Experimental investigation on the effects of inclined grooves on flow boiling heat transfer and instability in a minichannel heat sink

Composite cooling technology combining micro/minichannel and flow boiling has shown great potential in enhancing heat transfer. However, improving their heat transfer efficiency and reducing flow boiling instability is necessary for high heat flux devices to achieve more efficient operation. Therefore, this work first designs a minichannel heat sink with inclined grooves at the bottom and experimentally investigates two-phase flow boiling heat transfer under three mass fluxes (138.8, 230.32, and 331.90 kg/m²·s) and two inlet temperatures (70 and 80 °C). The minichannel with a length, width, and height of 200 mm, 2 mm, and 2 mm, respectively. The grooves are evenly arranged at the bottom of the minichannel, with a depth and width of 0.5 mm and an inclination angle of 45° to the flow direction. Results show that the inclined grooves not only provide more nucleation sites to generate more bubbles but also hinder the excessive growth and coalescence of bubbles, delaying the transition from bubbly flow to annular flow. In addition, compared to the smooth minichannel heat sink, the minichannel heat sink with bottom groove can achieve boiling at lower wall superheat and smaller effective heat flux, and the onset of nucleate boiling is advanced. When the inlet temperature is T_in=80 °C and the mass flux is G ≈ 138.81 kg/(m²·s), the maximum average heat transfer coefficient of the minichannel heat sink with bottom grooves in the two-phase region is 30.70 kW/(m²·K), which is 18.31 % higher than that of the smooth minichannel heat sink. Moreover, the inclined grooves at the bottom generally reduce pressure drop, yield an excellent net effect for heat transfer intensification, and mitigate flow boiling instability. Therefore, this work demonstrates that setting inclined grooves at the bottom of minichannel heat sinks can significantly improve their overall performance and provide a reference for enhancing two-phase boiling heat transfer.