Effect of porosity on heat transfer and pressure drop characteristics of wet air in hydrophobic metal foam under dehumidifying conditions

In order to evaluate the performance of the hydrophobic metal foam heat exchangers under dehumidifying conditions, the effect of porosity on the heat transfer and pressure drop characteristics of wet air in hydrophobic metal foam was experimentally investigated and compared with that in uncoated ones. The test results show that, as the porosity decreases from 95% to 85%, the heat transfer coefficient and pressure drop in hydrophobic metal foams are increased by 6%-18% and 56%-162%, respectively. The heat transfer coefficient of wet air in metal foams is increased by the hydrophobic coating at most experimental conditions except for the porosity of 85% and relative humidity of 70%-90%, and the maximum increment is 33%. The pressure drop of wet air in hydrophobic metal foams is 3%-139% larger than that in uncoated ones. The comprehensive performance of hydrophobic metal foam is better than that of uncoated foams at porosity of 95% and relative humidity of 30%-50%, and it becomes worse than that of uncoated ones with the decreasing porosity and increasing relative humidity.