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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Dynamic response of film thickness in spiral-groove face seals

Tests were performed on an inward- and an outward-pumping spiral-groove face seal to experimentally determine the film thickness response to seal seat motions and to gain insight into the effect of secondary seal friction on film thickness behavior. Film thickness, seal seat axial motion, seal frictional torque, and film axial load were recorded as functions of time. The experiments revealed that for sinusoidal axial oscillations of the seal seat, the primary ring followed the seal seat motion very well. For a skewed seal seat, however, the primary ring did not follow the seal seat motion, and load-carrying capacity was degraded. Secondary seal friction was varied over a wide range to determine its effect on film thickness dynamics. The seals were tested with ambient air at room temperature and atmospheric pressure as the fluid medium. The test speed ranged from 7000 to 20,000 rpm. Seal tangential velocity ranged from 34 to 98 m/sec (113 to 323 ft/sec).

Dirusso, E.↗
NASA NTRS1986

Space-based laser-driven MHD generator: Feasibility study

The feasibility of a laser-driven MHD generator, as a candidate receiver for a space-based laser power transmission system, was investigated. On the basis of reasonable parameters obtained in the literature, a model of the laser-driven MHD generator was developed with the assumptions of a steady, turbulent, two-dimensional flow. These assumptions were based on the continuous and steady generation of plasmas by the exposure of the continuous wave laser beam thus inducing a steady back pressure that enables the medium to flow steadily. The model considered here took the turbulent nature of plasmas into account in the two-dimensional geometry of the generator. For these conditions with the plasma parameters defining the thermal conductivity, viscosity, electrical conductivity for the plasma flow, a generator efficiency of 53.3% was calculated. If turbulent effects and nonequilibrium ionization are taken into account, the efficiency is 43.2%. The study shows that the laser-driven MHD system has potential as a laser power receiver for space applications because of its high energy conversion efficiency, high energy density and relatively simple mechanism as compared to other energy conversion cycles.

Choi, S. H.↗
NASA NTRS1992

Completing the evolution of supernova remnants and their bubbles

The filling fraction of hot gas in the ISM is reexamined with new calculations of the very long term evolution of SNRs and their fossil hot bubbles. Results are presented of a 1D numerical solution of the evolution of an SNR in a homogeneous medium with a nonthermal pressure corresponding to a 5-micro-G magnetic field and density of 0.2/cu cm. Comparison is made with a control simulation having no magnetic field pressure. It is found that the evolutions, once they have become radiative, differ in several significant ways, while both differ appreciably from qualitative pictures presented in the past. Over most of the evolution of either case, the hot bubble in the interior occupies only a small fraction of the shocked volume, the remainder in a thick shell of slightly compressed material. Column densities and radial distributions of O VI, N V, C IV, and Si IV as well as examples of absorption profiles for their strong UV lines are presented.

Slavin, Jonathan D.↗
NASA NTRS1993

Acoustic Pump

Pump uses acoustic-radiation forces. Momentum transferred from sound waves to sound-propagating material in way resulting in net pumping action on material. Acoustic pump is solid-state pump. Requires no moving parts, entirely miniaturized, and does not invade pumped environment. Silent, with no conventional vibration. Used as pump for liquid, suspension, gas, or any other medium interacting with radiation pressure. Also used where solid-state pump needed for reliability and controllability. In microgravity environment, device offers unusual control for low flow rates. For medical or other applications in which contamination cannot be allowed, offers noninvasive pumping force.

Heyman, Joseph S.↗
NASA NTRS1992

Pressure-confined clumps in magnetized molecular clouds

A substantial fraction of the mass of a giant molecular cloud (GMC) in the Galaxy is confined to clumps which occupy a small fraction of the volume of the cloud. A majority of the clumps in several well-studied GMCs (Ophiuchus, Orion G, Rosette, Cepheus OB3) are not in gravitational virial equilibrium, but instead are confined by the pressure of the surrounding medium. These clumps thus violate one of 'Larson's (1981) laws'. Generalizing the standard virial analysis for spherical clouds to spheroidal clouds, we determine the Jeans mass and the magnetic critical mass for the clumps in these clouds. The Alfven Mach number, which is proportional to the internal velocity dispersion of the clumps divided by the Alfven velocity, is estimated to be of order unity for all the clumps. The more massive clumps, which are in gravitational virial equilibrium, are too massive to be supported by magnetic fields alone (i.e., they are magnetically supercritical). Internally generated turbulence must play a key role in supporting these clumps.

Bertoldi, Frank↗
NASA NTRS1926

Experimental investigation of the physical properties of medium and heavy oils, their vaporization and use in explosion engines. Part I

While little has been accomplished in obtaining an abundant supply of light oils from coal and heavy oils, progress has been made on engine design to make use of the heavier oils. Progress has been made in two different directions which are outlined in this paper: the group of engines with medium and high-pressure carburetion in the cylinder; and the group of engines with low-pressure carburetion of the heavy oils before reaching the cylinder.

