 2,000 degrees Fahrenheit) when re-entering the Earth's atmosphere. It was necessary to test and verify the heat shield materials on Earth before space flight. After exhaustive research and testing, NASA decided to use plasma heating as a heat source. This technique involves passing a strong electric current through a rarefied gas to create a plasma (ionized gas) that produces an intensely hot flame. Although NASA did not invent the concept, its work expanded the market for commercial plasma heating systems. One company, Plasma Technology Corporation (PTC), was founded by a member of the team that developed the Re-entry Heating Simulator at Ames Research Center (ARC). Dr. Camacho, President of PTC, believes the technology has significant environmental applications. These include toxic waste disposal, hydrocarbon, decomposition, medical waste disposal, asbestos waste destruction, and chemical and radioactive waste disposal.

  4. Development of Naphthalene PLIF for Making Quantitative Measurements of Ablation Products Transport in Supersonic Flows

    NASA Astrophysics Data System (ADS)

    Combs, Christopher; Clemens, Noel

    2014-11-01

    Ablation is a multi-physics process involving heat and mass transfer and codes aiming to predict ablation are in need of experimental data pertaining to the turbulent transport of ablation products for validation. Low-temperature sublimating ablators such as naphthalene can be used to create a limited physics problem and simulate ablation at relatively low temperature conditions. At The University of Texas at Austin, a technique is being developed that uses planar laser-induced fluorescence (PLIF) of naphthalene to visualize the transport of ablation products in a supersonic flow. In the current work, naphthalene PLIF will be used to make quantitative measurements of the concentration of ablation products in a Mach 5 turbulent boundary layer. For this technique to be used for quantitative research in supersonic wind tunnel facilities, the fluorescence properties of naphthalene must first be investigated over a wide range of state conditions and excitation wavelengths. The resulting calibration of naphthalene fluorescence will be applied to the PLIF images of ablation from a boundary layer plug, yielding 2-D fields of naphthalene mole fraction. These images may help provide data necessary to validate computational models of ablative thermal protection systems for reentry vehicles. Work supported by NASA Space Technology Research Fellowship Program under grant NNX11AN55H.

  5. Improved Ablation Resistance of Silicone Rubber Composites by Introducing Montmorillonite and Silicon Carbide Whisker

    PubMed Central

    Zhang, Guangwu; Wang, Fuzhong; Huang, Zhixiong; Dai, Jing; Shi, Minxian

    2016-01-01

    Montmorillonite (MMT) was added to silicone rubber (SR) to improve the ablation resistance of the silicone. Following this, different quantities of silicon carbide whiskers (SiCw) were incorporated into the MMT/SR to yield a hybrid, ablative composite. The tensile strength and elongation at break of the composite increased after the addition of MMT. The ablation test results showed that MMT helped to form a covering layer by bonding with the silica and other components on the ablated surface. The linear and mass ablation rates exhibited decreases of 22.5% and 18.2%, respectively, in comparison to a control sample. After further incorporation of SiCw as the second filler, the resulting composites exhibited significantly higher tensile strength and ablation resistance, but not particularly lower elongation at break in comparison to the control sample. The SiCw/MMT fillers were beneficial in forming a dense and compact covering layer that delayed the heat and oxygen diffusion into the inner layers, which improved the ablation properties effectively. The remaining whiskers acted as a micro skeleton to maintain the composite’s char strength. Compared to the control sample, the linear and mass ablation rates of the composite after incorporating 6 phr SiCw and 10 phr MMT decreased by 59.2% and 43.6%, respectively. These experimental results showed that the fabricated composites exhibited outstanding mechanical properties and excellent ablation resistance. PMID:28773846

  6. Improved Ablation Resistance of Silicone Rubber Composites by Introducing Montmorillonite and Silicon Carbide Whisker.

