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NASA NTRS1988

A new linearized theory of laminar film condensation of two phase annular flow in a capillary pumped loop

Future large space based facilities, such as Space Station, will require energy management systems capable of transporting tens of kilowatts of heat over a hundred meters or more. This represents better than an order of magnitude improvement over current technology. Two-phase thermal systems are currently being developed to meet this challenge. Condensation heat transfer plays a very important role in this system. The present study attempts an analytic solution to the set of linearized partial differential equations. The axial velocity and temperature functions were found to be Bessel functions which have oscillatory behavior. This result agrees qualitatively with the experimental evidence from tests at both NASA Goddard Space Flight Center and elsewhere.

Hsu, Y. K.↗

NASA NTRS1993

Experimental investigation of a simulated LOX injector flow field

Current development of liquid oxidizer injectors for liquid rocket engines is highly dependent upon experimental investigations of the two-phase liquid oxidizer/gaseous fuel injection plume characteristics. This paper describes an effort to increase the applicability of optical diagnostic approaches to such flow fields find includes an innovative approach for interpreting laser-induced fluorescence signals from axisymmetric two-phase flows. The usefulness of both laser-induced fluorescence and surface scattering techniques are explored herein. The flow field selected for this investigation is an oxidizer-swirled, coaxial flow produced using an injector design under consideration for use in the Space Transportation Main Engine (STME). The liquid oxygen (LOX) flow through this injector is simulated using water. Photographs of laser-induced fluorescence and particle scattering and measured profiles of the mass distribution in this flow field are presented and discussed herein.

Hartfield, Roy J., Jr.↗

NASA NTRS1985

Thermal management of high power space based systems

Conventional techniques of using a portion of the spacecraft skin for radiation of waste heat will be inadequate for high powered payloads (50 to 100 kWe) due to the lack of sufficient area. A Shuttle type system using a pumped single phase fluid loop could be scaled up to higher power but this type of system would require excessive pump power and weight. A pumped two-phase heat transfer loop has a much lower pumping requirement due to the higher latent heat of vaporization of the fluid in comparison to the sensible heat it can absorb through a temperature change. Concepts for an evaporator and a condenser for a pumped two-phase system are described. The condenser uses capillary grooves and a separate pumped condensate return line to achieve high heat transfer coefficients and stable operation due to the separation of the vapor and liquid flows. The cold plate evaporator uses wicks to contain the liquid and transport it to the heated surface. It can also function as a condenser for warming components. Control concepts for the cold plate are discussed. Concepts for deployment or erection of large space radiators are also considered.

Hwangbo, H.↗

NASA NTRS1989

An analytic study of nonsteady two-phase laminar boundary layer around an airfoil

Recently, NASA, FAA, and other organizations have focused their attention upon the possible effects of rain on airfoil performance. Rhode carried out early experiments and concluded that the rain impacting the aircraft increased the drag. Bergrum made numerical calculation for the rain effects on airfoils. Luers and Haines did an analytic investigation and found that heavy rain induces severe aerodynamic penalties including both a momentum penalty due to the impact of the rain and a drag and lift penalty due to rain roughening of the airfoil and fuselage. More recently, Hansman and Barsotti performed experiments and declared that performance degradation of an airfoil in heavy rain is due to the effective roughening of the surface by the water layer. Hansman and Craig did further experimental research at low Reynolds number. E. Dunham made a critical review for the potential influence of rain on airfoil performance. Dunham et al. carried out experiments for the transport type airfoil and concluded that there is a reduction of maximum lift capability with increase in drag. There is a scarcity of published literature in analytic research of two-phase boundary layer around an airfoil. Analytic research is being improved. The following assumptions are made: the fluid flow is non-steady, viscous, and incompressible; the airfoil is represented by a two-dimensional flat plate; and there is only a laminar boundary layer throughout the flow region. The boundary layer approximation is solved and discussed.

