EFFECTS OF DC GAS-FLOW ON PERFORMANCE OF 2-STAGE 4 K PULSE TUBE COOLERS

DC flow was found to exist in most double-inlet pulse tube coolers fro m theoretical simulations. DC flow effects in a 4 K pulse tube cooler were studied by numerical analysis and experiment. Numerical predictio ns 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 perfor mance: (1) increasing cooling capacity of the pulse tube; and (2) diss ipating the enthalpy flow at the hot end of the pulse tube. Several fu nctions which cause DC flow, such as valve timing and geometry of doub le-inlet valve and DC flow bypass, were tested in the two-stage 4 K pu lse tube cooler. The predictions and experiment both show that the neg ative DC flow leads to change of temperature profiles in pulse tube an d regenerator. Experiments verify that cooling power at 4.2 K of the t wo-stage pulse tube cooler can be considerably improved with aid of a suitable negative DC flow. (C) 1998 Elsevier Science Ltd. All rights r eserved.