Flow boiling characteristics in a microchannel with various wettability patterned surfaces

Abstract

Flow boiling in a microchannel is an effective and attractive solution for thermal management. In this work, flow boiling was performed in microchannels with various wettability-patterned dotted surfaces. Pitch distances of dots were changed to study the wettability pattern effects on microchannel flow boiling. Glass-silicon-glass microchannels integrated with internal platinum heaters and various wettability patterns were fabricated and characterized using MEMS techniques. The transparent top of the channel allowed visualization of bubble dynamics and flow patterns. The hydraulic diameter of the microchannel is 338 μm, the side length of hydrophobic dots is 72 μm and the pitch distances of hydrophobic dots change from 122 μm to 172 μm. Bubble dynamics and flow patterns were visualized using a high-speed camera and a microscope. Heat transfer performance, including boiling curves and heat transfer coefficients (HTC), were explored experimentally under different mass flux. It is found that bubbles coalesce more frequently and flow pattern transitions are more intense with the decrease of pitch distance. In the low mass flux region, better heat transfer capability can be observed on the surface with larger pattern pitch distance, while with the increase of mass flux, a microchannel with smaller dot pitch distance presents better heat dissipation ability. Moreover, the critical heat flux (CHF) decreases with the decrease of dot pitch distance. The reasons behind these phenomena are related to the bubble coalescence, bubble density, and flow movement.