SUMMARY

A parametric study of pool boiling at atmospheric pressure from single-layered enhanced structures was conducted for a dielectric fluorocarbon liquid (PF 5060). The enhanced structures studied were fabricated in copper, had an overall size of 10 mm  10 mm and were 1 mm thick. The parameters investigated in this study were the heat flux, the width of the microchannels and the microchannel pitch. The boiling performance of the enhanced structures was found to increase with increase in channel width and decrease in channel pitch. The modes of boiling from an enhanced structure proposed by previous researchers were unable to explain the boiling curves obtained in this study. The present data are explained in light of the contribution from the top finned surface of the enhanced structure. Pool boiling experiments employing enhanced structures under top confinement were also conducted. The main parameter investigated was the top space (0 mm  13 mm). A high-speed camera with attached magnifying lens allowed precise observation of the evaporation process inside the structure as well as the liquid/vapor flow in the space above the structure. For the total confinement ( = 0 mm), the heat transfer performance of the enhanced structures was found to depend weakly on the channel width. For >0 mm, 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 oC 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. A semi-analytical predictive model applicable to pool boiling under confinement is developed. The model requires a limited number of empirical constants and is capable of predicting the experimental heat flux within 30%.