Search NASA⌕ Search

SEARCH · Search NASA

Results for “SUPERFLUID MODEL”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Dewar to dewar model for superfluid helium transfer

A model has been developed to predict the flow of He II between a source and a receiving dewar. The model uses a finite difference aproximation to integrate the describing equations. The transfer path may contain porous plugs or mechanical pumps, heater sections, heat leaks, constrictions due to valves, and bends. These line elements may occur in any order and in any quantity. The line elements are easily reconfigured by changing the input data. The input consists of the number of finite element cells, the pressure in each dewar, the heat input to each section and the dimensions of each section. The output is the temperature, pressure, flow rate, velocities and heat flux in each section. An internal reference table provides the properties of He II. The model is programmed for a LOTUS work sheet. It converges rapidly and usually requires 10 to 15 iterations. For most applications an iteration takes 30 s on an AT. The predictions agree well with experimental data.

Snyder, H. A.↗
NASA NTRS1988

JPL pulsar timing observations. V - Macro and microjumps in the Vela pulsar 0833-45

In this paper, 14.5 yr of JPL timing data are analyzed to study the spindown of the Vela pulsar. Discontinuities in the spin frequency and its derivatives have bimodal amplitude distributions. Macrojumps are characterized by relative changes in spin rate of about 10 to the -6th with a derivative of 0.01, while microjumps have relative changes in spin rate of less than about 10 to the -9th with derivative of less than about 0.0001. Macrojumps display a (+,-) signature with a well-defined ratio of the amplitudes. Microjumps, however, show all possible signs of events and a larger range in signature. Six macrojumps and their associated transients are quantified using a 10-parameter model for each jump. Amplitude and decay time parameters vary by a factor of about five over the set of jumps. The results are discussed in terms of superfluid vortex models. The macrojumps are consistent with a model in which angular momentum is suddenly transferred to the crust from a more rapidly rotating superfluid core, followed by relaxation of the spin-down rate.

Cordes, J. M.↗
NASA NTRS1997

Dynamics of Superfluid Helium in Low-Gravity

This report summarizes the work performed under a contract entitled 'Dynamics of Superfluid Helium in Low Gravity'. This project performed verification tests, over a wide range of accelerations of two Computational Fluid Dynamics (CFD) codes of which one incorporates the two-fluid model of superfluid helium (SFHe). Helium was first liquefied in 1908 and not until the 1930s were the properties of helium below 2.2 K observed sufficiently to realize that it did not obey the ordinary physical laws of physics as applied to ordinary liquids. The term superfluidity became associated with these unique observations. The low temperature of SFHe and it's temperature unifonrmity have made it a significant cryogenic coolant for use in space applications in astronomical observations with infrared sensors and in low temperature physics. Superfluid helium has been used in instruments such as the Shuttle Infrared Astronomy Telescope (IRT), the Infrared Astronomy Satellite (IRAS), the Cosmic Background Observatory (COBE), and the Infrared Satellite Observatory (ISO). It is also used in the Space Infrared Telescope (SIRTF), Relativity Mission Satellite formally called Gravity Probe-B (GP-B), and the Test of the Equivalence Principle (STEP) presently under development. For GP-B and STEP, the use of SFHE is used to cool Superconducting Quantum Interference Detectors (SQUIDS) among other parts of the instruments. The Superfluid Helium On-Orbit Transfer (SHOOT) experiment flown in the Shuttle studied the behavior of SFHE. This experiment attempted to get low-gravity slosh data, however, the main emphasis was to study the low-gravity transfer of SFHE from tank to tank. These instruments carried tanks of SFHE of a few hundred liters to 2500 liters. The capability of modeling the behavior of SFHE is important to spacecraft control engineers who must design systems that can overcome disturbances created by the movement of the fluid. In addition instruments such as GP-B and STEP are very sensitive to quasi-steady changes in the mass distribution of the liquid. The CFD codes were used to model the fluid's dynamic motion. Tests in one-g were performed with the main emphasis on being able to compute the actual damping of the fluid. A series of flights on the NASA Lewis reduced gravity DC-9 aircraft were performed with the Jet Propulsion Laboratory (JPL) Low Temperature Flight Facility and a superfluid Test Cell. The data at approximately 0.04g, lg and 2g were used to determine if correct fundamental frequencies can be predicted based on the acceleration field. Tests in zero gravity were performed to evaluate zero gravity motion.