    PubMed

    Zhang, Guangwu; Wang, Fuzhong; Huang, Zhixiong; Dai, Jing; Shi, Minxian

    2016-08-24

    Montmorillonite (MMT) was added to silicone rubber (SR) to improve the ablation resistance of the silicone. Following this, different quantities of silicon carbide whiskers (SiCw) were incorporated into the MMT/SR to yield a hybrid, ablative composite. The tensile strength and elongation at break of the composite increased after the addition of MMT. The ablation test results showed that MMT helped to form a covering layer by bonding with the silica and other components on the ablated surface. The linear and mass ablation rates exhibited decreases of 22.5% and 18.2%, respectively, in comparison to a control sample. After further incorporation of SiCw as the second filler, the resulting composites exhibited significantly higher tensile strength and ablation resistance, but not particularly lower elongation at break in comparison to the control sample. The SiCw/MMT fillers were beneficial in forming a dense and compact covering layer that delayed the heat and oxygen diffusion into the inner layers, which improved the ablation properties effectively. The remaining whiskers acted as a micro skeleton to maintain the composite's char strength. Compared to the control sample, the linear and mass ablation rates of the composite after incorporating 6 phr SiCw and 10 phr MMT decreased by 59.2% and 43.6%, respectively. These experimental results showed that the fabricated composites exhibited outstanding mechanical properties and excellent ablation resistance.

  7. Toward a comprehensive UV laser ablation modeling of multicomponent materials—A non-equilibrium investigation on titanium carbide

    NASA Astrophysics Data System (ADS)

    Ait Oumeziane, Amina; Parisse, Jean-Denis

    2018-05-01

    Titanium carbide (TiC) coatings of great quality can be produced using nanosecond pulsed laser deposition (PLD). Because the deposition rate and the transfer of the target stoichiometry depend strongly on the laser-target/laser-plasma interaction as well as the composition of the laser induced plume, investigating the ruling fundamental mechanisms behind the material ablation and the plasma evolution in the background environment under PLD conditions is essential. This work, which extends previous investigations dedicated to the study of nanosecond laser ablation of pure target materials, is a first step toward a comprehensive non-equilibrium model of multicomponent ones. A laser-material interaction model coupled to a laser-plasma interaction one is presented. A UV 20 ns KrF (248 nm) laser pulse is considered. Ablation depths, plasma ignition thresholds, and shielding rates have been calculated for a wide range of laser beam fluences. A comparison of TiC behavior with pure titanium material under the same conditions is made. Plasma characteristics such as temperature and composition have been investigated. An overall correlation between the various results is presented.

  8. Meteoroid/Debris Shielding

    NASA Technical Reports Server (NTRS)

    Christiansen, Eric L.

    2003-01-01

    This report provides innovative, low-weight shielding solutions for spacecraft and the ballistic limit equations that define the shield's performance in the meteoroid/debris environment. Analyses and hypervelocity impact testing results are described that have been used in developing the shields and equations. Spacecraft shielding design and operational practices described in this report are used to provide effective spacecraft protection from meteoroid and debris impacts. Specific shield applications for the International Space Station (ISS), Space Shuttle Orbiter and the CONTOUR (Comet Nucleus Tour) space probe are provided. Whipple, Multi-Shock and Stuffed Whipple shield applications are described.

  9. A Novel Microwave Catheter Can Perform Noncontact Circumferential Endocardial Ablation in a Model of Pulmonary Vein Isolation.

    PubMed

    Qian, Pierre; Barry, Michael Anthony; Nguyen, Trang; Ross, David; Kovoor, Pramesh; McEwan, Alistair; Thomas, Stuart; Thiagalingam, Aravinda

    2015-07-01

    Pulmonary vein isolation is an effective treatment for atrial fibrillation. Current endocardial ablation techniques require catheter contact for lesion formation. Inadequate or inconsistent catheter contact results in difficulty with achieving acute and long-term isolation and consequent atrial arrhythmia recurrence. Microwave energy produces radiant heating and therefore can be used for noncontact catheter ablation. We hypothesized that it is possible to design a microwave catheter to produce a circumferential transmural thermal lesion in an in vitro model of a pulmonary vein antrum. A monopole microwave catheter with a sideways firing axially symmetrical heating pattern was designed. Noncontact ablations were performed in a perfused pulmonary vein model constructed from microwave myocardial phantom embedded with a sheet of thermochromic liquid crystal to permit visualization and measurement of thermal lesions from color changes. 1200 J ablations were performed at 150 W for 80 seconds and 120 W for 100 seconds at high (0.8 L/min) and low (0.06 L/min) flow through the modeled pulmonary vein. Myocardial tissue was substituted for the phantom material and ablations repeated at 150 W for 180 seconds and stained with nitro-blue tetrazolium. The catheter was able to induce deep circumferential antral lesions in myocardial phantom and myocardial tissue. Higher power and shorter ablations delivering the same amount of microwave energy resulted in larger lesions with less surface sparing. A microwave catheter can be designed to produce a circumferential thermal lesion on noncontact ablation and may have possible applications for pulmonary vein isolation. © 2015 Wiley Periodicals, Inc.

