Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “pore sizes”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Feasibility of SiC composite structures for 1644 deg gas turbine seal applications

The feasibility of silicon carbide composite structures was evaluated for 1644 K gas turbine seal applications. The silicon carbide composites evaluated consisted of Si/SiC Silcomp (Trademark) - and sintered silicon carbide as substrates, both with attached surface layers containing BN as an additive. A total of twenty-eight candidates with variations in substrate type and density, and layer chemistry, density, microstructure, and thickness were evaluated for abradability, cold particle erosion resistance, static oxidation resistance, ballistic impact resistance, and fabricability. The BN-free layers with variations in density and pore size were later added for evaluation. The most promising candidates were evaluated for Mach 1.0 gas oxidation/erosion resistance from 1477 K to 1644 K. The as-fabricated rub layers did not perform satisfactorily in the gas oxidation/erosion tests. However, preoxidation was found to be beneficial in improving the hot gas erosion resistance. Overall, the laboratory and rig test evaluations show that material properties are suitable for 1477 K gas turbine seal applications.

Darolia, R.↗
NASA NTRS1980

Superfluid plug as a control device for helium coolant

New results are obtained on the characteristics of a superfluid plug as a nonmechanical control device for supplying cold helium vapor on demand from a superfluid-helium container. The data reported are for an Al2O3 ceramic plug having a nominal 5-micron pore size. A theoretical background and steady-state data are presented on mass flow rates and pressures as a function of liquid temperature. It is demonstrated that the superfluid plug can be employed as a flow control device in a control system designed to provide coolant on demand.

Karr, G. R.↗
NASA NTRS1981

Vapor-liquid phase separator permeability results

Continued studies are described in the area of vapor-liquid phase separator work with emphasis on permeabilities of porous sintered plugs (stainless steel, nominal pore size 2 micrometer). The temperature dependence of the permeability has been evaluated in classical fluid using He-4 gas at atmospheric pressure and in He-2 on the basis of a modified, thermosmotic permeability of the normal fluid.

Yuan, S. W. K.↗
NASA NTRS1980

Vacuum applications of metal foams

Several vacuum applications of copper foams in the density range 2-5% and pore sizes of 0.5-0.7 mm are discussed, such as a foreline hydrocarbon trap in a mechanical vacuum pump, a molecular-flow resistor, a diffuser, and a water injector. Other suggested applications include the use of foam copper in the form of an externally heated plug to remove traces of oxygen from inert gases bled into a vacuum system through a stainless steel line and the use of the porous surface for minimizing release of secondary electrons from electrodes in the path of charged particle beams.

Kendall, B. R. F.↗
NASA NTRS1982

Design of a 35-kilowatt bipolar nickel-hydrogen battery for low Earth orbit application

The needs of multikilowatt storage for low Earth orbit applications are featured. The modular concept, with projected energy densities of 20-24 W-hr/lb and 700-900 W-hr/ft3, has significant improvements over state of the art capabilities. Other design features are; active cooling, a new scheme for H2-O2 recombination, and pore size engineering of all cell components.

Cataldo, R. L.↗
NASA NTRS1982

Altered bone turnover during spaceflight

Modifications in calcium metabolism during spaceflight were studied, using parameters that reflect bone turnover. Bone formation rate, medullary area, bone length, bone density, pore size distribution, and differential bone cell number were evaluated in growing rate both immediately after and 25 days after orbital spaceflights aboard the Soviet biological satellites Cosmos 782 and 936. The primary effect of space flight on bone turnover was a reversible inhibition of bone formation at the periosteal surface. A simultaneous increase in the length of the periosteal arrest line suggests that bone formation ceased along corresponding portions of that surface. Possible reasons include increased secretion of glucocorticoids and mechanical unloading of the skeleton due to near-weightlessness, while starvation and immobilization are excluded as causes.

Turner, R. T.↗
NASA NTRS1982

Electrolyte management in porous battery components. Static measurements

The interaction between the porous hydrogen and nickel electrodes and microporous separator with respect to electrolyte management in nickel/hydrogen cells has been investigated. The distribution of electrolyte among the components has been measured and correlated with the pore size distributions, total void volume, and resistance of a variety of electrodes and separators. Calculations are used to show the effects of systematically varying these properties.

