접이식 버블젯 루프 히트파이프의 열전달 특성에 관한 연구

Abstract

Bubble jet loop heat pipe was designed to operate in a horizontal state. So it has been applied to the device of floor heating and root heating of green house farms. However, it was inconvenient to carry and did not work properly because it has a too long length and deflection of condensing part. In order to resolve the problem of conventional bubble jet loop heat pipe, the foldable bubble jet loop heat pipe was developed and to improve the performance of foldable bubble jet loop heat pipe, three kinds of experiments were conducted. First, the visualization of bubble jet loop heat pipe was performed to understand the operating principle. Bubbles made by the narrow gap between inner tube and outer tube of evaporating part generate pulsation at liquid surface of working fluid. The pulsation had slug flow, wavy flow and stratified flow. So working fluid circulates in the bubble jet loop heat pipe as two phase flow pattern. And large amount of heat is transferred by the latent heat from evaporating part to condensing part. Second, experiment that heat transfer characteristics depending on the changes in the folding angle of condensing part was conducted. This experiment was conducted under next conditions : Working fluid was R-134a, charging ratio was 50%, folding angle was from 0° to 5°(interval 0.5°). Heat flux of evaporating part was 9.65 kW/m2, respectively. The experimental results, show that bubble jet loop heat pipe had a high effective thermal conductivity of 2087 kW/m² in case of folding angle 1.5° and it has a uniform temperature profiles throughout the experiment. So the bubble jet loop heat pipe has a possibility for appling of the floor heating system. Finally, experiment that heat transfer characteristics depending on the changes in the charging ratio and heat flux of evpaorating part was conducted. This experiment was implemented under next conditions : Working fluid was R-134a, charging ratio was 30～70%(interval 10%), folding angle was 0°. Heat flux of evaporating part was 4.82, 7.23, 9.65, 12.06, 14.47 kW/m². In case of charging ratio 60%(inner volume), it has higher effective thermal conductivity than the others. And in case of from 4.82 to 9.65 kW/m² of heat flux, effective thermal conductivity increased. But in case of the others, effective thermal conductivity decreased because of the exceed of limit heat flux.