Experimental study of pool boiling on micro-cavities structured surfaces

The saturated and subcooled boiling experiments on micro-cavities structured surfaces are conducted in this work at atmospheric pressure. Micro-cavity structures on copper surface (i.e., MC200, MC400, MC600 and MC800) are prepared by nanosecond laser micro-nano processing technology. Bubble dynamics, mainly including active nucleation sites density, are comparatively discussed to further disclose the mechanism of boiling enhancement. Bubbles are easily nucleated inside micro-cavity structure and achieved higher local heat flux for bubble growth, thus exhibiting better heat transfer coefficient (HTC) on surface with micro-cavity structure pitch of 200 mu m at low heat fluxes. Under subcooled boiling, obvious bubble coalescence is observed at smaller micro-cavity structure pitch, indicating that the increase in nucleated bubble leads to the bubble coalescence. Compared to flat surface, a higher CHF is obtained on micro-cavities structured surfaces due to the uniformly distributed bubbles, and surface with micro-cavity structure pitch of 400 mu m exhibits the highest CHF since the counterflow between liquid inflow and vapor outflow is alleviate when the bubble departure diameter under large mushroom clouds is almost closed to the pitch of micro-cavity structure.