Investigation of pool boiling heat transfer under high centrifugal accelerations in radially rotating heat pipes

Pool boiling heat transfer plays a critical role in determining the thermal performance of radially rotating heat pipes (RRHPs). The enclosed geometric structure and operating mechanism of RRHPs lead to unique pool boiling heat transfer characteristics under high centrifugal accelerations. In this study, experimental investigations were conducted on RRHPs to address three critical issues: (1) measurement of the saturation temperature inside the RRHP, (2) the effect of subcooling on pool boiling regimes, and (3) the development of correlations for predicting pool boiling heat transfer. RRHPs with 100 % filling ratio and 40 mm pool depth were tested under heat inputs ranging from 40 W to 320 W and centrifugal accelerations ranging from 300 g to 2100 g . The results revealed that the liquid pool was not entirely saturated due to a significant temperature difference between the liquid pool and the vapor—a phenomenon measured for the first time. Three pool boiling regimes—natural convection, subcooled boiling, and saturated boiling—were distinguished based on theoretically derived local equivalent wall superheat and pool subcooling. With the increasing centrifugal acceleration, both the liquid–vapor saturation temperature difference and the pool subcooling were significantly increased, leading to suppressed nucleate boiling and expanded subcooled boiling regime within the liquid pool of the RRHP. Furthermore, two new empirical correlations of N u NC = 1.765 R a 0.13 and N u NB = 242 R e b 0.248 P r l − 1 B o − 0.351 were developed based on experimental data to predict pool boiling heat transfer in the natural convection and nucleate boiling regimes within the RRHP.