Simulation Study Of Direct Contact Heat Transfer Characteristics Of Molten Salt

In view of the low vapor pressure of molten salt and immiscible with the gas,direct-contact heat transfer of molten salt and gas was employed to effectively enhance the heat transfer rate and achieve full heat transfer.Based on this,this project was analyzed the heat transfer characteristics of the gas in direct contact with the molten salt,and coupled with the interphase heat transfer model in Eulerian model.The interfacial area concentration model was used to characterize the coalescence and breakage of bubbles.The following details and results were discussed.In this paper,air and heat conducting oil are the research object.Experiments and simulations of gas-liquid direct contact heat exchange at low temperature were carried out.The overall gas holdup,rate of temperature rise and volumetric heat transfer coefficient were measured by the experimental method.The experimental results show that the rate of temperature rise increases with the increase of superficial gas velocity and the temperature difference,and decreases with the increase of the initial liquid height.The volumetric heat transfer coefficient increases with the increase of the superficial gas velocity and decreases with the increase of the initial liquid height and the temperature difference.The numerical simulation results are in good agreement with the experimental ones.Then,the direct contact heat transfer characteristics of gas and nitric acid molten salt were analyzed,including the influence of operating parameters(including superficial gas velocity,gas inlet temperature and initial liquid height)and physical parameters(including gas species and initial molten salt temperature).The numerical results show that when the gas inlet temperature and the initial liquid height are the same,with the increase of superficial gas velocity,the degree of liquid turbulence in the bubble column increases,and the rate of temperature rise of molten salt and the volumetric heat transfer coefficient increases greatly.When the superficial gas velocity and the initial liquid height are unchanged,with the increase of gas inlet temperature,the interfacial area concentration increases,and the rate of temperature rise of molten salt increases,and the volumetric heat transfer coefficient decreases.When the superficial gas velocity and the gas inlet temperature are constant,as the initial liquid height increases,the heat gain per unit volume of molten salt decreases,the rate of temperature rise of molten salt and the volumetric heat transfer coefficient decreases slightly.When the superficial gas velocity and initial temperature of the molten salt are constant,the larger the Reynolds number,the faster the heat transfer rate.Carbon dioxide carries more heat than air and nitrogen.When carbon dioxide is used as heat transfer gas,the rate of temperature rise and the volumetric heat transfer coefficient of molten salt are obviously greater than air and nitrogen,and the air is slightly larger than the nitrogen.When the superficial gas velocity and the gas inlet temperature are the same,the fluidity of the molten salt and the specific heat capacity increase with the increase of the initial temperature of the molten salt.Therefor more heat will be needed to increase the unit volume of molten salt by 1K.The rate of temperature rise of molten salt decreases,and the volumetric heat transfer coefficient increases.