OILS↗
NASA NTRS1993

The theory of QSO absorption line systems and their relationship to the galaxies

The fundamental goal of this effort is to paint a picture of what the Ly-alpha forest clouds are and how they are distributed in space. Progress during the first phase of this program involved development of the 'Cheshire Cat Model' of Ly-alpha clouds in which systems over a large range of column densities are produced by disks with somewhat smaller column densities than those of normal galaxies. A prediction of the slab model of Ly-alpha clouds was confirmed by a new observational result, and the comparison of models to the new data allowed an estimate of the pressure of the intergalactic medium. This result should be forthcoming in pre-print form within the next month. The various results will now be described in more detail.

Charlton, Jane↗
NASA NTRS1995

Solar wind composition

Advances in instrumentation have resulted in the determination of the average abundances of He, C, N, O, Ne, Mg, Si, S, and Fe in the solar wind to approximately 10%. Comparisons with solar energetic particle (SEP) abundances and galactic cosmic ray abundances have revealed many similarities, especially when compared with solar photospheric abundances. It is now well established that fractionation in the corona results in an overabundance (with respect to the photosphere) of elements with first ionization potentials less than 10 eV. These observations have in turn led to the development of fractionation models that are reasonably successful in reproducing the first ionization (FIP) effect. Under some circumstances it has been possible to relate solar wind observations to particular source regions in the corona. The magnetic topologies of the source regions appear to have a strong influence on the fractionation of elements. Comparisons with spectroscopic data are particularly useful in classifying the different topologies. Ions produced from interstellar neutral atoms are also found in the solar wind. These ions are picked up by the solar wind after ionization by solar radiation or charge exchange and can be identified by their velocity in the solar wind. The pick-up ions provide most of the pressure in the interplanetary medium at large distances. Interstellar abundances can be derived from the observed fluxes of solar wind pick-up ions.

Ogilvie, K. W.↗
NASA NTRS1995

Hot shocked gas along the jets of NGC 4258 (M106)

The ROSAT High Resolution Interferometer (HRI) and Position Sensitive Proportional Counter (PSPC) detectors have been used to study the soft X-ray emission of the nearby SABbc galaxy NGC 4258 (M106). The helically twisted, nuclear jets, previously detected in radio continuum and visual emission-line studies, are found to dominate the X-ray images. After correcting pointing errors of up to +/- 7 sec in our HRI observation, we find that the southeast jet is spatially unresolved transversely along much of its 2.5 min (5 kpc) length. The northwest jet is more diffuse, and the extensive radio 'plateaus' also emit X-rays. The energy spectrum of the jets from the PSPC exposure is noisy but is best fitted as a Raymond-Smith plasma with kT = 0.3 keV, log N(sub H) approximately = 20.0/sq cm, and luminosity 1.6 x 10(exp 40) ergs/s between 0.1 and 2.4 keV. Gas at this temperature can arise from planar shocks of 500 km/s and may have been entrained as the jets scrape along the molecular clous that are known to be adjacent to the jets. The range of radial velocities from our published visual emission-line spectra of the jet are consistent with such a shock speed. We estimate that the mass of hot gas in the jets is 6 x 10(exp 4) (1/cc/n(sub e)) solar mass, with n(sub e) the average electron density. The inferred pressure of hot gas in the southeast jet may be similar to the radio equipartition pressure and to the ambient pressure of the interstellar medium (ISM). The X-ray spectral fit is poor above 0.7 keV and requires an additional hard component that peaks near the nucleus.

Cecil, G.↗
NASA NTRS1998

Magnetohydrodynamic Origin of Jets from Accretion Disks

A review is made of magnetohydrodynamic (MHD) theory and simulation of outflows from disks for different distributions of magnetic field threading the disk. In one limit of a relatively weak, initially diverging magnetic field, both thermal and magnetic pressure gradients act to drive matter to an outflow, while a toroidal magnetic field develops which strongly collimates the outflow. The collimation greatly reduces the field divergence and the mass outflow rate decreases after an initial peak. In a second limit of a strong magnetic field, the initial field configuration was taken with the field strength on the disk decreasing outwards to small values so that collimation was reduced. As a result, a family of stationary solutions was discovered where matter is driven mainly by the strong magnetic pressure gradient force. The collimation in this case depends on the pressure of an external medium. These flows are qualitatively similar to the analytic solutions for magnetically driven outflows. The problem of the opening of a closed field line configuration linking a magnetized star and an accretion disk is also discussed.

