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Sample records for pulsating tube flow

  1. Total-pressure-tube averaging in pulsating flows.

    NASA Technical Reports Server (NTRS)

    Krause, L. N.

    1973-01-01

    A number of total-pressure tubes were tested in a nonsteady flow generator in which the fraction of period that pressure is a maximum is approximately 0.8, thereby simulating turbomachine-type flow conditions. The tests were performed at a pressure level of 1 bar, for Mach numbers up to near 1, and frequencies up to 3 kHz. Most of the tubes indicated a pressure which was higher than the true average. Organ-pipe resonances which further increased the indicated pressure were 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.

  2. Influence of a pulsating flow on the transfer of heat from cylinders and finned tubes

    NASA Astrophysics Data System (ADS)

    Perwaiz, J.; Base, T. E.

    The effect of pulsations in the flow on forced convective heat transfer coefficients around a circular cylinder and a finned tube is studied. Convection measurement experiments were performed to determine the rate of heat transfer (average Nusselt numbers) from a circular cylinder and a finned tube in a pulsating crossflow. The experiments were performed using the unsteady flow inducer wind tunnel, which had facility for generating time-dependent flow. The forced convective heat transfer in steady crossflows was checked for both the circular cylinder and the finned tube to validate the experimental techniques and apparatus. The findings indicate the dependence of heat transfer on the dimensionless frequency of the crossflow. Specifically, at higher mean flows there is considerable discrepancy between the Nusselt number for steady flows and the Nusselt number for unsteady flows with the same mean flow value. The effects on the variation in the heat transfer must be carefully taken into account in the design and analysis of thermal systems exposed to pulsating flows.

  3. 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.

    2015-10-01

    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.

  4. Characteristics of heat transfer and flow of Al2O3/water nanofluid in a spiral-coil tube for turbulent pulsating flow

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

    In the past two decades, enhancement of heat transfer characteristics of original fluid using nanofluids has been proposed by a large number of researchers. In this paper, an experimental study was carried out to investigate effect of pulsation on heat transfer of fluid flow inside a spiral-coil tube. In order to perform the experiments, a hot water reservoir tank was prepared and the spiral-coil was immersed horizontally inside the tank. Average temperature of the hot water bath was kept constant at 60 °C to establish a quiescent region of uniform temperature. The experiments were conducted in turbulent flow regime using distilled water and Al2O3/water nanofluid at 0.5, 1, and 1.5 % particle volume concentration. Results showed that overall heat transfer coefficient of the base fluid flow increases by using nanofluid or pulsation into the base fluid flow up to 14 %. Heat transfer results also indicated that combination of the nanofluid and the pulsation into the fluid flow can increase significantly the overall heat transfer coefficient up to 23 %.

  5. Characteristics of heat transfer and flow of Al2O3/water nanofluid in a spiral-coil tube for turbulent pulsating flow

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

    In the past two decades, enhancement of heat transfer characteristics of original fluid using nanofluids has been proposed by a large number of researchers. In this paper, an experimental study was carried out to investigate effect of pulsation on heat transfer of fluid flow inside a spiral-coil tube. In order to perform the experiments, a hot water reservoir tank was prepared and the spiral-coil was immersed horizontally inside the tank. Average temperature of the hot water bath was kept constant at 60 °C to establish a quiescent region of uniform temperature. The experiments were conducted in turbulent flow regime using distilled water and Al2O3/water nanofluid at 0.5, 1, and 1.5 % particle volume concentration. Results showed that overall heat transfer coefficient of the base fluid flow increases by using nanofluid or pulsation into the base fluid flow up to 14 %. Heat transfer results also indicated that combination of the nanofluid and the pulsation into the fluid flow can increase significantly the overall heat transfer coefficient up to 23 %.

  6. Understanding thermo-fluidic characteristics of a glass tube closed loop pulsating heat pipe: flow patterns and fluid oscillations

    NASA Astrophysics Data System (ADS)

    Karthikeyan, V. K.; Ramachandran, K.; Pillai, B. C.; Brusly Solomon, A.

    2015-12-01

    An experimental program has been carried out to understand the thermo-fluidic characterization of deionized (DI) water charged closed loop pulsating heat pipe (CLPHP) with flow patterns and fluid oscillations. The CLPHP is examined under vertical and horizontal heating modes with varying heat power. The flow patterns along with fluid oscillations are correlated with thermal performance of the CLPHP. Further, the CLPHP with copper oxide nanofluid study is carried out to understand operational behavior of the device. Fast Fourier frequencies, average frequency of the internal fluid temperature are investigated. Several important features of CLPHP operation are identified by the visual study.

  7. 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 nonsteady 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 with 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.

  8. 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.

  9. Convective heat transfer characteristics of laminar pulsating pipe air flow

    NASA Astrophysics Data System (ADS)

    Habib, M. A.; Attya, A. M.; Eid, A. I.; Aly, A. Z.

    Heat transfer characteristics to laminar pulsating pipe flow under different conditions of Reynolds number and pulsation frequency were experimentally investigated. The tube wall of uniform heat flux condition was considered. Reynolds number was varied from 780 to 1987 while the frequency of pulsation ranged from 1 to 29.5Hz. The results showed that the relative mean Nusselt number is strongly affected by pulsation frequency while it is slightly affected by Reynolds number. The results showed enhancements in the relative mean Nusselt number. In the frequency range of 1-4Hz, an enhancement up to 30% (at Reynolds number of 1366 and pulsation frequency of 1.4Hz) was obtained. In the frequency range of 17-25Hz, an enhancement up to 9% (at Reynolds number of 1366 and pulsation frequency of 17.5Hz) was indicated. The rate of enhancement of the relative mean Nusselt number decreased as pulsation frequency increased or as Reynolds number increased. A reduction in relative mean Nusselt number occurred outside these ranges of pulsation frequencies. A reduction in relative mean Nusselt number up to 40% for pulsation frequency range of 4.1-17Hz and a reduction up to 20% for pulsation frequency range of 25-29.5Hz for Reynolds numbers range of 780-1987 were considered. This reduction is directly proportional to the pulsation frequency. Empirical dimensionless equations have been developed for the relative mean Nusselt number that related to Reynolds number (750

  10. 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.

  11. Some spectral and pulsation characteristics of the horizontal flow of a gas-liquid suspension

    NASA Astrophysics Data System (ADS)

    Krokovnyi, P. M.

    1980-02-01

    In the experiments described, the turbulence characteristics of a two-phase gas-liquid pipe flow were studied, using a 6 m long, 19-mm-diam tube. The inlet temperature of the suspension was maintained at 25 C. The friction energy spectra and the relative intensity of the friction pulsations were measured. The spectral and pulsation characteristics were obtained by an electrodiffusion technique which provided reliable data on the pulsations of the wall shear stress.

  12. 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).

  13. An experimental investigation of heat transfer to pulsating pipe air flow with different amplitudes

    NASA Astrophysics Data System (ADS)

    Zohir, A. E.; Habib, M. A.; Attya, A. M.; Eid, A. I.

    2006-05-01

    Heat transfer characteristics to both laminar and turbulent pulsating pipe flows under different conditions of Reynolds number, pulsation frequency, pulsator location and tube diameter were experimentally investigated. The tube wall of uniform heat flux condition was considered for both cases. Reynolds number varied from 750 to 12,320 while the frequency of pulsation ranged from 1 to 10 Hz. With locating the pulsator upstream of the inlet of the test section tube, results showed an increase in heat transfer rate due to pulsation by as much as 30% with flow Reynolds number of 1,643 and pulsation frequency of 1 Hz, depending on the upstream location of the pulsator valve. Closer the valve to the tested section inlet, the better improvement in the heat transfer coefficient is achieved. Upon comparing the heat transfer results of the upstream and the downstream pulsation, at Reynolds number of 1,366 and 1,643, low values of the relative mean Nusselt number were obtained with the upstream pulsation. Comparing the heat transfer results of the two studied test sections tubes for Reynolds number range from 8,000 to 12,000 and pulsation frequency range from 1.0 to 10 Hz showed that more improvement in heat transfer rate was observed with a larger tube diameter. For Reynolds number ranging from 8,000 to 12,000 and pulsation frequency of 10 Hz, an improvement in the relative mean Nusselt number of about 50% was obtained at Reynolds number of 8,000 for the large test section diameter of 50 mm. While, for the small test section diameter of 15 mm, at same conditions of Reynolds number and frequency, a reduction in the relative mean Nusselt number of up to 10% was obtained.

  14. The Effect of Flow Pulsations on Coriolis Mass Flow Meters

    NASA Astrophysics Data System (ADS)

    Cheesewright, R.; Clark, C.

    1998-11-01

    It has been reported that the accuracy of Coriolis mass flow meters can be adversely affected by the presence of pulsations (at particular frequencies) in the flow. A full analysis of the transient performance of a commercial Coriolis meter is only possible using finite element techniques. However, this is a transient, nonlinear problem in which the space and time variables are not (strictly) separable and the finite element techniques for tackling such problems make it desirable to have an analytical solution for a simplified meter, against which the finite element solution can be compared. This paper reports such a solution. The solution will also provide guidance for experiments. Existing analytical solutions for the performance of Coriolis meters in steady flow (a complex eigenvalue problem) are not easily extended to the transient flow case. The paper thus begins with the presentation of an alternative solution for steady flow through a simple, straight tube, Coriolis meter and it is notable that this solution gives a simple analytical expression for the experimentally observed small change in the resonant frequency of the meter, with flow rate, as well as an analytical expression for the meter sensitivity. The analysis is extended to the transient case, using classical, forced vibration, modal decomposition techniques. The solution shows that, unlike the steady flow case where the detector signals contain components at the drive frequency and the second mode frequency (Coriolis frequency), for pulsatile flow the detector signals will in general contain components involving at least four frequencies. It is demonstrated that the meter error depends on the algorithm used to estimate the phase difference from the detector signals. The particular flow pulsation frequencies which could possibly lead to large meter errors are identified.

  15. Theoretical and experimental investigations of flow pulsation effects in Coriolis mass flowmeters

    NASA Astrophysics Data System (ADS)

    Svete, A.; Kutin, J.; Bobovnik, G.; Bajsić, I.

    2015-09-01

    An understanding of the effects of flow pulsations on the dynamic behavior of Coriolis flowmeters is very important for their further development. In order to determine the phase difference between the vibrational signals, which represents the basic measurement effect of Coriolis flowmeters, there are many methods that include the proper filtering of all the signal components, except those with frequencies close to the drive frequency. Therefore, an understanding of the phenomenon of exciting the meter at its first natural frequency is very important. The results of a simple, linear, two-degree-of-freedom, lumped-parameter, dynamic model of a flowmeter show that the flow pulsations can degrade the accuracy of such a flowmeter as a result of indirect excitations of the measuring tube at the first natural frequency through the second-order perturbations by means of the Coriolis forces induced in pulsating flow conditions. In order to experimentally investigate these flow pulsation effects, a prototype of a straight-tube Coriolis mass flowmeter was developed to enable the processing of the response signals logged directly from the flow tube's sensors with the dual quadrature demodulation method, and therefore to provide the information available within the phase-difference data. The experimental results show that the flow pulsations upset the meter at its first natural frequency indirectly, as well as directly at the frequency of the pulsations due to the geometric imperfections of the measuring tube.

  16. A statistical method for draft tube pressure pulsation analysis

    NASA Astrophysics Data System (ADS)

    Doerfler, P. K.; Ruchonnet, N.

    2012-11-01

    Draft tube pressure pulsation (DTPP) in Francis turbines is composed of various components originating from different physical phenomena. These components may be separated because they differ by their spatial relationships and by their propagation mechanism. The first step for such an analysis was to distinguish between so-called synchronous and asynchronous pulsations; only approximately periodic phenomena could be described in this manner. However, less regular pulsations are always present, and these become important when turbines have to operate in the far off-design range, in particular at very low load. The statistical method described here permits to separate the stochastic (random) component from the two traditional 'regular' components. It works in connection with the standard technique of model testing with several pressure signals measured in draft tube cone. The difference between the individual signals and the averaged pressure signal, together with the coherence between the individual pressure signals is used for analysis. An example reveals that a generalized, non-periodic version of the asynchronous pulsation is important at low load.

  17. 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

  18. Pulsating laminar fully developed channel and pipe flows.

    PubMed

    Haddad, Kais; Ertunç, Ozgür; Mishra, Manoranjan; Delgado, Antonio

    2010-01-01

    Analytical investigations are carried out on pulsating laminar incompressible fully developed channel and pipe flows. An analytical solution of the velocity profile for arbitrary time-periodic pulsations is derived by approximating the pulsating flow variables by a Fourier series. The explicit interdependence between pulsations of velocity, mass-flow rate, pressure gradient, and wall shear stress are shown by using the proper dimensionless parameters that govern the flow. Utilizing the analytical results, the scaling laws for dimensionless pulsation amplitudes of the velocity, mass-flow rate, pressure gradient, and wall shear stress are analyzed as functions of the dimensionless pulsation frequency. Special attention has been given to the scaling laws describing the flow reversal phenomenon occurring in pulsating flows, such as the condition for flow reversal, the dependency of the reversal duration, and the amplitude. It is shown that two reversal locations away from the wall can occur in pulsating flows in pipes and channels and the reversed amount of mass per period reaches a maximum at a certain dimensionless frequency for a given amplitude of mass-flow rate fluctuations. These analyses are numerically conducted for pipe and channel flows over a large frequency range in a comparative manner. PMID:20365456

  19. Heat transfer coefficients for drying in pulsating flows

    SciTech Connect

    Fraenkel, S.L.

    1998-05-01

    Pulsating flows generated by a Rijke type combustor are studied for drying of grains and food particles. It is assumed that the velocity fluctuations are the main factor in the enhancement of the drying process. The heat transfer coefficients for drying in vibrating beds are utilized to estimate the heat transfer coefficients of fixed beds in pulsating and permeating flows and are compared to the steady flow heat transfer coefficients obtained for solid porous bodies, after perturbing the main flow. The cases considered are compared to the convective heat transfer coefficients employed in non-pulsating drying.

  20. Flow and mixing characteristics of an elevated pulsating transverse jet

    NASA Astrophysics Data System (ADS)

    Huang, Rong F.; Hsu, Ching M.

    2012-01-01

    Flow-evolution processes as well as the penetration, spread, and dispersion characteristics of elevated pulsating transverse jets were studied experimentally in a wind tunnel. Jet pulsations were induced by means of acoustic excitation. Streak pictures of the smoke-flow patterns, illuminated by a laser-light sheet in the median plane, were recorded by a high-speed digital camera. A hot-wire anemometer was used to digitize instantaneous velocities of instabilities in the flow. Penetration height and spread width were obtained through a binary edge identification technique. Tracer-gas concentrations were measured to provide information on jet dispersions and trajectories. Three characteristic flow modes (synchronized flapping jet, transition, and synchronized shear-layer vortices) were identified in the domain of the jet-to-crossflow momentum-flux ratio and the excitation Strouhal number. At low excitation Strouhal numbers, the jet column near the tube exit flapped back-and-forth periodically at the excitation frequency and induced large up-down motions of the deflected jet. The penetration, spread, and dispersion of the jet increased drastically compared with the non-excited jet because the up-down oscillating motions of the deflected jet transformed the axial momentum into oscillating lateral momentum. Forcing the jet into the transition and synchronized shear-layer vortices regimes caused the vortices to appear along the upwind shear layer of the deflected jet. Under these conditions, the penetration, spread, and dispersion of the jet presented insignificant increases because the entrainment effect induced by the shear-layer vortices was not as large as that produced by the jet oscillating motions in the synchronized flapping jet regime.

  1. Heat transfer characteristics of pulsated turbulent pipe flow

    NASA Astrophysics Data System (ADS)

    Habib, M. A.; Said, S. A. M.; Al-Farayedhi, A. A.; Al-Dini, S. A.; Asghar, A.; Gbadebo, S. A.

    Heat Transfer characteristics of pulsated turbulent pipe flow under different conditions of pulsation frequency, amplitude and Reynolds number were experimentally investigated. The pipe wall was kept at uniform heat flux. Reynolds number was varied from 5000 to 29 000 while frequency of pulsation ranged from 1 to 8 Hz. The results show an enhancement in the local Nusselt number at the entrance region. The rate of enhancement decreased as Re increased. Reduction of heat transfer coefficient was observed at higher frequencies and the effect of pulsation is found to be significant at high Reynolds number. It can be concluded that the effect of pulsation on the mean Nusselt numbers is insignificant at low values of Reynolds number.

  2. 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.

  3. 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.

  4. 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.

