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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Modeling Heat Flow In a Calorimeter Equipped With a Textured Solar Collector

Heat engines are being considered for generating electric power for minisatellite applications, particularly for those missions in high radiation threat orbits. To achieve this objective, solar energy must be collected and transported to the hot side of the heat engine. A solar collector is needed having the combined properties of high solar absorptance, low infrared emittance, and high thermal conductivity. To test candidate solar collector concepts, a simple calorimeter was designed, manufactured, and installed in a bench top vacuum chamber to measure heat flow. In addition, a finite element analysis model of the collector/calorimeter combination was made to model this heat flow. The model was tuned based on observations from the as-manufactured collector/calorimeter combination. In addition, the model was exercised to examine other collector concepts, properties, and scale up issues.

Jaworske, Donald A.↗
NASA NTRS1985

Heat flow in eastern Egypt - The thermal signature of a continental breakup

It is noted that the Red Sea is a modern example of continental fragmentation and incipient ocean formation. A consistent pattern of high heat flow in the Red Sea margins and coastal zone, including Precambrian terrane up to at least 30 km from the Red Sea, has emerged from the existing data. It is noted that this pattern has important implications for the mode and mechanism of Red Sea opening. High heat flow in the Red Sea shelf requires either a high extension of the crust in this zone (probably with major basic magmatic activity) or young oceanic crust beneath this zone. High heat flow in the coastal thermal anomaly zone may be caused by lateral conduction from the offshore lithosphere and/or from high mantle heat flow. It is suggested that new oceanic crust and highly extended continental crust would be essentially indistinguishable with the available data in the Red Sea margins, and are for many purposes essentially identical.

Morgan, P.↗
NASA NTRS1984

Megaregolith thickness, heat flow, and the bulk composition of the Moon

Models developed to assess the effects of megaregolith on lunar thermal evolution are discussed. It is confirmed that the two sites where lunar heat flow was measured are probably unrepresentative, with heat flows about 25% higher than regional averages, due to focussing of heat flow towards regions with thin megaregolith. Numerous lines of evidence indicate that the megaregolith is generally 2 to 3 km thick under highlands (which cover about 83% of the total lunar surface), and 1 km thick under maria. In most models, megaregolith thickness is assumed to be roughly 6x greater over highlands than over maria. Based on sparse data for porosity among lunar rock types, and the correlation between thermal conductivity and porosity, it is assumed that megaregolith conductivity is roughly 20 kiloerg s(-1)cm(-1)K(-1), and bedrock conductivity is roughly 7x greater. It is also found that insulation by megaregolith exacerbates the problem of reconciling modest temperatures inferred for the (present) matle with a high rate of heat production; an upper limit of 30 ng/g for the bulk-Moon U content can be derived from this constraint alone.

Warren, P. H.↗
NASA NTRS1985

Megaregolith thickness, heat flow, and the bulk composition of the moon

Models developed to assess the effects of megaregolith on lunar thermal evolution are discussed. It is confirmed that the two sites where lunar heat flow was measured are probably unrepresentative, with heat flows about 25 percent higher than regional averages, due to focussing of heat flow towards regions with thin megaregolith. Numerous lines of evidence indicate that the megaregolith is generally 2 to 3 km thick under highlands (which cover about 83 percent of the total lunar surface), and 1 km thick under maria. In most models, megaregolith thickness is assumed to be roughly 6x greater over highlands than over maria. Based on sparse data for porosity among lunar rock types, and the correlation between thermal conductivity and porosity, it is assumed that megaregolith conductivity is roughly 20 kiloerg s(-1)cm(-1)K(-1), and bedrock conductivity is roughly 7x greater. It is also found that insulation by megaregolith exacerbates the problem of reconciling modest temperatures inferred for the (present) mantle with a high rate of heat production; an upper limit of 30 ng/g for the bulk-Moon U content can be derived from this constraint alone.

