Experimental investigation on heat transfer characteristics in circulatory flash vaporization of aqueous NaCl solution

In this work, a series of experiments on circulatory flash vaporization of 10% and 20% NaCl solution was performed. The heat transfer characteristics in circulatory flash vaporization under different experimental conditions were presented. The non-equilibrium fraction of circulatory flash vaporization (NEF) was adopted to describe the extent of flash vaporization process completion. A volumetric heat transfer coefficient of circulatory flash vaporization (h_v) was introduced in the present study to evaluate the heat flux evolution from per unit volume of liquid pool under unit superheat degree. Moreover, the influences of superheat degree, pressure of flash evaporator, initial liquid level, circulating flow rate and concentration of NaCl solution on the volumetric heat transfer coefficient were also analyzed. Results suggested that the volumetric heat transfer coefficient increased with the superheat degree and flash chamber pressure. Lowering the initial liquid level and brine concentration promoted the heat transfer intensity. And Nusselt number of circulatory flash vaporization Nu_A was proposed to describe the heat transfer performance of circulatory flash vaporization according to the definition of volumetric heat transfer coefficient. Moreover, a correlation between Nusselt number of circulatory flash vaporization and dimensionless parameters was obtained with the relative error between −31.1% and 32.8% for 1.5 ≤ ΔT ≤ 20 K, 400≤Q≤1200 L h⁻¹, 7.4 ≤ P_f ≤ 31.2 kPa and 0.05 ≤ f_m ≤ 0.2.