  5. The Simulation of Coriolis Meter Response to Pulsating Flow Using a General Purpose F.E. Code

    NASA Astrophysics Data System (ADS)

    Belhadj, A.; Cheesewright, R.; Clark, C.

    2000-07-01

    The publication of a theoretical analysis of the response of a simple straight-tube Coriolis meter to flow pulsations raised the question of the extent to which the results of that analysis are generic over the wide range of geometric configurations used in commercially available meters. A procedure for using a general purpose finite element (FE) code to investigate this question is presented. The dual time scales, which are an essential feature of pulsating flow through a Coriolis meter, are used to minimize the amount of computation required to simulate the meter response. The FE model is developed in a full 3-D form with shear deflection and axial forces, and the computation of the simulated response for the geometrically most complex meter currently available shows that this level of representation is necessary to reveal the full details of the response. The response derived from the FE simulation for straight-tube meters, is compared with the published theoretical response and to experimental data. Over a range of different meters, the characteristics of the sensor signals in the presence of flow pulsations are shown to be generally similar. In all cases, the simulated sensor signals contain components corresponding to beating between the pulsation frequency and the meter drive frequency, in addition to the main component at the drive frequency. Spectra are computed from the simulated meter responses and these are used to show that the relationship between the mass flow rate and the phase difference between the component of the sensor signals at the drive frequency, is not significantly affected by the pulsations. Thus, the work suggests that the reports of changes in meter calibration due to certain frequencies of flow pulsation represent errors in signal processing rather than fundamental changes in the meter characteristics.

  6. 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.

  7. 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.

  8. Vibration of a Flexible Pipe Conveying Viscous Pulsating Fluid Flow

    NASA Astrophysics Data System (ADS)

    GORMAN, D. G.; REESE, J. M.; ZHANG, Y. L.

    2000-02-01

    The non-linear equations of motion of a flexible pipe conveying unsteadily flowing fluid are derived from the continuity and momentum equations of unsteady flow. These partial differential equations are fully coupled through equilibrium of contact forces, the normal compatibility of velocity at the fluid- pipe interfaces, and the conservation of mass and momentum of the transient fluid. Poisson coupling between the pipe wall and fluid is also incorporated in the model. A combination of the finite difference method and the method of characteristics is employed to extract displacements, hydrodynamic pressure and flow velocities from the equations. A numerical example of a pipeline conveying fluid with a pulsating flow is given and discussed.

  9. 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.

  10. Turbulent flow and heat transfer in rotating channels and tubes

    NASA Astrophysics Data System (ADS)

    Mitiakov, V. Y.; Petropavlovskii, R. R.; Ris, V. V.; Smirnov, E. M.; Smirnov, S. A.

    This document is a reduction of the author's experimental results on turbulent flow characteristics and heat transfer in rotating channels whose axes are parallel to the plane of rotation. Substantial dissimilarities of longitudinal velocity field profile and pulsational characteristics are caused by effects of stabilization and destabilization and secondary flow production. Local heat transfer coefficients vary over the perimeter of the tube section connecting detected flow peculiarities. It is shown that the increase in rotational intensity caused an increase in the relative dissimilarity of the local heat transfer coefficients and increased their mean value.

  11. 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.

  12. 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.

  13. Heat transfer from a fully-developed pulsating flow in a curved pipe

    NASA Astrophysics Data System (ADS)

    Chung, Jae Hwa; Hyun, Jae Min

    1994-01-01

    Numerical studies are made of the flow and heat transfer characteristics of a fully-developed pulsating flow in a strongly curved pipe. Emphasis is placed on delineating the effects of the Reynolds number, and pulsation amplitude and frequency. By using a toroidal coordinate system, the complete, time-dependent incompressible Navier-Stokes equations are formulated. The peripherally-uniform temperature condition is imposed on the pipe wall. Particular attention is given to heat transfer properties over substantially extended parameter ranges of the Reynolds number Re and the Womersley number Wo. Use is made of a well-established numerical solution procedure, with minor amendments. The computed results on the flow field are in close agreement with the existing data in the overlapping parameter ranges. The spatial distributions of axial and secondary flows are depicted. The time variations of flow structure are displayed. The numerical results on the spatial and temporal variations of the thermal field are presented. The circumferential profiles of local Nusselt number are plotted at selected instants. When Wo is small, the time- and space-averaged Nusselt numbers, bar-Nu(sub w), is lower for a pulsating flow than for a corresponding non-pulsating flow. At moderate and high Wo, however, the difference in bar-Nu(sub w) between a pulsating and a non-pulsating flow is insignificant.

  14. Milk flow-controlled changes of pulsation ratio and pulsation rate affect milking characteristics in dairy cows.

    PubMed

    Ambord, Sarah; Bruckmaier, Rupert M

    2009-08-01

    To test a system with milk flow-controlled pulsation, milk flow was recorded in 29 Holstein cows during machine milking. The three different treatments were routine milking (including a pre-stimulation of 50-70 s), milking with a minimum of teat preparation and milking with milk flow-controlled b-phase, i.e. with a gradually elongated b-phase of the pulsation cycle with increasing milk flow rate and shortening again during decreasing milk flow. For data evaluation the herd was divided into three groups based on the peak flow rate at routine milking (group 1: <3.2 kg/min; group 2: 3.2-4.5 kg/min; group 3: >4.5 kg/min). Compared with routine milking, milking with milk flow-controlled b-phase caused a significant elevation of the peak flow rate and the duration of incline lasted longer especially in cows with a peak flow rate of >3.2 kg/min in routine milking. In milking with a minimum of teat preparation the duration of incline lasted longer compared with the two other treatments. Bimodality of milk flow, i.e. delayed milk ejection at the start of milking, was most frequent at milking with a minimum of teat preparation. No significant differences between routine milking and milking with milk flow-controlled b-phase were detected for all other milking characteristics. In summary, milking with milk flow-controlled b-phase changes the course of milk removal, however mainly in cows with high peak flow rates. PMID:19250576

  15. Effect on the flow and heat transfer characteristics for sinusoidal pulsating laminar flow in a heated square cylinder

    NASA Astrophysics Data System (ADS)

    Yu, Jiu-Yang; Lin, Wei; Zheng, Xiao-Tao

    2014-06-01

    Two-dimensional numerical simulation is performed to understand the effect of flow pulsation on the flow and heat transfer from a heated square cylinder at Re = 100. Numerical calculations are carried out by using a finite volume method based on the pressure-implicit with splitting of operators algorithm in a collocated grid. The effects of flow pulsation amplitude (0.2 ≤ A ≤ 0.8) and frequency (0 ≤ f p ≤ 20 Hz) on the detailed kinematics of flow (streamlines, vorticity patterns), the macroscopic parameters (drag coefficient, vortex shedding frequency) and heat transfer enhancement are presented in detail. The Strouhal number of vortices shedding, drag coefficient for non-pulsating flow are compared with the previously published data, and good agreement is found. The lock-on phenomenon is observed for a square cylinder in the present flow pulsation. When the pulsating frequency is within the lock-on regime, time averaged drag coefficient and heat transfer from the square cylinder is substantially augmented, and when the pulsating frequency in about the natural vortex shedding frequency, the heat transfer is also substantially enhanced. In addition, the influence of the pulsating amplitude on the time averaged drag coefficient, heat transfer enhancement and lock-on occurrence is discussed in detail.

  16. Effects of pulsation on separated flow and heat transfer in enlarged channel

    NASA Astrophysics Data System (ADS)

    Yoshikawa, Hiroyuki; Kai, Tomonori; Munekata, Mizue; Ohba, Hideki

    2011-03-01

    Numerical results of three-dimensional separated flow and heat transfer in an enlarged rectangular channel are presented in this paper. The expansion ratio and aspect ratio of the channel are 2.0 and 16.0, respectively. Reynolds number of the flow is 200 and it is over the critical Reynolds number. Over the critical Reynolds number, the flow in the symmetric channel becomes asymmetric and deflects to one side of the walls. Effects of the pulsating fluctuation at the inlet upon the flow in the channel are investigated. It is clarified that the inlet flow with a pulsating fluctuation of Strouhal number 0.05 and 0.10 strongly affects on the flow in the channel, and heat transfer on the walls is enhanced, especially on the wall surface covered with long separation bubble. On the other hand, the pulsation of St = 0.0125 oscillates the shear layer more weakly than that of St = 0.05, 0.10 and the enhancement of heat transfer is smaller, though some vortices are shed from the vicinity of the side wall near the reattachment region. The oscillation of the main flow calms down gradually as the Strouhal number of the pulsation increases over 0.10. The influence of pulsation of St = 0.20 on the flow is restricted in the near downstream of the step, and heat transfer on the walls is almost similar to that of the steady flow in the channel.

  17. Siphon flows in isolated magnetic flux tubes

    NASA Technical Reports Server (NTRS)

    Thomas, John H.

    1988-01-01

    The paper considers steady siphon flows in isolated thin magnetic flux tubes surrounded by field-free gas, with plasma beta greater than or equal to 1, appropriate for conditions in the solar photosphere. The cross-sectional area of the flux tube varies along the tube in response to pressure changes induced by the siphon flow. Consideration is also given to steady isothermal siphon flows in arched magnetic flux tubes in a stratified atmosphere. Applications of the results to intense magnetic flux tubes in the solar photosphere and to the photospheric Evershed flow in a sunspot penumbra are addressed.

  18. 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.

  19. Detection of apparent skin motion using optical flow analysis: Blood pulsation signal obtained from optical flow sequence

    NASA Astrophysics Data System (ADS)

    Nakajima, Kazuki; Maekawa, Tsuyoshi; Miike, Hidetoshi

    1997-02-01

    A skin motion imaging system with two modes of operation, diffusive and specular reflections, was developed. The system consists of image capturing and processing elements. Using optical flow analyses of skin motion at the wrist, we have detected successfully a blood pulsation signal that concurs with the electrocardiogram. The signal provides information not only about blood pulsation, but also about blood circulation and the biomechanical properties of the skin. This system may have other applications in the future, such as noncontact blood pulsation detection and evaluation of the biomechanical properties of skin, for example.

  20. 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)

  1. Investigation of the mixed flow turbine performance under inlet pulsating flow conditions

    NASA Astrophysics Data System (ADS)

    Hamel, Mohammed; Abidat, Miloud; Litim, Sid Ali

    2012-03-01

    Turbochargers are widely used in Diesel engines as a means of increasing the output power. Most of them are fitted with radial or mixed flow turbines. In applications where high boost pressure is required, radial turbines are replaced by mixed flow turbines which can achieve a maximum efficiency at a lower value of blade speed to isentropic expansion velocity ratio than the usual 0.7 (for radial turbines). This study, performed with the ANSYS-CFX software, presents a numerical performance prediction of a mixed flow turbine under inlet pulsating flow conditions. In addition, the influence of the pulse frequency is studied and the numerical results are compared with those of a one-dimensional model and experimental data.

  2. Characteristics of velocity pulsations in a turbulent recirculated melt flow

    NASA Astrophysics Data System (ADS)

    Kirpo, M.; Jakovics, A.; Baake, E.

    2005-06-01

    For the modern industrial applications it is necessary to develop and investigate metallic and oxide materials of high purity or predicted composition. Such materials can be produced by the induction melting method, especially in inductor and cold crucible furnaces. Measurements taken in experimental furnaces show that the velocity pulsations dominate for the heat and mass exchange in the melt, especially in a zone between typical upper and lower eddies. Understanding of the pulsation mechanism and development of models to estimate the exchange characteristics are very important for the development and optimisation of industrial furnaces. The authors present experimental results and propose a simple 3D large eddy simulation (LES) model of the induction furnace that can be adapted to qualitative analysis of experimental data. Tables 2, Figs 13, Refs 7.

  3. LDA measurements on swirling flows in tubes

    NASA Astrophysics Data System (ADS)

    Kok, M.; Rosendal, F. J.; Brouwers, J. J.

    1993-08-01

    As part of research on swirler stabilized combustors, swirling flows in an expanding and, after a length L, contracting tube are investigated. If the flow is given sufficient rotation in a flow pattern with central recirculation area is measured in a tube with expansion ratio 0.69. In a larger tube with expansion ratio 0.23 a toroidal recirculation area is found. The time dependence of the flow is investigated by determining the autocorrelation function of the velocity signal. In the range of rotational velocities of the flow the flow field is shown to be periodic in time. This is a very interesting phenomenon that occurs only in sufficiently large tubes, with expansion ratio normally encountered in industrial furnaces. Numerical simulation of this flow will be difficult as it is periodically oscillating and probably not axisymmetric.

  4. 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.

  5. Numerical study of unsteady convective heat transfer in pulsating duct flows

    NASA Astrophysics Data System (ADS)

    Stosic, N.; Hanjalic, K.

    Numerical study results are presented for hydrodynamic parameters and heat transfer in a periodic gas flow, within a circular pipe in which flow oscillations were generated by pressure variation at one of the pipe ends. A comparison of experimental and numerical results has demonstrated satisfactory agreement, as well as the significant augmentation of the heat transfer coefficient under those resonant conditions in which the flow pulsation incitement frequencies correspond to the natural frequencies of the duct.

  6. Study on transient local entropy generation in pulsating fully developed laminar flow through an externally heated pipe

    NASA Astrophysics Data System (ADS)

    Yapıcı, Hüseyin; Kayataş, Nesrin; Baştürk, Gamze; Kahraman, Nafiz

    2006-11-01

    This study presents the investigation of transient local entropy generation rate in pulsating fully developed laminar flow through an externally heated pipe. The flow inlet to the pipe is considered as pulsating at a constant period and amplitude (only the velocity oscillates). The simulations are extended to include different pulsating flow cases (sinusoidal flow, step flow, and saw-down flow). To determine the effects of the mean velocity, the period and the amplitude of the pulsating flow on the entropy generation rate, the pulsating flow is examined for various cases of these parameters. Two-dimensional flow and temperature fields are computed numerically with the help of the fluent computational fluid dynamics (CFD) code. In addition to this CFD code, a computer program has been developed to calculate numerically the entropy generation and other thermodynamic parameters by using the results of the calculations performed for the flow and temperature fields. In all investigated cases, the irreversibility due to the heat transfer dominates. The step flow constitutes the highest temperature (about 919 K) and generates the highest total entropy rate (about 0.033 W/K) within the pipe. The results of this study indicate that in the considered situations, the inverse of square of temperature (1/ T 2) is more dominant on the entropy generation than the temperature gradients, and that the increase of the mean velocity of the pulsating flow has an adverse effect on the ratio of the useful energy transfer rate to irreversibility rate.

  7. Average Nusselt number correlation in the thermal entrance region of steady and pulsating turbulent pipe flows

    NASA Astrophysics Data System (ADS)

    Gbadebo, S. A.; Said, S. A. M.; Habib, M. A.

    Empirical correlation has been developed for local and average Nusselt numbers in the thermal entrance region of steady and pulsating turbulent air-flows in a pipe. The correlation was based on experimental data obtained from experiment carried out on a pipe heated under uniform heat flux conditions. The rate of flow was periodically varied at frequencies ranging from 1Hz to 13Hz while the average Reynolds number varied from 6400 to 42000.

  8. 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.

  9. 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%.

  10. Reduced order model of draft tube flow

    NASA Astrophysics Data System (ADS)

    Rudolf, P.; Štefan, D.

    2014-03-01

    Swirling flow with compact coherent structures is very good candidate for proper orthogonal decomposition (POD), i.e. for decomposition into eigenmodes, which are the cornerstones of the flow field. Present paper focuses on POD of steady flows, which correspond to different operating points of Francis turbine draft tube flow. Set of eigenmodes is built using a limited number of snapshots from computational simulations. Resulting reduced order model (ROM) describes whole operating range of the draft tube. ROM enables to interpolate in between the operating points exploiting the knowledge about significance of particular eigenmodes and thus reconstruct the velocity field in any operating point within the given range. Practical example, which employs axisymmetric simulations of the draft tube flow, illustrates accuracy of ROM in regions without vortex breakdown together with need for higher resolution of the snapshot database close to location of sudden flow changes (e.g. vortex breakdown). ROM based on POD interpolation is very suitable tool for insight into flow physics of the draft tube flows (especially energy transfers in between different operating points), for supply of data for subsequent stability analysis or as an initialization database for advanced flow simulations.

  11. Heat transfer in pulsating laminar flow in a pipe - A constant wall temperature

    NASA Astrophysics Data System (ADS)

    Kita, Y.; Hirose, K.; Hayashi, T.