  10. Ablative and transport fractionation of trace elements during laser sampling of glass and copper

    NASA Astrophysics Data System (ADS)

    Outridge, P. M.; Doherty, W.; Gregoire, D. C.

    1997-12-01

    The fractionation of trace elements due to ablation and transport processes was quantified during Q-switched infrared laser sampling of glass and copper reference materials. Filter-trapping of the ablated product at different points in the sample introduction system showed ablation and transport sometimes caused opposing fractionation effects, leading to a confounded measure of overall (ablative + transport) fractionation. An unexpected result was the greater ablative fractionation of some elements (Au, Ag, Bi, Te in glass and Au, Be, Bi, Ni, Te in copper) at a higher laser fluence of 1.35 × 10 4W cm -2 than at 0.62 × 10 4W cm -2, which contradicted predictions from modelling studies of ablation processes. With glass, there was an inverse logarithmic relationship between the extent of ablative and overall fractionation and element oxide melting point (OMPs), with elements with OMPs < 1000° C exhibiting overall concentration increases of 20-1340%. Fractionation during transport was quantitatively important for most certified elements in copper, and for the most volatile elements (Au, Ag, Bi, Te) in glass. Elements common to both matrices showed 50-100% higher ablative fractionation in copper, possibly because of greater heat conductance away from the ablation site causing increased element volatilisation or zone refinement. These differences between matrices indicate that non-matrix-matched standardisation is likely to provide inaccurate calibration of laser ablation inductively coupled plasma-mass spectrometry analyses of at least some elements.

  11. Evaluation of coated columbian alloy heat shields for space shuttle thermal protection system application. Volume 1: Phase 1 - Environmental criteria and material characterization, October 1970 - March 1972

    NASA Technical Reports Server (NTRS)

    Black, W. E.

    1972-01-01

    The studies presented are directed toward establishing criteria for a niobium alloy thermal protection system for the space shuttle. Evaluation of three niobium alloys and two silicon coatings for heat shield configurations culminated in the selection of two coating/substrate combinations for environmental criteria and material characterization tests. Specimens were exposed to boost and reentry temperatures, pressure, and loads simulating a space shuttle orbiter flight profile.

  12. Precision ablation of dental enamel using a subpicosecond pulsed laser.

    PubMed

    Rode, A V; Gamaly, E G; Luther-Davies, B; Taylor, B T; Graessel, M; Dawes, J M; Chan, A; Lowe, R M; Hannaford, P

    2003-12-01

    In this study we report the use of ultra-short-pulsed near-infrared lasers for precision laser ablation of freshly extracted human teeth. The laser wavelength was approximately 800nm, with pulsewidths of 95 and 150fs, and pulse repetition rates of 1kHz. The laser beam was focused to an approximate diameter of 50microm and was scanned over the tooth surface. The rise in the intrapulpal temperature was monitored by embedded thermocouples, and was shown to remain below 5 degrees C when the tooth was air-cooled during laser treatment. The surface preparation of the ablated teeth, observed by optical and electron microscopy, showed no apparent cracking or heat effects, and the hardness and Raman spectra of the laser-treated enamel were not distinguishable from those of native enamel. This study indicates the potential for ultra-short-pulsed lasers to effect precision ablation of dental enamel.

  13. Advanced Multifunctional MMOD Shield: Radiation Shielding Assessment

    NASA Technical Reports Server (NTRS)

    Rojdev, Kristina; Christiansen, Eric

    2013-01-01

    Deep space missions must contend with a harsh radiation environment Impacts to crew and electronics. Need to invest in multifunctionality for spacecraft optimization. MMOD shield. Goals: Increase radiation mitigation potential. Retain overall MMOD shielding performance.

  14. Microwave ablation versus radiofrequency ablation in the kidney: high-power triaxial antennas create larger ablation zones than similarly sized internally cooled electrodes.

