PERFORMANCE-CHARACTERISTICS OF PULSE TUBE REFRIGERATORS

In the present study experiments were carried out to investigate the p erformance characteristics of pulse tube refrigerators. It was found t hat the cool-down time t(c) during the transient or start-up period is dominated by the time constant of the pulse tube wall tau(pt) and tha t the dynamics of a basic pulse tube (BPT) refrigerator approaches tha t of a first-order system. For steady state operation, the cold-end te mperature T(L) was found to vary with tau(pt), and the cooling load Q( L) increases monotonically with increasing tau(pt). This indicates tha t heat pumped by the gas from the cold to the hot end increases with d ecreasing h(pt) (i.e. less energy exchange between the gas and wall). The process of heat storage or release of the pulse tube wall is thus shown to have a negative effect on the performance of a B PT refrigera tor. It was thus found experimentally that the gas compression/expansi on process inside the pulse tube, which is similar to a Brayton cycle but lies between isothermal and adiabatic, can explain the performance of BPT refrigerators. The present experiment also shows that the perf ormance of a pulse tube refrigerator at transient and steady states is mainly dominated by the time constant of the pulse tube wall tau(pt).