Heat transfer and pressure drop characteristics of wet air flow in metal foams with different structures and surface wettability during dehumidifying conditions.

Abstract

To optimize the metal foam heat exchangers under dehumidifying conditions, the heat transfer coefficient (HTC) and pressure drop of wet air in metal foams with different structure and surface wettability were obtained experimentally. The pore density of tested metal foams is 5-40 PPI, and the porosity is 0.85-0.95. The wettability includes the hydrophobic, hydrophilic and uncoated surface, with proceeding contact angles from 15.4° to 161.2°. The results show that, the HTC of wet air in metal foams are enhanced by 4%-33% and 2-21% by hydrophobic and hydrophilic coating, respectively; the pressure drops are obviously increased by hydrophobic coating and maximumly decreased by 20% by hydrophilic coating; as PPI increases, the pressure drop in metal foams are increased, while the HTC is firstly increased then decreased at most dehumidifying conditions; as porosity increases, the HTC and pressure drop are both decreased. Considering the comprehensive performance, 20PPI is the best metal foam pore density with best comprehensive performance, while 0.85 and 0.95 are the best porosity for hydrophobic and uncoated metal foams, respectively.