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Sample records for pulsating tube flow

  1. An experimental investigation of heat transfer in a spiral-coil tube with pulsating turbulent water flow

    NASA Astrophysics Data System (ADS)

    Kharvani, H. Ramezani; Doshmanziari, F. Ilami; Zohir, A. E.; Jalali-Vahid, D.

    2016-09-01

    In this study, in order to increase the heat transfer rate in a spiral-coil tube by an active method, a rotating ball valve was mounted downstream/upstream of the spiral-coil tube and used as a pulse generator. Influence of pulsation on heat transfer in the spiral-coil tube was experimentally investigated. Cold water was used as a working fluid inside the spiral-coil that was immersed horizontally in a hot water reservoir tank. The Average temperature of the hot water bath was kept constant at 60 °C to establish a uniform temperature. All experiments for both pulsator locations (upstream and downstream pulsation) were performed at fixed pulsation amplitude. Reynolds number was ranged from 6220 to 16,300 while pulsation frequency was varied from 0 to 20 Hz. It can be clearly observed from heat transfer results that the overall average heat transfer coefficient was enhanced up to 26 % for pulsating flow compared to steady flow without pulsation at all pulsation frequencies. It is also clear that the relative overall average heat transfer coefficient is strongly affected by Reynolds number. Finally, it was obtained that the upstream pulsation heat transfer coefficient has better heat transfer results than the corresponding ones of downstream pulsation in the studied range of Reynolds number.

  2. Pulsating slurry flow in pipelines

    NASA Astrophysics Data System (ADS)

    El Masry, O. A.; El Shobaky, K.

    1989-07-01

    An experimental study on pulsating turbulent flow of sand-water suspension was carried out. The objective was to investigate the effect of pulsating flow parameters, such as, frequency and amplitude on the critical velocity, the pressure drop per unit length of pipeline and hence the energy requirements for hydraulic transportation of a unit mass of solids. The apparatus was constructed as a closed loop of 11.4 m length and 3.3 cm inner diameter of steel tubing. Solid volumetric concentrations of up to 20% were used in turbulent flow at a mean Reynolds number of 33,000 82,000. Pulsation was generated using compressed air in a controlled pulsation unit. Frequencies of 0.1 1.0 Hz and amplitude ratios of up to 30% were used. Instantaneous pressure drop and flow rate curves were digitized to calculate the energy dissipation associated with pulsation. The critical velocity in pulsating flow was found to be less than that for the corresponding steady flow at the same volumetric concentration. Energy dissipation for pulsating flow was found to be a function of both frequency and amplitude of pulsation. A possible energy saving was indicated at frequencies of 0.4 0.8 Hz and moderate amplitudes ratios of less than 25%.

  3. Total pressure averaging in pulsating flows

    NASA Technical Reports Server (NTRS)

    Krause, L. N.; Dudzinski, T. J.; Johnson, R. C.

    1972-01-01

    A number of total-pressure tubes were tested in a non-steady flow generator in which the fraction of period that pressure is a maximum is approximately 0.8, thereby simulating turbomachine-type flow conditions. Most of the tubes indicated a pressure which was higher than the true average. Organ-pipe resonance which further increased the indicated pressure was encountered within the tubes at discrete frequencies. There was no obvious combination of tube diameter, length, and/or geometry variation used in the tests which resulted in negligible averaging error. A pneumatic-type probe was found to measure true average pressure, and is suggested as a comparison instrument to determine whether nonlinear averaging effects are serious in unknown pulsation profiles. The experiments were performed at a pressure level of 1 bar, for Mach number up to near 1, and frequencies up to 3 kHz.

  4. Hydrodynamics and heat transfer for pulsating laminar flow in channels

    NASA Astrophysics Data System (ADS)

    Valueva, E. P.; Purdin, M. S.

    2015-09-01

    The problem about laminar pulsating flow and heat transfer with high pulsation amplitudes of average cross-section velocity in a round tube and in a flat channel is solved using the finite element method. The difference scheme's optimal parameters are determined. Data on the pulsation amplitude and phase are obtained for the hydraulic friction coefficient, tangential stress on the wall, liquid temperature, heat flux on the wall q w (at ϑw = const), and wall temperature ϑw (at q w = const) are obtained. Two characteristic modes, namely, quasi steady-state and high-frequency ones are separated based on the value of dimensionless pulsation frequency. During operation in the quasi steady-state mode, the values of all hydrodynamic and thermal quantities correspond to the values of time-average velocity at the given time instant. For operation in the high-frequency mode, it is shown that the dependences of the pulsating components of hydrodynamic and thermal quantities on the dimensionless pulsation frequency have the same pattern for rectilinear channels having different shapes of their cross section. It is found that certain nodal points exist on the distribution of thermal characteristics along the tube (liquid temperature, heat flux density on the wall at ϑw = const, and wall temperature at q w = const) in which the values of these quantities remain unchanged. The distances between the nodal points decrease with increasing the pulsation frequency. The pulsations of thermal quantities decay over the tube length.

  5. Transition to turbulence in pulsating pipe flow

    NASA Astrophysics Data System (ADS)

    Xu, Duo; Warnecke, Sascha; Hof, Bjoern; Avila, Marc

    2014-11-01

    We report an experimental investigation of the transition to turbulence in a pulsating pipe flow. This flow is a prototype of various pulsating flows in both nature and engineering, such as in the cardiovascular system where the onset of turbulence is often possibly related to various diseases (e.g., the formation of aneurysms). The experiments are carried out in a straight rigid pipe using water with a sinusoidal modulation of the flow rate. The governing parameters, Reynolds number, Womersley number α (dimensionless pulsating frequency) and the pulsating amplitude A, cover a wide range 3 < α < 23 and 0 < A < 1 . To characterize the transition to turbulence, we determine how the characteristic lifetime of turbulent spots (/puffs) are affected by the pulsation. While at high pulsation frequencies (α > 12) lifetimes of turbulent spots are entirely unaffected by the pulsation, at lower frequencies they are substantially affected. With decreasing frequency much larger Reynolds numbers are needed to obtain spots of the same characteristic lifetime. Hence at low frequency transition is delayed significantly. In addition the effect of the pulsation amplitude on the transition delay is quantified. Duo Xu would like to acknowledge the support from Humboldt Foundation.

  6. Transition to turbulence in pulsating pipe flow

    NASA Astrophysics Data System (ADS)

    Hof, Bjorn; Warnecke, Sascha; Xu, Duo

    2013-11-01

    We report an experimental study of the transition to turbulence in a pulsating pipe flow the most important example of pulsating flows is the cardiovascular system where the onset of fluctuations and turbulence can be a possible cause for various diseases such as the formation of aneurysms. The present study is limited to a straight rigid pipe, sinusoidal modulation of the flow rate and a Newtonian fluid. The dimensionless parameters (Womersley and Reynolds numbers) were chosen to include the parameter range encountered in larger arteries. We observe that at large frequencies the critical point for the onset of turbulence remains completely unaffected by pulsation for all amplitudes investigated (up to 40%). However for smaller frequencies (Womersley numbers below 10) the critical point considerably increases. Furthermore we investigate how the transition scenario is affected for a fixed frequency and increasing amplitudes (approaching oscillatory flow).

  7. The research on flow pulsation characteristics of axial piston pump

    NASA Astrophysics Data System (ADS)

    Wang, Bingchao; Wang, Yulin

    2017-01-01

    The flow pulsation is an important factor influencing the axial piston pump performance. In this paper we implement modeling and simulation of the axial piston pump with AMESim software to explore the flow pulsation characteristics under various factors . Theory analysis shows the loading pressure, angular speed, piston numbers and the accumulator impose evident influence on the flow pulsation characteristics. This simulation and analysis can be used for reducing the flow pulsation rate via properly setting the related factors.

  8. Amplitude of Supersonic Diffuser Flow Pulsations

    NASA Technical Reports Server (NTRS)

    Sterbentz, William H.; Davids, Joseph

    1952-01-01

    A theoretical method for evaluating the stability characteristics and the amplitude and the frequency of pulsation of ram-jet engines without heat addition is presented herein. Experimental verification of the theoretical results are included where data were available. Theory and experiment show that the pulsation amplitude of a high mass-flow-ratio diffuser having no cone surface flow separation increases with decreasing mass flow. The theoretical trends for changes in amplitude, frequency, and mean-pressure recovery with changes in plenum-chamber volume were experimentally confirmed. For perforated convergent-divergent-type diffusers, a stability hysteresis loop was predicted on the pressure-recovery mass-flow-ratio curve. At a given mean mass-flow ratio, the higher.value of mean pressure recovery corresponded to oscillatory flow in the diffuser while the lower branch was stable. This hysteresis has been observed experimentally. The theory indicates that for a ram-jet engine of given diameter, the amplitude of pulsation of a supersonic diffuser is increased by decreasing the relative size of the plenum chamber with respect to the diffuser volume down to a critical value at which oscillations cease. In the region of these critical values, the stable mass-flow range of the diffuser may be increased either by decreasing the combustion chamber volume or by increasing the length of the diffuser.

  9. Guide tube flow diffuser

    SciTech Connect

    Berringer, R.T.; Myron, D.L.

    1980-11-04

    A nuclear reactor upper internal guide tube has a flow diffuser integral with its bottom end. The guide tube provides guidance for control rods during their ascent or descent from the reactor core. The flow diffuser serves to divert the upward flow of reactor coolant around the outside of the guide tube thereby limiting the amount of coolant flow and turbulence within the guide tube, thus enhancing the ease of movement of the control rods.

  10. Turbulence models in pulsating flows

    NASA Astrophysics Data System (ADS)

    Scotti, Alberto; Piomelli, Ugo

    2001-11-01

    We compare the performance of four low-Reynolds-number models for the unsteady Reynolds-averaged Navier-Stokes equations applied to the flow in a channel driven by a pressure gradient oscillating around a non-zero mean. The models considered are the one-equation Spalart-Allmaras model, the k-\\varepsilon model with the wall functions of Lam and Bremhorst, the k-ω^2 model of Saffman and Wilcox, and the k-\\varepsilon-v^2 model of Durbin. The results are compared with experiments, direct simulations and large-eddy simulations. The models give similar and reasonably accurate results as far as predicting the velocity profile in the channel as a function of the phase, and reproduce the observed behavior during part of the cycle. However, large differences exist between the models themselves, as well as with respect to the LES, at the level of the Reynolds shear stress, turbulent kinetic energy and dissipation rate. The k-\\varepsilon-v^2 model is overall superior to the other models considered.

  11. Determination of discharge during pulsating flow

    USGS Publications Warehouse

    Thompson, T.H.

    1968-01-01

    Pulsating flow in an open channel is a manifestation of unstable-flow conditions in which a series of translatory waves of perceptible magnitude develops and moves rapidly downstream. Pulsating flow is a matter of concern in the design and operation of steep-gradient channels. If it should occur at high stages in a channel designed for stable flow, the capacity of the channel may be inadequate at a discharge that is much smaller than that for which the channel was designed. If the overriding translatory wave carries an appreciable part of the total flow, conventional stream-gaging procedures cannot be used to determine the discharge; neither the conventional instrumentation nor conventional methodology is adequate. A method of determining the discharge during pulsating flow was tested in the Santa Anita Wash flood control channel in Arcadia, Calif., April 16, 1965. Observations of the dimensions and velocities of translatory waves were made during a period of controlled reservoir releases of about 100, 200, and 300 cfs (cubic feet per second). The method of computing discharge was based on (1) computation of the discharge in the overriding waves and (2) computation of the discharge in the shallow-depth, or overrun, part of the flow. Satisfactory results were obtained by this method. However, the procedure used-separating the flow into two components and then treating the shallow-depth component as though it were steady--has no theoretical basis. It is simply an expedient for use until laboratory investigation can provide a satisfactory analytical solution to the problem of computing discharge during pulsating flow. Sixteen months prior to the test in Santa Anita Wash, a robot camera had been designed .and programmed to obtain the data needed to compute discharge by the method described above. The photographic equipment had been installed in Haines Creek flood control channel in Los Angeles, Calif., but it had not been completely tested because of the infrequency of

  12. Experimental and Theoretical Studies of Pulsating Turbulent Flow. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Kingston, G. C.

    1975-01-01

    The objective of this investigation was to study the effects of small amplitude sinusoidal pulsations on fully developed turbulent flow in a tube from both experimental and theoretical viewpoints. Theoretical models for the macroscopic behavior of pulsating turbulent tube flow were developed for the two cases of very low and very high pulsation frequencies. The models are based on assumptions of quasi-steady and frozen eddy viscosity flow behavior, respectively. The models successfully predict unsteady velocity profiles, thereby supporting the currently proposed definitions of frequency regimes in pulsating turbulent flow. Experimental measurements were made of the time-dependent pressure drop and velocity profiles over the range of frequency-to-Reynolds number ratios from 0.0095 to 0.24. The two macroscopic models developed in this study predict unsteady velocity profiles which are in moderately good agreement with the experiments in their respective frequency regimes, and a previously developed quasi-steady model is found to predict experimental velocity profiles well in both the quasisteady and the frozen eddy viscosity frequency regimes. The effect of flow pulsations on the dissipation of turbulence energy in the vicinity of the wall was measured in the lower transition frequency regime. The long-time averaged dissipation was observed to be unchanged from the steady flow dissipation, within the accuracy of the experiment. A theoretical model of the periodic viscous sublayer was also developed and applied to pulsating flow in a tube, in order to investigate the effects of flow pulsations on the rate of production of turbulence in the region of the wall. The periodic viscous sublayer model predicts sublayer growth periods in steady flow which agree with the published experimental data. When the model is applied to pulsating flow, the response of the sublayer growth period falls into three frequency regimes, the parameters of which are in approximate agreement

  13. Numerical simulation of pulsating turbulent channel flow

    NASA Astrophysics Data System (ADS)

    Scotti, Alberto; Piomelli, Ugo

    2001-05-01

    Direct and large-eddy simulations of the Navier-Stokes equations are used to study the pulsating flow in a channel. The cases examined span a wide range of frequencies of the driving pressure gradient, and encompass different physical behaviors, from the quasi-Stokes flow observed at high frequencies, to a quasisteady behavior at the lowest ones. The validity of the dynamic Smagorinsky model to study this kind of unsteady flow is established by a posteriori comparison with direct simulations and experimental data. It is shown that the fluctuations generated in the near-wall region by the unsteady pressure gradient do not propagate beyond a certain distance lt from the wall, which can be estimated quite accurately by a simple eddy viscosity argument. No substantial departure from the Stokes regime at very high frequency (ω+ as high as 0.1) is observed. The time-dependent characteristics of the flow are examined in detail, as well as the topology of the coherent structures.

  14. Study of the velocity distribution influence upon the pressure pulsations in draft tube model of hydro-turbine

    NASA Astrophysics Data System (ADS)

    Sonin, V.; Ustimenko, A.; Kuibin, P.; Litvinov, I.; Shtork, S.

    2016-11-01

    One of the mechanisms of generation of powerful pressure pulsations in the circuit of the turbine is a precessing vortex core, formed behind the runner at the operation points with partial or forced loads, when the flow has significant residual swirl. To study periodic pressure pulsations behind the runner the authors of this paper use approaches of experimental modeling and methods of computational fluid dynamics. The influence of velocity distributions at the output of the hydro turbine runner on pressure pulsations was studied based on analysis of the existing and possible velocity distributions in hydraulic turbines and selection of the distribution in the extended range. Preliminary numerical calculations have showed that the velocity distribution can be modeled without reproduction of the entire geometry of the circuit, using a combination of two blade cascades of the rotor and stator. Experimental verification of numerical results was carried out in an air bench, using the method of 3D-printing for fabrication of the blade cascades and the geometry of the draft tube of hydraulic turbine. Measurements of the velocity field at the input to a draft tube cone and registration of pressure pulsations due to precessing vortex core have allowed building correlations between the velocity distribution character and the amplitude-frequency characteristics of the pulsations.

  15. The Effects of Pulsating Flow on Eruption Column Dynamics

    NASA Astrophysics Data System (ADS)

    Black, T.; Dufek, J.; Benage, M. C.

    2015-12-01

    Pulsating flow, at frequencies ranging from 10-2 to 101 Hz, has been recorded in explosive eruptions through video, thermal imagery, and infrasonic and seismic data. Such pulsating flow can be generated from instabilities in bubbly magma, and from granular instabilities in post-fragmentation conduit flow. Variable fluxes of gas and particles at the vent can alter entrainment conditions, and consequently affect eruption column stability. However, volcanic eruption models typically assume steady flow from the vent, and regime diagrams of eruption column stability are based on such steady flow assumptions. Using Eulerian-Eulerian multiphase numerical simulations of eruption columns with both steady and pulsating sources, we compared the relative behavior of steady and pulsed columns across a range of pulse frequencies and mass fluxes at the vent (mass flux is time-averaged for pulsating cases). Preliminary results suggest that pulsating flow increases air entrainment into the column relative to steady flow for otherwise constant eruption conditions, and that entrainment increases with decreasing pulse frequency. Increased entrainment at low frequency implies that low-frequency pulsed columns are more buoyant and potentially more stable than their steady counterparts, for a given mass flux. This effect disrupts the steady flow-based understanding of eruption column stability regimes and may be a factor to consider for future assessment of volcanic hazards and interpreting mass flux conditions from deposits.

  16. Effects of pulsating flow on current meter performance

    USGS Publications Warehouse

    Fulford, Janice M.; ,

    1995-01-01

    Summarized are laboratory tests for current meter response to pulsating flows. Included are results for mechanical and electromagnetic water-current meters that are commonly used for stream gaging. Most of the vertical-axis and horizontal-axis types of mechanical meters that were tested significantly underregistered the mean flow velocity when the magnitude of the pulsating portion of the flow velocity was greater than half the mean velocity but less than the mean velocity. Errors for all meters tested were largest at the lowest mean flow velocity, 0.076 m/s.

  17. CFD simulation of pulsation noise in a small centrifugal compressor with volute and resonance tube

    NASA Astrophysics Data System (ADS)

    Wakaki, Daich; Sakuka, Yuta; Inokuchi, Yuzo; Ueda, Kosuke; Yamasaki, Nobuhiko; Yamagata, Akihiro

    2015-02-01

    The rotational frequency tone noise emitted from the automobile turbocharger is called the pulsation noise. The cause of the pulsation noise is not fully understood, but is considered to be due to some manufacturing errors, which is called the mistuning. The effects of the mistuning of the impeller blade on the noise field inside the flow passage of the compressor are numerically investigated. Here, the flow passage includes the volute and duct located downstream of the compressor impeller. Our numerical approach is found to successfully capture the wavelength of the pulsation noise at given rotational speeds by the comparison with the experiments. One of the significant findings is that the noise field of the pulsation noise in the duct is highly one-dimensional although the flow fields are highly three-dimensional.

  18. Draft tube pressure pulsation predictions in Francis turbines with transient Computational Fluid Dynamics methodology

    NASA Astrophysics Data System (ADS)

    Melot, M.; Nennemann, B.; Désy, N.

    2014-03-01

    An automatic Computational Fluid Dynamics (CFD) procedure that aims at predicting Draft Tube Pressure Pulsations (DTPP) at part load is presented. After a brief review of the physics involved, a description of the transient numerical setup is given. Next, the paper describes a post processing technique, namely the separation of pressure signals into synchronous, asynchronous and random pulsations. Combining the CFD calculation with the post-processing technique allows the quantification of the potential excitation of the mechanical system during the design phase. Consequently it provides the hydraulic designer with a tool to specifically target DTPP and thus helps in the development of more robust designs for part load operation of turbines.

  19. The pulsating laminar flow in a rectangular channel

    NASA Astrophysics Data System (ADS)

    Valueva, E. P.; Purdin, M. S.

    2015-11-01

    The finite difference method is used to solve the task of the developed pulsating laminar flow in a rectangular channel. The optimum of the difference scheme parameters was determined. Data on the amplitude and phase of the longitudinal velocity oscillations, the hydraulic and friction drag coefficients, the shear stress on the wall have been obtained. Using the dimensionless value of the frequency pulsations two characteristic regimes — the quasisteady-state regime and the high-frequency regime have been identified. In the quasi-steady-state regime, the values of all hydrodynamic quantities at each instant of time correspond to the velocity value averaged over the cross section at a given moment of time. It is shown that in the high-frequency regime, the dependences on the dimensionless oscillation frequency of oscillating components of hydrodynamic quantities are identical for rectilinear channels with a different cross-sectional form (round pipe, flat and a rectangular channels). The effect of the aspect ratio of the rectangular channel sides channel on the pulsating flow dynamics has been analyzed.

  20. Numerical investigation of draft tube pressure pulsations in a Francis turbine with splitter blades

    NASA Astrophysics Data System (ADS)

    Kassanos, I.; Anagnostopoulos, J.; Papantonis, D.

    2017-04-01

    Operation of Francis turbines at part load conditions is related to the appearance of the draft tube helical vortex rope. Splitter blades have been employed in high head Francis turbines in order to improve performance as well as their unsteady characteristics. In this work the draft tube unsteady characteristics of a Francis runner with splitter blades are investigated numerically. Two different splitter designs were analysed, and the performance results were compared to the baseline runner with no splitter blades used. The amplitude of pressure pulsation caused by the precessing vortex rope as well as the related frequency was compared for all cases, for two different operating conditions. From the results a relationship between the pulsation frequency and splitter blade geometry was observed.

  1. Hydroacoustic pulsating jet generator

    NASA Astrophysics Data System (ADS)

    Unrau, A.; Meier, G. E. A.

    1987-04-01

    A high pressure turbulent jet generator connected to a low pressure hydraulic tube is studied to investigate water hammer in tubes with fast flow variations, generating high pressure pulsating water jets. The pulsating jet generator consists of a tube, a hydraulic valve, a spring, and a water container. The jet is the effect of the combination of turbulent pipe flow with a valve for flow nozzle. The jet pressure depends on specific oscillation impedance and flow velocity variations. For inlet pressure of 0.5 to 2 bar the pressure rises to 40 bar. The described pulsating jet generator is more effective than the earlier model. A piezoelectric pressure controller is used to register pressure signals and high speed photos are made of the jet. Test results are consistent with theoretical calculation.

  2. Investigations on the Aerodynamic Characteristics and Blade Excitations of the Radial Turbine with Pulsating Inlet Flow

    NASA Astrophysics Data System (ADS)

    Liu, Yixiong; Yang, Ce; Yang, Dengfeng; Zhang, Rui

    2016-04-01

    The aerodynamic performance, detailed unsteady flow and time-based excitations acting on blade surfaces of a radial flow turbine have been investigated with pulsation flow condition. The results show that the turbine instantaneous performance under pulsation flow condition deviates from the quasi-steady value significantly and forms obvious hysteretic loops around the quasi-steady conditions. The detailed analysis of unsteady flow shows that the characteristic of pulsation flow field in radial turbine is highly influenced by the pulsation inlet condition. The blade torque, power and loading fluctuate with the inlet pulsation wave in a pulse period. For the blade excitations, the maximum and the minimum blade excitations conform to the wave crest and wave trough of the inlet pulsation, respectively, in time-based scale. And toward blade chord direction, the maximum loading distributes along the blade leading edge until 20% chord position and decreases from the leading to trailing edge.

  3. Deformation Behavior of a Thin-Walled Tube in Hydroforming with Radial Crushing Under Pulsating Hydraulic Pressure

    NASA Astrophysics Data System (ADS)

    Yang, Lianfa; Rong, Haisong; He, Yulin

    2013-11-01

    Loading path plays a dominant role in tube hydroforming (THF), and the pulsating loading path has been reported capable of improving the formability of a tube in hydrobulging with axial feeding. As a new THF process, the tube hydroforming with radial crushing (THFRC) is receiving increasing attention; however, knowledge on the process still remains insufficient to extend its application to various other fields. In this study, the experiments of THFRC under both the pulsating and the linear hydraulic pressures were carried out to investigate the deformation behavior. The influences of the amplitude and the frequency of the pulsating hydraulic pressure on the shape precision, wall thickness, and the microstructures of the deformed parts were analyzed. Subsequently, metallographic examinations of the deformed specimens were conducted in an attempt to clarify the relationship between the microstructural evolution and deformation behavior. The mechanism of formability improvement in THFRC by the pulsating hydraulic pressure was explored from the perspective of microstructure. Compared with the linear hydraulic pressure, the pulsating hydraulic pressure could generate a higher shape precision, a more uniform wall thickness, as well as less martensites, and larger grain. The microstructural evolution induced by the pulsating loading path is supposed to contribute to the formability improvement of SUS304 stainless steel tubes.

  4. Carreau model for oscillatory blood flow in a tube

    NASA Astrophysics Data System (ADS)

    Tabakova, S.; Nikolova, E.; Radev, St.

    2014-11-01

    The analysis of the blood flow dynamics (hemodynamics) in tubes is crucial when investigating the rupture of different types of aneurysms. The blood viscosity nonlinear dependence on the flow shear rate creates complicated manifestations of the blood pulsations. Although a great number of studies exists, experimental and numerical, this phenomenon is still not very well understood. The aim of the present work is to propose a numerical model of the oscillatory blood flow in a tube on the basis of the Carreau model of the blood viscosity (nonlinear model with respect to the shear rate). The obtained results for the flow velocity and tangential stress on the tube wall are compared well with other authors' results.

  5. Nonisothermal flow of a polymeric liquid under a pulsating pressure gradient

    SciTech Connect

    Shul'man, Z.P.; Khusid, B.M.; Shabunina, Z.A.

    1987-03-01

    Increasing flow rates is a major problem in transporting petroleum as well as polymer solutions and melts. Industrial methods are often directed to reducing the effective viscosity: heating and pulsation. The latter is related to the nonlinearity in the properties. This paper studies the effects of pressure-gradient pulsations on the nonisothermal flow of a nonlinear liquid with memory in an annular channel.

  6. Enhancing cell viability with pulsating flow in a hollow fiber bioartificial liver.

    PubMed

    Nguyen, Diem T; Brotherton, John D; Chau, Pao C

    2005-10-01

    A pulsating flow of medium was used to alleviate diffusion and transport limitations in a hollow fiber bioreactor containing a human hepatoblastoma cell line. The strategy is easy to implement but effective. The pulsating flow is introduced by a solenoid pinch valve at the outlet of the bioreactor and regulated by a timing circuit. In a permeability test, the system with pulsating flow had much less membrane fouling as compared to the control, a conventional hollow fiber unit. In hepatocyte culture test runs, the pulsating-flow bioreactor demonstrated the ability to maintain a higher cell viability. Histological sections indicated significantly smaller necrotic regions in the pulsating-flow bioreactor as compared to the conventional unit.

  7. Nonsteady Flow in Capillary Tubes

    NASA Astrophysics Data System (ADS)

    Hara, Ayako

    2000-03-01

    Surface phenomena in the field of electron devices and the problem of how long. It takes plants to absorb water during their growth in hydroponic cultivation is attraching the attention of riseachers. However, the related study of non-steady flow in capillary tubes has a number of issues that require investigation. In response to this situation, we made attempted to assess nonsteady fiow in capillary tubes, the liquid rise time and other issues, using a motion equation that takes factors including the friction force of the tube and the surface tension into consideration.

  8. Multiobjective optimal design of runner blade using efficiency and draft tube pulsation criteria

    NASA Astrophysics Data System (ADS)

    Pilev, I. M.; Sotnikov, A. A.; Rigin, V. E.; Semenova, A. V.; Cherny, S. G.; Chirkov, D. V.; Bannikov, D. V.; Skorospelov, V. A.

    2012-11-01

    In the present work new criteria of optimal design method for turbine runner [1] are proposed. Firstly, based on the efficient method which couples direct simulation of 3D turbulent flow and engineering semi empirical formulas, the combined method is built for hydraulic energy losses estimation in the whole turbine water passage and the efficiency criterion is formulated. Secondly, the criterion of dynamic loads minimization is developed for those caused by vortex rope precession downstream of the runner. This criterion is based on the finding that the monotonic increase of meridional velocity component in the direction to runner hub, downstream of its blades, provides for decreasing the intensity of vortex rope and thereafter, minimization of pressure pulsation amplitude. The developed algorithm was applied to optimal design of 640 MW Francis turbine runner. It can ensure high efficiency at best efficiency operating point as well as diminished pressure pulsations at full load regime.

  9. Mass flow and its pulsation measurements in supersonic wing wake

    NASA Astrophysics Data System (ADS)

    Shmakov, A. S.; Shevchenko, A. M.; Yatskikh, A. A.; Yermolaev, Yu. G.

    2016-10-01

    The results of experimental study of the flow in the wing wake are presented. Experiments were carried out in supersonic wind tunnel T-325 of ITAM SB RAS. Rectangle half-wing with sharp edges with a chord length of 30 mm and semispan of 95 mm was used to generate vortex wake. Experimental data were obtained in the cross section located 6 chord length downstream of the trailing edge at Mach numbers of 2.5 and 4 and at wing angles of attack of 4 and 10 degrees. Constant temperature hot-wire anemometer was used to measure disturbances in supersonic flow. Hot-wire was made of a tungsten wire with a diameter of 10 μm and length of 1.5 mm. Shlieren flow visualization were performed. As a result, the position and size of the vortex core in the wake of a rectangular wing were determined. For the first time experimental data on the mass flow distribution and its pulsations in the supersonic longitudinal vortex were obtained.

  10. Numerical analysis of unsteady flow behaviour and pressure pulsation in pump turbine with misaligned guide vanes

    NASA Astrophysics Data System (ADS)

    Xiao, Y. X.; Sun, D. G.; Wang, Z. W.; Zhang, J.; Peng, G. Y.

    2012-11-01

    The unsteady flow within the entire flow passage of a pump-turbine with misaligned guide vanes (MGV) device under the rated speed was simulated using the Reynolds-averaged Navier-Stokes equations together with the k-ω based SST turbulence model. Three kinds of MGV arrangement of different opening angles were chosen to analyse the influence of MGV on the pressure pulsation in the flow passages of spiral case, stay vanes, guide vanes, rotating runner blades and draft tube. The characteristics of the dominant frequency of the unsteady flows in different flow parts under different misaligned guide vane arrangement/openings and the hydraulic performance of the pump-turbine were investigated at the turbine operating condition. The computation result shows that the MGV can decrease the peak-to-peak amplitude of the pressure fluctuation in the whole flow passage except the rotating runner blades. The low frequencies and the influence of Rotor Stator Interaction (RSI) in the entire flow passage vary with the arrangement/ openings of MGV.

  11. Venturi Tube with Varying Mass Flow

    NASA Technical Reports Server (NTRS)

    Regenscheit, B.

    1948-01-01

    Measurements on three tubes with flow regulated by suction at the trainling edge of the tube are described. It was possible to vary the mass of air flowing through the tube over a large range. Such tubes could be used for shrouded propellers.

  12. Darkening of the Sun prior to surface appearance of sunspot flux tubes and magneto-thermal pulsation of the Sun

    NASA Astrophysics Data System (ADS)

    Yoshimura, H.

    1994-08-01

    We found an evidence that the luminosity of the Sun systematically decreased about 20 days before sunspot surface appearance by analyzing time-lag correlation of time derivatives of running mean time profiles of the data ofthe Active Cavity Radiometer Irradiance Monitor (ACRIM) I experiment on board of Solar Maximum Mission (SMM) and of the data of the daily sunspot number. This indicates that sunspot flux tube cooling and heat transfer blocking by the flux tubes start to take place in the interior of the solar convection zone well before the sunspot surface appearance. From this finding and our previous finding that the luminosity of the Sun systematically increased and the blocked heat appeared on the surface about 50 days after the sunspot surface appearance, a new view of sunspot formation and dynamics and a new view of the luminosity modulation emerged. (1) Sunspots of a solar cycle are formed from clusters of flux tubes which can be seen in the running time mean profile of the sunspot number as a peak with duration on the order of 100 to 200 days. (2) Heat flow is blocked by the cluster of sunspot flux tubes inside the convection zone to decrease the luminosity about 20 days before the surface emergence of the sunspot cluster. (3) The blocked heat appears on the surface about 50 days after the surface emergence of the cluster of sunspot flux tubes to heat up the surface. This appears as a thermal pulse in the running mean time profile of the ACRIM data in between the peaks of the sunspot running mean time profile. This process of heating the surface makes the temperature gradient less steep and weakens the bouyancy of sunspot flux tubes below the surface. (4) The radiative cooling of the surface layer by the excess heat release steepens the temperature gradient so that the bouyancy of the sub-surface magnetic flux tubes becomes stronger to cause the next surge of emergence of a cluster of sunspots and other magnetic activities, which creates a peak in the

  13. Flow tube wall regenerator performance

    NASA Astrophysics Data System (ADS)

    Decher, Reiner

    1990-07-01

    The performance of a regenerator processing a fluid in a reciprocating manner is described in terms of the fluid and the wall material characteristics as well as the geometry of the flow tubes through which the fluid is forced. It is shown that the effectiveness cannot exceed 50 percent and that it requires a wall material of low thermal heat capacity with good thermal contact between wall and fluid. Quantitative results are presented for a representative analysis model.

  14. On Flow Stagnation in a Tube Radiator

    NASA Technical Reports Server (NTRS)

    Motil, Brian; Chao, David F.; Sankovic, John M.; Zhang, Nengli

    2007-01-01

    An analysis of the physical process for occurrence of flow stagnation in a space tube-radiator is performed and the mechanism and mathematic description for the flow stagnation are presented. Two causes for pressure drop unbalance between tubes of the radiator are identified: non-uniform cooling environment and different local flow resistances between the tubes. This analysis provides a theoretical basis for experimental simulations of the flow stagnation in a ground-based lab as well as two suggested methods to experimentally simulate flow stagnation. Criteria for the flow stagnation, depending on the viscosity data regressive polynomial, are derived from the extreme condition of the pressure drop in colder tubes. A preliminary numerical calculation is conducted for a space tube-radiator model which confirms the physical and mathematical analyses. The prediction by the criteria for flow stagnation in the tube-radiator model coincides with the numerical calculation result.

  15. On the effect of pulsating flow on surge margin of small centrifugal compressors for automotive engines

    SciTech Connect

    Galindo, J.; Climent, H.; Guardiola, C.; Tiseira, A.

    2009-11-15

    Surge is becoming a limiting factor in the design of boosting systems of downsized diesel engines. Although standard compressor flowcharts are used for the selection of those machines for a given application, on-engine conditions widely differ from steady flow conditions, thus affecting compressor behaviour and consequently surge phenomenon. In this paper the effect of pulsating flow is investigated by means of a steady gas-stand that has been modified to produce engine-like pulsating flow. The effect of pressure pulses' amplitude and frequency on the compressor surge line location has been checked. Results show that pulsating flow in the 40-67 Hz range (corresponding to characteristic pulsation when boosting an internal combustion engine) increases surge margin. This increased margin is similar for all the tested frequencies but depends on pulsation amplitude. In a further step, a non-steady compressor model is used for modelling the tests, thus allowing a deeper analysis of the involved phenomena. Model results widely agree with experimental results. (author)

  16. Flow and convective cooling in lava tubes

    NASA Astrophysics Data System (ADS)

    Sakimoto, S. E. H.; Zuber, M. T.

    1998-11-01

    Tube-fed basaltic lava flows with lengths ranging from 10 to 200 km are inferred to exhibit similar amounts of cooling. To explain the wide range of implied cooling rates, we consider forced convection as a dominant cooling process in lava tubes and present solutions that express mean temperature versus distance down the tube as a function of flow rate and flow cross section. Our models treat forced convective thermal losses in steady laminar flow through a lava tube with constant temperature walls and constant material properties. We explore the effects of different wall temperature and heat flux rate boundary conditions for circular tube and parallel plate flows over a range of tube sizes, plate spacings, eruption temperatures, and volume flow rates. Results show that nonlinear cooling rates over distance are characteristic of constant wall temperature for a piecewise parallel plate/circular tube model. This provides the best fit to temperature observations for Hawaiian tubes. Such a model may also provide an explanation for the very low (˜10°C) cooling observed in ˜10 km long Hawaii tube flows and inferred in longer ˜50 to 150 km tube-fed flows in Queensland. The forced convective cooling model may also explain similar flow morphologies for long tube-fed basaltic lava flows in a wide variety of locations, since small variations in eruption temperature or flow rate can accommodate the entire range of flow lengths and cooling rates considered. Our results are consistent with previous suggestions that long basaltic flows may be a reflection of low slopes, a particularly steady moderate eruption rate, and well-insulated flow, rather than of high discharge rates.

  17. Cross Flow Boiling in Tube Bundles.

    DTIC Science & Technology

    1982-10-01

    subsequent corrosion induced failure of the heating tube , an understanding of the fluid motion and heat transfer behavior in confined spaces will be...1-1982A U Cross Flowing Boiling in Tube Bundles Annual Technical Report October 1982 LOD S.C. Yao Associate Professor Department of Mechanical...Subtitle) S. TYPE OF REPORT & PERIOD COVERED Annual Technical Report CROSS FLOW BOILING IN TUBE BUNDLES Aug. 1, 1981 to Aug. 1, 1982 - 6. PERFORMING ORG

  18. 3D Numerical Simulation versus Experimental Assessment of Pressure Pulsations Using a Passive Method for Swirling Flow Control in Conical Diffusers of Hydraulic Turbines

    NASA Astrophysics Data System (ADS)

    TANASA, C.; MUNTEAN, S.; CIOCAN, T.; SUSAN-RESIGA, R. F.

    2016-11-01

    The hydraulic turbines operated at partial discharge (especially hydraulic turbines with fixed blades, i.e. Francis turbine), developing a swirling flow in the conical diffuser of draft tube. As a result, the helical vortex breakdown, also known in the literature as “precessing vortex rope” is developed. A passive method to mitigate the pressure pulsations associated to the vortex rope in the draft tube cone of hydraulic turbines is presented in this paper. The method involves the development of a progressive and controlled throttling (shutter), of the flow cross section at the bottom of the conical diffuser. The adjustable cross section is made on the basis of the shutter-opening of circular diaphragms, while maintaining in all positions the circular cross-sectional shape, centred on the axis of the turbine. The stagnant region and the pressure pulsations associated to the vortex rope are mitigated when it is controlled with the turbine operating regime. Consequently, the severe flow deceleration and corresponding central stagnant are diminished with an efficient mitigation of the precessing helical vortex. Four cases (one without diaphragm and three with diaphragm), are numerically and experimentally investigated, respectively. The present paper focuses on a 3D turbulent swirling flow simulation in order to evaluate the control method. Numerical results are compared against measured pressure recovery coefficient and Fourier spectra. The results prove the vortex rope mitigation and its associated pressure pulsations when employing the diaphragm.

  19. An investigation into inflection-point instability in the entrance region of a pulsating pipe flow

    PubMed Central

    Wang, R. H.; Jian, T. W.; Hsu, Y. T.

    2017-01-01

    This paper investigates the inflection-point instability that governs the flow disturbance initiated in the entrance region of a pulsating pipe flow. Under such a flow condition, the flow instability grows within a certain phase region in a pulsating cycle, during which the inflection point in the unsteady mean flow lifts away from the viscous effect-dominated region known as the Stokes layer. The characteristic frequency of the instability is found to be in agreement with that predicted by the mixing-layer model. In comparison with those cases not falling in this category, it is further verified that the flow phenomenon will take place only if the inflection point lifts away sufficiently from the Stokes layer. PMID:28265188

  20. Clinical Trial of Thermal Pulsation (LipiFlow) in Meibomian Gland Dysfunction With Preteatment Meibography

    PubMed Central

    Zhao, Yang; Veerappan, Anuradha; Yeo, Sharon; Rooney, David M.; Acharya, Rajendra U.; Tan, Jen Hong

    2016-01-01

    Objectives: Thermal pulsation (LipiFlow) has been advocated for meibomian gland dysfunction (MGD) treatment and was found useful. We aimed to evaluate the efficacy and safety of thermal pulsation in Asian patients with different grades of meibomian gland loss. Methods: A hospital-based interventional study comparing thermal pulsation to warm compresses for MGD treatment. Fifty patients were recruited from the dry eye clinic of a Singapore tertiary eye hospital. The ocular surface and symptom were evaluated before treatment, and one and three months after treatment. Twenty-five patients underwent thermal pulsation (single session), whereas 25 patients underwent warm compresses (twice daily) for 3 months. Meibomian gland loss was graded using infrared meibography, whereas function was graded using the number of glands with liquid secretion. Results: The mean age (SD) of participants was 56.4 (11.4) years in the warm compress group and 55.6 (12.7) years in the thermal pulsation group. Seventy-six percent of the participants were female. Irritation symptom significantly improved over 3 months in both groups (P<0.01), whereas tear breakup time (TBUT) was modestly improved at 1 month in only the thermal pulsation group (P=0.048), without significant difference between both groups over the 3 months (P=0.88). There was also no significant difference in irritation symptom, TBUT, Schirmer test, and gland secretion variables between patients with different grades of gland loss or function at follow-ups. Conclusions: A single session of thermal pulsation was similar in its efficacy and safety profile to 3 months of twice daily warm compresses in Asians. Treatment efficacy was not affected by pretreatment gland loss. PMID:26825281

  1. Siphon flows in isolated magnetic flux tubes. II - Adiabatic flows

    NASA Technical Reports Server (NTRS)

    Montesinos, Benjamin; Thomas, John H.

    1989-01-01

    This paper extends the study of steady siphon flows in isolated magnetic flux tubes surrounded by field-free gas to the case of adiabatic flows. The basic equations governing steady adiabatic siphon flows in a thin, isolated magnetic flux tube are summarized, and qualitative features of adiabatic flows in elevated, arched flux tubes are discussed. The equations are then cast in nondimensional form and the results of numerical computations of adiabatic siphon flows in arched flux tubes are presented along with comparisons between isothermal and adiabatic flows. The effects of making the interior of the flux tube hotter or colder than the surrounding atmosphere at the upstream footpoint of the arch is considered. In this case, is it found that the adiabatic flows are qualitatively similar to the isothermal flows, with adiabatic cooling producing quantitative differences. Critical flows can produce a bulge point in the rising part of the arch and a concentration of magnetic flux above the bulge point.

  2. Lattice Boltzmann simulation to laminar pulsating flow past a circular cylinder with constant temperature

    NASA Astrophysics Data System (ADS)

    Zheng, Youqu; Li, Guoneng; Guo, Wenwen; Dong, Cong

    2017-09-01

    In order to investigate the heat transfer characteristics of pulsating flows past a circular cylinder, a Lattice Boltzmann (LB) numerical code based on a 2-dimension-9-velocity frame is developed. The local Nusselt number and the dimensionless viscous force around the cylinder surface are explored in detail. Double Particle Distribution Function model and the second order extrapolation method for the curve boundary of the cylinder are employed in the LB numerical code. Numerical results found that the spatial averaged Nusselt number of the cylinder is oscillating with the same pulsating frequency of the incoming air flows. The heat transfer enhancement is mainly located in the windward side of the cylinder, and the heat transfer enhancement only happens in one half cycle of the pulsation. Whereas the heat transfer in the leeward side of the cylinder is found to be unaffected, and the heat transfer is slightly deteriorated in the other half cycle of the pulsation. Further analysis showed that the heat transfer enhancement is proportional to the magnitude of dimensionless viscous force.

  3. Analytic description of vibrations in a piping system with pulsating flow

    NASA Technical Reports Server (NTRS)

    Bosnyatskiy, G. P.; Grossman, R. I.; Kozobkov, A. A.; Koppel, A. I.

    1973-01-01

    Various calculation schemes were proposed for describing vibrations in a piping system with pulsating flow. Methods were selected and applied according to the type of irregularities examined: concentrated ones, extended ones, or complex ones. The selection of a method also depends on comparability of the extent of the irregularities with the pressure wavelength and velocity in the flow. Relations were found which permit a description of the interaction of a pulsating flow with any irregularity in the system. For complex systems with varying temperatures and some irregularities, relations were obtained, which reflect the varying phase displacement of the forces in these irregularities. The effect of the frictional torque on pipeline supports, in the presence of flexural and torsional vibrations was investigated, on the assumption that the frictional torque depends linearly on the angular velocity.

  4. Discrete-vortex simulation of pulsating flow on a turbulent leading-edge separation bubble

    NASA Technical Reports Server (NTRS)

    Sung, Hyung Jin; Rhim, Jae Wook; Kiya, Masaru

    1992-01-01

    Studies are made of the turbulent separation bubble in a two-dimensional semi-infinite blunt plate aligned to a uniform free stream with a pulsating component. The discrete-vortex method is applied to simulate this flow situation because this approach is effective for representing the unsteady motions of the turbulent shear layer and the effect of viscosity near the solid surface. The numerical simulation provides reasonable predictions when compared with the experimental results. A particular frequency with a minimum reattachment is related to the drag reduction. The most effective frequency is dependent on the amplified shedding frequency. The turbulent flow structure is scrutinized. This includes the time-mean and fluctuations of the velocity and the surface pressure, together with correlations between the fluctuating components. A comparison between the pulsating flow and the non-pulsating flow at the particular frequency of the minimum reattachment length of the separation bubble suggests that the large-scale vortical structure is associated with the shedding frequency and the flow instabilities.

  5. Pulsating electrolyte flow in a full vanadium redox battery

    NASA Astrophysics Data System (ADS)

    Ling, C. Y.; Cao, H.; Chng, M. L.; Han, M.; Birgersson, E.

    2015-10-01

    Proper management of electrolyte flow in a vanadium redox battery (VRB) is crucial to achieve high overall system efficiency. On one hand, constant flow reduces concentration polarization and by extension, energy efficiency; on the other hand, it results in higher auxiliary pumping costs, which can consume around 10% of the discharge power. This work seeks to reduce the pumping cost by adopting a novel pulsing electrolyte flow strategy while retaining high energy efficiency. The results indicate that adopting a short flow period, followed by a long flow termination period, results in high energy efficiencies of 80.5% with a pumping cost reduction of over 50%.

  6. High Speed Flow in Tubes

    DTIC Science & Technology

    1987-04-14

    variables such as density or pressure are assumed to depend only on time and not on position along the tube so that only some of the 1-D effects are...ideal gas law). 2) The local linear burning rate (rb) depends on the spatial- average pressure within the tube assembly. 3) The ratio of specific... depends on local pressure . 3) Case AD is the same as case AC except that the ratio of specific heats is no longer constant (i.e., Eq. (2.20) is used to

  7. Laboratory modeling of flow regimes in a draft tube of Francis hydro-turbine

    NASA Astrophysics Data System (ADS)

    Shtork, Sergey; Litvinov, Ivan; Mitryakov, Andrey; Hanjalic, Kemal

    The paper reports on some results of the experimental study of flow and pressure pulsations in a laboratory model of the draft tube (DT) of Francis-99 hydro-turbine over a broad range of operating regimes. Velocity distributions at the model inlet varied within 866 modes of the turbine load conditions, including those with maximum coherent pressure pulsations on the model walls. The contact and non-contact methods were used to measure pressure pulsations on the model walls using acoustic sensors and to measure the averaged velocity distribution with a laser Doppler anemometer "LAD-06i". Analysis of the results have showed that in the model cone there are flow modes with forming of precessing vortex cores, accompanied by a sharp increase in the amplitude of coherent pressure pulsations on the wall and the velocity field rearrangement. It is shown that the vortex core starts forming with an increase in the integral parameter of swirl up to S>0.5. A novelty of the work is the combination of the rapid prototyping (3-d printing) of the inflow swirl generators and computerized measurement techniques that makes it possible to acquire rapidly a large amount of experimental data for a variety of designs and operating conditions. The results can provide insight into the effect of various design and operating parameters on the flow physics, as well as serve for verification of the numerical simulations.

  8. Reducing the effect of penstock pressure pulsations on hydro electric plant power system stabilizer signals

    SciTech Connect

    Nettleton, L.D.; Gurney, J.H.; Bollinger, K.E.

    1993-12-01

    A characteristic trait of Francis turbines operating at low-head is pressure pulsations that occur during certain load levels of the generator. These stem from pressure variations across the turbine due to pulsating flow in the draft-tube. This surging action of the water column is related to draft-tube geometry and flow-rate of water in the penstock. The pressure pulsations cause torque variations on the turbine and corresponding electric power pulsations. If electric power is used as a feedback signal to the Power System Stabilizer (PSS), then Mvar and terminal voltage pulsations will occur when the generator is operating in the ``rough zone``. This paper describes field test results for investigating feedforward control from the penstock, draft tube and spiral case pressure to reduce the effects of Mw pulsations on PSS output signals. This investigation involved a PSS with generator power as the feedback signal and the PSS tuned for local and inter-area damping.

  9. Technical note: Reduced pulsation chamber vacuum at normal pulsation rate and ratio provides adequate prestimulation to induce oxytocin release and milk ejection while simultaneous milk flow is prevented.

    PubMed

    Neuheuser, Anna-Lena; Belo, Claire; Bruckmaier, Rupert M

    2017-10-01

    In the present study we investigated the milking characteristics and the oxytocin release in dairy cows milked after either manual prestimulation or a premilking period with pulsating liners at normal pulsation rate (60) and ratio (60:40) while the pulsation chamber vacuum (PCV) was reduced to 20 kPa to prevent the opening of the liners. During the milking trial with 8 cows the PCV reduction was started either before attachment (PCV-1) or immediately after attachment (PCV-2) of the teat cups. Milk yields, total milking times, average milk flows, peak flow rates, the duration of milk flow plateaus, and the duration of milk flow declines did not differ among the 3 treatments. Only the time to reach peak milk flow was prolonged when the vacuum reduction was started after teat cup attachment (PCV-2). In this treatment, milk flow >200 g/min already occurred during the premilking period, resulting in bimodal milk flow curves. In 5 of the 8 cows, plasma oxytocin (OT) concentrations were measured from -2 min before the start of milking until 3 min of milking to compare the OT release in response to manual prestimulation and during PCV-1. In both treatments, OT increased similarly and remained elevated until the end of measurements. Consequently, the areas under the curve of OT concentrations did not differ between treatments. In conclusion, milking performance is similar if milking is performed after manual prestimulation or after normal pulsation at reduced PCV. To prevent milk flow during the prestimulation period, it is of crucial importance to start the reduction of the PCV before cluster attachment. Copyright © 2017 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

  10. Evaluation of pump pulsation in respirable size-selective sampling: part I. Pulsation measurements.

    PubMed

    Lee, Eun Gyung; Lee, Larry; Möhlmann, Carsten; Flemmer, Michael M; Kashon, Michael; Harper, Martin

    2014-01-01

    Pulsations generated by personal sampling pumps modulate the airflow through the sampling trains, thereby varying sampling efficiencies, and possibly invalidating collection or monitoring. The purpose of this study was to characterize pulsations generated by personal sampling pumps relative to a nominal flow rate at the inlet of different respirable cyclones. Experiments were conducted using a factorial combination of 13 widely used sampling pumps (11 medium and 2 high volumetric flow rate pumps having a diaphragm mechanism) and 7 cyclones [10-mm nylon also known as Dorr-Oliver (DO), Higgins-Dewell (HD), GS-1, GS-3, Aluminum, GK2.69, and FSP-10]. A hot-wire anemometer probe cemented to the inlet of each cyclone type was used to obtain pulsation readings. The three medium flow rate pump models showing the highest, a midrange, and the lowest pulsations and two high flow rate pump models for each cyclone type were tested with dust-loaded filters (0.05, 0.21, and 1.25mg) to determine the effects of filter loading on pulsations. The effects of different tubing materials and lengths on pulsations were also investigated. The fundamental frequency range was 22-110 Hz and the magnitude of pulsation as a proportion of the mean flow rate ranged from 4.4 to 73.1%. Most pump/cyclone combinations generated pulse magnitudes ≥10% (48 out of 59 combinations), while pulse shapes varied considerably. Pulsation magnitudes were not considerably different for the clean and dust-loaded filters for the DO, HD, and Aluminum cyclones, but no consistent pattern was observed for the other cyclone types. Tubing material had less effect on pulsations than tubing length; when the tubing length was 183cm, pronounced damping was observed for a pump with high pulsation (>60%) for all tested tubing materials except for the Tygon Inert tubing. The findings in this study prompted a further study to determine the possibility of shifts in cyclone sampling efficiency due to sampling pump pulsations

  11. Pulsating-flow measurement with an orifice flange

    NASA Astrophysics Data System (ADS)

    Bossart, L. M.

    1981-05-01

    A measurement problem encountered during instrumentation of a geothermal air drilling operation on the Baca Ranch in the Jemez Mountains in New Mexico was how to measure the flow of ammonia water solution injected into the air line. The pump that develops the pressure in the ammonia line is not a positive displacement pump, therefore, counting pump strokes does not determine the number of gal/min of ammonia flow. The flow was measured using an orifice flange differential pressure technique but, the range of flow measured, exceeded the 4:1 range ability of an orifice. A computer smoothing of the differential pressure and the line pressure together with a scaling factor, determined by the shape of the raw differential pressure, provided a smoothing of the flow data which was checked against the actual flow over a long time period to determine the volume of solution injected into the system per hour. An instantaneous reading of ammonia flow was thereby determined. It showed small variations in corrosion rate measured in the standpipe that may have been caused by a momentary variation in the flow of ammonia solution.

  12. Air flow exploration of abrasive feed tube

    NASA Astrophysics Data System (ADS)

    Zhang, Shijin; Li, Xiaohong; Gu, Yilei

    2009-12-01

    An abrasive water-jet cutting process is one in which water pressure is raised to a very high pressure and forced through a very small orifice to form a very thin high speed jet beam. This thin jet beam is then directed through a chamber and then fed into a secondary nozzle, or mixing tube. During this process, a vacuum is generated in the chamber, and garnet abrasives and air are pulled into the chamber, through an abrasive feed tube, and mixes with this high speed stream of water. Because of the restrictions introduced by the abrasive feed tube geometry, a vacuum gradient is generated along the tube. Although this phenomenon has been recognized and utilized as a way to monitor nozzle condition and abrasive flowing conditions, yet, until now, conditions inside the abrasive feed line have not been completely understood. A possible reason is that conditions inside the abrasive feed line are complicated. Not only compressible flow but also multi-phase, multi-component flow has been involved in inside of abrasive feed tube. This paper explored various aspects of the vacuum creation process in both the mixing chamber and the abrasive feed tube. Based on an experimental exploration, an analytical framework is presented to allow theoretical calculations of vacuum conditions in the abrasive feed tube.

  13. A search for p-mode pulsations in white dwarf stars using the Berkeley Visible Imaging Tube detector

    NASA Astrophysics Data System (ADS)

    Kilkenny, D.; Welsh, B. Y.; Koen, C.; Gulbis, A. A. S.; Kotze, M. M.

    2014-01-01

    We present high-speed photometry (resolution 0.1 s) obtained during the commissioning of the Berkely Visible Imaging Tube system on the Southern African Large Telescope (SALT). The observations were an attempt to search for very rapid p-mode oscillations in white dwarf stars and included three DA stars known to be g-mode pulsators (ZZ Cet, HK Cet and AF Pic), one other DA star (WD 1056-384) not known to be variable and one AM Cvn star (HP Lib). No evidence was found for any variations greater than about 1 mmag in amplitude (˜0.1 per cent) at frequencies in excess of 60 mHz (periods <17 s) in any of the target stars, though several previously known g-mode frequencies were recovered.

  14. Estimation of anisotropic factor and turbulent mixing rate in rod bundles based on the flow pulsation phenomenon

    SciTech Connect

    Kim, S.; Park, G.C.

    1997-03-01

    The anisotropic turbulent diffusion and the turbulent mixing phenomena in rod bundle flow fields are studied. The former is a distinguishing feature of the flow through rod bundles, and the latter is essential to the subchannel thermal-hydraulic analysis. On the basis of the flow pulsation, which is suggested as a main process of turbulent mixing, scale relations for principal parameters such as the anisotropic factor and mixing rate are derived. To obtain a scale relation for the anisotropic factor, eddy viscosities are classified into isotropic and flow pulsation parts. Scales of each part are estimated using the scale analysis method. For the purpose of determining the length and velocity scales of the pulsating flow, a hypothetical circulating flow with a period corresponding to the frequency of the pulsation is assumed. The scale relation is compared with the experimental data and shows good agreement both with respect to trend and magnitude for various geometries. Thus, it is concluded that the flow pulsation is a significant contributor to the strong anisotropy in the rod bundle flow field. Also, the mixing rate is predicted by estimating the effective mixing velocity. The estimated mixing rate is transformed into well-known dimensionless numbers, which are compared with the experimental data and with correlations to verify the predictability.

  15. Shock Tube Flow Uniformity Experiments.

    DTIC Science & Technology

    1979-09-23

    S . CONTRACT OR GRANT NUMBTIRrs- ames E. Craig -’ -DNA001-79-C-0329 f-" 9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT. PROJECT...Mach angles all flalr-Seiween 28 and 32 degrees; because of flow field disto ion of the optical image, the measurement accuracy was( degrees. For a

  16. Research of working pulsation in closed angle based on rotating-sleeve distributing-flow system

    NASA Astrophysics Data System (ADS)

    Zhang, Yanjun; Zhang, Hongxin; Zhao, Qinghai; Jiang, Xiaotian; Cheng, Qianchang

    2017-08-01

    In order to reduce negative effects including hydraulic impact, noise and mechanical vibration, compression and expansion of piston pump in closed volume are used to optimize the angle between valve port and chamber. In addition, the mathematical model about pressurization and depressurization in pump chamber are analyzed based on distributing-flow characteristic, and it is necessary to use simulation software Fluent to simulate the distributing-flow fluid model so as to select the most suitable closed angle. As a result, when compression angle is 3°, the angle is closest to theoretical analysis and has the minimum influence on flow and pump pressure characteristic. Meanwhile, cavitation phenomenon appears in pump chamber in different closed angle on different degrees. Besides the flow pulsation is increasingly smaller with increasing expansion angle. Thus when expansion angle is 2°, the angle is more suitable for distributing-flow system.

  17. Investigation of the effect of external periodic flow pulsation on a cylinder wake using linear stability analysis

    NASA Astrophysics Data System (ADS)

    Lu, Liang; Papadakis, George

    2011-09-01

    The aim of this paper is to investigate the receptivity of cylinder wake to external periodic flow pulsation at low Reynolds number using linear stability analysis. The inlet flow pulsation appears as a forcing term in the linearised equation set. The full non-linear N-S equations as well as the linearised set for small perturbations around the time-averaged flow are solved using an in-house finite volume solver. The results are first validated against reference data for growth rate and frequency of the most unstable eigenmode for flow past a fixed cylinder with steady base flow at various Reynolds numbers. A special numerical technique is developed to separate the components of the solution in the wake that vary with the natural shedding frequency and the external pulsating frequency. The developed approach requires temporal integration over one period of vortex shedding and solution of a 4×4 linear system at every cell of the domain. The results show that both cross-stream and streamwise velocity components in the near cylinder region are strongly affected by flow pulsation, and its effect is spatially localised in the near wake. Increasing the pulsation frequency reduces the spatial extent within which pulsation plays an important role. A symmetric shedding pattern is established and at every period of external pulsation, two pairs of symmetric vortices are shed from the top and bottom of the cylinder. The width of the wake periodically widens and narrows, which is similar to "wake breathing" observed in a streamwise oscillating cylinder.

  18. Interaction of a pulsating vortex rope with the local velocity field in a Francis turbine draft tube

    NASA Astrophysics Data System (ADS)

    Müller, A.; Bullani, A.; Dreyer, M.; Roth, S.; Favrel, A.; Landry, C.; Avellan, F.

    2012-11-01

    Acoustic resonances in Francis turbines often define undesirable limitations to their operating ranges at high load. The knowledge of the mechanisms governing the onset and the sustenance of these instabilities in the swirling flow leaving the runner is essential for the development of a reliable hydroacoustic model for the prediction of system stability. The present work seeks to study experimentally the unstable draft tube flow by conducting a series of measurements on a reduced Francis Turbine model. The key physical parameters and their interaction with the hydraulic and mechanical system are studied and quantified. In particular, the evolution of the axial and tangential velocity components in the draft tube cone is analysed by means of Laser Doppler Anemometry. Combined with the calculation of the instantaneous vortex rope volume based on flow visualization and the measurement of the pressure fluctuations, the nature of the auto-oscillation in the draft tube flow is investigated.

  19. Study of mixed refrigerant undergoing pulsating flow in micro coolers with pre-cooling

    NASA Astrophysics Data System (ADS)

    Lewis, Ryan; Wang, Yunda; Schneider, Hayley; Lee, Y. C.; Radebaugh, Ray

    2013-10-01

    Micro cryogenic coolers can provide low temperatures with a smaller volumetric footprint and smaller power draw than their conventional-scale counterparts. However, they can exhibit lower-than-desired cooling power. We measure the specific cooling power of a refrigerant expanding from a high pressure of 0.6 MPa to a low pressure of 0.1 MPa, while undergoing pulsating flow in a micro cryogenic cooler with pre-cooling. We further observe that the pulses in the flow-rate occur due to a volume of liquid forming in the high-pressure coupling mini-channel. The composition of the flowing refrigerant is analyzed with gas chromatography and thermal conductivity detection (GC/TCD), showing that there is no overall composition change in the refrigerant after it enters the pre-cooling lines. A model of the cooling power under such a pulsating flow regime is developed with good agreement to measured values. An improved refrigerant mixture is designed with this model, and subsequently tested, showing increased specific cooling power.

  20. Incompressible viscous flow in tubes with occlusions

    NASA Astrophysics Data System (ADS)

    Huang, Huaxiong

    Viscous, incompressible flow in tubes with partial occlusion is investigated using numerical and experimental procedures. The study is related to the problem of atherosclerosis, one of the most common diseases of the circulatory system. One of the computational difficulties in solving the incompressible Navier-Stokes equations is the lack of pressure or vorticity boundary conditions. A finite difference approach, referred to as the interior constraint (IC) method, is proposed to resolve this difficulty. As a general numerical method, it is formulated for both the stream function-vorticity and primitive (physical) variable formulations. The procedure is explained using a one dimensional model with extensive numerical tests presented for two dimensional cases, including flow in a driven cavity and flow over a backward facing step. Results are obtained with second-order accuracy. Next, the IC method is applied to flow in a tube with an occlusion, which is used as the model for blood flow in stenosed arteries in the study of the pathology of atherosclerosis. Numerical results are obtained for both steady and pulsatile flows. Results are compared with those of SIMPLE, one of the commercially available numerical algorithms. The pulsatile flow study revealed several interesting new features. It suggested that the high shear stress is not likely to initiate atherosclerosis lesions. The recirculation region, which is a prominent feature of the unsteady flow, is more likely to cause the initiation and development of the disease. Experimental measurements for steady flow complement the numerical study and show qualitative agreement.

  1. Numerical investigation of flow structure and pressure pulsation in the Francis-99 turbine during startup

    NASA Astrophysics Data System (ADS)

    Minakov, A.; Sentyabov, A.; Platonov, D.

    2017-01-01

    We performed numerical simulation of flow in a laboratory model of a Francis hydroturbine at startup regimes. Numerical technique for calculating of low frequency pressure pulsations in a water turbine is based on the use of DES (k-ω Shear Stress Transport) turbulence model and the approach of “frozen rotor”. The structure of the flow behind the runner of turbine was analysed. Shows the effect of flow structure on the frequency and intensity of non-stationary processes in the flow path. Two version of the inlet boundary conditions were considered. The first one corresponded measured time dependence of the discharge. Comparison of the calculation results with the experimental data shows the considerable delay of the discharge in this calculation. Second version corresponded linear approximation of time dependence of the discharge. This calculation shows good agreement with experimental results.

  2. Numerical simulation of pulsation processes in hydraulic turbine based on 3D model of cavitating flow

    NASA Astrophysics Data System (ADS)

    Panov, L. V.; Chirkov, D. V.; Cherny, S. G.; Pylev, I. M.

    2014-01-01

    A new approach was proposed for simulation of unsteady cavitating flow in the flow passage of a hydraulic power plant. 1D hydro-acoustics equations are solved in the penstock domain. 3D equations of turbulent flow of isothermal compressible liquid-vapor mixture are solved in the turbine domain. Cavitation is described by a transfer equation for liquid phase with a source term which is responsible for evaporation and condensation. The developed method was applied for simulation of pulsations in pressure, discharge, and total energy propagating along the flow conduit of the hydraulic power plant. Simulation results are in qualitative and quantitative agreement with experiment. The influence of key physical and numerical parameters like discharge, cavitation number, penstock length, time step, and vapor density on simulation results was studied.

  3. High-Speed Ion Flow, Substorm Current Wedge, and Multiple Pi 2 Pulsations

    DTIC Science & Technology

    2007-11-02

    5.76 65.8 22.96 -20.5 03 6. 66 23 -2 20 3 .5 .19 D.6 Figure 12. Magnetic field data measured on the ISEE 1 satellite in the GSE...ISMC-TR-99-04 AEROSPACE REPORT NO. TR-99(8570)- 3 iHigh-Speed Ion Flow, Substorm Current Wedge, land Multiple Pi 2 Pulsations >0 December 1998...and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20S03. 1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 20 December 1998 3

  4. An Experimental Investigation of Flow Across Tube Banks

    NASA Technical Reports Server (NTRS)

    Brevoort, M.J.; Tifford, A.N.

    1942-01-01

    Flow across tube banks was investigated by surveys of total dynamic and static pressure by visualization of the flow through the use of titanium tetrachloride smoke, by thermocouple surveys of heated tubes, and by hot-wire surveys of both heated and unheated tubes. It was found that turbulence increased as the depth of the bank increased and that the broad wake behind each tube affected flow over the succeeding tubes.

  5. Effects of Pump Pulsation on Hydrodynamic Properties and Dissolution Profiles in Flow-Through Dissolution Systems (USP 4).

    PubMed

    Yoshida, Hiroyuki; Kuwana, Akemi; Shibata, Hiroko; Izutsu, Ken-Ichi; Goda, Yukihiro

    2016-06-01

    To clarify the effects of pump pulsation and flow-through cell (FTC) dissolution system settings on the hydrodynamic properties and dissolution profiles of model formulations. Two FTC systems with different cell temperature control mechanisms were used. Particle image velocimetry (PIV) was used to analyze the hydrodynamic properties of test solutions in the flow-through dissolution test cell. Two pulsation pumps (semi-sine, full-sine) and a non-pulsatile pump were used to study the effects of varied flows on the dissolution profiles of United States Pharmacopeia standard tablets. PIV analysis showed periodic changes in the aligned upward fluid flow throughout the dissolution cell that was designed to reduce the temperature gradient during pump pulsation (0.5 s/pulse). The maximum instantaneous flow from the semi-sine pump was higher than that of the full-sine pump under all conditions. The flow from the semi-sine wave pump showed faster dissolution of salicylic acid and prednisone tablets than those from other pumps. The semi-sine wave pump flow showed similar dissolution profiles in the two FTC systems. Variations in instantaneous fluid flow caused by pump pulsation that meets the requirements of pharmacopoeias are a factor that affects the dissolution profiles of tablets in FTC systems.

  6. Motions of a liquid in a pulsating bulb with application to problems of blood flow

    NASA Technical Reports Server (NTRS)

    Jones, R. T.

    1976-01-01

    Potential flows may be utilized to represent motions produced in pulsating bulbs. While the initial bulb shape may be arbitrary, sequential shapes are related by affine transformations. Two components appear in the distribution of pressure, one dependent on the instantaneous velocity and the other on the acceleration. For flows with stationary streamlines the inertial impedance is that of a simple mass, and is proportional to the first moment of the actual mass of fluid contained within the bulb. Examples treated are: (1) Expanding and collapsing circular cylinders, and (2) elliptical cylinders in which the perimeter is held constant. The thickness of the pulsatile laminar boundary layer is found to be approximately on millimeter for conditions in the vicinity of the heart. Conditions for separation and turbulence differ from those in steady flow.

  7. A hybrid method of estimating pulsating flow parameters in the space-time domain

    NASA Astrophysics Data System (ADS)

    Pałczyński, Tomasz

    2017-05-01

    This paper presents a method for estimating pulsating flow parameters in partially open pipes, such as pipelines, internal combustion engine inlets, exhaust pipes and piston compressors. The procedure is based on the method of characteristics, and employs a combination of measurements and simulations. An experimental test rig is described, which enables pressure, temperature and mass flow rate to be measured within a defined cross section. The second part of the paper discusses the main assumptions of a simulation algorithm elaborated in the Matlab/Simulink environment. The simulation results are shown as 3D plots in the space-time domain, and compared with proposed models of phenomena relating to wave propagation, boundary conditions, acoustics and fluid mechanics. The simulation results are finally compared with acoustic phenomena, with an emphasis on the identification of resonant frequencies.

