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Sample records for jet impingement cooling

  1. Comparison of burnout characteristics in jet impingement cooling and stray cooling

    NASA Astrophysics Data System (ADS)

    Cho, C. S. K.; Wu, K.

    Characteristics of spray cooling and jet impingement methods were investigated. The jet impingement cooling method created a large dry area on the test surface when the burnout heat flux was approached. In the spray cooling method, a liquid film with nucleate boiling was maintained for the entire experiment until a burnout was occurred. The spray cooling method produced a higher burnout heat flux than the jet impingement cooling method for the same liquid flow rate. In the spray cooling method, sprayed droplet velocity was a parameter for determining the burnout heat flux. The burnout heat flux in jet impingement cooling also showed dependency on the liquid jet velocity. Results of two methods for cooling the surface area were compared and correlated with the Weber number.

  2. Rewetting of hot vertical rod during jet impingement surface cooling

    NASA Astrophysics Data System (ADS)

    Agrawal, Chitranjan; Kumar, Ravi; Gupta, Akhilesh; Chatterjee, Barun

    2016-06-01

    A stainless steel (SS-316) vertical rod of 12 mm diameter at 800 ± 10 °C initial temperature was cooled by normal impinging round water jet. The surface rewetting phenomenon was investigated for a range of jet diameter 2.5-4.8 mm and jet Reynolds number 5000-24,000 using a straight tube type nozzle. The investigation were made from the stagnation point to maximum 40 mm downstream locations, simultaneously for both upside and downside directions. The cooling performance of the vertical rod was evaluated on the basis of rewetting parameters i.e. rewetting temperature, wetting delay, rewetting velocity and the maximum surface heat flux. Two separate Correlations have been proposed for the dimensionless rewetting velocity in terms of rewetting number and the maximum surface heat flux that predicts the experimental data within an error band of ±20 and ±15 % respectively.

  3. Modeling Single-Phase and Boiling Liquid Jet Impingement Cooling in Power Electronics

    SciTech Connect

    Narumanchi, S. V. J.; Hassani, V.; Bharathan, D.

    2005-12-01

    Jet impingement has been an attractive cooling option in a number of industries over the past few decades. Over the past 15 years, jet impingement has been explored as a cooling option in microelectronics. Recently, interest has been expressed by the automotive industry in exploring jet impingement for cooling power electronics components. This technical report explores, from a modeling perspective, both single-phase and boiling jet impingement cooling in power electronics, primarily from a heat transfer viewpoint. The discussion is from the viewpoint of the cooling of IGBTs (insulated-gate bipolar transistors), which are found in hybrid automobile inverters.

  4. Unsteady conjugate heat transfer analysis for impinging jet cooling

    NASA Astrophysics Data System (ADS)

    Tejero, F.; Flaszyński, P.; Szwaba, R.; Telega, J.

    2016-10-01

    The paper presents the numerical investigations of the heat transfer on a flat plate cooled by a single impinging jet. The thermal conductivity of the plate was modified from a high thermal case (steel -λ= 35 W/m/K) to a low one (steel alloy Inconel -λ= 9.8 W/m/K). The numerical simulations results are compared with the experimental data from the Institute of Fluid-Flow Machinery Polish Academy of Sciences, Gdansk (Poland). The numerical simulations are carried out by means of Ansys/Fluent and k-ω SST turbulence model and the temperature evolution on the target plate is investigated by conjugated heat transfer computations.

  5. Jet Impingement and Forced Convection Cooling Experimental Study in Rotating Turbine Blades

    NASA Astrophysics Data System (ADS)

    Li, Hsin-Lung; Chiang, Hsiao-Wei D.; Hsu, Chih-Neng

    2011-06-01

    Both jet impingement and forced convection are attractive cooling mechanisms widely used in cooling gas turbine blades. Convective heat transfer from impinging jets is known to yield high local and area averaged heat transfer coefficients. Impingement jets are of particular interest in the cooling of gas turbine components where advancement relies on the ability to dissipate extremely large heat loads. Current research is concerned with the measurement and comparison of both jet impingement and forced convection heat transfer in the Reynolds number range of 10,000 to 30,000. This study is aimed at experimentally testing two different setups with forced convection and jet impingement in rotating turbine blades up to 700 RPM. This research also observes Coriolis force and impingement cooling inside the passage during rotating conditions within a cooling passage. Local heat transfer coefficients are obtained for each test section using thermocouple technique with slip rings. The cross section of the passage is 10 mm × 10 mm without ribs and the surface heating condition has enforced uniform heat flux. The forced convection cooling effects were studied using serpentine passages with three corner turns under different rotating speeds and different inlet Reynolds numbers. The impingement cooling study uses a straight passage with a single jet hole under different Reynolds numbers of the impingement flow and the cross flow. In summary, the main purpose is to study the rotation effects on both the jet impingement and the serpentine convection cooling types. Our study shows that rotation effects increase serpentine cooling and reduce jet impingement cooling.

  6. Modular jet impingement assemblies with passive and active flow control for electronics cooling

    DOEpatents

    Zhou, Feng; Dede, Ercan Mehmet; Joshi, Shailesh

    2016-09-13

    Power electronics modules having modular jet impingement assembly utilized to cool heat generating devices are disclosed. The modular jet impingement assemblies include a modular manifold having a distribution recess, one or more angled inlet connection tubes positioned at an inlet end of the modular manifold that fluidly couple the inlet tube to the distribution recess and one or more outlet connection tubes positioned at an outlet end of the modular manifold that fluidly coupling the outlet tube to the distribution recess. The modular jet impingement assemblies include a manifold insert removably positioned within the distribution recess and include one or more inlet branch channels each including an impinging slot and one or more outlet branch channels each including a collecting slot. Further a heat transfer plate coupled to the modular manifold, the heat transfer plate comprising an impingement surface including an array of fins that extend toward the manifold insert.

  7. Traction Drive Inverter Cooling with Submerged Liquid Jet Impingement on Microfinned Enhanced Surfaces (Presentation)

    SciTech Connect

    Waye, S.; Narumanchi, S.; Moreno, G.

    2014-09-01

    Jet impingement is one means to improve thermal management for power electronics in electric-drive traction vehicles. Jet impingement on microfin-enhanced surfaces further augments heat transfer and thermal performance. A channel flow heat exchanger from a commercial inverter was characterized as a baseline system for comparison with two new prototype designs using liquid jet impingement on plain and microfinned enhanced surfaces. The submerged jets can target areas with the highest heat flux to provide local cooling, such as areas under insulated-gate bipolar transistors and diode devices. Low power experiments, where four diodes were powered, dissipated 105 W of heat and were used to validate computational fluid dynamics modeling of the baseline and prototype designs. Experiments and modeling used typical automotive flow rates using water-ethylene glycol as a coolant (50%-50% by volume). The computational fluid dynamics model was used to predict full inverter power heat dissipation. The channel flow and jet impingement configurations were tested at full inverter power of 40 to 100 kW (output power) on a dynamometer, translating to an approximate heat dissipation of 1 to 2 kW. With jet impingement, the cold plate material is not critical for the thermal pathway. A high-temperature plastic was used that could eventually be injection molded or formed, with the jets formed from a basic aluminum plate with orifices acting as nozzles. Long-term reliability of the jet nozzles and impingement on enhanced surfaces was examined. For jet impingement on microfinned surfaces, thermal performance increased 17%. Along with a weight reduction of approximately 3 kg, the specific power (kW/kg) increased by 36%, with an increase in power density (kW/L) of 12% compared with the baseline channel flow configuration.

  8. Two dimensional impinging jet cooling of high heat flux surface in magnetic confinement fusion reactor

    SciTech Connect

    Inoue, A.; Tanno, T.; Takahashi, M.

    1994-12-31

    Divertor surface of a magnetic confinement fusion reactor is exposed to strong radiation heating by high flux charged particles. According to standard design of the ITER, the heat flux of the divertor surface becomes average 15MW/m{sup 2} or more. In this study, a cooling by a two dimensional impinging jet flow is proposed to cool such high heat flux surface. For an impinging jet flow to flat heated surface, such as CHF is obtained only in the limited surface region where the jet flow hits directly. Apart from the region, the CHF decreases abruptly with the distance from the center. The main reason is that the pressure decreases abruptly as apart from the center region and the liquid flow is spread away from the heated surface region by the strong boiling. To overcome these difficulties, the authors propose that the impinging jet is applied to the heat transfer wall with a concave surface, because the pressure change becomes mild by the centrifugal force along the curved surface. The increase of the radial pressure gradient in the vertical direction to the curved surface promotes the departure of vapor bubbles near the wall region. It is expected that this mechanism as well as keeping high pressure along the flow works to enhance the CHF. To obtain the high heat flux in the wide region, a use of a two-dimensional impinging jet is suitable instead of a round jet.

  9. Numerical simulation of transient cooling of a hot solid by an impinging free surface jet

    SciTech Connect

    Fujimoto, Hitoshi; Takuda, Hirohiko; Hatta, Natsuo; Viskanta, R.

    1999-12-01

    In iron- and steel-making industries, jet impingement is widely used to cool hot strips and slabs. In the hot rolling process a hot strip passing through the finishing rolls is cooled along a runout table from an austenitic finishing temperature to a coiling temperature by means of impinging water jets. The upper surface of the strip is cooled by impingement of water sheets or bars, and the lower surface is cooled by water sprays. This paper treats transient cooling of a hot solid by an impinging circular free surface liquid jet. The flow and thermal fields in the liquid as well as the temperature distributions in the hot solid have been predicted numerically. The Navier-Stokes equations for incompressible fluid flow in an axisymmetric coordinate system and the transient heat conduction equation for a solid have been solved by a finite difference method. The hydrodynamics of the liquid film and the heat transfer processes have been investigated to understand the physics of the phenomena.

  10. Transient cooling of a hot metal plate with an impinging water jet

    SciTech Connect

    Kumagai, Satoshi; Suzuki, Shinju; Kubo, Ryo; Kawazoe, Masataka

    1995-12-31

    Transient boiling heat-transfer rate of a two-dimensional impinging water jet was measured throughout the surface of a 20 x 150 mm rectangle, during cooling from approximately 400 C to 100 C. Time-dependent surface-temperature distributions and the progress of a solid-liquid contact front were obtained for jet subcooling from 14 K to 50 K. Solid-liquid contact at the stagnation line starts from the moment of jet impingement, where violent boiling occurs and generated vapor splashes the water film; this results in deprivation of water supply to the outer region of the surface. The temperature of the outer surface remains high up to the time when the solid-liquid contact front reaches it and a large temperature gradient appears near the front. The surface temperature for the initiation of solid-liquid contact is higher at locations nearer the stagnation line and with higher jet subcooling.

  11. Advanced Liquid Cooling for a Traction Drive Inverter Using Jet Impingement and Microfinned Enhanced Surfaces: Preprint

    SciTech Connect

    Waye, S. K.; Narumanchi, S.; Mihalic, M.; Moreno, G.; Bennion, K.; Jeffers, J.

    2014-08-01

    Jet impingement on plain and micro-finned enhanced surfaces was compared to a traditional channel flow configuration. The jets provide localized cooling to areas heated by the insulated-gate bipolar transistor and diode devices. Enhanced microfinned surfaces increase surface area and thermal performance. Using lighter materials and designing the fluid path to manage pressure losses increases overall performance while reducing weight, volume, and cost. Powering four diodes in the center power module of the inverter and computational fluid dynamics (CFD) modeling was used to characterize the baseline as well as jet-impingement-based heat exchangers. CFD modeling showed the thermal performance improvements should hold for a fully powered inverter. Increased thermal performance was observed for the jet-impingement configurations when tested at full inverter power (40 to 100 kW output power) on a dynamometer. The reliability of the jets and enhanced surfaces over time was also investigated. Experimentally, the junction-to- coolant thermal resistance was reduced by up to 12.5% for jet impingement on enhanced surfaces s compared to the baseline channel flow configuration. Base plate-to-coolant (convective) resistance was reduced by up to 37.0% for the jet-based configuration compared to the baseline, suggesting that while improvements to the cooling side reduce overall resistance, reducing the passive stack resistance may contribute to lowering overall junction-to-coolant resistance. Full inverter power testing showed reduced thermal resistance from the middle of the module baseplate to coolant of up to 16.5%. Between the improvement in thermal performance and pumping power, the coefficient of performance improved by up to 13% for the jet-based configuration.

  12. Correlating equations for impingement cooling of small heat sources with multiple circular liquid jets

    NASA Astrophysics Data System (ADS)

    Womac, D. J.; Incropera, F. P.; Ramadhyani, S.

    1994-05-01

    Experiments were performed to investigate single-phase heat transfer from a 12.7 mm x 12.7 mm heat source to 2 x 2 and 3 x 3 arrays of free-surface and submerged jets. The objective was to study the efficacy of using arrays of free surface or submerged liquid jets to cool a small, chip-like heat source. The data are correlated by obtaining area-weighted combinations of separate correlations associated with impingement and wall jet region.

  13. Liquid jet impingement cooling with diamond substrates for extremely high heat flux applications

    SciTech Connect

    Lienhard, J.H. V; Khounsary, A.M.

    1993-09-01

    The combination of impinging jets and diamond substrates may provide an effective solution to a class of extremely high heat flux problems in which very localized heat loads must be removed. Some potential applications include the cooling of high-heat-load components in synchrotron x-ray, fusion, and semiconductor laser systems. Impinging liquid jets are a very effective vehicle for removing high heat fluxes. The liquid supply arrangement is relatively simple, and low thermal resistances can be routinely achieved. A jet`s cooling ability is a strong function of the size of the cooled area relative to the jet diameter. For relatively large area targets, the critical heat fluxes can approach 20 W/mm{sup 2}. In this situation, burnout usually originates at the outer edge of the cooled region as increasing heat flux inhibits the liquid supply. Limitations from liquid supply are minimized when heating is restricted to the jet stagnation zone. The high stagnation pressure and high velocity gradients appear to suppress critical flux phenomena, and fluxes of up to 400 W/mm{sup 2} have been reached without evidence of burnout. Instead, the restrictions on heat flux are closely related to properties of the cooled target. Target properties become an issue owing to the large temperatures and large temperature gradients that accompany heat fluxes over 100 W/mm{sup 2}. These conditions necessitate a target with both high thermal conductivity to prevent excessive temperatures and good mechanical properties to prevent mechanical failures. Recent developments in synthetic diamond technology present a possible solution to some of the solid-side constraints on heat flux. Polycrystalline diamond foils can now be produced by chemical vapor deposition in reasonable quantity and at reasonable cost. Synthetic single crystal diamonds as large as 1 cm{sup 2} are also available.

  14. Effect of surface thickness on the wetting front velocity during jet impingement surface cooling

    NASA Astrophysics Data System (ADS)

    Agrawal, Chitranjan; Gotherwal, Deepesh; Singh, Chandradeep; Singh, Charan

    2017-02-01

    A hot stainless steel (SS-304) surface of 450 ± 10 °C initial temperature is cooled with a normally impinging round water jet. The experiments have been performed for the surface of different thickness e.g. 1, 2, 3 mm and jet Reynolds number in the range of Re = 26,500-48,000. The cooling performance of the hot test surface is evaluated on the basis of wetting front velocity. The wetting front velocity is determined for 10-40 mm downstream spatial locations away from the stagnation point. It has been observed that the wetting front velocity increase with the rise in jet flow rate, however, diminishes towards the downstream spatial location and with the rise in surface thickness. The proposed correlation for the dimensionless wetting front velocity predicts the experimental data well within the error band of ±30 %, whereas, 75 % of experimental data lies within the range of ±20 %.

  15. High heat flux accelerator targets cooling with liquid-metal jet impingement

    NASA Astrophysics Data System (ADS)

    Silverman, I.; Arenshtam, A.; Kijel, D.; Nagler, A.

    2005-12-01

    Accelerator targets for radioisotope production generate very high density of thermal energy in the target material, which absorbs the particles beam. The design of these targets requires efficient heat removal techniques in order to preserve the integrity of the target. Normal average heat fluxes from these targets are around 1 kW/cm2 and may reach order of magnitude higher values at hot spots. Few techniques exist to deal with such high heat fluxes. One of them is jet impingement that has been proved to be able to deal with heat fluxes as high as 40 kW/cm2 using water as coolant. However, this requires very high jet velocities of more than 100 m/s. A few theoretical and experimental studies indicate that liquid-metal coolants (e.g., gallium or gallium alloys) can improve the heat transfer efficiency in this configuration. Experimental cooling loops based on water and liquid-metal jet impingement have been designed and built at Soreq to evaluate this method. For the current liquid-metal system an eutectic alloy of gallium and indium (GaIn) is used. Initial experiments demonstrate that the GaIn cooling system can deal with heat flux of about 2 kW/cm2 over an area of 1 cm2. The jet velocity is less than 4 m/s and the required differential pressure from the pump is less than 1 bar.

  16. Large Eddy Simulation of a cooling impinging jet to a turbulent crossflow

    NASA Astrophysics Data System (ADS)

    Georgiou, Michail; Papalexandris, Miltiadis

    2015-11-01

    In this talk we report on Large Eddy Simulations of a cooling impinging jet to a turbulent channel flow. The impinging jet enters the turbulent stream in an oblique direction. This type of flow is relevant to the so-called ``Pressurized Thermal Shock'' phenomenon that can occur in pressurized water reactors. First we elaborate on issues related to the set-up of the simulations of the flow of interest such as, imposition of turbulent inflows, choice of subgrid-scale model and others. Also, the issue of the commutator error due to the anisotropy of the spatial cut-off filter induced by non-uniform grids is being discussed. In the second part of the talk we present results of our simulations. In particular, we focus on the high-shear and recirculation zones that are developed and on the characteristics of the temperature field. The budget for the mean kinetic energy of the resolved-scale turbulent velocity fluctuations is also discussed and analyzed. Financial support has been provided by Bel V, a subsidiary of the Federal Agency for Nuclear Control of Belgium.

  17. SiO2 nanofluid planar jet impingement cooling on a convex heated plate

    NASA Astrophysics Data System (ADS)

    Asghari Lafmajani, Neda; Ebrahimi Bidhendi, Mahsa; Ashjaee, Mehdi

    2016-12-01

    The main objective of this paper is to investigate the heat transfer coefficient of a planar jet of SiO2 nanofluid that impinges vertically on the middle of a convex heated plate for cooling purposes. The planar jet issues from a rectangular slot nozzle. The convex aluminum plate has a thickness, width and length of 0.2, 40 and 130 mm, respectively, and is bent with a radius of 200 mm. A constant heat-flux condition is employed. 7 nm SiO2 particles are added to water to prepare the nanofluid with 0.1, 1 and 2 % (ml SiO2/ml H2O) concentrations. The tests are also performed at different Reynolds numbers from 1803 to 2782. Results indicate that adding the SiO2 nanoparticles can effectively increase both local and average heat transfer coefficients up to 39.37 and 32.78 %, respectively. These positive effects often are more pronounced with increasing Reynolds numbers. This enhancement increases with ascending the concentration of nanofluid, especially from 0.1 to 1 %.

  18. Use of thermochromic liquid crystals in the study of jet impingement cooling: Sensitivity of transient heating methods

    SciTech Connect

    Owens, R.; Liburdy, J.A.

    1995-12-31

    In the cooling of surfaces jet impingement arrays have been found to provide effective surface heat transfer. Considerable work has been doe in identifying the optimal jet array geometry, including jet diameter, spacing and relative distance to the surface to be cooled. Most all of these studies rely on surface averaged heat transfer results. However, there are applications where the local distribution of the impingement heat transfer is important. The magnitude of the local variations may cause serious problems in terms of surface temperature gradients. Thermochromic liquid crystals provide a means to directly measure the surface temperature which can be used to study the local heat transfer coefficient distribution. Both steady state and transient methods have been identified. The steady state method is a direct application of Newton`s Law of Cooling. The transient method establishes a step change in the surface boundary condition and solves the conduction problem in the surface substrate. This method can have advantages of lower experimental uncertainty. However, there are practical issues of time response that need to be addressed to determine actual local heat transfer coefficient. This paper addresses the issues associated with the transient method and provides results of impingement cooling. Of primary concern is the transient response and how that is related to the actual instantaneous convective condition at the surface. Results show a non-steady convective coefficient which must be corrected based on the experimental design parameters.

  19. Use of thermochromatic liquid crystals in the study of jet impingement cooling: sensitivity of transient heating methods

    NASA Astrophysics Data System (ADS)

    Owens, Robin; Liburdy, James A.

    1995-09-01

    In the cooling of surfaces jet impingement arrays have been found to provide effective surface heat transfer. Considerable work has been done in identifying the optimal jet array geometry, including jet diameter, spacing and relative distance to the surface to be cooled. Most all of these studies rely on surface averaged heat transfer results. However, there are applications where the local distribution of the impingement heat transfer is important. The magnitude of the local variations may cause serious problems in terms of surface temperature gradients. Thermochromic liquid crystals provide a means to directly measure the surface temperature which can be used to study the local heat transfer coefficient distribution. Both steady state and transient methods have been identified. The steady state method is a direct application of Newton's Law of Cooling. The transient method establishes a step change in the surface boundary condition and solves the conduction problem in the surface substrate. This method can have advantages of lower experimental uncertainty. However, there are practical issues of time response that need to be addressed to determine actual local heat transfer coefficient. This paper addresses the issues associated with the transient method and provides results of impingement cooling. Of primary concern is the transient response and how that is related to the actual instantaneous convective condition at the surface. Results show a nonsteady convective coefficient which must be corrected based on the experimental design parameters.

  20. Analysis of liquid-metal-jet impingement cooling in a corner region and for a row of jets

    NASA Technical Reports Server (NTRS)

    Siegel, R.

    1975-01-01

    A conformal mapping method was used to analyze liquid-metal-jet impingement heat transfer. The jet flow region and energy equation are transformed to correspond to uniform flow in a parallel plate channel with nonuniform heat addition along a portion of one wall. The exact solution for the wall-temperature distribution was obtained in the transformed channel, and the results are mapped back into the physical plane. Two geometries are analyzed. One is for a single slot jet directed either into an interior corner formed by two flat plates, or over the external sides of the corner; the flat plates are uniformly heated, and the corner can have various included angles. The heat-transfer coefficient at the stagnation point at the apex of the plates is obtained as a function of the corner angle, and temperature distributions are calculated along the heated walls. The second geometry is an infinite row of uniformly spaced parallel slot jets impinging normally against a uniformly heated plate. The heat-transfer behavior is obtained as a function of the spacing between the jets. Results are given for several jet Peclet numbers from 5 to 50.

  1. Design Of A Hybrid Jet Impingement / Microchannel Cooling Device For Densely Packed PV Cells Under High Concentration

    NASA Astrophysics Data System (ADS)

    Barrau, Jérôme; Rosell, Joan; Ibañez, Manel

    2010-10-01

    A hybrid jet impingement / microchannel cooling scheme was designed and applied to densely packed PV cells under high concentration. An experimental study allows validating the principles of the design and confirming its applicability to the cited system. In order to study the characteristics of the device in a wide range of conditions, a numerical model was developed and experimentally validated. The results allow evaluating the contributions of the cooling device to the performances of densely packed PV cells under high concentration. The main advantages of the system are related to its compactness, its good capacity of heat extraction associated to relatively low pressure losses and its capability to improve the temperature uniformity of the PV receiver with respect to other cooling schemes. These features improve the net electric output of the whole system and its reliability.

  2. Additions to compact heat exchanger technology: Jet impingement cooling & flow & heat transfer in metal foam-fins

    NASA Astrophysics Data System (ADS)

    Onstad, Andrew J.

    Compact heat exchangers have been designed following the same basic methodology for over fifty years. However, with the present emphasis on energy efficiency and light weight of prime movers there is increasing demand for completely new heat exchangers. Moreover, new materials and mesoscale fabrication technologies offer the possibility of significantly improving heat exchanger performance over conventional designs. This work involves fundamental flow and heat transfer experimentation to explore two new heat exchange systems: in Part I, large arrays of impinging jets with local extraction and in Part II, metal foams used as fins. Jet impingement cooling is widely used in applications ranging from paper manufacturing to the cooling of gas turbine blades because of the very high local heat transfer coefficients that are possible. While the use of single jet impingement results in non-uniform cooling, increased and more uniform mean heat transfer coefficients may be attained by dividing the total cooling flow among an array of smaller jets. Unfortunately, when the spent fluid from the array's central jets interact with the outer jets, the overall mean heat transfer coefficient is reduced. This problem can be alleviated by locally extracting the spent fluid before it is able to interact with the surrounding jets. An experimental investigation was carried out on a compact impingement array (Xn/Djet = 2.34) utilizing local extraction of the spent fluid (Aspent/Ajet = 2.23) from the jet exit plane. Spatially resolved measurements of the mean velocity field within the array were carried out at jet Reynolds numbers of 2300 and 5300 by magnetic resonance velocimetry, MRV. The geometry provided for a smooth transition from the jet to the target surface and out through the extraction holes without obvious flow recirculation. Mean Nusselt number measurements were also carried out for a Reynolds number range of 2000 to 10,000. The Nusselt number was found to increase with the

  3. Rotational effects on impingement cooling

    NASA Technical Reports Server (NTRS)

    Epstein, A. H.; Kerrebrock, J. L.; Koo, J. J.; Preiser, U. Z.

    1987-01-01

    The present consideration of rotation effects on heat transfer in a radially exhausted, impingement-cooled turbine blade model gives attention to experimental results for Reynolds and Rossby numbers and blade/coolant temperature ratio values that are representative of small gas turbine engines. On the basis of a model that encompasses the effects of Coriolis force and buoyancy on heat transfer, bouyancy is identified as the cause of an average Nusselt number that is 20-30 percent lower than expected from previous nonrotating data. A heuristic model is proposed which predicts that the impingement jets nearest the blade roots should deflect inward, due to a centripetal force generated by their tangential velocity counter to the blade motion. Potentially serious thermal stresses must be anticipated from rotation effects in the course of blade design.

  4. Rotational effects on impingement cooling

    NASA Astrophysics Data System (ADS)

    Epstein, A. H.; Kerrebrock, J. L.; Koo, J. J.; Preiser, U. Z.

    The present consideration of rotation effects on heat transfer in a radially exhausted, impingement-cooled turbine blade model gives attention to experimental results for Reynolds and Rossby numbers and blade/coolant temperature ratio values that are representative of small gas turbine engines. On the basis of a model that encompasses the effects of Coriolis force and buoyancy on heat transfer, bouyancy is identified as the cause of an average Nusselt number that is 20-30 percent lower than expected from previous nonrotating data. A heuristic model is proposed which predicts that the impingement jets nearest the blade roots should deflect inward, due to a centripetal force generated by their tangential velocity counter to the blade motion. Potentially serious thermal stresses must be anticipated from rotation effects in the course of blade design.

  5. Enhancement of Nucleate Boiling Heat Flux on Macro/Micro-Structured Surfaces Cooled by Multiple Impinging Jets

    NASA Technical Reports Server (NTRS)

    Kugler, Scott Lee

    1997-01-01

    An experimental investigation of nucleate boiling heat transfer from modified surfaces cooled by multiple in-line impinging circular jets is reported and found to agree with single jet results. A copper block is heated from the back by two electrical arcs, and cooled on the opposite side by three identical liquid jets of distilled water at subcoolings of 25 C 50 C and 77 C and Freon 113 at 24 C subcooling. Liquid flow rates are held constant at 5, 10, and 15 GPH for each of the three jets with jet velocities ranging from 1.4 m/s to 1 1.2 m/s and jet diameters from 0.95 mm to 2.2 mm. To increase the maximum heat flux (CHF) and heat removal rate, the boiling surface was modified by both macro and micro enhancements. Macro modification consists of machined radial grooves in the boiling surface arranged in an optimally designed pattern to allow better liquid distribution along the surface. These grooves also reduce splashing of liquid droplets, and provide 'channels' to sweep away bubbles. Micro modification was achieved by flame spraying metal powder on the boiling surface, creating a porous, sintered surface. With the addition of both micro and macro structured enhancements, maximum heat flux and nucleate boiling can be enhanced by more than 200%. Examination of each surface modification separately and together indicates that at lower superheats, the micro structure provides the enhanced heat transfer by providing more nucleation sites, while for higher superheats the macro structure allows better liquid distribution and bubble removal. A correlation is presented to account for liquid subcoolings and surface enhancements, in addition to the geometrical and fluid properties previously reported in the literature.

  6. Impinging jets atomization

    NASA Technical Reports Server (NTRS)

    Ibrahim, E. A.; Przekwas, A. J.

    1991-01-01

    An analysis of the characteristics of the spray produced by an impinging-jet injector is presented. Predictions of the spray droplet size and distribution are obtained through studying the formation and disintegration of the liquid sheet formed by the impact of two cylindrical jets of the same diameter and momentum. Two breakup regimes of the sheet are considered depending on Weber number, with transition occurring at Weber numbers between 500 and 2000. In the lower Weber number regime, the breakup is due to Taylor cardioidal waves, while at Weber number higher than 2000, the sheet disintegration is by the growth of Kelvin-Helmholtz instability waves. Theoretical expressions to predict the sheet thickness and shape are derived for the low Weber number breakup regime. An existing mathematical analysis of Kelvin-Helmholtz instability of radially moving liquid sheets is adopted in the predictions of resultant drop sizes by sheet breakup at Weber numbers greater than 2000. Comparisons of present theoretical results with experimental measurements and empirical correlations reported in the literature reveal favorable agreement.

  7. Regeneratively cooled transition duct with transversely buffered impingement nozzles

    DOEpatents

    Morrison, Jay A; Lee, Ching-Pang; Crawford, Michael E

    2015-04-21

    A cooling arrangement (56) having: a duct (30) configured to receive hot gases (16) from a combustor; and a flow sleeve (50) surrounding the duct and defining a cooling plenum (52) there between, wherein the flow sleeve is configured to form impingement cooling jets (70) emanating from dimples (82) in the flow sleeve effective to predominately cool the duct in an impingement cooling zone (60), and wherein the flow sleeve defines a convection cooling zone (64) effective to cool the duct solely via a cross-flow (76), the cross-flow comprising cooling fluid (72) exhausting from the impingement cooling zone. In the impingement cooling zone an undimpled portion (84) of the flow sleeve tapers away from the duct as the undimpled portion nears the convection cooling zone. The flow sleeve is configured to effect a greater velocity of the cross-flow in the convection cooling zone than in the impingement cooling zone.

  8. Theoretical model for high-power diamond laser optics using high-velocity liquid-metal jet impingement cooling

    NASA Astrophysics Data System (ADS)

    Palmer, James R.

    1993-02-01

    In 1988 I presented a paper, `Fly's Eye Modular Optic,' in the Los Angeles Symposium that described an optic for high power laser systems that provided for a modular system of hexagonal components that were independently cooled using a high velocity jet pointed normal to the back surface of the optical faceplate. In this paper we look at the use of diamond optical materials in concert with high velocity jet impingement heat transfer of various liquid metal mediums. By using this combination of techniques and materials we can push the laser damage threshold of optical components to even higher levels of absorbed flux density. The thrust of this paper is to develop a theoretical model for use on optical elements subject to very high continuous flux density lasers and to evaluate the use of commercial diamond substrates with conventional optical thin films and conventional substrates with CVD diamond films. In order to assume the very high absorbed flux densities, it is necessary to have a heat transfer technique capable of maintaining the optical component at a stable temperature and below the damage threshold of the optical materials. For the more common materials, thermal shock and subsequent failure in bi-axial shear have proven to be one of the major constituents of the optical damage. In this paper we look at the thermal shock, vis-a-vis, the melting point of some of the materials.

  9. Liquid jet impingement cooling with diamond substrates for extremely high heat flux applications

    NASA Astrophysics Data System (ADS)

    Lienhard V, John H.; Khounsary, Ali M.

    1993-11-01

    This paper considers the potential of jet/diamond systems for removing localized high heat fluxes. Diamond substrates are compared to other candidate materials. Limits on usable thermal resistances and heat transfer rates are estimated.

  10. Liquid jet impingement heat transfer with or without boiling

    NASA Astrophysics Data System (ADS)

    Ma, C. F.; Gan, Y. P.; Tian, Y. C.; Lei, D. H.; Gomi, T.

    1993-03-01

    The purpose of this paper is to summarize the important studies in the area of impingement heat transfer with or without phase change, with emphasis on the research conducted at Beijing Polytechnic University mainly with circular jets. Heat transfer characteristics of single phase jets are discussed in detail. Comment is presented on boiling heat transfer of impinging jets for steady and transient states. Some special cooling configurations of two-phase jets are also introduced.

  11. Jet array impingement flow distributions and heat transfer characteristics. Effects of initial crossflow and nonuniform array geometry. [gas turbine engine component cooling

    NASA Technical Reports Server (NTRS)

    Florschuetz, L. W.; Metzger, D. E.; Su, C. C.; Isoda, Y.; Tseng, H. H.

    1982-01-01

    Two-dimensional arrays of circular air jets impinging on a heat transfer surface parallel to the jet orifice plate are considered. The jet flow, after impingement, is constrained to exit in a single direction along the channel formed by the jet orifice plate and the heat transfer surface. The configurations considered are intended to model those of interest in current and contemplated gas turbine airfoil midchord cooling applications. The effects of an initial crossflow which approaches the array through an upstream extension of the channel are considered. Flow distributions as well as heat transfer coefficients and adiabatic wall temperatures resolved to one streamwise hole spacing were measured as a function of the initial crossflow rate and temperature relative to the jet flow rate and temperature. Both Nusselt number profiles and dimensionless adiabatic wall temperature (effectiveness) profiles are presented and discussed. Special test results which show a significant reduction of jet orifice discharge coefficients owing to the effect of a confined crossflow are also presented, along with a flow distribution model which incorporates those effects. A nonuniform array flow distribution model is developed and validated.

  12. Modelling techniques for jet impingement

    NASA Technical Reports Server (NTRS)

    Haviland, J. K.; Herling, W. W.

    1977-01-01

    A technique for testing scale models for the determination of fluctuating pressure loads due to jet impingement has been investigated using a quarter-scale model of a boilerplate test facility in which a JT-15D engine with a rectangular outer nozzle blows over a small curved airfoil representing the upper-surface of a wing. When model and full-scale spectra of fluctuating surface pressures are reduced to plots of pressure coefficient power-spectral density vs Strouhal number, moderate agreement is obtained, but a shift of spectral peaks is noted. However, when a correction for the ratio of average jet to ambient temperature is applied, the spectral peaks agree.

  13. Nanofluid impingement jet heat transfer

    PubMed Central

    2012-01-01

    Experimental investigation to study the heat transfer between a vertical round alumina-water nanofluid jet and a horizontal circular round surface is carried out. Different jet flow rates, jet nozzle diameters, various circular disk diameters and three nanoparticles concentrations (0, 6.6 and 10%, respectively) are used. The experimental results indicate that using nanofluid as a heat transfer carrier can enhance the heat transfer process. For the same Reynolds number, the experimental data show an increase in the Nusselt numbers as the nanoparticle concentration increases. Size of heating disk diameters shows reverse effect on heat transfer. It is also found that presenting the data in terms of Reynolds number at impingement jet diameter can take into account on both effects of jet heights and nozzle diameter. Presenting the data in terms of Peclet numbers, at fixed impingement nozzle diameter, makes the data less sensitive to the percentage change of the nanoparticle concentrations. Finally, general heat transfer correlation is obtained verses Peclet numbers using nanoparticle concentrations and the nozzle diameter ratio as parameters. PMID:22340669

  14. Experimental simulation of impingement cooling in midchord region of turbine blade

    NASA Astrophysics Data System (ADS)

    Li, Liguo; Jiang, Jun; Chang, Haiping; Zhang, Donglia

    1989-10-01

    Simulation experiments have been completed to research the characteristics of impingement cooling in the midchord region of a turbine blade for a given geometric parameter of jet array, initial crossflow, and pressure ratios of the film-cooling exhaust. Comparative experiments have been made on curvilinear and flat plate impinged surfaces, and impinged surfaces with and without a chordwise fin. Moreover, the thermal patterns from a liquid crystal show that the jet hole arrangement and distance between cooled surface and jet plate affect the heat transfer distributions for jet array impingement. Finally, the effects of the cooling air axially injected into guide tube on radial jet flow have also been determined.

  15. Impingement Heat Transfer of Reciprocating Jet Array

    NASA Astrophysics Data System (ADS)

    Su, Lo May; Chang, Shyy Woei; Chiou, Shyr Fuu

    This paper describes an experimental study of impingement heat transfer of reciprocating jet-array with piston cooling application for marine heavy-duty diesel engine. A selection of heat transfer measurements illustrates the manner by which the individual and interactive influences of reciprocating force and buoyancy on heat transfer for the impinging jet-array. It is demonstrated that the reciprocating force coupled with buoyancy interaction causes considerable heat transfer modifications from the static results. The isolated reciprocating force effect could initially reduce heat transfer to a level about 0.45 of static level with weak reciprocation but recovers when the reciprocating force increases. Heat transfer improvement and impediment could be aided by the location-dependent buoyancy effect in addition to the reciprocating force effect. An empirical heat transfer correlation, which is physically consistent, has been developed to permit the evaluation of the individual and synergistic effects of reciprocating force and buoyancy interaction on local heat transfer of the impinging jet-array.

  16. Active Control of Supersonic Impinging Jets

    DTIC Science & Technology

    2001-06-01

    UNCLASSIFIED Defense Technical Information Center Compilation Part Notice ADPO11106 TITLE: Active Control of Supersonic Impinging Jets DISTRIBUTION...component part numbers comprise the compilation report: ADPO11101 thru ADP011178 UNCLASSIFIED 8-1 Active Control of Supersonic Impinging Jets A...Street, Tallahassee, FL 32310, USA krotha &fmrl.fsu.edu Experimental studies of supersonic impinging jet flows suggest that they are greatly influenced

  17. Atomization characteristics of impinging liquid jets

    NASA Technical Reports Server (NTRS)

    Ryan, H. M.; Anderson, W. E.; Pal, S.; Santoro, R. J.

    1993-01-01

    A systematic study is presented of the atomization of impinging liquid jets investigating the effects of jet conditions (laminar versus turbulent), orifice diameter, impingement angle and jet velocity. Results are compared to current theories in terms of sheet breakup length, sheet shape and drop size. Experiments contrasting laminar and turbulent jet conditions clearly show that the jet conditions have a dramatic effect on the atomization process.

  18. Fundamental studies of impingement cooling thermal boundary conditions

    NASA Astrophysics Data System (ADS)

    Lucas, M. G.; Ireland, P. T.; Wang, Z.; Jones, T. V.; Pearce, W. J.

    1993-02-01

    Measurements were made of the local heat transfer at the surface of a flat plate underneath a confined impinging jet. Thermochromic liquid crystals were used to measure the surface temperature of a uniformly heated plate cooled by an impinging jet. The temperature of the wall through which the jet passes was controlled, and experiments were performed to measure the two heat transfer coefficients which arise from this three temperature problem. The effect of Reynolds number and plate to jet spacing on heat transfer was investigated. The heat transfer results are discussed in terms of the interpreted flow field.

  19. Confined Impinging Jets in Porous Media

    NASA Astrophysics Data System (ADS)

    Buonomo, B.; Cirillo, L.; Manca, O.; Mansi, N.; Nardini, S.

    2016-09-01

    Impinging jets are adopted in drying of textiles, paper, cooling of gas turbine components, freezing of tissue in cryosurgery and manufacturing, electronic cooling. In this paper an experimental investigation is carried out on impinging jets in porous media with the wall heated from below with a uniform heat flux. The fluid is air. The experimental apparatus is made up of a fun systems, a test section, a tube, to reduce the section in a circular section. The tube is long 1.0 m and diameter of 0.012 m. The test section has a diameter of 0.10 m and it has the thickness of 10, 20 and 40 mm. In the test section the lower plate is in aluminum and is heated by an electrical resistance whereas the upper plate is in Plexiglas. The experiments are carried out employing a aluminum foam 40 PPI at three thickness as the test section. Results are obtained in a Reynolds number range from 5100 to 15300 and wall heat flux range from 510 W/m2 to 1400 W/m2. Results are given in terms of wall temperature profiles, local and average Nusselt numbers, pressure drops, friction factor and Richardson number.

  20. Supersonic rectangular jet impingement noise experiments

    NASA Astrophysics Data System (ADS)

    Norum, Thomas D.

    1989-04-01

    The discrete frequency sound produced by jets issuing from a convergent, rectangular nozzle of aspect ratio 4.24 was investigated. Experiments were performed both with the free jet and with the jet impinging on a hard ground surface. The impingement tones that dominate the impinging jet spectra show a definite staging behavior which appears to be biased toward the free jet screech frequency once the separation distance exceeds the region of substantial shock cell development. The frequency variation of the impingement tone stages fit the details of a feedback cycle if the disturbance convection velocity is chosen to be 20 percent higher than that necessary to satisfy the screech feedback loop. Phase locked optical records show a flapping mode of jet oscillation with tones at or near the screech frequency, with superimposed symmetric oscillations when a second dominant tone of unrelated frequency appears in the spectrum.

  1. Thermal visualization of heat-transfer characteristics for single impinging jet

    NASA Astrophysics Data System (ADS)

    Li, Liguo; Zhu, Yun; Zhang, Jingzhou; Yu, Wei

    The local heat-transfer characteristics of an impingement-cooling jet are presently ascertained, for cases with and without crossflow, through the use of a combined metal heating-element and cholesteric liquid crystal system. The results obtained indicate that the impingement Nusselt numbers of double-peak values increase with rising jet Reynolds number. A moving cylindrical jet-source model is used to simulate and analyze the jet's impingement heat transfer.

  2. Calculations of slurry pump jet impingement loads

    SciTech Connect

    Wu, T.T.

    1996-03-04

    This paper presents a methodology to calculate the impingement load in the region of a submerged turbulent jet where a potential core exits and the jet is not fully developed. The profile of the jet flow velocities is represented by a piece-wise linear function which satisfies the conservation of momentum flux of the jet flow. The adequacy of the of the predicted jet expansion is further verified by considering the continuity of the jet flow from the region of potential core to the fully developed region. The jet impingement load can be calculated either as a direct impingement force or a drag force using the jet velocity field determined by the methodology presented.

  3. Microtextured Surfaces for Turbine Blade Impingement Cooling

    NASA Technical Reports Server (NTRS)

    Fryer, Jack

    2014-01-01

    Gas turbine engine technology is constantly challenged to operate at higher combustor outlet temperatures. In a modern gas turbine engine, these temperatures can exceed the blade and disk material limits by 600 F or more, necessitating both internal and film cooling schemes in addition to the use of thermal barrier coatings. Internal convective cooling is inadequate in many blade locations, and both internal and film cooling approaches can lead to significant performance penalties in the engine. Micro Cooling Concepts, Inc., has developed a turbine blade cooling concept that provides enhanced internal impingement cooling effectiveness via the use of microstructured impingement surfaces. These surfaces significantly increase the cooling capability of the impinging flow, as compared to a conventional untextured surface. This approach can be combined with microchannel cooling and external film cooling to tailor the cooling capability per the external heating profile. The cooling system then can be optimized to minimize impact on engine performance.

  4. Fluorescence Imaging Study of Impinging Underexpanded Jets

    NASA Technical Reports Server (NTRS)

    Inman, Jennifer A.; Danehy, Paul M.; Nowak, Robert J.; Alderfer, David W.

    2008-01-01

    An experiment was designed to create a simplified simulation of the flow through a hole in the surface of a hypersonic aerospace vehicle and the subsequent impingement of the flow on internal structures. In addition to planar laser-induced fluorescence (PLIF) flow visualization, pressure measurements were recorded on the surface of an impingement target. The PLIF images themselves provide quantitative spatial information about structure of the impinging jets. The images also help in the interpretation of impingement surface pressure profiles by highlighting the flow structures corresponding to distinctive features of these pressure profiles. The shape of the pressure distribution along the impingement surface was found to be double-peaked in cases with a sufficiently high jet-exit-to-ambient pressure ratio so as to have a Mach disk, as well as in cases where a flow feature called a recirculation bubble formed at the impingement surface. The formation of a recirculation bubble was in turn found to depend very sensitively upon the jet-exit-to-ambient pressure ratio. The pressure measured at the surface was typically less than half the nozzle plenum pressure at low jet pressure ratios and decreased with increasing jet pressure ratios. Angled impingement cases showed that impingement at a 60deg angle resulted in up to a factor of three increase in maximum pressure at the plate compared to normal incidence.

  5. Study of liquid jet impingement on screens

    NASA Technical Reports Server (NTRS)

    Dodge, F. T.; Ricker, R. E.

    1976-01-01

    A model is presented for an unconfined flow, such as a free jet, impinging on a screen which incorporates the influence of liquid deflection by the screen. The boundary layer blockage coefficient is introduced. This coefficient depends on the screen weave geometry and the jet impingement angle, and essentially accounts for the increase in fluid particle trajectory length through the screen resulting from the flow deflection. Comparisons were made with previous experimental studies to determine empirical values of the blockage coefficient. It is concluded that the new model reliably predicts the bulk flow and penetration characteristics of an impinging liquid jet interacting with a screen.

  6. Acoustics measurements in normal jet impingement

    NASA Technical Reports Server (NTRS)

    Kleis, S. J.

    1977-01-01

    The dependence of far field acoustic measurements for a uniform jet on nozzle to plate spacing for small dimensionless spacings (h/d - 0.75 to 3.0) was investigated. Spectra from a real time analyzer were read and processed by an HP 2116 minicomputer in on-line mode. Similar data was generated for a fully developed pipe flow exit condition jet to compare with other investigations. The data base for normal jet impingement was extended to smaller values of nozzle to plate spacing. The effects of slight noise heating (30 deg rise) of the jet on the far field noise produced by the impinging jet are demonstrated.

  7. Buoyancy and cross flow effects on heat transfer of multiple impinging slot air jets cooling a flat plate at different orientations

    NASA Astrophysics Data System (ADS)

    Nada, S. A.

    2009-06-01

    The present article reports on heat transfer characteristics associated with multiple laminar impinging air jet cooling a hot flat plat at different orientations. The work aims to study the interactions of the effects of cross flow, buoyancy induced flow, orientation of the hot surface with respect to gravity, Reynolds numbers and Rayleigh numbers on heat transfer characteristics. Experiments have been carried out for different values of jet Reynolds number, Rayleigh number and cross flow strength and at different orientations of the air jet with respect to the target hot plate. In general, the effective cooling of the plate has been observed to be increased with increasing Reynolds number and Rayleigh number. The results concluded that the hot surface orientation is important for optimum performance in practical applications. It was found that for Re ≥ 400 and Ra ≥ 10,000 (these ranges give 0.0142 ≤ Ri ≤ 1.59 the Nusselt number is independent on the hot surface orientation. However, for Re ≤ 300 and Ra ≥ 100,000 (these ranges give 1.59 ≤ Ri ≤ 42.85): (i) the Nusselt number for horizontal orientation with hot surface facing down is less that that of vertical orientation and that of horizontal orientation with hot surface facing up, and (ii) the Nusselt number of vertical orientation is approximately the same as that of horizontal orientation with hot surface facing up. For all surfaces orientations and for the entire ranges of Re and Ra, it was found that increasing the cross flow strength decreases the effective cooling of the surface.

  8. Polymer-induced turbulence modifications in an impinging jet

    NASA Astrophysics Data System (ADS)

    Mejia-Alvarez, R.; Christensen, K. T.

    2012-05-01

    This effort explores the impact of dilute polymer solutions on the turbulence characteristics in a submerged liquid impinging-jet configuration. Turbulent impinging jets are commonly used in technological applications such as drying, scouring, cooling, or heating due to an enhancement in transport characteristics in the impingement region under certain nozzle-to-wall configurations. Previous efforts have identified significant turbulence modifications in the presence of dilute concentrations of polymer in both bounded and unbounded flows, though the former has received considerably more attention. To this end, particle-image velocimetry measurements were taken for an axisymmetric turbulent impinging jet with a nozzle-to-wall distance H/ D = 6.8 and nominal Reynolds number of 26,000. Measurements were performed for both plain water and dilute polymer solutions of polyethylene oxide at concentrations of 50 and 100 ppm. The mean and turbulence characteristics of these three flows are contrasted and it is observed that the two polymer solutions modify both the mean and turbulent characteristics of the jet in all three regions of interest (the free-jet, impingement, and wall-jet regions). Of interest, the 50 ppm case yielded a slight suppression of the turbulence in the free-jet region accompanied by a longer axial length of the potential core compared to the case of plain water. In contrast, the 100 ppm case exhibits clear enhancement of the turbulence in the free-jet region and a shortening of the potential core length. The effect of polymer was opposite in the impingement and wall-jet regions wherein the turbulence was slightly suppressed in the 100 ppm case in a manner consistent with the onset of the Toms effect in this wall-bounded region of the flow.

  9. Convective heat transfer by impingement of circular liquid jets

    NASA Astrophysics Data System (ADS)

    Liu, X.; Lienhard, J. H. V.; Lombara, J. S.

    1991-08-01

    The impingement of circular, liquid jets provides a convenient method of cooling surfaces. Here, jet impingement cooling of uniformly heated surfaces is investigated analytically and experimentally for stable, unsubmerged, uniform velocity laminar jets in the absence of phase change. Analytical and numerical predictions are developed for a laminar radial film flow. Experiments using undisturbed laminar jets were performed to determine local Nusselt numbers from the stagnation point to radii of up to 40 diameters. Turbulent transition in the film flow is observed experimentally at a certain radius. Beyond this transition radius, a separate turbulent analysis is constructed. Integral method results are compared to numberical results, and Prandtl number effects are investigated. The predictions are found to agree well with the measurements for both laminar and turbulent flow. Predictive formulas are recommended for the entire range of radii.

  10. Convective heat transfer by impingement of circular liquid jets

    SciTech Connect

    Liu, X.; Lienhard, J.H. V; Lombara, J.S. )

    1991-08-01

    The impingement of circular, liquid jets provides a convenient method of cooling surfaces. Here, jet impingement cooling of uniformly heated surfaces is investigated analytically and experimentally for stable, unsubmerged, uniform velocity laminar jets in the absence of phase change. Analytical and numerical predictions are developed for a laminar radial film flow. Experiments using undisturbed laminar jets were performed to determine local Nusselt numbers from the stagnation point to radii of up to 40 diameters. Turbulent transition in the film flow is observed experimentally at a certain radius. Beyond this transition radius, a separate turbulent analysis is constructed. Integral method results are compared to numerical results, and Prandtl number effects are investigated. The predictions are found to agree well with the measurements for both laminar and turbulent flow. Predictive formulae are recommended for the entire range of radii.

  11. Extremely high heat fluxes beneath impinging liquid jets

    NASA Astrophysics Data System (ADS)

    Liu, X.; Lienhard, J. H., V.

    1993-05-01

    Measurements of jet-impingement heat fluxes up to 400 MW/sq m were obtained using a specially designed experimental arrangement where a thin metal plate was heated from one side with a plasma arc and cooled from the other side with an unsubmerged impinging water jet produced by a 34 MPa piston pump supplying a large cylindrical plenum. The results of this study, where heating was confined to the stagnation region, show no evidence of a critical heat flux, even up to the maximum power applied. The large fluxes were limited only by wall failure and the power of the heating source, and not by liquid-side thermal resistance.

  12. Liquid jet impinging orthogonally on a wettability-patterned surface

    NASA Astrophysics Data System (ADS)

    Koukoravas, Theodore; Ghosh, Aritra; Sinha Mahapatra, Pallab; Ganguly, Ranjan; Megaridis, Constantine

    2016-11-01

    Jet impingement has many technological applications because of its numerous merits, especially those related to the ability of liquids to carry away heat very efficiently. The present study introduces a new configuration employing a wettability-patterning approach to divert an orthogonally-impinging laminar water jet onto a predetermined portion of the target surface. Diverging wettable tracks on a superhydrophobic background provide the means to re-direct the impinging jet along paths determined by the shape of these tracks on the solid surface. In a heat transfer example of this method, an open-surface heat exchanger is constructed and its heat transfer performance is characterized. Since this approach facilitates prolonged liquid contact with the underlying heated surface through thin-film spreading, evaporative cooling is also promoted. We demonstrate flow cases extracting 100 W/cm2 at water flow rates of O(10 mL/min). By comparing with other jet-impingement cooling approaches, the present method provides roughly four times more efficient cooling by using less amount of coolant. The reduced coolant use, combined with the gravity-independent character of this technique, offer a new paradigm for compact heat transfer devices designed to operate in reduced- or zero-gravity environments.

  13. Spray formation processes of impinging jet injectors

    NASA Technical Reports Server (NTRS)

    Anderson, W. E.; Ryan, H. M.; Pal, S.; Santoro, R. J.

    1993-01-01

    A study examining impinging liquid jets has been underway to determine physical mechanisms responsible for combustion instabilities in liquid bi-propellant rocket engines. Primary atomization has been identified as an important process. Measurements of atomization length, wave structure, and drop size and velocity distribution were made under various ambient conditions. Test parameters included geometric effects and flow effects. It was observed that pre-impingement jet conditions, specifically whether they were laminar or turbulent, had the major effect on primary atomization. Comparison of the measurements with results from a two dimensional linear aerodynamic stability model of a thinning, viscous sheet were made. Measured turbulent impinging jet characteristics were contrary to model predictions; the structure of waves generated near the point of jet impingement were dependent primarily on jet diameter and independent of jet velocity. It has been postulated that these impact waves are related to pressure and momentum fluctuations near the impingement region and control the eventual disintegration of the liquid sheet into ligaments. Examination of the temporal characteristics of primary atomization (ligament shedding frequency) strongly suggests that the periodic nature of primary atomization is a key process in combustion instability.

  14. Spray formation processes of impinging jet injectors

    NASA Astrophysics Data System (ADS)

    Anderson, W. E.; Ryan, H. M.; Pal, S.; Santoro, R. J.

    1993-11-01

    A study examining impinging liquid jets has been underway to determine physical mechanisms responsible for combustion instabilities in liquid bi-propellant rocket engines. Primary atomization has been identified as an important process. Measurements of atomization length, wave structure, and drop size and velocity distribution were made under various ambient conditions. Test parameters included geometric effects and flow effects. It was observed that pre-impingement jet conditions, specifically whether they were laminar or turbulent, had the major effect on primary atomization. Comparison of the measurements with results from a two dimensional linear aerodynamic stability model of a thinning, viscous sheet were made. Measured turbulent impinging jet characteristics were contrary to model predictions; the structure of waves generated near the point of jet impingement were dependent primarily on jet diameter and independent of jet velocity. It has been postulated that these impact waves are related to pressure and momentum fluctuations near the impingement region and control the eventual disintegration of the liquid sheet into ligaments. Examination of the temporal characteristics of primary atomization (ligament shedding frequency) strongly suggests that the periodic nature of primary atomization is a key process in combustion instability.

  15. Improved Stirling engine performance using jet impingement

    NASA Technical Reports Server (NTRS)

    Johnson, D. C.; Britt, E. J.; Thieme, L. G.

    1982-01-01

    Of the many factors influencing the performance of a Stirling engine, that of transferring the combustion gas heat into the working fluid is crucial. By utilizing the high heat transfer rates obtainable with a jet impingement heat transfer system, it is possible to reduce the flame temperature required for engine operation. Also, the required amount of heater tube surface area may be reduced, resulting in a decrease in the engine nonswept volume and a related increase in engine efficiency. A jet impingement heat transfer system was designed by Rasor Associates, Inc., and tested in the GPU-3 Stirling engine at the NASA Lewis Research Center. For a small penalty in pumping power (less than 0.5% of engine output) the jet impingement heat transfer system provided a higher combustion-gas-side heat transfer coefficient and a smoothing of heater temperature profiles resulting in lower combustion system temperatures and a 5 to 8% increase in engine power output and efficiency.

  16. Improved Stirling engine performance using jet impingement

    NASA Technical Reports Server (NTRS)

    Johnson, D. C.; Britt, E. J.; Thieme, L. G.

    1982-01-01

    Of the many factors influencing the performance of a Stirling engine, that of transferring the combustion gas heat into the working fluid is crucial. By utilizing the high heat transfer rates obtainable with a jet impingement heat transfer system, it is possible to reduce the flame temperature required for engine operation. Also, the required amount of heater tube surface area may be reduced, resulting in a decrease in the engine nonswept volume and a related increase in engine efficiency. A jet impingement heat transfer system was designed by Rasor Associates, Inc., and tested in the GPU-3 Stirling engine at the NASA Lewis Research Center. For a small penalty in pumping power (less than 0.5% of engine output) the jet impingement heat transfer system provided a higher combustion-gas-side heat transfer coefficient and a smoothing of heater temperature profiles resulting in lower combustion system temperatures and a 5 to 8% increase in engine power output and efficiency.

  17. Axisymmetric wall jet development in confined jet impingement

    NASA Astrophysics Data System (ADS)

    Guo, Tianqi; Rau, Matthew J.; Vlachos, Pavlos P.; Garimella, Suresh V.

    2017-02-01

    The flow field surrounding an axisymmetric, confined, impinging jet was investigated with a focus on the early development of the triple-layered wall jet structure. Experiments were conducted using stereo particle image velocimetry at three different confinement gap heights (2, 4, and 8 jet diameters) across Reynolds numbers ranging from 1000 to 9000. The rotating flow structures within the confinement region and their interaction with the surrounding flow were dependent on the confinement gap height and Reynolds number. The recirculation core shifted downstream as the Reynolds number increased. For the smallest confinement gap height investigated, the strong recirculation caused a disruption of the wall jet development. The radial position of the recirculation core observed at this small gap height was found to coincide with the location where the maximum wall jet velocity had decayed to 15% of the impinging jet exit velocity. After this point, the self-similarity hypothesis failed to predict the evolution of the wall jet further downstream. A reduction in confinement gap height increased the growth rates of the wall jet thickness but did not affect the decay rate of the wall jet maximum velocity. For jet Reynolds numbers above 2500, the decay rate of the maximum velocity in the developing region of the wall jet was approximately -1.1, which is close to previous results reported for the fully developed region of radial wall jets. A much higher decay rate of -1.5 was found for the wall jet formed by a laminar impinging jet at Re = 1000.

  18. Single-phase liquid jet impingement heat transfer

    SciTech Connect

    Webb, B.W.; Ma, C.F.

    1995-12-31

    Impinging liquid jets have been demonstrated to be an effective means of providing high heat/mass transfer rates in industrial transport processes. When a liquid jet strikes a surface, thin hydrodynamic and thermal boundary layers from in the region directly beneath due to the jet deceleration and the resulting increase in pressure. The flow is then forced to accelerate in a direction parallel to the target surface in what is termed the wall jet or parallel flow zone. The thickness of the hydrodynamic and thermal boundary layers in the stagnation region may be of the order of tens of micrometers. Consequently, very high heat/mass transfer coefficients exist in the stagnation zone directly under the jet. Transport coefficients characteristic of parallel flow prevail in the wall jet region. The high heat transfer coefficients make liquid jet impingement an attractive cooling option where high heat fluxes are the norm. Some industrial applications include the thermal treatment of metals, cooling of internal combustion engines, and more recently, thermal control of high-heat-dissipation electronic devices. Both circular and planar liquid jets have attracted research attention. 180 refs., 35 figs., 11 tabs.

  19. Numerical investigation of heat transfer under confined impinging turbulent slot jets

    SciTech Connect

    Tzeng, P.Y.; Soong, C.Y.; Hsieh, C.D. )

    1999-06-01

    Impinging jet systems are extensively used to provide rapid heating, cooling, or drying in diverse industrial applications. Among these applications are the annealing of metals and plastic sheets; tempering and shaping of glass; drying of textiles, veneer, paper, and film materials; and cooling of combustion walls, turbine blades, and electronic components. This work numerically investigates confined impinging turbulent slot jets. Eight turbulence models, including one standard and seven low-Reynolds-number [kappa]-[epsilon] models, are employed and tested to predict the heat transfer performance of multiple impinging jets. Validation results indicate that the prediction by each turbulence model depends on grid distribution and numerical scheme used in spatial discretization. In addition, spent fluid exits are set between impinging jets to reduce the cross-flow effect in degradation of the heat transfer of downstream impinging jets. The overall heat transfer performance can be enhanced by proper spent fluid removal.

  20. Circular and Elliptic Submerged Impinging Water Jets

    NASA Astrophysics Data System (ADS)

    Claudey, Eric; Benedicto, Olivier; Ravier, Emmanuel; Gutmark, Ephraim

    1999-11-01

    Experiments and CFD have been performed to study circular and elliptic jets in a submerged water jet facility. The tests included discharge coefficient measurement to evaluate pressure losses encountered in noncircular nozzles compared to circular ones. Three-dimensional pressure mappings on the impingement surface and PIV measurement of the jet mean and turbulent velocity have been performed at different compound impingement angles relative to the impingement surface and at different stand-off distances. The objective was to investigate the effect of the non-circular geometry on the flow field and on the impact region. The tests were performed in a close loop system in which the water was pumped through the nozzles into a clear Plexiglas tank. The Reynolds numbers were typically in the range of 250000. Discharge coefficients of the elliptic nozzle was somewhat lower than that of the circular jet but spreading rate and turbulence level were higher. Pressure mapping showed that the nozzle exit geometry had an effect on the pressure distribution in the impact region and that high-pressure zones were generated at specific impact points. PIV measurements showed that for a same total exit area, the elliptic jets affected a surface area that is 8the equivalent circular. The turbulence level in the elliptic jet tripled due to the nozzle design. Results of the CFD model were in good agreement with the experimental data.

  1. Industrial stator vane with sequential impingement cooling inserts

    SciTech Connect

    Jones, Russell B; Fedock, John A; Goebel, Gloria E; Krueger, Judson J; Rawlings, Christopher K; Memmen, Robert L

    2013-08-06

    A turbine stator vane for an industrial engine, the vane having two impingement cooling inserts that produce a series of impingement cooling from the pressure side to the suction side of the vane walls. Each insert includes a spar with a row of alternating impingement cooling channels and return air channels extending in a radial direction. Impingement cooling plates cover the two sides of the insert and having rows of impingement cooling holes aligned with the impingement cooling channels and return air openings aligned with the return air channel.

  2. Drying hardwoods with impinging jets.

    Treesearch

    Howard N. Rosen

    1980-01-01

    Silver maple, yellow poplar, and black walnut lumber was dried in a prototype jet dryer over a range of temperatures from 120 degrees to 400 degrees Fahrenheit and air velocities from 1,000 to 9,000 fpm. Different drying schedules were developed for each type of wood. The quality of the jet-dried lumber was good and compared favorably with kiln-dried lumber.

  3. Gas turbine bucket with impingement cooled platform

    DOEpatents

    Jones, Raphael Durand

    2002-01-01

    In a turbine bucket having an airfoil portion and a root portion, with a substantially planar platform at an interface between the airfoil portion and root portion, a platform cooling arrangement including at least one bore in the root portion and at least one impingement cooling tube seated in the bore, the tube extending beyond the bore with an outlet in close proximity to a targeted area on an underside of the platform.

  4. An approximation technique for jet impingement flow

    SciTech Connect

    Najafi, Mahmoud; Fincher, Donald; Rahni, Taeibi; Javadi, KH.; Massah, H.

    2015-03-10

    The analytical approximate solution of a non-linear jet impingement flow model will be demonstrated. We will show that this is an improvement over the series approximation obtained via the Adomian decomposition method, which is itself, a powerful method for analysing non-linear differential equations. The results of these approximations will be compared to the Runge-Kutta approximation in order to demonstrate their validity.

  5. Investigations of scaling laws for jet impingement

    NASA Technical Reports Server (NTRS)

    Morton, J. B.; Haviland, J. K.; Catalano, G. D.; Herling, W. W.

    1976-01-01

    The statistical properties of tangential flows over surfaces were investigated by two techniques. In one, a laser-Doppler velocimeter was used in a smoke-laden jet to measure one-point statistical properties, including mean velocities, turbulent intensities, intermittencies, autocorrelations, and power spectral densities. In the other technique, free stream and surface pressure probes connected to 1/8 inch microphones were used to obtain single point rms and 1/3 octave pressures, as well as two point cross correlations, the latter being converted to auto spectra, amplitude ratios, phase lags, and coherences. The results of these studies support the vortex model of jets, give some insights into the effects of surface impingement, and confirm that jet diameter and velocity are the scaling parameters for circular jets, while Reynolds number is relatively unimportant.

  6. Sessile drop deformations under an impinging jet

    NASA Astrophysics Data System (ADS)

    Feng, James Q.

    2015-08-01

    The problem of steady axisymmetric deformations of a liquid sessile drop on a flat solid surface under an impinging gas jet is of interest for understanding the fundamental behavior of free surface flows as well as for establishing the theoretical basis in process design for the Aerosol direct-write technology. It is studied here numerically using a Galerkin finite-element method, by computing solutions of Navier-Stokes equations. For effective material deposition in Aerosol printing, the desired value of Reynolds number for the laminar gas jet is found to be greater than ~500. The sessile drop can be severely deformed by an impinging gas jet when the capillary number is approaching a critical value beyond which no steady axisymmetric free surface deformation can exist. Solution branches in a parameter space show turning points at the critical values of capillary number, which typically indicate the onset of free surface shape instability. By tracking solution branches around turning points with an arc-length continuation algorithm, critical values of capillary number can be accurately determined. Near turning points, all the free surface profiles in various parameter settings take a common shape with a dimple at the center and bulge near the contact line. An empirical formula for the critical capillary number for sessile drops with contact angle is derived for typical ranges of jet Reynolds number and relative drop sizes especially pertinent to Aerosol printing.

  7. Thermal chip fabrication with arrays of sensors and heaters for micro-scale impingement cooling heat transfer analysis and measurements.

    PubMed

    Shen, C H; Gau, C

    2004-07-30

    The design and fabrication for a thermal chip with an array of temperature sensors and heaters for study of micro-jet impingement cooling heat transfer process are presented. This thermal chip can minimize the heat loss from the system to the ambient and provide a uniform heat flux along the wall, thus local heat transfer processes along the wall can be measured and obtained. The fabrication procedure presented can reach a chip yield of 100%, and every one of the sensors and heaters on the chip is in good condition. In addition, micro-jet impingement cooling experiments are performed to obtain the micro-scale local heat transfer Nusselt number along the wall. Flow visualization for the micro-impinging jet is also made. The experimental results indicate that both the micro-scale impinging jet flow structure and the heat transfer process along the wall is significantly different from the case of large-scale jet impingement cooling process.

  8. Heat transfer from a row of impinging jets to concave cylindrical surfaces

    NASA Technical Reports Server (NTRS)

    Hrycak, P.

    1981-01-01

    Starting from the first principles, and with one experimentally obtained parameter, an expression for stagnation heat transfer is derived, applicable to round, impinging jets. The results obtained with a row of air jets impinging on an electrically-heated surface in a small-scale setup characteristic of a typical turbine blade have been found compatible with the average heat transfer from a geometrically similar, steam-heated surface scaled up ten times, and comparable with the results of other investigators. These findings were linked to the flow fields likely to exist in the gas turbine blades, internally cooled by a row of round jets or a single jet of equivalent width. The magnitude of heat-transfer coefficients obtained here with impinging jets approaches that normally associated with forced convection of water and evaporative cooling.

  9. Three-dimensional numerical study of laminar confined slot jet impingement cooling using slurry of nano-encapsulated phase change material

    NASA Astrophysics Data System (ADS)

    Mohib Ur Rehman, M.; Qu, Z. G.; Fu, R. P.