Frank, David J.↗
NASA NTRS1988

Space Cryogenics Workshop, University of Wisconsin, Madison, June 22, 23, 1987

Papers are presented on liquid helium servicing from the Space Station, performance estimates in the Superfluid Helium On-Orbit Transfer Flight Experiment, an analytical study of He II flow characteristics in the SHOOT transfer line, a Dewar to Dewar model for superfluid helium transfer, and mechanical pumps for superfluid helium transfer in space. Attention is also given to the cavitation characteristics of a small centrifugal pump in He I and He II, turbulent flow pressure drop in various He II transfer system components, slip effects associated with Knudsen transport phenomena in porous media, and an integrated fountain effect pump device for fluid management at low gravity. Other papers are on liquid/vapor phase separation in He-4 using electric fields, an enclosed capillary device for low-gravity management of He II, cavitation in flowing superfluid helium, the long-term performance of the passive thermal control systems of the IRAS spacecraft, and a novel approach to supercritical helium flight cryostat support structures.

Source record↗
NASA NTRS1982

Orbital performance of a one-year lifetime superfluid helium dewar based on ground testing and computer modelling

The ground-test results of the 550-liter superfluid-He dewar built for IRAS are presented and discussed, and a computer projection of its orbital performance life is developed. The ground-testing program included flow-swap, cold-flow, power-off, hot/cold-viewport, and strap-thermal-efficiency tests. After one set of trials, some design changes were made, and the thermal-network computer model of the system was modified as well. The driving boundary conditions of dewar orbital operation used in this model are vacuum-shell temperature = 170 K, aperture heating = 8.0 mW, and focal-plane power dissipation = 16.2 mW. An operational lifetime of 319 days and an He loss rate of 2.54 mg/sec are predicted.

Hopkins, R. A.↗
NASA NTRS2012

A Superfluid Pulse Tube Refrigerator Without Moving Parts for Sub-Kelvin Cooling

A report describes a pulse tube refrigerator that uses a mixture of He-3 and superfluid He-4 to cool to temperatures below 300 mK, while rejecting heat at temperatures up to 1.7 K. The refrigerator is driven by a novel thermodynamically reversible pump that is capable of pumping the He-3 He-4 mixture without the need for moving parts. The refrigerator consists of a reversible thermal magnetic pump module, two warm heat exchangers, a recuperative heat exchanger, two cold heat exchangers, two pulse tubes, and an orifice. It is two superfluid pulse tubes that run 180 out of phase. All components of this machine except the reversible thermal pump have been demonstrated at least as proof-of-concept physical models in previous superfluid Stirling cycle machines. The pump consists of two canisters packed with pieces of gadolinium gallium garnet (GGG). The canisters are connected by a superleak (a porous piece of VYCOR glass). A superconducting magnetic coil surrounds each of the canisters.

Miller, Franklin K.↗
NASA NTRS1990

Experimental verification of a tank to tank He II transfer model with trade study results

A computer program has been developed to study the thermodynamics of tank to tank superfluid helium transfer. The model includes a supply and a receiver tank connected by a transfer line. The convey of He II from one tank to the other is controlled by a fountain effect pump (FEP). Phase separators are present in both the supply and receiver tank to regulate the bath temperature. Description of this model has been published elsewhere. In the present paper, data from a transfer experiment are used to verify the accuracy of this model. The experiment consisted of an FEP made of a 2-micron sintered stainless steel porous plug. Superfluid has been transferred from a liquid helium bath into a glass beaker. Bath temperatures, flowrate and heater power records are available. These results are compared to the predictions of the computer program and good agreement is found between the two. This model is very useful for the study and design of superfluid transfer systems, e.g., the Superfluid Helium Tanker (SFHT) and the Particle Astrophysics Magnet Facility (ASTROMAG).

Yuan, S. W. K.↗
NASA NTRS1993

Thermal evolution of neutron stars with internal frictional heating

It has been suggested that the frictional interaction of neutron superfluids with normal matter in the inner crust of neutron stars dissipates rotational energy of superfluids and generates heat. Incorporating a general formula of internal heating into the detailed numerical codes of thermal evolution, we examine the effects of the internal heating on thermal evolution of neutron stars. We find that when a very stiff equation of state is used, it takes as long as about 2 x 10 exp 4 yr for the interior of a neutron star to reach the isothermal state, even if a strong heat source is placed in a thin layer of the inner crust. This time scale reduces to a few hundred years or less when medium to soft equations of state are used. A neutron star cools by neutrino emissions during the earlier stages referred to as the neutrino cooling era, while during the later photon cooling era it cools primarily by emission of photons from its surface. We show that heating rates expected in the current superfluid-crust interaction model can greatly increase the surface temperature in the photon cooling era, significantly changing the thermal evolution of relatively old neutron stars if a stiff equation of state is adopted.

