Experimental study and optimization of pin fin shapes in flow boiling of micro pin fin heat sinks

Micro pin fin heat sinks show their great merits of thermal management in high heat flux devices in microelectronic, energy, aerospace, and military areas. The design optimization of micro pin fin shapes is a critical issue for their applications, especially in two-phase flow boiling conditions. In this study, four types of staggered micro pin fins with different cross-section shapes, i.e., square, circular, diamond and streamline, were fabricated by a laser micromilling method, and constructed for heat sinks cooling systems. Flow boiling performance of the micro pin fin heat sinks (MPFHSs) was characterized using deionized water as coolant. The effect of cross-section shape on flow boiling characteristics of MPFHSs was examined. Test results showed that the square micro pin fins presented the best boiling heat transfer, followed by circular and streamline ones. The diamond micro pin fins performed worst in boiling heat transfer and suffered severe two-phase flow instabilities at moderate to high heat fluxes, whereas they introduced the smallest pressure drop. The streamline micro pin fins presented the largest two-phase pressure drop. The square and circular micro pin fins showed their superiority in the mitigation of two-phase flow instabilities. The square micro pin fins seem to be the optimum choice and should be selected for heat sink cooling systems. The results in this study provide critical information for the design optimization of micro pin fins heat sinks for the high heat-flux applications, and are of considerable practical importance.