Experimental Investigation on Falling Film Heat Transfer Characteristics in Radially Rotating Heat Pipe Evaporator

Radially rotating heat pipes (RRHPs) offer an innovative and efficient approach for cooling rotary equipment. The falling film heat transfer within the evaporator section plays a pivotal role in determining the overall thermal performance of the RRHP. This study delves into the characteristics of falling film heat transfer in the RRHP evaporator at filling ratio of 16%. Experiments were conducted across a broad spectrum of heat inputs, ranging from 40 W to 320 W, and centrifugal accelerations, spanning from 300 g to 2100 g. The findings revealed that falling film boiling was the dominating heat transfer mechanism under the experimental conditions in the RRHP evaporator, contributing to excellent thermal performance characterized by a low equivalent thermal resistance of less than 0.08 K/W and a high heat transfer coefficient exceeding 27000 W/(m²·K). The film Reynolds number, ranging from 4 to 160, indicated a laminar film regime. The study further demonstrated that the falling film heat transfer was significantly enhanced by increasing heat input and operating temperature. Conversely, the influence of centrifugal acceleration on falling film boiling was found to be minimal, highlighting a notable distinction between falling film boiling and pool boiling. A correlation based on the film Reynolds number and Prandtl number was established to describe falling film boiling in the RRHP evaporator, with deviations within ±25% from the experimental data.