DESIGN AND APPLICATION OF GAS-GAP HEAT SWITCHES Final Report C. K. Chan and R. G. Ross, Jr. 15 Mar. 1990 62 p Prepared for Air Force Space Technology Center, Kirtland AFB, NM (Contract NAS7-918) (NASA-CR-187339; JPL-Publ-90-38; NAS 1.26:187339) Avail: NTIS HC/MF A04 CSCL 09C Gas-gap heat switches can serve as an effective means of thermally disconnecting a standby cryocooler when the primary (operating) cooler is connected and vice versa. The final phase of the development and test of a cryogenic heat switch designed for loads ranging from 2 watts at 8 K, to 100 watts at 80 K are described. Achieved heat-switch on/off conductance ratio ranged from 11,000 at 8 K to 2200 at 80 K. A particularly challenging element of heat-switch design is achieving satisfactory operation when large temperatures differentials exist across the switch. A special series of tests and analyses was conducted and used in this Phase-2 activity to evaluate the developed switches for temperature differentials ranging up to 200 K. Problems encountered at the maximum levels are described and analyzed, and means of avoiding the problems in the future are presented. A comprehensive summary of the overall heat-switch design methodology is also presented with special emphasis on lessons learned over the course of the 4-year development effort. N91-10223# Author Johns Hopkins Univ., Baltimore, MD. Dept. of (Contracts DE-AC03-76SF-00098; LBL-4539610) The role of passive films in aqueous solutions has been studied extensively, yet the passivity of metals and alloys in non-aqueous solutions has received comparatively little attention despite its importance to such technologies as lithium batteries, chemical processing, and fuel processing. Long term integrity depends on the protective ability of the passive film in the non-aqueous electrolytes employed. By understanding the nature of passivity in non-aqueous solvents, and factors which cause its breakdown, improvements in the corrosive behavior of structural alloys and electrode materials in lithium batteries and other commercial applications in non-aqueous solutions can be made. The overall objective is to enhance the understanding of the major processes affecting corrosion in non-aqueous solvents: passivity and breakdown of passivity. Since passive layers control corrosion, the achievement of such an understanding especially in regards to how alloys composition affects these layers is crucial to the development of alloys more corrosion resistant in non-aqueous solvents. This research addresses the following fundamental questions: (1) Are the films found in organic solvents different from those produced in aqueous environments; (2) Can passive layers form on bare metals in the absence of water, and if they can, what is their nature; and (3) What are the kinetics of passive film formation, breakdown and repassivation. DOE the 1990's, Oak Ridge, TN, 23-27 Apr. 1990 (Contract DE-AC05-84OR-21400) (DE90-016849; CONF-900450-10) Avail: NTIS HC/MF A03 GAMMASPHERE is one of a new generation of gamma ray detector arrays. It consists of 110 Compton-suppressed large volume Ge detectors. The design goal is to achieve high efficiency and peak-to-total value for four to five fold coincidence experiments. Such highfold coincidence capability will provide new physics opportunities in areas such as high spins, transfer reactions, giant resonances, and astrophysics. The design of the detector and shield has been developed through extensive simulation calculations and an electronic honeycomb design was chosen. The electronics and computer systems are capable of operating at 50,000 event/sec. The design and development tasks are being carried out at several laboratories in the U.S. The project is expected to be funded in the fall of 1990. The first experiment is planned in the summer of 1992. DOE N91-10225# Technische Univ., Delft (Netherlands). AN AVALANCHE ELECTRON EMITTING DIODE IN GALLIUM ARSENIDE Ph.D. Thesis Tom vanZutphen 1990 122 p (Contract STW-DTN33-467) (ETN-90-97746) Avail: NTIS HC/MF A06 The development of an electron emitter based on a shallow pn-junction made of gallium arsenide is reported. Desirable properties of an electron gun are outlined and the attractive aspects and specific possibilities of the Avalanche Electron Emitting Diode (AEED) are discussed. Fabrication, including the self-made gold-germanium sputter and gold evaporation equipment, is explained. Ultrahigh vacuum measurement and cleaning setup and properties of the low energy argon ion sputter source and method of measurement are presented. Experimental results