Rasmussen, K. L.↗
NASA NTRS1993

The effects of orbital and climatic variations on Martian surface heat flow

Large changes in the orbital elements of Mars on timescales of 10(exp 4) to 10(exp 6) years will cause widely varying climate, specifically surface temperatures, as a result of varying insolation. These surface temperature oscillations will produce subsurface thermal gradients which contribute to the total surface heat flux. We investigate the thermal behavior of the Martian regolith on orbital timescales and show that this climatological surface heat flux is spatially variable and contributes significantly to the total surface heat flux at many locations. We model the thermal behavior of the Martian regolith by calculating the mean annual surface temperatures for each epoch (spaced 1000 years apart to resolve orbital variations) for the past 200,000 years at a chosen location on the surface. These temperatures are used as a boundary condition for the deeper regolith and subsurface temperature oscillation are then computed. The surface climatological heat flux due to past climate changes can then be found from the temperature gradient between the surface and about 150 m depth (a fraction of the thermal skin depth on these timescales). This method provides a fairly accurate determination of the climatological heat flow component at a point; however, this method is computationally time consuming and cannot be applied to all points on the globe. To map the spatial variations in the surface heat flow we recognize that the subsurface temperature structure will be largely dominated by the most recent surface temperature oscillations. In fact, the climate component of the surface heat flow will be approximately proportional to the magnitude of the most recent surface temperature change. By calculating surface temperatures at all points globally for the present epoch and an appropriate past epoch, and combining these results with a series of more precise calculations described above, we estimate the global distribution of climatological surface heat flow.

Mellon, Michael T.↗
NASA NTRS1992

A model for the global variation in oceanic depth and heat flow with lithospheric age

Variations in sea-floor depth and heat flow with age provide the main constraints on the thermal structure and evolution of the oceanic lithosphere. Joint fitting of heat flow and bathymetry yields a model with a hotter, thinner lithosphere than in previous models. The new model provides a significantly better fit to the data, including those from older lithosphere previously treated as anomalous. This will facilitate the analysis of lithospheric processes, including the effects of mid-plate volcanism and swells, regional subsidence, and hydrothermal circulation near spreading centers.

Stein, Carol A.↗
NASA NTRS1983

Heat Flow in Horizontal Ribbon Growth

Recent theoretical study reveals some important effects of heat flow in horizontal ribbon growth. Particular attention is paid to heat flow due to laminar convection current in melt induced by horizontal motion of ribbonshaped semiconductor crystal being pulled from melt. Analysis focuses on conditions required for stable growth.

Zontendyk, J. A.↗
NASA NTRS1970

Apollo 13 lunar heat flow experiment

Apollo 13 lunar surface heat flow experiment to measure vertical temperature gradients as function of time and soil thermal conductivity

Chute, J., Jr.↗
NASA NTRS1990

Convective heat flow in space cryogenics plugs - Critical and moderate He II heat flux densities

Plug flow rates of entropy, heat and normal fluid in phase separators and in zero net mass flow systems are, to some extent, quite similar. A simplified analysis of critical conditions is presented in agreement with data trends. A critical temperature gradient arises on the basis of the He II two-fluid model at the stability limit constraining the thermohydrodynamics of the system. Thus, the question of critical thermodynamic fluctuations associated with nucleation versus the possibility of critical gradients in externally imposed parameters is answered in favor of the latter route toward turbulence. Furthermore, a similarity equation is presented which incorporates size dependent rates for moderate heat flow densities observed in experiments.

Yuan, S. W. K.↗
NASA NTRS1976

Modeling studies for a Mars penetrator heat flow measurement

There were, two different design concepts considered for the purpose of measuring heat flow as part of a Mars penetrator mission. The first of the tentative designs utilizes temperature sensors emplaced along the trailing umbilicus at regularly spaced intervals, no greater than 1m, which is thermally coupled to the adjacent regolith radiatively and possibly convectively or conductively. The second of the heat flow designs considered requires the radial deployment of two or more low thermal mass temperature sensors outward from the penetrator body over a vertical (depth) range on the order of 1m.

