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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Streakline flow visualization study of a horseshoe vortex in a large-scale, two-dimensional turbine stator cascade

Neutrally bouyant helium-filled bubbles were observed as they followed the streamlines in a horseshoe vortex system around the vane leading edge in a large scale, two dimensional, turbine stator cascade. Inlet Reynolds number, based on true chord, ranged between 100,000 to 300,000. Bubbles were introduced into the endwall boundary layer through a slot upstream of the vane leading edge. The paths of the bubbles were recorded photographically as streaklines on 16 mm movie film. Individual frames from the film were selected, and overlayed to show the details of the horseshoe vortex around the leading edge. The transport of the vortex across the passage near the leading edge is clearly seen when compared to the streaks formed by bubbles carried in the main stream. Limiting streamlines on the endwall surface were traced by the flow of oil drops.

Gaugler, R. E.↗
NASA NTRS1980

Streakline flow visualization study of a horseshoe vortex in a large-scale, two-dimensional turbine stator cascade

Neutrally buoyant helium-filled bubbles were observed as they followed the streamlines in a horseshoe vortex system around the vane leading edge in a large-scale, two-dimensional, turbine stator cascade. Bubbles were introduced into the endwall boundary layer through a slot upstream of the vane leading edge. The paths of the bubbles were recorded photographically as streaklines on 16-mm movie film. Individual frames from the film have been selected, and overlayed to show the details of the horseshoe vortex around the leading edge. The transport of the vortex across the passage near the leading edge is clearly seen when compared to the streaks formed by bubbles carried in the main stream. Limiting streamlines on the endwall surface were traced by the flow of oil drops.

Gaugler, R. E.↗
NASA NTRS2019

Predicted Ice Shape Formations on a Boundary Layer Ingesting Engine Inlet

Computational ice shapes were generated on the boundary layer ingesting engine nacelle of the D8 Double Bubble aircraft. The computations were generated using LEWICE3D, a well-known CFD icing post processor. A 50-bin global drop diameter discretization was used to capture the collection efficiency due to the direct impingement of water onto the engine nacelle. These discrete results were superposed in a weighted fashion to generate six drop size distributions that span the Appendix C and O regimes. Due to the presence of upstream geometries, i.e. the fuselage nose, the trajectories of the water drops are highly complex. Since the ice shapes are significantly correlated with the collection efficiency, the upstream fuselage nose has a significant impact on the ice accretion on the engine nacelle. These complex trajectories are caused by the ballistic nature of the particles and are thus exacerbated as particle size increases. Shadowzones are generated on the engine nacelle, and due to the curvature of the nose of the aircraft the shadowzone boundary moves from lower inboard to upper outboard as particle size increases. The largest particle impinging one the engine nacelle from the 50-bin discretization was the 47 um drop diameter. As a result, the MVD greater than 40 um Appendix O conditions were characterized by extremely low collection efficiency on the engine nacelle for these direct impingement simulations.

Porter, Christopher↗
NASA NTRS1989

A free surface vortex method with weak viscous effects

The advantage of vortex methods for inviscid flows of several fluids separated by interfaces is that problems of this kind may be posed and solved numerically entirely on the interface surface. For free surface problems, where one of the fluids has negligible inertia, a small amount of viscosity produces a thin, weak rotational layer adjacent to the potential flow vortex sheet. Here, a method is described for including this weak viscous effect as a modification of the boundary conditions for the potential part of the flow, thus allowing this slightly viscous flow to be formulated as a vortex method on the free surface. This is important for unsupported free drops where the viscosity at the free surface is the only source of damping for oscillations, and for gas-filled bubbles, where it provides both drag and damping. Small applied shear stresses from aerodynamic, electrostatic, or other sources may be included provided they are of the same order as the potential flow shear stress or smaller.

Lundgren, T. S.↗
NASA NTRS1999

Enhanced Boiling on Micro-Configured Composite Surfaces Under Microgravity Conditions