and theoretical calculations are given. The Ga AEED device is concluded to be of not good enough quality for fair comparison to the silicon AEED. ESA N91-10226# Technische Univ., Delft (Netherlands). The behavior of first order oscillators is studied in order to present the designer with the knowledge to change the oscillator properties. The understanding is based mainly on qualitative aspects. Regenerative and nonregenerative memory implementations for the binary memory function are discussed. The influence of noise is discussed. Electronic circuits which were integrated and verified experimentally are given. Bipolar technology was used. For exact numerical predictions of oscillator behavior, computer simulators such as SPICE can be used. ESA light leads assembly area at RISTS, Telford, is performed. The objectives are the followings: to examine the organization and tasking structure to evaluate the effectiveness of the manufacturing control procedures; to review the quality procedures and to comment their effectiveness; to assess machine utilization to identify potential problem areas; to investigate and to comment on machine serviceability, reliability, and maintainability; to identify factors to reduce machine down time and any other factors affecting production. Conclusions and recommendations are given, particularly concerning the needs of infrastructure of the factory, taking into account that it is in the process of major expansion. ESA N91-10229# Oxford Univ. (England). Dept. of Engineering (OUEL-1823/90; ETN-90-97921) Avail: NTIS HC/MF A03 The central task in power station control is to meet the system demand while minimizing state and input variations in the plant. In order to achieve good set point following, the control system must make good use of coupling between the different control loops and if possible use information about future set points to smooth out the control activity. Characteristic Generalized Predictive Control (GPC) sets out to achieve both these objectives and hence would seem ideally suited to power station control. The presence of some fast and slow dynamics implies that the boiler turbine system is in essence a stiff problem; the characteristic GPC algorithm is suitably extended to take direct account of this. Simulation results show that the characteristic GPC algorithm provides the systematic means of approaching the boilier-turbine problem and affords some improvements in performance over traditional proportional integral derivative control schemes. N91-10348# Meteorological Satellite Center, Tokyo (Japan). ANTENNA/TRANSMITTER CONTROL UNIT ESA Seiji Kawabata and Masahiro Sasaki In its Meteorological Satellite Center Technical Note. Special Issue (1989). Summary of GMS System. 1: Telecommunication System Mar. 1989 p 91-95 In JAPANESE; ENGLISH summary (For primary document see N91-10338 01-42) Avail: NTIS HC/MF A08 34 FLUID MECHANICS AND HEAT TRANSFER Includes boundary layers; hydrodynamics; fluidics; mass transfer; and ablation cooling. For related information see also 02 Aerodynamics and 77 Thermodynamics and Statistical Physics. N91-10230# Ballistic Research Labs., Aberdeen Proving Ground, MD. LARGE BLAST AND THERMAL SIMULATOR ADVANCED CONCEPT DRIVER DESIGN BY COMPUTATIONAL FLUID DYNAMICS Final Report, 1987 - 1989 Klaus O. Opalka Aug. 1989 12 P (AD-A211364; BRL-TR-3026) Avail: NTIS HC/MF A03 CSCL 20/4 The construction of a large test facility is proposed for simulating the blast and thermal environment resulting from nuclear explosions. This facility would be used to test the survivability and vulnerability of military equipment such as trucks, tanks and helicopters in a simulated thermal and blast environment, and to perform research into nuclear blast phenomenology. The proposed advanced design concepts, heating of driver gas and fast-acting N91-10231# National Inst. of Standards and Technology, Gaithersburg, MD. Center for Chemical Engineering. MEASUREMENTS OF COEFFICIENTS OF DISCHARGE FOR CONCENTRIC FLANGE-TAPPED SQUARE-EDGED ORIFICE METERS IN NATURAL GAS OVER THE REYNOLDS NUMBER RANGE 25,000 TO 16,000,000 Final Report J. R. Whetstone, W. G. Cleveland, B. R. Bateman, and C. F. Sindt Sep. 1989 369 p Sponsored by American Petroleum Inst., Washington, DC (PB90-219601; NIST/TN-1270) Avail: NTIS HC/MF A16; also available SOD HC $18.00 as 003-003-02974-2 CSCL 20D The report describes the data acquisition systems and procedures used in the American Petroleum Institute (API)-sponsored orifice discharge coefficient project performed in natural gas flows and conducted at the test loop of the Natural