    1982-02-01

    An analytical model of heat transfer in a pulsating laminar pipe flow with a constant wall temperature is presented. Governing equations for the velocity profile and the wall shear stress are defined and the temperature field is studied for an instantaneous Nusselt number. Cases of steady and unsteady temperature fields are considered, along with the heat flux in the unsteady state, and a ratio for the Nusselt number in the steady state to that in the pulsating flow is obtained. A method for deriving the instantaneous pipe friction factor is demonstrated and the range of the pressure-gradient amplitudes is determined. Finally, conditions are formulated in which the temperature field, including the heat flux, at the wall are equal to that of the steady state.

  12. Evaluation of Pump Pulsation in Respirable Size-Selective Sampling: Part I. Pulsation Measurements

    PubMed Central

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

    2015-01-01

    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 1.25 mg) 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 183 cm, 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

  13. Siphon flows in isolated magnetic flux tubes. IV - Critical flows with standing tube shocks

    NASA Technical Reports Server (NTRS)

    Thomas, John H.; Montesinos, Benjamin

    1991-01-01

    Critical siphon flows in arched, isolated magnetic flux tubes are studied within the thin flux tube approximation, with a view toward applications to intense magnetic flux concentrations in the solar photosphere. The results of calculations of the strength and position of the standing tube shock in the supercritical downstream branch of a critical siphon flow are presented, as are calculations of the flow variables all along the flux tube and the equilibrium path of the flux tube in the surrounding atmosphere. It is suggested that arched magnetic flux tubes, with magnetic field strength increased by a siphon flow, may be associated with some of the intense, discrete magnetic elements observed in the solar photosphere.

  14. Effect of flow pulsation on mass transport in a cathode channel of polymer electrolyte membrane fuel cell

    NASA Astrophysics Data System (ADS)

    Han, Hun Sik; Kim, Yun Ho; Kim, Seo Young; Hyun, Jae Min

    2012-09-01

    An experimental and theoretical study on the cathode flow pulsation in a polymer electrolyte membrane (PEM) fuel cell is performed. A 10-cell PEM fuel cell stack with open-air cathode channels is employed to investigate the effects of the cathode flow pulsation on the overall performance. The polarization and corresponding power curves obtained show that both the limiting current density and the maximum power density are substantially enhanced when the pulsating component is added to the cathode mainstream flow. The flow pulsation at Re = 77 provides the maximum increment of 40% and 35.5% in the limiting current density and in the maximum power density, respectively. The enhancement of the overall performance is more pronounced at low Reynolds numbers. Also, the theoretical mass transport analysis in the pulsating cathode flow channel is carried out to verify the present experimental results. The momentum and species conservation equations are analytically solved, and the effective time-averaged dispersion coefficient is defined to account for the enhanced mass transport by the flow pulsation. Comprehensive analytical solutions show that the effect of the relevant parameters is in well accordance with the experimental results.

  15. Pulsation-driven mean zonal and meridional flows in rotating massive stars

    NASA Astrophysics Data System (ADS)

    Lee, Umin; Mathis, Stéphane; Neiner, Coralie

    2016-04-01

    Zonal and meridional axisymmetric flows can deeply impact the rotational and chemical evolution of stars. Therefore, momentum exchanges between waves propagating in stars, differential rotation, and meridional circulation must be carefully evaluated. In this work, we study axisymmetric mean flows in rapidly and initially uniformly rotating massive stars driven by small amplitude non-axisymmetric κ-driven oscillations. We treat them as perturbations of second order of the oscillation amplitudes and derive their governing equations as a set of coupled linear ordinary differential equations. This allows us to compute 2D zonal and meridional mean flows driven by low frequency g and r modes in slowly pulsating B stars and p modes in β Cephei stars. Oscillation-driven mean flows usually have large amplitudes only in the surface layers. In addition, the kinetic energy of the induced 2D zonal rotational motions is much larger than that of the meridional motions. In some cases, meridional flows have a complex radial and latitudinal structure. We find pulsation-driven and rotation-driven meridional flows can have similar amplitudes. These results show the importance of taking wave - mean flow interactions into account when studying the evolution of massive stars.

  16. 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.

  17. Calculation of He II flow in tubes

    SciTech Connect

    Snyder, H.A.; Mord, A.J. )

    1992-02-01

    The equations for the flow of He II are integrated using a new one-dimensional, steady state model to study the flow in a tube. A wide range of driving conditions is studied. The temperature and pressure profiles along the tube fall into four classes. A dimensionless parameter called {sigma} is defined which determines the progression through the four classes of behavior. The deviation of the flow from Newtonian is measured by {sigma}. Significant maxima of the temperature and pressure can occur between the ends of the tube for large values of {sigma}. The shapes of the profiles and the mass flux depend primarily on {sigma}, the geometry and the boundary conditions. Formulas are presented which relate the variables of interest to the boundary conditions. These formulas result from averaging the equations of motion along the tube. A general and unified approach, based on {sigma}, is presented for analyzing experimental data and designing new experiments. It is shown that the common practice of neglecting the pressure term in the energy equation results in poor prediction for many situations. The occurrence of large maxima of pressure and temperature imply that the interpretation of some of the experimental data of the literature should be reconsidered.

  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. Fluid dynamics and vibration of tube banks in fluid flow

    SciTech Connect

    Zukauskas, A.; Ulinskas, R.; Katinas, V.

    1988-01-01

    This work presents results derived in fluid dynamics, hydraulic drag and flow-induced vibrations within transverse and yawed tube banks. The studies encompass banks of smooth, rough and finned tubes at Reynolds numbers from 1 to 2x10/sup 6/. Highlighted in the text are fluid dynamic parameters of tube banks measured at inter-tube spaces and tube surfaces.

  20. 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.

  1. The effect of pressure pulsations and vibrations on fully developed pipe flow

    NASA Astrophysics Data System (ADS)

    Barnett, D. O.

    1981-08-01

    An analysis is presented of the effect of longitudinal pressure pulsations or vibrations on the velocity distribution in laminar or turbulent fully developed pipe flow. Specifically, the Reynolds equations are formulated in a noninertial reference frame so that the influence of pressure pulsations, vibrations, or a combined pressure and vibrational oscillation can be obtained from a single solution. For axisymmetric developed flow of a constant property (incompressible) fluid, the radial and circumferential momentum equations can be solved and the axial momentum equation is linearized so that the velocity field can be obtained as the sum of a steady and a time-dependent component. By obtaining a solution for the case where the pressure (or amplitude of vibration) varies sinusoidally, one obtains the solution for disturbances of arbitrary waveform through a Fourier series expansion of the disturbance. Results are presented that show that the velocity field is dependent upon the mean flow Reynolds number, a vibrational Reynolds number, and the amplitude of the forcing function. In general, the fluid response to differing waveforms is similar to that obtained for simple harmonic oscillations with respect to the various parameters explored.

  2. Some spectral and pulsation characteristics of a horizontal gas-liquid stream

    NASA Astrophysics Data System (ADS)

    Krokovnyi, P. M.

    1980-07-01

    In the experiments described, the turbulence characteristics of a two-phase gas-liquid pipe flow were studied, using a 6 m long, 19-mm-diam tube. The inlet temperature of the suspension was maintained at 25 C. The friction energy spectra and the relative intensity of the friction pulsations were measured. The spectral and pulsation characteristics were obtained by an electrodiffusion technique which provided reliable data on the pulsations of the wall shear stress.

  3. Long range effect of turbulent pressure pulsations in plane-parallel flows at different velocities with various flame fronts

    NASA Astrophysics Data System (ADS)

    Abramovich, G. N.; Rutovskiy, V. B.

    1985-01-01

    The levels of turbulent velocity and pressure pulsations in a diffusion flare both with and without a slipstream in the flow are calculated. The analytical expressions are derived from a plane model in which the vortices are replaced by rotating cylinders having axes perpendicular to the flow and radii proportional to an integral turbulence scale; the flow originates from two planar nozzles of substantially different size. The resulting formulas for these pulsations and the estimate of the increase in the turbulence in the presence of a flame front are in good agreement with test data. Pressure pulsations are independent of the density distribution at a nozzle section, while this density is the critical factor in determining the pulsation velocity field. When the nozzles are sufficiently close together, two velocity pulsation maxima are to be expected and their position can be computed beforehand. The case when the distance to the boundary of the second nozzle is small and both streams merge rapidly into a common flow is also considered.

  4. 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.

  5. Effects of bulk flow pulsations on film cooling from different length injection holes at different blowing ratios

    SciTech Connect

    Seo, H.J.; Lee, J.S.; Ligrani, P.M.

    1999-07-01

    Bulk flow pulsations in the form of sinusoidal variations of velocity and static pressure at injectant Strouhal numbers from 0.8 to 10.0 are investigated as they affect film cooling from a single row of simple angle holes. Similar flow variations are produced by potential flow interactions and passing shock waves near turbine surfaces in gas turbine engines. Time-averaged temperature distributions, phase-averaged temperature distributions, adiabatic film cooling effectiveness values, and iso-energetic Stranton numbers show that important alterations to film cooling protection occur as pulsation frequency, coolant Strouhal number, blowing ratio, and nondimensional injection hole length are changed. Overall, the pulsations affect film performance and behavior more significantly both as L/D decreases, and as blowing ratio decreases.

  6. The Selective Myosin II Inhibitor Blebbistatin Reversibly Eliminates Gastrovascular Flow and Stolon Tip Pulsations in the Colonial Hydroid Podocoryna carnea

    PubMed Central

    Connally, Noah; Anderson, Christopher P.; Bolton, Jules E.; Bolton, Edward W.; Buss, Leo W.

    2015-01-01

    Blebbistatin reversibly disrupted both stolon tip pulsations and gastrovascular flow in the colonial hydroid Podocoryna carnea. Epithelial longitudinal muscles of polyps were unaffected by blebbistatin, as polyps contracted when challenged with a pulse of KCl. Latrunculin B, which sequesters G actin preventing F actin assembly, caused stolons to retract, exposing focal adhesions where the tip epithelial cells adhere to the substratum. These results are consistent with earlier suggestions that non-muscle myosin II provides the motive force for stolon tip pulsations and further suggest that tip oscillations are functionally coupled to hydrorhizal axial muscle contraction. PMID:26605798

  7. 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.

  8. 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.

  9. 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. PMID:25348647

  10. Problems of unsteady temperature measurements in a pulsating flow of gas

    NASA Astrophysics Data System (ADS)

    Olczyk, A.

    2008-05-01

    Unsteady flow temperature is one of the most difficult and complex flow parameters to measure. Main problems concern insufficient dynamic properties of applied sensors and an interpretation of recorded signals, composed of static and dynamic temperatures. An attempt is made to solve these two problems in the case of measurements conducted in a pulsating flow of gas in the 0-200 Hz range of frequencies, which corresponds to real conditions found in exhaust pipes of modern diesel engines. As far as sensor dynamics is concerned, an analysis of requirements related to the thermometer was made, showing that there was no possibility of assuring such a high frequency band within existing solutions. Therefore, a method of double-channel correction of sensor dynamics was proposed and experimentally tested. The results correspond well with the calculations made by means of the proposed model of sensor dynamics. In the case of interpretation of the measured temperature signal, a method for distinguishing its two components was proposed. This decomposition considerably helps with a correct interpretation of unsteady flow phenomena in pipes.

  11. 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.

  12. Experimental investigation of flow and heating in a resonance tube

    NASA Technical Reports Server (NTRS)

    Sarohia, V.; Back, L. H.

    1979-01-01

    Experiments have been performed to determine the basic mechanism of heating in resonance tubes of square section with constant area excited by underexpanded jet flows. The jet flow between the nozzle exit and the tube inlet plays a key role in the performance of a resonance tube. A detailed and systematic investigation of the unsteady complex shock structure in this part of the flow region has led to a better understanding of the fundamental mechanisms associated with the gas heating in such tubes. A study of the effects of tube location in relation to free-jet shock location (without the presence of the resonance tube) has shed further light on the underlying mechanism of sustained oscillations of the flow in a resonance tube.

  13. Ionospheric outflows as possible source of the low-energy plasma flux tubes controlling the dimension of pulsating auroral patches

    NASA Astrophysics Data System (ADS)

    Liang, J.; Donovan, E.; Nishimura, T.; Yang, B.; Angelopoulos, V.

    2014-12-01

    Conjunctive observations of low-Earth-orbit satellites and optical auroral imagers have indicated that, a majority of pulsating auroral patches (PAPs) are associated with low-energy ion (LEI) precipitation structures with core energies ranging from several tens of eV up to a few hundred eV. This result is consistent with a long-standing proposal that the PAPs connect to flux tubes filled with enhanced "cold" plasma. To further explore the origin and generation mechanism of those LEI structures, we investigate a few THEMIS events when the in-situ probes are conceived as conjugate to PAPs, judging by an apparent correlation between the in-situ whistler-mode chorus and the oscillation of the PAP luminosity [Nishimura et al., 2011]. We notice a common existence of LEI structures from THEMIS in-situ data during those conjugacy event intervals. Such LEI structures are always strongly field-aligned, with core energies ranging from several tens of eV up to a few hundred eV, and often exhibit distinct energy dispersion features. Contingent upon the energy range and time, the pitch-angle distribution of the LEI structures can be either heavily biased toward parallel direction, or biased toward anti-parallel direction, or roughly symmetric between parallel and anti-parallel directions. The above observations allude to the ion outflows from the ionosphere as a plausible origin of the observed LEI structures. To check the above notion, we perform particle simulations assuming that the low-energy ions originate from the ion outflows in topside ionosphere and bounce between hemispheres while convecting with EXB drift. The simulation results can reproduce some of the basic observable features of the LEI structures, such as the energy dispersion and the variation of pitch-angle distribution versus time and energy. Combining the results from low-Earth-orbit satellites observations, THEMIS in-situ observations, and simulations, we propose that the ion outflows into the magnetosphere

  14. Leakage-flow-induced vibration of a tube-in-tube slip joint. [LMFBR

    SciTech Connect

    Mulcahy, T.M.

    1983-06-01

    The susceptibility of a cantilevered tube conveying water to self-excitation by leakage flow through a slip joint is assessed experimentally. The slip joint is formed by inserting a smaller, rigid tube into the free end of the cantilevered tube. Variations of the slip joint annular gaps and engagement lengths are tested, and several mechanisms for self-excitation are described.

  15. Leakage-flow-induced vibration of a tube-in-tube slip joint

    SciTech Connect

    Mulcahy, T.M.

    1984-01-01

    The susceptibility of a cantilevered tube conveying water to self-excitation by leakage flow through a slip joint is assessed experimentally. The slip joint is formed by inserting a smaller, rigid tube into the free end of the cantilevered tube. Variations of the slip joint annular gaps and engagement lengths are tested, and several mechanisms for self-excitation are described.

  16. Gas-solid flow in vertical tubes

    SciTech Connect

    Pita, J.A.; Sundaresan, S. )

    1991-07-01

    This paper reports on a computational study of fully-developed flow of gas-particle suspensions in vertical pipes which was carried out, using the model proposed recently by Sinclair and Jackson, to understand the predicted scale-up characteristics. It was shown that the model can capture the existence of steady-state multiplicity wherein different pressure gradients can be obtained for the same gas and solids fluxes. A pronounced and nonmonotonic variation of the pressure gradient required to achieve desired fluxes of solid and gas with tube diameter was predicted by the model, and this is explained on a physical basis. The computed results were compared with the experimental data. The model manifests an unsatisfactory degree of sensitivity to the inelasticity of the particle-particle collisions and the damping of particle-phase fluctuating motion by the gas.

  17. Mass Transfer in a Rigid Tube With Pulsatile Flow and Constant Wall Concentration

    PubMed Central

    Moschandreou, T. E.; Ellis, C. G.; Goldman, D.

    2011-01-01

    An approximate-analytical solution method is presented for the problem of mass transfer in a rigid tube with pulsatile flow. For the case of constant wall concentration, it is shown that the generalized integral transform (GIT) method can be used to obtain a solution in terms of a perturbation expansion, where the coefficients of each term are given by a system of coupled ordinary differential equations. Truncating the system at some large value of the parameter N, an approximate solution for the system is obtained for the first term in the perturbation expansion, and the GIT-based solution is verified by comparison to a numerical solution. The GIT approximate-analytical solution indicates that for small to moderate nondimensional frequencies for any distance from the inlet of the tube, there is a positive peak in the bulk concentration C1b due to pulsation, thereby, producing a higher mass transfer mixing efficiency in the tube. As we further increase the frequency, the positive peak is followed by a negative peak in the time-averaged bulk concentration and then the bulk concentration C1b oscillates and dampens to zero. Initially, for small frequencies the relative Sherwood number is negative indicating that the effect of pulsation tends to reduce mass transfer. There is a band of frequencies, where the relative Sherwood number is positive indicating that the effect of pulsation tends to increase mass transfer. The positive peak in bulk concentration corresponds to a matching of the phase of the pulsatile velocity and the concentration, respectively, where the unique maximum of both occur for certain time in the cycle. The oscillatory component of concentration is also determined radially in the tube where the concentration develops first near the wall of the tube, and the lobes of the concentration curves increase with increasing distance downstream until the concentration becomes fully developed. The GIT method proves to be a working approach to solve the first

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. Measuring and metering of unsteady flows

    SciTech Connect

    Padmanabhan, M.; Dodge, F.T.; Heidrick, T.R.

