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NASA NTRS1979

Gravitational potential energy of the earth - A spherical harmonic approach

A spherical harmonic equation for the gravitational potential energy of the earth is derived for an arbitrary density distribution by conceptually bringing in mass-elements from infinity and building up the earth shell upon spherical shell. The zeroth degree term in the spherical harmonic expansion agrees with the usual expression for the energy of a radial density distribution. The second degree terms give a maximum nonhydrostatic energy in the crust and mantle of -2.77 x 10 to the 29th ergs, an order of magnitude below McKenzie's (1966) estimate. McKenzie's result stems from mathematical error. Our figure is almost identical with Kaula's (1963) estimate of the minimum shear strain energy in the mantle, a not unexpected result on the basis of the virial theorem. If the earth is assumed to be a homogeneous viscous oblate spheroid relaxing to an equilibrium shape, then a lower limit to the mantle viscosity of 1.3 x 10 to the 20th P is found by assuming that the total geothermal flux is due to viscous dissipation of energy. This number is almost six orders of magnitude below MacDonald's (1966) estimate of the viscosity and removes his objection to convection. If the nonequilibrium figure is dynamically maintained by the earth acting as a heat engine at 1% efficiency, then the viscosity is 10 to the 22nd P, a number preferred by Cathles (1975) and Peltier and Andrew (1976) as the viscosity of the mantle.

Rubincam, D. P.↗

NASA NTRS1980

Electroepitaxy of multicomponent systems - Ternary and quarternary compounds

A theoretical model is presented which accounts for the electroepitaxial growth kinetics and composition of multicomponent compounds in terms of mass transport in the liquid and phase diagram relationships. The mass transport in the interface is dominated by electromigration in the absence of convection and by diffusion in the presence of convection. The composition of the solid is controlled by the Peltier effect at the growth interface and by the diffusion and mobility constants of the solute components and the growth velocity (current density). Thus, for a given solution composition, the composition of the solid can be varied by varying the current density. For a given current density the composition remains constant even in the case of relatively thick epitaxial layers. All aspects of the model were found to be in good agreement with the growth and composition characteristics of Ga/x-1/Al/x/As layers.

Bryskiewicz, T.↗

NASA NTRS1981

A study of low-noise preamplifier systems for use with room temperature mercuric iodide /HgI2/ X-ray detectors

An analysis of different preamplification systems for use with room temperature mercuric iodide X-ray detectors has been performed. Resistor-, drain-, and light-feedback preamplifiers have been studied. Energy resolution values of 295 eV (FWHM) for an Fe-55 source (5.9 keV) and 225 eV (FWHM) for a pulser have been obtained with both the detector and the input FET at room temperature using a pulsed-light feedback preamplifier. Improvement in energy resolution by cooling the input FET using a small Peltier element has been discussed.

Iwanczyk, J. S.↗

NASA NTRS1982

Heat flow control and segregation in directional solidification

Optimization of the vertical Bridgman technique for growth of electronic materials in single crystal form was investigated. The limitations of the crystal growth configuration were experimentally determined and heat transfer related deficiencies identified. Design of an alternate system was based on the use of heat pipes separated by a gradient region. Heat transfer analyses based on one and two dimensional models indicated the necessity of a flexible gradient zone configuration. Directional melting of binary systems as encountered during seeding in melt growth was analysed for concurrent compositional changes at the crystal-metal interface, and the theoretical treatment numerically applied to HgCdTe and Ga doped germanium. A theoretical and experimental study of the thermal effects associated with current flow was conducted. It was found that experimental measurements of dc induced growth during crystal pulling can be used for the precise determination of the Peltier coefficient.

Witt, A. F.↗

NASA NTRS1982

Computer modeling of thermoelectric generator performance

Features of the DEGRA 2 computer code for simulating the operations of a spacecraft thermoelectric generator are described. The code models the physical processes occurring during operation. Input variables include the thermoelectric couple geometry and composition, the thermoelectric materials' properties, interfaces and insulation in the thermopile, the heat source characteristics, mission trajectory, and generator electrical requirements. Time steps can be specified and sublimation of the leg and hot shoe is accounted for, as are shorts between legs. Calculations are performed for conduction, Peltier, Thomson, and Joule heating, the cold junction can be adjusted for solar radition, and the legs of the thermoelectric couple are segmented to enhance the approximation accuracy. A trial run covering 18 couple modules yielded data with 0.3% accuracy with regard to test data. The model has been successful with selenide materials, SiGe, and SiN4, with output of all critical operational variables.

