EXPERIMENTAL STUDY OF SINGLE-BUBBLE DYNAMICS AND MICROLAYER CHARACTERISTICS IN POOL BOILING ON DIFFERENT WETTABILITY SURFACES

Nucleate boiling is the most effective mode of heat transfer in pool boiling, exploring the morphological changes of bubbles under different conditions is of great help in improving the heat transfer mechanism of nucleate boiling. This study obtains hydrophilic, smooth, and hydrophobic surfaces with contact angles of 40.3 degrees, 69.3 degrees, and 90 degrees by grinding, oxidizing, and corroding copper surface with 276 um machined cavity, respectively, and then build a boiling experimental bench that can stably generate single-bubble, and the PIV technique is used to carry out single-bubble experiments on heat transfer surfaces with different wettability to observe the morphology of single-bubble and the trend of their surrounding fluids. The experimental results show that as the hydrophobicity of the heat transfer surface increases, the volume, the base circle radius, etc., and the thickness of the microlayer beneath the bubble will increase, the heat carried away by the single bubble will be more, and the replenishment rate of liquid due to the evaporation of microlayer at the moment of bubble detachment will also be faster, which will lead to the formation of a new bubble and help it detach from the surface and enhance the heat transfer.