Study On Flow And Heat Transfer Of PTT Model Fluid System With High Zeta Potential In Parallel Micropipes

In recent years,microsystems based on chemical and biological analysis have received widespread attention.Biological fluids are often used in these microsystems,and most of them are viscoelastic non-Newtonian fluids with complex models and rheological behaviors,which can be described by the simplified Phan-Thien-Tanner(PTT)model.In this thesis,the flow and heat transfer characteristics for single-layer and twolayer fluid systems in parallel microchannels are investigated under high Zeta potential.For the single-layer fluid system filled with conductive viscoelastic fluid,which is described by the PTT model constitutive equation,and the flow is driven by the mixed action of pressure,electric field force and magnetic field force.For the two-layer fluid system,the lower fluid is electrolyte solution,which is Newtonian fluid,and it flows under the mixed action of pressure,electric field force and magnetic field force;the upper fluid is a nonconductive viscoelastic fluid,which is described by the constitutive equation of PTT model,and the flow is dragged by the viscous shear force of the lower fluid to it at the interface of two-layer fluid.For these two kinds of fluid systems,the numerical solutions for the potential distribution are obtained by using finite difference method to solve the nonlinear Poisson-Boltzmann equation,and the approximate solutions of velocity,volume flow rate,temperature and entropy generation distribution are given by solving numerically the Cauchy momentum equation,continuity equation,energy equation and PTT model constitutive equation.The results show that:(1)the fluid velocity increase with the increase of Zeta potentials in two kinds of fluid systems;(2)with the increase of Zeta potential,the fluid temperature in the two-layer fluid system presents an obvious upward trend,and the temperature variation trend of single-layer system is mainly related to the geometry of microchannel;(3)for the two-layer fluid system,when the Hartman number of the external magnetic field exceeds a certain range,the fluid flow will be hindered;(4)for the two kinds of fluid systems,the application of reverse pressure gradients in both types of fluid systems can promote fluid flow,while the application of positive pressure gradients can hinder the fluid flow.