    1986-01-01

    This book presents the papers given at a conference on unsteady flow. Topics considered at the conference included the identification of pulsation induced orifice metering errors including gage line shift, electromagnetic flowmeters, mass flow measurements on the flue of a woodburning stove, fluid excitation forces acting on a tube array, and a numerical analysis of pulsating laminar flow through a pipe orifice.

  3. Flow and heat transfer of petal shaped double tube

    NASA Astrophysics Data System (ADS)

    Shakouchi, Toshihiko; Kawashima, Yuki; Tsujimoto, Koichi; Ando, Toshitake

    2014-06-01

    In this study, the flow and heat transfer characteristics of petal-shaped double tube with 6 petals are examined experimentally for a compact heat exchanger. As results, the heat transfer rate, Q, of the 6 petal shaped double tube (6-p tube) is much larger than that, Qp, of conventional circular double tube in all Reynolds number Rein,h (where, the reference length is hydraulic diameter) ranges. For example, at Rein,h =(0.5~1.0)× 104 it is about 4 times of Qp. The heat transfer enhancement of 6-p tube is by the increase of heat transfer area, wetting perimeter, and a highly fluctuating flow, and Q of the 6-p tube can be expressed by Q [kW/m] = 0.54Rein,h + 2245.

  4. 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.

  5. 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

  6. 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. PMID:24672370

  7. Test flow disturbances in an expansion tube

    NASA Technical Reports Server (NTRS)

    Paull, A.; Stalker, R. J.

    1992-01-01

    The operation of an expansion tube is investigated theoretically with emphasis on the factors that have limited the utility of the expansion tube in the past. It is shown why the window of steady test conditions is narrow and how this window can be expanded so that these facilities can be used in a variety of hypersonic research. The theoretical predictions are supported by centerline Pitot pressure measurements using air as the test gas.

  8. A numerical investigation of the effects of flow pulsations over a cylinder on dynamic forces and heat transfer

    NASA Astrophysics Data System (ADS)

    D'herde, Eric J.

    Flow over a fixed circular cylinder is a fundamental fluid mechanics problem that involves a simple geometry; yet, as the Reynolds number is incremented, increasingly complex flow patterns emerge. Most notably, when the Reynolds number exceeds a value of about 46, a Benard-von Karman vortex street pattern appears. It is associated with a characteristic natural vortex shedding frequency. The objectives of this study are to numerically investigate the effects of an incoming free-stream velocity pulsation with a mean Reynolds number of 100 on the dynamic forces acting on a fixed circular cylinder, on the flow regimes behind the cylinder, and on heat transfer between the cylinder and surrounding fluid. Sinusoidal free-stream pulsations with velocity amplitude Av values of 25%, 50% and 75% that of the mean free-stream velocity, and selected frequencies in the range of one fourth the natural shedding frequency fs to five times fs were considered. Of particular interest, is the interaction between forced pulsating frequencies and the natural vortex shedding frequency. At frequencies close to the natural frequency, and to twice the natural frequency, sudden reductions in the mean value of the drag coefficient are observed, as the imposed frequency increases. These sudden reductions are accompanied by complex changes in flow regimes and vortex shedding patterns. The complexity of flow regimes as a function of the imposed pulsation variables was compiled into a frequency-amplitude map. This original map enables one to correlate changes in flow regimes to both dynamic forces and heat transfer characteristics. No net mean drag reduction was observed in the range of dimensionless amplitudes and frequencies considered, at a Reynolds number of 100. Local heat transfer enhancements of up to 86% were achieved for a specific frequency-amplitude pair. A particular finding is the appearance, for a narrow range of frequencies, of a non-zero mean lift coefficient, despite the overall

  9. 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.

  10. 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.

  11. Unexpected water flow through Nafion-tube punctures

    NASA Astrophysics Data System (ADS)

    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.

  12. 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. PMID:21728645

  13. 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.

  14. 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. PMID:20355928

  15. Stokes flow through a tube with bumpy wall

    NASA Astrophysics Data System (ADS)

    Wang, C. Y.

    2006-07-01

    The Stokes flow through a tube with a bumpy wall is solved through a perturbation in the small amplitude of the three-dimensional bumps. The solution can be expressed in terms of modified Bessel functions. For given area or volume of a bump, there exists an optimum circumferential wave number and an optimum aspect ratio for which the flow rate is maximized.

  16. 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.

  17. 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.

  18. Unexpected water flow through Nafion-tube punctures

    PubMed Central

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

    2011-01-01

    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. PMID:21728645

  19. Detection of Anisotropic Pulsating Flow and Its Velocity-Fluctuation Rate in Fertilized Bird Eggs by NMR Microimaging

    NASA Astrophysics Data System (ADS)

    Görke, U.; Kimmich, R.; Weis, J.

    1996-06-01

    Coherent and incoherent flows in fertilized quail and bantam eggs have been studied with the aid of NMR microimaging techniques in the course of incubation until the end of the sixth day. The methods employed were multiplane tagging NMR imaging and a NMR gradient-echo imaging pulse sequence supplemented by bipolar gradient pulses in the coherence-evolution interval. The latter technique is suited for recording of velocity maps as well as for localizing of regions with enhanced echo attenuation by incoherent motions. Slight coherent displacements in the middle of the upper part of the egg white were found after the fourth day of incubation with the aid of both pulse schemes. The maximum velocity was estimated to be 1 mm/s. More pronounced effects revealed themselves in the examination of incoherent motions. After the same time of incubation and in a somewhat more restricted area of the upper part of the egg white, distinct motions could be localized consistently with either technique. It is shown that these motions are directed to and from the yolk. Furthermore, the analysis of the time fluctuations of the local signals with the aid of a Fourier transformation showed that the flow is largely of a pulsating nature. The pulsation frequency was found to be 0.4 Hz.

  20. Blood viscosity in tube flow: dependence on diameter and hematocrit.

    PubMed

    Pries, A R; Neuhaus, D; Gaehtgens, P

    1992-12-01

    Since the original publications by Martini et al. (Dtsch. Arch. Klin. Med. 169: 212-222, 1930) and Fahraeus and Lindqvist (Am. J. Physiol. 96: 562-568, 1931), it has been known that the relative apparent viscosity of blood in tube flow depends on tube diameter. Quantitative descriptions of this effect and of the dependence of blood viscosity on hematocrit in the different diameter tubes are required for the development of hydrodynamic models of blood flow through the microcirculation. The present study provides a comprehensive data base for the description of relative apparent blood viscosity as a function of tube diameter and hematocrit. Data available from the literature are compiled, and new experimental data obtained in a capillary viscometer are presented. The combined data base comprises measurements at high shear rates (u > or = 50 s-1) in tubes with diameters ranging from 3.3 to 1,978 microns at hematocrits of up to 0.9. If corrected for differences in suspending medium viscosity and temperature, the data show remarkable agreement. Empirical fitting equations predicting relative apparent blood viscosity from tube diameter and hematocrit are presented. A pronounced change in the hematocrit dependence of relative viscosity is observed in a range of tube diameters in which viscosity is minimal. While a linear hematocrit-viscosity relationship is found in tubes of < or = 6 microns, an overproportional increase of viscosity with hematocrit prevails in tubes of > or = 9 microns. This is interpreted to reflect the hematocrit-dependent transition from single- to multifile arrangement of cells in flow. PMID:1481902

  1. Three-dimensional freezing of flowing water in a tube cooled by air flow

    NASA Astrophysics Data System (ADS)

    Sugawara, M.; Komatsu, Y.; Beer, H.

    2015-05-01

    The 3-D freezing of flowing water in a copper tube cooled by air flow is investigated by means of a numerical analysis. The air flows normal to the tube axis. Several parameters as inlet water mean velocity w m , inlet water temperature T iℓ t , air flow temperature T a and air flow velocity u a are selected in the calculations to adapt it to a winter season actually encountered. The numerical results present the development of the ice layer mean thickness and its 3-D morphologies as well as the critical ice layer thickness in the tube choked by the ice layer.

  2. Gas flow between coaxial tubes: impedance to gas flow in an endotracheal tube increases with a catheter within.

    PubMed

    Magee, Patrick T

    2012-06-01

    The insertion of a suction catheter or a bronchoscope down an endotracheal tube increases the resistance to gas flow down the tube. The extent to which this occurs depends on the relative diameters of the endotracheal tube and the coaxially introduced catheter. This study utilises a laboratory model to quantify this effect, using a steady flow down an annulus between two tubes whose long axes lie co-axially. Two diameters of an endotracheal tube were modelled to represent flow down adult and neonatal endotracheal tubes; these were of internal diameter (d(o)) 6.3 mm and 3.2 mm, and of length (L) 555 mm. A steady flow of air was generated to pass through the model 'endotracheal' tube. Flowrates were calculated to give Re of approximately 5000 for the larger endotracheal tube, and of approximately 1300 for the smaller. These values correspond to clinically appropriate flowrates in adult and neonatal patients, respectively. The pressure drop deltaPo down the endotracheal tube was measured initially without any obstruction, using a calibrated pressure transducer. Catheters of diameter (d(i)) 0.8 mm, 1.6 mm, and 3.2 mm were introduced into the larger diameter endotracheal tube, while catheters of 0.8 mm and 1.6 mm were introduced into the smaller one, and flow was restored to its original value. The pressure drops deltaP down the endotracheal tubes were measured with the catheters introduced a length 'x' into the tube, to x = L/2 and to x = L. Results are compared with a theoretical calculation on the basis of laminar flow for concentric tubes. If a sampling tube or suction catheter is used down the length of an infant's endotracheal tube, the results show that for most values of do/di, there is a significant rise in deltaP/deltaPo. Where a flexible bronchoscope is used down an endotracheal tube or a telescope down a rigid bronchoscope, the value of deltaP/deltaP(o) may also increase unacceptably where d(o)/d(i) is low. The results show that for equal d(o)/d(i), and

  3. Slow viscous flow of two particles in a cylindrical tube

    NASA Astrophysics Data System (ADS)

    Yao, Xin; Wong, Teck Neng; Marcos, -

    2015-11-01

    The slow viscous flow around two particles in a cylindrical tube is obtained theoretically. We employ the Lamb's general solution based on spherical harmonics and cylindrical harmonics to solve the flow field around the particles and the flow within the tube, respectively. We compute the drag and torque coefficients of the particles which are dependent on the distance among the cylinder wall and the two particles. The hydrodynamic forces are also a function of particle velocities and background velocity. Our results are in agreement with the existing theory of a single particle traveling in the tube when the distance between the two particles increases. We found that particle-particle interactions can be neglected when the separation distance is three times larger than the sum of particles radii. Furthermore, such analysis can give us insights to understand the mechanisms of collision and aggregation of particles.

  4. 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.

  5. Viscous effects in tube flow initiated by an expansion wave

    NASA Technical Reports Server (NTRS)

    Tong, K.-O.; Russell, D. A.

    1977-01-01

    An examination is made of the effect of the turbulent boundary layer on the uniformity of the flow initiated by a nonsteady expansion wave traveling in a long, constant-area tube. Closed-form expressions for the flow perturbations first are obtained from the linearized equations of motion. Measured static pressure histories for both lowand high-tube Mach numbers are used for comparison. Detailed discussions of the limitations of the linearized model and its extension to high-tube Mach numbers are given. Agreement is shown between a modified version of the linearized model and the experimental results. A model of viscous nonsteady pipe flow is used to explain the nonlinear pressure decay observed at very large length-to-diameter ratios.

  6. Experimental research on heat transfer of pulsating heat pipe

    NASA Astrophysics Data System (ADS)

    Li, Jia; Yan, Li

    2008-06-01

    Experimental research was conducted to understand heat transfer characteristic of pulsating heat pipe in this paper, and the PHP is made of high quality glass capillary tube. Under different fill ratio, heat transfer rate and many other influence factors, the flow patterns were observed in the start-up, transition and stable stage. The effects of heating position on heat transfer were discussed. The experimental results indicate that no annular flow appears in top heating condition. Under different fill ratios and heat transfer rate, the flow pattern in PHP is transferred from bulk flow to semi-annular flow and annular flow, and the performance of heat transfer is improved for down heating case. The experimental results indicate that the total heat resistant of PHP is increased with fill ratio, and heat transfer rate achieves optimum at filling rate 50%. But for pulsating heat pipe with changing diameters the thermal resistance is higher than that with uniform diameters.

  7. Stability of a helical vortex tube with axial flow

    NASA Astrophysics Data System (ADS)

    Hattori, Yuji; Fukumoto, Yasuhide

    2011-11-01

    The stability of a helical vortex tube with axial flow is studied analytically. The base flow is obtained by solving the Euler equation perturbatively assuming small ratio of core to curvature radius, which is denoted by ɛ, and Rankine vortex with uniform axial flow at the leading order. We apply both local and modal stability analysis. By local stability analysis we show that the flow is subject to not only curvature instability but also Coriolis instability, both having the same resonance condition. The unstable growth rate is O(ɛ) and given by the magnitude of a sum of the complex numbers corresponding to the two instabilities. Combined effects of the axial flow and the torsion of the helical vortex tube appear as O(ɛ2) modification. These results are confirmed by the modal stability analysis.

  8. 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.

  9. 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.

  10. Period variations in pulsating X-ray sources. I - Accretion flow parameters and neutron star structure from timing observations

    NASA Technical Reports Server (NTRS)

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

    1978-01-01

    Torque fluctuations which can lead to variations in the periods of pulsating X-ray sources are examined. A description of torque variations in terms of noise processes is developed, and the resulting noise models are applied to observations of several pulsating X-ray sources. It is shown that fluctuations in accretion torque could account for the observed period variations and spindown episodes in Her X-1 and Cen X-3. The values of the torque noise strengths inferred from either a nonresonant response or, in the case of Her X-1, a Tkachenko-mode interpretation of the data are found to be consistent with those expected from processes at the magnetospheric boundary of an accreting neutron star. Ways to distinguish among the various interpretations of the period variations are considered. It is noted that fluctuating mass-flow rates may be responsible for other phenomena observed in compact X-ray sources, such as wobble with zero initial amplitude and binary period variations in close binary systems experiencing mass transfer.

  11. 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.

  12. 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.

  13. Numerical computation of transient coaxial entry tube flows

    NASA Technical Reports Server (NTRS)

    Wieber, P. R.; Dewitt, K. J.

    1976-01-01

    A numerical program was developed to compute transient laminar flows in two dimensions including multicomponent mixing and chemical reaction. The program can compute both incompressible flows and compressible flows at all speeds, and it is applied to describe transient and steady state solutions for low subsonic, coaxial entry, tue flows. Single component, nonreacting flows comprise most of the solutions, but one steady state solution is presented for trace concentration constituents engaging in a second order reaction. Numerical stability was obtained by adding at each calculation point a correction for numerical diffusion errors caused by truncation of the Taylor series used to finite difference the conservation equations. Transient computations were made for fluids initially at rest, then subjected to step velocity inputs that were uniform across each region of the entry plane and were held constant throughout the computation period. For center tube to annulus velocity ratios of 0.5 and 2.0, the bulk fluid in the tube initially moved in plug flow, but strong radial flows developed near the injection plane which moved the fluid into the high shear region between the jets and away from the tube wall.

  14. An Experimental Investigation of Fluid Flow and Heating in Various Resonance Tube Modes

    NASA Technical Reports Server (NTRS)

    Sarohia, V.; Back, L. H.; Roschke, E. J.; Pathasarathy, S. P.

    1976-01-01

    Experiments have been performed to study resonance phenomena in tubes excited by underexpanded jet flows. This investigation comprised the following: Study of the various resonance tube modes under a wide range of nozzle pressure, spacing between nozzle and tube mouth, and different tube length; the effects of these modes on the endwall pressure and gas temperature; flow visualization of both jet and tube flows by spark shadowgraph technique; and measurement of wave speed inside the tube by the laser-schlieren techniques. An extensive study of the free-jet flow was undertaken to explain important aspects of various modes of operation of resonance tube flows.

