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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Experimental Study of Low Temperature Behavior of Aviation Turbine Fuels in a Wing Tank Model

An experimental investigation was performed to study aircraft fuels at low temperatures near the freezing point. The objective was an improved understanding of the flowability and pumpability of the fuels under conditions encoutered during cold weather flight of a long range commercial aircraft. The test tank simulated a section of an outer wing tank and was chilled on the upper and lower surfaces. Fuels included commercial Jet A and Diesel D-2; JP-5 from oil shale; and Jet A, intermediate freeze point, and D-2 fuels derived from selected paraffinic and naphthenic crudes. A pour point depressant was tested.

Stockemer, Francis J.↗
NASA NTRS1978

Evaluation of the application of some gas chromatographic methods for the determination of properties of synthetic fuels

The purpose of the investigation was to evaluate the applicability, to some synthetic fuels, of some gas chromatographic methods now under development for use with petroleum based fuels. Thirty-two jet and diesel fuel samples which were prepared from oil shale and coal syncrudes were examined. The boiling range distribution of each was determined by gas chromatography, and from that data distillation properties were calculated. The calculated results gave sufficient agreement with the measured values that the equations could be useable in their present form. Bulk fuel properties were calculated for the 16 JP-5 and Diesel No. 2 type fuels. The results show that the equations would not give useable results. Capillary column gas chromatography was used to determine the n-alkane content of the eight JP-5 type samples and the results related to the observed freezing points. The results show that the concentrations of the long straight chain molecules in the fuels exert influence on the freezing point but are not the complete controlling factor.

Antoine, A. C.↗
NASA NTRS1979

Ammonia photolysis and the greenhouse effect in the primordial atmosphere of the earth

Photochemical calculations indicate that in the prebiotic atmosphere of earth ammonia would have been irreversibly converted to N2 in less than 40 years if the ammonia surface mixing ratio were no more than 0.0001. However, if a continuous outgassing of ammonia were maintained, radiative-equilibrium calculations indicate that a surface mixing ratio of ammonia of 0.0001 or greater would provide a sufficient greenhouse effect to keep the surface temperature above freezing. With a 0.0001 mixing ratio of ammonia, 60% to 70% of the present-day solar luminosity would be adequate to maintain surface temperatures above freezing. A lower limit to the time constant for accumulation of an amount of nitrogen equivalent to the present day value is 10 my if the outgassing were such as to provide a continuous surface mixing ratio of ammonia of at least 0.00001.

Kuhn, W. R.↗
NASA NTRS1980

Another look at aircraft-triggered lightning

There is positive evidence that a rapidly moving aircraft charged to high potentials by triboelectric processes can trigger lightning discharges by passage through freezing precipitation. The freezing zone in a nonstormy rain cloud is shown to be an electrically volatile region because of the potent charge exchange mechanisms which are active in agitated mixtures of supercooled water droplet and ice. Several intensifying effects are suggested which can be produced by the passage of an aircraft through this precipitation, resulting in a highly-ionized wake which acts like a trailing conductor. If weak charge centers are present in the cloud, the ionized wake acts to short out the gradient field resulting in very high potentials at the aircraft. The high potentials explain the electrical activity at the aircraft described by pilots, including intense corona, sparks and radio interference terminating in a loud discharge. Lightning strikes to naval aircraft towing gunnery targets at the end of long steel cables are described, showing that the same triggering mechanism may be involved in those cases. Recommendations are made to include triggering experiments in government flight programs now in progress.

