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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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Stationary Testing of a Pulse Tube Cryocooler Designed to Rotate at 6800 RPM with the Superconducting Rotor of an Electric Machine

Electrified aircraft are being developed to increase the efficiency and reduce the cost of operating subsonic transport aircraft. Achieving a substantial impact necessitates focusing on single- and twin-aisle aircraft which use propulsion systems with >20 MW ratings. For these aircraft, multi-MW superconducting electric machines are being developed due to their high specific power and high efficiency. Most of these electric machines employ superconductors on their rotor, thereby requiring cryogenic cooling of the rotating system. An attractive solution is to conductively cool the rotor using a cryocooler that rotates with the rotor. NASA has been developing a 50 K pulse tube cryocooler for its High Efficiency Megawatt Motor (HEMM) that can operate while rotating at up to 6,800 rpm. The first non-rotating tests of the fully assembled HEMM cryocooler have been completed, and initial testing has yielded a no-load temperature of 112 K. A small helium leak into the vacuum system has been identified as the major bottleneck to performance, and based on measurements with the motor turned off there is an observed vacuum-side heat leak of approximately 30 W at 115 K. Immediate next steps for testing are to locate and mitigate the apparent helium leaks into the vacuum chamber. Thus far, compressor performance and the apparent heat lift after correcting for the heat leak are on par with expectations.

Electrified Aircraft Propulsion↗

NASA NTRS1978

The thermal phase of a large solar flare

EUV and X-ray observations are used to derive the differential emission measures, temperatures, densities, radiative and conductive cooling rates, and thermal energy content of a class 2B flare that occurred on September 7, 1973. The results of the analysis indicate that (1) most of the flare plasma was at temperatures between 3 and 10 million degrees; (2) the peak temperature decreased with time from about 8 million K to 5 million K over a period of 3.5 hours; (3) the differential emission measure steadily decreased with time at nearly all temperatures; (4) both radiation and conduction were important cooling mechanisms for the plasma at temperatures above 100,000 K; and (5) a substantial amount of energy, of the order of 3 x 10 to the 31st power ergs, was deposited in the flare loops after flare maximum. The empirically determined flare parameters are compared with similar parameters derived from a simple theoretical loop model.

Withbroe, G. L.↗

NASA NTRS1992

Isolation of major Venus thermospheric cooling mechanism and implications for earth and Mars

The additional cooling mechanism responsible for the unexpectedly cold dayside Venus thermosphere is isolated. Consideration is given not only to the condition that the calculated temperatures must be reduced to the observed dayside temperatures but also that the theoretical temperature variations must be in accord with the observed low amplitude of temperature variations associated with the 27-d variations of the sun. It is found that the low amplitude of the 27-d oscillations, combined with the cooling necessary for observed 300-K dayside temperatures, cannot be explained by eddy conduction cooling and can only be explained by very strong 15-micron cooling. Implications of the decrease in amplitude of the 11-yr Venus thermospheric variability due to the 15-micron thermostat effect are examined.

Keating, Gerald M.↗

NASA NTRS1988

The structure of shocks with thermal conduction and radiative cooling

A general analysis is presented of the structure of a steady state, plane-parallel shock wave in which both thermal conduction and radiative cooling are important. The fluid is assumed to have a perfect-gas equation of state, with radiative cooling a function only of its temperature and density. Conduction in both diffusive and saturated regimes is treated. For the case of a strong shock, with conductivity and cooling function varying as power laws in temperature, approximate analytic solutions describing the shock wave are derived. For a plasma of solar composition, conduction is found to have a significant effect on the shock temperature and overall thickness of the postshock layer only for shock velocities greater than about 30,000 km/s, corresponding to shock temperatures greater than about 10 to the 10th K, but it affects the local structure of parts of the shock wave at much lower velocities. The effects of conduction are greatly enhanced if the heavy-element abundance is increased.