Abbey, K. M.↗
NASA NTRS1983

Experimental design

The design of long life, low weight nickel cadmium cells is studied. The status of a program to optimize nickel electrodes for the best performance is discussed. The pore size of the plaque, the mechanical strength and active material loading are considered in depth.

Lim, H. S.↗
NASA NTRS1981

Detection of strength limiting defects in cellular glasses by dielectric measurements

The foamed glasses that are being considered for structural support in solar thermal energy system silvered glass concentrator mirrors are assessed for strength-limiting defects by a nondestructive technique which measures the capacitance of well defined regions. The feasibility of locating large defects is demonstrated for the case of one type of cellular mass. Observed capacitance variations are believed to be due to small voids or other irregularities in the material. If the defects are equal to or greater than approximately 20 times the glass matrix pore size, they can be resolved with sufficient accuracy to delineate their spatial extent.

Gammell, P. M.↗
NASA NTRS1983

Propagation of sound in highly porous open-cell elastic foams

This work presents both theoretical predictions and experimental measurements of attenuation and progressive phase constants of sound in open-cell, highly porous, elastic polyurethane foams. The foams are available commercially in graded pore sizes for which information about the static flow resistance, thermal time constant, volume porosity, dynamic structure factor, and speed of sound is known. The analysis is specialized to highly porous foams which can be efficient sound absorbers at audio frequencies. Negligible effect of internal wave coupling on attenuation and phase shift for the frequency range 16-6000 Hz was predicted and no experimentally significant effects were observed in the bulk samples studied. The agreement between predictions and measurements in bulk materials is excellent. The analysis is applicable to both the regular and compressed elastic open-cell foams.

Lambert, R. F.↗
NASA NTRS1983

Strength and fracture toughness of reaction-bonded Si3N4

Fracture strength and fracture toughness measurements were made on reaction-bonded Si3N4 materials with a range of alpha/beta ratios. The results do not indicate any clear relation between the modulus of rupture and the alpha/beta ratio over the range 1.5-9. Values for the modulus of rupture range from 219 to 290 MN per sq m, with an overall average of 238 MN per sq m. The notched beam fracture toughness is found to be constant over the range of microstructures produced, indicating that of the various microstructural features (e.g., alpha/beta ratio and pore size and distribution) no single element has a controlling influence over fracture toughness and the fracture surface energy.

Danforth, S. C.↗
NASA NTRS1983

A Report on Superfluid Helium Flow Through Porous Plugs for Space Science Applications

As a background for the study of the nature of superfluid helium flow through porous plugs for other space science uses, preliminary tests on various plugs of a given material, diameter, height, and filtration grade have been performed. Two characteristics of the plugs, pore size and number of channels, have been determined by the bubble test and warm flow test of helium gas through the plugs, respectively. Tests on the flow of He II through the plugs have also been performed. An obvious feature of the results of these tests is that for isothermal measurements of pressure versus mass flow rate below approximately 2.10 K, the flow is separated into two different regimes, indicative of the occurrence of a critical phenomenon.

Mason, F. C.↗
NASA NTRS1983

Long life nickel electrodes for a nickel-hydrogen cell. I Initial performance

In order to develop a long life nickel electrode for a Ni/H2 cell, an investigation was begun to study the effects of sinter structure and active material loading level on the long life performance of nickel electrodes. This paper is a report on the initial performance of these electrodes as a part of an accelerated life test program. Seven different types of nickel plaques were made which included three levels of both their mechanical strength and median pore size. These plaques were impregnated with three levels of active material loading. The resultant electrodes were tested by a 200-cycle stress test which was conducted in flooded electrolyte, and also for initial performance in a Ni/H2 boiler plate cell. An interesting and unexpected observation was that an increased initial utilization of the active material was due more to its complete discharge to the lower average oxidation state than its increased charge acceptance in the charged state.