  15. Flow tube used to cool solar-pumped laser

    NASA Technical Reports Server (NTRS)

    1968-01-01

    A flow tube has been designed and constructed to provide two major functions in the application of a laser beam for transmission of both sound and video. It maintains the YAG laser at the proper operating temperature of 300 degrees K under solar pumping conditions, and it serves as a pump cavity for the laser crystal.

  16. RAPID COMMUNICATION Time-resolved measurements with a vortex flowmeter in a pulsating turbulent flow using wavelet analysis

    NASA Astrophysics Data System (ADS)

    Laurantzon, F.; Örlü, R.; Segalini, A.; Alfredsson, P. H.

    2010-12-01

    Vortex flowmeters are commonly employed in technical applications and are obtainable in a variety of commercially available types. However their robustness and accuracy can easily be impaired by environmental conditions, such as inflow disturbances and/or pulsating conditions. Various post-processing techniques of the vortex signal have been used, but all of these methods are so far targeted on obtaining an improved estimate of the time-averaged bulk velocity. Here, on the other hand, we propose, based on wavelet analysis, a straightforward way to utilize the signal from a vortex shedder to extract the time-resolved and thereby the phase-averaged velocity under pulsatile flow conditions. The method was verified with hot-wire and laser Doppler velocimetry measurements.

  17. 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. PMID:25611216

  18. Margination of leukocytes in blood flow through small tubes.

    PubMed

    Goldsmith, H L; Spain, S

    1984-03-01

    Leukocyte margination in the vessels of the microcirculation has been attributed to a flow-dependent interaction with red cells. To determine the extent of this effect, experiments with human blood were done in 100- to 180-micron tubes to detect changes in cell distribution as a function of hematocrit and flow rate. Using a flow visualization technique, the leukocyte concentration distribution was determined in 45% ghost cell suspensions. Migration of cells toward the wall was observed at centerline velocities greater than 1 mm sec-1 and increased with increasing flow rate. The effect was probably due to a more rapid inward migration of ghosts than leukocytes because of fluid inertia and cell density differences. Experiments were therefore carried out in whole blood at hematocrits from 20 to 60%, measuring the number concentration of leukocytes and erythrocytes within the tube, nt, and comparing it to that in the infusing reservoir, no, (Fahraeus effect). At mean tube shear rates G less than 100 sec-1, nt/no less than 1 for both leukocytes and erythrocytes showing net migration of cells away from the wall, although at nearly all hematocrits there was an enrichment of leukocytes relative to erythrocytes in the tubes. At G less than 50 sec-1, nt/no remained less than 1 for erythrocytes but increased to greater than 1 for leukocytes showing migration toward the wall, the increase being greatest at 20% hematocrit in the 100-micron tubes. The nature of the effect was revealed by cine films which showed that, as the flow rate decreased, erythrocytes formed rouleaux which migrated inward creating a core and displacing leukocytes to the periphery. In control experiments using washed blood cells in phosphate buffer-albumin, nt/no less than 1 for both leukocytes and erythrocytes at all G and hematocrits, and leukocytes were now distributed. Cine films of washed blood confirmed that, in the absence of rouleaux, no significant inward migration of erythrocytes occurred. PMID

  19. 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. PMID:10562643

  20. Leakage flow-induced vibrations for variations of a tube-in-tube slip joint

    SciTech Connect

    Mulcahy, T.M.

    1986-01-01

    Variations in the design of a specific slip joint separating two cantilevered, telescoping tubes conveying water were studied to determine their effect upon the leakage flow-induced vibration self-excitation mechanism known to exist for the original slip joint geometry. The important parameters controlling the self-excitation mechanism were identified, which, along with previous results, allowed the determination of a comprehensive set of design rules to avoid unstable vibrations. This was possible even though a new self-excitation mechanism was found when the engagement of the two tubes was small. 9 refs.

  1. Evaluation of compressible-flow Preston tube calibrations

    NASA Technical Reports Server (NTRS)

    Allen, J. M.

    1973-01-01

    An experimental and analytical study has been made of the accuracy of various Preston tube calibration equations to determine local skin friction in two-dimensional supersonic and low-hypersonic flows. Experimental Preston tube calibration data from the present and previous studies were used to evaluate the calibration equations. The maximum value of the calibration parameters of the present data is more than an order of magnitude larger than that previously obtained; thereby, the evaluation of the various calibration equations is facilitated. The Preston tube technique was found to be very inaccurate in the low range of the calibration parameters. Above this range, there was a steady increase in accuracy with increasing values of the calibration parameters. No critical maximum tube diameter was found even with tubes about twice as large as the theoretical maximum allowable diameter. Of the two forms of the calibration equation previously existing, the logarithmic laws gave more accurate results than the power laws over an extended range of the calibration parameters in supersonic adiabatic flow.

  2. Choked flow mechanism of HFC-134a flowing through short-tube orifices

    SciTech Connect

    Nilpueng, Kitti; Wongwises, Somchai

    2011-02-15

    This paper is a continuation of the author's previous work. New experimental data on the occurrence of choked flow phenomenon and mass flow rate of HFC-134a inside short-tube orifices under choked flow condition are presented. Short-tube orifices diameters ranging from 0.406 mm to 0.686 mm with lengths ranging from 1 mm to 3 mm which can be applied to a miniature vapour-compression refrigeration system are examined. The experimental results indicated that the occurrence of choked flow phenomena inside short-tube orifices is different from that obtained from short-tube orifice diameters of greater than 1 mm, which are typically used in air-conditioner. The beginning of choked flow is dependent on the downstream pressure, degree of subcooling, and length-to-diameter ratio. Under choked flow condition, the mass flow rate is greatly varied with the short-tube orifice dimension, but it is slightly affected by the operating conditions. A correlation of mass flow rate through short-tube orifices is proposed in terms of the dimensionless parameters. The predicted results show good agreement with experimental data with a mean deviation of 4.69%. (author) transfer coefficient was also proposed. (author)

  3. Properties of a constricted-tube air-flow levitator

    NASA Technical Reports Server (NTRS)

    Rush, J. E.; Stephens, W. K.; Ethridge, E. C.

    1982-01-01

    The properties of a constricted-tube gas flow levitator first developed by Berge et al. (1981) have been investigated experimentally in order to predict its behavior in a gravity-free environment and at elevated temperatures. The levitator consists of a constricted (quartz) tube fed at one end by a source of heated air or gas. A spherical sample is positioned by the air stream on the downstream side of the constriction, where it can be melted and resolidified without touching the tube. It is shown experimentally that the kinematic viscosity is the important fluid parameter for operation in thermal equilibrium at high temperatures. If air is heated from room temperature to 1200 C, the kinematic viscosity increases by a factor of 14. To maintain a given value of the Reynolds number, the flow rate would have to be increased by the same factor for a specific geometry of tube and sample. Thus, to maintain stable equilibrium, the flow rate should be increased as the air or other gas is heated. The other stability problem discussed is associated with changes in the shape of a cylindrical sample as it melts.

  4. Axisymmetric Time-Dependent Computations of Expansion Tube Flow

    NASA Technical Reports Server (NTRS)

    Wilson, Gregory J.; Arnold, James O. (Technical Monitor)

    1994-01-01

    The goal of this work is to add insight about the flow within expansion tubes by using computational fluid dynamics. This is accomplished by comparing the results of axisymmetric numerical simulations with finite-rate chemistry to data from the HYPULSE expansion tube facility which was previously the NASA Langley expansion tube. The numerical simulations begin at the opening of the primary diaphragm and compute the flow throughout the whole facility and, thus, are able to follow and assess the effect of many of the flow features created during operation of the facility. One particular issue that will be investigated is the effect of boundary layer formation in the acceleration tube on the test gas volume and test gas conditions. Both laminar and turbulent boundary layers will be implemented. The effect of momentary shock reflection off the secondary diaphragm will also be investigated. There is concern that such a reflection will stagnate the test gas and create high levels of dissociated molecules. This is particularly important in propulsion experiments where a freestream composition different from flight conditions may influence ignition and burning data. Several different models of diaphragm rupture will be implemented in order to help understand the importance of this issue.

  5. Limestone calcination during pulsating combustion

    SciTech Connect

    James, R.E. III ); Richards, G.A. )

    1992-01-01

    METC is currently conducting research on enhanced calcination during pulsating combustion as part of the Heat Engines program. It has been shown elsewhere that rapid, high temperature calcination will result in a calcined product with relatively large surface area, as desired for sulfur capture. It is proposed that such a process may occur during pulsating combustion where the oscillating pressure/velocity field around a particle increases the heat/mass transfer to and from the particle. To test this hypothesis, calcination tests in progress at METC use a novel form of pulse combustion called thermal'' pulse combustion, operating at 60000 BTUH, 100 Hz, and 5--15 psig peak-to- peak amplitude. Two configurations are being studied during the testing: one configuration is injection of sorbent into a refractory lined drop tube being heated by the pulse combustor, and the other configuration is injection of the sorbent into the pulse combustor through its centerbody and along the tailpipe at various positions. To understand the observed behavior, a characterization study of the pulse combustor is being conducted. Different flow rates, equivalence ratios, and injection positions are being tested.

  6. Flow-induced vibrations-1987

    SciTech Connect

    Au-Yang, M.K.; Chen, S.S.

    1987-01-01

    This book contains 20 selections. Some of the titles are: Acoustic resonance in heat exchanger tube bundles--Part 1. Physical nature of the phenomenon; Theoretical and experimental studies on heat exchanger U-bend tube bundle vibration characteristics; Experimental model analysis of metallic pipeline conveying fluid; Leakage flow-induced vibration of an eccentric tube-in-tube slip joint; and A study on the vibrations of pipelines caused by internal pulsating flows.

  7. Steady flow through a curved tube with wavy walls

    NASA Astrophysics Data System (ADS)

    Peterson, Sean D.

    2010-02-01

    The problem of fully developed steady flow of an incompressible Newtonian fluid through a mildly curved tube with wavy walls of small amplitude-to-wavelength ratio around the tube circumference is solved via a perturbation solution. Dean's original solution for tubes with circular cross-section is used as the foundation to solve the current regular perturbation problem. In general, the wavy walls are found to mitigate the effect of a given term in Dean's expansion. For instance, the first order effect of the wavy walls is to reduce the strength of the secondary flow vortices and minimize the reduction of the volumetric flow rate caused by the curvature. A related effect is a general reduction in the average axial and circumferential wall shear stresses. The local wall shear stress, however, increases at the points of maximum incursion of the protrusions into the flow and decreases in the valleys between the protuberances. The general form of the solution for an arbitrary number of protuberances is presented to first order in the geometric perturbation and to fourth order in the Dean number.

  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. Siphon flows in isolated magnetic flux tubes. V - Radiative flows with variable ionization

    NASA Technical Reports Server (NTRS)

    Montesinos, Benjamin; Thomas, John H.

    1993-01-01

    Steady siphon flows in arched isolated magnetic flux tubes in the solar atmosphere are calculated here including radiative transfer between the flux tube and its surrounding and variable ionization of the flowing gas. It is shown that the behavior of a siphon flow is strongly determined by the degree of radiative coupling between the flux tube and its surroundings in the superadiabatic layer just below the solar surface. Critical siphon flows with adiabatic tube shocks in the downstream leg are calculated, illustrating the radiative relaxation of the temperature jump downstream of the shock. For flows in arched flux tubes reaching up to the temperature minimum, where the opacity is low, the gas inside the flux tube is much cooler than the surrounding atmosphere at the top of the arch. It is suggested that gas cooled by siphon flows contribute to the cool component of the solar atmosphere at the height of the temperature minimum implied by observations of the infrared CO bands at 4.6 and 2.3 microns.

  10. Visualising Plasma Flow in Current-carrying Magnetic Flux Tubes

    NASA Astrophysics Data System (ADS)

    You, Setthivoine; Bellan, Paul M.

    2003-10-01

    Laboratory experiments at Caltech [1], designed to study the formation and dynamics of spheromaks, solar prominences [2] and astrophysical jets, have motivated a theory for plasma flow within current-carrying magnetic flux tubes [3]. The spheromak and jet plasmas studied are formed by the merging of several plasma-filled magnetic flux tubes. These flux tubes ingest gas puffed in by pulsed gas valves and have current driven along a bias field. The apparatus is now being modified to permit injection of two different gas species into the same flux tube from different ports, corresponding to opposite footpoints of the flux tube. The new gas delivery system allows for simultaneous injection of various combinations of gas species (H, D, He, N, Ne, Ar, Kr) through various gas nozzle locations (inner or outer gun electrodes, left hand side or right hand side series). During the discharge, the multi-species plasmas are to be imaged with high speed, single- and multiple-frame, intensified CCD cameras and will be differentiated by narrow band optical filters. Other diagnostics include a magnetic probe array, soft x-ray diodes and an optical multichannel analyser to monitor the magnetic field evolution, particle velocities and energies. [1] S. C. Hsu and P. M. Bellan, Mon. Not. R. Astron. Soc., 334, 257-261 (2000). [2] J. F. Hansen and P. M. Bellan, Astrophys. J., 563, L183-L186, (2001). [3] P. M. Bellan, Phys. Plasmas, 10, 1999-2008 (2003).

  11. Flow separation in a straight draft tube, particle image velocimetry

    NASA Astrophysics Data System (ADS)

    Duquesne, P.; Maciel, Y.; Ciocan, G. D.; Deschênes, C.

    2014-03-01

    As part of the BulbT project, led by the Consortium on Hydraulic Machines and the LAMH (Hydraulic Machine Laboratory of Laval University), the efficiency and power break off in a bulb turbine has been investigated. Previous investigations correlated the break off to draft tube losses. Tuft visualizations confirmed the emergence of a flow separation zone at the wall of the diffuser. Opening the guide vanes tends to extend the recirculation zone. The flow separations were investigated with two-dimensional and two-component particle image velocimetry (PIV) measurements designed based on the information collected from tuft visualizations. Investigations were done for a high opening blade angle with a N11 of 170 rpm, at best efficiency point and at two points with a higher Q11. The second operating point is inside the efficiency curve break off and the last operating point corresponds to a lower efficiency and a larger recirculation region in the draft tube. The PIV measurements were made near the wall with two cameras in order to capture two measurement planes simultaneously. The instantaneous velocity fields were acquired at eight different planes. Two planes located near the bottom wall were parallel to the generatrix of the conical part of the diffuser, while two other bottom planes diverged more from the draft tube axis than the cone generatrix. The last four planes were located on the draft tube side and diverged more from the draft tube axis than the cone generatrix. By combining the results from the various planes, the separation zone is characterized using pseudo-streamlines of the mean velocity fields, maps of the Reynolds stresses and maps of the reverse-flow parameter. The analysis provides an estimation of the separation zone size, shape and unsteady character, and their evolution with the guide vanes opening.

  12. 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.

  13. Leakage flow-induced vibration of an unconstricted tube-in-tube slip joint

    SciTech Connect

    Mulcahy, T.M.

    1986-03-01

    The conditions are given for which the more flexible of two cantilevered, telescoping tubes conveying fluid can be self-excited by flow leaking from an unconstricted slip joint. Also, a physical explanation of the excitation mechanism is discussed, and a design rule to avoid the mechanism is presented. In addition, the results for the unconstricted slip joint are shown to be similar to those for slip joints having annulus constrictions at very short engagement lengths.

  14. Leakage flow-induced vibration of an unconstricted tube-in-tube slip joint

    SciTech Connect

    Mulcahy, T.M.

    1986-12-01

    The conditions are given for which the more flexible of two cantilevered, telescoping tubes conveying fluid can be self-excited by flow leaking from an unconstricted slip joint. Also, a physical explanation of the excitation mechanism is discussed, and a design rule to avoid the mechanism is presented. In addition, the results for the unconstricted slip joint are shown to be similar to those for slip joints having annulus constrictions at very short engagement lengths.

  15. 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)

  16. 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.

  17. 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.

  18. Siphon flows in isolated magnetic flux tubes. III - The equilibrium path of the flux-tube arch

    NASA Technical Reports Server (NTRS)

    Thomas, John H.; Montesinos, Benjamin

    1990-01-01

    It is shown how to calculate the equilibrium path of a thin magnetic flux tube in a stratified, nonmagnetic atmosphere when the flux tube contains a steady siphon flow. The equilbrium path of a static thin flux tube in an infinite stratified atmosphere generally takes the form of a symmetric arch of finite width, with the flux tube becoming vertical at either end of the arch. A siphon flow within the flux tube increases the curvature of the arched equilibrium path in order that the net magnetic tension force can balance the inertial force of the flow, which tries to straighten the flux tube. Thus, a siphon flow reduces the width of the arched equilibrium path, with faster flows producing narrower arches. The effect of the siphon flow on the equilibrium path is generally greater for flux tubes of weaker magnetic field strength. Examples of the equilibrium are shown for both isothemal and adiabatic siphon flows in thin flux tubes in an isothermal external atmosphere.

