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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 NTRS1997

Determination of the Peltier Coefficient of Germanium in a Vertical Bridgeman-Stockbarger Furnace

The Peltier effect is the fundamental mechanism that makes interface demarcation through current pulsing possible. If a method for calculating the necessary current density for effective demarcation is to be developed, it will be necessary to know the value of the Peltier coefficient. This study determined experimentally the value of the Peltier coefficient for gallium-doped germanium by comparing the change in average growth rates between current-on and current-off periods. Current-on and current-off layer thickness measurements were made using differential interference contrast microscopy and atomic force microscopy. It was found that the Joule and Thomson effects could not be neglected. Peltier coefficients calculated from the experimental data with an analysis that accounts for Joule, Thomson, and Peltier effects yielded an average value for the Peltier coefficient of 0.076 +/- 0.015 V.

Weigel, Michaela E. K.↗
NASA NTRS1984

Thermoelectric and morphological effects of Peltier pulsing on directional solidification of eutectic Bi-Mn

Extensive in situ thermal measurements using Peltier Interface Demarcation (PID) during directional solidification of eutectic Bi/MnBi were carried out. Observations indicate that significant thermal transients occur throughout the sample as a result of the Peltier pulsing. The contributions of the Peltier, Thomson, and Joule heats were separated and studied as a function of pulse intensity and polarity. The Joule and the combined Peltier and Thomson thermal contributions were determined as a function of time during and after the current pulses, close to the solid/liquid interface. Variations of the Bi/MnBi particle morphology clearly reveal the interface shape, changes in interface velocity, meltback, and temporary loss of cooperative growth, as a result of the pulsing.

Silberstein, R. P.↗
NASA NTRS1986

Studying Crystal Growth With the Peltier Effect

Peltier interface demarcation (PID) shown useful as aid in studying heat and mass transfer during growth of crystals from molten material. In PID, two dissimilar "metals" solid and liquid phases of same material. Current pulse passed through unidirectionally solidifying sample to create rapid Peltier thermal disturbance at liquid/solid interface. Disturbance, measured by thermocouple stationed along path of solidification at or near interface, provides information about position and shape of interface.

Larsen, David J., Jr.↗
NASA NTRS1987

Spatial profile of thermoelectric effects during Peltier pulsing in Bi and Bi/MnBi eutectic

The spatial profile of the thermal transients that occur during and following the current pulsing associated with Peltier Interface Demarcation during directional solidification is studied. Results for pure Bi are presented in detail and compared with corresponding results for the Bi/MnBi eutectic. Significant thermal transients occur throughout the sample that can be accounted for by the Peltier effect, the Thomson effect, and Joule heating. These effects are separated and their behavior is studied as a function of time, current density, and position with respect to the solid/liquid interface.

Silberstein, R. P.↗
NASA NTRS2000

Melt Motion Due to Peltier Marking During Bridgman Crystal Growth with an Axial Magnetic Field

This paper treats a liquid-metal flow inside an electrically insulating cylinder with electrically conducting solids above and below the liquid region. There is a uniform axial magnetic field, and there is an electric current through the liquid and both solids. Since the lower liquid-solid interface is concave into the solid and since the liquid is a better electrical conductor than the adjacent solid, the electric current is locally concentrated near the centerline. The return to a uniform current distribution involves a radial electric current which interacts with the axial magnetic field to drive an azimuthal flow. The axial variation of the centrifugal force due to the azimuthal velocity drives a meridional circulation with radial and axial velocities. This problem models the effects of Peltier marking during the vertical Bridgman growth of semiconductor crystals with an externally applied magnetic field, where the meridional circulation due to the Peltier Current may produce important mixing in the molten semiconductor.

Sellers, C. C.↗
NASA NTRS1990

External Peltier Cooler For Low-Noise Amplifier

Inexpensive Peltier-effect cooling module made of few commercially available parts used to reduce thermal noise in microwave amplifier. Retrofitted to almost any microwave low-noise amplifier or receiver preamplifier used in communication, telemetry, or radar. Includes copper or aluminum cold plate held tightly against unit to be cooled by strap-type worm-gear clamps.