    PubMed

    Laeseke, Paul F; Lee, Fred T; Sampson, Lisa A; van der Weide, Daniel W; Brace, Christopher L

    2009-09-01

    To determine whether microwave ablation with high-power triaxial antennas creates significantly larger ablation zones than radiofrequency (RF) ablation with similarly sized internally cooled electrodes. Twenty-eight 12-minute ablations were performed in an in vivo porcine kidney model. RF ablations were performed with a 200-W pulsed generator and either a single 17-gauge cooled electrode (n = 9) or three switched electrodes spaced 1.5 cm apart (n = 7). Microwave ablations were performed with one (n = 7), two (n = 3), or three (n = 2) 17-gauge triaxial antennas to deliver 90 W continuous power per antenna. Multiple antennas were powered simultaneously. Temperatures 1 cm from the applicator were measured during two RF and microwave ablations each. Animals were euthanized after ablation and ablation zone diameter, cross-sectional area, and circularity were measured. Comparisons between groups were performed with use of a mixed-effects model with P values less than .05 indicating statistical significance. No adverse events occurred during the procedures. Three-electrode RF (mean area, 14.7 cm(2)) and single-antenna microwave (mean area, 10.9 cm(2)) ablation zones were significantly larger than single-electrode RF zones (mean area, 5.6 cm(2); P = .001 and P = .0355, respectively). No significant differences were detected between single-antenna microwave and multiple-electrode RF. Ablation zone circularity was similar across groups (P > .05). Tissue temperatures were higher during microwave ablation (maximum temperature of 123 degrees C vs 100 degrees C for RF). Microwave ablation with high-power triaxial antennas created larger ablation zones in normal porcine kidneys than RF ablation with similarly sized applicators.

  15. Ablation mass features in multi-pulses femtosecond laser ablate molybdenum target

    NASA Astrophysics Data System (ADS)

    Zhao, Dongye; Gierse, Niels; Wegner, Julian; Pretzler, Georg; Oelmann, Jannis; Brezinsek, Sebastijan; Liang, Yunfeng; Neubauer, Olaf; Rasinski, Marcin; Linsmeier, Christian; Ding, Hongbin

    2018-03-01

    In this study, the ablation mass features related to reflectivity of bulk Molybdenum (Mo) were investigated by a Ti: Sa 6 fs laser pulse at central wavelength 790 nm. The ablated mass removal was determined using Confocal Microscopy (CM) technique. The surface reflectivity was calibrated and measured by a Lambda 950 spectrophotometer as well as a CCD camera during laser ablation. The ablation mass loss per pulse increase with the increasing of laser shots, meanwhile the surface reflectivity decrease. The multi-pulses (100 shots) ablation threshold of Mo was determined to be 0.15 J/cm2. The incubation coefficient was estimated as 0.835. The reflectivity change of the Mo target surface following multi-pulses laser ablation were studied as a function of laser ablation shots at various laser fluences from 1.07 J/cm2 to 36.23 J/cm2. The results of measured reflectivity indicate that surface reflectivity of Mo target has a significant decline in the first 3-laser pulses at the various fluences. These results are important for developing a quantitative analysis model for laser induced ablation and laser induced breakdown spectroscopy for the first wall diagnosis of EAST tokamak.

  16. Flexible microwave ablation applicator for the treatment of pulmonary malignancies

    NASA Astrophysics Data System (ADS)

    Pfannenstiel, Austin; Keast, Tom; Kramer, Steve; Wibowo, Henky; Prakash, Punit

    2017-02-01

    Microwave ablation (MWA) is an emerging minimally invasive treatment option for malignant lung tumors. Compared to other energy modalities, such as radiofrequency ablation, MWA offers the advantages of deeper penetration within high impedance tissues such as aerated lung, shorter treatment times, and less susceptibility to the cooling heat-sink effects of air and blood flow. Previous studies have demonstrated clinical use of MWA for treating lung tumors; however, these procedures have relied upon the percutaneous application of rigid microwave antennas. The objective of our work was to develop and characterize a novel flexible microwave applicator which could be integrated with a bronchoscopic imaging and software guidance platform to expand the use of MWA as a treatment option for small (< 2cm) pulmonary tumors. This applicator would allow physicians an even less invasive, immediate treatment option for lung tumors identified within the scope of current medical procedures. It may also improve applicator placement accuracy and increase efficacy while minimizing the risk of procedural complications. A 2D-axisymmetric coupled FEM electromagnetic-heat transfer model was implemented to characterize expected antenna radiation patterns, ablation size and shape, and optimize antenna design for lung tissue. A prototype device was fabricated and evaluated in ex vivo tissues to verify simulation results and serve as proof-of-concept. Additional experiments were conducted in an in vivo animal model to further characterize the proposed system.

