Effects of Aspect Ratios on Internal Flow Patterns of an Inclined Closed Two-Phase Thermosyphon at Normal Operating Condition

摘要

A visual study of internal flow patterns inside an inclined closed two-phase thermosyphon at normal operating conditions for several aspect ratios has been conducted. The article describes the details of the flow patterns varying with inclination angles and aspect ratios. A thermosyphon with a diameter of 11.1 mm was used. R123 was selected as the working fluid, with a vapor temperature of 30℃ and a filling 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 of 30, 10, and 5. Flow phenomena were recorded with a standard video camera and a still camera, and the corresponding heat transfer rate was also monitored. It was observed that the basic internal flow patterns could be classified according to the aspect ratios as follows: At an aspect ratio of 10 and higher, the internal flow changed from annular and churn flow at the vertical position to a stratified slug flow in the inclined position, and there was an improvement in heat transfer rates between the vertical and the inclined positions. However, in the case of an aspect ratio less than 10, tilting the thermosyphon from vertical did not result in changing the internal bubbly flow. It was observed that the improvement in heat transfer rates in this case was likely to be higher than in the previous case.