Hsu, Yu-Kao↗

NASA NTRS1985

Aerothermal modeling program, phase 2

The main objectives of the Aerothermal Modeling Program, Phase 2 are: to develop an improved numerical scheme for incorporation in a 3-D combustor flow model; to conduct a benchmark quality experiment to study the interaction of a primary jet with a confined swirling crossflow and to assess current and advanced turbulence and scalar transport models; and to conduct experimental evaluation of the air swirler interaction with fuel injectors, assessments of current two-phase models, and verification the improved spray evaporation/dispersion models.

Mongia, H. C.↗

NASA NTRS1990

In-Space technology experiments program. A high efficiency thermal interface (using condensation heat transfer) between a 2-phase fluid loop and heatpipe radiator: Experiment definition phase

Space Station elements and advanced military spacecraft will require rejection of tens of kilowatts of waste heat. Large space radiators and two-phase heat transport loops will be required. To minimize radiator size and weight, it is critical to minimize the temperature drop between the heat source and sink. Under an Air Force contract, a unique, high-performance heat exchanger is developed for coupling the radiator to the transport loop. Since fluid flow through the heat exchanger is driven by capillary forces which are easily dominated by gravity forces in ground testing, it is necessary to perform microgravity thermal testing to verify the design. This contract consists of an experiment definition phase leading to a preliminary design and cost estimate for a shuttle-based flight experiment of this heat exchanger design. This program will utilize modified hardware from a ground test program for the heat exchanger.

Pohner, John A.↗

NASA NTRS1995

Low gravity transfer line chilldown

Antar, B. N.↗

NASA NTRS1989

Low gravity transfer line chilldown

A code has been developed that solves for the transfer line chilldown time and flow and heat transfer characteristics in one-g environment. The code solves the transient, one dimensional, space averaged mass, momentum, and energy conservation equations for liquid-vapor two-phase flow in tubes. The physical configuration solved is that appropriate for bottom coolant injection in a vertically supported heated tube. Four distinct regions are considered consecutively: fully liquid, inverted annular, dispersed, and fully vapor flow. The conservation equations for both the liquid and the vapor are solved in each region separately. Also, in each region the mass and energy transport between each phase as well as the energy and momentum transport between the tube wall and the fluid are accounted for. A finite wall thickness is also considered. The model described above was solved numerically through a mixed finite difference scheme with forward time marching. The inverted annular regime was resolved using a semi-implicit finite differencing while the dispersed regime was solved explicitly. Also, a staggered mesh was used in which the velocity was resolved at mesh boundaries while all other field variables were resolved at the mesh centroids. Different mesh sizes were used depending on the region of solution. A coarse mesh was used in the dispersed flow region while a much finer mesh was used in both the inverted annular flow region and the tube walls.

B. N. Antar↗

NASA NTRS1992

A prototype heat pipe heat exchanger for the capillary pumped loop flight experiment

A Capillary Pumped Two-Phase Heat Transport Loop (CAPL) Flight Experiment, currently planned for 1993, will provide microgravity verification of the prototype capillary pumped loop (CPL) thermal control system for EOS. CAPL employs a heat pipe heat exchanger (HPHX) to couple the condenser section of the CPL to the radiator assembly. A prototype HPHX consisting of a heat exchanger (HX), a header heat pipe (HHP), a spreader heat pipe (SHP), and a flow regulator has been designed and tested. The HX transmits heat from the CPL condenser to the HHP, while the HHP and SHP transport heat to the radiator assembly. The flow regulator controls flow distribution among multiple parallel HPHX's. Test results indicated that the prototype HPHX could transport up to 800 watts with an overall heat transfer coefficient of more than 6000 watts/sq m-deg C. Flow regulation among parallel HPHX's was also demonstrated.