    2016-10-01

    This Article presents a three dimensional numerical model investigating thermal performance and hydrodynamics features of the confined slot jet impingement using slurry of Nano Encapsulated Phase Change Material (NEPCM) as a coolant. The slurry is composed of water as a base fluid and n-octadecane NEPCM particles with mean diameter of 100nm suspended in it. A single phase fluid approach is employed to model the NEPCM slurry.The thermo physical properties of the NEPCM slurry are computed using modern approaches being proposed recently and governing equations are solved with a commercial Finite Volume based code. The effects of jet Reynolds number varying from 100 to 600 and particle volume fraction ranging from 0% to 28% are considered. The computed results are validated by comparing Nusselt number values at stagnation point with the previously published results with water as working fluid. It was found that adding NEPCM to the base fluid results with considerable amount of heat transfer enhancement.The highest values of heat transfer coefficients are observed at H/W=4 and Cm=0.28. However, due to the higher viscosity of slurry compared with the base fluid, the slurry can produce drastic increase in pressure drop of the system that increases with NEPCM particle loading and jet Reynolds number.

  10. Heat transfer from a square source to an impinging liquid jet confined by an annular wall

    SciTech Connect

    Besserman, D.L. ); Incropera, F.P.; Ramadhyani, S. )

    1992-02-01

    The objective of this study has been to consider experimentally impingement cooling of a chiplike source by a liquid, circular jet under conditions for which single-phase convection heat transfer from the source may be influenced by annular collection of the spent fluid. The experiments were performed with water and for operating conditions that are consistent with ship cooling requirements.

  11. Magnetic Resonance Velocimetry analysis of an angled impinging jet

    NASA Astrophysics Data System (ADS)

    Irhoud, Alexandre; Benson, Michael; Verhulst, Claire; van Poppel, Bret; Elkins, Chris; Helmer, David

    2016-11-01

    Impinging jets are used to achieve high heat transfer rates in applications ranging from gas turbine engines to electronics. Despite the importance and relative simplicity of the geometry, simulations historically fail to accurately predict the flow behavior in the vicinity of the flow impingement. In this work, we present results from a novel experimental technique, Magnetic Resonance Velocimetry (MRV), which measures three-dimensional time-averaged velocity without the need for optical access. The geometry considered in this study is a circular jet angled at 45 degrees and impinging on a flat plate, with a separation of approximately seven jet diameters between the jet exit and the impingement location. Two flow conditions are considered, with Reynolds numbers of roughly 800 and 14,000. Measurements from the MRV experiment are compared to predictions from Reynolds Averaged Navier Stokes (RANS) simulations, thus demonstrating the utility of MRV for validation of numerical analyses of impinging jet flow.

  12. The effect of drainage configuration on heat transfer under an impinging liquid jet array

    SciTech Connect

    Garrett, K.; Webb, B.W.

    1999-11-01

    Impinging jets provide high transport coefficients which make them attractive for use in applications such as paper drying, quenching of metals, turbine blade cooling, and thermal control of a variety of high heat flux devices (electronics, X-ray optics, etc.). Here, the heat transfer characteristics of single and dual-exit drainage configurations for arrays of liquid jets impinging normal to a heated isoflux plate has been studied experimentally. The interaction of drainage channel crossflow from upstream jets and the stagnation jets and its impact on heat transfer was the focus of the investigation. Infrared thermography was used to measure the local temperature distribution on the heated plate, from which local heat transfer coefficients were determined. A single jet diameter was used, and jet arrays with jet-to-jet spacings of 4.8, 6, 9, and 12 jet diameters were studied. Average jet Reynolds numbers in the range 400--5,000 were investigated for jet nozzle-to-impingement plate spacings of 1, 2, and 4 jet diameters for fully flooded (submerged) drainage flow. A single jet-to-plate spacing large enough to yield free-surface jets was also studied. The data reveal a complex dependence of local and average Nusselt numbers on the geometric parameters which describe the problem configuration.

  13. Outdoor Performance Analysis of a Photovoltaic Thermal (PVT) Collector with Jet Impingement and Compound Parabolic Concentrator (CPC)

    PubMed Central

    Jaaz, Ahed Hameed; Hasan, Husam Abdulrasool; Sopian, Kamaruzzaman; Kadhum, Abdul Amir H.; Gaaz, Tayser Sumer

    2017-01-01

    This paper discusses the effect of jet impingement of water on a photovoltaic thermal (PVT) collector and compound parabolic concentrators (CPC) on electrical efficiency, thermal efficiency and power production of a PVT system. A prototype of a PVT solar water collector installed with a jet impingement and CPC has been designed, fabricated and experimentally investigated. The efficiency of the system can be improved by using jet impingement of water to decrease the temperature of the solar cells. The electrical efficiency and power output are directly correlated with the mass flow rate. The results show that electrical efficiency was improved by 7% when using CPC and jet impingement cooling in a PVT solar collector at 1:00 p.m. (solar irradiance of 1050 W/m2 and an ambient temperature of 33.5 °C). It can also be seen that the power output improved by 36% when using jet impingement cooling with CPC, and 20% without CPC in the photovoltaic (PV) module at 1:30 p.m. The short-circuit current ISC of the PV module experienced an improvement of ~28% when using jet impingement cooling with CPC, and 11.7% without CPC. The output of the PV module was enhanced by 31% when using jet impingement cooling with CPC, and 16% without CPC. PMID:28763048

  14. Outdoor Performance Analysis of a Photovoltaic Thermal (PVT) Collector with Jet Impingement and Compound Parabolic Concentrator (CPC).

    PubMed

    Jaaz, Ahed Hameed; Hasan, Husam Abdulrasool; Sopian, Kamaruzzaman; Kadhum, Abdul Amir H; Gaaz, Tayser Sumer; Al-Amiery, Ahmed A

    2017-08-01

    This paper discusses the effect of jet impingement of water on a photovoltaic thermal (PVT) collector and compound parabolic concentrators (CPC) on electrical efficiency, thermal efficiency and power production of a PVT system. A prototype of a PVT solar water collector installed with a jet impingement and CPC has been designed, fabricated and experimentally investigated. The efficiency of the system can be improved by using jet impingement of water to decrease the temperature of the solar cells. The electrical efficiency and power output are directly correlated with the mass flow rate. The results show that electrical efficiency was improved by 7% when using CPC and jet impingement cooling in a PVT solar collector at 1:00 p.m. (solar irradiance of 1050 W/m² and an ambient temperature of 33.5 °C). It can also be seen that the power output improved by 36% when using jet impingement cooling with CPC, and 20% without CPC in the photovoltaic (PV) module at 1:30 p.m. The short-circuit current ISC of the PV module experienced an improvement of ~28% when using jet impingement cooling with CPC, and 11.7% without CPC. The output of the PV module was enhanced by 31% when using jet impingement cooling with CPC, and 16% without CPC.

  15. Detailed heat transfer coefficient distributions under an array of impinging jets with coolant extraction

    SciTech Connect

    Huang, Y.; Ekkad, S.V.; Han, J.C.

    1996-12-31

    Jet impingement cooling is a high performance technique for heat transfer enhancement. Local heat transfer distributions are presented for an array of jets impinging on a target plate with a series of coolant extraction holes. The flow enters the pressure channel, impinges on the target plate and exits toward the sides and through the coolant extraction holes. The impingement plate has four rows of 12 jet holes and the target plate has three rows of 11 coolant extraction holes. The jet holes and the coolant extraction holes have the same diameters and are staggered such that the air impinging from the jet hole does not exit directly through the extraction hole. The detailed heat transfer coefficient distributions are measured using a transient technique and liquid crystal coating. Results are presented for a range of jet Reynolds numbers between 4,000 and 20,000. The effect of crossflow is also studied by changing the exit opening of the impingement channel to provide three different spent air exit directions. Heat transfer results for the target plate with coolant extraction are compared with those without coolant extraction at the same flow conditions.

  16. Round impinging jets with relatively large stand-off distance

    NASA Astrophysics Data System (ADS)

    Shademan, Mehrdad; Balachandar, Ram; Roussinova, Vesselina; Barron, Ron

    2016-07-01

    Large eddy simulation and particle image velocimetry measurements have been performed to evaluate the characteristics of a turbulent impinging jet with large nozzle height-to-diameter ratio (H/D = 20). The Reynolds number considered is approximately 28 000 based on the jet exit velocity and nozzle diameter. Mean normalized centerline velocity in both the free jet and impingement regions and pressure distribution over the plate obtained from simulations and experiments show good agreement. The ring-like vortices generated due to the Kelvin-Helmholtz instabilities at the exit of the nozzle merge, break down and transform into large scale structures while traveling towards the impingement plate. A Strouhal number of 0.63 was found for the vortices generated at the exit of the nozzle. However, this parameter is reduced along the centerline towards the impingement zone. A characteristic frequency was also determined for the large scale structures impinging on the plate. The expansion, growth, tilt, and three-dimensionality of the impinging structures cause dislocation of the impinging flow from the centerline, which is significantly larger when compared with flows having small H/D ratios. Contrary to the behavior of impinging jets with small stand-off distance, due to the loss of coherence, the large scale structures do not result in significant secondary vortices in the wall jet region and consequently less fluctuations were observed for wall shear stress.

  17. Nanofluid jet impingement heat transfer characteristics in the rectangular mini-fin heat sink

    NASA Astrophysics Data System (ADS)

    Naphon, Paisarn; Nakharintr, Lursukd

    2012-11-01

    The nanofluid jet impingement heat transfer characteristics in a rectangular mini-fin heat sink are studied. The heat sink is fabricated from aluminum by a wire electrical discharge machine. The nanofluid is a mixture of deionized water and nanoscale TiO2 particles with a volume nanoparticle concentration of 0.2%. The results obtained for nanofluid jet impingement cooling in the rectangular mini-fin heat sink are compared with those found in the water jet impingement cooling. The effects of the inlet temperature of the nanofluid, its Reynolds number, and the heat flux on the heat transfer characteristics of the rectangular mini-fin heat sink are considered. It is found that the average heat transfer rates for the nanofluid as coolant are higher than those for deionized water.

  18. Experimental study of turbulence in isothermal jet impingement at intermediate plate spacings

    NASA Astrophysics Data System (ADS)

    Landfried, D. Tyler; Valentino, Alex; Mazumdar, Sagnik; Jana, Anirban; Kimber, Mark

    2013-11-01

    One fundamental problem in fluid dynamics is that of the axisymmetric round flow impinging on a plate placed some distance downstream of the jet. Impinging jets have a rich history of applications including small plate spacings, H/D ~ 1, such as encountered in electronics cooling, or large plate spacings, H/D ~ 102, such as vertical takeoff aircrafts and rocket engines. However, intermediate plate spacings, such as the lower plenum of the next generation nuclear reactors, are not typically studied. In this paper, an experimental study is conducted investigating the effect of the impingement plate on the flow behavior compared to the near free jet behavior when the plate is removed. Using air as the working fluid, a single jet is considered at jet Reynolds numbers of 10000, 20000, and 30000. A three-wire anemometer probe is used to quantify the mean components of velocities as well as the Reynolds stress and the third-order moments in the flow field at various distances between the jet outlet and the impingement plate. When present, the impingement plate is placed a distance of 8, 11, 14, and 17 diameters downstream of the jet. Additionally trends in the kinetic energy and dissipation are investigated for validation with numerical models.

  19. Active Control of Supersonic Impinging Jets Using Supersonic Microjets

    DTIC Science & Technology

    2005-01-01

    impinging jet experiments . control technique, which utilizes supersonic microjets and significantly alleviates the...an Obstacle", NASA TT F-15719, 1974. 15. Phalnikar, K. A., Alvi, F. S. and Shih, C. "Behavior of Free and Impinging Supersonic Microjets ," AIAA Paper...S., "Active Control of Supersonic Impingement Tones Using Steady and Pulsed Microjets ," submitted to Experiments in Fluids, August 2005, under

  20. Confined jet impingement of liquid nitrogen onto different heat transfer surfaces

    NASA Astrophysics Data System (ADS)

    Zhang, P.; Xu, G. H.; Fu, X.; Li, C. R.

    2011-06-01

    Jet impingement of liquid nitrogen owns many applications in the cryogenic cooling aspects, such as, cooling of high-power chips in the electronic devices and cryoprobes in the cryosurgery. In the present study, we systematically investigated the confined jet impingement of liquid nitrogen from a tube of about 2.0 mm in diameter onto the heat transfer surfaces of about 5.0 mm in basement diameter with different heat transfer surface geometries and conditions, i.e., flat surface, hemispherical surface and flat surface with a needle. The effects of many influential factors, such as, the geometry of the heat transfer surface, jet velocity, distance between the nozzle exit and heat transfer surface, heat transfer surface condition, and some other, on the heat transfer were investigated. The heat transfer correlations were also proposed by using the experimental data, and it was found that the heat transfer mechanism of liquid impingement in the confined space was dominated by the convective evaporation rather than the nucleate boiling in the present case. The critical heat flux (CHF) of the confined jet impingement was measured and the visualization of the corresponding flow patterns of the confined jet impingement of liquid nitrogen was also conducted simultaneously to understand the heat transfer phenomena.

  1. Flow Visualization and Heat Transfer Characteristics of Liquid Jet Impingement

    NASA Astrophysics Data System (ADS)

    Jafar, Farial A.; Thorpe, Graham R.; Turan, Özden F.

    2012-07-01

    Equipment used to cool horticultural produce often involves three-phase porous media. The flow field and heat transfer processes that occur in such equipment are generally quantified by means of empirical relationships amongst dimensionless groups. This work represents a first step towards the goal of harnessing the power of computational fluid dynamics (CFD) to better understand the heat transfer processes that occur in beds of irrigated horticultural produce. The primary objective of the present study is to use numerical predictions towards reducing the energy and cooling water requirement in cooling horticultural produce. In this paper, flow and heat transfer predictions are presented of a single slot liquid jet impinging on flat and curved surfaces using a CFD code (FLUENT) for 2D configurations. The effects of Reynolds number, nozzle to plate spacing, nozzle width, and target surface configuration have been studied. Reynolds numbers of 250, 375, 500, 700, 1000, 1500, 1800, and 1900 are studied where the liquid medium is water. Here, the Reynolds number is defined in terms of the hydraulic nozzle diameter, inlet jet velocity, and fluid kinematic viscosity. The results show that Reynolds numbers, nozzle to plate spacing, and nozzle width have a significant effect on the flow field and heat transfer characteristics, whereas the target surface configuration at the stagnation area has no substantial impact. The use of a numerical tool has resulted in a detailed investigation of these characteristics, which has not been available in the literature previously.

  2. Two stage serial impingement cooling for isogrid structures

    SciTech Connect

    Lee, Ching-Pang; Morrison, Jay A.

    2014-09-09

    A system for cooling a wall (24) of a component having an outer surface with raised ribs (12) defining a structural pocket (10), including: an inner wall (26) within the structural pocket and separating the wall outer surface within the pocket into a first region (28) outside of the inner wall and a second region (40) enclosed by the inner wall; a plate (14) disposed atop the raised ribs and enclosing the structural pocket, the plate having a plate impingement hole (16) to direct cooling air onto an impingement cooled area (38) of the first region; a cap having a skirt (50) in contact with the inner wall, the cap having a cap impingement hole (20) configured to direct the cooling air onto an impingement cooled area (44) of the second region, and; a film cooling hole (22) formed through the wall in the second region.

  3. Numerical study of a confined slot impinging jet with nanofluids

    PubMed Central

    2011-01-01

    Background Heat transfer enhancement technology concerns with the aim of developing more efficient systems to satisfy the increasing demands of many applications in the fields of automotive, aerospace, electronic and process industry. A solution for obtaining efficient cooling systems is represented by the use of confined or unconfined impinging jets. Moreover, the possibility of increasing the thermal performances of the working fluids can be taken into account, and the introduction of nanoparticles in a base fluid can be considered. Results In this article, a numerical investigation on confined impinging slot jet working with a mixture of water and Al2O3 nanoparticles is described. The flow is turbulent and a constant temperature is applied on the impinging. A single-phase model approach has been adopted. Different geometric ratios, particle volume concentrations and Reynolds number have been considered to study the behavior of the system in terms of average and local Nusselt number, convective heat transfer coefficient and required pumping power profiles, temperature fields and stream function contours. Conclusions The dimensionless stream function contours show that the intensity and size of the vortex structures depend on the confining effects, given by H/W ratio, Reynolds number and particle concentrations. Furthermore, for increasing concentrations, nanofluids realize increasing fluid bulk temperature, as a result of the elevated thermal conductivity of mixtures. The local Nusselt number profiles show the highest values at the stagnation point, and the lowest at the end of the heated plate. The average Nusselt number increases for increasing particle concentrations and Reynolds numbers; moreover, the highest values are observed for H/W = 10, and a maximum increase of 18% is detected at a concentration equal to 6%. The required pumping power as well as Reynolds number increases and particle concentrations grow, which is almost 4.8 times greater than the

  4. Impinging jet separators for liquid metal magnetohydrodynamic power cycles

    NASA Technical Reports Server (NTRS)

    Bogdanoff, D. W.

    1973-01-01

    In many liquid metal MHD power, cycles, it is necessary to separate the phases of a high-speed liquid-gas flow. The usual method is to impinge the jet at a glancing angle against a solid surface. These surface separators achieve good separation of the two phases at a cost of a large velocity loss due to friction at the separator surface. This report deals with attempts to greatly reduce the friction loss by impinging two jets against each other. In the crude impinging jet separators tested to date, friction losses were greatly reduced, but the separation of the two phases was found to be much poorer than that achievable with surface separators. Analyses are presented which show many lines of attack (mainly changes in separator geometry) which should yield much better separation for impinging jet separators).

  5. Supersonic moist air jet impingements on flat surface

    NASA Astrophysics Data System (ADS)

    Alam, Miah Md. Ashraful; Matsuo, Shigeru; Setoguchi, Toshiaki

    2010-02-01

    Pronounced aeroacoustic resonances are exhibited in the flowfield where a jet emerges from an orifice or a nozzle and impinges on a solid surface. One instance where such resonances are produced is in a high speed jet impingement, such as in the space launch vehicle systems, jet-engine exhaust impingement, and in the short take-off and vertical landing (STOVL) aircraft, etc. A highly unsteady flowfield leading to a drastic increase of noise level with very high dynamic pressure and thermal loads are noticed on nearby surfaces results dramatic lift loss, severe ground erosion and hot gas ingestion to the inlet in the jet engines. This highly unsteady behavior of the impinging jets is due to a feedback loop between the fluid and acoustic fields. In actual jet flow, the working gas may contain condensable gas such as steam or moist air. In these cases, the non-equilibrium condensation may occur at the region between nozzle exit and an object. The jet flow with non-equilibrium condensation may be quite different from that without condensation. Therefore, in this study, the effect of the non-equilibrium condensation of moist air on the axisymmetric under-expanded supersonic impinging jet on a vertical flat plate was investigated numerically.

  6. Water cooled steam jet

    DOEpatents

    Wagner, Jr., Edward P.

    1999-01-01

    A water cooled steam jet for transferring fluid and preventing vapor lock, or vaporization of the fluid being transferred, has a venturi nozzle and a cooling jacket. The venturi nozzle produces a high velocity flow which creates a vacuum to draw fluid from a source of fluid. The venturi nozzle has a converging section connected to a source of steam, a diffuser section attached to an outlet and a throat portion disposed therebetween. The cooling jacket surrounds the venturi nozzle and a suction tube through which the fluid is being drawn into the venturi nozzle. Coolant flows through the cooling jacket. The cooling jacket dissipates heat generated by the venturi nozzle to prevent vapor lock.

  7. Water cooled steam jet

    DOEpatents

    Wagner, E.P. Jr.

    1999-01-12

    A water cooled steam jet for transferring fluid and preventing vapor lock, or vaporization of the fluid being transferred, has a venturi nozzle and a cooling jacket. The venturi nozzle produces a high velocity flow which creates a vacuum to draw fluid from a source of fluid. The venturi nozzle has a converging section connected to a source of steam, a diffuser section attached to an outlet and a throat portion disposed there between. The cooling jacket surrounds the venturi nozzle and a suction tube through which the fluid is being drawn into the venturi nozzle. Coolant flows through the cooling jacket. The cooling jacket dissipates heat generated by the venturi nozzle to prevent vapor lock. 2 figs.

  8. Dynamics of laminar circular jet impingement upon convex cylinders

    NASA Astrophysics Data System (ADS)

    New, T. H.; Long, J.

    2015-02-01

    Flow dynamics associated with a laminar circular jet impinging upon a convex cylinder has been investigated by laser-induced fluorescence and digital particle-image velocimetry techniques. Cylinder-to-jet diameter ratios of 1, 2, and 4 were investigated, while the jet-to-cylinder separation distance was kept at four jet diameters throughout. Flow visualization and λ2 criterion results show that once the jet ring-vortices impinge upon the cylindrical surface, they move away from the impingement point by wrapping themselves partially around the surface. As the cylinder diameter increases, wall boundary layer separation, vortex dipole formation, and separation locations are initiated earlier along the cylindrical surface, producing significantly larger wakes. Along the cylinder straight-edges, ring-vortex cores are significantly smaller after impingement. This is due to accentuated vortex-stretching caused by partial wrapping around the cylindrical surface by the ring-vortices, on top of their movement away from the impingement point. Interestingly, vortex dipoles demonstrate a strong tendency to travel upstream and interact with other upstream vortex dipoles, instead of moving downstream gradually seen for flat-surface jet-impingements. Wall shear stress results are also presented to quantify the effects of cylinder diameter-ratio on surface skin friction distribution. Finally, these preceding observations are corroborated and explained in a three-dimensional flow dynamics model presented here.

  9. Shear layer characteristics of supersonic free and impinging jets

    NASA Astrophysics Data System (ADS)

    Davis, T. B.; Kumar, R.

    2015-09-01

    The initial shear layer characteristics of a jet play an important role in the initiation and development of instabilities and hence radiated noise. Particle image velocimetry has been utilized to study the initial shear layer development of supersonic free and impinging jets. Microjet control employed to reduce flow unsteadiness and jet noise appears to affect the development of the shear layer, particularly near the nozzle exit. Velocity field measurements near the nozzle exit show that the initially thin, uncontrolled shear layer develops at a constant rate while microjet control is characterized by a rapid nonlinear thickening that asymptotes downstream. The shear layer linear growth rate with microjet control, in both the free and the impinging jet, is diminished. In addition, the thickened shear layer with control leads to a reduction in azimuthal vorticity for both free and impinging jets. Linear stability theory is used to compute unstable growth rates and convection velocities of the resultant velocity profiles. The results show that while the convection velocity is largely unaffected, the unstable growth rates are significantly reduced over all frequencies with microjet injection. For the case of the impinging jet, microjet control leads to near elimination of the impingement tones and an appreciable reduction in broadband levels. Similarly, for the free jet, significant reduction in overall sound pressure levels in the peak radiation direction is observed.

  10. Measurements in a large angle oblique jet impingement flow

    NASA Technical Reports Server (NTRS)

    Foss, J. F.

    1978-01-01

    The flow field associated with the oblique impingement of an axisymmetric jet was investigated in the externally blown flap configuration for the STOL aircraft. The passive and active spreading characteristics of the shallow angle (a greater than or = approximately to 15 degrees) oblique impingement flow, the role of the initially azimuthal vorticity field, and the stagnation point region were studied, and compared to the large ( a = 45 degres) oblique jet impingement flow. A description of the characteristics of the large angle impingement flow is presented: A flow field near the plate as showing two distinct patterns, one near the location of the maximum surface pressure, and another about the geometric intersection of the jet axis with the plate; and turbulence in the region above the plate which is greater than the one accounted for by the convection of turbulence energy by the mean motion.

  11. Measurements of a single pulse impinging jet. A CFD reference

    NASA Astrophysics Data System (ADS)

    Bovo, Mirko; Rojo, Borja; Golubev, Maxim

    2014-03-01

    This paper reports three sets of measurements of a single pulse impinging jet. The purpose is to serve as a reference for CFD validation. A gas injector generates a single pulse jet at Re ~90000. The jet impinges on a temperature controlled flat target at different angles (0º, 30º, 45º and 60º). The jet velocity field is measured with PIV. The evolution of the jet velocity profile in time is reported at two different locations (suitable as CFD inlet conditions). At the same locations also turbulence quantities are reported. The impingement wall temperature is measured with fast responding thermocouples and infrared camera. These give high time and space resolution respectively. Results are reported in a format suitable for comparison with CFD simulations. The results show that the heat transfer effects are highest for the jet impinging normally on the target. Target inclination has remarkable effects on the jet penetration rate and repeatability. Even small target inclinations result creates a preferential direction for the jet flow and cause a shift in the position of the stagnation region.

  12. Synergistic degradation of chitosan by impinging stream and jet cavitation.

    PubMed

    Huang, Yongchun; Wang, Pengfei; Yuan, Yuan; Ren, Xian'e; Yang, Feng

    2015-11-01

    Chitosan degradation was investigated using a combination of jet cavitation and impinging stream. Different operating parameters such as the initial concentration (1-5 g L(-1)), initial pH (3.2-4.8), solution temperature (30, 40, 50, 60, and 70°C), inlet pressure (0.1-0.45 MPa), and treatment time (0-120 min) were optimized to achieve the maximum degradation of chitosan. After the optimization of jet cavitation parameters, chitosan degradation was carried out using venturi tubes of different structures (the fluidic generator). The efficiency of the jet cavitation degradation was improved significantly by combining with impinging stream. The structures of the degradation products were characterized by Fourier-transform infrared spectroscopy and X-ray diffraction. This study has conclusively established that a combination of jet cavitation and impinging stream can be effectively used for the complete degradation of chitosan.

  13. Supersonic impinging jet noise reduction using a hybrid control technique

    NASA Astrophysics Data System (ADS)

    Wiley, Alex; Kumar, Rajan

    2015-07-01

    Control of the highly resonant flowfield associated with supersonic impinging jet has been experimentally investigated. Measurements were made in the supersonic impinging jet facility at the Florida State University for a Mach 1.5 ideally expanded jet. Measurements included unsteady pressures on a surface plate near the nozzle exit, acoustics in the nearfield and beneath the impingement plane, and velocity field using particle image velocimetry. Both passive control using porous surface and active control with high momentum microjet injection are effective in reducing nearfield noise and flow unsteadiness over a range of geometrical parameters; however, the type of noise reduction achieved by the two techniques is different. The passive control reduces broadband noise whereas microjet injection attenuates high amplitude impinging tones. The hybrid control, a combination of two control methods, reduces both broadband and high amplitude impinging tones and surprisingly its effectiveness is more that the additive effect of the two control techniques. The flow field measurements show that with hybrid control the impinging jet is stabilized and the turbulence quantities such as streamwise turbulence intensity, transverse turbulence intensity and turbulent shear stress are significantly reduced.

  14. Thermal Management Using Pulsating Jet Cooling Technology

    NASA Astrophysics Data System (ADS)

    Alimohammadi, S.; Dinneen, P.; Persoons, T.; Murray, D. B.

    2014-07-01

    The existing methods of heat removal from compact electronic devises are known to be deficient as the evolving technology demands more power density and accordingly better cooling techniques. Impinging jets can be used as a satisfactory method for thermal management of electronic devices with limited space and volume. Pulsating flows can produce an additional enhancement in heat transfer rate compared to steady flows. This article is part of a comprehensive experimental and numerical study performed on pulsating jet cooling technology. The experimental approach explores heat transfer performance of a pulsating air jet impinging onto a flat surface for nozzle-to-surface distances 1 <= H/D <= 6, Reynolds numbers 1,300 <= Re <= 2,800 pulsation frequency 2Hz <= f <= 65Hz, and Strouhal number 0.0012 <= Sr = fD/Um <= 0.084. The time-resolved velocity at the nozzle exit is measured to quantify the turbulence intensity profile. The numerical methodology is firstly validated using the experimental local Nusselt number distribution for the steady jet with the same geometry and boundary conditions. For a time-averaged Reynolds number of 6,000, the heat transfer enhancement using the pulsating jet for 9Hz <= f <= 55Hz and 0.017 <= Sr <= 0.102 and 1 <= H/D <= 6 are calculated. For the same range of Sr number, the numerical and experimental methods show consistent results.

  15. Thermal-hydraulic performance of convective boiling jet array impingement

    NASA Astrophysics Data System (ADS)

    Jenkins, R.; De Brún, C.; Kempers, R.; Lupoi, R.; Robinson, A. J.

    2016-09-01

    Jet impingement boiling is investigated with regard to heat transfer and pressure drop performance using a novel laser sintered 3D printed jet impingement manifold design. Water was the working fluid at atmospheric pressure with inlet subcooling of 7oC. The convective boiling performance of the impinging jet system was investigated for a flat copper target surface for 2700≤Re≤5400. The results indicate that the heat transfer performance of the impinging jet is independent of Reynolds number for fully developed boiling. Also, the investigation of nozzle to plate spacing shows that low spacing delays the onset of nucleate boiling causing a superheat overshoot that is not observed with larger gaps. However, no sensitivity to the gap spacing was measured once boiling was fully developed. The assessment of the pressure drop performance showed that the design effectively transfers heat with low pumping power requirements. In particular, owing to the insensitivity of the heat transfer to flow rate during fully developed boiling, the coefficient of performance of jet impingement boiling in the fully developed boiling regime deteriorates with increased flow rate due to the increase in pumping power flux.

  16. Modeling 2-D jets impinging on Stirling regenerators

    NASA Technical Reports Server (NTRS)

    Gedeon, David

    1989-01-01

    The extent to which flow leaving Stirling coolers or heaters in the form of high-velocity jets penetrate the regenerator matrix is visually modeled using a computer program. Two-dimensional laminar jets are shown impinging on regenerator samples of variable permeability ranging from no matrix at all to matrices dense enough to stop the jet dead on. The results lend credibility to a simple tension for flow uniformity as a function of penetration depth.

  17. Numerical investigation of mist/air impingement cooling on ribbed blade leading-edge surface.

    PubMed

    Bian, Qingfei; Wang, Jin; Chen, Yi-Tung; Wang, Qiuwang; Zeng, Min

    2017-05-23

    The working gas turbine blades are exposed to the environment of high temperature, especially in the leading-edge region. The mist/air two-phase impingement cooling has been adopted to enhance the heat transfer on blade surfaces and investigate the leading-edge cooling effectiveness. An Euler-Lagrange particle tracking method is used to simulate the two-phase impingement cooling on the blade leading-edge. The mesh dependency test has been carried out and the numerical method is validated based on the available experimental data of mist/air cooling with jet impingement on a concave surface. The cooling effectiveness on three target surfaces is investigated, including the smooth and the ribbed surface with convex/concave columnar ribs. The results show that the cooling effectiveness of the mist/air two-phase flow is better than that of the single-phase flow. When the ribbed surfaces are used, the heat transfer enhancement is significant, the surface cooling effectiveness becomes higher and the convex ribbed surface presents a better performance. With the enhancement of the surface heat transfer, the pressure drop in the impingement zone increases, but the incremental factor of the flow friction is smaller than that of the heat transfer enhancement. Copyright © 2017 Elsevier Ltd. All rights reserved.

  18. Influence of elliptical structure on impinging-jet-array heat transfer performances

    NASA Astrophysics Data System (ADS)

    Arjocu, Simona C.; Liburdy, James A.

    1997-11-01

    A three-by-three square array of submerged, elliptic, impinging jets in water was used to study the heat transfer distribution in the cooling process of a constant heat flux surface. Tow jet aspect ratios were used, 2 and 3, both with the same hydraulic diameter. The array was tested at Reynolds numbers from 300 to 1500 and impinging distances of 1 to 5 hydraulic diameters. Thermochromic liquid crystals wee used to map the local heat transfer coefficient using a transient method, while the jet temperature was kept constant. The liquid crystal images were recorded through an optical fiber coupled with a CCD camera and a frame grabber and analyzed based on an RGB-temperature calibration technique. The results are reported relative to the unit cell that is used to delimitate the central jet. The heat transfer variation is shown to depend on the impingement distance and Reynolds number. The elliptic jets exhibit axis switching, jet column instability and jet swaying. All of these mechanisms affect the enhancement of the heat transfer rate and its distribution. The results are compared in terms of average and local heat transfer coefficients, for both major and minor planes for the two jet aspect ratios.

  19. Experimental and Computational Study of Underexpanded Jet Impingement Heat Transfer

    NASA Technical Reports Server (NTRS)

    Rufer, Shann J.; Nowak, Robert J.; Daryabeigi, Kamran; Picetti, Donald

    2009-01-01

    An experiment was performed to assess CFD modeling of a hypersonic-vehicle breach, boundary-layer flow ingestion and internal surface impingement. Tests were conducted in the NASA Langley Research Center 31-Inch Mach 10 Tunnel. Four simulated breaches were tested and impingement heat flux data was obtained for each case using both phosphor thermography and thin film gages on targets placed inside the model. A separate target was used to measure the surface pressure distribution. The measured jet impingement width and peak location are in good agreement with CFD analysis.

  20. Average heat-transfer characteristics of a row of circular air jets impinging on a concave surface

    NASA Technical Reports Server (NTRS)

    Livingood, J. N. B.; Gauntner, J. W.

    1972-01-01

    A study of the average heat-transfer characteristics of air jets impinging on the concave side of a right-circular semicylinder is reported. Results from existing correlating are compared with each other and with experimental heat-transfer data for a row of circular jets. Two correlations available in the literature are recommended for use in designing cooled turbine vanes and blades.

  1. Flow field and noise characteristics of a supersonic impinging jet

    NASA Astrophysics Data System (ADS)

    Krothapalli, A.; Rajkuperan, E.; Alvi, F.; Lourenco, L.

    1999-08-01

    This paper describes the results of a study examining the flow and acoustic characteristics of an axisymmetric supersonic jet issuing from a sonic and a Mach 1.5 converging diverging (C D) nozzle and impinging on a ground plane. Emphasis is placed on the Mach 1.5 nozzle with the sonic nozzle used mainly for comparison. A large-diameter circular plate was attached at the nozzle exit to measure the forces generated on the plate owing to jet impingement. The experimental results described in this paper include lift loss, particle image velocimetry (PIV) and acoustic measurements. Suckdown forces as high as 60% of the primary jet thrust were measured when the ground plane was very close to the jet exit. The PIV measurements were used to explain the increase in suckdown forces due to high entrainment velocities. The self-sustained oscillatory frequencies of the impinging jet were predicted using a feedback loop that uses the measured convection velocities of the large-scale coherent vortical structures in the jet shear layer. Nearfield acoustic measurements indicate that the presence of the ground plane increases the overall sound pressure levels (OASPL) by approximately 8 dB relative to a corresponding free jet. For moderately underexpanded jets, the influence of the shock cells on the important flow features was found to be negligible except for close proximity of the ground plane.

  2. Measurements of mean flow and acoustic power for a subsonic jet impinging normal to a large rigid surface

    NASA Technical Reports Server (NTRS)

    Schloth, A. P.

    1976-01-01

    An experimental study was made to measure the mean flow field and acoustic power of a subsonic jet impinging normal to a large rigid surface. A 6.25 cm diameter, circular cool air jet was used at heights of 20, 10, and 5 jet diameters above the surface. The jet exit Mach number was varied from 0.28 to 0.93. Impact and static pressure surveys were made in directions both axial and lateral to the jet axis and also parallel and perpendicular to the surface. Acoustic power was calculated from microphone measurements made during each test run using a diffuse field calibration for the test facility. Results indicate that the flow field for jet impingement is characterized mainly by a strong rise in static pressure in the impingement region near the surface and by boundary layer development in the wall jet region. Acoustic power measurements generally followed a U(8) law for both the free jet and jet impingement although there was some variation especially at high Mach number and for close impingement distances. Overall noise levels increased with decreasing jet-to-surface height. Normalized power spectra correlated well for all cases when the Strouhal number was greater than 0.2; the correlation was poor when the Strouhal number was low.

  3. Numerical study of an impinging jet to a turbulent channel flow in a T-Junction configuration

    NASA Astrophysics Data System (ADS)

    Georgiou, Michail; Papalexandris, Miltiadis

    2016-11-01

    In this talk we report on Large Eddy Simulations of an impinging planar jet to a turbulent channel flow in a T-Junction configuration. Due to its capacity for mixing and heat transfer enhancement, this type of flow is encountered in various industrial applications. In particular, our work is related to the emergency cooling systems of pressurized water reactors. As is well known, this type of flow is dominated by a large separation bubble downstream the jet impingement location. Secondary regions of flow separation are predicted both upstream and downstream the impinging jet. We describe how these separation regions interact with the shear layer that is formed by the injection of the jet to the crossflow, and how they affect the mixing process. In our talk we further examine the influence of the jet's velocity to characteristic quantities of the jet, such as penetration length and expansion angle, as well as to the first and second-order statistics of the flow.

  4. Splattering during turbulent liquid jet impingement on solid targets

    SciTech Connect

    Bhunia, S.K.; Lienhard, J.H. V . Dept. of Mechanical Engineering)

    1994-06-01

    In turbulent liquid jet impingement, a spray of droplets often breaks off of the liquid layer formed on the target. This splattering of liquid alters the efficiencies of jet impingement heat transfer processes and chemical containment safety devices, and leads to problems of aerosol formation in jet impingement cleaning processes. In this paper, the authors present a more complete study of splattering and improved correlations that extend and supersede the previous reports on this topic. The authors report experimental results on the amount of splattering for jets of water, isopropanol-water solutions, and soap-water mixtures. Jets were produced by straight tube nozzles of diameter 0.8--5.8 mm, with fully developed turbulent pipe-flow upstream of the nozzle exist. These experiments cover Weber numbers between 130--31,000, Reynolds numbers between 2,700--98,000, and nozzle-to-target separations of 0.2 [<=]l/d[<=]125. Splattering of up to 75 percent of the incoming jet liquid is observed. The results show that only the Weber number and l/d affect the fraction of jet liquid splattered. The presence of surfactants does not alter the splattering. A new correlation for the onset condition for splattering is given. In addition, the authors establish the range of applicability of the model of Lienhard et al. and the authors provide a more accurate set of coefficients for their correlation.

  5. The Effect of Impingement on Transitional Behavior in Underexpanded Jets

    NASA Technical Reports Server (NTRS)

    Inman, Jennifer A.; Danehy, Paul M.; Nowak, Robert J.; Alderfer, David W.

    2009-01-01

    An investigation into the development of flow unsteadiness in impinging axisymmetric underexpanded jets has been conducted at NASA Langley Research Center. The study has examined the effect of an impingement target placed at various distances and angles on transitional behavior of such jets. Two nozzles, with exit Mach numbers of 1.0 and 2.6, were used in this investigation. Planar laser-induced fluorescence of nitric oxide (NO PLIF) has been used to identify flow unsteadiness and to image transitional and turbulent flow features. Measurements of the location of the onset of various degrees of unsteady flow behavior have been made using these PLIF images. Both qualitative and quantitative comparisons are presented to demonstrate the observed effects of impingement and flow parameters on the process of the transition to turbulence. The presence of the impingement target was found to significantly shorten the distance to transition to turbulence by up to a factor of approximately three, with closer targets resulting in slightly shorter distance to transition and turbulence. The location at which the flow first exhibits unsteadiness was found to have a strong dependence on the presence and location of key flow structures. This paper presents quantitative results on transition criteria for free and impinging jets.

  6. Experimental Study of Impinging Jets Flow-Fields

    DTIC Science & Technology

    2016-07-27

    the jet plumes and outwash flow . Lift plate surface pressure measurements have also been made. The unsteady flow , known to have significant large...contributed to the identification and measurement of the major features of the flow -field generated by the two parallel impinging model jets. These...and outwash flow . 3 Laser Doppler Velocimeter Measurements Highlights of the LDV measurements are presented in the next two figures

  7. Experimental modeling of jet-ring turbine disk cooling

    NASA Technical Reports Server (NTRS)

    Metzger, D. E.; Kim, Y. W.

    1991-01-01

    The experimental facility and some early results are described from a current research program modeling turbine disk cooling with multiple impinging jets, such as employed on the Space Shuttle Main Engine oxygen turbopump. The study is designed to obtain detailed local convection heat transfer rates on specially constructed turbine disk models that employ either multiple cooling jet impingement near the disk outer radius from a jet ring, or alternatively, single entrance coolant supply into the center of the disk cavity. Jet impingement is an effective scheme for cooling of turbine disks at or near the blade attachment region, but the heat transfer mechanisms and merits relative to other schemes are not well understood. The present study employs two specially constructed full scale plastic model disks, contoured and plane, together with the corresponding stators. Local heat transfer rates are determined by a computer vision system from the response of thin liquid crystal coatings applied to the disk test faces. The present results indicate that multiple jet impingement directed at the blade attachment region results in higher cooling rates in that region than does the same flow supplied to the disk center, but this conclusion must be regarded as tentative.

  8. Local heat transfer in a rotating square channel with jet impingement

    SciTech Connect

    Hsieh, S.S.; Huang, J.T.; Liu, C.F.

    1999-11-01

    Jet impingement cooling has long been an area of active research, and with an ever-increasing scope of applications, the field continues to attract plenty of attention. The influence of rotation and jet mass flow rate on the local heat transfer coefficient for a single confined impinging round jet with a fixed jet-to-wall spacing of H/d = 5 was studied for the jet Reynolds number from 6,500 to 26,000 and the rotational Reynolds number from 0 to 112,000. The local heat transfer coefficient along the surface is measured and the effect of the rotation on the stagnation (peak) point, local and average Nusselt number, is presented and discussed. Furthermore, a correlation was developed for the average Nusselt number in terms of the parameters of Re{sub j} and Re{sub {Omega}}. In general, the combined jet impingement and rotation effect are shown to affect the heat transfer response. Rotation decreases the average Nusselt number values from 15 to 25% in outward and inward radial flow, respectively. Finally, comparisons of the present data with existing results for multijets with rotation were also made.

  9. Numerical evaluation of single central jet for turbine disk cooling

    NASA Technical Reports Server (NTRS)

    Subbaraman, M. R.; Hadid, A. H.; Mcconnaughey, P. K.

    1992-01-01

    The cooling arrangement of the Space Shuttle Main Engine High Pressure Oxidizer Turbopump (HPOTP) incorporates two jet rings, each of which produces 19 high-velocity coolant jets. At some operating conditions, the frequency of excitation associated with the 19 jets coincides with the natural frequency of the turbine blades, contributing to fatigue cracking of blade shanks. In this paper, an alternate turbine disk cooling arrangement, applicable to disk faces of zero hub radius, is evaluated, which consists of a single coolant jet impinging at the center of the turbine disk. Results of the CFD analysis show that replacing the jet ring with a single central coolant jet in the HPOTP leads to an acceptable thermal environment at the disk rim. Based on the predictions of flow and temperature fields for operating conditions, the single central jet cooling system was recommended for implementation into the development program of the Technology Test Bed Engine at NASA Marshall Space Flight Center.

  10. Mixing Characteristics of Turbulent Twin Impinging Axisymmetric Jets at Various Impingement Angles

    NASA Astrophysics Data System (ADS)

    Landers, Brian Donn

    An experimental study is first presented on the comparison between two commonly used velocity measurement techniques applied in experimental fluid dynamics: Constant Temperature Anemometry (CTA) and Particle Image Velocimetry (PIV). The comparison is performed in the near-field region of an axisymmetric circular turbulent jet where the flow field contains large scale turbulent structures. The comparison was performed for five Reynolds numbers, based on diameter, between 5,000 and 25,000. The Reynolds numbers selected cover the critical Reynolds number range, 10,000 to 20,000 where the characteristics of the flow transition to a fully developed turbulent mixing layer. A comparison between these two measurement techniques was performed in order to determine the differences between an intrusive (CTA) and non-intrusive (PIV) method when applied to a practical application. The results and observations obtained from the comparison between the two techniques were applied to better characterize the time-averaged characteristics of a single axisymmetric turbulent jet with a Reynolds number of 7,500. The mean and fluctuating velocities, turbulent kinetic energy (TKE), and vorticity were measured as a baseline case. Additionally, smoke visualization was utilized to determine the mixing characteristics of the transient start of an axisymmetric turbulent jet. The shedding frequencies, also known as, the `preferred mode were investigated for a single jet. Particle Image Velocimetry (PIV) was also utilized to characterize the pre-and post-regions of the interaction region of two axisymmetric, incompressible turbulent jets at included angles: 30, 45, and 60 degrees. The Reynolds number selected (7,500) was within the range of critical Reynolds numbers and the geometrical distance to twin jet impingement, X0, remained constant at 10.33D for each impingement angle. The mean and fluctuating velocities, vorticity, and turbulent kinetic energy (TKE) were measured. Smoke Visualization

  11. Impinging Jets and the Erodibility of Cohesive Sediment

    NASA Astrophysics Data System (ADS)

    Karamigolbaghi, M.; Bennett, S. J.; Ghaneeizad, S. M.; Atkinson, J. F.

    2016-12-01

    Defining the erodibility of cohesive sediment remains a critical challenge in Earth surface systems. The primary geomorphic law used in such applications relates erosion rate to an erodibility coefficient and an excess shear stress term. To assess erodibility, an inverse modeling approach can be adopted, wherein a known stress is applied to the cohesive sediment, and the erodibility parameters can be deduced through observation of erosion as a function of time. An impinging jet, as used in the jet erosion test, would appear to be an ideal flow (stress) source for erosion assessment. Recent work, however, has demonstrated that jet hydrodynamics can depart significantly from ideal flow conditions when employed for in situ erosion assessment. Here we will review jet theory and the use of jets for assessing the erodibility of cohesive sediment. Our results show that (1) flow confinement and the generation of secondary circulation can significantly change bed shear stress near and downstream of impingement, (2) the evolving scour hole shape, as conditioned by material characteristics and the erosion process, can significantly alter jet hydrodynamics and bed shear stress magnitudes and distributions near and downstream of impingement, and (3) incidental variations in material characteristics in carefully-executed, long-lived experiments can produce markedly different scour hole shapes and derived erodibility indices. Examples from experimental, numerical, and field observations will be used to illustrate these hydrodynamic and material effects on observed and predicted erosion rates. Because such effects are difficult to anticipate, the uncertainty of in situ cohesive sediment assessments using impinging jets can be quite large.

  12. Directional transport of impinging capillary jet on wettability engineered surfaces

    NASA Astrophysics Data System (ADS)

    Ghosh, Aritra; Chatterjee, Souvick; Sinha Mahapatra, Pallab; Ganguly, Ranjan; Megaridis, Constantine

    2015-11-01

    Impingement of capillary jet on a surface is important for applications like heat transfer, or for liquid manipulation in bio-microfluidic devices. Using wettability engineered surfaces, we demonstrate pump-less and directional transport of capillary jet on a flat surface. Spatial contrast of surface energy and a wedge-shape geometry of the wettability confined track on the substrate facilitate formation of instantaneous spherical bulges upon jet impingement; these bulges are further transported along the superhydrophilic tracks due to Laplace pressure gradient. Critical condition warranted for formation of liquid bulge along the varying width of the superhydrophilic track is calculated analytically and verified experimentally. The work throws light on novel fluid phenomena of unidirectional jet impingement on wettability confined surfaces and provides a platform for innovative liquid manipulation technique for further application. By varying the geometry and wettability contrast on the surface, one can achieve volume flow rates of ~ O(100 μL/sec) and directionally guided transport of the jet liquid, pumplessly at speeds of ~ O(10cm/sec).

  13. Spray Formation of Herschel-Bulkley Fluids using Impinging Jets

    NASA Astrophysics Data System (ADS)

    Rodrigues, Neil; Gao, Jian; Chen, Jun; Sojka, Paul E.

    2015-11-01

    The impinging jet spray formation of two non-Newtonian, shear-thinning, Herschel-Bulkley fluids was investigated in this work. The water-based gelled solutions used were 1.0 wt.-% agar and 1.0 wt.-% kappa carrageenan. A rotational rheometer and a capillary viscometer were used to measure the strain-rate dependency of viscosity and the Herschel-Bulkley Extended (HBE) rheological model was used to characterize the shear-thinning behavior. A generalized HBE jet Reynolds number Rej , gen - HBE was used as the primary parameter to characterize the spray formation. A like-on-like impinging jet doublet was used to produce atomization. Shadowgraphs were captured in the plane of the sheet formed by the two jets using a CCD camera with an Nd:YAG laser beam providing the back-illumination. Typical behavior for impinging jet atomization using Newtonian liquids was not generally observed due to the non-Newtonian, viscous properties of the agar and kappa carrageenan gels. Instead various spray patterns were observed depending on Rej , gen - HBE. Spray characteristics of maximum instability wavelength and sheet breakup length were extracted from the shadowgraphs. Multi-University Research Initiative Grant Number W911NF-08-1-0171.

  14. Visualization of the flow field in a confined and submerged impinging jet

    SciTech Connect

    Fitzgerald, J.A.; Garimella, S.V.

    1997-07-01

    The high heat transfer rates that can be obtained through the use of jet impingement cooling have led to its use in a variety of applications, including paper drying, glass manufacturing, turbine-blade cooling, and electronics cooling. Here, the flow field of a normally impinging, axisymmetric, confined and submerged liquid kit is studied using flow visualization. The results are compared with computations and experimental measurements of the flow field, and are used to describe the position of the recirculating toroid in the outflow region which is characteristic of the confined flow field. Changes in the features of the recirculation pattern due to changes in Reynolds number, nozzle diameter and nozzle-to-target plate spacing are documented. Results are presented for nozzle diameters of 3.18, 6.35, and 12.7 mm, at jet Reynolds numbers in the range of 2,000 to 23,000, and nozzle-to-target plate spacings of 1, 2, 3, and 4 jet diameters. Up to three interacting vertical structures are observed in the confinement region at the smaller Reynolds numbers. The center of the primary recirculation pattern moves away from the centerline of the jet with an increase in Reynolds number, nozzle diameter, and nozzle-to-target plate spacing. As the recirculating toroid moves away from the jet axis, more of the ambient fluid is entrained into the confinement region.

  15. Effect of impinging plate geometry on the self-excitation of subsonic impinging jets

    NASA Astrophysics Data System (ADS)

    Vinoth, B. R.; Rathakrishnan, E.

    2011-11-01

    In the generation of discrete tones by subsonic impinging jets, there exists a difference of opinion as how the feedback is achieved, i.e., the path of the feedback acoustic waves is whether inside the jet or outside the jet? The only available model (Tam and Ahuja model) for the prediction of an average subsonic jet impingement tone frequency assumes that the upstream part of the feedback loop is closed by an upstream propagating neutral wave of the jet. But, there is no information about the plate geometry in the model. The present study aims at understanding the effect of the plate geometry (size and co-axial hole in the plate) on the self-excitation process of subsonic impinging jets and the path of the acoustic feedback to the nozzle exit. The present results show that there is no effect of plate diameter on the frequency of the self-excitation. A new type of tones is generated for plates with co-axial hole (hole diameter is equal to nozzle exit diameter) for Mach numbers 0.9 and 0.95, in addition to the axisymmetric and helical mode tones observed for plates without co-axial hole. The stability results show that the Strouhal number of the least dispersive upstream propagating neutral waves match with the average Strouhal number of the new tones observed in the present experiments. The present study extends the validity of the model of Tam and Ahuja to a plate with co-axial hole (annular plate) and by doing so, we indirectly confirmed that the major acoustic feedback path to the nozzle exit is inside the jet.

  16. Cryogenic Impinging Jets Subjected to High Frequency Transverse Acoustic Forcing in a High Pressure Environment

    DTIC Science & Technology

    2016-07-27

    numerical study on the physical mechanism of impact waves and mixing process, and atomization of impinging jets. Chen et al carried out his numerical...used to capture the physical response of impact waves present on impingement sheet formed by two like on like impinging jets. Dynamic mode...speed, backlit imaging was used to capture the physical response of impact waves present on impingement sheet formed by two like on like impinging

  17. Impinging jet atomization at elevated and supercritical ambient conditions

    NASA Astrophysics Data System (ADS)

    Shen, Yunbiao

    This thesis presents an experimental study of the atomization of two impinging jets at elevated pressure and temperature conditions up to the supercritical ambient states. This problem is of central importance to the modeling of the mixing and combustion processes in modern liquid propellant rocket engines. Liquid nitrogen, as well as water, ethanol and 59% water glycerol solution are used as the test fluids. Sprays of various fluid properties are injected into the specially designed test chambers at temperatures as high as 600 K and elevated pressures up to the critical pressure of nitrogen. The thickness of a spreading sheet formed by the impingement of low speed jets is measured by real time interferometry. The results verified previous theoretical prediction. Double pulse, two reference beam holography is improved and applied in the droplet size and velocity measurements. Experiments indicate that in elevated but subcritical ambient conditions, the increase of ambient temperature will generally improve the fineness and uniformity of the spray. However, increase of the ambient pressure initially deteriorates the atomization quality. Further increase in the pressure improves the atomization quality. At supercritical ambient conditions, droplet formation is no longer the ultimate reason of spray atomization. The mechanism of spray mixing is found to be 'diffusion controlled' rather than 'evaporation controlled' as in subcritical conditions. Explanations of the experimental results are provided through the temperature and pressure dependence of the aerodynamic disturbances on the spray surface, heat and mass transport, aerodynamic drag and surface tension. The effects of jet diameter, impingement angle and jet velocity are also investigated in both subcritical and supercritical conditions. The atomization quality is found to be generally improved by smaller jet diameter, larger impingement angle and higher jet velocity.

  18. Jet array impingement with crossflow-correlation of streamwise resolved flow and heat transfer distributions

    NASA Technical Reports Server (NTRS)

    Florschuetz, L. W.; Metzger, D. E.; Truman, C. R.

    1981-01-01

    Correlations for heat transfer coefficients for jets of circular offices and impinging on a surface parallel to the jet orifice plate are presented. The air, following impingement, is constrained to exit in a single direction along the channel formed by the jet orifice plate and the heat transfer (impingement) surface. The downstream jets are subjected to a crossflow originating from the upstream jets. Impingement surface heat transfer coefficients resolved to one streamwise jet orifice spacing, averaged across the channel span, are correlated with the associated individual spanwise orifice row jet and crossflow velocities, and with the geometric parameters.

  19. Impingement flow heat transfer measurements of turbine blades using a jet array

    NASA Astrophysics Data System (ADS)

    Vantreuren, Kenneth W.

    1994-08-01

    The requirement for increased gas turbine engine performance has led to the use of much higher turbine entry temperature (TET). The higher temperatures require active cooling of the turbine blade using compressor bleed air. Arrays of impinging jets are one method currently used to reduce the blade temperature on the midspan and leading edge. Air flows through small holes in a blade insert and is directed on the inside surface of a turbine blade to reduce local surface temperature. The engine situation was represented by a 10-20 times scale model tested in the internal cooling transient facility at the University of Oxford. The geometry chosen was for a widely spaced array with a jet spacing of 8d and a plate thickness to jet diameter of 1.2. Experiments were accomplished for a range of impingement plate to target surface spacings, z/d, (1, 2 and 4) and jet Reynolds numbers, Re(sub j), (10,000 - 40,000) with both staggered and inline array hole configurations. The transient liquid crystal technique, both peak intensity narrowband and hue temperature history wideband, enabled the determination of heat transfer coefficient and adiabatic wall temperature. For the first time, local detail of heat transfer on the target surface as well as observation of the crossflow influence on the jet at the target surface are possible. A large variation in heat transfer exists between the stagnation point and channel passage between jets (2-4 times) which was unknown in previous experiments.

  20. Mach number effect on jet impingement heat transfer.

    PubMed

    Brevet, P; Dorignac, E; Vullierme, J J

    2001-05-01

    An experimental investigation of heat transfer from a single round free jet, impinging normally on a flat plate is described. Flow at the exit plane of the jet is fully developed and the total temperature of the jet is equal to the ambient temperature. Infrared measurements lead to the characterization of the local and averaged heat transfer coefficients and Nusselt numbers over the impingement plate. The adiabatic wall temperature is introduced as the reference temperature for heat transfer coefficient calculation. Various nozzle diameters from 3 mm to 15 mm are used to make the injection Mach number M vary whereas the Reynolds number Re is kept constant. Thus the Mach number influence on jet impingement heat transfer can be directly evaluated. Experiments have been carried out for 4 nozzle diameters, for 3 different nozzle-to-target distances, with Reynolds number ranging from 7200 to 71,500 and Mach number from 0.02 to 0.69. A correlation is obtained from the data for the average Nusselt number.

  1. Performance analysis and design optimization of micro-jet impingement heat sink

    NASA Astrophysics Data System (ADS)

    Husain, Afzal; Kim, Sun-Min; Kim, Kwang-Yong

    2013-11-01

    This study evaluated a silicon-based micro-jet impingement heat sink for electronic cooling applications. First, the pressure-drop and thermal characteristics were investigated for steady incompressible and laminar flow by solving three-dimensional Navier-Stokes equations, and the performance enhancement was carried out through parametric and optimization studies. Several parallel and staggered micro-jet configurations consisting of a maximum of 16 jet impingements were tested. The effectiveness of the micro-jet configurations, i.e. inline 2 × 2, 3 × 3 and 4 × 4 jets, and staggered 5-jet and 13-jet arrays with nozzle diameters 50, 76, and 100 μm, were analyzed at various flow rates for the maximum temperature-rise and pressure-drop characteristics. A design with a staggered 13-jet array showed the best performance among the various configurations investigated in the present study. The design optimization based on three-dimensional numerical analysis, surrogate modeling and a multi-objective evolutionary algorithm were carried out to understand the thermal resistance and pumping power correlation of the micro-jet impingement heat sink. Two design variables, the ratio of height of the channel and nozzle diameter, and the ratio of nozzle diameter and interjet spacing, were chosen for design optimization. The global Pareto-optimal front was achieved for overall thermal resistance and required pumping power of the heat sink. The Pareto-optimal front revealed existing correlation between pumping power and thermal resistance of the heat sink. Of the range of Pareto-optimal designs available, some representative designs were selected and their functional relationships among the objective functions and design variables were examined to understand the Pareto-optimal sensitivity and optimal design space. A minimum of 66 °C of maximum-temperature-rise was obtained for a heat flux of 100 W/cm2 at a pressure drop of about 24 kPa.

  2. The jet impingement phase of molten core-concrete interactions

    SciTech Connect

    Sienicki, J.J.; Spencer, B.W.

    1986-01-01

    Scoping calculations have been carried out demonstrating that a significant and abrupt reduction in the corium temperature may be realized when molten corium drains as a jet from a localized breach in the RPV lower head to impinge upon the concrete basemat. The temperature decrease may range from a value of approx.170 K (approx.140 K) for limestone (basaltic) aggregate concrete to a value approaching the initial corium superheat depending upon whether the forced convection impingement heat flux is assumed to be controlled by either thermal conduction across a slag film layer or the temperature boundary condition represented by a corium crust. The magnitude of the temperature reduction remains significant as the initial corium temperature, impinging corium mass, and initial localized breach size are varied over their range of potential values.

  3. Computational analysis for dry-ice sublimation assisted CO2 jet impingement flow

    NASA Astrophysics Data System (ADS)

    Kwak, Songmi; Lee, Jaeseon

    2015-11-01

    The flow and heat transfer characteristics of the novel gas-solid two-phase jet impingement are investigated computationally. When the high pressure carbon dioxide (CO2) flow passes through a nozzle or orifice, it experiences the sudden expansion and the rapid temperature drop occurred by Joule-Thomson effect. This temperature drop causes the lower bulk jet fluid temperature than the CO2 sublimation line, so dry-ice becomes formed. By using CO2 gas-solid mixture as a working fluid of jet impingement, it is expected the heat transfer enhancement can be achieved due to the low bulk temperature and the additional phase change latent heat. In this study, 2D CFD model is created to predict the cooling effect of gas-solid CO2 jet. The gas-solid CO2 flow is considered by Euler-Lagrangian approach of mixed phase and the additional heat transfer module is embedded to account for the sublimation phenomena of the solid state CO2. The jet flow and heat transfer performance of gas-solid CO2 jet is investigated by the variance of flow parameter like Reynolds number, solid phase concentration and jet geometries.

  4. Experimental study of highly viscous impinging jets

    SciTech Connect

    Gomon, M.

    1998-12-01

    The objective of this research is to study the behavior of highly viscous gravity-driven jets filling a container. Matters of interest are the formation of voids in the fluid pool during the filling process and the unstable behavior of the fluid in the landing region which manifests itself as an oscillating motion. The working fluids used in this research are intended to simulate the flow behavior of molten glass. Qualitative and quantitative results are obtained in a parametric study. The fraction of voids present in the fluid pool after the filling of the container is measured for different parameter values of viscosity and mass flow rate. Likewise, frequencies of the oscillating jet are measured. Results are inconclusive with regard to a correlation between parameter settings and void fractions. As for frequencies, power law correlations are established.

  5. Two-phase structure above hot surfaces in jet impingement boiling

    NASA Astrophysics Data System (ADS)

    Bogdanic, L.; Auracher, H.; Ziegler, F.

    2009-05-01

    Jet impingement boiling is very efficient in cooling of hot surfaces as a part of the impinging liquid evaporates. Several studies have been carried out to measure and correlate the heat transfer to impinging jets as a function of global parameters such as jet subcooling, jet velocity, nozzle size and distance to the surface, etc. If physically based mechanistic models are to be developed, studies on the fundamentals of two-phase dynamics near the hot surface are required. In the present study the vapor-liquid structures underneath a subcooled (20 K) planar (1 mm × 9 mm) water jet, impinging the heated plate vertically with a velocity of 0.4 m/s, were analyzed by means of a miniaturized optical probe. It has a tip diameter of app. 1.5 μm and is moved toward the plate by a micrometer device. The temperature controlled experimental technique enabled steady-state experiments in all boiling regimes. The optical probe data provides information about the void fraction, the contact frequencies and the distribution of the vapor and liquid contact times as a function of the distance to the surface. The measured contact frequencies range from 40 Hz at the onset of nucleate boiling to nearly 20,000 Hz at the end of the transition boiling regime. Due to condensation in the subcooled jet vapor disappears at a distance to the surface of app. 1.2 mm in nucleate boiling. This vapor layer becomes smaller with increasing wall superheat. In film boiling a vapor film thickness of 8 ± 2 μm was found.

  6. Heat transfer measurements and CFD simulations of an impinging jet

    NASA Astrophysics Data System (ADS)

    Petera, Karel; Dostál, Martin

    2016-03-01

    Heat transport in impinging jets makes a part of many experimental and numerical studies because some similarities can be identified between a pure impingement jet and industrial processes like, for example, the heat transfer at the bottom of an agitated vessel. In this paper, experimental results based on measuring the response to heat flux oscillations applied to the heat transfer surface are compared with CFD simulations. The computational cost of a LES-based approach is usually too high therefore a comparison with less computationally expensive RANS-based turbulence models is made in this paper and a possible improvement of implementing an anisotropic explicit algebraic model for the turbulent heat flux model is evaluated.

  7. Turbulence measurements in a rectangular mesoscale confined impinging jets reactor

    NASA Astrophysics Data System (ADS)

    Somashekar, Vishwanath; Liu, Ying; Fox, Rodney O.; Olsen, Michael G.

    2012-12-01

    Mesoscale chemical reactors capable of operating in the turbulent flow regime, such as confined impinging jets reactors (CIJR), offer many advantages for rapid chemical processing at the microscale. One application where these reactors are used is flash nanoprecipitation, a method for producing functional nanoparticles. Because these reactors often operate in a flow regime just beyond transition to turbulence, modeling flows in these reactors can be problematic. Moreover, validation of computational fluid dynamics models requires detailed and accurate experimental data, the availability of which has been very limited for turbulent microscale flows. In this work, microscopic particle image velocimetry (microPIV) was performed in a mesoscale CIJR at inlet jet Reynolds numbers of 200, 1,000, and 1,500. Pointwise and spacial turbulence statistics were calculated from the microPIV data. The flow was observed to be laminar and steady in the entire reactor at a Reynolds number of 200. However, at jets Reynolds numbers of 1,000 and 1,500, instabilities as a result of the jets impinging along the centerline of the reactor lead to a highly turbulent impingement region. The peak magnitude of the normalized Reynolds normal and shear stresses within this region were approximately the same for the Reynolds numbers of 1,000 and 1,500. The Reynolds shear stress was found to exhibit a butterfly shape, consistent with a flow field dominated by an oblique rocking of the impingement zone about the center of the reactor. Finally, the spatial auto- and cross-correlations velocity fluctuations were calculated and analyzed to obtain an understanding of size of the coherent structures.

  8. Ground Impingement of a Fan Jet Exhaust Plume

    DTIC Science & Technology

    1978-05-01

    1 - 100, where a very heavy oil line appears in Fig. lOb due to vane dcflection. A Vh/df 2 xd . qfIqc, w 6 h/drd, qf~ j ~ t+ + + + ++4+t444 4...Memorandum RN- -653 j ’~,i7) GROUND IMPINGEMENT OF A FAN JET EXHIAUST PLUME* C I DO William C/Hill, Jr. Richard C ./Jenkins Fluid Dynamics May 1078...19 13 Wall Jot Profiles for Vate ic 0..................... 20 14 Wall Jet Profiles for Vane w +200,....................... 21 15 Effects of Vae

  9. Hybrid RANS/LES of round impinging jets

    NASA Astrophysics Data System (ADS)

    Kubacki, Slawomir; Rokicki, Jacek; Dick, Erik

    2011-12-01

    Fluid flow and heat transfer characteristics are presented for simulations of round impinging jets at two nozzle-plate distances H/D = 2 and 10 (D is the nozzle exit diameter) and two Reynolds numbers Re = 5000 and 70,000 with hybrid RANS/LES (Reynolds-averaged Navier-Stokes/Large Eddy Simulation), dynamic Smagorinsky LES and RANS k-ω models. Three k-ω based hybrid RANS/LES models are analyzed. With the hybrid RANS/LES models, improved heat transfer results are obtained, when compared to RANS, in the impact region and in the developing wall-jet region. For accurate predictions at low nozzle-plate distance, it is necessary to sufficiently resolve the formation and development of the near-wall vortices in the jet impingement region. At high nozzle-plate distance, it is important to capture the evolution and breakup of the unsteady vortices in the shear layer of the jet, so that realistic mean and fluctuating velocity profiles are obtained in the impact jet region.

  10. Experimental Optimisation of the Thermal Performance of Impinging Synthetic Jet Heat Sinks

    NASA Astrophysics Data System (ADS)

    Marron, Craig; Persoons, Tim

    2014-07-01

    Zero-net-mass flow synthetic jet devices offer a potential solution for energy- efficient cooling of medium power density electronic components. There remains an incomplete understanding of the interaction of these flows with extended surfaces, which prevents the wider implementation of these devices in the field. This study examines the effect of the main operating parameters on the heat transfer rate and electrical power consumption for a synthetic jet cooled heat sink. Three different heat sink geometries are tested. The results find that a modified sink with a 14 × 14 pin array with the central 6 × 6 pins removed provides superior cooling to either a fully pinned sink or flat plate. Furthermore each heat sink is found to have its own optimum jet orifice-to-sink spacing for heat transfer independent of flow conditions. The optimum heat transfer for the modified sink is H = 34 jet diameters. The effect of frequency on heat transfer is also studied. It is shown that heat transfer increases superlinearly with frequency at higher stroke lengths. The orientation of the impingement surface with respect to gravity has no effect on the heat transfer capabilities of the tested device. These tests are the starting point for further investigation into enhanced synthetic jet impingement surfaces. The equivalent axial fan cooled pinned heat sink (Malico Inc. MFP40- 18) has a thermal resistance of 1.93K/W at a fan power consumption of 0.12W. With the modified pinned heat sink, a synthetic jet at Re = 911, L0/D = 10, H/D = 30 provides a thermal resistance of 2.5K/W at the same power consumption.

  11. Defrosting of a Heat Exchanger for Precooled Turbojet Engines Using Jet Impingement

    NASA Astrophysics Data System (ADS)

    Fukiba, Katsuyoshi; Inoue, Shou; Sato, Tetsuya; Ohkubo, Hidetoshi

    An innovative defrosting method for precooled turbojet engines are presented, and validated in this study using experimental methods. High speed gas jet was impinged on the cooling tubes of a heat exchanger for the purpose of defrosting. The coolant of the heat exchanger was liquid nitrogen, and whose temperature was 83K. The air flow speed, the air temperature and the air humidity were 1.0m/s, 23ºC and 59%, respectively. The effects of the jet duration, jet intervals and humidity of the jet gas on the heat exchange were assessed. As a result, we found that the presenting defrosting method is valid for the defrosting of the precooler.