Lacey, Cedric G.↗

NASA NTRS2004

Droplet-surface Impingement Dynamics for Intelligent Spray Design

VanderWal, Randy L.↗

NASA NTRS2004

Droplet-Surface Impingement Dynamics for Intelligent Spray Design

Spray cooling has high potential in thermal management and life support systems by overcoming the deleterious effect of microgravity upon two-phase heat transfer. In particular spray cooling offers several advantages in heat flux removal that include the following: 1) By maintaining a wetted surface, spray droplets impinge upon a thin fluid film rather than a dry solid surface; 2. Most heat transfer surfaces will not be smooth but rough. Roughness can enhance conductive cooling, aid liquid removal by flow channeling; and 3. Spray momentum can be used to a) substitute for gravity delivering fluid to the surface, b) prevent local dryout and potential thermal runaway and c) facilitate liquid and vapor removal. Yet high momentum results in high We and Re numbers characterizing the individual spray droplets. Beyond an impingement threshold, droplets splash rather than spread. Heat flux declines and spray cooling efficiency can markedly decrease. Accordingly we are investigating droplet impingement upon a) dry solid surfaces, b) fluid films, c) rough surfaces and determining splashing thresholds and relationships for both dry surfaces and those covered by fluid films. We are presently developing engineering correlations delineating the boundary between splashing and non-splashing regions. Determining the splash/non-splash boundary is important for many practical applications. Coating and cooling processes would each benefit from near-term empirical relations and subsequent models. Such demonstrations can guide theoretical development by providing definitive testing of its predictive capabilities. Thus, empirical relations describing the boundary between splash and non-splash are given for drops impinging upon a dry solid surface and upon a thin fluid film covering a similar surface. Analytical simplification of the power laws describing the boundary between the splash and non-splash regions yields insight into the engineering parameters governing the splash and non-splash outcomes of the fluid droplets. The power law correlation is shown separating the splashing versus non-splashing regions as developed for droplets impinging upon a dry solid surface. Splashing upon a dry surface is reasonably described by Ca greater than 0.85, reflecting the competing roles of surface tension and viscosity. The power law correlation is shown separating the splashing versus non-splashing regions as developed for droplets impinging upon a thin fluid film covering the solid surface. Splashing upon a thin fluid film, as described by v (pd/s) greater than 63, is governed by fluid density and surface tension, but is rather independent of viscosity. Finally, the data presented here suggests that a more direct dependence upon the surface tension and viscosity, given a better understanding of their interplay, would allow accurate description of the droplet-surface impacts for more complicated situations involving non-Newtonian fluids, specifically those exhibiting viscoelastic behavior.

Wal, Randy L. Vander↗

NASA NTRS1992

Chemical differentiation of a convecting planetary interior: Consequences for a one-plate planet such as Venus

Chemically depleted mantle forming a buoyant, refractory layer at the top of the mantle can have important implications for the evolution of the interior and surface. On Venus, the large apparent depths of compensation for surface topographic features might be explained if surface topography were supported by variations in the thickness of a 100-200 km thick chemically buoyant mantle layer or by partial melting in the mantle at the base of such a layer. Long volcanic flows seen on the surface may be explained by deep melting that generates low-viscosity MgO-rich magmas. The presence of a shallow refractory mantle layer may also explain the lack of volcanism associated with rifting. As the depleted layer thickens and cools, it becomes denser than the convecting interior and the portion of it that is hot enough to flow can mix with the convecting mantle. Time dependence of the thickness of a depleted layer may create episodic resurfacing events as needed to explain the observed distribution of impact craters on the venusian surface. We consider a planetary structure consisting of a crust, depleted mantle layer, and a thermally and chemically well-mixed convecting mantle. The thermal evolution of the convecting spherical planetary interior is calculated using energy conservation: the time rate of change of thermal energy in the interior is equated to the difference in the rate of radioactive heat production and the rate of heat transfer across the thermal boundary layer. Heat transfer across the thermal boundary layer is parameterized using a standard Nusselt number-Rayleigh number relationship. The radioactive heat production decreases with time corresponding to decay times for the U, Th, and K. The planetary interior cools by the advection of hot mantle at temperature T interior into the thermal boundary layer where it cools conductively. The crust and depleted mantle layers do not convect in our model so that a linear conductive equilibrium temperature distribution is assumed. The rate of melt production is calculated as the product of the volume flux of mantle into the thermal boundary layer and the degree of melting that this mantle undergoes. The volume flux of mantle into the thermal boundary layer is simply the heat flux divided by amount of heat lost in cooling mantle to the average temperature in the thermal boundary layer. The degree of melting is calculated as the temperature difference above the solidus, divided by the latent heat of melting. A maximum degree of melting is prescribed corresponding to the maximum amount of basaltic melt that the mantle can initially generate. As the crust thickens, the pressure at the base of the crust becomes high enough and the temperature remains low enough for basalt to transform to dense eclogite.

