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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

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NASA NTRS1950

Two-dimensional compressible flow in centrifugal compressors with straight blades

Six numerical examples are presented for steady, two-dimensional, compressible, nonviscous flow in centrifugal compressors with thin straight blades, the center lines of which generate the surface of a right circular cone when rotated about the axis of the compressor. A seventh example is presented for incompressible flow. The solutions were obtained in a region of the compressors, including the impeller tip, that was considered to be unaffected by the diffuser vanes or by the impeller-inlet configuration. Each solution applies to radial and mixed flow compressors with various cone angles but with the same angle between blades on the conic flow surface. The solution also apply to radial and mixed flow turbines with the rotation and the flow direction reversed. The effects of variations in the following parameters were investigated: (1) flow rate, (2) impeller-tip speed, (3) variation of passage height with radius, and (4) angle between blades on conic flow surface. The numerical results are presented in plots of the streamlines and constant Mach number lines. Correlation equations are developed whereby the flow conditions in any impeller with straight blades can be determined (in the region investigated by this analysis) for all operating conditions.

Stanitz, John D↗

NASA NTRS2001

Modeling Biogeochemical-Physical Interactions and Carbon Flux in the Sargasso Sea (Bermuda Atlantic Time-series Study site)

An ecosystem-carbon cycle model is used to analyze the biogeochemical-physical interactions and carbon fluxes in the Bermuda Atlantic Time-series Study (BATS) site for the period of 1992-1998. The model results compare well with observations (most variables are within 8% of observed values). The sea-air flux ranges from -0.32 to -0.50 mol C/sq m/yr, depending upon the gas transfer algorithm used. This estimate is within the range (-0.22 to -0.83 mol C/sq m/yr) of previously reported values which indicates that the BATS region is a weak sink of atmospheric CO2. The overall carbon balance consists of atmospheric CO2 uptake of 0.3 Mol C/sq m/yr, upward dissolved inorganic carbon (DIC) bottom flux of 1.1 Mol C/sq m/yr, and carbon export of 1.4 mol C/sq m/yr via sedimentation. Upper ocean DIC levels increased between 1992 and 1996 at a rate of approximately 1.2 (micro)mol/kg/yr, consistent with observations. However, this trend was reversed during 1997-1998 to -2.7 (micro)mol/kg/yr in response to hydrographic changes imposed by the El Nino-La Nina transition, which were manifested in the Sargasso Sea by the warmest SST and lowest surface salinity of the period (1992-1998).

Signorini, Sergio R.↗

NASA NTRS1972

Atmospheric helium and geomagnetic field reversals.

The problem of the earth's helium budget is examined in the light of recent work on the interaction of the solar wind with nonmagnetic planets. It is proposed that the dominant mode of helium (He4) loss is ion pumping by the solar wind during geomagnetic field reversals, when the earth's magnetic field is very small. The interaction of the solar wind with the earth's upper atmosphere during such a period is found to involve the formation of a bow shock. The penetration altitude of the shock-heated solar plasma is calculated to be about 700 km, and ionization rates above this level are estimated for a cascade ionization (electron avalanche) process to average 10 to the 9th power ions/sq cm/sec. The calculated ionization rates and the capacity of the solar wind to remove ionized helium (He4) from the upper atmosphere during geomagnetic dipole reversals are sufficient to yield a secular equilibrium over geologic time scales. The upward transport of helium from the lower atmosphere under these conditions is found to be adequate to sustain the proposed loss rate.

Sheldon, W. R.↗

NASA NTRS2018

HST/GHRS Observations of Cool, Low-Gravity Stars. VI. Mass-Loss Rates and Wind Parameters for M Giants

The photon-scattering winds of M giants absorb parts of the chromospheric emission lines and produce self-reversed spectral features in high-resolution Hubble Space Telescope (HST)/GHRS spectra. These spectra provide an opportunity to assess fundamental parameters of the wind, including flow and turbulent velocities, the optical depth of the wind above the region of photon creation, and the star’s mass-loss rate. This paper is the last paper in the series “GHRS Observations of Cool, Low-Gravity Stars”; the last several have compared empirical measurements of spectral emission lines with models of the winds and mass loss of K giants and supergiants. We have used the Sobolev with Exact Integration radiative transfer code, along with simple models of the outer atmosphere and wind, to determine and compare the wind characteristics of the two M-giant stars, gamma Cru (M3.5III) and mu Gem (M3IIIab), with previously derived values for low-gravity K-stars. The analysis specifies the wind parameters and calculates line profiles for the Mg II resonance lines, in addition to a range of unblended Fe II lines. Our line sample covers a large range of wind opacities and, therefore, probes a range of heights in the atmosphere. Our results show that mu Gem has a slower and more turbulent wind than gamma Cru. Also, mu Gem has a weaker chromosphere, in terms of surface flux, with respect to gamma Cru. This suggests that mu Gem is more evolved than gamma Cru. Comparing the two M giants in this work with previously studied K-giant and supergiant stars (alpha Tau, gamma Dra, and lambda Vel) reveals that the M giants have slower winds than the earlier giants, but exhibit higher mass-loss rates. Our results are interpreted in the context of the winds being driven by Alfvén waves.