Lovelace, R. V. E.↗
DOE OSTI2021

Hydrogen Component Leak Rate Quantification for System Risk and Reliability Assessment through QRA and PHM Frameworks: Preprint

The National Renewable Energy Laboratory's (NREL) Hydrogen Safety Research and Development (HSR&D) program in collaboration with the University of Maryland's Systems Risk and Reliability Analysis Laboratory (SyRRA) are working to improve reliability and reduce risk in hydrogen systems. This approach strives to use quantitative data on component leaks and failures, together with Prognosis and Health Management (PHM), and Quantitative Risk Assessment (QRA) to identify at-risk components, reduce component failures and downtime, and predict when components require maintenance. Hydrogen component failures increase facility maintenance cost, facility downtime, and reduce public acceptance of hydrogen technologies, ultimately increasing facility size and cost because of potentially overly conservative requirements. Leaks are a predominant failure mode for hydrogen components. However, uncertainties in the amount of hydrogen emitted from leaking components and the frequency of those failure events limit the understanding of the risks that they present under real-world operational conditions. NREL has deployed a test fixture, the Leak Rate Quantification Apparatus (LRQA), to quantify the mass flow rate of leaking gases from medium and high-pressure components that have failed while in service. Quantitative hydrogen leak rate data from this system could ultimately be used to better inform risk assessment and Regulation Codes and Standards (RCS). Parallel activity explores the use of PHM and QRA techniques to assess and reduce risk, thereby improving safety and reliability of hydrogen systems. The results of QRAs could further provide a systematic and science-based foundation for the design and implementation of RCS, as in the latest versions of the NFPA 2 code for gaseous hydrogen stations. Alternatively, data-driven techniques of PHM could provide new damage diagnosis and health-state prognosis tools. This research will help end users, station owners and operators, and regulatory bodies move towards risk-informed preventative maintenance versus emergency corrective maintenance, reducing cost and improving reliability. Predictive modelling of failures could improve safety and affect RCS requirements such as setback distances at liquid refuelling sites. The combination of leak rate quantification research, PHM, and QRA can lead to better informed models enabling data-based decision to be made for hydrogen system safety improvements.

codes and standards↗
NASA NTRS1993

Overview 1993: Chemical propulsion at CSTAR

Chemical Propulsion at CSTAR continues to expand its activities and areas of interest. Several new initiatives are being developed which are extensions of, or replacements for, earlier projects. One current focus is on reassessing promising engine cycles and the enabling technologies for implementing them. These engine cycles which include advanced hybrids, and staged combustion cycles have the use of oxygen as a working fluid and coolant in common. Oxygen is used as a turbine drive gas, tank pressurant and as a cooling medium for combustion devices. CSTAR has interest in the propellant feed systems for advanced rocket engines, including propellant conditioning and tank pressurization, gas generators, and turbomachinery. CSTAR's interests also include propellant injection into the main chamber. These aspects of rocket propulsion embody a diverse range of technical disciplines and technologies, critical to the pursuit of low cost space access. The chemical propulsion program at CSTAR includes active projects investigating hybrid rocket engine oxygen feed systems, hybrid rocket injectors, gas fed hybrid rocket combustion, elements of main injectors for staged combustion devices. CSTAR is actively seeking industrial partners interested in joint participation in one or more phases of the analyses, design, development and application of propulsion technologies and related technical disciplines.

Knuth, William H.↗
NASA NTRS1995

High Pressure Earth Storable Rocket Technology Program: Basic Program

The HIPES Program was conducted for NASA-LeRC by TRW. The Basic Program consisted of system studies, design of testbed engine, fabrication and testing of engine. Studies of both pressure-fed and pump-fed systems were investigated for N2O4 and both MMH and N2H4 fuels with the result that N2H4 provides the maximum payload for all satellites over MMH. The higher pressure engine offers improved performance with smaller envelope and associated weight savings. Pump-fed systems offer maximum payload for large and medium weight satellites while pressure-fed systems offer maximum payload for small light weight satellites. The major benefits of HIPES are high performance within a confined length maximizing payload for lightsats which are length (volume) constrained. Three types of thrust chambers were evaluated -- Copper heatsink at 400, 500 and 600 psia chamber pressures for performance/thermal; water cooled to determine heat absorbed to predict rhenium engine operation; and rhenium to validate the concept. The HIPES engine demonstrated very high performance at 50 lbf thrust (epsilon = 150) and Pc = 500 psia with both fuels: Isp = 337 sec using N2O4-N2H4 and ISP = 327.5 sec using N2O4-MMH indicating combustion efficiencies greater than 98%. A powder metallurgy rhenium engine demonstrated operation with high performance at Pc = 500 psia which indicated the viability of the concept.

