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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2022

GBaTSv2: a revised synthesis of the likely basal thermal state of the Greenland Ice Sheet

The basal thermal state (frozen or thawed) of the Greenland Ice Sheet is under-constrained due to few direct measurements, yet knowledge of this state is becoming increasingly important to interpret modern changes in ice flow. The first synthesis of this state relied on inferences from widespread airborne and satellite observations and numerical models, for which most of the underlying datasets have since been updated. Further, new and independent constraints on the basal thermal state have been developed from analysis of basal and englacial reflections observed by airborne radar sounding. Here we synthesize constraints on the Greenland Ice Sheet's basal thermal state from boreholes, thermomechanical ice-flow models that participated in the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6; Coupled Model Intercomparison Project Phase 6), IceBridge BedMachine Greenland v4 bed topography, Making Earth Science Data Records for Use in Research Environments (MEaSUREs) Multi-Year Greenland Ice Sheet Velocity Mosaic v1 and multiple inferences of a thawed bed from airborne radar sounding. Most constraints can only identify where the bed is likely thawed rather than where it is frozen. This revised synthesis of the Greenland likely Basal Thermal State version 2 (GBaTSv2) indicates that 33 % of the ice sheet's bed is likely thawed, 40 % is likely frozen and the remainder (28 %) is too uncertain to specify. The spatial pattern of GBaTSv2 is broadly similar to the previous synthesis, including a scalloped frozen core and thawed outlet-glacier systems. Although the likely basal thermal state of nearly half (46 %) of the ice sheet changed designation, the assigned state changed from likely frozen to likely thawed (or vice versa) for less than 6 % of the ice sheet. This revised synthesis suggests that more of northern Greenland is likely thawed at its bed and conversely that more of southern Greenland is likely frozen, both of which influence interpretation of the ice sheet's present subglacial hydrology and models of its future evolution. The GBaTSv2 dataset, including both code that performed the analysis and the resulting datasets, is freely available at https://doi.org/10.5281/zenodo.6759384 (MacGregor, 2022).

Joseph A. MacGregor↗
NASA NTRS1972

The present thermal state of the terrestrial planets

The thermal state of bodies is discussed as an aspect of their internal dynamics for bodies of roughly meteoritic composition in the range of sizes of planetary objects. The rheological behaviour of planetary material is assumed to be represented by a Newtonian viscosity varying exponentially with temperature, and only the consistency of this assumption with the elastic view of the planets is considered. It is shown that for the whole range of physically plausible values of the material parameters, the temperature distribution associated with a solution to the problem of internal dynamics for bodies with external radii larger than about 800 km departs significantly from that predicted on conduction theory arguments. For bodies in the range of sizes of the terrestrial planets, the viscosity-temperature relationship plays a dominant role in setting the absolute temperature of the central regions.

Tozer, D. C.↗
NASA NTRSDate not supplied

Electric Aircraft Thermal Management Using a Two-Phase Heat Transport System with Solid-State Thermal Switching Capability

Advanced Cooling Technologies, Inc. (ACT) is collaborating with NASA Glenn Research Center (GRC) to develop a heat pipe-based thermal delivery system to efficiently manage the waste heat generated onboard an electric aircraft. The heat pipe system will interface with NASA GRC’s thermoacoustic heat pump in order to recycle waste heat by transporting thermal energy to various end users onboard the aircraft. This paper discusses the layout of theoretical heat pipe networks for a MW-class commercial electric aircraft. This is followed by a discussion of progress made on the development of a novel two-phase heat transport system with solid-state thermal switching and control capabilities.

Exergy↗
NASA NTRS1980

Effect of production microclimate on female thermal state with increased temperature and air humidity

The thermal state of women during the effect of high air temperature and relative humidity with a varying degree of physical loads was studied. Parameters for air temperature, relative humidity, and air movement were established. It was established that in women the thermo-regulatory stress occurs at lower air temperatures and with lower physical loads than in men. The accumulation of heat in women was revealed with lower air temperature than in men. It is concluded that to preserve the normal physiological state of the female organism it is necessary to create more favorable microclimate conditions and decrease the physical loads.

Machablishvili, O. G.↗
NASA NTRS1984

The initial thermal state of the Moon

It is argued that the initial thermal state of the Moon was molten. The existence of young thrust fault scarps in the highlands and kbar stress drop, shallow moonquakes both suggest that the thermoelastic stresses in the outer crust are currently in the kbar range. This is expected if the Moon was initially molten, but not if the Moon had a magma ocean only a few hundred km deep. The thesis is also supported by reference to model studies of the concentrations of refractory incompatible elements.

