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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS2019

Thermal Model of a Zero Boil Off System for the Nuclear Thermal Propulsion System

NASA is currently developing an updated concept for a nuclear thermal propulsion (NTP) system. To enable this concept, efficient thermal insulation and cryocooler heat exchanger systems are required to eliminate boil-off of propellant. This paper presents the results of a thermal model used to assess the feasibility of using active cooling with a tube-on-tank heat exchanger configuration for the inline tank of the NTP system. Results show that: cryocooler working fluid temperature and mass flow rate can be adjusted to achieve zero boil off (ZBO) with broad area cooling, over-sizing the cryocooler lift directly translates into a reduction in tank pressure, and broad area cooling may still maintain ZBO despite the reduced heat transfer between tank wall and propellant that is expected in reduced gravity.

zero boil off↗
NASA NTRSDate not supplied

Flow Boiling in Microgap Coolers - Suborbital Flight Results

Flow Boiling in Microgap Coolers (FBMC) is a thermal management technique that provides embedded, on-site heat removal for power dense electronic components and systems. The dielectric coolant undergoes liquid-to-vapor phase change as it passes through channels integrated within or between devices. By facilitating direct contact between the coolant and heat-generating devices and relying on phase change, the system provides tight temperature control, hot spot mitigation, very high heat transfer coefficients, and low pumping power. Ground tests demonstrated removal of high heat fluxes (up to 500 kW/m2), very high coefficients of performance (up to 40 W of heat transferred per W of pumping power), and consistent performance across five evaporator orientations under the appropriate conditions. As a follow-on study and to better assess the role of gravity on such two-phase systems, the FBMC payload was developed and flown twice aboard the Blue Origin New Shepard space vehicle in January and May 2019. Each flight exposed the payload to weightlessness (150 seconds below 0.01 g) and shorter periods of high-g during ascent (up to 3 g) and descent (up to 5 g). The flow boiling performance was consistent independent of the acceleration levels, which provides confidence that such systems will provide consistent performance when tested on the ground, orbiting or traveling through weightlessness, and operating on the surface of the Moon, Mars, and other planetary bodies. Details of the flight results, payload development, flight environment, and planned future testing will be presented.

Flow boiling↗
NASA NTRS2021

Topical: Boiling, Condensation and Two-Phase Flows in Microgravity

The white paper addresses both fundamental and technological questions in the science of phase-change fluid flows aimed at understanding thermal transport in flow boiling and condensation and the use of these processes in space and terrestrial thermal systems. While flow boiling and condensation are widely employed in Earth-based thermal equipment to reduce the cost, size, and power required to transfer heat, a lack of data and predictive models on the impact of gravity on these phenomena hinders the use of two-phase heat transport in a low-gravity environment. The white paper presents research tasks in long-duration microgravity recommended to expand our knowledge on phase-changing flows. Due to elimination of the masking gravity effects, the proposed research will provide a unique opportunity to bring new insights into the role of capillary and hydrodynamic forces in phase-changing flows. The potential impact of the proposed research ranges from the space power, thermal and cryogenic systems to various terrestrial applications in the petrochemical, pharmaceutical, biochemical, nuclear, and metallurgical industries.

Phase-change fluid flow↗
NASA NTRS2021

Experimental Results and Interfacial Lift-off Model Predictions of Critical Heat Flux for Flow Boiling with Subcooled Inlet Conditions – In Preparation for Experiments Onboard the International Space Station

This study investigates critical heat flux (CHF) for subcooled flow boiling of n-Perfluorohexane based on results of pre-launch Earth-gravity Mission Sequence Tests (MSTs) of the Flow Boiling and Condensation Experiment (FBCE), which was launched to the International Space Station (ISS) in August 2021. CHF measurements were made in a rectangular channel having a 2.5 mm by 5 mm cross-section and a 114.6-mm long heated segment. Both single-sided and double-sided heating were tested in vertical upflow in Earth gravity for a variety of inlet conditions. The inlet subcooling was varied in the range of 0.4 – 32.0°C and encompassed both near-saturated and highly subcooled conditions. Experimental trends and high-speed video records were investigated to better understand the mechanism of CHF. Overall trends show CHF increases as flow rate and/or inlet subcooling are increased. Flow features from the events around CHF justify the applicability of the Interfacial Lift-off Model and the determination of limiting criteria for its application. The present experimental data are combined with prior databases for various flow orientations with respect to Earth gravity and microgravity data collected on parabolic flights. Predictions are made using the Interfacial Lift-off Model for this consolidated subcooled-inlet FBCE-CHF database. A heat utility ratio was included in the model to capture the effects of subcooling and corresponding thermodynamic non-equilibrium. An overall mean absolute error of 19.04% indicates good predictive capability of the model for both heating configurations, different gravity environments, and a wide range of inlet subcooling.

flow boiling↗
NASA NTRS2023

NASA Team Develops a Test Article to Demonstrate “Zero Boil-Off” Storage of Liquid Hydrogen via Cryocoolers and a Two-Stage Cooling Approach

Funded by NASA’s Technology Demonstration Mission Program and managed by the Cryogenic Fluid Management Portfolio Project, a NASA team is developing a test article to demonstrate the “zero boil-off” storage of liquid hydrogen using active cooling (cryocoolers) and a two-stage cooling approach. The current state of the art for storage of liquid hydrogen on-orbit is on the order of hours while future missions may require storage for months or even years. To enable such extended storage durations, “near zero” propellant loss, or “zero boil-off”, must be achieved. This may be accomplished with the implementation of “near zero” leakage components, a high performing suite of passive technologies to minimize the environmental heat loads, and active cooling via cryocoolers to intercept and remove heat from the propellant tanks and associated structure. Of course, with any cryogenic vehicle and mission, a mass and power trade should be conducted to determine if it is indeed feasible to carry the additional dry mass associated with active cooling, or if one could simply carry additional propellants to accommodate propellant loss which is typically not an option for a long duration mission.