  12. A computational study of highly viscous impinging jets

    SciTech Connect

    Silva, M.W.

    1998-11-01

    Two commercially-available computational fluid dynamics codes, FIDAP (Fluent, Inc., Lebanon, NH) and FLOW-3D (Flow Science, Inc., Los Alamos, NM), were used to simulate the landing region of jets of highly viscous fluids impinging on flat surfaces. The volume-of-fluid method was combined with finite difference and finite element approaches to predict the jet behavior. Several computational models with varying degrees of physical realism were developed, and the results were compared with experimental observations. In experiments, the jet exhibited several complex behaviors. As soon as it exited the nozzle, the jet began to neck down and become narrower. When it impacted the solid surface, the jet developed an instability near the impact point and buckled to the side. This buckling became a spiraling motion, and the jet spiraled about the impact point. As the jet spiraled around, a cone-shaped pile was build up which eventually became unstable and slumped to the side. While all of these behaviors were occurring, air bubbles, or voids, were being entrapped in the fluid pool. The results obtained from the FLOW-3D models more closely matched the behavior of real jets than the results obtained from /the FIDAP models. Most of the FLOW-3D models predicted all of the significant jet behaviors observed in experiments: necking, buckling, spiraling, slumping, and void entrapment. All of the FIDAP models predicted that the jet would buckle relatively far from the point of impact, whereas the experimentally observed jet behavior indicates that the jets buckle much nearer the impact point. Furthermore, it was shown that FIDAP is incapable of incorporating heat transfer effects into the model, making it unsuitable for this work.

  13. Reduction of glycine particle size by impinging jet crystallization.

    PubMed

    Tari, Tímea; Fekete, Zoltán; Szabó-Révész, Piroska; Aigner, Zoltán

    2015-01-15

    The parameters of crystallization processes determine the habit and particle size distribution of the products. A narrow particle size distribution and a small average particle size are crucial for the bioavailability of poorly water-soluble pharmacons. Thus, particle size reduction is often required during crystallization processes. Impinging jet crystallization is a method that results in a product with a reduced particle size due to the homogeneous and high degree of supersaturation at the impingement point. In this work, the applicability of the impinging jet technique as a new approach in crystallization was investigated for the antisolvent crystallization of glycine. A factorial design was applied to choose the relevant crystallization factors. The results were analysed by means of a statistical program. The particle size distribution of the crystallized products was investigated with a laser diffraction particle size analyser. The roundness and morphology were determined with the use of a light microscopic image analysis system and a scanning electron microscope. Polymorphism was characterized by differential scanning calorimetry and powder X-ray diffraction. Headspace gas chromatography was utilized to determine the residual solvent content. Impinging jet crystallization proved to reduce the particle size of glycine. The particle size distribution was appropriate, and the average particle size was an order of magnitude smaller (d(0.5)=8-35 μm) than that achieved with conventional crystallization (d(0.5)=82-680 μm). The polymorphic forms of the products were influenced by the solvent ratio. The quantity of residual solvent in the crystallized products was in compliance with the requirements of the International Conference on Harmonization. Copyright © 2014 Elsevier B.V. All rights reserved.

  14. Discharge coefficients of impingement and film cooling holes

    NASA Astrophysics Data System (ADS)

    Chu, T.; Brown, A.; Garret, S.

    1985-03-01

    In this article measurements of fluid flow through impingement and film cooling holes for typical turbine blade cooling systems are presented. The purpose of the measurements was to determine hole discharge coefficients over a range of Reynolds numbers from 5,000 to 30,000 and to observe in this range the dependence of discharge coefficient on Reynolds number. The effect of hole geometry, that is, sharp edged inlet or corner radius inlet, on discharge coefficients is also measured. Correlations relating discharge coefficients to Reynolds number, corner radius to hole diameter ratio, and blowing parameter are suggested.

  15. Sound source mechanisms in under-expanded impinging jets

    NASA Astrophysics Data System (ADS)

    Sinibaldi, Giorgia; Marino, Luca; Romano, Giovanni Paolo

    2015-05-01

    Experiments on the aeroacoustics of an under-expanded supersonic jet impinging on a flat plate are presented and thoroughly discussed. A wide range of nozzle pressure ratios and of nozzle-to-plate distances has been analyzed with particular attention to the behavior of the discrete component of the noise. The investigation has been carried out by means of acoustic, particle image velocimetry and wall pressure measurements. The analysis of the relationship between the acoustic data and the fluid dynamic fields allows to examine the different source mechanisms of the discrete component of the noise and to evaluate the link between the jet flow structure and the acoustic tone features. Specifically, two ranges of nozzle pressure ratio have been observed showing different acoustic behaviors, characterized by distinct mechanisms of discrete noise generation. These regions are separated by a range of nozzle pressure ratios where impinging tones are not observed. The present experimental data extend previously published results, improving the analysis of the connection between fluid dynamic and acoustic fields and leading to a better comprehension of the impinging tone source mechanisms.

  16. Numerical predictions of local entropy generation for an impinging jet

    SciTech Connect

    White, M.D.; Drost, M.K.

    1989-04-01

    Predictions of local volumetric entropy generation rates were made numerically for the convective heat transfer problems of a fluid jet impinging on isothermal and constant heat flux surfaces. The solution technique yielded a scalar field of volumetric entropy generation rates that extends over the fluid domain. For isotropic and Newtonian fluids local entropy generation rates, that stem from the irreversible phenomena of heat transfer across a finite temperature difference and viscous fluid flow, may be computed from fields of temperature, local temperature gradients, and the local viscous dissipation function. The primary points of interest for this problem were to investigate the surface heat transfer rates as a function of inlet jet velocities, and the apportionment between viscous and thermal source entropy generation. The problem investigated was restricted to two-dimensional slot jet flow with two fluids, helium and glycerin. 12 refs., 9 figs., 4 tabs.

  17. Large-eddy simulation of heat transfer from impinging slot jets

    SciTech Connect

    Cziesla, T.; Tandogan, E.; Mitra, N.K.

    1997-07-01

    Impinging jet flows have become a well-established object of investigation in recent years because of their increasing significance in both fundamental and applied fluid mechanics. Examples of a wide range of applications, are the drying of textiles, film, and paper; annealing of glass; processing of some metals and glass; cooling of gas turbine components and the outer wall of combustors and electronic equipment; and freezing of tissue. Here Nusselt number distributions are presented for impinging jet flow of an array of slot nozzles (rectangular jets). The tools to calculate the present turbulent flow are large-eddy simulation (LES) using a dynamic subgrid stress model and the direct numerical simulation (DNS). The numerical code has been validated by comparing computed Nusselt number distributions on the impingement plate for two-dimensional flow with experimental results. A comparison between LES using a logarithmic law of the wall and the DNS shows good agreement of Nusselt number in the Reynolds number range of 600--3,000. The velocity profile at the feed tube exit strongly influences the maximum heat transfer at the stagnation point.

  18. Impinging jet spray formation using non-Newtonian liquids

    NASA Astrophysics Data System (ADS)

    Rodrigues, Neil S.

    Over the past two decades there has been a heightened interest in implementing gelled propellants for rocket propulsion, especially for hypergolic bi-propellants such as monomethylhydrazine (MMH) and nitrogen tetroxide oxidizer (NTO). Due to the very high level of toxicity of hypergolic liquid rocket propellants, increasing safety is an important area of need for continued space exploration and defense operations. Gelled propellants provide an attractive solution to meeting the requirements for safety, while also potentially improving performance. A gelling agent can be added to liquid propellants exhibiting Newtonian behavior to transform the liquid into a non-Newtonian fluid with some solid-like behavior, i.e. a gel. Non-Newtonian jet impingement is very different from its Newtonian counterpart in terms of fluid flow, atomization, and combustion. This is due to the added agents changing physical properties such as the bulk rheology (viscosity) and interfacial rheology (surface tension). Spray characterization of jet impingement with Newtonian liquids has been studied extensively in existing literature. However, there is a scarcity in literature of studies that consider the spray characterization of jet impingement with gelled propellants. This is a rather critical void since a major tradeoff of utilizing gelled propellants is the difficulty with atomization due to the increased effective viscosity. However, this difficulty can be overcome by using gels that exhibit shear-thinning behavior---viscosity decreases with increasing strain rate. Shear-thinning fluids are ideal because they have the distinct advantage of only flowing easily upon pressure. Thereby, greatly reducing the amount of propellant that could be accidentally leaked during both critical functions such as liftoff or engagement in the battlefield and regular tasks like refilling propellant tanks. This experimental work seeks to help resolve the scarcity in existing literature by providing drop size

  19. Kinetics of particle deposition in the oblique impinging jet cell.

    PubMed

    Adamczyk, Zbigniew; Musiał, Elizeusz; Siwek, Barbara

    2004-01-01

    A new oblique impinging-jet (OBIJ) cell was developed, suitable for colloid deposition studies at various interfaces. In contrast to previously used orthogonal cells, the OBIJ construction makes possible direct microscope observations of particle deposition on nontransparent substrates. The cell performance was tested by studying kinetics of polystyrene latex particle deposition on mica. Two limiting cell configuration were used in the experiments: (i) the lower position (inverted microscope observation of substrate surface through air) and (ii) the upper position (observation of the substrate surface with adsorbed particles through the suspension layer). The dependence of local mass transfer rate (particle flux) on the position over the substrate surface was studied for various flow Reynolds numbers. It was demonstrated that deposition rate attained maximum at the flow stagnation point whose position was dependent on Re number. Moreover, it was shown that the local flux decreased at much slower rate when moving in the downstream direction, than for previously used impinging-jet cells. Consequently, the area of uniform transport conditions was larger, enabling more precise determination of the limiting particle flux at the stagnation-point. The dependence of the flux on Re number was systematically studied for various ionic strength of the suspension. It was demonstrated, in accordance with previous results for the ordinary impinging-jet, that the flux increased significantly for low ionic strength and high Re number. This phenomenon, referred to as the inverse salt effect, was interpreted in terms of the convective diffusion theory. The governing transport equation originating from this theory was solved numerically, for the region near the stagnation point, using the finite-difference method. These numerical solutions were used for nonlinear fitting of the flow intensity parameter dependence on the Re number. In this way the flow field in the vicinity of the

  20. An Experimental Study of Jet Impingement on a Circular Cylinder.

    DTIC Science & Technology

    1984-08-01

    4, pp. 72--676. 22. Beltaos , S ., and Rajaratnam, N., "Impinging Circular Turbulent Jets," Proceedings of the ASCE Journal of Hydralics Division, Vol...11. CONTRACT OR GRANT NUMBER( s ) 00 Dennis W. Potts ID WI) :-wiFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT. PROJECT. TASK - ANT STUDENT...necessary and identify by block niber) 70.1. AB6S M’AGC - Contlnu* on reverie side If necessary end vdentify by block number) S ATTACH ED [))"~- 1473

  1. Impingement Flow Heat Transfer Measurements of Turbine Blades Using a Jet Array

    DTIC Science & Technology

    1994-08-01

    wooawrrculatmo sysam 62 pm t 4.9 TlAR of aceilito wth ja pkoue box ......... 62 Rpmg 4. 10 TIU gravity uwtuald fw ating vahv desiged to tisoae the pe, i...fatigue and higher sre problems for the designer. With hot section design life equiments now 50% of the airframe life, users are demanding reliable...different arrays of impinging jets. This gives an indication of where hot spots or problem areas might occur on the blade. The heat transfer or cooling

  2. Conformal mapping technique for two-dimensional porous media and jet impingement heat transfer

    NASA Technical Reports Server (NTRS)

    Siegel, R.

    1974-01-01

    Transpiration cooling and liquid metals both provide highly effective heat transfer. Using Darcy's law in porous media and the inviscid approximation for liquid metals, the local fluid velocity in these flows equals the gradient of a potential. The energy equation and flow region are simplified when transformed into potential plane coordinates. In these coordinates, the present problems are reduced to heat conduction solutions which are mapped into the physical geometry. Results are obtained for a porous region with simultaneously prescribed surface temperature and heat flux, heat transfer in a two-dimensional porous bed, and heat transfer for two liquid metal slot jets impinging on a heated plate.

  3. Conformal mapping technique for two-dimensional porous media and jet impingement heat transfer

    NASA Technical Reports Server (NTRS)

    Siegel, R.

    1973-01-01

    Transpiration cooling and liquid metals both provide highly effective heat transfer. Using Darcy's law in porous media, and the inviscid approximation for liquid metals, the local fluid velocity in these flows equals the gradient of a potential, The energy equation and flow region are simplified when transformed into potential plane coordinates. In these coordinates the present problems are reduced to heat conduction solutions which are mapped into the physical geometry. Results are obtained for a porous region with simultaneously prescribed surface temperature and heat flux, heat transfer in a two-dimensional porous bed, and heat transfer for two liquid metal slot jets impinging on a heated plate.

  4. Conformal mapping technique for two-dimensional porous media and jet impingement heat transfer

    NASA Technical Reports Server (NTRS)

    Siegel, R.

    1974-01-01

    Transpiration cooling and liquid metals both provide highly effective heat transfer. Using Darcy's law in porous media and the inviscid approximation for liquid metals, the local fluid velocity in these flows equals the gradient of a potential. The energy equation and flow region are simplified when transformed into potential plane coordinates. In these coordinates, the present problems are reduced to heat conduction solutions which are mapped into the physical geometry. Results are obtained for a porous region with simultaneously prescribed surface temperature and heat flux, heat transfer in a two-dimensional porous bed, and heat transfer for two liquid metal slot jets impinging on a heated plate.

  5. Numerical study of twin-jet impingement upwash flow

    NASA Technical Reports Server (NTRS)

    Pegues, W. J.; Vanka, S. P.

    1990-01-01

    Two horizontally spaced jets impinging normally on a flat surface create a fountain upwash flow due to the collision of the radially flowing wall jets. This fountain flow is of importance to the dynamics and propulsion of STOVL aircraft. The fountain flow influences the lift forces on the aircraft and the ingestion of hot gases and debris by the engine inlet. In this paper, a multigrid based finite-difference numerical procedure has been applied to solve the equations governing this three-dimensional flow. The standard k-epsilon turbulence model has been used. Comparisons with experimental data reveal that while the mean velocities are predicted with reasonable accuracy, the turbulent kinetic energies are seriously in error. The reasons for this discrepancy could be the intense unsteadiness and large-scale structures of the flow in the near-wall region, which cannot be captured well by any Reynolds-averaged turbulence model.

  6. A simple confined impingement jets mixer for flash nanoprecipitation.

    PubMed

    Han, Jing; Zhu, Zhengxi; Qian, Haitao; Wohl, Adam R; Beaman, Charles J; Hoye, Thomas R; Macosko, Christopher W

    2012-10-01

    Johnson and Prud'homme (2003. AICHE J 49:2264-2282) introduced the confined impingement jets (CIJ) mixer to prepare nanoparticles loaded with hydrophobic compounds (e.g., drugs, inks, fragrances, or pheromones) via flash nanoprecipitation (FNP). We have modified the original CIJ design to allow hand operation, eliminating the need for a syringe pump, and we added a second antisolvent dilution stage. Impingement mixing requires equal flow momentum from two opposing jets, one containing the drug in organic solvent and the other containing an antisolvent, typically water. The subsequent dilution step in the new design allows rapid quenching with high antisolvent concentration that enhances nanoparticle stability. This new CIJ with dilution (CIJ-D) mixer is a simple, cheap, and efficient device to produce nanoparticles. We have made 55 nm diameter β-carotene nanoparticles using the CIJ-D mixer. They are stable and reproducible in terms of particle size and distribution. We have also compared the performance of our CIJ-D mixer with the vortex mixer, which can operate at unequal flow rates (Liu et al., 2008. Chem Eng Sci 63:2829-2842), to make β-carotene-containing particles over a series of turbulent conditions. On the basis of dynamic light scattering measurements, the new CIJ-D mixer produces stable particles of a size similar to the vortex mixer. Our CIJ-D design requires less volume and provides an easily operated and inexpensive tool to produce nanoparticles via FNP and to evaluate new nanoparticle formulation.

  7. Numerical study of multiple impinging slot jets with an inclined confinement surface

    SciTech Connect

    Yang, Y.T.; Shyu, C.H.

    1998-01-01

    This study presents numerical predictions on the fluid flow and heat transfer characteristics of multiple impinging slot jets with an inclined confinement surface. A nonorthogonal body-fitted coordinate system was used to handle the complexity of the geometry, and a control volume based finite difference method was employed to solve the governing equations. Two turbulence models are used to describe the turbulent structure: the standard {kappa}-{var_epsilon} turbulent model associated with wall function and the Lam-Bremhorst version of the low-Re {kappa}-{var_epsilon} model. The parameters studied include the angle of inclined confinement surface {theta}(0 {degree} {theta} 15{degree}) and entrance Reynolds number (11,000 {le} Re {le} 21,000). The numerical results show that the maximum local Nusselt number and maximum pressure on the impinging surface move downstream while the inclination angle {theta} is increased. The maximum local Nusselt number decreases while the value of the local Nusselt number downstream increases with increasing inclination angle {theta}. The calculated streamline contours are also noted, in that the entrance Re has little effect on the size of the recirculation region, but the inclination angle {theta} has a significant effect on the recirculation zones. Inclination of the confined surface to accelerate the fluid flow was found to level the local Nusselt number distribution on the impingement surface. Multiple turbulent jets are found in many practical applications, e.g., cooling of turbine blades and electrical equipment, drying of paper, textiles, and annealing of metals.

  8. Noise generated by impingement of a jet upon a large flat board

    NASA Technical Reports Server (NTRS)

    Olsen, W. A.; Miles, J. H.; Dorsch, R. G.

    1972-01-01

    Data were obtained on the noise generated by an air jet impinging on a large flat board. The board was large enough so that the flow leaving the edges of the board generated no significant noise. The impingement angle, nozzle shape and size, jet velocity, and the distance from the nozzle to the board were varied in the experiment. Far-field noise data are presented. The nozzle-alone noise contribution to the total noise was generally small and was subtracted from the total, leaving the impingement-only noise. The impingement-only noise was adequately correlated by eighth power of the peak impingement velocity and first power of the impingement area. The spectral data were correlated by a Strouhal number based on the peak impingement velocity and a characteristic impingement diameter.

  9. Two-Phase Flow in High-Heat-Flux Micro-Channel Heat Sink for Refrigeration Cooling Applications. Part 2: Low Temperature Hybrid Micro-Channel/Micro-Jet Impingement Cooling

    DTIC Science & Technology

    2008-09-01

    Boiling and Two-Phase Flow Laboratory 9 empirical two-phase heat transfer correlation is developed for... flow rates, the highest single-phase heat transfer Boiling and Two-Phase Flow Laboratory 55 65 , i q",, = 36.0 W/cm 2, fit = 11.1 g/s, Tin = 20’C (Dec...5.3 Variation of heat transfer coefficient with mean jet Reynolds number for different jet patterns. Boiling and Two-Phase Flow Laboratory 62 Nu

  10. Multiple jet impingement heat transfer characteristic: Experimental investigation of in-line and staggered arrays with crossflow

    NASA Technical Reports Server (NTRS)

    Florschuetz, L. W.; Metzger, D. E.; Takeuchi, D. I.; Berry, R. A.

    1980-01-01

    Heat transfer characteristics were obtained for configurations designed to model the impingement cooled midchord region of air cooled gas turbine airfoils. The configurations tested were inline and staggered two-dimensional arrays of circular jets with ten spanwise rows of holes. The cooling air was constrained to exit in the chordwise direction along the channel formed by the jet orifice plate and the heat transfer surface. Tests were run for chordwise jet hole spacings of five, ten, and fifteen hole diameters; spanwise spacings of four, six, and eight diameters; and channel heights of one, two, three, and six diameters. Mean jet Reynolds numbers ranged from 5000 to 50,000. The thermal boundary condition at the heat transfer test surface was isothermal. Tests were run for sets of geometrically similar configurations of different sizes. Mean and chordwise resolved Nusselt numbers were determined utilizing a specially constructed test surface which was segmented in the chordwise direction.

  11. Void fraction in two-phase flow in liquid impingement cooling system

    SciTech Connect

    Ohsone, Yasuo; Nakajima, Tadakatsu; Sasaki, Shigeyuki; Nishihara, Atsuo; Hirasawa, Shigeki

    1995-12-31

    Void fractions in forced-convection subcooled boiling were analyzed to gain information for designing a liquid impingement cooling system for electronic devices. The boiling vessel used in this study has a 160 mm x 160 mm heater. The heater is positioned to face jets of dielectric fluorocarbon (C{sub 6}F{sub 14},FC-72) liquid from circular nozzles 4 mm in diameter. The distance between the heater surface and the nozzles is 6 mm. The test section, which can be rotated 360 degrees, consists of 1.03-m-long acrylic pipes, 20 mm and 15 mm in diameter allows experiments to be conducted for both horizontal and vertical flow. Void fractions in the test section were examined with respect to variations in liquid jet temperature (T{sub Lin} = 26 C and 36C); nozzle exit velocity (U = 0.37--10 m/s); liquid pressure in the vessel (P{sub m} = 115--118 kPa); and heat flux in the heater (q = 3--50 W/cm{sup 2}). Results show that the effects on void fractions during liquid jet impingement flow boiling of nozzle exit velocity, pressure in the vessel, and heat flux in the heater, can be estimated by revising the exponents of these variables depending on the pressure of Miropolskii`s correlation of channel flow boiling.

  12. Normal Impingement of a Circular Liquid Jet onto a Screen in a Weightless Environment

    NASA Technical Reports Server (NTRS)

    Symons, E. P.

    1976-01-01

    The normal impingement of a circular liquid jet onto a fine-mesh screen in a weightless environment was investigated. Equations were developed to predict the velocity of the emerging jet on the downstream side of the screen as a function of screen and liquid parameters and of the velocity of the impinging jet. Additionally, the stability of the emerging jet was found to be Weber number dependent. In general, excepting at high velocities, the screen behaved much as a baffle, deflecting the major portion of the impinging flow.

  13. Global mode decomposition of supersonic impinging jet noise

    NASA Astrophysics Data System (ADS)

    Hildebrand, Nathaniel; Nichols, Joseph W.

    2015-11-01

    We apply global stability analysis to an ideally expanded, Mach 1.5, turbulent jet that impinges on a flat surface. The analysis extracts axisymmetric and helical instability modes, involving coherent vortices, shocks, and acoustic feedback, which we use to help explain and predict the effectiveness of microjet control. High-fidelity large eddy simulations (LES) were performed at nozzle-to-wall distances of 4 and 4.5 throat diameters with and without sixteen microjets positioned uniformly around the nozzle lip. These flow configurations conform exactly to experiments performed at Florida State University. Stability analysis about LES mean fields predicted the least stable global mode with a frequency that matched the impingement tone observed in experiments at a nozzle-to-wall distance of 4 throat diameters. The Reynolds-averaged Navier-Stokes (RANS) equations were solved at five nozzle-to-wall distances to create base flows that were used to investigate the influence of this parameter. A comparison of the eigenvalue spectra computed from the stability analysis about LES and RANS base flows resulted in good agreement. We also investigate the effect of the boundary layer state as it emerges from the nozzle using a multi-block global mode solver. Computational resources were provided by the Argonne Leadership Computing Facility.

  14. Liquid jet impingement normal to a disk in zero gravity

    NASA Technical Reports Server (NTRS)

    Labus, T. L.; Dewitt, K. J.

    1978-01-01

    An experimental and analytical investigation was conducted to determine the free surface shapes of circular jets impinging normal to sharp-edged disks in zero gravity. Experiments conducted in a zero gravity drop tower yielded three distinct flow patterns which were classified in terms of the relative effects of surface tension and inertial forces. An order of magnitude analysis was conducted indicating regions where viscous forces were not significant when computing free surface shapes. The free surface analysis was simplified by transforming the governing potential flow equations and boundary conditions into the inverse plane. The resulting nonlinear equations were solved numerically and comparisons were made with the experimental data for the inertia dominated regime.

  15. Measurements in a large angle oblique jet impingement flow

    NASA Technical Reports Server (NTRS)

    Foss, J. F.

    1974-01-01

    Velocity and surface pressure measurements, in the flow field of an obliquely impinging jet, and their interpretation as regards the governing mechanics and the aerodynamic noise generation characteristics of such a flow are reported. A computer controlled probe positioning mechanism allowed the measurement of the velocity magnitude and direction in the plane parallel to the plate. The mean velocity and Reynolds stress components were recorded. Measures of the terms in the momentum equation reveal the character of the pressure gradients in the neighborhood of the stagnation point. The effects of the stagnation streamline location on the vorticity field and the vortex sound considerations are discussed in relationship to the aerodynamic noise generation effects of this flow.

  16. Jet array impingement flow distributions and heat transfer characteristics: Effects of initial crossflow and nonuniform array geometry

    NASA Technical Reports Server (NTRS)

    Florschuetz, L. W.; Metzger, D. E.

    1982-01-01

    Flow distributions and heat transfer characteristics for two-dimensional arrays of circular air jets impinging on a surface parallel to the jet orifice plate were determined. The configurations considered were intended to model those of interest in current and contemplated gas turbine airfoil midchord cooling applications. The geometry of the airfoil applications considered dictates that all of the jet flow, after impingement, exit in the chordwise (i.e., streamwise) direction toward the trailing edge. Experimental results for the effect of an initial crossflow on both flow distributions and heat transfer characteristics for a number of the prior uniform array geometries. The effects of nonuniform array geometries on flow distributions and heat transfer characteristics for noninitial crossflow configurations are discussed.

  17. The connection between sound production and jet structure of the supersonic impinging jet

    NASA Astrophysics Data System (ADS)

    Henderson, Brenda

    2002-02-01

    An experimental investigation into the sound-producing characteristics of moderately and highly underexpanded supersonic impinging jets exhausting from a round convergent nozzle is presented. The production of large plate tones by impingement on a square plate with a side dimension equal to 12 nozzle exit diameters is studied using random and phase-locked shadowgraph photography. Discrete frequency sound is produced in the near-wall region of the jet when a Mach disk occurs upstream of the standoff shock wave. Tones cease when the plate distance is approximately 2.2 free-jet cell lengths and the first and second shock waves are located in the free-jet positions. The production of impulsive sound appears to be associated with the collapse of the standoff shock wave during a portion of the oscillation cycle. Results from unsteady plate-pressure measurements indicate that plane-wave motion occurs in the impingement region and a secondary pressure maximum is observed on the plate adjacent to the flow region where sound appears to originate.

  18. A Single Parameter to Characterize Wall Shear Stress Developed from an Underexpanded Axisymmetric Impinging Jet

    NASA Astrophysics Data System (ADS)

    Fillingham, Patrick; Murali, Harikrishnan

    2016-11-01

    Wall shear stress is characterized for underexpanded axisymmetric impinging jets for the application of aerodynamic particle resuspension from a surface. Analysis of the flow field and the wall shear stress resulted from normally impinging axisymmetric jets is conducted using Computational Fluid Dynamics. A normally impinging jet is modeled with a constant area nozzle, while varying height to diameter ratio (H/D) and inlet pressures. Schlieren photography is used to visualize the density gradient of the flow field for validation of the CFD. The Dimensionless Jet Parameter (DJP) is developed to describe flow regimes and characterize the shear stress. The DJP is defined as being proportional to the jet pressure ratio divided by the H/D ratio squared. Maximum wall shear stress is examined as a function of DJP with three distinct regimes: (i) subsonic impingement (DJP<1), (ii) transitional (1impingement (DJP>2). Due to the jet energy dissipation in shock structures, which become a dominant dissipation mechanism in the supersonic impingement regime, wall shear stress is limited to a finite value. Additionally, formation of shock structures in the wall flow were observed for DJP>2 resulting in difficulties with dimensionless analysis. In the subsonic impingement and transitional regimes equations as a function of the DJP are obtained for the maximum wall shear stress magnitude, maximum shear stress location, and shear stress decay. Using these relationships wall shear stress can be predicted at all locations along the impingement surface.

  19. Jet-regulated cooling catastrophe

    NASA Astrophysics Data System (ADS)

    Dubois, Yohan; Devriendt, Julien; Slyz, Adrianne; Teyssier, Romain

    2010-12-01

    We present the first implementation of active galactic nuclei (AGN) feedback in the form of momentum-driven jets in an adaptive mesh refinement (AMR) cosmological resimulation of a galaxy cluster. The jets are powered by gas accretion on to supermassive black holes (SMBHs) which also grow by mergers. Throughout its formation, the cluster experiences different dynamical states: both a morphologically perturbed epoch at early times and a relaxed state at late times allowing us to study the different modes of black hole (BH) growth and associated AGN jet feedback. BHs accrete gas efficiently at high redshift (z > 2), significantly pre-heating proto-cluster haloes. Gas-rich mergers at high redshift also fuel strong, episodic jet activity, which transports gas from the proto-cluster core to its outer regions. At later times, while the cluster relaxes, the supply of cold gas on to the BHs is reduced leading to lower jet activity. Although the cluster is still heated by this activity as sound waves propagate from the core to the virial radius, the jets inefficiently redistribute gas outwards and a small cooling flow develops, along with low-pressure cavities similar to those detected in X-ray observations. Overall, our jet implementation of AGN feedback quenches star formation quite efficiently, reducing the stellar content of the central cluster galaxy by a factor of 3 compared to the no-AGN case. It also dramatically alters the shape of the gas density profile, bringing it in close agreement with the β model favoured by observations, producing quite an isothermal galaxy cluster for gigayears in the process. However, it still falls short in matching the lower than universal baryon fractions which seem to be commonplace in observed galaxy clusters.

  20. Erosion and transport of particulates by forced jet impinging jet on a mobile sediment bed

    NASA Astrophysics Data System (ADS)

    Corfman, Kyle; Mulinti, Rahul; Kiger, Kenneth

    2013-11-01

    The work reports on the erosion and suspended flux characteristics of a forced impinging jet, as a prototypical surrogate to better understand the problem of rotorcraft brownout. Coherent vortex rings are generated through oscillatory forcing of a vertical impinging jet onto a sediment bed. Early in the flow development, annular ripple dunes are formed and steadily grow, the wavelength and growth rate depending largely on the particle size and flow conditions. In order to provide a reliable prediction of erosion for more realistic flows, such as those found in rotorcrafts, a parametric study was performed for several particle sizes and mixtures. PTV is used to correlate vertical and horizontal fluxes with resulting changes in the ground profiles. A single-phase PIV study detailing the changes in the vortex ring characteristics after the bed has reached a stable erosion pattern is also reported. This work is supported by the AFSOR under grant FA95500810406.

  1. Sensitivity analysis for the control of supersonic impinging jet noise

    NASA Astrophysics Data System (ADS)

    Nichols, Joseph W.; Hildebrand, Nathaniel

    2016-11-01

    The dynamics of a supersonic jet that impinges perpendicularly on a flat plate depend on complex interactions between fluid turbulence, shock waves, and acoustics. Strongly organized oscillations emerge, however, and they induce loud, often damaging, tones. We investigate this phenomenon using unstructured, high-fidelity Large Eddy Simulation (LES) and global stability analysis. Our flow configurations precisely match laboratory experiments with nozzle-to-wall distances of 4 and 4.5 jet diameters. We use multi-block shift-and-invert Arnoldi iteration to extract both direct and adjoint global modes that extend upstream into the nozzle. The frequency of the most unstable global mode agrees well with that of the emergent oscillations in the LES. We compute the "wavemaker" associated with this mode by multiplying it by its corresponding adjoint mode. The wavemaker shows that this instability is most sensitive to changes in the base flow slightly downstream of the nozzle exit. By modifying the base flow in this region, we then demonstrate that the flow can indeed be stabilized. This explains the success of microjets as an effective noise control measure when they are positioned around the nozzle lip. Computational resources were provided by the Argonne Leadership Computing Facility.

  2. Mathematical Modeling of Impinging Gas Jets on Liquid Surfaces

    NASA Astrophysics Data System (ADS)

    Hwang, Ho Yong; Irons, Gordon A.

    2011-06-01

    In top-blowing operations, the gas jet is a major source of momentum, so to model the momentum exchange properly with the liquid, the full-stress boundary conditions must be applied. A new mathematical method for better representation of the surface boundary condition was developed by combining the Cartesian cut cell method and volume of fluid method. The computational code was validated with the broken dam problem and reported critical phenomena in wave generation. The model was applied to impinging jets on liquid surfaces in two dimensions. The cavity depth was in good agreement with experimental measurements. The process of ligament and droplet formation was reproduced. The extent of momentum transfer to the liquid was investigated, and the trends with lance height and gas flow rate were similar to experimental evidence. The following important aspects of momentum transfer were identified: surface roughness as well as the development of local pressure gradients around wave crests. Kelvin-Helmholtz instability theory was used to interpret the results with respect to critical velocity for the onset of droplet formation. These principles were extended to conditions relevant to basic oxygen furnace (BOF) steelmaking. The critical velocities for droplets were calculated as functions of the physical properties for the gas-steel, gas-slag, slag-steel interfaces. The implications for BOF steelmaking were discussed. The mathematical model was applied to a simplified configuration of full-scale BOF steelmaking, and the local force balance was well described.

  3. Impingement cooling for modern combustors: experimental analysis of heat transfer and effectiveness

    NASA Astrophysics Data System (ADS)

    Facchini, B.; Surace, M.

    2006-04-01

    This paper presents results obtained from a wide-ranging experimental investigation into impingement cooling from multiple jet arrays which reproduced real LPP combustor liner geometries. The work was performed during the four years of the European project LOPOCOTEP. Two sparse, staggered impingement arrays were examined in detail and each case was compared with data from the literature relating to the same configuration and jet Reynolds numbers. As a result of this study, it has been possible to obtain detailed data about local distribution of the heat-transfer coefficient and spanwise row-averaged effectiveness, by using a new method which combined transient and steady-state thermochromic liquid-crystal (TLC) techniques. It was found that the data obtained in this work were in good agreement with results presented in the literature. This study shows that measured, row-by-row effectiveness values can be usefully employed in a preliminary design stage. Some data relating to hole-discharge coefficients are also presented.

  4. Mean flow characteristics for the oblique impingement of an axisymmetric jet

    NASA Technical Reports Server (NTRS)

    Foss, J. F.; Kleis, S. J.

    1975-01-01

    The oblique impingement of an axisymmetric jet has been investigated. A summary of the data and the analytical interpretations of the dominant mechanisms which influence the flow are reported. The major characteristics of the shallow angle oblique jet impingement flow field are: (1) minimal dynamic spreading as revealed by the surface pressure field, (2) pronounced kinematic spreading as revealed by the jet flow velocity field, (3) a pronounced upstream shift of the stagnation point from the maximum pressure point, (4) the production of streamwise vorticity by the impingement process.

  5. Oil-in-water emulsification using confined impinging jets.

    PubMed

    Siddiqui, Shad W; Norton, Ian T

    2012-07-01

    A confined impinging jet mixing device has been used to investigate the continuous sunflower oil/water emulsification process under turbulent flow conditions with oil contents between 5% (v/v) and 10% (v/v). Various emulsifiers (Tween20, Span80, Whey Protein, Lecithin and Sodium Dodecylsulphate) varying in molecular weights have been studied. Mean droplet sizes varied with the emulsifiers used and smallest droplets were obtained under fully turbulent flow regime, i.e. at the highest jet flow rate and highest jet Reynolds Number conditions. Sodium Dodecylsulfate (SDS) produced droplets in the range of 3.8 μm while 6 μm droplets were obtained with Whey Protein. Similar droplet sizes were obtained under fully turbulent flow conditions (610 mL/min; Reynolds Number=13,000) for oil content varying between 5% (v/v) and 10% (v/v). To investigate the smallest droplet size possible in the device, the emulsion was passed through the geometry multiple times. Multi-pass emulsification resulted in reduction in droplet size indicating that longer residence in the flow field under high shear condition allowed for breakage of droplets as well as the time for the emulsifier to stabilize the newly formed droplets, decreasing the impact of coalescence. This was confirmed by timescale analysis of the involved process steps for the droplet data obtained via experiments. Dependence of mean droplet size on the o/w interfacial tension and peak energy dissipation was also investigated. Copyright © 2012 Elsevier Inc. All rights reserved.

  6. Effects of Surface Roughness on Stagnation Heat Transfer of Impinging Liquid Jet on Metal Surface

    NASA Astrophysics Data System (ADS)

    Lee, Jungho

    The liquid jet impingement with phase change heat transfer has long been an attractive method of cooling especially in steelmaking process and heat treatment in metals. The current study focuses on making detailed measurements of the stagnation-point heat transfer as a jet impinges on the rough metal surfaces at high temperature nominally up to 900°C. The local heat flux measurements are introduced by a novel experimental technique in which test block assemblies with cartridge heaters and thermocouples are used to measure the heat flux distribution on the surface of hot steel plate as a function of heat flux gauge. The effects of surface roughness on the stagnation-point heat transfer were investigated for well-characterized four rough surfaces with root-mean-square average roughness heights ranging from 40 to 80 µm. The results show that surface protrusions on rough surface can penetrate the thermal sublayer in the stagnation point and thus increase the heat transfer. The heat transfer enhancement mechanism on roughened surface can be investigated by the different boiling regimes.

  7. PIV measurements of isothermal plane turbulent impinging jets at moderate Reynolds numbers

    NASA Astrophysics Data System (ADS)

    Khayrullina, A.; van Hooff, T.; Blocken, B.; van Heijst, G. J. F.

    2017-04-01

    This paper contains a detailed experimental analysis of an isothermal plane turbulent impinging jet (PTIJ) for two jet widths at moderate Reynolds numbers (7200-13,500) issued on a horizontal plane at fixed relative distances equal to 22.5 and 45 jet widths. The available literature on such flows is scarce. Previous studies on plane turbulent jets mainly focused on free jets, while most studies on impinging jets focused on the heat transfer between the jet and an impingement plane, disregarding jet development. The present study focuses on isothermal PTIJs at moderate Reynolds numbers characteristic of air curtains. Flow visualisations with fluorescent dye and 2D particle image velocimetry (PIV) measurements have been performed. A comparison is made with previous studies of isothermal free turbulent jets at moderate Reynolds numbers. Mean and instantaneous velocity and vorticity, turbulence intensity, and Reynolds shear stress are analysed. The jet issued from the nozzle with higher aspect ratio shows more intensive entrainment and a faster decay of the centreline velocity compared to the jet of lower aspect ratio for the same value of jet Reynolds number. The profiles of centreline and cross-jet velocity and turbulence intensity show that the PTIJs behave as a free plane turbulent jet until 70-75% of the total jet height. Alongside the information obtained on the jet dynamics, the data will be useful for the validation of numerical simulations.

  8. Impingement.

    ERIC Educational Resources Information Center

    Uziel, Mary S.

    1978-01-01

    Presents a literature review of the impact of impingement in fishery resources at different power plants in the United States, covering publications of 1976-77. Consideration is given to engineering studies and biological effects for reducing impingement. A list of 96 references is also presented. (HM)

  9. Impingement.

    ERIC Educational Resources Information Center

    Uziel, Mary S.

    1978-01-01

    Presents a literature review of the impact of impingement in fishery resources at different power plants in the United States, covering publications of 1976-77. Consideration is given to engineering studies and biological effects for reducing impingement. A list of 96 references is also presented. (HM)

  10. Effects of surface roughness on the average heat transfer of an impinging air jet

    SciTech Connect

    Beitelmal, A.H.; Saad, M.A.; Patel, C.D.

    2000-01-01

    Localized cooling by impinging flow has been used in many industrial applications such as in cooling of gas turbine blades and drying processes. Here, effect of surface roughness of a uniformly heated plate on the average heat transfer characteristics of an impinging air jet was experimentally investigated. Two aluminum plates, one with a flat surface and the second with some roughness added to the surface were fabricated. The roughness took the shape of a circular array of protrusions of 0.5mm base and 0.5mm height. A circular Kapton heater of the same diameter as the plates (70mm) supplied the necessary power. The surfaces of the plates were polished to reduce radiation heat losses and the back and sides insulated to reduce conduction heat losses. temperatures were measured over a Reynolds number ranging from 9,600 to 38,500 based on flow rate through a 6.85mm diameter nozzle. The temperature measurements were repeated for nozzle exit-to-plate spacing, z/d, ranging from 1 to 10. The average Nusselt number for both cases was plotted versus the Reynolds number and their functional correlation was determined. The results indicate an increase of up to 6.0% of the average Nusselt number due to surface roughness. This modest increase provides evidence to encourage further investigation and characterization of the surface roughness as a parameter for enhancing heat transfer.

  11. Effect of flow rate on the spray characteristics of impinging water jets

    NASA Astrophysics Data System (ADS)

    Vassallo, P.; Ashgriz, N.; Boorady, F. A.

    1992-10-01

    An experimental study of the spray characteristics of impinging turbulent water jets is conducted using a phase Doppler particle analyzer (PDPA). Both two and four impinging jet injectors are examined. The Reynolds number of the jets is varied in the range 3000-7500. Detailed distribution of diameter, velocity number density, and volume flux for each case is reported. For the injector with two jets impinging on each other at a 90-deg angle, mean drop size reduces, and mean velocity and number density increase as the jet velocities increase. The volume flux increases or decreases depending on the location on the cross section of the spray. The four-impinging-jet injector is made up of two parallel jets at the center and two other side jets, at the same plane, impinging on them at 45-deg angle. For this injector, as the flow rate of two parallel jets increases, a critical flow rate is obtained, below which the mean drop size and velocity increase and above which they decrease.

  12. Mixing and Noise Benefit Versus Thrust Penalty in Supersonic Jets Using Impingement Tones

    NASA Technical Reports Server (NTRS)

    Raman, Ganesh; Rice, Edward J.

    1994-01-01

    This paper reports the results of an experimental investigation on the effect of impingement tones generated by obstacles of various geometries on the spreading of a supersonic jet flow. A rectangular supersonic jet was produced using a convergent-divergent nozzle that was operated near its design point (with shocks minimized). The immersion of obstacles in the flow produced an intense impingement tone which then propagated upstream (as feedback) to the jet lip and excited the antisymmetric hydrodynamic mode in the jet, thus setting up a resonant self-sustaining loop. The violent flapping motion of the jet due to excitation of the antisymmetric mode, combined with the unsteady wakes of the obstacles, produced large changes in jet mixing. It was possible to control the frequency and amplitude of the impingement tone excitation by varying the nozzle-to-obstacle distance and the obstacle immersion. By proper shaping of the obstacles it was possible to reduce the thrust penalty significantly.

  13. Experimental Investigation of Jet Impingement Heat Transfer Using Thermochromic Liquid Crystals

    NASA Technical Reports Server (NTRS)

    Dempsey, Brian Paul

    1997-01-01

    Jet impingement cooling of a hypersonic airfoil leading edge is experimentally investigated using thermochromic liquid crystals (TLCS) to measure surface temperature. The experiment uses computer data acquisition with digital imaging of the TLCs to determine heat transfer coefficients during a transient experiment. The data reduction relies on analysis of a coupled transient conduction - convection heat transfer problem that characterizes the experiment. The recovery temperature of the jet is accounted for by running two experiments with different heating rates, thereby generating a second equation that is used to solve for the recovery temperature. The resulting solution requires a complicated numerical iteration that is handled by a computer. Because the computational data reduction method is complex, special attention is paid to error assessment. The error analysis considers random and systematic errors generated by the instrumentation along with errors generated by the approximate nature of the numerical methods. Results of the error analysis show that the experimentally determined heat transfer coefficients are accurate to within 15%. The error analysis also shows that the recovery temperature data may be in error by more than 50%. The results show that the recovery temperature data is only reliable when the recovery temperature of the jet is greater than 5 C, i.e. the jet velocity is in excess of 100 m/s. Parameters that were investigated include nozzle width, distance from the nozzle exit to the airfoil surface, and jet velocity. Heat transfer data is presented in graphical and tabular forms. An engineering analysis of hypersonic airfoil leading edge cooling is performed using the results from these experiments. Several suggestions for the improvement of the experimental technique are discussed.

  14. Measurement and visualization of impingement cooling in narrow channels

    NASA Astrophysics Data System (ADS)

    Kaiser, E.

    Experimental measurement techniques such as naphthalene sublimation, liquid crystal thermography and real-time holographic interferometry are standard. Their application in narrow channels causes problems and is therefore limited. The channel width must not change too much because the naphthalene sublimation and the liquid crystal coating necessary for the thermography may cause non-negotiable variations. The interferometry fails in turbulent flow area. The diffraction along the channel edges is an additional difficulty. A comparison of the results obtained from the application of all three techniques, which has not been considered in earlier publications, is made here. The methods were used to measure and visualize the heat transfer characteristics of an array of 1.2mm diameter impinging jets in an enclosed channel (>=2.2mm) with single-sided flow-off at Reynolds numbers of about Rez 20,000. Scale-up ratios as low as 2.4 have been used in order to maintain similarity as it has not been previously reported. The naphthalene technique provided a high spatially resolved measurement of the Sherwood number along a downstream line. The liquid crystal thermography technique provided 2D contours of the Nusselt number. The temperature distribution within dead water zones was visualized with holographic interferometry. The cross-flow effects caused a shift in the stagnation point and a monotone decrease in the Nusselt number in the downstream direction.

  15. Physics of Particle Entrainment Under the Influence of an Impinging Jet

    DTIC Science & Technology

    2008-12-01

    Blown Sand and Desert Dunes, Methuen, London. Beltaos, S. and Rajaratnam, N., 1974: Impinging circular turbulent jets, Journal Hydraulic Division...entrainment function.” J. of Hydraulic Engineering, 123:3, 233-236. Doorschot, J.J.J. and M. Lehning, 2001: Equilibrium saltation: mass fluxes...H., P. Leister and B. Westrich, 1979: Flow field and scouring effects of steady and pulsating jets impinging on a movable bed. J. of Hyd. Res. 17

  16. The oblique impingement of an axisymmetric jet. [flow characteristics of jet flow over flat plates

    NASA Technical Reports Server (NTRS)

    Foss, J. F.; Kleis, S. J.

    1976-01-01

    The mechanics of the oblique impingement of an axisymmetric jet on a plane surface are examined in detail. The stagnation point is discussed. A schematic drawing of the problem and coordinate system used to describe the flow field are given. The kinematic features of the flow above the plate are examined in the context of the conservation of mass, the vorticity of the jet, and the vorticity introduced by the jetplate interaction. The dynamic features of the flow are examined in terms of the surface pressure distribution and the cause-effect relationships which exist between the pressure and velocity/vorticity distributions. Flow calculations performed are given. The investigation is relevant to the flow resulting from the interaction of the propulsion jet with the main airfoil (STOL aircraft), and is appropriate to an over- or under- wing configuration.

  17. Enhancement of single-phase heat transfer and critical heat flux from an ultra-high-flux simulated microelectronic heat source to a rectangular impinging jet of dielectric liquid

    SciTech Connect

    Wadsworth, D.C.; Mudawar, I. )

    1992-08-01

    Jet impingement is encountered in numerous applications demanding high heating or cooling fluxes. Examples include annealing of metal sheets and cooling of turbine blades, x-ray medical devices, laser weapons, and fusion blankets. The attractive heat transfer attributes of jet impingement have also stimulated research efforts on cooling of high-heat-flux microelectronic devices. These devices are fast approaching heat fluxes in excess of 100 W/cm[sup 2], which have to be dissipated using coolants that are both electrically and chemically compatible with electronic components. Unfortunately, fluids satisfying these requirements tend to possess poor transport properties, creating a need for significant enhancement in the heat transfer coefficient by such means as increased coolant flow rate and phase change. The cooling problem is compounded by a need to cool large arrays of heat sources in minimal volume, and to reduce the spacing between adjacent circuit boards. These requirements place severe constraints on the packaging of jet impingement cooling hardware.

  18. Fluorescence imaging study of free and impinging supersonic jets: Jet structure and turbulent transition

    NASA Astrophysics Data System (ADS)

    Inman, Jennifer Ann

    A series of experiments into the behavior of underexpanded jet flows has been conducted at NASA Langley Research Center. This work was conducted in support of the Return to Flight effort following the loss of the Columbia. The tests involved simulating flow through a hypothetical breach in the leading edge of the Space Shuttle Orbiter along its reentry trajectory, with the goal of generating a data set with which other researchers can test and validate computational modeling tools. Two nozzles supplied with high-pressure gas were used to generate axisymmetric underexpanded jets exhausting into a low-pressure chamber. These nozzles had exit Mach numbers of 1 and 2.6. Reynolds numbers based on nozzle exit conditions ranged from about 200 to 35,000, and nozzle exit-to-ambient jet pressure ratios ranged from about 1 to 37. Both free and impinging jets were studied, with impingement distances ranging from 10 to 40 nozzle diameters, and impingement angles of 45°, 60°, and 90°. For the majority of cases, the jet fluid was a mixture of 99.5% nitrogen seeded with 0.5% nitric oxide (NO). Planar laser-induced fluorescence (PLIF) of NO was used to non-intrusively visualize the flow with a temporal resolution on the order of lets. PLIF images were used to identify and measure the location and size of flow structures. PLIF images were further used to identify unsteady jet behavior in order to quantify the conditions governing the transition to turbulent flow. This dissertation will explain the motivation behind the work, provide details of the laser system and test hardware components, discuss the theoretical aspects of laser-induced fluorescence, give an overview of the spectroscopy of nitric oxide, and summarize the governing fluid mechanical concepts. It will present measurements of the size and location of flow structures, describe the basic mechanisms and origins of unsteady behavior in these flows, and discuss the dependence of such behavior on particular flow

  19. Trailing edge cooling using angled impingement on surface enhanced with cast chevron arrangements

    SciTech Connect

    Lee, Ching-Pang; Heneveld, Benjamin E.; Brown, Glenn E.; Klinger, Jill

    2015-05-26

    A gas turbine engine component, including: a pressure side (12) having an interior surface (34); a suction side (14) having an interior surface (36); a trailing edge portion (30); and a plurality of suction side and pressure side impingement orifices (24) disposed in the trailing edge portion (30). Each suction side impingement orifice is configured to direct an impingement jet (48) at an acute angle (52) onto a target area (60) that encompasses a tip (140) of a chevron (122) within a chevron arrangement (120) formed in the suction side interior surface. Each pressure side impingement orifice is configured to direct an impingement jet at an acute angle onto an elongated target area that encompasses a tip of a chevron within a chevron arrangement formed in the pressure side interior surface.

  20. Interfacial condensation induced by sub-cooled liquid jet

    NASA Astrophysics Data System (ADS)

    Rame, Enrique; Balasubramaniam, R.

    2016-11-01

    When a sub-cooled liquid jet impinges on the free surface between a liquid and its vapor, vapor will condense at a rate dependent on the sub-cooling, the jet strength and fluid properties. In 1966 and during the examination of a different type of condensation flow, Shekriladeze found an approximate result, valid at large condensation rates, that decouples the flow in the liquid phase from that of the vapor, without putting it in the context of a formal asymptotic approximation. In this talk we will develop an asymptotic approximation that contains Shekriladze's result, and extend the calculations to the case when a non-condensable gas is present in the vapor phase.

  1. Experimental and numerical investigation of liquid jet impingement on superhydrophobic and hydrophobic convex surfaces

    NASA Astrophysics Data System (ADS)

    Kibar, Ali

    2017-02-01

    Experiments and numerical simulations were carried out to examine the vertical impingement a round liquid jet on the edges of horizontal convex surfaces that were either superhydrophobic or hydrophobic. The experiments examine the effects on the flow behaviour of curvature, wettability, inertia of the jet, and the impingement rate. Three copper pipes with outer diameters of 15, 22, and 35 mm were investigated. The pipes were wrapped with a piece of a Brassica oleracea leaf or a smooth Teflon sheet, which have apparent contact angles of 160° and 113°. The Reynolds number ranged from 1000 to 4500, and the impingement rates of the liquid jets were varied. Numerical results show good agreement with the experimental results for explaining flow and provide detailed information about the impingement on the surfaces. The liquid jet reflected off the superhydrophobic surfaces for all conditions. However, the jet reflected or deflected off the hydrophobic surface, depending on the inertia of the jet, the curvature of the surface, and the impingement rate. The results suggest that pressure is not the main reason for the bending of the jet around the curved hydrophobic surface.

  2. On the effect of fractal generated turbulence on the heat transfer of circular impinging jets

    NASA Astrophysics Data System (ADS)

    Astarita, Tommaso; Cafiero, Gioacchino; Discetti, Stefano

    2013-11-01

    The intense local heat transfer achieved by circular impinging jets is exploited in countless industrial applications (cooling of turbine blades, paper drying, tempering of glass and metals, etc). The heat transfer rate depends mainly on the Reynolds number, the nozzle-to-plate distance and the upstream turbulence. It is possible to enhance the heat transfer by exciting/altering the large scale structures embedded within the jet. In this work turbulent energy is injected by using a fractal grid at the nozzle exit. Fractal grids can generate more intense turbulence with respect to regular grids with the same blockage ratio by enhancing the jet turbulence over different scales. Consequently, they are expected to improve the convective heat transfer. The results outline that a significant improvement is achieved (for small nozzle-to-plate distances up to 100% at the stagnation point and more than 10% on the integral heat transfer over a circular area of 3 nozzle diameters) under the same power input.

  3. Jet Velocity Profile Effects on Spray Characteristics of Impinging Jets at High Reynolds and Weber Numbers

    NASA Astrophysics Data System (ADS)

    Rodrigues, Neil S.; Kulkarni, Varun; Sojka, Paul E.

    2014-11-01

    While like-on-like doublet impinging jet atomization has been extensively studied in the literature, there is poor agreement between experimentally observed spray characteristics and theoretical predictions (Ryan et al. 1995, Anderson et al. 2006). Recent works (Bremond and Villermaux 2006, Choo and Kang 2007) have introduced a non-uniform jet velocity profile, which lead to a deviation from the standard assumptions for the sheet velocity and the sheet thickness parameter. These works have assumed a parabolic profile to serve as another limit to the traditional uniform jet velocity profile assumption. Incorporating a non-uniform jet velocity profile results in the sheet velocity and the sheet thickness parameter depending on the sheet azimuthal angle. In this work, the 1/7th power-law turbulent velocity profile is assumed to provide a closer match to the flow behavior of jets at high Reynolds and Weber numbers, which correspond to the impact wave regime. Predictions for the maximum wavelength, sheet breakup length, ligament diameter, and drop diameter are compared with experimental observations. The results demonstrate better agreement between experimentally measured values and predictions, compared to previous models. U.S. Army Research Office under the Multi-University Research Initiative Grant Number W911NF-08-1-0171.

  4. Visualization of impingement field of real-rocket-exhausted jets by using moire deflectometry

    NASA Astrophysics Data System (ADS)

    He, An-Zhi; Yan, Da-Peng; Miao, Peng C.; Wang, Hai-Ling

    1991-12-01

    The experimental methods and results of an impingement field of a real rocket exhausted jet are presented. By using large aperture and long path moire deflector, the moire deflectograms of rocket free jet and rocket jet impingement field are obtained. From these moire deflectograms, the location of the Mach disk, the oblique shock wave, and the value of boundary are calculated quantitatively and compared with the results of numerical simulating and wind tunnel simulating. At the same time, we have found five new shock wave structures from the experiments.

  5. Heat transfer and flow characteristics of jets impinging on a concave hemispherical plate

    NASA Technical Reports Server (NTRS)

    Hrycak, P.

    1982-01-01

    The present study is concerned with an experimental investigation of the flow characteristics and heat transfer from turbulent air jets impinging normally on a concave hemispherical plate (CHP). It is found that the incompressible, turbulent jets impinging on a CHP are in many respects similar to the jets impinging on a flat plate. The observed differences are due to effects of curvature and to a slightly higher turbulence level inside of the CHP. Attention is given to the experimental apparatus, aspects of inner boundary layer development, the maximum velocity decay in a wall jet, the derivation of a maximum velocity decay formula, the influence of curvature on stagnation point heat transfer, and heat transfer calculations for a concave hemispherical plate.

  6. Conjugate heat transfer study of a turbulent slot jet impinging on a moving plate

    NASA Astrophysics Data System (ADS)

    Achari, A. Madhusudana; Das, Manab Kumar

    2017-03-01

    Numerical simulation of the flow field and conjugate heat transfer in an impinging jet with moving impingement plate is one of the important problems as it mimics closely with practical applications in industries. The Yang-Shih version of low Reynolds number k-ɛ model has been used to resolve the flow field and the temperature field in a two-dimensional, steady, incompressible, confined, turbulent slot jet impinging normally on a moving flat plate of finite thickness. The turbulence intensity and the Reynolds number considered at the inlet are 2 % and 15,000, respectively. The bottom face of the impingement plate has been maintained at a constant temperature higher than the nozzle exit temperature. The confinement plate has been considered to be adiabatic. The nozzle-to-surface spacing for the above study has been taken to be 6 and the surface-to-jet velocity ratios have been taken over a range of 0.25-1. The effects of impingement plate motion on the flow field and temperature field have been discussed elaborately with reference to stationary impingement plate. The dependence of flow field and fluid temperature field on impingement plate motion has been analyzed by plotting streamlines, isotherms for different plate speeds. A thorough study of flow characteristics for different surface-to-jet velocity ratios has been carried out by plotting profiles of mean vertical and horizontal components of velocity, pressure distribution, local shear stress distribution. The isotherms in the impingement plate of finite thickness, the distributions of solid-fluid interface temperature, the local Nusselt number, and the local heat flux for different surface-to-jet velocity ratios added to the understanding of conjugate heat transfer phenomenon.

  7. Analysis of impingement heat transfer for two parallel liquid-metal slot jets

    NASA Technical Reports Server (NTRS)

    Siegel, R.

    1974-01-01

    An analytical method is developed for determining heat transfer by impinging liquid-metal slot jets. The method involves mapping the jet flow region, which is bounded by free streamlines, into a potential plane where it becomes a uniform flow in a channel of constant width. The energy equation is transformed into potential plane coordinates and is solved in the channel flow region. Conformal mapping is then used to transform the solution back into the physical plane and obtain the desired heat-transfer characteristics. The analysis given here determines the heat-transfer characteristics for two parallel liquid-metal slot jets impinging normally against a uniformly heated flat plate. The liquid-metal assumptions are made that the jets are inviscid and that molecular conduction is dominating heat diffusion. Wall temperature distributions along the heated plate are obtained as a function of spacing between the jets and the jet Peclet number.

  8. Apparatus and methods for impingement cooling of a side wall of a turbine nozzle segment

    DOEpatents

    Burdgick, Steven Sebastian

    2002-01-01

    A gas turbine nozzle segment has outer and inner bands and a vane therebetween. Each band includes a nozzle wall, a side wall, a cover and an impingement plate between the cover and the nozzle wall defining two cavities on opposite sides of the impingement plate. Cooling steam is supplied to one cavity for flow through apertures of the impingement plate to cool the nozzle wall. The side wall of the band and inturned flange define with the nozzle wall an undercut region. The impingement plate has a turned flange welded to the inturned flange. A backing plate overlies the turned flange and aligned apertures are formed through the backing plate and turned flange to direct and focus cooling flow onto the side wall of the nozzle segment.

  9. Heat transfer from a liquid bath due to an impinging gas jet: A numerical study

    SciTech Connect

    Qian, F.; Farouk, B.; Mutharasan, R.

    1995-12-31

    An impinging gasjet on a liquid surface is found in many industrial processes such as electric arc furnace steel-making and welding. Fundamental understanding of the interaction of a gas or plasmajet impinging on a liquid pool can provide important insights into process behavior resulting in improved efficiency. A numerical model is developed for solving both the impinging gas jet and the liquid pool temperature and flow fields along with the deformed interface shape for the above processing operation. Using curvilinear coordinates, the Navier-Stokes equations of each phase are solved separately and then coupled via continuity of static pressure, shear stress, temperature and heat flux at the interface.

  10. Flow characteristics in free impinging jet reactor by particle image velocimetry (PIV) investigation

    NASA Astrophysics Data System (ADS)

    Zhang, Jun; Liu, Youzhi; Qi, Guisheng; Jiao, Weizhou; Yuan, Zhiguo

    2016-08-01

    The flow characteristics in free impinging jet reactors (FIJRs) were investigated using particle image velocimetry (PIV). The effects of the Reynolds number (Re) and the ratio of jet distance to jet diameter (w/d) on flow behavior were discussed for equal volumetric flow rates of the two jets. The impingement plane, instantaneous velocity, mean velocity, and turbulent kinetic energy (TKE) distribution of FIJRs are measured from captured images using the PIV technique. As Re increases, the average diameter of the impingement plane linearly increases. The instability of the liquid is closely related to the jet velocity or the Re. However, the stagnation point is insensitive to the variation of the Re. The droplets break up from the turbulent liquid in the ‘wall-free’ environment of FIJRs, so that the liquid back-flow found in confined impinging jet reactors (CIJRs) is not observed. Increasing the Re from 1800-4100 or decreasing the w/d from 20-6 plays a similar role in increasing the TKE values and intensifying turbulence, which promotes the momentum transfer and mixing efficiency in FIJRs.

  11. The effect of nozzle aspect ratio on the heat transfer characteristics of elliptic impinging jet

    SciTech Connect

    Lee, J.H.; Lee, S.J.

    1995-12-31

    The local heat transfer characteristics were investigated for a turbulent air jet issuing, normal to a heated flat plate, from an elliptic nozzle with various aspect ratios. Experimental parameters used in this study are the nozzle aspect ratio (AR = a/b) of 1, 1.5, 2, 3, and 4 having the same equivalent diameter D{sub e} and the nozzle-to-plate distance (L/D{sub e}) of 2, 4, 6, and 10. The temperature distribution on the heated flat plate was measured using a thermochromic liquid crystal and an improved image processing system that produced an unbiased color determination on liquid crystal. With varying the nozzle-to-plate distance, the isothermal contour on the heated flat plate showed an axis-switching phenomenon in its elliptical cross-section shape. As the aspect ratio of the elliptic nozzle increases, the heat transfer rate for the elliptic impinging jet with short nozzle-to-plate distance becomes larger than that of a circular jet in the impingement region. at L/D{sub e} = 2, the Nusselt number of an elliptic impinging jet with AR = 4 was maximum 15% higher than that of a circular impinging jet. This was caused by the engulfing large entrainment rate and large scale coherent structure of the elliptic jet.

  12. Particle removal from smooth and rough surfaces by turbulent jet impingement

    NASA Astrophysics Data System (ADS)

    Liebner, Thomas; Settles, Gary

    2006-11-01

    Recent experiments, e.g. Phares, Smedley & Flagan, J. Aerosol Sci. 31(11) 1335, 2000, have characterized monodisperse particle removal as a function of the theoretical wall shear stress induced by a free turbulent jet impinging upon a smooth surface. These experiments were done with variable jet impingement angle, duration, pressure, standoff distance, etc. The current research expands upon this theme through the experimental investigation of particle removal at larger standoff distances and correspondingly lower wall shear stress levels. We determine particle removal efficiency ratings as a function of the induced wall shear stress for particles of varying size and composition. Finally, we address the complications that arise in particle removal by turbulent jets if the impingement surface is no longer smooth (e.g. a fabric surface). This work has application to such problems as contamination control and the sampling of chemical traces from common surfaces.

  13. Penetration process and instabilities arisen on a liquid jet impinged to a liquid flowing in a channel

    NASA Astrophysics Data System (ADS)

    Hattori, Kaoru; Ueno, Ichiro

    2010-11-01

    We conduct a series of experiments with a special interest on a penetration process and instabilities arisen on a liquid jet impinged to a liquid of the same kind flowing in a channel. The impinged jet penetrates into the flowing bath accompanying with entrainment of the ambient immiscible gas, which results in the impinged jet wrapped by the entrained gas as a "sheath." This sheath formation enables the impinged jet to survive in the fluid in the channel without coalescing until the entrained-air sheath breaks down. Occasionally a "cap" of the entrained air is formed at the tip of the penetrated jet, and the jet elongates like a long balloon. Dynamic behaviors of the penetrated jet and the departure of the bubble of warring gas at the tip of the collapsing jet observed by use of a high-speed camera are discussed.

  14. Apparatus for impingement cooling a side wall adjacent an undercut region of a turbine nozzle segment

    DOEpatents

    Burdgick, Steven Sebastian

    2002-01-01

    A gas turbine nozzle segment has outer and inner bands and vanes therebetween. Each band includes a side wall, a cover and an impingement plate between the cover and nozzle wall defining two cavities on opposite sides of the impingement plate. Cooling steam is supplied to one cavity for flow through apertures of the impingement plate to cool the nozzle wall. The side wall of the band and inturned flange define with the nozzle wall an undercut region. Slots are formed through the inturned flange along the nozzle side wall. A plate having through-apertures extending between opposite edges thereof is disposed in each slot, the slots and plates being angled such that the cooling medium exiting the apertures in the second cavity lie close to the side wall for focusing and targeting cooling medium onto the side wall.

  15. Aeroacoustics and aerodynamics of impinging supersonic jets: Analysis of the screech tones

    NASA Astrophysics Data System (ADS)

    Sinibaldi, G.; Lacagnina, G.; Marino, L.; Romano, G. P.

    2013-08-01

    The interaction between acoustics and aerodynamics of a supersonic jet is an actual fundamental topic which has been a matter of discussion in the last decades. The present paper is devoted to the experimental analysis of free and impinging jets with particular attention on the effect of an impinging surface on screech tones. The acoustics is studied using free-field microphones, while Particle Image Velocimetry is used to investigate the velocity field. The analysis of acquired data allowed to verify and explain the coupling between acoustic discrete tones and mean and fluctuating flow velocities.

  16. Computation of Tone Noise From Supersonic Jet Impinging on Flat Plates

    NASA Technical Reports Server (NTRS)

    Loh, Ching Y.; Blech, Richard A. (Technical Monitor)

    2005-01-01

    A supersonic jet impinging normally on a flat plate has both practical importance and theoretical interests. The physical phenomenon is not fully understood yet. Research concentrates either on the hydrodynamics (e.g., lift loss for STOVL) or on the aeroacoustic loading. In this paper, a finite volume scheme - the space-time conservation element and solution element (CE/SE) method - is employed to numerically study the near-field noise of an underexpanded supersonic jet from a converging nozzle impinging normally on a flat plate. The numerical approach is of the MILES type (monotonically integrated large eddy simulation). The computed results compare favorably with the experimental findings.

  17. The Development and Validation of Simple Empirical Models of Impingement Cooling from Full Surface Heat Transfer Coefficient Distributions

    DTIC Science & Technology

    2003-03-01

    the impingement hole. More recently workers have investigated enhancing impingement heat transfer by employing extended surfaces, Taslim et al. (2000...ed. Oates, G.C.. Taslim , M.E., Setayeshgar, L., Spring, S.D., 2000, "An Experimental Evaluation of Advanced Leading Edge Impingement Cooling Concepts

  18. Spatial Characteristics of Water Spray Formed by Two Impinging Jets at Several Jet Velocities in Quiescent Air

    NASA Technical Reports Server (NTRS)

    Foster, Hampton H.; Heidmann, Marcus F.

    1960-01-01

    The spatial characteristics of a spray formed by two impinging water jets in quiescent air were studied over a range of nominal jet velocities of 30 to 74 feet per second. The total included angle between the 0.089-inch jets was 90 deg. The jet velocity, spray velocity, disappearance of the ligaments just before drop formation, mass distribution, and size and position of the largest drops were measured in a circumferential survey around the point of jet impingement. Photographic techniques were used in the evaluations. The distance from the point of jet impingement to ligament breakup into drops was about 4 inches on the spray axis and about 1.3 inches in the radial position +/-90 deg from the axis. The distance tended to increase slightly with increase in jet velocity. The spray velocity varied from about 99 to about 72 percent of the jet velocity for a change in circumferential position from the spray axis to the +/-80 deg positions. The percentages tended to increase slightly with an increase in jet velocity. Fifty percent of the mass was distributed about the spray axis in an included angle of slightly less than 40 deg. The effect of jet velocity was small. The largest observed drops (2260-micron or 0.090-in. diam.) were found on and about the spray axis. The size of the largest drops decreased for an increase in radial angular position, being about 1860 microns (0.074 in.) at the +/-90 deg positions. The largest drop sizes tended to decrease for an increase in jet velocity, although the velocity effect was small. A drop-size distribution analysis indicated a mass mean drop size equal to 54 percent of an extrapolated maximum drop size.