  8. Measurement of cryogenic regenerator characteristics under oscillating flow and pulsating pressure

    NASA Astrophysics Data System (ADS)

    Nam, Kwanwoo; Jeong, Sangkwon

    2003-10-01

    This paper describes an experimental apparatus developed to investigate detailed thermal and hydrodynamic characteristics of a regenerator at cryogenic temperature under oscillating flow and pulsating pressure conditions. Cold-end of the regenerator is maintained at approximately 85 K for G-M cryocooler type and 100 K for Stirling cryocooler type operations by means of two cryogenic heat exchangers. At both ends of the regenerator, fine hot wire probes are installed to measure the fast oscillating gas temperature and mass flow rate. The gas temperature sensors installed very close to the ends of the regenerator matrix assure precise gas temperature measurement in the regenerator. In this study, thermal and hydrodynamic behaviors of the well-defined wire-screen regenerator are fully characterized. First, pressure drop characteristics are discussed for different frequencies under room temperature. Second, ineffectiveness of the regenerator is obtained for different cold-end temperatures.

  9. Application of the results of experimental and numerical turbulent flow researches based on pressure pulsations analysis

    NASA Astrophysics Data System (ADS)

    Kovalnogov, Vladislav N.; Fedorov, Ruslan V.; Khakhalev, Yuri A.; Khakhaleva, Larisa V.; Chukalin, Andrei V.

    2017-07-01

    The numerical investigation of the turbulent flow with the impacts, based on a modified Prandtl mixing-length model with using of the analysis of pulsations of pressure, calculation of structure and a friction factor of a turbulent flow is made. These results under the study allowed us to propose a new design of a cooled turbine blade and gas turbine mobile. The turbine blade comprises a combined cooling and cylindrical cavity on the blade surface, and on the inner surfaces of the cooling channels too damping cavity located on the guide vanes of the compressor of a gas turbine engine, increase the supply of gas-dynamic stability of the compressor of a gas turbine engine, reduce the resistance of the guide blades, and increase the efficiency of the turbine engine.

  10. Vibration of Tube Bundles in Cross Water Flow

    NASA Astrophysics Data System (ADS)

    Dikarev, I. M.; Loshkareva, E. A.; Kartuesova, A. Yu.

    2017-03-01

    Results of vibration testing of an experimental tube bundle of 72 tubes of diameter 0.012 m in the case of cooling-water flow across the tubes with different versions of installation of baffles are described. The influence of the displacement of the baffles on the parameters of vibration of the tube bundle is determined.

  11. Information about accretion flows from X-ray timing of pulsating sources

    NASA Technical Reports Server (NTRS)

    Lamb, F. K.; Pines, D.; Shaham, J.

    1976-01-01

    The response was studied of a rotating neutron star to fluctuating torques and it was found that the observed variations in the pulsation periods of the compact X-ray sources Cen X-3 and Her X-1 could be caused by short time scale fluctuations in the accretion torques acting on the neutron stars. The sizes and rates of the required fluctuations are consistent with current accretion models. Such fluctuations can cause period variations either (a) directly, by causing a random walk of the star's angular velocity or (b) indirectly, by exciting a long-period mode of the neutron star, such as the Tkachenko mode of the rotating neutron superfluid. Phenomena in compact X-ray sources and cataclysmic variables which may be caused by fluctuating mass flow rates are also discussed.

  12. Information about accretion flows from X-ray timing of pulsating sources

    NASA Technical Reports Server (NTRS)

    Lamb, F. K.; Pines, D.; Shaham, J.

    1976-01-01

    The response was studied of a rotating neutron star to fluctuating torques and it was found that the observed variations in the pulsation periods of the compact X-ray sources Cen X-3 and Her X-1 could be caused by short time scale fluctuations in the accretion torques acting on the neutron stars. The sizes and rates of the required fluctuations are consistent with current accretion models. Such fluctuations can cause period variations either (a) directly, by causing a random walk of the star's angular velocity or (b) indirectly, by exciting a long-period mode of the neutron star, such as the Tkachenko mode of the rotating neutron superfluid. Phenomena in compact X-ray sources and cataclysmic variables which may be caused by fluctuating mass flow rates are also discussed.

  13. Effects of vacuum level and pulsation rate on milk ejection and milk flow traits in Tunisian dairy camels (Camelus dromedarius).

    PubMed

    Atigui, Moufida; Marnet, Pierre-Guy; Barmat, Ahmed; Khorchani, Touhami; Hammadi, Mohamed

    2015-01-01

    This work aims to compare the effects of milking at two vacuum levels (38 and 48 kPa) and three pulsation rates (60, 90, and 120 cpm) on milk production and milk flow characteristics. Six multiparous Maghrebi camels in late lactation and once daily milked were used. The best combination of setting for camel's milking was high vacuum and low pulsation rate (48 kPa/60 cpm). Milk yield and average and peak milk flow rate were the highest, while milking time was the shortest using this combination of setting (3.05 ± 0.30 kg, 1.52 ± 0.21 kg/min, 2.52 ± 0.21 kg/min, and 3.32 ± 0.31 min, respectively). Lower vacuum level lengthened milking time by more than 100 % and was not sufficient to extract milk correctly (1.69 to 2.48 times less milk yield harvested), suggesting a negative interaction with the stimulatory effect of pulsation. Higher pulsation rates did not better stimulate the camels and induced more bimodality and lower milk flow rates. Animal characteristics and liner/claw design affect machine milking and further investigations must be carried out to verify their effects and to study long-term effect of high vacuum level on udder health and teat condition.

  14. Numerical Investigation Of Nonlinear Waves Connected To Blood Flow In An Elastic Tube With Variable Radius

    NASA Astrophysics Data System (ADS)

    Dimitrova, Zlatinka I.

    2015-12-01

    We investigate flow of incompressible fluid in a cylindrical tube with elastic walls. The radius of the tube may change along its length. The discussed problem is connected to the fluid-structure interaction in large human arteries and especially to nonlinear effects. The long-wave approximation is applied to solve model equations. The obtained model Korteweg-deVries equation possessing a variable coefficient is reduced to a nonlinear dynamical system of three first order differential equations. The low probability of a solitary wave arising is shown. Periodic wave solutions of the model system of equations are studied and it is shown that the waves, that are consequence of the irregular heart pulsations may be modelled by a sequence of parts of such periodic wave solutions.

  15. Jet-flow from shock tubes

    NASA Astrophysics Data System (ADS)

    Kingery, Charles N.; Gion, Edmund J.

    1989-07-01

    This project was designed to map the magnitude and extent of the high velocity jet flow exiting shock tubes. The flow was measured by installing stagnation probes along three blast lines and by supplementing these measurements with calibrated displacement cubes. The side-on and stagnation overpressure versus time were measured, and from that, the side-on and stagnation impulse were calculated. The stagnation impulse showed a large drop in magnitude as the blast line was moved from the zero line to a 1.5 and then to a 3-diameter offset. A helium driver was used in the 2.54-cm-diameter shock tube to simulate an explosion in a storage magazine. Results are presented in the form of stagnation impulse versus distance along the three blast lines. The significance of these findings is that the present quantity-distance criteria for munitions stored in underground magazines are based on side-on peak overpressure, but our results show that the peak stagnation pressure and impulse are much greater. At a distance where 10.3-kPa (1.5 psi) side-on pressure was measured, a 49.6-kPa (7.2 psi) stagnation pressure was measured. At the same distance, a side-on impulse was 12.6 kPa-ms (1.83 psi-ms), while the stagnation impulse was 134 kPa-ms (20.2 psi-ms)--a dramatic difference.

  16. Investigation of the Plunging Pressure Pulsation in a Swirling Flow with Precessing Vortex Rope in a Straight Diffuser

    NASA Astrophysics Data System (ADS)

    Muntean, S.; Tănasă, C.; Bosioc, A. I.; Moş, D. C.

    2016-11-01

    The paper investigates an unexpected feature of the unsteady pressure field resulting from the self-induced instability of the decelerated swirling flow in a straight diffuser. Firstly, the self-induced instability is experimentally investigated on the swirl generator test rig. As a result, the asynchronous (rotating) pressure pulsation associated with the rotating vortex rope of 15 Hz and it second harmonic are discriminated. Also, a low frequency synchronous (plunging) pulsation around of 2.5 Hz is identified based on unsteady pressure field measured at the wall and LDV measurement of the velocity components in the flow. The low frequency plunging pressure fluctuations is superimposed on the rotating pressure pulsations associated with the vortex rope. The numerical simulations are performed to explore the vortex rope dynamics. The numerical results are compared against experimental data to assess the accuracy of the models. Next, the pressure pulsation dynamics is correlated with the time evolution of the vortex rope. The main conclusion emerging from the analysis of the vortex rope evolution in time is that the cycle with low frequency is responsible for the plunging (synchronous) pressure fluctuations superimposed over the rotating (asynchronous) pressure field associated with the precession of the vortex rope.

  17. Visualization of entry flow separation for oscillating flow in tubes

    NASA Technical Reports Server (NTRS)

    Qiu, Songgang; Simon, Terence W.

    1992-01-01

    Neutrally buoyant helium-filled soap bubbles with laser illumination are used to document entry flow separation for oscillating flow in tubes. For a symmetric entry case, the size of the separation zone appears to mildly depend on Reynolds number in the acceleration phase, but is roughly Reynolds number independent in the deceleration phase. For the asymmetric entry case, the separation zone was larger and appeared to grow somewhat during the deceleration phase. The separation zones for both entry geometry cases remain relatively small throughout the cycle. This is different from what would be observed in all-laminar, oscillator flows and is probably due to the high turbulence of the flow, particularly during the deceleration phase of the cycle.

  18. Visualization of entry flow separation for oscillating flow in tubes

    NASA Technical Reports Server (NTRS)

    Qiu, Songgang; Simon, Terence W.

    1992-01-01

    Neutrally buoyant helium-filled soap bubbles with laser illumination are used to document entry flow separation for oscillating flow in tubes. For a symmetric entry case, the size of the separation zone appears to mildly depend on Reynolds number in the acceleration phase, but is roughly Reynolds number independent in the deceleration phase. For the asymmetric entry case, the separation zone was larger and appeared to grow somewhat during the deceleration phase. The separation zones for both entry geometry cases remain relatively small throughout the cycle. This is different from what would be observed in all-laminar, oscillator flows and is probably due to the high turbulence of the flow, particularly during the deceleration phase of the cycle.

  19. Stability of Flow Through Collapsible Tubes

    NASA Astrophysics Data System (ADS)

    Hamadiche, M.; Gad-El-Hak, M.

    2000-11-01

    The stability of the Hagen--Poiseuille flow of a Newtonian fluid in an incompressible, collapsible, viscoelastic tube is determined using linear stability analysis. The temporal stability of the system subjected to infinitesimal axisymmetric or non-axisymmetric disturbances is considered. A novel numerical strategy is introduced to study the stability of the coupled fluid--structure system. The strategy alleviates the need for an initial guess and thus ensuring that all the unstable modes within a given closed region in the complex eigenvalue plane will be found. The parameters of the system are chosen such that it is stable if the duct is not allowed to collapse, in this way the unstable modes found are expected to be unique to collapsible tubes. Three different unstable modes are found and the present results are in excellent agreement with the experiments of Bertram and Godbole (J. Fluids & Structures 9, pp. 257--277,1995). Two of the unstable modes have approximately the same frequency which is about a third of the frequency of the third mode. Moreover, the high-frequency mode is non-axisymmetric while one of the low-frequency modes is axisymmetric and the other one non-axisymmetric. The variation of all three unstable modes with the pliability of the duct and the other control parameters of the system will be discussed.

  20. Hydraulic drag at the condensing steam flow in tubes

    NASA Astrophysics Data System (ADS)

    Leontiev, A. I.; Milman, O. O.

    2014-12-01

    The dependency of condensing steam flow parameters in tubes and channels was studied as a function of different flow modes for the coolant: counter-flow, co-flow, cross-flow. The drop for the total pressure of steam is higher for the counter-flow than for the co-flow or cross-flow modes. The pressure drop was estimated with different computation models as a function flow mode. Calculation results were compared with experimental data.

  1. Chaotic and mode-locked interactions between flow-induced collapsible-tube oscillation and pulsatile upstream forcing

    NASA Astrophysics Data System (ADS)

    Bertram, C. D.; She, Jianwei

    2000-02-01

    Interactions were examined between the otherwise periodic self-excited oscillation of a pneumatically compressed flexible tube conveying an aqueous flow, and pulsations induced by connecting the output of a hydraulically controlled piston pump executing sinusoidal piston displacements in parallel with the steady flow-driving head. Depending on pump amplitude and frequency, the oscillatory interaction consisted of either resonance, periodic entrainment or aperiodicity. Despite limitations imposed by intrinsic turbulent noise, aperiodic interactions were shown to exhibit characteristics of a low-dimensional chaotic attractor.

  2. Pulsating Stars

    NASA Astrophysics Data System (ADS)

    Catelan, M.; Smith, H. A.

    2015-03-01

    This book surveys our understanding of stars which change in brightness because they pulsate. Pulsating variable stars are keys to distance scales inside and beyond the Milky Way galaxy. They test our understanding not only of stellar pulsation theory but also of stellar structure and evolution theory. Moreover, pulsating stars are important probes of the formation and evolution of our own and neighboring galaxies. Our understanding of pulsating stars has greatly increased in recent years as large-scale surveys of pulsating stars in the Milky Way and other Local Group galaxies have provided a wealth of new observations and as space-based instruments have studied particular pulsating stars in unprecedented detail.

  3. CHARACTERIZING PULSATING MIXING OF SLURRIES

    SciTech Connect

    Bamberger, Judith A.; Meyer, Perry A.

    2007-12-01

    This paper describes the physical properties for defining the operation of a pulse jet mixing system. Pulse jet mixing operates with no moving parts located in the vessel to be mixed. Pulse tubes submerged in the vessel provide a pulsating flow due to a controlled combination of applied pressure to expel the fluid from the pulse tube nozzle followed by suction to refill the pulse tube through the same nozzle. For mixing slurries nondimensional parameters to define mixing operation include slurry properties, geometric properties and operational parameters. Primary parameters include jet Reynolds number and Froude number; alternate parameters may include particle Galileo number, particle Reynolds number, settling velocity ratio, and hindered settling velocity ratio. Rating metrics for system performance include just suspended velocity, concentration distribution as a function of elevation, and blend time.

  4. Construction of the prediction model between pressure and flow rate for pulsating flows based on the Greenfield-Fry model concerning wave dispersion

    NASA Astrophysics Data System (ADS)

    Chun, Sejong; Jin, Jonghan; Cho, Wan-Ho

    2017-05-01

    Wave dispersion is the key feature in understanding pulsating flows in a rigid circular pipe with small diameter. The wave dispersion makes flow signals distorted in the pulsating flows by boundary conditions due to pipe surface. Detailed description of this phenomenon can make the Greenfield-Fry model more practical. This model describes the relationship between the pressure gradient and the flow rate in the rigid circular pipe. Because pressure gradient measurement requires more than two pressure transducers, it would become more practical if only one pressure transducer is needed by applying the Taylor's frozen field hypothesis. This implies that only one pressure transducer is satisfactory for predicting flow signals with the Greenfield-Fry model. By applying the frequency variant convection velocity to consider the wave dispersion, the Taylor's frozen field hypothesis can relate the pressure signals with the flow signals according to the Greenfield-Fry model. In this study, the Taylor's frozen field hypothesis is reformulated into a simpler functional form with the frequency variant convection velocity in a zero-dimensional model with the Newtonian fluid, uniform, laminar, axially and one-dimensional pulsatile flow assumption. An experiment with a blood flow simulator is exemplified to demonstrate its usefulness to predict the flow signals from the pressure signals with the Greenfield-Fry model. Moreover, the three-element Windkessel model is compared to emphasize the importance of the physical model derived from the Navier-Stokes equation, such as the Greenfield-Fry model for the pulsating flows.

  5. Numerical simulation of flow characteristics in micro shock tubes

    NASA Astrophysics Data System (ADS)

    Zhang, Guang; Setoguchi, Toshiaki; Kim, Heuy Dong

    2015-06-01

    Recently micro shock tubes have been widely used in many engineering and industrial fields, but the characteristics of unsteady flow are not well known to date in micro shock tubes. Compared to conventional shock tubes with macro scales, flows related to shock waves in micro shock tubes are highly complicated. Stronger viscous and dissipative interactions make shock wave dynamic behaviors significantly different from theoretical predictions. In the present study, a CFD work was applied to the unsteady compressible Navier-Stokes equations which were solved using a fully implicit finite volume scheme. The diaphragm pressure ratio and shock tube diameter were varied to investigate their effects on micro shock tube flows. Different wall boundary conditions were also performed to observe shock wave and contact surface propagation with no slip and slip walls. Detailed flow characteristics at the foot of shock wave and contact surface propagation were known from the present numerical simulations.

  6. Osteocytes subjected to pulsating fluid flow regulate osteoblast proliferation and differentiation

    SciTech Connect

    Vezeridis, Peter S.; Chen Qian . E-mail: j.kleinnulend@vumc.nl

    2006-09-29

    Osteocytes are thought to orchestrate bone remodeling, but it is unclear exactly how osteocytes influence neighboring bone cells. Here, we tested whether osteocytes, osteoblasts, and periosteal fibroblasts subjected to pulsating fluid flow (PFF) produce soluble factors that modulate the proliferation and differentiation of cultured osteoblasts and periosteal fibroblasts. We found that osteocyte PFF conditioned medium (CM) inhibited bone cell proliferation, and osteocytes produced the strongest inhibition of proliferation compared to osteoblasts and periosteal fibroblasts. The nitric oxide (NO) synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) attenuated the inhibitory effects of osteocyte PFF CM, suggesting that a change in NO release is at least partially responsible for the inhibitory effects of osteocyte PFF CM. Furthermore, osteocyte PFF CM stimulated osteoblast differentiation measured as increased alkaline phosphatase activity, and L-NAME decreased the stimulatory effects of osteocyte PFF CM on osteoblast differentiation. We conclude that osteocytes subjected to PFF inhibit proliferation but stimulate differentiation of osteoblasts in vitro via soluble factors and that the release of these soluble factors was at least partially dependent on the activation of a NO pathway in osteocytes in response to PFF. Thus, the osteocyte appears to be more responsive to PFF than the osteoblast or periosteal fibroblast with respect to the production of soluble signaling molecules affecting osteoblast proliferation and differentiation.

  7. Siphon flows in isolated magnetic flux tubes. 3: The equilibrium path of the flux tube arch

    NASA Technical Reports Server (NTRS)

    Thomas, John H.; Montesinis, Benjamin

    1989-01-01

    The arched equilibrium path of a thin magnetic flux tube in a plane-stratified, nonmagnetic atmosphere is calculated for cases in which the flux tube contains a steady siphon flow. The large scale mechanical equilibrium of the flux tube involves a balance among the magnetic buoyancy force, the net magnetic tension force due to the curvature of the flux tube axis, and the inertial (centrifugal) force due to the siphon flow along curved streamlines. The ends of the flux tube are assumed to be pinned down by some other external force. Both isothermal and adiabatic siphon flows are considered for flux tubes in an isothermal external atmosphere. For the isothermal case, in the absence of a siphon flow the equilibrium path reduces to the static arch calculated by Parker (1975, 1979). The presence of a siphon flow causes the flux tube arch to bend more sharply, so that magnetic tension can overcome the additional straightening effect of the inertial force, and reduces the maximum width of the arch. The curvature of the arch increases as the siphon flow speed increases. For a critical siphon flow, with supercritical flow in the downstream leg, the arch is asymmetric, with greater curvature in the downstream leg of the arch. Adiabatic flow have qualitatively similar effects, except that adiabatic cooling reduces the buoyancy of the flux tube and thus leads to significantly wider arches. In some cases the cooling is strong enough to create negative buoyancy along sections of the flux tube, requiring upward curvature of the flux tube path along these sections and sometimes leading to unusual equilibrium paths of periodic, sinusoidal form.

  8. Siphon flows in isolated magnetic flux tubes. 3: The equilibrium path of the flux tube arch

    NASA Astrophysics Data System (ADS)

    Thomas, John H.; Montesinis, Benjamin

    1989-09-01

    The arched equilibrium path of a thin magnetic flux tube in a plane-stratified, nonmagnetic atmosphere is calculated for cases in which the flux tube contains a steady siphon flow. The large scale mechanical equilibrium of the flux tube involves a balance among the magnetic buoyancy force, the net magnetic tension force due to the curvature of the flux tube axis, and the inertial (centrifugal) force due to the siphon flow along curved streamlines. The ends of the flux tube are assumed to be pinned down by some other external force. Both isothermal and adiabatic siphon flows are considered for flux tubes in an isothermal external atmosphere. For the isothermal case, in the absence of a siphon flow the equilibrium path reduces to the static arch calculated by Parker (1975, 1979). The presence of a siphon flow causes the flux tube arch to bend more sharply, so that magnetic tension can overcome the additional straightening effect of the inertial force, and reduces the maximum width of the arch. The curvature of the arch increases as the siphon flow speed increases. For a critical siphon flow, with supercritical flow in the downstream leg, the arch is asymmetric, with greater curvature in the downstream leg of the arch. Adiabatic flow have qualitatively similar effects, except that adiabatic cooling reduces the buoyancy of the flux tube and thus leads to significantly wider arches. In some cases the cooling is strong enough to create negative buoyancy along sections of the flux tube, requiring upward curvature of the flux tube path along these sections and sometimes leading to unusual equilibrium paths of periodic, sinusoidal form.

  9. An experimental study of pulsatile flow through compliant tubes

    NASA Astrophysics Data System (ADS)

    Sturgeon, Victoria; Savas, Omer; Saloner, David

    2006-11-01

    An experimental investigation is made into transitional behaviors and instability of oscillatory input flows through elastic tubes, a problem with applications to hemodynamics and flows in the pulmonary system. Sinusoidal input flow is driven through a compliant silicone model in a series of experiments to investigate the effects of wall motion. A novel mechanism allows active control and feedback over the pressure on the tube exterior. By comparing the pressure within and outside of the tube and modifying the exterior pressure accordingly, the tube is inflated in a controlled manner without altering the input flow. In these experiments, the tube wall is deformed sinusoidally with an amplitude of approximately ten percent of its radius. Experiments are conducted using varying values of the parameters α= a √φν and β= δx √φν where a is the tube radius, φ the angular velocity of the input flow, ν the kinematic viscosity, and δx the cross-stream averaged periodic displacement of a fluid particle undergoing pulsatile motion. For a given α, it is found that indications of conditional turbulence appear in this flow through elastic tubes at far lower values of β - and thus at lower amplitudes of oscillation - than are reported in the literature for flows through rigid tubing.

  10. Boiling inside tubes: Critical heat flux for upward flow in uniformly heated vertical tubes

    NASA Astrophysics Data System (ADS)

    1986-11-01

    ESDU 85041 recommended a procedure for estimating the heat flux at different locations along a heated tube through which a boiling liquid is flowing, assuming that the wall is wetted by the liquid. The purpose of this Data Item (ESDU 86032) is to enable the reader to check, in the case of flow up a uniformly heated vertical tube, that the heat flux does not exceed the critical value above which the liquid would not wet the wall. This point marks the onset of dryout accompanied by an increase in resistance to heat transfer and the possible onset of corrosion and overheating of the tube. The open literature contains many experimental values of the critical heat flux (CHF) in flow up electrically heated vertical tubes, mostly with water or R.12. These results have been used to check various procedures for predicting CHF with flow up vertical tubes. The recommended procedure is given in detail and illustrated in an example.

  11. Numerical models of steady-state and pulsating flows of self-ionizing gas in plasma accelerator channels

    NASA Astrophysics Data System (ADS)

    Brushlinskii, K. V.; Kozlov, A. N.; Konovalov, V. S.

    2015-08-01

    This paper continues the series of numerical investigations of self-ionizing gas flows in plasma accelerator channels with an azimuthal magnetic field. The mathematical model is based on the equations of dynamics of a three-component continuous medium consisting of atoms, ions, and electrons; the model is supplemented with the equation of ionization and recombination kinetics within the diffusion approximation with account for photoionization and photorecombination. It also takes into account heat exchange, which in this case is caused by radiative heat conductance. Upon a short history of the issue, the proposed model, numerical methods, and results for steady-state and pulsating flows are described.

  12. Steady Slug Flow in a Circular Tube

    NASA Astrophysics Data System (ADS)

    Bian, Xiaoqiang; Perlin, Marc; Schultz, William W.

    2002-11-01

    The steady motion of a water slug in a circular tube is studied. When the contact lines completely stick to the tube, the axisymmetric surface modes are solved with a spectral method for originally spherical menisci. The results agree well with a simple 0-degree approximation for lowest slosh mode. The effects of slip in natural frequencies are also discussed. The velocity and menisci geometry are measured for slugs moving in a tilted tube for dry and pre-wetted inner tube surfaces. A custom glass tube has a square outer cross section for minimizing optic distortions and measuring velocity and meniscus geometry. Asymptotic methods and numerics solve the menisci sliding on pre-wetted inner surface. These results are qualitatively compared with our experiments and those in NASA TN-515. As expected, near-meniscus behavior plays a big role in the total resistance to the moving slug.

  13. Development of pulsating twin jets mechanism for mixing flow heat transfer analysis.

    PubMed

    Gitan, Ali Ahmed; Zulkifli, Rozli; Abdullah, Shahrir; Sopian, Kamaruzzaman

    2014-01-01

    Pulsating twin jets mechanism (PTJM) was developed in the present work to study the effect of pulsating twin jets mixing region on the enhancement of heat transfer. Controllable characteristics twin pulsed jets were the main objective of our design. The variable nozzle-nozzle distance was considered to study the effect of two jets interaction at the mixing region. Also, the phase change between the frequencies of twin jets was taken into account to develop PTJM. All of these factors in addition to the ability of producing high velocity pulsed jet led to more appropriate design for a comprehensive study of multijet impingement heat transfer problems. The performance of PTJM was verified by measuring the pulse profile at frequency of 20 Hz, where equal velocity peak of around 64 m/s for both jets was obtained. Moreover, the jet velocity profile at different pulsation frequencies was tested to verify system performance, so the results revealed reasonable velocity profile configuration. Furthermore, the effect of pulsation frequency on surface temperature of flat hot plate in the midpoint between twin jets was studied experimentally. Noticeable enhancement in heat transfer was obtained with the increasing of pulsation frequency.

  14. Development of Pulsating Twin Jets Mechanism for Mixing Flow Heat Transfer Analysis

    PubMed Central

    Abdullah, Shahrir

    2014-01-01

    Pulsating twin jets mechanism (PTJM) was developed in the present work to study the effect of pulsating twin jets mixing region on the enhancement of heat transfer. Controllable characteristics twin pulsed jets were the main objective of our design. The variable nozzle-nozzle distance was considered to study the effect of two jets interaction at the mixing region. Also, the phase change between the frequencies of twin jets was taken into account to develop PTJM. All of these factors in addition to the ability of producing high velocity pulsed jet led to more appropriate design for a comprehensive study of multijet impingement heat transfer problems. The performance of PTJM was verified by measuring the pulse profile at frequency of 20 Hz, where equal velocity peak of around 64 m/s for both jets was obtained. Moreover, the jet velocity profile at different pulsation frequencies was tested to verify system performance, so the results revealed reasonable velocity profile configuration. Furthermore, the effect of pulsation frequency on surface temperature of flat hot plate in the midpoint between twin jets was studied experimentally. Noticeable enhancement in heat transfer was obtained with the increasing of pulsation frequency. PMID:24672370

  15. Eruption constraints on tube-fed planetary lava flows

    NASA Astrophysics Data System (ADS)

    Sakimoto, Susan E. H.; Crisp, Joy; Baloga, Stephen M.

    1997-03-01

    We examine the role of pressure and gravity as driving forces in planetary lava tubes for Newtonian and power law rheologies. The tubes are assumed to have been filled with lava that was emplaced in constant diameter circular tubes in the laminar flow regime and had constant density, heat capacity, thermal conductivity, and viscosity. Our model provides relationships between tube dimensions, driving forces, and effusion rates and rheology parameters. In general, the pressure term in the driving force dominates for very small slopes, but the gravity term eclipses the pressure term as the slope increases. Applying the model to Alba Patera tube flows suggests effusion rates somewhere between 2 and 105m3/s and viscosities between 102 and 106Pas, with tighter constraints (2 to 4 orders of magnitude) for specific tube sizes and travel times. These effusion rate results are lower and the viscosity ranges are higher than those found in previous studies. This allows eruptions that are closer in style to terrestrial basaltic eruptions, although the flows are still considerably larger in scale than the Hawaiian tube flows. We find that very low lava viscosities are not essential for Alba Patera lava tubes and that tube formation may be a better indicator of the steadiness of the eruption and the presence of low slopes than it is of low viscosities (e.g., 102Pas). In addition, this analysis suggests that the tube systems on the steep flanks of Olympus Mons are fundamentally different from those at Alba Patera. The Olympus Mons flows could not have roofed over, been continuously full, or maintained a continuous lava tube transport system in the assumed full, steady, and fully developed conditions.

  16. Vertical, Bubbly, Cross-Flow Characteristics over Tube Bundles

    NASA Astrophysics Data System (ADS)

    Iwaki, C.; Cheong, K. H.; Monji, H.; Matsui, G.

    2005-12-01

    Two-phase flow over tube bundles is commonly observed in shell and tube-type heat exchangers. However, only limited amount of data concerning flow pattern and void fraction exists due to the flow complexity and the difficulties in measurement. The detailed flow structure in tube bundles needs to be understood for reliable and effective design. Therefore, the objective of this study was to clarify the two-phase structure of cross-flow in tube bundles by PIV. Experiments were conducted using two types of models, namely in-line and staggered arrays with a pitch-to-diameter ratio of 1.5. Each test section contains 20 rows of five 15 mm O.D. tubes in each row. The experiment’s data were obtained under very low void fraction (α<0.02). Liquid and gas velocity data in the whole flow field were measured successfully by optical filtering and image processing. The structures of bubbly flow in the two different configurations of tube bundles were described in terms of the velocity vector field, turbulence intensity and void fraction.

  17. Reevaluation of compressible-flow Preston tube calibrations

    NASA Technical Reports Server (NTRS)

    Allen, J. M.

    1977-01-01

    Revised zero-pressure-gradient, adiabatic wall skin-friction-balance data covering a Mach number range from 1.6 to 4.6 led to a reevaluation of existing compressible flow Preston tube calibration equations.

  18. Alleviating pulsations in turbines

    SciTech Connect

    Wedmark, A.B.

    1994-10-01

    Pressure pulsations resulting from vortices in the draft tube are a persistent problem with Francis turbines. Air injection through the turbine shaft often can solve the problem, but this approach may not be possible after the turbine unit has been manufactured. In such cases, new and innovative solutions may be required.

  19. Subcooled choked flow through steam generator tube cracks

    NASA Astrophysics Data System (ADS)

    Wolf, Brian J.

    The work presented here describes an experimental investigation into the choked flow of initially subcooled water through simulated steam generator tube cracks at pressures up to 6.9 MPa. The study of such flow is relevant to the prediction of leak flow rates from a nuclear reactor primary side to secondary side through cracks in steam generator tubes. An experimental approach to measuring such flow is de- scribed. Experimental results from data found in literature as well as the data collected in this work are compared with predictions from presented models as well as predictions from the thermal-hydraulic system code RELAP5. It is found that the homogeneous equilibrium model underpredicts choked flow rates of subcooled water through slits and artificial steam generator tube cracks. Additional modeling of thermal non-equilibrium improves the predictibility of choking mass flux for homogeneous models, however they fail to account for the characteristics of the two-phase pressure drop. An integral modeling approach is enhanced using a correlation developed from the data herein. Also, an assessment of the thermal-hydraulics code RELAP5 is performed and it’s applicability to predict choking flow rates through steam generator tube cracks is addressed. This assessment determined that the Henry & Fauske model, as coded in RELAP5, is best suited for modeling choked flow through steam generator tube cracks. Finally, an approach to applying choked flow data that is not at the same thermo-dynamic conditions as a prototype is developed.

  20. Unexpected water flow through Nafion-tube punctures.

    PubMed

    O'Rourke, Colin; Klyuzhin, Ivan; Park, Ji Sun; Pollack, Gerald H

    2011-05-01

    When a Nafion tube is immersed in water and a small hole is punched in the tube's wall, an unexpected phenomenon occurs: Water flows continuously into the tube through the hole. The phenomenon has proved repeatable, and dynamic aspects were therefore explored, including the effects of altered pH and introduction of a second hole. It appears that the flow is closely tied to the recently discovered "exclusion zone" that forms as an annulus inside the Nafion tube. These zones generate protons in the core of the tube, which exert pressure on the menisci; once a hole is punched, the pressure is relieved by sucking water through the hole. This hypothesis is consistent with the observed experimental evidence and may be relevant to the mechanism of water transport in trees.

  1. Nonlinear dynamics of tube arrays in cross flow

    SciTech Connect

    Chen, S.S.; Cai, Y.; Zhu, S.

    1994-04-01

    Fluidelastic instability of loosely supported tube arrays was studied analytically and experimentally. This is one of the important practical problems of autonomous fluid-structure systems with many interesting motions. Both fluid-damping and fluid-stiffness controlled instabilities were investigated. Depending on the system parameter, the dynamic response of the tubes includes periodic, quasiperiodic, and chaotic motions. The analytical model is based on the unsteady flow theory, which can predict the nonlinear dynamics of tube arrays in cross flow. For fluid-damping controlled instability, analytical results and experimental data agree reasonably well. This study was applied to heat exchangers.

  2. 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.

  3. The effect of fluid flow on coiled tubing reach

    SciTech Connect

    Bhalla, K.; Walton, I.C.

    1996-12-31

    A critical parameter to the success of many coiled tubing (CT) operations in highly deviated or horizontal wells is the depth penetration that can be attained before the CT buckles and locks up. Achieving a desired depth is always critical in CT operations and attaining an additional reach of a few hundred feet can be crucial. This paper addresses the effect of fluid flow in the CT and in the CT/wellbore annulus on the state of force and stress in the CT, and thereby predicts its effect on the reach attainable by the CT. The flow of fluid through the CT and annulus between the CT and borehole modifies the pressures and the effective force which governs the mechanical stability of the CT. The net force per unit length due to fluid flow in the coiled tubing and annulus between the coiled tubing casing/well is calculated in terms of the shear stress and its effect on the onset of buckling and lockup is determined. The model is then implemented in a full tubing forces calculation and the effect of flowing fluids and producing fluids on reach is analyzed. The new model is utilized in the design of commercial jobs. The exact analytic model shows that fluid flow inside the CT has zero impact on reach, that downward flow in the annulus has a favourable impact, and upward flow in the annulus reduces the maximum attainable reach. Using the full tubing forces model, a coiled tubing job can be designed taking into account the flow of a fluid with a specified rheology, density and flow rate. Thus the feasibility of attaining a given reach can be more accurately determined. Results are presented in the form of the surface weight for commercial wells and compared to field jobs.

  4. Superhydrophobic copper tubes with possible flow enhancement and drag reduction.

    PubMed

    Shirtcliffe, Neil J; McHale, Glen; Newton, Michael I; Zhang, Yong

    2009-06-01

    The transport of a Newtonian liquid through a smooth pipe or tube is dominated by the frictional drag on the liquid against the walls. The resistance to flow against a solid can, however, be reduced by introducing a layer of gas at or near the boundary between the solid and liquid. This can occur by the vaporization of liquid at a surface at a temperature above the Leidenfrost point, by a cushion of air (e.g. below a hovercraft), or by producing bubbles at the interface. These methods require a continuous energy input, but a more recent discovery is the possibility of using a superhydrophobic surface. Most reported research uses small sections of lithographically patterned surfaces and rarely considers pressure differences or varying flow rates. In this work we present a method for creating a uniform superhydrophobic nanoribbon layer on the inside of round copper tubes of millimetric internal radius. Two types of experiments are described, with the first involving a simultaneous comparison of four tubes with different surface finishes (as received, as received with hydrophobic coating, nanoribbon, and nanoribbon with a hydrophobic coating) under constant flow rate conditions using water and water-glycerol mixtures. The results show that the superhydrophobic nanoribbon with a hydrophobic coating surface finish allows greater flow at low pressure differences but that the effect disappears as the pressure at the inlet of the tube is increased. The second experiment is a simple visual demonstration of the low-pressure behavior using two nominally identical tubes in terms of length and cross-section, but with one tube possessing a superhydrophobic internal surface finish. In this experiment a reservoir is allowed to feed the two tubes with open ends via a T-piece and it is observed that, once flow commences, it preferentially occurs down the superhydrophobic tube.

  5. How does the tubular embryonic heart work? Looking for the physical mechanism generating unidirectional blood flow in the valveless embryonic heart tube.

    PubMed

    Männer, Jörg; Wessel, Armin; Yelbuz, T Mesud

    2010-04-01

    The heart is the first organ to function in vertebrate embryos. The human heart, for example, starts beating around the 21st embryonic day. During the initial phase of its pumping action, the embryonic heart is seen as a pulsating blood vessel that is built up by (1) an inner endothelial tube lacking valves, (2) a middle layer of extracellular matrix, and (3) an outer myocardial tube. Despite the absence of valves, this tubular heart generates unidirectional blood flow. This fact poses the question how it works. Visual examination of the pulsating embryonic heart tube shows that its pumping action is characterized by traveling mechanical waves sweeping from its venous to its arterial end. These traveling waves were traditionally described as myocardial peristaltic waves. It has, therefore, been speculated that the tubular embryonic heart works as a technical peristaltic pump. Recent hemodynamic data from living embryos, however, have shown that the pumping function of the embryonic heart tube differs in several respects from that of a technical peristaltic pump. Some of these data suggest that embryonic heart tubes work as valveless "Liebau pumps." In the present study, a review is given on the evolution of the two above-mentioned theories of early cardiac pumping mechanics. We discuss pros and cons for both of these theories. We show that the tubular embryonic heart works neither as a technical peristaltic pump nor as a classic Liebau pump. The question regarding how the embryonic heart tube works still awaits an answer.

  6. Driver gas flow with fluctuations. [shock tube turbulent bursts

    NASA Technical Reports Server (NTRS)

    Johnson, J. A., III; Jones, W. R.; Santiago, J.

    1980-01-01

    A shock tube's driver gas can apparently provide flow with turbulent bursts. The fluctuations are interpreted using a boundary layer model of contact surface flow and results form a kinetic theory of turbulence. With this, a lower limit of 4 on the ratio of maximum to minimum turbulent intensities in contact surface instabilities has been estimated.

  7. Numerical simulation of transient hypervelocity flow in an expansion tube

    NASA Technical Reports Server (NTRS)

    Jacobs, P. A.

    1992-01-01

    Several numerical simulations of the transient flow of helium in an expansion tube are presented. The aim of the exercise is to provide further information on the operational problems of the NASA Langley expansion tube. The calculations were performed with an axisymmetric Navier-Stokes code based on a finite-volume formulation and upwinding techniques. Although laminar flow and ideal bursting of the diaphragms was assumed, the simulations showed some of the important features seen in the experiments. In particular, the discontinuity in the tube diameter at the primary diaphragm station introduced a transverse perturbation to the expanding driver gas, and this perturbation was seen to propagate into the test gas under some flow conditions. The disturbances seen in the test flow can be characterized as either 'small-amplitude' noise possibly introduced during shock compression or 'large-amplitude' noise associated with the passage of the reflected head of the unsteady expansion.

  8. Sunspots and the physics of magnetic flux tubes. V - Mutual hydrodynamic forces between neighboring tubes

    NASA Technical Reports Server (NTRS)

    Parker, E. N.

    1979-01-01

    The mutual hydrodynamic forces between parallel cylinders in a moving fluid are illustrated through several formal examples. Parallel tubes in a uniform flow are attracted or repelled depending on whether they are side by side or one ahead of the other, respectively. A pulsating or undulating tube attracts all other neighboring tubes toward itself. These hydrodynamic effects suggest that the separate flux tubes beneath the sunspots exert significant attractive forces on each other.

  9. Vortex tubes in turbulent flows: Identification, representation, reconstruction

    NASA Technical Reports Server (NTRS)

    Banks, David C.; Singer, Bart A.

    1994-01-01

    In many cases the structure of a fluid flow is well-characterized by its vortices, especially for the purpose of visualization. In this paper we present a new algorithm for identifying vortices in complex flows. The algorithm produces a skeleton line along the center of a vortex by using a two-step predictor-corrector scheme. The vorticity vector field serves as the predictor and the pressure gradient (in the perpendicular plane) serves as the corrector. We describe an economical description of the vortex tube's cross-section: a 5-term truncated Fourier series is generally sufficient, and it compresses the representation of the flow by a factor of 4000 or more. We reconstruct the vortex tubes as generalized cylinders, providing a polygonal mesh suitable for display on a graphics workstation. We show how the reconstructed geometry of vortex tubes can be enhanced to help visualize helical motion in a static image.

  10. Numerical simulation of transient hypervelocity flow in an expansion tube

    NASA Technical Reports Server (NTRS)

    Jacobs, P. A.

    1992-01-01

    Several numerical simulations of the transient flow of helium in an expansion tube are presented in an effort to identify some of the basic mechanisms which cause the noisy test flows seen in experiments. The calculations were performed with an axisymmetric Navier-Stokes code based on a finite volume formulation and upwinding techniques. Although laminar flow and ideal bursting of the diaphragms was assumed, the simulations showed some of the important features seen in experiments. In particular, the discontinuity in tube diameter of the primary diaphragm station introduced a transverse perturbation to the expanding driver gas and this perturbation was seen to propagate into the test gas under some flow conditions. The disturbances seen in the test flow can be characterized as either small amplitude, low frequency noise possibly introduced during shock compression or large amplitude, high frequency noise associated with the passage of the reflected head of the unsteady expansion.

  11. Unsteady turbulent shear flow in shock tube discontinuities

    NASA Technical Reports Server (NTRS)

    Johnson, J. A., III; Ramaiah, R.; Lin, I.

    1981-01-01

    A pressure-ruptured shock tube and an arc driven shock tube, have been used to study the evolution of turbulent fluctuations at contact surfaces with N2O4-2NO2 mixtures and at ionizing shock fronts in argon. The study has focused on point density diagnostics derived from crossed light beam correlations and electric probes. Turbulent bursts are found for which dynamical and spectral analyses suggest a particle-like evolution of fluctuation segments with a unique and characteristic frequency, independent of flow history and overall flow conditions.

  12. Draft tube discharge fluctuation during self-sustained pressure surge: fluorescent particle image velocimetry in two-phase flow

    NASA Astrophysics Data System (ADS)

    Müller, A.; Dreyer, M.; Andreini, N.; Avellan, F.

    2013-04-01

    Hydraulic machines play an increasingly important role in providing a secondary energy reserve for the integration of renewable energy sources in the existing power grid. This requires a significant extension of their usual operating range, involving the presence of cavitating flow regimes in the draft tube. At overload conditions, the self-sustained oscillation of a large cavity at the runner outlet, called vortex rope, generates violent periodic pressure pulsations. In an effort to better understand the nature of this unstable behavior and its interaction with the surrounding hydraulic and mechanical system, the flow leaving the runner is investigated by means of particle image velocimetry. The measurements are performed in the draft tube cone of a reduced scale model of a Francis turbine. A cost-effective method for the in-house production of fluorescent seeding material is developed and described, based on off-the-shelf polyamide particles and Rhodamine B dye. Velocity profiles are obtained at three streamwise positions in the draft tube cone, and the corresponding discharge variation in presence of the vortex rope is calculated. The results suggest that 5-10 % of the discharge in the draft tube cone is passing inside the vortex rope.

  13. Computations of Axisymmetric Flows in Hypersonic Shock Tubes

    NASA Technical Reports Server (NTRS)

    Sharma, Surendra P.; Wilson, Gregory J.

    1995-01-01

    A time-accurate two-dimensional fluid code is used to compute test times in shock tubes operated at supersonic speeds. Unlike previous studies, this investigation resolves the finer temporal details of the shock-tube flow by making use of modern supercomputers and state-of-the-art computational fluid dynamic solution techniques. The code, besides solving the time-dependent fluid equations, also accounts for the finite rate chemistry in the hypersonic environment. The flowfield solutions are used to estimate relevant shock-tube parameters for laminar flow, such as test times, and to predict density and velocity profiles. Boundary-layer parameters such as bar-delta(sub u), bar-delta(sup *), and bar-tau(sub w), and test time parameters such as bar-tau and particle time of flight t(sub f), are computed and compared with those evaluated by using Mirels' correlations. This article then discusses in detail the effects of flow nonuniformities on particle time-of-flight behind the normal shock and, consequently, on the interpretation of shock-tube data. This article concludes that for accurate interpretation of shock-tube data, a detailed analysis of flowfield parameters, using a computer code such as used in this study, must be performed.

  14. Laminar Flow Through Circular Tubes with Side Inlets

    NASA Astrophysics Data System (ADS)

    Abedian, Behrouz; Muhlanger, Eric

    2004-11-01

    We discuss experimental results on steady axisymmetric flow of a Newtonian incompressible fluid through circular pipes with side inlets. Circular tubes with a set of holes along their sidewalls are used in a number of medical procedures as straight catheters to transfer fluid into or out of the human body. For example, because of the small size of the incision required, they are commonly used in peritoneal dialysis. The internal diameter and the diameter of the side holes are often 1 mm and less, and as a result, the fluid flow is laminar in a typical medical procedure. An understanding of the flow inside the catheter tube in terms of its geometric parameters will be key in designing new catheters with optimal clinical performance for specific applications. In the experiments, water is withdrawn from a smooth tube with side holes and the local axial pressure and flow rates through the side holes are measured for different flow conditions. A nondimensionalization of the data shows a power-law behavior in only some cases. Using numerical simulations, it is shown how the interaction of the axial flow with the impinging jets from the side holes can change the overall behavior of the flow for a given suction pressure.

  15. Flow-induced oscillation of collapsed tubes and airway structures.

    PubMed

    Bertram, Christopher D

    2008-11-30

    The self-excited oscillation of airway structures and flexible tubes in response to flow is reviewed. The structures range from tiny airways deep in the lung causing wheezing at the end of a forced expiration, to the pursed lips of a brass musical instrument player. Other airway structures that vibrate include the vocal cords (and their avian equivalent, the syrinx) and the soft palate of a snorer. These biological cases are compared with experiments on and theories for the self-excited oscillation of flexible tubes conveying a flow on the laboratory bench, with particular reference to those observations dealing with the situation where the inertia of the tube wall is dominant. In each case an attempt is made to summarise the current state of understanding. Finally, some outstanding challenges are identified.

  16. Flow in tubes of non-circular cross-sections

    NASA Astrophysics Data System (ADS)

    Quadir, Raushan Ara

    Laminar, viscous, incompressible flow in tubes of noncircular cross sections is investigated. The specific aims of the investigation are (1) to look at the problems of both developing flow and fully developed flow, (2) to consider noncircular cross sections in a more systematic manner than has been done in the past, and (3) to develop a relatively simple finite element technique for producing accurate numerical solutions of flow in tubes of fairly arbitrary cross sections. Fully developed flow in tubes is governed by a Poisson type equation for the mainstream velocity. Both analytical and numerical solutions are considered. The cross sections studied include elliptic and rectangular cross sections of different aspect ratios, some triangular cross sections, and a series of crescent-shaped cross sections. The physical characteristics of the flow are examined in a systematic manner in order to determine how these characteristics are affected by certain geometrical features of the cross section. Solutions fall into three basic categories depending on the shape of the cross section. In the first category, which includes circular and elliptic cross sections, solutions are possible in closed form. In the second, including rectangular and some triangular cross sections, solutions are in the form of infinite series. In the third, including cross sections of more complicated or irregular shapes, only numerical solutions are possible. Results of calculations of velocity profiles, flow rate, pumping power, and friction factor are presented in a way which can be useful for engineering applications. In numerical studies of both developing and fully developed flow finite element techniques are used. Results are obtained for tubes of rectangular and elliptic cross sections of different aspect ratios, for tubes of crescent-shaped cross sections, and a tube whose cross section is an oval of Cassini. For fully developed flow, results are compared with the corresponding exact

  17. Pulsating Soft Corals

    NASA Astrophysics Data System (ADS)

    Khatri, Shilpa; Holzman, Roi; Miller, Laura; Samson, Julia; Shavit, Uri

    2016-11-01

    Soft corals of the family Xeniidae have a pulsating motion, a behavior not observed in many other sessile organisms. We are studying how this behavior may give these corals a competitive advantage. We will present experimental data and computational simulations of the pulsations of the coral. Video data and kinematic analysis will be shown from the lab and the field. We will present direct numerical simulations of the pulsations of the coral and the resulting fluid flow by solving the Navier-Stokes equations coupled with the immersed boundary method. Furthermore, parameter sweeps studying the resulting fluid flow will be discussed. This work is supported by NSF PoLS #1505061 (to S. Khatri) and #1504777 (to L. Miller).

  18. Mechanistic modeling of fingering, nonmonotonicity, fragmentation, and pulsation within gravity/buoyant destabilized two-phase/unsaturated flow

    NASA Astrophysics Data System (ADS)

    Glass, Robert J.; Yarrington, Lane

    2003-03-01

    Fingering, nonmonotonicity, fragmentation, and pulsation within gravity/buoyant destabilized two-phase/unsaturated flow systems has been widely observed with examples in homogeneous to heterogeneous porous media, in single fractures to fracture networks, and for both wetting and nonwetting invasion. To model this phenomena, we consider a mechanistic approach based on forms of modified invasion percolation (MIP) that include gravity, the influence of the local interfacial curvature along the phase-phase interface, and the simultaneous invasion and reinvasion of both wetting and nonwetting fluids. We present example simulations and compare them to experimental data for three very different situations: (1) downward gravity-driven fingering of water into a dry, homogeneous, water-wettable, porous medium; (2) upward buoyancy-driven migration of gas within a water saturated, heterogeneous, water-wettable, porous medium; and (3) downward gravity-driven fingering of water into a dry, water-wettable, rough-walled fracture.

  19. Flow chemistry: intelligent processing of gas-liquid transformations using a tube-in-tube reactor.

    PubMed

    Brzozowski, Martin; O'Brien, Matthew; Ley, Steven V; Polyzos, Anastasios

    2015-02-17

    reactive gas in a given reaction mixture. We have developed a tube-in-tube reactor device consisting of a pair of concentric capillaries in which pressurized gas permeates through an inner Teflon AF-2400 tube and reacts with dissolved substrate within a liquid phase that flows within a second gas impermeable tube. This Account examines our efforts toward the development of a simple, unified methodology for the processing of gaseous reagents in flow by way of development of a tube-in-tube reactor device and applications to key C-C, C-N, and C-O bond forming and hydrogenation reactions. We further describe the application to multistep reactions using solid-supported reagents and extend the technology to processes utilizing multiple gas reagents. A key feature of our work is the development of computer-aided imaging techniques to allow automated in-line monitoring of gas concentration and stoichiometry in real time. We anticipate that this Account will illustrate the convenience and benefits of membrane tube-in-tube reactor technology to improve and concomitantly broaden the scope of gas/liquid/solid reactions in organic synthesis.

  20. Modeling expiratory flow from excised tracheal tube laws.

    PubMed

    Aljuri, N; Freitag, L; Venegas, J G

    1999-11-01

    Flow limitation during forced exhalation and gas trapping during high-frequency ventilation are affected by upstream viscous losses and by the relationship between transmural pressure (Ptm) and cross-sectional area (A(tr)) of the airways, i.e., tube law (TL). Our objective was to test the validity of a simple lumped-parameter model of expiratory flow limitation, including the measured TL, static pressure recovery, and upstream viscous losses. To accomplish this objective, we assessed the TLs of various excised animal tracheae in controlled conditions of quasi-static (no flow) and steady forced expiratory flow. A(tr) was measured from digitized images of inner tracheal walls delineated by transillumination at an axial location defining the minimal area during forced expiratory flow. Tracheal TLs followed closely the exponential form proposed by Shapiro (A. H. Shapiro. J. Biomech. Eng. 99: 126-147, 1977) for elastic tubes: Ptm = K(p) [(A(tr)/A(tr0))(-n) - 1], where A(tr0) is A(tr) at Ptm = 0 and K(p) is a parametric factor related to the stiffness of the tube wall. Using these TLs, we found that the simple model of expiratory flow limitation described well the experimental data. Independent of upstream resistance, all tracheae with an exponent n < 2 experienced flow limitation, whereas a trachea with n > 2 did not. Upstream viscous losses, as expected, reduced maximal expiratory flow. The TL measured under steady-flow conditions was stiffer than that measured under expiratory no-flow conditions, only if a significant static pressure recovery from the choke point to atmosphere was assumed in the measurement.

  1. Flow equation for porous plug and capillary tube flow restrictors

    NASA Technical Reports Server (NTRS)

    Davis, W. S.

    1972-01-01

    Development of flow measuring apparatus for determining low flow performance of resistojet thruster is discussed. Diagram of test equipment is presented. Operation of test equipment is described and numerical relationships are explained.

  2. Oscillatory Flow in Curved and Straight Tubes: Transport and Transition.

    NASA Astrophysics Data System (ADS)

    Eckmann, David Matthew

    Transport of soluble material is analyzed for volume-cycled oscillatory flow in a curved tube. The Navier -Stokes equations of motion are solved using a regular perturbation method for small ratio of tube radius to radius of curvature and order unity amplitude over a range of the Womersley parameter. A stream function definition of the lateral velocities is defined to satisfy the conservation of mass equation exactly. A pressure-gradient amplitude is specified to satisfy the fluid volume-cycling constraint imposed. Axial velocity profiles and cross-sectional steady streaming velocity profiles are compared to previous theories and experiments. The convection-diffusion transport equation is similarly solved by a regular perturbation scheme where uniform steady end concentrations and no wall flux are assumed. The time-average axial transport, consisting of the diffusive and convective flux of solute is calculated. There is substantial modification of transport compared to the straight tube case and the results are interpreted with respect to pulmonary gas exchange. A Laser Doppler Anemometer is used to analyze volume-cycled oscillatory flow of a Newtonian viscous fluid in a straight circular tube. The working fluid is chosen to match index of refraction with the Plexiglas test section. The axial velocity is measured at radial positions across the diameter of the tube for a wide range of amplitude A = stroke distance/tube radius (2.4 <=q A <=q 21.6) and Womersley parameter (9 < alpha < 33). Transition to turbulence is detected during the decelerating phase of fluid motion for 500 < R_delta < 875, where R_delta = alphaAsurd2 is the Reynolds number based on Stokes layer thickness. This instability is confined to the viscous boundary layer and does not appear in the inviscid core as reported by previous investigators, unless a source of vorticity such as a hot -wire anemometer probe is resident in the flow.

  3. Simulation of cardiac motion on non-Newtonian, pulsating flow development in the human left anterior descending coronary artery

    NASA Astrophysics Data System (ADS)

    Theodorakakos, A.; Gavaises, M.; Andriotis, A.; Zifan, A.; Liatsis, P.; Pantos, I.; Efstathopoulos, E. P.; Katritsis, D.

    2008-09-01

    This study aimed at investigating the effect of myocardial motion on pulsating blood flow distribution of the left anterior descending coronary artery in the presence of atheromatous stenosis. The moving 3D arterial tree geometry has been obtained from conventional x-ray angiograms obtained during the heart cycle and includes a number of major branches. The geometry reconstruction model has been validated against projection data from a virtual phantom arterial tree as well as with CT-based reconstruction data for the same patient investigated. Reconstructions have been obtained for a number of temporal points while linear interpolation has been used for all intermediate instances. Blood has been considered as a non-Newtonian fluid. Results have been obtained using the same pulse for the inlet blood flow rate but with fixed arterial tree geometry as well as under steady-state conditions corresponding to the mean flow rate. Predictions indicate that myocardial motion has only a minor effect on flow distribution within the arterial tree relative to the effect of the blood pressure pulse.

  4. Development and characterization of a laminar aerosol flow tube

    NASA Astrophysics Data System (ADS)

    Khalizov, Alexei F.; Earle, Michael E.; Johnson, Wayde J. W.; Stubley, Gordon D.; Sloan, James J.

    2006-03-01

    We have developed a new laminar aerosol flow tube (AFT) to study transformations such as ice nucleation, deliquescence, and efflorescence in model atmospheric aerosols. The apparatus consists of four sections which can be independently cooled to reproduce temperature profiles relevant to the troposphere and stratosphere. An automatic control system maintains the average axial temperature along each section between 100 and 300K, within ±0.1K. Changes in aerosol composition, phase, and size distribution are monitored at the tube exit using infrared spectroscopy (AFT-IR). We used computational fluid dynamics simulations to investigate flow velocity and temperature distributions within the flow tube. Based on these computations, the final design was formulated to eliminate turbulent mixing zones and buoyancy-driven convection cells. The latter can occur even under conditions where the Reynolds number indicates laminar flow. In either case, recirculation causes aerosol residence times and temperature histories to be poorly defined, leading to erroneous interpretation of experimental measurements. The resulting AFT design used copper fins to reduce temperature gradients and axial mixing of aerosol and carrier gas flows in the inlet section to reduce turbulence. The performance of the new AFT is significantly better than for previous designs.

  5. Ordered and chaotic flow of red blood cells flowing in a narrow tube

    NASA Astrophysics Data System (ADS)

    Beams, Natalie N.; Freund, Jonathan B.

    2013-11-01

    Red blood cells are well known to line up in an orderly arrangement when forced to flow through a narrow capillary-scale round tube (diameter <= 8 μ m). However, in slightly larger tubes, small perturbations from the center of the tube can cause this order to break down, resulting in apparently chaotic flow. Investigating this breakdown using a high-fidelity boundary integral solver for flowing blood cells, we show the existence of a bifurcation point for the appearance of this non-orderly behavior. The bifurcation point is found to be dependent on the diameter of the tube and the density of the cells, with more cells required to instigate chaotic behavior in smaller tubes (e.g., 27.5% cells by volume for a 11.28 μ m diameter tube, but only 5.63% for similar behavior in a tube twice that width). Increasing the cell interior viscosity is also observed to increase the amplification of perturbations. Additionally, as a counterpoint, we show that cells flowing chaotically in D = 12 μ m tubes, apparently indefinitely, will slowly organize into a regular single file if D is decreased to D = 10 μ m. Supported by NSF.

  6. Influence of Test Tube Material on Subcooled Flow Boiling Critical Heat Flux in Short Vertical Tube

    SciTech Connect

    Koichi Hata; Masahiro Shiotsu; Nobuaki Noda

    2006-07-01

    The steady state subcooled flow boiling critical heat flux (CHF) for the flow velocities (u = 4.0 to 13.3 m/s), the inlet subcooling ({delta}T{sub sub,in} = 48.6 to 154.7 K), the inlet pressure (P{sub in} = 735.2 to 969.0 kPa) and the increasing heat input (Q{sub 0} exp(t/t), t = 10, 20 and 33.3 s) are systematically measured with the experimental water loop. The 304 Stainless Steel (SUS304) test tubes of inner diameters (d = 6 mm), heated lengths (L = 66 mm) and L/d = 11 with the inner surface of rough finished (Surface roughness, R{sub a} = 3.18 {mu}m), the Cupro Nickel (Cu-Ni 30%) test tubes of d = 6 mm, L = 60 mm and L/d = 10 with R{sub a} = 0.18 {mu}m and the Platinum (Pt) test tubes of d = 3 and 6 mm, L = 66.5 and 69.6 mm, and L/d 22.2 and 11.6 respectively with R{sub a} = 0.45 {mu}m are used in this work. The CHF data for the SUS304, Cu-Ni 30% and Pt test tubes were compared with SUS304 ones for the wide ranges of d and L/d previously obtained and the values calculated by the authors' published steady state CHF correlations against outlet and inlet subcooling. The influence of the test tube material on CHF is investigated into details and the dominant mechanism of subcooled flow boiling critical heat flux is discussed. (authors)

  7. Study of spectral characteristics of radiation from a thermal wake of a pulsating optical discharge in a supersonic air flow

    SciTech Connect

    Malov, A N; Orishich, A M; Terent'eva, Ya S

    2015-10-31

    The spectral characteristics of the thermal wake of a pulsating optical discharge (POD) in a supersonic air flow are studied. The POD is stimulated by radiation of a mechanically Q-switched, repetitively pulsed CO{sub 2} laser with a pulse repetition rate of 7 – 150 kHz and a power up to 4.5 kW. The flow is produced by means of the supersonic aerodynamic MAU-M setup having a conic nozzle with a critical cross-section size of 50 mm, the Mach number being 1.3 – 1.6. We describe in detail the system of optical diagnostics that allows the detection of the spectrum of the weak thermal wake glow against the background of high-power POD radiation. The glow of the thermal wake is due to the emission of light by atoms and ions of nitrogen and oxygen, carried by the flow in the form of hot low-density gas clouds (caverns). The wavelengths of the thermal wake emission and the data on the transitions, corresponding to the spectral lines are presented. (laser applications and other topics in quantum electronics)

  8. Flow and heat transfer enhancement in tube heat exchangers

    NASA Astrophysics Data System (ADS)

    Sayed Ahmed, Sayed Ahmed E.; Mesalhy, Osama M.; Abdelatief, Mohamed A.

    2015-11-01

    The performance of heat exchangers can be improved to perform a certain heat-transfer duty by heat transfer enhancement techniques. Enhancement techniques can be divided into two categories: passive and active. Active methods require external power, such as electric or acoustic field, mechanical devices, or surface vibration, whereas passive methods do not require external power but make use of a special surface geometry or fluid additive which cause heat transfer enhancement. The majority of commercially interesting enhancement techniques are passive ones. This paper presents a review of published works on the characteristics of heat transfer and flow in finned tube heat exchangers of the existing patterns. The review considers plain, louvered, slit, wavy, annular, longitudinal, and serrated fins. This review can be indicated by the status of the research in this area which is important. The comparison of finned tubes heat exchangers shows that those with slit, plain, and wavy finned tubes have the highest values of area goodness factor while the heat exchanger with annular fin shows the lowest. A better heat transfer coefficient ha is found for a heat exchanger with louvered finned and thus should be regarded as the most efficient one, at fixed pumping power per heat transfer area. This study points out that although numerous studies have been conducted on the characteristics of flow and heat transfer in round, elliptical, and flat tubes, studies on some types of streamlined-tubes shapes are limited, especially on wing-shaped tubes (Sayed Ahmed et al. in Heat Mass Transf 50: 1091-1102, 2014; in Heat Mass Transf 51: 1001-1016, 2015). It is recommended that further detailed studies via numerical simulations and/or experimental investigations should be carried out, in the future, to put further insight to these fin designs.

  9. Nonperiodic eddy pulsations

    USGS Publications Warehouse

    Rubin, David M.; McDonald, Richard R.

    1995-01-01

    Recirculating flow in lateral separation eddies is typically weaker than main stem flow and provides an effective environment for trapping sediment. Observations of recirculating flow and sedimentary structures demonstrate that eddies pulsate in size and in flow velocity even when main stem flow is steady. Time series measurements of flow velocity and location of the reattachment point indicate that these pulsations are nonperiodic. Nonperiodic flow in the lee of a channel margin constriction is grossly different from the periodic flow in the lee of a cylinder that is isolated in a flow. Our experiments demonstrate that placing a flow-parallel plate adjacent to a cylinder is sufficient to cause the leeside flow to change from a periodic sequence of vortices to a nonperiodically pulsating lateral separation eddy, even if flow conditions are otherwise unchanged. Two processes cause the leeside flow to become nonperiodic when the plate is added. First, vortices that are shed from the cylinder deform and become irregular as they impact the plate or interfere with remnants of other vortices near the reattachment point. Second, these deformed vortices and other flow structures are recirculated in the lateral separation eddy, thereby influencing the future state (pressure and momentum distribution) of the recirculating flow. The vortex deformation process was confirmed experimentally by documenting spatial differences in leeside flow; vortex shedding that is evident near the separation point is undetectable near the reattachment point. Nonlinear forecasting techniques were used in an attempt to distinguish among several possible kinds of nonperiodic flows. The computational techniques were unable to demonstrate that any of the nonperiodic flows result from low-dimensional nonlinear processes.

  10. Numerical simulations of the flow in the HYPULSE expansion tube

    NASA Technical Reports Server (NTRS)

    Wilson, Gregory J.; Sussman, Myles A.; Bakos, Robert J.

    1995-01-01

    Axisymmetric numerical simulations with finite-rate chemistry are presented for two operating conditions in the HYPULSE expansion tube. The operating gas for these two cases is nitrogen and the computations are compared to experimental data. One test condition is at a total enthalpy of 15.2 MJ/Kg and a relatively low static pressure of 2 kPa. This case is characterized by a laminar boundary layer and significant chemical nonequilibrium in the acceleration gas. The second test condition is at a total enthalpy of 10.2 MJ/Kg and a static pressure of 38 kPa and is characterized by a turbulent boundary layer. For both cases, the time-varying test gas pressure predicted by the simulations is in good agreement with experimental data. The computations are also found to be in good agreement with Mirels' correlations for shock tube flow. It is shown that the nonuniformity of the test gas observed in the HYPULSE expansion tube is strongly linked to the boundary layer thickness. The turbulent flow investigated has a larger boundary layer and greater test gas nonuniformity. In order to investigate possibilities of improving expansion tube flow quality by reducing the boundary layer thickness, parametric studies showing the effect of density and turbulent transition point on the test conditions are also presented. Although an increase in the expansion tube operating pressure level would reduce the boundary layer thickness, the simulations indicate that the reduction would be less than what is predicted by flat plate boundary layer correlations.

  11. Holographic flow visualization at the Langley Expansion Tube

    NASA Technical Reports Server (NTRS)

    Goad, W. K.; Burner, A. W.

    1981-01-01

    A holographic system used for flow visualization at the Langley Expansion Tube is described. A ruby laser which can be singly or doubly pulsed during the short run time of less than 300 microns is used as the light source. With holography, sensitivity adjustments can be optimized after a run instead of before a run as with conventional flow visualization techniques. This results in an increased reliability of the flow visualization available for the study of real-gas effects on flow about models. Holographic techniques such as single-plate schlieren and shadowgraph, two plate interferometry, double pulse interferometry for perfect infinite-fringe interferograms, and double-pulse interferometry used to examine changes in the flow over a short time period are described and examples presented.

  12. Heat transfer research on supercritical water flow upward in tube

    SciTech Connect

    Li, H. B.; Yang, J.; Gu, H. Y.; Zhao, M.; Lu, D. H.; Zhang, J. M.; Wang, F.; Zhang, Y.

    2012-07-01

    The experimental research of heat transfer on supercritical water has been carried out on the supercritical water multipurpose test loop with a 7.6 mm upright tube. The experimental data of heat transfer is obtained. The experimental results of thermal-hydraulic parameters on flow and heat transfer of supercritical water show that: Heat transfer enhancement occurs when the fluid temperature reaches pseudo-critical point with low mass flow velocity, and peters out when the mass flow velocity increases. The heat transfer coefficient and Nusselt number decrease with the heat flux or system pressure increases, and increase with the increasing of mass flow velocity. The wall temperature increases when the mass flow velocity decreases or the system pressure increases. (authors)

  13. Holographic flow visualization at the Langley Expansion Tube

    NASA Astrophysics Data System (ADS)

    Goad, W. K.; Burner, A. W.

    1981-06-01

    A holographic system used for flow visualization at the Langley Expansion Tube is described. A ruby laser which can be singly or doubly pulsed during the short run time of less than 300 microns is used as the light source. With holography, sensitivity adjustments can be optimized after a run instead of before a run as with conventional flow visualization techniques. This results in an increased reliability of the flow visualization available for the study of real-gas effects on flow about models. Holographic techniques such as single-plate schlieren and shadowgraph, two plate interferometry, double pulse interferometry for perfect infinite-fringe interferograms, and double-pulse interferometry used to examine changes in the flow over a short time period are described and examples presented.

  14. Gravity Flow in Proposed Enteral Tube Small-Bore Connectors.

    PubMed

    Hurt, Ryan T; Epp, Lisa M; Pattinson, Adele K; Duellman, Wanda M; Corner, Stephen M; Mundi, Manpreet S

    2017-04-01

    Enteral nutrition (EN) misconnections have been identified as a serious and potential deadly problem. An international effort led by EN industry leaders has developed a small-bore enteral connector (ENFit) that in theory will reduce the frequency of misconnections. Despite the potential benefit of preventing misconnections, the full impact of adoption of the ENFit connector is unknown. To assess the impact of transitioning to ENFit on our home EN (HEN) patients, the current study evaluated gravity feeding comparing 2 proposed small-bore connectors to the legacy (current connector) using various commercial formulas. Six commonly used enteral formulas in our facility with varying density and viscosity were tested in triplicate. Forty milliliters of formula was poured into a syringe connected to an ENFit or legacy (current) feeding connector attached to varying French size tubes. The time it took formula to flow through the connectors was recorded, and the test was repeated in triplicate. All formulas took significantly longer to flow through the first ENFit connector compared with the legacy connector ( P < .05). The second ENFit connector demonstrated similar flow dynamics to the legacy connector. There is wide variability in the flow dynamics in ENFit connectors with significant potential impact on many facets of HEN, including medicine delivery, blenderized feeds, venting, and compliance with EN due to increased time to administer feeds. We highly recommend additional testing of flow dynamics, including gravity flow, as ENFit tubes are being developed and adopted.

  15. Draft tube flow phenomena across the bulb turbine hill chart

    NASA Astrophysics Data System (ADS)

    Duquesne, P.; Fraser, R.; Maciel, Y.; Aeschlimann, V.; Deschênes, C.

