Influence of surface wettability on pool boiling heat transfer on metal foam covers

In the present study, the nucleate pool boiling heat transfer characteristics of water on the hydrophilic and uncoated metal foam covers were experimentally investigated, and were compared with those on hydrophobic metal foam covers to analyze the influence of surface wettability on pool boiling heat transfer on metal foam covers. The experimental conditions cover pore densities of 5-50 PPI (pores per inch), porosities of 85%-95%, average contact angles of 0 degrees-148.1 degrees, heat fluxes of 0-2 x 10(6) W/m(2). As the pore density increases from 5 PPI to 40 PPI, the pool boiling heat transfer coefficient in hydrophilic metal foam is increased by 10%-25%, and the critical heat flux is increased by 40%. As the porosity decreases from 95% to 85%, both the critical heat flux and the pool boiling heat transfer performance in hydrophilic metal foams are deteriorated. The surface modification effect factor EFsm for hydrophilic metal foam varies within 1.01-1.38; EFsm increases with the increasing heat flux, which is contrary to that for hydrophobic metal foam. The critical heat flux on hydrophilic metal foam covers with 5 PPI and 20 PPI are 1.2 x 10(6) W/m(2) and 1.36 x 10(6) W/m(2), respectively, which are larger than those on hydrophobic ones. A new correlation for pool boiling heat transfer coefficient on metal foam covers with different wettability was developed with an average deviation of 14.1%.