Visualization of DC Gas Flows in a Double-Inlet Pulse Tube Refrigerator with a Second Orifice Valve

Abstract

We have observed the secondary flow induced in a double-inlet pulse tube refrigerator by using a smoke-wire flow visualization method and investigated the effects of the opening of the bypass valve on the flow behavior of the secondary flow, especially of the DC flow. Also, the effect of a second orifice valve on the secondary flow has been visually investigated. Based on the observations, the relationship between the cooling performance and the dynamic behavior of the secondary flow has been determined. It has been found that for the double-inlet pulse tube refrigerator, a DC flow is induced by opening the bypass valve, and that the DC flow is strengthened with additional opening of the valve. Further, the behavior of secondary flow in the pulse tube is well modeled as a superposition of the DC flow and the convection of acoustic streaming driven by the oscillating main flow. The valve opening for optimum cooling performance is found to be that that balances the DC flow and the acoustic streaming to reduce the net velocity of the secondary flow to zero in the core region of the pulse tube. Similarly, it is found for a double-inlet pulse tube refrigerator with a second orifice valve, that the optimum cooling performance again corresponds to near zero secondary flow in the core region.

Visualization of oscillating flow in a double-inlet pulse tube refrigerator with a diaphragm inserted in a bypass-tube

“…Experimental condition suitable for smoke-wire visualization was determined based on the results of the preliminary and previous experiments using the pulse tube refrigerator with the valve configuration [10]. The frequency of the gas oscillation was 6 Hz, and the amplitude of the pressure wave defined as the compression ratio between the high and low pressures at the inlet of the regenerator was 1.2.…”

“…The cause of this difference in the velocities near the wall can be attributed to whether the DC gas flow exists or not. For the double-inlet refrigerator, it was already reported that the DC gas flow is induced and the overall secondary flow is formed as a superposition of the DC gas flow on the acoustic streaming, and that under the optimized opening of the bypass valve, the velocity of the overall secondary flow decreases to almost zero in the core region while it increases near the wall [10]. In the case of the diaphragm D50 refrigerator, the DC gas flow is not induced owing to the diaphragm unit and accordingly the secondary flow only results from the acoustic streaming so that the velocity of the secondary flow near the wall decreases as a result of a decrease of the velocity in the core region.…”

Control of Secondary Flow in a Double-inlet Pulse Tube Refrigerator

“…The resistance for air flow along the direction indicated by the arrow was larger than that along the opposite direction, although the difference was less than 12% under the experimental conditions used here [10]. The effect of valve configuration on the flow behavior of the secondary flow, on the cooling performance, and on the pressure-volume (P-V work) diagram for gas was investigated.…”

“…Acoustic streaming is an axisymmetric convection in the pulse tube where the fluid flows toward the cold end in the core region and the associated return flow goes toward the hot end along the peripheral wall [10]. In general, the larger the temperature difference, the better the performance.…”

“…Gravity-driven convective flow can be induced when the refrigerator is inclined from the vertical orientation with the cold end lower [5,6,7,8]. Our previous visualization experiments indicated that acoustic streaming and DC flow were induced as secondary flows and that overall secondary flow in a pulse tube is formed by superposition of DC flow on acoustic streaming [10]. Acoustic streaming always degrades the cooling performance, whereas DC flow degrades the cooling performance only when the DC flow is not counterbalanced by the acoustic streaming in the core region of the pulse tube [9].…”