In order to accommodate the growing thermal management needs of future space platforms, several two-phase active thermal control systems (ATCSs) have evolved and were included in the designs of space stations. Compared to the pumped single-phase liquid loops used in the conventional Space Transportation System and Spacelab, ATCSs offer significant benefits that may be realized by adopting a two-phase fluid-loop system. Alternately, dynamic power systems (DPSs), based on the Rankine cycle, seem inevitably to be required to supply the electrical power requirements of expanding space activities. Boiling heat transfer is one of the key technologies for both ATCSs and DPSs. Nucleate boiling near critical heat flux (CHF) can transport very large thermal loads with much smaller device size and much lower pumping power. However, boiling performance deteriorates in a reduced gravity environment and operation in the CHF regime is precarious because any slight overload will cause the heat transfer to suddenly move to the film boiling regime, which in turn, will result in burnout of the heat transfer surfaces. New materials, such as micro-configured metal-graphite composites, can provide a solution for boiling enhancement. It has been shown experimentally that this type of material manifests outstanding boiling heat transfer performance and their CHF is also extended to higher values. Due to the high thermal conductivity of graphite fiber (up to 1,200 W/m-K in the fiber direction), the composite surfaces are non-isothermal during the boiling process. The composite surfaces are believed to have a much wider safe operating region (a more uniform boiling curve in the CHF regime) because non-isothermal surfaces have been found to be less sensitive to variations of wall superheat in the CHF regime. The thermocapillary forces formed by the temperature difference between the fiber tips and the metal matrix play a more important role than the buoyancy in the bubble detachment, for the bubble detachment manifests itself by a necking process which should not be weakened by reduced gravity. In addition, the composite surfaces introduce no extra pressure drop, no fouling and do not impose significant primary or maintenance costs. All of these suggest that this type of composite is an ideal material for the challenge of accounting for both reliability and economy of the relevant components applied in the ATCSs, the DPSs and other devices in future space missions. The aim of the proposed work is to experimentally investigate high nucleate pool boiling performance on a micro-configured metal-graphite composite surface and to determine the mechanisms of the nucleate boiling heat transfer both experimentally and theoretically. Freon-113 and water will be used as the test liquids to investigate wettability effects on boiling characteristics. The Cu-Gr and Al-Gr composites with various volume fractions of graphite fibers will be tested to obtain the heat transfer characteristic data in the nucleate boiling region and in the CHF regime. In the experiments, the bubble emission and coalescence processes will be recorded by a video camera with a magnifying borescope probe immersed in the working fluid. The temperature profile in the thermal boundary layer on the composite surfaces will be measured by a group of micro thermocouples consisting of four ultra fine micro thermocouples. This instrument was developed and successfully used to measure the temperature profile of evaporating liquid thin layers by the proposers in a study performed at the NASA/Lewis Research Center. A two tier model to explain the nucleate boiling process and the performance enhancement on the composite surfaces has been suggested by the authors. According to the model, the thicknesses of the microlayer and the macrolayer underneath the bubbles and mushrooms, can be estimated by the geometry of the composite surface. The experimental results will be compared to the predictions from the model, and in turn, to revise and improve it.

Zhang, Nengli↗
NASA NTRS2000

Two-Phase Flow in Packed Columns and Generation of Bubbly Suspensions for Chemical Processing in Space

For long-duration space missions, the life support and In-Situ Resource Utilization (ISRU) systems necessary to lower the mass and volume of consumables carried from Earth will require more sophisticated chemical processing technologies involving gas-liquid two-phase flows. This paper discusses some preliminary two-phase flow work in packed columns and generation of bubbly suspensions, two types of flow systems that can exist in a number of chemical processing devices. The experimental hardware for a co-current flow, packed column operated in two ground-based low gravity facilities (two-second drop tower and KC- 135 low-gravity aircraft) is described. The preliminary results of this experimental work are discussed. The flow regimes observed and the conditions under which these flow regimes occur are compared with the available co-current packed column experimental work performed in normal gravity. For bubbly suspensions, the experimental hardware for generation of uniformly sized bubbles in Couette flow in microgravity conditions is described. Experimental work was performed on a number of bubbler designs, and the capillary bubble tube was found to produce the most consistent size bubbles. Low air flow rates and low Couette flow produce consistent 2-3 mm bubbles, the size of interest for the "Behavior of Rapidly Sheared Bubbly Suspension" flight experiment. Finally the mass transfer implications of these two-phase flows is qualitatively discussed.

Motil, Brian J.↗
NASA NTRS1982

Application of microgravity and containerless environments to the investigation of fusion target fabrication technology

After the first observation of the core-centering force within a liquid shell in the KC-135 flight experiment, this force was successfully reproduced in terrestrial laboratories using two experimental techniques. The core-centering force generated for a compound drop system in the neutral buoyancy tank provides the first correlation between theoretical and experimental results. When this force was generated in a more realistic fusion-pellet system using the focusing-radiator levitating system, it was shown that this is a very strong force indeed in view of the fact that the ratio of specific gravities between the water and the core is approximately five. It is believed that this centering force will contribute significantly to an overall understanding of the fabrication physics of a fusion target system. Results from experiments in a vertical drag-free wind tunnel and in a 16-ft low pressure drop furnace suggest that eliminating or reducing the aerodynamic drag on fusion pellets during their formation stage will prevent the decentering of the bubble. Metallic and metallic glass fusion targets are seen as holding promise for improving and simplifying the fabrication process for ablative-type fusion targets.

