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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 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Heat transfer and pressure drop in a compact pin-fin heat exchanger with pin orientation at 18 deg to the flow direction

The heat transfer and pressure drop characteristics of a novel, compact heat exchanger in helium gas were measured at 3.5 MPa and Reynolds numbers of 450 to 12,000. The pin-fin specimen consisted of pins, 0.51 mm high and spaced 2.03 mm on centers, spanning a channel through which the helium flows; the angle of the row of pins to the flow direction was 18 deg. The specimen was radiatively heated on the top side at heat fluxes up to 74 W/sq cm and insulated on the back side. Correlations were developed for the friction factor and Nusselt number. The Nusselt number compares favorably to those of past studies of staggered pin-fins, when the measured temperatures are extrapolated to the temperature of the wall-fluid interface.

Olson, D. A.↗
NASA NTRS1990

Splat-quench solidification of freely falling liquid-metal drops by impact on a planar substrate

Results are presented of a study of the splat-quench solidification of small, freely falling liquid drops of the alloy Nitronic 40W, which were allowed to impact on a solid, planar, horizontal substrate. The principal variable was the substrate material, with substrates of copper, alumina and fused quartz being used. The shapes of the solidified splats were correlated with a simplified model for the energetics of the splatting process and with the thermal conductivity of the substrate. The measured results are qualitatively in agreement with theoretical predictions, and suggestions are offered for a more comprehensive model of splat-quench solidification. A relationship between sessile droplet diameter and parent wire diameter is also presented and discussed.

Collings, E. W.↗
NASA NTRS1990

Mechanics of transport phenomena in multi-component sessile drops with solidification

The mechanics of transport phenomena in multicomponent sessile drops with internal solidification is determined on the basis of an experimental study. A shadowgraph-schlieren system and a microscope-video system are used for the study. It is suggested that present data can be used to enhance the solid or crystal quality in a reduced-gravity environment where both thermo- and diffuso-capillary effects of solidification and crystal growth are dominant.

Su, Yeong-Jen↗
NASA NTRS1991

Drop-tower experiments for capillary surfaces in an exotic container

Low-gravity drop-tower experiments are carried out for an 'exotic' rotationally-symmetric container, which admits an entire continuum of distinct equilibrium symmetric capillary free surfaces. It is found that an initial equilibrium planer interface, a member of the continuum, will reorient toward a non-symmetric interface, as predicted by recent mathematical theory.

Concus, Paul↗
NASA NTRS1991

Effects of brush seal morphology on leakage and pressure drops

Research on brush seals which was undertaken earlier by Braun et al. (1990) is continued. Particular attention is given to the effects of brush positioning, design, and morphology on sealing surfaces, fluid leakage, and associated pressure drops. It is found that both the structure and the design of the brush are important to its performance. High resistance to the flow of the brush/fence combination can result in catastrophic failure of the brush, while at lower flow resistances, the failure is more gradual.

Braun, M. J.↗
NASA NTRS1992

Dispersion Of Evaporating Drops In A Vortex

Report presents theoretical study of behavior of evaporating liquid drops entrained in annular cross section of long, coherent gas vortex. Dynamic and thermodynamic interactions described. Study contributes to understanding of evaporation and combustion of sprayed liquid fuels.

Bellan, Josette↗
NASA NTRS1992

Burning Of Dense Clusters Of Fuel Drops

Report presents theoretical study of evaporation, ignition, and combustion of rich and relatively dense clusters of drops of liquid fuel. Focus on interactions between heterogenous liquid/gas mixture in cluster and flame surrounding it. Theoretical model of evaporation, ignition, and combustion presented.

Bellan, Josette↗
NASA NTRS1992

Diffusion Of Mass In Evaporating Multicomponent Drops

Report summarizes study of diffusion of mass and related phenomena occurring in evaporation of dense and dilute clusters of drops of multicomponent liquids intended to represent fuels as oil, kerosene, and gasoline. Cluster represented by simplified mathematical model, including global conservation equations for entire cluster and conditions on boundary between cluster and ambient gas. Differential equations of model integrated numerically. One of series of reports by same authors discussing evaporation and combustion of sprayed liquid fuels.

Bellan, Josette↗
NASA NTRS1990

Pressure drop of He II flow through a porous media

The paper reports on measurements of He II pressure drop across two porous SiO2 ceramic filter materials. These materials vary only in porosity, having values of 0.94 and 0.96. The average fiber diameter in both cases is approximately 5 microns. The experiment consists of a glass tube containing a piece of this sponge in one end. The tube is rapidly displaced downward in a bath of helium and the liquid levels are allowed to equilibrate over time producing variable velocities up to 10 cm/sec. The results are compared with those previously obtained using fine mesh screens. Good qualitative agreement is observed for turbulent flow; however, the behavior in the laminar flow regime is not fully understood.

Maddocks, J. R.↗
NASA NTRS1992

A method for non-contact drop charge measurement

A new approach for detecting point type of charge has been developed. This system is based on the principle of reciprocal motion of a grounded conductor near a point charge. The current induced through such a process can then be used to determine the static field strength of the point charge, hence the quantity of the charge. Experiments were done to understand the characteristics of this new device. Test case indicates that the results are in good agreement with the theoretical prediction. This device shows extremely good linearity with respect to the strength of the input static field. The resolution of the system is better than 10 V/m, which is about two orders of magnitude in sensitivity higher than other types of field measuring apparatus. The high sensitivity of this system makes it possible to conduct charged drop experiments under microgravity conditions.