  19. Numerical Simulation of Bubble Growth in Liquid Jet Impingement on a Hot Plate

    NASA Astrophysics Data System (ADS)

    Kim, Kyungmin; Son, Gihun

    Complete numerical simulations are performed for bubble growth in water jet impingement on a hot plate. The governing equations for the conservation of mass, momentum and energy are numerically solved in the liquid, vapor and air phases. The liquid-vapor and liquid-air interfaces are tracked by a level-set method which is modified to include the effect of phase change at the liquid-vapor interface. The level-set approach is combined with a non-equilibrium k-ε turbulence model. The effects of jet velocity, jet temperature and wall superheat on the bubble growth in water jet and the associated flow and heat transfer are quantified.

  20. Investigation of impinging jet resonant modes using unsteady pressure-sensitive paint measurements

    NASA Astrophysics Data System (ADS)

    Davis, Timothy; Edstrand, Adam; Alvi, Farrukh; Cattafesta, Louis; Yorita, Daisuke; Asai, Keisuke

    2015-05-01

    At given nozzle to plate spacings, the flow field of high-speed impinging jets is known to be characterized by a resonance phenomenon. Large coherent structures that convect downstream and impinge on the surface create strong acoustic waves that interact with the inherently unstable shear layer at the nozzle exit. This feedback mechanism, driven by the coherent structures in the jet shear layer, can either be axisymmetric or helical in nature. Fast-response pressure-sensitive paint (PSP) is applied to the impingement surface to map the unsteady pressure distribution associated with these resonant modes. Phase-averaged results acquired at several kHz are obtained using a flush mounted unsteady pressure transducer on the impingement plate as a reference signal. Tests are conducted on a Mach 1.5 jet at nozzle to plate spacings of . The resulting phase-averaged distribution reveals dramatically different flow fields at the corresponding impingement heights. The existence of a purely axisymmetric mode with a frequency of 6.3 kHz is identified at and is characterized by concentric rings of higher/lower pressure that propagate radially with increasing phase. Two simultaneous modes are observed at with one being a dominant symmetric mode at 7.1 kHz and the second a sub-dominant helical mode at 4.3 kHz. Complimentary phase-conditioned Schlieren images are also obtained visualizing the flow structures associated with each mode and are consistent with the PSP results.

  1. Laser-Induced Fluorescence Velocity Measurements in Supersonic Underexpanded Impinging Jets

    NASA Technical Reports Server (NTRS)

    Inman, Jennifer A.; Danehy, Paul M.; Barthel, Brett; Alderfer, David W.; Novak, Robert J.

    2010-01-01

    We report on an application of nitric oxide (NO) flow-tagging velocimetry to impinging underexpanded jet flows issuing from a Mach 2.6 nozzle. The technique reported herein utilizes a single laser, single camera system to obtain planar maps of the streamwise component of velocity. Whereas typical applications of this technique involve comparing two images acquired at different time delays, this application uses a single image and time delay. The technique extracts velocity by assuming that particular regions outside the jet flowfield have negligible velocity and may therefore serve as a stationary reference against which to measure motion of the jet flowfield. By taking the average of measurements made in 100 single-shot images for each flow condition, streamwise velocities of between -200 and +1,000 m/s with accuracies of between 15 and 50 m/s are reported within the jets. Velocity measurements are shown to explain otherwise seemingly anomalous impingement surface pressure measurements.

  2. A study of jet impingement on curved surfaces followed by oblique introduction into a freestream flow

    NASA Technical Reports Server (NTRS)

    Tatom, J. W.; Schnurr, N. M.; Williamson, J. W.; Dunlap, J. H.

    1972-01-01

    An experimental investigation of the temperature and velocity fields generated by a two-dimensional transverse jet was conducted. An approximate analysis of a deflected radial plane jet was developed. An analytical model of aircraft ingestion was extended to include computation of the inlet flow field. An investigation of the use of flaps as thrust reversers was initiated. Analyses of the impingement of a round incompressible and a round compressible jet on a arbitrary axisymmetric surface were completed. A computer study of the effects on performance of thrust reverser geometry was completed and the results compared with existing data. An experimental investigation of three-dimensional jet impingement on nonplane surfaces was also initiated.

  3. Characterization of an impinging jet into porous media

    NASA Astrophysics Data System (ADS)

    Wang, Cong; Alhani, Salwan; Gharib, Morteza

    2015-11-01

    In this work, characteristic behavior of a liquid jet into porous hydrophobic / hydrophilic particle media is investigated. In porous media, the capillary effect becomes significant, especially when the jet Reynolds Number is low. To analyze the cavity creation phenomena, the effect of jet's diameter, speed and acceleration as well as particles' size are carefully studied. Such knowledge of fluid behavior will provide guidance for medicine injection process. This work is supported by Caltech GALCIT STEM program.

  4. Liquid jet impingement normal to a disk in zero gravity. Ph.D. Thesis - Toledo Univ.

    NASA Technical Reports Server (NTRS)

    Labus, T. L.

    1976-01-01

    An experimental and analytical investigation was conducted to determine the free surface shapes of circular liquid jets impinging normal to sharp-edged disks under both normal and zero gravity conditions. An order of magnitude analysis was conducted indicating regions where viscous forces were not significant when computing free surface shapes. The demarcation between the viscous and inviscid region was found to depend upon the flow Reynolds number and the ratio between the jet and disk radius.

  5. Investigation of flow structure and heat transfer characteristics in an array of impinging slot jets

    NASA Astrophysics Data System (ADS)

    Ozmen, Yucel; Ipek, Gokhan

    2016-04-01

    In this study, an experimental and numerical study is carried out to investigate flow field and heat transfer characteristics of unconfined and confined arrays of four turbulent slot air jets issuing from the lower surface and impinging normally on the upper surface. Pressure and temperature distributions on the surfaces were obtained for the nozzle-to-plate spacing (H/W) of 1-10 and for the Reynolds numbers in the range of 5000-15,000 at the jet-to-jet centerline spacing (S/W) of 9. The effects of jet confinement, Reynolds number and nozzle-to-plate spacing on the flow structure and heat transfer were investigated. Pressure distributions are obtained experimentally and numerically, while heat transfer distributions are computed numerically. It is observed that the surface pressure distributions on both impingement and confinement plates are independent from the Reynolds number, while they have been largely affected from the nozzle-to-plate spacing. Jet confinement causes a considerable difference at the flow field especially for small nozzle-to-plate spacings. Subatmospheric regions are not observed for unconfined jet. However three different types of subatmospheric pressure regions occur on both impingement and confinement plates for confined jet. Nusselt distributions on the impingement plate for both unconfined and confined jet configurations depend on the Reynolds number and nozzle-to-plate spacing. It is concluded that there is a strong correlation between subatmospheric regions and secondary peaks in Nusselt distributions. The numerical results obtained using the Realizable k-ɛ turbulence model is in good accordance with the experimental results for moderate values of nozzle-to-plate spacings.

  6. OVERFLOW Validation for Predicting Plume Impingement of Underexpanded Axisymmetric Jets onto Angled Flat Plates

    NASA Technical Reports Server (NTRS)

    Lee, Henry C.; Klopfer, Goetz

    2011-01-01

    This report documents how OVERFLOW, a computational fluid dynamics code, predicts plume impingement of underexpanded axisymmetric jets onto both perpendicular and inclined flat plates. The effects of the plume impinging on a range of plate inclinations varying from 90deg to 30deg are investigated and compared to the experimental results in Reference 1 and 2. The flow fields are extremely complex due to the interaction between the shock waves from the free jet and those deflected by the plate. Additionally, complex mixing effects create very intricate structures in the flow. The experimental data is very limited, so these validation studies will focus only on cold plume impingement on flat and inclined plates. This validation study will help quantify the error in the OVERFLOW simulation when applied to stage separation scenarios.

  7. Jet impingement heat transfer enhancement for the GPU-3 Stirling engine

    NASA Technical Reports Server (NTRS)

    Johnson, D. C.; Congdon, C. W.; Begg, L. L.; Britt, E. J.; Thieme, L. G.

    1981-01-01

    A computer model of the combustion-gas-side heat transfer was developed to predict the effects of a jet impingement system and the possible range of improvements available. Using low temperature (315 C (600 F)) pretest data in an updated model, a high temperature silicon carbide jet impingement heat transfer system was designed and fabricated. The system model predicted that at the theoretical maximum limit, jet impingement enhanced heat transfer can: (1) reduce the flame temperature by 275 C (500 F); (2) reduce the exhaust temperature by 110 C (200 F); and (3) increase the overall heat into the working fluid by 10%, all for an increase in required pumping power of less than 0.5% of the engine power output. Initial tests on the GPU-3 Stirling engine at NASA-Lewis demonstrated that the jet impingement system increased the engine output power and efficiency by 5% - 8% with no measurable increase in pumping power. The overall heat transfer coefficient was increased by 65% for the maximum power point of the tests.

  8. Synchronal measurement of flow structure and heat transfer of impingement jet

    NASA Astrophysics Data System (ADS)

    Matsuda, Shoichi; Saji, Naomichi; Yaga, Minoru; Ishikawa, Masaaki; Oyakawa, Kenyu

    2010-06-01

    This paper will present the characteristics of flow behavior and thermal field of both free and impingement jet issued from a circular orifice nozzle at Re = 8900. The flow behavior of a single round jet and impingement jet was observed by smoke flow visualization recorded by a high speed camera using 5000 frame per second. Heat transfer coefficient on the impingement surface was measured by means of infrared camera (TVS-8500, Avio) with a two-dimensional array of Indeum-Antimony (In Sb) sensors varying in the separation distance between the nozzle and the target plate. The heat transfer coefficient changes in time and spatial. Therefore, the root mean square distribution of the heat transfer was obtained from the data. As a result, it was confirmed that the longitudinal vortex was observed outside of the ring vortex, and then the longitudinal vortex was penetrated in the jet flow. Moreover, the high value of root mean square of the heat transfer coefficient has spread radially in stripy manner, which is caused as the results of the longitudinal vortexes flowing in the radial direction on the impingement plate.

  9. Heat transfer characteristics within an array of impinging jets. Effects of crossflow temperature relative to jet temperature

    NASA Astrophysics Data System (ADS)

    Florschuetz, L. W.; Su, C. C.

    1985-10-01

    Spanwise average heat fluxes, resolved in the streamwise direction to one stream-wise hole spacing were measured for two-dimensional arrays of circular air jets impinging on a heat transfer surface parallel to the jet orifice plate. The jet flow, after impingement, was constrained to exit in a single direction along the channel formed by the jet orifice plate and heat transfer surface. The crossflow originated from the jets following impingement and an initial crossflow was present that approached the array through an upstream extension of the channel. The regional average heat fluxes are considered as a function of parameters associated with corresponding individual spanwise rows within the array. A linear superposition model was employed to formulate appropriate governing parameters for the individual row domain. The effects of flow history upstream of an individual row domain are also considered. The results are formulated in terms of individual spanwise row parameters. A corresponding set of streamwise resolved heat transfer characteristics formulated in terms of flow and geometric parameters characterizing the overall arrays is described.

  10. Heat transfer characteristics within an array of impinging jets. Effects of crossflow temperature relative to jet temperature

    NASA Technical Reports Server (NTRS)

    Florschuetz, L. W.; Su, C. C.

    1985-01-01

    Spanwise average heat fluxes, resolved in the streamwise direction to one stream-wise hole spacing were measured for two-dimensional arrays of circular air jets impinging on a heat transfer surface parallel to the jet orifice plate. The jet flow, after impingement, was constrained to exit in a single direction along the channel formed by the jet orifice plate and heat transfer surface. The crossflow originated from the jets following impingement and an initial crossflow was present that approached the array through an upstream extension of the channel. The regional average heat fluxes are considered as a function of parameters associated with corresponding individual spanwise rows within the array. A linear superposition model was employed to formulate appropriate governing parameters for the individual row domain. The effects of flow history upstream of an individual row domain are also considered. The results are formulated in terms of individual spanwise row parameters. A corresponding set of streamwise resolved heat transfer characteristics formulated in terms of flow and geometric parameters characterizing the overall arrays is described.

  11. Turbulent Heat Transfer From a Slot Jet Impinging on a Flat Plate.

    PubMed

    Benmouhoub, Dahbia; Mataoui, Amina

    2013-10-01

    The flow field and heat transfer of a plane impinging jet on a hot moving wall were investigated using one point closure turbulence model. Computations were carried out by means of a finite volume method. The evolutions of mean velocity components, vorticity, skin friction coefficient, Nusselt number and pressure coefficient are examined in this paper. Two parameters of this type of interaction are considered for a given impinging distance of 8 times the nozzle thickness (H/e = 8): the jet-surface velocity ratio and the jet exit Reynolds number. The flow field structure at a given surface-to-jet velocity ratio is practically independent to the jet exit Reynolds number. A slight modification of the flow field is observed for weak surface-to-jet velocity ratios while the jet is strongly driven for higher velocity ratio. The present results satisfactorily compare to the experimental data available in the literature for Rsj ≤ 1.The purpose of this paper is to investigate this phenomenon for higher Rsj values (0 ≤ Rsj ≤ 4). It follows that the variation of the mean skin friction and the Nusselt number can be correlated according to the surface-to-jet velocity ratios and the Reynolds numbers.

  12. Excavation of Regolith by Impinging Jets of Gas

    NASA Technical Reports Server (NTRS)

    Metzger, Philip T.; Immer, Christopher D.; Vu, Bruce T.; Donahue, Carly M.

    2006-01-01

    There are many situations in nature and technology where particulate matter is excavated by a fluid jet. Such a process is often used to excavate soil or to dig wells. Air jets are often used to transport particulate matter such as powders in various industrial processes. Similar situations occur in nature, as when waterfalls scour holes in sand. In other cases, the excavation is unwanted such as when a rocket lands on the sandy or dusty surface of a planet or moon. Recent research into regolith excavation by gas jets has obtained new insights into the physical processes of that excavation, and these may lead to new advances in technology for more efficient fluid-jet excavation processes and for better control of the unwanted excavation effects of landing rockets. This talk will explain the new insights and point to future work supporting lunar exploration.

  13. An experimental study of the oscillatory flow structure of tone-producing supersonic impinging jets

    NASA Astrophysics Data System (ADS)

    Henderson, Brenda; Bridges, James; Wernet, Mark

    2005-10-01

    An experimental investigation into the structure of a supersonic jet impinging on a large plate is presented. Digital particle image velocimetry (DPIV), shadowgraph photography and acoustic measurements are used to understand the relationship between the unsteady jet structure and the production of tones for nozzle-to-plate spacings between 1 and 5 nozzle exit diameters at a nozzle pressure ratio equal to 4. Results indicate that the instability of the jet depends on the location of the plate in the shock cell structure of the corresponding free jet and the strength of the standoff shock wave, rather than on the occurrence of recirculation zones in the impingement region. Phase-locked studies show streamwise displacements of the stand-off shock wave, a moving recirculation zone in the subsonic flow in front of the plate, and significant oscillations of both the compression and expansion regions in the peripheral supersonic flow when tones are produced. Sound is shown to be generated by periodic pulsing of the wall jet boundary resulting from periodic motion of the flow in the impingement and near-wall regions of the flow.

  14. An Experimental Investigation of the Flow Structure of Supersonic Impinging Jets

    NASA Technical Reports Server (NTRS)

    Henderson, Brenda; Bridges, James; Wernet, Mark

    2002-01-01

    An experimental investigation into the jet structure associated with sound production by a supersonic impinging jet is presented. Large plate impinging tones are investigated for a nozzle pressure ratio (NPR) of 4 and nozzle-to-plate spacings between 1 and 5 nozzle exit diameters, where NPR is equal to the ratio of the stagnation pressure to the pressure at the nozzle lip. Results from phase-locked shadowgraph and phase-averaged digital particle image velocimetry (DPIV) studies indicate that, during the oscillation cycle, the Mach disk oscillates axially, a well defined recirculation zone is created in the subsonic impingement region and moves toward the plate, and the compression and expansion regions in the outer supersonic flow move downstream, Sound appears to be generated in the wall jet at approximately 2.6R from the jet axis, where R is the nozzle exit radius. The oscillatory motion in the wall jet is the result of the periodic fluid motion in the near wall region.

  15. ANSYS Fluent Modelling of an Underexpanded Supersonic Sootblower Jet Impinging into Recovery Boiler Tube Geometries

    NASA Astrophysics Data System (ADS)

    Doroudi, Shahed

    Sootblowers generate high pressure supersonic steam jets to control fireside deposition on heat transfer tubes of a kraft recovery boiler. Sootblowing is energy expensive, using 3-12% of the mill's total steam production. This motivates research on the dynamics of sootblower jet interaction with tubes and deposits, to optimize their use. A CFD investigation was performed using ANSYS Fluent 15.0 to model three-dimensional steady-state impingement of a Mach 2.5 mildly underexpanded (PR 1.2) air jet onto arrays of cylindrical tubes with and without fins, at various nozzle-to-tube centerline offsets. A free jet and four impingement cases for each of the economizer and generating bank geometries are compared to experimental visualizations. Pressure distributions on impinging surfaces suggest that the fins in the economizer produce a reduced but uniform sootblowing force. Pressure contours along the tubes (in the vertical direction) show a sharp decline one tube diameter away from the jet mid-plane.

  16. Development of an Impinging-jet Fuel-injection Valve Nozzle

    NASA Technical Reports Server (NTRS)

    Spanogle, J A; Hemmeter, G H

    1931-01-01

    During an investigation to determine the possibilities and limitations of a two-stroke-cycle engine and ignition, it was necessary to develop a fuel injection valve nozzle to produce a disk-shaped, well dispersed spray. Preliminary tests showed that two smooth jets impinging upon each other at an angle of 74 degrees gave a spray with the desired characteristics. Nozzles were built on this basis and, when used in fuel-injection valves, produced a spray that fulfilled the original requirements. The spray is so well dispersed that it can be carried along with an air stream of comparatively low velocity or entrained with the fuel jet from a round-hole orifice. The characteristics of the spray from an impinging-jet nozzle limits its application to situations where wide dispersion is required by the conditions in the engine cylinder and the combustion chamber.

  17. Analysis of heat transfer for a normally impinging liquid-metal slot jet

    NASA Technical Reports Server (NTRS)

    Siegel, R.

    1973-01-01

    A two-dimensional liquid-metal slot jet that is impinging normally against a uniformly heated flat plate is analyzed. The distributions of wall temperature and heat-transfer coefficient are obtained as functions of position along the plate. The liquid-metal assumptions are made that the jet is inviscid and that molecular condition is dominating heat diffusion. The solution is obtained by mapping the jet flow region into a potential plane where it occupies a strip of uniform width. The energy equation is transformed into potential coordinates, and an exact solution obtained in the strip region. Conformal mapping is then used to transform the solution into the physical plane.

  18. Noise Characteristics of a Four-Jet Impingement Device Inside a Broadband Engine Noise Simulator

    NASA Technical Reports Server (NTRS)

    Brehm, Christoph; Housman, Jeffrey A.; Kiris, Cetin C.; Hutcheson, Florence V.

    2015-01-01

    The noise generation mechanisms for four directly impinging supersonic jets are investigated employing implicit large eddy simulations with a higher-order accurate weighted essentially non-oscillatory shock-capturing scheme. Impinging jet devices are often used as an experimental apparatus to emulate a broadband noise source. Although such devices have been used in many experiments, a detailed investigation of the noise generation mechanisms has not been conducted before. Thus, the underlying physical mechanisms that are responsible for the generation of sound waves are not well understood. The flow field is highly complex and contains a wide range of temporal and spatial scales relevant for noise generation. Proper orthogonal decomposition of the flow field is utilized to characterize the unsteady nature of the flow field involving unsteady shock oscillations, large coherent turbulent flow structures, and the sporadic appearance of vortex tubes in the center of the impingement region. The causality method based on Lighthill's acoustic analogy is applied to link fluctuations of flow quantities inside the source region to the acoustic pressure in the far field. It will be demonstrated that the entropy fluctuation term in the Lighthill's stress tensor plays a vital role in the noise generation process. Consequently, the understanding of the noise generation mechanisms is employed to develop a reduced-order linear acoustic model of the four-jet impingement device. Finally, three linear acoustic FJID models are used as broadband noise sources inside an engine nacelle and the acoustic scattering results are validated against far-field acoustic experimental data.

  19. Analysis of reactor material experiments investigating corium crust stability and heat transfer in jet impingement flow

    SciTech Connect

    Sienicki, J.J.; Spencer, B.W.

    1985-01-01

    Presented is an analysis of the results of the CSTI-1, CSTI-3, and CWTI-11 reactor material experiments in which a jet of molten corium initially at 3080/sup 0/K was directed downward upon a stainless steel plate. The experiments are a continuation of a program of reactor material tests investigating LWR severe accident phenomena. Objective of the present analysis is to determine the existence or nonexistence of a corium crust during impingement from comparison of the measured heatup of the plate (as measured by thermocouples imbedded immediately beneath the steel surface) with model calculations assuming alternately the presence and absence of a stable crust during impingement.

  20. An experimental investigation into the effect of changes in the geometry of a slot nozzle on the heat transfer characteristics of an impinging air jet

    NASA Astrophysics Data System (ADS)

    Hardisty, H.; Can, M.

    1983-03-01

    High velocity, impinging, air jets are commonly used for heating, cooling, drying etc., because of the high heat transfer coefficients which occur in the impingement region. To provide data for design, a variety of slot nozzles has been tested to determine the effect on heat transfer of both nozzle shape and slot width. A small heat flux meter was used to measure local values of the heat transfer coefficient in the impingement zone, and these local values were integrated to yield space average values. As a necessary preliminary to the heat transfer investigation, the discharge coefficients of the nozzles were measured. From the first test series it was found that heat transfer results from differently shaped nozzles could be satisfactorily correlated provided that the effective slot width was used to characterize nozzle shape. From the second test series it was found that for geometrically similar arrangements, narrower slots gave higher heat transfer coefficients.

  1. Surface Pressure Fluctuations Produced by an Axisymmetric Impinging Jet: Spatio-Temporal Characteristics

    NASA Astrophysics Data System (ADS)

    Naguib, Ahmed; Al-Aweni, Malek

    2013-11-01

    This is the second of a sequence of two presentations concerned with understanding the nature and generation mechanisms of the unsteady surface pressure in impinging jet flows. In the first presentation, the mechanisms influencing the evolution of the surface pressure are studied by examining instantaneous realizations obtained from time-resolved flow visualization and concurrent surface-embedded microphone array measurements; along with numerical simulations of related model problems. In this presentation, the focus is on examining the statistical importance and persistence of these mechanisms by comparing knowledge obtained from the instantaneous analysis to that resulting from inspection of conditional spatio-temporal surface-pressure behaviors, frequency-wavenumber spectra and other statistical measures. Results are presented for surface-pressure measurements at a Reynolds number based on jet diameter of approximately 7000. Dependence of the results on the spacing between the impingement wall and the jet as well as the jet impingement angle is also considered. Partly funded by NSF grant OISE-0611984 and Libyan-North American Scholarship program.

  2. Effect of nonuniform geometries on flow distributions and heat transfer characteristics for arrays of impinging jets

    NASA Technical Reports Server (NTRS)

    Florschuetz, L. W.; Tseng, H. H.

    1984-01-01

    Two-dimensional arrays of circular jets impinging on a surface parallel to the jet orifice plate are considered. The jet flow, after impingement, is constrained to exit in a single direction along the channel formed by the jet orifice plate and the impingement surface. Experimental results for the effects of streamwise nonuniform array geometries on streamwise flow distributions and heat transfer characteristics are presented. A flow distribution model for nonuniform arrays is developed and validated by comparison with the measured flow distributions. The model is then employed to compare nonuniform array streamwise resolved heat transfer coefficient data with previously reported uniform array data and with a previously developed correlation based on the uniform array data. It was found that uniform array results can, in general, serve as a satisfactory basis from which to predict heat transfer coefficients at individual spanwise rows of nonuniform arrays. However, significant differences were observed in some cases over the first one or two rows downstream of the geometric transition line of the nonuniform array.

  3. Apparatus and methods for impingement cooling of an undercut region adjacent a side wall of a turbine nozzle segment

    DOEpatents

    Burdgick, Steven Sebastian; Itzel, Gary Michael

    2001-01-01

    A gas turbine nozzle segment has outer and inner bands. Each band includes a side wall, a cover and an impingement plate between the cover and nozzle wall defining two cavities on opposite sides of the impingement plate. Cooling steam is supplied to one cavity for flow through apertures of the impingement plate to cool the nozzle wall. The side wall of the band and inturned flange define with the nozzle wall an undercut region. The inturned flange has a plurality of apertures for directing cooling steam to cool the side wall between adjacent nozzle segments.

  4. Ice growth and interface oscillation of water droplets impinged on a cooling surface

    NASA Astrophysics Data System (ADS)

    Hagiwara, Yoshimichi; Ishikawa, Shoji; Kimura, Ryota; Toyohara, Kazumasa

    2017-06-01

    We focused on the attenuation of air-water interface oscillation for impinged water droplets freezing on a cooling surface. We carried out not only experiments but also two-dimensional numerical simulation on the droplets using a Phase-field method and an immersed boundary method. The Reynolds number and Weber number were in the range of 35-129 and 1.6-22, respectively. The experimental and computational results showed that the height of the impinged droplets on the symmetrical axis started to oscillate as a result of the impact of the collision of droplets with the surfaces in all the cases that we investigated. The measured frequency of the oscillations in the case of the adiabatic droplets was equal to the frequency estimated from the equation for the capillary-gravity waves on sessile droplets (Temperton, 2013) [30]. The oscillations converged rapidly in all impinged water droplets that froze on the cooling surface. This is due partly to the growth of ice shells along the air-water interface and partly to decreases in water volume as a result of the ice growth mainly on the cooling surface. In addition, the thermal field was disturbed not only by the latent heat transfer but also by the upward component of recirculating flow induced by the droplet impingement.

  5. Dynamics of fine particles during impingement of jets on a body with a needle

    NASA Astrophysics Data System (ADS)

    Alkhimov*, A. P.; Bedarev, I. A.; Fedorov, A. V.

    2013-07-01

    Numerical simulation of the impingement of a jet of a two-phase mixture of a gas with submicron metal particles on an obstacle with a needle located in front of it is carried out. The structure of a separated flow formed on impingement of a supersonic jet on a body with a needle has been studied. A comparison of various approximations for the law of resistance of spherical particles is made. It is shown that particles whose size exceeds 5 μm practically have a rectilinear trajectory and velocity sufficient for cold gas-dynamical deposition, whereas particles of diameter less than 0.2 μm envelope the separation zone being formed near the needle, and their velocity is much smaller than the critical one.

  6. Analysis of potential for jet-impingement erosion from leaking steam generator tubes during severe accidents.

    SciTech Connect

    Majumdar, S.; Diercks, D. R.; Shack, W. J.; Energy Technology

    2002-05-01

    This report summarizes analytical evaluation of crack-opening areas and leak rates of superheated steam through flaws in steam generator tubes and erosion of neighboring tubes due to jet impingement of superheated steam with entrained particles from core debris created during severe accidents. An analytical model for calculating crack-opening area as a function of time and temperature was validated with tests on tubes with machined flaws. A three-dimensional computational fluid dynamics code was used to calculate the jet velocity impinging on neighboring tubes as a function of tube spacing and crack-opening area. Erosion tests were conducted in a high-temperature, high-velocity erosion rig at the University of Cincinnati, using micrometer-sized nickel particles mixed in with high-temperature gas from a burner. The erosion results, together with analytical models, were used to estimate the erosive effects of superheated steam with entrained aerosols from the core during severe accidents.

  7. Channel flow modeling of impingement cooling of a rotating turbine blade

    NASA Technical Reports Server (NTRS)

    Koo, J. J.

    1984-01-01

    Local heat transfer distributions in impingement cooling have been measured by Kreatsoulas and Prieser for a range of conditions which model those in actual turbine blades, including the effects of rotation. These data were reported as local Nusselt numbers, but referred to coolant supply conditions. By means of a channel flow modeling of the flow in the supply and impingement passages, the same data are here presented in terms of local Nusselt number distributions such as are used in design. The results in this form are compared to the nonrotating impingement results of Chupp and to the rotating but nonimpingement results of Morris. Rotation reduces the mean Nusselt numbers from these found by Chupp by about 30 percent, and introduces important radial variations which are sensitive to rotation and to leading edge stagger angle.

  8. Heat Transfer from Impinging Jets. A Literature Review

    DTIC Science & Technology

    1981-06-01

    of r /Bo from 0 to 36 were considered. Maximum heat transfer was found for Zn/Bo = 8, in agreement with Gardon and Akfirat’s data. Cadek concluded...Investigations, Div. of Hydraulics, Chalmers Univ. of Technology, Goteborg, Sweden, 1953. 7. Gardon , R ., and Cobonpue, J.A., "Heat Transfer between a Flat Plate...a Turbulent Round Jet and a Segmented Plate Perpendicular to It," M.S. Thesis, Newark College of Engineering, 1966. 9. Gardon , R ., and Akfirat, J.C

  9. Heat transfer characteristics of a single circular air jet impinging on a concave hemispherical shell

    NASA Technical Reports Server (NTRS)

    Livingood, J. N. B.; Gauntner, J. W.

    1973-01-01

    An experimental study was made of the local and average heat-transfer characteristics of a single turbulent air jet impinging on the concave surface of a hemisphere. Correlations were developed for expressing the effects of a number of dimensionless variables on the local and average Nusselt numbers. Results of the present study are compared with those from a similar study concerning a concave surface of a semicylindrical shell.

  10. An Evaluation of Jet Impingement Heat Transfer Correlations for Piccolo Tube Application

    NASA Technical Reports Server (NTRS)

    Bond, Thomas (Technical Monitor); Wright, William B.

    2004-01-01

    Impinging jets have been used for a wide variety of applications where high rates of heat transfer are desired. This report will present a review of heat transfer correlations that have been published. The correlations were then added to the LEWICE software to evaluate the applicability of these correlations to a piccolo tube anti-icing system. The results of this analysis were then compared quantitatively to test results on a representative piccolo tube system.

  11. Air jet erosion test on plasma sprayed surface by varying erodent impingement pressure and impingement angle

    NASA Astrophysics Data System (ADS)

    Behera, Ajit; Behera, Asit; Mishra, S. C.; Pani, S.; Parida, P.

    2015-02-01

    Fly-ash premixed with quartz and illmenite powder in different weight proportions are thermal sprayed on mild steel and copper substrates at various input power levels of the plasma torch ranging from 11 kW to 21 kW DC. The erosion test has done using Air Jet erosion test Reg (As per ASTM G76) with silica erodent typically 150-250 pm in size. Multiple tests were performed at increasing the time duration from 60 sec to 180 sec with increasing pressure (from 1 bar to 2.5 bar) and angle (60° & 90°). This study reveals that the impact velocity and impact angle are two most significant parameters among various factors influencing the wear rate of these coatings. The mechanisms and microstructural changes that arise during erosion wear are studied by using SEM. It is found that, when erodent are impacting the fresh un-eroded surface, material removal occurs by the continuous evolution of craters on the surface. Upper layer splats are removed out after 60 sec and second layer splat erosion starts. Based on these observations Physical models are developed. Some graphs plotted between mass loss-rate versus time period/impact Pressure/impact Angle gives good correlation with surface features observed.

  12. Role of the confinement of a root canal on jet impingement during endodontic irrigation

    NASA Astrophysics Data System (ADS)

    Verhaagen, B.; Boutsioukis, C.; Heijnen, G. L.; van der Sluis, L. W. M.; Versluis, M.

    2012-12-01

    During a root canal treatment the root canal is irrigated with an antimicrobial fluid, commonly performed with a needle and a syringe. Irrigation of a root canal with two different types of needles can be modeled as an impinging axisymmetric or non-axisymmetric jet. These jets are investigated experimentally with high-speed Particle Imaging Velocimetry, inside and outside the confinement (concave surface) of a root canal, and compared to theoretical predictions for these jets. The efficacy of irrigation fluid refreshment with respect to the typical reaction time of the antimicrobial fluid with a biofilm is characterized with a non-dimensional Damköhler number. The pressure that these jets induce on a wall or at the apex of the root canal is also measured. The axisymmetric jet is found to be stable and its velocity agrees with the theoretical prediction for this type of jet, however, a confinement causes instabilities to the jet. The confinement of the root canal has a pronounced influence on the flow, for both the axisymmetric and non-axisymmetric jet, by reducing the velocities by one order of magnitude and increasing the pressure at the apex. The non-axisymmetric jet inside the confinement shows a cascade of eddies with decreasing velocities, which at the apex does not provide adequate irrigation fluid refreshment.

  13. Experiments and Modeling of Impinging Jets and Premixed Hydrocarbon Stagnation Flames

    DTIC Science & Technology

    2005-05-26

    coupling of the acoustic properties of the two jets could lead to oscillations and instabilities in the flames. Impinging-jet flames are found to be more...the Knudsen-Weber slip correction factor [see Eq. (A.10)], τS is the Stokes time, and σ = dup/dx ∼= duf /dx is the (local) velocity gradient [see...that act on a particle in a typical flow are ΣF = FPG + FFI + FUD + FG + FSD + FTP , (A.2) where FPG = ρf ρp mp duf dt (A.3) is the pressure-gradient

  14. Surface Pressure Fluctuations Produced by an Axisymmetric Impinging Jet: Generation Mechanisms

    NASA Astrophysics Data System (ADS)

    Al-Aweni, Malek; Naguib, Ahmed

    2013-11-01

    This study is motivated by understanding the mechanisms leading to unsteady surface pressure generation in impinging jet flows. Employing an extensive database of concurrent time-resolved flow visualization and time series from a surface-embedded microphone array, two dominant mechanisms are found to affect the space-time evolution of the pressure within the wall-jet zone: vortex-wall and vortex-vortex interaction. To gain deeper insight into these mechanisms, two closely-related model problems are studied computationally using Fluent. The problems involve the impingement of a single or two axisymmetric vortex rings on a flat wall. The resulting spatio-temporally resolved computations are used in conjunction with Possion's equation for pressure to investigate the nature of the pressure-generating sources, their relative importance, and their relation to the observed surface pressure signature. The findings provide significant information towards realization of efficient, structure-based models for computing the unsteady wall pressure in impinging jets. Partly funded by NSF grant OISE-0611984 and Libyan-North American Scholarship program.

  15. Optimization of an inclined elliptic impinging jet with cross flow for enhancing heat transfer

    NASA Astrophysics Data System (ADS)

    Heo, Man-Woong; Lee, Ki-Don; Kim, Kwang-Yong

    2011-06-01

    This work presents a parametric study and optimization of a single impinging jet with cross flow to enhance heat transfer with two design variables. The fluid flow and heat transfer have been analyzed using three-dimensional compressible Reynolds-averaged Navier-Stokes equations with a uniform heat flux condition being applied to the impingement plate. The aspect ratio of the elliptic jet hole and the angle of inclination of the jet nozzle are chosen as the two design variables, and the area-averaged Nusselt number on a limited target plate is set as the objective function. The effects of the design variables on the heat transfer performance have been evaluated, and the objective function has been found to be more sensitive to the angle of inclination of the jet nozzle than to the aspect ratio of the elliptic jet hole. The optimization has been performed by using the radial basis neural network model. Through the optimization, the area-averaged Nusselt number increased by 7.89% compared to that under the reference geometry.

  16. On the correspondence between flow structures and convective heat transfer augmentation for multiple jet impingement

    NASA Astrophysics Data System (ADS)

    Terzis, Alexandros

    2016-09-01

    The correspondence between local fluid flow structures and convective heat transfer is a fundamental aspect that is not yet fully understood for multiple jet impingement. Therefore, flow field and heat transfer experiments are separately performed investigating mutual-jet interactions exposed in a self-gained crossflow. The measurements are taken in two narrow impingement channels with different cross-sectional areas and a single exit design. Hence, a gradually increased crossflow momentum is developed from the spent air of the upstream jets. Particle image velocimetry (PIV) and liquid crystal thermography (LCT) are used in order to investigate the aerothermal characteristics of the channel with high spatial resolution. The PIV measurements are taken at planes normal to the target wall and along the centreline of the jets, providing quantitative flow visualisation of jet and crossflow interactions. Spatially resolved heat transfer coefficient distributions on the target plate are evaluated with transient techniques and a multi-layer of thermochromic liquid crystals. The results are analysed aiming to provide a better understanding about the impact of near-wall flow structures on the convective heat transfer augmentation for these complex flow phenomena.

  17. Erosion onset of a cohesionless granular medium by an immersed impinging round jet

    NASA Astrophysics Data System (ADS)

    Brunier-Coulin, Florian; Cuéllar, Pablo; Philippe, Pierre

    2017-03-01

    Among different devices developed quite recently to quantify the resistance to erosion of natural soil within the broader context of dyke safety, the most commonly used is probably the jet erosion test in which a scouring crater is induced by impingement of an immersed water jet. A comprehensive experimental investigation on the jet erosion in the specific situation of a cohesionless granular material is presented here. The tests were performed by combining special optical techniques allowing for an accurate measurement of the scouring onset and evolution inside an artificially translucent granular sample. The impinging jet hydrodynamics are also analyzed, empirically validating the use of a self-similar theoretical framework for the laminar round jet. The critical conditions at the onset of erosion appear to be best described by a dimensionless Shields number based on the inertial drag force created by the fluid flow on the eroded particles rather than on the pressure gradients around them. To conclude, a tentative empirical model for the maximal flow velocity initiating erosion at the bottom of the scoured crater is put forward and discussed in the light of some preliminary results.

  18. Self-induced sloshing caused by an upward round jet impinging on the free surface

    SciTech Connect

    Madarame, Haruki; Okamoto, Koji; Iida, Masao

    1995-11-01

    The demand for compact design of FBR made it necessary to study the interaction between high speed coolant flow and the free surface. Self-induced sloshing was found to occur with an upward round jet making a surface swell at the impinging point. The conditions under which the sloshing occurred were investigated experimentally together with the sloshing modes and frequencies. Without exception the induced mode had only one diametrical node, which was accompanied by the lateral motion of the swell. The mode was replaced by lower one with increasing the inlet-surface distance and the velocity, the reason of which was explained by the following assumption; the oscillation of water columns on both sides of the jet connected by a virtual cross flow through the jet, i.e., jet-flutter, was coupled with the sloshing and supplied energy to it.

  19. The Effects of Crossflow on the Pressures and Lift Induced by the Fountain Generated Between Two Impinging Jets

    NASA Technical Reports Server (NTRS)

    Kuhn, Richard E.

    1998-01-01

    When a jet STOVL aircraft is hovering, or in a crossflow, while close to the ground wall jets flowing radially outward from the impingement points of the jets are generated. An upflow, or fountain, is generated where the wall jets from adjacent jets meet on the ground surface. The induced lift and suckdown generated by the impingement of the fountain on the lower surface of the configuration has been the subject of previous studies. This study analyzes the limited available pressure and force data on the effect of crossflow on the fountain induced lift and suckdown. The analysis includes the effects of jet spacing, height and operating conditions. However, it is limited to twin jet configurations of circular, vertical jets operating at subcritical nozzle pressure ratios over a fixed ground surface.

  20. Passive control of wall shear stress and mass transfer generated by submerged lobed impinging jet

    NASA Astrophysics Data System (ADS)

    Sodjavi, Kodjovi; Montagné, Brice; Meslem, Amina; Byrne, Paul; Serres, Laurent; Sobolik, Vaclav

    2016-05-01

    Particle image velocimetry was used to investigate the flow field in an impinging lobed daisy hemispherical nozzle jet in comparison to its counterpart round jet, at a Reynolds number of 5620 based on the exit velocity and the equivalent diameter D e of the nozzle. The limitations of the PIV technique in the vicinity of the target wall due to the laser scattering were addressed by using the electrodiffusion (ED) technique to determine the wall shear rate distribution. The distribution of the mass transfer coefficient is also obtained using the ED technique. The target wall is placed at a distance H = 2 D e from the plane tangent to the nozzle, at the center of the orifice. The entrainment of ambient fluid in the free jet region, which is larger in the lobed jet compared to the round jet, feeds in turn the wall jet region. The maximum wall shear rate was found significantly higher in the daisy jet, with an excess of 93 % compared to the reference round jet. The maximum mass transfer is 35 % higher in the former compared to the latter. Therefore, the hemispherical daisy nozzle is an excellent candidate in passive strategies to enhance local skin-friction and the subsequent local mass transfer at a constant exit Reynolds number.

  1. The influence of the stagnation zone on the fluid dynamics at the nozzle exit of a confined and submerged impinging jet

    NASA Astrophysics Data System (ADS)

    Jeffers, Nicholas; Stafford, Jason; Conway, Ciaran; Punch, Jeff; Walsh, Edmond

    2016-02-01

    Low profile impinging jets provide a means to achieve high heat transfer coefficients while occupying a small quantity of space. Consequently, they are found in many engineering applications such as electronics cooling, annealing of metals, food processing, and others. This paper investigates the influence of the stagnation zone fluid dynamics on the nozzle exit flow condition of a low profile, submerged, and confined impinging water jet. The jet was geometrically constrained to a round, 16-mm diameter, square-edged nozzle at a jet exit to target surface spacing ( H/ D) that varied between 0.25 < {{ H}{/}{ D}} < 8.75. The influence of turbulent flow regimes is the main focus of this paper; however, laminar flow data are also presented between 1350 < Re < 17{,}300. A custom measurement facility was designed and commissioned to utilise particle image velocimetry in order to quantitatively measure the fluid dynamics both before and after the jet exits its nozzle. The velocity profiles are normalised with the mean velocity across the nozzle exit, and turbulence statistics are also presented. The primary objective of this paper is to present accurate flow profiles across the nozzle exit of an impinging jet confined to a low H/ D, with a view to guide the boundary conditions chosen for numerical simulations confined to similar constraints. The results revealed in this paper suggest that the fluid dynamics in the stagnation zone strongly influences the nozzle exit velocity profile at confinement heights between 0 < {{ H}{/}{ D}} < 1. This is of particular relevance with regard to the choice of inlet boundary conditions in numerical models, and it was found that it is necessary to model a jet tube length {{ L}{/}{ D}} > 0.5—where D is the inner diameter of the jet—in order to minimise modelling uncertainty.

  2. Rolling up of Large-scale Laminar Vortex Ring from Synthetic Jet Impinging onto a Wall

    NASA Astrophysics Data System (ADS)

    Xu, Yang; Pan, Chong; Wang, Jinjun; Flow Control Lab Team

    2015-11-01

    Vortex ring impinging onto a wall exhibits a wide range of interesting behaviors. The present work devotes to an experimental investigation of a series of small-scale vortex rings impinging onto a wall. These laminar vortex rings were generated by a piston-cylinder driven synthetic jet in a water tank. Laser Induced Fluorescence (LIF) and Particle Image Velocimetry (PIV) were used for flow visualization/quantification. A special scenario of vortical dynamic was found for the first time: a large-scale laminar vortex ring is formed above the wall, on the outboard side of the jet. This large-scale structure is stable in topology pattern, and continuously grows in strength and size along time, thus dominating dynamics of near wall flow. To quantify its spatial/temporal characteristics, Finite-Time Lyapunov Exponent (FTLE) fields were calculated from PIV velocity fields. It is shown that the flow pattern revealed by FTLE fields is similar to the visualization. The size of this large-scale vortex ring can be up to one-order larger than the jet vortices, and its rolling-up speed and entrainment strength was correlated to constant vorticity flux issued from the jet. This work was supported by the National Natural Science Foundation of China (Grants No.11202015 and 11327202).

  3. Splattering and heat transfer during impingement of a turbulent liquid jet

    SciTech Connect

    Lienhard, J.H. V; Liu, X.; Gabour, L.A. )

    1992-05-01

    Splattering and heat transfer due to impingement of an unsubmerged, fully turbulent liquid jet is investigated experimentally and analytically. Heat transfer measurements were made along a uniformly heated surface onto which a jet impacted, and a Phase Doppler Particle Analyzer was used to measure the size, velocity, and concentration of the droplets splattered after impingement. Splattering is found to occur in proportion to the magnitude of surface disturbances to the incoming jet, and it is observed to occur only within a certain radial range, rather than along the entire film surface. A nondimensional group developed from inviscid capillary disturbance analysis of the circular jet successfully scales the splattering data, yielding predictive results for the onset of splattering results is used to formulate a prediction of local Nusselt number. Both the prediction and the experimental data reveal that the Nusselt number is enhanced for radial locations immediately following splattering, but falls below the nonsplattering Nusselt number at larger radii. The turbulent heat transfer enhancement upstream of splattering is also characterized.

  4. Heat transfer and vortical structures of a plane impinging jet excited by spanwise periodic disturbances

    NASA Astrophysics Data System (ADS)

    Miyoshi, Yoshifumi; Kaneko, Jun-Ichi; Sakakibara, Jun

    2001-11-01

    Wall temperature and vorticity distribution of a stagnation region of a plane impinging jet with spanwise and temporal periodic disturbances has been measured by using thermochromic liquid crystal (TLC) and PIV. The plane jet of water was excited in time and space by adding suction/blowing type disturbances produced by servomotor-driven injectors. Stainless foil heaters with TLC coating glued on a Plexiglass plate was used as a heated impingement wall. The TLC surface was observed by 3 monochrome CCD cameras through RGB filters to acquire color distribution, and the velocity and vorticity field in a center-plane of the jet have been measured by PIV. Strouhal and Reynolds number were set respectively at St=0.45 and Re=2300. Surface temperature distribution showed unsteady streaks in parallel with a wall jet direction. It was evident from the PIV results that these streaks were caused by counter-rotating vortices induced on the wall. The vorticity magnitude and heat transfer rate could be modified by the temporal phase angle between disturbances added in adjacent spanwise locations.

  5. Determination of Cavity Dimensions Induced by Impingement of Gas Jets onto a Liquid Bath

    NASA Astrophysics Data System (ADS)

    Li, Mingming; Li, Qiang; Kuang, Shibo; Zou, Zongshu

    2016-02-01

    This paper presents an experimental and theoretical study on the cavity profile induced by the impingement of top-blown multiple gas jets onto a water or oil/water bath. The depth and diameter of the cavity were measured with respect to the lance height, gas flow rate, jets inclination angle, and oil volume. The experimental results show that the cavity depth increases with the increase of gas flow rate or oil thickness but the decrease of lance height or jets inclination angle. The cavity diameter is much less affected by gas flow rate compared to other variables. Then, the importance of the surface tension in the modeling of the cavity was theoretically identified. It was found that in the cratering process, the effect of the liquid surface tension on the cavity depth could be remarkably significant for a basic oxygen furnace (BOF) cold model but negligible for a real BOF steelmaking system. An improved theoretical model was hence proposed and validated using the experimental data obtained from both the single- or two-layer liquid baths. The new model includes not only the explicit consideration of the liquid surface tension but also that of the energy utilization efficiency of the jets impinging kinetic energy contributed to the cratering process.

  6. Rapid PCR amplification using a microfluidic device with integrated microwave heating and air impingement cooling.

    PubMed

    Shaw, Kirsty J; Docker, Peter T; Yelland, John V; Dyer, Charlotte E; Greenman, John; Greenway, Gillian M; Haswell, Stephen J

    2010-07-07

    A microwave heating system is described for performing polymerase chain reaction (PCR) in a microfluidic device. The heating system, in combination with air impingement cooling, provided rapid thermal cycling with heating and cooling rates of up to 65 degrees C s(-1) and minimal over- or under-shoot (+/-0.1 degrees C) when reaching target temperatures. In addition, once the required temperature was reached it could be maintained with an accuracy of +/-0.1 degrees C. To demonstrate the functionality of the system, PCR was successfully performed for the amplification of the Amelogenin locus using heating rates and quantities an order of magnitude faster and smaller than current commercial instruments.

  7. Numerical models of jet disruption in cluster cooling flows

    NASA Technical Reports Server (NTRS)

    Loken, Chris; Burns, Jack O.; Roettiger, Kurt; Norman, Mike

    1993-01-01

    We present a coherent picture for the formation of the observed diverse radio morphological structures in dominant cluster galaxies based on the jet Mach number. Realistic, supersonic, steady-state cooling flow atmospheres are evolved numerically and then used as the ambient medium through which jets of various properties are propagated. Low Mach number jets effectively stagnate due to the ram pressure of the cooling flow atmosphere while medium Mach number jets become unstable and disrupt in the cooling flow to form amorphous structures. High Mach number jets manage to avoid disruption and are able to propagate through the cooling flow.

  8. Experimental investigation of influence of Reynolds number on synthetic jet vortex rings impinging onto a solid wall

    NASA Astrophysics Data System (ADS)

    Xu, Yang; He, GuoSheng; Kulkarni, Varun; Wang, JinJun

    2017-01-01

    Time-resolved particle image velocimetry was employed to study the effect of Reynolds number ( Re sj) on synthetic jet vortex rings impinging onto a solid wall. Four Reynolds numbers ranging from 166 to 664 were investigated for comparison while other parameters were kept constant. It is found that the Reynolds number has a significant impact on the spatial evolution of near-wall vortical structures of the impinging synthetic jet. Velocity triple decomposition reveals that periodic Reynolds shear stresses produced by both impinging and secondary vortex rings agree well with a four-quadrant-type distribution rule, and the random velocity fluctuations are strengthened as Re sj increases. For radial wall jet, radial velocity profiles exhibit a self-similar behavior for all Re sj, and this self-similar profile gradually deviates from the laminar solution as Re sj is increased. In particular, the self-similar profile for low Re sj (166) coincides with the laminar solution indicating that periodic velocity fluctuations produced by vortex rings have little effect on the velocity profile of the laminar wall jet. This also provides evidence that the impinging synthetic jet is more effective in mixing than the continuous jet for the laminar flow. For the high Re sj, the mean skin friction coefficient has a slower decay rate after reaching peak, and the radial momentum flux has a higher value at locations far away from the impingement region, both of these can be attributed to the enhanced random fluctuations.

  9. Comparison of temperature data from an engine investigation for film-cooled and non-film-cooled, panwise-finned vanes incorporating impingement cooling

    NASA Technical Reports Server (NTRS)

    Gauntner, D. J.

    1973-01-01

    The experimental temperature characteristics of two spanwise-finned, impingement-cooled vanes, one with film cooling and one without film cooling, were investigated in a modified J-75 research turbojet engine. Values of maximum temperature, average temperature, and maximum chordwise temperature difference were compared for the two vanes at the midspan. An analytical redesign of the two vane configurations indicated that the maximum and average temperatures and the maximum chordwise temperature difference could be significantly lowered. The experimental tests indicated that suction-surface film cooling may cause increased heat transfer near the trailing edge of the vane.

  10. Experiments on the ground vortex formed by an impinging jet in cross flow

    NASA Technical Reports Server (NTRS)

    Blake, William B.; Stewart, Vearl R.

    1993-01-01

    An inclined jet impinging on the ground creates a wall flow that spreads radially from the point of impingement. If a cross-flow is introduced, the upstream component of the wall flow will separate from the ground and create what has been termed the 'ground vortex.' The ground vortex has been shown to have a significant impact on aircraft aerodynamics and is one of the major contributors to hot gas ingestion. The paper discusses a recent study which included a generic wing-body configuration for assessing the impact of the ground vortex on configuration aerodynamics. Wind tunnel tests using fixed ground boards, moving ground belts, and moving model tests are discussed. The emphasis of the data is macroscopic, i.e. forward location of the vortex, effects of ground height, etc.

  11. Effect of nozzle geometry on impingement heat transfer distribution from jet arrays

    SciTech Connect

    Owens, R.D.; Liburdy, J.A.

    1995-12-31

    Heat transfer distributions were determined for flat surfaces using three different 3 x 3 jet-impingement arrays. Each array used a different jet orifice cross sectional geometry, either circles, triangles, or ellipses. For each geometry, the jet-to-jet spacing divided by the hydraulic diameter, was three. Five flow rates were tested with Reynolds numbers ranging from 268 to 1,557. For each flow rate, the four jet array height-to-jet spacings (H/D) of 2, 3, 4, and 5 were tested. All of the parameters presented, such as the Reynolds and Nusselt numbers, were based on the orifice hydraulic diameter. In order to determine the heat transfer distributions for each condition tested, thermochromic liquid crystals were used as part of a transient heating testing method. In the majority of the tests, the ellipse array performed the best, with the triangular orifice close behind. Also, of the three orifice geometries, the ellipse had the lowest pressure drop. The heat transfer improvement was especially predominant at low Reynolds numbers.

  12. Confined swirling jet impingement on a flat plate at moderate Reynolds numbers

    NASA Astrophysics Data System (ADS)

    Herrada, M. A.; Del Pino, C.; Ortega-Casanova, J.

    2009-01-01

    The behavior of a swirling jet issuing from a pipe and impinging on a flat smooth wall is analyzed numerically by means of axisymmetric simulations. The axial velocity profile at the pipe outlet is assumed flat while the azimuthal velocity profile is a Burger's vortex characterized by two non-dimensional parameters; a swirl number S and a vortex core length δ. We concentrate on the effects of these two parameters on the mechanical characteristics of the flow at moderate Reynolds numbers. Our results for S =0 are in agreement with Phares et al. [J. Fluid Mech. 418, 351 (2000)], who provide a theoretical determination of the wall shear stress under nonswirling impinging jets at high Reynolds numbers. In addition, we show that the swirl number has an important effect on the jet impact process. For a fixed nozzle-to-plate separation, we found that depending on the value of δ and the Reynolds number Re, there is a critical swirl number, S =S∗(δ ,Re), above which recirculating vortex breakdown bubbles are observed in the near axis region. For S >S∗, the presence of these bubbles enhances the transition from a steady to a periodic regime. For S

  13. Mucosal deformation from an impinging transonic gas jet and the ballistic impact of microparticles

    NASA Astrophysics Data System (ADS)

    Hardy, M. P.; Kendall, M. A. F.

    2005-10-01

    By means of a transonic gas jet, gene guns ballistically deliver microparticle formulations of drugs and vaccines to the outer layers of the skin or mucosal tissue to induce unique physiological responses for the treatment of a range of conditions. Reported high-speed imaging experiments show that the mucosa deforms significantly while subjected to an impinging gas jet from a biolistic device. In this paper, the effect of this tissue surface deformation on microparticle impact conditions is simulated with computational fluid dynamics (CFD) calculations. The microparticles are idealized as spheres of diameters 26.1, 39 and 99 µm and a density of 1050 kg m-3. Deforming surface calculations of particle impact conditions are compared directly with an immobile surface case. The relative velocity and obliquity of the deforming surface decrease the normal component of particle impact velocity by up to 30% at the outer edge of the impinging gas jet. This is qualitatively consistent with reported particle penetration profiles in the tissue. It is recommended that these effects be considered in biolistic studies requiring quantified particle impact conditions.

  14. Vortex structure of a plane impinging jet with spanwise periodic forcing

    NASA Astrophysics Data System (ADS)

    Sakakibara, Jun; Anzai, Tomokuni

    1999-11-01

    Vortex structure of a plane impinging jet of water with spanwise periodic forcing has been experimentally measured using PIV. A plane nozzle, having a width of ( B=30 ) mm and aspect ratio of 10, issued water jet vertically and impinged on a plate set at a distance ( H=5.5B ) from the nozzle exit. Sixty rectangular slots (1mm (×) 4mm cross-section) aligned in spanwise direction are installed both side of the nozzle exit with 5mm interval. Each slots are connected via vinyl tubes to four of speaker boxes to add suction/blowing perturbations to the initial shear layer of the jet. The perturbation added by successive 3 slots, 15mm in spanwise length, have a phase lag (α) behind the perturbation by next 3 slots, and repeated in whole row of the slots. This configuration could make spanwise periodic perturbations, which have a wave length (λ=30)mm, to excite the secondary instability of the shear layer. As increasing phase lag (α) the intensity of the vorticity of the streamwise counter-rotating vortices on the stagnation plate was increased, and maximum intensity was achieved at (α=π). Time and spatial evolution of the vortex structures will be shown in the presentation.

  15. Jet stability and wall impingement flow field in a thermal striping experiment

    DOE PAGES

    Lomperski, S.; Obabko, A.; Merzari, E.; ...

    2017-08-10

    We present velocity and temperature field measurements for a 0.9 x 0.9 x 1.7 m glass tank in which two air jets at Re=10000 mix and impinge upon the lid at ambient temperature and pressure. Flow patterns are characterized across a 350 x 200 mm plane located 3 mm below the lid for two inlet geometries: 1) “extended”, in which inlet channels protrude above the tank base, and 2) “flush”, a flat base without protrusions. This minor geometry variation produced distinct changes in the lid flow field, appearing as three stagnant regions for the extended case and only one formore » flush. The dichotomy is attributed to system stability characteristics: jets are stable in the extended case and unstable for flush. In a separate set of nonisothermal tests, the impingement temperature field was measured for inlet temperature mismatches of 4 oC and jets near Re=10000. A 50 m-long fiber optic distributed temperature sensor positioned 2 mm below the lid measured at 1350 locations. Like the velocity fields, the temperature fields differ for the two inlet geometries: good thermal mixing for the flush case and subdued mixing for the extended case. Simulations with the spectral element code Nek5000 replicated the observed stability dichotomy, duplicating the number of stagnant regions observed in the experiment and matching their locations within ±10 mm. Simulation data suggests that flush case instability is due to interactions between jets and wall flows at the bottom of the tank. The clear flow dichotomy exhibited by this two-jet setup presents an unambiguous case to test the ability of CFD tools to predict subtle flow field changes driven by minor modifications in geometry in the context of thermal striping.« less

  16. Computation of Turbulent Recirculating Flow in Channels, and for Impingement Cooling

    NASA Technical Reports Server (NTRS)

    Chang, Byong Hoon

    1992-01-01

    Fully elliptic forms of the transport equations have been solved numerically for two flow configurations. The first is turbulent flow in a channel with transverse rectangular ribs, and the second is impingement cooling of a plane surface. Both flows are relevant to proposed designs for active cooling of hypersonic vehicles using supercritical hydrogen as the coolant. Flow downstream of an abrupt pipe expansion and of a backward-facing step were also solved with various near-wall turbulence models as benchmark problems. A simple form of periodicity boundary condition was used for the channel flow with transverse rectangular ribs. The effects of various parameters on heat transfer in channel flow with transverse ribs and in impingement cooling were investigated using the Yap modified Jones and Launder low Reynolds number k-epsilon turbulence model. For the channel flow, predictions were in adequate agreement with experiment for constant property flow, with the results for friction superior to those for heat transfer. For impingement cooling, the agreement with experiment was generally good, but the results suggest that improved modelling of the dissipation rate of turbulence kinetic energy is required in order to obtain improved heat transfer prediction, especially near the stagnation point. The k-epsilon turbulence model was used to predict the mean flow and heat transfer for constant and variable property flows. The effect of variable properties for channel flow was investigated using the same turbulence model, but comparison with experiment yielded no clear conclusions. Also, the wall function method was modified for use in the variable properties flow with a non-adiabatic surface, and an empirical model is suggested to correctly account for the behavior of the viscous sublayer with heating.

  17. Thermal performance analysis of optimized hexagonal finned heat sinks in impinging air jet

    SciTech Connect

    Yakut, Kenan; Yeşildal, Faruk; Karabey, Altuğ; Yakut, Rıdvan

    2016-04-18

    In this study, thermal performance analysis of hexagonal finned heat sinks which optimized according to the experimental design and optimization method of Taguchi were investigated. Experiments of air jet impingement on heated hexagonal finned heat sinks were carried out adhering to the L{sub 18}(2{sup 1*}3{sup 6}) orthogonal array test plan. Optimum geometries were determined and named OH-1, OH-2. Enhancement efficiency with the first law of thermodynamics was analyzed for optimized heat sinks with 100, 150, 200 mm heights of hexagonal fin. Nusselt correlations were found out and variations of enhancement efficiency with Reynolds number presented in η–Re graphics.

  18. Spectroscopy of jet-cooled tyrosine derivatives

    NASA Astrophysics Data System (ADS)

    Teh, Chin Khuan; Sulkes, Mark

    1991-05-01

    Using fluorescence-based techniques (excitation and emission spectra lifetimes), we have studied the jet-cooled tyrosine derivatives tyramine and 3-(4-hydroxyphenyl) propionic acid (HPA). For solvent addition resulting in small, mainly one adduct complexes, there is a high degree of analogy with the results for the corresponding analogs of the amino acid tryptophan. In particular, for tyramine, as had been the case with its tryptophan analog tryptamine, addition of one -OH bearing solvent molecule at the α-amine apparently results in a complex in a single conformation.

  19. An experimental flow field and heat transfer investigation of submerged double-sided reattachment and two-dimensional impingement slot jets

    NASA Astrophysics Data System (ADS)

    Narayanan, Vinod

    Reattachment nozzles have great potential for heating, cooling, or drying applications in process industries due to their favorable transport characteristics. This research investigates sub-sonic, turbulent, submerged impingement jet flow field and associated heat transfer from two nozzles: a 0° exit angle Slot Jet Reattachment (SJR) nozzle and a Slot Jet (SJ) nozzle. Both these nozzles are comprised of a rectangular region of aspect ratio 20:1 with circular ends. The 0° SJR nozzle has an additional bottom plate that causes the flow to exit the nozzle parallel to an adjacent flat impingement surface. It is essentially a double-sided reattachment jet with unconfined circular ends. Detailed heat transfer, impingement surface pressure and flow field measurements are presented for both nozzles. The documented quantities include mean velocities, rms Reynolds normal and shear stresses in the plane of measurement, two-dimensional contour maps of local heat transfer distribution, and mean and rms surface pressures. Four case studies are presented in detail---two for each nozzle at different nozzle-to-surface spacings. Contours of local heat transfer for the SJR nozzle exhibit three-dimensionality within the recirculation and reattachment regions, which increases with nozzle-to-surface spacing. Flow field measurements at close spacing indicate that high heat transfer in the reattachment region could be caused by high near-wall streamwise and shear Reynolds stresses, coupled with an intermittent flow impingement on the surface due to high normal Reynolds stress. At farther nozzle-to-surface spacing, the streamwise Reynolds stress is the primary turbulent quantity affecting heat transfer. In both cases, the jet curtain is unsteady due to high normal Reynolds stress in the lower side of the jet. A non-dimensional scheme for generalized representation of heat transfer data for separated/reattaching jet flows is developed and demonstrated. It is based on a length scale that

  20. Investigation into the effect of nozzle shape on the nozzle discharge coefficient and heat and mass transfer characteristics of impinging air jets

    NASA Astrophysics Data System (ADS)

    Etemoglu, A. B.; Isman, M. K.; Can, M.

    2010-12-01

    High velocity impinging air jets are commonly used for heating, cooling and drying, etc. because of the high heat and mass transfer coefficients which are developed in the impingement region. In order to provide data for the designers of industrial equipment, a variety of slot nozzles were tested to determine the effect on heat transfer of both nozzle shape and slot width. A large multi-nozzle rig was also used to measure average heat and mass transfer characteristics under arrays of both slot nozzles and circular holes. As a necessary preliminary to the heat transfer investigation, the discharge coefficients of the nozzles were measured. Then, the experimental results are compared with the simplified flow model. A good agreement was found between the theoretical and experimental results. From the tests, it was also found that the heat transfer results from differently shaped nozzles could be satisfactorily correlated provided that the effective slot width or hole diameter was used to characterize the nozzle shapes.

  1. Prediction of jet impingement heat transfer using a hybrid wall treatment with different turbulent Prandtl number functions

    SciTech Connect

    Morris, G.K.; Garimella, S.V.; Amano, R.S.

    1995-12-31

    The local heat transfer coefficient distribution on a square heat source due to a normally impinging, axisymmetric, confined and submerged liquid jet was computationally investigated. Numerical predictions were made for nozzle diameters of 3.18 and 6.35 mm at several nozzle-to-heat source spacings, with turbulent jet Reynolds numbers ranging from 8500 to 13000. The commercial finite-volume code FLUENT was used to solve the thermal and flow fields using the standard high-Reynolds number {kappa}-{epsilon} turbulence model. The converged solution obtained from the code was refined using a post-processing program that incorporated several near-wall models. The role of four alternative turbulent Prandtl number functions on the predicted heat transfer coefficients was investigated. The predicted heat transfer coefficients were compared with previously obtained experimental measurements. The predicted stagnation and average heat transfer coefficients agree with experiments to within a maximum deviation of 16% and 20%, respectively. Reasons for the differences between the predicted and measured heat transfer coefficients are discussed. This study is applicable to electronic cooling.

  2. Trajectory measurements of a wall jet impinging onto a forward facing step entering a cross-flow.

    PubMed

    Langer, D C; Fleck, B A; Wilson, D J

    2010-04-15

    This study examines a horizontal wall jet impinging onto a forward facing step in a cross-flow. Planar laser induced fluorescence (PLIF) experiments in a water channel indicate that the wall-jet flow after impinging onto the step, becomes a vertical jet with an elliptical cross section. Experiments indicate that the jet trajectory scales with the perimeter of the elliptical jet issuing vertically into the cross-flow. The trajectory consists of three regions: the near-field region which is well described by a power law with an exponent of 1/2, the mid-field region where the jet is fully bent over which is described by a power law with an exponent of 1/3, and a far-field region where the jet is dominated by the cross-flow. This paper provides a prediction of the plume behaviour based on the geometric and initial conditions of the jet (diameter, step height, distance from jet to step, and velocity ratio) alone. The Briggs entrainment model for a round jet was also used to predict the trajectories of the jet in the cross-flow. It was found that the entrainment coefficients, alpha and beta, for the elliptical jet case had average values of 0.15 and 0.58 respectively. 2009 Elsevier B.V. All rights reserved.

  3. Application of the Bernoulli enthalpy concept to the study of vortex noise and jet impingement noise

    NASA Technical Reports Server (NTRS)

    Yates, J. E.

    1978-01-01

    A complete theory of aeroacoustics of homentropic fluid media is developed and compared with previous theories. The theory is applied to study the interaction of sound with vortex flows, for the DC-9 in a standard take-off configuration. The maximum engine-wake interference noise is estimated to be 3 or 4 db in the ground plane. It is shown that the noise produced by a corotating vortex pair departs significantly from the compact M scaling law for eddy Mach numbers (M) greater than 0.1. An estimate of jet impingement noise is given that is in qualitative agreement with experimental results. The increased noise results primarily from the nonuniform acceleration of turbulent eddies through the stagnation point flow. It is shown that the corotating vortex pair can be excited or de-excited by an externally applied sound field. The model is used to qualitatively explain experimental results on excited jets.

  4. Measurements of turbulent velocity statistics in a microscale rectangular confined impinging jets reactor

    NASA Astrophysics Data System (ADS)

    Olsen, Michael; Somashekar, Vishwanath; Fox, Rodney

    2011-11-01

    Microscale chemical reactors capable of operating in the turbulent flow regime, such as the confined impinging jets reactor (CIJR), offer many advantages for rapid chemical processing at the microscale, especially in application such as flash nanoprecipitation used for the production of functional nanoparticles. In the presented work, microscopic particle image velocimetry (microPIV) was employed on a microscale rectangular CIJR to obtain instantaneous velocity fields at jet Reynolds numbers of 200, 1000 and 1500, which corresponds to completely laminar, weakly turbulent, and fully turbulent regimes respectively in the reaction zone. For each Reynolds number, approximately 2000 instantaneous velocity fields were collected to analyze the flow fields and calculate pointwise and spatial turbulence statistics. Large eddy simulation (LES) was then performed to obtain time resolved simulated velocity fields which were then compared with the experimental results. Good agreement was observed between the experimental results and the LES results, demonstrating the viability of LES could be used as a tool for designing microscale reactors.

