By A. J. Croft
This publication is intended for laboratory employees who for one cause or one other have a necessity to chill anything all the way down to temperatures lower than that of liquid nitrogen - particularly to four. 2°K and under. It doesn't care for experimental thoughts at low temperatures, yet i've got attempted to convey the reader nose to nose with the brutishrealities of the required undefined. As weIl as giving information regarding assets of provide of kit, i've got long past into so me element approximately how a few of it may be made in laboratory workshops for the sake of these who're in need of cash yet blessed with powerfuble technical help. as far as hugely really expert goods akin to liquefiers, fridges, refrigerant packing containers, cryostat dewars, and so forth. , are involved, i've got incorporated aIl assets of offer which i've got received to he ar of; on the subject of extra generaIly on hand gear in simple terms consultant assets of recognized reliability were quoted. Any omissions or mistakes needs to be positioned down both to my very own lack of information, stupidity, or loss of will toget concerning the global, or maybe to the trouble i've got had in extracting details from brands. although, such a lot have long gone to nice hassle to assist, and that i desire i've got performed them justice. mentioned to paintings indifferently in inches and centimetres and perched among the opposing puIls of the us and Europe, i've got used a mix of devices that can surprise the purist.
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Extra info for Cryogenic Laboratory Equipment
Thermal insulation is by me ans of a eylindrieal dewar vessel the bottom of whieh forms the reservoir for liquid helium and from which it has to be drawn off about every 2 hr. The helium gas is purified before it goes into the liquefier in one of two interchangeable adsorptive purifiers working at liquid-nitrogen temperature. 4 litres of liquid helium. The compressors are capable of working up to 130 atm, which enables standard storage cylinders to be Speci[ication Output of liquid helium Helium gas throughput Model VR4 Model VR8* litres-hr- I 4 8 litres-hr- 1 90 m 3 _hr- 1 45 m 3 -hr- 1 (One compressor) (Two compressors) Engine speed 7-800 rpm 11-1200 rpm 10 litres-hr- I Liquid nitrogen consumption 5 -6 litres-hr- 1 Electrical power consumption 9 kW 18 kW approx.
In this case the helium gas stream is cooled additionally by the liquid nitrogen, and, as will be seen below, the output of the liquefier is * See also footnote to p. 37. Sec. 2 Commercial External-Work Liqueflers and Refrigerators 37 thereby doubled. An outer cylindrical tank enables a high vacuum to be maintained in the space surrounding the enclosure described above and including the radiation shield. This construction is equivalent to putting the whole of the helium system into adewar vessel and has the advantage that there are few sources of possible leaks into the highvacuum insulation.
Another method of construction (Croft and Jones4 ) involves attaching two short legs ne ar to the ends of a length of copper tube. Thin-walled tubing is then hard-soldered to these legs and the complete inner tube inserted through a slot in the long copper tube, which is then closed by soft-solde ring on a copper strip. End caps are then softsoldered on. · Its advantages are that a seal of complete reliability can be made even by an amateur glassblower and that the thin section of the copper part of the seal provides a useful safety valve.
Cryogenic Laboratory Equipment by A. J. Croft