LAUSR

ABSTRACT Liquid-vapor flow separation is a major problem in the development of high-efficiency two phase thermosyphons. The closed loop thermosyphons with check valve (CLTP/CV) are able to completely separate the liquid-vapor flow and their efficiency is higher than conventional closed loop thermosyphon (CLTP) under lower budget. This study investigated the flow visualization to clearly understand the complex heat transfer mechanism of internal behavior comparison between the CLTP and CLTP/CV without reports. A high speed camera was employed to record videos and photographs in evaporator and condenser sections. The CLTP/CV was made of pyrex tube with inner diameter of 11.6 mm, the evaporator and condenser were of equal lengths of 300 mm. The check valve was installed in an upward flow direction at the adiabatic section. Hot water was applied to the evaporator section at 75, 85 and 95 oC. The experimental results indicated that the heat transfer rates of the CLTP and CLTP/CV increased with an increase in the evaporator temperature with the maximum heat transfer rates at 126.18 and 195.73 W, respectively. The flow behavior of the CLTP exhibited a bubble flow/stratified wavy flow where bubbles move from end to end in the evaporator section. On the other hand, the installation of a check valve changed the flow behavior from flow/stratified wavy flow to nucleate pool boiling only in CLTP/CV, resulting in the heat transfer coefficient increasing by 33% from the maximum heat transfer coefficient of 413.74 to 625.92 W/m2 oC when comparing between the CLTP and CLTP/CV, respectively, this being consequently the main reason for the higher heat transfer rate.