Cryogenic fluids, transfer

Cryogenic fluid transfer lines are generally classified as one of three types uninsulated, foam-insulated lines, and vacuum-insulated lines. The latter may entail vacuum insulation alone, evacuated powder insulation, or multilayer insulation. A vapor barrier must be applied to the outer surface of foam-insulated transfer lines to minimize the degradation of the insulation that occurs when water vapor and other condensables are permitted to diffuse through the insulation to the cold surface of the lines. 

Fig. 9-15. Dimensional drawing for 1 /2-inch oxygen connection for cryogenic fluid transfer, from CGA V-6—1993.

Some applications of cryogenic-fluid transfer require optimization of many aspects of transfer-system design. This study examines methods of transfer-line insulation, the problems of metal degassing, and line storage life. 

For further discussion of heat transfer in cryogenic fluids, see R. J. Donnelly, Cryogenics, Physics Vade Mecum, ed. H.L. Anderson, AIP, NY (1981). For a recent discussion of contact resistance see also H. Jones, L. Cowey, and D. Dew-Hughes, Cryogenics 29 795 (1989). 

Generally, a heat-transfer fluid should be noncorrosive to carbon steel because of its low cost. Carbon steel may be used with all the organic fluids, and with molten salts up to 450°C (842 °F) [6]. With the sodium-potassium alloys, carbon, and low-alloy steels can be used up to 540°C (1000 F), but above 540°C stainless steels should be used [6]. Stainless steels contain 12 to 30% Cr and 0 to 22% Ni, whereas a steel containing small amoimts of nickel and chromium, typically 1.85% Ni and 0.80% Cr, is referred to as a low alloy steel [6]. Cryogenic fluids require special steels. For example, liquid methane requires steels containing 9% nickel. To aid in the selection of a heat-transfer fluid. Woods [28] has constracted a tenperature-pressure chart for several fluids. 

In practice, the heat transfer rate to a cryogenic fluid may be limited by the nature of the contacting surface, fluid, or vapor. For example, when the fluid contacts an insulating material, the heat transfer rate... 

Most of the cryogenic fluids are now available commercially in many parts of the world. These are shipped and stored in special insulated containers from which they are either used directly or are transferred to portable dewars and used as required. However, liquid helium and some of the reactive fluids are ordinarily produced in laboratory liquefiers as they are needed. For simplicity, laboratory experiments may be conducted with these fluids directly in the liquefier storage vessel, although provisions are usually made for the withdrawal of the liquid through an evacuated transfer tube. 

Ansioer by Author A problem on which a considerable amount of work remains to be done is that of establishing a satisfactory heat transfer coefficient correlation between heated surfaces such as are obtained in a rocket nozzle and a cryogenic fluid such as hydrogen. Another problem is that of describing correctly two-phase flow of hydrogen in channels of variable geometry under conditions of high pressure and heat input. 

AN ANALYTICAL METHOD FOR ESTIMATING GAS REQUIREMENTS IN THE PRESSURIZATION AND TRANSFER OF CRYOGENIC FLUIDS... 

TESTS OF EQUIVALENT MASS MODEL. For all reported tests, reliable data were obtained on gas consuriiptions during the pressurization and transfer of cryogenic fluids. These data were compared with calculated results using the equivalent mass method. 

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