The new hydrogen liquefier at the Clarendon Laboratory

Abstract

IN 1961, a Joule-Thomson hydrogen liquefier producing 30 l./hr was designed and built in the Clarendon Laboratory. Some explanation is necessary of the reasons for doing this in a low temperature laboratory where the chemical properties of hydrogen are not merely of no interest but might be thought an argument for not using it at all. We have three applications for liquid hydrogen in Oxford: as a precoolant for our helium liquefier, as a pre-coolant for apparatus subsequently used with liquid helium, and to a small extent as a cryogenic liquid per se. Our helium liquefier ~ was built in 1956. It uses externally produced liquid hydrogen and produces 12 1./hr internally. Our experience with this liquefier has been good: it has the reliability characteristic of liquefiers which have no moving parts at low temperature and the only significant maintenance required is annual overhaul of the compressor and vacuum pumps. We can produce up to 100 I. of liquid helium in one day's run-our present consumption is just under 150 1. per week so that we have capacity in our plant for meeting increased demands. We felt, therefore, that we ought to provide for a continued supply of liquid hydrogen for many years to come. The hydrogen liquefier built in 19462 and largely rebuilt in 19543 was used with liquid air made by a condensation process in which the coolant was liquid oxygen. 4 In recent years it has become possible to procure bulk liquid nitrogen in Oxford. We therefore decided to change from liquid oxygen to liquid nitrogen as the primary source of cold and to abandon the use of liquid air. With two pumped liquid air baths, we were able to reach an average pre-cooling temperature of 59 ° K. Liquid nitrogen, however, has a triple point at 63-2 ° K and we found that when we used it the expected reduction in output to about 85 per cent in fact occurred. At this reduced output, the liquefier could not keep pace with the helium liquefier. We therefore had the alternatives of modifying the existing liquefier or building a new one of adequate output. The former would have been difficult and expensive, so we decided on the latter course. Our old liquefier is now in use in the University of Witwatersrand. Basis of design