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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

Miniature Loop Heat Pipe with Multiple Evaporators for Thermal Control of Small Spacecraft

This paper presents an advanced miniature heat transport system for thermal control of small spacecraft. The thermal system consists of a loop heat pipe (LHP) with multiple evaporators and multiple deployable radiators for heat transfer, and variable emittance coatings on the radiators for performance enhancement. Thermoelectric coolers are used to control the loop operating temperature. The thermal system combines the functions of variable conductance heat pipes, thermal switches, thermal diodes, and the state-of-the-art LHPs into a single integrated thermal system. It retains all the performance characteristics of state-of-the-art LHPs and offers additional advantages to enhance the functionality, performance, versatility, and reliability of the system. Steady state and transient analytical models have been developed, and scaling criteria have also been established. A breadboard unit has been built for functional testing in laboratory and thermal vacuum environments. Experimental results show excellent performance of the thermal system and correlate very well with theoretical predictions.

Ku, Jentung↗
NASA NTRS1997

On The Validity of the Assumed PDF Method for Modeling Binary Mixing/Reaction of Evaporated Vapor in GAS/Liquid-Droplet Turbulent Shear Flow

An Investigation of the statistical description of binary mixing and/or reaction between a carrier gas and an evaporated vapor species in two-phase gas-liquid turbulent flows is perfomed through both theroetical analysis and comparisons with results from direct numerical simulations (DNS) of a two-phase mixing layer.

Vapor Binary Mixing Turbulent flows↗
NASA NTRS2004

Large Eddy Simulation of jets laden with evaporating drops

LES of a circular jet laden with evaporating liquid drops are conducted to assess computational-drop modeling and three different SGS-flux models: the Scale Similarity model (SSC), using a constant coefficient calibrated on a temporal mixing layer DNS database, and dynamic-coefficient Gradient and Smagorinsky models.

drop laden jets sprays↗
NASA NTRS2006

A New Finite-Conductivity Droplet Evaporation Model Including Liquid Turbulence Effect

A new approach to account for finite thermal conductivity and turbulence effects within atomizing droplets of an evaporating spray is presented in this paper. The model is an extension of the T-blob and T-TAB atomization/spray model of Trinh and Chen [9]. This finite conductivity model is based on the two-temperature film theory in which the turbulence characteristics of the droplet are used to estimate the effective thermal diffusivity for the liquid-side film thickness. Both one-way and two-way coupled calculations were performed to investigate the performance cf this model against the published experimental data.

Balasubramanyam, M. S.↗
NASA NTRS2008

Thermal Vacuum Testing of a Multi-Evaporator Miniature Loop Heat Pipe

Under NASA's New Millennium Program Space Technology 8 Project, four experiments are being developed for future small system applications requiring low mass, low power, and compactness. GSFC is responsible for developing the Thermal Loop experiment, which is an advanced thermal control system consisting of a miniature loop heat pipe (MLHP) with multiple evaporators and condensers. The objective is to validate the operation of an MLHP, including reliable start-ups, steady operation, heat load sharing, and tight temperature control over the range of 273K to 308K. An MLHP Breadboard has been built and tested for 1200 hours under the laboratory environment and 500 hours in a thermal vacuum chamber. Results of the TV tests are presented here.

Ku, Jentung↗
NASA NTRS2008

Multi-Evaporator Miniature Loop Heat Pipe for Small Spacecraft Thermal Control

This paper presents the development of the Thermal Loop experiment under NASA's New Millennium Program Space Technology 8 (ST8) Project. The Thermal Loop experiment was originally planned for validating in space an advanced heat transport system consisting of a miniature loop heat pipe (MLHP) with multiple evaporators and multiple condensers. Details of the thermal loop concept, technical advances and benefits, Level 1 requirements and the technology validation approach are described. An MLHP breadboard has been built and tested in the laboratory and thermal vacuum environments, and has demonstrated excellent performance that met or exceeded the design requirements. The MLHP retains all features of state-of-the-art loop heat pipes and offers additional advantages to enhance the functionality, performance, versatility, and reliability of the system. In addition, an analytical model has been developed to simulate the steady state and transient operation of the MHLP, and the model predictions agreed very well with experimental results. A protoflight MLHP has been built and is being tested in a thermal vacuum chamber to validate its performance and technical readiness for a flight experiment.

Ku, Jentung↗
NASA NTRS2007

Construction of a Penrose Diagram for a Spatially Coherent Evaporating Black Hole

A Penrose diagram is constructed for an example black hole that evaporates at a steady rate as measured by a distant observer, until the mass vanishes, yielding a final state Minkowski space-time. Coordinate dependencies of significant features, such as the horizon and coordinate anomalies, are clearly demonstrated on the diagram. The large-scale causal structure of the space-time is briefly discussed.

