Experimental Study And Simulation Of Flash Evaporation

Flash evaporation is applied as an important technical process of desalination, wastingheat recovery, and food or drug drying industrial process. Strengthening its research not onlycan enhance the understanding of the heat transfer and flow mechanism, but also has a veryimportant significance to improve energy efficiency and the industrial output.Based on flashing heat and mass transfer experimental platform, distilled water is used asworking fluid in experiment, the initial conditions is following: the initial temperature is65℃to99℃, the initial superheat is2℃to25℃, the initial height is390mm,440mm,490mm and540mm. The flashing process can be divided into three phases: bubble generationphase, boiling development stage and boiling weakened stage, according to the nucleationtheory the bubble generation phase can be divided into three cases, and boiling developmentstage can be divided into four regions. The swelling height, the maximum of penetrationdepth and penetration velocity are defined to describe flash evaporation, the impact of initialtemperature, degree of superheat, the initial liquid level height on the above parameters arequalitatively and quantitatively analyzed.The evolution of the temperature of water during flashing and the non-equilibriumfraction (NEF) versus time are discussed, the impact of initial temperature, degree ofsuperheat, the initial liquid level height on the evolution are analyzed. The flashing time,NEF*and the non-equilibrium temperature difference are defined by the evolution of NEFversus time, the impact of the initial conditions on them are studied in detail, finally, relevantformulas are well fitted to predict the relationship and influence.Finally, based on conservation of energy and mass, both the equilibrium model and thenon-equilibrium model are developed based on reasonable assumptions, and simulationmodels are established by MATLAB/Simulink. The simulation results are compared with theexperimental results, the advantage and disadvantage of the two models are analyzed, and thecorresponding models are refined reasonably.The impact of the initial conditions on the flash evaporation is studied in detail; this canprovides good guidance for the industrial applications. And the two flashing simulationmodels are of great significance for the further study of the flash evaporation.