    2014-03-01

    In the framework of the BulbT project launched by the Consortium on Hydraulic Machines and the LAMH (Hydraulic Machine Laboratory of Laval University) in 2011, an intensive campaign to identify flow phenomena in the draft tube of a model bulb turbine has been done. A special focus was put on the draft tube component since it has a particular importance for recuperation in low head turbines. Particular operating points were chosen to analyse flow phenomena in this component. For each of these operating points, power, efficiency and pressure were measured following the IEC 60193 standard. Visualizations, unsteady wall pressure and efficiency measurements were performed in this component. The unsteady wall pressure was monitored at seven locations in the draft tube. The frequency content of each pressure signal was analyzed in order to characterize the flow phenomena across the efficiency hill chart. Visualizations were recorded with a high speed camera using tufts and cavitation bubbles as markers. The predominant detected phenomena were mapped and categorized in relation to the efficiency hill charts obtained for three runner blade openings. At partial load, the vortex rope was detected and characterized. An inflection in the partial load efficiency curves was found to be related to complex vortex rope instabilities. For overload conditions, the efficiency curves present a sharp drop after the best efficiency point, corresponding to an inflection on the power curves. This break off is more severe towards the highest blade openings. It is correlated to a flow separation at the wall of the draft tube. Also, due to the separation occurring in these conditions, a hysteresis effect was observed on the efficiency curves.

  16. Background noise measurements from jet exit vanes designed to reduced flow pulsations in an open-jet wind tunnel

    NASA Technical Reports Server (NTRS)

    Hoad, D. R.; Martin, R. M.

    1985-01-01

    Many open jet wind tunnels experience pulsations of the flow which are typically characterized by periodic low frequency velocity and pressure variations. One method of reducing these fluctuations is to install vanes around the perimeter of the jet exit to protrude into the flow. Although these vanes were shown to be effective in reducing the fluctuation content, they can also increase the test section background noise level. The results of an experimental acoustic program in the Langley 4- by 7-Meter Tunnel is presented which evaluates the effect on tunnel background noise of such modifications to the jet exit nozzle. Noise levels for the baseline tunnel configuration are compared with those for three jet exit nozzle modifications, including an enhanced noise reduction configuration that minimizes the effect of the vanes on the background noise. Although the noise levels for this modified vane configuration were comparable to baseline tunnel background noise levels in this facility, installation of these modified vanes in an acoustic tunnel may be of concern because the noise levels for the vanes could be well above background noise levels in a quiet facility.

  17. Viscoelastic changes in the blood and vascular wall in a pulsating circular flow

    NASA Astrophysics Data System (ADS)

    Beraia, Merab; Todua, Fridon; Khomeriki, Irina

    2010-01-01

    Altered flow conditions, such as separation and recirculationg zones, low and oscillatory shear stress, play an important role in the development of arterial disease. Endothelial denudation by the blood flow is the first step in atherosclerosis. The description of blood flow in vivo is complicated due to the viscoelasticity of vessel walls. However, conventional researches of the effect of the blood vessel viscoelasticity on the blood pressure wave propagation using non-linear one-dimensional models do not take into account the viscoelasticity, despite it being importance in the analysis of pulse wave propagation in arteries. The purpose of this paper is to study the impact of the arterial pulse wave on the viscoelastic blood flow and initial factors of atherosclerosis. In 12 healthy men (25-39 years of age) peak velocity, mean velocity, mean flow and net flow in the aorta have been investigated by MR angiography. Initial velocity was registered after 43msec of the ECG-R wave, and it differed from zero at all sites of the aorta, although net flow was equal to zero. Womersley's number from the ascending to the thoracic aorta decreased from 12.5 ± 1.5 to 7.3 ± 1.2; flow modified from inertio-elastic to viscous. Pulse pressure wave move on artery walls fifteen or more times more rapidly than the blood flow. In the aortic arch in protodiastole blood flow separated into the opposite directed streams resulting in wave superposition with the high net flow. At the isthmus area separated waves interferences and reflects to anterograde direction. Pulse oscillation increases strain rate to the contiguous vessel wall flow layers. At the sites with the flow wave negative interference vessel pulse oscillation attenuates and at the boundary reflection flow wave can shift the vessel wall.

  18. Wind tunnel experiments on chaotic dynamics of a flexible tube row in a cross flow

    SciTech Connect

    Muntean, G.; Moon, F.C.

    1994-12-31

    Flow visualization and dynamics measurements of flexible cylindrical tubes in a cross-flow are described. Five tubes mounted on flexible supports were subjected to cross flow in a low turbulence wind tunnel. Dynamic measurements of the tube motion are presented. The data suggests that a low dimensional attractor exists for tube flutter under impact constraints using fractal dimension calculations. There is also qualitative evidence for single tube flutter in-line with the flow. In another set of experiments, a flow visualization technique is used to examine the flow behind the vibrating cylinders. Four different configurations of the jet flow behind the cylinders are observed. Coupling of the jet dynamics and tube motion seems apparent from the video data. These experiments are being used to try and construct a low order nonlinear model for the tube-flow dynamics.

  19. Stability analysis of wall driven nanofluid flow through a tube

    NASA Astrophysics Data System (ADS)

    Hossain, M. Mainul; Khan, M. A. H.

    2017-06-01

    Wall driven incompressible viscous fluid flow with nanoparticles through a tube is considered where two different nanofluids (Cu-water, SiO2-water) are used separately. Flow becomes gradually unstable due to movement of wall and existence of nanoparticles. However, Reynolds number, volume fraction and density ratio are responsible for flow instability. The mathematical model of the problem is constructed and solved by means of series solution method. Special type Hermite-Padé approximation method is used to improve the series solution. The critical point for Reynolds number, volume fraction and density ratio are determined and described using approximation technique and bifurcation diagram for both nanofluids. Moreover, Interaction between these three numbers and their effect on velocity profile are discussed. To indicate the nanofluid which is more effective for flow stability is our major concerned.

  20. Ordered and random structures in pulsatile flow through constricted tubes

    NASA Astrophysics Data System (ADS)

    Lieber, B. B.

    The poststenotic flow field in a rigid tube was investigated under pulsatile conditions. The waveform employed in the present experiment was sinusoidal and three contoured constrictions with 50, 75, and 90% area reduction were investigated. The fluid dynamic similarity parameters were chosen to represent conditions found in large arteries of humans and of experimental animals, using a Reynolds number range of 200 to 1000 and a frequency parameter value of 5.3. The analysis techniques of autoregressive modeling, correlation methods, and phase-shift averaging were employed in order to extract the maximum information about flow behavior. Analysis focuses on identification and representation of coherent flow disturbances, and examination of the influence of core flow behavior on the cyclic wall shear stress.

  1. Sieve tube geometry in relation to phloem flow.

    PubMed

    Mullendore, Daniel L; Windt, Carel W; Van As, Henk; Knoblauch, Michael

    2010-03-01

    Sieve elements are one of the least understood cell types in plants. Translocation velocities and volume flow to supply sinks with photoassimilates greatly depend on the geometry of the microfluidic sieve tube system and especially on the anatomy of sieve plates and sieve plate pores. Several models for phloem translocation have been developed, but appropriate data on the geometry of pores, plates, sieve elements, and flow parameters are lacking. We developed a method to clear cells from cytoplasmic constituents to image cell walls by scanning electron microscopy. This method allows high-resolution measurements of sieve element and sieve plate geometries. Sieve tube-specific conductivity and its reduction by callose deposition after injury was calculated for green bean (Phaseolus vulgaris), bamboo (Phyllostachys nuda), squash (Cucurbita maxima), castor bean (Ricinus communis), and tomato (Solanum lycopersicum). Phloem sap velocity measurements by magnetic resonance imaging velocimetry indicate that higher conductivity is not accompanied by a higher velocity. Studies on the temporal development of callose show that small sieve plate pores might be occluded by callose within minutes, but plants containing sieve tubes with large pores need additional mechanisms.

  2. Particle seeding flow system for horizontal shock tube

    SciTech Connect

    Johnston, Stephen; Garcia, Nicolas J.; Martinez, Adam A.; Orlicz, Gregory C.; Prestridge, Katherine P.

    2012-08-01

    The Extreme Fluids Team in P-23, Physics Division, studies fluid dynamics at high speeds using high resolution diagnostics. The unsteady forces on a particle driven by a shock wave are not well understood, and they are difficult to model. A horizontal shock tube (HST) is being modified to collect data about the behavior of particles accelerated by shocks. The HST has been used previously for studies of Richtmyer-Meshkov instability using Planar Laser-Induced Fluorescence (PLIF) as well as Particle Image Velocimetry (PIV), diagnostics that measure density and velocity. The purpose of our project is to design a flow system that will introduce particles into the HST. The requirements for this particle flow system (PFS) are that it be non-intrusive, be able to introduce either solid or liquid particles, have an exhaust capability, not interfere with existing diagnostics, and couple with the existing HST components. In addition, the particles must flow through the tube in a uniform way. We met these design criteria by first drawing the existing shock tube and diagnostics and doing an initial design of the ducts for the PFS. We then estimated the losses through the particle flow system from friction and researched possible fans that could be used to drive the particles. Finally, the most challenging component of the design was the coupling to the HST. If we used large inlets, the shock would lose strength as it passed by the inlet, so we designed a novel coupling inlet and outlet that minimize the losses to the shock wave. Our design was reviewed by the Extreme Fluids Team, and it is now being manufactured and built based upon our technical drawings.

  3. Compressible flow in a long tube closed at one end

    NASA Astrophysics Data System (ADS)

    Bennett, M. D.; Wyatt, F. V.

    1985-12-01

    Attention is given to pressure variations in a line that terminates at a sensing instrument of negligible volume, constituting a long tube that is closed at one end. An elementary derivation of the response equation that evolves from the laminar flow of a gas moving at subsonic speed is obtained, together with a closed form solution for the limiting case of slowly varying pressure gradients. After the transient phase, the difference in pressures acting at the ends of the duct is proportional to the coefficient of fluid viscosity, the square of the tube length/diameter ratio, and the time rate of change of the applied pressure; it is also inversely proportional to the magnitude of the pressure.

  4. Suppression of flow pulsation activity by relaxation process of additive effect on viscous media transport

    NASA Astrophysics Data System (ADS)

    Kharlamov, S.; Dedeyev, P.; Meucci, L.; Shenderova, I.; Manastirniy, A.; Usenko, M.

    2015-11-01

    The article presents the analysis of the processes occurring together with the turbulent transfer of impulse in mixture of hydrocarbon fluid and polymer solutions (anti-turbulent additives). The study evaluates complex shear flows by popular theoretical and practical methods. Understanding of hydrodynamic and dissipative effects of laminar-turbulent transition tightening and turbulence suppression is provided. The peculiarities of "thin" flow structure in pipeline zones with complex shape walls are evaluated. Recommendations to forecast the local flow parameters, calculation of hydraulic resistance are given.

  5. Flow synthesis using gaseous ammonia in a Teflon AF-2400 tube-in-tube reactor: Paal-Knorr pyrrole formation and gas concentration measurement by inline flow titration.

    PubMed

    Cranwell, Philippa B; O'Brien, Matthew; Browne, Duncan L; Koos, Peter; Polyzos, Anastasios; Peña-López, Miguel; Ley, Steven V

    2012-08-14

    Using a simple and accessible Teflon AF-2400 based tube-in-tube reactor, a series of pyrroles were synthesised in flow using the Paal-Knorr reaction of 1,4-diketones with gaseous ammonia. An inline flow titration technique allowed measurement of the ammonia concentration and its relationship to residence time and temperature.

  6. Stabilization of the turbulent flows in anisotropic viscoelastic tubes

    NASA Astrophysics Data System (ADS)

    Kizilova, N.; Hamadiche, M.

    Flow around the aircrafts and marine vehicles is turbulized that increases the skin-friction drag and fuel consumption. Here stability of the fully developed turbulent flow of an incompressible fluid in the viscoelastic tube is considered. The eddy viscosity concept is considered to be adequate and the flow velocity, wall displacement and pressures in the fluid and solid wall are timeaveraged quantities. Continuity conditions for the components of the velocity and stress tensor at the fluid-wall interface and no displacement condition at the outer wall of the tube are considered. Solution of the coupled system has been found in the form of the normal mode and the obtained system has been studied using the numerical technique described in [1,2]. The temporal and spatial eigenvalues and the dependencies of the temporal and spatial amplification rates on the rheological parameters of the wall have been computed. It was shown stability of the modes can be increased by a proper choice of the wall parameters. Successful combinations of the wall thickness, elasticity and viscosity have been found for a large variety of materials. It was shown a substantial reduction in the viscous wall shear stress accompanied by a decrease in the turbulence production or Reynolds stress can be reached via using the viscoelastic coating on the rigid surface. The obtained results are in a good agreement with recent direct numerical computations [3].

  7. Sieve Tube Geometry in Relation to Phloem Flow

    PubMed Central

    Mullendore, Daniel L.; Windt, Carel W.; Van As, Henk; Knoblauch, Michael

    2010-01-01

    Sieve elements are one of the least understood cell types in plants. Translocation velocities and volume flow to supply sinks with photoassimilates greatly depend on the geometry of the microfluidic sieve tube system and especially on the anatomy of sieve plates and sieve plate pores. Several models for phloem translocation have been developed, but appropriate data on the geometry of pores, plates, sieve elements, and flow parameters are lacking. We developed a method to clear cells from cytoplasmic constituents to image cell walls by scanning electron microscopy. This method allows high-resolution measurements of sieve element and sieve plate geometries. Sieve tube–specific conductivity and its reduction by callose deposition after injury was calculated for green bean (Phaseolus vulgaris), bamboo (Phyllostachys nuda), squash (Cucurbita maxima), castor bean (Ricinus communis), and tomato (Solanum lycopersicum). Phloem sap velocity measurements by magnetic resonance imaging velocimetry indicate that higher conductivity is not accompanied by a higher velocity. Studies on the temporal development of callose show that small sieve plate pores might be occluded by callose within minutes, but plants containing sieve tubes with large pores need additional mechanisms. PMID:20354199

  8. A Comparison of Critical Regimes in Collapsible Tube, Pipe, Open Channel and Gas-Dynamic Flows

    NASA Astrophysics Data System (ADS)

    Arun, C. P.

    2003-11-01

    Though of considerable interest to clinical scientists, collapsible tubes are only recently receiving due interest by fluid physicists. The subject of critical phenomena in collapsible tube flow appears not to have been examined critically. For example, it has been proposed in the past that shock waves in physiological tubes are abnormal. We propose a classification of flow through collapsible tubes recognising that compressibility in gas-dynamic and pipe flow (cf.waterhammer) corresponds to distensibility in collapsible tube flow. Thus, opening and closing waves of collapsible tube flow (predistension regime) is subcritical flow and the post-distension regime, supercritical. Physiological tubes are often hyperelastic and contractile and often, when distension is very significant, a hypercritical regime corresponding to hypersonic gas-dynamic flow is admissible. Such a hypercritical regime would allow storage of energy and muscle contraction in the wall of the tube and hence continuance of propulsion in the essentially intermittent flow that is seen in collapsible tubes. Such a mechanism appears to be in operation in the human aorta, bowel and urethra. The present work offers a comparison of critical regimes in various fluid flow situations including collapsible tubes, that is in harmony with known phenomena seen in nature.

  9. The ALE Discontinuous Galerkin Method for the Simulatio of Air Flow Through Pulsating Human Vocal Folds

    NASA Astrophysics Data System (ADS)

    Feistauer, Miloslav; Kučera, Václav; Prokopová, Jaroslav; Horáček, Jaromír

    2010-09-01

    The aim of this work is the simulation of viscous compressible flows in human vocal folds during phonation. The computational domain is a bounded subset of IR2, whose geometry mimics the shape of the human larynx. During phonation, parts of the solid impermeable walls are moving in a prescribed manner, thus simulating the opening and closing of the vocal chords. As the governing equations we take the compressible Navier-Stokes equations in ALE form. Space semidiscretization is carried out by the discontinuous Galerkin method combined with a linearized semi-implicit approach. Numerical experiments are performed with the resulting scheme.

  10. Accurate modelling of unsteady flows in collapsible tubes.

    PubMed

    Marchandise, Emilie; Flaud, Patrice

    2010-01-01

    The context of this paper is the development of a general and efficient numerical haemodynamic tool to help clinicians and researchers in understanding of physiological flow phenomena. We propose an accurate one-dimensional Runge-Kutta discontinuous Galerkin (RK-DG) method coupled with lumped parameter models for the boundary conditions. The suggested model has already been successfully applied to haemodynamics in arteries and is now extended for the flow in collapsible tubes such as veins. The main difference with cardiovascular simulations is that the flow may become supercritical and elastic jumps may appear with the numerical consequence that scheme may not remain monotone if no limiting procedure is introduced. We show that our second-order RK-DG method equipped with an approximate Roe's Riemann solver and a slope-limiting procedure allows us to capture elastic jumps accurately. Moreover, this paper demonstrates that the complex physics associated with such flows is more accurately modelled than with traditional methods such as finite difference methods or finite volumes. We present various benchmark problems that show the flexibility and applicability of the numerical method. Our solutions are compared with analytical solutions when they are available and with solutions obtained using other numerical methods. Finally, to illustrate the clinical interest, we study the emptying process in a calf vein squeezed by contracting skeletal muscle in a normal and pathological subject. We compare our results with experimental simulations and discuss the sensitivity to parameters of our model.

  11. Advances in flowing afterglow and selected-ion flow tube techniques

    NASA Astrophysics Data System (ADS)

    Squires, Robert R.

    1992-09-01

    New developments in flowing afterglow and selected-ion flow tube (SIFT) techniques are briefly reviewed. Particular emphasis is given to the new chemical and physical information that can be obtained with use of the tandem flowing afterglow-triple quadrupole apparatus developed in the author's laboratory. Several outstanding recent achievements in the design and utilization of flowing afterglow and SIFT instruments in other laboratories are briefly highlighted that illustrate the power and flexibility of flow-tube-based methods. These include isotope tracer experiments with the tandem flowing afterglow-SIFT instrument in Boulder, studies of large molecular cluster ions with the variable temperature facility at Penn State, and gas-phase metal ion reactions with the laser ablation/fast flow reactor in Madison. Recent applications of the flowing afterglow-triple quadrupole instrument in our laboratory have made use of collision-induced dissociation (CID) as a tool for synthesizing novel ions and for obtaining new thermo-chemical information from threshold energy measurements. Collision-induced decar☐ylation of organic car☐ylate ions provides access to a variety of unusual and highly basic carbanions that cannot be generated with conventional ion sources. The formation and properties of saturated alkyl ions and studies of gas-phase reactions of the methyl anion are briefly described. We have developed a new method for carrying out "preparative CID" in a flowing afterglow with use of a mini-drift tube; some recent applications of this new ion source are presented. Measurement of CID thresholds for simple cleavage reactions of thermalized ions can provide accurate measures of bond strengths, gas-phase acidities and basicities, and heats of formation for ions and reactive neutral species. Applications of this approach in the thermochemical characterization of carbenes, benzynes and biradicals are described. Future prospects for the continued development of flow

  12. Stability of flow through collapsible tubes: new results

    NASA Astrophysics Data System (ADS)

    Hamadiche, M.; Gad-El-Hak, M.

    2002-11-01

    The stability of the Hagen--Poiseuille flow of a Newtonian fluid in an incompressible, collapsible, viscoelastic tube is determined using linear stability analysis. Differently from our 2000 report, the dependence of the tube's diameter in the base state on the axial distance is explicitly accounted for in the present paper. A novel numerical strategy is introduced to study the spatio--temporal stability of the coupled fluid--structure system subjected to infinitesimal axisymmetric or non-axisymmetric disturbances. Axisymmetric disturbances correspond to the azimuthal wavenumber n=0. There, we have identified two convective instability modes one propagating upstream and the other downstream. For each of the non-axisymmetric disturbances n=1,2,3,4,5,6, we have found one absolute instability propagating upstream, while for n=1,2, downstream-propagating convective modes are observed. In total, we have identified 10 instability modes. Two of the standing waves have equal frequencies at their respective cusp points, while a third absolute instability has triple that frequency, in excellent agreement with existing experiments. This frequency tripling is preserved for all Reynolds numbers. The n=1 absolute instability mode is replaced by a convective mode when the Reynolds number exceeds 200, while the other standing waves, at n=2--6, persist to high Re values. Increasing the solid's viscosity, thickness or shear modulus causes the absolute instability modes to become convective as well as to ultimately become stable. The boundary separating the zone of absolute instabilities from that of convective instabilities has been identified. As the unperturbed tube takes a convergent--divergent form under the action of the transmural pressure, the unstable modes are shifted toward the divergent part of the duct.

  13. Controlling methods of a newly developed extra aortic counter-pulsation device using shape memory alloy fibers.

    PubMed

    Hashem, Mohamed O; Yamada, A; Tsuboko, Y; Muira, H; Homma, D; Shiraishi, Y; Yambe, T

    2013-01-01

    Diastolic counter-pulsation has been used to provide circulatory augmentation for short term cardiac support. The success of intra-aortic balloon pump (IABP) therapy has generated interest in long term counter-pulsation strategies to treat heart failure patients. The authors have been developing a totally implantable extra aortic pulsation device for the circulatory support of heart failure patients, using 150 µm Ni-Ti anisotropic shape memory alloy (SMA) fibers. These fibers contract by Joule heating with an electric current supply. The special features of our design are as follow: non blood contacting, extra aortic pulsation function synchronizing with the native heart, a wrapping mechanical structure for the aorta in order to achieve its assistance as the aortomyoplsty and the extra aortic balloon pump. The device consisted of rubber silicone wall plates, serially connected for radial contraction. We examined the contractile function of the device, as well as it controlling methods; the phase delay parameter and the pulse width modulation, in a systemic mock circulatory system, with a pneumatically driven silicone left ventricle model, arterial rubber tubing, a peripheral resistance unit, and a venous reservoir. The device was secured around the aortic tubing with a counter-pulsation mode of 1:4 against the heartbeat. Pressure and flow waveforms were measured at the aortic outflow, as well as its driving condition of the contraction phase width and the phase delay. The device achieved its variable phase control for co-pulsation or counter-pulsation modes by changing the phase delay of the SMA fibers. Peak diastolic pressure significantly augmented, mean flow increased (p<0.05) according to the pulse width modulation. Therefore the newly developed extra aortic counter-pulsation device using SMA fibers, through it controlling methods indicated its promising alternative extra aortic approach for non-blood contacting cardiovascular circulatory support.

  14. Hypervelocity flows of argon produced in a free piston driven expansion tube

    NASA Technical Reports Server (NTRS)

    Neely, A. J.; Stalker, R. J.

    1992-01-01

    An expansion tube with a free piston driver has been used to generate quasi-steady hypersonic flows in argon at flow velocities in excess of 9 km/s. Irregular test flow unsteadiness has limited the performance of previous expansion tubes. Test section measurements of pitot pressure, static pressure, and flat plate heat transfer rates are used to confirm the presence of quasi-steady flow, and comparisons are made with predictions for the equilibrium flow of an ideal, ionizing, monatomic gas. The results of this work indicate that expansion tubes can be used to generate quasi-steady hypersonic flows in argon at speeds in excess of Earth orbital velocity.

  15. Hypervelocity flows of argon produced in a free piston driven expansion tube

    NASA Technical Reports Server (NTRS)

    Neely, A. J.; Stalker, R. J.

    1992-01-01

    An expansion tube with a free piston driver has been used to generate quasi-steady hypersonic flows in argon at flow velocities in excess of 9 km/s. Irregular test flow unsteadiness has limited the performance of previous expansion tubes. Test section measurements of pitot pressure, static pressure, and flat plate heat transfer rates are used to confirm the presence of quasi-steady flow, and comparisons are made with predictions for the equilibrium flow of an ideal, ionizing, monatomic gas. The results of this work indicate that expansion tubes can be used to generate quasi-steady hypersonic flows in argon at speeds in excess of Earth orbital velocity.

  16. Analysis of steady viscous flow in slender tubes

    NASA Astrophysics Data System (ADS)

    Bujurke, N. M.; Katagi, N. N.; Awati, V. B.

    2005-09-01

    The computer extended perturbation series method is used to analyze the problem of steady viscous flow in slender tubes. The objective is to obtain an expansion in a power series of λ (= ɛ R, ɛ is a small parameter and R = M/{Lν } is a streamwise Reynolds number) and look for its analytic continuation. Such an expansion was usually terminated at the second or third order term and consequently they have a very limited utility. Sufficiently large number of terms in the series, representing physical quantities are, generated for the detail analysis which enables to get converging Pade’ sums for large λ. Domb-Sykes plot enables in finding singularity restricting the convergence of the series. Useful results valid up to λ = 15 are obtained for different derived quantities whereas in earlier findings [6], analysis could be done only up to λ = 10 resulting into a substantial improvement in the present study.

  17. Head pulsations in a centrifugal pump

    NASA Astrophysics Data System (ADS)

    Boiko, V. S.; Sotnyk, M. I.; Moskalenko, V. V.

    2017-08-01

    This article investigated the factors, which affect to the character of the head pulsations of a centrifugal pump. We investigated the dependence of the shape and depth of these pulsations from the operation mode of the pump. Was determined, that the head pulsations at the outlet of the impeller (pulsations on the blade passing frequency) cause head pulsations at the outlet of the pump, that have the same frequency, but differ in shape and depth. These pulsations depend on the design features of the flow-through part of the pump (from the ratio of hydraulic losses on the friction and losses on the vortex formation). A feature of the researches that were conducted is also the using of not only hydraulic but also electric modeling methods. It allows determining the values of the components of hydraulic losses.

  18. Program and charts for determining shock tube, and expansion tunnel flow quantities for real air

    NASA Technical Reports Server (NTRS)

    Miller, C. G., III; Wilder, S. E.

    1975-01-01

    A computer program in FORTRAN 4 language was written to determine shock tube, expansion tube, and expansion tunnel flow quantities for real-air test gas. This program permits, as input data, a number of possible combinations of flow quantities generally measured during a test. The versatility of the program is enhanced by the inclusion of such effects as a standing or totally reflected shock at the secondary diaphragm, thermochemical-equilibrium flow expansion and frozen flow expansion for the expansion tube and expansion tunnel, attenuation of the flow in traversing the acceleration section of the expansion tube, real air as the acceleration gas, and the effect of wall boundary layer on the acceleration section air flow. Charts which provide a rapid estimation of expansion tube performance prior to a test are included.

  19. Industrial application of ultrasound based in-line rheometry: From stationary to pulsating pipe flow of chocolate suspension in precrystallization process

    NASA Astrophysics Data System (ADS)

    Ouriev, Boris; Windhab, Erich; Braun, Peter; Birkhofer, Beat

    2004-10-01

    In-line visualization and on-line characterization of nontransparent fluids becomes an important subject for process development in food and nonfood industries. In our work, a noninvasive Doppler ultrasound-based technique is introduced. Such a technique is applied for investigation of nonstationary flow in the chocolate precrystallization process. Unstable flow conditions were induced by abrupt flow interruption and were followed up by strong flow pulsations in the piping system. While relying on available process information, such as absolute pressures and temperatures, no analyses of flow conditions or characterization of suspension properties could possibly be done. It is obvious that chocolate flow properties are sensitive to flow boundary conditions. Therefore, it becomes essential to perform reliable structure state monitoring and particularly in application to nonstationary flow processes. Such flow instabilities in chocolate processing can often lead to failed product quality with interruption of the mainstream production. As will be discussed, a combination of flow velocity profiles, on-line fit into flow profiles, and pressure difference measurement are sufficient for reliable analyses of fluid properties and flow boundary conditions as well as monitoring of the flow state. Analyses of the flow state and flow properties of chocolate suspension are based on on-line measurement of one-dimensional velocity profiles across the flow channel and their on-line characterization with the power-law model. Conclusions about flow boundary conditions were drawn from a calculated velocity standard mean deviation, the parameters of power-law fit into velocity profiles, and volumetric flow rate information.

  20. Surface reaction and pore diffusion in flow-tube reactors

    NASA Technical Reports Server (NTRS)

    Keyser, Leon F.; Moore, Steven B.; Leu, Ming-Taun

    1991-01-01

    The interaction of gas diffusion with surface reaction in porous solids is discussed and applied specifically to heterogeneous rate measurements in flow-tube reactors. External diffusion to the outer surface of a reactive solid, internal diffusion within the pores, surface reaction, and laminar flow are considered. A procedure is developed to correct observed surface rate constants for the interaction of these processes. Measured surface areas and bulk densities are used to construct a semiempirical model for porous diffusion in vapor-formed HNO3-H2O ices which are used to simulate polar stratospheric cloud surfaces. The model is tested experimentally by varying the thickness of these ices from about 15 to 120 microns. The results are consistent with the model predictions and show that the HNO3-H2O ices used are highly porous, and the internal surface must be considered in calculating kinetic parameters from observed loss rates. The best fit of the data yields a tortuosity factor of 3.3 +/-1.1 for the ice substrates.

  1. Tracheostomy Tube Type and Inner Cannula Selection Impact Pressure and Resistance to Air Flow.

    PubMed

    Pryor, Lee N; Baldwin, Claire E; Ward, Elizabeth C; Cornwell, Petrea L; O'Connor, Stephanie N; Chapman, Marianne J; Bersten, Andrew D

    2016-05-01

    Advancements in tracheostomy tube design now provide clinicians with a range of options to facilitate communication for individuals receiving ventilator assistance through a cuffed tube. Little is known about the impact of these modern design features on resistance to air flow. We undertook a bench model test to measure pressure-flow characteristics and resistance of a range of tubes of similar outer diameter, including those enabling subglottic suction and speech. A constant inspiratory ± expiratory air flow was generated at increasing flows up to 150 L/min through each tube (with or without optional, mandatory, or interchangeable inner cannula). Driving pressures were measured, and resistance was calculated (cm H2O/L/s). Pressures changed with increasing flow (P < .001) and tube type (P < .001), with differing patterns of pressure change according to the type of tube (P < .001) and direction of air flow. The single-lumen reference tube encountered the lowest inspiratory and expiratory pressures compared with all double-lumen tubes (P < .001); placement of an optional inner cannula increased bidirectional tube resistance by a factor of 3. For a tube with interchangeable inner cannulas, the type of cannula altered pressure and resistance differently (P < .001); the speech cannula in particular amplified pressure-flow changes and increased tube resistance by more than a factor of 4. Tracheostomy tube type and inner cannula selection imposed differing pressures and resistance to air flow during inspiration and expiration. These differences may be important when selecting airway equipment or when setting parameters for monitoring, particularly for patients receiving supported ventilation or during the weaning process. Copyright © 2016 by Daedalus Enterprises.

  2. Study on flow instability and countermeasure in a draft tube with swirling flow

    NASA Astrophysics Data System (ADS)

    Nakashima, T.; Matsuzaka, R.; Miyagawa, K.; Yonezawa, K.; Tsujimoto, Y.

    2014-03-01

    The swirling flow in the draft tube of a Francis turbine can cause the flow instability and the cavitation surge and has a larger influence on hydraulic power operating system. In this paper, the cavitating flow with swirling flow in the diffuser was studied by the draft tube component experiment, the model Francis turbine experiment and the numerical simulation. In the component experiment, several types of fluctuations were observed, including the cavitation surge and the vortex rope behaviour by the swirling flow. While the cavitation surge and the vortex rope behaviour were suppressed by the aeration into the diffuser, the loss coefficient in the diffuser increased by the aeration. In the model turbine test the aeration decreased the efficiency of the model turbine by several percent. In the numerical simulation, the cavitating flow was studied using Scale-Adaptive Simulation (SAS) with particular emphasis on understanding the unsteady characteristics of the vortex rope structure. The generation and evolution of the vortex rope structures have been investigated throughout the diffuser using the iso-surface of vapor volume fraction. The pressure fluctuation in the diffuser by numerical simulation confirmed the cavitation surge observed in the experiment. Finally, this pressure fluctuation of the cavitation surge was examined and interpreted by CFD.

  3. Experimental study on cross-flow induced vibrations in heat exchanger tube bundle

    NASA Astrophysics Data System (ADS)

    Khushnood, Shahab; Nizam, Luqman Ahmad

    2017-03-01

    Vibration in heat exchangers is one of the main problems that the industry has faced over last few decades. Vibration phenomenon in heat exchangers is of major concern for designers and process engineers since it can lead to the tube damage, tube leakage, baffle damage, tube collision damage, fatigue, creep etc. In the present study, vibration response is analyzed on single tube located in the centre of the tube bundle having parallel triangular arrangement (60°) with P/ D ratio of 1.44. The experiment is performed for two different flow conditions. This kind of experiment has not been reported in the literature. Under the first condition, the tube vibration response is analyzed when there is no internal flow in the tube and under the second condition, the response is analyzed when the internal tube flow is maintained at a constant value of 0.1 m/s. The free stream shell side velocity ranges from 0.8 m/s to 1.3 m/s, the reduced gap velocity varies from 1.80 to 2.66 and the Reynolds number varies from 44500 to 66000. It is observed that the internal tube flow results in larger vibration amplitudes for the tube than that without internal tube flow. It is also established that over the current range of shell side flow velocity, the turbulence is the dominant excitation mechanism for producing vibration in the tube since the amplitude varies directly with the increase in the shell side velocity. Damping has no significant effect on the vibration behavior of the tube for the current velocity range.

  4. Experimental study of the interaction of pulsations of the neutron flux and the coolant flow in a boiling-water reactor

    SciTech Connect

    Leppik, P.A.

    1984-12-01

    This paper presents results of a study designed to confirm that the interaction of the neutron flux and the coolant flow plays an important role in the mechanism of high-frequency (HF) resonant instability of the VK-50 boiling water reactor. To do this and to check the working model, signals from probes measuring the flow rate of the coolant and the neutron flux were recorded simultaneously (with the help of a magnetograph) in experiments performed in 1981 on driving the VK-50 reactor into the HF reonant instability regimes. Estimates were then obtained for the statistical characteristics of the pulsations of the flow rate and of the neutron flux, including the cross-correlation functions and coherence functions. The basic results of these studies are reported here.

  5. Temperature and pressure measurements at cold exit of counter-flow vortex tube with flow visualization of reversed flow

    NASA Astrophysics Data System (ADS)

    Yusof, Mohd Hazwan bin; Katanoda, Hiroshi; Morita, Hiromitsu

    2015-02-01

    In order to clarify the structure of the cold flow discharged from the counter-flow vortex tube (VT), the temperature and pressure of the cold flow were measured, and the existence and behavior of the reversed flow at the cold exit was studied using a simple flow visualization technique consisting of a 0.75mm-diameter needle, and an oil paint droplet. It is observed through this experiment that the Pitot pressure at the cold exit center can either be lower or higher than atmospheric pressure, depending on the inlet pressure and the cold fraction, and that a reversed flow is observed when the Pitot pressure at the cold exit center is lower than atmospheric pressure. In addition, it is observed that when reducing the cold fraction from unity at any arbitrary inlet pressure, the region of reversed and colder flow in the central part of cold exit extends in the downstream direction.

  6. Shear thinning effects on blood flow in straight and curved tubes

    NASA Astrophysics Data System (ADS)

    Cherry, Erica M.; Eaton, John K.

    2013-07-01

    Simulations were performed to determine the magnitude and types of errors one can expect when approximating blood in large arteries as a Newtonian fluid, particularly in the presence of secondary flows. This was accomplished by running steady simulations of blood flow in straight and curved tubes using both Newtonian and shear-thinning viscosity models. In the shear-thinning simulations, the viscosity was modeled as a shear rate-dependent function fit to experimental data. Simulations in straight tubes were modeled after physiologically relevant arterial flows, and flow parameters for the curved tube simulations were chosen to examine a variety of secondary flow strengths. The diameters ranged from 1 mm to 10 mm and the Reynolds numbers from 24 to 1500. Pressure and velocity data are reported for all simulations. In the straight tube simulations, the shear-thinning flows had flattened velocity profiles and higher pressure gradients compared to the Newtonian simulations. In the curved tube flows, the shear-thinning simulations tended to have blunted axial velocity profiles, decreased secondary flow strengths, and decreased axial vorticity compared to the Newtonian simulations. The cross-sectionally averaged pressure drops in the curved tubes were higher in the shear-thinning flows at low Reynolds number but lower at high Reynolds number. The maximum deviation in secondary flow magnitude averaged over the cross sectional area was 19% of the maximum secondary flow and the maximum deviation in axial vorticity was 25% of the maximum vorticity.

  7. Internal thermal coupling in direct-flow coaxial vacuum tube collectors

    SciTech Connect

    Glembin, J.; Rockendorf, G.; Scheuren, J.

    2010-07-15

    This investigation covers the impact of low flow rates on the efficiency of coaxial vacuum tube collectors. Measurements show an efficiency reduction of 10% if reducing the flow rate from 78 kg/m{sup 2} h to 31 kg/m{sup 2} h for a collector group with 60 parallel vacuum tubes with a coaxial flow conduit at one-sided connection. For a more profound understanding a model of the coaxial tube was developed which defines the main energy fluxes including the internal thermal coupling. The tube simulations show a non-linear temperature profile along the tube with the maximum temperature in the outer pipe. Due to heat transfer to the entering flow this maximum is not located at the fluid outlet. The non-linearity increases with decreasing flow rates. The experimentally determined flow distribution allows simulating the measured collector array. The simulation results confirm the efficiency decrease at low flow rates. The flow distribution has a further impact on efficiency reduction, but even at an ideal uniform flow, a considerable efficiency reduction at low flow rates is to be expected. As a consequence, low flow rates should be prevented for coaxial tube collectors, thus restricting the possible operation conditions. The effect of constructional modifications like diameter or material variations is presented. Finally the additional impact of a coaxial manifold design is discussed. (author)

  8. Flow and axial dispersion in a sinusoidal-walled tube: Effects of inertial and unsteady flows

    SciTech Connect

    Richmond, Marshall C.; Perkins, William A.; Scheibe, Timothy D.; Lambert, Adam; Wood, Brian D.

    2013-12-01

    Dispersion in porous media flows has been the subject of much experimental, theoretical and numerical study. Here we consider a wavy-walled tube (a three-dimensional tube with sinusoidally-varying diameter) as a simplified conceptualization of flow in porous media, where constrictions represent pore throats and expansions pore bodies. A theoretical model for effective (macroscopic) longitudinal dispersion in this system has been developed by volume averaging the microscale velocity field. Direct numerical simulation using computational fluid dynamics (CFD) methods was used to compute velocity fields by solving the Navier-Stokes equations, and also to numerically solve the volume averaging closure problem, for a range of Reynolds numbers (Re) spanning the low-Re to inertial flow regimes, including one simulation at Re = 449 for which unsteady flow was observed. Dispersion values were computed using both the volume averaging solution and a random walk particle tracking method, and results of the two methods were shown to be consistent. Our results are compared to experimental measurements of dispersion in porous media and to previous theoretical results for the low-Re, Stokes flow regime. In the steady inertial regime we observe an power-law increase in effective longitudinal dispersion (DL) with Re, consistent with previous results. This rapid rate of increase is caused by trapping of solute in expansions due to flow separation (eddies). For the unsteady case (Re = 449), the rate of increase of DL with Re was smaller than that observed at lower Re. Velocity fluctuations in this regime lead to increased rates of solute mass transfer between the core flow and separated flow regions, thus diminishing the amount of tailing caused by solute trapping in eddies and thereby reducing longitudinal dispersion.

  9. Comparison of Gravity Flow Rates Between ENFit and Legacy Feeding Tubes.

    PubMed

    Mundi, Manpreet S; Duellman, Wanda; Epp, Lisa; Davidson, Jacob; Hurt, Ryan T

    2017-04-01

    Misconnections between enteral supplies and other access devices have led to significant morbidity and mortality. To reduce misconnections, a standard small-bore connector has been developed (International Organization for Standards 80369-8; ENFit). The full impact of transition to this connector is not known, however. Working with major manufacturers and Food and Drug Administration, we obtained ENFit and comparative legacy tubes of variable sizes (low-profile, 14F, 18F, 20F, and 24F balloon gastrostomies). Gravity enteral feeding was simulated with an empty bolus syringe attached to the feeding tube to be tested. The tube was clamped and filled to the 60-mL mark with liquid (water, Jevity 1 Cal, Isosource HN, Isosource 1.5 Cal, Two Cal HN, and Nourish). The clamp was released, and time for formula to leave the syringe was recorded. There was no difference in flow rate between the aggregate legacy and ENFit tubes for the low-profile, 18F, and 20F sizes. The ENFit 14F tubes had a lower flow rate versus the legacy tubes, largely due to the low flow rates seen with the 1 ENFit tube. Similarly, 24F ENFit tubes with some formulas yielded lower flow rates as opposed to legacy. Overall, for the low-profile, 18F, and 20F sizes, the ENFit tubes had similar flow rates when compared with the legacy tubes. For the 14F and 24F sizes, the flow rate of ENFit tubes was significantly lower, which could result in longer EN delivery for patients who are using these tubes to provide gravity feeding.

  10. Flow of Supercritical Hydrogen in a Uniformly Heated Circular Tube

    NASA Technical Reports Server (NTRS)

    Youn, B.; Mills, A. F.

    1993-01-01

    Turbulent flow of supercritical hydrogen through a uniformly heated circular tube has been investigated using numerical methods, for the range of 4 x 10(exp 5) less than Re less than 3 x 10(exp 6), 5 less than or equal to q(sub W) less than or equal to 10 MW/sq m, 30 less than or equal to T(sub in) less than or equal to 90 K, and 5 less than or equal to P(sub in) less than or equal to 15 MPa. The purpose is to validate a turbulence model and calculation method for the design of active cooling systems of hydrogen-fueled hypersonic aircraft, where the hydrogen fuel a used as coolant. The PHOENICS software package was used for the computations, which required special provision for evaluation of the thermophysical properties of the supercritical hydrogen, and a low Reynolds number form of the k-epsilon turbulence model. Pressure drop and heat transfer data were compared with experiment and existing correlations and good agreement was demonstrated. For the pressure range considered here a "thermal spike" was observed and shown to be due to the secondary peak in specific heat, rather than the primary peak.

  11. Uncertainty Analysis of the Grazing Flow Impedance Tube

    NASA Technical Reports Server (NTRS)

    Brown, Martha C.; Jones, Michael G.; Watson, Willie R.

    2012-01-01

    This paper outlines a methodology to identify the measurement uncertainty of NASA Langley s Grazing Flow Impedance Tube (GFIT) over its operating range, and to identify the parameters that most significantly contribute to the acoustic impedance prediction. Two acoustic liners are used for this study. The first is a single-layer, perforate-over-honeycomb liner that is nonlinear with respect to sound pressure level. The second consists of a wire-mesh facesheet and a honeycomb core, and is linear with respect to sound pressure level. These liners allow for evaluation of the effects of measurement uncertainty on impedances educed with linear and nonlinear liners. In general, the measurement uncertainty is observed to be larger for the nonlinear liners, with the largest uncertainty occurring near anti-resonance. A sensitivity analysis of the aerodynamic parameters (Mach number, static temperature, and static pressure) used in the impedance eduction process is also conducted using a Monte-Carlo approach. This sensitivity analysis demonstrates that the impedance eduction process is virtually insensitive to each of these parameters.

  12. A single LipiFlow® Thermal Pulsation System treatment improves meibomian gland function and reduces dry eye symptoms for 9 months.

    PubMed

    Greiner, Jack V

    2012-04-01

    To evaluate the effect of a single treatment with the LipiFlow(®) Thermal Pulsation System on signs of meibomian gland dysfunction (MGD) and dry eye symptoms over a 9-month period. Patients (n = 42 eyes, 21 subjects) diagnosed with MGD and dry eye symptoms were recruited for a non-significant risk, prospective, open-label, 1-month clinical trial. Patients received a single 12-minute treatment using the LipiFlow(®) Thermal Pulsation System on each eye. The LipiFlow(®) device applies heat to the conjunctival surfaces of the upper and lower inner eyelids while simultaneously applying pulsatile pressure to the outer eyelid surfaces to express the meibomian glands. Patient symptoms were evaluated using the Ocular Surface Disease Index (OSDI) and Standard Patient Evaluation for Eye Dryness (SPEED) dry eye questionnaires; tear break-up time was measured with the dry eye test (DET™); and meibomian gland function was evaluated using a standardized diagnostic expression technique. Data are presented for patient's pre-treatment (baseline) and at 1-month and 9-month post-treatment. Meibomian gland secretion scores improved significantly from baseline (4.4 ± 4.0) to 1-month post-treatment (11.3 ± 6.2; p < 0.0001) and this improvement was maintained with no significant regression at 9 months (11.7 ± 5.9). Similarly, baseline tear break-up time (4.8 ± 3.2) was significantly increased at 1 month (9.6 ± 7.6; p < 0.001) and this increase was maintained with no significant regression at 9 months (7.1 ± 5.6). Symptom scores on both OSDI and SPEED questionnaires improved significantly at 1 month (p < 0.0001) and this improvement was maintained at 9 months. With such prolonged improvement in signs and symptoms of dry eye disease, the LipiFlow(®) Thermal Pulsation System offers a technological advancement for the treatment of dry eye disease secondary to meibomian gland dysfunction. A single 12-minute LipiFlow(®) treatment results in up to 9

  13. Concentration and velocity measurements in the flow of droplet suspensions through a tube

    NASA Astrophysics Data System (ADS)

    Kowalewski, T. A.

    1984-12-01

    Two optical methods, light absorption and LDA, are applied to measure the concentration and velocity profiles of droplet suspensions flowing through a tube. The droplet concentration is non-uniform and has two maxima, one near the tube wall and one on the tube axis. The measured velocity profiles are blunted, but a central plug-flow region is not observed. The concentration of droplets on the tube axis and the degree of velocity profile blunting depend on relative viscosity. These results can be qualitatively compared with the theory of Chan and Leal.

  14. PIV measurements of the flow field just downstream of an oscillating collapsible tube.

    PubMed

    Bertram, C D; Truong, N K; Hall, S D

    2008-12-01

    We probed the time-varying flow field immediately downstream of a flexible tube conveying an aqueous flow, during flow-induced oscillation of small amplitude, at time-averaged Reynolds numbers (Re) in the range 300-550. Velocity vector components in the plane of a laser sheet were measured by high-speed ("time-resolved") particle image velocimetry. The sheet was aligned alternately with both the major axis and the minor axis of the collapsing tube by rotating the pressure chamber in which the tube was mounted. The Womersley number of the oscillations was approximately 10. In the major-axis plane the flow fields were characterized by two jets that varied in lateral spacing. The rapid deceleration of flow at maximal collapse caused the jets momentarily to merge about one diameter into the downstream pipe, and strengthened and enlarged the existing retrograde flow lateral to each jet. Collapse also spread the jets maximally, allowing retrograde flow between them during the ascent from its minimum of the pressure at the end of the flexible tube. The minor-axis flow fields showed that the between-jet retrograde flow at this time extended all the way across the pipe. Whereas the retrograde flow lateral to the jets terminated within three diameters of the tube end at Re=335 at all times, it extended beyond three diameters at Re=525 for some 25% of the cycle including the time of maximal flow deceleration. Off-axis sheet positioning revealed the lateral jets to be crescent shaped. When the pressure outside the tube was increased, flattening the tube more, the jets retained a more consistent lateral position. These results illuminate the flows created by collapsible-tube oscillation in a laminar regime accessible to numerical modeling.

  15. Experimental study of rarefied gas flow near sudden contraction junction of a tube

    NASA Astrophysics Data System (ADS)

    Varade, Vijay; Agrawal, Amit; Pradeep, A. M.

    2014-06-01

    An experimental study of nearly isothermal rarefied gas flow near the sudden contraction junction of a tube is presented in this paper. The measurements are performed with nitrogen gas flowing at low pressures in conventional tubes with sudden contraction area ratios of 1.48, 3.74, 12.43, and 64. The flow is dynamically similar to gas flow in a microchannel as the Knudsen number (0.0001 < Kn < 0.032) falls in the slip flow regime. The Reynolds number in the smaller section (Res) ranges between 0.2 and 837. The static pressure measurements are analyzed to understand the flow behavior. The static pressure variation along the wall and uniform radial pressure profile near the junction indicates absence of flow separation and vena contracta. The static pressure variation in both the tubes approaches the pressure variation as that of an isolated straight tube at a certain critical Knudsen number for a given area ratio. The velocity field is obtained through a momentum balance and using the flow measurements. The effect of larger momentum diffusivity and slip at the wall, restricts any deviation in velocity profile from its parabolic nature at the junction and suppresses flow separation and vena contracta. The larger inertia force at the sudden contraction junction causes larger acceleration of the flow near the junction in the smaller tube as compared to that of the straight tube. The larger pressure drop in the sudden contraction is a result of the extent of flow compression and additional acceleration near the junction in the smaller tube as compared to the straight tube. This paper reports a set of new results that are expected to help in improving understanding of gaseous slip flows.

  16. Forced convective flow and heat transfer of upward cocurrent air-water slug flow in vertical plain and swirl tubes

    SciTech Connect

    Chang, Shyy Woei; Yang, Tsun Lirng

    2009-10-15

    This experimental study comparatively examined the two-phase flow structures, pressured drops and heat transfer performances for the cocurrent air-water slug flows in the vertical tubes with and without the spiky twisted tape insert. The two-phase flow structures in the plain and swirl tubes were imaged using the computerized high frame-rate videography with the Taylor bubble velocity measured. Superficial liquid Reynolds number (Re{sub L}) and air-to-water mass flow ratio (AW), which were respectively in the ranges of 4000-10000 and 0.003-0.02 were selected as the controlling parameters to specify the flow condition and derive the heat transfer correlations. Tube-wise averaged void fraction and Taylor bubble velocity were well correlated by the modified drift flux models for both plain and swirl tubes at the slug flow condition. A set of selected data obtained from the plain and swirl tubes was comparatively examined to highlight the impacts of the spiky twisted tape on the air-water interfacial structure and the pressure drop and heat transfer performances. Empirical heat transfer correlations that permitted the evaluation of individual and interdependent Re{sub L} and AW impacts on heat transfer in the developed flow regions of the plain and swirl tubes at the slug flow condition were derived. (author)

  17. Study on turbulent flow and heat transfer performance of tubes with internal fins in EGR cooler

    NASA Astrophysics Data System (ADS)

    Liu, Lin; Ling, Xiang; Peng, Hao

    2015-01-01

    In this paper, flow and heat transfer performances of the tubes with internal longitudinal fins in Exhaust Gas Recirculation (EGR ) cooler were investigated by three-dimension computation and experiment . Each test tube was a single-pipe structure, without inner tube. Three-dimension computation was performed to determine the thermal characteristics difference between the two kinds of tubes, that is, the tube with an inner solid staff as a blocked structure and the tube without the blocked structure. The effects of fin width and fin height on heat transfer and flow are examined. For proving the validity of numerical method, the calculated results were compared with corresponding experimental data. The tube-side friction factor and heat transfer coefficient were examined. As a result, the maximum deviations between the numerical results and the experimental data are approximately 5.4 % for friction factor and 8.6 % for heat transfer coefficient, respectively. It is found that two types of internally finned tubes enhance significantly heat transfer. The heat transfer of the tube with blocked structure is better, while the pressure drop of the tube without blocked structure is lower. The comprehensive performance of the unblocked tube is better to applied in EGR cooler.

  18. Flow distribution analysis on the cooling tube network of ITER thermal shield

    SciTech Connect

    Nam, Kwanwoo; Chung, Wooho; Noh, Chang Hyun; Kang, Dong Kwon; Kang, Kyoung-O; Ahn, Hee Jae; Lee, Hyeon Gon

    2014-01-29

    Thermal shield (TS) is to be installed between the vacuum vessel or the cryostat and the magnets in ITER tokamak to reduce the thermal radiation load to the magnets operating at 4.2K. The TS is cooled by pressurized helium gas at the inlet temperature of 80K. The cooling tube is welded on the TS panel surface and the composed flow network of the TS cooling tubes is complex. The flow rate in each panel should be matched to the thermal design value for effective radiation shielding. This paper presents one dimensional analysis on the flow distribution of cooling tube network for the ITER TS. The hydraulic cooling tube network is modeled by an electrical analogy. Only the cooling tube on the TS surface and its connecting pipe from the manifold are considered in the analysis model. Considering the frictional factor and the local loss in the cooling tube, the hydraulic resistance is expressed as a linear function with respect to mass flow rate. Sub-circuits in the TS are analyzed separately because each circuit is controlled by its own control valve independently. It is found that flow rates in some panels are insufficient compared with the design values. In order to improve the flow distribution, two kinds of design modifications are proposed. The first one is to connect the tubes of the adjacent panels. This will increase the resistance of the tube on the panel where the flow rate is excessive. The other design suggestion is that an orifice is installed at the exit of tube routing where the flow rate is to be reduced. The analysis for the design suggestions shows that the flow mal-distribution is improved significantly.

  19. Dynamics of Magnetic Flux Tubes in an Advective Flow around a Black Hole

    NASA Astrophysics Data System (ADS)

    Deb, Arnab; Chakrabarti, Sandip Kumar; Giri, Kinsuk

    2016-07-01

    Magnetic fields cannibalized by an accretion flow would very soon have a dominant toroidal component. Without changing the topology, we study the movements of these flux tubes inside a geometrically thick advective disk which undergo centrifugal pressure supported shocks. We also consider the effects of the flux tubes on the flow. We use a finite element method (Total Variation Diminishing) for this purpose and specifically focussed whether the flux tubes contribute to changes in outflow properties in terms of its collimation and outflow rates. It is seen that depending upon the cross sectional radius of the flux tubes (which control the drag force), these field lines may move towards the central object or oscillate vertically before eventually escaping out of the funnel wall (pressure zero surface). These interesting results obtained with and without flux tubes point to the role the flux tubes play in collimation of jets and outflows.

  20. Stability of the flow in a soft tube deformed due to an applied pressure gradient

    NASA Astrophysics Data System (ADS)

    Verma, M. K. S.; Kumaran, V.

    2015-04-01

    A linear stability analysis is carried out for the flow through a tube with a soft wall in order to resolve the discrepancy of a factor of 10 for the transition Reynolds number between theoretical predictions in a cylindrical tube and the experiments of Verma and Kumaran [J. Fluid Mech. 705, 322 (2012), 10.1017/jfm.2011.55]. Here the effect of tube deformation (due to the applied pressure difference) on the mean velocity profile and pressure gradient is incorporated in the stability analysis. The tube geometry and dimensions are reconstructed from experimental images, where it is found that there is an expansion and then a contraction of the tube in the streamwise direction. The mean velocity profiles at different downstream locations and the pressure gradient, determined using computational fluid dynamics, are found to be substantially modified by the tube deformation. The velocity profiles are then used in a linear stability analysis, where the growth rates of perturbations are calculated for the flow through a tube with the wall modeled as a neo-Hookean elastic solid. The linear stability analysis is carried out for the mean velocity profiles at different downstream locations using the parallel flow approximation. The analysis indicates that the flow first becomes unstable in the downstream converging section of the tube where the flow profile is more pluglike when compared to the parabolic flow in a cylindrical tube. The flow is stable in the upstream diverging section where the deformation is maximum. The prediction for the transition Reynolds number is in good agreement with experiments, indicating that the downstream tube convergence and the consequent modification in the mean velocity profile and pressure gradient could reduce the transition Reynolds number by an order of magnitude.

  1. Numerical Analysis of the Turbine 99 Draft Tube Flow Field Provoked by Redesigned Inlet Velocity Profiles.

    NASA Astrophysics Data System (ADS)

    Galván, S.; Reggio, M.; Guibault, F.; Castro, L.

    2014-03-01

    In recent years, several investigations on hydraulic turbine draft tube performance have shown that the hydrodynamic flow field at the runner outlet determines the diffuser efficiency affecting the overall performance of the turbine. This flow field, for which the principal characteristics are the flow rate and the inlet swirling flow intensity, is mostly developed on turbines designed for low head (high specific velocity) and operated away from their best efficiency point. To identify factors of the flow field responsible for loosing draft- tube efficiency, the correlations between the flow pattern along the diffuser and both swirl intensity and flow rate have been examined. An analytical representation of inlet flow field has been manipulated by a Multi Island Genetic Algorithm through the automatic coupling of multidisciplinary commercial software systems in order to obtain redesigned inlet velocity profiles. This loop allowed determining the profile for which the minimum energy loss factor was reached. With different flow field patterns obtained during the optimization process it was possible to undertake a qualitative and quantitative analysis which has helped to understand how to suppress or at least mitigate undesirable draft tube flow characteristics. The direct correlation between the runner blade design and the kinematics of the swirl at the draft tube inlet should suppose the perfect coupling at the runner-draft tube interface without compromising the overall flow stability of the machine.

  2. High enthalpy, hypervelocity flows of air and argon in an expansion tube

    NASA Technical Reports Server (NTRS)

    Neely, A. J; Stalker, R. J.; Paull, A.

    1991-01-01

    An expansion tube with a free piston driver has been used to generate quasi-steady hypersonic flows in argon and air at flow velocities in excess of 9 km/s. Irregular test flow unsteadiness has limited the performance of previous expansion tubes, and it has been found that this can be avoided by attention to the interaction between the test gas accelerating expansion and the contact surface in the primary shock tube. Test section measurements of pitot pressure, static pressure and flat plate heat transfer are reported. An approximate analytical theory has been developed for predicting the velocities achieved in the unsteady expansion of the ionizing or dissociating test gas.

  3. High enthalpy, hypervelocity flows of air and argon in an expansion tube

    NASA Technical Reports Server (NTRS)

    Neely, A. J; Stalker, R. J.; Paull, A.

    1991-01-01

    An expansion tube with a free piston driver has been used to generate quasi-steady hypersonic flows in argon and air at flow velocities in excess of 9 km/s. Irregular test flow unsteadiness has limited the performance of previous expansion tubes, and it has been found that this can be avoided by attention to the interaction between the test gas accelerating expansion and the contact surface in the primary shock tube. Test section measurements of pitot pressure, static pressure and flat plate heat transfer are reported. An approximate analytical theory has been developed for predicting the velocities achieved in the unsteady expansion of the ionizing or dissociating test gas.

  4. Experimental investigation of turbulent flow in smooth and longitudinal grooved tubes

    NASA Technical Reports Server (NTRS)

    Nitschke, P.

    1984-01-01

    Turbulent flow in tubes with and without longitudinal grooves is examined. The discovery of fine grooves forming a sort of streamline pattern on the body of sharks led to the expectation that the grooves on a surface reduce the momentum change, and thus the drag. To test this thesis, drag law, velocity profile and the profile of the velocity fluctuation were determined. Results show that for moderate Reynolds numbers the drag coefficient for grooved tubes is about 3 percent smaller than that of the smooth tubes. At higher Reynolds numbers, however, the drag coefficient for grooved tubes becomes larger than that for smooth tubes. No significant differences in the velocity profiles between grooved tubes and smooth tubes are found.

  5. Tube-in-tube reactor as a useful tool for homo- and heterogeneous olefin metathesis under continuous flow mode.

    PubMed

    Skowerski, Krzysztof; Czarnocki, Stefan J; Knapkiewicz, Paweł

    2014-02-01

    A tube-in-tube reactor was successfully applied in homo- and heterogeneous olefin metathesis reactions under continuous flow mode. It was shown that the efficient removal of ethylene facilitated by connection of the reactor with a vacuum pump significantly improves the outcome of metathesis reactions. The beneficial aspects of this approach are most apparent in reactions performed at low concentration, such as macrocyclization reactions. The established system allows achievement of both improved yield and selectivity, and is ideal for industrial applications. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Numerical Investigation of the Flow Structure in a Kaplan Draft Tube at Part Load

    NASA Astrophysics Data System (ADS)

    Maddahian, R.; Cervantes, M. J.; Sotoudeh, N.

    2016-11-01

    This research presents numerical simulation of the unsteady flow field inside the draft tube of a Kaplan turbine at part load condition. Due to curvature of streamlines, the ordinary two-equations turbulence models fail to predict the flow features. Therefore, a modification of the Shear Stress Transport (SST-SAS) model is utilized to approximate the turbulent stresses. A guide vane, complete runner and draft tube are considered to insure the real boundary conditions at the draft tube inlet. The outlet boundary is assumed to discharge into the atmosphere. The obtained pressure fluctuations inside the draft tube are in good agreement with available experimental data. In order to further investigate the RVR formation and its movement, the λ2 criterion, relating the position of the vortex core and strength to the second largest Eigen value of the velocity gradient tensor, is employed. The method used for vortex identification shows the flow structure and vortex motion inside the draft tube accurately.

  7. Dissipative heating effects and end corrections for viscous Newtonian flow in high shear capillary tube viscometry

    NASA Technical Reports Server (NTRS)

    Jakobsen, J.; Winer, W. O.

    1974-01-01

    The effect of dissipation heating on the apparent viscosity measured in capillary tube viscometry is described in this paper. Conditions of low Reynolds number and high shear are assumed. End corrections to the tube flow are incorporated. The flow curves show decreasing apparent viscosity when the shear stress increases. The configuration of the flow curves plotted in logarithmic presentation are found to be identical for fluids with Newtonian behavior. Convection is the predominant mechanism in removal of the heat in short capillary tube. The estimated upper bound for the shear stress obtainable in short length capillary tubes appears to be of the order of magnitude of 10 MPa limited primarily by the pressure drop associated with the constant end correction from the flat ended inlet and exit of the tube.

  8. Gas flow and thermal mixing in a helically wound tube bundle

    SciTech Connect

    Chiger, H.D.

    1980-07-01

    The thermal dissipation of a hot gas streak flowing across a segment of a helically wound tube bundle and the bypass flow streaming between the tubes and the bundle wall were investigated experimentally in the range of 8000 < Re < 50,000. Two different modes of creating a hot streak were employed. A planar hot streak was (1) injected at the entrance to the tube bundle and (2) generated by electrically heating several tubes past the bundle inlet. In the first case the mixing occurs in a region of lower turbulence since it occurs near the bundle inlet. In the second case the mixing occurs in a region of higher turbulence since the flow has already passed over several tube rows before the hot streak is generated.

  9. Analyzing the effect on heat transfer due to nonuniform distribution of liquid flow among the tubes of a shell-and-tube heat exchanger

    NASA Astrophysics Data System (ADS)

    Zinkevich, A. I.; Sharifullin, V. N.; Sharifullin, A. V.

    2010-09-01

    A method is proposed using which nonuniform distribution of liquid flow among the tubes of a shell-and-tube apparatus can be taken into account by means of a statistical distribution function. A formula showing interrelation of this function with the indicator of heat transfer intensity in the apparatus tube space is given.

  10. Direct numerical simulation of transitional flow in a staggered tube bundle

    NASA Astrophysics Data System (ADS)

    Linton, D.; Thornber, B.

    2016-02-01

    A series of Direct Numerical Simulations (DNS) of the flow through a staggered tube bundle has been performed over the range 1030 ≤ Rem ≤ 5572 to capture the flow transition that occurs at the matrix transition point of Rem ≈ 3000. The matrix transition is the point at which a second frequency becomes prominent in tube bundles. To date, this is the highest published Reynolds number at which a DNS has been performed on cross-flow over a tube bundle. This study describes the flow behaviour in terms of: the mean flow field, Strouhal numbers, vortex shedding, 3-D flow features, and turbulence properties. These results support the hypothesis that the transition in the vortex shedding behaviour at Rem ≈ 3000 is similar to that which occurs in single cylinder flow at the equivalent Reynolds number. The visualisations presented also demonstrate the nature of the shedding mechanisms before and after the matrix transition point.

  11. Interface dynamics of capillary driven flow in a tube

    NASA Astrophysics Data System (ADS)

    Ichikawa, Naoki; Satoda, Yoko; Nakada, Takeshi

    This paper describes the dynamics of a liquid driven by capillary force in a tube. The movement of a gas-liquid interface in a horizontal tube as a result of capillary action has been investigated. A theoretical analysis of the interface dynamics is presented where dimensionless numbers representing time and distance scales are introduced, and a unique functional relation is derived. Experiments were carried out with distilled water as the test liquid in glass tubes of inner diameter from 0.5 mm to 4.0 mm. The position of the gas-liquid interface as a function of time was observed. The experimental results agree well with theory.

  12. Heat transfer and fluid flow behaviors in a five-start spiral corrugated tube

    NASA Astrophysics Data System (ADS)

    Promthaisong, Pitak; Jedsadaratanachai, Withada; Chuwattanakul, Varesa; Eiamsa-ard, Smith

    2017-08-01

    This paper presented a numerical investigation on turbulent periodic flow, heat transfer, pressure loss and thermal enhancement factor in a 3D five-start spiral corrugated tube. Air was used as the working fluids through the tube for Reynolds numbers of about 5000-20,000. In the current studied, the five-start spiral corrugated tube with six relative pitch ratios (p/D, PR=1.0, 1.5, 2.0, 2.5, 3.0 and 3.5) with constant depth ratio (e/D, DR=0.06). The numerical results reveal that the five-start spiral corrugated tube can generated a swirl flow, main swirl flow and five-secondary swirl flow. This behavior lead to the major change of temperature in transverse plane, reduced thermal layer thickness and enhanced heat transfer on the tube wall. The five-start spiral corrugated tube in range investigated provided the heat transfer rate and friction factor up to 2.02 and 6.12 times, respectively, over the straight circular tube. The thermal enhancement factor of the five-start spiral corrugated tube in the range of 0.89-1.16 where its maximum found as the optimum point is at PR=2.0.

  13. Flow and axial dispersion in a sinusoidal-walled tube: Effects of inertial and unsteady flows

    NASA Astrophysics Data System (ADS)

    Richmond, Marshall C.; Perkins, William A.; Scheibe, Timothy D.; Lambert, Adam; Wood, Brian D.

    2013-12-01

    In this work, we consider a sinusoidal-walled tube (a three-dimensional tube with sinusoidally-varying diameter) as a simplified conceptualization of flow in porous media. Direct numerical simulation using computational fluid dynamics (CFD) methods was used to compute velocity fields by solving the Navier-Stokes equations, and also to numerically solve the volume averaging closure problem, for a range of Reynolds numbers (Re) spanning the low-Re to inertial flow regimes, including one simulation at Re=449 for which unsteady flow was observed. The longitudinal dispersion observed for the flow was computed using a random walk particle tracking method, and this was compared to the longitudinal dispersion predicted from a volume-averaged macroscopic mass balance using the method of volume averaging; the results of the two methods were consistent. Our results are compared to experimental measurements of dispersion in porous media and to previous theoretical results for both the low-Re, Stokes flow regime and for values of Re representing the steady inertial regime. In the steady inertial regime, a power-law increase in the effective longitudinal dispersion (DL) with Re was found, and this is consistent with previous results. This rapid rate of increase is caused by trapping of solute in expansions due to flow separation (eddies). One unsteady (but non-turbulent) flow case (Re=449) was also examined. For this case, the rate of increase of DL with Re was smaller than that observed at lower Re. Velocity fluctuations in this regime lead to increased rates of solute mass transfer between the core flow and separated flow regions, thus diminishing the amount of tailing caused by solute trapping in eddies and thereby reducing longitudinal dispersion. The observed tailing was further explored through analysis of concentration skewness (third moment) and its assymptotic convergence to conventional advection-dispersion behavior (skewness = 0). The method of volume averaging was

  14. Measurements and computations of mass flow and momentum flux through short tubes in rarefied gases

    NASA Astrophysics Data System (ADS)

    Lilly, T. C.; Gimelshein, S. F.; Ketsdever, A. D.; Markelov, G. N.

    2006-09-01

    Gas flows through orifices and short tubes have been extensively studied from the 1960s through the 1980s for both fundamental and practical reasons. These flows are a basic and often important element of various modern gas driven instruments. Recent advances in micro- and nanoscale technologies have paved the way for a generation of miniaturized devices in various application areas, from clinical analyses to biochemical detection to aerospace propulsion. The latter is the main area of interest of this study, where rarefied gas flow into a vacuum through short tubes with thickness-to-diameter ratios varying from 0.015 to 1.2 is investigated both experimentally and numerically with kinetic and continuum approaches. Helium and nitrogen gases are used in the range of Reynolds numbers from 0.02 to 770 (based on the tube diameter), corresponding to Knudsen numbers from 40 down to about 0.001. Propulsion properties of relatively thin and thick tubes are examined. Good agreement between experimental and numerical results is observed for mass flow rate and momentum flux, the latter being corrected for the experimental facility background pressure. For thick-to-thin tube ratios of mass flow and momentum flux versus pressure, a minimum is observed at a Knudsen number of about 0.5. A short tube propulsion efficiency is shown to be much higher than that of a thin orifice. The effect of surface specularity on a thicker tube specific impulse was found to be relatively small.

  15. PIV measurement of the vertical cross-flow structure over tube bundles

    NASA Astrophysics Data System (ADS)

    Iwaki, C.; Cheong, K. H.; Monji, H.; Matsui, G.

