HEAT TRANSFER ENHANCEMENT CHARACTERISTICS OF GRAVITY HEAT PIPE WITH SEGMENTED INTERNAL HELICAL MICROFIN

The heat transfer characteristics of gravity heat pipes (GHPs) with internal helical microfins (IHMs) were investigated experimentally, in comparison with smooth GHPs. The influence of different IHM arrangements on the GHPs was obtained. Four types of GHPs were designed and fabricated: GH-PIHM1 (GHP with IHM arranged only in the condenser section); GHPIHM2 (GHP with IHM arranged in both the condenser and adiabatic sections); GHPIHM3 (GHP with IHM arranged in all inner surfaces); and GHP (smooth GHP). The results showed that applying IHMs on the inner surface enhances the performance of the GHP; typically, by lowering the operating temperature and thermal resistance. All of the GHPs with IHMs demonstrated lower working temperatures than the smooth GHP; in particular, GHPIHM2 and GHPIHM3 decreased the working temperature by 23°C at 240 W. For most of the tested cases, the thermal resistance of GHPs with IHMs was reduced, as presented in ascending order: GHPIHM3 < GHPIHM2 < GHPIHM1 < GHP. For the condensation heat transfer coefficient, all three GHPs with IHMs can be improved; for the evaporation heat transfer coefficient, GHPIHM1 became worse while GHPIHM2 and GHPIHM3 performed better.