Gas Pipeline Company of America (NGPL) in Joliet, Illinois. Measurements of orifice discharge coefficients for 6- and 10-inch diameter orifice meter runs were made using critical venturis for mass flowrate measurement with associated measurement of pressures and temperatures. Eleven venturis were calibrated at the Colorado Engineering Experiment Station, Inc. (CEESI). Measurements of absolute and differential pressure and temperature for venturi and orifice meter conditions were made using an automated data acquisition system. Temperature and pressure measurements were directly related to U.S. national measurement standards. Daily calibration of absolute and differential pressure transducers using pressure working standards was designed into the measurement procedures. Collected over a 2-year period, the database contains tests on 44 orifice plates in 8 beta ratios for two meter sizes (6- and 10-inches). The database contains 1,345 valid test points. GRA N91-10232# National Aeronautical Lab., Bangalore (India). R. Gopinath Jun. 1990 25 p (PD-CF-9012) Avail: NTIS HC/MF A03 A closing report on the activity, Wall Interference Studies, is presented. Codes were developed to assess wall interference both for 2-D and 3-D cases, where the test section is ventilated, and validated. TSFOIL code was adapted for operation on the Univac computer. Instrumentation was developed for measuring the pressures on a control surface in the 1.2 m facility and once this is installed in the above facility, correcting the data from it for wall interference effects should be a routine affair. Author N91-10233 Rockefeller Univ., New York, NY. Alessandro Campa 1989 170 p The dynamical properties, at the molecular level, of binary fluid mixtures in equilibrium are studied; binary fluid mixtures are fluids consisting of two different components. As for simple fluids, the main experimental probes for the study of these properties of binary mixtures are light and neutron scattering. To connect the dynamics with scattering experiments the kinetic theory of fluids is used. The kinetic theory was applied to binary mixtures where the atomic masses of the molecules of the two components are very different. Both dilute (gaseous) mixtures and dense mixtures were studied. In the description of the dynamics of the fluid through the density-density correlation functions, one can introduce modes, which can be thought of as the different channels by which the correlations decay in time. Some modes are propagating, in the sense that they describe propagating, and damped, processes. Others are not propagating, and describe diffusive, purely damped processes. The results concern the appearance of a fast propagating mode, in disparate-mass binary mixtures, in a vast range of densities, from dilute gas mixtures to rather high (liquid) densities. This fast mode appears beyond the hydrodynamic regime. One can call this mode fast sound, because, like ordinary sound, it propagates, but it is faster. The most important point is that the fast sound is associated with dynamics of the light component only. How this phenomenon could be observed in light and neutron scattering experiments is explained. If it is detected in actual scattering experiments on disparate-mass binary mixtures it would be the first time that a non hydrodynamic mode in a fluid is clearly seen. Dissert. Abstr. N91-10234 lowa State Univ. of Science and Technology, Ames. Avail: Univ. Microfilms Order No. DA9014903 Four time-dependent numerical algorithms for the prediction of unsteady, viscous compressible flows are compared. The analyses are based on the time-dependent Navier-Stokes equations expressed in a generalized curvilinear coordinate system. The methods tested include three traditional central-difference algorithms, and a new upwind-biased algorithm utilizing an implicit, time-marching relaxation procedure based on Newton iteration. Aerodynamic predictions are compared for internal duct-type flows and cascaded turbomachinery flows with spatial periodicity. Two-dimensional internal duct-type flow predictions are performed using an H-type grid system. Planar cascade flows are analyzed using a numerically generated, capped, body-centered, O-type grid system. Initial results are presented for critical and supercritical steady inviscid flow about an isolated cylinder. These predictions are verified by comparisons with published computational results from a similar calculation. Results from each method are then further verified by comparison with experimental data for the more demanding case of flow through a