Clifford, D. W.↗
NASA NTRS1980

Solar energy system performance evaluation-seasonal report for Elcam San Diego, San Diego, California

The solar energy system, Elcam San Diego, was designed to supply domestic hot water heating for a single family residence located in Encinitas, California. System description, performance assessment, operating energy, energy savings, maintenance, and conclusions are presented. The system is a 'Sunspot' two tank cascade type, where solar energy is supplied to either a 66 gallon preheat tank (solar storage) or a 40 gallon domestic hot water tank. Water is pumped directly from one of the two tanks, through the 65 square feet collector array and back into the same tank. Freeze protection is provided by automatically circulating hot water from the hot water tank through the collectors and exposed plumbing when freezing conditions exist. Auxiliary energy is supplied by natural gas. Analysis is based on instrumented system data monitored and collected for one full season of operation.

Source record↗
NASA NTRS1980

Fuel system technology overview

Fuel system research and technology studies are being conducted to investigate the correlations and interactions of aircraft fuel system design and environment with applicable characteristics of the fuel. Topics include: (1) analysis of in-flight fuel temperatures; (2) fuel systems for high freezing point fuels; (3) experimental study of low temperature pumpability; (4) full scale fuel tank simulation; and (5) rapid freezing point measurement.

Friedman, R.↗
NASA NTRS1980

A short-range objective nocturnal temperature forecasting model

A relatively simple, objective, nocturnal temperature forecasting model suitable for freezing and near-freezing conditions has been designed so that a user, presumably a weather forecaster, can put in standard meteorological data at a particular location and receive an hour-by-hour prediction of surface and air temperatures for that location for an entire night. The user has the option of putting in his own estimates of wind speeds and background sky radiation which are treated as independent variables. An analysis of 141 test runs show that 57.4% of the time the model predicts to within 1 C for the best cases and to within 3 C for 98.0% of all cases.

Sutherland, R. A.↗
NASA NTRS1978

Phase diagram of KHF2 and non-equilibrium effects

The equilibrium diagram for the KHF2-H2O system was constructed from cooling and heating curves for the compositions between 5 wt% and 40 wt% KHF2 and the results are shown. The phase diagrams shown is typical of that of a two component system with miscible liquid phases and whole solid phases consist of pure components. A eutectic point was found at approximately 15% KHF2 which remains completely liquid down to a temperature of -9.0 C. No hydrate formation was observed and no anomalous behavior such as the occurrence of solid transitions or metastable states was observed. The effect of rapid freezing on the equilibrium diagram did not appear, and cooling curves exhibited only one halt. Also, at rapid freezing rates, the supercooling of the solutions was smaller than those observed at the slow cooling rates. The existence of a eutectic composition and the slow rate of dissolution of the salt are used to interpret heat absorption behavior in practical applications of the KHF2-H2O system.

Hobson, M. C.↗
NASA NTRS1951

An Instrument Employing a Coronal Discharge for the Determination of Droplet-Size Distribution in Clouds

A flight instrument that uses electric means for measuring the droplet-size distribution in above-freezing clouds has been devised and given preliminary evaluation in flight. An electric charge is placed on the droplets and they are separated aerodynamically according to their mass. Because the charge placed on the droplets is a. function of the droplet size, the size spectrum can 'be determined by measurement of the charge deposited on cylinders of several different sizes placed to intercept the charged droplets. An expression for the rate of charge acquisition by a water droplet in a field of coronal discharge is derived. The results obtained in flight with an instrument based on the method described indicate that continuous records of droplet-size spectrum variations in clouds can be obtained. The experimental instrument was used to evaluate the method and was not refined to the extent necessary for obtaining conclusive meteorological data. The desirable features of an instrument based on the method described are (i) The instrument can be used in clouds with temperatures above freezing; (2) the size and the shape of the cylinders do not change during the exposure time; (3) the readings are instantaneous and continuous; (4) the available sensitivity permits the study of variations in cloud structures of less than 200 feet in extent.

Brun, Rinaldo J.↗
NASA NTRS1981

Aviation turbine fuel properties and their trends

This paper is an examination of published Jet A inspection data covering selected property distributions, averages, and trends for the period from 1969 to 1979. Yearly median values of aromatics, mercaptan sulfur content, 10-percent distillation temperature, smoke point, and freezing point are changing with time, approaching their specification limit values, particularly in the last three years. A near-specification property is defined as one within a stated tolerance band around the specification limit. On this basis, most fuel samples have one to three near-specification properties, the most common being aromatics, smoke point, and freezing point.

