Internal flow patterns behavior of a top heat mode closed-loop oscillating heat pipe with check valves (THMCLOHP/CV)

Abstract

An experimental study of the internal flow patterns of a top heat mode closed-loop oscillating heat pipe with check valves (THMCLOHP/CV) was carried out. In this study, the heat pipe was made of a Pyrex tube with an inner diameter of 2.4 mm which was bent into 10 meandering turns and filled with ethanol, R141b and R123 at a filling ratio of 50% by total volume. The number of check valves was 2 sets. The length of evaporator, adiabatic and condenser sections was 50 mm. The pipe was operated at the top heat mode, and the heat applied at the evaporator section was controlled at 85, 105 and 125°C. The detailed flow patterns were recorded with a digital camera and a video camera. The experimental results showed that the operation of the THMCLOHP/CV included three main phenomena:Energy storage, movement of slug-train and restoration. At an evaporator section length of 50 mm, the maximum heat flux occurred with R123 as the working fluid at the evaporator temperature of 125°C. The total internal flow patterns occurred as slug flow/dispersed bubble flow/churn flow. In addition, the evaporator temperature increased from 85 to 105°C and 125°C with ethanol, R141b and R123 as working fluids. The average length of the vapor slug decreased and the average velocity of the vapor slug increased, respectively. Key words: Flow patterns, closed-loop oscillating heat pipe, top heat mode.