Experimental study on circulatory flash speed of aqueous NaCl solution circulatory flash evaporation

• Circulatory flash speed was defined as average drop rate of NEF during the residence time.
• The effect of main experimental parameters on circulatory flash was clarified thoroughly.
• With the increase of circulatory flash speed, non-equilibrium fraction has a minimum value.
• Comparative study on flash speed between static and circulatory flash evaporation was conducted.
• Volumetric heat transfer coefficient linearly increased with circulatory flash speed.

In present paper, a series of experiments on circulatory flash evaporation of 15% aqueous NaCl solution was carried out under various main experimental parameters. Circulatory flash speed, which represented the superheated energy consumed in unit time in flash chamber, was defined as average change rate of the non-equilibrium fraction during the residence time in flash chamber. It indicated the intensity of flash evaporation. The experiment results showed that circulatory flash speed quickly decreased to a lowest point, then increased monotonously with the increasing superheat and finally became flat. Influence of parameters, such as flow rate, initial height of water film and equilibrium pressure on circulatory flash speed was also investigated. As circulatory flash speed increased, NEF had a minimum value. At the same circulatory flash speed, NEF decreased when superheat degree and equilibrium pressure increased. And comparative study on flash speed between static and circulatory flash evaporation was also conducted. Both theoretical and experimental results of volumetric heat transfer coefficient showed a linear relationship with circulatory flash speed. However, the experimental values were greater than the calculated values due to the liquid droplets entrainment.