Chmielewski, A. B.↗

NASA NTRS1985

Faster Response for Memory-Metal Actuators

Cooling accelerated by attaching Peltier junction. Electric current carries heat to or from junction between two dissimilar metals, direction of heat flow depending on direction of current and particular metals used. Direction of current is opposite to that of same two metals operating as thermocouple.

Ruoff, C. F.↗

NASA NTRS1983

Postglacial rebound observed by Lageos and the effective viscosity of the lower mantle

Sixty-four observations of the orbital node made by the Lageos satellite over a five year time interval reveal an acceleration of (-8.1 + or 1.8) x 10 to the -8 power arcseconds day/2 due to a source which is not presently modeled in the GEODYN orbit determination computer program. This acceleration cannot be explained by the ocean tide with 18.6 year period, assuming it to be an equilibrium tide. Instead it seems to be due to postglacial rebound, which changes the J(2) coefficient in the spherical harmonic expansion of the earth's gravitational field at the rate of (-8.2 + or - 18) x 10 to the -19th power/s; this in turn accelerates the node. This rate does not agree with the -32 x 10 to the -19th power/s predicted by Wu and Peltier's (1982) L2 model, which has upper and lower mantle effective viscosities of 10 to the 21st and 22nd powers Pa's, respectively. it does agree well with their L1 model, which gives about 10 x 10 to the 19th power/s. Since the effective viscosity is 10 to the 21st power Pa s throughout the entire mantle in the L1 model, the results support the contentions that the effective viscosity is near 10 to the 21st power Pa s everywhere in the mantle, and this relatively low value for the effective viscosity may have permitted several degrees of polar wander due to glaciation during the Quaternary Ice Age.

Rubincam, D. P.↗

NASA NTRS1984

Postglacial rebound observed by Lageos and the effective viscosity of the lower mantle

Sixty-four observations of the orbital node made by the Lageos satellite over a five year time interval reveal an acceleration of (-8.1 + or - 1.8) x 10 to the -8 power arcseconds day/2 due to a source which is not presently modeled in the GEODYN orbit determination computer program. This acceleration cannot be explained by the ocean tide with 18.6 year period, assuming it to be an equilibrium tide. Instead it seems to be due to postglacial rebound, which changes the J(2) coefficient in the spherical harmonic expansion of the earth's gravitational field at the rate of (-8.2 + or - 18) x 10 to the -19th power/s; this in turn accelerates the node. This rate does not agree with the -32 x 10 to the -19th power/s predicted by Wu and Peltier's (1982) L2 model, which has upper and lower mantle effective viscosities of 10 to the 21st and 22nd powers Pa's, respectively. It does agree well with their L1 model, which gives about 10 x 10 to the 19th power/s. Since the effective viscosity is 10 to the 21st power Pa s throughout the entire mantle in the L1 model, the results support the contentions that the efective viscosity is near 10 to the 21st power Pa s everyhere in the mantle, and this relatively low value for the effective viscosity may have permitted several degrees of polar wander due to glaciation during the Quaternary Ice Age. Previously announced in STAR as N84-13705

Rubincam, D. P.↗

NASA NTRS1985

Memory metal actuator

A mechanical actuator can be constructed by employing a plurality of memory metal actuator elements in parallel to control the amount of actuating force. In order to facilitate direct control by digital control signals provided by a computer or the like, the actuating elements may vary in stiffness according to a binary relationship. The cooling or reset time of the actuator elements can be reduced by employing Peltier junction cooling assemblies in the actuator.

Ruoff, C. F.↗

NASA NTRS1986

Low energy X-ray spectra measured with a mercuric iodide energy dispersive spectrometer in a scanning electron microscope

A mercuric iodide energy dispersive X-ray spectrometer, with Peltier cooling provided for the detector and input field effect transistor, has been developed and tested in a scanning electron microscope. X-ray spectra were obtained with the 15 keV electron beam. An energy resolution of 225 eV (FWHM) for Mn-K(alpha) at 5.9 keV and 195 eV (FWHM) for the Mg-K line at 1.25 keV has been measured. Overall system noise level was 175 eV (FWHM). The detector system characterization with a carbon target demonstrated good energy sensitivity at low energies and lack of significant spectral artifacts at higher energies.

Iwanczyk, J. S.↗

NASA NTRS1987

Rapid melt/quench furnace using commercially available hardware

This report describes an off-the-shelf Orbital Tube Welder that can be easily used to melt and resolidify almost any electrically conductive material. This can be done on a KC-135 Aircraft within the microgravity period of one parabola. Melt sizes 3 mm diameter by 10 mm length and larger are feasible with most if not all materials. A highly reproducible, controlled, programmable heat and cool cycle can be provided. Sample measurements would have to be developed and could be as sophisticated or as simple as desired. These could include: optical and thermocouple temperature measurements, Peltier pulser for marking the solidification fronts, dimensional changes and whatever. Sample heat flows could be fixed over a very wide range being limited mostly by the cooling period, the desired sample size, and the 20 sec microgravity period of the KC-135 Aircraft parabola.

