Numerical Simulation Of Marangoni Effect In The Bubble Mass Transfer Process

Based on the flat interface model,this paper established the gas-liquid mass transfer equation and verified the feasibility of the equation in simulation.The mass transfer process of solute volatilization into gas-phase nitrogen in the single-bubble model and bubble bubbling model was further studied.The occurrence of the Marangoni convection at the interface and the effect of various parameters on the bubbling mass transfer were analyzed.In the flat interface model,the control equations and interfacial tensions were verified through simulation,the fluid mechanics calculation method was established.The influence of the Marangoni convection on the mass transfer results and the influence of the temperature gradient on the Marangoni convection were analyzed.The results showed that the occurrence of the Marangoni convection promoted the gas-liquid mass transfer and accelerated mass transfer.The existence of the temperature gradient can induce Marangoni convection earlier and enhance the mass transfer more obviously.In the single bubble model,a single bubble was generated by the patch method,and the simulation results without gravity and with gravity were investigated respectively.At the absence of gravity,both quantitative and qualitative results showed that the Marangoni convection was very obvious at the interface.The smaller the bubblediameter,the later the Marangoni convection occured,and the earlier the Marangoni convection took place with the presence of the temperature gradient.Under the condition of gravity,the occurrence of Marangoni convection can not be observed.It was considered that the macroscopic ascending movement of bubbles eliminated the occurrence of Marangoni convection.The effect of the bubble diameter was consistent with the case without gravity.The smaller the diameter,the faster the mass transfer approached to saturation.In the bubble column model,hydrodynamic analysis was carried out firstly.The effect of the surface tension,liquid viscosity and density on the bubble shape were investigated.The results showed that the bubble shape was affected by these parameters significantly.The bubble diameter increased with the increase of the surface tension,liquid viscosity and inlet velocity.In addition,these parameters also directly affected the number of bubble generated in the bubbling column,i.e.the gas holdup of the bubbling column,which provides a reference parameter for the feasible bubbling column design.Finally,based on the research of the fluid mechanics model,the physical property of the gas-liquid mass transfer system was changed for further investigation.Compared with the results of the single bubble mass transfer in the case with gravity in Chapter 3,the gas-liquid volatilization mass transfer model in the bubbling column was further analyzed.The reasons that the Marangoni convection was not observed at the single-bubble interface were analyzed.These analyses of the computational fluid dynamics should enhance understanding of the gas-liquid mass transfer in the bubbling column.