  19. Transitional flow in thin tubes for space station freedom radiator

    NASA Technical Reports Server (NTRS)

    Loney, Patrick; Ibrahim, Mounir

    1995-01-01

    A two dimensional finite volume method is used to predict the film coefficients in the transitional flow region (laminar or turbulent) for the radiator panel tubes. The code used to perform this analysis is CAST (Computer Aided Simulation of Turbulent Flows). The information gathered from this code is then used to augment a Sinda85 model that predicts overall performance of the radiator. A final comparison is drawn between the results generated with a Sinda85 model using the Sinda85 provided transition region heat transfer correlations and the Sinda85 model using the CAST generated data.

  20. Regional platelet concentration in blood flow through capillary tubes.

    PubMed

    Corattiyl, V; Eckstein, E C

    1986-09-01

    Platelet concentration was measured in samples from the various components of a bloodflow circuit, including the reservoir, the tube (with i.d. between 50 and 210 micron), and the discharge. The tube sample was collected by halting the flow and then flushing out a length of tube; thus, this sample collected equally from all radial locations. As the discharge sample was well mixed, it reflected the velocity field in the tube. Each reservoir sample was a traditional bulk collection. To ensure that the results represented the physical effects of flow on regional platelet concentration and could be interpreted with simple mass balance relationships, strong anticoagulation (sodium citrate and heparin) and platelet inhibition (prostaglandin E1) were used. Results for all tube diameters and for reservoir hematocrits from 5.5 to 77% and wall shear rates from 80 to 8000 sec-1 show that tubular platelet concentration is greater than reservoir or discharge platelet concentrations, which are equal. For platelet-rich plasma the tubular platelet concentration is decreased compared to the reservoir or discharge values. Mass balances show that the elevated tubular platelet concentration is due to an excess of platelets in radial locations with below average speeds; coupled with the need for red cells, this suggests that excess platelets have a near-wall location. Nonparametric statistical tests show that wall shear rate is a significant variable at a 0.05 confidence level; inner diameter is not found to be a significant variable, probably because of the limited diameter range studied and the experimental errors involved in determining platelet concentrations. PMID:3762431

  1. 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.

  2. A proposal to induce pulsating aurora by injecting ions from a rocket at the magnetic conjugate ionosphere to modify the flowing cyclotron maser

    NASA Astrophysics Data System (ADS)

    Chernouss, S.; Mogilevsky, M.; Trakhtengerts, V.; Deehr, C.; Stenbaek-Nielsen, H.

    2005-08-01

    There is experimental evidence for the artificial induction of Flowing Cyclotron Maser (FCM) by reflection coefficient modification. It is the close correlation of auroral pulsations and auroral VLF emissions that is the experimental basis of the theory. We review experiments with ionospheric barium vapor releases, when auroral pulsations were apparently triggered. This effect has been observed during a Ba-release rocket campaign in Alaska. In this experiment, the stimulation of auroral pulsations generated by a Ba-release during special auroral activity was clearly observed. Similar results were obtained during a Russian rocket campaign to release barium vapor in the ionosphere over the North Atlantic. It seems that changing the reflection coefficient is a main reason for the generation of auroral pulsations in both Ba release experiments. Thus, the apparent dependence of the cyclotron instability increment on the reflection coefficient of the FCM foot point parameters give us the possibility of modifying FCM by creating ion clouds in the ionosphere. It is proposed as a part of the RESONANCE satellite project to create an artificial ion cloud at the magnetic conjugate point of the satellite from Poker Flat Research Range during the satellite passage over Alaska. The details of the proposed experiment and the necessary geophysical situation are still under discussion.

  3. 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.

  4. 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].

  5. 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

  6. Pulsating blood-flow monitoring in developing fish embryos and rat mesentery by laser Doppler microscopy

    NASA Astrophysics Data System (ADS)

    Bikkulova, K. F.; Lapteva, N. B.; Levenko, Borislav A.; Polyakova, Marina S.; Priezzhev, Alexander V.; Proskurin, Sergei G.; Romanovsky, Yuri A.; Sokolova, Irina A.

    1993-07-01

    Laser Doppler (LD) microscopy is a technique, providing high-resolution noninvasive measurements of microstructures dynamics. It can be used in different fields of biophysics and biomedicine. This technique yields quantitative information on diffusion coefficients, velocities, and velocity profiles of dynamic microstructures in vivo and in vitro. LD microscopy is an alternative method of velocity measurement to such methods as computer- aided microphotography and imaging, diffraction grating microscopy, FRAP, etc. In this paper we describe the results of our LDM measurements of one of the main hemodynamic parameters -- the blood-flow velocities in the microvessels of Salmo salar and Danio rerio fish embryos, as well as of the rat mesentery.

  7. 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.

  8. Lava tube morphology on Etna and evidence for lava flow emplacement mechanisms

    NASA Astrophysics Data System (ADS)

    Calvari, Sonia; Pinkerton, Harry

    1999-06-01

    Lava tubes play a pivotal role in the formation of many lava flow fields. A detailed examination of several compound `a`a lava flow fields on Etna confirmed that a complex network of tubes forms at successively higher levels within the flow field, and that tubes generally advance by processes that include flow inflation and tube coalescence. Flow inflation is commonly followed by the formation of major, first-order ephemeral vents which, in turn, form an arterial tube network. Tube coalescence occurs when lava breaks through the roof or wall of an older lava tube; this can result in the unexpected appearance of vents several kilometers downstream. A close examination of underground features allowed us to distinguish between ephemeral vent formation and tube coalescence, both of which are responsible for abrupt changes in level or flow direction of lava within tubes on Etna. Ephemeral vent formation on the surface is frequently recorded underground by a marked increase in size of the tube immediately upstream of these vents. When the lining of an inflated tube has collapsed, `a`a clinker is commonly seen in the roof and walls of the tube, and this is used to infer that inflation has taken place in the distal part of an `a`a lava flow. Tube coalescence is recognised either from the compound shape of tube sections, or from breached levees, lava falls, inclined grooves or other structures on the walls and roof. Our observations confirm the importance of lava tubes in the evolution of extensive pahoehoe and `a`a flow fields on Etna.

  9. Separation phenomena for gaseous mixture flowing through a long tube into vacuum

    NASA Astrophysics Data System (ADS)

    Sharipov, Felix; Kalempa, Denize

    2005-12-01

    A gaseous mixture flow through a long tube into vacuum is considered assuming the pressure to be arbitrary at the tube entrance. Thus, the flow regime can vary from hydrodynamic at the entrance to free molecular at the tube exit. The distributions of density and concentration along the tube were obtained for the mixture helium-xenon at various values of the concentration and rarefaction at the tube entrance. It was shown that the variation of the concentration along the tube can be significant. The flow rates of both species determining the chemical composition in the down flow container were calculated. An analysis of these data shows that the chemical composition in the down flow container can be different from that in the up flow one, i.e., the separation phenomenon takes place. The results presented in the article can be used in practice to avoid the separation phenomenon or to intensify it if necessary.

  10. Investigation on the Oscillating Gas Flow Along AN Inertance Tube by Experimental and Cfd Methods

    NASA Astrophysics Data System (ADS)

    Chen, Houlei; Zhao, Miguang; Yang, Luwei; Cai, Jinghui; Hong, Guotong; Liang, Jingtao

    2010-04-01

    To investigate the oscillating gas flow along an inertance tube used in pulse tube coolers, a CFD model is set up for FLUENT and an experimental measuring cell is designed and optimized by CFD results. Some characteristics of oscillating flow are demonstrated and discussed. Then, the flow status along an inertance tube is measured by the optimized measuring cell. The experimental results validate the simulating results.

  11. INVESTIGATION ON THE OSCILLATING GAS FLOW ALONG AN INERTANCE TUBE BY EXPERIMENTAL AND CFD METHODS

    SciTech Connect

    Chen Houlei; Zhao Miguang; Yang Luwei; Cai Jinghui; Hong Guotong; Liang Jingtao

    2010-04-09

    To investigate the oscillating gas flow along an inertance tube used in pulse tube coolers, a CFD model is set up for FLUENT and an experimental measuring cell is designed and optimized by CFD results. Some characteristics of oscillating flow are demonstrated and discussed. Then, the flow status along an inertance tube is measured by the optimized measuring cell. The experimental results validate the simulating results.

  12. 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.

  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. PMID

  14. Automated library synthesis of cyclopropyl boronic esters employing diazomethane in a tube-in-tube flow reactor.

    PubMed

    Koolman, Hannes F; Kantor, Stanislaw; Bogdan, Andrew R; Wang, Ying; Pan, Jeffrey Y; Djuric, Stevan W

    2016-07-01

    The efficient synthesis of cyclopropyl boronic esters in library format using a diazomethane flow reactor has been achieved. A pivotal component of the system is a fully automated tube-in-tube reactor allowing for safe handling of hazardous diazomethane on repeated small scale and for the generation of larger quantities of product. The setup enables the repeated execution of Pd-catalyzed cyclopropanation reactions without compromising its operation over time. PMID:27314279

  15. 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.

  16. Electropolishing the bore of metal capillary tubes: A technique for adjusting the critical flow.

    PubMed

    Stoffels, J J; Ells, D R

    1979-12-01

    A technique has been developed for electropolishing the bore of metal capillary tubes. Although developed specifically for stainless-steel tubes, the technique should be directly applicable to other metals. Tubes with inside diameter as small as 0.20 mm and 110 mm long have been successfully electropolished. The electropolishing technique can be used to increase the critical flow of a capillary tube in a controllable way. PMID:18699437

  17. 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.

  18. Flow of superfluid helium in tubes with heated walls

    NASA Technical Reports Server (NTRS)

    Snyder, H. A.; Mord, A. J.

    1991-01-01

    The equations for superfluid helium flowing through a straight tube with heated walls are integrated. The model equations are based on those of Landau as modified for superfluid turbulence by Gorter and Mellink (1949). The model is implemented by the program SUPERFLOW which runs on a personal computer. The effect of the heating level on the mass flux, the energy flux, and the pressure and temperature profiles is investigated. The four types of profiles which occur without sidewall heating are also found with heated walls. The progression through these four types is shown to depend primarily on the dimensionless parameter, defined previously to characterize the unheated profiles, and a dimensionless ratio of heat fluxes. The pressure and temperature maxima which rise well above the boundary values increase significantly with sidewall heating. Approximate design equations for estimating the mass flux and the profiles are presented. The physical basis of the results is discussed. These results are useful in the design of optimal cooling loops and other superfluid flow systems.

  19. Study on the burnout with variations of flow twisting over tube length

    NASA Astrophysics Data System (ADS)

    Pometko, R. S.; Gorban, L. M.

    Results of experimental investigation into regularities of heat transfer intensification in tubes with transition from untwisting flows to twisting ones and vice versa are given. Experiments were conducted on flowing freon-12 in a tube 10 mm in dia with two zones of independent heating at 1.06 MPa pressure, 500 to 3000 kg/m(2)s flow rate, 80 mm screw twisting pitch. Characteristic specific features of interaction processes of flow core with the screw and untwisting band. Main trends of changing critical heat flux in tubes with varied, in length, flow twisting are qualitatively explained.

  20. 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.

  1. 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.

  2. Columbia University flow instability experimental program: Volume 3. Single tube parallel flow tests

    SciTech Connect

    Dougherty, T.; Maciuca, C.; McAssey, E.V. Jr.; Reddy, D.G.; Yang, B.W.

    1990-06-01

    The coolant in the Savannah River Site (SRS) production nuclear reactor assemblies is circulated as a subcooled liquid under normal operating conditions. This coolant is evenly distributed throughout multiple annular flow channels with a uniform pressure profile across each coolant flow channel. During the postulated Loss of Coolant Accident (LOCA), which is initiated by a hypothetical guillotine pipe break, the coolant flow through the reactor assemblies is significantly reduced. The flow reduction and accompanying power reduction (after shutdown is initiated) occur in the first 1--2 seconds of the LOCA. This portion of the LOCA is referred to as the Flow Instability phase. A series of down flow experiments have been conducted on three different size single tubes. The objective of these experiments was to determine the effect of a parallel flow path on the occurrence of flow instability. In all cases, it has been shown that the point of flow instability (OFI) determined under controlled flow operation does not change when operating in a controlled pressure drop mode (parallel path operation).

  3. ANGULAR FLOW INSENSITIVE PITOT TUBE SUITABLE FOR USE WITH STANDARD STACK TESTING EQUIPMENT

    EPA Science Inventory

    Five pitot tube designs were tested under various gas flow conditions for accuracy in measuring static and total pressure. The static- and impact-pressure measuring tubes least affected by angular flow were combined and then evaluated in the presence of standard particulate sampl...

  4. The effect of asymmetric heating on flow stability and heat transfer for flow in a vertical tube

    SciTech Connect

    Tappan, C.H.

    1987-11-01

    This study presents experimental results of combined free and forced convection heat transfer in a vertical tube with a circumferentially nonuniform constant wall heat flux. The effect of an asymmetric wall heat flux on flow stability and on the rate of heat transfer for water flowing downward in a vertical tube was investigated. Experimental results were used to develop two stability maps which identify various flow regimes, corresponding to different thermal and hydraulic conditions. Heat transfer coefficients were also determined. Experimental results in the present investigation were compared to those with uniform heating in horizontal and vertical tube flow situations discussed in the literature. 23 refs., 12 figs., 1 tab.

  5. 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.

  6. Visualization and void fraction measurement of decompressed boiling flow in a capillary tube

    NASA Astrophysics Data System (ADS)

    Asano, H.; Murakawa, H.; Takenaka, N.; Takiguchi, K.; Okamoto, M.; Tsuchiya, T.; Kitaide, Y.; Maruyama, N.

    2011-09-01

    A capillary tube is often used as a throttle for a refrigerating cycle. Subcooled refrigerant usually flows from a condenser into the capillary tube. Then, the refrigerant is decompressed along the capillary tube. When the static pressure falls below the saturation pressure for the liquid temperature, spontaneous boiling occurs. A vapor-liquid two-phase mixture is discharged from the tube. In designing a capillary tube, it is necessary to calculate the flow rate for given boundary conditions on pressure and temperature at the inlet and exit. Since total pressure loss is dominated by frictional and acceleration losses during two-phase flow, it is first necessary to specify the boiling inception point. However, there will be a delay in boiling inception during decompressed flow. This study aimed to clarify the boiling inception point and two-phase flow characteristics of refrigerant in a capillary tube. Refrigerant flows in a coiled copper capillary tube were visualized by neutron radiography. The one-dimensional distribution of volumetric average void fraction was measured from radiographs through image processing. From the void fraction distribution, the boiling inception point was determined. Moreover, a simplified CT method was successfully applied to a radiograph for cross-sectional measurements. The experimental results show the flow pattern transition from intermittent flow to annular flow that occurred at a void fraction of about 0.45.

  7. 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.

  8. 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.

  9. 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)

  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. Analysis of single phase flow pressure drop and heat transfer in a horizontal rifled tube

    NASA Astrophysics Data System (ADS)

    Lam, Soo Poey; Wahab, Abas Abdul; Ariffin, Saparudin; Kiow, Lee Woon

    2012-06-01

    Analysis by using Fluent® has been carried out to investigate the pressure drop and heat transfer of single phase flow (Reynolds number ranging from 2.0×104 - 1.4×105) in a 2 meter long of rifled tube and smooth tube which are heated at the outer wall at constant temperature. The rifled tube or also known as spiral internally ribbed tube which is used in this investigation has an outside diameter 45.0 mm and inside equivalent diameter of 33.1 mm while the smooth tube has an outside diameter 45.0 mm and inside diameter 34.1 mm. The working fluid that is used in this investigation is water. In this analysis, realizable k-epsilon model has been chosen to solve the fully developed turbulence flow in both the tubes. The result from simulation shows that the pressure drop in rifled tube is about 1.69-2.0 times higher than in the smooth tube while the heat transfer coefficient of water in the rifle tube is 0.97-1.27 times than in the smooth tube. The high pressure drop and heat transfer coefficient in rifled tube comparing to smooth tube is due to the helical rib in the rifled tube which not only acted as rough surface, but also causes swirling effect near the wall which enhance heat transfer. The present study has proved that although the rifled tube produces high pressure drop but it is good in heat transfer enhancement through the ratio of heat flux to the pumping power. Correlations have been proposed for the single phase friction factor and Nusselt number of the rifled tube.

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

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

    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.

  14. 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.

