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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 991 records · Page 55
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Evaluation of the importance of the relative velocity during evaporation of drops in sprays

The importance of relative velocity past individual drops composing a burning spray with an envelope flame is estimated by applying the Bellan and Cuffel (1983) spray evaporation model to an ambient flow going around the spray without penetrating it. The model assumes a spherical spray composed of monodisperse uniformly distributed droplets which all move at the same speed, and relative gas/spray velocities, and spray radii used were representative of boiler and furnace operations. Numerical calculations indicate that the spray is more prone to ambient flow penetration for leaner mixtures (particularly for n = 1/cu cm), lower initial temperatures of gas phase and droplet, and more dilute spray configurations.

Bellan, J.↗
NASA NTRS1987

Forced-Flow Evaporative Cooler

Evaporative cooler absorbs heat efficiently under unusual gravitational conditions by using centrifugal force and vapor vortexes to maintain good thermal contact between heat-transfer surface and vaporizable coolant. System useful for cooling electronic or other equipment under low gravity encountered in spacecraft or under multiple-gravity conditions frequently experienced in high-performance airplanes.

Ellis, Wilbert E.↗
NASA NTRS1986

Observational study of ion-electron equilibration and of cloud evaporation in supernova remnants under the HEAO-2 guest investigator program

Observations of three selected supernovae remnants (Cygnus Loop, IC 443, and Puppis A) were made in the forbidden coronal iron lines (Fe X) lambda 6374 and (Fe XIV) lambda 5303. The resulting data was compared quantitatively with Einstein images of the same objects, and an attempt was made to determine (a) the process by which ion and electron energies are equilibrated behind the shock front in the ISM and (b) whether cloud evaporation occurs within the hot remnant interiors. Spatially-resolved X ray emission were modeled for Sedov-Taylor blast wave models of supernovae remnants (SNR) under conditions of non-equlibrium ionization. The computations are intended to provide results that can be directly compared with Einstein high resolution image (HRI) and imaging proportional counter (IPS) data. The computer program for predicting the spatial distribution of HRI and IPS counting rates was completed, and final testing of it had begun.

Teske, R. G.↗
NASA NTRS1987

Forbidden coronal iron line images of Puppis A - Cloud evaporation or shocked cloud?

Calibrated CCD images of the eastern X-ray knot in Puppis A, made in the forbidden red and green coronal Fe lines, are discussed. They show the high-temperature gas to have a rich morphology, with the scale of some features approaching the 2.6 arcsec resolution of the data. The pictures have been compared with an Einstein HRI soft X-ray image; there is close correspondence in the position and size of structures seen in the optical forbidden lines and in the X-rays. Located near the shock front a cloud of about 0.4 pc x 0.9 pc dimension shines brilliantly in the 5303 A line. To test the hypothesis that the cloud might be evaporating into the remnant interior, the 5303 A and 6374 A intensity distributions expected for a steady state, one-fluid evaporatig model have been computed.

Teske, Richard G.↗
NASA NTRS1987

Design and test of a prototype thermal bus evaporator reservoir aboard the KC-135 0-g aircraft

The Thermal Bus Zero-G Reservoir Demonstration Experiment (RDE) has currently undergone two flights on the NASA-JSC KC-135 Reduced Gravity Aircraft. The objective of the experiment, which uses a smaller version of the evaporator reservoirs being designed for the Prototype Thermal Bus for Space Station, is to demonstrate proper 0-g operation of the reservoir in terms of fluid positioning, draining, and filling. The KC-135 was chosen to provide a cost-effective and timely evaluation of 0-g design issues that would be difficult to predict analytically. A total of fifty 0-g parabolas have been flown, each providing approximately 25-30 seconds of 0-g time. While problems have been encountered, the experiment has provided valuable design data on the 0-g operation of the reservoir. This paper documents the design of the experiment; the results of both flights, based on the high-speed movies taken during the flight and the visual observations of the experimenters; and the design modifications made as a result of the first flight and planned as a result of the second flight.

Brown, Richard F.↗
NASA NTRS1988

Evaporation And Ignition Of Dense Fuel Sprays

Simple theoretical model makes useful predictions of trends. Pair of reports presents theoretical model of evaporation and ignition of sprayed liquid fuel. Developed as part of research in combustion of oil and liquid fuels derived from coal, tar sand, and shale in furnace. Work eventually contributes to increase efficiency of combustion and decrease pollution generated by burning of such fuels.

Bellan, Josette↗
NASA NTRS1987

Method of evaporation

Liquids, such as juices, milk, molten metal and the like are concentrated by forming uniformly-sized, small droplets in a precision droplet forming assembly and deploying the droplets in free fall downwardly as a central column within an evacuated column with cool walls. A portion of the solvent evaporates. The vapor flows to the wall, condenses, and usually flows down the wall as a film to condensate collector and drain. The vertical column of freely falling droplets enters the splash guard. The condensate can be collected, sent to other towers or recycled.