Lee, M. C.↗
DOE OSTI2022

Numerical Simulation and Modeling of Hydrogen Gas Evolution on Planar and Microwire Array Electrodes

The impact of gas evolution on the electrochemical characteristics of planar electrodes and microwire array electrodes has been analyzed using modeling and simulation. The impacts can mainly be broken into three phenomena: a) a shift in the local reversible hydrogen electrode potential; b) hyperpolarization; and c) an increase in the solution resistance of the electrolyte. The local reversible hydrogen electrode potential shift was found to play the most important role, constituting >40% of the total potential drop between the cathode and reference electrode, following correction for cell resistance. Compared to planar electrodes, a microwire array structure reduces the impact of bubbles on the solution conductance, but the shift in the local reversible hydrogen electrode potential varies with distance from the actual electrode surface.

25 ENERGY STORAGE↗
NASA NTRS1985

Fluid surface behavior in low gravity. Center discretionary fund no. 83-21

Measurements of rotating equilibrium bubble shapes in the low-gravity environment of a free-falling aircraft are presented. Emphasis is placed on bubbles which intersect the container boundaries. These data are compared with theoretical profiles derived from Laplace's formula and are in good agreement with the measurements. Two types of instability are explored. The first occurs when the baffle spacing is too large for the bubble to intersect both the top and bottom boundaries. The second occurs when the hydrostatic pressure beneath a displaced free surface does not compensate for pressure change due to capillary forces. The interface shape depends on the contact angle, the radius of intersection with container, and the parameter F which is a measure of the relative importance of centrifugal force to surface tension. For isolated bubbles, F has a maximum value of 1/2. A further increase in F causes the bubble to break contact with the axis of rotation. For large values of F, the bubble becomes more cylindrical and the capillary rise occurs over a thinner layer so that the small radius of curvature can generate enough pressure drop to balance the increased hydrostatic contribution.

Leslie, F.↗
NASA NTRS2003

Insights into the Processing of Carbon by Early Microbial Ecosystems

Interactions between Earth and the biosphere that were crucial for early biological evolution also influenced substantially the processes that circulate C between its reservoirs in the atmosphere, ocean, crust and mantle. The C-13 C-12 values of crustal carbonates and organics have recorded changes both in biological discrimination and in the relative rates of burial of organics and carbonates. A full interpretation of these patterns needs further isotopic studies of microbial ecosystems and individual anaerobes. Thus we measured carbon isotope discrimination during autotrophic and heterotrophic growth of pure cultures of sulfate-reducing bacteria and archaea (SRB and SRA). Discrimination during CO2 assimilation is significantly larger than during heterotrophic growth on lactate or acetate. SRB grown lithoautotrophically consumed less than 3% of available CO2 and exhibited substantial discrimination, as follows: Desulfobacterium autotrophicum (alpha 1.0100 to 1.0123), Desulfobacter hydrogenophilus (alpha = 0.0138), and Desulfotomuculum acetoxidans (alpha = 1.0310). Mixotrophic growth of Desulfovibrio desulfuricans on acetate and CO2 resulted in biomass with delta C-13 composition intermediate to that of the substrates. We have recently extended these experiments to include the thermophilic SRA Archeoglobus spp. Ecological forces also influence isotopic discrimination. Accordingly, we quantified the flow of C and other constituents in modern marine cyanobacterial mats, whose ancestry extends back billions of years. Such ecosystem processes shaped the biosignatures that entered sediments and atmospheres. At Guerrero Negro, BCS, Mexico, we examined mats dominated by Microcoleus (subtidal) and Lyngbya (intertidal to supratidal) cyanobacteria. During 24 hour cycles, we observed the exchange of O2 and dissolved inorganic C (DIC) between mats and the overlying water. Microcoleus mats assimilated near-equal amounts of DIC during the day as they released at night, but Lyngbya mats typically showed net uptake of DIC over the diel cycle. Patterns of O2 daytime release and nighttime uptake mirrored these DIC trends in both mat types. Nighttime DIC effluxes from Microcoleus mats were equivalent in the presence versus absence of O2, whereas nighttime DIC effluxes from Lyngbya mats dropped markedly in the absence of O2. Thus aerobic diagenesis was more important in Lyngbya mats than in Microcoleus mats, perhaps because trapped O2 bubbles persist only in Lyngbya mats at night and thus sustain populations of aerbes. In both mat types, effluxes of H2, CH4 and short-chain fatty acids were much greater at night in the absence of 02, emphasizing the importance of fermentation. Differences observed between Microcoleus versus Lyngbya mats forecast differences in their microbial populations and in their patterns of gene expression.

