EXPERIMENTAL STUDY ON PHASE CHANGE HEAT TRANSFER ENHANCEMENT OF A NOVEL LOOP HEAT PIPE BY USING SURFACE MICRO-STRUCTURES

A novel loop heat pipe (NLHP) with an evaporator and a boiling pool can provide excellent heat dissipation for electronic chips due to the high critical heat flux density of boiling heat transfer. The surface micro-structure can improve heat transfer performance of the boiling pool of the NLHP by increasing the number of nucleation sites and the heat transfer area. In the present study, V-shaped groove surface and quadrangular pyramid surface micro-structures were designed and fabricated, and then applied to the boiling pool of the NLHP. It was found that the surface micro-structures not only improve the startup characteristics of the NLHP by reducing the peak temperature and the time to reach the peak value but they also improve the thermal performance of the NLHP by reducing the steady-state temperature and the time to reach steady state. Compared to a flat boiling pool, the V-shaped groove micro-structure expands the maximum power to 200 W (heat flux of 41.32 W/cm(2)) while the quadrangular pyramid micro-structure reduces it to 140 W (heat flux of 28.93 W/cm(2)) since the latter possesses more nucleation sites and a more efficient boiling process. The system thermal resistance of the NLHP decreases with increasing heat loads and is remarkably reduced by the surface micro-structures, with a minimum value of 0.157 K/W obtained by the V-shaped groove micro-structure at 200 W.