Hydrogen Storage↗
NASA NTRSDate not supplied

A CFD Framework for Film Boiling and Quenching in Cryogenic Chilldown

Tests of cryogenic chilldown in a vertical stainless steel tube are simulated using computational fluid dynamics (CFD). Subcooled liquid nitrogen enters the room-temperature tube at one end, resulting in film boiling and eventual quenching of the tube walls. A CFD-based modeling framework employing the mixture multiphase model has been developed to simulate this chilldown process and applied to validate it against experimental data. Extensive sensitivity studies have been performed to create a consistent modeling framework, and a two test conditions are simulated to test the modeling capability. The importance of the rewetting temperature and its relation to the foam limit temperature is discussed and is considered in the CFD model. The presented results demonstrate a qualitatively consistent representation of the film boiling and quenching regime. However, the quantitative accuracy of the simulations varies with the test conditions. Simulated vapor volume fraction distributions are also presented, although the current lack of experimental volume fraction data does not permit a comparison.

Computational Fluid Dynamics↗
NASA NTRSDate not supplied

A CFD Framework for Film Boiling and Quenching in Cryogenic Chilldown

Tests of cryogenic chilldown in a vertical stainless-steel tube are simulated using computational fluid dynamics (CFD). Subcooled liquid nitrogen enters a room-temperature tube at one end, resulting in film boiling and eventual quenching of the tube walls. A CFDbased modeling framework employing the mixture multiphase model was developed to simulate this chilldown process and was applied to validate it against experimental data. Extensive sensitivity studies have been performed to create a consistent modeling framework, and a range of test conditions are simulated to assess the modeling capability. The importance of the rewetting temperature and its relation to the foam limit temperature is discussed and considered in the CFD framework. The presented results demonstrate a qualitatively consistent representation of the film boiling and quenching regime. However, the quantitative accuracy of the simulations varies with the test conditions. In addition, simulated distributions of the vapor volume fraction are presented, but the current lack of experimental volume fraction data prevents comparisons.

Computational Fluid Dynamics↗
NASA NTRSDate not supplied

A CFD Framework for Film Boiling and Quenching in Cryogenic Chilldown

Tests of cryogenic chilldown in a vertical stainless-steel tube are simulated using computational fluid dynamics (CFD). Subcooled liquid nitrogen enters a room-temperature tube at one end, resulting in film boiling and eventual quenching of the tube walls. A CFDbased modeling framework employing the mixture multiphase model was developed to simulate this chilldown process and was applied to validate it against experimental data. Extensive sensitivity studies have been performed to create a consistent modeling framework, and a range of test conditions are simulated to assess the modeling capability. The importance of the rewetting temperature and its relation to the foam limit temperature is discussed and considered in the CFD framework. The presented results demonstrate a qualitatively consistent representation of the film boiling and quenching regime. However, the quantitative accuracy of the simulations varies with the test conditions. In addition, simulated distributions of the vapor volume fraction are presented, but the current lack of experimental volume fraction data prevents comparisons.

Computational Fluid Dynamics↗
NASA NTRS2026

Decoupling Surface Topography from Gravitational Acceleration in Cryogenic Pool Boiling

Boiling heat transfer is governed by a complex interplay between surface conditions and gravitational acceleration. To isolate the sole effects of gravity, we investigated the pool boiling characteristics of liquid nitrogen on atomically smooth silicon dioxide (SiO 2 ) surfaces under terrestrial (1-g) and reduced gravity (0±0.02 g) conditions achieved via parabolic flight. Our results quantify a drastic reduction in the critical heat flux (CHF) in reduced gravity, decreasing from 16.15 W/cm 2 at 1-g to 5−6 W/cm 2 at μ-g due to the suppression of buoyancy. Conversely, we observed a distinct increase in the heat transfer coefficient (HTC) in the reduced gravity condition prior to CHF. By utilizing a surface with a maximum peak-to-valley height of ≈36.7 nm and low contact angle hysteresis (<10°), we confirm this HTC enhancement is an intrinsic response to the gravitational environment, decoupled from surface-defect-induced nucleation. These findings demonstrate that the influence of surface topography is significantly more prominent in reduced gravity than in terrestrial conditions, providing a critical baseline for rationalizing the design of cryogenic thermal management systems in space and quantum applications.

Liquid nitrogen↗
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 NTRS1972

Liquid metal boiling inception

An experimental study of the inception of boiling in potassium in forced convection is reported. The boiler consisted of a 0.19-inch inside diameter, niobium-1% zirconium boiler tube approximately six feet long. Heating was accomplished by direct electrical tube wall conduction. Experiments were performed with both all-liquid fill and two-phase fill startup sequences and with a range of flow rates, saturation temperatures, inert gas levels, and fill liquid temperatures. Superheat of the liquid above the equilibrium saturation temperature was observed in all the experiments. Incipient boiling liquid superheat ranged from a few degrees to several hundred. Comparisons of these data with other data and with several analytical treatments are presented.

Sabin, C. M.↗
NASA NTRS1971

The boiling point of stratospheric aerosols.

A photoelectric particle counter was used for the measurement of aerosol boiling points. The operational principle involves raising the temperature of the aerosol by vigorously heating a portion of the intake tube. At or above the boiling point, the particles disintegrate rather quickly, and a noticeable effect on the size distribution and concentration is observed. Stratospheric aerosols appear to have the same volatility as a solution of 75% sulfuric acid. Chemical analysis of the aerosols indicates that there are other substances present, but that the sulfate radical is apparently the major constituent.

Rosen, J. M.↗