다각적 분석 기법을 통한 고발열체 냉각기술 개발

Abstract

The need for innovative thermal control systems for space equipment such as satellites and spacecrafts has been addressed to keep the electronic components within the maximum allowable temperature limit. To accommodate high heat flux electronic devices in space equipment, a pulsating heat pipe (PHP) has been gaining much attention as an ideal candidate for space applications due to its simple wickless structure and its long-distance heat transport capability. A thermally-driven two-phase flow inside the PHP is known to transfer heat very efficiently until the heat input is below a certain limit. If the applied heat input exceeds the maximum allowable limit, the thermal performance of the PHP is significantly degraded as a result of the so-called dryout phenomenon. In this study, a systematic investigation is carried out on the heat transport capability of the PHP. As the preliminary study, flow visualization is performed using high-speed photography together with our image-processing algorithm: Based on the flow visualization results, it is postulated that the heat transport capability is significantly affected by the effective void fraction, which is defined as the average length of the vapor region occupied by vapor plugs (enclosed by liquid films) over the effective length of the PHP. This postulate is experimentally confirmed with PHPs with different lengths and various filling ratios. The optimum value for the effective void fraction is shown to decrease with increasing effective length or alternatively the optimum filling ratio increases with increasing effective length. Finally, a correlation of the optimum filling ratio is developed and found to be accurate in predicting the experimental data. This correlation provides a design guideline for choosing the optimum filling ratio for each PHP with a specified length to achieve its highest heat transport capability.