1) The use of microbubbles to enhance mass transfer in a compact bubble column has become a valuable topic recently. When the liquid flow induced by the presence of microbubbles is taken into account, the behavior of the microbubbles may differ widely from simple estimations. One example is the change of the residence time, which is determined not only by slip velocity but also the velocity of the surrounding liquid. In the present study the effect of the bubble-induced liquid flow on mass transfer in microbubble plumes is analyzed numerically. A two-way coupling Eulerian-Lagrangian approach is used to simulate oxygen bubble plumes with initial bubble diameters from 100 μm to 1 mm and a maximum local void fraction of less than 2% in compact rectangular tanks. The simulations illustrate that the effect of bubble-induced liquid velocity on the residence time of microbubbles increases with the decrease of initial bubble diameters, and also increases with the reduction of initial water depth. The differences between the concentrated and uniform bubble injections are compared. The results show that the uniform injection of microbubbles provides much better mass transfer efficiency than the concentrated injection, because the bubble-induced liquid flow is suppressed when bubbles are injected uniformly over the entire bottom of the tank.
2) There are two types of modeling for the lipid bilayer bio-membrane. One is a two-dimensional fluid membrane which reflects the fluidity of the lipid molecules. The other is a hyperelastic membrane which reflects the stiffness of cytoskeleton structure. Liposome is usually modeled as a fluid membrane and Red Blood Cell (RBC) is as a hyperelastic one. We discuss how these differences of membrane models affect the behaviors of vesicles under the presence of shear flow. It is shown that the hyperelastic membrane model for RBC shows a less inclination angle of tank-treading motion and early transition from tank-treading to tumbling.
The deformation of multiple red blood cells in a capillary flow is studied numerically. The immersed boundary method is used for the fluid-red blood cells interaction. The membrane of the red blood cell is modeled as a hyper-elastic thin shell. The numerical results show that the apparent viscosity in the capillary flow is more sensitive to the change of shear coefficient of the membrane than the bending coefficient and surface dilation coefficient, and the increase of the shear coefficient results in an increase of the pressure drop in the blood flow in capillary vessels in order to sustain the same flux rate of red blood cells.