Visualization of oscillatory flow phenomena in tapered pulse tube refrigerators

Abstract

An oscillating flow in a pulse tube refrigerator with a tapered pulse tube was observed by a smoke wire flow visualization method. Effects of a tapered tube on flow phenomena were investigated from the view point of suppressing secondary streamings. Two kinds of tapered pulse tubes, a converging and a diverging tapered tube, were tested and the result was compared to that of cylindrical pulse tubes with the same interior volume as the tapered ones. It was observed in the converging tube that the velocity profile of the streaming is much more flattened compared to that in the cylindrical tube, and gas moves not only in the axial direction but in the radial direction substantially. It is also found that the performance of the converging tapered pulse tube is slightly improved compared to that of the cylindrical one, but it is not clearly distinguished from the observation whether the improvement is due to the suppression of the secondary streaming or not. On the other hand, the secondary streaming in the diverging tube is enhanced and the performance is deteriorated compared to those of both cylindrical and converging tubes.