Temperature visualization and investigation inside evaporator of pulsating heat pipe using temperature-sensitive paint

Abstract The mechanism of pulsating heat pipe (PHP) is still unclear because of its complex thermal fluid property, and a few studies have measured the temperature distribution inside PHPs. In this study, the temperature distribution inside a PHP was visualized. Temperature-sensitive paint (TSP) was applied on the optical window and was excited using UV LED light. The luminescence intensity was captured using a CMOS camera. The fluid and wall temperatures inside the PHP were measured instantaneously, with an accuracy of 0.263 °C. The thermal flow induced by evaporation and oscillation was captured. The temperature of working fluid adhering to the wall surface was lesser than the ambient temperature. When oscillatory flow was generated, the temperature at an arbitrary point inside the channel fluctuated. In contrast, when circulatory flow was generated, the temperature in the channel became stable. Based on the frequency analysis, the circulatory flow showed the periodic property. Measured data was in qualitative agreement with known PHP properties. Temperature measurement by TSP is considered effective in evaluating the performance and flow mechanism of PHPs.