Convective Heat Transfer Motivated by Liquid-to-Vapor Density Difference in Centrifugal Force Field of Axially Rotating Loop Thermosyphons

The innovative rotating looped thermosyphons (RLTs) with and without a coil insert were proposed with cooling applications in rotating machinery. The spatial gradients of body forces among the vapor–liquid mixture of the distilled water in a strong centrifugal acceleration field motivated the flow circulation in a RLT to facilitate the latent heat transmissions. The effective thermal conductivity (Keff), the thermal resistance (Rth), the Nusselt numbers in the condenser (Nucon) and evaporator (Nueva), and the Nusselt number of the airflow induced by the rotating bend of the condenser (Nuext,con) of each RLT were measured at various rotating speeds and heat powers with two filling ratios of 0.5 and 0.8. The increase of filling ratio from 0.5 to 0.8 to maintain a thin liquid film along the rotating inner leg of each RLT substantially improved the heat transfer performances. The Keff, Nucon, Nueva, and Nuext,con were increased with rotating speed, leading to the corresponding reduction of Rth. On the basis of the experimental data, the empirical correlations that were used to calculate Rth, Keff, Nucon, Nueva, and Nuext,con of the RLTs at the two filling ratios with and without coil were proposed to assist the relevant design applications.