  5. Flow structure and heat transfer characteristics of an unconfined impinging air jet at high jet Reynolds numbers

    NASA Astrophysics Data System (ADS)

    Ozmen, Y.; Baydar, E.

    2008-09-01

    The flow and heat transfer characteristics of an unconfined air jet that is impinged normally onto a heated flat plate have been experimentally investigated for high Reynolds numbers ranging from 30,000 to 70,000 and a nozzle-to-plate spacing range of 1-10. The mean and turbulence velocities by using hot-wire anemometry and impingement surface pressures with pressure transducer are measured. Surface temperature measurements are made by means of an infrared thermal imaging technique. The effects of Reynolds number and nozzle-to-plate spacing on the flow structure and heat transfer characteristics are described and compared with similar experiments. It was seen that the locations of the second peaks in Nusselt number distributions slightly vary with Reynolds number and nozzle-to-plate spacing. The peaks in distributions of Nusselt numbers and radial turbulence intensity are compatible for spacings up to 3. The stagnation Nusselt number was correlated for the jet Reynolds number and the nozzle-to-plate spacing as Nu st∝ Re 0.69( H/D)0.019.

  6. Spectrum of the sound produced by a jet impinging on the gas-water interface of a supercavity

    NASA Astrophysics Data System (ADS)

    Foley, A. W.; Howe, M. S.; Brungart, T. A.

    2010-02-01

    An analysis is made of the sound generated by the impingement of an air jet on the gas-water interface of a supercavity. The water is in uniform low Mach number motion over the interface. The interface is rippled by the jet, which produces an unsteady surface force on the water that behaves as a dipole or monopole acoustic source, respectively, at high and low frequencies. In a first approximation the very large difference in the gas density and that of water implies that the surface force is similar to that occurring when a jet impinges on a rigid wall. Data from recent measurements by Foley (2009, Ph.D. Dissertation, Department of Mechanical Engineering, Boston University) of the frequency spectrum of the surface force produced by the impact of a turbulent jet on a wall are used to formulate an analytical representation of the spectrum and thence to predict the sound produced in water when the same jet impinges on the cavity interface. The prediction is used to estimate the characteristics of gas jet impingement noise for an experimental supercavitating vehicle in use at the Applied Research Laboratory of Penn State University.

  7. Verification and validation of impinging round jet simulations using an adaptive FEM

    NASA Astrophysics Data System (ADS)

    Pelletier, Dominique; Turgeon, Éric; Tremblay, Dominique

    2004-03-01

    This paper illustrates the use of an adaptive finite element method as a means of achieving verification of codes and simulations of impinging round jets, that is obtaining numerical predictions with controlled accuracy. Validation of these grid-independent solution is then performed by comparing predictions to measurements. We adopt the standard and accepted definitions of verification and validation (Technical Report AIAA-G-077-1998, American Institute of Aeronautics and Astronautics, 1998; Verification and Validation in Computational Science and Engineering. Hermosa Publishers: Albuquerque, NM, 1998). Mesh adaptation is used to perform the systematic and rigorous grid refinement studies required for both verification and validation in CFD. This ensures that discrepancies observed between predictions and measurements are due to deficiencies in the mathematical model of the flow. Issues in verification and validation are discussed. The paper presents an example of code verification by the method of manufactured solution. Examples of successful and unsuccessful validation for laminar and turbulent impinging jets show that agreement with experiments is achieved only with a good mathematical model of the flow physics combined with accurate numerical solution of the differential equations. The paper emphasizes good CFD practice to systematically achieve verification so that validation studies are always performed on solid grounds.

  8. CFD study of Jet Impingement Test erosion using Ansys Fluent® and OpenFOAM®

    NASA Astrophysics Data System (ADS)

    López, Alejandro; Nicholls, William; Stickland, Matthew T.; Dempster, William M.

    2015-12-01

    The initial aim of this study was to compare OpenFoam and Ansys Fluent in order to verify OpenFoam's Lagrangian Library and erosion capabilities. However, it was found that previous versions of Fluent have been providing wrong results for the discrete phase and the differences with the latest version (Ansys Fluent 15) are shown. A Submerged Jet Impingement Test is an effective method for studying erosion created by solid particles entrained in a liquid. When considering low particle concentrations a Lagrangian modeling of the particulate phase is a reasonable approach. Proper linkage between OpenFOAM's Lagrangian library and the solver pimpleFoam for incompressible transient flows allows two-phase simulations to be undertaken for comparison with Ansys Fluent with the aim of verifying OpenFoam's accuracy. Steady state convergence for the fluid flow is first accomplished and the results are compared, confirming a good agreement between the two packages. A transient simulation was then set up and spherical particles incorporated into the fluid flow. An assessment of the two codes' discrete phase models was carried out, focusing on the differences between impact angles and velocities yielded at the impingement plate's surface employing a similar strategy to that outlined first by Hattori et al. (2008) and later by Gnanavelu et al. (2009, 2011). In the comparison of OpenFoam with the latest version of Fluent, the main differences between the injection models are highlighted and the coupling possibilities between phases are taken into consideration. Agreement between trends for both impact angles and velocities is satisfactory when the last version of the commercial package is considered and the average discrepancy between numerical values is very low, verifying OpenFoam's Lagrangian library. Two different Jet Impingement Test configurations are also compared and the differences highlighted.

  9. Cooling of a multichip electronic module by means of confined two-dimensional jets of dielectric liquid

    NASA Astrophysics Data System (ADS)

    Wadsworth, D. C.; Mudawar, I.

    1990-11-01

    Experiments were performed to investigate single-phase heat transfer from a smooth 12.7 x 12.7-sq-mm simulated chip to a two-dimensional jet of dielectric FC-72 liquid issuing from a thin rectangular slot into a channel confined between the chip surface and nozzle plate. The effects of jet width, confinement channel height, and impingement velocity have been examined. Channel height had a negligible effect on the heat-transfer performance of the jet. A correlation for the convective heat-transfer coefficient is presented as a function of jet width, heater length, flow velocity, and fluid properties. A self-contained multichip cooling module consisting of a 3 x 3 array of heat sources confirmed the uniformity and predictability of cooling for each of the nine chips, and proved the cooling module is well suited for packaging large arrays of high-power-density chips.

  10. Cooling of a multichip electronic module by means of confined two-dimensional jets of dielectric liquid

    SciTech Connect

    Wadsworth, D.C.; Mudawar, I. )

    1990-11-01

    Experiments were performed to investigate single-phase heat transfer froma smooth 12.7 {times} 12.7 mm{sup 2} simulated chip to a two-dimensional jet of dielectric Fluorinert FC-72 liquid issuing from a thin rectangular slot into a channel confined between the chip surface and nozzle plate. The effects of jet width, confined channel height, and impingement velocity have been examined. Channel height had a negligible effect ont eh theat transfer performance of the jet for the conditions of the present study. A correlation for the convective heat transfer coefficient is presented as a function of jet, width, heat length, flow velocity, and fluid properties. A self-contained multichip cooling module consisting of a 3 {times} 3 array of heat sources confirmed the uniformity and predictability of cooling for each of the nine chips, and proved the cooling module is well suited for packaging large arrays of high-power density chips.

  11. Liquid and gelled sprays for mixing hypergolic propellants using an impinging jet injection system

    NASA Astrophysics Data System (ADS)

    James, Mark D.

    The characteristics of sprays produced by liquid rocket injectors are important in understanding rocket engine ignition and performance. The includes, but is not limited to, drop size distribution, spray density, drop velocity, oscillations in the spray, uniformity of mixing between propellants, and the spatial distribution of drops. Hypergolic ignition and the associated ignition delay times are also important features in rocket engines, providing high reliability and simplicity of the ignition event. The ignition delay time is closely related to the level and speed of mixing between a hypergolic fuel and oxidizer, which makes the injection method and conditions crucial in determining the ignition performance. Although mixing and ignition of liquid hypergolic propellants has been studied for many years, the processes for injection, mixing, and ignition of gelled hypergolic propellants are less understood. Gelled propellants are currently under investigation for use in rocket injectors to combine the advantages of solid and liquid propellants, although not without their own difficulties. A review of hypergolic ignition has been conducted for selected propellants, and methods for achieving ignition have been established. This research is focused on ignition using the liquid drop-on-drop method, as well as the doublet impinging jet injector. The events leading up to ignition, known as pre-ignition stage are discussed. An understanding of desirable ignition and combustion performance requires a study of the effects of injection, temperature, and ambient pressure conditions. A review of unlike-doublet impinging jet injection mixing has also been conducted. This includes mixing factors in reactive and non-reactive sprays. Important mixing factors include jet momentum, jet diameter and length, impingement angle, mass distribution, and injector configuration. An impinging jet injection system is presented using an electro-mechanically driven piston for injecting liquid

  12. Characterization of an inline row impingement channel for turbine blade cooling applications

    NASA Astrophysics Data System (ADS)

    Ricklick, Mark A.

    Gas turbines have become an intricate part of today's society. Besides powering practically all 200,000+ passenger aircraft in use today, they are also a predominate form of power generation when coupled with a generator. The fact that they are highly efficient, and capable of large power to weight ratios, makes gas turbines an ideal solution for many power requirement issues faced today. Designers have even been able to develop small, 'micro' turbines capable of producing efficient portable power. Part of the turbine's success is the fact that their efficiency levels have continuously risen since their introduction in the early 1800's. Along with improvements in our understanding and designs of the aerodynamic components of the turbine, as well as improvements in the areas of material design and combustion control, advances in component cooling techniques have predominantly contributed to this success. This is the result of a simple thermodynamic concept; as the turbine inlet temperature is increased, the overall efficiency of the machine increases as well. Designers have exploited this fact to the extent that modern gas turbines produce rotor inlet temperatures beyond the melting point of the sophisticated materials used within them. This has only been possible through the use of sophisticated cooling techniques, particularly in the 1st stage vanes and blades. Some of the cooling techniques employed today have been internal cooling channels enhanced with various features, film and showerhead cooling, as well as internal impingement cooling scenarios. Impingement cooling has proven to be one of the most capable heat removal processes, and the combination of this cooling feature with that of channel flow, as is done in impingement channel cooling, creates a scenario that has understandably received a great deal of attention in recent years. This study has investigated several of the unpublished characteristics of these impingement channels, including the channel

  13. Detailed measurements of local heat transfer coefficient and adiabatic wall temperature beneath an array of impinging jets

    SciTech Connect

    Van Treuren, K.W.; Wang, Z.; Ireland, P.T.; Jones, T.V. . Dept. of Engineering Science)

    1994-07-01

    A transient method of measuring the local heat transfer under an array of impinging jets has been developed. The use of a temperature-sensitive coating consisting of three encapsulated thermochromic liquid crystal materials has allowed the calculation of both the local adiabatic wall temperature and the local heat transfer coefficient over the complete surface of the target plate. The influence of the temperature of the plate through which the impingment gas flows on the target plate heat transfer has been quantified. Results are presented for a single in-line array configuration over a range of jet Reynolds numbers.

  14. Numerical simulation of liquid-layer breakup on a moving wall due to an impinging jet

    NASA Astrophysics Data System (ADS)

    Yu, Taejong; Moon, Hojoon; You, Donghyun; Kim, Dokyun; Ovsyannikov, Andrey

    2014-11-01

    Jet wiping, which is a hydrodynamic method for controlling the liquid film thickness in coating processes, is constrained by a rather violent film instability called splashing. The instability is characterized by the ejection of droplets from the runback flow and results in an explosion of the film. The splashing phenomenon degrades the final coating quality. In the present research, a volume-of-fluid (VOF)-based method, which is developed at Cascade Technologies, is employed to simulate the air-liquid multiphase flow dynamics. The present numerical method is based on an unstructured-grid unsplit geometric VOF scheme and guarantees strict conservation of mass of two-phase flow, The simulation results are compared with experimental measurements such as the liquid-film thickness before and after the jet wiping, wall pressure and shear stress distributions. The trajectories of liquid droplets due to the fluid motion entrained by the gas-jet operation, are also qualitatively compared with experimental visualization. Physical phenomena observed during the liquid-layer breakup due to an impinging jet is characterized in order to develop ideas for controlling the liquid-layer instability and resulting splash generation and propagation. Supported by the Grant NRF-2012R1A1A2003699, the Brain Korea 21+ program, POSCO, and 2014 CTR Summer Program.

  15. Unsteady Surface-Pressure Measurements and Time-Resolved Flow Visualization of a Normally and Obliquely Impinging Jet

    NASA Astrophysics Data System (ADS)

    Al-Aweni, Malek; Naguib, Ahmed

    2012-11-01

    In comparison to heat transfer and flow field data, there is little information regarding the space-time characteristics of the surface pressure fluctuations in impinging jets. Moreover, when available, such measurements are rarely accompanied by flow field information, making it difficult to identify the mechanisms/flow structures leading to pressure generation. The current work employs an axisymmetric air jet impinging on a flat wall to identify the flow features associated with significant wall-pressure signatures. To this end, unsteady surface-pressure measurements, using an embedded electret microphone array in the impingement plate, and time-resolved smoke-wire flow visualization are carried out for normal and oblique incidence of the jet. The results show the presence of two dominant modes of pressure oscillation, one is observed throughout the measurement domain and the other found primarily within the wall-jet zone. Links are drawn between these modes and the flow structures, yielding information useful for constructing structure-based models of the surface pressure in impinging jets.

  16. Computational analysis of embedded droplet impingement for integrated cooling of electronics

    NASA Astrophysics Data System (ADS)

    Wu, Chi-fu; Murthy, Jayathi Y.; Yao, S. C.

    1999-08-01

    An embedded droplet impingement device is being designed for cooling electronic chip packages which utilizes the latent heat of vaporization of dielectric coolants and provides adaptive on-demand cooling. The device must generate micro- droplets in the 50 - 250 micron range and must be small enough to be embedded in the chip package. A simplex swirl atomizer is one of the designs being considered to generate the spray. This numerical study investigates the design and performance of a micro-scale simplex swirl atomizer. Alternative atomizer designs are considered, and the flow field inside the atomizer is computed over a range of operating parameters. Local and global flow quantities, including exit swirl velocity and pressure profiles, as well as overall pressure drop parameters are computed to characterize alternative designs. These indices are useful in predicting spray quality and in identifying important geometric variables.

  17. Role of fluid elasticity on the dynamics of rinsing flow by an impinging jet

    NASA Astrophysics Data System (ADS)

    Hsu, Tienyi T.; Walker, Travis W.; Frank, Curtis W.; Fuller, Gerald G.

    2011-03-01

    Rinsing flows are common processes where a jet of one liquid impinges upon a layer of a second liquid for the purpose of removing the second liquid. An imaging setup has been developed to obtain both qualitative and quantitative data on the rinsing flow of a jet of water impinging on either layers of Newtonian or elastic fluids. Three classes of test fluids have been investigated: a Newtonian glycerol-water solution, a semidilute aqueous solution of high molecular weight polyacrylamide solution displaying both elasticity and shear thinning, and an elastic but non-shear thinning Boger fluid. The fluids were designed to have approximately equal zero-shear viscosities. For all cases, a circular hydraulic jump occurs and Saffman-Taylor instabilities were observed at the interface between the low viscosity jet and the higher viscosity coating liquids. Results show that the elasticity (extensional viscosity) of the samples influences the pattern of the instabilities and contributes to dampening surface disturbances in the vicinity of the hydraulic jump. Quantitative measurements of liquid layer thicknesses were obtained using a laser triangulation technique. We observed that shear thinning contributes to increasing the velocity of the hydraulic jump circle growth, and the growth profile appears to be linear instead of logarithmic-like as in the Newtonian fluids. Shear thinning characteristics of the samples also contribute to a larger vertical height of the hydraulic jump and an undercutting phenomenon. The elasticity of the fluids contributes to a "recoil" of the hydraulic jump circle, causing the circle, after initial expansion, to shrink in size before expanding again.

  18. Mounding of a non-Newtonian jet impinging on a solid substrate.

    SciTech Connect

    Schunk, Peter Randall; Grillet, Anne Mary; Roberts, Scott A.; Baer, Thomas A.; Rao, Rekha Ranjana

    2010-06-01

    When a fluid jet impinges on a solid substrate, a variety of behaviors may occur around the impact region. One example is mounding, where the fluid enters the impact region faster than it can flow away, forming a mound of fluid above the main surface. For some operating conditions, this mound can destabilize and buckle, entraining air in the mound. Other behaviors include submerging flow, where the jet impinges into an otherwise steady pool of liquid, entraining a thin air layer as it enters the pool. This impact region is one of very high shear rates and as such, complex fluids behave very differently than do Newtonian fluids. In this work, we attempt to characterize this range of behavior for Newtonian and non-Newtonian fluids using dimensionless parameters. We model the fluid as a modified Bingham-Carreau-Yasuda fluid, which exhibits the full range of pseudoplastic flow properties throughout the impact region. Additionally, we study viscoelastic effects through the use of the Giesekus model. Both 2-D and 3-D numerical simulations are performed using a variety of finite element method techniques for tracking the jet interface, including Arbitrary Lagrangian Eulerian (ALE), diffuse level sets, and a conformal decomposition finite element method (CDFEM). The presence of shear-thinning characteristics drastically reduces unstable mounding behavior, yet can lead to air entrainment through the submerging flow regime. We construct an operating map to understand for what flow parameters mounding and submerging flows will occur, and how the fluid rheology affects these behaviors. This study has many implications in high-speed industrial bottle filling applications.

  19. Investigation of impingement region and wall jets formed by the interaction of high aspect ratio lift jets and a ground plane

    NASA Technical Reports Server (NTRS)

    Kotansky, D. R.; Glaze, L. W.

    1978-01-01

    Flow characteristics of impinging jets emanating from rectangular exit area converging nozzles of exit area aspect ratio four, six, and eight were investigated. Azimuthal distributions of wall jet radial momentum flux in the ground plane were strongly directional and sensitive to rectangular nozzle exit area aspect ratio, jet impingement angle, and height above ground, H/D. Effects of jet exit velocity profile nonuniformities were also investigated. Data from the single nozzle rectangular jet impringement investigations were incorporated into an existing VTOL aircraft ground flow field computer program. It is suggested that this program together with the Douglas Neumann program modified for V/STOL applications may be used for the analysis and prediction of flow fields and resulting forces and moments on multijet V/STOL aircraft hovering in ground effect.

  20. Spectroscopy of jet-cooled Bi3.

    PubMed

    Arrington, Caleb A; Morse, Michael D

    2008-12-18

    A resonant two-photon ionization spectroscopic study of jet-cooled Bi3 has identified two band systems in the molecule in the 9600-10 600 and 15 250-16 050 cm(-1) range. The latter of these has been previously observed in matrix isolation spectroscopy and tentatively attributed to Bi4; the mass-resolved work presented here reassigns it to Bi3. A review of all previously observed electronic states is presented, and it is argued that the new band system lying in the range 9600-10 600 cm(-1) corresponds to the spin-forbidden A' 4A1" <-- X1 2E" (E1/2 component) band system.

  1. Fluid dynamics and convective heat transfer in impinging jets through implementation of a high resolution liquid crystal technique

    NASA Technical Reports Server (NTRS)

    Kim, K.; Wiedner, B.; Camci, C.

    1993-01-01

    A combined convective heat transfer and fluid dynamics investigation in a turbulent round jet impinging on a flat surface is presented. The experimental study uses a high resolution liquid crystal technique for the determination of the convective heat transfer coefficients on the impingement plate. The heat transfer experiments are performed using a transient heat transfer method. The mean flow and the character of turbulent flow in the free jet is presented through five hole probe and hot wire measurements, respectively. The flow field character of the region near the impingement plate plays an important role in the amount of convective heat transfer. Detailed surveys obtained from five hole probe and hot wire measurements are provided. An extensive validation of the liquid crystal based heat transfer method against a conventional technique is also presented. After a complete documentation of the mean and turbulent flow field, the convective heat transfer coefficient distributions on the impingement plate are presented. The near wall of the impingement plate and the free jet region is treated separately. The current heat transfer distributions are compared to other studies available from the literature. The present paper contains complete sets of information on the three dimensional mean flow, turbulent velocity fluctuations, and convective heat transfer to the plate. The experiments also prove that the present nonintrusive heat transfer method is highly effective in obtaining high resolution heat transfer maps with a heat transfer coefficient uncertainty of 5.7 percent.

  2. Fluid dynamics and convective heat transfer in impinging jets through implementation of a high resolution liquid crystal technique

    NASA Astrophysics Data System (ADS)

    Kim, K.; Wiedner, B.; Camci, C.

    A combined convective heat transfer and fluid dynamics investigation in a turbulent round jet impinging on a flat surface is presented. The experimental study uses a high resolution liquid crystal technique for the determination of the convective heat transfer coefficients on the impingement plate. The heat transfer experiments are performed using a transient heat transfer method. The mean flow and the character of turbulent flow in the free jet is presented through five hole probe and hot wire measurements, respectively. The flow field character of the region near the impingement plate plays an important role in the amount of convective heat transfer. Detailed surveys obtained from five hole probe and hot wire measurements are provided. An extensive validation of the liquid crystal based heat transfer method against a conventional technique is also presented. After a complete documentation of the mean and turbulent flow field, the convective heat transfer coefficient distributions on the impingement plate are presented. The near wall of the impingement plate and the free jet region is treated separately. The current heat transfer distributions are compared to other studies available from the literature. The present paper contains complete sets of information on the three dimensional mean flow, turbulent velocity fluctuations, and convective heat transfer to the plate. The experiments also prove that the present nonintrusive heat transfer method is highly effective in obtaining high resolution heat transfer maps with a heat transfer coefficient uncertainty of 5.7 percent.

  3. The Stability of Radiatively Cooling Jets I. Linear Analysis

    NASA Technical Reports Server (NTRS)

    Hardee, Philip E.; Stone, James M.

    1997-01-01

    The results of a spatial stability analysis of a two-dimensional slab jet, in which optically thin radiative cooling is dynamically important, are presented. We study both magnetized and unmagnetized jets at external Mach numbers of 5 and 20. We model the cooling rate by using two different cooling curves: one appropriate to interstellar gas, and the other to photoionized gas of reduced metallicity. Thus, our results will be applicable to both protostellar (Herbig-Haro) jets and optical jets from active galactic nuclei. We present analytical solutions to the dispersion relations in useful limits and solve the dispersion relations numerically over a broad range of perturbation frequencies. We find that the growth rates and wavelengths of the unstable Kelvin-Helmholtz (K-H) modes are significantly different from the adiabatic limit, and that the form of the cooling function strongly affects the results. In particular, if the cooling curve is a steep function of temperature in the neighborhood of the equilibrium state, then the growth of K-H modes is reduced relative to the adiabatic jet. On the other hand, if the cooling curve is a shallow function of temperature, then the growth of K-H modes can be enhanced relative to the adiabatic jet by the increase in cooling relative to heating in overdense regions. Inclusion of a dynamically important magnetic field does not strongly modify the important differences between an adiabatic jet and a cooling jet, provided the jet is highly supermagnetosonic and not magnetic pressure-dominated. In the latter case, the unstable modes behave more like the transmagnetosonic magnetic pressure-dominated adiabatic limit. We also plot fluid displacement surfaces associated with the various waves in a cooling jet in order to predict the structures that might arise in the nonlinear regime. This analysis predicts that low-frequency surface waves and the lowest order body modes will be the most effective at producing observable features in

  4. Heat transfer and material temperature conditions in the leading edge area of impingement-cooled turbine vanes

    NASA Astrophysics Data System (ADS)

    Berg, H. P.; Pfaff, K.; Hennecke, D. K.

    The resultant effects on the cooling effectiveness at the leading edge area of an impingement-cooled turbine vane by varying certain geometrical parameters is described with reference to local internal heat transfer coefficients determined from experiment and temperature calculations. The local heat transfer on the cooling-air side is determined experimentally with the aid of the analogy between heat- and mass transfer. The impingement cooling is provided from an inserted sheet-metal containing a single row of holes. The Reynolds Number and several of the cooling geometry parameters were varied. The results demonstrate the high local resolution of the method of measurement, which allows improved analytical treatment of the leading-edge cooling configuration. These experiments also point to the necessity of not always performing model tests under idealized conditions. This becomes very clear in the case of the tests performed on an application-oriented impingement-cooling configuration like that often encountered in engine manufacture. In conclusion, as an example, temperature calculations are employed to demonstrate the effect on the cooling effectiveness of varying the distances between insert and inner surface of the leading edge. It shows how the effectiveness of the leading edge cooling can be increased by simple geometrical measures, which results in a considerable improvement in service life.

  5. Secondary peak in the Nusselt number distribution of impinging jet flows: A phenomenological analysis

    NASA Astrophysics Data System (ADS)

    Aillaud, P.; Duchaine, F.; Gicquel, L. Y. M.; Didorally, S.

    2016-09-01

    This paper focuses on a wall-resolved Large Eddy Simulation (LES) of an isothermal round submerged air jet impinging on a heated flat plate, at a Reynolds number of 23 000 (based on the nozzle diameter and the bulk velocity at the nozzle outlet) and for a nozzle to plate distance of two jet diameters. This specific configuration is known to lead to a non-monotonic variation of the temporal-mean Nusselt number as a function of the jet center distance, with the presence of two distinct peaks located on the jet axis and close to two nozzle diameters from the jet axis. The objectives are here twofold: first, validate the LES results against experimental data available in the literature and second to explore this validated numerical database by the use of high order statistics such as skewness and probability density functions of the temporal distribution of temperature and pressure to identify flow features at the origin of the second Nusselt peak. Skewness (Sk) of the pressure temporal distribution reveals the rebound of the primary vortices located near the location of the secondary peak and allows to identify the initiation of the unsteady separation linked to the local minimum in the mean heat transfer distribution. In the region of mean heat transfer enhancement, joint velocity-temperature analyses highlight that the most probable event is a cold fluid flux towards the plate produced by the passage of the vortical structures. In parallel, heat transfer distributions, analyzed using similar statistical tools, allow to connect the above mentioned events to the heat transfer on the plate. Thanks to such advanced analyses, the origin of the double peak is confirmed and connected to the flow dynamics.

  6. Unsteady computational analysis of shrouded plug nozzle flows and reacting impinging jets

    NASA Astrophysics Data System (ADS)

    Kapilavai, Dheeraj S. K.

    The computations of a non-reacting nozzle-flow problem and a reacting impinging jet problem using a unified numerical methodology is presented. The nozzle problem is a shrouded plug configuration that operates at nozzle pressure ratio (NPR, ratio of inlet pressure to ambient pressure) between one to a design NPR of 6.23 for supersonic applications. An sub-scale model with extensive instrumentation is the basis of axisymmetric and three-dimensional computations done as both steady and unsteady problems with an aim to understand nozzle flow physics. The pressure distribution and shock structure predicted by steady computations not only detailed the shock physics but were also in close agreement with measured pressure data and visualization. The nozzle is observed to transition from normal shock at NPR's just above one to a lambda shock below NPR of 2.0 and then from a Mach reflection to a regular reflection within NPR range 2.25 to 3.1. A barrel oblique shock is observed above NPR of 3.1 before achieving perfect expansion at design NPR. During the shock transition the separation region behind the shock is observed to be fully attached for NPR's below 2.0, a regime called free shock separation (FSS), followed by reattached flow on plug wall called restricted shock separation (RSS) at higher NPR's. The unsteady computational analysis explained the shifts in frequencies observed in measurements. The unsteady computations at NPR of 1.26 show that the measured frequency of 170Hz is because of periodic choking and unchoking driven by large scale shock motion. In the FSS regime identified by computations the measured frequency remains constant at 200Hz. Following this the frequency shifts to above 300Hz and increases monotonically as the nozzle transitions from FSS to RSS observed to occur between NPR of 2.0 and approximately 2.25. Unsteady 3-D computations showed axisymmetric instantaneous flowfield at NPR of 1.26 while at NPR of 1.59 the dynamic flowfield was observed to

  7. On the tones of round choked jets impinging on normal flat plates

    NASA Technical Reports Server (NTRS)

    Powell, Alan; Henderson, Brenda

    1990-01-01

    An experimental investigation of the sound produced by an axisymmetric supersonic jet impinging on plates with variable size and nozzle-to-plate spacings was performed. Spectral analysis and schlieren photography were used to determine the sound characteristics and flow disturbances associated with the production of discrete tones. Two classes of tones, associated with small and large plates, existed for pressure ratios above 2.70. For lower pressure ratios, however, only large plate tones occurred for all plate sizes with choked jet screech appearing at the largest spacings. Reflector tests indicated that both classes of tones were part of a feedback loop to the nozzle. Schlieren photography revealed both symmetric and asymmetric disturbances in the large plate jet flows which corresponded to symmetrical and helical modes of oscillation in the cross-spectrum studies. In addition to this, both symmetric and asymmetric oscillations of the shock waves occurred in the large plate case while symmetric oscillations of the shock wave occurred in the small plate case.

  8. Surface curvature effects on flow and heat transfer from a round impinging jet

    SciTech Connect

    Lee, D.H.; Chung, Y.S.; Kim, D.S.

    1996-12-31

    Effects of the hemispherically convex surface curvature on the local heat transfer from a round impinging jet were experimentally investigated. The flow at the nozzle exit has a fully developed velocity profile. The jet Reynolds number (Re) ranges from 11,000 to 50,000, the nozzle-to-surface distance (L/d) from 2 to 10, and the hemisphere-to-nozzle diameter ratio (D/d) from 11.2 to 29.3. The results show that the stagnation point Nusselt number (Nu{sub st}) increases with increasing curvature (i.e., decreasing value of D/d). The maximum Nusselt number at the stagnation point occurs at L/d {approx_equal} 6 to 8 for all Re`s and D/d`s tested. Nu{sub st} are well correlated with Re, L/d, and D/d. For larger L/d, Nu{sub st} dependency on Re is stronger due to an increase of turbulence in the approaching jet as a result of the more active exchange of momentum with a surrounding air. The local Nusselt number decreases monotonically from its maximum value at the stagnation point. However, for L/d = 2 and Re = 23,000, and for L/d {le} 4 and Re = 50,000, the streamwise Nusselt number distributions exhibit secondary maxima at r/d {approx_equal} 2.2.

  9. Impingement heat transfer within arrays of circular jets. II - Effects of crossflow in the presence of roughness elements

    NASA Astrophysics Data System (ADS)

    Trabold, T. A.; Obot, N. T.

    1987-05-01

    An experimental investigation was carried out to determine the effects of jet-induced crossflow on impingement heat transfer from rough surfaces. The jets impinged on surfaces having repeated square ribs, with transverse flow of the spent air. Two crossflow schemes were tested: discharge of the spent air through two opposite sides (intermediate crossflow) and through one side (complete or maximum crossflow) of the rectangular impingement surface. The rib height was fixed at 0.813 mm, while the pitch-to-height ratio (p/e) was varied between 6 and 10. The study covered standoff spacing and jet Reynolds number in the range 2 to 16 jet hole diameters and, 1300 to 21,000, respectively. Three nozzle plates, having 48, 90 and 180 square-edged holes, were tested. For the maximum crossflow scheme, the presence of roughness results in small upstream reductions in heat transfer coefficient, with marked improvement in the downstream section; indicating that roughness elements can be used to compensate for the degradation that is usually associated with impingement on smooth surfaces.

  10. Fuel Regression Characteristics of Cascaded Multistage Impinging-Jet (CAMUI) Type Hybrid Rocket

    NASA Astrophysics Data System (ADS)

    Itoh, Mitsunori; Maeda, Takenori; Kakikura, Akihito; Kaneko, Yudai; Mori, Kazuhiro; Nakashima, Takuji; Wakita, Masashi; Uematsu, Tsutomu; Totani, Tsuyoshi; Oshima, Nobuyuki; Nagata, Harunori

    A series of lab-scale firing tests was conducted to investigate the fuel regression characteristics of Cascaded Multistage Impinging-jet (CAMUI) type hybrid rocket. The alternative fuel grain used in this rocket consists of a number of cylindrical fuel blocks with two ports, which were aligned along the axis of the combustion chamber with a small gap. The ports are aligned staggered with respect to ones of neighboring blocks so that the combustion gas flow impinges on the forward-end surface of each block. In this fuel grain, forward-end surfaces, back-end surfaces and ports of fuel blocks contribute as burning surfaces. Polyethylene and LOX were used as a propellant, and the tests were conducted at the chamber pressure of 0.5 2MPa and the mass flux of 50 200kg/m2s. Main results obtained in this study are in the followings: The regression rate of each surface was obtained as a function of the propellant mass flux and local equivalent ratio of the combustion gas. At back-end surfaces the regression rate has a high sensitivity on the gap height of neighboring fuel blocks. These fuel regression characteristics will contribute as fundamental data to improve the optimum design of the fuel grain.

  11. A Water Model Study of Impinging Gas Jets on Liquid Surfaces

    NASA Astrophysics Data System (ADS)

    Hwang, Ho Yong; Irons, Gordon A.

    2012-04-01

    Water modeling experiments were designed to observe the deformation of a liquid surface by impinging the gas jet. Video images were taken and processed in a systematic way. The important surface cavity parameters, such as depth, width, and their frequency of oscillation, were obtained. The relation between surface depression depth and the supplied gas momentum were consistent with previous findings and were extended to higher flow rates. The surface instability and the onset of splashing were observed and interpreted with the Blowing number. The wave behaviors were described qualitatively with a combination of photographic evidence and power spectral density analysis to extract the characteristic wave numbers for each gas flow rate. The analysis of the time series of the surface variables showed a connection to the attenuation of turbulence gas pressure fluctuation and the surface deformation by the gas impingement. Bath velocities were measured with a particle image velocimetry (PIV) technique. To quantify the transfer of kinetic energy from the gas to the liquid, an energy transfer index was defined and calculated with the PIV data. The index was insensitive to gas flow rate but increased with cavity width. The momentum transfer across the interface was also analyzed, and a similar cavity width dependence was found. A correlation between the cavity shape and momentum transfer was proposed.

  12. Liquid jet impingement normal to a disk in zero gravity. Ph.D. Thesis Toledo Univ.

    NASA Technical Reports Server (NTRS)

    Labus, T. L.

    1977-01-01

    The free surface shapes of circular liquid jets impinging normal to sharp-edged disks in zero gravity are determined. Zero gravity drop tower experiments yielded three distinct flow patterns that were classified in terms of the relative effects of surface tension and inertial forces. An order of magnitude analysis was conducted that indicated regions where viscous forces were not significant in the computation of free surface shapes. The free surface analysis was simplified by transforming the governing potential flow equations and boundary conditions into the inverse plane, where the stream function and velocity potential became the coordinates. The resulting nonlinear equations were solved by standard finite difference methods, and comparisons were made with the experimental data for the inertia dominated regime.

  13. Numerical Study of Impingement Location of Liquid Jet Poured from a Tilting Ladle with Lip Spout

    NASA Astrophysics Data System (ADS)

    Castilla, R.; Gamez-Montero, P. J.; Raush, G.; Khamashta, M.; Codina, E.

    2017-04-01

    A new approach for simulating liquid poured from a tilting lip spout is presented, using neither a dynamic mesh nor the moving solid solution method. In this case only the tilting ladle is moving, so we propose to rotate the gravitational acceleration at an angular velocity prescribed by a geometrical and dynamical calculation to keep the poured flow rate constant. This angular velocity is applied to modify the orientation of the gravity vector in computational fluid dynamics (CFD) simulations using the OpenFOAM® toolbox. Also, fictitious forces are considered. The modified solver is used to calculate the impingement location for six spout geometries and compare the jet dispersion there. This method could offer an inexpensive tool to calculate optimal spout geometries to reduce sprue size in the metal casting industry.

  14. Two-phase liquid-liquid flows generated by impinging liquid jets

    NASA Astrophysics Data System (ADS)

    Tsaoulidis, Dimitrios; Li, Qi; Angeli, Panagiota

    2015-11-01

    Two-phase flows in intensified small-scale systems find increasing applications in (bio)chemical analysis and synthesis, fuel cells, polymerisation, and separation processes (solvent extraction). Current nuclear spent fuel reprocessing separation technologies have been developed many decades ago and have not taken account recent advances on process intensification which can drive down plant size and economics. In this work, intensified impinging jets will be developed to create dispersions by bringing the two liquid phases into contact through opposing small channels. A systematic set of experiments has been undertaken, to investigate the hydrodynamic characteristics, to develop predictive models, and enable comparisons with other contactors. Drop size distribution and mixing intensity will be investigated for liquid-liquid mixtures as a function of various parameters using high speed imaging and conductivity probes.

  15. An Analysis of the Pressures, Forces and Moments Induced by the Ground Vortex Generated by a Single Impinging Jet

    NASA Technical Reports Server (NTRS)

    Kuhn, Richard E.

    1997-01-01

    When a jet STOVL aircraft is in STOL operation the jets impinge on the ground and generate wall jets flowing radially outward from the points at which the jets impinge. When the forward flowing part of a wall jet meets the free stream flow it is rolled back on itself forming a parabolic shaped ground vortex. Positive pressures are induced on the lower surface of the configuration ahead of the ground vortex and suction pressures are induced over the ground vortex itself. In addition, the suction pressures induced aft of the jet out of ground effect are reduced and lifting pressures are induced on the upper surface. This study analyzes available pressure and force data and develops a method for estimating the forces and moments induced in ground effect. The method includes the effects of configuration variables, height and operating conditions, as well as the effects of the location, deflection and shape of the jet. However, it is limited to single jets at subcritical nozzle pressure ratios. An analysis of the effects of moving over the ground vs. tests over a fixed ground plane is included.

  16. On jet impingement and thin film breakup on a horizontal superhydrophobic surface

    NASA Astrophysics Data System (ADS)

    Prince, Joseph F.; Maynes, Daniel; Crockett, Julie

    2015-11-01

    When a vertical laminar jet impinges on a horizontal surface, it will spread out in a thin film. If the surface is hydrophobic and a downstream depth is not maintained, the film will radially expand until it breaks up into filaments or droplets. We present the first analysis and model that describes the location of this transition for both isotropic and anisotropic structured superhydrophobic (SH) surfaces. All surfaces explored are hydrophobic or SH, where the SH surfaces exhibit an apparent slip at the plane of the surface due to a shear free condition above the air filled cavities between the structures. The influence of apparent slip on the entire flow field is significant and yields behavior that deviates notably from classical behavior for a smooth hydrophilic surface where a hydraulic jump would form. Instead, break up into droplets occurs where the jet's outward radial momentum is balanced by the inward surface tension force of the advancing film. For hydrophobic surfaces, or SH surfaces with random micropatterning, the apparent slip on the surface is uniform in all directions and droplet breakup occurs in a circular pattern. When alternating rib/cavity microstructures are used to create the SH surface, the apparent slip varies as a function of the azimuthal coordinate, and thus, the breakup location is elliptically shaped. The thin film dynamics are modeled by a radial momentum analysis for a given jet Weber number and specified slip length and the location of breakup for multiple surfaces over a range of jet Weber numbers and realistic slip length values is quantified. The results of the analysis show that the breakup radius increases with increasing Weber number and slip length. The eccentricity of the breakup ellipse for the rib/cavity SH structures increases with increasing Weber number and slip length as well. A generalized model that allows prediction of the transition (break-up) location as a function of all influencing parameters is presented

  17. Local distribution of wall static pressure and heat transfer on a rough flat plate impinged by a slot air jet

    NASA Astrophysics Data System (ADS)

    Meda, Adimurthy; Katti, Vadiraj V.

    2017-02-01

    The present work experimentally investigates the local distribution of wall static pressure and the heat transfer coefficient on a rough flat plate impinged by a slot air jet. The experimental parameters include, nozzle-to-plate spacing (Z/D h = 0.5-10.0), axial distance from stagnation point (x/D h ), size of detached rib (b = 4-12 mm) and Reynolds number (Re = 2500-20,000). The wall static pressure on the surface is recorded using a Pitot tube and a differential pressure transmitter. Infrared thermal imaging technique is used to capture the temperature distribution on the target surface. It is observed that, the maximum wall static pressure occurs at the stagnation point (x/D h = 0) for all nozzle-to-plate spacing (Z/D h ) and rib dimensions studied. Coefficient of wall static pressure (C p ) decreases monotonically with x/D h . Sub atmospheric pressure is evident in the detached rib configurations for jet to plate spacing up to 6.0 for all ribs studied. Sub atmospheric region is stronger at Z/D h = 0.5 due to the fluid accelerating under the rib. As nozzle to plate spacing (Z/D h ) increases, the sub-atmospheric region becomes weak and vanishes gradually. Reasonable enhancement in both C p as well as Nu is observed for the detached rib configuration. Enhancement is found to decrease with the increase in the rib width. The results of the study can be used in optimizing the cooling system design.

  18. Local distribution of wall static pressure and heat transfer on a rough flat plate impinged by a slot air jet

    NASA Astrophysics Data System (ADS)

    Meda, Adimurthy; Katti, Vadiraj V.

    2017-08-01

    The present work experimentally investigates the local distribution of wall static pressure and the heat transfer coefficient on a rough flat plate impinged by a slot air jet. The experimental parameters include, nozzle-to-plate spacing (Z /D h = 0.5-10.0), axial distance from stagnation point ( x/D h ), size of detached rib ( b = 4-12 mm) and Reynolds number ( Re = 2500-20,000). The wall static pressure on the surface is recorded using a Pitot tube and a differential pressure transmitter. Infrared thermal imaging technique is used to capture the temperature distribution on the target surface. It is observed that, the maximum wall static pressure occurs at the stagnation point ( x/D h = 0) for all nozzle-to-plate spacing ( Z/D h ) and rib dimensions studied. Coefficient of wall static pressure ( C p ) decreases monotonically with x/D h . Sub atmospheric pressure is evident in the detached rib configurations for jet to plate spacing up to 6.0 for all ribs studied. Sub atmospheric region is stronger at Z/D h = 0.5 due to the fluid accelerating under the rib. As nozzle to plate spacing ( Z/D h ) increases, the sub-atmospheric region becomes weak and vanishes gradually. Reasonable enhancement in both C p as well as Nu is observed for the detached rib configuration. Enhancement is found to decrease with the increase in the rib width. The results of the study can be used in optimizing the cooling system design.

  19. Effect of coating material on heat transfer and skin friction due to impinging jet onto a laser producedhole

    NASA Astrophysics Data System (ADS)

    Shuja, S. Z.; Yilbas, B. S.

    2013-07-01

    Jet impingement onto a two-layer structured hole in relation to laser drilling is investigated. The hole consists of a coating layer and a base material. The variations in the Nusselt number and the skin friction are predicted for various coating materials. The Reynolds stress turbulent model is incorporated to account for the turbulence effect of the jet flow and nitrogen is used as the working fluid. The study is extended to include two jet velocities emanating from the conical nozzle. It is found that coating material has significant effect on the Nusselt number variation along the hole wall. In addition, the skin friction varies considerably along the coating thickness in thehole.

  20. Vortex dynamics and wall shear stress behaviour associated with an elliptic jet impinging upon a flat plate

    NASA Astrophysics Data System (ADS)

    Long, J.; New, T. H.

    2016-07-01

    Vortical structures and dynamics of a Re h = 2100 elliptic jet impinging upon a flat plate were studied at H/ d h = 1, 2 and 4 jet-to-plate separation distances. Flow investigations were conducted along both its major and minor planes using laser-induced fluorescence and digital particle image velocimetry techniques. Results show that the impingement process along the major plane largely consists of primary jet ring-vortex and wall-separated secondary vortex formations, where they subsequently separate from the flat plate at smaller H/ d h = 1 and 2 separation distances. Key vortex formation locations occur closer to the impingement point as the separation distance increases. Interestingly, braid vortices and rib structures begin to take part in the impingement process at H/ d h = 4 and wave instabilities dominate the flow field. In contrast, significantly more coherent primary and secondary vortices with physically larger vortex core sizes and higher vortex strengths are observed along the minor plane, with no signs of braid vortices and rib structures. Lastly, influences of these different flow dynamics on the major and minor plane instantaneous and mean skin friction coefficient levels are investigated to shed light on the effects of separation distance on the wall shear stress distributions.

  1. Investigation of the flow-field of two parallel round jets impinging normal to a flat surface

    NASA Astrophysics Data System (ADS)

    Myers, Leighton M.

    The flow-field features of dual jet impingement were investigated through sub-scale model experiments. The experiments were designed to simulate the environment of a Short Takeoff, and Vertical Landing, STOVL, aircraft performing a hover over the ground, at different heights. Two different dual impinging jet models were designed, fabricated, and tested. The Generation 1 Model consisted of two stainless-steel nozzles, in a tandem configuration, each with an exit diameter of approximately 12.7 mm. The front convergent nozzle was operated at the sonic Mach number of 1.0, while the rear C-D nozzle was generally operated supersonically. The nozzles were embedded in a rectangular flat plate, referred to as the lift plate, which represents a generic lifting surface. The lift plate was instrumented with 36 surface pressure taps, which were used to examine the flow entrainment and recirculation patterns caused by varying the stand-off distance from the nozzle exits to a flat ground surface. The stand-off distance was adjusted with a sliding rail frame that the ground plane was mounted to. Typical dimensionless stand-off distances (ground plane separation) were H/DR = 2 to 24. A series of measurements were performed with the Generation 1 model, in the Penn State High Speed Jet Aeroacoustics Laboratory, to characterize the basic flow phenomena associated with dual jet impingement. The regions of interest in the flow-field included the vertical jet plume(s), near impingement/turning region, and wall jet outwash. Other aspects of interest included the loss of lift (suckdown) that occurs as the ground plane separation distance becomes small, and azimuthal variation of the acoustic noise radiation. Various experimental methods and techniques were used to characterize the flow-field, including flow-visualization, pressure rake surveys, surface mounted pressure taps, laser Doppler velocimetry, and acoustic microphone arrays. A second dual impinging jet scale model, Generation 2

  2. A simplified analog for a rotorcraft-in-ground-effect flow using a forced impinging jet

    NASA Astrophysics Data System (ADS)

    Geiser, Jayson; Kiger, Ken

    2010-11-01

    The phenomenon of rotorcraft brown-out is defined as the intense suspension and re-ingestion of sand during the take-off and landing of a rotor-lifted aircraft. To mitigate the problem of rotorcraft brown-out, the non-equilibrium sediment suspension process that occurs within a typical rotorcraft wake must be understood. We attempt to understand the most basic aspects of this complex flow through the use of an axisymmetric forced impinging jet. While this flow neglects the swirl component associated with a rotorcraft, it does reproduce the typical coherent vortex structures, and permits their repeatable generation within an axisymmetric mean stagnation flow. The goal of the current work is to determine the forcing conditions that produce isolated, but intense and repeatable structures that can be followed through their interaction with the wall boundary. Stereo PIV imaging is applied to detail the breakdown of a vortex ring in the wall jet zone. The secondary vortex generation and decay are observed experimentally with 3-D vector fields, and their results are interpreted with respect to their significance in the context of sediment mobilization.

  3. Large-eddy simulations of impinging jets at high Reynolds numbers

    NASA Astrophysics Data System (ADS)

    Wu, Wen; Piomelli, Ugo

    2013-11-01

    We have performed large-eddy simulations of an impinging jet with embedded azimuthal vortices. We used a hybrid approach in which the near-wall layer is modelled using the RANS equations with the Spalart-Allmaras model, while away from the wall Lagrangian-averaged dynamic eddy-viscosity modelled LES is used. This method allowed us to reach Reynolds numbers that would be prohibitively expensive for wall-resolving LES. First, we compared the results of the hybrid calculation with a wall-resolved one at moderate Reynolds number, Re = 66 , 000 (based on jet diameter and velocity). The mean velocity and Reynolds stresses were in good agreement between the simulations, and, in particular, the generation of secondary vorticity at the wall and its liftup were captured well. The simulation cost was reduced by 86%. We then carried out simulations at Re = 266 , 000 and 1.3 million. The effect of Reynolds number on vortex development will be discussed. Canada Research Chair in Computational Turbulence, HPCVL-Sun Microsystems Chair in Computational Science and Engineering.

  4. Organic-vapor-liquid-solid deposition with an impinging gas jet

    NASA Astrophysics Data System (ADS)

    Shaw, Daniel W.; Bufkin, Kevin; Baronov, Alexandr A.; Johnson, Brad L.; Patrick, David L.

    2012-04-01

    A method for rapid, mass-efficient deposition of highly crystalline organic films under near ambient conditions of pressure and temperature is reported based on delivery of an organic precursor via an impinging gas jet to a substrate coated by a thin liquid solvent layer. Films of the organic semiconductor tetracene were deposited by sublimation into a flow of argon carrier gas directed at an indium-tin-oxide/glass substrate coated by a thin layer of bis(2-ethylhexyl)sebecate, and growth was followed in situ with optical microscopy. A fluid dynamics model is applied to account for the gas phase transport and aggregation, and the results compared to experiment. The combination of gas jet delivery with an organic-vapor-liquid-solid growth mechanism leads to larger crystals and lower nucleation densities than on bare surfaces, with markedly different nucleation and growth kinetics. An explanation based on enhanced solution-phase diffusivity and a larger critical nucleus size in the liquid layer is proposed to account for the differences.

  5. Drop Characteristics of non-Newtonian Impinging Jets at High Generalized Bird-Carreau Jet Reynolds Numbers

    NASA Astrophysics Data System (ADS)

    Sojka, Paul E.; Rodrigues, Neil S.

    2015-11-01

    The current study investigates the drop characteristics of three Carboxymethylcellulose (CMC) sprays produced by the impingement of two liquid jets. The three water-based solutions used in this work (0.5 wt.-% CMC-7MF, 0.8 wt.-% CMC-7MF, and 1.4 wt.-% CMC-7MF) exhibited strong shear-thinning, non-Newtonian behavior - characterized by the Bird-Carreau rheological model. A generalized Bird-Carreau jet Reynolds number was used as the primary parameter to characterize the drop size and the drop velocity, which were measured using Phase Doppler Anemometry (PDA). PDA optical configuration enabled a drop size measurement range of approximately 2.3 to 116.2 μm. 50,000 drops were measured at each test condition to ensure statistical significance. The arithmetic mean diameter (D10) , Sauter mean diameter (D32) , and mass median diameter (MMD) were used as representative diameters to characterize drop size. The mean axial drop velocity Uz -mean along with its root-mean square Uz -rms were used to characterize drop velocity. Incredibly, measurements for all three CMC liquids and reference DI water sprays seemed to follow a single curve for D32 and MMD drop diameters in the high generalized Bird-Carreau jet Reynolds number range considered in this work (9.21E +03

  6. Simulation of jet cooling effects on Czochralski crystal growth

    NASA Technical Reports Server (NTRS)

    Srivastava, R. K.; Ramachandran, P. A.; Dudukovic, M. P.

    1986-01-01

    The effects of cooling the crystal side surface by blowing a jet of an inert gas are examined in detail for Czochralski crystal growth. A combined model of the crystal + melt, which incorporates the detailed radiation calculations, the shape of the melt-gas meniscus, predicts the growth rate and the crystal-melt interface shape, is used for this study. The convective heat transfer coefficient for the jet is estimated from the correlation available in the literature. The effect of the jet cooling on the interface shape and the pulling rate is significant. The crystal diameter as well as the interface shape tend to be more stable in the environment of the rapid cooling of the crystal by the jet. The crystal diameter or the interface shape can be easily controlled by adjusting the gas flow rate through the jet. This gives the Czochralski pulling an additional degree of freedom facilitating the control of crystal diameter and interface shape.

  7. Simulation of jet cooling effects on Czochralski crystal growth

    NASA Technical Reports Server (NTRS)

    Srivastava, R. K.; Ramachandran, P. A.; Dudukovic, M. P.

    1986-01-01

    The effects of cooling the crystal side surface by blowing a jet of an inert gas are examined in detail for Czochralski crystal growth. A combined model of the crystal + melt, which incorporates the detailed radiation calculations, the shape of the melt-gas meniscus, predicts the growth rate and the crystal-melt interface shape, is used for this study. The convective heat transfer coefficient for the jet is estimated from the correlation available in the literature. The effect of the jet cooling on the interface shape and the pulling rate is significant. The crystal diameter as well as the interface shape tend to be more stable in the environment of the rapid cooling of the crystal by the jet. The crystal diameter or the interface shape can be easily controlled by adjusting the gas flow rate through the jet. This gives the Czochralski pulling an additional degree of freedom facilitating the control of crystal diameter and interface shape.

  8. Spatially-resolved, three-dimensional spray characterization of impinging jets by digital in-line holography

    NASA Astrophysics Data System (ADS)

    Gao, Jian; Rodrigues, Neil; Sojka, Paul; Chen, Jun

    2014-11-01

    The impinging jet injector is a preferred method for the atomization of liquid rocket propellants. The majority of experimental studies in literature are not spatially-resolved due to the limitations of widely available point-wise and two-dimensional (2D) diagnostic techniques such as phase Doppler anemometry (PDA), which requires significant experimental repetitions to give spatially-resolved measurements. In the present study, digital in-line holography (DIH) is used to provide spatially-resolved, three-dimensional (3D) characteristics of impinging jet sprays. A double-exposure DIH setup is configured to measure droplet 3D, three-component velocity as well as the size distribution. The particle information is extracted by the hybrid method, which is recently proposed as a particle detection method. To enlarge the detection volume, two parallel, collimated laser beams are used to simultaneously probe the spray at two locations, and two identical cameras are used to record the corresponding holograms. Such a setup has a detection volume of approximately 20 cm by 3.6 cm by 4.8 cm. Sprays of both Newtonian and non-Newtonian liquids corresponding to regimes at relatively lower jet Reynolds and Weber numbers are investigated. Measurements from DIH are further verified by comparison with experimental data obtained from shadowgraph and PDA. It is revealed that DIH is particularly suitable to provide spatially-resolved, 3D measurements of impinging jet sprays that are not particularly dense.

  9. Experimental Investigation of the Discharge Coefficient and Impingement Heat Transfer Characteristics of a Single Jet in Cross Flow

    NASA Astrophysics Data System (ADS)

    Roberts, Brian

    This experimentation investigates the local heat transfer characteristics of an impinging jet with the effects of cross flow. The jet is formed by a single round hole with a diameter of 0.25 inches, sharp edges and a length to diameter ratio of 4. For one combination of impingement plate spacing and cross flow to jet flow mass velocity ratio, detailed photographs of a sheet of liquid crystal were taken. These photographs were then used to create a Nusselt number contour plot. Observations are made regarding the comparison of the Nusselt number contour plots with and without cross flow. Comparisons are also made to data in open literature citing the degradation of the average Nusselt number with cross flow to that without cross flow. While the main focus of this study was the heat transfer of an impinging jet, a large amount of discharge coefficient data was also gathered for a single, sharp edged, round hole in the presence of cross flow. It compared very well to other investigator's data and a correlation relating the discharge coefficient to the mass velocity ratio is reported.

  10. The Stability of Radiatively Cooling Jets. 2: Nonlinear Evolution

    NASA Technical Reports Server (NTRS)

    Stone, James M.; Xu, Jianjun; Hardee, Philip

    1997-01-01

    We use two-dimensional time-dependent hydrodynamical simulations to follow the growth of the Kelvin-Helmholtz (K-H) instability in cooling jets into the nonlinear regime. We focus primarily on asymmetric modes that give rise to transverse displacements of the jet beam. A variety of Mach numbers and two different cooling curves are studied. The growth rates of waves in the linear regime measured from the numerical simulations are in excellent agreement with the predictions of the linear stability analysis presented in the first paper in this series. In the nonlinear regime, the simulations show that asymmetric modes of the K-H instability can affect the structure and evolution of cooling jets in a number of ways. We find that jets in which the growth rate of the sinusoidal surface wave has a maximum at a so-called resonant frequency can be dominated by large-amplitude sinusoidal oscillations near this frequency. Eventually, growth of this wave can disrupt the jet. On the other hand, nonlinear body waves tend to produce low-amplitude wiggles in the shape of the jet but can result in strong shocks in the jet beam. In cooling jets, these shocks can produce dense knots and filaments of cooling gas within the jet. Ripples in the surface of the jet beam caused by both surface and body waves generate oblique shock "spurs" driven into the ambient gas. Our simulations show these shock "spurs" can accelerate ambient gas at large distances from the jet beam to low velocities, which represents a new mechanism by which low-velocity bipolar outflows may be driven by high-velocity jets. Rapid entrainment and acceleration of ambient gas may also occur if the jet is disrupted. For parameters typical of protostellar jets, the frequency at which K-H growth is a maximum (or highest frequency to which the entire jet can respond dynamically) will be associated with perturbations with a period of - 200 yr. Higher frequency (shorter period) perturbations excite waves associated with body

  11. The effect of ordered structure of turbulence on momentum, heat and mass transfer of impinging round jets

    NASA Astrophysics Data System (ADS)

    Popiel, C. O.; Trass, O.

    The interaction of vortex structure of the round free jet with the plane solid surface has been investigated using the 'smoke wire' flow visualization and skin friction measurements. The more precise explanation of the mechanism of the influence of the large-scale ordered flow structure on the heat or mass convective processes in the transient region of the impinging round jet has been presented. It was observed that toroidal vortices are periodically generated at the edge of the nozzle and grow to produce the well ordered flow structure at the plate. A periodic appearance of ring-like wall eddies which are rolled up on the wall surface between the radially stretched large-scale toroidal vortices has been recorded. The radial distribution of the skin friction obtained with the thermoanemometry flush mounted probe appears to be generally consistent with the impingement heat transfer data with the exception of the strong acceleration zone in the stagnation point vicinity.

  12. Analysis of a Cylindrical Specimen Heated by an Impinging Hot Hydrogen Jet

    NASA Technical Reports Server (NTRS)

    Wang, Ten-See; Luong, Van; Foote, John; Litchford, Ron; Chen, Yen-Sen

    2006-01-01

    A computational conjugate heat transfer methodology was developed, as a first step towards an efficient and accurate multiphysics, thermo-fluid computational methodology to predict environments for hypothetical solid-core, nuclear thermal engine thrust chamber and components. A solid conduction heat transfer procedure was implemented onto a pressure-based, multidimensional, finite-volume, turbulent, chemically reacting, thermally radiating, and unstructured grid computational fluid dynamics formulation. The conjugate heat transfer of a cylindrical material specimen heated by an impinging hot hydrogen jet inside an enclosed test fixture was simulated and analyzed. The solid conduction heat transfer procedure was anchored with a standard solid heat transfer code. Transient analyses were then performed with ,variable thermal conductivities representing three composites of a material utilized as flow element in a legacy engine test. It was found that material thermal conductivity strongly influences the transient heat conduction characteristics. In addition, it was observed that high thermal gradient occur inside the cylindrical specimen during an impulsive or a 10 s ramp start sequence, but not during steady-state operations.

  13. Megahertz rate Schlieren visualization of underexpanded, impinging jet using pulsed high power LED

    NASA Astrophysics Data System (ADS)

    Willert, Christian; Mitchell, Daniel; Soria, Julio

    2010-11-01

    Recent advances in light emitting diode (LED) technology has resulted in high power, single chip devices that provide luminous radiant fluxes exceeding several watts. Operated in pulsed current mode the instantaneous light emission of an LED can be further increased to levels comparable to that of photographic (xenon) flash units making it a suitable light source for Schlieren imaging. Compared to the commonly used xenon flash units an LED can be triggered within tens of nanoseconds at rise times on the order of 100 ns thereby enabling stroboscopic illumination at megahertz rates. In the present application the LED's driving electronics were synchronized to a high speed camera to provide time-resolved Schlieren images of an underexpanded free jet impinging on a flat plate (nozzle pressure ratio 2.0 to 5.2). The LED was pulsed in burst mode for 102 images at currents of up to 120 A at 500 ns per pulse. Compared to images obtained with a xenon white light flash the nearly monochromatic green light of the LED results in much crisper flow features with superior repeatability in intensity without any speckle artifacts commonly found with laser illumination.

  14. Performance Enhancement of a High Speed Jet Impingement System for Nonvolatile Residue Removal

    NASA Technical Reports Server (NTRS)

    Klausner, James F.; Mei, Renwei; Near, Steve; Stith, Rex

    1996-01-01

    A high speed jet impingement cleaning facility has been developed to study the effectiveness of the nonvolatile residue removal. The facility includes a high pressure air compressor which charges the k-bottles to supply high pressure air, an air heating section to vary the temperature of the high pressure air, an air-water mixing chamber to meter the water flow and generate small size droplets, and a converging- diverging nozzle to deliver the supersonic air-droplet mixture flow to the cleaning surface. To reliably quantify the cleanliness of the surface, a simple procedure for measurement and calibration is developed to relate the amount of the residue on the surface to the relative change in the reflectivity between a clean surface and the greased surface. This calibration procedure is economical, simple, reliable, and robust. a theoretical framework is developed to provide qualitative guidance for the design of the test and interpretation of the experimental results. The result documented in this report support the theoretical considerations.

  15. Experimental investigation of impinging jet erosion on model cohesive granular materials

    NASA Astrophysics Data System (ADS)

    Brunier-Coulin, Florian; Sarrat, Jean-Loup; Cuéllar, Pablo; Philippe, Pierre

    2017-06-01

    Erosion of soils affects both natural landscapes and engineering constructions as embankment dams or levees. Improving the safety of such earthen structures requires in particular finding out more about the elementary mechanisms involved in soil erosion. Towards this end, an experimental work was undertaken in three steps. First, several model materials were developed, made of grains (mostly glass beads) with solid bridges at particle contacts whose mechanical yield strength can be continuously varied. Furthermore, for most of them, we succeeded in obtaining a translucent system for the purpose of direct visualization. Second, these materials were tested against surface erosion by an impinging jet to determine a critical shear stress and a kinetic coefficient [2, 3]. Note that an adapted device based on optical techniques (combination of Refractive Index Matching and Planar Laser Induced Fluorescence [3]) was used specifically for the transparent media. Third, some specifically developed mechanical tests, and particularly traction tests, were implemented to estimate the mechanical strength of the solid bridges both at micro-scale (single contact) and at macro-scale (sample) and to investigate a supposed relationship with soil resistance to erosion.

  16. Consider the cold facts about steam-jet vacuum cooling

    SciTech Connect

    Decker, L.O. )

    1993-01-01

    This article compares the advantages of steam-jet vacuum cooling systems with mechanical compression or absorption systems. Steam-jet vacuum systems are popular where large flow rates of cool water are continuously required. Some utility and cogeneration plants find steam-jet cooling a convenient use for excess summer steam to improve the summer load balance between steam production and electric power generation. Initial costs depend on size and capacity. A 100-200 ton unit may be comparable to a mechanical system of the same size. In addition a cooling tower will be needed where river, pond, or lake water is not available. Simplicity and reliability of the system means savings in maintenance costs.

  17. A DPIV study on the effects of separation distance upon the vortical behaviour of jet-cylinder impingements

    NASA Astrophysics Data System (ADS)

    Long, J.; New, T. H.

    2015-07-01

    An experimental investigation based on laser-induced fluorescence (LIF) and digital particle image velocimetry (DPIV) was conducted to provide a better understanding into the effects of jet-cylinder separation distance on the vortical structures and dynamic behaviour resulting from jet impingements upon convex cylinders. Separation distances of 1, 2 and 4 jet diameters were investigated, while cylinder-jet diameter ratio was maintained at 2 throughout. LIF and DPIV results show that jet ring-vortex initiation, wall-separated vortex initiation, vortex dipole formation and vortex separation occur further away from the impingement point as the separation distance decreases. Varying the separation distance also influences the recirculating wake region size at the cylinder lee sides, as well as producing two distinct flow modes between adjacent vortex dipoles along the cylinder straight edges. Mean and instantaneous skin friction coefficient distributions determined from DPIV results not only showcase the different effects of separation distance on the wall shear stress, but also illustrate how the flow dynamics influence the local wall shear stress levels. On the other hand, wall-separated vortex initiation, vortex dipole formation and separation events incur little distinctive changes upon the local wall shear stress distributions that may ease their unique identification.

  18. Numerical Investigation of the Flow Dynamics and Evaporative Cooling of Water Droplets Impinging onto Heated Surfaces: An Effective Approach To Identify Spray Cooling Mechanisms.

    PubMed

    Chen, Jian-Nan; Zhang, Zhen; Xu, Rui-Na; Ouyang, Xiao-Long; Jiang, Pei-Xue

    2016-09-13

    Numerical investigations of the dynamics and evaporative cooling of water droplets impinging onto heated surfaces can be used to identify spray cooling mechanisms. Droplet impingement dynamics and evaporation are simulated using the presented numerical model. Volume-of-fluid method is used in the model to track the free surface. The contact line dynamics was predicted from a dynamic contact angle model with the evaporation rate predicted by a kinetic theory model. A species transport equation was solved in the gas phase to describe the vapor convection and diffusion. The numerical model was validated by experimental data. The physical effects including the contact angle hysteresis and the thermocapillary effect are analyzed to offer guidance for future numerical models of droplet impingement cooling. The effects of various parameters including surface wettability, surface temperature, droplet velocity, droplet size, and droplet temperature were numerically studied from the standpoint of spray cooling. The numerical simulations offer profound analysis and deep insight into the spray cooling heat transfer mechanisms.

  19. A study of heat transfer in the surface layer of metal during the impingement of a liquid jet

    NASA Astrophysics Data System (ADS)

    Koldin, A. V.; Platonov, N. I.

    2008-03-01

    We propose a model of heat transfer that takes place when a sheet of metal heated to a high temperature is cooled by a jet. The model takes into account transition and film boiling of liquid, as well as convective and radiant heat transfer in air medium. Examples are given illustrating how the temperature field of a movable metal sheet cooled by a system of jets is calculated.

  20. Numerical heat transfer during partially-confined, confined, and free liquid jet impingement with rotation and chemical mechanical planarization process modeling

    NASA Astrophysics Data System (ADS)

    Lallave Cortes, Jorge C.

    This work presents the use of numerical modeling for the analysis of transient and steady state liquid jet impingement for cooling application of electronics, and energy dissipation during a CMP process under the influence of a series of parameters that controls the transport phenomena mechanism. Seven thorough studies were done to explore how the flow structure and conjugated heat transfer in both the solid and fluid regions was affected by adding a secondary rotational flow during the jet impingement process. Axis-symmetrical numerical models of round jets with a spinning or static nozzle were developed using the following configurations: confined, partially-confined, and free liquid jet impingement on a rotating or stationary uniformly heated disk of finite thickness and radius. Calculations were done for various materials, namely copper, silver, Constantan, and silicon with a solid to fluid thermal conductivity ratio covering a range of 36.91.2222, at different laminar Reynolds numbers ranging from 220 to 2,000, under a broad rotational rate range of 0 to 1,000 RPM (Ekman number=infinity--3.31x10--5), nozzle-to-plate spacing (beta=0.25.5.0), dimensionless disk thicknesses (b/dn=0.167.1.67), confinement ratio (rp/rd=0.2.0.75), and Prandtl number (1.29.124.44) using NH3, H2O, FC.77 and MIL.7808 as working fluids. An engineering correlation relating the average Nusselt number with the above parameters was developed for the prediction of system performance. The simulation results compared reasonably well with previous experimental studies. The second major contribution of this research was the development of a three dimensional CMP model that shows the temperature distributions profile as an index of energy dissipation at the wafer and pad surfaces, and slurry interface. A finite element analysis was done with FIDAP 8.7.4 package under the influence of physical parameters, such as slurry flow rates (0.5.1.42 cc/s), polishing pressures (17.24.41.37 kPa), pad

  1. Ultra-high-speed 3D astigmatic particle tracking velocimetry: application to particle-laden supersonic impinging jets

    NASA Astrophysics Data System (ADS)

    Buchmann, N. A.; Cierpka, C.; Kähler, C. J.; Soria, J.