DesMarais, D.↗
DOE OSTI2023

Methane foam performance in oil-wet unconsolidated porous media: A systematic experimental investigation at reservoir conditions

Methane foam performance was systematically evaluated using high-pressure and high-temperature experiments performed on oil-wet proppant packs. The sensitivities of foam performance to various key factors, including surfactant concentration, foam quality, total injection rate, salinity, operating pressure, and initial oil saturation were examined. The results showed that even though the foamability and foam strength in oil-wet proppant packs were adversely affected by wettability and presence of oil, the steady-state pressure drops across the proppant packs were insensitive to the quantity of oil initially present. The presence of oil above the critical oil saturation impeded the onset of foam generation. This suggested that the foamability of surfactants depends on the synergetic effects of surfactant’s ionic nature and foam parameters, such as foam quality and total injection rate, on their ability to reduce the oil saturation to a threshold value below which favorable bubble generation sites could be created. It was observed that, for low injection rate, anionic surfactant was ineffective at low salinity conditions, while amphoteric agent performed well at all salinities. Additionally, an increase in salinity resulted in enhanced pressure drop across the proppant packs for both anionic and amphoteric surfactants. Further, the results also established that too high operating pressures are somewhat detrimental to the foam strength and stability, irrespective of the ionic nature of foaming agents and the wettability of the porous medium. For the anionic surfactant, the increase in the total flow rate was found to mitigate the adverse effects of low salt concentration and operating pressure. Results from quality-sensitivity foam tests identified two regions for the foam behavior, named low-quality and high-quality regimes, separated by the transition foam quality. Finally, we discuss the implications of the results for the design and effective implementation of enhanced oil recovery (EOR) schemes that deploy hydrocarbon-based foams.

02 PETROLEUM↗
NASA NTRS1985

Measurements of rotating bubble shapes in low-gravity environment

Measurements of rotating equilibrium bubble shapes in the low-gravity environment of a free-falling aircraft are presented. Emphasis is placed on bubbles which intersect the container boundaries. These data are compared with theoretical profiles derived from Laplace's formula and are in good agreement with the measurements. The interface shape depends on the contact angle, the radius of intersection with the container, and the parameter F, which is a measure of the relative importance of centrifugal force to surface tension. For isolated bubbles F has a maximum value of 1/2. A further increase in F causes the bubble to break contact with the axis of rotation. For large values of F the bubble becomes more cylindrical and the capillary rise occurs over a thinner layer in order that the small radius of curvature can generate a sufficient pressure drop to account for the increased hydrostatic contribution.

Leslie, F.↗
NASA NTRS1996

Observations of Gas-Liquid Flows Through Contractions in Microgravity

Tests were conducted for an air-water flow through two sudden contractions aboard the NASA DC-9 low gravity aircraft. Flow rate, residual accelerations, void fraction, film thickness, and pressure drop data were recorded and flow visualization at 250 images per second were recorded. Some preliminary results based on the flow visualization data are presented for bubbly, slug and annular flow.

McQuillen, John↗
NASA NTRS2005

Synthetic Vortex Generator Jets Used to Control Separation on Low-Pressure Turbine Airfoils

Low-pressure turbine (LPT) airfoils are subject to increasingly stronger pressure gradients as designers impose higher loading in an effort to improve efficiency and lower cost by reducing the number of airfoils in an engine. When the adverse pressure gradient on the suction side of these airfoils becomes strong enough, the boundary layer will separate. Separation bubbles, particularly those that fail to reattach, can result in a significant loss of lift and a subsequent degradation of engine efficiency. The problem is particularly relevant in aircraft engines. Airfoils optimized to produce maximum power under takeoff conditions may still experience boundary layer separation at cruise conditions because of the thinner air and lower Reynolds numbers at altitude. Component efficiency can drop significantly between takeoff and cruise conditions. The decrease is about 2 percent in large commercial transport engines, and it could be as large as 7 percent in smaller engines operating at higher altitudes. Therefore, it is very beneficial to eliminate, or at least reduce, the separation bubble.

