Numerical Simulation Of Boundary Slip Characteristics Of Microchannel In Mesoscale

Compared with macro scale flows, the influence of boundary conditions on the fluid flow in micro channels is more significant. With the scale of micro channel decreasing, the effect of boundary conditions can even play the leading role, therefore, for getting a specific function, the researches on the characteristics of boundary slip in micro channel possesses important theoretical significance and practical value. In this paper, the effect of boundary slip properties and surface wettability on boundary slip in mesoscale are studied by using dissipative particle dynamics (DPD) method.Based on Poiseuille flow, the influence of index of weight function of dissipative force in DPD model (s) on diffusion coefficient (D), the dissipative viscosity (ηD), viscosity (η) and Schmidt number (Sc) was analyzed. The boundary slip velocity of Poiseuille flow under different interaction strength coefficient in mesoscale was simulated in the condition of dissipative force with s=2.0, by freezing double-deck DPD particles as the solid wall, and the slip model assumed as Navier linear slip. By changing the solid-liquid particle repulsion coefficient awf, the dissipation coefficient y, the solid wall particle density pw and the distance between wall particles and the solid-liquid boundary a, the influences of different parameters on the solid boundary flow were discussed. The results show that the slip velocity has a linear relationship with the solid-liquid repulsion coefficient αwf, and increases with αwf growing. The relationship between the slip velocity and solid-liquid dissipative force coefficient y is exponential and the slip velocity gradually reduces with the increasing of y. The slip velocity and solid wall particle density pw has a linear relationship, as pw increases, the slip velocity increases linearly. The slip velocity has a logarithmic normal relationship with a, with the increasing of a, the slip velocity increases first and then decreases. Finally, the dissipative particle dynamics simulation method is improved by using smooth cubic spline curve to set up potential function. The feature of the conservative force weight function derived from the above potential function is that the interaction presents to be repulsive when the distance between two particles is short, otherwise attractive.The solid wall wettability was simulated by using the improved method. The results show that, the contact angle of the droplet on solid surface has a quadratic relationship with αwf/αf, and decreases with the increase of αwf/αf. In the simulation of the flow in micro channel with different surface wettability, the results show that when the hydrophobicity of solid surface is strong, the micro channel has a small resistance, and with the hydrophilicity of solid wall increasing, the resistance of wall increases.The simulation results of steady flow in micro channel show that slip velocity change significantly with the change of contact angle when the wall is hydrophobic, while with the surface become hydrophilic, the slip velocity is essentially stable. After the analysis of flow velocity, it can be found that, the flow in micro channel with hydrophobic boundary condition is greater than that with hydrophilic boundary condition. It follows that the boundary slip can reduce the energy loss during flowing process efficiently.