Numerical Simulation Of Fluid Flow And Heat Transfer In Microchannels

During the last decades, microfluidic devices have emerged as an important area of research due to rapid development of Micro Electromechanical Systems (MEMS). Throughout understanding of fluid flow and heat transfer in microfluidics is significant to design better devices. Therefore, liquid flow and heat transfer in microchannels are numerically simulated from three aspects in this work.In an attempt to quantify the electrokinetic effects, the pressure driven liquid flow and heat transfer in parallel-plate microchannels and rectangular microchannels are numerically simulated based on the Poisson-Boltzmann, Navier-Stokes, energy equations, and the newest data ofξpotential and surface conductanceλ_s . Velocity and temperature fields are all determined for hydrodynamically fully developed and thermally developing laminar flows. For rectangular microchannels, the calculation is made subject to two sets of thermal boundary conditions: circumferentially-constant wall temperature and axially-constant wall heat flux, and uniform wall heat flux both axially and circum-ferentially. Also obtained are friction coefficients and Nusselt numbers for both channels with/without the electrokinetic effects. The electrokinetic effects are discussed for various channel sizes, various zeta potentials, different ionic concentrations and different thermal boundary conditions. The electrokinetic effects for the two channels are also compared with each other. Some new beneficial results are obtained.The governing equations for a two-fluid two-dimensional Stokes flow are presented in the third part of this work. The dynamic and kinematic boundary conditions at the free interface between the two immiscible fluids are given together with a choice for a non-dimensional scaling of the equations. Based on a second-order Runge-Kutta time integration scheme, a numerical model for the simulation of a two-phase flow in two-dimensional T-shaped microchannels is developed. The governing equations are solved by using the commercial finite-element program COSMOL that interfaces with MATLAB through a scripting language. Then the code is applied to a numerical investigation of the time-dependent dynamics of the creation of gas bubbles in T-shaped microchannels Besides, the final bubble sizes are discussed for various gas pressures, surface tensions, liquid dynamic viscosities, and liquid inlet velocities.