    2014-11-01

    The paper demonstrates ultra-high-speed three-component, three-dimensional (3C3D) velocity measurements of micron-sized particles suspended in a supersonic impinging jet flow. Understanding the dynamics of individual particles in such flows is important for the design of particle impactors for drug delivery or cold gas dynamic spray processing. The underexpanded jet flow is produced via a converging nozzle, and micron-sized particles ( d p = 110 μm) are introduced into the gas flow. The supersonic jet impinges onto a flat surface, and the particle impact velocity and particle impact angle are studied for a range of flow conditions and impingement distances. The imaging system consists of an ultra-high-speed digital camera (Shimadzu HPV-1) capable of recording rates of up to 1 Mfps. Astigmatism particle tracking velocimetry (APTV) is used to measure the 3D particle position (Cierpka et al., Meas Sci Technol 21(045401):13, 2010) by coding the particle depth location in the 2D images by adding a cylindrical lens to the high-speed imaging system. Based on the reconstructed 3D particle positions, the particle trajectories are obtained via a higher-order tracking scheme that takes advantage of the high temporal resolution to increase robustness and accuracy of the measurement. It is shown that the particle velocity and impingement angle are affected by the gas flow in a manner depending on the nozzle pressure ratio and stand-off distance where higher pressure ratios and stand-off distances lead to higher impact velocities and larger impact angles.

  2. Evaluation of sensing and actuation capabilities of piezoelectric composites in the impingement surface of a supersonic jet

    NASA Astrophysics Data System (ADS)

    Freeborn-Scott, Christopher

    A short takeoff and vertical landing aircraft in hover creates a highly unsteady flowfield dominated by resonance. The supersonic impinging jet created by this aircraft causes damage to the aircraft and nearby structures, lift loss, hot exhaust/debris ingestion by the engine inlet and it is harmful to people in the vicinity. This unsteadiness is caused by a feedback loop, which begins with a disturbance as the nozzle exit that excites the shear layer causing an instability to travel down through the shear layer. As that instability travels downward, it grows and impinges on the ground creating a strong acoustic wave that travels up through the ambient air to the nozzle lip, thus closing the loop. The harmful effects of this flowfield are the motivation for this study. Many flow control techniques have been attempted to reduce the detrimental impact of this flowfield, most notably microjet injection around the periphery of the nozzle exit. This method has been shown to work well; however, this study focuses on implementing ground-based control. Piezoelectric composites have been successful both as frequency sensors and as actuators for vibration suppression. By implementing two piezoelectric composites, the macro-fiber composite and Quick Pack, into the impingement surface of a supersonic jet, an evaluation of the sensing and control capabilities of the devices can be evaluated. Both elements are glued to the underside of a thin, flexible plate, which is placed in the ground, and subjected to a supersonic impinging jet. The jet is ideally expanded at Mach 1.5 with a stagnation temperature equal to the ambient temperature. Narrowband acoustic and unsteady pressure spectra show that at h/d = 4, the presence of a compliant plate causes a shift in the dominant mode, which amounts to a shift in the main impingement tone frequency from 5.7 Hz to 7.1 Hz. Comparison of the power spectral density to the noise and pressure spectra showed that the piezofiber composites are

  3. Film cooling: case of double rows of staggered jets.

    PubMed

    Dorignac, E; Vullierme, J J; Noirault, P; Foucault, E; Bousgarbiès, J L

    2001-05-01

    An experimental investigation of film cooling of a wall in a case of double rows of staggered hot jets (65 degrees C) in an ambient air flow. The wall is heated at a temperature value between the one of the jets and the one of the main flow. Experiments have been carried out for different injection rates, the main flow velocity is maintained at 32 m/s. Association of the measures of temperature profiles by cold wire and the measures of wall temperature by infrared thermography allows us to describe the behaviour of the flows and to propose the best injection which assures a good cooling of the plate.

  4. Gas-Jet Cooling Would Improve Czochralski Process

    NASA Technical Reports Server (NTRS)

    Dudukovic, M. P.; Ramachandran, P. A.; Srivastava, R. K.

    1989-01-01

    Controlled cooling by jets of gas improves growth of single crystals of silocon by Czochralski process, according to study. Rate of cooling by jets joins temperature of crucible and pulling rate as input variable of process adjusted to achieve required diameter of crystal and shape of crystal/melt interface. Critical parameters of growing crystal, output variables of Czochralski process controlled via two or all three of input variables. One input variable, usually speed, held constant while other two adjusted to achieve required diameter and interface.

  5. Analysis of noise produced by jet impingement near the trailing edge of a flat and a curved plate

    NASA Technical Reports Server (NTRS)

    Mckinzie, D. J., Jr.; Burns, R. J.

    1975-01-01

    The sound fields produced by the interaction of a subsonic cold gas jet with the trailing edge of a large flat plate and a curved plate were analyzed. The analyses were performed to obtain a better understanding of the dominant noise source and the mechanism governing the peak sound-pressure-level frequencies of the broadband spectra. An analytical expression incorporating an available theory and experimental data predicts sound field data over an arc of approximately 105 deg measured from the upstream jet axis for the two independent sets of data. The dominant noise as detected on the impingement side of either plate results from the jet impact (eighth power of the velocity dependence) rather than a trailing-edge disturbance (fifth or sixth power of the velocity dependence). Also, the frequency of the peak SPL may be governed by a phenomenon which produces periodic formation and shedding of ring vortices from the nozzle lip.

  6. Local heat transfer distribution between smooth flat surface and impinging air jet from a circular nozzle at low Reynolds numbers

    NASA Astrophysics Data System (ADS)

    Katti, Vadiraj V.; Yasaswy, S. Nagesh; Prabhu, S. V.

    2011-03-01

    An experimental investigation is performed to study the effect of jet to plate spacing and low Reynolds number on the local heat transfer distribution to normally impinging submerged circular air jet on a smooth and flat surface. A single jet from a straight circular nozzle of length-to-diameter ratio ( l/d) of 83 is tested. Reynolds number based on nozzle exit condition is varied between 500 and 8,000 and jet-to-plate spacing between 0.5 and 8 nozzle diameters. The local heat transfer characteristics are obtained using thermal images from infrared thermal imaging technique. It was observed that at lower Reynolds numbers, the effect of jet to plate distances covered during the study on the stagnation point Nusselt numbers is minimal. At all jet to plate distances, the stagnation point Nusselt numbers decrease monotonically with the maximum occurring at a z/d of 0.5 as opposed to the stagnation point Nusselt numbers at high Reynolds numbers which occur around a z/d of 6.

  7. Experimental estimation of convective heat transfer coefficient from pulsating semi-confined impingement air slot jet by using inverse method

    NASA Astrophysics Data System (ADS)

    Farahani, Somayeh Davoodabadi; Kowsary, Farshad

    2017-09-01

    An experimental study on pulsating impingement semi-confined slot jet has been performed. The effect of pulsations frequency was examined for various Reynolds numbers and Nozzle to plate distances. Convective heat transfer coefficient is estimated using the measured temperatures in the target plate and conjugate gradient method with adjoint equation. Heat transfer coefficient in Re < 3000 tended to increase with increasing frequency. The pulsations enhance mixing, which results in an enhancement of mean flow velocity. In case of turbulent jet (Re > 3000), heat transfer coefficient is affected by the pulsation from particular frequency. In this study, the threshold Strouhal number (St) is 0.11. No significant heat transfer enhancement was obtained for St < 0.11. The thermal resistance is smaller each time due to the newly forming thermal boundary layers. Heat transfer coefficient increases due to decrease thermal resistance. This study shows that maximum enhancement in heat transfer due to pulsations occurs in St = 0.169. Results show the configuration geometry has an important effect on the heat transfer performances in pulsed impinging jet. Heat transfer enhancement can be described to reflect flow by the confinement plate.

  8. Electronic Spectra of the Jet-Cooled Acetaminophen

    NASA Astrophysics Data System (ADS)

    Lee, Seung Jun; Min, Ahreum; Kim, Yusic; Choi, Myong Yong; Chang, Jinyoung; Lee, Sang Hak; Kim, Seong Keun

    2010-06-01

    Resonant two-photon ionization (R2PI), laser induced fluorescence (LIF) and UV-UV double resonance spectra of the jet-cooled acetaminophen, widely used as a pain reliever and fever reducer, were obtained in the gas phase. Conformational characterizations for acetaminophen will be presented with an aid of spectroscopic techniques and DFT B3LYP calculations.

  9. Physical and Mathematical Modeling of Thin Steel Slab Continuous Casting Secondary Cooling Zone Air-Mist Impingement

    NASA Astrophysics Data System (ADS)

    de León B., Melecio; Castillejos E., A. Humberto

    2015-10-01

    This study is an attempt to unveil the fluid dynamic phenomena occurring during interaction of air-mists with the surface of the steel strand during its pass through the continuous casting secondary cooling system. Air-mists generated under conditions of practical interest are studied while impacting on a vertical wall at room temperature. Experimentally a spatial multiple-counting technique based on capturing instantaneous double-exposure shadowgraphs is used to visualize the internal structure of mists at distances between 0 and 4 mm from the wall. Analysis of single exposure images allows determination of size distributions of primary (impinging) and secondary (ejecting) drops and of fluctuating thickness of water films formed on the wall surface. Besides, examination of image pairs enables measurement of velocity and trajectory angles of both kinds of drops. These results aided in the formulation and validation of a transient, turbulent, 3D, multiphase fluid dynamic model for simulating impinging air-mists. The model is based on KIVA-3V and for simulating the airborne mist region it solves the continuity equations—mass, momentum, turbulence quantities—for the air coupled with the equation of motion for drops sampled randomly from distributions assumed to govern their size and volume flux at the nozzle orifice. While for the impingement region submodels are established to estimate the results of drop/wall interaction, i.e., the dynamics of secondary drops and water films formed by the impingement of primary drops. The model forecasts reasonably well the random distributions of diameters, velocities, trajectory angles, and Weber numbers of both kind of drops moving near the wall. Additionally, it predicts well the average thickness of the water film and the important effect that air nozzle pressure has on the normal impinging velocity of drops; high pressures result in large drop velocities favoring intimate contact with the surface.

  10. A jet-driven dynamo (JEDD) from jet-inflated bubbles in cooling flows

    NASA Astrophysics Data System (ADS)

    Soker, Noam

    2017-04-01

    I suggest that the main process that amplifies magnetic fields in cooling flows in clusters and group of galaxies is a jet-driven dynamo (JEDD). The main processes that are behind the JEDD is the turbulence that is formed by the many vortices formed in the inflation processes of bubbles, and the large scale shear formed by the propagating jet. It is sufficient that a strong turbulence exits in the vicinity of the jets and bubbles, just where the shear is large. The typical amplification time of magnetic fields by the JEDD near the jets and bubbles is approximately hundred million years. The amplification time in the entire cooling flow region is somewhat longer. The vortices that create the turbulence are those that also transfer energy from the jets to the intra-cluster medium, by mixing shocked jet gas with the intra-cluster medium gas, and by exciting sound waves. The JEDD model adds magnetic fields to the cyclical behaviour of energy and mass in the jet-feedback mechanism in cooling flows.

  11. A jet-driven dynamo (JEDD) from jets-inflated bubbles in cooling flows

    NASA Astrophysics Data System (ADS)

    Soker, Noam

    2017-01-01

    I suggest that the main process that amplifies magnetic fields in cooling flows in clusters and group of galaxies is a jet-driven dynamo (JEDD). The main processes that are behind the JEDD is the turbulence that is formed by the many vortices formed in the inflation processes of bubbles, and the large scale shear formed by the propagating jet. It is sufficient that a strong turbulence exits in the vicinity of the jets and bubbles, just where the shear is large. The typical amplification time of magnetic fields by the JEDD near the jets and bubbles is approximately hundred million years. The amplification time in the entire cooling flow region is somewhat longer. The vortices that create the turbulence are those that also transfer energy from the jets to the intra-cluster medium, by mixing shocked jet gas with the intra-cluster medium gas, and by exciting sound waves. The JEDD model adds magnetic fields to the cyclical behavior of energy and mass in the jet-feedback mechanism (JFM) in cooling flows.

  12. Analysis of reactor material experiments investigating oxide fuel crust stability and heat transfer in jet impingement flow

    SciTech Connect

    Sienicki, J.J.; Spencer, B.W.

    1985-01-01

    An analysis is presented of the crust stability and heat transfer behavior in the CSTI-1, CSTI-3, and CWTI-11 reactor material experiments in which a jet of molten oxide fuel at approx. 160/sup 0/K above its freezing temperature was impinged normally upon stainless steel plates initially at 300 and 385 K. The major issue is the existence of nonexistence of a stable solidified layer of fuel, or crust, interstitial to the flowing hot fuel and the steel substrate, tending to insulate the steel from the hot molten fuel. A computer model was developed to predict the heatup of thermocouples imbedded immediately beneath the surface of the plate for both of the cases in which a stable crust is assumed to be either present or absent during the impingement phase. Comparison of the model calculations with the measured thermocouple temperatures indicates that a protective crust was present over nearly all of the plate surface area throughout the impingement process precluding major melting of the plate steel. However, the experiments also show evidence for very localized and isolated steel melting as revealed by localized and isolated pitting of the steel surface and the response of thermocouples located within the pitted region.

  13. Numerical thermal analysis of water's boiling heat transfer based on a turbulent jet impingement on heated surface

    NASA Astrophysics Data System (ADS)

    Toghraie, D.

    2016-10-01

    In this study, a numerical method for simulation of flow boiling through subcooled jet on a hot surface with 800 °C has been presented. Volume fraction (VOF) has been used to simulate boiling heat transfer and investigation of the quench phenomena through fluid jet on a hot horizontal surface. Simulation has been done in a fixed Tsub=55 °C, Re=5000 to Re=50,000 and also in different Tsub =Tsat -Tf between 10 °C and 95 °C. The effect of fluid jet velocity and subcooled temperature on the rewetting temperature, wet zone propagation, cooling rate and maximum heat flux has been investigated. The results of this study show that by increasing the velocity of fluid jet of water, convective heat transfer coefficient at stagnation point increases. More ever, by decreasing the temperature of the fluid jet, convective heat transfer coefficient increases.

  14. Heat Transfer Characteristics of Impinging Jets by Four Circular Nozzles Arranged in Square-type

    NASA Astrophysics Data System (ADS)

    Ichimiya, Koichi

    This paper presents the experimental results on the impingement heat transfer by 4-circular nozzles arranged in square type. Experiments were performed for the dimensionless space H(= h/D)=0.5-8,the Reynolds number Re(= VoD/v)=3000-40000, and the dimensionless pitch Pi(= pi/D)=8. The two-dimensional behavior of the local Nusselt number was corresponded to the flow visualization by oil film method on the impingement surface. The average Nusselt number was expressed by the geometric function and Re2/3. The maximum average Nusselt number was obtained at the dimensionless nozzle-impingement surface spacing H=2 for constant Reynolds number.

  15. Drop Impingement on Highly Wetting Micro/Nano Porous Surfaces

    NASA Astrophysics Data System (ADS)

    Buie, Cullen; Joung, Youngsoo

    2011-11-01

    Recently, we developed a novel fabrication method using a combination of electrophoretic deposition (EPD) and break down anodization (BDA) to achieve highly wetting nanoporous surfaces with microscale features. In this study we investigate droplet impingement behavior on these surfaces as a function of impact velocity, droplet size, and liquid properties. We observe impingement modes we denote as ``necking'' (droplet breaks before full penetration in the porous surface), ``spreading'' (continuous wicking into the porous surface), and ``jetting'' (jets of liquid emanate from the edges of the wicking liquid). To predict the droplet impingement modes, we've developed a non-dimensional parameter that is a function of droplet velocity, dynamic viscosity, effective pore radius and contact angle. The novel dimensionless parameter successfully predicts drop impingement modes across multiple fluids. Results of this study will inform the design of spray impingement cooling systems for electronics applications where the ``spreading'' mode is preferred.

  16. Normal impingement loads due to small air jets issuing from a base plate and reflecting off a platform for various jet Mach numbers, separation distances, and ambient pressures

    NASA Technical Reports Server (NTRS)

    Hoffman, S.

    1972-01-01

    An investigation was conducted in a 12.5-meter-diameter vacuum sphere to determine the impingement loads due to air jets issuing from and perpendicular to a circular base and reflecting off a square platform, that is, a simulation of rendezvous maneuvering, docking, launch, impact dampers etc. The nozzles had exit Mach numbers of 1, 3, 5, and 7. The ambient pressures were 0.0006, 5, 225, and 760 torr. Under near-field separation distances and at 0.0006 torr, reflections were significant; and ratios of the impingement force to thrust on both plates in the biplane arrangement varied from about 750 for exit Mach number 1 to 120 for exit Mach number 7. The far-field force ratios were near unity for the platform and zero for the base and indicated few, if any, reflections. Some reversals and rapid changes in loads were obtained at transition distances between the near and far fields. In general, increasing the exit Mach number or ambient pressure reduced the impingement loads.

  17. Spot cooling. Part 1: Human responses to cooling with air jets

    SciTech Connect

    Melikov, A.K.; Halkjaer, L.; Arakelian, R.S.; Fanger, P.O.

    1994-12-31

    Eight standing male subjects and a thermal manikin were studied for thermal, physiological, and subjective responses to cooling with an air jet at room temperatures of 28 C, 33 C, and 38 C and a constant relative humidity of 50%. The subjects wore a standard uniform and performed light work. A vertical jet and a horizontal jet were employed The target area of the jet, i.e., the cross section of the jet where it first met the subject, had a diameter of 0.4 m and was located 0.5 m from the outlet. Experiments were performed at average temperatures at the jet target area of 20 C, 24 C, and 28 C. Each experiment lasted 190 minutes and was performed with three average velocities at the target area: 1 and 2 m/s and the preferred velocity selected by the subjects. The impact of the relative humidity of the room air, the jet`s turbulence intensity, and the use of a helmet on the physiological and subjective responses of the eight subjects was also studied The responses of the eight subjects were compared with the responses of a group of 29 subjects. The spot cooling improved the thermal conditions of the occupants. The average general thermal sensation for the eight subjects was linearly correlated to the average mean skin temperature and the average sweat rate. An average mean skin temperature of 33 C and an average sweat rate of 33 g{center_dot}h{sup {minus}1} m{sup {minus}2} were found to correspond to a neutral thermal sensation. The local thermal sensation at the neck and at the arm exposed to the cooling jet was found to be a function of the room air temperature and the local air velocity and temperature of the jet. The turbulence intensity of the cooling jet and the humidity of the room air had no impact on the subjects` physiological and subjective responses. Large individual differences were observed in the evaluation of the environment and in the air velocity preferred by the subjects.

  18. Optimal design of an air jet for spot cooling

    SciTech Connect

    Tillman, F.A.; Hwang, C.L.; Lin, M.J.

    1984-01-01

    In a heat-stressed industry where process loads are very high and/or there are comparatively few workers or work stations, total area air conditioning is prohibitively expensive and wasteful of energy. In such situations, spot (area of localized) cooling systems may be used to provide environmental conditions proper for worker comfort, or stress avoidance, only in the immediate vicinity of the worker. The optimization problem is to minimize the system's energy requirement by determining the optimum jet size, cooling jet air velocity, and the temperature and humidity from a refrigerating system that provides the proper environment for workers within the permissible physiological strain. The problem is a nonlinear programming problem and is solved by a generalized reduced-gradient (GRG) method. In the case study, effects of outdoor weather conditions, factory air conditions, worker loading, and worker's clothing on optimal system design and control are investigated.

  19. 2D numerical simulation of impinging jet onto the concave surface by k - w - overline{{v2 }} - f turbulence model

    NASA Astrophysics Data System (ADS)

    Seifi, Zeinab; Nazari, Mohammad Reza; Khalaji, Erfan

    2017-01-01

    In the present article, the characteristics of turbulent jet impinging onto a concave surface is studied using k - w - overline{{v2 }} - f turbulence model. Dependent parameters such as inlet Reynolds number (2960 < Re < 12,000), nozzle-plate distance (4 < H/B < 10), concavity (D/B = 30, 60) of confined and unconfined impinging jet are scrutinized to find out whether this approach would bring any privileges compared to other investigations or not. The obtained results indicate better performance in low nozzle-plate distance in comparison with those mentioned in other literatures. Furthermore, the average Nusselt number of confined impinging jet overtakes unconfined one (similar circumstances) while this trend will decline as relative concavity increases. Moreover, local heat transfer of stagnation area and wall jet goes up and down through nozzle-plate distance enhancement respectively. Finally, the effects of sinusoidal pulsed inlet profile on heat transfer of unconfined impinging jet indicate direct affiliation of amplitude and neutral impact of frequency on Nusselt number distribution.

  20. Thermal characteristics of air-water spray impingement cooling of hot metallic surface under controlled parametric conditions

    NASA Astrophysics Data System (ADS)

    Nayak, Santosh Kumar; Mishra, Purna Chandra

    2016-06-01

    Experimental results on the thermal characteristics of air-water spray impingement cooling of hot metallic surface are presented and discussed in this paper. The controlling input parameters investigated were the combined air and water pressures, plate thickness, water flow rate, nozzle height from the target surface and initial temperature of the hot surface. The effects of these input parameters on the important thermal characteristics such as heat transfer rate, heat transfer coefficient and wetting front movement were measured and examined. Hot flat plate samples of mild steel with dimension 120 mm in length, 120 mm breadth and thickness of 4 mm, 6 mm, and 8 mm respectively were tested. The air assisted water spray was found to be an effective cooling media and method to achieve very high heat transfer rate from the surface. Higher heat transfer rate and heat transfer coefficients were obtained for the lesser i.e, 4 mm thick plates. Increase in the nozzle height reduced the heat transfer efficiency of spray cooling. At an inlet water pressure of 4 bar and air pressure of 3 bar, maximum cooling rates 670°C/s and average cooling rate of 305.23°C/s were achieved for a temperature of 850°C of the steel plate.

  1. Local distribution of wall static pressure and heat transfer on a smooth flat plate impinged by a slot air jet

    NASA Astrophysics Data System (ADS)

    Adimurthy, M.; Katti, Vadiraj V.

    2016-06-01

    Local distribution of wall static pressure and heat transfer on a smooth flat plate impinged by a normal slot air jet is experimental investigated. Present study focuses on the influence of jet-to-plate spacing (Z/D h ) (0.5-10) and Reynolds number (2500-20,000) on the fluid flow and heat transfer distribution. A single slot jet with an aspect ratio (l/b) of about 22 is chosen for the current study. Infrared Thermal Imaging technique is used to capture the temperature data on the target surface. Local heat transfer coefficients are estimated from the thermal images using `SMART VIEW' software. Wall static pressure measurement is carried out for the specified range of Re and Z/D h . Wall static pressure coefficients are seen to be independent of Re in the range between 5000 and 15,000 for a given Z/D h . Nu values are higher at the stagnation point for all Z/D h and Re investigated. For lower Z/D h and higher Re, secondary peaks are observed in the heat transfer distributions. This may be attributed to fluid translating from laminar to turbulent flow on the target plate. Heat transfer characteristics are explained based on the simplified flow assumptions and the pressure data obtained using Differential pressure transducer and static pressure probe. Semi-empirical correlation for the Nusselt number in the stagnation region is proposed.

  2. Local distribution of wall static pressure and heat transfer on a smooth flat plate impinged by a slot air jet

    NASA Astrophysics Data System (ADS)

    M, Adimurthy; Katti, Vadiraj V.

    2017-02-01

    Local distribution of wall static pressure and heat transfer on a smooth flat plate impinged by a normal slot air jet is experimental investigated. Present study focuses on the influence of jet-to-plate spacing ( Z/D h ) (0.5-10) and Reynolds number (2500-20,000) on the fluid flow and heat transfer distribution. A single slot jet with an aspect ratio ( l/b) of about 22 is chosen for the current study. Infrared Thermal Imaging technique is used to capture the temperature data on the target surface. Local heat transfer coefficients are estimated from the thermal images using `SMART VIEW' software. Wall static pressure measurement is carried out for the specified range of Re and Z/D h . Wall static pressure coefficients are seen to be independent of Re in the range between 5000 and 15,000 for a given Z/D h . Nu values are higher at the stagnation point for all Z/D h and Re investigated. For lower Z/D h and higher Re, secondary peaks are observed in the heat transfer distributions. This may be attributed to fluid translating from laminar to turbulent flow on the target plate. Heat transfer characteristics are explained based on the simplified flow assumptions and the pressure data obtained using Differential pressure transducer and static pressure probe. Semi-empirical correlation for the Nusselt number in the stagnation region is proposed.

  3. Numerical Analysis of an Impinging Jet Reactor for the CVD and Gas-Phase Nucleation of Titania

    NASA Technical Reports Server (NTRS)

    Gokoglu, Suleyman A.; Stewart, Gregory D.; Collins, Joshua; Rosner, Daniel E.

    1994-01-01

    We model a cold-wall atmospheric pressure impinging jet reactor to study the CVD and gas-phase nucleation of TiO2 from a titanium tetra-iso-propoxide (TTIP)/oxygen dilute source gas mixture in nitrogen. The mathematical model uses the computational code FIDAP and complements our recent asymptotic theory for high activation energy gas-phase reactions in thin chemically reacting sublayers. The numerical predictions highlight deviations from ideality in various regions inside the experimental reactor. Model predictions of deposition rates and the onset of gas-phase nucleation compare favorably with experiments. Although variable property effects on deposition rates are not significant (approximately 11 percent at 1000 K), the reduction rates due to Soret transport is substantial (approximately 75 percent at 1000 K).

  4. Effect of nozzle-to-plate spacing on the development of a plane jet impinging on a heated plate

    NASA Astrophysics Data System (ADS)

    Rim, Ben Kalifa; Saïd, Nejla Mahjoub; Bournot, Hervé; Le Palec, Georges

    2017-04-01

    An experimental investigation was carried out to study the behavior of a turbulent air jet impinging on a heated plate. The study of the flow field was performed using a particle image velocimetry. A three-dimensional numerical model with Reynolds stress model has been conducted to examine the global flow. Numerical results agree well with experimental data. The main properties of the fluid occurring between the nozzle and the flat plate are presented. In addition, the effect of the distance between the nozzle exit and the plate (h/e = 14 and 28) were investigated and detailed analysis of the dynamic, turbulent distribution and temperature fields were performed. The wall shear stress and the pressure fields near the heated plate are then explored. Results showed that the mean velocity and the heat transfer characteristics of small nozzle-to-plate spacing are significantly different from those of large nozzle-to-plate spacing.

  5. Effect of nozzle-to-plate spacing on the development of a plane jet impinging on a heated plate

    NASA Astrophysics Data System (ADS)

    Rim, Ben Kalifa; Saïd, Nejla Mahjoub; Bournot, Hervé; Le Palec, Georges

    2016-09-01

    An experimental investigation was carried out to study the behavior of a turbulent air jet impinging on a heated plate. The study of the flow field was performed using a particle image velocimetry. A three-dimensional numerical model with Reynolds stress model has been conducted to examine the global flow. Numerical results agree well with experimental data. The main properties of the fluid occurring between the nozzle and the flat plate are presented. In addition, the effect of the distance between the nozzle exit and the plate (h/e = 14 and 28) were investigated and detailed analysis of the dynamic, turbulent distribution and temperature fields were performed. The wall shear stress and the pressure fields near the heated plate are then explored. Results showed that the mean velocity and the heat transfer characteristics of small nozzle-to-plate spacing are significantly different from those of large nozzle-to-plate spacing.

  6. Numerical investigation on super-cooled large droplet icing of fan rotor blade in jet engine

    NASA Astrophysics Data System (ADS)

    Isobe, Keisuke; Suzuki, Masaya; Yamamoto, Makoto

    2014-10-01

    Icing (or ice accretion) is a phenomenon in which super-cooled water droplets impinge and accrete on a body. It is well known that ice accretion on blades and vanes leads to performance degradation and has caused severe accidents. Although various anti-icing and deicing systems have been developed, such accidents still occur. Therefore, it is important to clarify the phenomenon of ice accretion on an aircraft and in a jet engine. However, flight tests for ice accretion are very expensive, and in the wind tunnel it is difficult to reproduce all climate conditions where ice accretion can occur. Therefore, it is expected that computational fluid dynamics (CFD), which can estimate ice accretion in various climate conditions, will be a useful way to predict and understand the ice accretion phenomenon. On the other hand, although the icing caused by super-cooled large droplets (SLD) is very dangerous, the numerical method has not been established yet. This is why SLD icing is characterized by splash and bounce phenomena of droplets and they are very complex in nature. In the present study, we develop an ice accretion code considering the splash and bounce phenomena to predict SLD icing, and the code is applied to a fan rotor blade. The numerical results with and without the SLD icing model are compared. Through this study, the influence of the SLD icing model is numerically clarified.

  7. Evaluation of the sensitivity and response of IR thermography from a transparent heater under liquid jet impingement

    NASA Astrophysics Data System (ADS)

    Haustein, H. D.; Rohlfs, W.; Al-Sibai, F.; Kneer, R.

    2012-11-01

    The feasibility of a visible/IR transparent heater and its suitability for IR thermography is experimentally examined. The most common transparent conductive coating, Indium Tin Oxide (ITO), is quite reflective and its optical properties depend on thickness and manufacturing process. Therefore, the optical properties of several thicknesses and types of ITO, coated on an IR window (BaF2), are examined. A highly transparent Cadmium Oxide (CdO) coating on a ZnS window, also examined, is found to be unusable. Transmissivity is found to increase with a decrease in coating thickness, and total emittance is relatively low. A thick ITO coating was examined for IR thermography in the challenging test case of submerged water jet impingement, where temperature differences were characteristically small and distributed. The measurements under steady state conditions were found to agree well with the literature, and the method was validated. Comparison of two IR cameras did not show the LWIR low-temperature advantage, up to the maximal acquisition rate examined, 1.3KHz. Rather the MWIR camera had a stronger signal to noise ratio, due to the higher emissivity of the heater in this range. The transient response of the transparent heater showed no time-delay, though the substrate dampens the thermal response significantly. Therefore, only qualitative transient measurements are shown for the case of pulsating free-surface jet impingement, showing that the motion of the hydraulic jump coincides with thermal measurements. From these results, recommendations are made for coating/window combination in IR thermography.

  8. Morphology of an aluminum alloy eroded by a jet of angular particles impinging at normal incidence

    NASA Technical Reports Server (NTRS)

    Rao, P. V.; Young, S. G.; Buckley, D. H.

    1983-01-01

    The erosion of an aluminum alloy impinged by crushed glass particles at normal incidence was studied. The erosion patterns were analyzed by scanning electron microscopy, energy dispersive X-ray spectroscopy, and surface profilometer measurements. From the analysis of specimens tested at various driving gas pressures and time intervals, four distinct erosion regions were identified. A study of pit morphology and its relationship to cumulative erosion was made. Cutting wear is believed to be the predominant material removal mechanism; some evidence of deformation wear was found during the incubation period.

  9. Studies on Impingement Effects of Low Density Jets on Surfaces — Determination of Shear Stress and Normal Pressure

    NASA Astrophysics Data System (ADS)

    Sathian, Sarith. P.; Kurian, Job

    2005-05-01

    This paper presents the results of the Laser Reflection Method (LRM) for the determination of shear stress due to impingement of low-density free jets on flat plate. For thin oil film moving under the action of aerodynamic boundary layer the shear stress at the air-oil interface is equal to the shear stress between the surface and air. A direct and dynamic measurement of the oil film slope is measured using a position sensing detector (PSD). The thinning rate of oil film is directly measured which is the major advantage of the LRM over LISF method. From the oil film slope history, direct calculation of the shear stress is done using a three-point formula. For the full range of experiment conditions Knudsen numbers varied till the continuum limit of the transition regime. The shear stress values for low-density flows in the transition regime are thus obtained using LRM and the measured values of shear show fair agreement with those obtained by other methods. Results of the normal pressure measurements on a flat plate in low-density jets by using thermistors as pressure sensors are also presented in the paper. The normal pressure profiles obtained show the characteristic features of Newtonian impact theory for hypersonic flows.

  10. Analysis of Material Sample Heated by Impinging Hot Hydrogen Jet in a Non-Nuclear Tester

    NASA Technical Reports Server (NTRS)

    Wang, Ten-See; Foote, John; Litchford, Ron

    2006-01-01

    A computational conjugate heat transfer methodology was developed and anchored with data obtained from a hot-hydrogen jet heated, non-nuclear materials tester, as a first step towards developing an efficient and accurate multiphysics, thermo-fluid computational methodology to predict environments for hypothetical solid-core, nuclear thermal engine thrust chamber. The computational methodology is based on a multidimensional, finite-volume, turbulent, chemically reacting, thermally radiating, unstructured-grid, and pressure-based formulation. The multiphysics invoked in this study include hydrogen dissociation kinetics and thermodynamics, turbulent flow, convective and thermal radiative, and conjugate heat transfers. Predicted hot hydrogen jet and material surface temperatures were compared with those of measurement. Predicted solid temperatures were compared with those obtained with a standard heat transfer code. The interrogation of physics revealed that reactions of hydrogen dissociation and recombination are highly correlated with local temperature and are necessary for accurate prediction of the hot-hydrogen jet temperature.

  11. Adiabatic cooling of the artificial Porcupine plasma jet

    NASA Astrophysics Data System (ADS)

    Ruizhin, Iu. Ia.; Treumann, R. A.; Bauer, O. H.; Moskalenko, A. M.

    1987-01-01

    Measurements of the plasma density obtained during the interaction of the artificial plasma jet, fired into the ionosphere with the body of the Porcupine main payload, have been analyzed for times when there was a well-developed wake effect. Using wake theory, the maximum temperature of the quasi-neutral xenon ion beam has been determined for an intermediate distance from the ion beam source when the beam has left the diamagnetic region but is still much denser than the ionospheric background plasma. The beam temperature is found to be about 4 times less than the temperature at injection. This observation is very well explained by adiabatic cooling of the beam during its initial diamagnetic and current-buildup phases at distances r smaller than 10 m. Outside this region, the beam conserves the temperature achieved. The observation proves that the artificial plasma jet passes through an initial gas-like diamagnetic phase restricted to the vicinity of the beam source, where it expands adiabatically. Partial cooling also takes place outside the diamagnetic region where the beam current still builds up. The observations also support a recently developed current-closure model of the quasi-neutral ion beam.

  12. A compressible wall-adapting similarity mixed model for large-eddy simulation of the impinging round jet

    NASA Astrophysics Data System (ADS)

    Lodato, Guido; Vervisch, Luc; Domingo, Pascale

    2009-03-01

    Wall-jet interaction is studied with large-eddy simulation (LES) in which a mixed-similarity subgrid scale (SGS) closure is combined with the wall-adapting local eddy-viscosity (WALE) model for the eddy-viscosity term. The macrotemperature and macropressure are introduced to deduce a weakly compressible form of the mixed-similarity model, and the relevant formulation for the energy equation is deduced accordingly. LES prediction capabilities are assessed by comparing flow statistical properties against experiment of an unconfined impinging round jet at Reynolds numbers of 23 000 and 70 000. To quantify the benefit of the proposed WALE-similarity mixed model, the lower Reynolds number simulations are also performed using the standard WALE and Lagrangian dynamic Smagorinsky approaches. The unsteady compressible Navier-Stokes equations are integrated over 2.9 M, 3.5 M, and 5.5 M node Cartesian grids with an explicit fourth-order finite volume solver. Nonreflecting boundary conditions are enforced using a methodology accounting for the three-dimensional character of the turbulent flow at boundaries. A correct wall scaling is achieved from the combination of similarity and WALE approaches; for this wall-jet interaction, the SGS closure terms can be computed in the near-wall region without the necessity of resorting to additional specific treatments. The possible impact of turbulent energy backscatter in such flow configurations is also addressed. It is found that, for the present configuration, the correct reproduction of reverse energy transfer plays a key role in the estimation of near-wall statistics, especially when the viscous sublayer is not properly resolved.

  13. Effects of geometry on slot-jet film cooling performance

    SciTech Connect

    Hyams, D.G.; McGovern, K.T.; Leylek, J.H.

    1995-10-01

    The physics of the film cooling process for shaped, inclined slot-jets with realistic slot-length-to-width ratios (L/s) is studied for a range of blowing ratio (M) and density ratio (DR) parameters typical of gas turbine operations. For the first time in the open literature, the effect of inlet and exit shaping of the slot-jet on both flow and thermal field characteristics is isolated, and the dominant mechanisms responsible for differences in these characteristics are documented. A previously documented computational methodology was applied for the study of four distinct configurations: (1) slot with straight edges and sharp corners (reference case); (2) slot with shaped inlet region; (3) slot with shaped exit region; and (4) slot with both shaped inlet and exit regions. Detailed field results as well as surface phenomena involving adiabatic film effectiveness ({eta}) and heat transfer coefficient (h) are presented. It is demonstrated that both {eta} and h results are vital in the proper assessment of film cooling performance. All simulations were carried out using a multi-block, unstructured/adaptive grid, fully explicit, time-marching solver with multi-grid, local time stepping, and residual smoothing type acceleration techniques. Special attention was paid to and full documentation provided for: (1) proper modeling of the physical phenomena; (2) exact geometry and high quality grid generation techniques; (3) discretization schemes; and (4) turbulence modeling issues. The key parameters M and DR were varied from 1.0 to 2.0 and 1.5 to 2.0, respectively, to show their influence. Simulations were repeated for slot length-to-width ratio (L/s) of 3.0 and 4.5 in order to explain the effects of this important parameter. Additionally, the performance of two popular turbulence models, standard k-F, and RNG k-E, were studied to establish their ability to handle highly elliptic jet/crossflow interaction type processes.

  14. Comparison of central axis and jet ring coolant supply for turbine disk cooling on a SSME-HPOTP model

    NASA Technical Reports Server (NTRS)

    Kim, Y. W.; Metzger, D. E.

    1992-01-01

    The test facility, test methods and results are presented for an experimental study modeling the cooling of turbine disks in the blade attachment regions with multiple impinging jets, in a configuration simulating the disk cooling method employed on the Space Shuttle Main Engine oxygen turbopump. The study's objective was to provide a comparison of detailed local convection heat transfer rates obtained for a single center-supply of disk coolant with those obtained with the present flight configuration where disk coolant is supplied through an array of 19 jets located near the disk outer radius. Specially constructed disk models were used in a program designed to evaluate possible benefits and identify any possible detrimental effects involved in employing an alternate disk cooling scheme. The study involved the design, construction and testing of two full scale rotating model disks, one plane and smooth for baseline testing and the second contoured to the present flight configuration, together with the corresponding plane and contoured stator disks. Local heat transfer rates are determined from the color display of encapsulated liquid crystals coated on the disk in conjunction with use of a computer vision system. The test program was composed of a wide variety of disk speeds, flowrates, and geometrical configurations, including testing for the effects of disk boltheads and gas ingestion from the gas path region radially outboard of the disk-cavity.

  15. The ground vortex flow field associated with a jet in a cross flow impinging on a ground plane for uniform and annular turbulent axisymmetric jets. M.S. Thesis

    NASA Technical Reports Server (NTRS)

    Cavage, William M.; Kuhlman, John M.

    1993-01-01

    An experimental study was conducted of the impingement of a single circular jet on a ground plane in a cross flow. This geometry is a simplified model of the interaction of propulsive jet exhaust from a V/STOL aircraft with the ground in forward flight. Jets were oriented normal to the cross flow and ground plane. Jet size, cross flow-to-jet velocity ratio, ground plane-to-jet board spacing, and jet exit turbulence level and mean velocity profile shape were all varied to determine their effects on the size of the ground vortex interaction region which forms on the ground plane, using smoke injection into the jet. Three component laser Doppler velocimeter measurements were made with a commercial three color system for the case of a uniform jet with exit spacing equal to 5.5 diameters and cross flow-to-jet velocity ratio equal to 0.11. The flow visualization data compared well for equivalent runs of the same nondimensional jet exit spacing and the same velocity ratio for different diameter nozzles, except at very low velocity ratios and for the larger nozzle, where tunnel blockage became significant. Variation of observed ground vortex size with cross flow-to-jet velocity ratio was consistent with previous studies. Observed effects of jet size and ground plane-to-jet board spacing were relatively small. Jet exit turbulence level effects were also small. However, an annular jet with a low velocity central core was found to have a significantly smaller ground vortex than an equivalent uniform jet at the same values of cross flow-to-jet velocity ratio and jet exit-to-ground plane spacing. This may suggest a means of altering ground vortex behavior somewhat, and points out the importance of proper simulation of jet exit velocity conditions. LV data indicated unsteady turbulence levels in the ground vortex in excess of 70 percent.

  16. Fundamental research on convective heat transfer in electronic cooling technology

    NASA Astrophysics Data System (ADS)

    Ma, C. F.; Gan, Y. P.; Tian, Y. Q.; Lei, D. H.

    1992-03-01

    During the past six years comprehensive research programs have been conducted at the Beijing Polytechnic University to provide a better understanding of heat transfer characteristics of existing and condidate cooling techniques for electronic and microelectronic devices. This paper provides a review and summary of the programs with emphasis on direct liquid cooling. Included in this review are the heat transfer investigations related to the following cooling modes: liquid free, mixed and forced convection, liquid jet impingement, flowing liquid film cooling, pool boiling, spray cooling, foreign gas jet impingement in liquid pool, and forced convection air-cooling.

  17. Research on free and impinging jets for the development of STOL aircraft

    NASA Technical Reports Server (NTRS)

    Foss, J. F.; Kleis, S. J.

    1974-01-01

    The effect of the exit plane conditions on the initial region of an axisymmetric jet was systematically investigated. An essentially top-hat mean velocity profile and a homogeneous turbulence structure were maintained at the exit plane for eight distinct scale and intensity conditions. Mass and momentum flux values are independent of the exit turbulence structure for the range investigated; however, a significant (approximately 25%) increase in the latter implies a pronounced static pressure decrement inside the jet. Details of the velocity profile and turbulence structure are influenced by the exit plane conditions. The three radial-axial components of the Reynolds stress tensor have been conditionally sampled and are analyzed to show the initial condition effects.

  18. An Experimental Investigation of Ice-melting and heat transfer rates from submerged warm water jets upward impinging into ice-blocks as analogous for water-filled cavities formed during subglacial eruptions.

    NASA Astrophysics Data System (ADS)

    Jamshidnia, Hamidreza; Gudmundsson, Magnus Tumi

    2016-11-01

    Rates of energy transfer in water-filled cavities formed under glaciers by geothermal and volcanic activity are investigated by conducting experiments in which hot water jets (10°- 90°C) impinging into an ice block for jet Reynolds numbers in turbulent regime of 10000 -70000. It is found that heat flux is linearly dependent on jet flow temperature. Water jet melts a cavity into an ice block. Cavities had steep to vertical sides with a doming roof. Some of ice blocks used had trapped air bubbles. In these cases that melting of the ice could have led to trapping of air at the top of cavity, partially insulating the roof from hot water jet. The overall heat transfer rate in cavity formation varied with jet temperature from <100 kW m-2 to 900 kW m-2 while melting rates in the vertical direction yield heat transfer rates of 200-1200 kW m-2. Experimental heat transfer rates can be compared to data on subglacial melting observed for ice cauldrons in Iceland. For lowest temperatures the numbers are comparable to those for geothermal water in cool, subglacial water bodies and above subglacial flowpaths of jökulhlaups. Highest experimental rates for 80-90°C jets are 3-10 times less than inferred from observations of recent subglacial eruptions (2000-4000 kW m-2) . This can indicate that single phase liquid water convection alone may not be sufficient to explain the rates seen in recent subglacial eruptions, suggesting that forced 2 or 3 phase convection can be common.

  19. Cool and hot emission in a recurring active region jet

    NASA Astrophysics Data System (ADS)

    Mulay, Sargam M.; Zanna, Giulio Del; Mason, Helen

    2017-09-01

    Aims: We present a thorough investigation of the cool and hot temperature components in four recurring active region jets observed on July 10, 2015 using the Atmospheric Imaging Assembly (AIA), X-ray Telescope (XRT), and Interface Region Imaging Spectrograph (IRIS) instruments. Methods: A differential emission measure (DEM) analysis was performed on areas in the jet spire and footpoint regions by combining the IRIS spectra and the AIA observations. This procedure better constrains the low temperature DEM values by adding IRIS spectral lines. Plasma parameters, such as Doppler velocities, electron densities, nonthermal velocities and a filling factor were also derived from the IRIS spectra. Results: In the DEM analysis, significant cool emission was found in the spire and the footpoint regions. The hot emission was peaked at log T [K] = 5.6-5.9 and 6.5 respectively. The DEM curves show the presence of hot plasma (T = 3 MK) in the footpoint region. We confirmed this result by estimating the Fe XVIII emission from the AIA 94 Å channel which was formed at an effective temperature of log T [K] = 6.5. The average XRT temperatures were also found to be in agreement with log T [K] = 6.5. The emission measure (EM) was found to be three orders of magnitude higher in the AIA-IRIS DEM compared with that obtained using only AIA. The O IV (1399/1401 Å) electron densities were found to be 2.0×1010 cm-3 in the spire and 7.6 × 1010 cm-3 in the footpoint. Different threads along the spire show different plane-of-sky velocities both in the lower corona and transition region. Doppler velocities of 32 km s-1 (blueshifted) and 13 km s-1 (redshifted) were obtained in the spire and footpoint, respectively from the Si IV 1402.77 Å spectral line. Nonthermal velocities of 69 and 53 km s-1 were recorded in the spire and footpoint region, respectively. We obtained a filling factor of 0.1 in the spire at log T [K] = 5. Conclusions: The recurrent jet observations confirmed the presence of

  20. Heat transfer in two-dimensional jet impingement of a dielectric liquid on to a flat plate with uniform heat flux

    NASA Astrophysics Data System (ADS)

    Gil, C. B.; Su, G. S.; Chow, L. C.; Beam, J. E.

    1992-10-01

    Experiments were performed to investigate the convective heat transfer from a two-dimensional slot jet of the dielectric liquid PAO to a smooth 15.2 mm by 9.5 mm film resistor surface. The effects of nozzle width, nozzle-to-plate distance, impinging velocity, and liquid properties bave been examined. Heat transfer correlations and a discussion of relative parametric effects are provided.

  1. Jet-Cooled Emission Spectra of the Xylyl Radicals

    NASA Astrophysics Data System (ADS)

    Selco, J. I.; Carrick, P. G.

    1995-09-01

    Jet-cooled electronic emission spectra from ortho-, meta-, and para-xylyl (methylbenzyl) radicals have been recorded with a corona excited supersonic expansion (CESE) apparatus. A full vibronic analysis of the D1 → D0 transitions for all three isomers has been carried out, allowing for unambiguous assignments of the gas-phase ground state vibrational frequencies. For modes exhibiting progressions (numbering according to Green and Wilson) (11 (18a), 29 (6b), 10 (6a), 9 (1), 25 (3) and 5 (14) in ortho-xylyl; 10 (6b) in meta-xylyl; and 5 (1), 6 (6a), 3 (7a), and 17 (10a) in para-xylyl), anharmonicity constants are calculated and reported. Although CESE excitation of the xylenes (used in this study as precursors) did not result in the interconversion of isomers, it does occur along with homolytic methyl C-H bond dissociation during the formation of the radicals.

  2. Unsteady numerical simulation of a round jet with impinging microjets for noise suppression

    PubMed Central

    Lew, Phoi-Tack; Najafi-Yazdi, Alireza; Mongeau, Luc

    2013-01-01

    The objective of this study was to determine the feasibility of a lattice-Boltzmann method (LBM)-Large Eddy Simulation methodology for the prediction of sound radiation from a round jet-microjet combination. The distinct advantage of LBM over traditional computational fluid dynamics methods is its ease of handling problems with complex geometries. Numerical simulations of an isothermal Mach 0.5, ReD = 1 × 105 circular jet (Dj = 0.0508 m) with and without the presence of 18 microjets (Dmj = 1 mm) were performed. The presence of microjets resulted in a decrease in the axial turbulence intensity and turbulent kinetic energy. The associated decrease in radiated sound pressure level was around 1 dB. The far-field sound was computed using the porous Ffowcs Williams-Hawkings surface integral acoustic method. The trend obtained is in qualitative agreement with experimental observations. The results of this study support the accuracy of LBM based numerical simulations for predictions of the effects of noise suppression devices on the radiated sound power. PMID:23967931

  3. Unsteady numerical simulation of a round jet with impinging microjets for noise suppression.

    PubMed

    Lew, Phoi-Tack; Najafi-Yazdi, Alireza; Mongeau, Luc

    2013-09-01

    The objective of this study was to determine the feasibility of a lattice-Boltzmann method (LBM)-Large Eddy Simulation methodology for the prediction of sound radiation from a round jet-microjet combination. The distinct advantage of LBM over traditional computational fluid dynamics methods is its ease of handling problems with complex geometries. Numerical simulations of an isothermal Mach 0.5, Re(D) = 1 × 10(5) circular jet (D(j) = 0.0508 m) with and without the presence of 18 microjets (D(mj) = 1 mm) were performed. The presence of microjets resulted in a decrease in the axial turbulence intensity and turbulent kinetic energy. The associated decrease in radiated sound pressure level was around 1 dB. The far-field sound was computed using the porous Ffowcs Williams-Hawkings surface integral acoustic method. The trend obtained is in qualitative agreement with experimental observations. The results of this study support the accuracy of LBM based numerical simulations for predictions of the effects of noise suppression devices on the radiated sound power.

  4. Preparation of poly(MePEGCA-co-HDCA) nanoparticles with confined impinging jets reactor: experimental and modeling study.

    PubMed

    Lince, Federica; Bolognesi, Sara; Marchisio, Daniele L; Stella, Barbara; Dosio, Franco; Barresi, Antonello A; Cattel, Luigi

    2011-06-01

    In this work, the biodegradable copolymer poly(methoxypolyethyleneglycolcyanoacrylate-co-hexadecylcyanoacrylate) is used to prepare nanoparticles via solvent displacement in a confined impinging jets reactor (CIJR). For comparison, nanoparticles constituted by the homopolymer counterpart are also investigated. The CIJR is a small passive mixer in which very fast turbulent mixing of the solvent (i.e., acetone and tetrahydrofuran) and of the antisolvent (i.e., water) solutions occurs under controlled conditions. The effect of the initial copolymer concentration, solvent type, antisolvent-to-solvent ratio, and mixing rate inside the mixer on the final nanoparticle size distribution, surface properties, and morphology is investigated from the experimental point of view. The effect of some of these parameters is studied by means of a computational fluid dynamics (CFD) model, capable of quantifying the mixing conditions inside the CIJR. Results show that the CIJR can be profitably used for producing nanoparticles with controlled characteristics, that there is a clear correlation between the mixing rate calculated by CFD and the mean nanoparticle size, and therefore that CFD can be used to design, optimize, and scale-up these processes.

  5. Cratering Soil by Impinging Jets of Gas, with Application to Landing Rockets on Planetary Surfaces

    NASA Technical Reports Server (NTRS)

    Metzger, Philip T.; Vu, B. T.; Taylor, D. E.; Kromann, M. J.; Fuchs, M.; Yutko, B.; Dokos, A.; Immer, Christopher D.; Lane, J. E.; Dunkel, Michael B.; hide

    2007-01-01

    Several physical mechanisms are involved in excavating granular materials beneath a vertical jet of gas. These occur, for example, beneath the exhaust plume of a rocket landing on the soil of the Moon or Mars. A series of experiments and simulations have been performed to provide a detailed view of the complex gas/soil interactions. Measurements have also been taken from the Apollo lunar landing videos and from photographs of the resulting terrain, and these help to demonstrate how the interactions extrapolate into the lunar environment. It is important to understand these processes at a fundamental level to support the ongoing design of higher-fidelity numerical simulations and larger-scale experiments. These are needed to enable future lunar exploration wherein multiple hardware assets will be placed on the Moon within short distances of one another. The high-velocity spray of soil from landing spacecraft must be accurately predicted and controlled lest it erosively damage the surrounding hardware.

  6. Transpiring Cooling of a Scram-Jet Engine Combustion Chamber

    NASA Technical Reports Server (NTRS)

    Choi, Sang H.; Scotti, Stephen J.; Song, Kyo D.; Ries,Heidi

    1997-01-01

    The peak cold-wall heating rate generated in a combustion chamber of a scram-jet engine can exceed 2000 Btu/sq ft sec (approx. 2344 W/sq cm). Therefore, a very effective heat dissipation mechanism is required to sustain such a high heating load. This research focused on the transpiration cooling mechanism that appears to be a promising approach to remove a large amount of heat from the engine wall. The transpiration cooling mechanism has two aspects. First, initial computations suggest that there is a reduction, as much as 75%, in the heat flux incident on the combustion chamber wall due to the transpirant modifying the combustor boundary layer. Secondly, the heat reaching the combustor wall is removed from the structure in a very effective manner by the transpirant. It is the second of these two mechanisms that is investigated experimentally in the subject paper. A transpiration cooling experiment using a radiant heating method, that provided a heat flux as high as 200 Btu/sq ft sec ( approx. 234 W/sq cm) on the surface of a specimen, was performed. The experiment utilized an arc-lamp facility (60-kW radiant power output) to provide a uniform heat flux to a test specimen. For safety reasons, helium gas was used as the transpirant in the experiments. The specimens were 1.9-cm diameter sintered, powdered-stainless-steel tubes of various porosities and a 2.54cm square tube with perforated multi-layered walls. A 15-cm portion of each specimen was heated. The cooling effectivenes and efficiencies by transpiration for each specimen were obtained using the experimental results. During the testing, various test specimens displayed a choking phenomenon in which the transpirant flow was limited as the heat flux was increased. The paper includes a preliminary analysis of the transpiration cooling mechanism and a scaling conversion study that translates the results from helium tests into the case when a hydrogen medium is used.

  7. Fish mortality by impingement on the cooling-water intake screens of Britain's largest direct-cooled power station.

    PubMed

    Greenwood, M F D

    2008-04-01

    An estimated 5.66 x 10(7) fish (summed quarterly 95% confidence intervals: 3.01 x 10(7)-1.07 x 10(8)) weighing 258.4 t (143.2-467.9 t) were killed on the cooling-water intake screens of the 2400 MW Longannet Power Station (Forth estuary) in January 1999--December 2000. Abundance and number of species (40) collected were close to predictions for a power station of this size and latitude. Potential losses of equivalent adult whiting (Merlangius merlangus), cod (Gadus morhua), and plaice (Pleuronectes platessa) through deaths of juveniles were estimated at 353.1 t (208.0-603.2 t) worth approximately euro 429,266 (euro 246,592-752,765) in 1999--2000. Fish catch-per-trawl in the estuary was generally not noticeably greater during a year of low water withdrawal (coal miners' strike of 1984--1985) when compared to other years from 1982 to 2001, except for gobies (Pomatoschistus spp.). A fish-return system is being tested at Longannet to reduce mortality.

  8. Direct Flame Impingement

    SciTech Connect

    2005-09-01

    During the DFI process, high velocity flame jets impinge upon the material being heated, creating a high heat transfer rate. As a result, refractory walls and exhaust gases are cooler, which increases thermal efficiency and lowers NOx emissions. Because the jet nozzles are located a few inches from the load, furnace size can be reduced significantly.

  9. High-resolution photoabsorption spectrum of jet-cooled propyne

    SciTech Connect

    Jacovella, U.; Holland, D. M. P.; Boyé-Péronne, S.; Joyeux, D.; Archer, L. E.; Oliveira, N. de; Nahon, L.; Lucchese, R. R.; Xu, Hong; Pratt, S. T.

    2014-09-21

    The absolute photoabsorption cross section of propyne was recorded between 62 000 and 88 000 cm{sup −1} by using the vacuum-ultraviolet, Fourier-transform spectrometer at the Synchrotron Soleil. This cross section spans the region including the lowest Rydberg bands and extends above the Franck-Condon envelope for ionization to the ground electronic state of the propyne cation, X{sup ~+}. Room-temperature spectra were recorded in a flowing cell at 0.9 cm{sup −1} resolution, and jet-cooled spectra were recorded at 1.8 cm{sup −1} resolution and a rotational temperature of ∼100 K. The reduced widths of the rotational band envelopes in the latter spectra reveal new structure and simplify a number of assignments. Although nf Rydberg series have not been assigned previously in the photoabsorption spectrum of propyne, arguments are presented for their potential importance, and the assignment of one nf series is proposed. As expected from previous photoelectron spectra, Rydberg series are also observed above the adiabatic ionization threshold that converge to the v{sub 3}{sup +} = 1 and 2 levels of the C≡C stretching vibration.

  10. Free and Impinging Supersonic Microjets - An Experimental Study

    NASA Astrophysics Data System (ADS)

    Phalnikar, Koustubh; Alvi, Farrukh; Shih, Chiang

    2000-11-01

    Recent years have seen considerable research in the fluid dynamics of microjets due to their potential use in applications such as micro-propulsion, cooling of MEMS components and fine particle deposition and removal. To date, most of this work has been limited to low velocity flows. The present study examines supersonic microjets in the range of 50 - 400 microns with exit velocities in the range of 400-500 m/s. Such microjets are presently being used to actively control supersonic impinging jets which occur in STOVL (Short Takeoff and Vertical Landing) aircraft. The flow field is visualized using a lens based micro-Schlieren system with effective magnifications greater than 100 x. Schlieren images, which to the best of our knowledge have never before been obtained at this scale, clearly show the characteristic shock cell structure observed in large-scale jets. Based on these images, the jet is clearly supersonic as far as 10-12 diameters downstream. Quantitative measurements providing jet decay and spreading rates are also obtained via pressure surveys using micro-pitot probes. In addition to free microjets, the impingement of these supersonic microjets on flat surfaces is also studied. Based on visual data, the flow structure of impinging microjets strongly resembles that of larger, macro supersonic impinging jets.

  11. Design an efficient air impingement nozzle array

    SciTech Connect

    Steinberg, N.I.

    1995-08-01

    Direct air impingement is the most commonly used system for heating, cooling,and drying webs and films. Air impingement heat-transfer systems blow jets of air (or other gas) perpendicular to the web from an array of nozzles. These may be slot nozzles positioned across the web or a two-dimensional array of round nozzles, typically holes in a plate. Designing air impingement systems essentially means specifying the key geometric parameters that control the heat-transfer coefficient: slot width, slot-to-slot pitch, and slot-to-web stand-off distance, as well as some secondary parameters that affect heat transfer uniformity in the longitudinal and transverse directions. Slot nozzle array designs based on published optimization correlations usually have a near-maximum heat-transfer coefficient for a given impingement velocity, but an accessibly high nozzle area per unit impinged area. This increase construction and operating cost because the air volumes are too high. This article addresses that problem by providing a systematic design procedure along with the required design data.

  12. Femoroacetabular Impingement

    DTIC Science & Technology

    2008-04-01

    or pincer type impingement. On conventional radiographs, prominence of the anterolateral femoral head-neck junction, a “pistol grip deformity,” and...morphologic abnormalities of the hip. There are two types of FAI, termed cam impingement and pincer impingement, which have distinct imaging...to several different morphologic abnormalities of the hip. There are two types of FAI, termed cam impingement and pincer impingement. Though each

  13. Jet-Cooled Chlorofluorobenzyl Radicals: Spectroscopy and Mechanism

    NASA Astrophysics Data System (ADS)

    Yoon, Young; Lee, Sang

    2016-06-01

    Whereas the benzyl radical, a prototypic aromatic free radical, has been the subject of numerous spectroscopic studies, halo-substituted benzyl radicals have received less attention, due to the difficulties associated with production of radicals from precursors. In particular, chloro-substituted benzyl radicals have been much less studied because of the weak visible emission intensity and weak C-Cl bond dissociation energy. The jet-cooled chlorofluorobenzyl radicals were generated in a technique of corona excited supersonic jet expansion using a pinhole-type glass nozzle for the vibronic assignments and measurements of electronic energies of the D_1 → D_0 transition. The 2,4-,2.5-, and 2.6- chlorofluorobenzyl radicals were generated by corona discharge of corresponding precursors, chlorofluorotoluenes seeded in a large amount of helium carrier gas. The vibronic emission spectra were recorded with a long-path monochromator in the visible region. The emission spectra show the vibronic bands originating from two types of benzyl-type radicals, chlorofluorobenzyl and fluorobenzyl benzyl radicals, in which fluorobenzyl radicals were obtained by displacement of Cl by H produced by dissociation of methyl C-H bond. From the analysis of the spectra observed, we could determine the electronic energies in D_1 → D_0 transition and vibrational mode frequencies at the D_0 state of chlorofluorobenzyl radicals, which show the origin band of the electronic transition to be shifted to red region, comparing with the parental benzyl radical. From the quantitative analysis of the red-shift, it has been found that the additivity rule can be applied to dihalo-substituted benzyl radicals. In this presentation, the dissociation process of precursors in corona discharge is discussed in terms of bond dissociation energy as well as the spectroscopic analysis of the radicals. C. S. Huh, Y. W. Yoon, and S. K. Lee, J. Chem. Phys. 136, 174306 (2012). Y. W. Huh, S. Y. Chae, and S. K. Lee, Chem

  14. Active Control of Jets in Cross-Flow for Film Cooling Applications

    NASA Technical Reports Server (NTRS)

    Nikitopoulos, Dimitris E.

    2003-01-01

    Jets in cross-flow have applications in film cooling of gas turbine vanes, blades and combustor liners. Their cooling effectiveness depends on the extent to which the cool jet-fluid adheres to the cooled component surface. Lift-off of the cooling jet flow or other mechanisms promoting mixing, cause loss of cooling effectiveness as they allow the hot "free-stream" fluid to come in contact with the component surface. The premise of this project is that cooling effectiveness can be improved by actively controlling (e.9. forcing, pulsing) the jet flow. Active control can be applied to prevent/delay lift-off and suppress mixing. Furthermore, an actively controlled film-cooling system coupled with appropriate sensory input (e.g. temperature or heat flux) can adapt to spatial and temporal variations of the hot-gas path. Thus, it is conceivable that the efficiency of film-cooling systems can be improved, resulting in coolant fluid economy. It is envisioned that Micro Electro-Mechanical Systems (MEMS) will play a role in the realization of such systems. As a first step, a feasibility study will be conducted to evaluate the concept, identify actuation and sensory elements and develop a control strategy. Part of this study will be the design of a proof-of-concept experiment and collection of necessary data.

  15. Influence of the elliptical and circular orifices on the local heat transfer distribution of a flat plate impinged by under-expanded jets

    NASA Astrophysics Data System (ADS)

    Vinze, Ravish; Limeye, M. D.; Prabhu, S. V.

    2017-04-01

    Experimental study is carried out to explore the influence of nozzle profile on heat transfer for underexpanded impinging jets. Circular and elliptical orifices are used to generate underexpanded jets for underexpantion ratio ranging from 1.25 to 2.67. The supply pressure maintained in the present study ranges from 2.36 to 5.08 times the ambient pressure. IR thermal imaging camera is used to measure surface temperature of thin foil at different nozzle to plate distances. Shadowgraph and pressure distribution are used to understand the flow structure and distribution of circular and elliptical nozzle. It is observed that plate shock and pressure distribution over the plate have significant influence on the local heat transfer. The performance of the circular orifice is far better at lower z/d. The axis switching is observed for an elliptical orifice. Correlation for local heat transfer predicts Nusselt number comparable within 15 % of experimental results.

  16. Jet-Cooled Broad Range Near-Ir Scan of Reactive Intermediates Using Cavity Ringdown Spectroscopy

    NASA Astrophysics Data System (ADS)

    Kline, Neal D.; Codd, Terrance J.; Chen, Ming-Wei; Miller, Terry A.

    2012-06-01

    A technique has been developed for obtaining broad range scans of jet-cooled radicals using cavity ringdown spectroscopy. The talk will describe a method that uses a slit jet expansion in tandem with an electrical discharge to produce the reactive intermediates and obtain rotational temperatures of 15-30 K and effective vibrational temperatures of 0 K. The spectrum can be recorded by scanning the second stokes of an H_2 Raman shifted YAG-pumped dye laser with bandwidth of ≈ 0.1 cm-1. This technique has been used to obtain the jet-cooled widetilde{A} - widetilde{X} spectra of the NO_3 radical and the 2,1-hydroxypropyl peroxy radical (2,1-HPP). Obtaining the jet-cooled spectra helped to identify hot bands present in the room temperature spectrum of NO_3 and also helped to identify cold, low-frequency fundamental bands present in the 2,1-HPP spectrum.

  17. Combustion of LOX with H2(sub g) under subcritical, critical, and supercritical conditions and experimental observation of dense spray and mixing of impinging jets

    NASA Technical Reports Server (NTRS)

    Kuo, Kenneth K.; Hsieh, W. H.; Yang, A. S.; Brown, J. J.; Cheung, F. B.; Woodward, R. D.; Kline, M. C.

    1992-01-01

    Progress made during the period of February 1 to October 15, 1992 is reported. The overall objective of Task 1 of the investigation is to achieve a better understanding of the combustion processes of liquid oxygen and gaseous hydrogen under subcritical, critical, and supercritical conditions. Specific objectives of the research program are: (1) to determine the evaporation- and burning-rate characteristics of LOX in hydrogen/helium environments under broad ranges of operating conditions; (2) to measure species concentration profile and surface temperature of LOX employing the gas chromatography and fine-wire thermocouples under non-reacting flow situations; (3) to perform a fugacity-based multicomponent thermodynamic phase equilibrium analysis for examining the high-pressure vapor-liquid equilibrium behavior at the liquid surface of LOX; (4) to formulate and solve a theoretical model for simulating the evaporation and combustion processes in a LOX/H2/He system; and (5) to validate the theoretical model with the measured experimental data. Task 2 of the investigation is described. Observation of a like-on-like injector element in the near-injector region performed in the previous phase of this project has identified the existence of a high Reynolds number regime in which the pre-impingement jets are fully turbulent and undergoing surface breakup. The new spray regime, which has not been observed by previous investigators, is characterized by the presence of many fine droplets and the disappearance of the well-defined liquid breakup wave pattern in the post-impingement region. It is speculated that a cavitating region may be present within the orifice so that it could induce strong turbulence, leading to an onset of atomization of the jets prior to impingement. To further investigate the dense spray behavior of the impinging jets in the high Reynolds number region, experiments were conducted using Plexiglas injector components for direct internal flow observation

  18. Experimental investigation of cross-over jets in a rib-roughened trailing-edge cooling channel

    NASA Astrophysics Data System (ADS)

    Xue, Fei

    Increasing the rotor inlet temperature can dramatically increase the efficiency and power output of the gas turbine engine. However, the melting point of turbine blade material limits the realistic upper bound of the rotor inlet temperature. As a result, the development of high temperature turbine blade material and advanced turbine blade cooling technology determines the future of turbine blade engine. Adding impingement jet holes and rib turbulators in the inner cooling channel of the gas turbine blades are two effective ways to enhance the cooling effects. The purpose of this study is to figure out the influence of different combinations of jet holes and rib turbulators on the heat transfer efficiency. A tabletop scale test model is used in the study to simulate the cooling cavity of trailing edge and its feed channel in a real gas turbine blade. The Dimensional Analysis Theory is used in the study to eliminate the influence of scaling. Two different crossover slots are tested with 5 different rib arrangements, and each of the test geometries is tested for 6 jet Reynolds numbers ranging from 10,000 to 36,000. The two different crossover slots are the crossover slots with 0 and 5 degree tilt angles. The four different rib arrangements are ribs with 0 degree, 45 degree, 90 degree and 135 degree angles of attack with respect to the flow direction. Furthermore, a smooth test section (no ribs) was also tested. The steady state liquid crystal thermography is used to quantify the heat transfer performance of the target areas. The variation of Nusselt number versus Reynolds number is plotted for each of the 10 geometries. Also, the variation of Nusselt number versus Reynolds number are compared for different rib angles of attack with the same crossover slot tilt angle, and between different crossover slots tilt angles with the same rib angle. The results show that, the area-weighted average Nusselt number increases monotonically with the Reynolds number; the target

  19. Comparison of temperature data from a four-vane static cascade and a research gas turbine engine for a chordwise-finned, impingement- and film-cooled vane

    NASA Technical Reports Server (NTRS)

    Gladden, H. J.; Livingood, J. N. B.; Gauntner, D. J.

