Slip Boundary-based Simulation About Two Types Of Flows Propelled By Concentrations Gradient With Micro-/nanoscale

Microfluidic system is the general classification for fluid flow,which characterized by micro-or nanometer level.The characteristic size and the related size effect of the system made the boundary slip,an important factor that influences its performance,become innegligible.In a chemical potential-driven flow caused by concentration gradient of solutes,the boundary slip may influence the distribution of flow field mainly by inducing a flow at fluid-solid interface in microflow,and in turn affects the performance of the system.The osmosis phenomena in micro-or nano-scale,as one of important phenomena used in microfluidic system,has the high application value in biomedicine,microfluidic flow and environmental monitoring.Therefore,it is significant to study the boundary slip effect in the micro-/nano-scale osmosis phenomena.By analyzing the flow characteristics of the fluid-solid interface in the osmosis phenomenon,this paper establishes the model of slip velocity,which satisfies the flow characteristics of the solid-liquid interface and is used as the boundary condition to study the boundary slip effect in the osmosis phenomena of micro-/nanoscale.The simulation is conducted on the simulation platform,COMSOL Multiphysics,which enables coupling multiphysic fields.Firstly,the steady permeation phenomenon of channel with the initial concentration gradient is investigated.The flow field distribution,pressure distribution and stress distribution in the channel are studied by establishing the boundary slip modified flow model,which can help us further understand the penetration phenomena and provide theoretical guidance for their application in interdisciplinary disciplines.Secondly,the self-propelled characteristics of Janus particles in transient condition are investigated,which can self-establish the concentration gradient.By establishing a self-propulsion model with boundary slip modification,the distribution of flow field under the concentration gradient by the catalytic reaction and the viscous stress distribution at the solid-liquid interface are studied,and the mechanism of the bubble position of the catalytic reaction is further understood,and the theoretical guidance is provided for the directional motion of Janus particles.For the study of osmosis phenomena in micro-/nanochannel,it mainly include laminar flow module and dilute matter transfer module under steady state conditions.A two-dimensional axisymmetric seepage model coupling slip velocity is established,and the numerical solution and analysis are carried out.By representing the physical characteristic parameters of the solute permeability,the simulation process is conducted.Then we compare the simulation results and that of the classical K-K model to validate the effectness of the present model.The results show that the flow field distribution inside the channel is the superimposing of the piston distribution and parabolic distribution,and the velocity distribution after superposition depends on the contribution of the two flows with different conditions.The pressure distribution indicates that osmotic pressure could make the deformation at inlet and outlet,which widened inlet to outward and shrink outlet to the medial,and the hydraulic pressure difference will make the inlet and outlet produce synchrony deformation,which both widened to outward,and the inlet deformation is more pronounced.The stress distribution shows that the osmotic pressure has no obvious pressure effect on the lateral orifice,i.e.the lateral pore has no obvious transformation,but the hydraulic pressure difference will make the lateral pore apparent displacement,which is consistent with the relevant research conclusion.For the study of the self-propulsion motion characteristics of Janus particles,it mainly relates to the laminar flow module and the dilute material transfer module in the transient condition.A two-dimensional axisymmetric Janus spherical particle model with coupling slip velocity is established to determine the position of the bubble generated by the catalytic reaction.The results show that the flow field near the reaction side will generate the flow velocity to the 100 ?m/s when the reaction sustained about 15 ms.A two-dimensional Janus cylindrical model is constructed and be solved,the significance of vortex generation in two-dimensional axisymmetric Janus spherical particle model is to indicate the bubble position,and the analysis finds that there are two points in the reaction side that deviate from the axis position,and can induce the bubble formation and stabilize.By analyzing the viscous stress of the Janus spherical particle surface,it was found that the direction of viscous stress is changed with the velocity of particle surface,and further verifies the bubble location.The establishment of the dynamic model provides a theoretical basis for further study on the self-driven motion characteristics of Janus particles and its application.