Brown, Beth A.↗
NASA NTRS2007

Evaporation-Cooled Protective Suits for Firefighters

Suits cooled by evaporation of water have been proposed as improved means of temporary protection against high temperatures near fires. When air temperature exceeds 600 F (316 C) or in the presence of radiative heating from nearby sources at temperatures of 1,200 F (649 C) or more, outer suits now used by firefighters afford protection for only a few seconds. The proposed suits would exploit the high latent heat of vaporization of water to satisfy a need to protect against higher air temperatures and against radiant heating for significantly longer times. These suits would be fabricated and operated in conjunction with breathing and cooling systems like those with which firefighting suits are now equipped

Weinstein, Leonard Murray↗
NASA NTRS2010

Hollow Fiber Spacesuit Water Membrane Evaporator Development and Testing for Advanced Spacesuits

The spacesuit water membrane evaporator (SWME) is being developed to perform the thermal control function for advanced spacesuits to take advantage of recent advances in micropore membrane technology in providing a robust heat-rejection device that is potentially less sensitive to contamination than is the sublimator. Principles of a sheet membrane SWME design were demonstrated using a prototypic test article that was tested in a vacuum chamber at JSC in July 1999. The Membrana Celgard X50-215 microporous hollow fiber (HoFi) membrane was selected after recent contamination tests as the most suitable candidate among commercial alternatives for HoFi SWME prototype development. A design that grouped the fiber layers into stacks, which were separated by small spaces and packaged into a cylindrical shape, was developed into a full-scale prototype consisting 14,300 tube bundled into 30 stacks, each of which are formed into a chevron shape and separated by spacers and organized into three sectors of ten nested stacks. Vacuum chamber testing has been performed characterize heat rejection as a function of inlet water temperature and water vapor backpressure and to show contamination resistance to the constituents expected to be found in potable water produced by the distillation processes. Other tests showed the tolerance to freezing and suitability to reject heat in a Mars pressure environment.

Bue, Grant C.↗
NASA NTRS2010

Hollow Fiber Ground Evaporator Unit Testing

A candidate technology for 1-atmosphere suited heat rejection was developed and tested at NASA Johnson Space Center. The concept is to use a collection of microporous hydrophobic tubes potted between inlet and outlet headers with water as coolant. A pump provides flow between headers through the tubes which are subjected to fan driven cross flow of relatively dry air. The forced ventilation would sweep out the water vapor from the evaporation of the coolant rejecting heat from the coolant stream. The hollow fibers are obtained commercially (X50-215 Celgard) which are arranged in a sheet containing 5 fibers per linear inch. Two engineering development units were produced that vary the fold direction of the fiber sheets relative to the ventilation. These units were tested at inlet water temperatures ranging from 20 deg C to 30 deg C, coolant flow rates ranging from 10 to 90 kg/hr, and at three fan speeds. These results were used to size a system that could reject heat at a rate of 340 W.

Bue, Grant↗
NASA NTRS2010

Multi-Evaporator Miniature Loop Heat Pipe for Small Spacecraft Thermal Control: Validation Results - Part 2

Under NASA s New Millennium Program Space Technology 8 (ST 8) Project, Goddard Space Fight Center has conducted a Thermal Loop experiment to advance the maturity of the Thermal Loop technology from proof of concept to prototype demonstration in a relevant environment , i.e. from a technology readiness level (TRL) of 3 to a level of 6. The thermal Loop is an advanced thermal control system consisting of a miniature loop heat pipe (MLHP) with multiple evaporators and multiple condensers designed for future small system applications requiring low mass, low power, and compactness. The MLHP retains all features of state-of-the-art loop heat pipes (LHPs) and offers additional advantages to enhance the functionality, performance, versatility, and reliability of the system. An MLHP breadboard was built and tested in the laboratory and thermal vacuum environments for the TRL 4 and TRL 5 validations, respectively, and an MLHP proto-flight unit was built and tested in a thermal vacuum chamber for the TRL 6 validation. In addition, an analytical model was developed to simulate the steady state and transient behaviors of the MLHP during various validation tests. The MLHP demonstrated excellent performance during experimental tests and the analytical model predictions agreed very well with experimental data. All success criteria at various TRLs were met. Hence, the Thermal Loop technology has reached a TRL of 6. This paper presents the validation results, both experimental and analytical, of such a technology development effort.

Ku, Jentung↗