  15. Avoiding leakage flow-induced vibration by a tube-in-tube slip joint

    SciTech Connect

    Mulcahy, T.M.

    1985-01-01

    Parameters and operating conditions (a stability map) were determined for which a specific slip-joint design did not cause self-excited lateral vibration of the two cantilevered, telescoping tubes forming the joint. The joint design featured a localized annular constriction. Flowrate, modal damping, tube engagement length, and eccentric positioning were among the parameters tested. Interestingly, all self-excited vibrations could be avoided by following a simple design rule: place constrictions only at the downstream end of the annular region between the tubes. Also, overall modal damping decreased with increased flowrate, at least initially, for upstream constrictions while the damping increased for downstream constrictions.

  16. Avoiding leakage flow-induced vibration by a tube-in-tube slip joint

    SciTech Connect

    Mulcahy, T.M.

    1984-10-01

    Parameters and operating conditions (a stability map) were determined for which a specific slip-joint design did not cause self-excited lateral vibration of the two cantilevered, telescoping tubes forming the joint. The joint design featured a localized annular constriction. Flowrate, modal damping, tube engagement length, and eccentric positioning were among the parameters tested. Interestingly, all self-excited vibrations could be avoided by following a simple design rule: place constrictions only at the downstream end of the annular region between the tubes. Also, overall modal damping decreased with increased flowrate, at least initially, for upstream constrictions while the damping increased for downstream constrictions.

  17. Synchronization Model for Pulsating Variables

    NASA Astrophysics Data System (ADS)

    Takahashi, S.; Morikawa, M.

    2013-12-01

    A simple model is proposed, which describes the variety of stellar pulsations. In this model, a star is described as an integration of independent elements which interact with each other. This interaction, which may be gravitational or hydrodynamic, promotes the synchronization of elements to yield a coherent mean field pulsation provided some conditions are satisfied. In the case of opacity driven pulsations, the whole star is described as a coupling of many heat engines. In the case of stochastic oscillation, the whole star is described as a coupling of convection cells, interacting through their flow patterns. Convection cells are described by the Lorentz model. In both models, interactions of elements lead to various pulsations, from irregular to regular. The coupled Lorenz model also describes a light curve which shows a semi-regular variability and also shows a low-frequency enhancement proportional to 1/f in its power spectrum. This is in agreement with observations (Kiss et al. 2006). This new modeling method of ‘coupled elements’ may provide a powerful description for a variety of stellar pulsations.

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

    PubMed

    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)]. 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. PMID:25974574

  19. 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.

  20. 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.

  1. Effect of Non-Uniform Inlet Temperature on Flow Stagnation in a Pumped Fluid Tube Radiator

    NASA Astrophysics Data System (ADS)

    Reavis, Gretchen

    2008-01-01

    The effect of a non-uniform inlet temperature on the panel fluid tube flow stagnation point is examined using a spacecraft radiator panel model with 20 fluid tubes constructed in Thermal Desktop®. Fluid temperature variations due to panel edge effect and localized hot and cold spots in the flow path were simulated by varying the fluid inlet temperature on one or more tubes. Results show that a large fluid inlet temperature difference between tubes can decrease the fluid system stability and increase the possibility of fluid stagnation with the coldest fluid tube initiating stagnation. Conversely, a small fluid inlet temperature difference between tubes can, in some cases, increase the fluid system stability and decrease the possibility of fluid stagnation. A uniform fluid inlet temperature provides for a near optimization of the stagnation point as compared to fluid temperature gradients across the panel.

  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. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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

  8. Lava Tube Flow Models at Alba Patera, Mars: Topographic Constraints on Eruption Rates

    NASA Technical Reports Server (NTRS)

    Riedel, S. J.; Sakimoto, S. E. H.; Bradley, B. A.; DeWet, A.

    2001-01-01

    Alba Patera has some of the longest lava tubes over some of the shallowest slopes on Mars. We use Mars Orbiter Laser Altimeter (MOLA) topography to model eruption rates for several Alba Patera lava tubes and compare them within Alba and with flows from other martian volcanic regions. Additional information is contained in the original extended abstract.

  9. 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...

  10. CFD simulation of the gas flow in a pulse tube cryocooler with two pulse tubes

    NASA Astrophysics Data System (ADS)

    Yin, C. L.

    2015-12-01

    In this paper, in order to instruct the next optimization work, a two-dimension Computational Fluid Dynamics (CFD) model is developed to simulate temperature distribution and velocity distribution of oscillating fluid in the DPTC by individual phase-shifting. It is found that the axial temperature distribution of regenerator is generally uniform and the temperatures near the center at the same cross setion of two pulse tubes are obviously higher than their near wall temperatures. The wall temperature difference about 0-7 K exists between the two pulse tubes. The velocity distribution near the center of the regenerator is uniform and there is obvious injection stream coming at the center of the pulse tubes from the hot end. The formation reason of temperature distribution and velocity distribution is explained.

  11. Methods for numerical study of tube bundle vibrations in cross-flows

    NASA Astrophysics Data System (ADS)

    Longatte, E.; Bendjeddou, Z.; Souli, M.

    2003-11-01

    In many industrial applications, mechanical structures like heat exchanger tube bundles are subjected to complex flows causing possible vibrations and damage. Part of fluid forces are coupled with tube motion and the so-called fluid-elastic forces can affect the structure dynamic behaviour generating possible instabilities and leading to possible short term failures through high amplitude vibrations. Most classical fluid force identification methods rely on structure response experimental measurements associated with convenient data processes. Owing to recent improvements in Computational Fluid Dynamics, numerical simulation of flow-induced vibrations is now practicable for industrial purposes. The present paper is devoted to the numerical identification of fluid-elastic effects affecting tube bundle motion in presence of fluid at rest and one-phase cross-flows. What is the numerical process? When fluid-elastic effects are not significant and are restricted to added mass effects, there is no strong coupling between structure and fluid motions. The structure displacement is not supposed to affect flow patterns. Thus it is possible to solve flow and structure problems separately by using a fixed nonmoving mesh for the fluid dynamic computation. Power spectral density and time record of lift and drag forces acting on tube bundles can be computed numerically by using an unsteady fluid computation involving for example a large Eddy simulation. Fluid force spectra or time record can then be introduced as inlet conditions into the structure code providing the tube dynamic response generated by flow. Such a computation is not possible in presence of strong flow structure coupling. When fluid-elastic effects cannot be neglected, in presence of tube bundles subjected to cross-flows for example, a coupling between flow and structure computations is required. Appropriate numerical methods are investigated in the present work. The purpose is to be able to provide a numerical

  12. Experiments on vibration of heat-exchanger tube arrays in cross flow

    SciTech Connect

    Blevins, R.D.; Gibert, R.J.; Villard, B.

    1981-04-01

    A series of tests has been made at the Commissariat a L Energie Atomique, Saclay, France, in cooperation with General Atomic Company, San Diego, on flow-induced vibration of simulated heat exchanger tube bundles in a cross flow of air. The tests were of two types. In the first type, a tube instrumented with pressure transducers was inserted at various locations in a tube bundle. Measurements were made of pressure spectra, coherence, and lift force. It was found that the turbulence-induced pressures rise from a low value at the bundle entrance to a relatively high value within the bundle. In the second type of test, tube bundles were fabricated from flexible plastic tubes, cantilevered off a tube sheet, and the vibration induced by cross flow was observed. An investigation was made of the effect of tube-to-tube frequency difference and spacing on the onset of instability. It was found that while present theory often qualitatively predicts the correct trends, it may not be quantitatively accurate in many cases.

  13. Investigation of an innovative method for DC flow suppression of double-inlet pulse tube coolers

    NASA Astrophysics Data System (ADS)

    Hu, J. Y.; Luo, E. C.; Wu, Z. H.; Dai, W.; Zhu, S. L.

    2007-05-01

    The use of double-inlet mode in the pulse tube cooler opens up a possibility of DC flow circulating around the regenerator and the pulse tube. The DC flow sometimes deteriorates the performance of the cryocooler because such a steady flow adds an unwanted thermal load to the cold heat exchanger. It seems that this problem is still not well solved although a lot of effort has been made. Here we introduce a membrane-barrier method for DC flow suppression in double-inlet pulse tube coolers. An elastic membrane is installed between the pulse tube cooler inlet and the double-inlet valve to break the closed-loop flow path of DC flow. The membrane is acoustically transparent, but would block the DC flow completely. Thus the DC flow is thoroughly suppressed and the merit of double-inlet mode is remained. With this method, a temperature reduction of tens of Kelvin was obtained in our single-stage pulse tube cooler and the lowest temperature reached 29.8 K.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. Effects of Red Blood Cell Aggregation on the Apparent Viscosity of Blood Flow in Tubes.

    NASA Astrophysics Data System (ADS)

    Hitt, Darren L.; Lowe, Mary L.

    1996-11-01

    In arterioles and venules (20-200μ diameter), the low shear rates enable red blood cells to form aggregate structures of varying sizes and morphology. The size and distribution of the aggregates affect the flow impedance within a microvascular network; this effect may be characterized by an "apparent viscosity". In this study, we measure the apparent viscosity of blood flow in 50μ glass tubes as a function of shear rate and red blood cell volume fraction (hematocrit); for a fixed tube geometry and an imposed flow rate, the viscosity is determined by measuring the pressure drop across the tube. To correlate the apparent viscosity with the size and spatial distribution of the aggregates in the flow, video images of the flow are recorded and analyzed using power spectral techniques. Pig blood and sheep blood are used as the models for aggregating and non-aggregating blood, respectively. Supported by NSF PFF Award CTS-9253633

  19. Effects of tangential velocity distribution on flow stability in a draft tube

    NASA Astrophysics Data System (ADS)

    Dou, Huashu; Niu, Lin; Cao, Shuliang

    2014-10-01

    Numerical simulations of the flow in the draft tube of a Francis turbine are carried out in order to elucidate the effects of tangential velocity on flow stability. Influence of the location of the maximum tangential velocity is explored considering the equality of the total energy at the inlet of the draft tube. It is found that the amplitude of the pressure fluctuation decreases when the location of the maximum of the tangential velocity moves from the centre to the wall on the cross section. Thus, the stability of the flow in the draft tube increases with the moving of the location of the maximum tangential velocity. However, the relative hydraulic loss increases and the recovery coefficient of the draft tube decreases slightly.

  20. 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.

  1. An experimental study of fluidelastic instability and draf force on a tube in two-phase cross flow

    SciTech Connect

    Joo, Youngcheol

    1994-12-31

    Two-phase cross flow over heat exchanger tubes creates vibrations which contribute greatly to the wear on the tubes. Fluidelastic instability is a major mechanism by which tubes can fail. In this work, the fluidelastic instability of a tube placed in an array subjected to two-phase cross flow has been studied. For the determination of fluidelastic instability, a triangular tube array was used. The tubes were made of acrylic and were 2.2 cm or 2.37 cm in diameter and 20 cm in length. Eighteen tubes and 4 half tubes formed 5 rows with a pitch to diameter ratio of 1.4. All of the tubes except the test tube were rigidly supported at the text section wall. The test tube was flexibly supported with two cantilever beams. By installing cantilever beams horizontally and vertically, drag and lift direction tube vibration were studied. Parameters of tube mass, structural stiffness, natural frequency, and pitch to diameter ratio were varied. The drag coefficients on a rigidly held tube in an array subjected to two-phase cross flow were measured. The tube in an array was located at displaced positions as well as at the normal position in order to study the variation of fluid force as the tube vibrates. In the experiments, gap Reynolds numbers up to 1 x 10{sup 5} were obtained, while void fraction was varied from zero to 0.5. The drag coefficients in two-phase flow are much higher than those in single phase flow. The ratio of two-phase to single phase drag coefficient decreases as Reynolds number increases. The drag coefficient on a tube in an array increases as the tube is displaced in the direction of flow. The drag coefficient increases rapidly when the tube is displaced more than a certain critical distance.

  2. Condensation of refrigerants flowing inside smooth and corrugated tubes

    SciTech Connect

    Hinton, D.L.; Conklin, J.C.; Vineyard, E.A.

    1995-07-01

    Because heat exchanger thermal performance has a direct fluence on the overall cycle performance of vapor-compression refrigeration machinery,enhanced heat transfer surfaces are of interest to improve the efficiency of heat pumps and air conditioners. We investigated R-22 and a nonazeotropic refrigerant mixture (NARM) of 75% R-143a and 25% R-124 (by mass) to study their thermal performance in a condenser made of conventional smooth tubes and another condenser made of corrugated, or spirally indented, tubes. We investigated the condensing heat transfer and pressure drop characteristics in an experimental test loop model of a domestic beat pump system employing a variable speed compressor. The refrigerant circulates inside the central tube and the water circulates in the annulus. At refrigerant mass fluxes of approximately 275--300 kg/m{sup 2}s, the measured irreversible pressure drop of the corrugated surface was 23% higher than that of the smooth surface for the R-22. At refrigerant mass fluxes of 350-370 kg/m{sup 2}s, the irreversible pressure drop of the corrugated surface was 36% higher than that of the smooth surface for the NARM. The average heat transfer coefficient for the corrugated surface for R-22 was roughly 40% higher than that for the smooth tube surface at refrigerant mass fluxes of 275--295 kg/m{sup 2}s. The average heat transfer coefficient for the corrugated surface for the NARM was typically 70% higher than that for the smooth tube surface at refrigerant mass fluxes of 340--385 kg/m{sup 2}s.

  3. Study of junction flows in louvered fin round tube heat exchangers using the dye injection technique

    SciTech Connect

    Huisseune, H.; Willockx, A.; De Paepe, M.; T'Joen, C.; De Jaeger, P.

    2010-11-15

    Detailed studies of junction flows in heat exchangers with an interrupted fin design are rare. However, understanding these flow structures is important for design and optimization purposes, because the thermal hydraulic performance of heat exchangers is strongly related to the flow behaviour. In this study flow visualization experiments were performed in six scaled-up models of a louvered fin round tube heat exchanger. The models have three tube rows in a staggered layout and differ only in their fin spacing and louver angle. A water tunnel was designed and built and the flow visualizations were carried out using dye injection. At low Reynolds numbers the streakline follows the tube contours, while at higher Reynolds numbers a horseshoe vortex is developed ahead of the tubes. The two resulting streamwise vortex legs are destroyed by the downstream louvers (i.e. downstream the turnaround louver), especially at higher Reynolds numbers, smaller fin pitches and larger louver angles. Increasing the fin spacing results in a larger and stronger horseshoe vortex. This illustrates that a reduction of the fin spacing results in a dissipation of vortical motion by mechanical blockage and skin friction. Furthermore it was observed that the vortex strength and number of vortices in the second tube row is larger than in the first tube row. This is due to the thicker boundary layer in the second tube row, and the flow deflection, which is typical for louvered fin heat exchangers. Visualizations at the tube-louver junction showed that in the transition part between the angled louver and the flat landing a vortex is present underneath the louver surface which propagates towards the angled louver. (author)

  4. Leakage flow-induced vibration of an eccentric tube-in-tube slip joint

    SciTech Connect

    Mulcahy, T.M.

    1985-08-01

    Eccentricity of a specific slip-joint design separating two cantilevered, telescoping tubes did not create any self-excited lateral vibrations that had not been observed previously for a concentric slip joint. In fact, the eccentricity made instabilities less likely to occur, but only marginally. Most important, design rules previously established to avoid instabilities for the concentric slip joint remain valid for the eccentric slip joint. 6 refs., 9 figs., 2 tabs.

  5. 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)

  6. 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.

  7. 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.

  8. Exact solution of cilia induced flow of a Jeffrey fluid in an inclined tube.

    PubMed

    Maqbool, K; Shaheen, S; Mann, A B

    2016-01-01

    The present study investigated the cilia induced flow of MHD Jeffrey fluid through an inclined tube. This study is carried out under the assumptions of long wavelength and low Reynolds number approximations. Exact solutions for the velocity profile, pressure rise, pressure gradient, volume flow rate and stream function are obtained. Effects of pertinent physical parameters on the computational results are presented graphically. PMID:27610298

  9. Pressure drop and pumping power for fluid flow through round tubes

    NASA Technical Reports Server (NTRS)

    Jelinek, D.

    1973-01-01

    Program, written for Hewlett-Packard 9100A electronic desk computer provides convenient and immediate solution to problem of calculating pressure drop and fluid pumping power for flow through round tubes. Program was designed specifically for steady-state analysis and assumes laminar flow.