two-dimensional turbine cascade. Inviscid predictions are presented for two different transonic turbine cascade flows. Dissert. Abstr. Analytical and experimental methods are addressed for increasing industrial and home drying efficiency via pulse combustors. A fundamental scientific methodology is being developed for the momentum, heat, and mass transfer in oscillating (on the mean) turbulent flows. The approach follows the intuitive ideas of Taylor and Kolmogorov on the construction of microscales of turbulence. A parallel experimental program was carried out by the pulse combustor of the Continuous Combustion Lab of Sandia-Livermore National Labs. A droplet sizing technique and a quasi-steady computer model were developed. The unsteady analytical model determines the range of the quasi-steady model and provides also a mass transfer correlation beyond this range. The scales of mass transfer in oscillating turbulent flows were developed. A mass transfer correlation based on these scales was proposed. The correlation agrees well with the results so far obtained in the experimental program. Author N91-10236# Argonne National Lab., IL. Materials and Components Technology Div. TWO-PHASE FLOW PATTERNS AND FRICTIONAL PRESSURE GRADIENTS IN A SMALL, HORIZONTAL, RECTANGULAR CHANNEL M. W. Wambsganss, J. A. Jendrzejczyk, D. M. France, and N. T. Obot (Clarkson Univ., Potsdam, NY.) May 1990 112 p (Contract W-31-109-eng-38) (DE90-014802; ANL-90/19) Avail: NTIS HC/MF A06 Two-phase flow patterns and frictional pressure gradients in flow in small, rectangular channels are being studies as part of a larger research program addressing phase change heat transfer of pure refrigerants and refrigerant mixtures in plate-fin heat exchangers. Small rectangular flow channels were selected as representative of plain fin geometries. The particular channel reported herein has dimensions of 19.05 x 3.18 mm. Adiabatic flows of air/water mixtures, with the flow channel horizontal and the channel exit at near-atmospheric conditions, were utilized in the experiments. Analysis and interpretation of the pressure data relative to observed flow pattern transitions led to an objective method for determining the plug/bubble-to-slug flow transition. This method, together with visual observations, supplemented with photographic data, was used to develop a flow pattern map. A comparison of existing flow pattern maps for circular pipes, capillary tubes, and larger rectangular channels led to the conclusion that, while qualitative agreement exists, these maps are not generally applicable on a quantitative basis to the subject small rectangular channel. Two state-of-the-art correlations for frictional pressure gradient were evaluated, with particular emphasis on the practically important ranges of total mass quality and mass flux, from the standpoint of plate-fin heat exchangers designed as evaporators. Neither correlation was in good agreement over the entire range of interest. A modified, semiempirical correlation was developed to predict, with satisfactory accuracy for design purposes, the measured data of these experiments. DOE N91-10237*# Institute for Computer Applications in Science and Engineering, Hampton, VA. BOUNDED ENERGY STATES IN HOMOGENEOUS TURBULENT (NASA-CR-187439; NAS 1.26:187439; ICASE-90-66) Avail: NTIS HC/MF A03 CSCL 20D The equilibrium structure of homogeneous turbulent shear flow is investigated from a theoretical standpoint. Existing turbulence models, in apparent agreement with physical and numerical experiments, predict an unbounded exponential time growth of the turbulent kinetic energy and dissipation rate; only the anisotropy tensor and turbulent time scale reach a structural equilibrium. It is shown that if vortex stretching is accounted for in the dissipation rate transport equation, then there can exist equilibrium solutions, with bounded energy states, where the turbulence production is balanced by its dissipation. Illustrative calculations are present for a k-epsilon model modified to account for vortex stretching. The calculations indicate an initial exponential time growth of the turbulent kinetic energy and dissipation rate for elapsed times that are as large as those considered in any of the previously conducted physical or numerical experiments on homogeneous shear flow. However, vortex stretching eventually takes over and forces a production-equals-dissipation equilibrium with bounded energy states. The validity of this result is further supported by an independent theoretical argument. It is concluded that the generally accepted structural