Dufresne, Eugene R.↗
NASA NTRS1987

The details of the convective evaporation of dense and dilute clusters of drops

A global model describing the convective evaporation of dense and dilute clusters of drops has been formulated starting from first principles. The volume of the cluster and the number of drops in a given cluster are fixed, and the drops do not move with respect to each other. The model has been tested for three different drag models and shows less than 10-percent sensitivity in the prediction of the droplet lifetime. The initial relative velocity between drops and gases is a weak control parameter in the 40-1000-cm/s regime.

Bellan, J.↗
NASA NTRS1987

Thermoelectric integrated membrane evaporation subsystem testing

An advanced preprototype Thermoelectric Integrated Membrane Evaporation Subsystem (TIMES) has been developed to provide high quality water recovery from various types of wastewater on extended duration space flights. The subsystem has undergone extensive wastewater processing testing, in order to evaluate its potential as an essential part of the Space Station Water Reclamation System. A discussion of the operating performance of the TIMES is presented in this paper, with special attention given to the water quality attained for a number of simulated Space Station wastewater feedstocks.

Dehner, Gerard F.↗
NASA NTRS1987

Containerless study of metal evaporation by laser induced fluorescence

Laser induced fluorescence (LIF) detection of atomic vapors was used to study evaporation from electromagnetically levitated and CW CO2 laser-heated molybdenum spheres and resistively-heated tungsten filaments. Electromagnetic (EM) levitation in combination with laser heating of tungsten, zirconium, and aluminum specimens was also investigated. LIF intensity vs temperature data were obtained for molybdenum atoms and six electronic states of atomic tungsten, at temperatures up to the melting point of each metal. The detected fraction of the emitted radiation was reduced by self-absorption effects at the higher experimental temperatures. Vaporization enthalpies derived from data for which less than half the LIF intensity was self-absorbed were -636 + or - 24 kJ/g-mol for Mo and 831 + or - 32 kJ/g-mol for W. Space-based applications of EM levitation in combination with radiative heating are discussed.

Schiffman, Robert A.↗
NASA NTRS1988

Sequentially evaporated thin Y-Ba-Cu-O superconductor films: Composition and processing effects

Thin films of YBa2Cu3O(7-beta) have been grown by sequential evaporation of Cu, Y, and BaF2 on SrTiO3 and MgO substrates. The onset temperatures were as high as 93 K while T sub c was 85 K. The Ba/Y ratio was varied from 1.9 to 4.0. The Cu/Y ratio was varied from 2.8 to 3.4. The films were then annealed at various times and temperatures. The times ranged from 15 min to 3 hr, while the annealing temperatures used ranged from 850 C to 900 C. A good correlation was found between transition temperature (T sub c) and the annealing conditions; the films annealed at 900 C on SrTiO3 had the best T sub c's. There was a weaker correlation between composition and T sub c. Barium poor films exhibitied semiconducting normal state resistance behavior while barium rich films were metallic. The films were analyzed by resistance versus temperature measurements and scanning electron microscopy. The analysis of the films and the correlations are reported.

Valco, George J.↗
NASA NTRS1988

Deposition and characterization of ZnS/Si heterojunctions produced by vacuum evaporation

Isotype heterojunctions of ZnS (lattice constant 5.41 A) were grown on silicon (lattice constant 5.43 A) p-n junctions to form a minority-carrier mirror. The deposition process was vacuum evaporation from a ZnS powder source onto a heated (450 C) substrate. Both planar (100) and textured (111) surfaces were used. A reduction of the minority-carrier recombination at the surface was seen from increased short-wavelength quantum response and increased illuminated open-circuit voltage. The minority-carrier diffusion length was not degraded by the process.

Landis, Geoffrey A.↗
NASA NTRS1988

Characterization of ZrO2 buffer layers for sequentially evaporated Y-Ba-CuO on Si and Al2O3 substrates

Thin film high temperature superconductors have the potential to change the microwave technology for space communications systems. For such applications it is desirable that the films be formed on substrates such as Al2O3 which have good microwave properties. The use of ZrO2 buffer layers between Y-Ba-Cu-O and the substrate has been investigated. These superconducting films have been formed by multilayer sequential electron beam evaporation of Cu, BaF2 and Y with subsequent annealing. The three layer sequence of Y/BaF2/Cu is repeated four times for a total of twelve layers. Such a multilayer film, approximately 1 micron thick, deposited directly on SrTiO3 and annealed at 900 C for 45 min produces a film with a superconducting onset of 93 K and critical temperature of 85 K. Auger electron spectroscopy in conjunction with argon ion sputtering was used to obtain the distribution of each element as a function of depth for an unannealed film, the annealed film on SrTiO3 and annealed films on ZrO2 buffer layers. The individual layers were apparent. After annealing, the bulk of the film on SrTiO3 is observed to be fairly uniform while films on the substrates with buffer layers are less uniform. The Y-Ba-Cu-O/ZrO2 interface is broad with a long Ba tail into the ZrO2, suggesting interaction between the film and the buffer layer. The underlying ZrO2/Si interface is sharper. The detailed Auger results are presented and compared with samples annealed at different temperatures and durations.