Lin, K. C.↗
NASA NTRS1992

Pressure drop in fully developed, turbulent, liquid-vapor annular flows in zero gravity

The prediction of frictional pressure drop in fully developed, turbulent, annular liquid-vapor flows in zero gravity using simulation experiments conducted on earth is described. The scheme extends the authors' earlier work on dispersed flows. The simulation experiments used two immiscible liquids of identical density, namely, water and n-butyl benzoate. Because of the lack of rigorous analytical models for turbulent, annular flows, the proposed scheme resorts to existing semiempirical correlations. Results based on two different correlations are presented and compared. Others may be used. It was shown that, for both dispersed and annular flow regimes, the predicted frictional pressure gradients in 0-g are lower than those in 1-g under otherwise identical conditions. The physical basis for this finding is given.

Sridhar, K. R.↗
NASA NTRS1993

Evaporation Of Clusters Of Drops In A Jet

Report presents theoretical study of evaporation of clusters of liquid drops injected with gas jet flowing into hot ambient gas. One in series of studies of various aspects of behavior of sprays. Simplified mathematical models used to extract qualitative information on trends in interactions.

Bellan, Josette↗
NASA NTRS1992

Drop tube research

This report covers the activities performed in the Drop Tube Study which The University of Alabama in Huntsville designed, fabricated and performed various low gravity experiments in materials processing from November 1, 1991 through October 30, 1992. During the performance of this contract the utilization of these ground-based containerless processing facilities has been instrumental in providing the opportunity to determine the feasibility of performing a number of solidification experiments in a simulated space environment, without the expense of a space-based experiment. A number of periodic reports have been given to the TCOR during the course of this contract hence this final report is meant only to summarize the many activities performed and not redundantly cover materials already submitted.

Workman, Gary L.↗
NASA NTRS1993

Velocity and drop size measurements in a swirl-stabilized, combusting spray

Velocity and drop size measurements are reported for a swirl-stabilized, combusting spray. For the gas phase, three components of mean and fluctuating velocity are reported. For the droplets, three components of mean and fluctuating velocity, diameter, and number flux are reported. The liquid fuel utilized for all the tests was heptane. The fuel was injected using an air-assist atomizer. The combustor configuration consisted of a center-mounted, air-assist atomizer surrounded by a coflowing air stream. Both the coflow and the atomizing air streams were passed through 45 degree swirlers. The swirl was imparted to both streams in the same direction. The combustion occurred unconfined in stagnant surroundings. The nonintrusive measurements were obtained using a two-component phase/Doppler particle analyzer. The laser-based instrument measured two components of velocity as well as droplet size at a particular point. Gas phase measurements were obtained by seeding the air streams with nominal 1 micron size aluminum-oxide particles and using the measured velocity from that size to represent the gas phase velocity. The atomizing air, coflow air, and ambient surroundings were all seeded with the aluminum-oxide particles to prevent biasing. Measurements are reported at an axial distance of 5 mm from the nozzle. Isothermal single-phase gas velocities are also reported for comparison with the combusting case.

Bulzan, Daniel L.↗
NASA NTRS1992

Laser scattering in a hanging drop vapor diffusion apparatus for protein crystal growth in a microgravity environment

One type of hardware used to grow protein crystals in the microgravity environment aboard the U.S. Space Shuttle is a hanging drop vapor diffusion apparatus (HDVDA). In order to optimize crystal growth conditions, dynamic control of the HDVDA is desirable. A critical component in the dynamically controlled system is a detector for protein nucleation. We have constructed a laser scattering detector for the HDVDA capable of detecting the nucleation stage. The detector was successfully tested for several scatterers differing in size using dynamic light scattering techniques. In addition, the ability to detect protein nucleation using the HDVDA was demonstrated for lysozyme.

Casay, G. A.↗
NASA NTRS1993

Self-rectifying electron beam melter for pendant-drop containerless processing

A self-rectifying electron beam melting technique is described. Utilizing an ac power supply, in contrast to the more usual dc supply, the in situ self-rectifying approach offers a simple and very inexpensive means of producing metallic pendant drops for use in containerless melt-processing experiments.

Pyun, D. S.↗
NASA NTRS1993

A mixed formulation for interlaminar stresses in dropped-ply laminates

A structural model is developed for the linear elastic response of structures consisting of multiple layers of varying thickness such as laminated composites containing internal ply drop-offs. The assumption of generalized plane deformation is used to reduce the solution domain to two dimensions while still allowing some out-of-plane deformation. The Hellinger-Reissner variational principle is applied to a layerwise assumed stress distribution with the resulting governing equations solved using finite differences.

Harrison, Peter N.↗
NASA NTRS1991

A potential method for the estimation of drop size distribution from a dual-wavelength airborne radar

In order to investigate the role of the drop size distribution (DSD) from a dual-wavelength airborne radar and to recover profiled rain rates, a procedure is described for the purpose of estimating the DSD. The method differs from previous approaches in that it provides 2n + 1 parameters of the profiled DSD (where n is the number of range gates) and it uses a recursive procedure beginning at the range gate near the surface progressing backwards toward the storm top. The method is argued to be useful both as a diagnostic tool and as a means by which more detailed information on the vertical structure of the precipitation can be obtained.

Meneghini, R.↗