equilibrium for homogeneous shear flow with unbounded component energies is in need of re-examination. FLUID MECHANICS AND HEAT TRANSFER image transmission which allows the user to have direct interaction with the solution development. In addition to theory and results, the hardware and software requirements are discussed. Author N91-10239# Los Alamos National Lab., NM. AFDM: AN ADVANCED FLUID-DYNAMICS MODEL. VOLUME 1: SCOPE, APPROACH, AND SUMMARY W. R. Bohl, F. R. Parker, D. Wilhelm, J. Berthier, L. Goutagny (Commissariat a l'Energie Atomique, Cadarache, France ), and H. Ninokata Sep. 1990 109 p (Contract W-7405-eng-36) (DE90-016723; LA-11692-MS-Vol-1) Avail: NTIS HC/MF A06 AFDM, or the Advanced Fluid-Dynamics Model, is a computer code that investigates new approaches simulating the multiphase-flow fluid-dynamics aspects of severe accidents in fast reactors. The AFDM formalism starts with differential equations similar to those in the SIMMER-II code. These equations are modified to treat three velocity fields and supplemented with a variety of new models. The AFDM code has 12 topologies describing what material contacts are possible depending on the presence or absence of a given material in a computational cell, on the dominant liquid, and on the continuous phase. Single-phase, bubbly, churn-turbulent, cellular, and dispersed flow regimes are permitted for the pool situations modeled. Virtual mass terms are included for vapor in liquid-continuous flow. Interfacial areas between the continuous and discontinuous phases are convected to allow some tracking of phenomenological histories. Interfacial areas are also modified by models of nucleation, dynamic forces, turbulence, flashing, coalescence, and mass transfer. Heat transfer is generally treated using engineering correlations. Liquid-vapor phase transitions are handled with the nonequilibrium, heat-transfer-limited model, whereas melting and freezing processes are based on equilibrium considerations. Convection is treated using a fractional-step method of time integration, including a semi-implicit pressure iteration. A higher-order differencing option is provided to control numerical diffusion. The Los Alamos SESAME equation-of-state has been implemented using densities and temperatures as the independent variables. N91-10240# Los Alamos National Lab., NM. DOE (Contract W-7405-eng-36) (DE90-017535; LA-11692-MS-Vol-4) Avail: NTIS HC/MF A04 This report gives the Advanced Fluid-Dynamics Model (AFDM) solution algorithm describing vaporization/condensation (V/C) and melting/freezing processes. The finite-difference equations used are derived from the general AFDM differential equations with convection ignored. In two-phase cells, V/C is determined by a simultaneous iterative solution. The objective is to retain stability and energy conservation with consistent interfacial and bulk conditions describing vapor/liquid densities and temperatures. Particular attention is given in the special cases required to obtain a solution. In single-phase cells, the heat transfer is determined first; then, a vapor composition is updated for the (alpha) (sub 0) volume based on the saturation pressures for the individual liquids. Melting/freezing rates are determined based on equilibrium considerations. Mass-transfer-induced velocity changes are calculated implicitly so as to conserve momentum. In addition to the treatment of the standard models, a description is provided on the energy transfers used for the simplified NOPHASE option. N91-10241# Los Alamos National Lab., NM. (Contract W-7405-eng-36) (DE90-017536; LA-11692-MS-Vol-5) Avail: NTIS HC/MF A07 DOE This report gives the details for the convection of mass, (AFDM) code. Steps 2 to 4 of the AFDM algorithm are described. Step 2 explicitly convects the results of Step 1 intracell transfers. Step 3 performs an iteration to obtain consistent end-of-time-step cell-edge velocities and cell-centered pressures. Step 4 convects all cell variables with converged Step 3 velocities and includes the effects of interfacial dissipation. The unique AFDM higher-order spatial differencing format and the iterative solution for velocities based on three-field momentum coupling coefficients are described. The rationale for the momentum convection relationships selected is discussed. Details are provided on the linear equation-solver options available to treat the five-diagonal pressure-coefficient matrix formulated in the Step 3 iteration. N91-10242# Los Alamos National Lab., NM. DOE J. Berthier, D. Wilhelm, and W. R. Bohl Sep. 1990 85 p (Contract