Dependence of convective secondary flow on inclination angle in an inclined pulse tube refrigerator revealed by visualization

Secondary flow in an inclined orifice pulse tube refrigerator at typical inclination angles of 0–180° was studied by using a smoke-wire flow visualization technique. It was revealed that the secondary flow formed a unicellular convective flow in the pulse tube and had two flow patterns depending on the angle. This dependence of flow pattern on the inclination angle is well explained by the superposition of gravity-driven convective flow on acoustic streaming. Even if the cold end was lower than the hot end, the gravity-driven convective flow occurred and the secondary flow was affected by gravity.