Indigenous Development of Helium Liquefier

On August 14, 2010 at 21.15 hrs we achieved Helium liquefaction in fully indigenously designed and developed system for the first time. The system was further modified to liquefy and collect liquid helium in an external Dewar.

On October 13, 2010 we could collect liquid helium in an external Dewar. During its maiden trail itself, the system was operated for more than 25 hours continuously and more than 150 liters of liquid helium was collected in an external Dewar (Make CryoFab, Cap: 250 liters). The liquefaction rate achieved was about 6 lit/ hour.

On October 26, 2010. During second run the system was operated for more than 36 hours and more than 200 liters of liquid helium was collected in the external Dewar.

Photograph shows Helium Liquefaction system developed at RRCAT. It produced more than 150 Litres of Liquid helium in its first trail run

Helium Liquefiers basically comprises of following components: expansion devices with work extraction mechanism, a train of efficient heat exchangers, pressure regulating devices etc.

Helium Liquefier system developed by us is based on two Reciprocating type expansion engines operating at 50K and 20K. These engines consist of extended length FRP pistons. FRP and long length results in reduction of heat in leaks form room temperature to the expansion space (Locally made FRP is used). Due to this length, the expansion process takes place deep inside the cold box, whereas other components of expansion engines such as fly wheel, inlet and exhaust valve actuators, work extraction mechanism (Brake), etc operates at room temperature. The gaps between the piston and liner, also called “void volume”, plays an important role in achieving the required expansion efficiency. Work extraction device used is alternator, used in automobiles, which is modified to suit the requirements. We have used six numbers of cross counter flow type heat exchangers operating between different temperature ranges.

High pressure helium gas finally cooled to about 7K or lower, with the combination of expansion engine and a train of heat exchangers, enters a Joule Thomson (J-T) expansion valve. On expansion through J-T valve, a fraction of the flow forms helium mist. This fraction depends on the temperature and pressure of helium gas at the beginning of J-T expansion (High Pressure) and the final expansion pressure. The J-T valve also, was designed and fabricated in house. Amount of this mist, to condense as liquid in the Dewar, strongly depends on the stability of pressure inside the Dewar. Achieving liquefaction for more than 36 hours continuously implies the stable pressure and temperature conditions maintained over the period. The other deciding factor for operation over long period is the handling of impurities in high pressure helium gas stream, especially oil carry over from main process compressor. An efficient oil removal system has to be employed for this purpose.

The oil removal system is also designed by us and fabricated by local fabricators. In addition to its design and fabrication, processing of components plays an important role in it. Locally available activated charcoal has been used in our system; its processing parameters were also established. Standard oil coalescing filters are used in this system.

The main process compressor, which maintains supply of pure oil free high pressure helium gas at about 230 psig and return low pressure of about 2 psig, is also procured from Indian manufacturer. It is an open type (belt driven), oil lubricated - air cooled - four stage - compressor supplied by M/s Sulzer, India, Model C4U217.4G. To handle the high heat of compression for helium gas, manufacturer has provided additional cooling. To avoid air in-leaks in the compressor during suction cycle, minor alterations were done in the process circuit of the compressor by us, after commissioning at RRCAT.