    Shell and tube heat exchangers are among the most commonly used types of heat exchangers. Shell-side cross-flow in tube bundles has received considerable attention and has been investigated extensively. However, the microscopic flow structure including velocity distribution, wake, and turbulent structure in the tube bundles needs to be determined for more effective designs. Therefore, in this study, in order to clarify the detailed structure of cross-flow in tube bundles with particle image velocimetry (PIV), experiments were conducted using two types of model; in-line and staggered bundles with a pitch-to-diameter ratio of 1.5, containing 20 rows of five 15 mm O.D. tubes in each row. The velocity data in the whole flow field were measured successfully by adjusting the refractive index of the working fluid to that of the tube material. The flow features were characterized in different tube bundles with regards to the velocity vector field, vortex structure, and turbulent intensity.

  16. New understanding of the role of cerebrospinal fluid: offsetting of arterial and brain pulsation and self-dissipation of cerebrospinal fluid pulsatile flow energy.

    PubMed

    Min, Kyung Jay; Yoon, Soo Han; Kang, Jae-Kyu

    2011-06-01

    Many theories have been postulated to date regarding the mechanisms involved in the absorption of the intracranial arterial blood flow energy in the intracranial space, but it is as yet nor clearly defined. The blood flow energy that is transmitted from the heart formulates the cerebrospinal fluid (CSF) pulsatile flow, and is known to constitute the major energy of the CSF flow, while the bulk flow carries only small energy. The intracranial space that is enclosed in a solid cranium and is an isolate system as in the Monroe-Kellie doctrine, and the authors propose to re-analyze the Monroe-Kellie doctrine concept in terms of energy transfer and dissipation of the Windkessel effect. We propose that the large blood flow energy that initiates in the heart is transferred in order of precedence to the arteries, arterioles, brain parenchyma, and finally to CSF within the cranium, in which the energy is confined and unable to be transferred, so that the final transfer of energy to the CSF pulsatile flow is self-dissipated in terms of direction and chronology in CSF pulsatile flow. In order for the CSF pulsatile flow that is transferred from arterial blood flow energy to be dissipated in the intracranial space, this cannot be explained with bulk flow energy in any perspective, since the pulsatile flow kinetic energy is greater than the bulk flow kinetic energy by at least a 100-fold. The pulsatile flow energy within the closed intracranial space cannot be transferred and is confined, as postulated by the Monroe-Kellie doctrine, and therefore the authors propound that the pulsatile flow dissipates by itself. The dissipation of the CSF pulsatile flow kinetic energy will be in all directions in a diffuse and random manner, and is offset by the CSF flow energy vector due to the CSF mixing process. Such energy dissipation will lead to maintenance of low CSF flow energy, which will result in maintaining low intracranial pressure (ICP), and sufficient brain perfusion. It is our

  17. TWO-PHASE FLOW OF TWO HFC REFRIGERANT MIXTURES THROUGH SHORT-TUBE ORIFICES

    EPA Science Inventory

    The report gives results of an experimental investigation to develop an acceptable flow model for short tube orifice expansion devices used in heat pumps. The refrigerants investigated were two hydrofluorocarbon (HFC) mixtures considered hydrochlorofluorocarbon (HCFC)-22 replacem...

  18. Computational model for the transition from peristaltic to pulsatile flow in the embryonic heart tube.

    PubMed

    Taber, Larry A; Zhang, Jinmei; Perucchio, Renato

    2007-06-01

    Early in development, the heart is a single muscle-wrapped tube without formed valves. Yet survival of the embryo depends on the ability of this tube to pump blood at steadily increasing rates and pressures. Developmental biologists historically have speculated that the heart tube pumps via a peristaltic mechanism, with a wave of contraction propagating from the inflow to the outflow end. Physiological measurements, however, have shown that the flow becomes pulsatile in character quite early in development, before the valves form. Here, we use a computational model for flow though the embryonic heart to explore the pumping mechanism. Results from the model show that endocardial cushions, which are valve primordia arising near the ends of the tube, induce a transition from peristaltic to pulsatile flow. Comparison of numerical results with published experimental data shows reasonably good agreement for various pressure and flow parameters. This study illustrates the interrelationship between form and function in the early embryonic heart.

  19. Velocity and shear rate estimates of some non-Newtonian oscillatory flows in tubes

    NASA Astrophysics Data System (ADS)

    Kutev, N.; Tabakova, S.; Radev, S.

    2016-10-01

    The two-dimensional Newtonian and non-Newtonian (Carreau viscosity model used) oscillatory flows in straight tubes are studied theoretically and numerically. The corresponding analytical solution of the Newtonian flow and the numerical solution of the Carreau viscosity model flow show differences in velocity and shear rate. Some estimates for the velocity and shear rate differences are theoretically proved. As numerical examples the blood flow in different type of arteries and the polymer flow in pipes are considered.

  20. Simulation and System Analysis of Flow Pulsation at Normal and Emergency for Advanced On-line Monitoring and Control of NPP

    SciTech Connect

    Proskouriakov, K.N.; Moukhine, V.S.

    2002-07-01

    In addition to investigation of thermal-hydraulic processes on NPP with use of computer codes the new system analysis of flow pulsation is worked out. System analysis shows that properties of heat rejection circuits of NPP as oscillatory system are not equal the sum of properties of its separate elements but gives the new properties which must be taken into account. Methods have been worked out for calculating and identifying the sources of thermal-hydraulic disturbances are intended to improve the means of early diagnostics of anomalies in the technological process, to forecast their development, to improve the efficiency of overhauling operations and safety in operation, and also to create advanced on-line monitoring and control of NPP. Conception of the control system development presents. Proposal for main topics R and D areas for advanced NPP monitoring, diagnostic and control are identified. (authors)

  1. Two-phase flow of HFC-134a and CFC-12 through short-tube orifices

    SciTech Connect

    Kim, Y.; O`Neal, D.L.; Yuan, X.

    1994-12-31

    Short-tube orifices have been widely used as an expansion device on automotive and residential-sized air conditioners in the United States. The design for optimum performance of these systems requires predicting correct flow characteristics through short tubes for a given set of operating conditions. Insufficient data are available on how any of the new replacement refrigerants will perform in short-tube orifices relative to conventional refrigerants. This paper compares experimental mass flow results with HFC-134a and CFC-12 for a variety of inlet conditions and short-tube geometries. Five sharp-edged short-tube orifices with 7 < LID < 20 and 1.10 mm (0.0435 in.) < D < 1.72 mm (0.0676 in.) were tested with HFC-134a and CFC-12. Both two-phase and subcooled liquid flow conditions entering the short tube were examined for condensing temperatures ranging from 35.4 C (96 F) to 53.8 C (129 F), for subcooling as high as 13.9 C (25 F), and for qualities as high as 10% at the inlet of the short tube. The effects of downstream pressure were also investigated by lowering the downstream pressure from the upstream saturation pressure down to 310 kPa (45 psia). For HFC-134a, two types of measurements were made during this study-mass flow tests and pressure distribution inside the orifice. For CFC-12, only mass flow tests were performed The results with CFC-12 were compared with those of HFC-134a with the same upstream temperature conditions. A comparison of these two refrigerants was made as a function of the main operating variables (upstream pressure, subcooling, and downstream pressure) and short-tube geometry. Semi-empirical models for both HFC-134a and CFC-12 were developed for the prediction of mass flow rate through short tubes.

  2. Effects of airfoil-probe tubes on the flow field of a compressor cascade

    NASA Astrophysics Data System (ADS)

    Ma, Hongwei; Jin, Chao; Zhao, Lianpeng; Ma, Rong

    2017-08-01

    To explore the effects of airfoil-probe tubes and its installment position on the flow field of the compressor cascade, and find out the mechanism that how the airfoil-probes affect the aerodynamic characteristics of the compressor cascade, this paper performed both numerical and experimental works on the same compressor cascade. The experiment mainly focused on the cases of low Mach number (Ma = 0.1), and cases with different Mach numbers (0.1, 0.3, 0.7) and different incidence angles (-5, 0, 5) are investigated by the numerical method. The case without the airfoil-probe tube was referenced as the baseline, and other three cases with the airfoil-probe tubes installed in different chordwise positions (30%, 50%, 70% of the chord length) were studied. The diameter of the airfoil-probe tube is 3mm, which is configured as 300% amplification of some particular airfoil-probe according to the geometrical similarity principle. The results show that the airfoil-probe tubes have a negative influence on the flow capacity of the cascade at all investigation points. The separations and the large scale streamwise vortices that induced by the airfoil-probe tube on the pressure side cause most the losses at the high Mach number. The influence of the airfoil-probe tube on the flow field in the vicinity of the pressure side surface is local separation at the low Mach number. The airfoil-probe tubes also have a clearly effect on the leakage flow. It decreases the mass flow of the leakage flow and weakens the intensity of the leakage vortex, but enlarges the influence area. The total pressure loss of the case that the tube is installed at the half chordwise position is generally lower than other cases especially at the high Mach number, it can even decrease the losses compared with the basic case.

  3. Analysis of flow parameters of a Newtonian fluid through a cylindrical collapsible tube.

    PubMed

    Kanyiri, Caroline W; Kinyanjui, Mathew; Giterere, Kang'ethe

    2014-01-01

    In this research study, fluid flow through a cylindrical collapsible tube has been investigated. Of particular interest is the effect of flow parameters on the cross sectional area of a collapsible tube, flow velocity and internal pressure of the fluid. The flow parameters considered are longitudinal tension and volumetric flow rate. The tube is considered collapsible in the transverse direction, taken to be perpendicular to the main flow direction. Collapse happens when external pressure exceeds internal pressure and hence the tube results to a highly noncircular cross sectional area. The fluid flow in consideration is steady and incompressible. Equations governing the flow are non-linear and cannot be solved analytically. Therefore an approximate solution to the equations has been determined numerically. In this case, finite difference method has been used. A computer program has then been used to generate the results which are presented in form of graphs. The results show that the longitudinal tension is directly proportional to both the cross sectional area and internal pressure and inversely proportional to the flow velocity and that change in volumetric flow rate has no effect on the cross sectional area but it is directly proportional to the flow velocity and inversely proportional to the internal pressure.

  4. Riemannian geometry of twisted magnetic flux tubes in almost helical plasma flows

    SciTech Connect

    Garcia de Andrade, L.C.

    2006-02-15

    Riemannian geometry of curves applied recently by Ricca [Fluid Dyn. Res 36, 319 (2005)] in the case of inflectional disequilibrium of twisted magnetic flux tubes is used here to compute the magnetic helicity force-free field case. Here the application of Lorentz force-free to the magnetic flux tube in tokamaks allows one to obtain an equation that generalizes the cylindrical tokamak equation by a term that contains the curvature of the magnetic flux tube. Another example of the use of the magnetic flux tube is done by taking the electron magnetohydrodynamics (MHD) fluid model (EMHD) of plasma physics that allows one to compute the velocity of the fluid in helical and almost helical flows in terms of the Frenet torsion of thin magnetic flux tubes. The cases of straight and curved twisted tubes are examined. Second-order effects on the Frenet torsion arise on the poloidal component of the magnetic field, while curvature effects appear in the toroidal component. The magnetic fields are computed in terms of the penetration depth used in superconductors. The ratio between poloidal and toroidal components of the magnetic field depends on the torsion and curvature of the magnetic flux tube. It is shown that the rotation of the almost helical plasma flow contributes to the twist of the magnetic flux tube through the total Frenet torsion along the tube.

  5. Experimental investigation of the draft tube inlet flow of a bulb turbine

    NASA Astrophysics Data System (ADS)

    Vuillemard, J.; Aeschlimann, V.; Fraser, R.; Lemay, S.; Deschênes, C.

    2014-03-01

    In the BulbT project framework, a bulb turbine model was studied with a strongly diverging draft tube. At high discharge, flow separation occurs in the draft tube correlated to significant efficiency and power drops. In this context, a focus was put on the draft tube inlet flow conditions. Actually, a precise inlet flow velocity field is required for comparison and validation purposes with CFD simulation. This paper presents different laser Doppler velocimetry (LDV) measurements at the draft tube inlet and their analysis. The LDV was setup to measure the axial and circumferential velocity on a radius under the runner and a diameter under the hub. A method was developed to perform indirect measurement of the mean radial velocity component. Five operating conditions were studied to correlate the inlet flow to the separation in the draft tube. Mean velocities, fluctuations and frequencies allowed characterizing the flow. Using this experimental database, the flow structure was characterized. Phase averaged velocities based on the runner position allowed detecting the runner blade wakes. The velocity gradients induced by the blade tip vortices were captured. The guide vane wakes was also detected at the draft tube inlet. The recirculation in the hub wake was observed.

  6. Evaluation of hydro-mechanical pulsation for rocket injector research

    NASA Astrophysics Data System (ADS)

    Wilson, Matthew B.

    The Propulsion Research Center at the University of Alabama in Huntsville has designed and built a hydro-mechanical pulsator to simulate the pressure fluctuations created by high frequency combustion instability. The pressure response characteristics were evaluated in an atmospheric test rig using filtered de-ionized water as the working fluid. The outlet of the pulsator was connected to a swirl injector post to provide downstream flow resistance. Previous low pressure and mass flow experimental data revealed a complex relationship between the control parameters and the pulsation response. For each test, the average mass flow rates of the waste water, water lost through the seals, and injector mass flow rates are measured. A dynamic pressure transducer at the pulsator exit measures and records the pressure waveform. Pulsation magnitude, reliability, repeatability, pulsation effects, and detailed variable control are examined. The data shows the pulsator is capable of generating 30% pulsation at 1575 Hz input. The repeatability of the pulsator is questionable because the standard deviations exceeded 40% of the average. The detailed data obtained during this research provides is sufficient to develop a pulsator tuning procedure for future applications.

  7. Reactions of Ions with Ionic Liquid Vapors by Selected-Ion Flow Tube Mass Spectrometry

    DTIC Science & Technology

    2011-03-04

    similar to one we have used for sulfuric acid. 21 A ¼” glass tube is wrapped with insulated heating wire in two zones, a short one near the tip and a...steel shim connected to ground. Glass wool is inserted inside the length of the glass tube and a small amount of ionic liquid is distributed...throughout the glass wool by syringe injection. Helium flush gas of up to 145 sccm is used to transport the ionic liquid to the flow tube, and a He flow

  8. Pressure drop and temperature rise in He II flow in round tubes, Venturi flowmeters and valves

    NASA Technical Reports Server (NTRS)

    Walstrom, P. L.; Maddocks, J. R.

    1988-01-01

    Pressure drops in highly turbulent He II flow were measured in round tubes, valves, and Venturi flowmeters. Results are in good agreement with single-phase flow correlations for classical fluids. The temperature rise in flow in a round tube was measured, and found to agree well with predictions for isenthalpic expansion. Cavitation was observed in the venturis under conditions of low back pressure and high flow rate. Metastable superheating of the helium at the venturi throat was observed before the helium made a transition to saturation pressure.

  9. Investigation of an anomalous flow condition of the Langley pilot model expansion tube

    NASA Technical Reports Server (NTRS)

    Friesen, W. J.

    1974-01-01

    Free-stream flow velocity measurements were made in the Langley pilot model expansion tube during the test flow interval. During this interval, an anomalous dip in pitot pressure occurs for the expansion tube operating conditions employed. Within the test flow interval, the main conclusions reached from comparison of the measured flow velocity, pitot pressure, and tube wall pressure are: the variations which occur in velocity and wall pressure are small compared with the variations in pitot pressure; a corresponding dip in the derived flow density is associated with the dip in pitot pressure; and the value of the average density over the interval, which results from the expansion from the shocked intermediate chamber condition, is approximately one-half of the value that can result from only an isentropic process.

  10. Air-water two-phase flow in a 3-mm horizontal tube

    NASA Astrophysics Data System (ADS)

    Chen, Ing Youn; Chang, Yu-Juei; Wang, Chi-Chung

    2000-01-01

    Two-phase flow pattern and friction characteristics for air-water flow in a 3.17 mm smooth tube are reported in this study. The range of air-water mass flux is between 50 to 700 kg/m2.s and gas quality is between 0.0001 to 0.9. The pressure drop data are analyzed using the concept of the two-phase frictional multipliers and the Martinelli parameter. Experimental data show that the two-phase friction multipliers are strongly related to the flow pattern. Taitel & Dukler flow regime map fails to predict the stratified flow pattern data. Their transition lines between annular-wavy and annular-intermittent give fair agreement with data. A modified correlation from Klimenko and Fyodoros criterion is able to distinguish the annular and stratified data. For two-phase flow in small tubes, the effect of surface tension force should be significantly present as compared to gravitational force. The tested empirical frictional correlations couldn't predict the pressure drop in small tubes for various working fluids. It is suggested to correlate a reliable frictional multiplier for small horizontal tubes from a large database of various working fluids, and to develop the flow pattern dependent models for the prediction of two-phase pressure drop in small tubes. .

  11. The influence of tripwires on the stability of tube bundles subjected to cross-flow

    SciTech Connect

    Romberg, O.; Popp, K.

    1996-12-01

    In heat exchanger tube arrays subjected to cross flow fluidelastic instability is a dangerous excitation mechanism. This paper reports on experimental investigations concerning the influence of disturbed flow on the stability behavior of normal and rotated triangular tube arrays of different pitch-to-diameter ratios as well as to in-line square arrays. The excitation is due to air cross flow in a wind tunnel. The experimental apparatus allows to measure the stability boundaries of fully flexible bundles as well as single flexibly mounted tubes with variable equilibrium position in otherwise fixed arrays as a function of the mass-damping parameter {delta}{sub r} and the reduced gap velocity V{sub r}. A disturbance of the flow channels between the tubes is achieved by application of thin Prandtl-tripwires with a diameter of 1/80 of tube diameter on the top and the bottom of each tube. This leads in most of the cases to a shift of the stability boundaries often to higher reduced gap velocities or even to stability in the entire parameter region, depending on the bundle configuration and equilibrium position. To understand these effects a simultaneous flow visualization based on the laser-light-sheet procedure has been carried out.

  12. Heat Exchange Between a Liquid Flowing in a Tube and an External Flow Around it with Intense Stirring

    NASA Astrophysics Data System (ADS)

    Moshinskii, A. I.

    2014-11-01

    A mathematical model of heat exchange between a tube (a coil) with a liquid flowing inside it and an external flow around it is considered. Limiting equations of the process with intense stirring are derived. Some solutions of the proposed equations are obtained that can be used in modeling the processes occurring in heat exchangers.

  13. Kinetic theory and turbulent discontinuities. [shock tube flow

    NASA Technical Reports Server (NTRS)

    Johnson, J. A., III; I, L.; Li, Y.; Ramaian, R.; Santigo, J. P.

    1981-01-01

    Shock tube discontinuities were used to test and extend a kinetic theory of turbulence. In shock wave and contact surface fluctuations, coherent phenomena were found which provide new support for the microscopic nonempirical approach to turbulent systems, especially those with boundary layer-like instabilities.

  14. Numerical study on coupled fluid flow and heat transfer process in parabolic trough solar collector tube

    SciTech Connect

    Tao, Y.B.; He, Y.L.

    2010-10-15

    A unified two-dimensional numerical model was developed for the coupled heat transfer process in parabolic solar collector tube, which includes nature convection, forced convection, heat conduction and fluid-solid conjugate problem. The effects of Rayleigh number (Ra), tube diameter ratio and thermal conductivity of the tube wall on the heat transfer and fluid flow performance were numerically analyzed. The distributions of flow field, temperature field, local Nu and local temperature gradient were examined. The results show that when Ra is larger than 10{sup 5}, the effects of nature convection must be taken into account. With the increase of tube diameter ratio, the Nusselt number in inner tube (Nu{sub 1}) increases and the Nusselt number in annuli space (Nu{sub 2}) decreases. With the increase of tube wall thermal conductivity, Nu{sub 1} decreases and Nu{sub 2} increases. When thermal conductivity is larger than 200 W/(m K), it would have little effects on Nu and average temperatures. Due to the effect of the nature convection, along the circumferential direction (from top to down), the temperature in the cross-section decreases and the temperature gradient on inner tube surface increases at first. Then, the temperature and temperature gradients would present a converse variation at {theta} near {pi}. The local Nu on inner tube outer surface increases along circumferential direction until it reaches a maximum value then it decreases again. (author)

  15. Dynamic and Stagnating Plasma Flow Leading to Magnetic-Flux-Tube Collimation

    NASA Astrophysics Data System (ADS)

    You, Setthivoine

    2006-10-01

    This talk presents experimental observations, first reported by You, Yun, Bellan in PRL (art. 045002, 2005), strongly supporting the ``MHD pump-collimation'' model proposed by Bellan in Phys. Plasmas (vol. 10, p.1999, 2003). Collimated, plasma-filled, magnetic flux tubes are observed over a tremendous range of scales. In laboratory plasmas, on the surface of the Sun, or jetting out of galactic cores, these flux tubes are extremely collimated, with cross-sections that do not vary much along the length of the tube even in the absence of external magnetic fields or any significant ambient medium pressure. Furthermore, these flux tubes are not in static equilibrium but exhibit strong plasma flows on a rapid time-scale compared to their overall motion within their surroundings. The Caltech experiment simulates magnetically-driven astrophysical jets at the laboratory scale by imposing boundary conditions analogous to astrophysical jet boundary conditions and with plasma dimensionless numbers comparable to numerical MHD simulations. Observations show a distinct sequence of events. The initial flux tubes flare out into the large vacuum, because the magnetic field weakens away from the source. As electrical current flows, the flux tubes become denser and more collimated while sucking plasma from gas sources at the system boundary, effectively acting like a magnetohydrodynamic pump. These flux tubes then merge together into a single column which jets out into the vacuum. The jet continues the same pumping process, to become even denser and more collimated, until either the electrical current or the supply of particles stop. The strong plasma flow convects frozen-in magnetic flux to regions of weaker magnetic field at the end of the tube, and as the flow stagnates there, magnetic flux piles up, pinching the tube into a collimated filament.

  16. Gas-liquid pipe flow under microgravity conditions: influence of tube diameter on flow patterns and pressure drops

    NASA Astrophysics Data System (ADS)

    Colin, C.; Fabre, J.

    1995-08-01

    Gas-liquid flow experiments have been performed in small tubes of 19 mm, 10 mm and 6 mm diameter, during parabolic flights, for a range of superficial liquid velocities from 0.1 to 2 m/s and superficial gas velocities from 0.05 m/s to 10 m/s. Results are compared to those previously obtained by Colin et al., /1/, in a 40 mm i.d. tube. The flow patterns identified are: bubbly flow, slug flow and a pattern halfway between slug and annular flows. The main difference between the experiments in small tubes and the previous ones, concerns the transition between bubbly flow and slug flow, the role of coalescence and the wall friction factor. Coalescence is shown to play a major role in the transition from bubbly to slug flow. In particular at small Reynolds number coalescence seems to be partly inhibited. Single-phase flow correlations for wall shear stress underestimate the wall friction factor in the intermediate range of Reynolds number between laminar and turbulent flow.

  17. Numerical Simulation of Two-Phase Critical Flow with the Phase Change in the Nozzle Tube

    NASA Astrophysics Data System (ADS)

    Ishigaki, Masahiro; Watanabe, Tadashi; Nakamura, Hideo

    Two-phase critical flow in the nozzle tube is analyzed numerically by the best estimate code TRACE and the CFD code FLUENT, and the performance of the mass flow rate estimation by the numerical codes is discussed. For the best estimate analysis by the TRACE code, the critical flow option is turned on. The mixture model is used with the cavitation model and the evaporation-condensation model for the numerical simulation by the FLUENT code. Two test cases of the two-phase critical flow are analyzed. One case is the critical flashing flow in a convergent-divergent nozzle (Super Moby Dick experiment), and the other case is the break nozzle flow for a steam generator tube rupture experiment of pressurized water reactors at Large Scale Test Facility of Japan Atomic Energy Agency. The calculation results of the mass flow rates by the numerical simulations show good agreements with the experimental results.

  18. Detailed flow and force measurements in a rotated triangular tube bundle subjected to two-phase cross-flow

    NASA Astrophysics Data System (ADS)

    Pettigrew, M. J.; Zhang, C.; Mureithi, N. W.; Pamfil, D.

    2005-05-01

    Two-phase cross-flow exists in many shell-and-tube heat exchangers. A detailed knowledge of the characteristics of two-phase cross-flow in tube bundles is required to understand and formulate flow-induced vibration parameters such as damping, fluidelastic instability, and random excitation due to turbulence. An experimental program was undertaken with a rotated-triangular array of cylinders subjected to air/water flow to simulate two-phase mixtures. The array is made of relatively large diameter cylinders (38 mm) to allow for detailed two-phase flow measurements between cylinders. Fiber-optic probes were developed to measure local void fraction. Local flow velocities and bubble diameters or characteristic lengths of the two-phase mixture are obtained by using double probes. Both the dynamic lift and drag forces were measured with a strain gauge instrumented cylinder.

  19. Development of a compact laminar flow heat exchanger with stainless steel micro-tubes

    NASA Astrophysics Data System (ADS)

    Saji, N.; Nagai, S.; Tsuchiya, K.; Asakura, H.; Obata, M.

    2001-05-01

    The present paper describes the design concept and manufacturing of a new compact laminar flow heat exchanger with stainless-steel micro-tubes for helium refrigerators. In the temperature range of less than 20 K, aluminum plate fin type heat exchangers exhibit a remarkable fall of performance characteristics as a compact heat exchanger. We presented in a previous paper that some compact heat exchangers with good performance in the temperature range of less than 4 K are required for a subcooled He II refrigerator cycle to be worked with 3He turbo-compressors (F. Doty, et al., A new look at the closed brayton cycle, Proceedings, IECEC-90 Reno, NV, 1991, p. 116). For this requirement, we developed a micro-tube strip counter flow type heat exchanger, which consists of 12 elements with a total of 4800 stainless steel micro-tubes. Each element is formed with 400 tubes and a newly developed vacuum brazing method was applied for the bonding to the side plate. Each tube has an inner diameter of 0.5 mm, an outer diameter of 0.7 mm and is 310 mm long. We developed a cladding plate with two layers of gold brazing sheet sandwiched inside. In aerodynamic and thermal design of the element, the laminar flow conditions were adopted for the flows of inner and outer tubes to keep a high heat transfer rate and a low pressure loss.

  20. A file of red blood cells in tube flow: A three-dimensional numerical study

    NASA Astrophysics Data System (ADS)

    Ye, Ting; Phan-Thien, Nhan; Khoo, Boo Cheong; Lim, Chwee Teck

    2014-09-01

    The rheology of a file of red blood cells (RBCs) in a tube flow is investigated based on a three-dimensional (3D) computational model using the dissipative particle dynamics (DPD) method. The 3D model consists of a discrete RBC model to describe the RBC deformation, a Morse potential model to characterize the cell-cell interaction, and a DPD model to provide all the relevant information on the suspension flow. Three important features of the suspension flow are simulated and analyzed, (i) the effect of the tube hematocrit, (ii) the effect of the cell spacing, and (iii) the effect of the flow velocity. We first study the cell deformation and the rheology of suspension at different tube hematocrit. The results show that the cell deformation decreases with increasing tube hematocrit, and a good agreement between the simulation and available experiments is found for the discharge hematocrit and relative apparent viscosity of RBC suspension. We then analyze the effect of non-uniform cell spacing, where the cell-cell interaction goes into effect, showing that a non-uniform cell spacing has a slight effect on the cell deformation, and almost has no effect on the rheology of suspension. We finally study the effect of the flow velocity and show that a typical plug-flow velocity profile is observed. The results also show that the cell deformation increases with increasing flow velocity, as expected. The discharge hematocrit also increases, but the relative apparent viscosity decreases, with increasing flow velocity.

  1. Active Learning in Fluid Mechanics: Youtube Tube Flow and Puzzling Fluids Questions

    ERIC Educational Resources Information Center

    Hrenya, Christine M.

    2011-01-01

    Active-learning exercises appropriate for a course in undergraduate fluid mechanics are presented. The first exercise involves an experiment in gravity-driven tube flow, with small groups of students partaking in a contest to predict the experimental flow rates using the mechanical energy balance. The second exercise takes the form of an…

  2. Active Learning in Fluid Mechanics: Youtube Tube Flow and Puzzling Fluids Questions

    ERIC Educational Resources Information Center

    Hrenya, Christine M.

    2011-01-01

    Active-learning exercises appropriate for a course in undergraduate fluid mechanics are presented. The first exercise involves an experiment in gravity-driven tube flow, with small groups of students partaking in a contest to predict the experimental flow rates using the mechanical energy balance. The second exercise takes the form of an…

  3. Thermodynamic Analysis and Optimization Based on Exergy Flow for a Two-Staged Pulse Tube Refrigerator

    DTIC Science & Technology

    2010-01-01

    includes flow conductance, heat transfer effectiveness, and conduction heat transfer parameters for regenerators in both stages. It is assumed that...performance of the refrigerator. The effects of the allocation of the values of flow conductance and ineffectiveness parameters in the regenerators ...irreversibility in the regenerators , is developed and discussed. KEYWORDS: Exergy analysis, Multi-stage, Cryocoolers, Pulse tubes, Irreversibility 113

  4. Liquid circulation in a stirred system with an axial flow impeller and a cylindrical draft tube

    NASA Astrophysics Data System (ADS)

    Fořt, Ivan; Vlček, Petr; Jirout, Tomáš

    2017-07-01

    This study deals with a CFD simulation of the turbulent flow of a homogeneous liquid in a cylindrical stirred system with a pitched-blade impeller and a cylindrical draft tube. Design of investigated pilot plant equipment corresponds to the shape of agitated crystallizer with a draft tube - additional cooling heat exchanger. The results of the computation are expressed by means of the circulation pattern of a stirred liquid and the main flow characteristics of the system - the flow rate numbers and the impeller power number.

  5. Numerical simulation of pressure pulsations in Francis turbines

    NASA Astrophysics Data System (ADS)

    Magnoli, M. V.; Schilling, R.

    2012-11-01

    In the last decades, hydraulic turbines have experienced the increase of their power density and the extension of their operating range, leading the fluid and mechanical dynamic effects to become significantly more pronounced. The understanding of the transient fluid flow and of the associated unsteady effects is essential for the reduction of the pressure pulsation level and improvement of the machine dynamic behaviour. In this study, the instationary fluid flow through the complete turbine was numerically calculated for an existing Francis machine with high specific speed. The hybrid turbulence models DES (detached eddy simulation) and SAS (scale adaptive simulation) allowed the accurate simulation of complex dynamic flow effects, such as the rotor-stator-interaction and the draft tube instabilities. Different operating conditions, as full load, part load, higher part load and deep part load, were successfully simulated and showed very tight agreement with the experimental results from the model tests. The transient pressure field history, obtained from the CFD (computational fluid dynamics) simulation and stored for each time step, was used as input for the full instationary FEA (finite element analysis) of turbine components. The assessment of the machine dynamic motion also offered the possibility to contribute to the understanding of the pressure pulsation effects and to further increase the turbine stability. This research project was developed at the Institute of Fluid Mechanics of the TU München.

  6. Interaction of heat transfer and gas flow in a vertical hot tube

    NASA Astrophysics Data System (ADS)

    Abolpour, Bahador; Afsahi, M. Mehdi; Yaghobi, Mohsen; Goharrizi, Ataallah Soltani; Azizkarimi, Mehdi

    2017-02-01

    One of the main interests in industries, especially metallurgical industries, is improving the overall rate of the processes. A solution for this issue in the processes including gas phase (such as gas-solid reactions) is operating at high temperature. Mechanism of heat transfer to the gas phase at this condition is complex regarding effect of temperature on the gas properties. In this study, interaction of heat transfer and gas flow in a vertical hot tube has been investigated, experimentally and numerically. Finally, effects of inlet volumetric flow rate, gaseous type, extent of the tube wall heat flux and tube diameter on temperature and velocity distributions of the gaseous phase inside the tube have been studied.

  7. Interaction of heat transfer and gas flow in a vertical hot tube

    NASA Astrophysics Data System (ADS)

    Abolpour, Bahador; Afsahi, M. Mehdi; Yaghobi, Mohsen; Goharrizi, Ataallah Soltani; Azizkarimi, Mehdi

    2017-07-01

    One of the main interests in industries, especially metallurgical industries, is improving the overall rate of the processes. A solution for this issue in the processes including gas phase (such as gas-solid reactions) is operating at high temperature. Mechanism of heat transfer to the gas phase at this condition is complex regarding effect of temperature on the gas properties. In this study, interaction of heat transfer and gas flow in a vertical hot tube has been investigated, experimentally and numerically. Finally, effects of inlet volumetric flow rate, gaseous type, extent of the tube wall heat flux and tube diameter on temperature and velocity distributions of the gaseous phase inside the tube have been studied.

  8. A numerical study of steady flow through a curved tube with wavy walls

    NASA Astrophysics Data System (ADS)

    Prince, Chekema; Gu, Mingyao; Peterson, Sean

    2011-11-01

    Flow through curved tubes has been studied for nearly a century owing to the practical industrial applications and general academic interest. More recently, interest in curved tubes has resurfaced due to the ubiquity of curvature in the vasculature and the resulting need to accurately model arterial vessels. Previous studies have focused primarily on circular cross sections and the roles of the Dean number and curvature ratio on the flow physics. In this study we examine the effect of wavy walls, that is, axially aligned ribs extending the length of the tube, on steady flow through mildly and finite curved tubes using computational fluid dynamics. Analytical work on the subject has been limited to low Dean numbers and small bump heights, thus we primarily focus on the impact of higher Dean number with large protrusions on the flow physics. The results are compared with those in circular cross section tubes at the same Dean number. Particular attention is paid to flow characteristics of interest in the vasculature, such as wall shear stress, that have been shown to stimulate biochemical pathways that trigger cell growth.

  9. Measurement and analysis of energy flow in Stirling-type pulse tube refrigerator

    NASA Astrophysics Data System (ADS)

    Ki, Taekyung; Jeong, Sangkwon; Seo, Mansu; Park, Inmyong

    2012-06-01

    The analysis of energy flow is a useful method for understanding a system. This paper focuses on the instantaneous measurement of physical conditions and analysis of energy flow in the Stirling-type pulse tube refrigerator. For measuring physical conditions of the working fluid such as the mass flow rate, the temperature, and the pressure, several cryogenic sensors are installed in the Stirling-type pulse tube refrigerator optimally designed in the operating condition of 60 Hz and 2.5 MPa. The physical conditions of the working fluid in the Stirling-type pulse tube refrigerator are carefully measured as varying the operating frequency and the charging pressure. From the measured results, the enthalpy, the PV work, and the loss are quantified in each location of the PTR and the conversion of energy flows is experimentally confirmed. The results of this paper can be used for understanding the optimal operating condition and modifying correlations of various losses in the Stirling-type pulse tube refrigerator. KEYWORDS: Energy flow, Loss, Pulse tube refrigerator

  10. Effects of the geometry of the exit of a tube in an oscillating flow

    NASA Astrophysics Data System (ADS)

    Echeverría, Elia; Málaga, Carlos; Czitrom, Steven; Olvera, Arturo; Stern, Catalina

    2014-11-01

    The problem of optimizing the performance of a wave-driven seawater pump - comprising a resonant duct and an exhaust duct joined by a variable volume air-compression chamber - it is explored by studying oscillating flows at the exit of a tube. It is known that the performance of this pump depends on the geometry of the mouth of its intake tube. An inspection of the integral expression of the Navier-Stokes equation along a central streamline of this flow shows that changing the shape of the tube's mouth modifies only the inertia and energy losses terms because both depend on the flow field at the chosen streamline. These changes must be such that the integral relation is preserved. Therefore, by measuring the inertial term (known as added mass), the term for losses can be measured indirectly. We developed a method to measure the added mass for oscillating flows in tubes with different mouth shapes and compared these measurements with those obtained for a model of the flow through the pump. Our results suggest a way to find a criterion for choosing the geometry of the mouth of the tubes in order to minimize dissipation and improve efficiency of the pump. This work was supported by funds provided by DGAPA-UNAM (Project PAPITT-IN1188608).

  11. Investigation on internal flow of draft tube at overload condition in low specific speed Francis turbine

    NASA Astrophysics Data System (ADS)

    Tamura, Yuta; Tani, Kiyohito

    2016-11-01

    The cavitating vortices causes the unsteady phenomena like the pressure fluctuation, the noise and the vibration in the draft tube at the overload condition which is the far operating point from the design point. Because the full load was normally near the design point, there were few troubles due to cavitating vortices at the full load. Today, however, the design point is sometimes set to lower load to achieve the high efficiency from the partial load to the full load in low specific speed Francis turbines, which have good performance to a change in a discharge. Then, the full load is relatively further from the design point. As the result, the potential for the cavitating vortices at the full load is increased. To control of the unsteady phenomena at the full load, the study focused on the cavitating vortices at the overload condition is important. This paper presents the unsteady behavior of the cavitating vortices at the overload condition with the scaled model of specific speed NQE=0.083. On the experimental approach, the pressure pulsation in the upper draft tube was measured and the unsteady behavior of cavitating vortices was taken movies with a high speed camera. On the numerical approach, Computational Fluid Dynamics (CFD) adopting a two-phase unsteady analysis was carried out. The pressure fluctuation and the velocity distribution of two runners, an original and a newly designed, were compared.

  12. Conveyor belt effect in the flow through a tube of a viscous fluid with spinning particles.

    PubMed

    Felderhof, B U

    2012-04-28

    The extended Navier-Stokes equations describing the steady-state hydrodynamics of a viscous fluid with spinning particles are solved for flow through a circular cylindrical tube. The flow caused by an applied torque density in the azimuthal direction and linear in the radial distance from the axis is compared with the flow caused by a uniform applied force density directed along the axis of the tube. In both cases the flow velocity is of Poiseuille type plus a correction. In the first case the flow velocity is caused by the conveyor belt effect of spinning particles. The corrections to the Poiseuille flow pattern in the two cases differ only by a proportionality factor. The spin velocity profiles in the two cases are also proportional.

  13. Effect of flow rate and insulin priming on the recovery of insulin from microbore infusion tubing.

    PubMed

    Fuloria, M; Friedberg, M A; DuRant, R H; Aschner, J L

    1998-12-01

    A retrospective medical record review of 13 consecutive, hyperglycemic, extremely low birth weight (ELBW) infants treated with continuous insulin infusions revealed a 14- to 24-hour delay (mean, 19 hours) in blood glucose normalization despite stepwise increases in insulin infusion rates. This in vitro study examined the effects of flow rate and insulin priming on insulin recovery from polyvinyl chloride (PVC) tubing and polyethylene (PE)-lined PVC tubing infused with a standard insulin stock solution. Stock insulin solution (0.2 U/mL) was infused through microbore PVC or PE-lined tubing at flow rates of 0.05 and 0.2 mL/h. To determine if saturation of nonspecific binding sites would alter effluent insulin concentration, we compared insulin recovery from tubing previously flushed with the stock solution and tubing primed with 5 U/mL of insulin for 20 minutes. Effluent samples, which were collected at baseline and at six time points during a 24-hour period, were immediately frozen at -20 degreesC. Insulin concentration was measured by IMx immunoassay. Data were analyzed using general linear modeling with repeated measures. At 0.05 mL/h flow rate, insulin recovery from unprimed PVC tubing at 1, 2, 4, and 8 hours was 17%, 11%, 27%, and 55%, respectively, with 100% recovery at 24 hours. From insulin-primed tubing, insulin recovery was approximately 70% at 1, 2, and 4 hours, and close to 100% at 8 hours. At a faster flow rate of 0.2 mL/h, insulin recovery at 1, 2, 4, and 8 hours was 22%, 38%, 67%, and 75% vs 42%, 85%, 91% and 95% from unprimed and insulin-primed PVC tubing, respectively. Similar results were obtained from unprimed and insulin-primed PE-lined tubing at 0.2 mL/h flow rate. Priming of microbore tubing with 5 U/mL of insulin solution for 20 minutes to block nonspecific binding sites enhances delivery of a standard insulin stock at infusion rates typically used to treat hyperglycemic ELBW infants. We conclude that priming the tubing with a higher

  14. Flow of two immiscible fluids in a periodically constricted tube: Transitions to stratified, segmented, churn, spray, or segregated flow

    NASA Astrophysics Data System (ADS)

    Fraggedakis, D.; Kouris, Ch.; Dimakopoulos, Y.; Tsamopoulos, J.

    2015-08-01

    We study the flow of two immiscible, Newtonian fluids in a periodically constricted tube driven by a constant pressure gradient. Our volume-of-fluid algorithm is used to solve the governing equations. First, the code is validated by comparing its predictions to previously reported results for stratified and pulsing flow. Then, it is used to capture accurately all the significant topological changes that take place. Initially, the fluids have a core-annular arrangement, which is found to either remain the same or change to a different arrangement depending on the fluid properties, the pressure driving the flow, or the flow geometry. The flow-patterns that appear are the core-annular, segmented, churn, spray, and segregated flow. The predicted scalings near pinching of the core fluid concur with similarity predictions and earlier numerical results [I. Cohen et al., "Two fluid drop snap-off problem: Experiments and theory," Phys. Rev. Lett. 83, 1147-1150 (1999)]. Flow-pattern maps are constructed in terms of the Reynolds and Weber numbers. Our result provides deeper insights into the mechanism of the pattern transitions and is in agreement with previous studies on core-annular flow [Ch. Kouris and J. Tsamopoulos, "Core-annular flow in a periodically constricted circular tube, I. Steady state, linear stability and energy analysis," J. Fluid Mech. 432, 31-68 (2001) and Ch. Kouris et al., "Comparison of spectral and finite element methods applied to the study of interfacial instabilities of the core-annular flow in an undulating tube," Int. J. Numer. Methods Fluids 39(1), 41-73 (2002)], segmented flow [E. Lac and J. D. Sherwood, "Motion of a drop along the centreline of a capillary in a pressure-driven flow," J. Fluid Mech. 640, 27-54 (2009)], and churn flow [R. Y. Bai et al., "Lubricated pipelining—Stability of core annular-flow. 5. Experiments and comparison with theory," J. Fluid Mech. 240, 97-132 (1992)].

  15. Transition to Non-Newtonian behavior of blood suspensions flowing in small tubes

    NASA Astrophysics Data System (ADS)

    Caswell, Bruce; Lei, Huan; Fedosov, Dmitry; Karniadakis, George

    2011-11-01

    Blood flow in tubes is widely considered to be Newtonian down to diameters of about 200 microns. We have employed a multi-scale, Dissipative Particle Dynamics (DPD) model of the red blood cell (RBC) to investigate suspensions driven through small tubes (diameters 20-150 microns). The cross-stream stress gradient induces radial migration of the suspended RBCs resulting in the formation of a hematocrit (H) peak at the centerline, and at the wall a cell-free layer (CFL) whose edge is the point of maximum RBC distortion. This suggests that hard-sphere suspension theories will not capture well blood flow in tubes. For the larger tubes the velocity profiles beyond the CFL are essentially parabolic even though the core H is non-uniform. As the diameter decreases: (1) the CFL moves inward and the central H peak grows, but for the smallest (20 microns) the H peak is shifted off-center, (2) the bulk velocity profiles become similar to those of a shear-thinning non-Newtonian fluid. However, accurate modeling of the velocity field of the bulk flow in small tubes as a homogeneous non-Newtonian fluid can only be achieved if model parameters are taken to depend on tube diameter and pressure drop.

  16. Inspiratory Tube Condensation During High-Flow Nasal Cannula Therapy: A Bench Study.

    PubMed

    Chikata, Yusuke; Unai, Kazuaki; Izawa, Masayo; Okuda, Nao; Oto, Jun; Nishimura, Masaji

    2016-03-01

    High-flow nasal cannula (HFNC) therapy provides better humidification than conventional oxygen therapy. To allay loss of vapor as condensation, a servo-controlled heating wire is incorporated in the inspiratory tube, but condensation is not completely avoidable. We investigated factors that might affect condensation: thermal characteristics of the inspiratory tube, HFNC flow, and ambient temperature. We evaluated 2 types of HFNC tubes, SLH Flex 22-mm single tube and RT202. Both tubes were connected to a heated humidifier with water reservoir. HFNC flow was set at 20, 40, and 60 L/min, and FIO2 was set at 0.21. Air conditioning was used maintain ambient temperature at close to either 20 or 25°C. We weighed the tubes on a digital scale before (0 h) and at 3, 6, and 24 h after, turning on the heated humidifier, and calculated the amount of condensation by simple subtraction. The amount of distilled water used during 24 h was also recorded. At 25°C, there was little condensation, but at 20°C and HFNC flow of 20, 40, and 60 L/min for 24 h, the amount of condensation with the SLH was 50.2 ± 10.7, 44.3 ± 17.7, and 56.6 ± 13.9 mg, and the amount with the RT202 was 96.0 ± 35.1, 72.8 ± 8.2, and 64.9 ± 0.8 mg. When ambient temperature was set to 20°C, condensation with the RT202 was statistically significantly greater than with the SLH at all flow settings (P < .001). Ambient temperature statistically significantly influenced the amount of condensation in the tubes. Copyright © 2016 by Daedalus Enterprises.

  17. Coalescence phenomena of droplets with suspended particles in a tube flow at low Reynolds number

    NASA Astrophysics Data System (ADS)

    Muraoka, Masahiro; Ueno, Ichiro; Mizoguchi, Hiroshi; Kamiyama, Toshihiko; Wada, Takuma

    Coalescence phenomena of droplets in a tube flow at low Reynolds number are expected to be useful for fluid handling technique, controlling chemical reaction and so on. In the case of motion of droplets with suspended particles, Drug delivery system can be cited as one of applications. The coalescence phenomena are also underlying basis on analyzing the flow of multiphase fluids through porous media. Such phenomena can be seen, for instance, in enhanced oil recovery, breaking of emulsions in porous coalescers and so on. In this experiment, a glass tube of 2.0 mm in inner diameter, 7.0 mm in outer diameter, and 1500 mm in length is used as a test tube. Silicones oil is employed as the test fluid for the droplet. Mixture fluid of glycerol and pure water is used for a surrounding fluid in the tube flow. The density of the droplets is matched to that of the surrounding fluid by adding carbon tetrachloride. An over flow tank is used to keep the flow in the tube steady at a designated averaged velocity. The test tube is surrounded by a tank filled with a temperature-controlled water to keep the temperature of the system constant. Droplets are injected into the test tube using micro-syringes in front of inlet of the test tube. Behaviors of droplets and suspended particles are monitored by a digital video camera and high speed cameras placed on a sliding stage. The motion of the stage is electrically controlled to follow the travelling droplets in the test tube. Coalescence time of two droplets is measured. The coalescence time indicates a period between the instant when relative velocity of two droplets becomes zero after their apparent contact and the instant when the coalescence takes place. The coalescence time is compared with semi-theoretical formulas obtained using resistance exerted on liquid droplet in a tube creeping flow. When relative velocity of two droplets becomes zero after their apparent contact, clearance diameter of clearance area between droplets is

  18. VFLOW2D - A Vorte-Based Code for Computing Flow Over Elastically Supported Tubes and Tube Arrays

    SciTech Connect

    WOLFE,WALTER P.; STRICKLAND,JAMES H.; HOMICZ,GREGORY F.; GOSSLER,ALBERT A.

    2000-10-11

    A numerical flow model is developed to simulate two-dimensional fluid flow past immersed, elastically supported tube arrays. This work is motivated by the objective of predicting forces and motion associated with both deep-water drilling and production risers in the oil industry. This work has other engineering applications including simulation of flow past tubular heat exchangers or submarine-towed sensor arrays and the flow about parachute ribbons. In the present work, a vortex method is used for solving the unsteady flow field. This method demonstrates inherent advantages over more conventional grid-based computational fluid dynamics. The vortex method is non-iterative, does not require artificial viscosity for stability, displays minimal numerical diffusion, can easily treat moving boundaries, and allows a greatly reduced computational domain since vorticity occupies only a small fraction of the fluid volume. A gridless approach is used in the flow sufficiently distant from surfaces. A Lagrangian remap scheme is used near surfaces to calculate diffusion and convection of vorticity. A fast multipole technique is utilized for efficient calculation of velocity from the vorticity field. The ability of the method to correctly predict lift and drag forces on simple stationary geometries over a broad range of Reynolds numbers is presented.

  19. Flow through a circular tube with a permeable Navier slip boundary

    PubMed Central

    2011-01-01

    For Newtonian fluid flow in a right circular tube, with a linear Navier slip boundary, we show that a second flow field arises which is different to conventional Poiseuille flow in the sense that the corresponding pressure is quadratic in its dependence on the length along the tube, rather than a linear dependence which applies for conventional Poiseuille flow. However, assuming that the quadratic pressure is determined, say from known experimental data, then the new solution only exists for a precisely prescribed permeability along the boundary. While this cannot occur for conventional pipe flow, for fluid flow through carbon nanotubes embedded in a porous matrix, it may well be an entirely realistic possibility, and could well explain some of the high flow rates which have been reported in the literature. Alternatively, if the radial boundary flow is prescribed, then the new flow field exists only for a given quadratic pressure. Our primary purpose here is to demonstrate the existence of a new pipe flow field for a permeable Navier slip boundary and to present a numerical solution and two approximate analytical solutions. The maximum flow rate possible for the new solution is precisely twice that for the conventional Poiseuille flow, which occurs for constant inward directed flow across the boundary. PMID:21711926

  20. Flow through a circular tube with a permeable Navier slip boundary.

    PubMed

    Cox, Barry James; Hill, James Murray

    2011-05-17

    For Newtonian fluid flow in a right circular tube, with a linear Navier slip boundary, we show that a second flow field arises which is different to conventional Poiseuille flow in the sense that the corresponding pressure is quadratic in its dependence on the length along the tube, rather than a linear dependence which applies for conventional Poiseuille flow. However, assuming that the quadratic pressure is determined, say from known experimental data, then the new solution only exists for a precisely prescribed permeability along the boundary. While this cannot occur for conventional pipe flow, for fluid flow through carbon nanotubes embedded in a porous matrix, it may well be an entirely realistic possibility, and could well explain some of the high flow rates which have been reported in the literature. Alternatively, if the radial boundary flow is prescribed, then the new flow field exists only for a given quadratic pressure. Our primary purpose here is to demonstrate the existence of a new pipe flow field for a permeable Navier slip boundary and to present a numerical solution and two approximate analytical solutions. The maximum flow rate possible for the new solution is precisely twice that for the conventional Poiseuille flow, which occurs for constant inward directed flow across the boundary.

  1. Flow and Temperature Distribution Evaluation on Sodium Heated Large-sized Straight Double-wall-tube Steam Generator

    SciTech Connect

    Kisohara, Naoyuki; Moribe, Takeshi; Sakai, Takaaki

    2006-07-01

    The sodium heated steam generator (SG) being designed in the feasibility study on commercialized fast reactor cycle systems is a straight double-wall-tube type. The SG is large sized to reduce its manufacturing cost by economics of scale. This paper addresses the temperature and flow multi-dimensional distributions at steady state to obtain the prospect of the SG. Large-sized heat exchanger components are prone to have non-uniform flow and temperature distributions. These phenomena might lead to tube buckling or tube to tube-sheet junction failure in straight tube type SGs, owing to tubes thermal expansion difference. The flow adjustment devices installed in the SG are optimized to prevent these issues, and the temperature distribution properties are uncovered by analysis methods. The analysis model of the SG consists of two parts, a sodium inlet distribution plenum (the plenum) and a heat transfer tubes bundle region (the bundle). The flow and temperature distributions in the plenum and the bundle are evaluated by the three-dimensional code 'FLUENT' and the two dimensional thermal-hydraulic code 'MSG', respectively. The MSG code is particularly developed for sodium heated SGs in JAEA. These codes have revealed that the sodium flow is distributed uniformly by the flow adjustment devices, and that the lateral tube temperature distributions remain within the allowable temperature range for the structural integrity of the tubes and the tube to tube-sheet junctions. (authors)

  2. Pulsatility Index as a Diagnostic Parameter of Reciprocating Wall Shear Stress Parameters in Physiological Pulsating Waveforms.

    PubMed

    Avrahami, Idit; Kersh, Dikla; Liberzon, Alexander

    2016-01-01

    Arterial wall shear stress (WSS) parameters are widely used for prediction of the initiation and development of atherosclerosis and arterial pathologies. Traditional clinical evaluation of arterial condition relies on correlations of WSS parameters with average flow rate (Q) and heart rate (HR) measurements. We show that for pulsating flow waveforms in a straight tube with flow reversals that lead to significant reciprocating WSS, the measurements of HR and Q are not sufficient for prediction of WSS parameters. Therefore, we suggest adding a third quantity-known as the pulsatility index (PI)-which is defined as the peak-to-peak flow rate amplitude normalized by Q. We examine several pulsating flow waveforms with and without flow reversals using a simulation of a Womersley model in a straight rigid tube and validate the simulations through experimental study using particle image velocimetry (PIV). The results indicate that clinically relevant WSS parameters such as the percentage of negative WSS (P[%]), oscillating shear index (OSI) and the ratio of minimum to maximum shear stress rates (min/max), are better predicted when the PI is used in conjunction with HR and Q. Therefore, we propose to use PI as an additional and essential diagnostic quantity for improved predictability of the reciprocating WSS.

  3. Pulsatility Index as a Diagnostic Parameter of Reciprocating Wall Shear Stress Parameters in Physiological Pulsating Waveforms

    PubMed Central

    Avrahami, Idit; Kersh, Dikla

    2016-01-01

    Arterial wall shear stress (WSS) parameters are widely used for prediction of the initiation and development of atherosclerosis and arterial pathologies. Traditional clinical evaluation of arterial condition relies on correlations of WSS parameters with average flow rate (Q) and heart rate (HR) measurements. We show that for pulsating flow waveforms in a straight tube with flow reversals that lead to significant reciprocating WSS, the measurements of HR and Q are not sufficient for prediction of WSS parameters. Therefore, we suggest adding a third quantity—known as the pulsatility index (PI)—which is defined as the peak-to-peak flow rate amplitude normalized by Q. We examine several pulsating flow waveforms with and without flow reversals using a simulation of a Womersley model in a straight rigid tube and validate the simulations through experimental study using particle image velocimetry (PIV). The results indicate that clinically relevant WSS parameters such as the percentage of negative WSS (P[%]), oscillating shear index (OSI) and the ratio of minimum to maximum shear stress rates (min/max), are better predicted when the PI is used in conjunction with HR and Q. Therefore, we propose to use PI as an additional and essential diagnostic quantity for improved predictability of the reciprocating WSS. PMID:27893801

  4. Vibration of a tube bundle in two-phase Freon cross-flow

    SciTech Connect

    Pettigrew, M.J.; Taylor, C.E.; Jong, J.H.; Currie, I.G.

    1995-11-01

    Two-phase cross-flow exists in many shell-and-tube heat exchangers. The U-bend region of nuclear steam generators is a prime example. Testing in two-phase flow simulated by air-water provides useful results inexpensively. However, two-phase flow parameters, in particular surface tension and density ratio, are considerably different in air-water than in steam-water. A reasonable compromise is testing in liquid-vapor Freon, which is much closer to steam-water while much simpler experimentally. This paper presents the first results of a series of tests on the vibration behavior of tube bundles subjected to two-phase Freon cross-flow. A rotated triangular tube bundle of tube-to-diameter ratio of 1.5 was tested over a broad range of void fractions and mass fluxes. Fluidelastic instability, random turbulence excitation, and damping were investigated. Well-defined fluidelastic instabilities were observed in continuous two-phase flow regimes. However, intermittent two-phase flow regimes had a dramatic effect on fluidelastic instability. Generally, random turbulence excitation forces are much lower in Freon than in air-water. Damping is very dependent on void fraction, as expected.

  5. Response of periodontal ligament fibroblasts and gingival fibroblasts to pulsating fluid flow: nitric oxide and prostaglandin E2 release and expression of tissue non-specific alkaline phosphatase activity.

    PubMed

    van der Pauw, M T; Klein-Nulend, J; van den Bos, T; Burger, E H; Everts, V; Beertsen, W

    2000-12-01

    The capacity of the periodontal ligament to alter its structure and mass in response to mechanical loading has long been recognized. However, the mechanism by which periodontal cells can detect physical forces and respond to them is largely unknown. Besides transmission of forces via cell-matrix or cell-cell interactions, the strain-derived flow of interstitial fluid through the periodontal ligament may mechanically activate the periodontal cells, as well as ensure transport of cell signaling molecules, nutrients and waste products. Mechanosensory cells, such as endothelial and bone cells, are reported to respond to a flow of fluid with stimulated prostaglandin E2 (PGE2) and nitric oxide production. Therefore, we examined the PGE2 and nitric oxide response of human periodontal ligament and gingival fibroblasts to pulsating fluid flow and assessed the expression of tissue non-specific alkaline phosphatase activity. Periodontal ligament and gingival fibroblasts were subjected to a pulsating fluid flow (0.7 +/- 0.02 Pa, 5 Hz) for 60 min. PGE2 and nitric oxide concentrations were determined in the conditioned medium after 5, 10, 30 and 60 min of flowing. After fluid flow the cells were cultured for another 60 min without mechanical stress. Periodontal ligament fibroblasts, but not gingival fibroblasts, responded to fluid flow with significantly elevated release of nitric oxide and decreased expression of tissue non-specific alkaline phosphatase activity. In both periodontal ligament and gingival fibroblasts, PGE2 production was significantly increased after 60 min of flowing. Periodontal ligament fibroblasts, but not gingival fibroblasts, produced significantly higher levels of PGE2 during the postflow culture period. We conclude that human periodontal ligament fibroblasts are more responsive to pulsating fluid flow than gingival fibroblasts. The similarity of the early nitric oxide and PGE2 responses to fluid flow in periodontal fibroblasts with bone cells and

  6. Enthalpy, Entropy, and Exergy Flows — Real Gas Effects in Ideal Pulse Tube Cryocoolers

    NASA Astrophysics Data System (ADS)

    Kittel, P.

    2006-04-01

    The enthalpy, entropy, and exergy flows in ideal pulse tube cryocoolers and some of the losses in non-ideal pulse tube cryocoolers have been described previously. This paper will describe how these flows are affected by real gas phenomena in ideal pulse tube cryocoolers. Frequently such descriptions take an energy-centric view, concentrating on the first law of thermodynamics, the conservation of energy. This approach can result in a complex description of the cooler in terms of energy and enthalpy flows. An alternative is to take an entropy-centric approach. Closely related to this is the exergy-centric approach. These descriptions concentrate on the second law of thermodynamics, the generation of entropy or the destruction of exergy. Both the energy-centric and exergy/entropy-centric approaches make use of both the laws of thermodynamics and both approaches give equivalent descriptions of a cryocooler. However, the latter approach can be more useful as it can yield a simpler description, one that emphasis loss mechanisms. This paper applies the second law approach to pulse tube cryocoolers. The non-ideal gas effects in the various components on the exergy, entropy, and enthalpy flows are discussed. The discussion applies to basic, orifice, and inertance type pulse tubes and can be easily extended to other types of regenerative cryocoolers such as Gifford-McMahon and Stirling cryocoolers.

  7. Resistance of pediatric and neonatal endotracheal tubes: influence of flow rate, size, and shape.

    PubMed

    Manczur, T; Greenough, A; Nicholson, G P; Rafferty, G F

    2000-05-01

    The aim of this study was to determine the resistances of endotracheal tubes (ETTs) commonly used in neonatal and pediatric intensive care units and the relationship of resistance to flow rate, size, and shape of ETT. Laboratory-based measurements. We examined straight tubes with inner diameters between 2.5 and 6 mm and shouldered (Cole) tubes with inner diameter/outer diameter between 2.5/4 and 3.5/5 mm. We assessed ETT resistance at standard and "appropriate for patient use" lengths at flow rates from 0 L/min to 30 L/min. We used calibrated rotameters to control the flow of gas and proximal static pressure measured by using either an industrial draft gauge or a differential pressure transducer. The ETT resistance was calculated by dividing the proximal ETT pressure by the measured flow and expressed as the mean of three measurements at each flow rate. Resistance increased as ETT diameter decreased; at flows of 5 L/min and 10 L/min, the resistances of the 6 mm inner diameter ETT were 3.1 H2O/L/sec and 4.6 cm H20/L/ sec, respectively, and the resistances of the 2.5 mm inner diameter ETT were 81.2 H2O/L/sec and 139.4 cm H20/L/sec, respectively. Shortening an ETT to a length appropriate for patient use (e.g., a 4.0 mm inner diameter, from 20.7 to 11.3 cm) reduced its resistance on average by 22%. The resistance of a Cole tube was approximately 50% lower than that of a straight tube with an inner diameter corresponding to the narrow part of the shouldered tube. Our results suggest that the use of a small-diameter, straight ETT will significantly increase the work of breathing.

  8. Calculation of unsteady flow in tubes of combustion engines with special regard to multiple branching

    NASA Astrophysics Data System (ADS)

    Goerg, K. A.

    1982-12-01

    A theoretical basis for numerical analysis of unsteady flow in internal combustion engines is suggested. By a general study of an arbitrary throttle point as control volume, only two flow conditions-inlet flow and outlet flow-have to be computed. The throttle-point function is reduced to linking tube parts in a logical way. The convergence criteria of the solution methods used (Lax-Wendroff, Hartree, Predictor Corrector, and fixed point method) guarantee that the solutions are unequivocal. Limiting value studies lead to the formulation of an algorithm, which allows the computation of the throttle flow by multiple branching.

  9. Pressure losses during steam flow and condensation in tubes and channels

    NASA Astrophysics Data System (ADS)

    Leontiev, A. I.; Milman, O. O.

    2014-12-01

    Theoretical and experimental investigations have revealed the dependence of parameters of the process of steam condensation in tubes and channels on the scheme of heat-exchange fluid flow, including counter, forward, and cross flow systems. The total pressure losses in the case of counter flow are greater than those in the case of forward and cross flow. This dependence is valid for the flow of gases and plasma in channels with significant density variation (e.g., due to heating and cooling). Pressure losses have been evaluated using various computational models, and the results are compared to experimental data.

  10. Flow properties in expansion tube with helium, argon, air, and CO2

    NASA Technical Reports Server (NTRS)

    Miller, C. G.

    1974-01-01

    Test flow velocities from 5 to 7 km/sec were generated in a 6-in. expansion tube using helium, argon, air, and CO2 test gases. Pitot pressure profiles across the flow at the test section are presented for the four test gases, and measured flow quantities are compared to computer predicted values. Comparison of predicted and measured flow quantities suggests the expansion to be near thermochemical equilibrium for all test gases and implies the existence of a totally reflected shock at the secondary diaphragm. Argon, air, and CO2 flows were observed to attenuate while traversing the acceleration section, whereas no attenuation was observed for helium.

  11. Influence of outlet geometry on strongly swirling turbulent flow through a circular tube

    NASA Astrophysics Data System (ADS)

    Escudier, M. P.; Nickson, A. K.; Poole, R. J.

    2006-12-01

    The results are reported for an extensive series of measurements (using laser Doppler anemometry) of the mean and fluctuating flow fields for swirling turbulent flow downstream of an orifice in a tube. The influence of a concentric outlet contraction is found to be negligible for low "supercritical" swirl. For high "subcritical" swirl, the outlet geometry is found to have a significant influence throughout the flow field and, in the case of an eccentric (i.e., offset) outlet, to lead to an asymmetric flow with a distorted core. In no case was the core found to precess or the flow to be periodic.

  12. Free-stream temperature, density, and pressure measurements in an expansion tube flow

    NASA Technical Reports Server (NTRS)

    Haggard, K. V.

    1973-01-01

    An experimental study was conducted to determine test-flow conditions in the Langley pilot model expansion tube. Measurements of temperature, density, wall pressure, pitot pressure, and shock and interface velocities were compared with theoretical calculations based on various models of the flow cycle. The vibrational temperature and integrated density of the molecular oxygen component of the flow were measured by use of vacuum ultraviolet absorption techniques. These measurements indicate both the presence and possible degree of nonequilibrium in the flow. Data are compared with several simplified models of the flow cycle, and data trends are discussed.

  13. Simulation of turbulent non-isothermal polydisperse bubbly flow behind a sudden tube expansion

    NASA Astrophysics Data System (ADS)

    Pakhomov, M. A.; Terekhov, V. I.

    2016-09-01

    The results of numerical simulation of the structure of non-isothermal polydisperse bubbly turbulent flow and heat transfer behind a sudden tube expansion are presented. The study was carried out at a change in the initial diameter of the air bubbles within d m1 = 1-5 mm and their volumetric void fraction β = 0-10 %. Small bubbles are available in almost the entire cross section of the tube, while the large bubbles pass mainly through the flow core. An increase in the size of dispersed phase causes the growth of turbulence in the liquid phase due to flow turbulization, when there is a separated flow of liquid past the large bubbles. Adding the air bubbles causes a significant reduction in the length of the separation zone and heat transfer enhancement, and these effects increase with increasing bubble size and their gas volumetric flow rate ratio.

  14. Flow Rate Driven by Peristaltic Movement in Plasmodial Tube of Physarum Polycephalum

    NASA Astrophysics Data System (ADS)

    Yamada, Hiroyasu; Nakagaki, Toshiyuki

    2008-07-01

    We report a theoretical analysis of protoplasmic streaming driven by peristaltic movement in an elastic tube of an amoeba-like organism. The Plasmodium of Physarum polycephalum, a true slime mold, is a large amoeboid organism that adopts a sheet-like form with a tubular network. The network extends throughout the Plasmodium and enables the transport and circulation of chemical signals and nutrients. This tubular flow is driven by periodically propagating waves of active contraction of the tube cortex, a process known as peristaltic movement. We derive the relationship between the phase velocity of the contraction wave and the flow rate, and we discuss the physiological implications of this relationship.

  15. Transition to chaos of a vertical collapsible tube conveying air flow

    NASA Astrophysics Data System (ADS)

    Castillo Flores, F.; Cros, A.

    2009-05-01

    "Sky dancers", the large collapsible tubes used as advertising, are studied in this work through a simple experimental device. Our study is devoted to the nonlinear dynamics of this system and to its transition to chaos. Firstly, we have shown that after a collapse occurs, the air fills the tube at a different speed rate from the flow velocity. Secondly, the temporal intermittency is studied as the flow rate is increased. A statistical analysis shows that the chaotic times maintain roughly the same value by increasing air speed. On the other hand, laminar times become shorter, until the system reaches a completely chaotic state.

  16. Shock-wave-induced flow past a circular cylinder in a dusty-gas shock tube

    NASA Astrophysics Data System (ADS)

    Sugiyama, Hiromu; Shirota, Takahiro; Doi, Hiromichi; Takayama, Kazuyoshi

    1990-05-01

    An experimental investigation of a shock-wave-induced flow past a circular cylinder in a dusty-gas shock tube was made. The shock tubes used for the present research had test sections of identical geometry. For a frozen-shock Mach number of 1.3, flow visualization studies were conducted by the schlieren method, using a high-speed camera and a pulsed-laser holographic interferometer. The behavior of shock waves past a circular cylinder in a dusty-gas, the development of dust-free regions, and the formation of vortices behind a circular cylinder were observed in detail.

  17. Laminar flow studies of a low-temperature space radiator model using D-shaped tubes

    NASA Technical Reports Server (NTRS)

    Cintula, T. C.; Prok, G. M.; Johnston, D. B.

    1972-01-01

    Test results of a low-temperature space radiator model are presented. Radiator performance is evaluated with a low-thermal-conductivity fluid in laminar flow in D-shaped cross-section tubes. The test covered a Reynolds number range from 50 to 4500 and a fluid temperature range from 294 to 414 K (70 to 286 F). For low-temperature radiators, the fluid-to-surface temperature differential was predominately influenced by fluid temperature in laminar flow. Heat transfer and pressure drop for the radiator tube could be predicted within engineering accuracy from existing correlations.

  18. Analysis of laminar flow heat transfer in uniform temperature circular tubes with tape inserts

    NASA Astrophysics Data System (ADS)

    Manglik, R. M.; Bergles, A. E.

    1986-05-01

    Constant property, laminar flow heat transfer in a semicircular tube with uniform wall temperature has been analyzed to define the lower bound of heat transfer augmentation in circular tubes with twisted-tape inserts. Two thermal boundary conditions, which correspond to the two extremes of the fin effect of twisted tapes encountered in practical applications, are considered. Numerical solutions, employing finite-difference formulations for the governing momentum and energy equations were carried out for the thermal entrance region and for fully developed flow.