  10. RECOMMENDED PRACTICE FOR FLOW MEASUREMENT IN WASTEWATER TREATMENT PLANTS WITH VENTURI TUBES AND VENTURI NOZZLES

    EPA Science Inventory

    Venturi tubes and venturi nozzles are suitable for in-plant flow measurement of raw influent, treated effluent, return activated sludge, certain digested sludges, and for air and gas flows. However, they are not generally recommended for measurement of raw primary sludge. For cla...

  11. 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.

  12. 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…

  13. Pulsating incinerator hearth

    SciTech Connect

    Basic, J.N. Sr.

    1984-10-09

    A pulsating hearth for an incinerator wherein the hearth is suspended on a fixed frame for movement in a limited short arc to urge random size particles burning in a pile on the hearth in a predetermined path intermittently across the surface of the heart. Movement is imparted to the hearth in periodic pulses preferably by inflating sets of air bags mounted on the frame, which stroke the hearth to move it a short distance from an initial position and jar it against the frame, thus impelling the burning particles a short distance by inertia and concurrently stoking the burning pile upon each stroke, and then returning the hearth to its initial position. The hearth may also have a plurality of nozzles connected to a source of air for delivering gently flowing air to the burning pile on the hearth.

  14. Modeling flow through inline tube bundles using an adaptive immersed boundary method

    NASA Astrophysics Data System (ADS)

    Liang, Chunlei; Luo, Xiaoyu; Griffith, Boyce

    2007-11-01

    Fluid flow and its exerted forces on the tube bundle cylinders are important in designing mechanical/nuclear heat exchanger facilities. In this paper, we study the vortex structure of the flow around the tube bundle for different tube spacing. An adaptive, formally 2^nd order immersed boundary (IB) method is used to simulate the flow. One advantage of the IB method is its great flexibility and ease in positioning solid bodies in the fluid domain. Our IB approach uses a six-point regularized delta function and is a type of continuous forcing approach. Validation results obtained using the IB method for two-in-tandem cylinders compare well with those obtained using the finite volume or spectral element methods on unstructured grids. Subsequently, we simulated flow through six-row inline tube bundles with pitch-to-diameter ratios of 2.1, 3.2, and 4, respectively, on structured adaptively refined Cartesian grids. The IB method enables us to study the critical tube spacing when the flow regime switches from the vortex reattachment pattern to alternative individual vortex shedding.

  15. 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).

  16. 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.

  17. 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. PMID:22559504

  18. 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)].

  19. 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.

  20. 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.

  1. 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

  2. Prediction of refrigerant void fraction in horizontal tubes using probabilistic flow regime maps

    SciTech Connect

    Jassim, E.W.; Newell, T.A.; Chato, J.C.

    2008-04-15

    A state of the art review of two-phase void fraction models in smooth horizontal tubes is provided and a probabilistic two-phase flow regime map void fraction model is developed for refrigerants under condensation, adiabatic, and evaporation conditions in smooth, horizontal tubes. Time fraction information from a generalized probabilistic two-phase flow map is used to provide a physically based weighting of void fraction models for different flow regimes. The present model and void fraction models in the literature are compared to data from multiple sources including R11, R12, R134a, R22, R410A refrigerants, 4.26-9.58 mm diameter tubes, mass fluxes from 70 to 900 kg/m{sup 2} s, and a full quality range. The present model has a mean absolute deviation of 3.5% when compared to the collected database. (author)

  3. Analytical comparison of condensing flows inside tubes under earth-gravity and space environments

    NASA Astrophysics Data System (ADS)

    Keshock, E. G.; Sadeghipour, M. S.

    1981-09-01

    The heat transfer behavior of flow condensation inside horizontal tubes under conditions of zero gravity and earth gravity is modeled and analyzed. For earth conditions for wetting fluids, the annular flow region changes to a stratified flow pattern as a result of gravity drainage of the condensate from the upper portion of the tube. The stratified condensate layer is considered inactive in the heat transfer process; its magnitude is determined along the tube length from the analytical results of Rufer and Kezios (1966). Under zero-gravity conditions, where no such gravity drainage is observed, the flow is considered to be annular along the complete length of the tube. The analytical approach of Bae (1970) is used to evaluate the heat transfer rates under zero-gravity conditions. The results suggest a substantially poorer condensing performance under zero-gravity conditions. It is pointed out that these results can be simply explained in terms of the smaller condensate film thickness over the upper portion of the tube periphery at any axial location under earth-gravity conditions because of gravity drainage of the condensate.

  4. 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.

  5. 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.

  6. Fluid-elastic Instability of Helical Tubes Subjected to Single-Phase External Flow and Two-Phase Internal Flow

    SciTech Connect

    Jong Chull Jo; Myung Jo Jhung; Woong Sik Kim; Hho Jung Kim

    2004-07-01

    This study investigates the fluid-elastic instability characteristics of steam generator helical type tubes in operating nuclear power plants. The thermal-hydraulic conditions of both tube side and shell side flow fields are predicted by a general purpose computational fluid dynamics code employing the finite volume element modeling. To get the natural frequency, corresponding mode shape and participation factor, modal analyses are performed for helical type tubes with various conditions. Investigated are the effects of the helix angle, the number of supports and the status of the inner fluid on the modal, and fluid-elastic instability characteristics of the tubes, which are expressed in terms of the natural frequency, corresponding mode shape, and stability ratio. (authors)

  7. Pressure maxima in the flow of superfluid [sup 4]He in tubes

    SciTech Connect

    Mills, G.L.; Mord, A.J.; Snyder, H.A. University of Colorado, Campus Box 429, Boulder, Colorado 80309 )

    1994-01-01

    Calculations based on the standard equations for the flow He II in tubes predict large pressure and moderate temperature maxima when the tube is long and narrow. This effect has not, to our knowledge, been previously observed. Experimental data are presented that confirm the existence of the pressure maxima in capillaries of diameter 0.3 [mu]m. The measured data are in good agreement with predictions. The data validate the model equations for flow in capillaries and porous media using the bulk value of the Gorter-Mellink parameter. This effect may impact interpretations of experimental searches for size effects.

  8. 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.

  9. A historical pyroclastic flow emplaced within a pre-existing Pleistocene lava tube: Silidong, Tianchi Volcano, Changbaishan, northeastern China

    NASA Astrophysics Data System (ADS)

    Chen, Zhengquan; Wei, Haiquan; Liu, Yongshun; Tilling, Robert I.; Xu, Jiandong; Wu, Chengzhi; Nie, Baofeng

    2015-06-01

    Pyroclastic flow deposits recently found within a pre-existing lava tube at Tianchi Volcano represent, to the best of our knowledge, the only such reported occurrence worldwide. In this case, pyroclastic flow of Tianchi's "Millennium eruption" (~1 ka) traveled about 18 km from the summit eruptive source and poured successively into the ~560-m-long accessible segment of Silidong lava tube. Mapping of tube morphology, combined with detailed characterization of the features associated with the pumice flow deposits (e.g., adhering of pyroclastic materials on tube walls, fumarole pipes, rootless vents, and flow fronts of the deposit surface) has enabled plausible inferences regarding the original within-tube conditions and dynamic flow regime during emplacement. We propose a model of an aggrading pyroclastic flow which locally varies its sedimentation rate. The pyroclastic deposit is thicker in locations of reduced flow mobility, and the resultant variations in deposit thickness appear to control the distribution of fumarole pipes and rootless vents.

  10. 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

  11. 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. PMID:27529137

  12. 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

  13. Effect of draft tube size on the performance of a cross-flow turbine

    SciTech Connect

    Reddy, H.; Seshadri, V.; Kothari, D.P.

    1996-03-01

    The cross-flow turbine has attracted the attention of several investigators working in the area of microhydroelectric power generation. This type of turbine, although primarily an impulse type, is suitable for operation at low and medium heads. This article describes the effect of using different sizes of draft tubes on the performance of a 5-kW cross-flow turbine. An effort is made to arrive at an optimum size for the particular turbine tested, as the existing draft tube (203 mm) had an adverse effect on the performance at higher heads. The study involved variation of different performance parameters such as output, efficiency, runaway speed, and speed ratio for four different cases, viz., without the draft tube and with three different sizes of draft tubes (203, 250, and 300 mm) in the head range 3--9 m. The investigation shows that a properly sized draft tube enhances the efficiency of a cross-flow turbine over the entire space of its operation.

  14. 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.

  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. 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.

  17. Evidence for siphon flows with shocks in solar magnetic flux tubes

    NASA Technical Reports Server (NTRS)

    Degenhardt, D.; Solanki, S. K.; Montesinos, B.; Thomas, J. H.

    1993-01-01

    We synthesize profiles of the infrared line Fe I 15648.5 A (g = 3) for a recently developed theoretical model of siphon flows along photospheric magnetic loops. The synthesized line profiles are compared with the observations from which Rueedi et al. (1992) deduced the presence of such flows across the neutral line of an active region plage. This comparison supports the interpretation of Rueedi et al. (1992). It also suggests that the average footpoint separation of the observed loops carrying the siphon flow is 8-15 sec and that the siphon flow experiences a standing tube shock in the downstream leg near the top of the arch.

  18. Numerical study of shock tube flows with homogeneous and heterogeneous condensations in rarefaction wave

    NASA Astrophysics Data System (ADS)

    Nagao, Junji; Matsuo, Shigeru; Setoguchi, Toshiaki; Kim, Heuy Dong

    2010-08-01

    Shock tubes are devices in which the state of a gas is changed suddenly from one uniform state to another by the passage of shock and expansion waves. In the theory of ideal shock tube flow, it is customarily assumed that the unsteady expansion and shock waves generated by diaphragm rupture are a perfectly centered plane wave. However, such waves are generally not centered, or may not even by plane in practice. In the present research, the time-dependent behavior of homogeneous and heterogeneous condensation of moist air in the shock tube is investigated by using a computational fluid dynamics work. Further, the numerical and experimental studies were carried out in order to investigate the effect of the diaphragm rupture process on the flow characteristics of expansion and shock waves generated near the diaphragm.

  19. 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. PMID:27112856

  20. Diagnostic suite for study of corpuscular flow dynamics in ion-optical system of neutron tube

    NASA Astrophysics Data System (ADS)

    Dolgov, A. N.; Markov, V. G.; Kanshin, I. A.; Prokhorovich, D. E.; Sadilkin, A. G.; Vizgalov, I. V.; Rashchikov, V. I.; Mamedov, N. V.; Kolodko, D. V.

    2016-01-01

    In this work we developed a combined approach based on the experimental investigation of corpuscular flow at the outlet of an ion source and the computer simulations of beam transport inside ion-optical system that enabled us to recover the parameters of neutron tube operation.

  1. Transfer of heat by self-induced flow in a rotating tube

    NASA Astrophysics Data System (ADS)

    Gilham, S.; Ivey, P. C.; Owen, J. M.

    1994-04-01

    This paper provides a review of recently published research on self-induced flow and heat transfer in a rotating tube, together with additional theoretical work on heat transfer to the cylindrical wall of the tube. Earlier work has shown that self-induced flow can occur when a tube, with one end open and the other sealed, is rotated about its axis: Fluid flows along the axis toward the sealed end and returns in an annular layer on the cylindrical wall. The flow and heat transfer on the end wall are similar to those associated with the so-called free disk, and measured velocity distributions in the tube and Nusselt numbers for the end wall are in good agreement with those computed from numerical solutions of the Navier-Stokes and energy equations. The Reynolds analogy is used in this paper to provide a correlation for the computed Nusselt numbers for the cylindrical wall, and design correlations are provided to enable the results to be applied to anti-icing systems for the nose bullets of aero-engines.

  2. Flow field for an underexpanded, supersonic nozzle exhausting into an expansive launch tube

    NASA Technical Reports Server (NTRS)

    Morris, R. R.; Bertin, J. J.; Batson, J. L.

    1976-01-01

    Static pressure distributions along the launcher wall and pitot pressure measurements from the annular region between the rocket and the launcher were made as an underexpanded supersonic nozzle exhausted into an expansive launch tube. The flow remained supersonic along the entire length of the launcher for all nozzle locations studied.

  3. 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.

  4. 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.

  5. Effects of axial flow on the stability of a helical vortex tube

    NASA Astrophysics Data System (ADS)

    Hattori, Y.; Fukumoto, Y.

    2012-05-01

    The effects of axial flow on the stability of a helical vortex tube are studied by short-wavelength stability analysis. By axial flow we mean the flow along the helical tube inside the vortex core. At the leading order the base flow is set to the Rankine vortex with uniform velocity along the helical tube. The exponential growth rate is obtained analytically as the magnitude of the sum of three O(ɛ) and five O(ɛ2) complex numbers, where ɛ is the ratio of the core to curvature radius. At O(ɛ) the effect of axial flow can be regarded as the effect of the Coriolis force; as a result the instability is the superposition of the curvature instability and the Coriolis or precessional instability since the two instabilities occur under the same resonance condition. At O(ɛ2) combined effects of the axial flow and the torsion appear; the maximum growth rate increases when the period of particle motion increases.

  6. Ultrasonic observation of blood disturbance in a stenosed tube: effects of flow acceleration and turbulence downstream.

    PubMed

    Nam, Kweon-Ho; Paeng, Dong-Guk; Choi, Min Joo; Shung, K Kirk

    2008-01-01

    Red blood cell (RBC) aggregation is known to be highly dependent on hemodynamic parameters such as shear rate, flow turbulence and flow acceleration under pulsatile flow. The effects of all three hemodynamic parameters on RBC aggregation and echogenicity of porcine whole blood were investigated downstream of an eccentric stenosis in a mock flow loop using B-mode images with Doppler spectrograms of a commercial ultrasonic system. A hyperechoic parabolic profile appeared downstream during flow acceleration, yielding another piece of evidence suggesting that the enhancement of rouleaux formation may be caused by flow acceleration. It was also found that echogenicity increased locally at a distance of three tube diameters downstream from the stenosis. The local increase of echogenicity is thought to be mainly due to flow turbulence. The hypoechoic "black hole" was also seen at the center of the tube downstream of the stenosis where blood flow was disturbed, and this may be caused by the compound effect of flow turbulence and shear rate. PMID:17900794

  7. A correlation method for determining the number of sampling cycles required for pulsating flow analysis using a LDA.

    PubMed

    Jin, W; Clark, C

    1994-09-01

    A correlation method has been developed for pulsatile flow analysis, which allows justification of the minimum number of cycles for ensemble averaging, to satisfy ergodicity. It can also be used to identify cycles with excessive fluctuations caused by artefact or incidental errors and, hence, enhance the accuracy of analysis. PMID:7929467

  8. Investigation of DC flow effects on a 4K two-stage pulse tube cryocooler

    NASA Astrophysics Data System (ADS)

    Tsuchiya, A.; Xu, M. Y.

    2014-05-01

    Sumitomo Heavy Industries, Ltd. (SHI) has been continuously developing 4K GM-type pulse tube cryocoolers for cooling superconducting magnets and pre-cooling ultra-low temperature refrigerators, such as dilution refrigerators, etc. In a double-inlet or a 4-valve GM-type pulse tube cryocooler, there is a gas circulation, called DC flow, generated by the pulse tube, the regenerator and the orifice. The performance of a pulse tube cryocooler is strongly dependent on the rate of such kind of flow. It is possible to improve the performance by optimizing the rate. In order to optimize the rate, a bypass line with a small valve is installed between the warm end of the pulse tube and the low pressure side of the compressor. The second stage cooling capacity at 4.2 K was improved by about 0.25 W after optimization of the rate by adjusting the opening of the valve. The details of the experiment results will be reported in this paper.

  9. 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

  10. Operation of the ISL transonic shock tube in a high subsonic flow regime

    NASA Astrophysics Data System (ADS)

    Seiler, F.; Havermann, M.; Boller, F.; Mangold, P.; Takayama, K.

    The transonic flow regime plays an important role in experimental aerodynamic research. Modern civil aircraft fly up to a Mach number of M ≈ 0.9 in the high subsonic speed regime, as, for example, the Boeing or Airbus passenger aircraft. Nearly sonic Mach numbers are foreseen for innovative airplane concepts like the sonic cruiser by Boeing. In the military domain, guided missiles like the cruise missile also fly in the high subsonic flow regime. For testing purposes, transonic wind tunnels are mainly used for sub- as well as supersonic design applications. These wind tunnels have normally very large dimensions, which makes their operation quite expensive. If only small scale tests are required, a cheap working facility turns out to be more beneficial. For this purpose, a conventional shock tube operated at transonic flow conditions has been put into operation at the ISL. In the transonic flow regime, however, the reduction of the tube cross section by the model can produce severe distortions followed by a choking of the shock tube flow in the test section. Extensive experimental investigations were performed to determine the subsonic choking Mach number as a function of the model size. These results are compared with theoretical estimations and, more in detail, with CFD calculations.