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Dotson K.T.,University of Maryland University College | Sunderland P.B.,University of Maryland University College | Yuan Z.-G.,National Center for Space Exploration Research | Urban D.L.,NASA
Fire Safety Journal | Year: 2011

Laminar smoke points were measured in nonbuoyant laminar jet diffusion flames in coflowing air. Microgravity was obtained on board the International Space Station. A total of 55 smoke points were found for ethylene, propane, propylene, and propylene/nitrogen mixtures. Burner diameters were 0.41, 0.76, and 1.6 mm, and coflow velocities varied from 5.4 to 65 cm/s. These flames allow extensive control over residence time via variations in dilution, burner diameter, and coflow velocity. The measured smoke-point lengths scaled with d-0.91uair0.41, where d is burner diameter and uair is coflow velocity. The measurements yielded estimates of sooting propensities of the present fuels in microgravity diffusion flames. Analytical models of residence times in gas jet flames are presented, and although residence time helps explain many of the observed trends it does not correlate the measured smoke points. © 2011 Elsevier Ltd. All rights reserved.

Meyer M.E.,NASA | Mulholland G.W.,University of Maryland University College | Mulholland G.W.,U.S. National Institute of Standards and Technology | Bryg V.,National Center for Space Exploration Research | And 5 more authors.
Aerosol Science and Technology | Year: 2015

The Smoke Aerosol Measurement Experiment (SAME) has been conducted twice by the National Aeronautics and Space Administration and provided real-time aerosol data in a spacecraft micro-gravity environment. Flight experiment results have been recently analyzed with respect to comparable ground-based experiments. The ground tests included an electrical mobility analyzer as a reference instrument for measuring particle size distributions of the smoke produced from overheating five common spacecraft materials. Repeatable sample surface temperatures were obtained with the SAME ground-based hardware, and measurements were taken with the aerosol instruments returned from the International Space Station comprising two commercial smoke detectors, three aerosol instruments, which measure moments of the particle size distribution, and a thermal precipitator for collecting smoke particles for transmission electron microscopy (TEM). Moment averages from the particle number concentration (zeroth moment), the diameter concentration (first moment), and the mass concentration (third moment) allowed calculation of the count mean diameter and the diameter of average mass of smoke particles. Additional size distribution information, including geometric mean diameter and geometric standard deviations, can be calculated if the particle size distribution is assumed to be lognormal. Both unaged and aged smoke particle size distributions from ground experiments were analyzed to determine the validity of the lognormal assumption. Comparisons are made between flight experiment particle size distribution statistics generated by moment calculations and microscopy particle size distributions (using projected area equivalent diameter) from TEM grids, which have been returned to the Earth. © 2015 This article not subject to United States copyright law.

Zimmerli G.A.,NASA | Asipauskas M.,National Center for Space Exploration Research | Van Dresar N.T.,NASA
Cryogenics | Year: 2010

We have analyzed data published by others reporting the solubility of helium in liquid hydrogen, oxygen, and methane, and of nitrogen in liquid oxygen, to develop empirical correlations for the mole fraction of these pressurant gases in the liquid phase as a function of temperature and pressure. The data, compiled and provided by NIST, are from a variety of sources and covers a large range of liquid temperatures and pressures. The correlations were developed to yield accurate estimates of the mole fraction of the pressurant gas in the cryogenic liquid at temperature and pressures of interest to the propulsion community, yet the correlations developed are applicable over a much wider range. The mole fraction solubility of helium in all these liquids is less than 0.3% at the temperatures and pressures used in propulsion systems. When nitrogen is used as a pressurant for liquid oxygen, substantial contamination can result, though the diffusion into the liquid is slow. © 2010 Elsevier Ltd. All rights reserved.

