Effects of DC gas flow on performance of two-stage 4 K pulse tube coolers

DC flow was found to exist in most double-inlet pulse tube coolers from theoretical simulations. DC flow effects in a 4 K pulse tube cooler were studied by numerical analysis and experiment. Numerical predictions show that a negative DC flow from the hot end of the pulse tube to the inlet of regenerator has two positive effects on the cooler performance: (1) increasing cooling capacity of the pulse tube; and (2) dissipating the enthalpy flow at the hot end of the pulse tube. Several functions which cause DC flow, such as valve timing and geometry of double-inlet valve and DC flow bypass, were tested in the two-stage 4 K pulse tube cooler. The predictions and experiment both show that the negative DC flow leads to change of temperature profiles in pulse tube and regenerator. Experiments verify that cooling power at 4.2 K of the two-stage pulse tube cooler can be considerably improved with aid of a suitable negative DC flow. (C) 1998 Elsevier Science Ltd. All rights reserved.