A visual study of internal flow patterns inside all inclined closed two-phase thermosyphon at normal operating conditions for several aspect ratios has been conducted. The article describes the derails of the flow patterns varying with inclination angles and aspect ratios, A thermosvphon with a diameter of I I. I mm was used. R I23 was selected as the working fluid, with a vapor temperature of 30'C and a fillillg ratio of 80%. Observation of the flow phenomena was conducted at selected inclination angles of 90', 30', and 5°from the horizontal axis, with aspect ratios of30, 10, and 5. Flow phenomena were recorded with a standard video camera and a still camera, and the corresponding heat transfer rate was a/so monitored. It was observed that the basic internal flow patterns could be classified according 10 the aspect ratios as follows: At all aspect ratio of 10 and higher, the internal flow changed from annular and churn flow at the vertical position to a stratified slug flow ill the inclined position, and there was all improvement in heat transfer rates between the vertical and the inclined positions. However, ill the case ofall aspect ratio less than 10. tilting the thermosvphon from vertical did not result ill changing the internal bubbly flow. II was observed thai the improvement ill heal transfer rates in this case was likely 10 be higher than in the previous case.The thermosyphon has been proven as a promising heat transfer device with very high thermal conductivity. Employing an evaporation and condensation principle of working fluid, which is in a closed container,
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.
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