A narrow shape double-layer microchannel heat sink (DL-MCHS) designed for high-power laser crystal

Abstract

• A narrow shape DL-MCHS is designed for the small-size high power laser crystal. • The multi-layers are inner-soldered to enhance the vertical heat transfer rate. • Extension of DL-MCHS in the length enhances the overall heat transfer capability. • Heat diffusion reduces the influence of fluid flow rate ratio in the two layers. • The DL-MCHS exhibits a low pumping power. The thermal effect-induced problem has become a bottleneck in high power laser systems. The laser crystal, which dissipates a heat flux over 150 W/cm 2 , is the most challenging component when considering the solution of the thermal problem. In this work, we designed a double-layer microchannel heat sink (DL-MCHS) for the heat release of a small-size laser crystal. The main constraints, including the high power density of the laser crystal, space restriction, and the fabrication method are taking into account. A narrow shape DL-MCHS is proposed. The microchannels are fabricated micro-mechanically, and the layers of the DL-MCHS are welded together using a vacuum brazing method. A systematic experimental study is performed to evaluate the performance of the DL-MCHS. The results show that the narrow shape DL-MCHS, which extends the volume only in its length, shows good heat transfer capability. The overall heat transfer coefficient reaches 42 × 10 3 W/(m 2 ·K). The surface temperature of the heating source is well controlled below 55 °C at a typical heat power of 234 W. When the same fluid flow rates are adopted in the two microchannel layers, the first microchannel layer (bottom) absorbs two thirds of the total heat, while the rest is absorbed in the second layer (top). In the solid base of the DL-MCHS, thermal resistance in the vertical direction is over three times that in the longitudinal direction. When the fluid flow ratio in the first microchannel layer increases, the overall heat transfer coefficient is enhanced slightly, while the temperature distribution on the heating head is little affected. Comparing the single-layer cooling pattern, the double-layer flow pattern improves the uniformity of temperature distribution on the heat sink when the counter-current flow is used, and saves the pumping power by up to 60%.