Numerical Study Of Multiphase Channel Flows With Multiphysics By A Front-tracking Method

A front tracking/finite volume method is employed to solve the two-phase flow.The energy conservation equation and an electrical force term are coupled with the Navier-Stokes equation,respectively,to study the thermocapillary motion and electrohydrodynamic of multiphase flows,which involves a number of energy and power industry processes.Firstly,the thermocapillary motion of two-and three-dimensional fully deformable bubble in a channel with an obstruction is studied.The results show that,for a fixed obstruction and channel size,the influence coefficient α,defined as the ratio of arrival time in channels with and without obstruction,increases with increasing Marangoni(Ma)number for both two-and three-dimensional flows,whereas an increase of Reynolds(Re)number leads to an increase of influence coefficient in two-dimensions but a decrease in three-dimensional flows.Moreover,a change of Capillary(Ca)number does not have a visible effect on the thermocapillary motion,which is different from bubble motion driven by other body forces.Results for two-dimensional flows show that the influence coefficient increases dramatically with an increase of the obstruction size W,and a larger obstruction makes the dependence of a on the fluid parameters more obviously.The effect of electrostatic forces on the distribution of drops in turbulent channel flows is also examined.The droplets and suspending fluid are assumed to be leaky dielectric fluids.We set the electrical conductivity ratio(R=σi/σo)smaller than the dielectric permittivity ratio(S-1=εi/εo)to drive the flow from the drop poles to their equators.The results show that an applied external electric field has a significant effect on the microstructure and the flow properties.For flows without an electric field,where the Mason(Mn)number is infinity,the drops aggregated in the core of the channel and the liquid streamwise velocity are similar to those in single-phase flow.For Mn=0.1,a low electric intensity,most of the drops are driven to the walls due to the unbalanced electric force on the drop interface.Form Mn=0.05,drops are more likely to stick together because of the stronger combination of electrohydrodynamic effect and dielectrophoretic force between drops.Therefore,the number of drops in the middle of the channel increases while still many drops are in the wall layer.For Mn=0.007,the electric intensity is very strong and all the drops in the channel tend to line up and form columns spanning the channel width.These columns become unstable when the flow drives them close to each other.It is also found that an increase of the electric intensity can lead to an increase in the average wall shear stress.In addition,the liquid streamwise velocity will become more uniform,which means the effective viscosity of the system is increased,when Mn=0.007.