Experimental Study on the Pulse Tube Refrigerator with Two Relief Valves

Abstract

In this paper we report on the performance of a pulse tube refrigerator with two relief valves. Pulse tube refrigerators have no moving parts in the cold end so there is the possibility of achieving long life. However, the pulse tube refrigerator has not achieved enough cooling power. One candidate approach to increasing the cooling power without increasing the size, operating frequency, or the cost is to more precisely control the pattern of the compression (expansion) and the travelling wave.

To this end, we have adopted two relief valves, instead of an orifice, to control the patterns of the compression (expansion) and of the travelling wave. The refrigerator consists of a piston, a regenerator, a pulse tube, a buffer tank, and two relief valves. The two relief valves are placed between the hot end of pulse tube and the buffer tank. The two relief valves divide the compression (expansion) time and the traveling time during which the gas moves at constant pressure. The two relief valves open when the pressure achieves a fixed value and make the travelling wave into a square wave. Thus, the PV diagram becomes similar to that of the Ericson cycle.

In our test apparatus, the pulse tube refrigerator with two relief valves achieved a minimum temperature of 69 K. The maximum cooling power measured at 90 K was 4.7 W, with an indicated work of 204 W — this corresponds to a 5.3 % Carnot efficiency. When using an orifice instead of the two relief valves, the pulse tube refrigerator achieved a 74 K lower temperature limit; the maximum cooling power measured at 90 K was 3.6 W, with an indicated work of 209 W — this corresponds to a 4.0% Carnot efficiency.