The enhancement of the efficiency of evaporation of liquid water, for water evaporation and steam generation, is of major technological as well as scientific interest, with applications ranging from water heaters to distillation and desalination. The use of solar radiation for this purpose amounts to a better utilization of an abundant energy resource.
The relative influence of the capillary, Marangoni, and hydrophobic forces in mediating the evaporation of water from carbon foam based porous media, in response to incident solar radiation, are investigated. It is indicated that inducing hydrophilic interactions on the surface, through nitric acid treatment of the foams, has a similar effect to reduced pore diameter and the ensuing capillary forces. The efficiency of water evaporation may be parameterized through the Capillary number (Ca), with a lower Ca being preferred. The proposed study is of much relevance to efficient solar energy utilization.
We specifically indicate that enhanced capillary pressures, either due to a decreased pore size or the chemical modification of the surfaces would serve to increase the evaporative efficiency of water through light absorbing (where it is indicated that the absorption could be of the order of 93%-95%) porous media. The proposed media may also be used for desalination where the larger electrical conductivity may be of advantage; additionally, a decreased interfacial thermal resistance in ionic solutions may also be beneficial.