Influence of surface wettability on heat transfer and pressure drop characteristics of wet air in metal foam under dehumidifying conditions

Abstract

The surface wettability determines the condensate mode and the adhesive force of condensate on the metal fiber surface, which can directly affect the heat transfer and pressure drop characteristics of wet air in metal foams. In the present study, the heat transfer and pressure drop characteristics of wet air in metal foams with different surface wettability under dehumidifying conditions were investigated experimentally. The tested samples include the hydrophobic, hydrophilic and uncoated metal foams, and the experimental conditions cover the inlet air temperatures of 27oC-35 °C, the inlet air relative humidity of 30%–90% and the air velocities of 0.5–1.0 m/s. The experimental results show that, the heat transfer coefficients in hydrophobic and hydrophilic metal foams are larger by 4%–33% and 3–21% than that in uncoated metal foams, respectively, and the heat transfer enhancement of the hydrophobic coating is more obvious; compared with the uncoated metal foams, the pressure drop in hydrophobic metal foams is increased by 3%–139%, while the pressure drop in hydrophilic metal foams is reduced by 1%–20%. The heat transfer and pressure drop characteristics of wet air in metal foams were evaluated by the comprehensive performance index (j·f−1/3), and the comprehensive performance of hydrophilic metal foam is better than that of hydrophobic and uncoated metal foams.