    1972-01-01

    Experimental heat-transfer data obtained for a chordwise-finned, impingement- and film-cooled turbine vane tested in a four-vane static cascade to a gas temperature and a gas pressure of 2250 F and 80 psia, respectively, are presented. Average and local vane temperatures are correlated and compared with correlations of temperature data obtained from tests of the same vane in a modified J-75 turbojet engine. The measured vane temperatures obtained from these tests in the two test stands are also compared with analytically determined temperatures.

  20. Comparison of heat-transfer test data for a chordwise-finned, impingement-cooled turbine vane tested in a four-vane cascade and a research engine

    NASA Technical Reports Server (NTRS)

    Gladden, H. J.; Yeh, F. C.

    1972-01-01

    The heat-transfer characteristics of a chordwise-finned, impingement-cooled vane were investigated in both a modified J-57 research engine and a four-vane cascade. The data were compared by a correlation of temperature difference ratio with coolant- to gas-flow ratio and also by two modifications of this correlation. The results indicated that the cascade vane temperature data can generally be used to represent the engine vane temperature data. A discussion of engine and cascade gas-side heat-transfer coefficients is also presented. A redesign of the vane leading edge could significantly increase the potential turbine-inlet temperature operating limit.

  1. On sound generated by gas-jet impingement on a bubbly gas-water interface, with application to supercavity self-noise

    NASA Astrophysics Data System (ADS)

    Gilbert, J. B.; Howe, M. S.; Koch, R. M.

    2012-09-01

    An analysis is made of the sound produced when a high speed turbulent gas jet impinges at normal incidence on a planar gas-water interface in the presence of a uniform, thin homogeneous bubble layer between the gas and the water. It is shown that the bubble layer exhibits a behaviour similar to a 'quarter-wave' resonator, storing energy supplied by gas impingement which is subsequently released as high amplitude sound into the water. In the absence of bubbles the radiation into the water has dipole characteristics, peaking strongly in the direction normal to the interface. The bubbles diffuse this sharp dipole lobe, and are predicted to increase the sound power in the water by up to 10 dB or more over a range of intermediate frequencies when the layer properties are similar to those encountered in experiments using a model scale supercavitating vehicle. At higher frequencies, in the range important for vehicle guidance and control, the bubble layer tends to reduce this source of self-noise. The same mechanism of resonant amplification should be effective more generally, when the bubbles lie within a more confined surface envelope, such as the surface 'wake' of the jet impact zone, whose shape defines a different set of interior eigenmodes.

  2. Experimental study of cooling performance of pneumatic synthetic jet with singular slot rectangular orifice

    NASA Astrophysics Data System (ADS)

    Yu, Roger Ho Zhen; Ismail, Mohd Azmi bin; Ramdan, Muhammad Iftishah; Mustaffa, Nur Musfirah binti

    2017-03-01

    Synthetic Jet generates turbulence flow in cooling the microelectronic devices. In this paper, the experiment investigation of the cooling performance of pneumatic synthetic jet with single slot rectangular orifices at low frequency motion is presented. The velocity profile at the end of the orifice was measured and used as characteristic performance of synthetic jet in the present study. Frequencies of synthetic jet and the compressed air pressure supplied to the pneumatic cylinder (1bar to 5bar) were the parameters of the flow measurement. The air velocity of the synthetic jet was measured by using anemometer air flow meter. The maximum air velocity was 0.5 m/s and it occurred at frequency motion of 8 Hz. The optimum compressed air supplied pressure of the synthetic jet study was 4 bar. The cooling performance of synthetic jet at several driven frequencies from 0 Hz to 8 Hz and heat dissipation between 2.5W and 9W were also investigate in the present study. The results showed that the Nusselt number increased and thermal resistance decreased with both frequency and Reynolds number. The lowest thermal resistance was 5.25°C/W and the highest Nusselt number was 13.39 at heat dissipation of 9W and driven frequency of 8Hz.

  3. Liquid film target impingement scrubber

    DOEpatents

    McDowell, William J.; Coleman, Charles F.

    1977-03-15

    An improved liquid film impingement scrubber is provided wherein particulates suspended in a gas are removed by jetting the particle-containing gas onto a relatively small thin liquid layer impingement target surface. The impingement target is in the form of a porous material which allows a suitable contacting liquid from a pressurized chamber to exude therethrough to form a thin liquid film target surface. The gas-supported particles collected by impingement of the gas on the target are continuously removed and flushed from the system by the liquid flow through each of a number of pores in the target.

  4. Into Mesh Lubrication of Spur Gears with Arbitrary Offset Oil Jet. 2: for Jet Velocities Equal to or Greater than Great Velocity

    NASA Technical Reports Server (NTRS)

    Akin, L. S.; Townsend, D. P.

    1982-01-01

    An analysis was conducted for into mesh oil jet lubrication with an arbitrary offset and inclination angle from the pitch point for the case where the oil jet velocity is equal to or greater than gear pitch line velocity. Equations were developed for minimum and maximum oil jet impingement depth. The analysis also included the minimum oil jet velocity required to impinge on the gear or pinion and the optimum oil jet velocity required to obtain the best lubrication condition of maximum impingement depth and gear cooling. It was shown that the optimum oil jet velocity for best lubrication and cooling is when the oil jet velocity equals the gear pitch line velocity. When the oil jet velocity is slightly greater than the pitch line velocity the loaded side of the driven gear and the unloaded side of the pinion receive the best lubrication and cooling with slightly less impingement depth. As the jet velocity becomes much greater than the pitch line velocity the impingement depth is considerably reduced and may completely miss the pinion.

  5. Characteristics of the air supply envelop of the cooled flooded air jet

    NASA Astrophysics Data System (ADS)

    Timofeevskiy, A. L.; Sulin, A. B.; Ryabova, T. N.; Neganov, D. V.

    2017-08-01

    The characteristics of a plane-parallel non-isothermal airflow (which is fed into the room in the form of a flooded jet) were investigated,. The temperature and velocity fields were measured experimentally in the cross section of the supply air flare. The results of the theoretical calculation and numerical simulation of temperature and velocity profiles were compared with experimental data in a flat cooled supply jet.

  6. Numerical investigation on laminar round-jet impinging on a surface at uniform heat flux in a channel partially filled with a porous medium

    NASA Astrophysics Data System (ADS)

    Buonomo, B.; Diana, A.; Manca, O.; Nardini, S.

    2017-01-01

    Horizontal channel partially filled with porous media and a single round jet impinging on the porous medium are numerically investigated. The wall facing the round jet is partially heated at uniform heat flux. A two-dimensional axial symmetric flow in the channel is assumed to evaluate the thermal behavior within the channel. The analysis in the porous medium is accomplished in local thermal equilibrium conditions and under the Brinkman–Forchheimer-extended Darcy law assumption. The problem is solved employing the Ansys-Fluent code. Results are given in terms of stream function and temperature fields of fluid and solid matrix, wall temperature profiles, air velocity and temperature profiles along the transversal section of channel. The Peclet number ranges from 1 to 1000 and Rayleigh number values are 10, 50, 100 and 1000. Reynolds jet number, solid wall distance and wall heat flux effects on thermal and fluid dynamic behaviors are investigated. Results indicate that Nusselt number has the highest value for the channel with a porous medium of thickness equal to the channel gap, whereas it presents very small changes increasing the porous medium length on the heated wall. Correlations among average Nusselt, Peclet and Rayleigh numbers are proposed.

  7. Experiments With Radiatively Cooled Supersonic Plasma Jets Generated in Conical Wire Array Z-Pinches

    NASA Astrophysics Data System (ADS)

    Lebedev, S. V.; Ampleford, D. J.; Bland, S. N.; Chittenden, J. P.; Ciardi, A.; Naz, N.; Haines, M. G.; Frank, A.; Blackman, E.; Gardiner, T.

    2002-12-01

    We present results of astrophysically relevant experiments where highly supersonic plasma jets are generated via conically convergent plasma flows in a conical wire array Z-pinch. Stagnation of plasma flow on the axis of symmetry forms a standing conical shock effectively collimating the flow in the axial direction. This scenario is essentially similar to that discussed by Canto and collaborators [1] as a purely hydrodynamic mechanism for jet formation in astrophysical systems. Experiments using different materials (Al, Fe and W) show that a hypersonic (M ~ 20), well-collimated jet is generated when the radiative cooling rate of the plasma is significant.

  8. Astrophysical Jets with Conical Wire Arrays: Radiative Cooling, Rotation and Deflection

    SciTech Connect

    Ampleford, D. J.; Jennings, C. A.; Lebedev, S. V.; Bland, S. N.; Hall, G. N.; Suzuki-Vidal, F.; Palmer, J. B. A.; Chittenden, J. P.; Ciardi, A.; Bott, S. C.

    2009-01-21

    Highly collimated outflows or jets are produced by a number of astrophysical objects including protostars. The morphology and collimation of these jets is thought to be strongly influenced by the effects of radiative cooling, angular momentum and the interstellar medium surrounding the jet. Astrophysically relevant experiments are performed with conical wire array z-pinches investigating each of these effects. It is possible in each case to enter the appropriate parameter regime, leading the way towards future experiments where these different techniques can be more fully combined.

  9. Numerical optimization of a multi-jet cooling system for the blown film extrusion

    NASA Astrophysics Data System (ADS)

    Janas, M.; Wortberg, J.

    2015-05-01

    The limiting factor for every extrusion process is the cooling. For the blown film process, this task is usually done by means of a single or dual lip air ring. Prior work has shown that two major effects are responsible for a bad heat transfer. The first one is the interaction between the jet and the ambient air. It reduces the velocity of the jet and enlarges the straight flow. The other one is the formation of a laminar boundary layer on the film surface due to the fast flowing cooling air. In this case, the boundary layer isolates the film and prevents an efficient heat transfer. To improve the heat exchange, a novel cooling approach is developed, called Multi-Jet. The new cooling system uses several slit nozzles over the whole tube formation zone for cooling the film. In contrast to a conventional system, the cooling air is guided vertically on the film surface in different heights to penetrate the boundary sublayer. Simultaneously, a housing of the tube formation zone is practically obtained to reduce the interaction with the ambient air. For the numerical optimization of the Multi-Jet system, a new procedure is developed. First, a prediction model identifies a worth considering cooling configuration. Therefore, the prediction model computes a film curve using the formulation from Zatloukal-Vlcek and the energy balance for the film temperature. Thereafter, the optimized cooling geometry is investigated in detail using a process model for the blown film extrusion that is able to compute a realistic bubble behavior depending on the cooling situation. In this paper, the Multi-Jet cooling system is numerically optimized for several different process states, like mass throughputs and blow-up ratios using one slit nozzle setting. For each process condition, the best cooling result has to be achieved. Therefore, the height of any nozzle over the tube formation zone is adjustable. The other geometrical parameters of the cooling system like the nozzle diameter or the

  10. Design and Testing of an Automated System using Thermochromatic Liquid Crystals to Determine Local Heat Transfer Coefficients for an Impinging Jet

    NASA Technical Reports Server (NTRS)

    Tan, Benjamin

    1995-01-01

    Using thermochromatic liquid crystal to measure surface temperature, an automated transient method with time-varying free-stream temperature is developed to determine local heat transfer coefficients. By allowing the free-stream temperature to vary with time, the need for complicated mechanical components to achieve a step temperature change is eliminated, and by using the thermochromatic liquid crystals as temperature indicators, the labor intensive task of installing many thermocouples is omitted. Bias associated with human perception of the transition of the thermochromatic liquid crystal is eliminated by using a high speed digital camera and a computer. The method is validated by comparisons with results obtained by the steady-state method for a circular Jet impinging on a flat plate. Several factors affecting the accuracy of the method are evaluated.

  11. Jet impinging onto a laser drilled tapered hole: Influence of tapper location on heat transfer and skin friction at hole surface

    NASA Astrophysics Data System (ADS)

    Shuja, S. Z.; Yilbas, B. S.

    2013-02-01

    Jet emerging from a conical nozzle and impinging onto a tapered hole in relation to laser drilling is investigated and the influence taper location on the heat transfer and skin friction at the hole wall surface is examined. The study is extended to include four different gases as working fluid. The Reynolds stress model is incorporated to account for the turbulence effect in the flow field. The hole wall surface temperature is kept at 1500 K to resemble the laser drilled hole. It is found that the location of tapering in the hole influences the heat transfer rates and skin friction at the hole wall surface. The maximum skin friction coefficient increases for taper location of 0.25 H, where H is the thickness of the workpiece, while Nusselt number is higher in the hole for taper location of 0.75 H.

  12. Rapid preparation of high electrochemical performance LiFePO4/C composite cathode material with an ultrasonic-intensified micro-impinging jetting reactor.

    PubMed

    Dong, Bin; Huang, Xiani; Yang, Xiaogang; Li, Guang; Xia, Lan; Chen, George

    2017-11-01

    A joint chemical reactor system referred to as an ultrasonic-intensified micro-impinging jetting reactor (UIJR), which possesses the feature of fast micro-mixing, was proposed and has been employed for rapid preparation of FePO4 particles that are amalgamated by nanoscale primary crystals. As one of the important precursors for the fabrication of lithium iron phosphate cathode, the properties of FePO4 nano particles significantly affect the performance of the lithium iron phosphate cathode. Thus, the effects of joint use of impinging stream and ultrasonic irradiation on the formation of mesoporous structure of FePO4 nano precursor particles and the electrochemical properties of amalgamated LiFePO4/C have been investigated. Additionally, the effects of the reactant concentration (C=0.5, 1.0 and 1.5molL(-1)), and volumetric flow rate (V=17.15, 51.44, and 85.74mLmin(-1)) on synthesis of FePO4·2H2O nucleus have been studied when the impinging jetting reactor (IJR) and UIJR are to operate in nonsubmerged mode. It was affirmed from the experiments that the FePO4 nano precursor particles prepared using UIJR have well-formed mesoporous structures with the primary crystal size of 44.6nm, an average pore size of 15.2nm, and a specific surface area of 134.54m(2)g(-1) when the reactant concentration and volumetric flow rate are 1.0molL(-1) and 85.74mLmin(-1) respectively. The amalgamated LiFePO4/C composites can deliver good electrochemical performance with discharge capacities of 156.7mAhg(-1) at 0.1C, and exhibit 138.0mAhg(-1) after 100 cycles at 0.5C, which is 95.3% of the initial discharge capacity. Copyright © 2017. Published by Elsevier B.V.

  13. A simple counter-flow cooling system for a supersonic free-jet beam source assembly

    NASA Astrophysics Data System (ADS)

    Barr, M.; Fahy, A.; Martens, J.; Dastoor, P. C.

    2016-05-01

    A simple design for an inexpensive, cooled, free-jet beam source is described. The source assembly features an integrated cooling system as supplied by a counter-flow of chilled nitrogen, and is composed primarily of off-the-shelf tube fittings. The design facilitates rapid implementation and eases subsequent alignment with respect to any downstream beamline aperture. The source assembly outlined cools the full length of the stagnation volume, offering temperature control down to 100 K and long-term temperature stability better than ±1 K.

  14. A simple counter-flow cooling system for a supersonic free-jet beam source assembly.

    PubMed

    Barr, M; Fahy, A; Martens, J; Dastoor, P C

    2016-05-01

    A simple design for an inexpensive, cooled, free-jet beam source is described. The source assembly features an integrated cooling system as supplied by a counter-flow of chilled nitrogen, and is composed primarily of off-the-shelf tube fittings. The design facilitates rapid implementation and eases subsequent alignment with respect to any downstream beamline aperture. The source assembly outlined cools the full length of the stagnation volume, offering temperature control down to 100 K and long-term temperature stability better than ±1 K.

  15. Transpiration cooling in the locality of a transverse fuel jet for supersonic combustors

    NASA Astrophysics Data System (ADS)

    Northam, G. Burton; Capriotti, Diego P.; Byington, Carl S.

    1990-07-01

    The objective of the current work was to determine the feasibility of transpiration cooling for the relief of the local heating rates in the region of a sonic, perpendicular, fuel jet of gaseous hydrogen. Experiments were conducted to determine the interaction between the cooling required and flameholding limits of a transverse jet in a high-enthalpy, Mach 3 flow in both open-jet and direct-connect test mode. Pulsed shadowgraphs were used to illustrate the flow field. Infrared thermal images indicated the surface temperatures, and the OH(-) emission of the flame was used to visualize the limits of combustion. Wall, static presures indicated the location of the combustion within the duct and were used to calculate the combustion efficiency. The results from both series of tests at facility total temperatures of 1700 K and 2000 K are presented.

  16. Transpiration cooling in the locality of a transverse fuel jet for supersonic combustors

    NASA Technical Reports Server (NTRS)

    Northam, G. Burton; Capriotti, Diego P.; Byington, Carl S.

    1990-01-01

    The objective of the current work was to determine the feasibility of transpiration cooling for the relief of the local heating rates in the region of a sonic, perpendicular, fuel jet of gaseous hydrogen. Experiments were conducted to determine the interaction between the cooling required and flameholding limits of a transverse jet in a high-enthalpy, Mach 3 flow in both open-jet and direct-connect test mode. Pulsed shadowgraphs were used to illustrate the flow field. Infrared thermal images indicated the surface temperatures, and the OH(-) emission of the flame was used to visualize the limits of combustion. Wall, static presures indicated the location of the combustion within the duct and were used to calculate the combustion efficiency. The results from both series of tests at facility total temperatures of 1700 K and 2000 K are presented.

  17. Severe local hypothermia from laparoscopic gas evaporative jet cooling: a mechanism to explain clinical observations.

    PubMed

    Gray, R I; Ott, D E; Henderson, A C; Cochran, S A; Roth, E A

    1999-01-01

    Explanations for laparoscopic-induced hypothermia fail to explain clinical observations. It is possible that water evaporation occurs from the jet stream of gas inflation resulting in tissue surface super-cooling leading to tissue damage and drying. Theoretical calculations based on thermal conductivity, mass transfer effects and heat flux considerations correlated closely with synthetic and tissue experiments. Thermocouple measurements at a rate of 15 data points per second were performed. Cooling rates of 10 to 25 degrees centigrade per second for high flow rates were found based on gas flow rate and effective size of gas delivery site. These rapid temperature drops extended beyond a 2 cm2 diameter. Evaporative cooling accounts for significant hypothermia. The cooling is dependent on the lack of water vapor in the gases currently used during laparoscopy. Cooling rates are independent of height from tissue and geometry of delivery port. Heating and hydrating the gas to a physiologic condition eliminates hypothermia and tissue dessication.

  18. Design, Fabrication, and Testing of an Auxiliary Cooling System for Jet Engines

    NASA Technical Reports Server (NTRS)

    Leamy, Kevin; Griffiths, Jim; Andersen, Paul; Joco, Fidel; Laski, Mark; Balser, Jeffrey (Technical Monitor)

    2001-01-01

    This report summarizes the technical effort of the Active Cooling for Enhanced Performance (ACEP) program sponsored by NASA. It covers the design, fabrication, and integrated systems testing of a jet engine auxiliary cooling system, or turbocooler, that significantly extends the use of conventional jet fuel as a heat sink. The turbocooler is designed to provide subcooled cooling air to the engine exhaust nozzle system or engine hot section. The turbocooler consists of three primary components: (1) a high-temperature air cycle machine driven by engine compressor discharge air, (2) a fuel/ air heat exchanger that transfers energy from the hot air to the fuel and uses a coating to mitigate fuel deposits, and (3) a high-temperature fuel injection system. The details of the turbocooler component designs and results of the integrated systems testing are documented. Industry Version-Data and information deemed subject to Limited Rights restrictions are omitted from this document.

  19. Combined Effects of Wakes and Jet Pulsing on Film Cooling

    DTIC Science & Technology

    2008-10-01

    water as a refer- ence. Constant current cold- wire and constant temperature hot - wire anemometry were used to measure flow temperature and velocity...Temperature measurements were made using an infrared camera, thermocouples, and constant current (cold wire ) anemometry . The local film cooling effectiveness...and heat transfer coefficient were de- termined from the measured temperatures. Phase locked flow temperature fields were determined from cold- wire

  20. Combined Effects of Wakes and Jet Pulsing on Film Cooling

    DTIC Science & Technology

    2008-08-01

    water as a refer- ence. Constant current cold- wire and constant temperature hot - wire anemometry were used to measure flow temperature and velocity...Temperature measurements were made using an infrared camera, thermocouples, and constant current (cold wire ) anemometry . The local film cooling effectiveness...and heat transfer coefficient were de- termined from the measured temperatures. Phase locked flow temperature fields were determined from cold- wire

  1. Laboratory Astrophysics and Collimated Stellar Outflows: The Production of Radiatively Cooled Hypersonic Plasma Jets

    NASA Astrophysics Data System (ADS)

    Lebedev, S. V.; Chittenden, J. P.; Beg, F. N.; Bland, S. N.; Ciardi, A.; Ampleford, D.; Hughes, S.; Haines, M. G.; Frank, A.; Blackman, E. G.; Gardiner, T.

    2002-01-01

    We present the first results of astrophysically relevant experiments where highly supersonic plasma jets are generated via conically convergent flows. The convergent flows are created by electrodynamic acceleration of plasma in a conical array of fine metallic wires (a modification of the wire array Z-pinch). Stagnation of plasma flow on the axis of symmetry forms a standing conical shock effectively collimating the flow in the axial direction. This scenario is essentially similar to that discussed by Cantó and collaborators as a purely hydrodynamic mechanism for jet formation in astrophysical systems. Experiments using different materials (Al, Fe, and W) show that a highly supersonic (M~20), well-collimated jet is generated when the radiative cooling rate of the plasma is significant. We discuss scaling issues for the experiments and their potential use for numerical code verification. The experiments also may allow direct exploration of astrophysically relevant issues such as collimation, stability, and jet-cloud interactions.

  2. Research into the process of impingement of two plane jets of an ideal fluid with free boundaries

    NASA Astrophysics Data System (ADS)

    Baskakov, V. D.; Karnaukhov, K. A.

    2016-07-01

    The problem of finding parameters stationary jets, outgoing from a place of impact of two incoming flat ideal jets with free boundaries and possessing the identical speed, but various width, has no decision. Various models are widely used for a conclusion of the missing equation now, but they lead to contradictory results. The new model is offered. Adequacy to the offered model was checked by comparison results with data of the numerical calculations in ANSYS AUTODYN. The dependence approximating results of numerical calculations is developed to increase accuracy in calculations of angular provision of the internal outgoing jet.First of all, the executed researches are interesting to experts, who works on behavior low- value technological errors in shaped charges.

  3. Recent developments in turbine blade internal cooling.

    PubMed

    Han, J C; Dutta, S

    2001-05-01

    This paper focuses on turbine blade internal cooling. Internal cooling is achieved by passing the coolant through several rib-enhanced serpentine passages inside the blade and extracting the heat from the outside of the blades. Both jet impingement and pin-fin-cooling are also used as a method of internal cooling. In the past number of years there has been considerable progress in turbine blade internal cooling research and this paper is limited to reviewing a few selected publications to reflect recent developments in turbine blade internal cooling.

  4. Corrosion studies of carbon steel under impinging jets of simulated slurries of neutralized current acid waste (NCAW) and neutralized cladding removal waste (NCRW)

    SciTech Connect

    Smith, H.D.; Elmore, M.R.

    1992-01-01

    Plans for the disposal of radioactive liquid and solid wastes presently stored in double-shell tanks at the Hanford Site call for retrieval and processing of the waste to create forms suitable for permanent disposal. Waste will be retrieved from a tank using a submerged slurry pump in conjunction with one or more rotating slurry jet mixer pumps. Pacific Northwest Laboratory (PNL) has conducted tests using simulated waste slurries to assess the effects of a impinging slurry jet on the corrosion rate of the tank wall and floor, an action that could potentially compromise the tank's structural integrity. Corrosion processes were investigated on a laboratory scale with a simulated neutralized cladding removal waste (NCRW) slurry and in a subsequent test with simulated neutralized current acid waste (NCAW) slurry. The test slurries simulated the actual NCRW and NCAW both chemically and physically. The tests simulated those conditions expected to exist in the respective double-shell tanks during waste retrieval operations. Results of both tests indicate that, because of the action of the mixer pump slurry jets, the waste retrieval operations proposed for NCAW and NCRW will moderately accelerate corrosion of the tank wall and floor. Based on the corrosion of initially unoxidized test specimens, and the removal of corrosion products from those specimens, the maximum time-averaged corrosion rates of carbon steel in both waste simulants for the length of the test was {approximately}4 mil/yr. The protective oxide layer that exists in each storage tank is expected to inhibit corrosion of the carbon steel.

  5. Corrosion studies of carbon steel under impinging jets of simulated slurries of neutralized current acid waste (NCAW) and neutralized cladding removal waste (NCRW)

    SciTech Connect

    Smith, H.D.; Elmore, M.R.

    1992-01-01

    Plans for the disposal of radioactive liquid and solid wastes presently stored in double-shell tanks at the Hanford Site call for retrieval and processing of the waste to create forms suitable for permanent disposal. Waste will be retrieved from a tank using a submerged slurry pump in conjunction with one or more rotating slurry jet mixer pumps. Pacific Northwest Laboratory (PNL) has conducted tests using simulated waste slurries to assess the effects of a impinging slurry jet on the corrosion rate of the tank wall and floor, an action that could potentially compromise the tank`s structural integrity. Corrosion processes were investigated on a laboratory scale with a simulated neutralized cladding removal waste (NCRW) slurry and in a subsequent test with simulated neutralized current acid waste (NCAW) slurry. The test slurries simulated the actual NCRW and NCAW both chemically and physically. The tests simulated those conditions expected to exist in the respective double-shell tanks during waste retrieval operations. Results of both tests indicate that, because of the action of the mixer pump slurry jets, the waste retrieval operations proposed for NCAW and NCRW will moderately accelerate corrosion of the tank wall and floor. Based on the corrosion of initially unoxidized test specimens, and the removal of corrosion products from those specimens, the maximum time-averaged corrosion rates of carbon steel in both waste simulants for the length of the test was {approximately}4 mil/yr. The protective oxide layer that exists in each storage tank is expected to inhibit corrosion of the carbon steel.

  6. The cool component and the dichotomy, lateral expansion, and axial rotation of solar X-ray jets

    SciTech Connect

    Moore, Ronald L.; Sterling, Alphonse C.; Falconer, David A.; Robe, Dominic

    2013-06-01

    We present results from a study of 54 polar X-ray jets that were observed in coronal X-ray movies from the X-ray Telescope on Hinode and had simultaneous coverage in movies of the cooler transition region (T ∼ 10{sup 5} K) taken in the He II 304 Å band of the Atmospheric Imaging Assembly (AIA) on Solar Dynamics Observatory. These dual observations verify the standard-jet/blowout-jet dichotomy of polar X-ray jets previously found primarily from XRT movies alone. In accord with models of blowout jets and standard jets, the AIA 304 Å movies show a cool (T ∼ 10{sup 5} K) component in nearly all blowout X-ray jets and in a small minority of standard X-ray jets, obvious lateral expansion in blowout X-ray jets but none in standard X-ray jets, and obvious axial rotation in both blowout X-ray jets and standard X-ray jets. In our sample, the number of turns of axial rotation in the cool-component standard X-ray jets is typical of that in the blowout X-ray jets, suggesting that the closed bipolar magnetic field in the jet base has substantial twist not only in all blowout X-ray jets but also in many standard X-ray jets. We point out that our results for the dichotomy, lateral expansion, and axial rotation of X-ray jets add credence to published speculation that type-II spicules are miniature analogs of X-ray jets, are generated by granule-size emerging bipoles, and thereby carry enough energy to power the corona and solar wind.

  7. Evaporative cooling by a pulsed jet spray of binary ethanol-water mixture

    NASA Astrophysics Data System (ADS)

    Karpov, P. N.; Nazarov, A. D.; Serov, A. F.; Terekhov, V. I.

    2015-07-01

    We have experimentally studied the heat transfer under conditions of pulsed multinozzle jet spray impact onto a vertical surface. The working coolant fluid was aqueous ethanol solution in a range of concentrations K 1 = 0-96%. The duration of spray pulses was τ = 2, 4, and 10 ms at a repetition frequency of 10 Hz. The maximum heat transfer coefficient was achieved at an ethanol solution concentration within 50-60%. The thermal efficiency of pulsed spray cooling grows with increasing ethanol concentration and decreasing jet spray pulse duration.

  8. High-sensitivity laser spectroscopy with atoms from a cooled helium jet

    SciTech Connect

    Lewis, D.A.; Evans, R.M.; Davids, C.N.; Finn, M.A.; Kaufman, S.L.; Greenlees, G.W.

    1983-01-01

    We have developed a cryogenic He-jet system which efficiently transports radioactive atoms produced on-line at the Argonne National Laboratory Tandem-Linac Accelertor away from the production region and forms them into a cool atomic beam. This atomic beam will be probed with high sensitivity laser spectroscopy using the photon burst method. The ultimate goal of this work is to determine the sizes, shapes, and magnetic moments of short-lived nuclei through their atomic hyperfine structure. Preliminary measurements with the He-jet system and the adaption of the photon burst method to this new geometry are described.

  9. Interaction of radiatively cooled plasma jets with static gas and collimated supersonic gas jets

    NASA Astrophysics Data System (ADS)

    Suzuki-Vidal, F.; Lebedev, S. V.; Skidmore, J.; Bocchi, M.; Bland, S. N.; Burdiak, G.; Chittenden, J. P.; de Grouchy, P.; Hall, G. N.; Harvey-Thompson, A. J.; Khoory, E.; Pickworth, L. A.; Suttle, L.; Swadling, G. F.; Krishnan, M.; Madden, R. E.; Elliot, K. W.; Coleman, P. L.; Ciardi, A.

    2011-10-01

    The MAGPIE generator (1.4 MA, 240 ns) drives an ablative plasma from a thin Al foil. The convergence of the plasma from the foil on its axis leads to the formation of a supersonic plasma jet, with a typical velocity of ~100 km/s. Jet-ambient interactions are studied either by injecting a highly-collimated, supersonic, cold gas jet above the foil using a nozzle, or by enclosing the foil inside a cell filled with neutral, static gas. In both cases, the plasma jet creates several shock features in the ambient medium. Experimental results from varied ambient parameters such as gas pressure and composition are presented together with 3-D MHD simulations. Work supported at AASC by DOE SBIR Grant DE-FG02-08ER85030, and at Imperial College by EPSRC Grant No. EP/G001324/1, by the NNSA under DOE Cooperative Agreements No. DE-F03-02NA00057 and No. DE-SC-0001063, and by a Marie Curie ERG grant.

  10. The spatial and temporal structure of thermal fluctuations associated with a vertical turbulent jet impinging a water surface: laboratory experiments and field observations

    NASA Astrophysics Data System (ADS)

    Judd, K. Peter; Savelyev, Ivan B.; Smith, Geoffrey B.; Marmorino, George

    2012-06-01

    Infrared imaging, in both laboratory and field settings, has become a vital tool in diagnosing near-surface thermalhydrodynamic phenomena such as convective cells, accumulation of surfactant, and coherent turbulent structures. In this presentation, we initially focus on a laboratory scale (0.01-1m) subsurface vertical turbulent water jet that serves as a canonical flow. The jet has a slightly elevated temperature thus the warmer fluid serves as a passive marker. Infrared image sequences of the surface thermal field were collected for various water jet flow rates and for both "clean" and surfactant-contaminated surface conditions. Turbulent characteristics of the near-surface flow field were measured by means of Digital Particle Image Velocimetry (DPIV), and these are used to examine the statistical nature of the coupled thermal-hydrodynamic field. An analog of the laboratory jet is the discharge of power-plant cooling water through a vertical pipe on the ocean floor. High-resolution airborne infrared imagery has recently been acquired of such a discharge (from the Huntington Beach Generating Station, CA), and these data are compared with the laboratory results in an attempt to understand striking spatial patterns discovered on the ocean surface.

  11. Evidence for Coexisting Hot and Cool Polar Coronal Jets - Coordinated Observations of SOHO and TRACE

    NASA Astrophysics Data System (ADS)

    Dobrzycka, D.; Raymond, J. C.; Deluca, E. E.; Gurman, J.; Biesecker, D.; Fludra, A.

    2004-05-01

    The polar coronal jets were first observed by SOHO instruments (EIT, LASCO, UVCS) during the last solar minimum. They were small, fast ejections originating from flaring UV bright points within large polar coronal holes. The polar holes disappeared at solar maximum and the jets were not visible anymore. Currently, however, as the Sun's activity declines, the polar holes again became permanent structures and new polar coronal jets were observed by specially designed SOHO Joint Observing Program (JOP 155). Their frequency of several events per day appear comparable to the frequency from last solar minimum. Also, the speed of ˜ 400~km~s-1 at 1.6~R⊙ is consistent with typical velocities of polar jets in 1996-1998. The ejections are believed to be triggered by the field line reconnection between the emerging magnetic dipole and pre-existing unipolar field. Existing models predict that the hot jet is ejected together with another jet made of cool material. The coordinated SOHO and TRACE observations within JOP 155 provide unique opportunity to test this prediction. We will present observations and discuss evidence supporting the model.

  12. Lif Spectroscopy of Jet Cooled MgOH

    NASA Astrophysics Data System (ADS)

    Fukushima, Masaru; Ishiwata, Takashi

    2014-06-01

    We have generated MgOH in supersonic free jet expansions, and observed the laser induced fluorescence ( LIF ) of the tilde{A} ^2Π - tilde{X} ^2Σ^+ transition. We have reported rotational analyses of the bending vibronic bands, 2_0^n, n = 0, 2, and 4, and it has been found that the spin-orbit constant of the bending vibronic levels, tilde{A} ^2Π (0n^00) μ ^2Π, increases with increasing the bending vibrational quantum number, n. This observation is interpreted as the lower level possessing primarily bent character and the higher level possessing linear character. The bending potential surface of the tilde{A} ^2Π state is thought to be the reason for the present observation and interpretation. This potential surface is thought to be fairly flat and anharmonic with bent and linear geometries at the r_e and r_0 structures, respectively. We also observed the other two vibronic bands at almost the middle between the 2_0^2 and 2_0^4 bands. One of the two has a similar rotational structure with that of the origin band, 0_0^0, and is assigned to be the Mg-OH stretching vibronic band, tilde{A} ^2Π (00^01) - tilde{X} ^2Σ^+ (00^00). The rotational structure of another vibronic band is very complex, and it seems to overlap, at least, two vibronic bands, ^2Π - and ^2Σ(+) - ^2Σ^+. More precise analysis is underway. M. Fukushima and T. Ishiwata, The 21st Colloquium on High-Resolution Molecular Spectroscopy, F8 (2009).

  13. Supersonic jet cooled rotational spectrum of 2,4-difluorophenol

    NASA Astrophysics Data System (ADS)

    Nair, K. P. Rajappan; Dewald, David; Wachsmuth, Dennis; Grabow, Jens-Uwe

    2017-05-01

    The microwave spectrum of the cis form of aromatic 2,4-difluorophenol (DFP) has been recorded and analyzed in the frequency range of 5-25 GHz using a pulsed-jet Fourier transform microwave spectrometer. Rotational transitions were measured for the parent and all unique single 13C substituted isotopologues and 18O in natural abundance and on enriched deuterium species on the hydroxyl group. The rotational (MHz), centrifugal distortion (kHz), and quadrupole coupling constants (MHz) in deuterium species were determined. The rotational constants for the parent species are obtained as A = 3125.04158(43) MHz, B = 1290.154481(54) MHz, C = 913.197424(36) MHz, DJ = 0.020899(162) kHz, DK = 0.9456(100) kHz, DJK = 0.09273(65) kHz, d1 = -0.00794(14) kHz, d2 = -0.002356(93) kHz and for the deuterated species A = 3125.38579(44) MHz, B = 1261.749784(48) MHz, C = 898.927184(27) MHz, DJ = 0.02096(19) kHz, DK = 0.379(74) kHz, DJK = 0.0880(11) kHz, d1 = -0.00691(11) kHz, d2 = -0.00183(11) kHz. The deuterium quadrupole coupling constants are χaa = -0.0109(33) MHz, and (χbb - χcc) = 0.2985(59) MHz. The rs substitution structure was determined using the measured rotational constants of the isotopologues, a nonlinear least squares fit was performed to obtain the best fit gas phase r0 effective structure. Supporting ab initio (MP2) and density functional calculations provided consistent values for the rotational parameters, and molecular structure.

  14. Heating cold clumps by jet-inflated bubbles in cooling flow clusters

    NASA Astrophysics Data System (ADS)

    Hillel, Shlomi; Soker, Noam

    2014-12-01

    We simulate the evolution of dense-cool clumps embedded in the intracluster medium (ICM) of cooling flow clusters of galaxies in response to multiple jet-activity cycles, and find that the main heating process of the clumps is mixing with the hot shocked jets' gas, the bubbles, while shocks have a limited role. We use the PLUTO hydrodynamical code in two dimensions with imposed axisymmetry, to follow the thermal evolution of the clumps. We find that the inflation process of hot bubbles, which appear as X-ray deficient cavities in observations, is accompanied by complicated induced vortices inside and around the bubbles. The vorticity induces efficient mixing of the hot bubbles' gas with the ICM and cool clumps, resulting in a substantial increase of the temperature and entropy of the clumps. For the parameters used by us, heating by shocks barely competes with radiative cooling, even after 25 consecutive shocks excited during 0.5 Gyr of simulation. Some clumps are shaped to filamentary structure that can turn to observed optical filaments. We find that not all clumps are heated. Those that cool to very low temperatures will fall in and feed the central supermassive black hole, hence closing the feedback cycle in what is termed the cold feedback mechanism.

  15. Rotationally resolved spectra of jet-cooled RuSi

    NASA Astrophysics Data System (ADS)

    Lindholm, Ned; Morse, Michael D.

    2007-08-01

    We report the first gas-phase spectroscopic investigation of diatomic ruthenium silicide (RuSi). The molecules were produced by laser ablation of a Ru disk into a flow of helium carrier gas containing 0.5% SiH4, and were cooled in a supersonic expansion. The RuSi molecules were then studied using resonant two-photon ionization spectroscopy. Investigations conducted in the spectral range from 18800to23800cm-1 show a large number of excited vibronic levels that cannot readily be grouped into electronic band systems. The ground state is been demonstrated to be of Δ33 symmetry, deriving from the 2δ314σ1 electronic configuration. Correcting for the effects of the spin-uncoupling operator, the ground state bond length (r0) is determined to be 2.0921±0.0004Å (1σ error limit). Diatomic RuSi is shown to have strong dπ-pπ bonds, unlike the isovalent AlCo molecule.

  16. Spectroscopic evidence of jet-cooled o-chloro-alpha-methylbenzyl radical in corona excitation.

    PubMed

    Ahn, Hyeon Geun; Lee, Gi Woo; Lee, Sang Kuk

    2008-12-25

    We report the first spectroscopic evidence of the o-chloro-alpha-methylbenzyl radical. The electronically hot but jet-cooled o-chloro-alpha-methylbenzyl radical was formed from precursor o-chloro-ethylbenzene seeded in a large amount of inert carrier gas helium, by employing the technique of corona excited supersonic expansion with a pinhole-type glass nozzle. The vibronic emission spectrum was recorded with a long path monochromator in the D(1) --> D(0) electronic transition in the visible region. By comparing the observed spectrum with that of the o-chlorobenzyl radical reported previously, we could easily identify the spectroscopic evidence of the jet-cooled o-chloro-alpha-methylbenzyl radical generated in the corona discharge of o-chloro-ethylbenzene, from which the electronic transition energy and several vibrational mode frequencies in the ground electronic state were accurately determined.

  17. Spectroscopic evidence of jet-cooled p-methyl-α-methylbenzyl radical

    NASA Astrophysics Data System (ADS)

    Chae, Sang Youl; Yoon, Young Wook; Lim, Manho; Lee, Sang Kuk

    2015-08-01

    We report spectroscopic evidence of the jet-cooled p-methyl-α-methylbenzyl radical in corona discharge. The visible vibronic emission spectra were recorded from the corona discharge of three precursors, p-xylene, p-ethyltoluene, and p-isopropyltoluene seeded in a large amount of carrier gas helium using a pinhole-type glass nozzle. From the analysis of the vibronic spectra observed from each precursor and the bond dissociation energies of precursor molecules, we are able to confirm the formation of the jet-cooled p-methyl-α-methylbenzyl radical in corona discharge, and determine the energy of the D1 → D0 transition and a few vibrational mode frequencies in the D0 state.

  18. Pressure-loss and flow coefficients inside a chordwise-finned, impingement, convection, and film air-cooled turbine vane

    NASA Technical Reports Server (NTRS)

    Hippensteele, S. A.

    1974-01-01

    Total-pressure-loss coefficients, flow discharge coefficients, and friction factors were determined experimentally for the various area and geometry changes and flow passages within an air-cooled turbine vane. The results are compared with those of others obtained on similar configurations, both actual and large models, of vane passages. The supply and exit air pressures were controlled and varied. The investigation was conducted with essentially ambient-temperature air and without external flow of air over the vane.

  19. Analysis of heat-transfer tests of an impingement-convection- and film-cooled vane in a cascade

    NASA Technical Reports Server (NTRS)

    Gladden, H. J.; Gauntner, D. J.; Livingood, J. N. B.

    1971-01-01

    Experimental flow and heat transfer data obtained for an air-cooled turbine vane tested in a static cascade at gas temperatures and pressures to 1644 K (2500 F) and 31 N/cm2 (45 psia), respectively, are presented. Average and local vane temperatures were correlated in several ways. Calculated and measured coolant flows and vane temperatures are compared. Potential allowable increases in gas temperature are also discussed.

  20. Jet streak modification via diabatic heating during periods of intense cool-season precipitation

    NASA Astrophysics Data System (ADS)

    Market, Patrick Shawn

    The propagation of a jet streak in the presence of predominately stable latent heat release is examined. Unlike many prior studies which emphasized latent heat release due to mesoscale convective system activity this work addresses cool season mid-latitude weather systems in which stable latent heat release played a significant role. In both cool and warm seasons, the result is the same: the amplification of a pre-existing jet streak, or the in situ development of a new jet streak. The former situation is more typical of the cool season when thermal gradients and the jet stream are both stronger and more conducive to the transient baroclinic waves which engender streaks in the jet stream flow, while the latter development tends to be the product of a warm season environment when the background thermal and flow patterns are weaker. In this work, the development of a pre-existing straight- line jet streak upstream of its prior location (``backbuilding'') presumably due to latent heat release is studied. Both dry and moist adiabatic simulations with a mesoscale numerical model indicate that backbuilding occurs in the absence of latent heat release (dry run) due to confluence but is enhanced when such heating is included (moist run). This is due to the latent heat release and consequent warming of the column in which it occurs, thus altering the height gradient. Such a process causes accelerations in the flow. Moreover, the mid-tropospheric nature of the stable latent heating causes the backbuilding to be maximized in the mid-troposphere (500 to 400 hPa). Isentropic coordinate analyses of the model output are employed in the estimation of latent heating and ageostrophic wind components. In terms of sensible weather, the propagating jet streak tends to initiate precipitation in its right entrance region because of the induced ascent. In the present case, the latent heat release associated with this precipitation acted to anchor the jet streak in place and even build

  1. Cool Core Cycles: Cold Gas and AGN Jet Feedback in Cluster Cores

    NASA Astrophysics Data System (ADS)

    Prasad, Deovrat; Sharma, Prateek; Babul, Arif

    2015-10-01

    Using high-resolution 3D and 2D (axisymmetric) hydrodynamic simulations in spherical geometry, we study the evolution of cool cluster cores heated by feedback-driven bipolar active galactic nuclei (AGNs) jets. Condensation of cold gas, and the consequent enhanced accretion, is required for AGN feedback to balance radiative cooling with reasonable efficiencies, and to match the observed cool core properties. A feedback efficiency (mechanical luminosity ≈ ɛ {\\dot{M}}{{acc}}{c}2; where {\\dot{M}}{{acc}} is the mass accretion rate at 1 kpc) as small as 6 × 10-5 is sufficient to reduce the cooling/accretion rate by ˜10 compared to a pure cooling flow in clusters (with {M}200≲ 7× {10}14 {M}⊙ ). This value is much smaller compared to the ones considered earlier, and is consistent with the jet efficiency and the fact that only a small fraction of gas at 1 kpc is accreted onto the supermassive black hole (SMBH). The feedback efficiency in earlier works was so high that the cluster core reached equilibrium in a hot state without much precipitation, unlike what is observed in cool-core clusters. We find hysteresis cycles in all our simulations with cold mode feedback: condensation of cold gas when the ratio of the cooling-time to the free-fall time ({t}{{cool}}/{t}{{ff}}) is ≲10 leads to a sudden enhancement in the accretion rate; a large accretion rate causes strong jets and overheating of the hot intracluster medium such that {t}{{cool}}/{t}{{ff}}\\gt 10; further condensation of cold gas is suppressed and the accretion rate falls, leading to slow cooling of the core and condensation of cold gas, restarting the cycle. Therefore, there is a spread in core properties, such as the jet power, accretion rate, for the same value of core entropy or {t}{{cool}}/{t}{{ff}}. A smaller number of cycles is observed for higher efficiencies and for lower mass halos because the core is overheated to a longer cooling time. The 3D simulations show the formation of a few-kpc scale

  2. Synthesis of superior fast charging-discharging nano-LiFePO4/C from nano-FePO4 generated using a confined area impinging jet reactor approach.

    PubMed

    Liu, Xiao-min; Yan, Pen; Xie, Yin-Yin; Yang, Hui; Shen, Xiao-dong; Ma, Zi-Feng

    2013-06-14

    LiFePO4/C nanocomposites with excellent electrochemical performance is synthesized from nano-FePO4, generated by a novel method using a confined area impinging jet reactor (CIJR). When discharged at 80 C (13.6 Ag(-1)), the LiFePO4/C delivers a discharge capacity of 95 mA h g(-1), an energy density of 227 W h kg(-1) and a power density of 34 kW kg(-1).

  3. Microfog lubricant application system for advanced turbine engine components, phase 2. Tasks 3, 4 and 5: Wettability and heat transfer of microfog jets impinging on a heated rotating disc, and evaluation of reclassifying nozzles and a vortex mist generator

    NASA Technical Reports Server (NTRS)

    Shim, J.; Leonardi, S. J.

    1972-01-01

    The wettabilities and heat transfer rates of microfog jets (oil-mist nozzle flows) impinging on a heated rotating disc were determined under an inert atmosphere of nitrogen at temperatures ranging from 600 to 800 F. The results are discussed in relation to the various factors involved in the microfog lubricant application systems. Two novel reclassifying nozzles and a vortex mist generator were also studied.

  4. Analysis of a Free Surface Film from a Controlled Liquid Impinging Jet over a Rotating Disk Including Conjugate Effects, with and without Evaporation

    NASA Technical Reports Server (NTRS)

    Sankaran, Subramanian (Technical Monitor); Rice, Jeremy; Faghri, Amir; Cetegen, Baki M.

    2005-01-01

    A detailed analysis of the liquid film characteristics and the accompanying heat transfer of a free surface controlled liquid impinging jet onto a rotating disk are presented. The computations were run on a two-dimensional axi-symmetric Eulerian mesh while the free surface was calculated with the volume of fluid method. Flow rates between 3 and 15 1pm with rotational speeds between 50 and 200 rpm are analyzed. The effects of inlet temperature on the film thickness and heat transfer are characterized as well as evaporative effects. The conjugate heating effect is modeled, and was found to effect the heat transfer results the most at both the inner and outer edges of the heated surface. The heat transfer was enhanced with both increasing flow rate and increasing rotational speeds. When evaporative effects were modeled, the evaporation was found to increase the heat transfer at the lower flow rates the most because of a fully developed thermal field that was achieved. The evaporative effects did not significantly enhance the heat transfer at the higher flow rates.

  5. Assessment of the relative performance of a confined impinging jets mixer and a multi-inlet vortex mixer for curcumin nanoparticle production.

    PubMed

    Chow, Shing Fung; Sun, Changquan Calvin; Chow, Albert Hee Lum

    2014-10-01

    The relative performance of two specially designed mixers for nanoparticle production, namely, two-stream confined impinging jets with dilution mixer (CIJ-D-M) and four-stream multi-inlet vortex mixer (MIVM), was evaluated using the model compound, curcumin (CUR), under defined conditions of varying mixing rate and organic solvent. In the absence of turbulent fluctuations, higher mixing rate tended to generate finer particles. Among the three water-miscible organic solvents tested, acetone afforded the smallest particle size and the narrowest particle size distribution. Both mixers were capable of reproducibly fabricating CUR nanoparticles with particle size below 100 nm and high encapsulation efficiency (>99.9%). Specifically, CIJ-D-M yielded nanoparticles with smaller size and polydispersity index while the particles obtained by the MIVM displayed better short-term stability. In addition, CIJ-D-M tended to produce a mixture of irregular nanoaggregates and primary nanoparticles while roughly spherical nanoparticles were generated with the MIVM. The observed particle size and morphological differences could be attributed to the differences in the configuration of the mixing chamber and the related mixing order.

  6. Engine investigation of an air-cooled turbine rotor blade incorporating impingement-cooled leading edge, chordwise passages, and a slotted trailing edge

    NASA Technical Reports Server (NTRS)

    Dengler, R. P.; Yeh, F. C.; Gauntner, J. W.; Fallon, G. E.

    1972-01-01

    Experimental temperatures are presented for an air-cooled turbine rotor blade tested in an engine. The data were obtained for turbine stator inlet temperatures from 2000 to 2500 F and for turbine-inlet gas pressures from 32 to 46 psia. Average and local blade heat-transfer data are correlated. Potential allowable increases in gas temperature are also discussed.

  7. Vapor Jet Ejector Used to Generate Free Waste Heat Driven Cooling in Military Environmental Cooling Units

    DTIC Science & Technology

    2012-07-01

    vap erant vapor is or by a J-tub essure side of using similar pressure incre ump in order o the diesel-e per heat excha recovered at to the exhaus...top of the a tering the com at exchanger. g of the conve id flow. A nit essure pulsati tor where the ed in the cool erature level. ger where wa

  8. Ballistics Model for Particles on a Horizontal Plane in a Vacuum Propelled by a Vertically Impinging Gas Jet

    NASA Technical Reports Server (NTRS)

    Lane, J. E.; Metzger, P. T.

    2010-01-01

    A simple trajectory model has been developed and is presented. The particle trajectory path is estimated by computing the vertical position as a function of the horizontal position using a constant horizontal velocity and a vertical acceleration approximated as a power law. The vertical particle position is then found by solving the differential equation of motion using a double integral of vertical acceleration divided by the square of the horizontal velocity, integrated over the horizontal position. The input parameters are: x(sub 0) and y(sub 0), the initial particle starting point; the derivative of the trajectory at x(sub 0) and y(sub 0), s(sub 0) = s(x(sub 0))= dx(y)/dy conditional expectation y = y((sub 0); and b where bx(sub 0)/y(sub 0) is the final trajectory angle before gravity pulls the particle down. The final parameter v(sub 0) is an approximation to a constant horizontal velocity. This model is time independent, providing vertical position x as a function of horizontal distance y: x(y) = (x(sub 0) + s(sub 0) (y-y(sub 0))) + bx(sub 0) -(s(sub 0)y(sub 0) ((y - y(sub 0)/y(sub 0) - ln((y/y(sub 0)))-((g(y-y(sub 0)(exp 2))/ 2((v(sub 0)(exp 2). The first term on the right in the above equation is due to simple ballistics and a spherically expanding gas so that the trajectory is a straight line intersecting (0,0), which is the point at the center of the gas impingement on the surface. The second term on the right is due to vertical acceleration, which may be positive or negative. The last term on the right is the gravity term, which for a particle with velocities less than escape velocity will eventually bring the particle back to the ground. The parameters b, s(sub 0), and in some cases v(sub 0), are taken from an interpolation of similar parameters determined from a CFD simulation matrix, coupled with complete particle trajectory simulations.

  9. Numerical solution for the temperature distribution in a cooled guide vane blade of a radial gas turbine

    NASA Technical Reports Server (NTRS)

    Hosny, W. M.; Tabakoff, W.

    1977-01-01

    A two dimensional finite difference numerical technique is presented to determine the temperature distribution of an internal cooled blade of radial turbine guide vanes. A simple convection cooling is assumed inside the guide vane blade. Such cooling has relatively small cooling effectiveness at the leading edge and at the trailing edge. Heat transfer augmentation in these critical areas may be achieved by using impingement jets and film cooling. A computer program is written in FORTRAN IV for IBM 370/165 computer.

  10. Distribution of a pelagic tunicate, Salpa fusiformis in warm surface current of the eastern Korean waters and its impingement on cooling water intakes of Uljin nuclear power plant.

    PubMed

    Chae, Jinho; Choi, Hyun Woo; Lee, Woo Jin; Kim, Dongsung; Lee, Jae Hac

    2008-07-01

    Impingement of a large amount of gelatinous plankton, Salpa fusiformis on the seawater intake system-screens in a nuclear power plant at Uljin was firstly recorded on 18th June 2003. Whole amount of the clogged animals was estimated were presumptively at 295 tons and the shortage of cooling seawater supply by the animal clogging caused 38% of decrease in generation capability of the power plant. Zooplankton collection with a multiple towing net during the day and at night from 5 to 6 June 2003 included various gelatinous zooplanktons known to be warm water species such as salps and siphonophores. Comparatively larger species, Salpa fusiformis occupied 25.4% in individual density among the gelatinous plankton and showed surface distribution in the depth shallower than thermocline, performing little diel vertical migration. Temperature, salinity and satellite data also showed warm surface current predominated over the southern coastal region near the power plant in June. The results suggested that warm surface current occasionally extended into the neritic region may transfer S. fusiformis, to the waters off the power plant. The environmental factors and their relation to ecobiology of the large quantity of salpa population that are being sucked into the intake channel of the power plant are discussed.

  11. Assessment of subgrid-scale models with a large-eddy simulation-dedicated experimental database: The pulsatile impinging jet in turbulent cross-flow

    NASA Astrophysics Data System (ADS)

    Baya Toda, Hubert; Cabrit, Olivier; Truffin, Karine; Bruneaux, Gilles; Nicoud, Franck

    2014-07-01

    Large-Eddy Simulation (LES) in complex geometries and industrial applications like piston engines, gas turbines, or aircraft engines requires the use of advanced subgrid-scale (SGS) models able to take into account the main flow features and the turbulence anisotropy. Keeping this goal in mind, this paper reports a LES-dedicated experiment of a pulsatile hot-jet impinging a flat-plate in the presence of a cold turbulent cross-flow. Unlike commonly used academic test cases, this configuration involves different flow features encountered in complex configurations: shear/rotating regions, stagnation point, wall-turbulence, and the propagation of a vortex ring along the wall. This experiment was also designed with the aim to use quantitative and nonintrusive optical diagnostics such as Particle Image Velocimetry, and to easily perform a LES involving a relatively simple geometry and well-controlled boundary conditions. Hence, two eddy-viscosity-based SGS models are investigated: the dynamic Smagorinsky model [M. Germano, U. Piomelli, P. Moin, and W. Cabot, "A dynamic subgrid-scale eddy viscosity model," Phys. Fluids A 3(7), 1760-1765 (1991)] and the σ-model [F. Nicoud, H. B. Toda, O. Cabrit, S. Bose, and J. Lee, "Using singular values to build a subgrid-scale model for large eddy simulations," Phys. Fluids 23(8), 085106 (2011)]. Both models give similar results during the first phase of the experiment. However, it was found that the dynamic Smagorinsky model could not accurately predict the vortex-ring propagation, while the σ-model provides a better agreement with the experimental measurements. Setting aside the implementation of the dynamic procedure (implemented here in its simplest form, i.e., without averaging over homogeneous directions and with clipping of negative values to ensure numerical stability), it is suggested that the mitigated predictions of the dynamic Smagorinsky model are due to the dynamic constant, which strongly depends on the mesh resolution

  12. Severe Local Hypothermia from Laparoscopic Gas Evaporative Jet Cooling: A Mechanism To Explain Clinical Observations

    PubMed Central

    Gray, Robert I.; Henderson, A. Courtney; Cochran, Steve A.; Roth, Elizabeth A.

    1999-01-01

    Background and Objectives: Explanations for laparoscopic-induced hypothermia fail to explain clinical observations. It is possible that water evaporation occurs from the jet stream of gas inflation resulting in tissue surface super-cooling leading to tissue damage and drying. Methods: Theoretical calculations based on thermal conductivity, mass transfer effects and heat flux considerations correlated closely with synthetic and tissue experiments. Thermocouple measurements at a rate of 15 data points per second were performed. Results: Cooling rates of 10 to 25 degrees centigrade per second for high flow rates were found based on gas flow rate and effective size of gas delivery site. These rapid temperature drops extended beyond a 2 cm2 diameter. Conclusions: Evaporative cooling accounts for significant hypothermia. The cooling is dependent on the lack of water vapor in the gases currently used during laparoscopy. Cooling rates are independent of height from tissue and geometry of delivery port. Heating and hydrating the gas to a physiologic condition eliminates hypothermia and tissue dessication. PMID:10527326

  13. Jet model for slot film cooling with effect of free-stream and coolant turbulence

    NASA Technical Reports Server (NTRS)

    Simon, Frederick F.

    1986-01-01

    An analysis was performed utilizing the model of a wall jet for obtaining equations that will predict slot film-cooling efficiency under conditions of variable turbulence intensity, flow, and temperature. The analysis, in addition to assessing the effects of the above variables, makes a distinction between an initial region and a fully developed region. Such a distinction is important in determining the role that the turbulence intensity of the coolant plays in effecting film-cooling effectiveness in the area of the slot exit. The results of the analysis were used in the correlation of the results of a well-designed film-cooling experiment. The result of the analysis and experiment was equations that predicted film-cooling efficiency within + or - 4% average deviation for lateral free-stream turbulence intensities up to 24% and blowing rates up to 1.9. These equations should be useful in determining the optimum quantity of cooling air requried for protecting the wall of a combustor.

  14. Radiatively cooled supersonic plasma jets generated in wire array Z-pinches

    NASA Astrophysics Data System (ADS)

    Bland, Simon; Lebedev, Sergey; Chittenden, Jerry; Beg, F. N.; Ciardi, A.; Haines, M. G.

    2000-10-01

    We will present experiments on the generation of a highly supersonic plasma jet by a convergent plasma flow, produced by electrodynamic acceleration of plasma in a conical array of fine metallic wires (a modification of the wire array Z-pinch [1]). Stagnation of the plasma flow on the axis of symmetry forms a standing conical shock, which effectively collimates the flow in the axial direction. This scenario is essentially similar to that discussed by Cantó et al. [2] as a possible, purely hydrodynamic mechanism of jet formation in young stellar objects. Experiments using different materials (Al, Fe and W) show that a highly supersonic (M 20) and a well-collimated jet is generated when the radiative cooling rate of the plasma is significant. The interaction of this jet with a plasma target could be used for scaled [3] laboratory astrophysical experiments on hydrodynamic instabilities in decelerated plasma flow. [1] M.K. Matzen, Phys. Plasmas v.4, 1519 (1997) [2] J. Cantó, et. al. Astron. Astrophys. v.192, 287 (1994). [3] D. Ryutov et al., ApJ, v.518, 821 (1999)

  15. Jet-cooled infrared absorption spectrum of the v4 fundamental band of HCOOH and HCOOD

    NASA Astrophysics Data System (ADS)

    Luo, Wei; Zhang, Yulan; Li, Wenguang; Duan, Chuanxi

    2017-04-01

    The jet-cooled absorption spectrum of the v4 fundamental band of normal formic acid (HCOOH) and deuterated formic acid (HCOOD) was recorded in the frequency range of 1370-1392 cm-1 with distributed-feedback quantum cascade lasers (DFB-QCLs) as the tunable infrared radiations. A segmented rapid-scan data acquisition scheme was developed for pulsed supersonic jet infrared laser absorption spectroscopy based on DFB-QCLs with a moderate vacuum pumping capacity. The unperturbed band-origin and rotational constants in the excited vibrational state were determined for both HCOOH and HCOOD. The unperturbed band-origin locates at 1379.05447(11) cm-1 for HCOOH, and 1366.48430(39) cm-1 for HCOOD, respectively.

  16. Vibronic emission spectroscopy of benzyl-type radicals: Jet-cooled 2-fluoro-5-chlorobenzyl radical

    NASA Astrophysics Data System (ADS)

    Yoon, Young Wook; Chae, Sang Youl; Lee, Sang Kuk

    2014-07-01

    We produced the vibronically excited but jet-cooled 2-fluoro-5-chlorobenzyl radical by corona discharge of precursor 2-fluoro-5-chlorotoluene with a large amount of carrier gas He using a pinhole-type glass nozzle in a technique of corona excited supersonic jet expansion. The vibronic emission spectrum was recorded using a long-path double monochromator in the visible region. From an analysis of the spectrum, we determined the electronic energy of the D1 → D0 transition and vibrational mode frequencies in the ground electronic state of the 2-fluoro-5-chlorobenzyl radical for the first time. In addition, substituent effect on electronic transition energy was discussed for substituents on the benzene ring.

  17. n,. pi. /sup */ state of jet-cooled benzophenone as studied by sensitized phosphorescence excitation spectroscopy

    SciTech Connect

    Kamei, S.; Sato, T.; Mikami, N.; Ito, M.

    1986-10-23

    The sensitized phosphorescence excitation spectrum of jet-cooled benzophenone due to the S/sub 1/(n,..pi../sup */) produced from S/sub 0/ transition has been measured. It was found that the spectrum consists exclusively of several long progressions of 60 cm/sup -1/ which is the in-phase torsional mode of the phenyl rings. The vibrational analysis and the potential calculation shows that the in the S/sub 1/(n,..pi../sup */) state great geometry changes occur in the dihedral angle between the phenyl rings, the C=O bond distance, and the C-C bonds adjacent to the C=O bond.

  18. Fluorescence excitation spectrum and solvent-assisted conformational isomerization (SACI) of jet-cooled acetaminophen

    NASA Astrophysics Data System (ADS)

    Sohn, Woon Yong; Kang, Jeong Seok; Lee, So Young; Kang, Hyuk

    2013-08-01

    Fluorescence excitation spectrum of jet-cooled acetaminophen was obtained. When AAP was expanded with a buffer gas containing 0.3-1.1% of water, absorption peaks of the less stable trans conformer was significantly reduced by solvent-assisted conformational isomerization (SACI), which is confirmed by a separately measured UV-UV hole burning spectroscopy. It is also confirmed by quantum mechanical calculation and RRKM calculation that it is energetically and kinetically possible to induce SACI in AAP with water. The SACI mechanism suggests a possible pathway that acetaminophen can adopt an active conformation in vivo, which is need for molecular recognition and drug activity.

  19. Spectroscopic identification of dichlorobenzyl radicals: Jet-cooled 2,3-dichlorobenzyl radical

    NASA Astrophysics Data System (ADS)

    Chae, Sang Youl; Yoon, Young Wook; Lee, Sang Kuk

    2015-07-01

    The vibronically excited but jet-cooled 2,3-dichlorobenzyl radical was generated from the corona discharge of precursor 2,3-dichlorotoluene seeded in a large amount of carrier gas He using a pinhole-type glass nozzle. From an analysis of the visible vibronic emission spectrum observed, we obtained the electronic energy of the D1 → D0 transition and vibrational mode frequencies in the D0 state of the 2,3-dichlorobenzyl radical by comparing the observation with the results of ab initio calculations. In addition, we discussed substituent effect of Cls on electronic transition energy in terms of substituent orientation for the first time.

  20. High Temperature Ceramic Guide Vane Temperature and Pressure Distribution Calculation for Flow with Cooling Jets

    NASA Technical Reports Server (NTRS)

    Srivastava, Rakesh

    2004-01-01

    A ceramic guide vane has been designed and tested for operation under high temperature. Previous efforts have suggested that some cooling flow may be required to alleviate the high temperatures observed near the trailing edge region. The present report describes briefly a three-dimensional viscous analysis carried out to calculate the temperature and pressure distribution on the blade surface and in the flow path with a jet of cooling air exiting from the suction surface near the trailing edge region. The data for analysis was obtained from Dr. Craig Robinson. The surface temperature and pressure distribution along with a flowfield distribution is shown in the results. The surface distribution is also given in a tabular form at the end of the document.

  1. Heat transfer coefficient distribution over the inconel plate cooled from high temperature by the array of water jets

    NASA Astrophysics Data System (ADS)

    Malinowski, Z.; Telejko, T.; Cebo-Rudnicka, A.; Szajding, A.; Rywotycki, M.; Hadała, B.

    2016-09-01

    The industrial rolling mills are equipped with systems for controlled water cooling of hot steel products. A cooling rate affects the final mechanical properties of steel which are strongly dependent on microstructure evolution processes. In case of water jets cooling the heat transfer boundary condition can be defined by the heat transfer coefficient. In the present study one and three dimensional heat conduction models have been employed in the inverse solution to heat transfer coefficient. The inconel plate has been heated to about 900oC and then cooled by one, two and six water jets. The plate temperature has been measured by 30 thermocouples. The heat transfer coefficient distributions at plate surface have been determined in time of cooling.

  2. Investigation of flow characteristics effects on heat transfer in water-cooled cylinder heads

    NASA Astrophysics Data System (ADS)

    Hassan, M. A. M.; Abd El-Hameed, H. M.; Mahmoud, Osama E.

    2017-04-01

    An experimental and theoretical study has been performed to investigate the effect of flow characteristics on heat-transfer in water impingement-cooled cylinder heads. Numerous investigations have been made using a three-dimensional model, which is designed and solved by FLUENT software using both realizable k-ɛ turbulent and heat transfer models. The simulation investigates a fully developed turbulent-water flow in asymmetric heated circular passage cooled by parallel flow or impingement of circular submerged confined liquid jet. The following parameters were investigated for both parallel flow and jet impingement flow: flow velocities (1, 2 and 3 m/s), bulk fluid temperatures (50, 70 and 90 °C), main duct diameters (6, 8, 10 and 12 mm). While the following parameters were investigated for jet impingement flow, jet diameter ratio (0.6, 0.8 and 1) and jet inclination angles as measured from horizontal (45°, 60° and 90°). Experimental results were used to verify the theoretical model. Results indicate that, the normal jet (90°) gives the maximum cooling effect in comparison to other angles while the maximum heat transfer coefficient is found at jet interface position.

  3. Investigation of flow characteristics effects on heat transfer in water-cooled cylinder heads

    NASA Astrophysics Data System (ADS)

    Hassan, M. A. M.; Abd El-Hameed, H. M.; Mahmoud, Osama E.

    2016-08-01

    An experimental and theoretical study has been performed to investigate the effect of flow characteristics on heat-transfer in water impingement-cooled cylinder heads. Numerous investigations have been made using a three-dimensional model, which is designed and solved by FLUENT software using both realizable k-ɛ turbulent and heat transfer models. The simulation investigates a fully developed turbulent-water flow in asymmetric heated circular passage cooled by parallel flow or impingement of circular submerged confined liquid jet. The following parameters were investigated for both parallel flow and jet impingement flow: flow velocities (1, 2 and 3 m/s), bulk fluid temperatures (50, 70 and 90 °C), main duct diameters (6, 8, 10 and 12 mm). While the following parameters were investigated for jet impingement flow, jet diameter ratio (0.6, 0.8 and 1) and jet inclination angles as measured from horizontal (45°, 60° and 90°). Experimental results were used to verify the theoretical model. Results indicate that, the normal jet (90°) gives the maximum cooling effect in comparison to other angles while the maximum heat transfer coefficient is found at jet interface position.

  4. Influence of wire mesh at nozzle exit on heat transfer from square jets - An experimental investigation

    NASA Astrophysics Data System (ADS)

    Muvvala, Pullarao; Balaji, C.; Venkateshan, S. P.

