ELECTROHYDRODYNAMICS OF SUPERFLUID HELIUM IN NARROW CHANNELS
Electrohydrodynamics of superfluid helium in narrow channels
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Electrohydrodynamics of superfluid helium in narrow channels
The Superfluid Helium On-Orbit Transfer (SHOOT) Flight Demonstration was an attached Shuttle payload mounted on a Hitchhiker cross-bay carrier which flew on STS-57 in June of 1993. SHOOT successfully demonstrated the handling and transfer of superfluid helium between two containers, called dewars, in low gravity. SHOOT was a class C payload and for the STS-57 mission was termed a complex secondary payload. The primaries were the retrieval of the EURECA carrier and a collection of modular experiments contained in SPACEHAB. Because the liquid helium was continuously boiling off, SHOOT's activities were scheduled for the first three days of the mission, concurrent with some SPACEHAB experiments, but well before the EURECA retrieval. Control of the SHOOT experiment was highly interactive and originated primarily from the Goddard Payload Operations and Control Center (POCC). Transfer and calibration activities required continuous command windows of up to 50 minutes duration and up to 80 minutes out of each orbit. Occasionally the crew controlled the experiment using the Payload General Support Computer (PGSC) when near-real time control and monitoring was required. SHOOT also placed considerable demands on the orbiter, including a pitch rotation of 3 deg./sec for 15 minutes, and translational burns using both the aft and forward RCS jets to generate accelerations up to 7 milli-g. The basis for these and other requirements are discussed. Interacion with the crew and timing of crew activity during the mission will be detailed. The processing flow of SHOOT at KSC is described with emphasis on the tradeoffs for vertical, as opposed to horizontal, installation in the orbiter. Finally, some lessons learned are presented that are relevant to future cryogenic and Hitchhiker payloads.
The results are presented of a study program directed toward evaluating the problems associated with cooling an LST instrument to 2 K for a year by using superfluid helium as the cooling means. The results include the parametric analysis of systems using helium only, and systems using helium plus a shield cryogen. A baseline system, using helium only is described. The baseline system is sized for an instrument heat leak of 50 mw. It contains 71 Kg of superfluid helium and has a total, filled weight of 217 Kg. A brief assessment of the technical problems associated with a long life, spaceborne superfluid helium storage system is also made. It is concluded that a one year life, superfluid helium cooling system is feasible, pending experimental verification of a suitable low g vent system.
An experiment to investigate the properties of superfluid helium in a microgravity environment flew on the Shuttle on the Spacelab 2 mission in July and August of 1985. This paper summarizes the flight experiment and describes the preliminary results. The experiment comprised an investigation of long-wavelength third-sound waves in micron-thick films, a study of the motions of superfluid helium under milli-g and micro-g accelerations, and measurements of the fluctuations in temperature associated with the small motions of the bulk helium. An additional accomplishment was to qualify and characterize a reflyable, space compatible cryostat.
An experiment to investigate the properties of superfluid helium in a microgravity environment flew on the Shuttle on the Spacelab 2 mission in July and August of 1985. This paper summarizes the flight experiment and describes some preliminary results. The experiment comprised an investigation of long-wavelength third-sound waves in micron-thick films, a study of the motions of superfluid helium under milli-g and micro-g accelerations, and measurements of the fluctuations in temperature associated with the small motions of the bulk helium. An additional objective was to qualify and characterize a reflyable, space-compatible cryostat.
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.
A number of space flight experiments and entire facilities require superfluid helium as a coolant. Among these are the Space Infrared Telescope Facility (SIRTF), the Large Deployable Reflector (LDR), the Advanced X-ray Astrophysics Facility (AXAF), the Particle Astrophysics Magnet Facility (PAMF or Astromag), and perhaps even a future Hubble Space Telescope (HST) instrument. Because these systems are required to have long operational lifetimes, a means to replenish the liquid helium, which is exhausted in the cooling process, is required. The most efficient method of replenishment is to refill the helium dewars on orbit with superfluid helium (liquid helium below 2.17 Kelvin). To develop and prove the technology required for this liquid helium refill, a program of ground and flight testing was begun. The flight demonstration is baselined as a two flight program. The first, described in this paper, will prove the concepts involved at both the component and system level. The second flight will demonstrate active astronaut involvement and semi-automated operation. The current target date for the first launch is early 1991.
A prototype superfluid helium bayonet for potential space applications has been developed and evaluated with a low heat leak test apparatus. Measured heat leak of the 13 mm (1/2 inch) bayonet pair is 0.21 W at 1.8 K with an uncertainty of +0.09/-0.05 W. Bayonets are fabricated with thin, electron beam (EB) welded tubes which are EB welded to machined nose and flange pieces. Low heat leak structural integrity is provided by a 0.9 mm thickness of filament wound fiberglass-epoxy. Superfluid creep is restricted by KEL-F nose seals which form vacuum-tight extensions to the bayonet cold end pieces.