Nayagam V.,National Center for Space Exploration Research | Dietrich D.L.,NASA | Ferkul P.V.,National Center for Space Exploration Research | Hicks M.C.,NASA | Williams F.A.,University of California at San Diego
Combustion and Flame | Year: 2012

Experimental observations of anomalous combustion of n-heptane droplets burning in microgravity are reported. Following ignition, a relatively large n-heptane droplet first undergoes radiative extinction, that is, the visible flame ceases to exist because of radiant energy loss. But the droplet continues to experience vigorous vaporization for an extended period according to a quasi-steady droplet-burning law, ending in a secondary extinction at a finite droplet diameter, after which a vapor cloud rapidly appears surrounding the droplet. We hypothesize that the second-stage vaporization is sustained by low-temperature, soot-free, "cool-flame" chemical heat release. Measured droplet burning rates and extinction diameters are used to extract an effective heat release, overall activation energy, and pre-exponential factor for this low-temperature chemistry, and the values of the resulting parameters are found to be closer to those of "cool-flame" overall reaction-rate parameters, found in the literature, than to corresponding hot-flame parameters. © 2012 The Combustion Institute.

Balasubramaniam R.,National Center for Space Exploration Research | Gokoglu S.,NASA | Hegde U.,National Center for Space Exploration Research
International Journal of Mineral Processing | Year: 2010

The processing of lunar regolith for the production of oxygen is a key component of the In-Situ Resource Utilization plans currently being developed by NASA. In the carbothermal process, a portion of the surface of the regolith in a container is heated by exposure to a heat source so that a small zone of molten regolith is established. A continuous flow of methane is maintained over the molten regolith zone. In this paper, we discuss the development of a chemical conversion model of the carbothermal process to predict the rate of production of carbon monoxide. Our model is based on a mechanism where methane pyrolyzes when it comes in contact with the surface of the hot molten regolith to form solid carbon and hydrogen gas. Carbon is deposited on the surface of the melt, and hydrogen is released into the gas stream above the melt surface. We assume that the deposited carbon mixes in the molten regolith and reacts with metal oxides in a reduction reaction by which gaseous carbon monoxide is liberated. Carbon monoxide bubbles through the melt and is released into the gas stream. It is further processed downstream to ultimately produce oxygen. © 2010 Elsevier B.V. All rights reserved.

Olson S.L.,NASA | Ferkul P.V.,National Center for Space Exploration Research
42nd International Conference on Environmental Systems 2012, ICES 2012 | Year: 2012

Drop tower tests are conducted at Martian gravity to determine the flammability of three materials compared to previous tests in other normal gravity and reduced gravity environments. The comparison is made with consideration of a modified NASA standard test protocol. Material flammability limits in the different gravity and flow environments are tabulated to determine the factor of safety associated with normal gravity flammability screening. Previous testing at microgravity and Lunar gravity indicated that some materials burned to lower oxygen concentrations in low gravity than in normal gravity, although the low g extinction limit criteria are not the same as 1g due to time constraints in drop testing. Similarly, the data presented in this paper for Martian gravity suggest that there is a gravity level below Earth's at which materials burn more readily than on Earth. If proven for more materials, this may indicate the need to include a factor of safety on 1g flammability limits.

Olson S.L.,NASA | Gokoglu S.A.,NASA | Urban D.L.,NASA | Ruff G.A.,NASA | Ferkul P.V.,National Center for Space Exploration Research
Proceedings of the Combustion Institute | Year: 2015

Upward flame spread tests were conducted on thin fuels in a sealed chamber capable of accommodating large-scale samples (1 m length). The primary objective of these tests was to measure flame spread and pressure rise in a large sealed chamber during and after flame spread and to characterize that data as a function of sample material, initial pressure, and sample size. The flame spread rate as a function of initial pressure has been measured for a given fuel and found to vary as ∼P2 in agreement with Grash of number scaling. The burning rate per unit area for a fixed pressure has been shown to be a constant independent of fuel area density or quantity of fuel burned. A steady upward flame spread was observed only at low pressure. The pressure rise in a sealed chamber has been shown to scale with the quantity of fuel burned, and the peak pressure has been shown to scale inversely with initial pressure, in agreement with the pressure dependence of the characteristic time associated with a simple analytical solution of an energy balance. The pressure rise per mass of fuel burned exhibits an exponential decay with burn-time, also in agreement with the analytical solution.