chromospheric emission lines↗

NASA NTRS1982

Voltage reapplication rate control for commutation of thyristors

A circuit for commutating a thyristor (21) by shunting its current for a minimum interval, thereby removing sustaining voltage to said thyristor, then subsequently restoring voltage to said thyristor at a predetermined rate, utilizes a series combination of a commutation electronic switch (22) and an isolated dc voltage supply (23) connected in parallel with the thyristor. The voltage supply is arranged with a polarity that permits the current flowing through the thyristor in one direction to be bypassed through the series combination while the commutation switch is turned on and to reverse bias the thyristor when the commutation switch is fully on. A dv/dt control circuit (24) limits the rate of rise of voltage across the commutation switch (22) as it is turned off in response to a command input signal. The dv/dt control circuit is comprised of a constant current drive (31) and a capacitor (32) connected between the output terminal of the commutation switch and the control input terminal of the commutation switch. The thyristor may be a triac (40) with two commutation switches (42, 43), one for current of each polarity, or with a single commutation switch (55) and a bridge circuit (52-55) for selecting the polarity of the switch (56).

Rippel, Wally E.↗

NASA NTRS1967

Laboratory pulse modulator uses minority carrier storage diodes

Pulse modulator is capable of continuously variable pulse width over a 10 to 1 range of 1.0 microsecond to 0.1 microsecond and operates over a wide range of pulse repetition rates. Pulse width diversity is obtained by operating step-recovery diodes in the reverse conduction mode.

Source record↗

NASA NTRS1976

Impact ejecta on the moon

The partitioning of energy and the distribution of the resultant ejecta on the moon is numerically modeled using a Eulerian finite difference grid. The impact of an iron meteoroid at 15 km/sec on a gabbroic anorthosite lunar crust is examined. The high speed impact induced flow is described over the entire hydrodynamic regime from a time where the peak pressures are 6 Mbar until the stresses everywhere in the flow are linearly elastic, and less than 5 kbar. Shock-induced polymorphic phase changes, (plagioclase and pyroxene to hollandite and perovskite), and the subsequent reversion to low pressure phases are demonstrated to enhance shock wave attenuation. A rate-dependent equation of state is used for describing the hysteretic effect of the phase change. Ballistic equations for a spherical planet are then applied to material with net velocity away from the moon.

Okeefe, J. D.↗

NASA NTRS1995

The 3-D effects in the long-term solar wind speed rise observed by Voyager 2 in early 1994

In early 1994, Voyager 2 at 42-43 AU near heliolatitude 10 deg S observed over a period of approximately 100 days a remarkable sequence of quasi-recurrent stream fronts, wherein the background (ambient) speed rose steadily from approximately 450 to approximately 550 km/s while the mean period of the streams decreased from the usual 25 days down to approximately 20 days. A qualitative explanation for this effect can be derived from IMP observations, which show that the amplitude of the stream structure at 1 AU increased monotonically in late 1993, concurrent with major secular evolution in the corona. The reduction in period, then, amounts to a doppler shift due to the progressive overtaking of successively faster streams in the sequence. Attempts to model this process quantitatively with 1-D dynamic simulations falter on three accounts: (1) the reduction in period is overestimated, (2) the simulation predicts many more fronts surviving to 43 AU than are observed by Voyager; (3) the density variations are much too large. It is argued that inclusion of the 3-D geometry in the simulation would resolve most all these shortcomings. Using a series of calculations executed with 1-D, 2-D, and 3-D MHD models of hypothetical tilted-dipole flows, we show that: (1) the radial propagation velocities of 3-D fronts are less than those of 1-D or 2-D fronts, owing to the tilt of (and increased shearing across) the interaction surfaces hence the overtaking rate of successive streams is reduced; (2) in a tilted-dipole geometry, the reverse fronts should largely disappear from the equatorial plane by 43 AU, effectively halving the number of fronts to be observed (see companion paper on predominance of forward fronts at Voyager); and (3) the density enhancements would be much smaller than predicted by a 1-D model.