Parmentier, E. M.↗

NASA NTRS1985

Spatial and temporal variations of solar coronal loops

Skylab EUV observations of an active region near the solar limb with both hot and cool loops present were analyzed. The observed intensity variations for hot loops were small, typically a few percent over a period of 30 min. The cool loops exhibited stronger variations, sometimes appearing and disappearing in 5 to 10 min. Most of the cool material observed in the loops appeared to be caused by the downward flow of coronal rain and by the upward ejection of chromospheric material in surges. The frequent EUV brightenings observed near the loop footpoints appear to have been produced by both in situ transient energy releases and the infall/impact of coronal rain. The mean energy input required to balance the radiative and conductive cooling of the hot loops is approximately 0.003 erg/cu cm/s.

Habbal, S. R.↗

NASA NTRS2004

Qualification of Laser Diode Arrays for Mercury Laser Altimeter Mission

NASA's requirements for high reliability, high performance satellite laser instruments have driven the investigation of many critical components; specifically, 808 nm laser diode array (LDA) pump devices. The MESSENGER mission is flying the Mercury Laser Altimeter (MLA) which is a diode-pumped Nd:YAG laser instrument designed to map the topography of Mercury. The environment imposed on the instrument by the orbital dynamics places special requirements on the laser diode arrays. In order to limit the radiative heating of the satellite from the surface of Mercury, the satellite is designed to have a highly elliptical orbit. The satellite will heat near perigee and cool near apogee. The laser power is cycled during these orbits so that the laser is on for only 30 minutes (perigee) in a 12 hour orbit. The laser heats 10 C while powered up and cools while powered down. In order to simulate these operational conditions, we designed a test to measure the LDA performance while being temperature and power cycled. Though the mission requirements are specific to NASA and performance requirements are derived from unique operating conditions, the results are general and widely applicable. We present results on the performance of twelve LDAs operating for several hundred million pulses. The arrays are 100 watt, quasi-CW, conductively-cooled, 808 nm devices. Prior to testing, we fully characterize each device to establish a baseline for individual array performance and status. Details of this characterization can be found in reference. Arrays are divided into four groups and subjected to the temperature and power cycling matrix are shown.

Stephen, Mark↗

NASA NTRS1979

The evolution of soft X-ray-emitting flare loops

We have constructed a numerical model for a cooling flare loop in which the complete set of single-fluid equations in a one-dimensional geometry (i.e., parallel to the magnetic field) is solved. Both evaporative and static boundary conditions for the chromosphere-corona interface have been developed. This model is used to investigate the effects of initial temperature and density, loop geometry, and boundary conditions on the form of the plasma evolution and the soft X-ray emission. The results are then compared with Skylab S-056 observations of the 1973 August 9 flare. For this comparison, and under the present assumptions, we conclude that even highly compact flares must have a multiloop structure similar to large flares, and that both radiative and conductive cooling are necessary to explain the observations. The data appear to be consistent with the predicted emission from a combination of evaporative cooling loops.

Antiochos, S. K.↗

NASA NTRS1975

Electrochemical oxygen concentrator as an oxygen compressor

A solid polymer electrolyte (SPE) oxygen compressor is described which generates pressures of 3000 psi. The SPE is a cation exchange membrane with chemical compatibility, and has the capability of withstanding 5000 psi. Other features of the compressor described include: gasketless sealing, porus plate cell supports, and conductive cooling. Results are presented of a computer program which defines the power of the system as a function of density, temperature, pressure, membrane thickness, and water content.

Source record↗

NASA NTRS1979

Description of a 2.3 kW power transformer for space applications

The principle features and special testing of a high voltage high power transformer designed and developed for space application are described. The transformer is operated in a series resonant inverter supplying beam power to a 30 cm mercury ion thruster. Electrical requirements include operation of 2.3 kW continuous power output, primary currents to 35 amps rms, and frequencies up to 20 kHz. High efficiency was obtained through detailed considerations of the tradeoffs available in core materials, wire selection, coil configurations and thermal control. A number of novel heat removal techniques are discussed which control the winding temperature using only the available conductive cooling.

