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  • 1
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    High-performance heat pipes for heat recovery applications (1980)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Methods to improve the performance of reflux heat pipes for heat recovery applications were examined both analytically and experimentally. Various models for the estimation of reflux heat pipe transport capacity were surveyed in the literature and compared with experimental data. A high transport capacity reflux heat pipe was developed that provides up to a factor of 10 capacity improvement over conventional open tube designs; analytical models were developed for this device and incorporated into a computer program HPIPE. Good agreement of the model predictions with data for R-11 and benzene reflux heat pipes was obtained.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-163816
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Two-phase working fluids for the temperature range of 50 to 350 deg, phase 2 (1980)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Several two phase heat transfer fluids were tested in aluminum and carbon steel reflux capsules for over 25,000 hours at temperatures up to 300 C. Several fluids showed very good stability and would be useful for long duration heat transfer applications over the range 100 to 350 C. Instrumentation for the measurement of surface tension and viscosity were constructed for use with heat transfer fluids over the temperature range 0 to 300 C and with pressures from 0 to 10 atmospheres. The surface tension measuring device constructed requires less than a 1.0 cc sample and displays an accuracy of about 5 percent in preliminary tests, while the viscometer constructed for this program requires a 0.05 cc sample and shows an accuracy of about 5 percent in initial tests.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-159847
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  • 3
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    Two-Phase Working Fluids for the Temperature Range 50 to 350 C (1977)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The decomposition and corrosion of two-phase heat transfer liquids and metal envelopes have been investigated on the basis of molecular bond strengths and chemical thermodynamics. Potentially stable heat transfer fluids for the temperature range 100 C to 350 C have been identified, and reflux heat pipes tests initiated with 10 fluids and carbon steel and aluminum envelopes to experimentally establish corrosion behavior and noncondensable gas generation rates.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-135255
    Format: application/pdf
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  • 4
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    Heat pipe temperature control utilizing a soluble gas absorption reservior (1976)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A new gas-controlled heat pipe design is described which uses a liquid matrix reservior, or sponge, to replace the standard gas reservior. Reservior volume may be reduced by a factor of five to ten for certain gas-liquid combinations, while retaining the same level of temperature control. Experiments with ammonia, butane, and carbon dioxide control gases with methanol working fluid are discussed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-137792
    Format: application/pdf
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  • 5
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    Study of a high performance evaporative heat transfer surface (1977)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: An evaporative surface is described for heat pipes and other two-phase heat transfer applications that consists of a hybrid composition of V-grooves and capillary wicking. Characteristics of the surface include both a high heat transfer coefficient and high heat flux capability relative to conventional open-faced screw thread surfaces. With a groove density of 12.6 cm/1 and ammonia working fluid, heat transfer coefficients in the range of 1 to 2 W/sq cm have been measured along with maximum heat flux densities in excess of 20 W/sq cm. A peak heat transfer coefficient in excess of 2.3 W/sq cm was measured with a 37.8 cm/1 hybrid surface.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-152008
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  • 6
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    Investigation of an inverted meniscus heat pipe wick concept (1975)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A wicking concept is described for efficient evaporation of heat pipe working fluids under diverse conditions. It embodies the high heat transfer coefficient of the circumferential groove while retaining the circumferential fluid transport capability of a thick porous wick or screen. Experimental tests are described which substantiate the efficacy of the evaporation technique for a circumferentially-grooved heat pipe charged alternately with ammonia and R-ll (CCl3F). With ammonia, heat transfer coefficients in the range of 2 to 2.7 W/sq cm K were measured at heat flux densities up to 20 W/sq cm while, with R-ll, a heat transfer coefficient of l.0 W/sq cm K was measured with flux densities up to 5 W/sq cm. Heat transfer coefficients and flux densities were unusually high compared to literature data for other nonboiling evaporative surfaces.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-137724
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  • 7
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    An investigation of condensation heat transfer in a closed tube containing a soluble noncondensable gas (1976)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: An exact one-dimensional condensation heat transfer model for insoluble gases has been developed and compared with experimental data. Modifications to this model to accommodate soluble gas behavior have also been accomplished, and the effects on gas front behavior demonstrated. Analytical models for condensation heat transfer are documented, and a novel optical method used for measuring gas concentration profiles is outlined.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-137811
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  • 8
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    An investigation of condensation heat transfer in a closed tube containing a soluble noncondensable gas (1976)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A more exact one-dimensional condensation heat transfer model for insoluble gases was developed and compared with experimental data. Modifications to this model to accommodate soluble gas behavior were also accomplished, and the effects on gas front behavior demonstrated. Analytical models for condensation heat transfer are documented, and an optical method used for measuring gas concentration profiles is outlined. Experimental data is then presented and interpreted.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-149095
    Format: application/pdf
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  • 9
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    An investigation of heat pipe meniscus heat transfer (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The use of grooved evaporator surfaces in heat pipes has increased in popularity in the past few years primarily due to the reproducibility achievable with grooved walls and the relatively low costs of the threading or extrusion processes involved in their production. The present study combines both analyses and experiments on square groove geometries, with special emphasis on overcoming the limitations of earlier analyses with finite-difference methods and groove-fillet hydrodynamic simplifications. The groove fillet, which has in previous analyses been assumed constant in radius of curvature, is permitted to change in thickness and curvature consistent with hydrodynamics and heat loss from the groove. A model is developed for accurate determination of the effect of constriction resistance on groove performance. The grooved-surface tests to be conducted are briefly described which will provide data under closely controlled operation to allow comparison and verification of the analyses.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 78-405 , International Heat Pipe Conference; May 22, 1978 - May 24, 1978; Palo Alto, CA
    Format: text
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    NASA TECHNICAL REPORTS
  • 10
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    Arterial gas occlusions in operating heat pipes (1975)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The effect of noncondensable gases on high performance arterial heat pipes has been investigated both analytically and experimentally. Models have been generated which characterize the dissolution of gases in condensate and the diffusional loss of dissolved gases from condensate in arterial flow. These processes, and others, have been used to postulate stability criteria for arterial heat pipes. Experimental observations of gas occlusions were made using a stainless steel heat pipe equipped with viewing ports, and the working fluids methanol and ammonia with the gas additives helium, argon, and xenon. Observations were related to gas transport models.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 75-657 , American Institute of Aeronautics and Astronautics, Thermophysics Conference; May 27, 1975 - May 29, 1975; Denver, CO
    Format: text
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