Keihm, S. J.↗
NASA NTRS1977

Lunar heat-flow experiment

The principal components of the experiment were probes, each with twelve thermometers of exceptional accuracy and stability, that recorded temperature variations at the surface and in the regolith down to 2.5 m. The Apollo 15 experiment and the Apollo 17 probes recorded lunar surface and subsurface temperatures. These data provided a unique and valuable history of the interaction of solar energy with lunar surface and the effects of heat flowing from the deep interior out through the surface of the moon. The interpretation of these data resulted in a clearer definition of the thermal and mechanical properties of the upper two meters of lunar regolith, direct measurements of the gradient in mean temperature due to heat flow from the interior and a determination of the heat flow at the Apollo 15 and Apollo 17 sites.

Langseth, M. G.↗
NASA NTRS1986

Measurement of the thermal conductivity of composites using heat flow sensors

A thermal conductivity measuring apparatus that uses heat flow sensors to measure the heat flux through samples was constructed of inexpensive materials. This device was used to measure the thermal conductivity (k) of two composites used in the space program that consist of fibrous or granular components embedded in a resin matrix. The k-values that were determined ranged from 0.035 to 0.059 Btu/h sq ft-F/ft (-163 to 553 F) and 0.029 to 0.035 Btu/h-sq ft-F/ft (77 to 212 F). Thermal conductivity values of the composites conformed to the rule of mixture. The accuracy of the system was found to be comparable to the guarded hotplate and it requires neither a skilled operator nor extensive maintenance.

Penn, B. G.↗
NASA NTRS1994

Volcanic Eruptions on Io: Heat Flow, Resurfacing, and Lava Composition

In this paper we consider the infrared outbursts on Io reported over the last 15 years and examine the implications for resurfacing rates and heat flow using a recent, well observed, eruption sequence. A large change was observed in Io's infrared emission on January 9, 1990 at several different wavelengths. We model this event as due to a large actively erupting lava flow. The flow increased its area at a rate of 1.5 x 10 5 m 2 s -1 and cooled from 1225 K to 555 K over about 2.6 hours. This event is consistent with other Io infrared outbursts and is used in this paper to estimate the more general characteristics of Ionian volcanism, resurfacing, and heat flow. The inferred eruption rate of 3 x 10 5 m 3 s -1 is very high, but is not unprecedented on the Earth.

Io↗
NASA NTRS1995

The direction of heat flow in an expanding current free stellar atmosphere

The energy budgets of the corona are substantially influenced by losses attributed to thermal conduction losses down the transition region, towards the chromosphere. Although Fourier law for such a plasma regime is now universally criticized as inappropriate, the direction of this heat flow seems to be certain. The purpose of this paper is to point out, based on conservation laws, the direction in which the heat must flow in this regime, provided it is known that there is a time independent expansion devoid of parallel currents. It will be argued that the direction of the heat flux is from the base of the transition region up into the corona, rather than the opposite. Under the circumstances mentioned above, the direction of the heat flow should be opposite to the gradient of the electron pressure gradient. Although the transition region is modeled as isobaric, this is only approximately true. Such a likely scenario makes the heat flow almost certainly to flow from the lower temperature base of the TR up into the incipient corona if a steady state current free expansion is to be maintained.

Scudder, J. D.↗
NASA NTRS1973

Apollo 17 heat flow and convection experiments: Final data analyses results

A group of experiments called the Apollo 17 heat flow and convection (HFC) experiments was conducted, aboard the Apollo 17 spacecraft while in translunar coast on the way to the moon. These experiments together with the HFC experiments flown on Apollo 14 demonstrated and provided data on two types of low-g natural convection: cellular, surface tension-driven convection and convection in confined fluids caused by spacecraft and astronaut movements. Observed convection onset times show that surface tension-driven convection occurs at lower temperature gradients in low-g than in one-g environments. Data on heat flow in confined fluids show that spacecraft and astronaut movements can cause significant degrees of convection.

Bannister, T. C.↗