Abstract
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.
Highlights
Prior to the examination of the thermal performances of the rotating looped thermosyphons (RLTs), the variations of the measured RLTs’ pressures at the evaporator (Peva ) and the condenser (Pcon ) and the corresponding saturated temperatures Tsat,eva and Tsat,con caused by varying centrifugal acceleration (Ca) (Q*) at the similar Q* (Ca) for the RLTs with and without coil are exhibited in Figure 3 at (a,c) filling ratios (FR) = 0.5 and (b,d) FR = 0.8
The present study proposed the rotating loop thermosyphon (RLT) as a passive heat transfer measure for rotor cooling of an electric motor or a rotating machinery
For all the RLTs tested, numbers of the evaporator (Nueva) were decreased with Q* but increased with Ca due to the attendant increases of evaporator pressure and Tsat,eva with the improved vapor–liquid circulation when Ca was increased
Summary
Thermal physics in a rotating heat pipe (RHP) is analogous, to a certain extent, with the free convection motivated by the gradients of fluid density in the earth’s gravity. The large vapor-to-liquid density difference in a much stronger centrifugal acceleration field with latent heat transmissions, differentiates and promotes the heat transfer mechanisms in a RHP from that with free convective flows. Li and Liu [1] conducted a review to highlight the effects of rotation mode and speed, capillary structure and geometries of condenser and evaporator, heat power, filling ratio, and working fluid on the performances of RHPs. The uniqueness of the thermal flow phenomena in an RHP originated from the particular interfacial segregation of the liquid flowing in the direction of centrifugal force.
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