Observation of DC Flows in a Double Inlet Pulse Tube

Abstract

Pulse tube cryocoolers using the double inlet configuration have demonstrated increased performance over the single orifice configuration. However, the double inlet has an internal closed loop fluid path that can allow a dc fluid current to flow unregenerated from ambient temperatures to the cold end, which can impose a significant heat load on the cold stage. As pointed out by Gedeon2, there are hydrodynamic mechanisms in pulse tube cryocoolers that generate these flows. These mechanisms include “streaming”, where oscillating flow and pressure fields viscously interacting with boundaries lead to non-zero time-averaged mass flows, and asymmetric pressure drops due to asymmetric entrance/exit effects. Recently, several investigators have demonstrated that dc flows are present in double inlet pulse tubes. To investigate this further, we have intentionally introduced dc circulating flow into a double inlet pulse tube, controlling both the magnitude and direction of the flow. We observed shifts in the temperature profiles of both regenerator and pulse tube, with the directions and magnitudes consistent with the magnitude and direction of the dc flow. We have measured significant loss of cooling power as the dc flows increased. We have also observed that dc flows can be highly unstable under certain conditions, with sudden onsets of large flows with only minor changes in operating conditions.