Simulation Study Of Direct Contact Heat Transfer And Flow Of Molten Salt In Bubble Column

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,A direct contact heat transfer model is obtained by analyzing the heat transfer process of a single bubble in the molten salt.The mixing and heat transfer process of gas and molten salt in the bubble column are simulated.based on the two-fluid model,which coupling the interfacial area transport equation?IATE?and the direct contact heat transfer model.The simulations are partly verified by the experimental data.The effects of superficial gas velocity,operating pressure,different kinds of gases,different kinds of molten salts,different heat transfer models in bubble column are discussed.The following are details and results.In this paper,by analyzing the heat transfer process of a single bubble in the molten salt obtained the energy equation and then the direct contact heat transfer model is obtained by numerical calculation.Taking air and paraffin as research objects,The overall gas holdup,volumetric heat transfer coefficient and the temperature distribution of the paraffin wax in the tower are discussed.when apparent gas velocity is during 0.04 m·s^-1 to 0.1 m·s^-1.The experimental results show that as the superficial gas velocity increases,the overall gas holdup and volumetric heat transfer coefficient increase.Mere 7%deviation is found between the overall gas holdup obtained through simulation and experiment,Mere 2%deviation is found between the volumetric heat transfer coefficient obtained through simulation and experiment,the temperature distribution is uniform.and the temperature difference between the bottom and the top of the column is 2 K.Based on the two-fluid model,which coupling the interfacial area transport equation?IATE?and the direct contact heat transfer model.the direct contact heat transfer characteristics of gas and molten salt were analyzed,including the influence of operating parameters?including superficial gas velocity,operating pressure?,physical parameters?including gas species and molten salt species?.and different heat transfer models.The results show that with the increase of superficial gas velocity,the liquid phase turbulence in the tower increases obviously,the overall gas hold up in the bubble column increases,and the temperature drop rate and volumetric heat transfer coefficient of the molten salt increase greatly.with the operating pressure increases,the temperature drop rate of the molten salt and the volume heat transfer coefficient increase;When different kinds of gases direct contact with the same molten salt,The gas density is large and the overall gas content is large.The gas density multiplied heat capacity is large,and volumetric heat transfer coefficient is large.the temperature drop rate of the molten salt is positively correlated with the volumetric heat transfer coefficient;When different kinds of molten salt are direct contact with the same gas for heat exchange,The continuous phase has a large surface tension and the overall gas content is large.The salt density multiplied heat capacity is large,and the volumetric heat transfer coefficient is large.The temperature drop rate of the molten salt is positively correlated with the volumetric heat transfer coefficient;When different heat transfer models participate in the heat transfer,the volumetric heat transfer coefficient of the single bubble heat transfer model is large.Under the same amount of heat exchange,the temperature drop rate of the melt salt and the volumetric heat transfer coefficient have opposite trends.