  17. Structural Design and Thermal Analysis for Thermal Shields of the MICE Coupling Magnets

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Green, Michael A.; Pan, Heng; Liu, X. K.

    2009-07-01

    A superconducting coupling magnet made from copper matrix NbTi conductors operating at 4 K will be used in the Muon Ionization Cooling Experiment (MICE) to produce up to 2.6 T on the magnet centerline to keep the muon beam within the thin RF cavity indows. The coupling magnet is to be cooled by two cryocoolers with a total cooling capacity of 3 W at 4.2 K. In order to keep a certain operating temperature margin, the most important is to reduce the heat leakage imposed on cold surfaces of coil cold mass assembly. An ntermediate temperature shield system placed betweenmore » the coupling coil and warm vacuum chamber is adopted. The shield system consists of upper neck shield, main shields, flexible connections and eight supports, which is to be cooled by the first stage cold heads of two ryocoolers with cooling capacity of 55 W at 60 K each. The maximum temperature difference on the shields should be less than 20 K, so the thermal analyses for the shields with different thicknesses, materials, flexible connections for shields' cooling and structure design for heir supports were carried out. 1100 Al is finally adopted and the maximum temperature difference is around 15 K with 4 mm shield thickness. The paper is to present detailed analyses on the shield system design.« less

  18. Ablation of gold irradiated by femtosecond laser pulse: Experiment and modeling

    NASA Astrophysics Data System (ADS)

    Ashitkov, S. I.; Komarov, P. S.; Zhakhovsky, V. V.; Petrov, Yu V.; Khokhlov, V. A.; Yurkevich, A. A.; Ilnitsky, D. K.; Inogamov, N. A.; Agranat, M. B.

    2016-11-01

    We report on the ablation phenomena in gold sample irradiated by femtosecond laser pulses of moderate intensity. Dynamics of optical constants and expansion of a heated surface layer was investigated in a range from picosecond up to subnanosecond using ultrafast interferometry. Also morphology of the ablation craters and value of an ablation threshold (for absorbed fluence) were measured. The experimental data are compared with simulations of mass flows obtained by two-temperature hydrodynamics and molecular dynamics methods. Simulation shows evolution of a thin surface layer pressurized by a laser pulse. Unloading of the pressurized layer proceeds together with electron-ion thermalization, melting, cavitation and spallation of a part of surface liquid layer. The experimental and simulation results on two-temperature physics and on a fracture, surface morphology and strength of liquid gold at a strain rate ∼ 109 s-1 are discussed.

  19. Split-core heat-pipe reactors for out-of-pile thermionic power systems.

    NASA Technical Reports Server (NTRS)

    Niederauer, G.; Lantz, E.; Breitweiser, R.

    1971-01-01

    Description of the concept of splitting a heat-pipe reactor for out-of-core thermionics into two identical halves and using the resulting center gap for reactivity control. Short Li-W reactor heat pipes penetrate the axial reflectors and form a heat exchanger with long heat pipes which wind through the shield to the thermionic diodes. With one reactor half anchored to the shield, the other is attached to a long arm with a pivot behind the shield and swings through a small arc for reactivity control. A safety shim prevents large reactivity inputs, and a fueled control arm drive shaft acts as a power stabilizer. Reactors fueled with U-235C and with U-233C have been studied.-

  20. Global ablation techniques.

    PubMed

    Woods, Sarah; Taylor, Betsy

    2013-12-01

    Global endometrial ablation techniques are a relatively new surgical technology for the treatment of heavy menstrual bleeding that can now be used even in an outpatient clinic setting. A comparison of global ablation versus earlier ablation technologies notes no significant differences in success rates and some improvement in patient satisfaction. The advantages of the newer global endometrial ablation systems include less operative time, improved recovery time, and decreased anesthetic risk. Ablation procedures performed in an outpatient surgical or clinic setting provide advantages both of potential cost savings for patients and the health care system and improved patient convenience. Copyright © 2013. Published by Elsevier Inc.