Ashpis, David E.↗
NASA NTRS1977

Experimental investigations on sodium-filled heat pipes

The possibilities of producing heat pipes and, especially, the necessary capillary structures are discussed. Several types of heat pipes were made from stainless steel and tested at temperatures between 400 and 1055 deg C. The thermal power was determined by a calorimeter. Results indicate: bubble-free evaporation of sodium from rectangular open chennels is possible with a heat flux of more than 1,940 W/sq cm at 1055 C. The temperature drop along the tube could be measured only at low temperatures. A subdivided heat pipe worked against the gravitational field. A heat pipe with a capillary structure made of a rolled screen was supported by rings and bars operated at 250 W/sq cm heat flux in the evaporating region.

Dorner, S.↗
NASA NTRS1994

Interferometric investigations of compressible dynamic stall over a transiently pitching airfoil

The compressible dynamic stall flowfield over a NACA 0012 airfoil transiently pitching from 0 to 60 deg at a constant rate under compressible flow conditions has been studied using real-time interferometry. A quantitative description of the overall flowfield, including the finer details of dynamic stall vortex formation, growth, and the concomitant changes in the airfoil pressure distribution, has been provided by analyzing the interferograms. For Mach numbers above 0.4, small multiple shocks appear near the leading edge and are present through the initial stages of dynamic stall. Dynamic stall was found to occur coincidentally with the bursting of the separation bubble over the airfoil. Compressibility was found to confine the dynamic stall vortical structure closer to the airfoil surface. The measurements show that the peak suction pressure coefficient drops with increasing freestream Mach number, and also it lags the steady flow values at any given angle of attack. As the dynamic stall vortex is shed, an anti-clockwise vortex is induced near the trailing edge, which actively interacts with the post-stall flow.

Chandrasekhara, M. S.↗
NASA NTRS1982

Dynamic load measurements with delta wings undergoing self-induced roll-oscillations

The aerodynamic forces acting on a delta wing, mounted on a free-to-roll sting-balance apparatus, were measured. Two wing planforms having leading edge sweeps of 76 and 80 deg were tested, but only the wing with the 80 deg sweep would undergo periodic self-induced roll oscillation. The time dependent forces and roll angles for this wing were then recorded for various test conditions. In these tests a considerable drop in the average normal force of the free-to-roll wing was measured, relative to the normal force obtained in the static tests. Also, the helium-bubble flow visualization technique was used to gain some insight into the periodic motion of the separated leading edge vortices.

Levin, D.↗
NASA NTRS2004

Module for Oxygenating Water without Generating Bubbles

A module that dissolves oxygen in water at concentrations approaching saturation, without generating bubbles of oxygen gas, has been developed as a prototype of improved oxygenators for water-disinfection and water-purification systems that utilize photocatalyzed redox reactions. Depending on the specific nature of a water-treatment system, it is desirable to prevent the formation of bubbles for one or more reasons: (1) Bubbles can remove some organic contaminants from the liquid phase to the gas phase, thereby introducing a gas-treatment problem that complicates the overall water-treatment problem; and/or (2) in some systems (e.g., those that must function in microgravity or in any orientation in normal Earth gravity), bubbles can interfere with the flow of the liquid phase. The present oxygenation module (see Figure 1) is a modified version of a commercial module that contains >100 hollow polypropylene fibers with a nominal pore size of 0.05 m and a total surface area of 0.5 m2. The module was originally designed for oxygenation in a bioreactor, with no water flowing around or inside the tubes. The modification, made to enable the use of the module to oxygenate flowing water, consisted mainly in the encapsulation of the fibers in a tube of Tygon polyvinyl chloride (PVC) with an inside diameter of 1 in. (approx.=25 mm). In operation, water is pumped along the insides of the hollow fibers and oxygen gas is supplied to the space outside the hollow tubes inside the PVC tube. In tests, the pressure drops of water and oxygen in the module were found to be close to zero at water-flow rates ranging up to 320 mL/min and oxygen-flow rates up to 27 mL/min. Under all test conditions, no bubbles were observed at the water outlet. In some tests, flow rates were chosen to obtain dissolved-oxygen concentrations between 25 and 31 parts per million (ppm) . approaching the saturation level of approx.=35 ppm at a temperature of 20 C and pressure of 1 atm (approx.=0.1 MPa). As one would expect, it was observed that the time needed to bring a flow of water from an initial low dissolved-oxygen concentration (e.g., 5 ppm) to a steady high dissolved-oxygen concentration at or near the saturation level depends on the rates of flow of both oxygen and water, among other things. Figure 2 shows the results of an experiment in which a greater flow of oxygen was used during the first few tens of minutes to bring the concentration up to approx.=25 ppm, then a lesser flow was used to maintain the concentration.

Gonzalez-Martin, Anuncia↗