Pressure measurements in pure superfluid helium 2 flow at subcritical velocities, showing quantitative agreement with Euler equation with zero curl
An apparatus which forces liquid helium from a calibrated bellows through a flow meter is used to calibrate turbine and Venturi flow meters in both normal and superfluid helium. The bellows are driven by an ambient temperature stepping motor. Flow rates range up to 0.35 L/s, and helium temperatures range from 1.25-4.0 K. For the case of a 9.3-mm bore turbine meter, identical meter factors are found for normal and superfluid helium. For the Venturi meter, discharge coefficients between 0.98 and 1.0 are found with normal and superfluid helium.
The Space Infrared Telescope Facility (SIRTF) is a 1 m class cryogenically cooled observatory for infrared astronomy. The SIRTF cryogenic system has to satisfy the five year mission lifetime requirement as well as to provide sufficient cooling for the science instruments and optical system. A 4000 cu dm superfluid helium dewar has been selected for the current baseline cryogenic system which represents the largest superfluid helium dewar proposed to date for a long lifetime space-borne application. This paper discusses the design and predicted performance of the current cryogenic system, as well as its comparison with IRAS and other space-borne superfluid helium dewars currently under development.
The design of a superfluid helium space tanker is described, which has the characteristics of minimum boil-off, low-g venting and maintenance of the superfluid state, transfer operations that include a pumping method, the additional fluid conditioning required during transfer, and a liquid acquisition system for transfer in a weightless environment. A concept for loading and ground conditioning of He, that simplifies launch operations and maximizes the quantity available at launch is presented. Configuration diagrams are included.
The in-flight tests and the operational sequences of the Superfluid Helium On-Orbit Transfer (SHOOT) experiment are outlined. These tests include the transfer of superfluid helium at a variety of rates, the transfer into cold and warm receivers, the operation of an extravehicular activity coupling, and tests of a liquid acquisition device. A variety of different types of instrumentation will be required for these tests. These include pressure sensors and liquid flow meters that must operate in liquid helium, accurate thermometry, two types of quantity gauges, and liquid-vapor sensors.
The in-flight tests and the operational sequences of the Superfluid Helium On-Orbit Transfer (SHOOT) experiment are outlined. These tests include the transfer of superfluid helium at a variety of rates, the transfer into cold and warm receivers, the operation of an extravehicular activity coupling, and tests of a liquid acquisition device. A variety of different types of instrumentation will be required for these tests. These include pressure sensors and liquid flow meters that must operate in liquid helium, accurate thermometry, two types of quantity gauges, and liquid-vapor sensors.
The rapid increase in resistance of high purity semi-conducting germanium with decreasing temperature in the superfluid helium range of temperatures makes this material highly adaptable as a very sensitive thermometer. Also, a germanium thermometer exhibits a highly reproducible resistance versus temperature characteristic curve upon cycling between liquid helium temperatures and room temperature. These two factors combine to make germanium thermometers ideally suited for measuring temperatures in many cryogenic studies at superfluid helium temperatures. One disadvantage, however, is the relatively high cost of calibrated germanium thermometers. In space helium cryogenic systems, many such thermometers are often required, leading to a high cost for calibrated thermometers. The construction of a thermometer calibration cryostat and probe which will allow for calibrating six germanium thermometers at one time, thus effecting substantial savings in the purchase of thermometers is considered.
The SHOOT Flight Demonstration will provide the technology necessary to resupply superfluid helium in space. The helium dewars in SHOOT have unique requirements, including no detectable leaks, demonstrated structural integrity to allow flight aboard the Space Shuttle, and low parasitic heat leak. The requirements, materials, and processes used to fabricate the two superfluid helium dewars, particularly as they apply to welding, are presented.
The Superfluid Helium On-Orbit Transfer Flight Experiment (SHOOT) is designed to demonstrate the techniques and components required for orbital superfluid (He II) replenishment of observatories and satellites. One of the tasks planned in the experiment is to cool a warm cryogen tank and a warm transfer line to liquid helium temperature. A math model, based on single-phase vapor flow heat transfer, has been developed to predict the cooldown time, component temperature histories, and helium consumption rate, for various initial conditions of the components and for the thermomechanical pump heater powers of 2 W and 0.5 W. This paper discusses the model and the analytical results, which can be used for planning the experiment operations and determining the pump heater power required for the cooldown operation.
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.