Poorman, Richard M.↗

NASA NTRS1986

Intensified-CCD focal plane detector for space applications A second generation

An intensified-CCD detector system developed for space applications from commercially available components is described. This detector uses components which are readily available and are mechanically, thermally, and optically coupled to produce the final compact system. The CCD is cooled using a Peltier-effect thermoelectric cooler to reduce thermal noise. The image is formed on the photocathode of a proximity-focused image intensifier and is transferred fiber-optically from the intensifier to the CDD. Various photocathode and window materials are used to optimize the system for use within the wavelength range extending from the far UV to the near IR. The basic design, including the image intensifier, intensifier-CCD interface, CCD array, cooling, electronics, and mounting, and the detector performance are described in detail.

Torr, M. R.↗

NASA NTRS1987

On the control of flexible structures by applied thermal gradients

Thermal, elastic, and feedback analyses are applied to the case of a beam with a distributed thermal actuator. The actuator is capable of producing a thermal gradient across the section of the beam. One candidate for such an actuator uses the Peltier effect, which appears in certain semiconductors. These devices act as heat pumps when a voltage is applied, causing a temperature gradient. It is shown that the thermal gradients can induce deflection in the beam. If the thermal gradients are applied in the proper sense to a vibrating beam, it is possible to increase the vibration damping exhibited by the structure. Experimental results are given for a cantilever beam, whose first vibrational mode damping ratio was increased from 0.81 to 7.4 percent with a simple lead compensation.

Edberg, D. L.↗

NASA NTRS1987

Control of flexible structures by applied thermal gradients

Edberg, Donald L.↗

NASA NTRS1989

Phase Separators And Fountain-Effect Pumps For He 11

Fused-glass microchannel arrays for use as HE 11 phase separators and fountain-effect pumps. Microchannel devices for use in low-gravity storage and cooling systems containing superfluid helium. Phase separators and pumps take advantage of thermomechanical effect peculiar to He 11 in restricted spaces. By creating thermal gradient in porous plug, direction of flow reversed, turning phase separator into pump. However, addition of heat disadvantage. Thermal gradient created by using Peltier effect to transfer heat across array, removing heat from He 11 supply and overcoming undesirable addition of heat.

Whitehouse, Paul L.↗

NASA NTRS1988

The influences of convection on directional solidification of eutectic Bi/MnBi

Eutectic alloys of Bi-Mn were directionally solidified using the Bridgman-Stockbarger technique to determine the influences of gravitationally-driven thermo-solutal convection on the Bi-MnBi rod eutectic. Experiments were conducted that varied the level of convection by varying the growth parameters and growth orientation, by microgravity damping, by applied magnetic field damping, and by imposing forced convection. Peltier interface demarcation and in situ thermocouple measurements were used to monitor interface velocity and thermal gradient and to evaluate interface planarity.

Larson, David J., Jr.↗

NASA NTRS1990

A technique to measure the thermal diffusivity of high T(sub c) superconductors

High T(sub c) superconducting electrical current leads and ground straps will be used in cryogenic coolers in future NASA Goddard Space Flight Center missions. These superconducting samples will be long, thin leads with a typical diameter of two millimeters. A longitudinal method is being developed to measure the thermal diffusivity of candidate materials for this application. This technique will use a peltier junction to supply an oscillatory heat wave into one end of a sample and will use low mass thermocouples to follow the heat wave along the sample. The thermal diffusivity will be calculated using both the exponential decay of the heat wave and the phase shift of the wave. Measurements will be done in a cryostat between 10 K and room temperature.

Powers, Charles E.↗

NASA NTRS1986

Process for detecting the likelihood of ice formation, ice warning system for carrying out the process, and utilization thereof

An ice warning system comprising a diaphragm set into vibration at one of its frequencies of resonance by a piezoelectric cell. The diaphragm is coupled thermally to a metallic plate alternately cooled and heated respectively below and above the ambient temperature by Peltier elements connected to a reversible DC current generator. A microprocessor measures any variation of the resonance frequency caused by a deposit of ice on the diaphragm during the cooling or heating periods and delivers an alarm signal if this variation of frequency reaches and/ or exceeds a predetermined value. The microprocessor controls the period, intensity and direction of the current delivered by the DC current generator as a function of the ambient temperature and the temperature of the diaphragm. The ice warning system is preferably utilized in the aeronautical field for indicating the likelihood of natural ice formation on the engines and the wings of aircraft.

Martin Lustenberger↗