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At least 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Temperature Rises In Pumps For Superfluid Helium

Report discusses increases in temperature of superfluid helium in centrifugal and fountain-effect pumps. Intended for use in transfers of superfluid helium in outer space. Increases in temperature significantly affect losses during transfers and are important in selection of temperatures of supply tanks. Purpose of study, increase in temperature in fountain-effect pump calculated on basis of thermodynamic considerations, starting from assumption of ideal pump. Results of recent tests of ceramic material intended for use in such pumps support this assumption. Overall, centrifugal pumps more effective because it produces smaller rise in temperature.

Kittel, Peter↗
NASA NTRS1989

Thermophysical properties of Helium-4 from 0.8 to 1500 K with pressures to 2000 MPa

Tabular summary data of the thermophysical properties of fluid helium are given for temperatures from 0.8 to 1500 K, with pressures to 2000 MPa between 75 and 300 K, or to 100 MPa outside of this temperature band. Properties include density, specific heats, enthalpy, entropy, internal energy, sound velocity, expansivity, compressibility, thermal conductivity, and viscosity. The data are calculated from a computer program which is available from the National Institute of Standards and Technology. The computer program is based on carefully fitted state equations for both normal and superfluid helium.

Arp, Vincent D.↗
NASA NTRS1989

Non-LTE analysis of extremely helium-rich stars. The hot sdO stars LSE 153, 259 and 263

Results of a non-LTE fine analysis based mainly on high-resolution CASPEC spectra for three extremely helium-rich sdO stars are discussed in order to explain hydrogen deficiency in single stars. High temperature (Teff = 70,000 to 75,000 K) and a position in the log Teff - log g diagram were found close to the Eddington limit. Various abundance estimates are derived for hydrogen (upper limits only), carbon, nitrogen, and magnesium. Hydrogen is reduced to less than 10 percent by number in LSE 153 and LSE 263, and to less than 5 percent in LSE 259. The hydrogen deficiency is accompanied by nitrogen- and carbon-enrichment in LSE 153 and LSE 259 only. In LSE 263, carbon is depleted by about 1 dex. Stellar masses obtained by assuming that a core mass-luminosity relation holds for these stars, were found to be in the range 0.6-0.9 solar mass, yielding luminosities log L/L:solar = 3.7-4.5. Two of the program stars (LSE 153 and 259) appear to be possible successors of the R CrB and helium B stars, whereas the third star (LSE 263) displays a much lower carbon content in its photosphere making it an exceptional case among the known hydrogen deficient stars.

Husfeld, D.↗
NASA NTRS1990

The discovery of magnetically controlled circumstellar matter in the helium-weak stars HD 5737 and HD 79158

The paper reports the discovery, using combined IUE spectroscopy and Zeeman polarimetric magnetic field measurements, of magnetically controlled circumstellar material in two helium-weak stars. HD 5737 = Alpha Sculptoris is, except for its extreme helium deficiency, similar to the He weak sn star HD 21699. A unique period for the magnetic and C IV and Si IV variations of 21.65 days is reported. The effective (longitudinal) field nulls coincide extremely well with C IV line strength maxima. The magnetic field and equatorial trapped plasma are highly oblique to the rotation axis (about 70 deg), and the line variations appear to be stable. Similar magnetospheric variations in HD 79158 = 36 Lyncis have been discovered, for which no period had been previously available. The period is 3.84 days, yet it too displays magnetic-equatorial plasma. The magnetospheric axis is highly oblique to the rotation axis, around 80 deg.

Shore, Steven N.↗
NASA NTRS1990

Pressure drop in the SHOOT superfluid helium acquisition system

Central to the upcoming Superfield Helium On-Orbit Transfer (SHOOT) demonstration is the fluid acquisition system. The main component of the system is a rectangular cross-section gallery area with one side fabricated from a fine mesh screen. He II enters through the screen and is delivered to a fountain effect pump. A model is proposed to predict the pressure drop as fluid flows through the screen and an expression is derived for the required gallery arm length as a function of flow rate demand. The model is compared with measurement of pressure drop in a full scale SHOOT gallery arm operated with flow rates of up to 850 cu dm/hr. The tests were conducted in the University of Wisconsin horizontal liquid helium flow facility to minimize gravitational effects.

Nissen, J. A.↗
NASA NTRS1990

The helium strong stars of the Ori OB1 association

International Ultraviolet Explorer (IUE) fluxes for the helium strong stars of the orion OB1b association and the physical parameters implied by these data are discussed. The helium strong stars are found to be main sequence, or only slightly evolved, stars between about 7 and 12 solar mass.

