DC flow in pulse tube coolers

Abstract

A single stage four-valve pulse tube cooler is operated thus that a steady gas flow (DC flow) is superimposed on the oscillating flow. Both, the measured refrigeration power and the temperature profiles are found to be in qualitative agreement with numeric simulations based on a simplified thermoacoustic model. Furthermore such calculations are being applied to a two-stage pulse tube cooler with 45 K and 5 K stage temperatures. It is shown that moderate positive DC flow (steady gas flow from the regenerator to the pulse tube) can be advantageous. There is a relatively small improvement at the first stage, but for the second stage DC flow is shown to be essential. In the special case considered here, no 5 K refrigeration power is expected to be achieved without DC flow, whereas more than 1 W is predicted when there is a DC flow rate amounting to about 0.4% of the alternating flow going into the second stage regenerator. The temperature profile within the pulse tube is shown to be a very sensitive parameter for the control of the DC flow.