Increasing the evaporation rate for fresh water production-application to energy saving in renewable energy sources

This paper is centered on the study of the energy saving in the obtaining of drinking water from salty or contaminated water by reduction of the latent heat of evaporation. This is procured by a reduction of the surface tension of the liquid mixture by adding nonvolatile surfactants to the water to be distilled. It has been proven that there exists a direct relationship between the evaporation rates of the salty, or contaminated water and the pure water, a relationship that is dependent on time. Also, the reason for the respective evaporation rates is inversely proportional to the surface tension, so that if the latter is reduced, the former is increased. Thus, the drinking water production could be increased using the same energy, i.e. less energy would be spent to produce the same quantity of drinking water, improving the yield of the process. The proportionality constant between the reason for evaporation rates and the surface tension of the mixture is a dependent function of the type of surfactant, its concentration and the operation conditions (ambient and mixture temperature, relative dampness, etc.). The characteristic values of the constant have been determined for the tests accomplished which will permit a quantified energy saving in the obtaining of drinking water by evaporation for a certain process. The generalization of the characterization process of the value of the constant will simplify the calculations and create an expression that determines the energy in all cases. (C) 1997 Elsevier Science Ltd.