Shore, Steven N.↗
NASA NTRS1991

Tests in Helium Illustrate High Mach Number Inlet-Forebody Interactions

High Mach helium tests are described in the form of the view-graphs. The following topics are included: high-speed inlet-forebody interaction tests; helium tunnel; boundary layer approaching inlet; ramp surface pressure distribution; static pressure on ramp; and pressure variation across wedge and ramp.

Weidner, John↗
NASA NTRS1990

Hydrogen, helium, and other solar-wind components in lunar soil - Abundances and predictions

The lack of a shielding atmosphere on the moon permits solar-wind particles to impinge upon the lunar soil and become implanted into the various phases which comprise the soil. Relatively large quantities of solar-wind implanted hydrogen (50-100 ppm) and helium (10-50 ppm) are present. The measured parameter of I(s)FeO, a direct indicator of maturity and exposure age, can be used as a first approximation to predict the abundances of many solar-wind components in the soils. However, because ilmenite acts as a 'sponge' for the retention of certain elements, the TiO2 content of the soil is a better indicator for hydrogen and helium contents.

Taylor, Lawrence A.↗
NASA NTRS1991

Lithium in halo stars - Constraining the effects of helium diffusion on globular cluster ages and cosmology

Stellar evolutionary models with diffusion are used to show that observations of lithium in extreme halo stars provide crucial constraints on the magnitude of the effects of helium diffusion. The flatness of the observed Li-T(eff) relation severely constrains diffusion Li isochrones, which tend to curve downward toward higher T(eff). It is argued that Li observations at the hot edge of the plateau are particularly important in constraining the effects of helium diffusion; yet, they are currently few in number. It is proposed that additional observations are required there, as well as below 5500 K, to define more securely the morphology of the halo Li abundances. Implications for the primordial Li abundance are considered. It is suggested that a conservative upper limit to the initial Li abundance, due to diffusive effects alone, is 2.35.

Deliyannis, Constantine P.↗
NASA NTRS1992

Helium bubble flow visualization of the spanwise separation on a NACA 0012 with simulated glaze ice

Research was performed to experimentally visualize and document the flow separation due to simulated glaze ice accretion on a NACA 0012 semispan with 30 deg sweep using helium bubbles as flow tracers. Results are compared to Navier-Stokes computational simulations for different angles of attack. Prior to acquiring data for the semispan model, a two dimensional experiment was conducted to determine the accuracy of using the helium bubbles as flow tracers. Results from the three dimensional experiment compare well to the computational simulations.

Kerho, M.↗
NASA NTRS1990

Superfluid helium on-orbit resupply

The requirements for superfluid helium (SFHe) resupply were investigated, and the results were used to develop a conceptual design for a superfluid helium tanker (SFHT) which is designed to meet a 50-mission requirement. The SFHT design uses a conventional dewar approach with multiple vapor cooled shields, and a porous-plug phase separator for on-orbit temperature control. An open loop refrigeration approach is used for ground conversion of normal He to SFHe, allowing near-total fill of the supply tank. Design diagrams of the SFHT concept and of various SFHT subsystems are presented.

Eberhardt, Ralph N.↗
NASA NTRS1990

Liquid helium Dewar for one meter mirror testing

The NASA Ames Research Center has developed a baseline design for a One Meter Cryogenic Optical Test Facility (OMF) incorporating a liquid helium Dewar for cryogenic optical testing of one-meter-class mirrors, principally the Space Infrared Telescope Facility (SIRTF) primary mirror. The primary requirements for the test facility are as follows: (1) the facility must be capable of interferometrically testing any mirror, positioned face-up or face-down, with a diameter less than 1.5 meters and a radius of curvature from 1.5 to 5.5 meters; (2) the facility must achieve and maintain, for 24 hours, a mirror temperature of 4 K with a maximum radiative heat load of less than 500 mW to the mirror, using stored liquid helium and liquid nitrogen; (3) the facility must include a vibration-isolated metrology structure between the test mirror and an external interferometer, and (4) the facility must be operated by two persons and a test, starting from the mounting of a mirror to the removal of a mirror, must be conducted within one week.