Pizzo, V. J.↗

NASA NTRS2015

Loop Heat Pipe Temperature Oscillation Induced by Gravity Assist and Reservoir Heating

The Laser Thermal Control System (LCTS) for the Advanced Topographic Laser Altimeter System (ATLAS) to be installed on NASA's Ice, Cloud, and Land Elevation Satellite (ICESat-2) consists of a constant conductance heat pipe and a loop heat pipe (LHP) with an associated radiator. During the recent thermal vacuum testing of the LTCS where the LHP condenser/radiator was placed in a vertical position above the evaporator and reservoir, it was found that the LHP reservoir control heater power requirement was much higher than the analytical model had predicted. Even with the control heater turned on continuously at its full power, the reservoir could not be maintained at its desired set point temperature. An investigation of the LHP behaviors found that the root cause of the problem was fluid flow and reservoir temperature oscillations, which led to persistent alternate forward and reversed flow along the liquid line and an imbalance between the vapor mass flow rate in the vapor line and liquid mass flow rate in the liquid line. The flow and temperature oscillations were caused by an interaction between gravity and reservoir heating, and were exacerbated by the large thermal mass of the instrument simulator which modulated the net heat load to the evaporator, and the vertical radiator/condenser which induced a variable gravitational pressure head. Furthermore, causes and effects of the contributing factors to flow and temperature oscillations intermingled.

Thermal Control Systems↗

NASA NTRS2015

Loop Heat Pipe Temperature Oscillation Induced by Gravity Assist and Reservoir Heating

0000↗

NASA NTRS2017

Packaging Technology for Dielectric-Coating-Less Heavy Ion Radiation Testing of High-Voltage (HV) Electronic Parts

Testing high voltage (HV) electronic parts (greater than 300 V) for sudden event effects (SEE) caused by cosmic rays in the space environment, consisting of energetic heavy-ions, and neutron radiation in the upper atmosphere is a crucial step towards using these parts in spacecraft and aircraft. Due to the nature of cosmic radiation and neutrons, electronic parts are tested for SEE without any packaging and/or shielding over the top of the device. In the case of commercial HV parts, the top of the packaging is etched off and then a thin dielectric coating is placed over the part in order to avoid electrical arcing between the device surface and wire bonds and other components. Even though the effects of the thin dielectric layer on SEE testing can be accounted for, the dielectric layer significantly hinders post testing failure analysis. Replicating the test capability of state-of-the-art packaging while eliminating the need for post radiation test processing of the die surface (that obscures failure analysis) is the goal. To that end, a new packaging concept for HV parts has been developed that requires no dielectric coating over the part. Testing of prototype packages used with Schottky diodes (rated at 1200V) has shown no electrical arcing during testing and leakage currents during reverse bias testing are within the manufactures specifications.

High Voltage↗

NASA NTRS2024

GVIPS Prediction of Cyclic Ratchetting Behavior and Cycles With Interrupted Relaxation Periods of TIMETAL 21S at 650 oC

The predictive performance of a multimechanism GVIPS model with saturating hardening function is assessed against a set of high temperature cyclic experiments under both strain-control and stress-control at varying rates of loading as well as several complex interrupted cyclic responses. The material specimens were composed of the titanium alloy, TIMETAL 21S, and tested at 650oC, see Lissenden et al., 2007. The model did a very good job of predicting the variety of tests, particularly given the fact that only monotonic loading tests (tensile, creep, relaxation) and a single fully reversed cycle was used for characterization. It was particularly interesting that the model was capable of reasonably capturing the rate of accumulated strain during ratchetting under tensile mean stress. Given complex interrupted cyclic response, the model was able to both qualitatively and even quantitatively predict reasonably well both the cyclic and associated relaxation periods (in all quadrants of the stress-strain space) thus confirming the validity of the chosen functional forms for both hardening and thermal recovery. The quantitative inaccuracy is associated with the fact that the material specimens tested by Lissenden et al., 2007 was significantly “softer” than those tested by Castelli in Saleeb et al., 1994 which were used for characterization of the GVIPS model parameters.

Viscoplaticity↗

NASA NTRS2026

GVIPS Prediction of Cyclic Ratchetting Behavior and Cycles with Interrupted Relaxation Periods of TIMETAL 21S at 650 °C

The predictive performance of a multimechanism GVIPS model with saturating hardening function is assessed against a set of high temperature cyclic experiments under both strain-control and stress-control at varying rates of loading as well as several complex interrupted cyclic responses. The material specimens were composed of the titanium alloy, TIMETAL 21S, and tested at 650 °C, see Lissenden et al., 2007. The model did a very good job of predicting the variety of tests, particularly given the fact that only monotonic loading tests (tensile, creep, relaxation) and a single fully reversed cycle was used for characterization. It was particularly interesting that the model was capable of reasonably capturing the rate of accumulated strain during ratchetting under tensile mean stress. Given complex interrupted cyclic response, the model was able to both qualitatively and even quantitatively predict reasonably well both the cyclic and associated relaxation periods (in all quadrants of the stress-strain space) thus confirming the validity of the chosen functional forms for both hardening and thermal recovery. The quantitative inaccuracy is associated with the fact that the material specimens tested by Lissenden et al., 2007 was significantly “softer” than those tested by Castelli in Saleeb et al., 1994 which were used for characterization of the GVIPS model parameters.

