We tried to observe the flow behavior in typical pulse tube refrigerators (i.e., basic, orifice and double-inlet pulse tube refrigerators) using a smoke-wire flow visualization technique, and discuss the fundamental flow behavior in those pulse tube refrigerators. The pulse tube is made of a transparent acrylate tube having the effective length of 280mm, an inner diameter of 16mm and a wall thickness of 4mm. The regenerator is composed of a stainless-steel housing and a bakelite tube, 18mm in diameter and 168mm long packed with 770 discs of 100-mesh stainless-steel screen. The reservoir has a volume of about 3×10^-4m³, which is 5.5 times larger than the pulse tube volume. Air is used as the working gas and pressure oscillation is generated by introducing pressurized air of about 0.2MPa into the rotary valve and releasing it to the atmosphere. Visualization is done under the conditions of frequency of 5Hz and compression ratio of about 1.2.
The flow behavior throughout the pulse tube during one cycle is cleared. It was found that typical velocity profiles of the viscous oscillating flow are observed for all pulse tube refrigerators, and that the orifice and double-inlet types have larger velocity and displacement compared to the basic one. It was also found that the thickness of velocity boundary layer for oscillating flow is estimated to be about 30% of the radius of the pulse tube. Secondary streaming in the pulse tube, which flows in the direction from cold- to hot-end in the core region and the opposite direction in the boundary region, was recognized for all refrigerators.