Valco, George J.↗
NASA NTRS1988

Evaporation over land surfaces - First results from HAPEX-MOBILHY Special Observing Period

Preliminary results are presented from the May 7-July 15, 1986 Special Observing Period (SOP) of the HAPEX-MOBILHY program, which examines the hydrological budget and evaporation flux at the scale of a 10,000 sq km GCM grid square to determine soil moisture, surface-energy budgets, and surface hydrology. The SOP used two highly instrumented remote sensing aircraft to obtain detailed measurements of atmospheric fluxes and surface properties. It is noted that the measurements are reliable at spatially local and short time scales, as well as on the monthly time scale. The data base obtained may be used in parametrization schemes against which land-surface water budgets can be tested.

Andre, Jean-Claude↗
NASA NTRS1986

Laboratory studies of the deposition of alkali sulfate vapors from combustion gases using a flash-evaporation technique

A relatively simple experimental technique is proposed and demonstrated for making measurements of absolute dewpoints and relative deposition rates from flowing combustion gases containing condensible inorganic vapors. The method involves first accumulating condensate on a Pt ribbon target maintained below the dewpoint and then flash-evaporating the condensate into the filament wake, where its alkali content is monitored by alkali-atom emission spectroscopy. The advantages of the method over others are demonstrated; in particular, the method can detect liquid condensate inventories which are small enough to be negligibly influenced by surface runoff produced by gas-side shear stress and liquid condensate surface tension gradients. Illustrative Na2SO4 and K2SO4 deposition rate data and corresponding dewpoint data obtained in a series of alkali-seeded propane/air atmospheric flames are presented and discussed.

Rosner, Daniel E.↗
NASA NTRS1989

Highly oriented Tl2Ba2Ca2Cu3O10 thin films by pulsed laser evaporation

Superconducting thin films on MgO (100) substrates with nearly pure Tl2Ba2Ca2Cu3O10 (2:2:2:3) phase using pulsed laser evaporation and postannealing have been fabricated. The films had c axes perpendicular to the substrates. Superconducting films with onset temperatures of 125 K and zero resistance at 110 K were obtained. X-ray microprobe fluorescence measurements indicate that a typical composition of films is Tl(0.66)Ba(1.77)Ca(1.46)Cu3O(x) which is low in Tl compared to that expected for the 2:2:2:3 phase. A typical grain size is greater than 10 microns revealed by scanning electron microscopy.

Liou, S. H.↗
NASA NTRS1988

Evaporation, ignition and combustion of nondilute clusters of drops

A theory of evaporation, ignition, and burning of moderately dense spherical drop clusters has been developed. The theory takes into account burning of premixed air and fuel internal to the cluster at ignition and subsequent burning of fuel emitted from the cluster by a flame sheet surrounding it. The model considers interdrop interaction, momentum exchange between drops and gas, and turbulent exchange processes between the cluster and its surroundings. Calcualtions are performed for varying initial air to fuel mass ratios, initial cluster radii, ambient gas temperatures, and initial drop temperatures. Results are presented for fuel burn fractions at ignition and at the moment of drop disappearance, as well as jump conditions at ignition.

Bellan, J.↗
NASA NTRS1989

Computations of turbulent evaporating sprays

A computational study of turbulent evaporating sprays is reported. The major focus is to examine the sensitivity of the vaporization behavior of turbulent sprays to the transient liquid-phase processes. Three models considered to represent these processes are the thin skin, infinite diffusion, and diffusion limit models. Favre-averaged equations with k-epsilon-g turbulence model are employed for the gas phase. The Lagrangian approach with a stochastic separated flow method is used for the liquid phase where the effects of gas turbulence on droplet trajectories and interphase transport rates are considered using random-walk computations. Also the variable-property effects are considered in detail. Results indicate that, depending upon the boiling temperature and heat of vaporization of the fuel considered, the vaporization behavior of turbulent sprays may be quite sensitive to the modeling of transient liquid-phase processes. Thus, it is important that for most hydrocarbon fuels these processes be adequately represented in any comprehensive spray computations. The present results also provide further support to the conclusions of earlier studies which have been based on simplified spray configurations.

Aggarwal, S. K.↗