Pool Boiling Using Thin Enhanced Structures Under Top-Confined Conditions

An experimental study of pool boiling using enhanced structures under top-confined conditions was conducted with a dielectric fluorocarbon liquid (PF 5060). The single layer enhanced structures studied were fabricated in copper and quartz, had an overall size of $10×10mm2$⁠, and were $1mm$ thick. The parameters investigated in this study were the heat flux $(0.8-34W∕cm2)$ and the top space $S$$(0-13mm)$⁠. High-speed visualizations were performed to elucidate the liquid/vapor flow in the space above the structure. The enhancement observed for plain surfaces in the low heat fluxes regime is not present for the present enhanced structure. On the other hand, the maximum heat flux for a prescribed $85°C$ surface temperature limit increased with the increase of the top spacing, similar to the plain surfaces case. Two characteristic regimes of pool boiling have been identified and described: isolated flattened bubbles regime and coalesced bubbles regime.