THE refrigerants available in a number of laboratories which have entered the low temperature field in recent years are often limited to liquid helium and liquid nitrogen. A small supply of liquid hydrogen would provide a valuable extension of the facilities available in these laboratories, as well as providing a more economical alternative to liquid helium, to workers whose requirements do not call for temperatures below 10Β°K. For these reasons the design of a small and accessible hydrogen liquefier, of simple construction, is presented here in a form which will enable other workers to design liquefiers with outputs to meet their particular requirements.
The definitions of the symbols used in the equations are collected in the Appendix.
Basic initial considerations
From a knowledge of the variation of the enthalpy of hydrogen with temperature and pressure it is possible to calculate the rate of liquefaction at an expansion valve situated at the end of a countercurrent interchanger carrying gas under known conditions from the equation
Using data from the work of Woolley, Scott, and Brickwedde,1 and assuming a 100 per cent efficient interchanger, operating with a fore temperature of 70 Β° K, calculation showed that an average of about 0.68 1. of liquid could be expected from a 165 ft 3 cylinder, the pressure of which fell from 120 to 30 atm durir/g the liquefaction process, Allowing for the gas passed before the onset of liquefaction eight such cylinders are used in producing approximately 5 1. of liquid hydrogen.