Ku, Jentung↗

NASA NTRS1979

Proceedings of the 25th International Instrumentation Symposium, May 7-10, 1979, Anaheim, California

The papers deal essentially with the instrumentation needs of the transportation industry, machinery diagnostics, and energy research. The sessions covered include: acoustic emission, reentry vehicle ground and flight testing, performance of nose tip materials, instrumentation for solar heating and cooling systems, vibration measurement, data acquisition and analysis, system for aerospace pressure measurements, wind tunnel instrumentation and control, energy source instrumentation, nondestructive testing, pressure and flow measurements, automated test facilities, strain measurements, electrooptical instrumentation, thermal measurements, microcomputer applications in instrumentation and automation, flight testing, blast pressure measurement, two-phase liquid/gas mass flow measurement, and machinery monitoring and instrumentation.

Conferences↗

NASA NTRS1993

Validation of a nonintrusive optical technique for the measurement of liquid mass distribution in a two-phase spray

This work is the continuation of an optical technique development program initiated as part of the 1992 Summer Faculty Fellowship Program. The 1992 work consisted of the formulation and implementation of a technique ivolving the spatial deconvolution of fluorescence data from a uniformly illuminated, seeded densed spray to obtain quantitative measurements of the liquid density profiles. This measurement approach largely overcomes substantial scattering problems associated with other optical approaches for two-phase flows. However, to apply this measurement approach with confidence to unknown flows, the technique must be validated. Consequently, technique validation using classical grid patternator techniques has been focus of the current work. This work has included the design and construction of a patternator rig and the implementation of a test program designed for the comparison of patternator data with the deconvolved optical data. The flow field used for the validation is the plume of an axisymetric swirl coaxial LOX injector being considered for use in the Space Transportation System Main Engine. The flow facility is an improved version of the test rig which was constructed in 1992 for the initial technique development. This report includes a brief description of the optical measurement technique and the patternator rig and a presentation of the data comparisons.

Hartfield, Roy, Jr.↗

NASA NTRS1972

Experimental investigation of two-phase heat transfer in a porous matrix.

One-dimensional two-phase flow transpiration cooling through porous metal is studied experimentally. The experimental data is compared with a previous one-dimensional analysis. Good agreement with calculated temperature distribution is obtained as long as the basic assumptions of the analytical model are satisfied. Deviations from the basic assumptions are caused by nonhomogeneous and oscillating flow conditions. Preliminary derivation of nondimensional parameters which characterize the stable and unstable flow conditions is given. Superheated liquid droplets observed sputtering from the heated surface indicated incomplete evaporation at heat fluxes well in access of the latent energy transport. A parameter is developed to account for the nonequilibrium thermodynamic effects. Measured and calculated pressure drops show contradicting trends which are attributed to capillary forces.

Von Reth, R.↗

NASA NTRS1957

The Effect of Solid Admixtures on the Velocity of Motion of a Free Dusty Air Jet

In dusty air flows occurring in industrial practice in transport by air pressure of friable materials, in the drying, annealing, and so forth, of a pulverized solid mass in suspension, and in other processes, the concentration of solid particles usually has a magnitude of the order of 1 kg per 1 kg of air. At such a concentration, the ratio of the volume of the particles to the volume of the air is small (less than one-thousandth part). However, regardless of this, the presence of a solid admixture manifests itself in the rules for the velocity distribution of the air in a dusty air flow. As a result, the rules of velocity change are different for clean and for dusty air flows. The estimation of the influence of the admixture on the velocity of the motion of the flow presents a definitive interest. One of the attempts to estimate that influence on the axial velocity of a free axially symmetrical jet with admixtures was made by Abramovich. Abramovich assumed beforehand that the fine particles of the admixture in the jet are subject to the motion of the air (that is, that the velocity of the admixture is approximately equal to the local velocity of the air); he then took as the basis of his considerations, in solving the problem, the condition that the amount of motion of the two-phase jet must be constant.

