Experimental study on heat transfer characteristics of circulatory flash evaporation

Flash evaporation with velocity in horizontal direction, called the circulatory flash evaporation, is the main mechanism in many industry processes such as multi-stage flash (MSF) desalination. The previous studies are mainly concerned about the characteristics of static flash evaporation or the flow pattern of the fluid in the single stage of the MSF. Little work has been performed on the heat transfer characteristics of circulatory flash evaporation. In the present paper a circulatory flash evaporation system was built. The experiments were carried out with flow rates of 400, 600, 800, 1000, 1200 L h^-1, initial water film heights ranging from 100 to 265 mm and at pressures of 7.4, 12.3, 19.9, 31.2 kPa, respectively. Results indicated that non-equilibrium fraction (NEF) augmented to a peak value at first and decreased monotonously when superheat increased. The heat transfer coefficient dropped with the increase in the superheat. The influence of flow rate, pressure in the flash chamber and initial water film height on the variation of NEF and heat transfer coefficient was also investigated. The NEF decreased with increasing flow rate and pressure in the flash chamber but increased as the initial water film height rising. However, the volumetric heat transfer coefficient showed an opposite law.