Philips 95-15 Cryogenerator

Philips 95-15 Cryogenerator

Type 95 –I5 beta type cryocooler (very low temperature refrigerator) for liquifying air.

Piston; 80mm diameter, 50mm stroke.  Displacer: 70mm diameter, 27mm stroke.

40 bar Hydrogen or Helium working fluid.

 During the 1930’s. Netherlands based electrical goods maker Philips recognized that with newly available materials and deeper understanding of thermodynamics, 19th century hot air engines could be markedly improved.  Their Stirling engine development program began in 1938 and continued through WW2 even while their facilities were under German occupation.  By pressurising the working fluid, specific output (power for size) could be improved by an order of magnitude or more, especially if hydrogen or helium was used instead of air (because of superior heat transfer properties).  Pressurisation was not a new idea (Robert Stirling’s brother James had built a pressurised engine in 1840) but their oilless sealing (which enabled fine mesh regenerators to be used without their clogging) was original. 

 Their first product was a quiet, efficient kerosene burning 300watt generator set for operating valve radios where reticulated electricity was not available.  Invention of the transistor (in 1948) killed this project, but Philips went on to develop Stirling cycle engines for many uses; ships, cars, satellites and etc.  Their licensees during the 1950 to 1990 period included Ford, GM, DAF, MAN, NASA and many others.  None of these developments resulted in successful commercial products, even though they achieved specific outputs (power for size) exceeding what was then available from internal combustion engines. The reason for this is that high output Stirling engines are very expensive to build and are temperamental because of seal unreliability and the very high temperatures (>700degrees C) that cylinder heads operate at.

 However, the Stirling cycle is reversable: powered by an electric motor, Stirling engines become very efficient refrigerators, quite capable of liquifying air for example.  From 1948, Philips set up a division under JWL Kohler to develop Stirling cycle-based units for this purpose and from 1954, began selling liquid air cryocoolers to commercial operators, universities and research laboratories.  They later developed micro units for cooling infrared sensors and much larger cryocoolers to reach the very low temperatures required for super conductivity.

 This is an original 1950’s Philips liquid air machine, ex Waikato University. The large drum-like object is its snow separator (water vapour and C02 extractor).

 Philips sold off their cryocooler division in 1990 and since then Stirling cycle cryocoolers from a range of manufacturers have become ubiquitous whenever very low temperatures are required.

Fabrum, a successful new Christchurch based business, makes liquid hydrogen cryocoolers for the global market that use the Stirling cycle (see their display in this collection).

Peter Lynn for the Mahan Heritage Centre, August 2023