Viscoplaticity↗

NASA NTRS1976

Mars - Chemical weathering as a massive volatile sink

The amounts of volatiles incorporated in the Martian regolith by photostimulated oxidation weathering of Fe(2+)-bearing minerals are estimated. The process of photostimulated oxidation weathering is described, and it is noted that all the necessary constituents for this process are present on Mars. The rates at which oxygen and hydrogen are irreversibly removed from the Martian atmosphere by the present process are determined, irreversible and reversible water losses are considered, and the loss of CO2 by carbonate formation is shown to be irreversible. The results suggest that photostimulated oxidation weathering has irreversibly consumed 100 to 100,000 g/sq cm of H2O and 10 to 10,000 g/sq cm of CO2, assuming a uniform rate over geologic time. It is concluded that if the amounts of H2O and CO2 actually removed by photostimulated oxidation are close to the upper limits of the present estimates, then that process may have had a major effect in limiting the amount of H2O and CO2 trapped in the regolith and polar caps.

Huguenin, R. L.↗

NASA NTRS1982

The mechanical design of a vapor compressor for a heat pump to be used in space

A heat pump developed for use in Spacelab as a stand-alone refrigeration unit as well as within a fluid loop system is discussed. It will provide an active thermal control for payloads. Specifications for the heat pump were established: (1) heat removal rates at the source; (2) heat source temperatures from room temperature; (3) heat-sink fluid temperatures at condenser inlet; and (4) minimum power consumption. A reversed Carnot cycle heat pump using Freon 12 as working fluid incorporating a one-cylinder reciprocating compressor was selected. The maximum crankshaft speed was fixed relatively high at 100 rpm. The specified cooling rates then made it necessary to select a cylinder volume of 10 cu cm, which was obtained with a bore of 40 mm and a stroke of 8 mm.

Berner, F.↗

NASA NTRS2017

Reversible and Irreversible Time-Dependent Behavior of GRCop-84

A series of mechanical tests were conducted on a high-conductivity copper alloy, GRCop-84, in order to understand the time dependent response of this material. Tensile, creep, and stress relaxation tests were performed over a wide range of temperatures, strain rates, and stress levels to excite various amounts of time-dependent behavior. At low applied stresses the deformation behavior was found to be fully reversible. Above a certain stress, termed the viscoelastic threshold, irreversible deformation was observed. At these higher stresses the deformation was observed to be viscoplastic. Both reversible and irreversible regions contained time dependent deformation. These experimental data are documented to enable characterization of constitutive models to aid in design of high temperature components.

viscoelasticity↗

NASA NTRS1981

Measurement of sound absorption in the air

The large temperature gradient in each section of the resonance tube resulting from the liquid nitrogen coolant necessitated a design modification to the cooling system. A timer and four solenoid valves were installed so that the coolant flow can be reversed periodically. The hardware and software for controlling the analog to digital converter and conversion rate were completed, and the system is operational. A duty cycle control circit was implemented so that on the sixteenth conversion a relay shuts off the vibration exciter used to generate the sound wave. Thus the starting point of each decay curve is exactly known. This information is necessary for evaluating the g digital decay information. The data acquisition and digital decay evaluation programs are described.

Meredith, R.↗

NASA NTRS1981

New technologies for solar energy silicon - Cost analysis of dichlorosilane process

A reduction in the cost of silicon for solar cells is an important objective in a project concerned with the reduction of the cost of electricity produced with solar cells. The cost goal for the silicon material is about $14 per kg (1980 dollars). The process which is currently employed to produce semiconductor grade silicon from trichlorosilane is not suited for meeting this cost goal. Other processes for producing silicon are, therefore, being investigated. A description is presented of results obtained for the DCS process which involves the production of dichlorosilane as a silicon source material for solar energy silicon. Major benefits of dichlorosilane as a silicon source material include faster reaction rates for chemical vapor deposition of silicon. The DCS process involves the reaction 2SiHCl3 yields reversibly SiH2Cl2 + SiCl4. The results of a cost analysis indicate a total product cost without profit of $1.29/kg of SiH2Cl2.

Yaws, C. L.↗