Heat transfer of isolated bubbles in microchannel boiling

In recent years, microchannel boiling heat transfer has become an effective solution for high heat flux electronic devices. This study explores the heat transfer mechanism of bubbles within microchannels by employing an integrated approach that combines experimental observations with numerical simulations. Through the study of heat transfer during the stages of free growth, restricted growth, and elongated growth of bubbles, a heat transfer model for bubble growth using water as the working fluid was developed. The bottom of the bubble was divided into convection, dry patch, and conduction zones based on the dominant heat transfer mechanism, with the convection zone showing higher heat transfer coefficients. As the bubble transitions into the elongation growth stage, its size undergoes rapid expansion. With the increase in the inlet velocity, the dry patch disappears, and the bubble is completely covered by liquid film. As the capillary number increases, the liquid film thickness and the dry patch length increase, and the dry patch area rapidly expands when bubbles enter the elongated growth stage. The existence of corner regions at the bottom of the rectangular channel results in leakage flow, where capillary forces replenish the liquid, and the action of evaporation reduces the temperature in these areas.