Lim, H. S.↗
NASA NTRS1985

High-thermal-gradient Superalloy Crystal Growth

Single, (001)-oriented crystals of PWA 1480 were processed in alumina/silica shell molds in a laboratory high gradient furnace. The furnace employs a graphite resistance heated element, a radiation baffle, and a water cooled radiation trap below the baffle. All crystals were grown in vacuum (10 torr) and all heat transfer was radiative. The element is constructed with a variable cross section that is tapered just above the baffle to maximize heat input and therefore thermal gradient. A maximum alloy temperature of 1600 C was used. A thermal gradient of 130 deg C/cm was recorded at 1370 C just above the solidus of the PWA 1480 alloys. Crystal bars with 14.4 and 17.5 mm diameters were grown in alumina/silica shell molds. Each crystal was started from a 1.6 mm pencil seed at a rate of 76 mm/hr and slowly accelerated to a rate of 200 mm/hr under computer control. Volume percent porosity and average pore size were measured as functions of distance in representative bars. Low cycle fatigue behavior and stress rupture properties were determined.

Pearson, D. D.↗
NASA NTRS1986

Lightweight nickel electrode for nickel hydrogen cells and batteries

The nickel electrode was identified as the heaviest component of the nickel hydrogen (NiH2) battery. The NASA Lewis Research Center is developing nickel electrodes for NiH2 battery devices which will be lighter in weight and have higher energy densities when cycled under a low Earth orbit regime at deep depths of discharge. Lightweight plaques are first exposed to 31 percent potassium hydroxide for 3 months to determine their suitability for use as electrode substrates from a chemical corrosion standpoint. Pore size distribution and porosity of the plaques are then measured. The lightweight plaques examined are nickel foam, nickel felt, nickel plastic and nickel plated graphite. Plaques are then electrochemically impregnated in an aqueous solution. Initial characterization tests of the impregnated plaques are performed at five discharge levels, C/2, 1.0 C, 1.37 C, 2.0C, and 2.74 C rates. Electrodes that passed the initial characterization screening test will be life cycle tested. Lightweight electrodes are approximately 30 to 50 percent lighter in weight than the sintered nickel electrode.

Britton, D. L.↗
NASA NTRS1986

Ultrasonic measurement of porosity in casts and welds

The development of a quantitative nondestructive method which involves ultrasonic attenuation measurements in frequency domain to determine volume fraction of porosity in aluminum cast is discussed. The aluminum alloy A357 casting samples were produced at the Ohio State University Foundry with controlled porosity contents ranging from 0% to 6%. A computer controlled system was used to direct ultrasonic beam to a test sample to different places to conduct ultrasonic attenuation measurements. The plot of attenuation coefficients as a function of frequency was then evaluated based on existing theories to determine volume fraction of porosity and pore size.

Adler, L.↗
NASA NTRS1986

Possible Mars brines - Equilibrium and kinetic considerations

To determine the fate of postulated near surface brines on Mars, the rate of H2O mass loss from subsurface brines was calculated as a function of latitude, depth, regolith porosity, eutectic temperature, and pore size. A model for a chemically reasonable brine that could reproduce Martian radar results was developed, and the escape rate of H2O molecules from such a brine was estimated. It is suggested that the presence of a low-permeability duricrust may be required to preserve such a brine for reasonable periods, and to prevent detection of an extensive subsurface system by the Viking MAWD instrument.

Zent, A. P.↗
NASA NTRS1986

A flooded-starved design for nickel-cadmium cells

A somewhat analogous situation among groupings of alkaline fuel cells is described where the stochastic aspects were much more accurately documented and then it was illustrated how this problem was eliminated using straight forward principles of pore size engineering. This is followed by a suggested method of adapting these same design principles to nickel-cadmium cells. It must be kept in mind that when cells are cycled to typically twenty percent depth of discharge that eighty percent of the weight of the cell is simply dead weight. Some of this dead weight might be put to better use by trading it for a scheme that would increase the time during which the cell would be working more closely to its optimum set of operating parameters.

Thaller, L. H.↗