Ajay Khatri

A throttle cycle refrigerator operating below 77 K

A cryocooler has been developed that uses a unique refrigerant in a throttle cycle to achieve temperatures below the normal boiling point of liquid nitrogen. 70 K was achieved at no load condition and continuous operation with a 1.5 W heat load below 77 K has been demonstrated. The refrigerator consists of a compressor package that is similar to a standard air conditioning system, a cold end which has no moving parts that consists of a heat exchanger with a cold plate, and two gas lines connecting the compressor and the cold end. The system requires no maintenance. Several prototypes have been built, tested and delivered to a customer for application in the field of high temperature superconducting filters for cellular phone communications. The cold end has the design flexibility to be customized for different applications. System performance can also be customized by designing different refrigerants that can be used without the need to modify the hardware.

Performance of a Mixed-Refrigerant System Designed for Computer Cooling

CMOS-based computer processors will operate at increased frequencies when cooled to sub-ambient temperatures by a refrigeration system. This benefit must be weighed against many refrigerator considerations, the most noteworthy being thermal performance, efficiency, reliability, and cost. With this in mind a throttle-cycle, mixed-refrigerant cryocooler using a single-stage, oil-lubricated compressor was modified for increased capacity at 173K (-100°C) and its thermal performance was characterized. This mixedrefrigerant system cooled 119 Watts (with an average heat flux of better than 5 Watts/cm2) at an interface temperature of 173K, with a Coefficient of Performance (COP) of more than 22%. The maximum in cooling capacity was 140 Watts at 183K (-90°C). The ratio of the COP relative to Carnot (ideal) efficiency held very constant at 16% over the temperature range of 153 to 183K (-120 to -90°C). This performance (relative to Carnot) is comparable to that of refrigeration systems with similar capacity operating at much higher temperatures. These results establish the good efficiency obtainable using mixedrefrigerant technology, making cooled CMOS applications attractive. Based on experimental data and computer simulations, we anticipate that better than 20% of Carnot efficiency can be achieved with a more optimal design.

Water trap refrigerated by a throttle-cycle cooler using mixed gas refrigerant

The design features and the performance of the cooler are discussed to emphasize characteristics of this refrigeration system compared to other cryocoolers used for water traps. A throttle-cycle cooler based on one-stage oil-lubricated compressor provides water trap temperature in a narrow range of 115 K to 130 K depending upon the heat load on the water trap surface.