Friedman, R.↗
NASA NTRS1982

Recent trends in aviation turbine fuel properties

Plots and tables, compiled from Department of Energy (and predecessor agency) inspection reports from 1969 to 1980, present ranges, averages, extremes, and trends for most of the 22 properties of Jet A aviation turbine fuel. In recent years, average values of aromatics content, mercaptan sulfur content, distillation temperature of 10 percent recovered, smoke point, and freezing point show small but recognizable trends toward their specification limits. About 80 percent of the fuel samples had at least one property near specification, defined as within a standard band about the specification limit. By far the most common near-specification properties were aromatics content, smoke point, and freezing point.

Friedman, R.↗
NASA NTRS1982

'Scaling' analysis of the ice accretion process on aircraft surfaces

A comprehensive set of scaling parameters is developed for the ice accretion process by analyzing the energy equations of the dynamic freezing zone and the already frozen ice layer, the continuity equation associated with supercooled liquid droplets entering into and impacting within the dynamic freezing zone, and energy equation of the ice layer. No initial arbitrary judgments are made regarding the relative magnitudes of each of the terms. The method of intrinsic reference variables in employed in order to develop the appropriate scaling parameters and their relative significance in rime icing conditions in an orderly process, rather than utilizing empiricism. The significance of these parameters is examined and the parameters are combined with scaling criteria related to droplet trajectory similitude.

Keshock, E. G.↗
NASA NTRS1983

Steady flow approximations to the helium r-process

A steady flow approximation to the r-process is presented and used for numerical experiments with physical quantities to determine the sensitivity of the process to variations in those quantities. The effect of neutron capture cross sections along the capture path and of recently available improved beta decay rates on the r-process are discussed. The peaks in the observed r-process yield curve near mass numbers 80 and 130 are roughly characterized by a neutron number density of 10 to the 20th per cu/cm; the mean beta decay rates are about 10/s, and the freezing time is comparable to or less than 0.1 s. The peak near mass number 195 is roughly characterized by a neutron number density of 10 to the 21st/cm, the mean beta decay rates are about 100/s, and the freezing time is comparable to or less than 0.01 s. The flow path of the steady state r-process is sensitively dependent upon the neutron capture cross sections in the flow network and on the values of the beta decay rates.

Cameron, A. G. W.↗
NASA NTRS1983

Magnetism and thermal evolution of the terrestrial planets

The absence in the cases of Venus and Mars of the substantial intrinsic magnetic fields of the earth and Mercury is considered, in light of thermal history calculations which suggest that, while the cores of Mercury and the earth are continuing to freeze, the cores of Venus and Mars may still be completely liquid. It is noted that completely fluid cores, lacking intrinsic heat sources, are not likely to sustain thermal convection for the age of the solar system, but cool to a subadiabatic, conductive state that cannot maintain a dynamo because of the gravitational energy release and the chemically driven convection that accompany inner core growth. The models presented include realistic pressure- and composition-dependent freezing curves for the core, and material parameters are chosen so that correct present-day values of heat outflow, upper mantle temperature and viscosity, and inner core radius, are obtained for the earth.