  19. Blood flow in small tubes: quantifying the transition to the non-continuum regime

    PubMed Central

    Lei, Huan; Fedosov, Dmitry A.; Caswell, Bruce; Karniadakis, George Em

    2013-01-01

    In small vessels blood is usually treated as a Newtonian fluid down to diameters of ~200 μm. We investigate the flow of red blood cell (RBC) suspensions driven through small tubes (diameters 10–150 μm) in the range marking the transition from arterioles and venules to the largest capillary vessels. The results of the simulations combined with previous simulations of uniform shear flow and experimental data show that for diameters less than ~100 μm the suspension’s stress cannot be described as a continuum, even a heterogeneous one. We employ the dissipative particle dynamics (DPD) model, which has been successfully used to predict human blood bulk viscosity in homogeneous shear flow. In tube flow the cross-stream stress gradient induces an inhomogeneous distribution of RBCs featuring a centreline cell density peak, and a cell-free layer (CFL) next to the wall. For a neutrally buoyant suspension the imposed linear shear-stress distribution together with the differentiable velocity distribution allow the calculation of the local viscosity across the tube section. The viscosity across the section as a function of the strain rate is found to be essentially independent of tube size for the larger diameters and is determined by the local haematocrit (H) and shear rate. Other RBC properties such as asphericity, deformation, and cell-flow orientation exhibit similar dependence for the larger tube diameters. As the tube size decreases below ~100 μm in diameter, the viscosity in the central region departs from the large-tube similarity function of the shear rate, since H increases significantly towards the centreline. The dependence of shear stress on tube size, in addition to the expected local shear rate and local haematocrit, implies that blood flow in small tubes cannot be described as a heterogeneous continuum. Based on the analysis of the DPD simulations and on available experimental results, we propose a simple velocity-slip model that can be used in

  20. Blood flow in small tubes: quantifying the transition to the non-continuum regime.

    PubMed

    Lei, Huan; Fedosov, Dmitry A; Caswell, Bruce; Karniadakis, George Em

    2013-05-01

    In small vessels blood is usually treated as a Newtonian fluid down to diameters of ~200 μm. We investigate the flow of red blood cell (RBC) suspensions driven through small tubes (diameters 10-150 μm) in the range marking the transition from arterioles and venules to the largest capillary vessels. The results of the simulations combined with previous simulations of uniform shear flow and experimental data show that for diameters less than ~100 μm the suspension's stress cannot be described as a continuum, even a heterogeneous one. We employ the dissipative particle dynamics (DPD) model, which has been successfully used to predict human blood bulk viscosity in homogeneous shear flow. In tube flow the cross-stream stress gradient induces an inhomogeneous distribution of RBCs featuring a centreline cell density peak, and a cell-free layer (CFL) next to the wall. For a neutrally buoyant suspension the imposed linear shear-stress distribution together with the differentiable velocity distribution allow the calculation of the local viscosity across the tube section. The viscosity across the section as a function of the strain rate is found to be essentially independent of tube size for the larger diameters and is determined by the local haematocrit (H) and shear rate. Other RBC properties such as asphericity, deformation, and cell-flow orientation exhibit similar dependence for the larger tube diameters. As the tube size decreases below ~100 μm in diameter, the viscosity in the central region departs from the large-tube similarity function of the shear rate, since H increases significantly towards the centreline. The dependence of shear stress on tube size, in addition to the expected local shear rate and local haematocrit, implies that blood flow in small tubes cannot be described as a heterogeneous continuum. Based on the analysis of the DPD simulations and on available experimental results, we propose a simple velocity-slip model that can be used in conjunction

  1. Excitation condition analysis of guided wave on PFA tubes for ultrasonic flow meter.

    PubMed

    Li, Xuan; Xiao, Xufeng; Cao, Li

    2016-12-01

    Impurity accumulation, which decreases the accuracy of flow measurement, is a critical problem when applying Z-shaped or U-shaped ultrasonic flow meters on straight PFA tubes. It can be expected that the guided wave can be used to implement flow measurement on straight PFA tubes. In this paper, the propagation of guided wave is explained by finite element simulations for the flow meter design. Conditions of guided wave generation, including the excitation frequency and the wedge structure, are studied in the simulations. The wedge is designed as a cone which is friendly to be manufactured and installed. The cone angle, the piezoelectric wafer's resonant frequency and the vibration directions are studied in the simulations. The simulations shows that the propagation of guided wave in thin PFA tubes is influenced by the piezoelectric wafers' resonant frequency and the vibration direction when the mode is on the 'water line'. Based on the results of the simulations, an experiment is conducted to verify the principles of excitation conditions, which performs flow measurement on a straight PFA tube well.

  2. Blood flow to the uterine tube (oviduct) of the early pregnant and pseudopregnant rabbit.

    PubMed

    Waldhalm, S J; Dickson, W M

    1976-07-01

    Blood flow to the uterus and uterine tube was measured in 46 rabbits in estrus and early pregnancy or pseudopregnancy. Uterine blood flow in estrus averaged 0.910 +/- 0.253 (SD) ml/g/minute and remained unchanged through postcoital day (PCD) 15. Blood flow to the uterine tube in estrus was 0.810 +/- 0.287 ml/g/minute. A peak blood flow of 1.323 +/- 0.424 ml/g/minute, was measured in the uterine tube on PCD 4, followed by a decrease of blood flow to estrous levels on PCD 8 to 15. The gross blood vasculature of the uterus uterine tube, and ovary was studied by intravascular silicone rubber injection in 17 rabbits. The architecture of the blood vascular system remained unchanged from estrus through early pregnancy or pseudopregnancy. The differences were vascularization of the corpus luteum, vascular accommodation of uterine distension, and enlargement of the lateral arcuate vein which spans the uterotubal junction.

  3. A Hands-on Exercise in Building Darcy Tubes to Improve Student Understanding of Groundwater Flow

    NASA Astrophysics Data System (ADS)

    Smith, J. A.

    2012-12-01

    Teaching undergraduate students about sustainability typically includes discussions of water resources and the flow of groundwater in aquifers. Understanding the flow of groundwater is a fundamental step for students, but one that can easily get mired in equations (e.g., Darcy's Law). In an effort to transform Darcy's Law, which describes flow of fluid through a porous medium, from an abstract concept to a hands-on experiment, I had undergraduate students build working "Darcy tubes" and calculate hydraulic conductivity during a three-hour lab period. At the beginning of the lab period, I presented the students with the materials: three pairs of plastic soda bottles with straight sides, glass tubing, pantyhose (for screens), rubber hosing, sieved sand in three grain sizes (1-2 mm, 0.5-1.0 mm, and 0.25-0.5 mm), and various types of tape and adhesive. After we discussed the basic design of a Darcy tube (inlet and outlet, with two piezometers), the students went to work. Real-time problem-solving was an integral (and exciting) part of the exercise. Within two hours, they had built three Darcy tubes, each filled with a different sand size. The students determined the cross-sectional area of each tube (A) and the distance between the two piezometers (L). We then ran the experiments, using tinted water so that we could more easily tell when the sand in the tubes was saturated. We measured discharge (Q) through the tube and marked the height of the water in each piezometer to calculate difference in hydraulic head (Δh). With the data we had collected, the students were able to calculate hydraulic conductivity (K) using a simple form of Darcy's Law: Q = -KA (Δh/L). Despite the simplicity of the Darcy tubes, the students' K values were reasonable for the sediment types that we used. Student comments on the Darcy tube exercise were overwhelmingly positive. The Darcy tubes could be used in a subsequent lab period for exploration of more advanced concepts, such as

  4. The motion of magnetic flux tube at the dayside magnetopause under the influence of solar wind flow

    SciTech Connect

    Liu, Z.X.; Hu, Y.D.; Li, F. ); Pu, Z.Y. )

    1990-05-01

    The authors propose that flux transfer events (FTEs) at the dayside magnetopause are formed by fluid vortices in the flow field. According to the view of vortex-induced reconnection a FTE tube is a magnetic fluid vortex tube (MF vortex tube). The motion of a FTE tube can be represented by that of a MF vortex in the formation region located in the dayside magnetopause region. This study deals with the internal and external influences governing the motion of MF vortex tubes. The equations of motion of a vortex tube are established and solved. It is found that a FTE tube moves frm low latitude to high latitude with a certain speed. However, the motional path is not a straight line but oscillates about the northward direction for the northern hemisphere. The motional velocity, amplitude and period of the oscillation depend on the flow field and magnetic field in the magnetosheath and magnetosphere as well as the size of the FTE tube.

  5. Experimental studies on pressure drop characteristics of cryogenic cross-counter flow coiled finned tube heat exchangers

    NASA Astrophysics Data System (ADS)

    Gupta, Prabhat Kumar; Kush, P. K.; Tiwari, Ashesh

    2010-04-01

    Cross-counter flow coiled finned tube heat exchangers used in medium capacity helium liquefiers/refrigerators were developed in our lab. These heat exchangers were developed using integrated low finned tubes. Experimental studies have been performed to know the pressure drop characteristics of tube side and shell side flow of these heat exchangers. All experiments were performed at room temperature in the Reynolds number range of 3000-30,000 for tube side and 25-155 for shell side. The results of present experiments indicate that available correlations for tube side can not be used for prediction of tube side pressure drop data due to complex surface formation at inner side of tube during formation of fins over the outer surface. Results also indicate that surface roughness effect becomes more pronounced as the value of di/ D m increases. New correlations based on present experimental data are proposed for predicting the friction factors for tube side and shell side.

  6. Influence of acute jugular vein compression on the cerebral blood flow velocity, pial artery pulsation and width of subarachnoid space in humans.

    PubMed

    Frydrychowski, Andrzej F; Winklewski, Pawel J; Guminski, Wojciech

    2012-01-01

    The aim of this study was to assess the effect of acute bilateral jugular vein compression on: (1) pial artery pulsation (cc-TQ); (2) cerebral blood flow velocity (CBFV); (3) peripheral blood pressure; and (4) possible relations between mentioned parameters. Experiments were performed on a group of 32 healthy 19-30 years old male subjects. cc-TQ and the subarachnoid width (sas-TQ) were measured using near-infrared transillumination/backscattering sounding (NIR-T/BSS), CBFV in the left anterior cerebral artery using transcranial Doppler, blood pressure was measured using Finapres, while end-tidal CO(2) was measured using medical gas analyser. Bilateral jugular vein compression was achieved with the use of a sphygmomanometer held on the neck of the participant and pumped at the pressure of 40 mmHg, and was performed in the bend-over (BOPT) and swayed to the back (initial) position. In the first group (n = 10) during BOPT, sas-TQ and pulse pressure (PP) decreased (-17.6% and -17.9%, respectively) and CBFV increased (+35.0%), while cc-TQ did not change (+1.91%). In the second group, in the initial position (n = 22) cc-TQ and CBFV increased (106.6% and 20.1%, respectively), while sas-TQ and PP decreases were not statistically significant (-15.5% and -9.0%, respectively). End-tidal CO(2) remained stable during BOPT and venous compression in both groups. Significant interdependence between changes in cc-TQ and PP after bilateral jugular vein compression in the initial position was found (r = -0.74). Acute bilateral jugular venous insufficiency leads to hyperkinetic cerebral circulation characterised by augmented pial artery pulsation and CBFV and direct transmission of PP into the brain microcirculation. The Windkessel effect with impaired jugular outflow and more likely increased intracranial pressure is described. This study clarifies the potential mechanism linking jugular outflow insufficiency with arterial small vessel cerebral disease.

  7. Influence of Acute Jugular Vein Compression on the Cerebral Blood Flow Velocity, Pial Artery Pulsation and Width of Subarachnoid Space in Humans

    PubMed Central

    Frydrychowski, Andrzej F.; Winklewski, Pawel J.; Guminski, Wojciech

    2012-01-01

    Purpose The aim of this study was to assess the effect of acute bilateral jugular vein compression on: (1) pial artery pulsation (cc-TQ); (2) cerebral blood flow velocity (CBFV); (3) peripheral blood pressure; and (4) possible relations between mentioned parameters. Methods Experiments were performed on a group of 32 healthy 19–30 years old male subjects. cc-TQ and the subarachnoid width (sas-TQ) were measured using near-infrared transillumination/backscattering sounding (NIR-T/BSS), CBFV in the left anterior cerebral artery using transcranial Doppler, blood pressure was measured using Finapres, while end-tidal CO2 was measured using medical gas analyser. Bilateral jugular vein compression was achieved with the use of a sphygmomanometer held on the neck of the participant and pumped at the pressure of 40 mmHg, and was performed in the bend-over (BOPT) and swayed to the back (initial) position. Results In the first group (n = 10) during BOPT, sas-TQ and pulse pressure (PP) decreased (−17.6% and −17.9%, respectively) and CBFV increased (+35.0%), while cc-TQ did not change (+1.91%). In the second group, in the initial position (n = 22) cc-TQ and CBFV increased (106.6% and 20.1%, respectively), while sas-TQ and PP decreases were not statistically significant (−15.5% and −9.0%, respectively). End-tidal CO2 remained stable during BOPT and venous compression in both groups. Significant interdependence between changes in cc-TQ and PP after bilateral jugular vein compression in the initial position was found (r = −0.74). Conclusions Acute bilateral jugular venous insufficiency leads to hyperkinetic cerebral circulation characterised by augmented pial artery pulsation and CBFV and direct transmission of PP into the brain microcirculation. The Windkessel effect with impaired jugular outflow and more likely increased intracranial pressure is described. This study clarifies the potential mechanism linking jugular outflow insufficiency with arterial small

  8. The influence of upstream turbulence on the stability of tube bundles subjected to cross-flow

    SciTech Connect

    Romberg, O.; Popp, K.

    1996-12-01

    Tube failures in heat exchangers are often caused by inadmissible vibrations. Especially the fluidelastic instability is a dangerous excitation mechanism. The investigations refer to the influence of isotropic upstream turbulence on the stability behavior of parallel and rotated triangular tube arrays of different pitch-to-diameter ratios. The excitation is due to air cross-flow in a wind tunnel. The experimental apparatus allows to measure the stability boundaries (Connors diagram) of fully flexible bundles as well as single flexibly mounted tubes with variable equilibrium position in otherwise fixed arrays. By using a turbulence grid with variable geometric properties it is possible to produce isotropic turbulence with variable turbulence intensity Tu and scale length L{sub x} at the inlet of the bundle. These values were determined using hot wire anemometers. The investigations show in most of the cases a stabilization of the tubes with increasing turbulence.

  9. CFD analysis of flow through Venturi tube and its discharge coefficient

    NASA Astrophysics Data System (ADS)

    Tukimin, A.; Zuber, M.; Ahmad, K. A.

    2016-10-01

    Venturi tube plays a very important role in different fields of engineering. It has a number of industrial applications in which its design is an essential factor. Venturi tube used in gas measurement applications provides an accurate critical gas flow measurement. There is a need to design Venturi tube with an effective analytical tool or software. In this work, two parameters: pressure drop and velocity discharge nozzle were analyzed using Computational Fluid Dynamics (CFD). The results obtained were then analyzed for accurate determination of the Venturi tube's discharge coefficient, Cd. It was found that there is less than 1% difference between the average values of the discharge coefficient obtained from the numerical analysis and experimental results.

  10. The Effects of Glucose Therapy Agents-Apple Juice, Orange Juice, and Cola-on Enteral Tube Flow and Patency.

    PubMed

    Steinberg, Daphna J; Montreuil, Jasmine; Santoro, Andrea L; Zettas, Antonia; Lowe, Julia

    2016-06-01

    To develop evidence-based hypoglycemia treatment protocols in patients receiving total enteral nutrition, this study determined the effect on enteral tube flow of glucose therapy agents: apple juice, orange juice, and cola, and it also examined the effects of tube type and feed type with these glucose therapy agents. For this study, 12 gastrostomy tubes (6 polyethylene and 6 silicone) were set at 50 mL/h. Each feeding set was filled with Isosource HN with fibre or Novasource Renal. Each tube was irrigated with 1 glucose therapy agent, providing approximately 20 g of carbohydrate every 4 h. Flow-rate measurements were collected at 2 h intervals. The results showed that the glucose therapy agent choice affected flow rates: apple juice and cola had higher average flow rates than orange juice (P = 0.01). A significant difference was found between tube type and enteral formula: polyethylene tubes had higher average flow rates than silicone tubes (P < 0.0001), and Isosource HN with fibre had higher flow rates than Novasource Renal (P = 0.01). We concluded that apple juice and cola have less tube clogging potential than orange juice, and thus may be considered as primary treatment options for hypoglycemia in enterally fed patients. Polyethylene tubes and Isosource HN with fibre were less likely to clog than silicone tubes and Novasource Renal.

  11. A new disruption mitigation valve (DMV) and gas flow in guiding tubes of different diameter

    NASA Astrophysics Data System (ADS)

    Finken, K. H.; Lehnen, M.; Bozhenkov, S. A.

    2011-03-01

    A new disruption mitigation valve, the DMV-30, has been developed and tested. The orifice output area of the valve is a factor of 2.4 and 12.25 times larger than that of its predecessors, DMV-20 and DMV-10, and the gas reservoir amounts to 1.3 L while the older version used at JET had only 0.65 L. The coil which provides the magnetic field pulse for the activation of the piston by an eddy current is outside of the working gas volume such that all gas volumes are now made of stainless steel. The valve has the advantages of the previous developments: it is robust and reproducible, opens fully within 3 ms and releases 50% of the gas within about 5 ms (He) to 10 ms (Ar). The valve is attached subsequently to two different guiding tubes, one with an inner diameter of 38 mm as used presently at JET and one with 102 mm inner diameter; the aim of this paper is the analysis of the gas flows for different diameters. The front of the gas pulse propagates with a Mach number of about 2.5 through the tubes, independent of the two diameters. This high speed agrees with theoretical expectations of flow expansion of a half infinite tube in vacuum. In the quasi-stationary phase of the expansion, the gas flows with about sound speed in the 102 mm tube and with about half of the sound speed in the 38 mm tube.

  12. Numerical prediction of flow and heat transfer in a tube with circumferential fins and circular disks

    SciTech Connect

    Jeon, K.; Seo, T.; Lee, C.; Kim, C.

    1999-07-01

    The characteristics of fluid flow and heat transfer were numerically analyzed for hydrodynamically and thermally developing laminar flow in a tube with circumferential fins and circular disks. Computations were carried out for a variety of flow conditions and geometric arrangements for the fins and disks, and the effects of these on heat transfer enhancement and pressure drop were studied. In order to quantify the heat transfer enhancement effects of the fins and disks in a tube, the Nusselt numbers for various configurations were compared to those for a corresponding smooth tube. In addition, the flow pattern and the local Nusselt number of developing flow as well as the overall Nusselt numbers for both developing and fully developed flows were presented with associated increase in pressure drop. It was found that the flow was fully developed after passing two consecutive fins from the entrance, and that not only heat transfer enhancement but also pressure drop increase were significant with the fins and disks. And, it was known that heat transfer enhancement and pressure drop increase are strongly dependent on Reynolds number and the fin height rather than the size of the disk.

  13. On the Quantitative Analysis of Liquid Flow in Physiological Tubes.

    DTIC Science & Technology

    1982-12-01

    SS - . .. 1 _ Table 2 Pump Contractile Tissue Cardiac Ciliated Skeletal Smooth System Muscle Epithelium Muscle Muscle CNS( Ventricles ...skeletal muscle compression....................... 33 2. Pressure effects ........................... 33 3. Viscous effects... muscle ................................. 68 VII. COMBINATION PUMPS .................................... 69 A. Pulsatile-Skeletal Flow Propulsion

  14. Application of Fast Optical Tomography to Flow Tubes

    DTIC Science & Technology

    2007-11-02

    electro-optics, quantum electronics, solid-state lasers , optical propagation and communications; microwave semiconductor devices, microwave /millimeter...34Application of Tomography in 3-D Transonic Flows, AIAA-87-1374, AIAA 19th Fluid Dynamics, Plasma Dynamics and Laser Conference, Honolulu, Hawaii...thermomechanics, gas kinetics and radiation; cw and pulsed chemical and excimer laser development including chemical kinetics, spectroscopy, optical

  15. Damping and fluidelastic instability in two-phase cross-flow heat exchanger tube arrays

    NASA Astrophysics Data System (ADS)

    Moran, Joaquin E.

    An experimental study was conducted to investigate damping and fluidelastic instability in tube arrays subjected to two-phase cross-flow. The purpose of this research was to improve our understanding of these phenomena and how they are affected by void fraction and flow regime. The model tube bundle had 10 cantilevered tubes in a parallel-triangular configuration, with a pitch ratio of 1.49. The two-phase flow loop used in this research utilized Refrigerant 11 as the working fluid, which better models steam-water than air-water mixtures in terms of vapour-liquid mass ratio as well as permitting phase changes due to pressure fluctuations. The void fraction was measured using a gamma densitometer, introducing an improvement over the Homogeneous Equilibrium Model (HEM) in terms of void fraction, density and velocity predictions. Three different damping measurement methodologies were implemented and compared in order to obtain a more reliable damping estimate. The methods were the traditionally used half-power bandwidth, the logarithmic decrement and an exponential fitting to the tube decay response. The decay trace was obtained by "plucking" the monitored tube from outside the test section using a novel technique, in which a pair of electromagnets changed their polarity at the natural frequency of the tube to produce resonance. The experiments showed that the half-power bandwidth produces higher damping values than the other two methods. The primary difference between the methods is caused by tube frequency shifting, triggered by fluctuations in the added mass and coupling between the tubes, which depend on void fraction and flow regime. The exponential fitting proved to be the more consistent and reliable approach to estimating damping. In order to examine the relationship between the damping ratio and mass flux, the former was plotted as a function of void fraction and pitch mass flux in an iso-contour plot. The results showed that damping is not independent of mass

  16. Hydrodynamic chromatography using flow of a highly concentrated dextran solution through a coiled tube.

    PubMed

    Miyagawa, Yoichi; Morisada, Shintaro; Ohto, Keisuke; Hidetaka, Kawakita

    2016-08-01

    Separation of colloidal particles in non-Newtonian fluid is important in food engineering. Using hydrodynamic chromatography, colloidal particles and starch granules originating from corn were individually injected into dextran solutions (Mw 2,000,000g/mol) flowing through a coiled tube for efficient size separation. Rheological properties of dextran solutions ranging from 50 to 250g/L were determined, revealing pseudoplastic fluid behavior. Velocity profiles for dextran solution flow in coiled tubes were obtained from rheological power law parameters. Suspensions of colloidal particles of diameters 1.0 and 20μm were individually injected into the dextran flows, demonstrating that dextran solutions at high concentration separated colloidal particles. Starch granules were separated by size using a dextran solution flow (250g/L). Thus, we expect to obtain efficient separation of colloidal particles in foods using highly concentrated dextran solutions. Copyright © 2016 Elsevier Ltd. All rights reserved.

  17. Influence of the gas-flow Reynolds number on a plasma column in a glass tube

    SciTech Connect

    Jin, Dong Jun; Uhm, Han S.; Cho, Guangsup

    2013-08-15

    Atmospheric-plasma generation inside a glass tube is influenced by gas stream behavior as described by the Reynolds number (Rn). In experiments with He, Ne, and Ar, the plasma column length increases with an increase in the gas flow rate under laminar flow characterized by Rn < 2000. The length of the plasma column decreases as the flow rate increases in the transition region of 2000 < Rn < 4000. For a turbulent flow beyond Rn > 4000, the length of the plasma column is short in front of the electrode, eventually leading to a shutdown.

  18. Analysis of the flow rate characteristics of valveless piezoelectric pump with fractal-like Y-shape branching tubes

    NASA Astrophysics Data System (ADS)

    Huang, Jun; Zhang, Jianhui; Wang, Shouyin; Liu, Weidong

    2014-05-01

    Microchannel heat sink with high heat transfer coefficients has been extensively investigated due to its wide application prospective in electronic cooling. However, this cooling system requires a separate pump to drive the fluid transfer, which is uneasy to minimize and reduces their reliability and applicability of the whole system. In order to avoid these problems, valveless piezoelectric pump with fractal-like Y-shape branching tubes is proposed. Fractal-like Y-shape branching tube used in microchannel heat sinks is exploited as no-moving-part valve of the valveless piezoelectric pump. In order to obtain flow characteristics of the pump, the relationship between tube structure and flow rate of the pump is studied. Specifically, the flow resistances of fractal-like Y-shape branching tubes and flow rate of the pump are analyzed by using fractal theory. Then, finite element software is employed to simulate the flow field of the tube, and the relationships between pressure drop and flow rate along merging and dividing flows are obtained. Finally, valveless piezoelectric pumps with fractal-like Y-shape branching tubes with different fractal dimensions of diameter distribution are fabricated, and flow rate experiment is conducted. The experimental results show that the flow rate of the pump increases with the rise of fractal dimension of the tube diameter. When fractal dimension is 3, the maximum flow rate of the valveless pump is 29.16 mL/min under 100 V peak to peak (13 Hz) power supply, which reveals the relationship between flow rate and fractal dimensions of tube diameter distribution. This paper investigates the flow characteristics of valveless piezoelectric pump with fractal-like Y-shape branching tubes, which provides certain references for valveless piezoelectric pump with fractal-like Y-shape branching tubes in application on electronic chip cooling.

  19. Heat transfer during intermittent/slug flow in horizontal tubes

    SciTech Connect

    Shoham, O.; Dukler, A.E.; Taitel, Y.

    1982-08-01

    Heat transfer characteristics for two-phase gas-liquid slug flow in a horizontal pipe have been measured. The time variation of temperature, heat transfer coefficients, and heat flux is reported for the different zones of slug flow: the mixing region at the nose, the body of the slug, the liquid film, and the gas bubble behind the slug. Substantial differences in heat transfer coefficient exist between the bottom and top of the slug. This results from the fact that each slug is effectively a thermally developing entry region caused by the presence of a hot upper wall just upstream of each slug. A qualitative theory is presented which explains this behavior. 18 refs.

  20. Thermochemical Nonequilibrium Analysis of Oxygen in Shock Tube Flows

    NASA Astrophysics Data System (ADS)

    Neitzel, Kevin; Kim, Jae Gang; Boyd, Iain D.

    The successful development of hypersonic vehicles requires a detailed knowledge of the flow physics around the vehicle. The physics knowledge and modeling confidence drives the development of the major vehicle flight systems including the thermal protection system and flight control system. Specifically, an understanding of the thermochemical nonequilibrium behavior is crucial for this flight regime. The hypersonic flight regime involves an extremely high level of energy so a small error in the modeling of the energy processes can result in drastic changes in the vehicle design, including prohibitive design requirements. This emphasizes the need for a deep understanding of the underlying flow phenomena and molecular energy transfer processes in order to adequately design a hypersonic vehicle computationally.

  1. Uniformity of Ludwieg tube flows. [temperature variations behind nonsteady expansion wave

    NASA Technical Reports Server (NTRS)

    Russell, D. A.; Knoke, G. S.; Wai, J. C.

    1975-01-01

    Pressure and speed of sound measurements are used to obtain averaged gas properties in a Ludwieg combustion tube in which the gas is burned just prior to use. Absorption of a laser beam in the exit flow is used to check the predicted temperature uniformity. The burning process and the heat transfer to the cold walls are modeled. Interferograms of Ludwieg tube boundary layers are utilized to develop a new semiempirical boundary layer expression referred to as the integral density thickness, which is then applied to a recently developed linearized analysis of the effects of this layer. Pressure-time histories are determined for a wide range of tube flow Mach number and aspect ratio. Viscous and nonviscous effects are considered. It is shown that although the influence of the integral density thickness on the flow can be large, a modified linear theory can be used to estimate the effects for arbitrary tube flow Mach number and values of the aspect ratio that include cases where the boundary layers have merged.

  2. Visualization and flow boiling heat transfer of hydrocarbons in a horizontal tube

    NASA Astrophysics Data System (ADS)

    Yang, Zhuqiang; Bi, Qincheng; Guo, Yong; Liu, Zhaohui; Yan, Jianguo

    2013-07-01

    Visualizations of a specific hydrocarbon fuel in a horizontal tube with 2.0 mm inside diameter were investigated. The experiments were conducted at mass velocity of 213.4, 426.5 and 640.2 kg/ (m2ṡs), diabatic lengths of 140, 240 and 420 mm under the pressure from 2.0-2.7 MPa. In the sub-pressure conditions, bubbly, intermittent, stratified-wave, churn and annular flow patterns were observed. The frictional pressure drops were also measured to distinguish the patterns. The development of flow patterns and frictional pressure drop were positively related to the mass velocity and the heat flux. However, the diabatic length of the tube takes an important part in the process. The residence time of the fluid does not only affect the transition of the patterns but influence the composition of the fuel manifested by the fuel color and carbon deposit. The special observational phenomenon was obtained for the supercritical pressure fluid. The flow in the tube became fuzzier and pressure drop changed sharply near the pseudocritical point. The flow boiling heat transfer characteristics of the hydrocarbons were also discussed respectively. The curve of critical heat flux about onset of nucleate boiling was plotted with different mass velocities and diabatic tube lengths. And heat transfer characteristics of supercritical fuel were proved to be better than that in subcritical conditions.

  3. A model of plasma membrane flow and cytosis regulation in growing pollen tubes.

    PubMed

    Chavarría-Krauser, Andrés; Yejie, Du

    2011-09-21

    A model of cytosis regulation in growing pollen tubes is developed and simulations presented. The authors address the question on the minimal assumptions needed to describe the pattern of exocytosis and endocytosis reported recently by experimental biologists. Biological implications of the model are also treated. Concepts of flow and conservation of membrane material are used to pose an equation system, which describes the movement of plasma membrane in the tip of growing pollen tubes. After obtaining the central equations, relations describing the rates of endocytosis and exocytosis are proposed. Two cytosis receptors (for exocytosis and endocytosis), which have different recycling rates and activation times, suffice to describe a stable growing tube. Simulations show a very good spatial separation between endocytosis and exocytosis, in which separation is shown to depend strongly on exocytic vesicle delivery. In accordance to measurements, most vesicles in the clear zone are predicted to be endocytic. Membrane flow is essential to maintain cell polarity, and bi-directional flow seems to be a natural consequence of the proposed mechanism. For the first time, a model addressing plasma membrane flow and cytosis regulation were posed. Therefore, it represents a missing piece in an integrative model of pollen tube growth, in which cell wall mechanics, hydrodynamic fluxes and regulation mechanisms are combined. Copyright © 2011 Elsevier Ltd. All rights reserved.

  4. Enhancement of Condensation Heat Transfer by Counter-Corrent Wavy Flow in a Vertical Tube

    NASA Astrophysics Data System (ADS)

    Teranishi, Tsunenobu; Ozawa, Takanori; Takimoto, Akira

    As a basic research for the development of a high-performance and environment-friendly thermal energy recovery system, detailed experiments have been conducted to investigate the mechanism of the enhancement of condensation heat transfer by the counter-current moist air flow in a vertical tube. From the results of visual observation of the phenomena by using a high-speed video recorder and the measurement of condensate rate respectively from an upper and a bottom end of a cooled tube, in which various humidity vapor of air and water flowed upward or downward, the dynamic behavior of liquid film condensed on cooled surface and moist air flow was classified into four distinctive patterns in quality and quantity. Further, the effect of the scale and the operating condition such as the diameter and the length of tube, the vapor concentration and the moist air temperature, on the condensation rate of counter-current wavy flow was clarified in relation to the pattern and condition of occurrence of the wavy flow of liquid film and flooding due to the shear forces between the interface of liquid and moist air flow.

  5. Effects of temporally varying inlet conditions on flow and particle deposition in the small bronchial tubes.

    PubMed

    Soni, Bela; Thompson, David

    2012-09-01

    The laminar flow in the small bronchial tubes is quite complex because of the presence of vortex-dominated, secondary flows. Factors contributing to this complexity are the unsteady nature of the inhale-exhale breathing cycle and the geometrical characteristics of the bronchial tubes. To investigate unsteady effects on flows and particle transport, unsteady inhalation flows at a 30-respiration-per-minute frequency, corresponding to a moderate activity level, were simulated for a three-generation, asymmetric, planar bronchial tube model. Ten-micron diameter water droplets were introduced at the inlet at different times during inhalation to develop particle destination maps. The differences in the flow fields and destination maps obtained at the unsteady peak flow and the comparable steady-state inflow condition were minimal. However, particles released at equivalent instantaneous off-peak inflow conditions produced different destination maps. The differences were attributed to the temporal variations of the fluid velocities and history effects. Copyright © 2012 John Wiley & Sons, Ltd.

  6. Pulsating white dwarfs

    NASA Astrophysics Data System (ADS)

    Kepler, S. O.; Romero, Alejandra D.

    2017-09-01

    The Sloan Digital Sky Survey has allowed us to increase the number of known white dwarfs by a factor of five and consequently the number of known pulsating white dwarfs also by a factor of five. It has also led to the discovery of new types of variable white dwarfs, as the variable hot DQs, and the pulsating Extremely Low Mass white dwarfs. With the Kepler Mission, it has been possible to discover new phenomena, the outbursts present in a few pulsating white dwarfs.

  7. A Calibration of the Preston Tube in Liquid Flow Systems.

    DTIC Science & Technology

    1979-12-01

    connected to a 40 in. mercury manometer bank. Two total pressure probe installations are available, with one located at the extreme outflow end of the pipe...versatile and assured both good probe alignment to the flow and negligible probe interference effects. The probe was connected to a single 30 in. mercury ... manometer which gave readings accurate to .05 in. Hg as did the 40 in. manometer bank. 17 *r4 $4 P., 0 ~r54 so 18 Additional features of the oil pipe

  8. Migration of a droplet in a cylindrical tube in the creeping flow regime

    NASA Astrophysics Data System (ADS)

    Nath, Binita; Biswas, Gautam; Dalal, Amaresh; Sahu, Kirti Chandra

    2017-03-01

    The migration of a neutrally buoyant droplet in a tube containing another immiscible liquid is investigated numerically in the creeping flow regime. A fully developed velocity profile is imposed at the inlet of the tube. The interface between the two immiscible fluids is captured using a coupled level-set and volume-of-fluid approach. The deformation and breakup dynamics of the droplet are investigated in terms of three dimensionless parameters, namely, the ratio between the radius of the undeformed droplet and the radius of the capillary tube, the viscosity ratio between the dispersed and the continuous phases, and the capillary number that measures the relative importance of the viscous force over the surface tension force. It has been observed that the droplet, while traversing through the tube, either approaches a steady bulletlike shape or develops a prominent reentrant cavity at its rear. Depending on the initial droplet size, there exists a critical capillary number for every flow configuration beyond which the drop fails to maintain a steady shape and breaks into fragments. The deformation and breakup phenomena depend primarily on the droplet size, the viscosity ratio, and the capillary number. Special attention has been given to the case where the drop diameter is comparable with the tube diameter. A thorough computational study has been conducted to find the critical capillary number for a range of droplets of varied sizes suspended in systems having different viscosity ratios.

  9. Reverse Fluid Transport Due to Boundary Pulsations

    NASA Astrophysics Data System (ADS)

    Coloma, Mikhail; Schaffer, David; Chiarot, Paul; Huang, Peter

    2016-11-01

    We investigate a reverse fluid transport mechanism consisting of peristaltic flow and boundary wave reflections. The reverse flow occurs in a rectangular conduit aligned in parallel between two cylindrical channels embedded in an elastic PDMS medium. The pulsating flow in the cylindrical channels, driven by a peristaltic pump, deform the PDMS medium and induce a pulsating flow in the rectangular conduit. Waveforms along the conduit boundaries, and their transmission and reflections, can be controlled by changing the PDMS rigidity. Our results show that while the overall wave propagation direction is in the forward direction, a reverse flow in the rectangular conduit can be preferentially induced by varying the elastic rigidity in one of the cylindrical channels. We study the overall flow velocity and direction under various PDMS rigidities. The identified set of experimental parameters that leads to a reverse flow will provide insights in understanding metabolic waste transport within the arterial walls in the brain.

  10. PHOS Experiment: Thermal Response of a Large Diameter Pulsating Heat Pipe on Board REXUS-18 Rocket

    NASA Astrophysics Data System (ADS)

    Creatini, F.; Guidi, G. M.; Belfi, F.; Cicero, G.; Fioriti, D.; Di Prizio, D.; Piacquadio, S.; Becatti, G.; Orlandini, G.; Frigerio, A.; Fontanesi, S.; Nannipieri, P.; Rognini, M.; Morganti, N.; Filippeschi, S.; Di Marco, P.; Fanucci, L.; Baronti, F.; Mameli, M.; Marengo, M.; Manzoni, M.

    2015-09-01

    In the present work, the results of two Closed Loop Pulsating Heat Pipes (CLPHPs) tested on board REXUS-1 8 sounding rocket in order to get experimental data over a relatively broad reduced gravity period (about 90 s) are thoroughly discussed. The CLPHPs are partially filled with refrigerant FC-72 and have, respectively, an inner tube diameter larger (3 .0 mm) and slightly smaller (1 .6 mm) than a critical diameter defined on Earth gravity conditions. On ground, the small diameter CLPHP works as a real Pulsating Heat Pipe (PHP): the typical capillary slug flow pattern forms inside the device and the heat exchange is triggered by self-sustained thermally driven oscillations of the working fluid. Conversely, the large diameter CLPHP behaves like a two-phase thermosyphon in vertical position while does not operate in horizontal position as the working fluid stratifies within the tube and surface tension is not able to balance buoyancy. Then, the idea to test the CLPHPs under reduced gravity conditions: as soon as gravity reduces, buoyancy becomes less intense and the typical capillary slug flow pattern can also forms within a tube with a larger diameter. Moreover, this allows to increase the heat transfer rate and, consequently, to decrease the overall thermal resistance. Even though it was not possible to experience the expected reduced gravity conditions due to a failure of the yo-yo de-spin system, the thermal response to the peculiar acceleration field (hyper-gravity) experienced on board are thoroughly described.

  11. Pulsating Heat pipe Only for Space (PHOS): results of the REXUS 18 sounding rocket campaign

    NASA Astrophysics Data System (ADS)

    Creatini, F.; Guidi, G. M.; Belfi, F.; Cicero, G.; Fioriti, D.; Di Prizio, D.; Piacquadio, S.; Becatti, G.; Orlandini, G.; Frigerio, A.; Fontanesi, S.; Nannipieri, P.; Rognini, M.; Morganti, N.; Filippeschi, S.; Di Marco, P.; Fanucci, L.; Baronti, F.; Mameli, M.; Manzoni, M.; Marengo, M.

    2015-11-01

    Two Closed Loop Pulsating Heat Pipes (CLPHPs) are tested on board REXUS 18 sounding rocket in order to obtain data over a relatively long microgravity period (approximately 90 s). The CLPHPs are partially filled with FC-72 and have, respectively, an inner tube diameter larger (3 mm) and slightly smaller (1.6 mm) than the critical diameter evaluated in static Earth gravity conditions. On ground, the small diameter CLPHP effectively works as a Pulsating Heat Pipe (PHP): the characteristic slug and plug flow pattern forms inside the tube and the heat exchange is triggered by thermally driven self-sustained oscillations of the working fluid. On the other hand, the large diameter CLPHP works as a two- phase thermosyphon in vertical position and doesn't work in horizontal position: in this particular condition, the working fluid stratifies within the device as the surface tension force is no longer able to balance buoyancy. Then, the idea to test the CLPHPs in reduced gravity conditions: as the gravity reduces the buoyancy forces becomes less intense and it is possible to recreate the typical PHP flow pattern also for larger inner tube diameters. This allows to increase the heat transfer rate and, consequently, to decrease the overall thermal resistance. Even though it was not possible to experience low gravity conditions due to a failure in the yoyo de-spin system, the thermal response to the peculiar acceleration field (hyper-gravity) experienced on board are thoroughly described.

  12. Creeping motion of single droplet and mixing behaviour of coalescing droplets in a tube flow

    NASA Astrophysics Data System (ADS)

    Muraoka, Masahiro; Ueno, Ichiro; Mizoguchi, Hiroshi; Toshihiko, Kamiyama; Wada, Takuma

    2012-07-01

    Creeping motion of single droplet and coalescence of droplets in a tube flow is expected to be useful for fluid handling technique, controlling chemical reaction and so on. In the case of motion of droplets with suspended particles, Drug delivery system can be cited as one of applications. The problem is also underlying basis on analyzing the flow of multiphase fluids through porous media. Such phenomena can be seen, for instance, in enhanced oil recovery, breaking of emulsions in porous coalescers and so on. Regarding examples of studies of creeping motion of droplets in a tube flow, Hetsroni G. et al[1] considered motion of droplets and bubbles with small d/D(d:undeformed diameter of droplet or bubble, D: tube diameter)theoretically. Higdon et al[2] obtained resistance functions for spherical particles, droplets and bubbles numerically. Olbricht at al.[3,4] investigated mainly coalescence time of coalescence phenomena of droplets. There exists little information, however, on mixing behaviour of coalescing droplets and effects of suspended particles in the droplets concerned on their coalescence. In this experiment, a glass tube of 2.0 mm in inner diameter, 7.0 mm in outer diameter, and 1500 mm in length is used as a test tube. Silicones oil of 50, 1000 and 6000cSt are employed as the test fluid for the droplet. Mixture fluid of glycerol and pure water is used for a surrounding fluid in the tube flow. The density of the droplets is matched to that of the surrounding fluid by adding carbon tetrachloride. An over flow tank is used to keep the flow in the tube steady at a designated averaged velocity V. The test tube is surrounded by a tank filled with a temperature-controlled water to keep the temperature of the system constant. Droplets are injected into the test tube using micro-syringes in front of inlet of the tube. Behaviours of droplets and suspended particles are monitored by a digital video camera and high speed cameras placed on a sliding stage. The motion

  13. Canyon air flow measurement utilizing ASME standard pitot tube arrays

    SciTech Connect

    Moncrief, B.R.

    1990-01-01

    The Savannah River Site produces nuclear materials for national defense. In addition to nuclear reactors, the site has separation facilities for reprocessing irradiated nuclear fuel. The chemical separation of highly radioactive materials takes place by remote control in large buildings called canyons. Personnel in these buildings are shielded from radiation by thick concrete walls. Contaminated air is exhausted from the canyons and contaminants are removed by sand filters prior to release to the atmosphere through a stack. When these facilities were built on a crash basis in the early 1950's, inadequate means were provided for pressure and air flow measurement. This presentation describes the challenge we faced in retrofitting a highly radioactive, heavily shielded facility with instrumentation to provide this capability.

  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. Application of program LAURA to perfect gas shock tube flows: A parametric study

    NASA Technical Reports Server (NTRS)

    Mitterer, K. F.; Mitcheltree, R. A.; Gnoffo, P. A.

    1992-01-01

    The Langley Aerothermodynamic Upwind Relaxation Algorithm (LAURA) was originally developed to solve steady-flow problems. The desire to validate the algorithm with shock tube experimental data motivated the development of a time-accurate version of the LAURA code. The current work presents a test of the Algorithm. Computational results are compared with the exact solution for a simple shock tube case. The parameters examined are Courant number, relaxation sweeps, grid spacing, and the inviscid relaxation factor. The results of the study indicate that LAURA is capable of producing accurate solutions when appropriate values are used for each parameter.

  16. Pseudocompressible approximation and statistical turbulence modeling: application to shock tube flows.

    PubMed

    Soulard, Olivier; Griffond, Jérôme; Souffland, Denis

    2012-02-01

    In this work, a pseudocompressible approximation relevant for turbulent mixing flows encountered in shock tubes is derived. The asymptotic analysis used for this purpose puts forward the role played by four dimensionless numbers on the flow compressibility, namely, the turbulent, deformation, stratification, and buoyancy force Mach numbers. The existence of rapid distortion and diffusion-dissipation regimes is also accounted for in the analysis. Some consequences of the derived pseudocompressible approximation on statistical turbulence models are discussed. In particular, the evolutions of the density variance and flux are examined, as well as the turbulent transport of energy. The different aspects of this study are assessed by performing a direct numerical simulation of a shock tube flow configuration.

  17. Modelling complex draft-tube flows using near-wall turbulence closures

    SciTech Connect

    Ventikos, Y.; Sotiropoulos, F.; Patel, V.C.

    1996-12-31

    This paper presents a finite-volume method for simulating flows through complex hydroturbine draft-tube configurations using near-wall turbulence closures. The method employs the artificial-compressibility pressure-velocity coupling approach in conjunction with multigrid acceleration for fast convergence on very fine grids. Calculations are carried out for a draft tube with two downstream piers on a computational mesh consisting of 1.2x10{sup 6} nodes. Comparisons of the computed results with measurements demonstrate the ability of the method to capture most experimental trends with reasonable accuracy. Calculated three-dimensional particle traces reveal very complex flow features in the vicinity of the piers, including horse-shoe longitudinal vortices and and regions of flow reversal.

  18. Analysis and testing of compressible flow ejectors with variable area mixing tubes.

    NASA Technical Reports Server (NTRS)

    Hickman, K. E.; Hill, P. G.; Gilbert, G. B.

    1972-01-01

    An analytical model has been developed to predict the flow behavior within axisymmetric single-nozzle ejectors employing variable-area mixing tubes. The primary flow may be supersonic or subsonic and may have a different stagnation temperature from the subsonic secondary flow. Tests were performed on an ejector with an 800 F supersonic (M = 2.72) primary jet to evaluate the analytical model. Measured velocity profiles, temperature profiles, and wall static pressure distributions are presented and compared to the analytical predictions. Agreement is generally good.

  19. Characteristics of Pulsating Aurora

    NASA Astrophysics Data System (ADS)

    Humberset, B. K.; Gjerloev, J. W.; Mann, I. R.; Samara, M.; Michell, R.

    2013-12-01

    We have investigated the spatiotemporal characteristics of pulsating auroral patches observed with an all-sky imager located at Poker Flat, Alaska. Pulsating aurora often covers the entire sky with intermixed large and small-scale patches that vary in intensity or disappear and reappear on different time scales and timings. The broad definition of pulsating aurora covers patches and bands from tens to several tens of km which have a quasi-periodic temporal variation from 1 s to tens of seconds. In this paper we examine >15 patches from different events. We analyze all-sky movies (557.7 nm, 3.31 Hz) with a simple, yet robust, technique that allows us to determine the scale size dependent variability of the >15 individual patches. A spatial 2D Fourier Transform is used to separate the aurora into different horizontal scale sizes, and by correlating each patch for all image separations and available scale sizes smaller than the patch itself, we reveal what scale sizes are pulsating and their variability. The patches are found to be persistent, meaning that we can follow them for typically 5 minutes. The period of the pulsations is often remarkably variable and it seems that only certain scale sizes pulsate (typically the size of the patch). The patches drift with the background ExB plasma drift indicating that the magnetospheric source mechanism drifts with the field lines.

  20. Cross-Roll Flow Forming of ODS Alloy Heat Exchanger Tubes For Hoop Creep Enhancement

    SciTech Connect

    Bimal K. Kad

    2006-09-30

    Mechanically alloyed oxide dispersion strengthened (ODS) Fe-Cr-Al alloy thin walled tubes and sheets, produced via powder processing and consolidation methodologies, are promising materials for eventual use at temperatures up to 1200 C in the power generation industry, far above the temperature capabilities of conventional alloys. Target end-uses range from gas turbine combustor liners to high aspect ratio (L/D) heat exchanger tubes. Grain boundary creep processes at service temperatures, particularly those acting in the hoop direction, are the dominant failure mechanisms for such components. The processed microstructure of ODS alloys consists of high aspect ratio grains aligned parallel to the tube axis, a result of dominant axial metal flow which aligns the dispersoid particles and other impurities in the longitudinal direction. The dispersion distribution is unaltered on a micro scale by recrystallization thermal treatments, but the high aspect ratio grain shape typically obtained limits transverse grain spacing and consequently the hoop creep response. Improving hoop creep in ODS-alloy components will require understanding and manipulating the factors that control the recrystallization behavior, and represents a critical materials design and development challenge that must be overcome in order to fully exploit the potential of ODS alloys. The objectives of this program are to (1) increase creep-strength at temperature in ODS-alloy tube and liner components by 100% via, (2) preferential cross-roll flow forming and grain/particle fibering in the critical hoop direction. The research program outlined here is iterative in nature and is intended to systematically (a) examine and identify post-extrusion forming methodologies to create hoop strengthened tubes, which will be (b) evaluated at ''in-service'' loads at service temperatures and environments. In this 12th quarter of performance, program activities are concluded for Task 2 and continuing for Tasks 3, 4 and

  1. Experiment on Flow Boiling of HFC134a in a Multi-port Extruded Tube

    NASA Astrophysics Data System (ADS)

    Kuwahara, Ken; Koyama, Shigeru; Kazari, Kengo; Nakahita, Kouichi

    In the present study, the local heat transfer and pressure drop characteristics are investigated experimentally for the flow boiling of refrigerant HFC134a in a multi-port extruded tube of 1.06mm in hydraulic diameter. The test tube is 865mm in total length made of aluminum. The pressure drop was measured at an interval of 191mm, the local heat transfer coefficient was measured in every subsection of 75mm in effective heating length. The measured pressure drop was compared with a few correlations. Those data agree with the correlation of Koyama et al., proposed for condensation process, and of Friedel. The local heat transfer coefficients were also compared with correlation of Yu et al. It is pointed out that multiplier of the convection term in a rectangular channel is different from that of circular tube.

  2. Micromachined lab-on-a-tube sensors for simultaneous brain temperature and cerebral blood flow measurements.

    PubMed

    Li, Chunyan; Wu, Pei-Ming; Hartings, Jed A; Wu, Zhizhen; Cheyuo, Cletus; Wang, Ping; LeDoux, David; Shutter, Lori A; Ramaswamy, Bharat Ram; Ahn, Chong H; Narayan, Raj K

    2012-08-01

    This work describes the development of a micromachined lab-on-a-tube device for simultaneous measurement of brain temperature and regional cerebral blood flow. The device consists of two micromachined gold resistance temperature detectors with a 4-wire configuration. One is used as a temperature sensor and the other as a flow sensor. The temperature sensor operates with AC excitation current of 500 μA and updates its outputs at a rate of 5 Hz. The flow sensor employs a periodic heating and cooling technique under constant-temperature mode and updates its outputs at a rate of 0.1 Hz. The temperature sensor is also used to compensate for temperature changes during the heating period of the flow sensor to improve the accuracy of flow measurements. To prevent thermal and electronic crosstalk between the sensors, the temperature sensor is located outside the "thermal influence" region of the flow sensor and the sensors are separated into two different layers with a thin-film Copper shield. We evaluated the sensors for accuracy, crosstalk and long-term drift in human blood-stained cerebrospinal fluid. These in vitro experiments showed that simultaneous temperature and flow measurements with a single lab-on-a-tube device are accurate and reliable over the course of 5 days. It has a resolution of 0.013 °C and 0.18 ml/100 g/min; and achieves an accuracy of 0.1 °C and 5 ml/100 g/min for temperature and flow sensors respectively. The prototype device and techniques developed here establish a foundation for a multi-sensor lab-on-a-tube, enabling versatile multimodality monitoring applications.

  3. Studies on heat transfer in flow of silver nanofluid through a straight tube with twisted tape inserts

    NASA Astrophysics Data System (ADS)

    Waghole, D. R.; Warkhedkar, R. M.; Kulkarni, V. S.; Shrivastva, R. K.

    2016-02-01

    Convective heat transfer in the flow of silver nanofluid through a straight tube with twisted tape inserts was investigated experimentally. This straight tube was used as absorber/receiver tube in parabolic trough collector. The experiments were conducted for Reynolds number range 500 < Re < 6000 with twisted tape inserts of different twist ratio range 0.577 < H/D < 1.732. This experimental study shows that twisted tape inserts enhances heat transfer rate in the tube. The heat transfer coefficient and friction factor in the flow of silver nanofliud with 5 % volume fraction (concentration) are higher compared to the flow of water. From this study, Nusselt number, friction factor and enhancement factor are found as 2.0-3.0 times, 10-48.5 and 135-175 %, respectively with silver nanofliud. Finally new possible correlations for predicting heat transfer and friction factor in the flow of silver nanofliud through the straight tube with twisted tape inserts are proposed.

  4. Nanofluids heat transfer and flow analysis in vertical spirally coiled tubes using Eulerian two-phase turbulent model

    NASA Astrophysics Data System (ADS)

    Naphon, P.; Arisariyawong, T.; Nualboonrueng, T.

    2017-02-01

    A computation fluid dynamics study has been performed to analyze the nanofluids heat transfer and flow characteristics in the spirally coiled tubes. Eulerian two-phase turbulent model is applied to simulate the heat transfer and flow characteristics in the vertical spirally coiled tube. The spirally coiled tubes are fabricated by bending a 8.50 mm inner diameter straight copper tube into a spiral-coil with two different curvature ratios of 0.035, 0.060. The predicted results are verified with the present measured data. Reasonable agreement is obtained from the comparison between the measured data and the predicted results. In addition, due to the centrifugal force, the induced secondary flow has significant effect on the heat transfer enhancement as flowing through the spirally coiled tube. Effects of curvature, nanofluids concentration and hot water temperature on the nanofluids heat transfer characteristics and pressure drop are considered.

  5. Nanofluids heat transfer and flow analysis in vertical spirally coiled tubes using Eulerian two-phase turbulent model

    NASA Astrophysics Data System (ADS)

    Naphon, P.; Arisariyawong, T.; Nualboonrueng, T.

    2017-07-01

    A computation fluid dynamics study has been performed to analyze the nanofluids heat transfer and flow characteristics in the spirally coiled tubes. Eulerian two-phase turbulent model is applied to simulate the heat transfer and flow characteristics in the vertical spirally coiled tube. The spirally coiled tubes are fabricated by bending a 8.50 mm inner diameter straight copper tube into a spiral-coil with two different curvature ratios of 0.035, 0.060. The predicted results are verified with the present measured data. Reasonable agreement is obtained from the comparison between the measured data and the predicted results. In addition, due to the centrifugal force, the induced secondary flow has significant effect on the heat transfer enhancement as flowing through the spirally coiled tube. Effects of curvature, nanofluids concentration and hot water temperature on the nanofluids heat transfer characteristics and pressure drop are considered.

  6. Numerical evaluation of laminar heat transfer enhancement in nanofluid flow in coiled square tubes.

    PubMed

    Sasmito, Agus Pulung; Kurnia, Jundika Candra; Mujumdar, Arun Sadashiv

    2011-05-09

    Convective heat transfer can be enhanced by changing flow geometry and/or by enhancing thermal conductivity of the fluid. This study proposes simultaneous passive heat transfer enhancement by combining the geometry effect utilizing nanofluids inflow in coils. The two nanofluid suspensions examined in this study are: water-Al2O3 and water-CuO. The flow behavior and heat transfer performance of these nanofluid suspensions in various configurations of coiled square tubes, e.g., conical spiral, in-plane spiral, and helical spiral, are investigated and compared with those for water flowing in a straight tube. Laminar flow of a Newtonian nanofluid in coils made of square cross section tubes is simulated using computational fluid dynamics (CFD)approach, where the nanofluid properties are treated as functions of particle volumetric concentration and temperature. The results indicate that addition of small amounts of nanoparticles up to 1% improves significantly the heat transfer performance; however, further addition tends to deteriorate heat transfer performance.

  7. Turbulent flow regime in coiled tubes: local heat-transfer coefficient

    NASA Astrophysics Data System (ADS)

    Bozzoli, F.; Cattani, L.; Mocerino, A.; Rainieri, S.

    2017-08-01

    Wall curvature represents a widely adopted technique for enhancing heat transfer: the fluid flowing inside a coiled pipe experiences the centrifugal force and this phenomenon induces local maxima in the velocity distribution that locally increase the temperature gradients at the wall by enhancing the heat transfer both in the laminar and in the turbulent flow regime. Consequently, the distribution of the velocity field over the cross-section of the tube is strongly uneven thus leading to significant variations along the circumferential angular coordinate of the convective heat-transfer coefficient at the wall internal surface: in particular, it shows higher values at the outer bend side of the coil than at the inner bend side. The aim of the present work is to estimate experimentally the local convective heat-transfer coefficient at the fluid wall interface in coiled tubes when turbulent flow regime occurs. In particular, the temperature distribution maps on the external coil wall are employed as input data of the inverse heat conduction problem in the wall and a solution approach based on the Tikhonov regularisation is implemented. The results, obtained with water as working fluid, are focused on the fully developed region in the turbulent flow regime in the Reynolds number range of 5000 to 12,000. For the sake of completeness, the overall efficiency of the coiled tubes under test is assessed under a first-law performance evaluation criterion.

  8. Numerical evaluation of laminar heat transfer enhancement in nanofluid flow in coiled square tubes

    PubMed Central

    2011-01-01

    Convective heat transfer can be enhanced by changing flow geometry and/or by enhancing thermal conductivity of the fluid. This study proposes simultaneous passive heat transfer enhancement by combining the geometry effect utilizing nanofluids inflow in coils. The two nanofluid suspensions examined in this study are: water-Al2O3 and water-CuO. The flow behavior and heat transfer performance of these nanofluid suspensions in various configurations of coiled square tubes, e.g., conical spiral, in-plane spiral, and helical spiral, are investigated and compared with those for water flowing in a straight tube. Laminar flow of a Newtonian nanofluid in coils made of square cross section tubes is simulated using computational fluid dynamics (CFD)approach, where the nanofluid properties are treated as functions of particle volumetric concentration and temperature. The results indicate that addition of small amounts of nanoparticles up to 1% improves significantly the heat transfer performance; however, further addition tends to deteriorate heat transfer performance. PMID:21711901

  9. Selected Ion Flow-Drift Tube Mass Spectrometry: Quantification of Volatile Compounds in Air and Breath.

    PubMed

    Spesyvyi, Anatolii; Smith, David; Španěl, Patrik

    2015-12-15

    A selected ion flow-drift tube mass spectrometric analytical technique, SIFDT-MS, is described that extends the established selected ion flow tube mass spectrometry, SIFT-MS, by the inclusion of a static but variable E-field along the axis of the flow tube reactor in which the analytical ion-molecule chemistry occurs. The ion axial speed is increased in proportion to the reduced field strength E/N (N is the carrier gas number density), and the residence/reaction time, t, which is measured by Hadamard transform multiplexing, is correspondingly reduced. To ensure a proper understanding of the physics and ion chemistry underlying SIFDT-MS, ion diffusive loss to the walls of the flow-drift tube and the mobility of injected H3O(+) ions have been studied as a function of E/N. It is seen that the derived diffusion coefficient and mobility of H3O(+) ions are consistent with those previously reported. The rate coefficient has been determined at elevated E/N for the association reaction of the H3O(+) reagent ions with H2O molecules, which is the first step in the production of H3O(+)(H2O)1,2,3 reagent hydrate ions. The production of hydrated analyte ion was also experimentally investigated. The analytical performance of SIFDT-MS is demonstrated by the quantification of acetone and isoprene in exhaled breath. Finally, the essential features of SIFDT-MS and SIFT-MS are compared, notably pointing out that a much lower speed of the flow-drive pump is required for SIFDT-MS, which facilitates the development of smaller cost-effective analytical instruments for real time breath and fluid headspace analyses.

  10. Experimental investigation of heat transfer performance coefficient in tube bundle of shell and tube heat exchanger in two-phase flow

    NASA Astrophysics Data System (ADS)

    Karaś, Marcin; Zając, Daniel; Ulbrich, Roman

    2014-03-01

    This paper presents the results of studies in two phase gasliquid flow around tube bundle in the model of shell tube heat exchanger. Experimental investigations of heat transfer coefficient on the tubes surface were performed with the aid of electrochemical technique. Chilton-Colburn analogy between heat and mass transfer was used. Twelve nickel cathodes were mounted on the outside surface of one of the tubes. Measurement of limiting currents in the cathodic reduction of ferricyanide ions on nickel electrodes in aqueous solution of equimolar quantities of K3Fe(CN)6 and K4Fe(CN)6 in the presence of NaOH basic solution were applied to determine the mass transfer coefficient. Controlled diffusion from ions at the electrode was observed and limiting current plateau was measured. Measurements were performed with data acquisition equipment controlled by software created for this experiment. Mass transfer coefficient was calculated on the basis of the limiting current measurements. Results of mass transfer experiments (mass transfer coefficient) were recalculated to heat transfer coefficient. During the experiments, simultaneously conducted was the the investigation of two-phase flow structures around tubes with the use of digital particle image velocimetry. Average velocity fields around tubes were created with the use of a number of flow images and compared with the results of heat transfer coefficient calculations.

  11. Hybrid modeling of convective laminar flow in a permeable tube associated with the cross-flow process

    NASA Astrophysics Data System (ADS)

    Venezuela, A. L.; Pérez-Guerrero, J. S.; Fontes, S. R.

    2009-03-01

    The confined flows in tubes with permeable surfaces are associated to tangential filtration processes (microfiltration or ultrafiltration). The complexity of the phenomena do not allow for the development of exact analytical solutions, however, approximate solutions are of great interest for the calculation of the transmembrane outflow and estimate of the concentration polarization phenomenon. In the present work, the generalized integral transform technique (GITT) was employed in solving the laminar and permanent flow in permeable tubes of Newtonian and incompressible fluid. The mathematical formulation employed the parabolic differential equation of chemical species conservation (convective-diffusive equation). The velocity profiles for the entrance region flow, which are found in the connective terms of the equation, were assessed by solutions obtained from literature. The velocity at the permeable wall was considered uniform, with the concentration at the tube wall regarded as variable with an axial position. A computational methodology using global error control was applied to determine the concentration in the wall and concentration boundary layer thickness. The results obtained for the local transmembrane flux and the concentration boundary layer thickness were compared against others in literature.

  12. A numerical investigation of the 3-D flow in shell and tube heat exchangers

    SciTech Connect

    Prithiviraj, M.; Andrews, M.J.

    1996-12-31

    A three-dimensional computer program for simulation of the flow and heat transfer inside Shell and Tube Heat Exchangers has been developed. The simulation of shell and tube heat exchangers is based on a distributed resistance method that uses a modified two equation {kappa}-{epsilon} turbulence model along with non-equilibrium wall functions. Volume porosities and non-homogeneous surface permeabilities account for the obstructions due to the tubes and arbitrary arrangement of baffles. Sub-models are described for baffle-shell and baffle-tube leakage, shellside and tubeside heat transfer, with geometry generators for tubes, baffles, and nozzle inlets and outlets. The sub-models in HEATX use parameters that have not been altered from their published values. Computed heat transfer and pressure drop are compared with experimental data from the Delaware project (Bell, 1963). Numerically computed pressure drops are also compared for different baffle cuts, and different number of baffles with the experiments of Halle et al. (1984) which were performed in an industrial sized heat exchanger at Argonne National Labs. Discussion of the results is given with particular reference to global and local properties such as pressure drop, temperature variation, and heat transfer coefficients. Good agreement is obtained between the experiments and HEATX computations for the shellside pressure drop and outlet temperatures for the shellside and tubeside streams.

  13. Investigation of the flow field inside flat-plate collector tube using PIV technique

    SciTech Connect

    Sookdeo, Steven; Siddiqui, Kamran

    2010-06-15

    The thermofluid process inside the tube of flat-plate collectors is complex because the non-uniform heating of the tube results in the formation of stably and unstably stratified layers of fluid that interact with each other. The measurement and investigation of the flow behaviour inside the collector tube is very challenging. We report on a novel application of the particle image velocimetry (PIV) technique to remotely measure the velocity field inside the collector tube. The two-dimensional velocity fields were measured in the midplane of a collector tube for the Reynolds number range of 150-900 at unheated and four different heating conditions. We have presented and discussed in detail the technique implementation and the associated challenges. The results have shown that the collector heating significantly alters the structure and magnitude of the mean velocity field and influences the heat transfer to the fluid. It is observed that the collector heating causes a significant asymmetry in the mean velocity profiles over the given range of Reynolds numbers and heating conditions. (author)

  14. The Flow and Pressure Relationships in Different Tubes Commonly Used for Semi-occluded Vocal Tract Exercises.

    PubMed

    Amarante Andrade, Pedro; Wistbacka, Greta; Larsson, Hans; Södersten, Maria; Hammarberg, Britta; Simberg, Susanna; Švec, Jan G; Granqvist, Svante

    2016-01-01

    This experimental study investigated the back pressure (P(back)) versus flow (U) relationship for 10 different tubes commonly used for semi-occluded vocal tract exercises, that is, eight straws of different lengths and diameters, a resonance tube, and a silicone tube similar to a Lax Vox tube. All tubes were assessed with the free end in air. The resonance tube and silicone tube were further assessed with the free end under water at the depths from 1 to 7 cm in steps of 1 cm. The results showed that relative changes in the diameter of straws affect P(back) considerably more compared with the same amount of relative change in length. Additionally, once tubes are submerged into water, P(back) needs to overcome the pressure generated by the water depth before flow can start. Under this condition, only a small increase in P(back) was observed as the flow was increased. Therefore, the wider tubes submerged into water produced an almost constant P(back) determined by the water depth, whereas the thinner straws in air produced relatively large changes to P(back) as flow was changed. These differences may be taken advantage of when customizing exercises for different users and diagnoses and optimizing the therapy outcome. Copyright © 2016 The Voice Foundation. Published by Elsevier Inc. All rights reserved.

  15. Modeling of surface-tension-driven flow of blood in capillary tubes.

    PubMed

    Wang, Jun; Huang, Wei; Bhullar, Raghbir S; Tong, Pin

    2004-06-01

    Surface-tension-driven blood flow into a capillary tube, as in some medical devices, is studied. In a previous article, we considered the early stages of the entry flow from a drop of blood into a capillary, and solved the problem analytically under the assumption that the resistance of the air is negligible. In the present note we consider a capillary tube of finite length, with the far end containing a small window which opens to the atmosphere. The dynamic reverberation of the air in the capillary tube is analyzed in conjunction with the dynamics of the blood. Existing computing programs are used to solve the Navier-Stokes equations. The interface is characterized by the surface tension between the blood and the air, and the contact angle at the triple point where the air-blood interface meets the capillary tube wall. The results tell us how good our earlier simplified analysis is. The new numerical results show that the smaller the window, the larger is the effect of aerodynamic reverberation. However, even for a window as small as 4% of the capillary cross section, and located at the end of the capillary, the difference of the time of arrival of the interface at the window is less than 5%.

  16. The Caltech Photooxidation Flow Tube reactor: design, fluid dynamics and characterization

    NASA Astrophysics Data System (ADS)

    Huang, Yuanlong; Coggon, Matthew M.; Zhao, Ran; Lignell, Hanna; Bauer, Michael U.; Flagan, Richard C.; Seinfeld, John H.

    2017-03-01

    Flow tube reactors are widely employed to study gas-phase atmospheric chemistry and secondary organic aerosol (SOA) formation. The development of a new laminar-flow tube reactor, the Caltech Photooxidation Flow Tube (CPOT), intended for the study of gas-phase atmospheric chemistry and SOA formation, is reported here. The present work addresses the reactor design based on fluid dynamical characterization and the fundamental behavior of vapor molecules and particles in the reactor. The design of the inlet to the reactor, based on computational fluid dynamics (CFD) simulations, comprises a static mixer and a conical diffuser to facilitate development of a characteristic laminar flow profile. To assess the extent to which the actual performance adheres to the theoretical CFD model, residence time distribution (RTD) experiments are reported with vapor molecules (O3) and submicrometer ammonium sulfate particles. As confirmed by the CFD prediction, the presence of a slight deviation from strictly isothermal conditions leads to secondary flows in the reactor that produce deviations from the ideal parabolic laminar flow. The characterization experiments, in conjunction with theory, provide a basis for interpretation of atmospheric chemistry and SOA studies to follow. A 1-D photochemical model within an axially dispersed plug flow reactor (AD-PFR) framework is formulated to evaluate the oxidation level in the reactor. The simulation indicates that the OH concentration is uniform along the reactor, and an OH exposure (OHexp) ranging from ˜ 109 to ˜ 1012 molecules cm-3 s can be achieved from photolysis of H2O2. A method to calculate OHexp with a consideration for the axial dispersion in the present photochemical system is developed.

  17. Numerical analysis of the steam flow field in shell and tube heat exchanger

    NASA Astrophysics Data System (ADS)

    Bartoszewicz, Jarosław; Bogusławski, Leon

    2016-06-01

    In the paper, the results of numerical simulations of the steam flow in a shell and tube heat exchanger are presented. The efficiency of different models of turbulence was tested. In numerical calculations the following turbulence models were used: k-ɛ, RNG k-ɛ, Wilcox k-ω, Chen-Kim k-ɛ, and Lam-Bremhorst k-ɛ. Numerical analysis of the steam flow was carried out assuming that the flow at the inlet section of the heat exchanger were divided into three parts. The angle of steam flow at inlet section was determined individually in order to obtain the best configuration of entry vanes and hence improve the heat exchanger construction. Results of numerical studies were verified experimentally for a real heat exchanger. The modification of the inlet flow direction according to theoretical considerations causes the increase of thermal power of a heat exchanger of about 14%.

  18. Saturated flow boiling heat transfer correlation for carbon dioxide for horizontal smooth tubes

    NASA Astrophysics Data System (ADS)

    Turgut, Oguz Emrah; Asker, Mustafa

    2017-01-01

    Literature comprises fewer studies about flow boiling modelling of refrigerants for in tube flows. In addition, researches on two phase flow heat transfer are based on the mathematical models which were derived in a very limited operational condition and correlated for their own measurements. In this study, a new flow boiling model including the superposed effects of nucleate and convective boiling mechanisms is proposed through the minimization of the cumulative error between the proposed mathematical model and actual data by means of artificial cooperative search algorithm and applied to the database of R-744 (carbon dioxide), available from different studies in the literature. Predictions obtained from the proposed model have been compared with those of retained from the literature correlations developed for flow boiling in tubes. The comparison results indicate that the new model outperforms the literature correlations in terms of prediction accuracy. Results of the comparisons reveal that the proposed flow boiling mathematical model has a mean absolute relative error of 14.6% and predicts 76.7% of the experimental data within ±20.0%.

