Transfer Processes Of Bubbles And Mass Transfer Intensification

Studies about gas-liquid phase flow are hot issues in science and technology.In recent decades,investigations of bubble behaviors and mass transfer processes have been implemented.However,there are still insufficiencies and even research gaps because of the high complexity and the limitation.Liquid-side fluid field and mass transfer process have been paid attention while gas-side studies need to be further investigated.It is meaningful to study the flow and mass transfer inside bubbles to deepen the understanding for mass transfer mechanism and explore mass transfer enhancement methods.In this paper,the single bubble behavior and flow insides bubbles,the interactions between gas-liquid mass transfer and behaviors,and the mass transfer processes inside bubbles and mass transfer enhancement were studied.The experiment about fluid behaviors inside bubbles was developed.Based on the PIV,a clear image was captured to show the flow field by selecting the tracer and analyzing its characteristics.The experiment lays the foundation for the studies of internal fluid flow and mass transfer mechanism.The combined method of experiment and simulation for bubble deformation and internal flow rules was established.For the bubble rising behaviors,the flow field parameters of bubbles and its surrounding liquid were obtained by image processing system.The results show that the bubble shape tends to be regular when the liquid viscosity increases.Based on the relation between Sh munber and Re number,it can be deduced that the mass transfer coefficient reduces with the velocity decreasing.The bubble shapes and flow inside and outside the bubble were calculated.The flow patterns inside bubbles were classified as“two main vortexes”pattern,“separate vortexs with two main vortexes”pattern and“scattered vortexes”pattern.The characteristics of each type was discussed.The correlation of internal velocity and bubble shape parameter was established.Based on the pressure difference?P₁ and P₂?,surface tension??P?and shape changes of boundary,the rules of bubble deformation were concluded and they can be used to estimate the trend of bubble shape changes.The CO₂-water system was set as the object and the interaction between the bubble behaviors and mass transfer process was studied.For the bubbles rising behaviors,the results show that small bubble diameter promotes the mass transfer.For the cutting behavior,the mass fraction change rate insides original bubble is less than the rate insides daughter bubbles.It means that the cutting behavior plays positive role on mass transfer based on the increase of mass transfer area and the enhancement of surface renewal.For the coalescence behavior,the critical intervals of bubbles were studied and the mass transfer process was analyzed.The results show that the coalescence behavior implements surface renewal but the area is reduced so it has negative impact on mass transfer.The fluid flow insides the bubble changes the diffusion into convective mass transfer.The display and analysis of the process was implemented by a chromogenic reaction experiment.The influences of the flow on the distribution were studied by analyzing flow patterns,velocity distribution and concentration distribution.The mass transfer with internal flow was compared with the mass transfer without internal flow.The results show that the internal flow can promote the mass transfer obviously?the mass transfer coefficient increases by 28.0%?.According to the area changes caused by deformation and concentration distribution changes inside the bubble,the mass transfer enhancement factor?was proposed to realize the quantitative analysis of convective mass transfer enhancement.???Based on the above studies,the effective ways to enhance mass transfer in industrial process were proposed.1.The mass transfer area can be increased significantly to enhance the mass transfer by reducing the bubble size such as bubble break.2.The internal flow insides bubbles can be strengthened by optimizing the operating parameters and the internals of the devices.Then the internal concentration gradient and the impetus of mass transfer can be increased so the mass transfer can be enhanced.3.Based on the methods such as multistage bubble break to break and coalesce bubbles constantly,the continuous surface renewal can be enhanced to promote the mass transfer.