Binder, A. B.↗
NASA NTRS2001

Observation of Sea Ice Surface Thermal States Under Cloud Cover

Clouds interfere with the distribution of short-wave and long-wave radiations over sea ice, and thereby strongly affect the surface energy balance in polar regions. To evaluate the overall effects of clouds on climatic feedback processes in the atmosphere-ice-ocean system, the challenge is to observe sea ice surface thermal states under both clear sky and cloudy conditions. From laboratory experiments, we show that C-band radar (transparent to clouds) backscatter is very sensitive to the surface temperature of first-year sea ice. The effect of sea ice surface temperature on the magnitude of backscatter change depends on the thermal regimes of sea ice thermodynamic states. For the temperature range above the mirabilite (Na2SO4.10H20) crystallization point (-8.2 C), C-band data show sea ice backscatter changes by 8-10 dB for incident angles from 20 to 35 deg at both horizontal and vertical polarizations. For temperatures below the mirabilite point but above the crystallization point of MgCl2.8H2O (-18.0 C), relatively strong backwater changes between 4-6 dB are observed. These backscatter changes correspond to approximately 8 C change in temperature for both cases. The backscattering mechanism is related to the temperature which determines the thermodynamic distribution of brine volume in the sea ice surface layer. The backscatter is positively correlated to temperature and the process is reversible with thermodynamic variations such as diurnal insolation effects. From two different dates in May 1993 with clear and overcast conditions determined by the Advanced Very High Resolution Radiometer (AVHRR), concurrent Earth Resources Satellite 1 (ERS-1) C-band ice observed with increases in backscatter over first-year sea ice, and verified by increases in in-situ sea ice surface temperatures measured at the Collaborative-Interdisciplinary Cryosphere Experiment (C-ICE) site.

Nghiem, S. V.↗
NASA NTRS1972

Origin, evolution and present thermal state of the moon

The relative absence of lunar volcanism in the last 3 b.y. and the Apollo 15 heat flow measurement suggest that present-day temperatures in the moon are approximately steady state to depths of 100 km. An exponential distribution of heat sources with depth is scaled by equating the surface heat flow to the integrated heat production of this exterior shell. Presumed present-day interior temperatures and the present-day surface heat flow of 30 ergs/cm2-sec are obtained. The estimated homogeneous concentrations of U, the chemistry of the lunar surface material and inferences to modest depth, and the short accretion time of the moon necessary to provide large-scale differentiation at 4.6 AE suggest that the moon had its origin in the rapid accretion of compounds first condensing from the protoplanetary nebula. The present thermal state of the moon may involve at least some partial melting through all the lunar interior deeper than 200 km. Such a thermal configuration is inconsistent neither with temperatures inferred from electrical conductivity studies nor with the nonhydrostatic shape of the moon.

Hanks, T. C.↗
NASA NTRS2016

A Synthesis of the Basal Thermal State of the Greenland Ice Sheet

Greenland's thick ice sheet insulates the bedrock below from the cold temperatures at the surface, so the bottom of the ice is often tens of degrees warmer than at the top, because the ice bottom is slowly warmed by heat coming from the Earth's depths. Knowing whether Greenland's ice lies on wet, slippery ground or is anchored to dry, frozen bedrock is essential for predicting how this ice will flow in the future. But scientists have very few direct observations of the thermal conditions beneath the ice sheet, obtained through fewer than two dozen boreholes that have reached the bottom. Our study synthesizes several independent methods to infer the Greenland Ice Sheet's basal thermal state -whether the bottom of the ice is melted or not-leading to the first map that identifies frozen and thawed areas across the whole ice sheet. This map will guide targets for future investigations of the Greenland Ice Sheet toward the most vulnerable and poorly understood regions, ultimately improving our understanding of its dynamics and contribution to future sea-level rise. It is of particular relevance to ongoing Operation IceBridge activities and future large-scale airborne missions over Greenland.

IceBridge↗
NASA NTRS1979

Convection, composition, and the thermal state of the lower mantle

A thermal model for the lower mantle is presented, which is constructed from the petrologically derived estimates of the temperature in the transition zone and from an adiabat based on the thermal properties of MgO and SiO2 measured at high pressures. Superadiabatic contributions to the geotherm through the lower mantle are negligibly small. A thermal boundary layer is required at the base of the mantle in order to satisfy an estimate of the lowest possible temperature in the core. It is suggested that a thermal boundary layer is associated with a chemical discontinuity either at the top of the lower mantle or near its base.

Jeanloz, R.↗
NASA NTRS1975

Solid state thermal control for spacecraft

The steady-state heat-pumping capabilities of thermoelectric devices are examined for spacecraft in earth orbit, using a simple model. Thermoelectric parameters for a standard Bi2Te, alloy are fitted with fourth-order polynomials in temperature. Parameters are used which are the average for the temperature difference across the p-n couple. Internal spacecraft temperatures are varied from 270 to 330 K, and absorbed incident radiation fluxes are varied from zero to 700 W per sq m. It is found that heat rejection can be optimized with respect to thermoelectric device and radiator fin geometries, as well as with respect to input electrical power and that these devices are most useful on the surfaces with highest incident radiant power. Maximum heat fluxes which can be pumped out of the spacecraft are on the order of 50-160 W per sq m for the various thermal environments examined. Input electrical powers corresponding to these maximum heat fluxes range from about 50-300 W per sq m. However, efficiency is greatly improved by operation at lower input-power levels.

Harpster, J. W. C.↗
NASA NTRS1974

Steady state thermal radiometers

A radiometer is described operating in a vacuum under steady state conditions. The front element is an aluminum sheet painted on the outer side with black or other absorptive material of selected characteristics. A thermocouple is bonded to the inner side of the aluminum sheet. That is backed by highly insulative layers of glass fiber and crinkled, aluminized Mylar polyester. Those layers are backed with a sturdy, polyester sheet, and the entire lamination is laced together by nylon cords. The device is highly reliable in that it does not drift out of calibration, and is significantly inexpensive.

Loose, J. D.↗