Experimental investigation on the characteristics of flash evaporation from superheated water jets for desalination

摘要

A promising method of desalination suitable for low-populated islands and remote areas is experimentally investigated at a small desalination plant capable of producing 15.2 tons of fresh water per day based on the flash evaporation from superheated water jets. In this method, water at a temperature ranging from 24 to 40 °C is brought to superheat condition through the injection into a depressurized chamber maintained below the boiling pressure that corresponds to the injected water temperature. A part of the injected water quickly evaporates in order to regain equilibrium at the reduced pressure, and the generated steam is condensed on a surface condenser supplied with the cold water. Even at very low degrees of superheat, flash evaporation from the superheated jets has shown high efficiency in converting the latent heat of the liquid water into vapor within the jet residence time which does not exceed a fraction of a second. An exponentially decaying curve model that simulates the temperature decline curves at the centerline of the upward flowing jet is developed and found matching the experimental data considerably. Influence of flow conditions on the characteristics of the flashing jet and on the intensity of the flash evaporation is also clarified.