Umeda, Hideyuki↗
NASA NTRS1989

Neutron star evolution with internal heating

The thermal evolution predicted by current models of the superfluid-crust interaction is noted to differ substantially from the thermal evolution predicted by models without internal heating as well as previous models of heating. Heating rates approaching the maximum predicted by current models enhance the photon luminosity of the star in the neutrino cooling era, and dramatically alter the thermal evolution in the photon cooling era. Standard cooling models are consistent with current pulsar temperature estimates and upper limits, except those for the Vela pulsar, which are lower than predicted.

Shibazaki, Noriaki↗
NASA NTRS1993

On quasiperiodic variations of pulsars' periods - An alternative to the planetary interpretation of PSR1257+12

The quasi-periodic timing residuals of PSR1257+12 are considered to be a result of two large-scale internal motions of the neutron star: core-crust relative motion and precession. The model requires that the superfluid core of a neutron star is not pinned to the solid crust. A very good fit to the observations is obtained for the set of parameters that corresponds to a nearly orthogonal rotator, and the period of the core-crust relative rotation that is nearly twice the period of precession.

Dolginov, A. Z.↗
NASA NTRS1986

Transferring superfluid helium in space

A simple thermodynamic model of a transfer system for resupplying liquid helium in space is presented, with application to NASA projects including the Space Infrared Telescope Facility, the Large Deployable Reflector, and the Hubble Space Telescope. The relations between different thermodynamic regimes that can be expected in the transfer line are used to study the relative efficiencies of various possible transfer techniques. Low heat leak into the transfer line, particularly at point sources such as the coupling, is necesssary for efficient transfer of liquid helium, and proper selection of supply tank temperature is important during helium resupply.

Kittel, Peter↗
NASA NTRS1991

Flow of superfluid helium in tubes with heated walls

The equations for superfluid helium flowing through a straight tube with heated walls are integrated. The model equations are based on those of Landau as modified for superfluid turbulence by Gorter and Mellink (1949). The model is implemented by the program SUPERFLOW which runs on a personal computer. The effect of the heating level on the mass flux, the energy flux, and the pressure and temperature profiles is investigated. The four types of profiles which occur without sidewall heating are also found with heated walls. The progression through these four types is shown to depend primarily on the dimensionless parameter, defined previously to characterize the unheated profiles, and a dimensionless ratio of heat fluxes. The pressure and temperature maxima which rise well above the boundary values increase significantly with sidewall heating. Approximate design equations for estimating the mass flux and the profiles are presented. The physical basis of the results is discussed. These results are useful in the design of optimal cooling loops and other superfluid flow systems.

Snyder, H. A.↗
NASA NTRS1971

Physics of the neutron star

Neutron star models, discussing crystalline crust, particle superfluid properties, rotational vortices and relation to Crab Nebula pulsar

Cameron, A. G. W.↗
NASA NTRS1995

A probabilistic model of a porous heat exchanger

This paper presents a probabilistic one-dimensional finite element model for heat transfer processes in porous heat exchangers. The Galerkin approach is used to develop the finite element matrices. Some of the submatrices are asymmetric due to the presence of the flow term. The Neumann expansion is used to write the temperature distribution as a series of random variables, and the expectation operator is applied to obtain the mean and deviation statistics. To demonstrate the feasibility of the formulation, a one-dimensional model of heat transfer phenomenon in superfluid flow through a porous media is considered. Results of this formulation agree well with the Monte-Carlo simulations and the analytical solutions. Although the numerical experiments are confined to parametric random variables, a formulation is presented to account for the random spatial variations.

Agrawal, O. P.↗
NASA NTRS1994

A Microgravity Helium Dilution Cooler

We are developing a He-3-He-4 dilution cooler to operate in microgravity. It uses charcoal adsorption pumps and heaters for its operation; it has no moving parts. It currently operates cyclically to well below 0.1 K and we have designed a version to operate continuously. We expect that the continuous version will be able to provide the long-duration cooling that many experiments need at temperatures down to 0.040 K. More importantly, such a dilution cooler could provide the precooling that enables the use of adiabatic demagnetization techniques that can reach temperatures below 0.001 K. At temperatures below 0.002 K many fascinating microgravity experiments on superfluid He-3 become possible. Among the possibilities are: research into a superfluid He-3 gyroscope, study of the nucleation of the B-phase of superfluid He-3 when the sample is floating out of contact with walls, study of the anisotropy of the surface tension of the B-phase, and NMR experiments on tiny free-floating clusters of superfluid He-3 atoms that should model the shell structure of nuclei.

Roach, Pat R.↗