  19. Saturated flow boiling heat transfer correlation for carbon dioxide for horizontal smooth tubes

    NASA Astrophysics Data System (ADS)

    Turgut, Oguz Emrah; Asker, Mustafa

    2017-06-01

    Literature comprises fewer studies about flow boiling modelling of refrigerants for in tube flows. In addition, researches on two phase flow heat transfer are based on the mathematical models which were derived in a very limited operational condition and correlated for their own measurements. In this study, a new flow boiling model including the superposed effects of nucleate and convective boiling mechanisms is proposed through the minimization of the cumulative error between the proposed mathematical model and actual data by means of artificial cooperative search algorithm and applied to the database of R-744 (carbon dioxide), available from different studies in the literature. Predictions obtained from the proposed model have been compared with those of retained from the literature correlations developed for flow boiling in tubes. The comparison results indicate that the new model outperforms the literature correlations in terms of prediction accuracy. Results of the comparisons reveal that the proposed flow boiling mathematical model has a mean absolute relative error of 14.6% and predicts 76.7% of the experimental data within ±20.0%.

  20. A Numerical Model for Time-Dependent Gravity-Driven Flow in a Collapsible Tube

    NASA Astrophysics Data System (ADS)

    Peters, Amanda; Borkin, Michelle; Mandre, Shreyas

    2009-11-01

    We present details of a Navier-Stokes solver to address fluid flows through a circular tube with elastic walls. This is the first implementation of a large structured-grid fluid dynamics code on this architecture. This class of problems, fluid flow through collapsible tubes, is very important to the study of biological systems (respiratory system, circulatory system, etc.) and physical systems (fluid dynamics, engineering, etc.). In contrast to other models, we focus on integrating wall elasticity and time dependance. We successfully model the flow of blood through the jugular vein of a giraffe over time by numerically evaluating a series of hyperbolic PDEs using Lax-Wendroff. Through careful error and stability analysis, we were able to create an accurate and stable simulation. We were able to examine the role that elasticity plays at various length scales and determine it has an impact on the flow velocity over large length scales (i.e. a giraffe) whereas it is negligible over small length scales (i.e. a human) as it is likely overwhelmed by factors such as lateral flow and viscosity. This work presents a strong framework for future CFD studies regarding various human blood flow physiologies including the abdominal aorta.

  1. Experimental perfect-gas study of expansion-tube flow characteristics

    NASA Technical Reports Server (NTRS)

    Shinn, J. L.; Miller, C. G., III

    1978-01-01

    Results of an experimental investigation of expansion tube flow characteristics performed with helium test gas and acceleration gas are presented. The use of helium, eliminates complex real gas chemistry in the comparison of measured and predicted flow quantities. The driver gas was unheated helium at a nominal pressure of 33 MN sq m. The quiescent test gas pressure and quiescent acceleration gas pressure were varied from 0.7 to 50 kN/sq m and from 2.5 to 53 N/sq m, respectively. The effects of tube-wall boundary layer growth and finite secondary diaphragm opening time were examined through the variation of the quiescent gas pressures and secondary diaphragm thickness. Optimum operating conditions for helium test gas were also defined.

  2. A One Dimensional Model to Predict Steady Flow Through a Collapsible Tube

    NASA Astrophysics Data System (ADS)

    Unhale, S. A.; Marino, G.; Parameswaran, S.

    2005-06-01

    Flow through tubes that can collapse during normal operation characterizes virtually every bodily fluid-carrying vessel. A MATLAB program was developed to solve a one-dimensional numerical model for steady state collapsible tube flow. The numerical results were then compared with experimental findings of Bertram [10]. The model included a novel polynomial-defined relationship between the Reynolds number and skin friction coefficient. The results are in strong agreement with experiment (r > 0.95). Further correlation analysis showed significance at the 0.025 level [r 14 = 0.986; r 17 = 0.975; r 15 = 0.990; r 15 = 0.956; r 19 = 0.943; p ≪ 0.001]. An average error of less than ten percent existed between computations and experiment.

  3. Magnetic field effect on flow parameters of blood along with magnetic particles in a cylindrical tube

    NASA Astrophysics Data System (ADS)

    Sharma, Shashi; Singh, Uaday; Katiyar, V. K.

    2015-03-01

    In this paper, the effect of external uniform magnetic field on flow parameters of both blood and magnetic particles is reported through a mathematical model using magnetohydrodynamics (MHD) approach. The fluid is acted upon by a varying pressure gradient and an external uniform magnetic field is applied perpendicular to the cylindrical tube. The governing nonlinear partial differential equations were solved numerically and found that flow parameters are affected by the influence of magnetic field. Further, artificial blood (75% water+25% Glycerol) along with iron oxide magnetic particles were prepared and transported into a glass tube with help of a peristaltic pump. The velocity of artificial blood along with magnetic particles was experimentally measured at different magnetic fields ranging from 100 to 600 mT. The model results show that the velocity of blood and magnetic particles is appreciably reduced under the influence of magnetic field, which is supported by our experimental results.

  4. Monitoring chloramines and bromamines in a humid environment using selected ion flow tube mass spectrometry.

    PubMed

    Hu, Wan-Ping; Langford, Vaughan S; McEwan, Murray J; Milligan, Daniel B; Storer, Malina K; Dummer, Jack; Epton, Michael J

    2010-06-30

    The selectivity and sensitivity of selected ion flow tube mass spectrometry (SIFT-MS) for individual breath analysis of haloamines has been improved by heating the flow tube in a commercial instrument to around 106 degrees C. Data is presented showing the marked reduction in the number density of water clusters of product ions of common breath metabolites that are isobaric with the product ions from monochloramine and monobromamine that are used to monitor the haloamine concentrations. These results have direct relevance to the real-time monitoring of chloramines in drinking water, swimming pools and food processing plants. However, once the isobaric overlaps from water cluster ions are reduced at the higher temperatures, there is no conclusive evidence showing the presence of haloamines on single breath exhalations in the mid parts per trillion range from examination of the breaths of volunteers. Copyright 2010 John Wiley & Sons, Ltd.

  5. Cross-Roll Flow Forming of ODS Alloy Heat Exchanger Tubes For Hoop Creep Enhancement

    SciTech Connect

    Bimal Kad

    2007-09-30

    Mechanically alloyed oxide dispersion strengthened (ODS) Fe-Cr-Al alloy thin walled tubes and sheets, produced via powder processing and consolidation methodologies are promising materials for eventual use at temperatures up to 1200 C in the power generation industry, far above the temperature capabilities of conventional alloys. Target end-uses range from gas turbine combustor liners to high aspect ratio (L/D) heat exchanger tubes. Grain boundary creep processes at service temperatures, particularly those acting in the hoop direction, are the dominant failure mechanisms for such components. The processed microstructure of ODS alloys consists of high aspect ratio grains aligned parallel to the tube axis, a result of dominant axial metal flow which aligns the dispersoid particles and other impurities in the longitudinal direction. The dispersion distribution is unaltered on a micro scale by recrystallization thermal treatments, but the high aspect ratio grain shape typically obtained limits transverse grain spacing and consequently the hoop creep response. Improving hoop creep in ODS-alloy components will require understanding and manipulating the factors that control the recrystallization behavior, and represents a critical materials design and development challenge that must be overcome in order to fully exploit the potential of ODS alloys. The objectives of this program were to (1) increase creep-strength at temperature in ODS-alloy tube and liner components by 100% via, (2) preferential cross-roll flow forming and grain/particle fibering in the critical hoop direction. The research program outlined was iterative and intended to systematically (i) examine and identify post-extrusion forming methodologies to create hoop strengthened tubes, to be (ii) evaluated at 'in-service' loads at service temperatures and environments. Our report outlines the significant hoop creep enhancements possible via secondary cross-rolling and/or flow-forming operations. Each of the

  6. Experimental and Numerical Modeling of Rarefied Gas Flows Through Orifices and Short Tubes

    DTIC Science & Technology

    2005-07-13

    approach (solution of the Navier - Stokes equations , NS hereafter). 437 Report Documentation Page Form ApprovedOMB No. 0704-0188 Public reporting burden for...Continuum approach. The Navier - Stokes computations were performed with commercial software, CFD- FASTRAN, which is a sophisticated compressible finite-volume...micro and nanotechnologies (such as lubrication problems that deal with transitional flows in long channels and tubes) and porous media (represented by a

  7. Loss of feed flow, steam generator tube rupture and steam line break thermohydraulic experiments

    SciTech Connect

    Mendler, O J; Takeuchi, K; Young, M Y

    1986-10-01

    The Westinghouse Model Boiler No. 2 (MB-2) steam generator test model at the Engineering Test Facility in Tampa, Florida, was reinstrumented and modified for performing a series of tests simulating steam generator accident transients. The transients simulated were: loss of feed flow, steam generator tube rupture, and steam line break events. This document presents a description of (1) the model boiler and the associated test facility, (2) the tests performed, and (3) the analyses of the test results.

  8. Uptake Study of Acetone On Ice Using A Vertical Coated Wall Flow Tube. Atmos Pheric Implications.

    NASA Astrophysics Data System (ADS)

    Peybernès, N.; Le Calvé, S.; Mirabel, Ph.

    The upper troposphere defines a region of the atmosphere (between 8 and 12 km) characterised by its low temperatures (-45 to -85 °C) and where cirrus clouds cover a substantial portion (~25 %) of the earth's surface . Some measurements in the upper troposphere showed the presence of high acetone concentrations (up to 3000 pptv) which lead to an enhanced abundance of HOX and likely modify the ozone cycles in this region of the atmosphere. The goal of this work is then to measure uptake coefficients of acetone on ice and to determine its surface coverage. The low pressure and low temperature flow tube (1-5 Torr) has been adapted to study the gas-ice interactions of atmospheric interest. By using this technique, it is possible to study kinetics of chemical reactions on ice which can be doped by adding chemical species 3, 4. This new set-up is coupled with a Mass Spectrometer which allows product identification and quantification. The vertical flow tube has a movable injector which permits to change the reaction distance and then the reaction time. The ice surface is prepared by totally wetting the inner wall of the flow tube with pure water which is then rapidly cooled down to ­20°C. The ice temperature is then regulated between -40°C and -80°C by circulating cool ethanol through a double jacket surrounding the flow tube. Our results permit to estimate the ratio of acetone molecules adsorbed by ice surface to the number of acetone molecules in the gas phase. One can then estimate the influence of its adsorption on ice on its atmospheric lifetime in the upper troposphere. 1Salomon et al., J. Geophys. Res. 102, 21411, (1997). 2S.A. Mckeen et al. Geophys. res. Lett. 24, 3177, (1997). 3 J.P.D. Abbatt et al., J. Geophys. Res. 97, 15819, (1992). 4 D.R. Hanson et al., J. Phys. Chem. 96, 2682, (1992).

  9. A quiet-flow Ludwieg tube for experimental study of high speed boundary layer transition

    NASA Technical Reports Server (NTRS)

    Schneider, Steven P.

    1992-01-01

    A new low Reynolds number quiet-flow Ludwieg tube facility, now under construction, is briefly described, and its advantages outlined. The facility is characterized by good optical access and may be particularly useful for the development of optical instrumentation for the generation and measurement of instability waves. Initial research plans also include work on hot-wire instrumentation, wave generation techniques, roughness and receptivity effects, and suction distribution effects.

  10. CROSS-ROLL FLOW FORMING OF ODS ALLOY HEAT EXCHANGER TUBES FOR HOOP CREEP ENHANCEMENT

    SciTech Connect

    Bimal K. Kad

    2005-06-27

    Mechanically alloyed oxide dispersion strengthened (ODS) Fe-Cr-Al alloy thin walled tubes and sheets, produced via powder processing and consolidation methodologies, are promising materials for eventual use at temperatures up to 1200 C in the power generation industry, far above the temperature capabilities of conventional alloys. Target end-uses range from gas turbine combustor liners to high aspect ratio (L/D) heat exchanger tubes. Grain boundary creep processes at service temperatures, particularly those acting in the hoop direction, are the dominant failure mechanisms for such components. The processed microstructure of ODS alloys consists of high aspect ratio grains aligned parallel to the tube axis, a result of dominant axial metal flow which aligns the dispersoid particles and other impurities in the longitudinal direction. The dispersion distribution is unaltered on a micro scale by recrystallization thermal treatments, but the high aspect ratio grain shape typically obtained limits transverse grain spacing and consequently the hoop creep response. Improving hoop creep in ODS-alloy components will require understanding and manipulating the factors that control the recrystallization behavior, and represents a critical materials design and development challenge that must be overcome in order to fully exploit the potential of ODS alloys. The objectives of this program are to (1) increase creep-strength at temperature in ODS-alloy tube and liner components by 100% via, (2) preferential cross-roll flow forming and grain/particle fibering in the critical hoop direction. Recent studies in cross-rolled ODS-alloy sheets (produced from flattened tubes) indicate that transverse creep is significantly enhanced via controlled transverse grain fibering, and similar improvements are expected for cross-rolled tubes. The research program outlined here is iterative in nature and is intended to systematically (i) prescribe extrusion consolidation methodologies via detailed

  11. Modelling flow pattern transitions for steady upward gas-liquid flow in vertical tubes. [Bubble, slug, churn and dispersed-annular; also existence regions and transitions

    SciTech Connect

    Taitel, Y.; Bornea, D.; Dukler, A.E.

    1980-05-01

    Models for predicting flow patterns in steady upward gas-liquid flow in vertical tubes (such as production-well tubing) delineate the transition boundaries between each of the four basic flow patterns for gas-liquid flow in vertical tubes: bubble, slug, churn, and dispersed-annular. Model results suggest that churn flow is the development region for the slug pattern and that bubble flow can exist in small pipes only at high liquid rates, where turbulent dispersion forces are high. Each transition depends on the flow-rate pair, fluid properties, and pipe size, but the nature of the dependence is different for each transition because of differing control mechanisms. The theoretical predictions are in reasonably good agreement with a variety of published flow maps based on experimental data.

  12. Simulations of transonic shock-tube flow with a model micro-cylinder in the driver.

    PubMed

    Liu, Yi; Kendall, Mark A F

    2007-02-01

    A unique hand-held needle-free powder injection system, using a transient shock-tube flow to deliver powder genes and drugs into human skin for a wide range of treatments, has been proposed. In the development of such devices, a strong non-linear phenomenon, possibly shock process instead of unsteady expansion waves, was observed in the driver portion of the shock-tube flow in the presence of a gas micro-cylinder. In this paper, we further investigate effects of a model micro-cylinder in the driver on the gas dynamics of a prototype clinical device numerically. To accurately simulate such complex shock-tube flows, an efficient numerical solver, MIFVS, is extended to incorporate with a transition-modified turbulence model. Comparison with experimental measurements shows that the extended MIFVS accurately predicts pressure traces in both laminar and turbulent regimes. The separation zone due to a strong non-linear process is properly captured via such transition-modified turbulence model. Numerical investigations and discoveries are presented and discussed.

  13. On the use of the periodicity condition in cross-flow tube

    NASA Astrophysics Data System (ADS)

    Beladjine, Boumedienne; Aounallah, Mohammed; Belkadi, Mustapha; Aadjlout, Lahouari; Imine, Omar

    2015-05-01

    This paper presents the results of measurements and numerical predictions of turbulent cross-flow through an in-line 7×7 bundle configuration with a constant transverse and longitudinal pitch-to-diameter ratio of 1.44. The experiments are conducted to measure the pressure around tubes, using DPS differential pressure scanner with air flow, in square channel at a Reynolds number of 35000 based on the gap velocity and the tube diameter. The commercial ANSYS FLUENT is used to solve the unsteady Reynolds-Averaged Navier-Stokes (RANS) equations. The primary aim of the present study is to search for a turbulent model that could serve as an engineering design tool at a relatively low computational cost. The performances of the Spalart-Allmaras, the RNG k-ɛ, the Shear Stress Transport k-ω and the second moment closure RSM models are evaluated by comparing their simulation results against experimental data. The second objective is to verify the validity of the periodicity assumption taken account in the most previous numerical works by considering the filled bundle geometry. The CFD results show that the Spalart-Allmaras model on the fine mesh are comparable to the experiments while the periodicity statement did not produce consistently the flow behavior in the 7×7 tube bundle configuration.

  14. A computer code for calculating subcooled boiling pressure drop in forced convective tube flows

    NASA Astrophysics Data System (ADS)

    Wong, Christopher F.

    1988-12-01

    A calculation procedure, embodied in a computer code, was developed to calculate the convective subcooled boiling (SCB) pressure drop of water flowing in small diameter vertical or horizontal tubes under the condition of high heat fluxes. The present investigation is an extension of previous work performed by C. T. Kline in 1985. The computer code, presented then and now, numerically integrates the single-phase and separated-flow-model pressure drop equations from the inlet to the outlet of a heated tube. Efforts in this study were concentrated on identifying weaknesses in Kline's best code version and investigating his recommendations for future work. The calculation procedures for each flow regime in the tube were modified to give better overall results. New work focused primarily on the partially-developed boiling (PDB) and fully-developed boiling (FDB) regimes. The pressure drop predictions from each code version were compared to the experimental pressure drop results from the experimental investigations of Dormer/Bergles, Owens/Schrock, and Reynolds.

  15. The effect of flat bar supports on the cross flow induced response of heat exchanger U-tubes

    SciTech Connect

    Weaver, D.S.; Schneider, W.

    1982-01-01

    A wind tunnel study was conducted to determine the effect of flat bar supports on the cross-flow induced response of heat exchanger U-tubes. The 13 mm diameter tubes formed a triangular array with a pitch ratio o 1.57 and a mean U-bend diameter of about 1.5 m. A 0.3 m long section of the array was exposed to a flow parallel to the plane of the U-bends. Experiments were conducted with no supports, with 1 set of flat bars at the apex and with 2 sets of flat bar supports at the apex and 45/sup 0/ points. In each case, the tube response was monitored to a flow velocity beyond that required for fluid elastic instability. Limited experiments were also conducted to examine the effect of tube support clearance on tube response. Conclusions are drawn regarding the effectiveness of flat bars as U-bend antivibration supports.

  16. Optimization and improvement of PM2.5 thermophoretic deposition efficiency in turbulent gas flowing over tube surfaces.

    PubMed

    Tao, Zhou; Zenghui, Wang; Ruichang, Yang

    2005-09-01

    PM2.5 thermophoretic deposition efficiency in turbulent gas flowing over tube surfaces is analyzed using the new concept of potential capacity and potential capacity variation. According to Romay's model, a thermophoretic deposition efficiency model in turbulent gas flowing over tube surfaces is built up based on the potential capacity. Through computing and analyzing thermophoretic deposition efficiency, PM2.5 thermophoretic deposition efficiency in turbulent gas flowing over tube surfaces in direct ratio to the potential capacity variation and in inverse ratio to the temperature ratio of tube wall to entrance gas-particle mixture. And the imprecise notion of thermophoretic deposition efficiency direct ratio to the temperature difference between tube wall and entrance gas-particle mixture is reviewed. There are credible foundations to be provided for improving and researching thermophoretic deposition efficiency in theory and experiment.

  17. Design and Operation of a Cryogenic Nitrogen Pulsating Heat Pipe

    NASA Astrophysics Data System (ADS)

    Diego Fonseca, Luis; Miller, Franklin; Pfotenhauer, John

    2015-12-01

    We report the design, experimental setup and successful test results using an innovative passive cooling system called a “Pulsating Heat Pipe” (PHP) operating at temperatures ranging from 77 K to 80 K and using nitrogen as the working fluid. PHPs, which transfer heat by two phase flow mechanisms through a closed loop tubing have the advantage that no electrical pumps are needed to drive the fluid flow. In addition, PHPs have an advantage over copper straps and thermal conductors since they are lighter in weight, exhibit lower temperature gradients and have higher heat transfer rates. PHPs consist of an evaporator section, thermally anchored to a solid, where heat is received at the saturation temperature where the liquid portion of the two-phase flow evaporates, and a condenser where heat is rejected at the saturation temperature where the vapor is condensed. The condenser section in our experiment has been thermally interfaced to a CT cryocooler from SunPower that has a cooling capacity of 10 W at 77 K. Alternating regions of liquid slugs and small vapor plugs fill the capillary tubing, with the vapor regions contracting in the condenser section and expanding in the evaporator section due to an electric heater that will generate heat loads up to 10 W. This volumetric expansion and contraction provides the oscillatory flow of the fluid throughout the capillary tubing thereby transferring heat from one end to the other. The thermal performance and temperature characteristics of the PHP will be correlated as a function of average condenser temperature, PHP fill liquid ratio, and evaporator heat load. The experimental data show that the heat transfer between the evaporator and condenser sections can produce an effective thermal conductivity up to 35000 W/m-K at a 3.5 W heat load.

  18. Nonlinear saturation of the Rayleigh instability due to oscillatory flow in a liquid-lined tube

    NASA Astrophysics Data System (ADS)

    Halpern, David; Grotberg, James B.

    2003-10-01

    In this paper, the stability of core annular flows consisting of two immiscible fluids in a cylindrical tube with circular cross-section is examined. Such flows are important in a wide range of industrial and biomedical applications. For example, in secondary oil recovery, water is pumped into the well to displace the remaining oil. It is also of relevance in the lung, where a thin liquid film coats the inner surface of the small airways of the lungs. In both cases, the flow is influenced by a surface-tension instability, which may induce the breakup of the core fluid into short plugs, reducing the efficiency of the oil recovery, or blocking the passage of air in the lung thus inducing airway closure. We consider the stability of a thin film coating the inner surface of a rigid cylindrical tube with the less viscous fluid in the core. For thick enough films, the Rayleigh instability forms a liquid bulge that can grow to eventually create a plug blocking the tube. The analysis explores the effect of an oscillatory core flow on the interfacial dynamics and particularly the nonlinear stabilization of the bulge. The oscillatory core flow exerts tangential and normal stresses on the interface between the two fluids that are simplified by uncoupling the core and film analyses in the thin-film high-frequency limit of the governing equations. Lubrication theory is used to derive a nonlinear evolution equation for the position of the air liquid interface which includes the effects of the core flow. It is shown that the core flow can prevent plug formation of the more viscous film layer by nonlinear saturation of the capillary instability. The stabilization mechanism is similar to that of a reversing butter knife, where the core shear wipes the growing liquid bulge back on to the tube wall during the main tidal volume stroke, but allows it to grow back as the stoke and shear turn around. To be successful, the leading film thickness ahead of the bulge must be smaller than the

  19. Numerical prediction of a draft tube flow taking into account uncertain inlet conditions

    NASA Astrophysics Data System (ADS)

    Brugiere, O.; Balarac, G.; Corre, C.; Metais, O.; Flores, E.; Pleroy

    2012-11-01

    The swirling turbulent flow in a hydroturbine draft tube is computed with a non-intrusive uncertainty quantification (UQ) method coupled to Reynolds-Averaged Navier-Stokes (RANS) modelling in order to take into account in the numerical prediction the physical uncertainties existing on the inlet flow conditions. The proposed approach yields not only mean velocity fields to be compared with measured profiles, as is customary in Computational Fluid Dynamics (CFD) practice, but also variance of these quantities from which error bars can be deduced on the computed profiles, thus making more significant the comparison between experiment and computation.

  20. A quiet flow Ludwieg tube for study of transition in compressible boundary layers: Design and feasibility

    NASA Technical Reports Server (NTRS)

    Schneider, Steven P.

    1990-01-01

    Since Ludwieg tubes have been around for many years, and NASA has already established the feasibility of creating quiet-flow wind tunnels, the major question addressed was the cost of the proposed facility. Cost estimates were obtained for major system components, and new designs which allowed fabrication at lower cost were developed. A large fraction of the facility cost comes from the fabrication of the highly polished quiet-flow supersonic nozzle. Methods for the design of this nozzle were studied at length in an attempt to find an effective but less expensive design. Progress was sufficient to show that a quality facility can be fabricated at a reasonable cost.

  1. Numerical simulation of transient inviscid gas flows in a shock tube

    NASA Technical Reports Server (NTRS)

    Yang, J. Y.; Lombard, C. K.; Nagaraj, N.; Bershader, D.

    1985-01-01

    Time-dependent upwind high resolution schemes for solving the Euler equations were developed and applied to simulate 1-D and 2-D transient inviscid gas flows in a shock tube. Using obstacles of different geometries, a series of calculations were carried out to investigate the transient complex shock-wave diffraction phenomena. Shock-wave and objects interactions with shock Mach-number Ms ranging from 2 to 20 were considered. Comparison with analytical and available experimental results indicate good agreement. Display of detailed flow structures including multiple Mach shocks, slip surfaces, and vortex are also given.

  2. Monte Carlo N-Particle Tracking of Ultrafine Particle Flow in Bent Micro-Tubes

    SciTech Connect

    Casella, Andrew M.; Loyalka, Sudarsham K.

    2016-02-16

    The problem of large pressure-differential driven laminar convective-diffusive ultrafine aerosol flow through bent micro-tubes is of interest in several contemporary research areas including; release of contents from pressurized containment vessels, aerosol sampling equipment, advanced scientific instruments, gas-phase micro-heat exchangers, and microfluidic devices. In each of these areas, the predominant problem is the determination of the fraction of particles entering the micro-tube that is deposited within the tube and the fraction that is transmitted through. Due to the extensive parameter restrictions of this class of problems, a Lagrangian particle tracking method making use of the coupling of the analytical stream line solutions of Dean and the simplified Langevin equation is quite a useful tool in problem characterization. This method is a direct analog to the Monte Carlo N-Particle method of particle transport extensively used in nuclear physics and engineering. In this work, 10 nm diameter particles with a density of 1 g/cm3 are tracked within micro-tubes with toroidal bends with pressure differentials ranging between 0.2175 and 0.87 atmospheres. The tubes have radii of 25 microns and 50 microns and the radius of curvature is between 1 m and 0.3183 cm. The carrier gas is helium, and temperatures of 298 K and 558 K are considered. Numerical convergence is considered as a function of time step size and of the number of particles per simulation. Particle transmission rates and deposition patterns within the bent micro-tubes are calculated.

  3. Numerical investigation on nonlinear effect and vortex formation of oscillatory flow throughout a short tube in a thermoacoustic Stirling engine

    NASA Astrophysics Data System (ADS)

    Yang, Peng; Chen, Hui; Liu, Yingwen

    2017-06-01

    In this paper, a two-dimensional axisymmetric model of a thermoacoustic Stirling engine with a short tube where the cross section narrows has been developed. The transient streamlines and vortex formation through short tubes with different diameters in oscillatory flow have been investigated visually by computational fluid dynamics. Three dimensionless parameters, Reynolds number (Re), Keulegan-Carpenter number (KC), and Womersley number (Wo), are used to describe the flow regime and vortex characteristic throughout the short tube. High Re and Wo numbers indicate that the oscillatory flow develops into the turbulent flow through the short tube. The KC number has a direct effect on the transition of streamlines and the development of the vortex. For a small cross section where KC ≈ 1, streamlines rotate and the vortex forms at both sides of the short tube. The vortex stays in the main flow region, and intensity varies as streamlines are convected downstream. The velocity along the radius presents a Poiseuille profile within the influence of the vortex. For a large cross section where KC < 1, streamlines pass the short tube with little rotation and the vortex disappears in the main flow region and confines near the short tube. The velocity profile tends to be flat. The nonlinear effects including instantaneous pressure drop and power dissipation throughout the short tube are also discussed. It shows that the time averaged pressure drop is generated at the cost of power dissipation. Finally, the "effectiveness" is applied to evaluate the performance of the short tube. The results suggest that increasing the diameter of the short tube is in favor of reducing power dissipation, which is beneficial to improve "effectiveness."

  4. Creeping gaseous flows through elastic tube and annulus micro-configurations

    NASA Astrophysics Data System (ADS)

    Elbaz, Shai; Jacob, Hila; Gat, Amir

    2016-11-01

    Gaseous flows in elastic micro-configurations is relevant to biological systems (e.g. alveolar ducts in the lungs) as well as to applications such as gas actuated soft micro-robots. We here examine the effect of low-Mach-number compressibility on creeping gaseous axial flows through linearly elastic tube and annulus micro-configurations. For steady flows, the leading-order effects of elasticity on the pressure distribution and mass-flux are obtained. For transient flow in a tube with small deformations, elastic effects are shown to be negligible in leading order due to compressibility. We then examine transient flows in annular configurations where the deformation is significant compared with the gap between the inner and outer cylinders defining the annulus. Both compressibility and elasticity are obtained as dominant terms interacting with viscosity. For a sudden flux impulse, the governing non-linear leading order diffusion equation is initially approximated by a porous-medium-equation of order 2.5 for the pressure square. However, as the fluid expand and the pressure decreases, the governing equation degenerates to a porous-medium-equation of order 2 for the pressure.

  5. Experimental investigation of ice slurry flow pressure drop in horizontal tubes

    SciTech Connect

    Grozdek, Marino; Khodabandeh, Rahmatollah; Lundqvist, Per

    2009-01-15

    Pressure drop behaviour of ice slurry based on ethanol-water mixture in circular horizontal tubes has been experimentally investigated. The secondary fluid was prepared by mixing ethyl alcohol and water to obtain initial alcohol concentration of 10.3% (initial freezing temperature -4.4 C). The pressure drop tests were conducted to cover laminar and slightly turbulent flow with ice mass fraction varying from 0% to 30% depending on test conditions. Results from flow tests reveal much higher pressure drop for higher ice concentrations and higher velocities in comparison to the single phase flow. However for ice concentrations of 15% and higher, certain velocity exists at which ice slurry pressure drop is same or even lower than for single phase flow. It seems that higher ice concentration delay flow pattern transition moment (from laminar to turbulent) toward higher velocities. In addition experimental results for pressure drop were compared to the analytical results, based on Poiseulle and Buckingham-Reiner models for laminar flow, Blasius, Darby and Melson, Dodge and Metzner, Steffe and Tomita for turbulent region and general correlation of Kitanovski which is valid for both flow regimes. For laminar flow and low buoyancy numbers Buckingham-Reiner method gives good agreement with experimental results while for turbulent flow best fit is provided with Dodge-Metzner and Tomita methods. Furthermore, for transport purposes it has been shown that ice mass fraction of 20% offers best ratio of ice slurry transport capability and required pumping power. (author)

  6. An analytical model for decaying swirl flow and heat transfer inside a tube

    SciTech Connect

    Wu, H.Y.; Cheng, H.E.; Shuai, R.J.; Zhou, Q.T.

    2000-02-01

    Decaying swirl flow can enhance the heat transfer inside a tube. For the decaying swirl flow of which maximum tangential velocity is located in the immediate vicinity of the wall, an analytical model based on the fluid theorem about the moment of momentum is proposed for the local maximum tangential velocity, local friction factor, and local Nusselt number in this paper. The analytical solutions compare favorably with the experimental data. Influences of the Reynolds number, wall roughness and initial tangential-to-axial velocity ratio on the decaying characteristics of the friction factor and Nusselt number have been analyzed. The analytical results show that the swirl flow decays more rapidly at the initial segment; for same conditions, the friction factor decays more severely than the Nusselt number; relative to the values of the nonswirl flow, the friction factor increases more intensely than the Nusselt number.

  7. Two phase choke flow in tubes with very large L/D

    NASA Technical Reports Server (NTRS)

    Hendricks, R. C.; Simoneau, R. J.

    1977-01-01

    Data were obtained for two phase and gaseous choked flow nitrogen in a long constant area duct of 16200 L/D with a diverging diffuser attached to the exit. Flow rate data were taken along five isotherms (reduced temperature of 0.81, 0.96, 1.06, 1.12, and 2.34) for reduced pressures to 3. The flow rate data were mapped in the usual manner using stagnation conditions at the inlet mixing chamber upstream of the entrance length. The results are predictable by a two phase homogeneous equilibrium choking flow model which includes wall friction. A simplified theory which in essence decouples the long tube region from the high acceleration choking region also appears to predict the data resonably well, but about 15 percent low.

  8. Convective heat transfer in foams under laminar flow in pipes and tube bundles

    PubMed Central

    Attia, Joseph A.; McKinley, Ian M.; Moreno-Magana, David; Pilon, Laurent

    2014-01-01

    The present study reports experimental data and scaling analysis for forced convection of foams and microfoams in laminar flow in circular and rectangular tubes as well as in tube bundles. Foams and microfoams are pseudoplastic (shear thinning) two-phase fluids consisting of tightly packed bubbles with diameters ranging from tens of microns to a few millimeters. They have found applications in separation processes, soil remediation, oil recovery, water treatment, food processes, as well as in fire fighting and in heat exchangers. First, aqueous solutions of surfactant Tween 20 with different concentrations were used to generate microfoams with various porosity, bubble size distribution, and rheological behavior. These different microfoams were flowed in uniformly heated circular tubes of different diameter instrumented with thermocouples. A wide range of heat fluxes and flow rates were explored. Experimental data were compared with analytical and semi-empirical expressions derived and validated for single-phase power-law fluids. These correlations were extended to two-phase foams by defining the Reynolds number based on the effective viscosity and density of microfoams. However, the local Nusselt and Prandtl numbers were defined based on the specific heat and thermal conductivity of water. Indeed, the heated wall was continuously in contact with a film of water controlling convective heat transfer to the microfoams. Overall, good agreement between experimental results and model predictions was obtained for all experimental conditions considered. Finally, the same approach was shown to be also valid for experimental data reported in the literature for laminar forced convection of microfoams in rectangular minichannels and of macrofoams across aligned and staggered tube bundles with constant wall heat flux. PMID:25552745

  9. Convective heat transfer in foams under laminar flow in pipes and tube bundles.

    PubMed

    Attia, Joseph A; McKinley, Ian M; Moreno-Magana, David; Pilon, Laurent

    2012-12-01

    The present study reports experimental data and scaling analysis for forced convection of foams and microfoams in laminar flow in circular and rectangular tubes as well as in tube bundles. Foams and microfoams are pseudoplastic (shear thinning) two-phase fluids consisting of tightly packed bubbles with diameters ranging from tens of microns to a few millimeters. They have found applications in separation processes, soil remediation, oil recovery, water treatment, food processes, as well as in fire fighting and in heat exchangers. First, aqueous solutions of surfactant Tween 20 with different concentrations were used to generate microfoams with various porosity, bubble size distribution, and rheological behavior. These different microfoams were flowed in uniformly heated circular tubes of different diameter instrumented with thermocouples. A wide range of heat fluxes and flow rates were explored. Experimental data were compared with analytical and semi-empirical expressions derived and validated for single-phase power-law fluids. These correlations were extended to two-phase foams by defining the Reynolds number based on the effective viscosity and density of microfoams. However, the local Nusselt and Prandtl numbers were defined based on the specific heat and thermal conductivity of water. Indeed, the heated wall was continuously in contact with a film of water controlling convective heat transfer to the microfoams. Overall, good agreement between experimental results and model predictions was obtained for all experimental conditions considered. Finally, the same approach was shown to be also valid for experimental data reported in the literature for laminar forced convection of microfoams in rectangular minichannels and of macrofoams across aligned and staggered tube bundles with constant wall heat flux.

  10. Combustor with two stage primary fuel tube with concentric members and flow regulating

    DOEpatents

    Parker, David Marchant; Whidden, Graydon Lane; Zolyomi, Wendel

    1999-01-01

    A combustor for a gas turbine having a centrally located fuel nozzle and inner, middle and outer concentric cylindrical liners, the inner liner enclosing a primary combustion zone. The combustor has an air inlet that forms two passages for pre-mixing primary fuel and air to be supplied to the primary combustion zone. Each of the pre-mixing passages has a circumferential array of swirl vanes. A plurality of primary fuel tube assemblies extend through both pre-mixing passages, with each primary fuel tube assembly located between a pair of swirl vanes. Each primary fuel tube assembly is comprised of two tubular members. The first member supplies fuel to the first pre-mixing passage, while the second member, which extends through the first member, supplies fuel to the second pre-mixing passage. An annular fuel manifold is divided into first and second chambers by a circumferentially extending baffle. The proximal end of the first member is attached to the manifold itself while the proximal end of the second member is attached to the baffle. The distal end of the first member is attached directly to the second member at around its mid-point. The inlets of the first and second members are in flow communication with the first and second manifold chambers, respectively. Control valves separately regulate the flow of fuel to the two chambers and, therefore, to the two members of the fuel tube assemblies, thereby allowing the flow of fuel to the first and second pre-mixing passages to be separately controlled.

  11. CROSS-ROLL FLOW FORMING OF ODS ALLOY HEAT EXCHANGER TUBES FOR HOOP CREEP ENHANCEMENT

    SciTech Connect

    Bimal K. Kad

    2004-05-31

    Mechanically alloyed oxide dispersion strengthened (ODS) Fe-Cr-Al alloy thin walled tubes and sheets, produced via powder processing and consolidation methodologies, are promising materials for eventual use at temperatures up to 1200 C in the power generation industry, far above the temperature capabilities of conventional alloys. Target end-uses range from gas turbine combustor liners to high aspect ratio (L/D) heat exchanger tubes. Grain boundary creep processes at service temperatures, particularly those acting in the hoop direction, are the dominant failure mechanisms for such components. The processed microstructure of ODS alloys consists of high aspect ratio grains aligned parallel to the tube axis, a result of dominant axial metal flow which aligns the dispersoid particles and other impurities in the longitudinal direction. The dispersion distribution is unaltered on a micro scale by recrystallization thermal treatments, but the high aspect ratio grain shape typically obtained limits transverse grain spacing and consequently the hoop creep response. Improving hoop creep in ODS-alloy components will require understanding and manipulating the factors that control the recrystallization behavior, and represents a critical materials design and development challenge that must be overcome in order to fully exploit the potential of ODS alloys. The objectives of this program are to (1) increase creep-strength at temperature in ODS-alloy tube and liner components by 100% via, (2) preferential cross-roll flow forming and grain/particle fibering in the critical hoop direction. Recent studies in cross-rolled ODS-alloy sheets (produced from flattened tubes) indicate that transverse creep is significantly enhanced via controlled transverse grain fibering, and similar improvements are expected for cross-rolled tubes. The research program outlined here is iterative in nature and is intended to systematically (1) prescribe extrusion consolidation methodologies via detailed

  12. CROSS-ROLL FLOW FORMING OF ODS ALLOY HEAT EXCHANGER TUBES FOR HOOP CREEP ENHANCEMENT

    SciTech Connect

    Bimal K. Kad

    2004-03-31

    Mechanically alloyed oxide dispersion strengthened (ODS) Fe-Cr-Al alloy thin walled tubes and sheets, produced via powder processing and consolidation methodologies, are promising materials for eventual use at temperatures up to 1200 C in the power generation industry, far above the temperature capabilities of conventional alloys. Target end-uses range from gas turbine combustor liners to high aspect ratio (L/D) heat exchanger tubes. Grain boundary creep processes at service temperatures, particularly those acting in the hoop direction, are the dominant failure mechanisms for such components. The processed microstructure of ODS alloys consists of high aspect ratio grains aligned parallel to the tube axis, a result of dominant axial metal flow which aligns the dispersoid particles and other impurities in the longitudinal direction. The dispersion distribution is unaltered on a micro scale by recrystallization thermal treatments, but the high aspect ratio grain shape typically obtained limits transverse grain spacing and consequently the hoop creep response. Improving hoop creep in ODS-alloy components will require understanding and manipulating the factors that control the recrystallization behavior, and represents a critical materials design and development challenge that must be overcome in order to fully exploit the potential of ODS alloys. The objectives of this program are to (1) increase creep-strength at temperature in ODS-alloy tube and liner components by 100% via, (2) preferential cross-roll flow forming and grain/particle fibering in the critical hoop direction. Recent studies in cross-rolled ODS-alloy sheets (produced from flattened tubes) indicate that transverse creep is significantly enhanced via controlled transverse grain fibering, and similar improvements are expected for cross-rolled tubes. The research program outlined here is iterative in nature and is intended to systematically (1) prescribe extrusion consolidation methodologies via detailed

  13. CROSS-ROLL FLOW FORMING OF ODS ALLOY HEAT EXCHANGER TUBES FOR HOOP CREEP ENHANCEMENT

    SciTech Connect

    Bimal K. Kad

    2005-02-28

    Mechanically alloyed oxide dispersion strengthened (ODS) Fe-Cr-Al alloy thin walled tubes and sheets, produced via powder processing and consolidation methodologies, are promising materials for eventual use at temperatures up to 1200 C in the power generation industry, far above the temperature capabilities of conventional alloys. Target end-uses range from gas turbine combustor liners to high aspect ratio (L/D) heat exchanger tubes. Grain boundary creep processes at service temperatures, particularly those acting in the hoop direction, are the dominant failure mechanisms for such components. The processed microstructure of ODS alloys consists of high aspect ratio grains aligned parallel to the tube axis, a result of dominant axial metal flow which aligns the dispersoid particles and other impurities in the longitudinal direction. The dispersion distribution is unaltered on a micro scale by recrystallization thermal treatments, but the high aspect ratio grain shape typically obtained limits transverse grain spacing and consequently the hoop creep response. Improving hoop creep in ODS-alloy components will require understanding and manipulating the factors that control the recrystallization behavior, and represents a critical materials design and development challenge that must be overcome in order to fully exploit the potential of ODS alloys. The objectives of this program are to (1) increase creep-strength at temperature in ODS-alloy tube and liner components by 100% via, (2) preferential cross-roll flow forming and grain/particle fibering in the critical hoop direction. Recent studies in cross-rolled ODS-alloy sheets (produced from flattened tubes) indicate that transverse creep is significantly enhanced via controlled transverse grain fibering, and similar improvements are expected for cross-rolled tubes. The research program outlined here is iterative in nature and is intended to systematically (i) prescribe extrusion consolidation methodologies via detailed

  14. CROSS-ROLL FLOW FORMING OF ODS ALLOY HEAT EXCHANGER TUBES FOR HOOP CREEP ENHANCEMENT

    SciTech Connect

    Bimal K. Kad

    2004-08-31

    Mechanically alloyed oxide dispersion strengthened (ODS) Fe-Cr-Al alloy thin walled tubes and sheets, produced via powder processing and consolidation methodologies, are promising materials for eventual use at temperatures up to 1200 C in the power generation industry, far above the temperature capabilities of conventional alloys. Target end-uses range from gas turbine combustor liners to high aspect ratio (L/D) heat exchanger tubes. Grain boundary creep processes at service temperatures, particularly those acting in the hoop direction, are the dominant failure mechanisms for such components. The processed microstructure of ODS alloys consists of high aspect ratio grains aligned parallel to the tube axis, a result of dominant axial metal flow which aligns the dispersoid particles and other impurities in the longitudinal direction. The dispersion distribution is unaltered on a micro scale by recrystallization thermal treatments, but the high aspect ratio grain shape typically obtained limits transverse grain spacing and consequently the hoop creep response. Improving hoop creep in ODS-alloy components will require understanding and manipulating the factors that control the recrystallization behavior, and represents a critical materials design and development challenge that must be overcome in order to fully exploit the potential of ODS alloys. The objectives of this program are to (1) increase creep-strength at temperature in ODS-alloy tube and liner components by 100% via, (2) preferential cross-roll flow forming and grain/particle fibering in the critical hoop direction. Recent studies in cross-rolled ODS-alloy sheets (produced from flattened tubes) indicate that transverse creep is significantly enhanced via controlled transverse grain fibering, and similar improvements are expected for cross-rolled tubes. The research program outlined here is iterative in nature and is intended to systematically (i) prescribe extrusion consolidation methodologies via detailed

  15. CROSS-ROLL FLOW FORMING OF ODS ALLOY HEAT EXCHANGER TUBES FOR HOOP CREEP ENHANCEMENT

    SciTech Connect

    Bimal K. Kad

    2004-11-30

    Mechanically alloyed oxide dispersion strengthened (ODS) Fe-Cr-Al alloy thin walled tubes and sheets, produced via powder processing and consolidation methodologies, are promising materials for eventual use at temperatures up to 1200 C in the power generation industry, far above the temperature capabilities of conventional alloys. Target end-uses range from gas turbine combustor liners to high aspect ratio (L/D) heat exchanger tubes. Grain boundary creep processes at service temperatures, particularly those acting in the hoop direction, are the dominant failure mechanisms for such components. The processed microstructure of ODS alloys consists of high aspect ratio grains aligned parallel to the tube axis, a result of dominant axial metal flow which aligns the dispersoid particles and other impurities in the longitudinal direction. The dispersion distribution is unaltered on a micro scale by recrystallization thermal treatments, but the high aspect ratio grain shape typically obtained limits transverse grain spacing and consequently the hoop creep response. Improving hoop creep in ODS-alloy components will require understanding and manipulating the factors that control the recrystallization behavior, and represents a critical materials design and development challenge that must be overcome in order to fully exploit the potential of ODS alloys. The objectives of this program are to (1) increase creep-strength at temperature in ODS-alloy tube and liner components by 100% via, (2) preferential cross-roll flow forming and grain/particle fibering in the critical hoop direction. Recent studies in cross-rolled ODS-alloy sheets (produced from flattened tubes) indicate that transverse creep is significantly enhanced via controlled transverse grain fibering, and similar improvements are expected for cross-rolled tubes. The research program outlined here is iterative in nature and is intended to systematically (i) prescribe extrusion consolidation methodologies via detailed

  16. Heat Transfer and Flow Characteristics of Flow Boiling of CO2-oil Mixtures in Horizontal Smooth and Micro-fin Tubes

    NASA Astrophysics Data System (ADS)

    Ono, Takashi; Gao, Lei; Honda, Tomohiro

    Experiments on flow pattern, heat transfer and pressure drop of flow boiling of pure CO2 and CO2-oil mixtures in horizontal smooth and micro-fin tubes have been carried out. The smooth tube is a stainless steel tube with an inner diameter of 3.76 mm. The micro-fin tube is a copper tube with a mean inner diameter of 3.75 mm. Experiments were carried out at mass velocities from 100 to 500 kg⁄(m2·s), saturation temperature of 10 °C, and the circulation ratio of lubricating oil (PAG) is from 0 to 1.0 mass%. Flow pattern observations mainly showed the slug and wavy flow for the smooth tube, but the annular flow for the micro-fin tube. As compared with flow patterns in case of pure CO2, an increase in frequency of slug occurrence in slug flow region, and a decrease in liquid amount at the top of the tube in annular flow region were observed in case of CO2-oil mixtures. For pure CO2, the flow boiling heat transfer was dominated by nucleate boiling at low vapor quality region, and the heat transfer coefficients for the micro-fin tube were higher than those of the smooth tube. For CO2-oil mixtures, the flow boiling heat transfer was dominated by convective evaporation especially at high vapor quality region. In addition, the heat transfer coefficient decreased remarkably when the oil circulation ratio was larger than 0.1 mass%. For pressure drop characteristics, in case of pure CO2, the homogeneous model agreed with the experimental results within ± 30 % for the smooth tube. The pressure drops of the micro-fin tube were 0˜70 % higher than those predicted with the homogeneous model. Furthermore, the pressure drops increased at the high oil circulation ratio and high vapor quality conditions. The increases in the pressure drops were considered due to the increase in the thickness of the oil film and the decrease in the effective flow cross-sectional area.

  17. The numerical modelling of falling film thickness flow on horizontal tubes

    NASA Astrophysics Data System (ADS)

    Hassan, I. A.; Sadikin, A.; Isa, N. Mat

    2017-04-01

    This paper presents a computational modelling of water falling film flowing over horizontal tubes. The objective of this study is to use numerical predictions for comparing the film thickness along circumferential direction of tube on 2-D CFD models. The results are then validated with a theoretical result in previous literatures. A comprehensive design of 2-D models have been developed according to the real application and actual configuration of the falling film evaporator as well as previous experimental parameters. A computational modelling of the water falling film is presented with the aid of Ansys Fluent software. The Volume of Fluid (VOF) technique is adapted in this analysis since its capabilities of determining the film thickness on tubes surface is highly reliable. The numerical analysis is carried out under influence of ambient pressures at temperature of 27 °C. Three types of CFD numerical models were analyzed in this simulation with inter tube spacing of 30 mm, 20 mm and 10 mm respectively. The use of a numerical simulation tool on water falling film has resulted in a detailed investigation of film thickness. Based on the numerical simulated results, it is found that the average values of water film thickness for each model are 0.53 mm, 0.58 mm, and 0.63 mm.

  18. Thermal and fluid flow characteristics in a tube equipped with peripherally-cut dual twisted tapes

    NASA Astrophysics Data System (ADS)

    Changcharoen, W.; Somravysin, P.; Eiamsa-ard, S.

    2014-12-01

    This article presents an experimental analysis of the turbulent flow of water in a heat exchanger tube fitted with peripherally-cut dual twisted tapes (PDTs) under a constant wall heat-flux condition. The peripherallycut dual twisted tapes with different cutting pitch ratios (l/y = 0.5, 0.75 and 1.0) were tested for Reynolds numbers in the range of 5400 to 14,000. The experimental results showed thatNusselt number and friction factor of the tubes fitted with PDTswere considerably higher than those of the plain tube and those of the tubes with single twisted tape (ST) and dual twisted tapes (DTs). It was found that PDTs with l/y = 0.5, 0.75 and 1.0 gave higher heat transfer rate than the typical DTs, with average Nusselt numbers greater by 12.1%, 7.8% and 3.8%, respectively. For the range investigated, PDTs with the smallest l/y ratio offered the highest thermal performance factor of 1.14.

  19. Numerical study of chemical reactions in a surface microdischarge tube with mist flow based on experiment

    NASA Astrophysics Data System (ADS)

    Shibata, T.; Nishiyama, H.

    2014-03-01

    Recently, a water treatment method of spraying solution into a discharge region has been developed and shows high energy efficiency. In this study, a simulation model of a water treatment method using a surface microdischarge (SMD) tube with mist flow is proposed for further understanding the detailed chemical reactions. Our model has three phases (plasma, gas and liquid) and three simulation steps. The carrier gas is humid air including 2% or 3% water vapour. The chemical species diffusion characteristics in the SMD tube and the concentrations in a droplet are clarified in a wide pH interval. The simulation results show that the chemical species generated on the SMD tube inner wall are diffused to the central axis and dissolved into fine droplets. Especially, OH radicals dissolve into droplets a few mm away from the SMD tube wall because of acidification of the droplets. Furthermore, the hydrogen peroxide density, which is the most important indicator of a radical reaction in water, is influenced by the initial solution pH. This pH dependence results from ozone self-decomposition in water.

  20. O(2) release from erythrocytes flowing in a narrow O(2)-permeable tube: effects of erythrocyte aggregation.

    PubMed

    Tateishi, N; Suzuki, Y; Cicha, I; Maeda, N

    2001-07-01

    The effects of erythrocyte aggregation on O(2) release were examined using O(2)-permeable fluorinated ethylenepropylene copolymer tubes (inner diameter, 25 microm; outer diameter, 100 microm). Measurements were performed using an apparatus built on an inverted microscope that contained a scanning-grating spectrophotometer with a photon count detector connected to two photomultipliers and an image processor through a video camera. The rate of O(2) release from the cells flowing in the narrow tube was determined based on the visible absorption spectrum and the flow velocity of the cells as well as the tube size. When the tube was exposed to nitrogen-saturated deoxygenated saline containing 10 mM sodium dithionite, the flowing erythrocytes were deoxygenated in proportion to the traveling distance, and the deoxygenation at a given distance increased with decreasing flow velocity and cell concentration (hematocrit). Adding Dextran T-70 to the cell suspension increased erythrocyte aggregation in the tube, which resulted in suppressed cell deoxygenation and increased marginal cell-free-layer thickness. The deoxygenation was inversely proportional to the cell-free-layer thickness. The relation was not essentially altered even when the medium viscosity was adjusted with Dextran T-40 to remain constant. The rate of O(2) release from erythrocytes in the tube was discussed in relation to the O(2) diffusion process. We conclude that the diffusion of O(2) from erythrocytes flowing in narrow tubes is inhibited primarily by erythrocyte aggregation itself and partly by thickening of the cell-free layer.

  1. Influence of lubricant oil on heat transfer performance of refrigerant flow boiling inside small diameter tubes. Part I: Experimental study

    SciTech Connect

    Wei, Wenjian; Ding, Guoliang; Hu, Haitao; Wang, Kaijian

    2007-10-15

    Two-phase flow pattern and heat transfer characteristics of refrigerant-oil mixture flow boiling inside small tubes with inside diameters of 6.34 mm and 2.50 mm are investigated experimentally. The test condition of nominal oil concentration is from 0% to 5%, mass flux from 200 to 400 kg m{sup -2} s{sup -1}, heat flux from 3.2 to 14 kW m{sup -2}, evaporation temperature of 5 C, inlet quality from 0.1 to 0.8, and quality change from 0.1 to 0.2. Wavy, wavy-annular, annular and mist-annular flow pattern in 6.34 mm tube are observed, while only slug-annular and annular flow pattern are observed in 2.50 mm tube. Oil presence can make annular flow to form early and to retard to diminish in quality direction at nominal oil concentration {>=}3%. Augmentation effect of oil on heat transfer coefficient becomes weakened or even diminishes for small diameter tube while detrimental effect of oil on small tube performance becomes more significant than large tube. For both test tubes, variation of heat transfer coefficient and enhanced factor with oil concentration is irregular. Two-phase heat transfer multiplier with refrigerant-oil mixture properties increases consistently and monotonically with local oil concentration at different vapor quality. (author)

  2. Study of the motion and deposition of micro particles in a vertical tube containing uniform gas flow

    NASA Astrophysics Data System (ADS)

    Abolpour, Bahador; Afsahi, M. Mehdi; Soltani Goharrizi, Ataallah; Azizkarimi, Mehdi

    2017-06-01

    In this study, effects of a gaseous jet, formed in a vertical tube containing a uniform gas flow, on the injected micro particles have been investigated. A CFD model has been developed to simulate the particle motion in the tube. This simulation is very close to the experimental data. The results show that, increasing the flow rate of carrier gas or decreasing the flow rate of surrounding gas increases the effect of gaseous jet and also increases trapping rate of the particles by the tube wall. The minimum and maximum residence times of particles approach together with increasing the size of solid particles. Particles larger than 60 μm have a certain and fixed residence time at different flow rates of the carrier or surrounding gas. About 40 μm particle size has minimal trapping by the tube wall at various experimental conditions.

  3. The development of asymmetry for oscillatory flow within a tube containing sharp edge periodic baffles

    NASA Astrophysics Data System (ADS)

    Zheng, Mingzhi; Li, Jie; Mackley, M. R.; Tao, Jianjun

    2007-11-01

    This paper investigates the evolution of asymmetric patterns for oscillatory flow in a baffled tube. A numerical simulation for three-dimensional flows in an axisymmetric geometry was developed and compared with experimental results obtained using particle image velocimetry (PIV). Sharp edged baffles were used for both numerical simulations and experiments. From the numerical simulation, a stability map of the flow symmetry was obtained as a function of Reynold-Strouhal numbers. The simulations show that for all Strouhal numbers, the flow was axisymmetric at Reynolds numbers less than 100 and asymmetric at Reynolds numbers larger than 225. The flow was less stable to asymmetric disturbances at small or large Strouhal numbers when compared to St =1.0. In particular, the flow in the region St <0.5 and Re >100 was asymmetric. Two mechanisms for vortex instability transition into three dimensions has been identified. At small Strouhal numbers, the primary mechanism is a shear (Kelvin-Helmholtz) instability. At larger Strouhal numbers, the axisymmetry of the flow is broken because of the collision of travelling eddies that have been shed from opposite baffles. The numerical results are in general in agreement quantitatively with the experimental observations and both experiment and simulation assist in understanding the development of unsteadiness in periodic reversing flows.

  4. CHF multiplier of subcooled flow boiling for non-uniform heating conditions in swirl tube

    SciTech Connect

    Inasaka, F.; Nariai, H.

    1994-12-31

    The high heat flux components of fusion reactors, such as divertor plates and beam dumps of neutral beam injectors, are estimated to be subjected to very high heat loads more than 10 MW/m{sup 2}. Critical heat flux (CHF), which determines the upper limit of heat removal, is one of the most important problems in designing cooling systems. For practical applications in cooling systems, subcooled flow boiling in water combined with swirl-flow in tubes with internal twisted tape is thought to be the most superior for CHF characteristics in fusion reactor components, heat by irradiation comes in from one side of the wall, and cooling channel is then under circumferentially non-uniform heating condition. Authors have conducted the experiments on the CHF with internal twisted tapes under circumferentially non-uniform heating conditions and showed that when the intensity of non-uniformity increased, q{sub cH} (peak heat flux at burnout under nonuniform heating condition) in tube with internal twisted tape increased above the q{sub c,unif} (CHF under uniform heating condition), though the average qualities were the same for both cases. They also showed that this CHF enhancement was not seen in smooth tubes without tape under the same average qualities.

  5. Experimental analysis of refrigerants flow boiling inside small sized microfin tubes

    NASA Astrophysics Data System (ADS)

    Diani, Andrea; Rossetto, Luisa

    2017-07-01

    The refrigerant charge reduction is one of the most challenging issues that the scientific community has to cope to reduce the anthropic global warming. Recently, mini microfin tubes have been matter of research, since they can reach better thermal performance in small domains, leading to a further refrigerant charge reduction. This paper presents experimental results about R134a flow boiling inside a microfin tube having an internal diameter at the fin tip of 2.4 mm. The mass flux was varied between 375 and 940 kg m-2 s-1, heat flux from 10 to 50 kW m-2, vapor quality from 0.10 to 0.99. The saturation temperature at the inlet of the test section was kept constant and equal to 30 °C. R134a thermal and fluid dynamic performances are presented and compared against those obtained with R1234ze(E) and R1234yf and against values obtained during R134a flow boiling inside a 3.4 mm ID microfin tube.

  6. Numerical modeling of condensation from vapor-gas mixtures for forced down flow inside a tube

    SciTech Connect

    Yuann, R Y; Schrock, V E; Chen, Xiang

    1995-09-01

    Laminar film condensation is the dominant heat transfer mode inside tubes. In the present paper direct numerical simulation of the detailed transport process within the steam-gas core flow and in the condensate film is carried out. The problem was posed as an axisymmetric two dimensional (r, z) gas phase inside an annular condensate film flow with an assumed smooth interface. The fundamental conservation equations were written for mass, momentum, species concentration and energy in the gaseous phase with effective diffusion parameters characterizing the turbulent region. The low Reynolds number two equation {kappa}-{epsilon} model was employed to determine the eddy diffusion coefficients. The liquid film was described by similar formulation without the gas species equation. An empirical correlation was employed to correct for the effect of film waviness on the interfacial shear. A computer code named COAPIT (Condensation Analysis Program Inside Tube) was developed to implement numerical solution of the fundamental equations. The equations were solved by a marching technique working downstream from the entrance of the condensing section. COAPIT was benchmarked against experimental data and overall reasonable agreement was found for the key parameters such as heat transfer coefficient and tube inner wall temperature. The predicted axial development of radial profiles of velocity, composition and temperature and occurrence of metastable vapor add insight to the physical phenomena.

  7. 3D Laboratory Measurements of Forces, Flows, and Collimation in Arched Flux Tubes

    NASA Astrophysics Data System (ADS)

    Haw, Magnus; Bellan, Paul

    2016-10-01

    Fully 3D, vector MHD force measurements from an arched, current carrying flux tube (flux rope) are presented. The experiment consists of two arched plasma-filled flux ropes each powered by a capacitor bank. The two loops are partially overlapped, as in a Venn diagram, and collide and reconnect during their evolution. B-field data is taken on the lower plasma arch using a 54 channel B-dot probe. 3D volumetric data is acquired by placing the probe at 2700 locations and taking 5 plasma shots at each location. The resulting data set gives high resolution (2cm, 10ns) volumetric B-field data with high reproducibility (deviation of 3% between shots). Taking the curl of the measured 3D B-field gives current densities (J) in good agreement with measured capacitor bank current. The JxB forces calculated from the data have a strong axial component at the base of the current channel and are shown to scale linearly with axial gradients in current density. Assuming force balance in the flux tube minor radius direction, we infer near-Alfvenic axial flows from the footpoint regions which are consistent with the measured axial forces. Flux tube collimation is observed in conjunction with these axial flows. These dynamic processes are relevant to the stability and dynamics of coronal loops. Supported provided by NSF, AFOSR.

  8. A Local Condensation Analysis Representing Two-phase Annular Flow in Condenser/radiator Capillary Tubes

    NASA Technical Reports Server (NTRS)

    Karimi, Amir

    1991-01-01

    NASA's effort for the thermal environmental control of the Space Station Freedom is directed towards the design, analysis, and development of an Active Thermal Control System (ATCS). A two phase, flow through condenser/radiator concept was baselined, as a part of the ATCS, for the radiation of space station thermal load into space. The proposed condenser rejects heat through direct condensation of ATCS working fluid (ammonia) in the small diameter radiator tubes. Analysis of the condensation process and design of condenser tubes are based on the available two phase flow models for the prediction of flow regimes, heat transfer, and pressure drops. The prediction formulas use the existing empirical relationships of friction factor at gas-liquid interface. An attempt is made to study the stability of interfacial waves in two phase annular flow. The formulation is presented of a stability problem in cylindrical coordinates. The contribution of fluid viscosity, surface tension, and transverse radius of curvature to the interfacial surface is included. A solution is obtained for Kelvin-Helmholtz instability problem which can be used to determine the critical and most dangerous wavelengths for interfacial waves.

  9. Analysis on the effect of venturi tube structural parameters on fluid flow

    NASA Astrophysics Data System (ADS)

    Zhang, J. X.

    2017-06-01

    Fluid flow occurring in a venturi tube was numerically simulated with the Fluent software, and several factors to affect the mass flux and an asymmetric flow were analyzed, including the contraction ratio, ratio of the throat section length to diameter, the diffusion angle and the inlet and outlet pressure difference. Results show that the minimum pressure point occurs at the intersection between the contraction and throat sections in the venturi tube. As the contraction ratio increases, vacuum degree ascends, and mass flux rises. While both vacuum degree and mass flux reduces as the diffusion angle increases. In addition, an increment in the contraction ratio shortens a fully developed section of velocity in the diffusion section. At the contraction ratio less than 0.2 or the diffusion angle less than 35°, velocity in the diffusion section shows an asymmetric and skewed flow. However, as the inlet and outlet pressure difference increases, mass flux goes up, and thereby occurring a back-flowing in the throat section. The calculated results were compared with the reference's data, both error is within 0.5% - -28%.

  10. Fluid particle diffusion through high-hematocrit blood flow within a capillary tube.

    PubMed

    Saadatmand, Maryam; Ishikawa, Takuji; Matsuki, Noriaki; Jafar Abdekhodaie, Mohammad; Imai, Yohsuke; Ueno, Hironori; Yamaguchi, Takami

    2011-01-04

    Fluid particle diffusion through blood flow within a capillary tube is an important phenomenon to understand, especially for studies in mass transport in the microcirculation as well as in solving technical issues involved in mixing in biomedical microdevices. In this paper, the spreading of tracer particles through up to 20% hematocrit blood, flowing in a capillary tube, was studied using a confocal micro-PTV system. We tracked hundreds of particles in high-hematocrit blood and measured the radial dispersion coefficient. Results yielded significant enhancement of the particle diffusion, due to a micron-scale flow-field generated by red blood cell motions. By increasing the flow rate, the particle dispersion increased almost linearly under constant hematocrit levels. The particle dispersion also showed near linear dependency on hematocrit up to 20%. A scaling analysis of the results, on the assumption that the tracer trajectories were unbiased random walks, was shown to capture the main features of the results. The dispersion of tracer particles was about 0.7 times that of RBCs. These findings provide good insight into transport phenomena in the microcirculation and in biomedical microdevices.

  11. Centrifugal scaling of isothermal gas-liquid flows in horizontal tubes

    NASA Astrophysics Data System (ADS)

    Geraets, Jacques Joseph Marie

    1986-05-01

    To test the similarity criteria of two-phase gas-liquid flows, arising from the governing equations and boundary conditions, the flow of air and a water-glycerine mixture in a 50 mm diameter horizontal tube is compared with a two-phase flow of helium and water in a 5 mm diameter tube rotating around a parallel vertical axis (the effective gravity is 113 g0). Results emphasize that in general only dimensionless correlations provide meaningful predictions. The homogeneous Dukler case 1 (1964b) correlation, which contains no two-phase information, provides the best fit (the standard deviation is 21%) with the measured pressure drops. For predicting flow pattern the most promising approach is that of Taitel and Dukler (1976). Examples of scaling down large diameter, high pressure pipelines are presented. With a scale factor of 1/30 equality of the Froude number, the gas-liquid density ratio, and either the Reynolds number or the Weber number can be realized. Compressibility and gas viscosity are not properly scaled.

  12. Condensation of Forced Convection Two-Phase Flow in a Miniature Tube

    NASA Technical Reports Server (NTRS)

    Begg, E.; Faghri, A.; Krustalev, D.

    1999-01-01

    A physical/mathematical model of annular film condensation at the inlet of a miniature tube has been developed. In the model, the liquid flow is coupled with the vapor flow along the liquid-vapor interface through the interfacial temperature, heat flux, shear stress, and pressure jump conditions due to surface tension effects. The model predicts the shape of the liquid-vapor interface along the condenser and leads to the conclusion that there is complete condensation at a certain distance from the condenser inlet. The numerical results show that complete condensation of the incoming vapor is possible at comparatively low heat loads and that this is a special case of a more general condensation regime with two-phase bubbly flow downstream of the initial annular film condensation region. Observations from the flow visualization experiment confirm the existence and qualitative features of annular film condensation leading to the complete condensation phenomenon in a small diameter (3.25 mm) circular tube condenser.

  13. Experimental measurement of oil-water two-phase flow by data fusion of electrical tomography sensors and venturi tube

    NASA Astrophysics Data System (ADS)

    Liu, Yinyan; Deng, Yuchi; Zhang, Maomao; Yu, Peining; Li, Yi

    2017-09-01

    Oil-water two-phase flows are commonly found in the production processes of the petroleum industry. Accurate online measurement of flow rates is crucial to ensure the safety and efficiency of oil exploration and production. A research team from Tsinghua University has developed an experimental apparatus for multiphase flow measurement based on an electrical capacitance tomography (ECT) sensor, an electrical resistance tomography (ERT) sensor, and a venturi tube. This work presents the phase fraction and flow rate measurements of oil-water two-phase flows based on the developed apparatus. Full-range phase fraction can be obtained by the combination of the ECT sensor and the ERT sensor. By data fusion of differential pressures measured by venturi tube and the phase fraction, the total flow rate and single-phase flow rate can be calculated. Dynamic experiments were conducted on the multiphase flow loop in horizontal and vertical pipelines and at various flow rates.