Chazen, M. L.↗
NASA NTRS1991

Lift producing device exhibiting low drag and reduced ventilation potential and method for producing the same

A lift producing device is disclosed which is adapted to be connected to a vehicle to provide lift to the vehicle when the vehicle is moved relative to a first fluid medium having a first density and viscosity and being in contact with a second fluid medium adjacent the vehicle. The second fluid medium has a second fluid density which is different from the first fluid density. The lift producing device comprises opposed first and second major surfaces joined at a longitudinally extending leading edge and at a longitudinally extending trailing edge, with at least a portion of the longitudinally extending leading edge being spaced from the longitudinally extending trailing edge by a predetermined mean chord length. When the vehicle is moved relative to the first fluid medium at a velocity within a range of predetermined velocities, with each of the velocities having a direction inclined from a plane extending through the leading edge and the trailing edge within a predetermined angular range, a region of high pressure is generated in the first fluid medium adjacent the first major surface and a region of low pressure is generated in the first fluid medium adjacent the second major surface. The lift producing device has a cross-sectional shape which will generate a pressure distribution around the device when the vehicle is moved relative to the first fluid medium at a velocity within the range of predetermined velocities such that the first fluid medium exhibits attached laminar flow along the device for a portion of the predetermined mean chord length from the leading edge to the trailing edge and will neither form a laminar separation bubble adjacent the second major surface of the device, nor exhibit turbulent separation adjacent the second major surface for substantially all of the predetermined mean chord length from the leading edge to the trailing edge. The portion along which attached laminar flow is maintained is the longest portion which will still fulfill the flow separation requirements. A method for producing the foil is also disclosed.

Caldwell, Richard A.↗
NASA NTRS1990

Radiative magnetized thermal conduction fronts

The evolution of plane-parallel magnetized thermal conduction fronts in the interstellar medium (ISM) was studied. Separating the coronal ISM phase and interstellar clouds, these fronts have been thought to be the site of the intermediate-temperature regions whose presence was inferred from O VI absorption-line studies. The front evolution was followed numerically, starting from the initial discontinuous temperature distribution between the hot and cold medium, and ending in the final cooling stage of the hot medium. It was found that, for the typical ISM pressure of 4000 K/cu cm and the hot medium temperature of 10 to the 6th K, the transition from evaporation to condensation in a nonmagnetized front occurs when the front thickness is 15 pc. This thickness is a factor of 5 smaller than previously estimated. The O VI column densities in both evaporative and condensation stages agree with observations if the initial hot medium temperature Th exceeds 750,000 K. Condensing conduction fronts give better agreement with observed O VI line profiles because of lower gas temperatures.

Borkowski, Kazimierz J.↗
DOE OSTI2024

Method and system for electrochemically compressing gaseous hydrogen

Method and system for electrochemically compressing hydrogen. In one embodiment, the system includes a membrane electrode assembly (MEA) that includes a polymer electrolyte membrane (PEM), an anode, and a cathode. First and second gas diffusion media are positioned adjacent the cathode and anode, respectively. A humidifying membrane is positioned next to the second gas diffusion medium on a side opposite the anode. A water supply is connected to the humidifying membrane, and a hydrogen gas supply is connected to the second gas diffusion medium. A hydrogen gas collector including a back pressure regulator is connected to the first gas diffusion medium. Separators, positioned on opposite sides of the MEA, are connected to a power source. In use, hydrogen is electrochemically pumped across the MEA and collected in the hydrogen gas collector. The PEM is kept properly humidified by the humidifying membrane, which releases water into the second gas diffusion medium.

Hamdan, Monjid↗
NASA NTRS1993

Electromagnetically driven relativistic jets - A class of self-consistent numerical solutions

We explore the generalized Grad-Shafranov (GS) equation (Lovelace et al. 1986), which describes the cross-field balance of the magnetic flux surfaces in a stationary, axisymmetric, cold relativistic MHD wind. We construct a family of self-consistent, jet-type, non-self-similar solutions in which flux surfaces thread the equatorial plane vertically and are eventually collimated into nested cylinders. These solutions conserve the total energy and angular momentum along each flux surface and satisfy the relativistic GS equation in the cross-field direction. We find that the total specific energy in the flow depends primarily on a dimensionless combination of the poloidal magnetic flux, the rotation, and the mass loading rate, which reduces to Michel's (1969) magnetization parameter for radial winds. The final width of the flow and its ratio of kinetic energy flux to Poynting flux depend sensitively on the pressure distribution of the ambient medium, which is required to contain the jet at its outer edge when no jet-confirming external toroidal magnetic field is present. Furthermore, we show that the magnetic pressure in the flow can be much higher near the axis than close to the edge, reflecting the 'pinching' effect of the toroidal magnetic field.

Li, Zhi-Yun↗