Influence of pore density on heat transfer and pressure drop characteristics of wet air in hydrophilic metal foams

•New data of heat transfer and pressure drop in metal foams were obtained.•Influence of pore density on wet air flow in metal foams was analyzed.•Hydrophilic influence factors for metal foams were analyzed.•Performance of hydrophilic metal foams and hydrophilic fins were compared. To optimize the performance of hydrophilic metal foam, the influence of pore density on heat transfer and pressure drop characteristics of wet air in hydrophilic metal foams is experimentally investigated. The experimental conditions include pore density from 5PPI to 40PPI. The results show that, as pore density increases from 5PPI to 40PPI, the overall heat transfer coefficient of wet air in hydrophilic metal foams always increases at relative humidity of 30–70%, while it initially increases then decreases at relative humidity of 90%, representing a maximum value at PPI of 20; the pressure drops always increase as pore density increases; the best comprehensive performance of hydrophilic metal foam is achieved at PPI of 20. Compared with the uncoated metal foam, the overall heat transfer coefficient of wet air in hydrophilic metal foam is increased by 2–21%, while the pressure drop of wet air in hydrophilic metal foam is decreased by 1–15% at most conditions; the hydrophilic metal foam provides better comprehensive performance than the uncoated metal foam and the hydrophilic fin-and-tube heat exchangers. Correlations for the Colburn j factor and Friction factor f are developed for the wet air flow in hydrophilic metal foams, and the maximal deviation of the correlation for the j and f factors are within ±15% and ±20%, respectively.