    2017-06-01

    The goal of this work is to compare the fluid flow and heat transfer characteristics of square jet in the presence of a wire mesh at the nozzle exit. Towards this, in-house experiments are carried out by impinging a square jet on a uniformly heated plate of finite thickness, with air as the cooling medium. Two different sets of square jets are employed in this study namely a jet in the absence of mesh and a jet in the presence of a wire mesh at the nozzle exit. Jet centerline mean velocity and turbulence intensity measurements are done with a hot-wire anemometer to support the heat transfer results.

  5. Hydrodynamics and PIV study in the impingement zone formed by a droplet train

    NASA Astrophysics Data System (ADS)

    Kanjirakat, Anoop; Sadr, Reza; Zhang, Taolue; Muthusamy, Jayaveera; Alvarado, Jorge; Texas A; M University at Qatar Collaboration; Texas A; M University College Station Collaboration

    2016-11-01

    Droplet impingement is encountered in numerous technical applications, such as ink jet printing, spray cooling, and fuel injection in internal combustion engines. Even though many studies in droplet impingement were conducted in past, not many have measured the near-wall velocities in the droplet impingement zone. With the goal of gaining a better understanding of the hydrodynamics in the impingement zone, well-controlled experiments are performed in combination with micro-PIV measurements and numerical simulations. Hydrodynamics of HFE-7100 droplets generated using a piezoelectric droplet generator, impinging on a pre-wetted surface is investigated. Micro-PIV studies in the high-velocity impingement zone are performed using one-micron meter fluorescent particles dispersed in HFE-7100 along with the double exposed images. Three-dimensional and 2D-axisymmetric numerical modeling for a transient droplet crown development is performed. The interface between the gas and the liquid is modeled using a Volume of Fluid (VOF) method. Numerical simulation results obtained are observed to be in good agreement with that of the experimental observations. Supported by National Priority Research Program (NPRP) of Qatar National Research Fund (QNRF), Grant No.: NPRP 6-1304-2-525.

  6. Spectral characteristics of heterocyclic compounds with a chain structure, cooled in an ultrasonic jet

    NASA Astrophysics Data System (ADS)

    Povedailo, V. A.; Yakovlev, D. L.

    2006-11-01

    We have recorded the fluorescence excitation spectra of three heterocyclic compounds with a chain structure [BPO (2-phenyl-5-(4-diphenylyl)oxazole), POPOP (1,4-di[2-(5-phenyloxazolyl)]benzene, and TOPOT (1,4-di[2-(5-n-tolyloxazolyl)]benzene] and the fluorescence spectra of POPOP, under conditions where the molecules were cooled in an ultrasonic helium jet. A line structure is observed in the spectra of POPOP and TOPOT; for the BPO molecules, whose configuration changes considerably during electronic excitation, vibrational structure is apparent only in the low-frequency region of the excitation spectrum, and a diffuse spectrum is recorded starting from ν 0 0 + 200 cm-1. For all the compounds, in the spectra we recorded vibrations with frequencies up to 100 cm-1, arising due to the flexibility of the molecular structure. The rotational contours of the lines for the electronic and vibronic transitions of the POPOP molecules (Trot = 10.5 K) and TOPOT molecules (Trot = 15 K) are structureless and bell-shaped. The degree of polarization of the fluorescence Pfl for the jet-cooled POPOP molecules for excitation of vibrations along the absorption band up to 2000 cm-1 above ν 0 0 is practically constant (˜8.4%) and matches Pfl for high-temperature vapors.

  7. Characterization of a cryogenically cooled high-pressure gas jet for laser/cluster interaction experiments

    NASA Astrophysics Data System (ADS)

    Smith, R. A.; Ditmire, T.; Tisch, J. W. G.

    1998-11-01

    We have developed and carried out detailed characterization of a cryogenically cooled (34-300 K), high-pressure (55 kTorr) solenoid driven pulsed valve that has been used to produce dense jets of atomic clusters for high intensity laser interaction studies. Measurements including Rayleigh scattering and short pulse interferometry show that clusters of controlled size, from a few to >104 atoms/cluster can be produced from a broad range of light and heavy gases, at average atomic densities up to 4×1019 atoms/cc. Continuous temperature and pressure control of the valve allows us to vary mean cluster size while keeping the average atomic density constant, and we find that many aspects of the valves behavior are consistent with ideal gas laws. However, we also show that effects including the build up of flow on milliseconds time scales, the cooling of gas flowing into the valve, and condensation of gas inside the valve body at temperatures well above the liquefaction point need to be carefully characterized in order to decouple the operation of the jet from the laser interaction physics.

  8. Multiple Null Point Reconnections in a limb faint cool jet ejection event

    NASA Astrophysics Data System (ADS)

    Tavabi, E.; Koutchmy, S.

    2016-09-01

    Giant spicules and macro- spicules are an important extended rather cool structure between the solar surface and the corona, partly filling the space inside the chromosphere and surrounded by a transition thin region. Their formation and dynamical properties are still mysterious. In order to explain solar limb and disc periodic recurrences of these events, a simulation model assuming quasi- random positions of spicules above the solar limb was studied. We allow a set number of spicules with different physical properties (such as height, lifetime and tilt angle as shown by an individual spicule) randomly occurring. It is assumed that after reaching a maximum length, the spicules are less rapidly falling back to the solar surface. This kind of limb event was often reported in the literature (spike; giant spicule; Ha ejection event; spray etc) but no serious quantitative analysis could be done. Indeed from ground-based observations, it is impossible to deduce precised parameters because the earth atmospheric turbulent effects makes impossible to make small scale measurements. SOT space-borne observations we use are unique in providing well reproducible observations permitting very precise measurements. The study of X-ray jets is an important topic to understand the heating of the solar corona and the origin of the fast wind. The recently launched Hinode mission permitted to observe the cool proxies of these jets with an unprecedented high spatial resolution of 120 km on the Sun. We selected a high cadence sequence of SOT (Hinode) observations taken with both the HCaII and the Hα filter to look at the details of the dynamics revealed by a large jet event. Both wavelet and amplitude spectra analysis were used to analyze the observed kink wave and the time variations of intensities during the event. The results are discussed in the frame of different models implying reconnections with the inference of the dynamical phenomena occurring in the vicinity of several null

  9. The Jet-Cooled High-Resolution IR Spectrum of Formic Acid Cyclic Dimer

    NASA Astrophysics Data System (ADS)

    Goubet, Manuel; Bteich, Sabath; Huet, Therese R.; Pirali, Olivier; Asselin, Pierre; Soulard, Pascale; Jabri, Atef; Roy, P.; Georges, Robert

    2017-06-01

    As the simplest carboxylic acid, formic acid (FA) is an excellent model molecule to investigate the general properties of carboxylic acids. FA is also an atmospherically and astrophysically relevant molecule. It is well known that its dimeric form is predominant in the gas phase at temperatures below 423 K. The cyclic conformation of the dimer (FACD) is an elementary system to be understood for the concerted hydrogen transfer through equivalent hydrogen bonds, an essential process within biomolecules. The IR range is a crucial spectral region, particularly the far-IR, as it gives a direct access to the intermolecular vibrational modes involved in this process. Moreover, due to its centrosymmetric conformation, the FACD exhibits no pure rotation spectrum and, due to spectral line congestion and Doppler broadening, IR bands cannot be rotationally resolved at room temperature. So far, only parts of the ν_{5}-GS band (C-O stretch) have been observed under jet-cooled conditions using laser techniques. We present here six rotationally resolved IR bands of FACD recorded under jet-cooled conditions using the Jet-AILES apparatus and the QCL spectrometer at MONARIS, including the far-IR ν_{24}-GS band (intermolecular in-plane bending). Splitting due to vibration-rotation-tunneling motions are clearly observed. A full spectral analysis is in progress starting from the GS constants obtained by Goroya et al. and with the support of electronic structure calculations. T. Miyazawa and K. S. Pitzer, J. Am. Chem. Soc. 81, 74, 1959 R. Georges, M. Freytes, D. Hurtmans, I. Kleiner, J. Vander Auwera, M. Herman, Chem. Phys. 305, 187, 2004 M. Ortlieb and M. Havenith, J. Phys. Chem. A 111, 7355, 2007; K. G. Goroya, Y. Zhu, P. Sun and C. Duan, J. Chem. Phys. 140, 164311, 2014 This work is supported by the CaPPA project (Chemical and Physical Properties of the Atmosphere) ANR-11-LABX-0005-01

  10. Cooling of Electronically-Excited He2 Molecules in a Microcavity Plasma Jet

    NASA Astrophysics Data System (ADS)

    Su, Rui; Houlahan, Thomas J., Jr.; Eden, J. Gary

    2016-06-01

    Helium dimers in the d3Σ+u excited electronic state with potential energy >24 eV and radiative lifetime of 25 ns have been generated in a microcavity plasma jet and rotationally cooled by supersonic expansion in vacuum. The dynamic process of cooling is recorded by imaging the axis of expansion onto the slit of Czerny-Turner spectrometer, yielding spatial-temporal spectrograms of d3Σ+u→b3Πg (v', v'')=(0, 0) emission. Analysis of the data shows the spatial-temporal evolution of the rotational temperature to be a damped sinusoid that reaches a minimum value of 100K. This reproducible behavior is attributed to the reflection of electrons from a virtual cathode located downstream of the nozzle and indicates that the spatially-averaged electron density is 108 cm-3. We present this observed rotational temperature oscillation during the supersonic cooling process as an example of the potential of our supersonic microplasma expansion as a tool to explore physical dynamics in diatomic molecules having high excitation energies and small lifetimes.

  11. Experiments on free and impinging supersonic microjets

    NASA Astrophysics Data System (ADS)

    Phalnikar, K. A.; Kumar, R.; Alvi, F. S.

    2008-05-01

    The fluid dynamics of microflows has recently commanded considerable attention because of their potential applications. Until now, with a few exceptions, most of the studies have been limited to low speed flows. This experimental study examines supersonic microjets of 100-1,000 μm in size with exit velocities in the range of 300-500 m/s. Such microjets are presently being used to actively control larger supersonic impinging jets, which occur in STOVL (short takeoff and vertical landing) aircraft, cavity flows, and flow separation. Flow properties of free as well as impinging supersonic microjets have been experimentally investigated over a range of geometric and flow parameters. The flowfield is visualized using a micro-schlieren system with a high magnification. These schlieren images clearly show the characteristic shock cell structure typically observed in larger supersonic jets. Quantitative measurements of the jet decay and spreading rates as well as shock cell spacing are obtained using micro-pitot probe surveys. In general, the mean flow features of free microjets are similar to larger supersonic jets operating at higher Reynolds numbers. However, some differences are also observed, most likely due to pronounced viscous effects associated with jets at these small scales. Limited studies of impinging microjets were also conducted. They reveal that, similar to the behavior of free microjets, the flow structure of impinging microjets strongly resembles that of larger supersonic impinging jets.

  12. Numerical study of metal foam heat sinks under uniform impinging flow

    NASA Astrophysics Data System (ADS)

    Andreozzi, A.; Bianco, N.; Iasiello, M.; Naso, V.

    2017-01-01

    The ever-increasing demand for performance improvement and miniaturization of electronics has led to a significant generation of waste heat that must be dissipated to ensure a reliable device operation. The miniaturization of the components complicates this task. In fact, reducing the heat transfer area, at the same required heat rate, it is necessary to increase the heat flux, so that the materials operate in a temperature range suitable to its proper functioning. Traditional heat sinks are no longer capable of dissipating the generated heat and innovative approaches are needed to address the emerging thermal management challenges. Recently, heat transfer in open-cell metal foams under an impinging jet has received attention due to the considerable heat transfer potential of combining two cooling technologies: impinging jet and porous medium. This paper presents a numerical study on Finned Metal Foam (FMF) and Metal Foam (MF) heat sinks under impinging air jet cooling. The analysis is carried out by means of the commercial software COMSOL Multiphysics®. The purpose is to analyze the thermal performance of the metal foam heat sink, finned or not, varying its geometric parameters. Results are presented in terms of predicted dissipated heat rate, convective heat transfer coefficient and pressure losses.

  13. Experimental investigation of impingement heat transfer from a round rib-roughened surface

    NASA Astrophysics Data System (ADS)

    Isman, Mustafa Kemal; Can, Muhiddin

    2017-04-01

    An experimental investigation on impingement heat transfer from a rib-roughened surface is performed. Single, double, and triple rib configurations are tested. The rib is also located at three different positions for a single rib case. The Reynolds number is varied from 10,000 to 50,000 whereas the dimensionless jet-to-surface distance (z/D) is kept constant as 8. Results show that, the Nusselt number decreases just before a rib. After the rib, however, the Nusselt number decreases by a larger amount. Since ribs cause a reincreasing in the Nusselt number after the stagnation point and since the stagnation point Nusselt number is not affected by ribs, they can be used to enhance heat transfer especially for spot cooling applications. It is also obtained that using ribs is more useful for low speed impinging jets, when heat transfer from the whole surface is considered.

  14. Femoroacetabular impingement.

    PubMed

    Volpon, José Batista

    2016-01-01

    The femoroacetabular impingement (FAI) is as condition recently characterized that results from the abnormal anatomic and functional relation between the proximal femur and the acetabular border, associated with repetitive movements, which lead labrum and acetabular cartilage injuries. Such alterations result from anatomical variations such as acetabular retroversion or decrease of the femoroacetabular offset. In addition, FAI may result from acquired conditions as malunited femoral neck fractures, or retroverted acetabulum after pelvic osteotomies. These anomalies lead to pathological femoroacetabular contact, which in turn create impact and shear forces during hip movements. As a result, there is early labrum injury and acetabulum cartilage degeneration. The diagnosis is based on the typical clinical findings and images. Treatment is based on the correction of the anatomic anomalies, labrum debridement or repair, and degenerate articular cartilage removal. However, the natural evolution of the condition, as well as the outcome from long-term treatment, demand a better understanding, mainly in the asymptomatic individuals.

  15. Pyrene measurements in sooting low pressure methane flames by jet-cooled laser-induced fluorescence.

    PubMed

    Wartel, M; Pauwels, J-F; Desgroux, P; Mercier, X

    2011-12-15

    This paper presents in detail the study we carried out concerning the pyrene measurement by jet-cooled laser-induced fluorescence (JCLIF) in different sooting low pressure methane flames. The aim of this paper is both to demonstrate the potentialities of this technique for the measurement of such moderately sized polycyclic aromatic hydrocarbons under sooting flame conditions and to provide new experimental data for the understanding and the development of chemical models of the soot formation processes. Several concentration profiles of pyrene measured in different sooting flame (various pressure and equivalence ratio) are presented. The validation of the JCLIF method for pyrene measurements is explained in detail as well as the calibration procedure, based on the standard addition method, which has been implemented for the quantification of the concentration profiles. Sensitivity lower than 1 ppb was obtained for the measurement of this species under sooting flame conditions.

  16. High-resolution spectroscopy of jet-cooled CH{sub 5}{sup +}: Progress

    SciTech Connect

    Savage, C.; Dong, F.; Nesbitt, D. J.

    2015-01-22

    Protonated methane (CH{sub 5}{sup +}) is thought to be a highly abundant molecular ion in interstellar medium, as well as a potentially bright μwave- mm wave emitter that could serve as a tracer for methane. This paper describes progress and first successful efforts to obtain a high resolution, supersonically cooled spectrum of CH{sub 5}{sup +} in the 2900-3100 cm{sup −1} region, formed in a slit supersonic discharge at low jet temperatures and with sub-Doppler resolution. Short term precision in frequency measurement (< 5 MHz on an hour time scale) is obtained from a thermally controlled optical transfer cavity servoloop locked onto a frequency stabilized HeNe laser. Long term precision (< 20 MHz day-to-day) due to pressure, temperature and humidity dependent index of refraction effects in the optical transfer cavity is also present and discussed.

  17. Identification of Structural Motifs of Imidazolium Based Ionic Liquids from Jet-Cooled Infrared Spectroscopy.

    NASA Astrophysics Data System (ADS)

    Young, Justin W.; Booth, Ryan S.; Annesley, Christopher; Stearns, Jaime A.

    2016-06-01

    Highly variable and potentially revolutionary, ionic liquids (IL) are a class of molecules with potential for numerous Air Force applications such as satellite propulsion, but the complex nature of IL structure and intermolecular interactions makes it difficult to adequately predict structure-property relationships in order to make new IL-based technology a reality. For example, methylation of imidazolium ionic liquids leads to a substantial increase in viscosity but the underlying physical mechanism is not understood. In addition the role of hydrogen bonding in ILs, especially its relationship to macroscopic properties, is a matter of ongoing research. Here, structural motifs are identified from jet-cooled infrared spectra of different imidazolium based ionic liquids, such as 1-ethyl-3-methylimidazolium bis(trifluoromethyl-sulfonyl)imide. Measurements of the C-H stretches indicate three structural families present in the gas phase.

  18. Vibronic spectrum of jet-cooled 2-chloro-5-fluorobenzyl radical: Assignments and substituent effect

    NASA Astrophysics Data System (ADS)

    Chae, Sang Youl; Yoon, Young Wook; Lee, Sang Kuk

    2014-09-01

    We report spectroscopic constants of the jet-cooled 2-chloro-5-fluorobenzyl radical which was generated by corona discharge of precursor 2-chloro-5-fluorotoluene seeded in a large amount of helium carrier gas using a pinhole-type glass nozzle. The visible vibronic emission spectrum was recorded with a long-path monochromator. From an analysis of the spectrum observed, the electronic energy of the D1 → D0 transition and vibrational mode frequencies in the D0 state were determined for the first time by comparing its vibronic data with those of a precursor and ab initio calculation. In addition, the substituent effect on electronic transition energy has been discussed.

  19. Spectroscopic observation of jet-cooled 2,5-dichlorobenzyl radical generated by corona discharge

    NASA Astrophysics Data System (ADS)

    Yi, Eun Hye; Yoon, Young Wook; Lee, Sang Kuk

    2014-07-01

    Vibronically excited but jet-cooled 2,5-dichlorobenzyl radical was generated from 2,5-dichlorotoluene precursor in a large excess of helium carrier gas, from which the visible vibronic emission spectrum was recorded. From an analysis of the spectrum observed, it was found that the origin band shows larger shift to red than those expected from mono-substitutions, which has been discussed in terms of orientation of substituents. Also, the electronic energy of the D1 → D0 transition and vibrational mode frequencies at the ground electronic state of the 2,5-dichlorobenzyl radical were determined in comparison with the known vibrational data of precursor and ab initio calculations.

  20. Spectroscopic study of jet-cooled deuterated porphycenes: unusual isotopic effects on proton tunneling.

    PubMed

    Mengesha, Ephriem T; Zehnacker-Rentien, Anne; Sepioł, J; Kijak, M; Waluk, J

    2015-02-12

    Porphycene (Pc) is a well-known model for studying double hydrogen transfer, which shows vibrational-mode-specific tunneling splitting when isolated in supersonic jets or helium nanodroplets. The effect of deuteration on tunneling splitting is reported for jet-cooled heterogeneous, deuterated Pc samples (Pc-d(mix)) with the prevailing contribution of Pc-d12 isotopologue. The sample introduced into the gas phase using laser desorption is studied by means of laser-induced fluorescence (LIF) and single vibronic level fluorescence (SVLF) measurements, in combination with quantum chemical calculations. The influence of molecular symmetry is studied by comparing Pc, Pc-d12, and Pc-d11. The spectra of Pc-d12 show strong similarity to those of the parent undeuterated porphycene (Pc). Comparable tunneling splitting is observed in the two isotopologues, both for the 0-0 transition and the most efficient promoting 2Ag mode. In contrast, an unusual isotopic effect is observed for the totally symmetrical 4Ag mode. While this vibration behaves as a neutral mode in Pc, neither enhancing nor decreasing the tunneling efficiency, it strongly promotes hydrogen transfer in Pc-d12. This observation is explained in terms of modification of the displacement vectors of the 4Ag mode upon deuteration. It demonstrates that isotope substitution affects hydrogen transfer even when the weak structural modifications are far from the reaction center, emphasizing the strongly multidimensional nature of the tunneling process.

  1. A Computational Study for the Utilization of Jet Pulsations in Gas Turbine Film Cooling and Flow Control

    NASA Technical Reports Server (NTRS)

    Kartuzova, Olga V.

    2012-01-01

    This report is the second part of a three-part final report of research performed under an NRA cooperative Agreement contract. The first part is NASA/CR-2012-217415. The third part is NASA/CR-2012-217417. Jets have been utilized in various turbomachinery applications in order to improve gas turbines performance. Jet pulsation is a promising technique because of the reduction in the amount of air removed from compressor. In this work two areas of pulsed jets applications were computationally investigated using the commercial code Fluent (ANSYS, Inc.); the first one is film cooling of High Pressure Turbine (HPT) blades and second one is flow separation control over Low Pressure Turbine (LPT) airfoil using Vortex Generator Jets (VGJ). Using pulsed jets for film cooling purposes can help to improve the effectiveness and thus allow higher turbine inlet temperature. Effects of the film hole geometry, blowing ratio and density ratio of the jet, pulsation frequency and duty cycle of blowing on the film cooling effectiveness were investigated. As for the low-pressure turbine (LPT) stages, the boundary layer separation on the suction side of airfoils can occur due to strong adverse pressure gradients. The problem is exacerbated as airfoil loading is increased. Active flow control could provide a means for minimizing separation under conditions where it is most severe (low Reynolds number), without causing additional losses under other conditions (high Reynolds number). The effects of the jet geometry, blowing ratio, density ratio, pulsation frequency and duty cycle on the size of the separated region were examined in this work. The results from Reynolds Averaged Navier-Stokes and Large Eddy Simulation computational approaches were compared with the experimental data.

  2. Jet-Cooled Spectroscopy on the Ailes Infrared Beamline of the Synchrotron Radiation Facility Soleil

    NASA Astrophysics Data System (ADS)

    Georges, Robert

    2015-06-01

    . Vervloet, Phys. Chem. Chem. Phys. 15, 10141-10150 (2013) The cyclic ground state structure of the HF trimer revealed by far-infrared jet-cooled Fourier transform spectroscopy. P. Asselin, P. Soulard, B. Madebène, M. Goubet, T. R. Huet, R. Georges, O. Pirali and P. Roy, Phys. Chem. Chem. Phys. 16(10), 4797-806 (2014) Standard free energy of the equilibrium between the trans-monomer and the cyclic-dimer of acetic acid in the gas phase from infrared spectroscopy. M. Goubet, P. Soulard, O. Pirali, P. Asselin, F. Réal, S. Gruet, T. R. Huet, P. Roy and R. Georges, Phys. Chem. Chem. Phys. DOI: 10.1039/c4cp05684a

  3. Gear Lubrication and Cooling Experiment and Analysis

    NASA Technical Reports Server (NTRS)

    Townsend, D. P.; Akin, L. S.

    1983-01-01

    A gear tooth temperature analysis was performed using a finite element method combined with a calculated heat input, a calculated oil jet impingement depth, and estimated heat transfer coefficients for the different parts of the gear tooth that are oil cooled and air cooled. Experimental measurements of gear tooth average surface temperature and gear tooth instantaneous surface temperature were made with a fast response, infrared, radiometric microscope. Increasing oil pressure has a significant effect on both average surface temperature and peak surface temperature at loads above 1895 N/cm(1083 lb/in) and speeds of 10,000 and 7500 rpm. Both increasing speed (from 5000 to 10,000 rpm) at constant speed cause a significant rise in the average surface temperature and in the instantaneous peak surface temperatures on the gear teeth. The oil jet pressure required to provide the best cooling for gears is the pressure required to obtain full gear tooth impingement. Calculated results for gear tooth temperatures were close to experimental results for various oil jet impingement depths for identical operating conditions.

  4. Bright Fans in Mars Cryptic Region Caused by Adiabatic Cooling of CO2 Gas Jets.

    NASA Astrophysics Data System (ADS)

    Titus, T. N.; Kieffer, H. H.; Langevin, Y.; Murchie, S.; Seelos, F.; Vincendon, M.

    2007-12-01

    Over the last decade, observations of the retreat of the southern seasonal cap of Mars have revealed the presence of exotic processes within an area now informally referred to as the cryptic region. The appearance of dark spots, fans, blotches, and halos have been a "hot" topic of scientific discussion since they were first observed by the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) [Malin et al., 1998]. Further observations by the Mars Odyssey (ODY) Thermal Emission Imaging System (THEMIS) showed that the dark features remained cold throughout the early-to-mid spring, suggesting that these features were either CO2 ice or were in thermal contact with CO2 ice [Kieffer et al., 2006]. In this paper, we present observations in the near-infrared at spatial resolutions that have previously been unavailable. We present further evidence that many of these features in the cryptic region are the result of cold jets, as first described by Kieffer [2000, 2007]. The adiabatic cooling of gas spewing downwind from the jets produces CO2 frost, thus forming the bright fans. The bright fans appear to be devoid of H2O ice, thus further supporting the hypothesis that they are formed from the downwind settling of CO2 frost. In some areas, the bright fans are adjacent to dark fans and appear to start from common vertices, while in other areas, bright fan-like deposits occur without the strong presence of dark fans. References: Kieffer, H.H. (2000) Annual Punctuated CO2 Slab-Ice and Jets on Mars, International Conference on Mars Polar Science and Exploration, p. 93. Kieffer, H.H. et al. (2006) Nature, 442,793-796. Kieffer, H.H. (2007) JGR, in press. Malin, M.C., M.H. Carr, G.E. Danielson, M.E. Davies, W.K. Hartmann, A.P. Ingersoll, P.B. James, H. Masursky, A.S. McEwen, L.A. Soderblom, P. Thomas, J. Veverka, M.A. Caplinger, M.A. Ravine, and T.A. Soulanille (1998) Early views of the Martian surface from the Mars orbiter camera of Mars global surveyor, Science, 279, 1681-1685.

  5. Laser Induced Fluorescence Spectroscopy of Jet-Cooled CaOCa

    NASA Astrophysics Data System (ADS)

    Sullivan, Michael N.; Frohman, Daniel J.; Heaven, Michael; Fawzy, Wafaa M.

    2016-06-01

    The group IIA metals have stable hypermetallic oxides of the general form MOM. Theoretical interest in these species is associated with the multi-reference character of the ground states. It is now established that the ground states can be formally assigned to the M+O^{2-M+} configuration, which leaves two electrons in orbitals that are primarily metal-centered ns orbitals. Hence the MOM species are diradicals with very small energy spacings between the lowest energy singlet and triplet states. Previously, we have characterized the lowest energy singlet transition (1Σ^{+u← X1Σ+g}) of BeOBe. In this study we obtained the first electronic spectrum of CaOCa. Jet-cooled laser induced fluorescence spectra were recorded for multiple bands that occured within the 14,800 - 15,900 cm-1 region. Most of the bands exhibited simple P/R branch rotational line patterns that were blue-shaded. Only even rotational levels were observed, consistent with the expected X 1Σ^{+g} symmetry of the ground state (40Ca has zero nuclear spin). A progression of excited bending modes was evident in the spectrum, indicating that the transition is to an upper state that has a bent equilibrium geometry. Molecular constants were extracted from the rovibronic bands using PGOPHER. The experimental results and interpretation of the spectrum, which was guided by the predictions of electronic structure calculation, will be presented.

  6. Laser Induced Fluorescence Spectroscopy of Jet-Cooled MgOMg

    NASA Astrophysics Data System (ADS)

    Sullivan, Michael N.; Frohman, Daniel J.; Heaven, Michael; Fawzy, Wafaa M.

    2017-06-01

    The group IIA metals have stable hypermetallic oxides of the general form MOM. Theoretical interest in these species is associated with the multi-reference character of the ground states. It is now established that the ground states can be formally assigned to the M^{+O^{2-}M^{+}} configuration, which leaves two electrons in orbitals that are primarily metal-centered ns orbitals. Hence the MOM species are diradicals with very small energy spacings between the lowest energy singlet and triplet states. Previously, we have characterized the lowest energy singlet transition (^{1Σ^{+}_{u}← ^{1}Σ^{+}_{g}}) of BeOBe. Preliminary data for the first electronic transition of the isovalent species, CaOCa, was presented previously (71^{st} ISMS, talk RI10). We now report the first electronic spectrum of MgOMg. Jet-cooled laser induced fluorescence spectra were recorded for multiple bands that occurred within the 21,000 - 24,000 cm^{-1} range. Most of the bands exhibited simple P/R branch rotational line patterns that were blue-shaded. Only even rotational levels were observed, consistent with the expected X ^{1Σ^{+}_{g}} symmetry of the ground state (^{24Mg} has zero nuclear spin). Molecular constants were extracted from the rovibronic bands using PGOPHER. The experimental results and interpretation of the spectrum, which was guided by the predictions of electronic structure calculation, will be presented.

  7. Electronic spectra of jet-cooled isoindoline: Spectroscopic determination of energy difference between conformational isomers

    NASA Astrophysics Data System (ADS)

    Tanaka, Sei'ichi; Okuyama, Katsuhiko

    2010-04-01

    The electronic spectra of jet-cooled isoindoline between the electronic ground (S0) state and the ππ ∗ lowest-excited singlet state (S1) were observed by the fluorescence excitation and single-vibronic-level dispersed fluorescence methods. The low-frequency progression due to the puckering vibration appeared in both spectra. Analysis of dispersed spectra together with geometry optimization at the level of B3LYP/6-311+G(d) indicated the presence of conformational isomers possessing axial and equatorial N-H bonds with respect to the molecular plane. The 0-0 bands of the axial and equatorial conformers were measured at 37 022 and 36 761 cm-1, respectively. Three common levels in the S1 state accessible from the respective S0-state zero levels were observed. From their transition frequencies, the S0-state energy difference between the isomers was determined to be 47.7±0.2 cm-1, where the axial conformer was more stable. In the S1 state, the energy difference was 213.7±0.2 cm-1, and the equatorial conformer was more stable. The cause of switching from a stable conformation upon excitation is discussed in terms of the electron conjugation between the π∗ orbital in benzene and the lone pair orbital of nitrogen.

  8. Dispersed Fluorescence Spectroscopy of Jet-Cooled Isobutoxy, 2-METHYL-1-BUTOXY, and Isopentoxy Radicals

    NASA Astrophysics Data System (ADS)

    Reza, Md Asmaul; Reilly, Neil J.; Alam, Jahangir; Mason, Amy; Liu, Jinjun

    2015-06-01

    It is well known that rate constants of certain reactions of alkoxy radicals, e.g., unimolecular dissociation (decomposition by C-C bond fission) and isomerization via 1,5 H-shift, are highly sensitive to the molecular structure. In the present and the next talks, we report dispersed fluorescence (DF) spectra of various alkoxy radicals obtained under supersonic jet-cooled conditions by pumping different vibronic bands of their tilde B ← tilde X laser induced fluorescence (LIF) excitation spectra. This talk focuses on the DF spectra of 2-methyl-1-propoxy (isobutoxy), 2-methyl-1-butoxy, and 3-methyl-1-butoxy (isopentoxy). In all cases, strong CO-stretch progressions were observed, as well as transitions to other vibrational levels, including low-frequency ones. Quantum chemical calculations were carried out to aid the assignment of the DF spectra. Franck-Condon factors were calculated using the ezSpectrum program. Wu, Q.; Liang, G.; Zu, L.; Fang, W. J. Phys. Chem A 2012, 116, 3156-3162. Lin, J.; Wu, Q.; Liang, G.; Zu, L.; Fang, W. RSC Adv. 2012, 2, 583-589. Liang, G.; Liu , C.; Hao, H.; Zu, L.; Fang, W. J. Phys. Chem. A 2013, 117, 13229- 13235. V. Mozhayskiy and A. I. Krylov, http://iopenshell.usc.edu/

  9. The UV Spectroscopy of Jet-Cooled 3-PHENYL-2-PROPYNENITRILE

    NASA Astrophysics Data System (ADS)

    Jawad, Khadija M.; Zwier, Timothy S.

    2016-06-01

    The atmosphere of Saturn's moon Titan is replete with hydrocarbons and nitriles, but knowledge of the formation and sink processes as well as the identities of molecules on the large end of photochemical models of the atmosphere is very limited. 3-phenyl-2-propynenitrile (Ph-C≡C-C≡N) is of potential importance in this atmosphere because it is a likely product of photochemical reaction between cyanoacetylene and benzene, bringing together two of the key functional groups in Titan's atmosphere in a single molecule. We present the UV spectrum of this molecule in the gas phase, under jet-cooled conditions, using 2-color resonant two-photon ionization. The spectrum was recorded from 292-208nm, taking advantage of the wide tunability of a BBO-based OPO as the excitation source. On its long wavelength end, the spectrum has sharp transitions arising from a ΠΠ* transition characteristic of a phenyl derivative, while deeper into the UV the spectrum is broadened in a manner reminiscent of cyanoacteylene.

  10. The introduction of tangential or perpendicular nonisothermic plane jets into a turbulent crossflow for the purpose of film cooling

    NASA Astrophysics Data System (ADS)

    Reinheimer, G.; Beer, H.

    1983-05-01

    Combustion-chamber-wall cooling by injection of a cold-air film through tangential or normal jets, a technique suitable for gas-turbine applications, is modelled mathematically in terms of adiabatic-wall-temperature distribution and cooling efficiency. The vector forms of the conservation equations for mass, energy, and momentum are developed in terms of a curvilinear orthogonal coordinate system and used to characterize the flow parameters; similarity-profile assumptions, boundary-layer simplifications, and an entrainment hypothesis based on the suction effect of the jet are applied to allow the modelling of normal, tangential, and mixed tangential/normal injection on a numerical basis. Model predictions are compared to original and published experimental measurements, and good agreement is found in most cases.

  11. The high-resolution infrared spectrum of the ν3 +ν5 combination band of jet-cooled propyne

    NASA Astrophysics Data System (ADS)

    Doney, K. D.; Zhao, D.; Bouwman, J.; Linnartz, H.

    2017-09-01

    We present the first detection of the high-resolution ro-vibrational spectrum of the ν3 +ν5 combination band of propyne around 3070 cm-1. The fully resolved spectrum is recorded for supersonically jet-cooled propyne using continuous wave cavity ring-down spectroscopy (cw-CRDS). The assignments are supported with the help of accurate ab initio vibration-rotation interaction constants (αi) and anharmonic frequencies. A detailed analysis of the rotationally cold spectrum is given.

  12. Effects of Nozzle Scale, Total Temperature and an Afterburner on Jet Noise from a Pre-Cooled Turbojet Engine

    NASA Astrophysics Data System (ADS)

    Araki, Mikiya; Sano, Takayuki; Fukuda, Masayuki; Kojima, Takayuki; Taguchi, Hideyuki; Nishida, Shunsuke; Imamura, Osamu; Shiga, Seiichi; Tsue, Mitsuhiro

    Effects of nozzle scale, total temperature, and an afterburner on jet noise characteristics from a pre-cooled turbojet engine are investigated experimentally. In JAXA (Japan Aerospace Exploration Agency), a pre-cooled turbojet engine for an HST (Hypersonic transport) is under development. In the present study, 1.0%- and 2.4%-scaled models of the rectangular plug nozzle (Nozzles I and II) are manufactured, and the jet noise characteristics are investigated under a wide range of total temperatures. For Nozzle I, no air-heater is utilized and the total temperature is 290K. For Nozzle II, a pebble heater and an afterburner (AB) are utilized upstream of the nozzle model, and the total temperature is varied from 520K (pebble heater) to 1540K (pebble heater + AB). The total pressure is set at 0.27 and 0.30MPa(a) for both nozzle models. Jet noise is measured using a high-frequency microphone set at 135 deg from the engine inlet, and normalized jet noise spectra are obtained based on AUjn law and Helmholtz number. For cases without afterburner, the normalized spectra agrees well regardless of the nozzle scale and total temperature where the velocity index lies from n = 7.7 to 9.2, and the correlation factor between the two facilities is shown to be about 1dB. For the case with afterburner, the normalized spectrum does not agree with other conditions where the velocity index n seems to be about 4.

  13. High-speed thermal imaging of yttria-stabilized zirconia droplet impinging on substrate in plasma spraying

    SciTech Connect

    Shinoda, Kentaro; Murakami, Hideyuki; Kuroda, Seiji; Oki, Sachio; Takehara, Kohsei; Etoh, Takeharu Goji

    2007-05-07

    The authors have developed an in situ monitoring system that captures the impacting phenomena of plasma-sprayed particles at 1x10{sup 6} frames/s. The system clearly captured deformation and cooling processes of an yttria-stabilized zirconia droplet of 50 {mu}m in diameter impinging at 170 m/s on a smooth quartz glass substrate kept at room temperature. The images show that the liquid sheet jetting out sideways from the droplet detached from the substrate and kept on spreading without disintegration until its maximum extent. While the sheet was spreading, the center region of the flattened droplet cooled down much more rapidly.

  14. Techniques for increasing the film cooling efficiency by means of the vortex near-wall jets

    NASA Astrophysics Data System (ADS)

    Terekhov, V. I.; Shishkin, N. E.

    2013-12-01

    Experimental results on the effect of the methods of gas cooling arrangement on thermal efficiency are presented. The swirl cooling is considered at both injecting along the axis and co-axial supply of the cooling gas. The influence of swirling degree, density ratio of both flows and flow regimes on the efficiency of near-wall cooling is considered.

  15. Techniques for increasing the film cooling efficiency by means of the vortex near-wall jets

    NASA Astrophysics Data System (ADS)

    Terekhov, V. I.; Shishkin, N. E.

    2014-12-01

    Experimental results on the effect of the methods of gas cooling arrangement on thermal efficiency are presented. The swirl cooling is considered at both injecting along the axis and co-axial supply of the cooling gas. The influence of swirling degree, density ratio of both flows and flow regimes on the efficiency of near-wall cooling is considered.

  16. Jet-Cooled Laser-Induced Fluorescence Spectroscopy of T-Butoxy

    NASA Astrophysics Data System (ADS)

    Reilly, Neil J.; Cheng, Lan; Stanton, John F.; Miller, Terry A.; Liu, Jinjun

    2015-06-01

    The vibrational structures of the tilde A ^2A_1 and tilde X ^2E states of t-butoxy were obtained in jet-cooled laser-induced fluorescence (LIF) and dispersed fluorescence (DF) spectroscopic measurements. The observed transitions are assigned based on vibrational frequencies calculated using Complete Active Space Self-Consistent Field (CASSCF) method and the predicted Franck-Condon factors. The spin-orbit (SO) splitting was measured to be 35(5) cm-1 for the lowest vibrational level of the ground (tilde X ^2E) state and increases with increasing vibrational quantum number of the CO stretch mode. Vibronic analysis of the DF spectra suggests that Jahn-Teller (JT)-active modes of the ground-state t-butoxy radical are similar to those of methoxy and would be the same if methyl groups were replaced by hydrogen atoms. Coupled-cluster calculations show that electron delocalization, introduced by the substitution of hydrogens with methyl groups, reduces the electronic contribution of the SO splittings by only around ten percent, and a calculation on the vibronic levels based on quasidiabatic model Hamiltonian clearly attributes the relatively small SO splitting of the tilde X ^2E state of t-butoxy mainly to stronger reduction of orbital angular momentum by the JT-active modes when compared to methoxy. The rotational and fine structure of the LIF transition to the first CO stretch overtone level of the tilde A^2A_1 state has been simulated using a spectroscopic model first proposed for methoxy, yielding an accurate determination of the rotational constants of both tilde A and tilde X states.

  17. The Penetration Behavior of an Annular Gas-Solid Jet Impinging on a Liquid Bath: The Effects of the Density and Size of Solid Particles

    NASA Astrophysics Data System (ADS)

    Chang, J. S.; Sohn, H. Y.

    2012-08-01

    Top-blow injection of a gas-solid jet through a circular lance is used in the Mitsubishi Continuous Smelting Process. One problem associated with this injection is the severe erosion of the hearth refractory below the lances. A new configuration of the lance to form an annular gas-solid jet rather than the circular jet was designed in this laboratory. With this new configuration, the solid particles fed through the center tube leave the lance at a much lower velocity than the gas, and the penetration behavior of the jet is significantly different from that with a circular lance where the solid particles leave the lance at the same high velocity as the gas. In previous cold-model investigations in this laboratory, the effects of the gas velocity, particle feed rate, lance height of the annular lance, and the cross-sectional area of the gas jet were studied and compared with the circular lance. This study examined the effect of the density and size of the solid particles on the penetration behavior of the annular gas-solid jet, which yielded some unexpected results. The variation in the penetration depth with the density of the solid particles at the same mass feed rate was opposite for the circular lance and the annular lance. In the case of the circular lance, the penetration depth became shallower as the density of the solid particles increased; on the contrary, for the annular lance, the penetration depth became deeper with the increasing density of particles. However, at the same volumetric feed rate of the particles, the density effect was small for the circular lance, but for the annular lance, the jets with higher density particles penetrated more deeply. The variation in the penetration depth with the particle diameter was also different for the circular and the annular lances. With the circular lance, the penetration depth became deeper as the particle size decreased for all the feed rates, but with the annular lance, the effect of the particle size was

  18. Posterior ankle impingement.

    PubMed

    Giannini, Sandro; Buda, Roberto; Mosca, Massimiliano; Parma, Alessandro; Di Caprio, Francesco

    2013-03-01

    Posterior ankle impingement is a common cause of chronic ankle pain and results from compression of bony or soft tissue structures during ankle plantar flexion. Bony impingement is most commonly related to an os trigonum or prominent trigonal process. Posteromedial soft tissue impingement generally arises from an inversion injury, with compression of the posterior tibiotalar ligament between the medial malleolus and talus. Posterolateral soft tissue impingement is caused by an accessory ligament, the posterior intermalleolar ligament, which spans the posterior ankle between the posterior tibiofibular and posterior talofibular ligaments. Finally, anomalous muscles have also been described as a cause of posterior impingement.

  19. Externally blown flap impingement noise.

    NASA Technical Reports Server (NTRS)

    Putnam, T. W.; Lasagna, P. L.

    1972-01-01

    An investigation of externally blown flap impingement noise was conducted using a full-scale turbofan engine and aircraft wing. The noise produced with a daisy nozzle installed on the engine exhaust system was greater than that produced by a conical nozzle at the same thrust. The daisy nozzle caused the jet velocity to decay about 35 percent at the flap. The presence of the wing next to the conical nozzle increased the noise, as did increasing the flap deflection. Compared with the conical nozzle, the daisy nozzle produced slightly less noise at a flap deflection of 60 deg but produced more noise at the lower flap deflections tested.

  20. Evaluation of Impinging Stream Vortex Chamber Concepts for Liquid Rocket Engine Applications

    NASA Technical Reports Server (NTRS)

    Trinh, Huu; Kopicz, Charles; Bullard, Brad; Michaels, Scott

    2003-01-01

    NASA Marshall Space Flight Center (MSFC) and the U. S. Army are jointly investigating vortex chamber concepts for cryogenic oxygen/hydrocarbon fuel rocket engine applications. One concept, the Impinging Stream Vortex Chamber Concept (ISVC), has been tested with gel propellants at AMCOM at Redstone Arsenal, Alabama. A version of this concept for the liquid oxygen (LOX)/hydrocarbon fuel (RP-1) propellant system is derived from the one for the gel propellant. An unlike impinging injector is employed to deliver the propellants to the chamber. MSFC has also designed two alternative injection schemes, called the chasing injectors, associated with this vortex chamber concept. In these injection techniques, both propellant jets and their impingement point are in the same chamber cross-sectional plane. One injector has a similar orifice size with the original unlike impinging injector. The second chasing injector has small injection orifices. The team has achieved their objectives of demonstrating the self-cooled chamber wall benefits of ISVC and of providing the test data for validating computational fluids dynamics (CFD) models. These models, in turn, will be used to design the optimum vortex chambers in the future.

  1. Fundamental Study of a Jet-in-Cross-Flow Interacting with a Vortex Generator for Film Cooling Applications

    NASA Technical Reports Server (NTRS)

    Zaman, Khairul; Rigby, David; Heidmann, James

    2009-01-01

    Results of an experimental study are presented on the effectiveness of a vortex generator (VG) in preventing lift-off of a jet-in-cross-flow (JICF). The study is pertinent to film-cooling applications and its relevance to NASA programs is first briefly discussed. In the experiment, the jet issues into the boundary layer at an angle of 20deg to the free-stream. The effect of a triangular, ramp-shaped VG is studied while varying its geometry and location. Detailed flow-field properties are obtained for a case in which the height of the VG and the diameter of the orifice are comparable to the approach boundary layer thickness. The VG produces a streamwise vortex pair with vorticity magnitude three times larger (and of opposite sense) than that found in the JICF alone. Such a VG appears to be most effective in keeping the jet attached to the wall. The effect of parametric variation is studied mostly from surveys ten diameters downstream from the orifice. Results over a range of jet-to-freestream momentum flux ratio (1jet. On the other hand, when the height is doubled, the jet core is dissipated due to larger turbulence intensity. Varying the location of the VG, over a distance of three diameters from the orifice, is found to have little impact.

  2. Jets.

    PubMed

    Rhines, Peter B.

    1994-06-01

    This is a discussion of concentrated large-scale flows in planetary atmospheres and oceans, argued from the viewpoint of basic geophysical fluid dynamics. We give several elementary examples in which these flows form jets on rotating spheres. Jet formation occurs under a variety of circumstances: when flows driven by external stress have a rigid boundary which can balance the Coriolis force, and at which further concentration can be caused by the beta effect; when there are singular lines like the line of vanishing windstress or windstress-curl, or the Equator; when compact sources of momentum, heat or mass radiate jet-like beta plumes along latitude circles; when random external stirring of the fluid becomes organized by the beta effect into jets; when internal instability of the mass field generates zonal flow which then is concentrated into jets; when bottom topographic obstacles radiate jets, and when frontogenesis leads to shallow jet formation. Essential to the process of jet formation in stratified fluids is the baroclinic life cycle described in geostrophic turbulence studies; there, conversion from potential to kinetic energy generates eddy motions, and these convert to quasibarotropic motions which then radiate and induce jet-like large-scale circulation. Ideas of potential vorticity stirring by eddies generalize the notion of Rossby-wave radiation, showing how jets embedded in an ambient potential vorticity gradient (typically due to the spherical geometry of the rotating planet) gain eastward momentum while promoting broader, weaker westward circulation. Homogenization of potential vorticity is an important limit point, which many geophysical circulations achieve. This well-mixed state is found in subdomains of the terrestrial midlatitude oceans, the high-latitude circumpolar ocean, and episodically in the middle atmosphere. Homogenization expels potential vorticity gradients vertically to the top and bottom of the fluid, and sideways to the edges of

  3. Jet fuel from 18 cool-season oilseed feedstocks in a semi-arid environment

    NASA Astrophysics Data System (ADS)

    Allen, Brett; Jabro, Jay

    2017-04-01

    Renewable jet fuel feedstocks can potentially offset the demand for petroleum based transportation resources, diversify cropping systems, and provide numerous ecosystem services . However, identifying suitable feedstock supplies remains a primary constraint to adoption. A 4-yr, multi-site experiment initiated in fall 2012 investigated the yield potential of six winter- and twelve spring-types of cool-season oilseed feedstocks. Sidney, MT (250 mm annual growing season precipitation) was one of eight sites in the western USA with others in Colorado, Idaho, Iowa, Minnesota, North Dakota, Oregon, and Texas. Winter types of Camelina sativa (1), Brassica napus (4), and B. rapa (1) were planted in mid-September, while spring types of Camelina sativa (1), B. napus (4), B. rapa (1), B. juncea (2), B. carinata (2), and Sinapis alba (2) were planted in early to late April. Seeding rates varied by entry and were between 4 to 11 kg/ha. All plots were under no-till management. Plots were 3 by 9 m with each treatment (oilseed entry) replicated four times. Camelina 'Joelle' was the only fall-seeded entry that survived winters with little to no snow cover on plots and where minimum air temperature reached -32°C. Stands of 'Joelle' in the spring of all years were excellent. 'Joelle' plots were typically harvested in July, while spring types were harvested 2-6 weeks later. Severe hailstorms during the late growing seasons of 2013 and 2015 resulted in up to 95% seed loss, preventing normal seed yield harvest of spring types. The B. carinata and spring camelina were the least and most susceptible to hail damage during plant maturity, respectively. 'Joelle' winter camelina was harvested before the severe weather in both years, showing the benefit of an early maturing crop in regions prone to late season hail. Overall, camelina was the only winter type that showed potential as an oilseed feedstock due to its superior winter hardiness. For spring types, B. napus, Camelina sativa, and B

  4. Occult hemoglobin as an indicator of impingement stress in fishes

    SciTech Connect

    Not Available

    1980-01-01

    During the process of impingement on cooling system intake screens, fish may be subject to different types of stress, the total of which often results in the death of individual fish. This report assesses the use of occult hemoglobin in fish demand mucus as an indicator of impingement stress. (ACR)

  5. Intelligent Engine Systems: Thermal Management and Advanced Cooling

    NASA Technical Reports Server (NTRS)

    Bergholz, Robert

    2008-01-01

    The objective is to provide turbine-cooling technologies to meet Propulsion 21 goals related to engine fuel burn, emissions, safety, and reliability. Specifically, the GE Aviation (GEA) Advanced Turbine Cooling and Thermal Management program seeks to develop advanced cooling and flow distribution methods for HP turbines, while achieving a substantial reduction in total cooling flow and assuring acceptable turbine component safety and reliability. Enhanced cooling techniques, such as fluidic devices, controlled-vortex cooling, and directed impingement jets, offer the opportunity to incorporate both active and passive schemes. Coolant heat transfer enhancement also can be achieved from advanced designs that incorporate multi-disciplinary optimization of external film and internal cooling passage geometry.

  6. Enhancement of Heat Transfer with Pool and Spray Impingement Boiling on Microporous and Nanowire Surface Coatings

    SciTech Connect

    Thiagarajan, S. J.; Wang, W.; Yang, R.; Narumanchi, S.; King, C.

    2010-09-01

    The DOE National Renewable Energy Laboratory (NREL) is leading a national effort to develop next-generation cooling technologies for hybrid vehicle electronics. The goal is to reduce the size, weight, and cost of power electronic modules that convert direct current from batteries to alternating current for the motor, and vice versa. Aggressive thermal management techniques help to increase power density and reduce weight and volume, while keeping chip temperatures within acceptable limits. The viability of aggressive cooling schemes such as spray and jet impingement in conjunction with enhanced surfaces is being explored. Here, we present results from a series of experiments with pool and spray boiling on enhanced surfaces, such as a microporous layer of copper and copper nanowires, using HFE-7100 as the working fluid. Spray impingement on the microporous coated surface showed an enhancement of 100%-300% in the heat transfer coefficient at a given wall superheat with respect to spray impingement on a plain surface under similar operating conditions. Critical heat flux also increased by 7%-20%, depending on flow rates.

  7. Plume impingement forces on inclined flat plates

    NASA Astrophysics Data System (ADS)

    Legge, H.

    Plume impingement from spacecraft control thrusters on vehicles in space is simulated in wind tunnel scale experiments. Pressure and shear stress are measured on flat plates inclined to the plume axis between 0 and 90 deg. In addition to a nozzle of a 0.5N thruster, a free jet from a thin plate orifice was used, by which the flow regime from nearly free molecular flow to continuum flow was covered. Simple pressure and shear stress laws are given by which the impingement pressure and shear stress can be estimated for engineering applications.

  8. Fluid flow and heat convection studies for actively cooled airframes

    NASA Astrophysics Data System (ADS)

    Mills, A. F.

    This report details progress made on the jet impingement - liquid crystal - digital imaging experiment. With the design phase complete, the experiment is currently in the construction phase. In order to reach this phase two design related issues were resolved. The first issue was to determine NASP leading edge active cooling design parameters. Meetings were arranged with personnel at SAIC International, Torrance, CA in order to obtain recent publications that characterized expected leading edge heat fluxes as well as other details of NASP operating conditions. The information in these publications was used to estimate minimum and maximum jet Reynolds numbers needed to accomplish the required leading edge cooling, and to determine the parameters of the experiment. The details of this analysis are shown in Appendix A. One of the concerns for the NASP design is that of thermal stress due to large surface temperature gradients. Using a series of circular jets to cool the leading edge will cause a non-uniform temperature distribution and potentially large thermal stresses. Therefore it was decided to explore the feasibility of using a slot jet to cool the leading edge. The literature contains many investigations into circular jet heat transfer but few investigations of slot jet heat transfer. The first experiments will be done on circular jets impinging on a fiat plate and results compared to previously published data to establish the accuracy of the method. Subsequent experiments will be slot jets impinging on full scale models of the NASP leading edge. Table 1 shows the range of parameters to be explored. Next a preliminary design of the experiment was done. Previous papers which used a similar experimental technique were studied and elements of those experiments adapted to the jet impingement study. Trade-off studies were conducted to determine which design was the least expensive, easy to construct, and easy to use. Once the final design was settled, vendors were

  9. Fluid flow and heat convection studies for actively cooled airframes

    NASA Technical Reports Server (NTRS)

    Mills, A. F.

    1993-01-01

    This report details progress made on the jet impingement - liquid crystal - digital imaging experiment. With the design phase complete, the experiment is currently in the construction phase. In order to reach this phase two design related issues were resolved. The first issue was to determine NASP leading edge active cooling design parameters. Meetings were arranged with personnel at SAIC International, Torrance, CA in order to obtain recent publications that characterized expected leading edge heat fluxes as well as other details of NASP operating conditions. The information in these publications was used to estimate minimum and maximum jet Reynolds numbers needed to accomplish the required leading edge cooling, and to determine the parameters of the experiment. The details of this analysis are shown in Appendix A. One of the concerns for the NASP design is that of thermal stress due to large surface temperature gradients. Using a series of circular jets to cool the leading edge will cause a non-uniform temperature distribution and potentially large thermal stresses. Therefore it was decided to explore the feasibility of using a slot jet to cool the leading edge. The literature contains many investigations into circular jet heat transfer but few investigations of slot jet heat transfer. The first experiments will be done on circular jets impinging on a fiat plate and results compared to previously published data to establish the accuracy of the method. Subsequent experiments will be slot jets impinging on full scale models of the NASP leading edge. Table 1 shows the range of parameters to be explored. Next a preliminary design of the experiment was done. Previous papers which used a similar experimental technique were studied and elements of those experiments adapted to the jet impingement study. Trade-off studies were conducted to determine which design was the least expensive, easy to construct, and easy to use. Once the final design was settled, vendors were

  10. Sequential cooling insert for turbine stator vane

    SciTech Connect

    Jones, Russell B; Krueger, Judson J; Plank, William L

    2014-04-01

    A sequential impingement cooling insert for a turbine stator vane that forms a double impingement for the pressure and suction sides of the vane or a triple impingement. The insert is formed from a sheet metal formed in a zigzag shape that forms a series of alternating impingement cooling channels with return air channels, where pressure side and suction side impingement cooling plates are secured over the zigzag shaped main piece. Another embodiment includes the insert formed from one or two blocks of material in which the impingement channels and return air channels are machined into each block.

  11. Sequential cooling insert for turbine stator vane

    SciTech Connect

    Jones, Russel B; Krueger, Judson J; Plank, William L

    2014-11-04

    A sequential impingement cooling insert for a turbine stator vane that forms a double impingement for the pressure and suction sides of the vane or a triple impingement. The insert is formed from a sheet metal formed in a zigzag shape that forms a series of alternating impingement cooling channels with return air channels, where pressure side and suction side impingement cooling plates are secured over the zigzag shaped main piece. Another embodiment includes the insert formed from one or two blocks of material in which the impingement channels and return air channels are machined into each block.

  12. Closed circuit steam cooled turbine shroud and method for steam cooling turbine shroud

    DOEpatents

    Burdgick, Steven Sebastian; Sexton, Brendan Francis; Kellock, Iain Robertson

    2002-01-01

    A turbine shroud cooling cavity is partitioned to define a plurality of cooling chambers for sequentially receiving cooling steam and impingement cooling of the radially inner wall of the shoud. An impingement baffle is provided in each cooling chamber for receiving the cooling media from a cooling media inlet in the case of the first chamber or from the immediately upstream chamber in the case of the second through fourth chambers and includes a plurality of impingement holes for effecting the impingement cooling of the shroud inner wall.

  13. Nozzle cavity impingement/area reduction insert

    DOEpatents

    Yu, Yufeng Phillip; Itzel, Gary Michael; Osgood, Sarah Jane

    2002-01-01

    A turbine vane segment is provided that has inner and outer walls spaced from one another, a vane extending between the inner and outer walls and having leading and trailing edges and pressure and suction sides, the vane including discrete leading edge, intermediate, aft and trailing edge cavities between the leading and trailing edges and extending lengthwise of the vane for flowing a cooling medium; and an insert sleeve within at least one of the cavities and spaced from interior wall surfaces thereof. The insert sleeve has an inlet for flowing the cooling medium into the insert sleeve and has impingement holes defined in first and second walls thereof that respectively face the pressure and suction sides of the vane. The impingement holes of at least one of those first and second walls are defined along substantially only a first, upstream portion thereof, whereby the cooling flow is predominantly impingement cooling along a first region of the insert wall corresponding to the first, upstream portion and the cooling flow is predominantly convective cooling along a second region corresponding to a second, downstream portion of the at least one wall of the insert sleeve.

  14. Excited-state structure, vibrations, and nonradiative relaxation of jet-cooled 5-fluorocytosine.

    PubMed

    Lobsiger, Simon; Trachsel, Maria A; Den, Takuya; Leutwyler, Samuel

    2014-03-20

    The S0 → S1 vibronic spectrum and S1 state nonradiative relaxation of jet-cooled keto-amino 5-fluorocytosine (5FCyt) are investigated by two-color resonant two-photon ionization spectroscopy at 0.3 and 0.05 cm(–1) resolution. The 0(0)(0) rotational band contour is polarized in-plane, implying that the electronic transition is (1)ππ*. The electronic transition dipole moment orientation and the changes of rotational constants agree closely with the SCS-CC2 calculated values for the (1)ππ* (S1) transition of 5FCyt. The spectral region from 0 to 300 cm(–1) is dominated by overtone and combination bands of the out-of-plane ν1′ (boat), ν2′ (butterfly), and ν3′ (HN–C6H twist) vibrations, implying that the pyrimidinone frame is distorted out-of-plane by the (1)ππ* excitation, in agreement with SCS-CC2 calculations. The number of vibronic bands rises strongly around +350 cm(–1); this is attributed to the (1)ππ* state barrier to planarity that corresponds to the central maximum of the double-minimum out-of-plane vibrational potentials along the ν1′, ν2′, and ν3′ coordinates, which gives rise to a high density of vibronic excitations. At +1200 cm(–1), rapid nonradiative relaxation (k(nr) ≥ 10(12) s(–1)) sets in, which we interpret as the height of the (1)ππ* state barrier in front of the lowest S1/S0 conical intersection. This barrier in 5FCyt is 3 times higher than that in cytosine. The lifetimes of the ν′ = 0, 2ν1′, 2ν2′, 2ν1′ + 2ν2′, 4ν2′, and 2ν1′ + 4ν2′ levels are determined from Lorentzian widths fitted to the rotational band contours and are τ ≥ 75 ps for ν′ = 0, decreasing to τ ≥ 55 ps at the 2ν1′ + 4ν2′ level at +234 cm(–1). These gas-phase lifetimes are twice those of S1 state cytosine and 10–100 times those of the other canonical nucleobases in the gas phase. On the other hand, the 5FCyt gas-phase lifetime is close to the 73 ps lifetime in room-temperature solvents. This lack of

  15. The excited-state structure, vibrations, lifetimes, and nonradiative dynamics of jet-cooled 1-methylcytosine

    NASA Astrophysics Data System (ADS)

    Trachsel, Maria A.; Wiedmer, Timo; Blaser, Susan; Frey, Hans-Martin; Li, Quansong; Ruiz-Barragan, Sergi; Blancafort, Lluís; Leutwyler, Samuel

    2016-10-01

    We have investigated the S0 → S1 UV vibronic spectrum and time-resolved S1 state dynamics of jet-cooled amino-keto 1-methylcytosine (1MCyt) using two-color resonant two-photon ionization, UV/UV holeburning and depletion spectroscopies, as well as nanosecond and picosecond time-resolved pump/delayed ionization measurements. The experimental study is complemented with spin-component-scaled second-order coupled-cluster and multistate complete active space second order perturbation ab initio calculations. Above the weak electronic origin of 1MCyt at 31 852 cm-1 about 20 intense vibronic bands are observed. These are interpreted as methyl group torsional transitions coupled to out-of-plane ring vibrations, in agreement with the methyl group rotation and out-of-plane distortions upon 1ππ∗ excitation predicted by the calculations. The methyl torsion and ν1 ' (butterfly) vibrations are strongly coupled, in the S1 state. The S0 → S1 vibronic spectrum breaks off at a vibrational excess energy Eexc ˜ 500 cm-1, indicating that a barrier in front of the ethylene-type S1⇝S0 conical intersection is exceeded, which is calculated to lie at Eexc = 366 cm-1. The S1⇝S0 internal conversion rate constant increases from kIC = 2 ṡ 109 s-1 near the S1(v = 0) level to 1 ṡ 1011 s-1 at Eexc = 516 cm-1. The 1ππ∗ state of 1MCyt also relaxes into the lower-lying triplet T1 (3ππ∗) state by intersystem crossing (ISC); the calculated spin-orbit coupling (SOC) value is 2.4 cm-1. The ISC rate constant is 10-100 times lower than kIC; it increases from kISC = 2 ṡ 108 s-1 near S1(v = 0) to kISC = 2 ṡ 109 s-1 at Eexc = 516 cm-1. The T1 state energy is determined from the onset of the time-delayed photoionization efficiency curve as 25 600 ± 500 cm-1. The T2 (3nπ∗) state lies >1500 cm-1 above S1(v = 0), so S1⇝T2 ISC cannot occur, despite the large SOC parameter of 10.6 cm-1. An upper limit to the adiabatic ionization energy of 1MCyt is determined as 8.41 ± 0.02 e

  16. The excited-state structure, vibrations, lifetimes, and nonradiative dynamics of jet-cooled 1-methylcytosine.

    PubMed

    Trachsel, Maria A; Wiedmer, Timo; Blaser, Susan; Frey, Hans-Martin; Li, Quansong; Ruiz-Barragan, Sergi; Blancafort, Lluís; Leutwyler, Samuel

    2016-10-07

    We have investigated the S0 → S1 UV vibronic spectrum and time-resolved S1 state dynamics of jet-cooled amino-keto 1-methylcytosine (1MCyt) using two-color resonant two-photon ionization, UV/UV holeburning and depletion spectroscopies, as well as nanosecond and picosecond time-resolved pump/delayed ionization measurements. The experimental study is complemented with spin-component-scaled second-order coupled-cluster and multistate complete active space second order perturbation ab initio calculations. Above the weak electronic origin of 1MCyt at 31 852 cm(-1) about 20 intense vibronic bands are observed. These are interpreted as methyl group torsional transitions coupled to out-of-plane ring vibrations, in agreement with the methyl group rotation and out-of-plane distortions upon (1)ππ(∗) excitation predicted by the calculations. The methyl torsion and ν1(') (butterfly) vibrations are strongly coupled, in the S1 state. The S0 → S1 vibronic spectrum breaks off at a vibrational excess energy Eexc ∼ 500 cm(-1), indicating that a barrier in front of the ethylene-type S1⇝S0 conical intersection is exceeded, which is calculated to lie at Eexc = 366 cm(-1). The S1⇝S0 internal conversion rate constant increases from kIC = 2 ⋅ 10(9) s(-1) near the S1(v = 0) level to 1 ⋅ 10(11) s(-1) at Eexc = 516 cm(-1). The (1)ππ(∗) state of 1MCyt also relaxes into the lower-lying triplet T1 ((3)ππ(∗)) state by intersystem crossing (ISC); the calculated spin-orbit coupling (SOC) value is 2.4 cm(-1). The ISC rate constant is 10-100 times lower than kIC; it increases from kISC = 2 ⋅ 10(8) s(-1) near S1(v = 0) to kISC = 2 ⋅ 10(9) s(-1) at Eexc = 516 cm(-1). The T1 state energy is determined from the onset of the time-delayed photoionization efficiency curve as 25 600 ± 500 cm(-1). The T2 ((3)nπ(∗)) state lies >1500 cm(-1) above S1(v = 0), so S1⇝T2 ISC cannot occur, despite the large SOC parameter of 10.6 cm(-1). An upper limit to the adiabatic

  17. Cold plate with combined inclined impingement and ribbed channels

    DOEpatents

    Parida, Pritish R.

    2015-12-22

    Heat transfer devices and methods for making the same that include a first enclosure having at least one inlet port; a second enclosure having a bottom plate and one or more dividing walls to establish channels, at least one internal surface of each channel having rib structures to create turbulence in a fluid flow; and a jet plate connecting the first enclosure and the second enclosure having impinging jets that convey fluid from the first enclosure to the channels, said impinging jets being set at an angular deviation from normal to cause local acceleration of fluid and to increase a local heat transfer rate.

  18. Jet-cooled infrared spectra of molecules and complexes with a cw mode-hop-free external-cavity QCL and a distributed-feedback QCL

    NASA Astrophysics Data System (ADS)

    Liu, X.; Xu, Y.; Su, Z.; Tam, W. S.; Leonov, I.

    2011-03-01

    The coupling of quantum cascade lasers (QCLs) with an off-axis cavity enhanced absorption (CEA) spectrometer and an astigmatic multiple pass absorption (MPA) spectrometer are described in this paper. A continuous wave (cw) liquid nitrogen cooled distributed-feedback QCL at 5.7 μm and a cw room temperature mode-hop-free external-cavity QCL at 6.1 μm were employed as the light source. For the CEA spectrometer, the effects of mirror size and laser scan rate were evaluated. For the MPA spectrometer, a pair of astigmatic mirrors with a 55 cm mirror distance was aligned to the 366-pass configuration. The jet-cooled samples were generated using a homemade pulsed slit jet nozzle assembly. Two LabVIEW programs were written to automate and synchronize the timing of the laser scan, the pulsed slit jet molecular expansion, and the data acquisition. Infrared spectra of jet-cooled methyl lactate and the Ar-H2O complex and room temperature N2O and NH3 samples were measured using both the rapid scan and the wavelength modulation methods to evaluate the sensitivity and resolution of the CEA and MPA spectrometers. The combination of the MPA spectrometer with the external-cavity QCL using the rapid scan method was found to be the best suited combination to measure high resolution jet-cooled infrared spectra.

  19. US in ankle impingement syndrome.

    PubMed

    Pesquer, Lionel; Guillo, Stephane; Meyer, Philippe; Hauger, Olivier

    2014-06-01

    Ankle impingement is a common condition occurring secondary to sprain or repeated microtrauma. Clinical symptoms are chronic pain located in the affected region and limited range of ankle motion. There are three types of ankle impingement syndrome: anterior impingement, which can be subdivided into anterolateral, anteromedial and purely anterior impingement; posterior impingement, which can be subdivided into posterior and posteromedial impingement; and calcaneal peroneal impingement which is secondary to planovalgus foot deformity. This paper evaluates physiological and clinical elements of these three types of ankle impingement syndrome as well as the role of ultrasound (US) imaging and US-guided treatment.

  20. Spray mist cooling heat transfer in glass tempering process

    NASA Astrophysics Data System (ADS)

    Sozbir, Nedim; Yao, S. C.

    2016-10-01

    Energy saving is a very important issue in glass plants, especially in a glass tempering process, where very high velocity air jet impingement is applied during the cooling process of glass tempering. In fact, air compressor energy may be reduced by a spray cooling due to its high heat transfer capabilities. Presently, in this paper, both pure air and water mist spray cooling are investigated in the glass tempering process. The test results indicate that thin and low-cost tempered glass can be made by mist cooling without fracture. It is possible to find the optimal water flux and duration of mist application to achieve a desirable temperature distribution in the glass for deep penetration of the cooling front but without inducing cracking during the tempering. The use of mist cooling could give about 29 % air pressure reduction for 2-mm glass plate and 50 % reduction for both 3- and 4-mm glass plates.