Soper, Terry A.↗
NASA NTRS1980

Liquid-phase electroepitaxy - Dopant segregation

A theoretical model is presented which accounts for the dopant segregation in liquid-phase electroepitaxy in terms of dopant transport in the liquid phase (by electromigration and diffusion), the growth velocity, and the Peltier effect at the substrate-solution interface. The contribution of dopant electromigration to the magnitude of the effective segregation coefficient is dominant in the absence of convection; the contribution of the Peltier effect becomes significant only in the presence of pronounced convection. Quantitative expressions which relate the segregation coefficient to the growth parameters also permit the determination of the diffusion constant and electromigration mobility of the dopant in the liquid phase. The model was found to be in good agreement with the measured segregation characteristics of Sn in the electroepitaxial growth of GaAs from Ga-As solutions. For Sn in Ga-As solution at 900 C the diffusion constant was found to be 4 x 10 to the -5 sq cm/s and the electromigration velocity (toward the substrate with a positive polarity 2 x 10 to the -5 cm/s current density of 10 A/sq cm.

Lagowski, J.↗
NASA NTRS1985

Measurement of the characteristic X ray of oxygen and other ultrasoft X rays using mercuric iodide detectors

This letter reports the detection and resolution of the characteristic X-ray of oxygen at 523 eV and other ultrasoft X-rays (photons energy less than 1 keV) using radiation detectors fabricated from the compound semi-insulator mercuric iodide (HgI2). These detectors are capable of operation at room ambient but in these experiments were slightly cooled using a Peltier element to 0 C. A pulsed light feedback preamplifier with a Peltier element cooled (to -30 deg) first stage field-effect transistor was used to amplify signals from the detector. Overall system noise level was 185 eV (full width at half-maximum) limited by the temperature of the first stage field-effect transistor. With optimal cooling of this element the characteristic X-ray of carbon at 282 eV should be measurable. These results would seem to be important in measurement of biological samples in electron column instruments.

Iwanczyk, J. S.↗
NASA NTRS1993

The inference of mantle viscosity from an inversion of the Fennoscandian relaxation spectrum

The theory of Peltier (1976) for mantle viscosity is adopted, within the framework of nonlinear Bayesian Inference, to invert the Fennoscandian relaxation spectra derived by McConnell (1968). A set of rigorous constraints which all models for the viscosity variation beneath Fennoscandian must satisfy is derived. These constraints are used to test the plausibility of a wide class of viscosity models. It is shown that a model with a weak asthenosphere overlying an isoviscous 10 exp 21 Pa s deep mantle provides to good fit to the relaxation spectrum. This is also true of models with a thin sublithospheric low-viscosity zone overlying a two-layer deep mantle with a moderate jump in viscosity across 670 km depth, and models with a viscosity jump of between four and six across isoviscous upper and lower mantle regions.

Mitrovica, J. X.↗
NASA NTRS1973

Thin film thermoelectric devices as thermal control coatings: A study

Peltier effect, Thomson effect, and Seeback effect are utilized in design of thermal control coating that serves as versatile means for controlling heat absorbed and radiated by surface. Coatings may be useful in extreme temperature environment enclosures or as heat shields.

Clemons, J. M.↗
NASA NTRS1975

Thermoelectrically-cooled quartz microbalance

Temperature of microbalance can be maintained at ambient temperature or held at some other desired temperature. Microbalance has tow-stage thermoelectric device that controls temperature of quartz crystal. Heat can be pumped to or from balance by Peltier effect.

Mckeown, D.↗
NASA NTRS1976

Thermal control systems for low temperature Shuttle payloads

Greater sensitivity and longer life for future space sensor systems place more stringent demands on cooling system technology. Results are presented for a study designed to determine and evaluate low-temperature thermal control system concepts for various cooling categories in the range 3-200 K and to generate hardware development plans for undeveloped viable system concepts. The study considered Shuttle launched payloads in the 1980-1991 time frame, with 1-5 yr of life. Cooling concepts are categorized as open-cycle (expendable), closed-cycle (mechanical), solid-state, and radiative. Particular attention is given to the concepts of multistage heat pipe radiator, diode heat pipe radiator, and radiator guarded cryostat. Results are given for parametric analyses of the Vuilleumier refrigerator, the rotary reciprocating refrigerator, the solid hydrogen refrigerator, the solid hydrogen/multistage radiator hybrid cooler, and the magneto-Peltier hybrid cooler.

Wright, J. P.↗
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.↗