POOL BOILING HEAT TRANSFER IN DIELECTRIC FLUIDS AND IMPACT OF SURFACES ON THE REPEATABILITY

This study presents an experimental investigation on the nucleate boiling heat transfer (NBHT) in deionized ( DI) water and HFE-7100 on bare copper surfaces. The experiments were performed under atmospheric condition at 0 and 10 K subcooling levels. The primary objective was to understand the effect of fluid property on critical heat flux (CHF) and heat transfer performance, where the occurrence of surface oxidation over the entire set of experiments were investigated for a range of operating conditions. In order to determine the onset and development of the latter phenomenon, experiments for the complete boiling process have been repeated three times under similar conditions. A detailed visualization study with a high-speed camera has been utilized to capture the dynamics of bubble formation and departure. Additionally, high-resolution microscopic images were captured, and contact angle measurements were used to express the experimental results conveniently. Microscopic images showed that using DI water leads to an intensified oxidization on the heater surface, while HFE-7100 yields a minor occurrence of oxide layer on the copper surfaces. The results indicated that CHF values remain constant for water at 0 K; however, a remarkable increase was observed for 10 K subcooling from the first to third run of successive measurements.