W-7405-eng-36) (DE90-017537; LA-11692-MS-Vol-3) Avail: NTIS HC/MF A05 This report consists of three parts. First, for the standard Advanced Fluid-Dynamics Model (AFDM), heat-transfer coefficients between components are worked out, depending on the different possible topologies. Conduction, convection, and radiative heat-transfer mechanisms are modeled. For solid particles, discontinuous phases that obey a rigid model, and components lacking relative motion, heat transfer is by conduction. Convection is represented for fluids in motion inside circulating bubbles and/or droplets. Radiation is considered between droplets in vapor continuous flow. In addition, a film-boiling model has been formulated, where radiation provides the lower limit on the fuel-to-coolant heat-transfer coefficient. Second, the momentum-exchange coefficients are defined for the standard AFDM. Between a continuous and discontinuous phase, the model consists of both laminar and turbulent terms. The most important feature is the drag coefficient in the turbulent term. It is calculated by a drag similarity hypothesis with limits for large Reynolds numbers, distorted particles, and churn-turbulent flow. A unique hysteresis algorithm exists to treat the liquid continuous to vapor continuous transition. Two discontinuous components are coupled using a turbulent term with an input drag coefficient. Fluid structure momentum exchange is represented with a standard friction-factor correlation. Third, the formulas used for the AFDM simplified Step 1 models are discussed. These include the heat-transfer coefficients, the momentum-exchange functions, and the manner in which interfacial areas are determined from input length scales. The simplified modeling uses steady-state engineering correlations, as in SIMMER-II. DOE N91-10243# Los Alamos National Lab., NM. (DE90-017538; LA-11692-MS-Vol-8) Avail: NTIS HC/MF A07 The T6P postprocessor analyzes data from TAPE6 and TAPE36. The processor calculates new variables, integrates variables over regions of the mesh, compares values of a variable of a given problem at selected times, compares values of a variable at selected times between problems for parameter studies, calculates derivatives of a variable with respect to time or another variable, and traces a variable at a requested location in the mesh over time. The data are presented to the user graphically, using two-dimensional graphs and three-dimensional perspective or contour plots. Interactive graphic techniques may be used with perspective plots. DOE range of densities, from dilute gas mixtures to rather high (liquid) densities. This fast mode appears beyond the hydrodynamic regime. One can call this mode fast sound, because, like ordinary sound, it propagates, but it is faster. The most important point is that the fast sound is associated with dynamics of the light component only. How this phenomenon could be observed in light and neutron scattering experiments is explained. If it is detected in actual scattering experiments on disparate-mass binary mixtures it would Dissert. Abstr. be the first time that a non hydrodynamic mode in a fluid is clearly seen. N91-10234 lowa State Univ. of Science and Technology, Ames. 282 p Avail: Univ. Microfilms Order No. DA9014903 Four time-dependent numerical algorithms for the prediction of unsteady, viscous compressible flows are compared. The analyses are based on the time-dependent Navier-Stokes equations expressed in a generalized curvilinear coordinate system. The methods tested include three traditional central-difference algorithms, and a new upwind-biased algorithm utilizing an implicit, time-marching relaxation procedure based on Newton iteration. Aerodynamic predictions are compared for internal duct-type flows and cascaded turbomachinery flows with spatial periodicity. Two-dimensional internal duct-type flow predictions are performed using an H-type grid system. Planar cascade flows are analyzed using a numerically generated, capped, body-centered, O-type grid system. Initial results are presented for critical and supercritical steady inviscid flow about an isolated cylinder. These predictions are verified by comparisons with published computational results from a similar calculation. Results from each method are then further verified by comparison with experimental data for the more demanding case of flow through a two-dimensional turbine cascade. Dissert. Abstr. Inviscid predictions are presented for two different transonic turbine cascade flows. N91-10235# Michigan Univ., Ann Arbor. Dept. of Mechanical MASS TRANSFER IN OSCILLATING FLOWS: EFFICIENT