Micromachined Joule-Thomson coolers

A MEMS-based Joule-Thomson cold stage was designed and prototypes were realized and tested. The cold stage consists of a stack of three glass wafers. In the top wafer, a high-pressure channel is etched that ends in a flow restriction with a height of typically 300 nm. An evaporator volume crosses the center wafer into the bottom wafer. This bottom wafer contains the low-pressure channel thus forming a counter-flow heat exchanger. A design aiming at a net cooling power of 10 mW at 96 K and operating with nitrogen as the working fluid was optimized based on the minimization of entropy production. A batch of prototype coolers ranging from 20 to 40 mm was made for a flow of typically 1mgCs-1 at a high pressure of 80 bar and a low pressure of 6 bar. The design and fabrication of the coolers will be discussed along with experimental results. A specific issue that will be addressed is the clogging of the restriction due to the deposition of ice crystals. Furthermore, introductory experiments with multistage microcoolers will be discussed. © 2008 American Institute of Physics.