Zimmerli G.A.,NASA | Metzger S.,Vantage Partners LLC | Asipauskas M.,National Center for Space Exploration Research
50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference 2014 | Year: 2014

A key requirement of a low-gravity screen-channel liquid acquisition device (LAD) is the need to retain 100% liquid in the channel in response to propellant outflow and spacecraft maneuvers. The point at which a screen-channel LAD ingests vapor is known as breakdown, and can be measured several different ways such as: visual observation of bubbles in the LAD channel outflow; a sudden change in pressure drop between the propellant tank and LAD sump outlet; or, an indication by wet-dry sensors placed in the LAD channel or outflow stream. Here we describe a new type of sensor for gauging a screen-channel LAD, the Radio Frequency Mass Gauge (RFMG). The RFMG measures the natural electromagnetic modes of the screen-channel LAD, which is very similar to an RF waveguide, to determine the amount of propellant in the channel. By monitoring several of the RF modes, we show that the RFMG acts as a global sensor of the LAD channel propellant fill level, and enables detection of LAD breakdown even in the absence of outflow. This paper presents the theory behind the RFMG-LAD sensor, measurements and simulations of the RF modes of a LAD channel, and RFMG detection of LAD breakdown in a channel using a simulant fluid during inverted outflow and long-term stability tests. © 2014 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Hegde U.,National Center for Space Exploration Research | Hegde U.,NASA | Gotti D.,National Center for Space Exploration Research | Hicks M.,NASA
Journal of Supercritical Fluids | Year: 2014

Observations of near-critical water jets are reported in the injection Reynolds number range of approximately 300-3000 to characterize their transition to turbulence. Three types of cases are described: (i) subcritical jet injected into subcritical water, (ii) supercritical jet injected into supercritical water, and (iii) supercritical jet injected into subcritical water. In each case, the working pressure was kept above the critical value to eliminate two-phase effects. For cases (i) and (ii), the transition behavior follows well known characteristics with transition to turbulence initially occurring near the tip of the jet with the transition location moving upstream nearer to the nozzle exit with an increase in injection Reynolds number. However, the transition behavior for case (iii) is quite different with significant buoyant effects leading to turbulent behavior at lower Reynolds numbers. Consideration of the pseudocritical region with strongly varying fluid properties, which is established in the mixing region between the jet and the cell fluid, yields an effective Froude number that is useful to elucidate this difference. The effective Froude number incorporates the Prandtl number of the mixing region to account for the large disparity between viscous and thermal length scales. © 2014 Elsevier B.V. All rights reserved.

Yuan Z.-G.,National Center for Space Exploration Research | Kleinhenz J.E.,NASA
41st International Conference on Environmental Systems 2011, ICES 2011 | Year: 2011

Gas phase pressure effects on the apparent thermal conductivity of a JSC-1A/air mixture have been experimentally investigated under steady state thermal conditions from 10 kPa to 100 kPa. The result showed that apparent thermal conductivity of the JSC-1A/air mixture decreased when pressure was lowered to 80 kPa. At 10 kPa, the conductivity decreased to 0.145 W/m/oC, which is significantly lower than 0.196 W/m/oC at 100 kPa. This finding is consistent with the results of previous researchers. The reduction of the apparent thermal conductivity at low pressures is ascribed to the Knudsen effect. Since the characteristic length of the void space in bulk JSC-1A varies over a wide range, both the Knudsen regime and continuum regime can coexist in the pore space. The volume ratio of the two regimes varies with pressure. Thus, as gas pressure decreases, the gas volume controlled by Knudsen regime increases. Under Knudsen regime the resistance to the heat flow is higher than that in the continuum regime, resulting in the observed pressure dependency of the apparent thermal conductivity.

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