V. S. Arpaci, R. Gemmen, and A. Selamet Apr. 1990 96 p (PB90-242389; GRI-90/0135) Avail: NTIS HC/MF A05 CSCL 20D Analytical and experimental methods are addressed for increasing industrial and home drying efficiency via pulse combustors. A fundamental scientific methodology is being developed for the momentum, heat, and mass transfer in oscillating (on the mean) turbulent flows. The approach follows the intuitive ideas of Taylor and Kolmogorov on the construction of microscales of turbulence. A parallel experimental program was carried out by the pulse combustor of the Continuous Combustion Lab of Sandia-Livermore National Labs. A droplet sizing technique and a quasi-steady computer model were developed. The unsteady analytical model determines the range of the quasi-steady model and provides also a mass transfer correlation beyond this range. The scales of mass transfer in oscillating turbulent flows were developed. A mass transfer correlation based on these scales Author was proposed. The correlation agrees well with the results so far obtained in the experimental program. N91-10236# Argonne National Lab., IL. Components Technology Div. TWO-PHASE FLOW PATTERNS AND FRICTIONAL PRESSURE GRADIENTS IN A SMALL, HORIZONTAL, RECTANGULAR CHANNEL M. W. Wambsganss, J. A. Jendrzejczyk, D. M. France, and N. T. Obot (Clarkson Univ., Potsdam, NY.) May 1990 112 p (Contract W-31-109-eng-38) (DE90-014802; ANL-90/19) Avail: NTIS HC/MF A06 FLUID MECHANICS AND HEAT TRANSFER Two-phase flow patterns and frictional pressure gradients in flow in small, rectangular channels are being studies as part of a larger research program addressing phase change heat transfer of pure refrigerants and refrigerant mixtures in plate-fin heat exchangers. Small rectangular flow channels were selected as representative of plain fin geometries. The particular channel reported herein has dimensions of 19.05 x 3.18 mm. Adiabatic flows of air/water mixtures, with the flow channel horizontal and the channel exit at near-atmospheric conditions, were utilized in the experiments. Analysis and interpretation of the pressure data relative to observed flow pattern transitions led to an objective method for determining the plug/bubble-to-slug flow transition. This method, together with visual observations, supplemented with photographic data, was used to develop a flow pattern map. A comparison of existing flow pattern maps for circular pipes, capillary tubes, and larger rectangular channels led to the conclusion that, while qualitative agreement exists, these maps are not generally applicable on a quantitative basis to the subject small rectangular channel. Two state-of-the-art correlations for frictional pressure gradient were evaluated, with particular emphasis on the practically important ranges of total mass quality and mass flux, from the standpoint of plate-fin heat exchangers designed as evaporators. Neither correlation was in good agreement over the entire range of interest. A modified, semiempirical correlation was developed DOE to predict, with satisfactory accuracy for design purposes, the measured data of these experiments. N91-10237*# Institute for Computer Applications in Science BOUNDED ENERGY STATES IN HOMOGENEOUS TURBULENT (NASA-CR-187439; NAS 1.26:187439; ICASE-90-66) Avail: NTIS The equilibrium structure of homogeneous turbulent shear flow is investigated from a theoretical standpoint. Existing turbulence models, in apparent agreement with physical and numerical experiments, predict an unbounded exponential time growth of the turbulent kinetic energy and dissipation rate; only the anisotropy tensor and turbulent time scale reach a structural equilibrium. It is shown that if vortex stretching is accounted for in the dissipation rate transport equation, then there can exist equilibrium solutions, with bounded energy states, where the turbulence production is balanced by its dissipation. Illustrative calculations are present for a k-epsilon model modified to account for vortex stretching. The calculations indicate an initial exponential time growth of the turbulent kinetic energy and dissipation rate for elapsed times that are as large as those considered in any of the previously conducted physical or numerical experiments on homogeneous shear flow. However, vortex stretching eventually takes over and forces & production-equals-dissipation equilibrium with bended energy states. The validity of this result is further independent theoretical ument. It is concl accepted structural equum for home unbounded component rgies is in Jed by an generally flow with mation. |