Experimental study on non-equilibrium fraction of NaCl solution circulatory flash evaporation

• A circulatory flash evaporation system was designed and built.
• Two methods for NEF calculation were compared to each other and a more reasonable method was chosen to calculate NEF.
• NEF augmented to a peak value at first and decreased monotonously when the superheat increased.
• NEF decreased with increasing flow rate and flash chamber pressure but increased with increasing initial water film height.
• The NEF curve of NaCl solution was coincident with that of pure water in presented 10% NaCl solution flash evaporation cases.

Non-equilibrium performance of NaCl solution is different from that of pure water due to boiling point elevation (BPE) of NaCl aqueous solution. It's necessary to conduct experiments for NaCl solution circulatory flash evaporation. Experiments were conducted with flow rates of 400, 600, 800, 1000, and 1200 L·h− 1, initial water film heights ranging from 100 to 265 mm, initial water film concentrations of 0, 5%,10% and at pressures of 7.4, 12.3, 19.9, and 31.2 kPa. Two different benchmarks using the saturate temperatures of pure water and NaCl solution were chosen to calculate the non-equilibrium fraction (NEF) for NaCl solution circulatory flash evaporation, and comparison between the two methods was also performed. Results showed that the method using the saturate temperature of NaCl solution was reasonable to reveal the essence of NaCl solution flash evaporation. NEF considering BPE augmented to a peak value at first and decreased monotonously when the superheat increased. The NEF value increased with the increasing initial water film height and concentration but decreased with the increasing mass flow rate and flash chamber pressure. Moreover, the NEF curve of NaCl solution was coincident with that of pure water in presented 10% NaCl solution flash evaporation cases.