Design and Development of Cryocooler Based Liquid Nitrogen Plant

Abstract

The advantage of cryocooler is the small size of its cold head due to this it can be mounted on top of a Dewar, thus reducing overall size of the liquefier setup making it possible to use it in demanding sites and laboratories where the consumption of liquid nitrogen is not in higher quantities. So the dewar which is mostly used to store liquid cryogen, here is used for production and storage purposes. A cryocooler based Nitrogen liquefaction system was designed and developed which can be an ideal solution to the liquid nitrogen usage in laboratories. This setup uses a Cryomech Single stage Gifford-Mcmahon cryocooler to provide cooling and condensation of nitrogen at 80 K with the refrigeration capacity of 266 W (Rated) at 80K and a dewar specially fabricated with wider neck than usual dewar to accommodate cold head. The Gifford-Mcmahon cryocooler consist of compressor package, Helium Flex lines and cold head which is the heart and soul of this setup. The cold head is mounted into the top of the dewar and it extends down into the neck of the dewar for the purpose of cooling the nitrogen entering the dewar to 80K (-193ºC) at 0.5 bar gauge pressure which is the operating pressure for this dewar. The nitrogen gas liquefies on contact with the cold head heat exchanger. The liquefied nitrogen drips off the heat exchanger down into the dewar. This process would typically lower the pressure inside the dewar, but the regulator allows more nitrogen gas to enter the dewar to maintain the pressure at the preset level. The flow rate of the nitrogen gas into the dewar is controlled by the rate of liquefaction inside the dewar. In the experimental dewar maximum liquefaction rate of 74 Ltr/day and in the main dewar liquefaction rate of 64 Ltr/day were achieved. The difference in liquefaction rate was due to the high radiation load coming on cryogen reservoir of main dewar.