Chernov, A. P.↗

NASA NTRS1962

STABILITY OF FILM BOILING TWO-PHASE FLOW IN CRYOGENIC SYSTEMS

The stability of film boiling two phase flow is investigated referring in particular to saturated cryogenic liquids. This type of fluid motion is unstable, such that a range of wave numbers will always be present in which disturbances are amplified. Further the mode of operation of the energy supply system may favour temperature fluctuations of large amplitude if the circuit does not provide feed-back compensation. The theoretically predicted stabilization due to capillarity is reduced considerably in liquefied gases with low surface tension, such as hydrogen. This effect causes the transition to turbulent flow to occur at low Reynolds numbers, and increases the heat transport in the turbulent regime. A comparison with experimental data, (horizontal cylinder), shows that the "critical" film Reynolds number ūδ/𝜈, at which instabilities become effective, is lowered from approximately 200, (O2), to about 30, (H2). Similar results have been found with other configurations. Therefore application of laminar film boiling solutions is restricted to small objects, entrance regions, or stagnation points. Turbulent correlations given so far are valid only for a certain group of substances with similar behavior.

LIQUID FLOW↗

NASA NTRS1983

A pumped two-phase cooling system for spacecraft

A pumped, two-phase heat-transport system is being developed for possible use for temperature control of scientific instruments on future NASA missions. As compared to a single-phase system, this two-phase system can maintain tighter temperature control with less pumping power. A laboratory model of the system has been built and tested. The measured heat transfer coefficients were approximately the same as in heat pipes, 220 Btu/hr-sq ft-F, as compared to 25 Btu/hr-sq ft-F for single-phase liquid flow. Heat shearing between experiments has been demonstrated wherein vapor generated in the cold plate of an active experiment was condensed in a cold, unheated experiment. System stability has been observed. However, additional development is needed. The use of non-azeotropic mixtures of coolants appears especially promising as a simple way to determine exit quality and thus control the flow rates to prevent dryout.

Ollendorf, S.↗

NASA NTRS1989

The modelling of heat, mass and solute transport in solidification systems

The aim of this paper is to explore the range of possible one-phase models of binary alloy solidification. Starting from a general two-phase description, based on the two-fluid model, three limiting cases are identified which result in one-phase models of binary systems. Each of these models can be readily implemented in standard single phase flow numerical codes. Differences between predictions from these models are examined. In particular, the effects of the models on the predicted macro-segregation patterns are evaluated.

Voller, V. R.↗

NASA NTRS1990

Effect of a crystal-melt interface on Taylor-vortex flow

The linear stability of circular Couette flow between concentric infinite cylinders is considered for the case that the stationary outer cylinder is a crystal-melt interface rather than a rigid surface. A radial temperature difference is maintained across the liquid gap, and equations for heat transport in the crystal and melt phases are included to extend the ordinary formulation of this problem. The stability of this two-phase system depends on the Prandtl number. For small Prandtl number the linear stability of the two-phase system is given by the classical results for a rigid-walled system. For increasing values of the Prandtl number, convective heat transport becomes significant and the system becomes increasingly less stable. Previous results in a narrow-gap approximation are extended to the case of a finite gap, and both axisymmetric and nonaxisymmetric disturbance modes are considered. The two-phase system becomes less stable as the finite gap tends to the narrow-gap limit. The two-phase system is more stable to nonaxisymmetric modes with azimuthal wavenumber n = 1; the stability of these n = 1 modes is sensitive to the latent heat of fusion.

Mcfadden, G. B.↗

NASA NTRS1990

Active thermal control systems for lunar and Martian exploration

Several ATCS options including heat pumps, radiator shading devices, and single-phase flow loops were considered. The ATCS chosen for both lunar and Martian habitats consists of a heat pump integral with a nontoxic fluid acquisition and transport loop, and vertically oriented modular reflux-boiler radiators. The heat pump operates only during the lunar day. The lunar and Martian transfer vehicles have an internal single-phase water-acquisition loop and an external two-phase ammonia rejection system with rotating inflatable radiators. The lunar and Martian excursion vehicles incorporate internal single-phase water acquisition, which is connected via heat exchangers to external body-mounted single-phase radiators. A water evaporation system is used for the transfer vehicles during periods of high heating.

Ewert, Michael K.↗