Sarver, George L., III↗
NASA NTRS1992

Helium bubble flow visualization of the spanwise separation on a NACA 0012 with simulated glaze ice

Research has been performed to experimentally visualize and document the flow separation due to simulated glaze ice accretion on a NACA 0012 semispan with 30-deg sweep using helium bubbles as flow tracers. Results are compared to Navier-Stokes computational simulations for different angles of attack. Prior to acquiring data for the semispan model, a two-dimensional experiment was conducted to determine the accuracy of using the helium bubbles as flow tracers. Results from the 3D experiment compare well to the computational simulations.

Kerho, M.↗
NASA NTRS1990

Superfluid helium needs and resupply on Space Station

Viewgraphs and discussion on superfluid helium needs and resupply on space station are presented. Topics covered include: uses of superfluid helium in space; space station He 2 technology issues; resupply - fluid management issues; liquid acquisition devices for on orbit transfer; and liquid acquisition devices for SHOOT.

Dipirro, Michael J.↗
NASA NTRS1992

Helium escape from the Earth's atmosphere - The charge exchange mechanism revisited

We have studied the escape of neutral helium from the terrestrial atmosphere through exothermic charge exchange reactions between He(+) ions and the major atmospheric constituents N2, O2 and O. Elastic collisions with the neutral background particles were treated quantitatively using a recently developed kinetic theory approach. An interhemispheric plasma transport model was employed to provide a global distribution of He(+) ions as a function of altitude, latitude and local solar time and for different levels of solar ionization. Combining these ion densities with neutral densities from an MSIS model and best estimates for the reaction rate coefficients of the charge exchange reactions, we computed the global distribution of the neutral He escape flux. The escape rates show large diurnal and latitudinal variations, while the global average does not vary by more than a factor of three over a solar cycle. We find that this escape mechanism is potentially important for the overall balance of helium in the Earth's atmosphere. However, more accurate values for the reaction rate coefficients of the charge exchange reactions are required to make a definitive assessment of its importance.

Lie-Svendsen, O.↗
NASA NTRS1992

A liquid-helium-cooled absolute reference cold load for long-wavelength radiometric calibration

Design, radiometric and thermal performance, and operation of a large diameter (78 cm) liquid-helium-cooled blackbody absolute reference cold load (CL) for the calibration of microwave radiometers is described. CL provides an absolute calibration near the liquid-helium (LHe) boiling point, with total uncertainty in the radiometric temperature of less than 30 mK over the 2.5-23 cm wavelength operating range. CL was used at several wavelengths at the South Pole, Antarctica and the White Mountain Research Center, California. Results show that, for the instruments operated at 20-, 12-, 7.9-, and 4.0 cm wavelength at the South Pole, the total corrections to the LHe boiling-point temperature (about 3.8 K) were 48 +/-23, 18 +/-10, 10 +/-18, and 15 +/-mK.

Bensadoun, Marc↗
NASA NTRS1993

Spectra of low-mass helium star models and the type Ic supernova SN 1987M

The question of whether the low-mass helium star models reproduce the helium-poor Type Ic spectrum of SN 1987M is investigated by comparing the theoretical spectrum from the 3.3-solar-mass model of Shigeyama et al. (1990) to observations of SN 1987M reported by Filippenko et al. (1990). The results indicate a number of positive correlations between the observed and the computed spectra. In both types of spectra, Ca II, O I, and Mg I emission lines dominate at late times, and, if extensive composition mixing is imposed, good fits can be made to the shapes of the emission features and good agreement can be found with the observed ratio of the forbidden and IR triplet blends of Ca II. The former indicates that the 3.3-solar-mass model predicts the proper density/velocity structure, and the latter indicates that the computed temperature structure is consistent with the observation though the lines are too strong relative to the continuum. This result is roughly independent of the He abundance. The computed and observed spectra are consistent with a small Ni-56 production in contrast to Type Ia thermonuclear events whose spectra are dominated by Fe-group lines at late times.

Swartz, Douglas A.↗
NASA NTRS1991

Slosh wave excitation of cryogenic liquid helium in gravity Probe-B rotating dewar

The dynamical behavior of fluids, in particular the effect of surface tension on partially-filled rotating fluids (cryogenic liquid helium and helium vapor) in a full scale Gravity Probe-B Spacecraft propellant dewar tank imposed by various frequencies of gravity jitters have been investigated. Fluid stress distribution, caused by the excitation of slosh waves and their associated large amplitude disturbances on the liquid-vapor interface, exerted on the outer and inner walls of rotating dewar container also have been investigated. Results show that fluid stress distribution exerted on the outer and inner walls of rotating dewar are closely related to the characteristics of slosh waves excited on the liquid-vapor interface in the rotating dewar tank.

Hung, R. J.↗