Small liquid hydrogen tanks

Metal hydrides can hold a large amount of hydrogen in a small volume. A metal hydride tank may be one third the volume of a 5,000 psi liquid hydrogen tank. Hydride tanks can take on different shapes depending on the vehicle design. 

Answer by Author Our studies indicate that the use of low-cost, low-density plastic foam encapsulated in a thin plastic membrane such as polyethylene or Mylar and subsequendy evacuated provides a low-cost method for providing auxiliary ground-based insulation for rocket vehicle liquid-hydrogen tanks. For the short storage time required for this particular application, the allowable loss rate was established as 2 per day. On this basis, the installed cost of the evacuated foam system was less than an evacuated powder system or any other system that requires a thick, rigid outer shell. For applications where the diameter of the tank is small, or with ex-... 

The main tank is filled with liquid hydrogen from a trailer. Despite the sophisticated heat insulation in any container for cryogenic liquids, the small amount of remaining heat input vfill trigger off a warming process in the tank which causes the liquid in the container to evaporate and the pressure to rise. After a certain pressure build-up time the maximum operating pressure of the tank is reached. The pressure relief valve has to be opened. From this point onwards, gas must be released (boil-off). The container now acts as an open system with gas usually being lost to the environment. 

As BMW has shown, care in design can provide a solution to the problem of transferring liquid hydrogen. The liquid line are be insulated by placing it coaxial inside the gas return line from the tank. An outer covering of thermal insulation in turn protects the gas return line. It is also be necessary to include a small vacuum pipeline from the dispenser to the interface between the fill line and the fill receptacle on the vehicle. These various lines will be incorporated into a fill line about 6 cm in diameter. Figure 7.2 shows BMW s excellent answer to this design problem. 

Slush hydrogen can be transported in the most efficient equipment now used for liquid hydrogen, with about 0.7 % melting of the solid for the same heat leak which causes 0.1 % evaporation of liquid. A four-day haul in the large railway car p] would cause a reduction in the solid fraction from 50 to about 40%. This quality can be upgraded back to 50% by a small vacuum pump on the launch site storage tank. 

PERFORMANCE OF HIGH-EFFICIENCY INSULATION ON A 35-LITER CONTAINER. After completing tests on the small sample, attention was directed to the practical applications of this insulation on a liquid-nitrogen and liquid-hydrogen container, A tank 1 ft in diameter by 2 ft tall (approximately 35-liter capacity) was built. 

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