  14. Evaporation heat transfer and friction characteristics of R-134a flowing downward in a vertical corrugated tube

    SciTech Connect

    Aroonrat, Kanit; Wongwises, Somchai

    2011-01-15

    Differently from most previous studies, the heat transfer and friction characteristics of the pure refrigerant HFC-134a during evaporation inside a vertical corrugated tube are experimentally investigated. The double tube test sections are 0.5 m long with refrigerant flowing in the inner tube and heating water flowing in the annulus. The inner tubes are one smooth tube and two corrugated tubes, which are constructed from smooth copper tube of 8.7 mm inner diameter. The test runs are performed at evaporating temperatures of 10, 15, and 20 C, heat fluxes of 20, 25, and 30 kW/m{sup 2}, and mass fluxes of 200, 300, and 400 kg/m{sup 2} s. The quality of the refrigerant in the test section is calculated using the temperature and pressure obtained from the experiment. The pressure drop across the test section is measured directly by a differential pressure transducer. The effects of heat flux, mass flux, and evaporation temperature on the heat transfer coefficient and two-phase friction factor are also discussed. It is found that the percentage increases of the heat transfer coefficient and the two-phase friction factor of the corrugated tubes compared with those of the smooth tube are approximately 0-10% and 70-140%, respectively. (author)

  15. Cross-Roll Flow Forming of ODS Alloy Heat Exchanger Tubes For Hoop Creep Enhancement

    SciTech Connect

    Bimal K. Kad

    2005-11-23

    Mechanically alloyed oxide dispersion strengthened (ODS) Fe-Cr-Al alloy thin walled tubes and sheets, produced via powder processing and consolidation methodologies, are promising materials for eventual use at temperatures up to 1200 C in the power generation industry, far above the temperature capabilities of conventional alloys. Target end-uses range from gas turbine combustor liners to high aspect ratio (L/D) heat exchanger tubes. Grain boundary creep processes at service temperatures, particularly those acting in the hoop direction, are the dominant failure mechanisms for such components. The processed microstructure of ODS alloys consists of high aspect ratio grains aligned parallel to the tube axis, a result of dominant axial metal flow which aligns the dispersoid particles and other impurities in the longitudinal direction. The dispersion distribution is unaltered on a micro scale by recrystallization thermal treatments, but the high aspect ratio grain shape typically obtained limits transverse grain spacing and consequently the hoop creep response. Improving hoop creep in ODS-alloy components will require understanding and manipulating the factors that control the recrystallization behavior, and represents a critical materials design and development challenge that must be overcome in order to fully exploit the potential of ODS alloys. The objectives of this program are to (1) increase creep-strength at temperature in ODS-alloy tube and liner components by 100% via, (2) preferential cross-roll flow forming and grain/particle fibering in the critical hoop direction. Recent studies in crossrolled ODS-alloy sheets (produced from flattened tubes) indicate that transverse creep is significantly enhanced via controlled transverse grain fibering, and similar improvements are expected for cross-rolled tubes. The research program outlined here is iterative in nature and is intended to systematically (1) examine and identify post-extrusion forming methodologies to

  16. Benefit of pulsation in soft corals

    PubMed Central

    Kremien, Maya; Shavit, Uri; Mass, Tali; Genin, Amatzia

    2013-01-01

    Soft corals of the family Xeniidae exhibit a unique, rhythmic pulsation of their tentacles (Movie S1), first noted by Lamarck nearly 200 y ago. However, the adaptive benefit of this perpetual, energetically costly motion is poorly understood. Using in situ underwater particle image velocimetry, we found that the pulsation motions thrust water upward and enhance mixing across the coral–water boundary layer. The induced upward motion effectively prevents refiltration of water by neighboring polyps, while the intensification of mixing, together with the upward flow, greatly enhances the coral’s photosynthesis. A series of controlled laboratory experiments with the common xeniid coral Heteroxenia fuscescens showed that the net photosynthesis rate during pulsation was up to an order of magnitude higher than during the coral’s resting, nonpulsating state. This enhancement diminished when the concentration of oxygen in the ambient water was artificially raised, indicating that the enhancement of photosynthesis was due to a greater efflux of oxygen from the coral tissues. By lowering the internal oxygen concentration, pulsation alleviates the problem of reduced affinity of ribulose-1,5-bisphosphate carboxylase oxygenase (RuBisCO) to CO2 under conditions of high oxygen concentrations. The photosynthesis–respiration ratio of the pulsating H. fuscescens was markedly higher than the ratios reported for nonpulsating soft and stony corals. Although pulsation is commonly used for locomotion and filtration in marine mobile animals, its occurrence in sessile (bottom-attached) species is limited to members of the ancient phylum Cnidaria, where it is used to accelerate water and enhance physiological processes. PMID:23610420

  17. Benefit of pulsation in soft corals.

    PubMed

    Kremien, Maya; Shavit, Uri; Mass, Tali; Genin, Amatzia

    2013-05-28

    Soft corals of the family Xeniidae exhibit a unique, rhythmic pulsation of their tentacles (Movie S1), first noted by Lamarck nearly 200 y ago. However, the adaptive benefit of this perpetual, energetically costly motion is poorly understood. Using in situ underwater particle image velocimetry, we found that the pulsation motions thrust water upward and enhance mixing across the coral-water boundary layer. The induced upward motion effectively prevents refiltration of water by neighboring polyps, while the intensification of mixing, together with the upward flow, greatly enhances the coral's photosynthesis. A series of controlled laboratory experiments with the common xeniid coral Heteroxenia fuscescens showed that the net photosynthesis rate during pulsation was up to an order of magnitude higher than during the coral's resting, nonpulsating state. This enhancement diminished when the concentration of oxygen in the ambient water was artificially raised, indicating that the enhancement of photosynthesis was due to a greater efflux of oxygen from the coral tissues. By lowering the internal oxygen concentration, pulsation alleviates the problem of reduced affinity of ribulose-1,5-bisphosphate carboxylase oxygenase (RuBisCO) to CO2 under conditions of high oxygen concentrations. The photosynthesis-respiration ratio of the pulsating H. fuscescens was markedly higher than the ratios reported for nonpulsating soft and stony corals. Although pulsation is commonly used for locomotion and filtration in marine mobile animals, its occurrence in sessile (bottom-attached) species is limited to members of the ancient phylum Cnidaria, where it is used to accelerate water and enhance physiological processes.

  18. Experimental study on flow boiling heat transfer of LNG in a vertical smooth tube

    NASA Astrophysics Data System (ADS)

    Chen, Dongsheng; Shi, Yumei

    2013-10-01

    An experimental apparatus is set up in this work to study the upward flow boiling heat transfer characteristics of LNG (liquefied natural gas) in vertical smooth tubes with inner diameters of 8 mm and 14 mm. The experiments were performed at various inlet pressures from 0.3 to 0.7 MPa. The results were obtained over the mass flux range from 16 to 200 kg m-2 s-1 and heat fluxes ranging from 8.0 to 32 kW m-2. The influences of quality, heat flux and mass flux, tube diameter on the heat transfer characteristic are examined and discussed. The comparisons of the experimental heat transfer coefficients with the predicted values from the existing correlations are analyzed. The correlation by Zou et al. [16] shows the best accuracy with the RMS deviation of 31.7% in comparison with the experimental data.

  19. Protective tubes for sodium heated water tubes

    DOEpatents

    Essebaggers, Jan

    1979-01-01

    A heat exchanger in which water tubes are heated by liquid sodium which minimizes the results of accidental contact between the water and the sodium caused by failure of one or more of the water tubes. A cylindrical protective tube envelopes each water tube and the sodium flows axially in the annular spaces between the protective tubes and the water tubes.

  20. The Effect of Fin Pitch on Fluid Elastic Instability of Tube Arrays Subjected to Cross Flow of Water

    NASA Astrophysics Data System (ADS)

    Desai, Sandeep Rangrao; Pavitran, Sampat

    2016-07-01

    Failure of tubes in shell and tube exchangers is attributed to flow induced vibrations of such tubes. There are different excitations mechanisms due to which flow induced vibration occurs and among such mechanisms, fluid elastic instability is the most prominent one as it causes the most violent vibrations and may lead to rapid tube failures within short time. Fluid elastic instability is the fluid-structure interaction phenomenon which occurs when energy input by the fluid force exceeds energy expended in damping. This point is referred as instability threshold and corresponding velocity is referred as critical velocity. Once flow velocity exceeds critical flow velocity, the vibration amplitude increases very rapidly with flow velocity. An experimental program is carried out to determine the critical velocity at instability for plain and finned tube arrays subjected to cross flow of water. The tube array geometry is parallel triangular with cantilever end condition and pitch ratios considered are 2.6 and 2.1. The objective of research is to determine the effect of increase in pitch ratio on instability threshold for plain tube arrays and to assess the effect of addition of fins as well as increase in fin density on instability threshold for finned tube arrays. Plain tube array with two different pitch ratios; 2.1 and 2.6 and finned tube arrays with same pitch ratio; 2.6 but with two different fin pitches; such as fine (10 fpi) and coarse (4 fpi) are considered for the experimentation. Connors' equation that relates critical velocity at instability to different parameters, on which instability depends, has been used as the basis for analysis and the concept of effective diameter is used for the present investigation. The modal parameters are first suitably modified using natural frequency reduction setup that is already designed and developed to reduce natural frequency and hence to achieve experimental simulation of fluid elastic instability within the limited

  1. A criterion to determine uniform and non-uniform stratified liquid-gas flow through horizontal tubes

    SciTech Connect

    Bishop, A.A.; Deshpande, S.D.

    1986-04-01

    Non-uniform liquid-gas stratified flow (i.e. flow with an interfacial level gradient, ILG) can exist when high viscosity liquids and/or large diameter tubes are used. The available data, covering a wide range of liquid viscosities (0.8 to 310 mPa.s) and tube diameters (0.0254 m to 0.216 m), are analyzed. It is shown that the Lockhart-Martinelli parameter, X less than or equal to 1 is a criterion to determine uniform stratified flow and disappearance of ILG. In addition, interfacial shear stress relationships are also shown to be indicative of different types of stratified flow.

  2. KELVIN-HELMHOLTZ INSTABILITY IN CORONAL MAGNETIC FLUX TUBES DUE TO AZIMUTHAL SHEAR FLOWS

    SciTech Connect

    Soler, R.; Terradas, J.; Oliver, R.; Ballester, J. L.; Goossens, M.

    2010-04-01

    Transverse oscillations of coronal loops are often observed and have been theoretically interpreted as kink magnetohydrodynamic (MHD) modes. Numerical simulations by Terradas et al. suggest that shear flows generated at the loop boundary during kink oscillations could give rise to a Kelvin-Helmholtz instability (KHI). Here, we investigate the linear stage of the KHI in a cylindrical magnetic flux tube in the presence of azimuthal shear motions. We consider the basic, linearized MHD equations in the beta = 0 approximation and apply them to a straight and homogeneous cylindrical flux tube model embedded in a coronal environment. Azimuthal shear flows with a sharp jump of the velocity at the cylinder boundary are included in the model. We obtain an analytical expression for the dispersion relation of the unstable MHD modes supported by the configuration, and compute analytical approximations of the critical velocity shear and the KHI growth rate in the thin tube limit. A parametric study of the KHI growth rates is performed by numerically solving the full dispersion relation. We find that fluting-like modes can develop a KHI in timescales comparable to the period of kink oscillations of the flux tube. The KHI growth rates increase with the value of the azimuthal wavenumber and decrease with the longitudinal wavenumber. However, the presence of a small azimuthal component of the magnetic field can suppress the KHI. Azimuthal motions related to kink oscillations of untwisted coronal loops may trigger a KHI, but this phenomenon has not been observed to date. We propose that the azimuthal component of the magnetic field is responsible for suppressing the KHI in a stable coronal loop. The required twist is small enough to prevent the development of the pinch instability.

  3. Pulsation dampening device for super critical fluid expansion engine, hydraulic engine or pump in cryogenic service

    SciTech Connect

    Ness, L.A.

    1989-11-07

    This patent describes a surge bottle or pressure pulsation dampening device for cryogenic services. It comprises: a liquid sump section, wherein the liquid sump section is comprised of an enclosed area containing a volume of an incompressible fluid; a warm gas volume section, wherein the warm gas volume section is comprised of an enclosed area containing a volume of a compressible warm gas; and a laminar flow section which connects and allows for communication between the liquid sump section and the warm gas volume section. The laminar flow section is comprised of a number of small bore, thin walled tubes which contain the incompressible fluid in the end connected to the liquid sump section and the compressible warm gas in the end connected to the warm gas volume section wherein the bore of the tubes are such that any movement of the either the compressible warm gas or the incompressible fluid would be laminar flow. During operation, the incompressible fluid and the warm compressible gas within the small bore, thin walled tubes move or oscillate a short distance in each of the tubes with minimal intermixing of the incompressible fluid and the warm compressible gas thereby minimizing heat leak from the warm gas volume section to the liquid sump section into the liquid in the sump.

  4. Experimental and numerical investigation of unsteady behavior of cavitating vortices in draft tube of low specific speed Francis turbine

    NASA Astrophysics Data System (ADS)

    Tamura, Y.; Tani, K.; Okamoto, N.

    2014-03-01

    At both partial and full load of Francis turbines, the unsteady behavior of cavitating draft tube vortices occurs and leads to undesirable matters such as power house vibration, noise and power swing in some cases. This paper presents the investigation of the interaction between the flow pattern at runner outlet and the unsteady behavior of cavitating vortices in draft tube with experimental and numerical approaches. On the experimental research, the pressure pulsation in the draft tube is measured and the unsteady behavior of cavitating vortices is taken pictures with a high speed camera in the model test. On the numerical research, by Computational Fluid Dynamics (CFD) adopting a two-phase unsteady analysis, the analysis domain from the guide vane to the draft tube is carried out for investigating the interaction between the runner outlet flow and the vortex pattern. The pressure pulsation at the upper draft tube and the unsteady behavior of cavitating vortices obtained from CFD results are similar to those obtained in the model test. Detailed analysis of CFD results at overload indicates the repeat of expansion and contraction of cavitating vortices, which were shaped helical vortices with opposite direction of runner rotation, and the corresponding flow pattern in every time step of the pressure pulsations.

  5. Velocity measurements of low Reynolds number tube flow using fiber-optic technology

    SciTech Connect

    Bianchi, J.C.

    1993-03-01

    In 1988 Nielsen started work to measure the spatial variability of the mass flux vector being transported in a porous medium. To measure the spatial variability of the mass flux vector, the spatial variability of its components(velocity, concentration) must be measured. Nielsen was successful in measuring the pore level concentration at many different pores and in verifying the assumption that a nonuniform concentration field exists within the mixing zone between two miscible fluids. However, Nielsen was unable to conduct the necessary pore level velocity measurements needed. Nielsen's work is being continued and a probe is being developed that will measure both velocity and concentration components at pore level. The probe is essentially the same probe used to make the pore level concentration measurements with added capabilities needed to make the velocity measurements. This probe has several design variables, dealing primarily with the velocity component, that need further investigation. The research presented in this thesis investigates these parameters by performing experiments in a capillary tube. The tube is a controlled system where the velocity of the fluid can be determined from the volumetric flow rate using Poiseuille's solution for viscous flow. Also, a statistically based relationship between the velocity measured with the probe and the velocity determined from the volumetric flow rate has been developed.

  6. Nanofluid heat transfer under mixed convection flow in a tube for solar thermal energy applications.

    PubMed

    Sekhar, Y Raja; Sharma, K V; Kamal, Subhash

    2016-05-01

    The solar flat plate collector operating under different convective modes has low efficiency for energy conversion. The energy absorbed by the working fluid in the collector system and its heat transfer characteristics vary with solar insolation and mass flow rate. The performance of the system is improved by reducing the losses from the collector. Various passive methods have been devised to aid energy absorption by the working fluid. Also, working fluids are modified using nanoparticles to improve the thermal properties of the fluid. In the present work, simulation and experimental studies are undertaken for pipe flow at constant heat flux boundary condition in the mixed convection mode. The working fluid at low Reynolds number in the mixed laminar flow range is undertaken with water in thermosyphon mode for different inclination angles of the tube. Local and average coefficients are determined experimentally and compared with theoretical values for water-based Al2O3 nanofluids. The results show an enhancement in heat transfer in the experimental range with Rayleigh number at higher inclinations of the collector tube for water and nanofluids.

  7. Tensile properties and flow behavior analysis of modified 9Cr-1Mo steel clad tube material

    NASA Astrophysics Data System (ADS)

    Singh, Kanwarjeet; Latha, S.; Nandagopal, M.; Mathew, M. D.; Laha, K.; Jayakumar, T.

    2014-11-01

    The tensile properties and flow behavior of modified 9Cr-1Mo steel clad tube have been investigated in the framework of various constitutive equations for a wide range of temperatures (300-923 K) and strain rates (3 × 10-3 s-1, 3 × 10-4 s-1 and 3 × 10-5 s-1). The tensile flow behavior of modified 9Cr-1Mo steel clad tube was most accurately described by Voce equation. The variation of instantaneous work hardening rate (θ = dσ/dε) and σθ with stress (σ) indicated two stage behavior characterized by rapid decrease at low stresses (transient stage) followed by a gradual decrease in high stresses (Stage III). The variation of work hardening parameters and work hardening rate in terms of θ vs. σ and σθ vs. σ with temperature exhibited three distinct regimes. Rapid decrease in flow stress and work hardening parameters and rapid shift of θ vs. σ and σθ vs. σ towards low stresses with increase in temperature indicated dynamic recovery at high temperatures. Tensile properties of the material have been best predicted from Voce equation.

  8. Experimental estimation of the local heat-transfer coefficient in coiled tubes in turbulent flow regime

    NASA Astrophysics Data System (ADS)

    Bozzoli, F.; Cattani, L.; Mocerino, A.; Rainieri, S.

    2016-09-01

    Wall curvature is a popular heat transfer enhancement technique since it gives origin to the centrifugal force in the fluid: this phenomenon promotes local maxima in the velocity distribution that locally increase the temperature gradients at the wall by enhancing the heat transfer both in the laminar and in the turbulent flow regime. This geometry produces an asymmetrical distribution of the velocity field over the cross-section of the tube which lead to a significant variation in the convective heat-transfer coefficient along the circumferential angular coordinate: it presents higher values at the outer bend side of the wall surface than at the inner bend side. Although the irregular distribution of the heat transfer coefficient may be critical in some industrial applications, most of the authors did not investigate this aspect, mainly due to the practical difficulty of measuring heat flux on internal wall surface of a pipe. In the present investigation the local convective heat-transfer coefficient is experimentally estimated at the fluid-wall interface in coiled tubes when turbulent flow regime occurs; in particular, temperature distribution maps on the external coil wall are employed as input data of the inverse heat conduction problem in the wall and a solution approach based on the Tikhonov regularisation is implemented. The results, obtained with water as working fluid, are focused on the fully developed region in the turbulent flow regime in the Reynolds number range of 5000 to 12000.

  9. Velocity measurements of low Reynolds number tube flow using fiber-optic technology

    SciTech Connect

    Bianchi, J. Christopher

    1993-03-01

    In 1988 Nielsen started work to measure the spatial variability of the mass flux vector being transported in a porous medium. To measure the spatial variability of the mass flux vector, the spatial variability of its components(velocity, concentration) must be measured. Nielsen was successful in measuring the pore level concentration at many different pores and in verifying the assumption that a nonuniform concentration field exists within the mixing zone between two miscible fluids. However, Nielsen was unable to conduct the necessary pore level velocity measurements needed. Nielsen`s work is being continued and a probe is being developed that will measure both velocity and concentration components at pore level. The probe is essentially the same probe used to make the pore level concentration measurements with added capabilities needed to make the velocity measurements. This probe has several design variables, dealing primarily with the velocity component, that need further investigation. The research presented in this thesis investigates these parameters by performing experiments in a capillary tube. The tube is a controlled system where the velocity of the fluid can be determined from the volumetric flow rate using Poiseuille`s solution for viscous flow. Also, a statistically based relationship between the velocity measured with the probe and the velocity determined from the volumetric flow rate has been developed.

  10. Influence of tube-entrance configuration on average heat-transfer coefficients and friction factors for air flowing in an Inconel tube

    NASA Technical Reports Server (NTRS)

    Lowdermilk, Warren H; Grele, Milton D

    1950-01-01

    A heat-transfer investigation was conducted with air flowing through an electrically heated Inconel tube having either a long-approach or a right-angle-edge entrance, an inside diameter of 0.402 inch, and a length of 24 inches over a range of Reynolds numbers up to 375,000 and average inside-tube-wall temperatures up to 2000 degrees R. Good correlation of heat-transfer data was obtained for both entrances, which substantiates work previously reported. A fair correlation of friction data was obtained for both entrances. The entrance configuration had little effect on the average heat-transfer and friction coefficients.

  11. High-speed flow visualization in hypersonic, transonic, and shock tube flows

    NASA Astrophysics Data System (ADS)

    Kleine, H.; Olivier, H.

    2017-02-01

    High-speed flow visualisation has played an important role in the investigations conducted at the Stoßwellenlabor of the RWTH Aachen University for many decades. In addition to applying the techniques of high-speed imaging, this laboratory has been actively developing new or enhanced visualisation techniques and approaches such as various schlieren methods or time-resolved Mach-Zehnder interferometry. The investigated high-speed flows are inherently highly transient, with flow Mach numbers ranging from about M = 0.7 to M = 8. The availability of modern high-speed cameras has allowed us to expand the investigations into problems where reduced reproducibility had so far limited the amount of information that could be extracted from a limited number of flow visualisation records. Following a brief historical overview, some examples of recent studies are given, which represent the breadth of applications in which high-speed imaging has been an essential diagnostic tool to uncover the physics of high-speed flows. Applications include the stability of hypersonic corner flows, the establishment of shock wave systems in transonic airfoil flow, and the complexities of the interactions of shock waves with obstacles of various shapes.

  12. Theoretical research of helium pulsating heat pipe under steady state conditions

    NASA Astrophysics Data System (ADS)

    Xu, D.; Liu, H. M.; Li, L. F.; Huang, R. J.; Wang, W.

    2015-12-01

    As a new-type heat pipe, pulsating heat pipe (PHP) has several outstanding features, such as great heat transport ability, strong adjustability, small size and simple construction. PHP is a complex two-phase flow system associated with many physical subjects and parameters, which utilizes the pressure and temperature changes in volume expansion and contraction during phase changes to excite the pulsation motion of liquid plugs and vapor bubbles in the capillary tube between the evaporator and the condenser. At present time, some experimental investigation of helium PHP have been done. However, theoretical research of helium PHP is rare. In this paper, the physical and mathematical models of operating mechanism for helium PHP under steady state are established based on the conservation of mass, momentum, and energy. Several important parameters are correlated and solved, including the liquid filling ratio, flow velocity, heat power, temperature, etc. Based on the results, the operational driving force and flow resistances of helium PHP are analysed, and the flow and heat transfer is further studied.

  13. ACCELEROMETERS IN FLOW FIELDS: A STRUCTURAL ANALYSIS OF THE CHOPPED DUMMY INPILE TUBE

    SciTech Connect

    Howard, T. K.; Marcum, W. R.; Latimer, G. D.; Weiss, A.; Jones, W. F.; Phillips, A. M.; Woolstenhulme, N.; Holdaway, K.; Campbell, J.

    2016-06-01

    Four tests characterizing the structural response of the Chopped-Dummy In-Pile tube (CDIPT) experiment design were measured in the Hydro-Mechanical Fuel Test Facility (HMFTF). Four different test configurations were tried. These configurations tested the pressure drop and flow impact of various plate configurations and flow control orifices to be used later at different reactor power levels. Accelerometers were placed on the test vehicle and flow simulation housing. A total of five accelerometers were used with one on the top and bottom of the flow simulator and vehicle, and one on the outside of the flow simulator. Data were collected at a series of flow rates for 5 seconds each at an acquisition rate of 2 kHz for a Nyquist frequency of 1 kHz. The data were then analyzed using a Fast Fourier Transform (FFT) algorithm. The results show very coherent vibrations of the CDIPT experiment on the order of 50 Hz in frequency and 0.01 m/s2 in magnitude. The coherent vibrations, although small in magnitude pose a potential design problem if the frequencies coincide with the natural frequency of the fueled plates or test vehicle. The accelerometer data was integrated and combined to create a 3D trace of the experiment during the test. The merits of this data as well as further anomalies and artifacts are also discussed as well as their relation to the instrumentation and experiment design.

  14. Computation of the Nusselt number asymptotes for laminar forced convection flows in internally finned tubes

    SciTech Connect

    Ledezma, G.A.; Campo, A.

    1999-04-01

    The utilization of internal longitudinal finned tubes has received unparallel attention in the heat transfer literature over the years as a result of its imminent application in high performance compact heat exchangers to enhance the heat transfer between laminar streams of viscous fluids and tube walls. Here, the central goal of this paper is to report a simple approximate way for the prediction of the two asymptotes for the local Nusselt number in laminar forced convection flows inside internal longitudinal finned tubes. The computational attributes of the Method Of Lines (MOL) are propitious for the determination of asymptotic temperature solutions and corresponding heat transfer rates (one for Z {r_arrow} 0 and the other for z {r_arrow} {infinity}). The two local Nusselt number sub-distributions, namely Nu{sub z{r_arrow}0} and Nu{sub z{r_arrow}{infinity}}, blend themselves into an approximate Nusselt number distribution that covers the entire z-domain in a natural way.

  15. Inducing gas flow and swirl in tubes using ionic wind from corona discharges

    NASA Astrophysics Data System (ADS)

    Weinberg, Felix; Carleton, Fred; Kara, Dhiren; Xavier, Agatha; Dunn-Rankin, Derek; Rickard, Matthew

    2006-02-01

    Air induction and rotation about the axis of a vertical tube is generated by an assembly of corona discharges between pinpoints and earthed electrodes, which induces a swirling ionic wind. The mechanism is elucidated and the geometrical configuration of the electric field lines of force is optimised by studying the deposition of charged particles on the earth electrodes, by numerical modelling of a simplified geometry and ultimately by maximising the measured tangential velocities. Upward convective flows of up to a litre per second are provided by an additional ionic wind pump at the base of the tube. With assemblies of up to three layers of six points each, tangential velocities of up to 3.3 m/s (≈900 rpm) are attained at the periphery, as recorded by small Pitot tubes. The concept, developed particularly for microgravity environments, appears suitable for adding a substantial centrifugal contribution to the operation of electrostatic precipitators and as a basis for further progress on electrical field-controlled burners.

  16. Vortex shedding and fluidelastic instability in a normal square tube array excited by two-phase cross-flow

    NASA Astrophysics Data System (ADS)

    Feenstra, P. A.; Weaver, D. S.; Nakamura, T.

    2003-05-01

    Laboratory experiments were conducted to determine the flow-induced vibration (FIV) response and fluidelastic stability threshold of a model heat exchanger tube bundle subjected to a cross-flow of refrigerant 11. The tube bundle consisted of a normal square array of 12 tubes with outer tube diameters of 7.11mm and a pitch over diameter ratio of 1.485. The experiments were conducted in a flow-loop that was capable of generating single- and two-phase cross-flows over a variety of mass fluxes and void fractions. The primary intent of the research was to improve our understanding of the FIVs of heat exchanger tube arrays subjected to two-phase cross-flow. Of particular concern was the effect of array pattern geometry on fluidelastic instability. The experimental results are analysed and compared with existing data from the literature using various methods of parameter definition. Comparison of tube vibration response in liquid flow with previous results shows a similar occurrence of symmetric vortex shedding that validates the scale model approach in single-phase flow. It was found that the introduction of a small amount of bubbles in the flow disrupted the vortex shedding and thereby caused a significant reduction in streamwise vibration amplitude. The fluidelastic stability thresholds for the present array agree well with results from previous studies. Furthermore, a good collapse of the stability data from various investigations is obtained when the fluid density is defined using the slip model of Feenstra et al. and when an effective two-phase flow velocity is defined using the interfacial velocity model of Nakamura et al.

  17. Circumventing Imprecise Geometric Information and Development of a Unified Modeling Technique for Various Flow Regimes in Capillary Tubes

    NASA Astrophysics Data System (ADS)

    Abbasi, Bahman

    2012-11-01

    Owing to their manufacturability and reliability, capillary tubes are the most common expansion devices in household refrigerators. Therefore, investigating flow properties in the capillary tubes is of immense appeal in the said business. The models to predict pressure drop in two-phase internal flows invariably rely upon highly precise geometric information. The manner in which capillary tubes are manufactured makes them highly susceptible to geometric imprecisions, which renders geometry-based models unreliable to the point of obsoleteness. Aware of the issue, manufacturers categorize capillary tubes based on Nitrogen flow rate through them. This categorization method presents an opportunity to substitute geometric details with Nitrogen flow data as the basis for customized models. The simulation tools developed by implementation of this technique have the singular advantage of being applicable across flow regimes. Thus the error-prone process of identifying compatible correlations is eliminated. Equally importantly, compressibility and chocking effects can be incorporated in the same model. The outcome is a standalone correlation that provides accurate predictions, regardless of any particular fluid or flow regime. Thereby, exploratory investigations for capillary tube design and optimization are greatly simplified. Bahman Abbasi, Ph.D., is Lead Advanced Systems Engineer at General Electric Appliances in Louisville, KY. He conducts research projects across disciplines in the household refrigeration industry.

  18. Cross-Roll Flow Forming of ODS Alloy Heat Exchanger Tubes for Hoop Creep Enhancement

    SciTech Connect

    Bimal K. Kad

    2006-04-10

    Mechanically alloyed oxide dispersion strengthened (ODS) Fe-Cr-Al alloy thin walled tubes and sheets, produced via powder processing and consolidation methodologies, are promising materials for eventual use at temperatures up to 1200 C in the power generation industry, far above the temperature capabilities of conventional alloys. Target end-uses range from gas turbine combustor liners to high aspect ratio (L/D) heat exchanger tubes. Grain boundary creep processes at service temperatures, particularly those acting in the hoop direction, are the dominant failure mechanisms for such components. The processed microstructure of ODS alloys consists of high aspect ratio grains aligned parallel to the tube axis, a result of dominant axial metal flow which aligns the dispersoid particles and other impurities in the longitudinal direction. The dispersion distribution is unaltered on a micro scale by recrystallization thermal treatments, but the high aspect ratio grain shape typically obtained limits transverse grain spacing and consequently the hoop creep response. Improving hoop creep in ODS-alloy components will require understanding and manipulating the factors that control the recrystallization behavior, and represents a critical materials design and development challenge that must be overcome in order to fully exploit the potential of ODS alloys. The objectives of this program are to (1) increase creep-strength at temperature in ODS-alloy tube and liner components by 100% via, (2) preferential cross-roll flow forming and grain/particle fibering in the critical hoop direction. The research program outlined here is iterative in nature and is intended to systematically (1) examine and identify post-extrusion forming methodologies to create hoop strengthened tubes, which will be (2) evaluated at ''in-service'' loads at service temperatures and environments. This research program is being conducted in collaboration with the DOE's Oak Ridge National Laboratory and the vested

  19. Rhythmic pulsations in inferior vena cava in pericardial constriction.

    PubMed

    Mittal, S R

    2016-09-01

    A case of pericardial constriction with rhythmic, nonrespiratory pulsations in inferior vena cava is presented. Hepatic vein flow showed wave form classical of pericardial constriction. Backward transmission of changes in right atrial pressure resulted in rhythmic, nonrespiratory pulsations in inferior vena cava. This echocardiographic finding could help in diagnosis of pericardial constriction. Copyright © 2015 Cardiological Society of India. Published by Elsevier B.V. All rights reserved.

  20. A theoretical computerized study for the electrical conductivity of arterial pulsatile blood flow by an elastic tube model.

    PubMed

    Shen, Hua; Zhu, Yong; Qin, Kai-Rong

    2016-12-01

    The electrical conductivity of pulsatile blood flow in arteries is an important factor for the application of the electrical impedance measurement system in clinical settings. The electrical conductivity of pulsatile blood flow depends not only on blood-flow-induced red blood cell (RBC) orientation and deformation but also on artery wall motion. Numerous studies have investigated the conductivity of pulsatile blood based on a rigid tube model, in which the effects of wall motion on blood conductivity are not considered. In this study, integrating Ling and Atabek's local flow theory and Maxwell-Fricke theory, we develop an elastic tube model to explore the effects of wall motion as well as blood flow velocity on blood conductivity. The simulation results suggest that wall motion, rather than blood flow velocity, is the primary factor that affects the conductivity of flowing blood in arteries.

  1. Experimental investigation of a bioartificial capsule flowing in a narrow tube

    NASA Astrophysics Data System (ADS)

    Risso, Frédéric; Collé-Paillot, Fabienne; Zagzoule, Mokhtar

    This work is an experimental study of the motion and deformation of a bioartificial capsule flowing in a tube of 4 mm diameter. The capsules, initially designed for medical applications, are droplets of salt water surrounded by a thin polymeric membrane. They are immersed in a very viscous Newtonian silicone oil that flows through a tube in the Stokes regime. The properties of the capsules were carefully determined. Two previous experimental papers were devoted to their characterization by osmotic swelling and compression between two plates. The present work also provides a series of tests that allows an accurate definition of the experimental model under investigation. The capsules are buoyant and initially quasi-spherical. Nevertheless, buoyancy and small departures from sphericity are shown to have no significant effects, provided the flowing velocity is large enough for the viscous stress to become predominant. The capsules are also initially slightly over-inflated, but there is no mass transfer through the membrane during the present experiments. Their volume therefore remains constant. The membrane can be described as an elastic two-dimensional material, the elastic moduli of which are independent of the deformation. Far from the tube ends, the capsule reaches a steady state that depends on two parameters: the capillary number, Ca; and the ratio of the radius of the capsule to that of the tube, a/R. The capillary number, which compares the hydrodynamic stresses to the elastic tensions in the membrane, was varied between 0 and 0.125. The radius ratio, which measures the magnitude of the confinement, was varied from 0.75 to 0.95. In the range investigated, the membrane material always remains in the elastic domain. At fixed a/R, the capsule is stretched in the axial direction when Ca is increased. The process of deformation involves two main stages. At small to moderate Ca, the lateral dimension of the capsule decreases whereas its axial length increases. The

  2. Physical hydrodynamic propulsion model study on creeping viscous flow through a ciliated porous tube

    NASA Astrophysics Data System (ADS)

    Akbar, Noreen Sher; Butt, Adil Wahid; Tripathi, Dharmendra; Bég, O. Anwar

    2017-03-01

    The present investigation focusses on a mathematical study of creeping viscous flow induced by metachronal wave propagation in a horizontal ciliated tube containing porous media. Creeping flow limitations are imposed, i.e. inertial forces are small compared to viscous forces and therefore a very low Reynolds number (Re ≪ 1) is taken into account. The wavelength of metachronal wave is also considered to be very large for cilia movement. The physical problem is linearized and exact solutions are developed for the differential equation problem. Mathematica software is used to compute and illustrate numerical results. The influence of slip parameter and Darcy number on velocity profile, pressure gradient and trapping of bolus are discussed with the aid of graphs. It is found that with increasing magnitude of the slip parameter, the trapped bolus inside the streamlines increases in size. The study is relevant to biological propulsion of medical micromachines in drug delivery.

  3. Analysis of Signal Propagation in an Elastic-Tube Flow Model

    NASA Astrophysics Data System (ADS)

    Waggy, Scott; Akman, Ozgur; Biringen, Sedat

    2009-11-01

    We combine linear and nonlinear signal analysis techniques to investigate the transmission of pressure signals along a one-dimensional model of fluid flow in an elastic tube. We derive a simple measure for the robustness of a simulated vessel against in vivo fluctuations in the pressure, based on quantifying the degree of synchronization between proximal and distal pressure pulses. The practical use of this measure will be in its application to simulated pulses generated in response to a stochastic forcing term mimicking biological variations of root pressure in arterial blood flow. Using spectral analysis methods based on synchronization theory, we introduce a novel nonlinear index for measuring the robustness of the model against fluctuations in the forcing signal, based on a general scheme for deriving low-dimensional measures of (biological) performance from higher-dimensional systems of equations.

  4. Flow boiling heat transfer characteristics of methane in a horizontal tube

    NASA Astrophysics Data System (ADS)

    Wang, S.; Gong, M. Q.; Chen, G. F.; Sun, Z. H.; Wu, J. F.

    2014-01-01

    Forced two-phase flow boiling heat transfer coefficients of methane through a smooth horizontal tube with an inner diameter of 6 mm were measured. Experimental investigations were carried out at a particular set of test variables with the pressure range from 0.3 MPa to 0.6 MPa, heat flux range from 5 kW/m2 to 63 kW/m2, mass flux from 110 kg/m2-s to 275 kg/m2-s, and the vapor quality from 0 to 0.25. The influences of different experimental parameters on the flow boiling heat transfer coefficient were discussed. The data were also compared against ten heat transfer coefficient predictive methods. The correlations suggested by Kew-Conwell and Lazarek-Black both show good agreements with a mean absolute relative deviation less than 10%, and over 95% points within an error bandwidth of ±30.0%.

  5. Study of blood viscosity at low shear rate and its flow through viscoelastic tubes and ducts

    NASA Astrophysics Data System (ADS)

    Misra, N.; Sarkar, A.; Srinivas, A.; Kapusetti, G.

    2012-02-01

    A nonlinear mathematical model is developed analytically to study the flow characteristics of visco-elastic fluid through a visco-elastic pipe when it is subjected to external body acceleration. The equations governing the motion of the system are solved analytically with the use of appropriate boundary conditions. For the present scope of study the flow of visco-elastic fluid (blood) in smaller artery which is visco-elastic in nature has been taken. The artery is assumed to be a flexible cylindrical tube containing a non-Newtonian fluid. The unsteady flow mechanism in the artery is subjected to a pulsatile pressure gradient arising from the normal functioning of the heart and also the external body acceleration. Numerical models have finally been developed for Newtonian and Non-Newtonian fluid in order to have a thorough quantitative measure of the effects of body acceleration on the flow velocity, volume flow rate and the wall shear stress of blood in normal human artery and when the artery gets stiffer, just to validate the applicability of the present mathematical model.

  6. Classical Cepheid pulsations

    SciTech Connect

    Moskalik, P.; Buchler, J.R.; Kovacs, G. )

    1990-12-01

    Theoretical models of classical Cepheid variable stars are examined by means of test computations focusing on (1) the systematic period change known as the Hertzsprung or bump progression and (2) the hypothesis (Simon and Schmidt, 1976) that (1) is due to a 2:1 resonance between the fundamental mode and the second overtone. One-parameter families or sequences of models are calculated which represent 'snapshots' of pulsational behavior at different points on the Cepheid evolutionary tracks, and a remarkable uniformity is found when the Fourier coefficients for sequences with moderate luminosity/mass ratios are plottted against the linear period ratio. The complete disappearance of this uniformity when the coefficients are plotted against the pulsation period itself is shown to be consistent with (2). The description of these phenomena with amplitude equations is explained, and expressions for estimating the width of the instability strip are derived. 32 refs.

  7. Attenuation of hydrogen radicals traveling under flowing gas conditions through tubes of different materials

    SciTech Connect

    Grubbs, R.K.; George, S.M.

    2006-05-15

    Hydrogen radical concentrations traveling under flowing gas conditions through tubes of different materials were measured using a dual thermocouple probe. The source of the hydrogen radicals was a toroidal radio frequency plasma source operating at 2.0 and 3.3 kW for H{sub 2} pressures of 250 and 500 mTorr, respectively. The dual thermocouple probe was comprised of exposed and covered Pt/Pt13%Rh thermocouples. Hydrogen radicals recombined efficiently on the exposed thermocouple and the energy of formation of H{sub 2} heated the thermocouple. The second thermocouple was covered by glass and was heated primarily by the ambient gas. The dual thermocouple probe was translated and measured temperatures at different distances from the hydrogen radical source. These temperature measurements were conducted at H{sub 2} flow rates of 35 and 75 SCCM (SCCM denotes cubic centimeter per minute at STP) inside cylindrical tubes made of stainless steel, aluminum, quartz, and Pyrex. The hydrogen radical concentrations were obtained from the temperatures of the exposed and covered thermocouples. The hydrogen concentration decreased versus distance from the plasma source. After correcting for the H{sub 2} gas flow using a reference frame transformation, the hydrogen radical concentration profiles yielded the atomic hydrogen recombination coefficient, {gamma}, for the four materials. The methodology of measuring the hydrogen radical concentrations, the analysis of the results under flowing gas conditions, and the determination of the atomic hydrogen recombination coefficients for various materials will help facilitate the use of hydrogen radicals for thin film growth processes.

  8. Numerical simulation of swirling flow in complex hydroturbine draft tube using unsteady statistical turbulence models

    SciTech Connect

    Paik, Joongcheol; Sotiropoulos, Fotis; Sale, Michael J

    2005-06-01

    A numerical method is developed for carrying out unsteady Reynolds-averaged Navier-Stokes (URANS) simulations and detached-eddy simulations (DESs) in complex 3D geometries. The method is applied to simulate incompressible swirling flow in a typical hydroturbine draft tube, which consists of a strongly curved 90 degree elbow and two piers. The governing equations are solved with a second-order-accurate, finite-volume, dual-time-stepping artificial compressibility approach for a Reynolds number of 1.1 million on a mesh with 1.8 million nodes. The geometrical complexities of the draft tube are handled using domain decomposition with overset (chimera) grids. Numerical simulations show that unsteady statistical turbulence models can capture very complex 3D flow phenomena dominated by geometry-induced, large-scale instabilities and unsteady coherent structures such as the onset of vortex breakdown and the formation of the unsteady rope vortex downstream of the turbine runner. Both URANS and DES appear to yield the general shape and magnitude of mean velocity profiles in reasonable agreement with measurements. Significant discrepancies among the DES and URANS predictions of the turbulence statistics are also observed in the straight downstream diffuser.

  9. Correlation for the Prediction of Flow Boiling Heat Transfer in Small Diameter Tubes

    NASA Astrophysics Data System (ADS)

    Miyata, Kazushi; Mori, Hideo; Hamamoto, Yoshinori

    The objective of the present study is to develop a correlation applicable to a prediction of an axially local heat transfer coefficient in flow boiling within small diameter tubes. From experimental data of authors obtained previously, it was found that, for the accurate prediction of the heat transfer in small diameter tubes, it was necessary to evaluate precisely the contribution of evaporation heat transfer of thin liquid film around vapor plugs in slug flow, adding to the forced convection heat transfer and nucleate boiling heat transfer. There are, however, only conventional heat transfer correlations which consider any two of the three contributions; forced convection and nucleate boiling in most cases. In this study, a new correlation considering all of three contributions was developed based on data of R 410A by authors and data of other Freons, water and CO2 by other researchers. In the new correlation, the liquid film evaporation heat transfer is evaluated using liquid film thickness correlated with the Capillary number, the forced convection heat transfer is calculated by use of the Dittus-Boelter correlation and the Lockhart-Martinelli parameter, and the nucleate boiling heat transfer is predicted from the Stephan-Abdelsalam correlation with the suppression factor. The new correlation showed higher prediction performance compared with conventional heat transfer correlations.

  10. Effects of oil on boiling of replacement refrigerants flowing normal to a tube bundle -- Part 1: R-123

    SciTech Connect

    Tatara, R.A.; Payvar, P.

    2000-07-01

    Local experimental heat transfer coefficients have been obtained for boiling refrigerant flowing up and across a tube bundle segment representing a full flooded evaporator tube bundle. R-123 data with a structured enhanced boiling tube are available.The refrigerant enters at 15% vapor quality and exits at nearly 100% vapor in order to simulate an actual flooded evaporator bundle. Both heat flux, 2,607 to 10,427 Btu/h{center_dot}ft{sup 2} (8,224 to 32,893 W/m{sup 2}), and oil content, 0--15% (by weight), are varied; the mass flux is not varied independently but set by the heat flux. Local tube and bulk fluid temperatures are measured directly, by thermocouples, to calculate the refrigerant-side heat transfer coefficients. The bundle segment saturation temperature set point (taken at the top of the tube bundle) is 40 F (4.4 C).

  11. Pulsating combustion of gas fuel in the combustion chamber with closed resonant circuit

    NASA Astrophysics Data System (ADS)

    Yallina, E. V.; Larionov, V. M.; Iovleva, O. V.

    2013-12-01

    In the combustion chambers of the pulsation of gas flow oscillation greatly accelerate heat dissipation to the walls of the combustion chamber and improve combustion efficiency as compared with a uniform combustion mode. This allows you to effectively solve a number of problems of industrial power, including an environmentally friendly combustion products. Significant drawback of such systems - the emitted noise exceeding the permissible requirements. One solution to this problem - the separation of the resonance tube into 2 parts connected at the output to the interference of sound waves. The results of theoretical studies pulsating combustion technical mixture of propane in the system, consisting of a combustion chamber and two resonance tubes forming a closed resonant circuit. Resonators have a variable length. Calculations have shown that under certain oscillation of the resonator length to the first resonant frequency of the system is achieved by reducing SPL more than 15 dB. For oscillations at a second resonant frequency is the complete elimination of noise while maintaining intense oscillations in the combustion chamber.

  12. Smooth- and enhanced-tube heat transfer and pressure drop : Part II. The role of transition to turbulent flow.

    SciTech Connect

    Obot, N. T.; Das, L.; Rabas, T. J.

    2000-11-14

    The objectives of this presentation are two-fold: first, to demonstrate the connection between the attainable coefficients and transition to turbulent flow by using the transition-based corresponding states method to generalize results obtained with smooth tubes and enhanced tubes, and second, to provide guidelines on the calculation of heat transfer coefficients from pressure-drop data and vice versa by using the transition concept or the functional law of corresponding states.

  13. Exchange flows of two immiscible Newtonian liquids in a vertical tube: From falling drops to falling slugs

    NASA Astrophysics Data System (ADS)

    Varges, P. R.; Fonseca, B. S.; Naccache, M. F.; de Souza Mendes, P. R.

    2017-06-01

    We present an experimental study of buoyancy-driven flows of two immiscible Newtonian liquids in a vertical tube where initially the heavier and more viscous one is placed on the top of the lighter one. Flow visualization was performed using a digital camera, and inversion velocities were determined through image analysis. The influence of the governing parameters on the speed and flow regime was examined for pairs of liquids with small density differences. Two different flow regimes were observed, namely, falling drops and falling slugs. In the first regime, spherical and ellipsoidal drops are obtained, depending on the ratio between the drop and tube diameters. The falling slug regime is a core-annular flow pattern above a critical value of interfacial tension, while no flow is noticed below this critical value. The experimental results are in good agreement with model predictions from the literature. Indeed, the results showed that terminal velocity can be estimated by empirical correlations for falling spheres.

  14. Influence of Hydraulic Design on Stability and on Pressure Pulsations in Francis Turbines at Overload, Part Load and Deep Part Load based on Numerical Simulations and Experimental Model Test Results

    NASA Astrophysics Data System (ADS)

    Magnoli, M. V.; Maiwald, M.

    2014-03-01

    Francis turbines have been running more and more frequently in part load conditions, in order to satisfy the new market requirements for more dynamic and flexible energy generation, ancillary services and grid regulation. The turbines should be able to be operated for longer durations with flows below the optimum point, going from part load to deep part load and even speed-no-load. These operating conditions are characterised by important unsteady flow phenomena taking place at the draft tube cone and in the runner channels, in the respective cases of part load and deep part load. The current expectations are that new Francis turbines present appropriate hydraulic stability and moderate pressure pulsations at overload, part load, deep part load and speed-no-load with high efficiency levels at normal operating range. This study presents series of investigations performed by Voith Hydro with the objective to improve the hydraulic stability of Francis turbines at overload, part load and deep part load, reduce pressure pulsations and enlarge the know-how about the transient fluid flow through the turbine at these challenging conditions. Model test measurements showed that distinct runner designs were able to influence the pressure pulsation level in the machine. Extensive experimental investigations focused on the runner deflector geometry, on runner features and how they could reduce the pressure oscillation level. The impact of design variants and machine configurations on the vortex rope at the draft tube cone at overload and part load and on the runner channel vortex at deep part load were experimentally observed and evaluated based on the measured pressure pulsation amplitudes. Numerical investigations were employed for improving the understanding of such dynamic fluid flow effects. As example for the design and experimental investigations, model test observations and pressure pulsation curves for Francis machines in mid specific speed range, around nqopt = 50 min

  15. Length and time for development of laminar flow in tubes following a step increase of volume flux

    NASA Astrophysics Data System (ADS)

    Chaudhury, Rafeed A.; Herrmann, Marcus; Frakes, David H.; Adrian, Ronald J.

    2015-01-01

    Laminar flows starting up from rest in round tubes are relevant to numerous industrial and biomedical applications. The two most common types are flows driven by an abruptly imposed constant pressure gradient or by an abruptly imposed constant volume flux. Analytical solutions are available for transient, fully developed flows, wherein streamwise development over the entrance length is absent (Szymanski in J de Mathématiques Pures et Appliquées 11:67-107, 1932; Andersson and Tiseth in Chem Eng Commun 112(1):121-133, 1992, respectively). They represent the transient responses of flows in tubes that are very long compared with the entrance length, a condition that is seldom satisfied in biomedical tube networks. This study establishes the entrance (development) length and development time of starting laminar flow in a round tube of finite length driven by a piston pump that produces a step change from zero flow to a constant volume flux for Reynolds numbers between 500 and 3,000. The flows are examined experimentally, using stereographic particle image velocimetry and computationally using computational fluid dynamics, and are then compared with the known analytical solutions for fully developed flow conditions in infinitely long tubes. Results show that step function volume flux start-up flows reach steady state and fully developed flow five times more quickly than those driven by a step function pressure gradient, a 500 % change when compared with existing estimates. Based on these results, we present new, simple guidelines for achieving experimental flows that are fully developed in space and time in realistic (finite) tube geometries. To a first approximation, the time to achieve steady spatially developing flow is nearly equal to the time needed to achieve steady, fully developed flow. Conversely, the entrance length needed to achieve fully developed transient flow is approximately equal to the length needed to achieve fully developed steady flow. Beyond this

  16. An experimental study of subcooled choked flow through steam generator tube cracks

    NASA Astrophysics Data System (ADS)

    Vadlamani, Ram Anand

    The Work conducted in this Research involved the simulation of Pressurized Water Reactor Conditions of Steam Generators to study the complex phenomenon of Subcooled Choked Flow or two-phase critical flow that occurs when water leaks from the primary side of a steam generator into the secondary side, thus making it highly relevant to Reactor Safety and Probabilistic Risk assessment methods. Slits of small L/D ratio were manufactured and tested on the Facility for Leak Rate Testing at pressures (6.89 MPa) and high temperatures (280°C) relevant to Pressurized Water Reactors over a range of subcooling. Small flow channel length was used (1.3mm) equivalent to steam generator tube thickness with the study of a variety of geometries with differences in surface roughness. Unique to literature, the samples had very small L/Ds and the study was a controlled parametric study of choked flow. The effect of L/D was examined, compared to recent studies conducted at Purdue University by Wolf and Revankar while contrasting with others in literature. Analytical models were applied highlighting the importance of non-equilibrium effects and contrasted with other studies of different L/Ds. RELAP5, a well developed code widely utilized in industry was studied to analyze its predictive capabilities and conditions for best estimate. L/D effects on mass fluxes were studied and it was observed that mass fluxes were affected to a very small degree by subcooling.

  17. Water flow in carbon nanotubes: The effect of tube flexibility and thermostat

    NASA Astrophysics Data System (ADS)

    Sam, Alan; Kannam, Sridhar Kumar; Hartkamp, Remco; Sathian, Sarith P.

    2017-06-01

    Although the importance of temperature control in nonequilibrium molecular dynamics simulations is widely accepted, the consequences of the thermostatting approach in the case of strongly confined fluids are underappreciated. We show the strong influence of the thermostatting method on the water transport in carbon nanotubes (CNTs) by considering simulations in which the system temperature is controlled via the walls or via the fluid. Streaming velocities and mass flow rates are found to depend on the tube flexibility and on the thermostatting algorithm, with flow rates up to 20% larger when the walls are flexible. The larger flow rates in flexible CNTs are explained by a lower friction coefficient between water and the wall. Despite the lower friction, a larger solid-fluid interaction energy is found for flexible CNTs than for rigid ones. Furthermore, a comparison of thermostat schemes has shown that the Berendsen and Nosé-Hoover thermostats result in very similar transport rates, while lower flow rates are found under the influence of the Langevin thermostat. These findings illustrate the significant influence of the thermostatting methods on the simulated confined fluid transport.

  18. Prediction of friction factor of pure water flowing inside vertical smooth and microfin tubes by using artificial neural networks

    NASA Astrophysics Data System (ADS)

    Çebi, A.; Akdoğan, E.; Celen, A.; Dalkilic, A. S.

    2017-02-01

    An artificial neural network (ANN) model of friction factor in smooth and microfin tubes under heating, cooling and isothermal conditions was developed in this study. Data used in ANN was taken from a vertically positioned heat exchanger experimental setup. Multi-layered feed-forward neural network with backpropagation algorithm, radial basis function networks and hybrid PSO-neural network algorithm were applied to the database. Inputs were the ratio of cross sectional flow area to hydraulic diameter, experimental condition number depending on isothermal, heating, or cooling conditions and mass flow rate while the friction factor was the output of the constructed system. It was observed that such neural network based system could effectively predict the friction factor values of the flows regardless of their tube types. A dependency analysis to determine the strongest parameter that affected the network and database was also performed and tube geometry was found to be the strongest parameter of all as a result of analysis.

  19. Prediction of friction factor of pure water flowing inside vertical smooth and microfin tubes by using artificial neural networks

    NASA Astrophysics Data System (ADS)

    Çebi, A.; Akdoğan, E.; Celen, A.; Dalkilic, A. S.

    2016-06-01

    An artificial neural network (ANN) model of friction factor in smooth and microfin tubes under heating, cooling and isothermal conditions was developed in this study. Data used in ANN was taken from a vertically positioned heat exchanger experimental setup. Multi-layered feed-forward neural network with backpropagation algorithm, radial basis function networks and hybrid PSO-neural network algorithm were applied to the database. Inputs were the ratio of cross sectional flow area to hydraulic diameter, experimental condition number depending on isothermal, heating, or cooling conditions and mass flow rate while the friction factor was the output of the constructed system. It was observed that such neural network based system could effectively predict the friction factor values of the flows regardless of their tube types. A dependency analysis to determine the strongest parameter that affected the network and database was also performed and tube geometry was found to be the strongest parameter of all as a result of analysis.

  20. Vibration analysis of shell-and-tube heat exchangers: an overview-Part 1: flow, damping, fluidelastic instability

    NASA Astrophysics Data System (ADS)

    Pettigrew, M. J.; Taylor, C. E.

    2003-11-01

    Design guidelines were developed to prevent tube failures due to excessive flow-induced vibration in shell-and-tube heat exchangers. An overview of vibration analysis procedures and recommended design guidelines is presented in this paper. This paper pertains to liquid, gas and two-phase heat exchangers such as nuclear steam generators, reboilers, coolers, service water heat exchangers, condensers, and moisture-separator-reheaters. Generally, a heat exchanger vibration analysis consists of the following steps: (i) flow distribution calculations, (ii) dynamic parameter evaluation (i.e. damping, effective tube mass, and dynamic stiffness), (iii) formulation of vibration excitation mechanisms, (iv) vibration response prediction, and (v) resulting damage assessment (i.e., comparison against allowables). The requirements applicable to each step are outlined in this paper. Part 1 of this paper covers flow calculations, dynamic parameters and fluidelastic instability.

  1. On the definition of dominant force regimes for flow boiling heat transfer by using single mini-tubes

    NASA Astrophysics Data System (ADS)

    Baba, Soumei; Sawada, Kenichiro; Kubota, Chisato; Kawanami, Osamu; Asano, Hitoshi; Inoue, Koichi; Ohta, Haruhiko

    Recent increase in the size of space platforms requires the management of larger amount of waste heat under high heat flux conditions and the transportation of it along a long distance to the radiator. Flow boiling applied to the thermal management system in space attracts much attention as promising means to realize high-performance heat transfer and transport because of large latent heat of vaporization. In microgravity two-phase flow phenomena are quite different from those under 1-g condition because buoyancy effects are significantly reduced and surface tension becomes dominant. By the similar reason, flow boiling characteristics in mini channels are not the same as those in channels of normal sizes. In the present stage, however, the boundary between the regimes of body force dominated and of surface tension dominated is not clear. The design of space thermal devices, operated under the conditions where no effect of gravity is expected, will improve the reliability of their ground tests, provided that the boundaries of dominant force regimes are clarified quantitatively in advance. In flow boiling in mini channels or in parallel channels, back flow could be occurred because of rapid growth of bubbles in a confined space, resulting flow rate fluctuation. Flow boiling heat transfer characteristics in mini channels can be changed considerably by the existence of inlet flow rate fluctuation. It is important to pay attention to experimental accuracy and to use a single circular mini-tube to compare heat transfer characteristics with those of normal size tubes. In the present paper, effects of tube orientations, i.e. vertical upward flow, vertical downward flow and horizontal flow, on flow boiling heat transfer characteristics is investigated for FC72 flowing in single mini-tubes with inner diameters of 0.13 and 0.51 mm to establish a reliable dominant force regime map. If the regime map is described by using dimensionless groups of Bond, Weber and Froude numbers

  2. Effects of self-pulsation on the spray characteristics of gas-liquid swirl coaxial injector

    NASA Astrophysics Data System (ADS)

    Kang, Zhongtao; Li, Qinglian; Cheng, Peng; Zhang, Xinqiao; Wang, Zhen-guo

    2016-10-01

    To understand the influence of self-pulsation on the spray characteristics of gas-liquid swirl coaxial injector, a back-lighting photography technique has been employed to capture the instantaneous self-pulsated spray and stable spray images with a high speed camera. The diameter and velocity of the droplets in the spray have been characterized with a Dantec Phase Doppler Anemometry (PDA) system. The effects of self-pulsation on the spray pattern, primary breakup, spray angle, diameter and velocity distribution and mass flow rate distribution are analyzed and discussed. The results show that the spray morphology is greatly influenced by self-pulsation. The stable spray has a cone shape, while the self-pulsated spray looks like a Christmas tree. The main difference of these two sprays is the primary breakup. The liquid film of stable spray keeps stable while that of self-pulsated spray oscillates periodically. The film width of self-pulsated spray varies in a large range with 'neck' and 'shoulder' features existing. The liquid film of self-pulsated spray breaks up at the second neck, and then the second shoulder begins to breakup into ligaments. The self-pulsated spray produces droplet clusters periodically, varies horizontal spray width and mass flux periodically. From the point of spatial distribution, self-pulsation is good for the spray, it uniformizes the mass flux along radius and increases the spray angle. However, when self-pulsation occurs, the SMD distribution varies from an inverted V shape to a hollow cone shape, and SMD increases at all the measuring points. Namely, from the point of atomization performance, self-pulsation has negative effects even when the breakup length is smaller. The effects of self-pulsation on the diameter and velocity distributions of the spray are mainly in the center part of the spray. The periphery of stable and self-pulsated spray has similar diameter and velocity distribution.

  3. Numerical heat and mass transfer analysis of a cross-flow indirect evaporative cooler with plates and flat tubes

    NASA Astrophysics Data System (ADS)

    Chua, K. J.; Xu, J.; Cui, X.; Ng, K. C.; Islam, M. R.

    2016-09-01

    In this study the performance of an indirect evaporative cooling system (IECS) of cross-flow configuration is numerically investigated. Considering the variation of water film temperature along the flowing path and the wettability of the wet channel, a two-dimensional theoretical model is developed to comprehensively describe the heat and mass transfer process involved in the system. After comparing the simulation results with available experimental data from literature, the deviation within ±5 % proves the accuracy and reliability of the proposed mathematical model. The simulation results of the plate type IECS indicate that the important parameters, such as dimension of plates, air properties, and surface wettability play a great effect on the cooling performance. The investigation of flow pattern shows that cross-flow configuration of primary air with counter-flow of secondary air and water film has a better cooling performance than that of the parallel-flow pattern. Furthermore, the performance of a novel flat tube working as the separating medium is numerically investigated. Simulation results for this novel geometry indicate that the tube number, tube long axis and short axis length as well as tube length remarkably affect its cooling performance.

  4. Influence of the Runner Gap on the Flow Field in the Draft Tube of a Low Head Turbine

    NASA Astrophysics Data System (ADS)

    Junginger, Bernd; Riedelbauch, Stefan

    2016-11-01

    The gap flow of axial turbines is usually neglected in the design process of hydraulic machines, although it can lead to a stabilization of the draft tube flow. Though, this negligence of the gap can falsify the flow field in the draft tube. Presented in this paper are simulations of an axial propeller turbine operated at Δγ = Δγ BEP with Q > Qbep . Simulations of four gap sizes, using a mesh with about 15 million elements for the entire machine, are performed. Additionally, two turbulence models are applied, the k-ω-SST and the SAS-SST model. At the evaluated operating point a full load vortex develops. Depending on the turbulence model the developing vortex rope can either arise from the hub in a straight shape or in a shape resembling a corkscrew. Integral quantities such as head and torque are compared with experimental model test results performed in the laboratory of the Institute. Flow field simulation results are evaluated for different gap widths. Furthermore, the impact of the gap flow respectively the gap size can be observed in velocity profiles evaluated at different positions downstream the runner until to the end of the draft tube cone. Moreover, the pressure signals recorded at the beginning of the draft tube cone are also affected by the gap flow.

  5. Dissipative particle dynamics simulations of deformation and aggregation of healthy and diseased red blood cells in a tube flow

    SciTech Connect

    Ye, Ting; Phan-Thien, Nhan Khoo, Boo Cheong; Lim, Chwee Teck

    2014-11-15

    In this paper, we report simulation results assessing the deformation and aggregation of mixed healthy and malaria-infected red blood cells (RBCs) in a tube flow. A three dimensional particle model based on Dissipative Particle Dynamics (DPD) is developed to predict the tube flow containing interacting cells. The cells are also modelled by DPD, with a Morse potential to characterize the cell-cell interaction. As validation tests, a single RBC in a tube flow and two RBCs in a static flow are simulated to examine the cell deformation and intercellular interaction, respectively. The study of two cells, one healthy and the other malaria-infected RBCs in a tube flow demonstrates that the malaria-infected RBC (in the leading position along flow direction) has different effects on the healthy RBC (in the trailing position) at the different stage of parasite development or at the different capillary number. With parasitic development, the malaria-infected RBC gradually loses its deformability, and in turn the corresponding trailing healthy RBC also deforms less due to the intercellular interaction. With increasing capillary number, both the healthy and malaria-infected RBCs are likely to undergo an axisymmetric motion. The minimum intercellular distance becomes small enough so that rouleaux is easily formed, i.e., the healthy and malaria-infected RBCs are difficultly disaggregated.

  6. Prototyping of Poly(dimethylsiloxane) Interfaces for Flow Gating, Reagent Mixing, and Tubing Connection in Capillary Electrophoresis

    PubMed Central

    Zhang, Qiyang; Gong, Maojun

    2014-01-01

    Integrated microfluidic systems coupled with electrophoretic separations have broad application in biological and chemical analysis. Interfaces for the connection of various functional parts play a major role in the performance of a system. Here we developed a rapid prototyping method to fabricate monolithic poly(dimethylsiloxane) (PDMS) Interfaces for flow-gated injection, online reagent mixing, and tube-to-tube connection in an integrated capillary electrophoresis (CE) system. The basic idea was based on the properties of PDMS: elasticity, transparency, and suitability for prototyping. The molds for these interfaces were prepared by using commercially available stainless steel wires and nylon lines or silica capillaries. A steel wire was inserted through the diameter of a nylon line and a cross format was obtained as the mold for PDMS casting of flow gates and 4-way mixers. These interfaces accommodated tubing connection through PDMS elasticity and provided easy visual trouble shooting. The flow gate used smaller channel diameters thus reducing flow rate by 25 fold for effective gating compared with mechanically machined counterparts. Both PDMS mixers and the tube-to-tube connectors could minimize the sample dead volume by using an appropriate capillary configuration. As a whole, the prototyped PDMS interfaces are reusable, inexpensive, convenient for connection, and robust when integrated with the CE detection system. Therefore, these interfaces could see potential applications in CE and CE-coupled systems. PMID:24331370

  7. Prototyping of poly(dimethylsiloxane) interfaces for flow gating, reagent mixing, and tubing connection in capillary electrophoresis.

    PubMed

    Zhang, Qiyang; Gong, Maojun

    2014-01-10

    Integrated microfluidic systems coupled with electrophoretic separations have broad application in biologic and chemical analysis. Interfaces for the connection of various functional parts play a major role in the performance of a system. Here, we developed a rapid prototyping method to fabricate monolithic poly(dimethylsiloxane) (PDMS) interfaces for flow-gated injection, online reagent mixing, and tube-to-tube connection in an integrated capillary electrophoresis (CE) system. The basic idea was based on the properties of PDMS: elasticity, transparency, and suitability for prototyping. The molds for these interfaces were prepared by using commercially available stainless steel wires and nylon lines or silica capillaries. A steel wire was inserted through the diameter of a nylon line and a cross format was obtained as the mold for PDMS casting of flow gates and 4-way mixers. These interfaces accommodated tubing connection through PDMS elasticity and provided easy visual trouble shooting. The flow gate used smaller channel diameters, thus reducing flow rate by 25-fold for effective gating compared with mechanically machined counterparts. Both PDMS mixers and the tube-to-tube connectors could minimize the sample dead volume by using an appropriate capillary configuration. As a whole, the prototyped PDMS interfaces are reusable, inexpensive, convenient for connection, and robust when integrated with the CE detection system. Therefore, these interfaces could see potential applications in CE and CE-coupled systems. Copyright © 2013 Elsevier B.V. All rights reserved.

  8. System and method having multi-tube fuel nozzle with differential flow

    DOEpatents

    Hughes, Michael John; Johnson, Thomas Edward; Berry, Jonathan Dwight; York, William David

    2017-01-03

    A system includes a multi-tube fuel nozzle with a fuel nozzle body and a plurality of tubes. The fuel nozzle body includes a nozzle wall surrounding a chamber. The plurality of tubes extend through the chamber, wherein each tube of the plurality of tubes includes an air intake portion, a fuel intake portion, and an air-fuel mixture outlet portion. The multi-tube fuel nozzle also includes a differential configuration of the air intake portions among the plurality of tubes.

  9. Columbia University flow instability experimental program: Volume 7. Single tube tests, critical heat flux test program

    SciTech Connect

    Dougherty, T.; Maciuca, C.; McAssey, E.V. Jr.; Reddy, D.G.; Yang, B.W.

    1992-09-01

    This report deals with critical heat flux (CHF) measurements in vertical down flow of water at low pressures in a round Inconel tube, 96 inches long and 0.62 inch inside diameter. A total of 28 CHF points were obtained. These data were found to correlate linearly with the single variable q, defined as the heat flux required to raise the enthalpy from the inlet value to the saturation value. These results were compared to the published results of Swedish investigators for vertical upflow of water at low pressures in round tubes of similar diameters and various lengths. The parameter q depends on the inlet enthalpy and is a nonlocal variable, thus this correlation is nonlocal unless the coefficients depend upon tube length in a particular prescribed manner. For the low pressure Swedish data, the coefficients are practically independent of length and hence the correlation is nonlocal. In the present investigation only one length was employed, so it is not possible to determine whether the correlation for these data is local or nonlocal, although there is reason to believe that it is local. The same correlation was applied to a large data base (thousands of CHF points) compiled from the published data of a number of groups and found to apply, with reasonable accuracy over a wide range of conditions, yielding sometimes local and sometimes nonlocal correlations. The basic philosophy of data analysis here was not to generate a single correlation which would reproduce all data, but to search for correlations which apply adequately over some range and which might have some mechanistic significance. The tentative conclusion is that at least two mechanisms appear operative, leading to two types of correlations, one local, the other nonlocal.

  10. Numerical study of the transient flow in the driven tube and the nozzle section of a shock tunnel

    NASA Technical Reports Server (NTRS)

    Tokarcik-Polsky, Susan; Cambier, Jean-Luc

    1993-01-01

    The initial flow in a shock tunnel was examined numerically using computational fluid dynamics (CFD). A finite-volume total variation diminishing (TVD) scheme was used to calculate the transient flow in a shock tunnel. Both viscous and inviscid, chemically nonreacting flows were studied. The study consisted of two parts, the first dealt with the transient flow in the driven-tube/nozzle interface region (inviscid calculations). The effects of varying the geometry in this region was examined. The second part of the study examined the transient flow in the nozzle (viscous calculations). The results were compared to experimental data.

  11. Pressure pulsation in Kaplan turbines: Prototype-CFD comparison

    NASA Astrophysics Data System (ADS)

    Rivetti, A.; Lucino1, C.; Liscia, S.; Muguerza, D.; Avellan, F.

    2012-11-01

    Pressure pulsation phenomena in a large Kaplan turbine are investigated by means of numerical simulations (CFD) and prototype measurements in order to study the dynamic behavior of flow due to the blade passage and its interaction with other components of the turbine. Numerical simulations are performed with the commercial software Ansys CFX code, solving the incompressible Unsteady Reynolds-Averaged-Navier Stokes equations under a finite volume scheme. The computational domain involves the entire machine at prototype scale. Special care is taken in the discretization of the wicket gate overhang and runner blade gap. Prototype measurements are performed using pressure transducers at different locations among the wicket gate outlet and the draft tube inlet. Then, CFD results are compared with temporary signals of prototype measurements at identical locations to validate the numerical model. A detailed analysis was focused on the tip gap flow and the pressure field at the discharge ring. From a rotating reference frame perspective, it is found that the mean pressure fluctuates accordingly the wicket gate passage. Moreover, in prototype measurements the pressure frequency that reveals the presence of modulated cavitation at the discharge ring is distinguished, as also verified from the shape of erosion patches in concordance with the number of wicket gates.

  12. Laminar boundary layer flow of saturated vapor and its condensate over a horizontal tube

    NASA Astrophysics Data System (ADS)

    Smyrnaios, D. N.; Pelekasis, N. A.; Tsamopoulos, J. A.