Hansen, I.↗

NASA NTRS1979

Description of A 2.3 kW power transformer for space applications

The paper describes the principal features and special testing of a high-frequency high-power low-specific-weight (0.57 kg/kW) 2.3-kW electronic power transformer developed for space applications. The transformer is operated in a series resonant inverter supplying beam power to a 30-cm mercury ion thruster. High efficiency (above 98.5%) is obtained through careful detailed design. A number of unique heat removal techniques are discussed which control the winding temperature using only the available conductive cooling.

Hansen, I.↗

NASA NTRS1980

Some experience with arc-heater simulation of outer planet entry radiation

An electric arc heater was operated at 800 amperes and 100,000 pa (1 atm) with hydrogen, helium, and two mixtures of hydrogen and helium. A VUV-scanning monochromator was used to record the spectra from an end view while a second spectrometer was used to determine the plasma temperature using hydrogen continuum radiation at 562 nm. Except for pure helium, the plasma temperature was found to be too low to produce significant helium radiation, and the measured spectra were primarily the hydrogen spectra with the highest intensity in the pure hydrogen case. A radiation computer code was used to compute the spectra for comparison to the measurements and to extend the study to simulation of outer planet entry radiation. Conductive cooling prevented ablation of phenolic carbon material samples mounted inside the arc heater during a cursory attempt to produce radiation absorption by ablation gases.

Wells, W. L.↗

NASA NTRS1980

An 8 x 10 to the 5th bit bubble memory cell for spacecraft applications

A multiple chip magnetic bubble memory cell design developed for NASA embodies the low power, low weight, environmental tolerance and reliability necessary for successful operation in spacecraft launch and mission environments. Packaging of multiple chips in a common magnetic bias, drive coil assembly reduces weight and volume overhead per chip and also reduces the number of coil drive components required. This 8 x 10 to the 5th bit cell is conduction cooled and provides a metal and ceramic sealed hermetic chip environment.

Becker, F. J.↗

NASA NTRS1982

Cryogenic testing of mirrors for infrared space telescopes

The Shuttle IR Telescope Facility (SIRTF) test apparatus can test candidate mirror materials as large as 66 cm in diameter, at temperatures as low as about 10 K, and is accurate enough to detect optical figure changes as small as a fraction of a wavelength from the room temperature figure. The fused silica mirrors currently undergoing testing in the SIRTF are sunk into a liquid He reservoir with copper straps, whose individual strands are soldered to small silver spots diffused throughout the unfigured side of the mirror to accomplish fast conductive cooling. Optical access to the cold mirror is by means of a small glass port in the vacuum chamber. An interferometer is used to examine the mirror figure throughout the cool-down. Interferograms are photographed, fringe patterns are digitized, and mirror figure contour plots are calculated by means of a computer.

Miller, J. H.↗

NASA NTRS1985

Superconducting magnet

Extensive computer based engineering design effort resulted in optimization of a superconducting magnet design with an average bulk current density of approximately 12KA/cm(2). Twisted, stranded 0.0045 inch diameter NbTi superconductor in a copper matrix was selected. Winding the coil from this bundle facilitated uniform winding of the small diameter wire. Test coils were wound using a first lot of the wire. The actual packing density was measured from these. Interwinding voltage break down tests on the test coils indicated the need for adjustment of the wire insulation on the lot of wire subsequently ordered for construction of the delivered superconducting magnet. Using the actual packing densities from the test coils, a final magnet design, with the required enhancement and field profile, was generated. All mechanical and thermal design parameters were then also fixed. The superconducting magnet was then fabricated and tested. The first test was made with the magnet immersed in liquid helium at 4.2K. The second test was conducted at 2K in vacuum. In the latter test, the magnet was conduction cooled from the mounting flange end.

Source record↗

NASA NTRS1985

Inhibition of conductive heat flow by magnetic constriction in the corona and transition region - Dependence on the shape of the constriction

Attention is given to the process by which the shape of the constriction of field lines inhibiting the conduction of heat down from the corona acts in conjunction with the degree of constriction to inhibit the heat flow. The analytical model for the heat flow involves tapered flux tubes in which the plasma properties are constant on cross sections, while the plasma is static and the only energy transfer is by thermal conduction. It is determined that only two specific solutions to the model are applicable to the solar atmosphere: the steady state, which is appropriate for quiet regions and for active ones that are not flaring, and the time-dependent case, in which no heat enters the hot end, which is appropriate for conductive cooling of flare loops.

Moore, R. L.↗