Numerical Analysis On Condensation Heat Transfer Characteristics Of CO₂/H₂O Mixture Outside Tube

A new type of coal gasification technology has gradually become the focus of attention in the energy field.Coal and supercritical water vapor are oxidized under high temperature,and the mixture of high temperature and high pressure water vapor and carbon dioxide is directly connected to the turbine,and the mixture after work is condensed into condensers for condensing separation.At present,the research on condensing heat transfer of condensers containing non condensable gases is mostly related to air,and the content of condensation of water vapor containing carbon dioxide is less.Therefore,this paper study the heat and mass transfer process of condensation heat transfer of carbon dioxide containing water vapor.The difficulty of the structural condensing model lies in the calculation of two phase flow and the interphase mass exchange.In this paper,the fluid volume model(VOF)in the multiphase flow model is used to solve the control equation of the two phase flow by introducing the concept of phase volume fraction.And the model of phase transition based on the theory of gas molecular dynamics is adopted,and a suitable user defined function(UDF)is written to calculate the mass transfer between two phases and be added into the control equation as a mass source term.In order to calculate the convection and diffusion process of mixed gases,a component transport model is introduced.Because the empirical coefficient of condensation is a semi empirical coefficient,in order to verify the reliability of the condensation coefficient,the numerical simulation of the condensation process of water vapor containing air outside the tube is first carried out,and the simulation results are compared with the data in the literature,and the appropriate condensation coefficient is analyzed and calculated,at the same time,the cooling is verified.The reliability and stability of the condensing model.The condensation model of the condensed coefficient of condensation is used to simulate the condensation process of water vapor containing carbon dioxide.It is found that the condensation heat transfer effect decreases rapidly with the increase of carbon dioxide concentration,and when the concentration of carbon dioxide increases to a certain extent,the trend of condensation heat transfer coefficient declines will be slowed down.Compared with the simulation results of carbon dioxide and air,it is found that the effect of non condensable gas on heat transfer effect is small when the content of non condensing gas is small,but when the content of non condensing gas rises to a certain concentration,the heat transfer coefficient of condensing of different non condensable gases is linear.The heat transfer of the tube bundle is usually more complicated than that of the single tube.Numerical simulations are carried out for the condensation process of the aligned and interlocked tubes.It can be seen from the analysis that the heat transfer effect of the fork tube bundle is stronger than that of the parallel row,and with the increase of the flow velocity,the disturbance is more intense and the heat transfer effect between the tube bundles is enhanced.The heat transfer coefficient of the rear tube is usually smaller than that of the front tube,and the last row is slightly higher than the front tube,but the last row is more than the saturated vapor contact surface.