Thermal characteristics of a low-loss liquid-helium dewar
A liquid helium dewar has been designed, fabricated, and operated successfully with a minimum background heat-loss rate of only a few milliwatts. The objective is to provide a facility that can be used to measure relatively low heat-loss rate (1--100 milliwatts) in a liquid helium environment. The experimental system consists mainly of an inner helium reservoir within an outer helium reservoir that is thermally shielded from the room-temperature environment by multiple insulation layers in a vacuum environment and a liquid nitrogen reservoir. The inner helium reservoir has a reduced cross-sectional (neck) area to minimize radiative and convective heat transfer to the liquid helium in the lower portion of the reservoir. Experimental results indicate that it takes a long time (>16 hours) for the system to cool down and reach the minimum heat-loss condition. Strong thermal interactions were observed between the inner and the outer reservoirs above the reduced cross-sectional area of the inner reservoir which is separated from the outer reservoir by a cylindrical stainless steel wall. Temperature measurements showed stratification in the vapor space above the liquid helium in the inner reservoir. Temperature distributions in the vapor space are not one-dimensional, and horizontal temperature gradients exist; this strongly suggests that natural convection may have persisted in the vapor space above the liquid helium in the inner reservoir. To alleviate the problem of strong thermal interactions between the inner and the outer reservoirs, we have since redesigned and tested an improved inner helium reservoir. The new reservoir has a heat intercept, an extended vacuum insulating space between the two helium reservoirs above the heat intercept, and an upper portion made of a thermally insulating epoxy fiberglass composite. Testing showed that interaction between the inner and the outer helium reservoirs of the new system is significantly lower than the original system.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- W-31-109-ENG-38
- OSTI ID:
- 88855
- Report Number(s):
- ANL/ET/CP-82236; CONF-950336-28; ON: DE95012271
- Resource Relation:
- Conference: American Society of Mechanical Engineers/Japanese Society of Mechanical Engineers/Japan Solar Energy Society international solar energy conference, Lahaina, HI (United States), 19-24 Mar 1995; Other Information: PBD: May 1994
- Country of Publication:
- United States
- Language:
- English
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