Stevenson, D. J.↗
NASA NTRS1982

Ground based studies for the space processing of lead-tin-telluride

This paper summarizes the results of a series of studies dealing with crystal growth from the melt and in particular, the growth of the narrow bandgap semiconductor PbSnTe by the Bridgman technique. Theoretical calculations have shown that for low Prandtl number fluids such as semiconductors, convection has no effect on the temperature field in the melt but has a significant effect on the compositional field. They also show that convective flow will exist in a Bridgman growth system on earth, even in the 'thermally stable' configuration. Measurements of the specific heat have been made up to temperatures of 722 C. The thermal diffusivity has been measured up to 1010 C which includes values for the melt. The interdiffusion coefficients for PbTe and SnTe in the melt have been determined. A technique has been developed and tested which provides a vacuum tight quartz ampoule with electrical feedthroughs for interface demarcation studies during the Bridgman growth. Analysis of crystals grown has indicated that the PbSnTe system is solutally unstable and the distribution of SnTe in the crystal, after an anomalous first to freeze region, follows that predicted by Pfann for convection controlled growth. Studies of the amount of supercooling in PbSnTe indicate that this may explain an anomalous composition distribution in the first to freeze region of an unseeded growth.

Crouch, R. K.↗
NASA NTRS1983

Interpreting the solar wind ionization state

The ionization state of the solar coronal expansion is frozen within a few solar radii of the solar photosphere, and spacecraft measurements of the solar wind heavy ion charge state can therefore yield information about coronal conditions (e.g., electron temperature). Previous interpretations of the frozen-in ionization state have always assumed that in the coronal freezing-in region, (1) all heavy ions flow at the same bulk speed as protons, (2) the electron velocity distribution function is Maxwellian, and (3) conditions vary in space but not in time. The consequences of relaxing these assumptions for the interpretation of solar wind charge state measurements are examined. It is found that: (1) the temperature inferred by traditional interpretation of the interplanetary ionization state overestimates (underestimate) the actual coronal electron temperature if higher ion charge stages flow systematically faster (slower) than lower stages at the coronal freezing radius; (2) temperatures inferred from relative abundance measurements of ion-charge-stages with high ionization potentials moderately overestimate the actual coronal electron temperature if the high-energy tail of the coronal electron velocity distribution is enhanced relative to a Maxwellian distribution; (3) the propagation of a disturbance, e.g., a shock wave, through the corona can strongly affect the frozen-in charge state, but only over a time (a few times ten minutes) corresponding to the coronal transit time for the disturbance.

Owocki, S. P.↗
NASA NTRS1983

The faint young sun-climate paradox - Crustal influences

The various mechanisms which have been proposed to compensate for the climatic effects of a 30 percent increase in the solar constant during the past 4.5 billion years are examined. Mechanisms besides the greenhouse effect could have provided significant compensation during the second half of this period. It is proposed that the development of continents during the past 2.5 billion years caused a secular evolution of the atmosphere-ocean heat transport system. As a result, past climates were less susceptible to complete freeze-over. The lower albedo of water would be another factor in this effect insofar as the early earth had smaller land masses. A complete or nearly complete freeze-over may have occurred as past glaciations were widespread. Climate models then suggest that the earth would have remained frozen through the present epoch and into a distant future. It is suggested that volcanic influences could allow a passage from the frozen branch onto the unfrozen branch of climate models should conditions on earth be suitable for that climate change. A broad equatorial belt of volcanic ash is one scenario which would allow a transfer from the frozen earth state into the unfrozen one.

Schatten, K. H.↗
NASA NTRS1983

The effect of a coronal shock wave on the solar wind ionization state

In connection with studies of solar wind ionization state freezing, it is shown that, by using a Lagrangian approach of following individual fluid parcels, the techniques used previously for calculating ionization state variations in a steady state case can be extended straightforwardly to time-varying flows. The specific ionization state calculations presented are for a relatively simple picture of time-dependent coronal flow, based on a well-known model of a self-similar shock wave propagating through the corona. Time-dependent ionization effects for the sudden transition between two otherwise steady flows are likely to be limited to a narrow range of gas parcels which, having been shocked within the coronal freezing-in radius, pass a fixed interplanetary observer in an interval of a few tens of minutes. The amplitude of any rise in interplanetary ionization temperature associated with the coronal shock is likely to be considerably smaller than the jump in electron temperature that actually occurs in the corona.

Owocki, S. P.↗