Effect of a new type staggered pin fin configuration on flow boiling characteristics of micro-heat sinks

Abstract

Flow boiling in micro-pin fn structured heat sinks is an up-to-date thermal management technique. However, due to microsized fow passages, bubble blockage is a problem for this type of heat sinks, too. In addition, mixing and bubble breakup are important phenomena for enhancement of heat transfer. Taking more advantages of potential of this unique technique depends on removing of relevant shortcomings and supporting infuential mechanisms; therefore, new geometries being designed based on bubble-dynamic characteristics should be developed, and relevant thermo-hydrodynamic characteristics should be analyzed. Therefore, the present paper experimentally analyzes boiling performance of water fow in a micro-pin fn heat sink having a new type of geometry. The heat sink has four sections, and in each section, the micro-fns are positioned in staggered form according to previous sections, also the number of fns in each section is fewer than the one of the former sections. In this paper, for the frst time in the literature, combined infuence of regional staggered pin fn arrangement and regional cross-sectional enlargement on thermo-hydrodynamic characteristics of fow boiling in micro-pin fn heat sinks is investigated. The new type of heat sink (NT) is compared with conventional type (CT) in which the micro-pin fns are uniformly located throughout the heat sink. Saturated fow boiling experiments are conducted at a heat fux range of 132–272 kW m−2 (90 W to 180 W with 10 W increments), and at a constant mass velocity of 174 kg m−2 s −1 for constant inlet temperature of 75 °C. It is concluded that staggered pin fns with decreasing number signifcantly boost thermal and fow characteristics. Compared to the conventional type, two-phase heat transfer coefcient increases up to 94.5%, and pressure drop decreases up to 18.3% via NT. The wall superheat for NT is lower than those obtained for CT for the whole database, which physically means that NT keeps the heating surface at lower temperature for the same heat load. Prevention of bubble blockage problem, suppression of fow reversal, enhancement of bubble disjunction, decrease of vapor-waiting time on heat transfer surface, and more efective convective boiling characteristics are the main underlying reasons of performance enhancement.