    2002-06-01

    The steady two-dimensional laminar flow of a stream of saturated vapor flowing over a tube that is kept at a uniform temperature, below the saturation temperature, is examined. Owing to the temperature difference between the vapor stream and the solid surface a film of condensate is generated that flows along the surface due to shear, pressure-drop, and gravity. In the limit as the boundary layer and film thickness remain smaller than the radius of curvature of the surface a simplified lubrication-type formulation describes the temperature and flow fields in the film, whereas the usual boundary layer formulation is applied in the vapor boundary layer. The case of flow past a horizontal cylinder of radius R is investigated numerically with the oncoming stream aligned with gravity. The parameters that control momentum and heat transfer in this problem are the viscosity ratio, μcs/μss, the density ratio, ρcs/ρss, the Prandtl number, Pr=cpcsμcs/kcs, the Froude number, Fr=U∞2/(gπR), and finally the thickness ratio between the condensate and the vapor boundary layer, ɛ, which is also a measure of the temperature difference between the vapor stream and the tube wall. Then, the Nusselt number and the skin friction coefficient, averaged over the upper half of the cylinder, are calculated for a wide parameter range. When Fr is very small and ɛ relatively large the flow remains attached until the trailing stagnation point of the cylinder. As the effect of adverse pressure drop becomes more pronounced (Fr increases or ɛ decreases) it is shown that the solution exhibits two different types of singularity in the rear part of the cylinder. The first one is a typical Goldstein singularity because it appears at the tube wall and it is associated with vanishing skin friction (wall shear) and rapidly increasing film thickness. The second one takes place near the interface between the vapor stream and the film of condensate in a region where very small velocities prevail in

  13. Investigations of Internal Flow Fields of Constant-Area Mixing-Tubes under Starting-Limit Conditions

    NASA Astrophysics Data System (ADS)

    Kitamura, Eijiro; Tomioka, Sadatake; Sakuranaka, Noboru; Watanabe, Syuichi; Masuya, Goro

    Flow fields in the constant-area mixing tubes of ejector jets were investigated under the starting-limit conditions of an aerodynamic choking mode by performing numerical simulations and cold flow experiments. Pressure recovery was almost completed in the shock-train region. The length of the shock-train region (Lst) was measured under various conditions. Lst was proportional to the mass flow rate ratio of the secondary flow to the primary flow when this ratio was less than 0.15. On the other hand, Lst became almost constant when the mass flow rate ratio exceeded 0.15. Numerical studies showed that this change was caused by the difference in the mechanism of the flow fields. In the cases with low air mass flow rates, the primary and secondary flows almost mixed in a region between the inlets of the mixing tubes and the choking points. The pressure was recovered by a pseudo-shock-wave generated downstream of the choking point. On the other hand, when the mass flow rate ratio was higher than 0.15, the primary and secondary flows were clearly separated at the choking point. The pressure recovery was achieved by the mixing between the primary and secondary flows downstream of the choking point.

  14. Measurement of the flow properties within a copper tube containing a deflagrating explosive

    SciTech Connect

    Hill, Larry G; Morris, John S; Jackson, Scott I

    2009-01-01

    We report on the propagation of deflagration waves in the high explosive (HE) PBX 9501 (95 wt % HMX, 5 wt% binder). Our test configuration, which we call the def1agration cylinder test (DFCT), is fashioned after the detonation cylinder test (DTCT) that is used to calibrate the JWL detonation product equation of state (EOS). In the DFCT, the HE is heated to a uniform slightly subcritical temperature, and is ignited at one end by a hot wire. For some configurations and initial conditions, we observe a quasi-steady wave that flares the tube into a funnel shape, stretching it to the point of rupture. This behavior is qualitatively like the DTCT, such that, by invoking certain additional approximations that we discuss, its behavior can be analyzed by the same methods. We employ an analysis proposed by G.I. Taylor to infer the pressure-volume curve for the burning, expanding flow. By comparing this result to the EOS of HMX product gas alone. we infer that only {approx}20 wt% of the HMX has burned at tube rupture. This result confirms pre-existing observations about the role of convective burning in HMX cookoff explosions.

  15. Microfilament Orientation Constrains Vesicle Flow and Spatial Distribution in Growing Pollen Tubes

    PubMed Central

    Kroeger, Jens H.; Daher, Firas Bou; Grant, Martin; Geitmann, Anja

    2009-01-01

    Abstract The dynamics of cellular organelles reveals important information about their functioning. The spatio-temporal movement patterns of vesicles in growing pollen tubes are controlled by the actin cytoskeleton. Vesicle flow is crucial for morphogenesis in these cells as it ensures targeted delivery of cell wall polysaccharides. Remarkably, the target region does not contain much filamentous actin. We model the vesicular trafficking in this area using as boundary conditions the expanding cell wall and the actin array forming the apical actin fringe. The shape of the fringe was obtained by imposing a steady state and constant polymerization rate of the actin filaments. Letting vesicle flux into and out of the apical region be determined by the orientation of the actin microfilaments and by exocytosis was sufficient to generate a flux that corresponds in magnitude and orientation to that observed experimentally. This model explains how the cytoplasmic streaming pattern in the apical region of the pollen tube can be generated without the presence of actin microfilaments. PMID:19804712

  16. Stability of viscous film flow coating the interior of a vertical tube with a porous wall

    NASA Astrophysics Data System (ADS)

    Liu, Rong; Ding, Zijing

    2017-05-01

    The stability of the gravity-driven flow of a viscous film coating the inside of a tube with a porous wall is studied theoretically. We used Darcy's law to describe the motion of fluids in a porous medium. The Beaver-Joseph condition is used to describe the discontinuity of velocity at the porous-fluid interface. We derived an evolution equation for the film thickness using a long-wave approximation. The effect of velocity slip at the porous wall is identified by a parameter β . We examine the effect of β on the temporal stability, the absolute-convective instability (AI-CI), and the nonlinear evolution of the interface deformation. The results of the temporal stability reveal that the effect of velocity slip at the porous wall is destabilizing. The parameter β plays an important role in determining the AI-CI behavior and the nonlinear evolution of the interface. The presence of the porous wall promotes the absolute instability and the formation of the plug in the tube.

  17. The Effect of Compressibility on the Pressure Reading of a Prandtl Pitot Tube at Subsonic Flow Velocity

    NASA Technical Reports Server (NTRS)

    Walchner, O

    1939-01-01

    Errors arising from yawed flow were also determined up to 20 degrees angle of attack. In axial flow, the Prandtl pitot tube begins at w/a approx. = 0.8 to give an incorrect static pressure reading, while it records the tank pressure correctly, as anticipated, up to sonic velocity. Owing to the compressibility of the air, the Prandtl pitot tube manifests compression shocks when the air speed approaches velocity of sound. This affects the pressure reading of the instrument. Because of the increasing importance of high speed in aviation, this compressibility effect is investigated in detail.

  18. Computational astrophysics: Pulsating stars

    NASA Astrophysics Data System (ADS)

    Davis, C. G.

    The field of computational astrophysics in pulsating star studies has grown considerably since the advent of the computer. Initially calculations were done on the IBM 704 with 32K of memory and now we use the CRAY YMP computers with considerably more memory. Our early studies were for models of pulsating stars using a 1D Lagrangian hydrodynamic code (SPEC) with radiation diffusion. The radiative transfer was treated in the equilibrium diffusion approximation and the hydrodynamics was done utilizing the approximation of artificial viscosity. The early calculations took many hours of 704 CPU time. Early in 1965 we decided to improve on the usual treatment of the radiative transfer used in our codes by utilizing the method of moments, the so-called variable Eddington approximation. In this approximation the material energy field is uncoupled from the radiation energy field and the angular dependence is introduced through the Eddington factor. A multigroup frequency dependent method may also be applied. The Eddington factor is determined by snapshots of the stars structure utilizing a y-line approximation. The full radiative transfer approximation appears necessary in order to understand the light curves for W Virginia stars and may be important for the light curves of RR Lyrae stars. A detailed radiative transfer method does not appear to be necessary for the understanding of Cepheid light curves. A recent improvement to our models for pulsating stars is in the use of an adaptive mesh scheme to resolve the sharp features in the nonlinear hydrodynamic structure. From these improved structures, better analysis of the radius, velocity, and light curves could be obtained.

  19. Film stability in a vertical rotating tube with a core-gas flow.

    NASA Technical Reports Server (NTRS)

    Sarma, G. S. R.; Lu, P. C.; Ostrach, S.

    1971-01-01

    The linear hydrodynamic stability of a thin-liquid layer flowing along the inside wall of a vertical tube rotating about its axis in the presence of a core-gas flow is examined. The stability problem is formulated under the conditions that the liquid film is thin, the density and viscosity ratios of gas to liquid are small and the relative (axial) pressure gradient in the gas is of the same order as gravity. The resulting eigenvalue problem is first solved by a perturbation method appropriate to axisymmetric long-wave disturbances. The damped nature (to within the thin-film and other approximations made) of the nonaxisymmetric and short-wave disturbances is noted. In view of the limitations on a truncated perturbation solution when the disturbance wavenumber is not small, an initial value method using digital computer is presented. Stability characteristics of neutral, growing, and damped modes are presented showing the influences of rotation, surface tension, and the core-gas flow. Energy balance in a neutral mode is also illustrated.

  20. Preliminary investigation of heat transfer to water flowing in an electrically heated Inconel tube

    NASA Technical Reports Server (NTRS)

    Kaufman, Samuel J; Isely, Francis D

    1950-01-01

    A heat-transfer investigation was conducted with water flowing in an electrically heated Inconel tube with an inside diameter of 0.204 inch and a length-diameter ratio of 50 for ranges of Reynolds number up to 100,000 and of entrance pressure up to 200 inches of mercury gage. Correlation of average heat-transfer coefficients was obtained by use of the familiar Nusselt relation, wherein the physical properties of water were evaluated at an average bulk temperature. For conditions in which no boiling occurred, the data gave a good correlation. Runs made in the nucleate-boiling region, however, gave higher values of heat-transfer coefficient than would be predicted by the Nusselt relation.

  1. Status of selected ion flow tube MS: accomplishments and challenges in breath analysis and other areas.

    PubMed

    Smith, David; Španěl, Patrik

    2016-06-01

    This article reflects our observations of recent accomplishments made using selected ion flow tube MS (SIFT-MS). Only brief descriptions are given of SIFT-MS as an analytical method and of the recent extensions to the underpinning analytical ion chemistry required to realize more robust analyses. The challenge of breath analysis is given special attention because, when achieved, it renders analysis of other air media relatively straightforward. Brief overviews are given of recent SIFT-MS breath analyses by leading research groups, noting the desirability of detection and quantification of single volatile biomarkers rather than reliance on statistical analyses, if breath analysis is to be accepted into clinical practice. A 'strengths, weaknesses, opportunities and threats' analysis of SIFT-MS is made, which should help to increase its utility for trace gas analysis.

  2. Structural isomers of C2N(+) - A selected-ion flow tube study

    NASA Technical Reports Server (NTRS)

    Knight, J. S.; Petrie, S. A. H.; Freeman, C. G.; Mcewan, M. J.; Mclean, A. D.

    1988-01-01

    Reactivities of the structural isomers CCN(+) and CNC(+) were examined in a selected-ion flow tube at 300 + or - 5 K. The less reactive CNC(+) isomer was identified as the product of the reactions of C(+) + HCN and C(+) + C2N2; in these reactions only CNC(+) can be produced because of energy constraints. Rate coefficients and branching ratios are reported for the reactions of each isomer with H2, CH4, NH3, H2O, C2H2, HCN, N2, O2, N2O, and CO2. Ab initio calculations are presented for CCN(+) and CNC(+); a saddle point for the reaction CCN(+) yielding CNC(+) is calculated to be 195 kJ/mol above CNC(+). The results provide evidence that the more reactive CCN(+) isomer is unlikely to be present in measurable densities in interstellar clouds.

  3. Spectropolarimetric Evidence for a Siphon Flow along an Emerging Magnetic Flux Tube

    NASA Astrophysics Data System (ADS)

    Requerey, Iker S.; Ruiz Cobo, B.; Del Toro Iniesta, J. C.; Orozco Suárez, D.; Blanco Rodríguez, J.; Solanki, S. K.; Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Riethmüller, T. L.; van Noort, M.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.

    2017-03-01

    We study the dynamics and topology of an emerging magnetic flux concentration using high spatial resolution spectropolarimetric data acquired with the Imaging Magnetograph eXperiment on board the sunrise balloon-borne solar observatory. We obtain the full vector magnetic field and the line of sight (LOS) velocity through inversions of the Fe i line at 525.02 nm with the SPINOR code. The derived vector magnetic field is used to trace magnetic field lines. Two magnetic flux concentrations with different polarities and LOS velocities are found to be connected by a group of arch-shaped magnetic field lines. The positive polarity footpoint is weaker (1100 G) and displays an upflow, while the negative polarity footpoint is stronger (2200 G) and shows a downflow. This configuration is naturally interpreted as a siphon flow along an arched magnetic flux tube.

  4. Reactions of Ions with Ionic Liquid Vapors by Selected-Ion Flow Tube Mass Spectrometry.

    PubMed

    Chambreau, Steven D; Boatz, Jerry A; Vaghjiani, Ghanshyam L; Friedman, Jeffrey F; Eyet, Nicole; Viggiano, A A

    2011-04-21

    Room-temperature ionic liquids exert vanishingly small vapor pressures under ambient conditions. Under reduced pressure, certain ionic liquids have demonstrated volatility, and they are thought to vaporize as intact cation-anion ion pairs. However, ion pair vapors are difficult to detect because their concentration is extremely low under these conditions. In this Letter, we report the products of reacting ions such as NO(+), NH4(+), NO3(-), and O2(-) with vaporized aprotic ionic liquids in their intact ion pair form. Ion pair fragmentation to the cation or anion as well as ion exchange and ion addition processes are observed by selected-ion flow tube mass spectrometry. Free energies of the reactions involving 1-ethyl-3-methylimidazolium bis-trifluoromethylsulfonylimide determined by ab initio quantum mechanical calculations indicate that ion exchange or ion addition are energetically more favorable than charge-transfer processes, whereas charge-transfer processes can be important in reactions involving 1-butyl-3-methylimidazolium dicyanamide.

  5. Analysis of radiative heat transfer impact in cross-flow tube and fin heat exchangers

    NASA Astrophysics Data System (ADS)

    Hanuszkiewicz-Drapała, Małgorzata; Bury, Tomasz; Widziewicz, Katarzyna

    2016-03-01

    A cross-flow, tube and fin heat exchanger of the water - air type is the subject of the analysis. The analysis had experimental and computational form and was aimed for evaluation of radiative heat transfer impact on the heat exchanger performance. The main element of the test facility was an enlarged recurrent segment of the heat exchanger under consideration. The main results of measurements are heat transfer rates, as well as temperature distributions on the surface of the first fin obtained by using the infrared camera. The experimental results have been next compared to computational ones coming from a numerical model of the test station. The model has been elaborated using computational fluid dynamics software. The computations have been accomplished for two cases: without radiative heat transfer and taking this phenomenon into account. Evaluation of the radiative heat transfer impact in considered system has been done by comparing all the received results.

  6. Experimental Study on the Flow and Heat Transfer Characteristics of TiO2-Water Nanofluids in a Spirally Fluted Tube

    NASA Astrophysics Data System (ADS)

    Qi, Cong; Li, Chunyang; Wang, Guiqing

    2017-09-01

    The flow and heat transfer characteristics of TiO2-water nanofluids with different nanoparticle mass fractions in a spirally fluted tube and a smooth tube are experimentally investigated at different Reynolds numbers. The effects of pH values and doses of dispersant agent on the stability of TiO2-water nanofluids are discussed. The effects of nanoparticle mass fractions and Reynolds numbers on Nusselt numbers and frictional resistance coefficients in the spirally fluted tube and the smooth tube are also investigated. It is found that TiO2-water nanofluids in the spirally fluted tube have a larger enhancement than that in the smooth tube. The heat transfer enhancement and the increase in frictional resistance coefficients of TiO2-water nanofluids in the spirally fluted tube and the smooth tube for laminar flow and turbulent flow are compared. It is found that there are a larger increase in heat transfer and a smaller increase in frictional resistance coefficients for turbulent flow than that for laminar flow of TiO2-water nanofluids in the spirally fluted tube. The comprehensive evaluations for the thermo-hydraulic performance of TiO2-water nanofluids in the smooth tube and spirally fluted tube are also discussed.

  7. Experimental Study on the Flow and Heat Transfer Characteristics of TiO2-Water Nanofluids in a Spirally Fluted Tube.

    PubMed

    Qi, Cong; Li, Chunyang; Wang, Guiqing

    2017-09-02

    The flow and heat transfer characteristics of TiO2-water nanofluids with different nanoparticle mass fractions in a spirally fluted tube and a smooth tube are experimentally investigated at different Reynolds numbers. The effects of pH values and doses of dispersant agent on the stability of TiO2-water nanofluids are discussed. The effects of nanoparticle mass fractions and Reynolds numbers on Nusselt numbers and frictional resistance coefficients in the spirally fluted tube and the smooth tube are also investigated. It is found that TiO2-water nanofluids in the spirally fluted tube have a larger enhancement than that in the smooth tube. The heat transfer enhancement and the increase in frictional resistance coefficients of TiO2-water nanofluids in the spirally fluted tube and the smooth tube for laminar flow and turbulent flow are compared. It is found that there are a larger increase in heat transfer and a smaller increase in frictional resistance coefficients for turbulent flow than that for laminar flow of TiO2-water nanofluids in the spirally fluted tube. The comprehensive evaluations for the thermo-hydraulic performance of TiO2-water nanofluids in the smooth tube and spirally fluted tube are also discussed.

  8. Analysis of heat transfer and fluid flow through a spirally fluted tube using a porous substrate approach

    SciTech Connect

    Srinivasan, V.; Vafai, K.; Christensen, R.N. )

    1994-08-01

    An innovative approach was opted for modeling the flow and heat transfer through spirally fluted tubes. The model divided the flow domain into two regions. The flutes were modeled as a porous substrate with direction-dependent permeabilities. This enabled modeling the swirl component in the fluted tube. The properties of the porous substrate such as its thickness, porosity, and ratio of the direction-dependent permeabilities were obtained from the geometry of the fluted tube. Experimental data on laminar Nusselt numbers and friction factors for different types of fluted tubes representing a broad range of flute geometry were available. Experimental data from a few of the tubes tested were used to propose a relationship between the permeability of the porous substrate and the flute parameters, particularly the flute spacing. The governing equations were discretized using the Finite Element Method. The model was verified and applied to the other tubes in the test matrix. Very good agreement was found between the numerical predictions and the experimental data. 20 refs., 13 figs., 4 tabs.

  9. Pulsation and mass loss in Mira variables

    NASA Technical Reports Server (NTRS)

    Wood, P. R.

    1980-01-01

    The behavior of pulsation in the outer layers of a typical Mira variable was studied in the adiabatic and isothermal limits. A shock wave propagates outward once per period and the radial velocity obtained from observations of hydrogen emission lines is identified with the velocity of gas in the post shock region. In the adiabatic case, mass loss in the form of a steady stellar wind was produced. In the isothermal case, no continuous mass loss was produced but occasional ejection of shells occur. Pulsation introduced into a star undergoing steady mass loss as a result of radiation pressure acting on grains caused the mass loss rate to increase by a factor of approximately 40, while the terminal velocity of the flow was almost unaltered.

  10. Influence of Reynolds number on coalescence of droplets with particle in flow through a tube at low Reynolds number

    NASA Astrophysics Data System (ADS)

    Muraoka, Masahiro; Yatagawa, Yuta; Kumagai, Yuki

    2016-07-01

    The coalescence of droplets in flow through a tube at low Reynolds number is potentially useful for different purposes including the handling of fluids, control of chemical reaction, and in drug delivery systems. The phenomenon is also the basis for analyzing the flow of multiphase fluids through porous media such as in enhanced oil recovery and the breaking of emulsions in porous coalescers. With regard to examples of studies on the creeping motion of droplets in a flow through a tube, Hetsroni G. et al.[1] theoretically examined the motion of a spherical droplet or bubble with small d/D, where d is the undeformed diameter of the droplet or bubble, and D is the tube diameter. Higdon J.J.L. and Muldowney G.P. [2] numerically obtained the resistance functions for a spherical particle, droplet, and bubble. Olbricht, W.L. and Kung D.M.[3] and Aul R.W. and Olbricht, W.L.[4] mainly investigated the coalescence time of droplets. Aul R.W. and Olbricht W.L. proposed a semi-theoretical formula of the coalescence time. Based on the formula by them, Muraoka, M. et al.[5] proposed other semi-theoretical formulas of the coalescence time in terms of the resistance experienced by the liquid droplet in creeping flow through a tube. The latter formulas take the eccentricity of the following droplets into consideration. In the present study, a glass tube of inner diameter 2.0mm, outer diameter 7.0mm, and length 1500 mm was used as the test tube. Silicon oil with a kinematic viscosity of 3000cSt was employed as the test fluid of the droplet. A mixture of glycerol and pure water was used as the surrounding fluid of the creeping flow through a tube. A large volumetric syringe pump was used to maintain steady flow through the tube at a designated average velocity. The test tube was immersed in temperature-controlled water contained in a tank to maintain constant temperature of the system. The droplets were injected into the test tube. The behaviors of the droplets were monitored by a

  11. Direct simulation Monte Carlo-based expressions for the gas mass flow rate and pressure profile in a microscale tube

    NASA Astrophysics Data System (ADS)

    Gallis, M. A.; Torczynski, J. R.

    2012-01-01

    The direct simulation Monte Carlo (DSMC) method of Bird is used to develop simple closed-form expressions for the mass flow rate and the pressure profile for the steady isothermal flow of an ideal gas through a microscale tube connecting two infinite reservoirs at different pressures but at the temperature of the tube wall. Gas molecules reflect from the tube wall according to the Maxwell model (a linear combination of specular and diffuse reflections at the wall temperature) with a unity or sub-unity value of the accommodation coefficient (the probability that molecules reflect diffusely from the wall). The DSMC-based expressions have four parameters. Two parameters are specified so that the mass flow rate reduces to the known expression in the free-molecular regime. One parameter was previously determined by comparison to DSMC simulations in the slip regime. The remaining parameter is determined by comparison to DSMC simulations for pressures spanning the transition regime with several values of the accommodation coefficient. The expressions for the mass flow rate and the pressure profile agree well with the DSMC simulations (rms and maximum differences of 2% and 5% for all cases examined), with other more complicated expressions and with recent experiments involving microscale tubes and channels for all flow regimes.

  12. Can blood flow in separate small tubes be quantitatively assessed by high-resolution laser Doppler imaging?

    PubMed

    Lindén, M

    1997-11-01

    A method is suggested for quantitative flow assessment of whole-blood perfusing tubes with diameters in the range from 500 microns to 1.5 mm, for velocities below 9 mm s-1. The algorithm is based both on the Doppler broadening of backscattered laser light and the magnitude of the diameter of the perfused tube. A bandwidth-modified high-resolution laser Doppler perfusion imaging system is used to record the Doppler broadening. A flow model, consisting of a linearly narrowing tube (inner diameter 620-1330 microns), is connected to a precision infusion pump and perfused by human whole blood of volume flows ranging from 0 to 6.6 mm3 s-1. Empirical data are fitted into a regression model, and the parameters of the algorithm can be determined, resulting in a correlation coefficient of 0.975 between the predicted and true volume flows. Using this algorithm, volume flows in tubes of inner diameters of 500 microns, 750 microns and 1.4 mm are predicted, with accuracies corresponding to correlation coefficients of 0.994, 0.993 and 0.996.

  13. Effects of oil on boiling R-123 and R-134a flowing normal to an integral-finned tube bundle

    SciTech Connect

    Tatara, R.A.; Payvar, P.

    1999-07-01

    Local, experimental heat transfer coefficients have been measured for boiling refrigerant flowing up and across a tube bundle segment representing a full flooded evaporator tube bundle. R-123 and R-134a data with 26 fins per inch (1,024 fins per meter) tubes have been obtained. The refrigerant enters at 15% vapor quality and exits at nearly 100% vapor in order to simulate an actual flooded evaporator bundle. The nominal area heat flux was varied from 2,607 to 10,427 Btu/h{center{underscore}dot}ft{sup 2} (8,224 to 32,893 W/m{sup 2}) as the tube bundle oil content ranged from 0 to 15% (by weight) for each refrigerant/tube combination. The performance of R-22 without oil has also been determined. Local tube and bulk fluid temperatures were measured directly by thermocouples to calculate the refrigerant-side heat transfer coefficients. The bundle segment saturation temperature set point (taken at the top of the tube bundle) is 40 F (4.4 C).

  14. Technical design and assessment of tube equipment using two-phase flow for cleaning and disinfection.

    PubMed

    Reinemann, D J

    1996-12-01

    Most pipeline systems in dairy and food processing plants are cleaned by circulating cleaning solutions under pressure with a liquid pump. The flow of the circulated solutions is single-phase or flooded flow. Milking system pipelines are subject to special requirements which distinguish them from those in dairy and other food processing plants. Milking system pipelines are considerably larger in diameter than product lines in dairy plants because they must carry both milk and air in a stratified flow condition during the milking process. Milking machine Clean-In-Place (CIP) systems have historically used flooded flow to circulate cleaning solutions. The force to move liquid, however, is typically the vacuum provided by the same vacuum pump used during milking, rather than a positive pressure liquid pump. As the size and complexity of milking machines has increased in recent years, flooded flow CIP systems have become inadequate. The amount of water required to fully flood a milking system becomes impractical with very long and/or large diameter pipelines. The power available to achieve adequate flow velocity is also limited. Air admission has been used to produce two-phase (air/water) slug flow and overcome some of the limitations of fully flooded CIP. Cycled air admission can reduce the amount of water required for circulation and increase flow velocities and thus enhance mechanical cleaning action. Cycled air admission has been implemented in the field largely through trial and error methods. There has been a lack of fundamental design information and testing protocols for air-injected milking machine CIP systems. This has resulted in mixed success in the application of air injected systems. This paper summarizes both laboratory and field research conducted at the University of Wisconsin Milking Research and Instruction lab to provide basic information for the design of air injected CIP systems and methods for field assessment of these systems. Just as properly

  15. The linear stability of a core annular flow in an asymptotically corrugated tube

    NASA Astrophysics Data System (ADS)

    Wei, Hsien-Hung; Rumschitzki, David S.

    2002-09-01

    This paper examines the core annular flow of two immiscible fluids in a straight circular tube with a small corrugation, in the limit where the ratio [epsilon] of the mean undisturbed annulus thickness to the mean core radius and the corrugation (characterized by the parameter [sigma]) are both asymptotically small and where the surface tension is small. It is motivated by the problems of liquid liquid displacement in irregular rock pores such as occur in secondary oil recovery and in the evolution of the liquid film lining the bronchii in the lungs whose diameters vary over different generations of branching. We investigate the asymptotic base flow in this limit and consider the linear stability of its leading order (in the corrugation parameter) solution. For the chosen scalings of the non-dimensional parameters the core's base flow slaves that of the annulus. The equation governing the leading-order interfacial position for a given wall corrugation function shows a competition between shear and capillarity. The former tends to align the interface shape with that of the wall and the latter tends to introduce a phase shift, which can be of either sign depending on whether the circumferential or the longitudinal component of capillarity dominates. The asymptotic linear stability of this leading-order base flow reduces to a single partial differential equation with non-constant coefficients deriving from the non-uniform base flow for the time evolution of an interfacial disturbance. Examination of a single mode k wall function allows the use of Floquet theory to analyse this equation. Direct numerical solutions of the above partial differential equation agree with the predictions of the Floquet analysis. The resulting spectrum is periodic in [alpha]- space, [alpha] being the disturbance wavenumber space. The presence of a small corrugation not only modifies (at order [sigma]2) the primary eigenvalue of the system. In addition, short-wave order-one disturbances that

  16. Application of J-Groove to the suppression of swirl flow in the draft tube of a Francis hydro turbine

    NASA Astrophysics Data System (ADS)

    Wei, Q. S.; Choi, Y. D.; Zhu, B. S.

    2012-11-01

    The purpose of this study is to examine the validity of J-Groove in controlling and suppressing the swirl flow in a draft tube of Francis hydro turbine which may cause draft surge. "J-Groove" composed of shallow grooves and mounted parallel to the pressure gradient on the draft tube wall is a very simple passive device to suppress several abnormal phenomena in turbomachinery. The CFD analysis has been performed using the draft tube of a Francis hydro turbine model. The calculated results of velocity distribution in the draft tube show that a considerable reduction of swirl velocity is attained by using J-Groove. Besides the vortex core around the dead water region near the draft inlet is reduced by J-Groove.

  17. Influence of lubricant oil on heat transfer performance of refrigerant flow boiling inside small diameter tubes. Part II: Correlations

    SciTech Connect

    Wei, Wenjian; Ding, Guoliang; Hu, Haitao; Wang, Kaijian

    2007-10-15

    The predictive ability of the available state-of-the-art heat transfer correlations of refrigerant-oil mixture is evaluated with the present experiment data of small tubes with inside diameter of 6.34 mm and 2.50 mm. Most of these correlations can be used to predict the heat transfer coefficient of 6.34 mm tube, but none of them can predict heat transfer coefficient of 2.50 mm tube satisfactorily. A new correlation of two-phase heat transfer multiplier with local properties of refrigerant-oil mixture is developed. This correlation approaches the actual physical mechanism of flow boiling heat transfer of refrigerant-oil mixture and can reflect the actual co-existing conditions of refrigerant and lubricant oil. More than 90% of the experiment data of both test tubes have less than {+-}20% deviation from the prediction values of the new correlations. (author)

  18. Acoustic radiation from a fluid-filled, subsurface vascular tube with internal turbulent flow due to a constriction.

    PubMed

    Yazicioglu, Yigit; Royston, Thomas J; Spohnholtz, Todd; Martin, Bryn; Loth, Francis; Bassiouny, Hisham S

    2005-08-01

    The vibration of a thin-walled cylindrical, compliant viscoelastic tube with internal turbulent flow due to an axisymmetric constriction is studied theoretically and experimentally. Vibration of the tube is considered with internal fluid coupling only, and with coupling to internal-flowing fluid and external stagnant fluid or external tissue-like viscoelastic material. The theoretical analysis includes the adaptation of a model for turbulence in the internal fluid and its vibratory excitation of and interaction with the tube wall and surrounding viscoelastic medium. Analytical predictions are compared with experimental measurements conducted on a flow model system using laser Doppler vibrometry to measure tube vibration and the vibration of the surrounding viscoelastic medium. Fluid pressure within the tube was measured with miniature hydrophones. Discrepancies between theory and experiment, as well as the coupled nature of the fluid-structure interaction, are described. This study is relevant to and may lead to further insight into the patency and mechanisms of vascular failure, as well as diagnostic techniques utilizing noninvasive acoustic measurements.

  19. Steady and transient forced convection heat transfer for water flowing in small tubes with exponentially increasing heat inputs

    NASA Astrophysics Data System (ADS)

    Shibahara, M.; Fukuda, K.; Liu, Q. S.; Hata, K.

    2017-03-01

    Steady and transient heat transfer coefficients for water flowing in small tubes with exponentially increasing heat inputs were measured. Platinum tubes with inner diameters of 1.0 and 2.0 mm were used as test tubes, which were mounted vertically in the experimental water loop. In the experiment, the upward flow velocity ranged from 2 to 16 m/s, and the corresponding Reynolds numbers ranged from 4.77 × 103 to 9.16 × 104 at the inlet liquid temperatures ranged from 298 to 343 K. The heat generation rate exponentially increased with the function. The period of the heat generation rate ranged from 24 ms to 17.5 s. Experimental results indicate that steady heat transfer coefficients decreased with the increase in the inner diameter of the small tube. Moreover, the ratio of bulk viscosity to near-wall viscosity of water increased with the rise in surface temperature of the vertical tube. From the experimental data, correlations of steady-state heat transfer for inner diameters of 1.0 and 2.0 mm were obtained. The heat transfer coefficient increased with decreasing the period of the heat generation rate as the flow velocity decreased. Moreover, the Nusselt number under the transient condition was affected by the Fourier number and the Reynolds number.

  20. Critical heat-flux characteristics of R-113 boiling two-phase flow in twisted-tape-inserted tubes

    SciTech Connect

    Lee, Sangryoul; Inoue, Akira; Takahashi, Minoru

    1996-07-01

    This paper presents experimental data on the critical heat flux (CHF) in twisted-tape-inserted tubes over a wide quality range of {minus}0.25 to 0.8. The influences of quality, twist ratio, mass velocity, and clearance between the twisted tape and tube inner wall on CHF were investigated. In the subcooled region, it was observed, using an infrared thermoviewer, that CHF was initiated locally at the wall near the twisted tape. Consequently, twisted tape insertion with small tape-well clearance decreased CHF to below the value of the empty tubes at a low flow rate. This decrease was found to be avoidable by adjusting the clearance. In the net quality region, CHF of the twisted-tape-inserted tubes increased with increasing flow rate contrary to the case of the empty tubes. However, CHF in the net quality region was also decreased by insertion of twisted tapes with high twist ratio (loosely twisted tapes) at a very low flow rate.

  1. Unsteady Flow Analysis of Pump Mode Small Discharge Condition for a Francis Pump-turbine

    NASA Astrophysics Data System (ADS)

    Xiaoran, ZHAO; Yexiang, XIAO; Jincai, XU; Wei, XU; Jianbo, SUN; Zhengwei, WANG; Yangyang, YAO

    2016-11-01

    Unsteady flow phenomena, including vortex flow at runner inlet, helical backflow in the draft tube and numerous vortexes inside the guide vanes, can occur in pump-turbines under off design conditions at pump mode and can impact normal operation of pump-turbines. All of these phenomena cause serious pressure pulsation, which is quite different from cases in normal pump mode. There is also a difference of pressure pulsation frequency and amplitude in different place through the runner. This paper builds a whole flow passage of a model pump-turbine, simulates flow characteristics in runner by CFD technology, analyses pressure pulsation in the runner and explores the origin and mechanism of pressure pulsations. The SST-CC turbulence model is adopted to perform unsteady simulations of the pump-turbine under 0.46Q BEP small discharge condition at pump mode. Unsteady flow structures are proceeded combined with hydraulic loss and pressure amplitude spectra. The results indicates that there is complicated disordered flow inside the runner under 0.46Q BEP small discharge condition at pump mode, shows the amplitude and frequency characteristic of pressure pulsations through runner flow passage.

  2. Using color flow detection of air insufflation to improve accuracy in verifying nasogastric tube position.

    PubMed

    Wong, Kin Wa; Chan, Hok Hang; Wong, Chi Pang; Chan, Ming Yin; Chau, Jeffrey Cheuk Wai; Wong, Tai Wai

    2017-02-01

    Previous studies have shown that ultrasonography (USG), as an alternative to radiography, has a good accuracy in confirming nasogastric tube (NGT) position. Color flow detection of air insufflation is a novel approach in verifying NGT position. In our study, we aimed at evaluating its sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy in confirming the NGT position, as compared with 2-dimensional (2D) USG. The study was conducted on adult patients over a period of 38months in an emergency department in Hong Kong. 2D USG and color flow Doppler imaging were conducted for each subject. Chest X-ray was used as the gold standard for NGT position confirmation. 100 patients (59 males and 41 females) were recruited totally. Their mean age was 82. The sensitivity, specificity, PPV and NPV of 2D USG were 11.1% (95% CI 4.6%-17.6%), 100% (95% CI 100%-100%), 100% (95% CI 100%-100%), and 11.1% (95% CI 4.6%-17.6%) respectively. For color flow Doppler USG, the sensitivity, specificity, PPV and NPV were 90% (95% CI 83.7%-96.2%), 80% (95% CI 55.2%-100%), 97.6% (95% CI 94.3%-100%), and 47.1% (95% CI 23.3%-70.8%) respectively. The overall accuracy of color Doppler imaging was 89%, which was higher than that of 2D USG (20% only). Color flow detection of air insufflation improves the diagnostic accuracy of ultrasound in verifying NGT position. It is a quick investigation such that fasting time of patients and their length of ED stay can be shortened. Copyright © 2016 Elsevier Inc. All rights reserved.

  3. Columbia University Flow Instability Experimental Program, Volume 1. Single tube uniformly heated tests: Part 1, Technical discussion

    SciTech Connect

    Dougherty, T.; Maciuca, C.; McAssey, E.V. Jr.; Reddy, D.G.; Yang, B.W.

    1990-01-01

    An experimental program has been conducted to investigate flow instability in circular tubes under vertical down-flow conditions. The test section L/D ratio range was 86 to 270. The maximum test section surface heat flux was one million Btu/hr-ft{sup 2}. Over 1700 data points were obtained. The effect of flowrate, inlet temperature, exit pressure, and heat flux on the initiation of flow instability was determined. In addition, the data was used to evaluate various methods of predicting the onset of flow instability. Using the measured wall temperatures, surface temperatures and heat transfer coefficients have been obtained. Correlations for the heat transfer coefficient along the tube under both single and two phase conditions were developed.

  4. A study of the influence of mean flow on the acoustic performance of Herschel-Quincke tubes

    PubMed

    Torregrosa; Broatch; Payri

    2000-04-01

    In this paper, a simple flow model is used in order to assess the influence of mean flow and dissipation on the acoustic performance of the classical two-duct Herschel-Quincke tube. First, a transfer matrix is obtained for the system, which depends on the values of the Mach number in the two branches. These Mach numbers are then estimated separately by means of an incompressible flow calculation. Finally, both calculations are used to study the way in which mean flow affects the position and value of the characteristic attenuation and resonances of the system. The results indicate the nontrivial character of the influence observed.

  5. Structure of black aurora associated with pulsating aurora

    NASA Astrophysics Data System (ADS)

    Fritz, Bruce A.; Lessard, Marc L.; Blandin, Matthew J.; Fernandes, Philip A.

    2015-11-01

    Morphological behavior of black aurora as it relates to pulsating aurora is investigated by examining a collection of ground-based observations from January 2007 in support of the Rocket Observations of Pulsating Aurora rocket campaign. Images were sampled from video recorded by a Xybion intensified camera (30 fps) at Poker Flat Research Range, AK. The primary observations of black aurora recorded during the substorm recovery phase were between separate patches of pulsating aurora as well as pulsating aurora separated from diffuse aurora. In these observations the black aurora forms an apparent firm boundary between the auroral forms in a new behavior that is in contrast with previously reported observations. Also presented for the first time are black curls in conjunction with pulsating aurora. Curl structures that indicate shear plasma flows in the ionosphere may be used as a proxy for converging/diverging electric fields in and above the ionosphere. This new subset of black auroral behavior may provide visual evidence of black aurora as an ionospheric feedback mechanism as related to pulsating aurora.

  6. A program for calculating expansion-tube flow quantities for real-gas mixtures and comparison with experimental results

    NASA Technical Reports Server (NTRS)

    Miller, C. G., III

    1972-01-01

    A computer program written in FORTRAN 4 language is presented which determines expansion-tube flow quantities for real test gases CO2 N2, O2, Ar, He, and H2, or mixtures of these gases, in thermochemical equilibrium. The effects of dissociation and first and second ionization are included. Flow quantities behind the incident shock into the quiescent test gas are determined from the pressure and temperature of the quiescent test gas in conjunction with: (1) incident-shock velocity, (2) static pressure immediately behind the incident shock, or (3) pressure and temperature of the driver gas (imperfect hydrogen or helium). The effect of the possible existence of a shock reflection at the secondary diaphragm of the expansion tube is included. Expansion-tube test-section flow conditions are obtained by performing an isentropic unsteady expansion from the conditions behind the incident shock or reflected shock to either the test-region velocity or the static pressure. Both a thermochemical-equilibrium expansion and a frozen expansion are included. Flow conditions immediately behind the bow shock of a model positioned at the test section are also determined. Results from the program are compared with preliminary experimental data obtained in the Langley 6-inch expansion tube.

  7. AEROSOL NUCLEATION AND GROWTH DURING LAMINAR TUBE FLOW: MAXIMUM SATURATIONS AND NUCLEATION RATES. (R827354C008)

    EPA Science Inventory

    An approximate method of estimating the maximum saturation, the nucleation rate, and the total number nucleated per second during the laminar flow of a hot vapour–gas mixture along a tube with cold walls is described. The basis of the approach is that the temperature an...

  8. AEROSOL NUCLEATION AND GROWTH DURING LAMINAR TUBE FLOW: MAXIMUM SATURATIONS AND NUCLEATION RATES. (R827354C008)

    EPA Science Inventory

    An approximate method of estimating the maximum saturation, the nucleation rate, and the total number nucleated per second during the laminar flow of a hot vapour–gas mixture along a tube with cold walls is described. The basis of the approach is that the temperature an...

  9. Dependency of the Reynolds number on the water flow through the perforated tube

    NASA Astrophysics Data System (ADS)

    Závodný, Zdenko; Bereznai, Jozef; Urban, František

    2016-06-01

    Safe and effective loading of nuclear reactor fuel assemblies demands qualitative and quantitative analysis of the relationship between the coolant temperature in the fuel assembly outlet, measured by the thermocouple, and the mean coolant temperature profile in the thermocouple plane position. It is not possible to perform the analysis directly in the reactor, so it is carried out using measurements on the physical model, and the CFD fuel assembly coolant flow models. The CFD models have to be verified and validated in line with the temperature and velocity profile obtained from the measurements of the cooling water flowing in the physical model of the fuel assembly. Simplified physical model with perforated central tube and its validated CFD model serve to design of the second physical model of the fuel assembly of the nuclear reactor VVER 440. Physical model will be manufactured and installed in the laboratory of the Institute of Energy Machines, Faculty of Mechanical Engineering of the Slovak University of Technology in Bratislava.

  10. Dependency of the Reynolds number on the water flow through the perforated tube

    SciTech Connect

    Závodný, Zdenko Bereznai, Jozef Urban, František

    2016-06-30

    Safe and effective loading of nuclear reactor fuel assemblies demands qualitative and quantitative analysis of the relationship between the coolant temperature in the fuel assembly outlet, measured by the thermocouple, and the mean coolant temperature profile in the thermocouple plane position. It is not possible to perform the analysis directly in the reactor, so it is carried out using measurements on the physical model, and the CFD fuel assembly coolant flow models. The CFD models have to be verified and validated in line with the temperature and velocity profile obtained from the measurements of the cooling water flowing in the physical model of the fuel assembly. Simplified physical model with perforated central tube and its validated CFD model serve to design of the second physical model of the fuel assembly of the nuclear reactor VVER 440. Physical model will be manufactured and installed in the laboratory of the Institute of Energy Machines, Faculty of Mechanical Engineering of the Slovak University of Technology in Bratislava.

  11. Flow resistance, work of breathing of humidifiers, and endotracheal tubes in the hyperbaric chamber.

    PubMed

    Arieli, Ran; Daskalovic, Yohanan; Ertracht, Ofir; Arieli, Yehuda; Adir, Yohai; Abramovich, Amir; Halpern, Pinchas

    2011-09-01

    Humidification of inspired gas is critical in ventilated patients, usually achieved by heat and moisture exchange devices (HMEs). HME and the endotracheal tube (ETT) add airflow resistance. Ventilated patients are sometimes treated in hyperbaric chambers. Increased gas density may increase total airway resistance, peak pressures (PPs), and mechanical work of breathing (WOB). We tested the added WOB imposed by HMEs and various sizes of ETT under hyperbaric conditions. We mechanically ventilated 4 types of HMEs and 3 ETTs at 6 minute ventilation volumes (7-19.5 L/min) in a hyperbaric chamber at pressures of 1 to 6 atmospheres absolute (ATA). Peak pressure increased with increasing chamber pressure with an HME alone, from 2 cm H₂O at 1 ATA to 6 cm H(2)O at 6 ATA. Work of breathing was low at 1 ATA (0.2 J/L) and increased to 1.2 J/L at 6 ATA at minute ventilation = 19.5 L/min. Connecting the HME to an ETT increased PP as a function of peak flow and chamber pressure. Reduction of the ETT diameter (9 > 8 > 7.5 mm) and increase in chamber pressure increased the PP up to 27.7 cm H₂O, resistance to 33.2 cmH₂O*s/L, and WOB to 3.76 J/L at 6 ATA with a 7.5-mm EET. These are much greater than the usually accepted critical peak pressures of 25 cm H₂O and WOB of 1.5 to 2.0 J/L. Endotracheal tubes less than 8 mm produce significant added WOB and airway pressure swings under hyperbaric conditions. The hyperbaric critical care clinician is advised to use the largest possible ETT. The tested HMEs add negligible resistance and WOB in the chamber. Copyright © 2011 Elsevier Inc. All rights reserved.

  12. Characterizing Accreting White Dwarf Pulsators

    NASA Astrophysics Data System (ADS)

    Szkody, Paula; Mukadam, Anjum

    2014-02-01

    Understanding the population, mass distribution, and evolution of accreting white dwarfs impacts the entire realm of binary interaction, including the creation of Type Ia supernovae. We are concentrating on accreting white dwarf pulsators, as the pulsation properties allow us a view of how the accretion affects the interior of the star. Our ground- based photometry on 11 accreting pulsators with corresponding temperatures from HST UV spectra suggest a broad instability strip in the range of 10500 to 16000K. Additionally, tracking a post-outburst heated white dwarf as it cools and crosses the blue edge and resumes pulsation provides an independent method to locate the empirical instability strip. Determining a post-outburst cooling curve yields an estimate of the amount of heating and the accreted mass during the outburst. We request additional photometry of 2 objects that present unique properties: GW Lib which has not yet returned to its pre-outburst pulsation spectrum after 6 yrs, and EQ Lyn which returned to its pre- outburst pulsation after 3 yrs but is now turning on and off without ongoing outbursts. Following the pulsation spectrum changes over stretches of several nights in a row will provide specific knowledge of the stability of the observed modes.

  13. Oscillatory fluid flow in deformable tubes: Implications for pore-scale hydromechanics from comparing experimental observations with theoretical predictions.

    PubMed

    Kurzeja, Patrick; Steeb, Holger; Strutz, Marc A; Renner, Jörg

    2016-12-01

    Oscillatory flow of four fluids (air, water, two aqueous sodium-tungstate solutions) was excited at frequencies up to 250 Hz in tubes of two materials (steel, silicone) covering a wide range in length, diameter, and thickness. The hydrodynamical response was characterized by phase shift and amplitude ratio between pressures in an upstream (pressure excitation) and a downstream reservoir connected by the tubes. The resulting standing flow waves reflect viscosity-controlled diffusive behavior and inertia-controlled wave behavior for oscillation frequencies relatively low and high compared to Biot's critical frequency, respectively. Rigid-tube theories correspond well with the experimental results for steel tubes filled with air or water. The wave modes observed for silicone tubes filled with the rather incompressible liquids or air, however, require accounting for the solid's shear and bulk modulus to correctly predict speed of pressure propagation and deformation mode. The shear mode may be responsible for significant macroscopic attenuation in porous materials with effective frame-shear moduli lower than the bulk modulus of the pore fluid. Despite notable effects of the ratio of densities and of acoustic and shear velocity of fluid and solid, Biot's frequency remains an approximate indicator of the transition from the viscosity to the inertia controlled regime.

  14. Effects of oil on boiling of replacement refrigerants flowing normal to a tube bundle -- Part 2: R-134a

    SciTech Connect

    Tatara, R.A.; Payvar, P.

    2000-07-01

    Local, experimental heat transfer coefficients have been obtained for boiling refrigerant flowing up and across a tube bundle segment representing a full flooded evaporator tube bundle. R-134a data with a structured enhanced boiling tube are available. This tube has reentrant cavities designed for higher saturation pressure of refrigerants. The refrigerant enters at 15% vapor quality and exits at nearly 100% vapor in order to simulate an actual evaporator bundle. Both heat flux, 2,607 to 10,427 Btu/h{center_dot}f{sup 2} (8,224 to 32,893 W/m{sup 2}), and oil content, 0--12% (by weight), are varied; the mass flux is not an independent variable but determined by the heat flux. Local tube and bulk fluid temperatures are measured directly, by thermocouples, to calculate the refrigerant-side heat transfer coefficients. The bundle segment saturation temperature setpoint (taken at the top of the tube bundle) is 40 F (4.4 C).

  15. a Numerical Study of Unsteady Fluid Flow in In-Line and Staggered Tube Banks

    NASA Astrophysics Data System (ADS)

    Beale, S. B.; Spalding, D. B.

    1999-08-01

    This paper is concerned with the results of numerical calculations for transient flow in in-line-square and rotated-square tube banks with a pitch-to-diameter ratio of 2:1, in the Reynolds number range of 30-3000. Transient-periodic behaviour is induced by the consideration of two or more modules, with a sinusoidal span-wise perturbation being applied in the upstream module. There is a triode-like effect, whereby the downstream response to the stimulus is amplified, and there is a net gain in the crosswise flow component. When an appropriate feedback mechanism is provided, a stable transient behaviour is obtained, with alternate vortices being shed from each cylinder. Flow visualization studies of the results of the calculations are presented together with quantitative details of pressure drop, lift, drag and heat transfer. For the staggered bank, a wake-switching or Coanda effect was observed as the serpentine-shaped wake attached to alternate sides of the downstream cylinder. The induced response is independent of the amplitude and frequency of the applied disturbance, including the case of spontaneous behaviour with no excitation mechanism. For the in-line case where each cylinder is in the shadow of the previous one, the motion is less pronounced; however, a shear-layer instability associated with the alternating spin of shed vortices was observed. In this case, the response was found to be somewhat dependent on the frequency of the applied disturbance, and a transient motion could not be induced spontaneously in the absence of an explicit feedback mechanism. Calculated Strouhal numbers were in fair agreement with experimental data: for the staggered geometry, they had values of between 0.26 and 0.35, or from -21 to +6% higher than measured values, while for the in-line geometry, the Strouhal numbers ranged between 0.09 and 0.12, or about 20-40% lower than experimental values.

  16. Evaluation of runner cone extension to dampen pressure pulsations in a Francis model turbine

    NASA Astrophysics Data System (ADS)

    Gogstad, Peter Joachim; Dahlhaug, Ole Gunnar

    2016-11-01

    Today's energy market has a high demand of flexibility due to introduction of other intermittent renewables as wind and solar. To ensure a steady power supply, hydro turbines are often forced to operate more at part load conditions. Originally, turbines were built for steady operation around the best efficiency point. The demand of flexibility, combined with old designs has showed an increase in turbines having problems with hydrodynamic instabilities such as pressure pulsations. Different methods have been investigated to mitigate pressure pulsations. Air injection shows a significant reduction of pressure pulsation amplitudes. However, installation of air injection requires extra piping and a compressor. Investigation of other methods such as shaft extension shows promising results for some operational points, but may significantly reduce the efficiency of the turbine at other operational points. The installation of an extension of the runner cone has been investigated at NTNU by Vekve in 2004. This has resulted in a cylindrical extension at Litjfossen Power Plant in Norway, where the bolt suffered mechanical failure. This indicates high amplitude pressure pulsations in the draft tube centre. The high pressure pulsation amplitudes are believed to be related to high tangential velocity in the draft tube. The mentioned runner cone extension has further been developed to a freely rotating extension. The objective is to reduce the tangential velocity in the draft tube and thereby the pressure pulsation amplitudes.

  17. Selected ion flow tube studies of air plasma cations reacting with alkylbenzenes

    SciTech Connect

    Arnold, S.T.; Dotan, I.; Williams, S.; Viggiano, A.A.; Morris, R.A.

    2000-02-10

    Rate constants and product branching fractions are reported for reactions of the air plasma cations NO{sup +}, O{sub 2}{sup +}, O{sup +}, N{sup +}, and N{sub 2}{sup +} with several alkylbenzenes: toluene, ethylbenzene, n-propylbenzene, and m-xylene. The measurements were made using a selected ion flow tube (SIFT) apparatus at 300 K. All reactions were found to proceed at the collision rate. NO{sup +} reactions yield exclusively nondissociative charge-transfer products. C{sub 7}H{sub 7}{sup +} is the dominant product ion observed in all the O{sup +}, N{sup +}, and N{sub 2}{sup +} reactions. Charge transfer and formation of C{sub 7}H{sub 7}{sup +} are the major product channels in the O{sub 2}{sup +} reactions. Product distributions were converted to crude breakdown diagrams, showing the relative abundance of each product ion as a function of the reactant ion recombination energy. The flow tube results exhibit a shift in the product ion threshold energies, an effect attributed to a kinetic shift resulting from slow fragmentation of the excited charge-transfer complex combined with collisional stabilization of the complex by the He buffer gas. Two isomeric forms of the C{sub 7}H{sub 7}{sup +} product ion are produced in these reactions: the benzyl (Bz{sup +}) and tropylium (Tr{sup +}) cations. The Bz{sup +}/Tr{sup +} isomeric mixture ratio was quantified as a function of energy for all four alkylbenzenes. Changes in the Bz{sup +}/Tr{sup +} mixture suggest that ethylbenzene has a relatively larger reverse activation barrier compared with toluene for forming Tr{sup +} from the charge-transfer complex, while formation of Tr{sup +} from the larger alkylbenzenes probably proceeds via a different mechanism altogether. For m-xylene, the formation of both Bz{sup +} and Tr{sup +} isomers likely proceeds via a different mechanism than for the n-alkylbenzenes.

  18. Flow and heat transfer characteristics of graphene oxide nanofluids in a horizontal tube

    NASA Astrophysics Data System (ADS)

    Nunna, Maheshwar Rao

    This thesis presents a fundamental study conducted on heat transfer and decrease in flow through a straight copper tube of a graphene oxide (GO) nanofluid developed in-house. The GO particles were synthesized using the modified Hummers method. The physicochemical properties of the fabricated GO were characterized using X-ray diffraction analysis (XRD), a scanning electron microscope (SEM), and UV-Vis spectrophotometry, and the particle size distribution was investigated using dynamic light scattering. GO nanofluids of 0.01 wt. % and 0.1 wt. % were prepared by dispersing GO sheets in de-ionized water. Thermo-physical properties of GO nanofluids were also measured at different temperatures. An experimental setup was developed to find the heat transfer characteristics and pressure drop of nanofluids in the test section. A flexible heater was used to provide the constant heat flux condition at the wall of the tube for all the experiments. In this study, the experimental investigations of flow regime, flowrates, pressure drop and heat transfer characteristics were performed by considering three different heat flux conditions (7.38 kW/m2, 9.08 kW/m2, and 12.55 kW/m2) at three different set points of variable frequency drive (VFD), 15, 20, and 25, connected to the pump. Due to the increase in viscosity, there was a decrease in flowrate and Reynolds number from 0.01 wt. % to 0.1 wt. % of GO nanofluids at constant pump frequency. Experimental data obtained for water was validated with available data from the literature, and the correlations were formulated for the Nusselt number and Reynolds number by considering the multiple regression analysis. Convective heat transfer coefficient and dimensionless wall temperature for water and GO nanofluids were investigated. A rise in dimensionless wall temperature with the increase of velocity and particle concentration was observed. The convective heat transfer coefficient for GO 0.01 wt. % was higher when compared to GO 0.1 wt

  19. Boiling Heat Transfer and Pressure Drop of a Refrigerant Flowing Vertically Downward in a Small Diameter Tube

    NASA Astrophysics Data System (ADS)

    Miyata, Kazushi; Mori, Hideo; Ohishi, Katsumi; Tanaka, Hirokazu

    Experiments were performed on boiling heat transfer and pressure drop of a refrigerant R410A flowing vertically downward in a copper smooth tube of 1.0 mm inside diameter for the development of a high-performance heat exchanger using small diameter tubes for air conditioning systems. Local heat transfer coefficients were measured in a range of mass fluxes from 30 to 200 kg/(m2•s), heat fluxes from 1 to 16 kW/m2 and quality from 0.1 to over 1 at evaporation temperature of 10°C. Pressure drops were measured and flow patterns were observed at mass fluxes from 30 to 200 kg/(m2•s) and quality from 0.1 to 0.9. The characteristics of frictional pressure drop, heat transfer coefficient and dryout qualities were clarified by comparing the measurements with the data for the vertically upward flow previously obtained.

  20. Modeling of pulsating heat pipes.

    SciTech Connect

    Givler, Richard C.; Martinez, Mario J.

    2009-08-01

    This report summarizes the results of a computer model that describes the behavior of pulsating heat pipes (PHP). The purpose of the project was to develop a highly efficient (as compared to the heat transfer capability of solid copper) thermal groundplane (TGP) using silicon carbide (SiC) as the substrate material and water as the working fluid. The objective of this project is to develop a multi-physics model for this complex phenomenon to assist with an understanding of how PHPs operate and to be able to understand how various parameters (geometry, fill ratio, materials, working fluid, etc.) affect its performance. The physical processes describing a PHP are highly coupled. Understanding its operation is further complicated by the non-equilibrium nature of the interplay between evaporation/condensation, bubble growth and collapse or coalescence, and the coupled response of the multiphase fluid dynamics among the different channels. A comprehensive theory of operation and design tools for PHPs is still an unrealized task. In the following we first analyze, in some detail, a simple model that has been proposed to describe PHP behavior. Although it includes fundamental features of a PHP, it also makes some assumptions to keep the model tractable. In an effort to improve on current modeling practice, we constructed a model for a PHP using some unique features available in FLOW-3D, version 9.2-3 (Flow Science, 2007). We believe that this flow modeling software retains more of the salient features of a PHP and thus, provides a closer representation of its behavior.

  1. Variability of Microcirculation Detected by Blood Pulsation Imaging

    PubMed Central

    Kamshilin, Alexei A.; Teplov, Victor; Nippolainen, Ervin; Miridonov, Serguei; Giniatullin, Rashid

    2013-01-01

    The non-invasive assessment of blood flow is invaluable for the diagnostic and monitoring treatment of numerous vascular and neurological diseases. We developed a non-invasive and non-contact method of blood pulsation imaging capable of visualizing and monitoring of the two-dimensional distribution of two key parameters of peripheral blood flow: the blood pulsation amplitude and blood pulsation phase. The method is based on the photoplethysmographic imaging in the reflection mode. In contrast with previous imaging systems we use new algorithm for data processing which allows two dimensional mapping of blood pulsations in large object's areas after every cardiac cycle. In our study we carried out the occlusion test of the arm and found (i) the extensive variability of 2D-distribution of blood pulsation amplitude from one cardiac cycle to another, and (ii) existence of the adjacent spots to which the blood is asynchronously supplied. These observations show that the method can be used for studying of the multicomponent regulation of peripheral blood circulation. The proposed technique is technologically simple and cost-effective, which makes it applicable for monitoring the peripheral microcirculation in clinical settings for example, in diagnostics or testing the efficiency of new medicines. PMID:23431399

  2. Secondary flow morphologies due to model stent-induced perturbations in a 180° curved tube during systolic deceleration

    NASA Astrophysics Data System (ADS)

    Bulusu, Kartik V.; Plesniak, Michael W.

    2013-03-01

    Morphological changes in secondary flow structures due to a stent model were investigated under physiological inflow conditions. The stent model was inserted upstream of a 180° curved tube artery model. A carotid artery flow rate with its characteristic systolic and diastolic phases was supplied by a pump to drive a blood-analog working fluid. Phase-averaged, two-component, two-dimensional (2C-2D) particle image velocimeter measurements revealed the changing morphologies of these secondary flow structures. Continuous wavelet transforms provided an enhanced means to detect coherent secondary flow structures in this bio-inspired experimental study. A two-dimensional Ricker wavelet was used, and the optimal wavelet scale was determined using Shannon entropy as a measure of randomness in the wavelet-transformed vorticity fields. Planar secondary flow vortical structures at the 90° location in the curved tube were observed to exhibit distinct spatio-temporal characteristics different than the baseline flow without the stent. Flow patterns observed at the systolic peak comprised of early Lyne-type, along with a deformed Dean-type pair of ordered, coherent, high-circulation and counter-rotating vortical structures. Systolic deceleration was marked by the breakdown of large-scale coherent vortices into multiple, disordered, low-circulation, coherent vortical structures, indicating new transitional secondary flow morphologies. These multi-scale secondary flow morphologies arise due to the combination of imbalances in centrifugal and pressure forces, and stent-induced flow perturbations. The detailed flow physics associated with the formation of Dean and Lyne vortices are described in previous publications that have been cited in the manuscript. The secondary flow structures reported here are driven by similar fundamental mechanisms, but additionally contain more complicated effects, such as asymmetry and multiple strengths, that cannot be predicted from simple theories.

  3. Heat transfer deterioration in tubes caused by bulk flow acceleration due to thermal and frictional influences

    SciTech Connect

    Jackson, J. D.

    2012-07-01

    Severe deterioration of forced convection heat transfer can be encountered with compressible fluids flowing through strongly heated tubes of relatively small bore as the flow accelerates and turbulence is reduced because of the fluid density falling (as the temperature rises and the pressure falls due to thermal and frictional influence). The model presented here throws new light on how the dependence of density on both temperature and pressure can affect turbulence and heat transfer and it explains why the empirical equations currently available for calculating effectiveness of forced convection heat transfer under conditions of strong non-uniformity of fluid properties sometimes fail to reproduce observed behaviour. It provides a criterion for establishing the conditions under which such deterioration of heat transfer might be encountered and enables heat transfer coefficients to be determined when such deterioration occurs. The analysis presented here is for a gaseous fluid at normal pressure subjected strong non-uniformity of fluid properties by the application of large temperature differences. Thus the model leads to equations which describe deterioration of heat transfer in terms of familiar parameters such as Mach number, Reynolds number and Prandtl number. It is applicable to thermal power plant systems such as rocket engines, gas turbines and high temperature gas-cooled nuclear reactors. However, the ideas involved apply equally well to fluids at supercritical pressure. Impairment of heat transfer under such conditions has become a matter of growing interest with the active consideration now being given to advanced water-cooled nuclear reactors designed to operate at pressures above the critical value. (authors)

  4. Uptake of gaseous formaldehyde onto soil surfaces: a coated-wall flow tube study

    NASA Astrophysics Data System (ADS)

    Li, Guo; Su, Hang; Li, Xin; Meusel, Hannah; Kuhn, Uwe; Pöschl, Ulrich; Shao, Min; Cheng, Yafang

    2015-04-01

    Gaseous formaldehyde (HCHO) is an important intermediate molecule and source of HO2 radicals. However, discrepancies exist between model simulated and observed HCHO concentrations, suggesting missing sources or sinks in the HCHO budget. Multiphase processes on the surface of soil and airborne soil-derived particles have been suggested as an important mechanism for the production/removal of atmospheric trace gases and aerosols. In this work, the uptake of gaseous HCHO on soil surfaces were investigated through coated-wall flow tube experiments with HCHO concentration ranging from 10 to 40 ppbv. The results show that the adsorption of HCHO occurred on soil surfaces, and the uptake coefficient dropped gradually (i.e., by a factor of 5 after 1 hour) as the reactive surface sites were consumed. The HCHO uptake coefficient was found to be affected by the relative humidity (RH), decreasing from (2.4 ± 0.5) × 10-4 at 0% RH to (3.0 ± 0.08) × 10-5 at 70% RH, due to competition of water molecule absorption on the soil surface. A release of HCHO from reacted soil was also detected by applying zero air, suggesting the nature of reversible physical absorption and the existence of an equilibrium at the soil-gas interface. It implies that soil could be either a source or a sink for HCHO, depending on the ambient HCHO concentration. We also develop a Matlab program to calculate the uptake coefficient under laminar flow conditions based on the Cooney-Kim-Davis method.

  5. Enhancement of CHF water subcooled flow boiling in tubes using helically coiled wires

    NASA Astrophysics Data System (ADS)

    Celata, G. P.; Cumo, M.; Mariani, A.

    1994-01-01

    The present paper reports the results of an experimental investigation about the occurrence of the critical heat flux (CHF) in subcooled flow boiling of water, carried out to ascertain the influence of thermal hydraulic parameters on CHF under conditions typical of themronuclear fusion divertor thermal hydraulic design. Helically coiled wires were used as turbulence promoters to enhance the CHF with respect to the smooth channel. Geometric characteristics of stainless steel 304 Type test sections were: 6.0 and 8.0 mm i.d., 0.25 mm wal thickness, 0.1 and 0.15 m heated length, horizontal and vertical (upflow) position. Test sections were uniformly heated using d.c. current. A maximum CHF of about 30 MW/sq m was reached with smooth tubes under the following conditions: T(sub in) = 30 C, p = 4.6 MPa, u = 10 m/s, D = 8.0 mm, L = 0.1 m. Helically coiled wires (d = 1.0 mm, pitch = 20.0 mm) allowed an increase of the CHF up to 50%, with reference to smooth channels, coupled with a moderate increase of pressure drop (down to 25%). Pressure revealed a negative effect on the efficiency of turbulence promoters. No observable influence of the channel orientation was detected.

  6. Numerical Investigation on Trapezoidal Cavity Receiver Used In LFR with Water Flow in Absorber Tubes

    NASA Astrophysics Data System (ADS)

    Duggal, Rohit; Jilte, Ravindra

    2017-03-01

    In the present study, numerical three dimensional model of trapezoidal cavity used in LFR was analysed. Results are presented in the form of Thermal losses occurring from the receiver operating with an absorber tube temperature from 350-550 K in step of 50 K and emissivity varied from 0.5-1.0. Effect of wind blowing below lower glass plate (cavity aperture) were also analysed considering the heat transfer coefficient from 5 to 25 W/m2K. At lower absorber temperature (350 K) convective losses is found to be 43% of the total heat loss whereas radiative losses accounted 57%. For higher absorber temperature radiative losses are dominant (77%) and convective losses are reduced to 23%. The air temperature gradient in the horizontal direction (parallel to lower glass plate) is found to be negligible whereas it is varied significantly in vertical direction (normal to lower glass plate). The average cavity air temperature is observed to be 480 K for low wind flow (h=5 W/m2K) and it reduces to 360 K for h=25 W/m2K. This has resulted in increased convective losses (27% higher).

  7. Microwave plasma ion sources for selected ion flow tube mass spectrometry

    NASA Astrophysics Data System (ADS)

    Spanel, Patrik; Dryahina, Kseniya; Smith, David

    2007-11-01

    The performance of the ion sources used in selected ion flow tube mass spectrometry, SIFT-MS, instruments is paramount in determining their sensitivities and detection limits for trace gas analysis. The microwave discharge plasma ion source that is currently used for the production of currents of the precursor H3O+, NO+ and O2+ ions for SIFT-MS is described, and the ion chemistry occurring within the plasma and the dissociation of the precursor ions on the helium carrier gas are considered. Thus, it is shown that the most suitable ion source gas composition is a mixture comprising maximal water vapour and minimal air at the lowest total pressure at which the discharge is sustained and stable. It is also shown that the injection energies of the precursor ions into the helium carrier gas must be kept low to minimize collisional dissociation of the ions and thus to minimize the fraction of reactive impurity ions in the carrier gas. Under these conditions, count rates greater than 106 s-1 of all three precursor ion species with less than 1% of impurity ions have been achieved, which has moved the detection limit of SIFT-MS analyses of the volatile metabolites present in exhaled breath and ambient air into the 0.1-1 parts-per-billion concentration regime.

  8. Quantification of methanol in the presence of ethanol by selected ion flow tube mass spectrometry.

    PubMed

    Chambers-Bédard, Catherine; Ross, Brian M

    The quantification of trace compounds in alcoholic beverages is a useful means to both investigate the chemical basis of beverage flavor and to facilitate quality control during the production process. One compound of interest is methanol which, due to it being toxic, must not exceed regulatory limits. The analysis of headspace gases is a desirable means to do this since it does not require direct sampling of the liquid material. One established means to conduct headspace analysis is selected ion flow tube mass spectrometry (SIFT-MS). The high concentration of ethanol present in the headspace of alcoholic drinks complicates the analysis, however, via reacting with the precursor ions central to this technique. We therefore investigated whether methanol could be quantified in the presence of a large excess of ethanol using SIFT-MS. We found that methanol reacted with ionized ethanol to generate product ions that could be used to quantify methanol concentrations and used this technique to quantify methanol in beverages containing different quantities of ethanol. We conclude that SIFT-MS can be used to quantify trace compounds in alcoholic beverages by determining the relevant reaction chemistry.

  9. Measurement of breath acetone concentrations by selected ion flow tube mass spectrometry in type 2 diabetes.

    PubMed

    Storer, Malina; Dummer, Jack; Lunt, Helen; Scotter, Jenny; McCartin, Fiona; Cook, Julie; Swanney, Maureen; Kendall, Deborah; Logan, Florence; Epton, Michael

    2011-12-01

    Selected ion flow tube-mass spectrometry (SIFT-MS) can measure volatile compounds in breath on-line in real time and has the potential to provide accurate breath tests for a number of inflammatory, infectious and metabolic diseases, including diabetes. Breath concentrations of acetone in type 2 diabetic subjects undertaking a long-term dietary modification programme were studied. Acetone concentrations in the breath of 38 subjects with type 2 diabetes were determined by SIFT-MS. Anthropomorphic measurements, dietary intake and medication use were recorded. Blood was analysed for beta hydroxybutyrate (a ketone body), HbA1c (glycated haemoglobin) and glucose using point-of-care capillary (fingerprick) testing. All subjects were able to undertake breath manoeuvres suitable for analysis. Breath acetone varied between 160 and 862 ppb (median 337 ppb) and was significantly higher in men (median 480 ppb versus 296 ppb, p = 0.01). In this cross-sectional study, no association was observed between breath acetone and either dietary macronutrients or point-of-care capillary blood tests. Breath analysis by SIFT-MS offers a rapid, reproducible and easily performed measurement of acetone concentration in ambulatory patients with type 2 diabetes. The high inter-individual variability in breath acetone concentration may limit its usefulness in cross-sectional studies. Breath acetone may nevertheless be useful for monitoring metabolic changes in longitudinal metabolic studies, in a variety of clinical and research settings.

  10. Heterogeneous oxidation of terbuthylazine by "dark" OH radicals under simulated atmospheric conditions in a flow tube.

    PubMed

    Pflieger, Maryline; Monod, Anne; Wortham, Henri

    2013-06-18

    In order to investigate the heterogeneous oxidation kinetics of the herbicide terbuthylazine (TERB), a stable and reproducible generation system of "dark" hydroxyl radical in the gas phase was developed and optimized using a PTR-MS. TERB was adsorbed on silica particles, which were coated on the walls of