UC Riverside

We developed a model for analyzing flows driven chemically by the joint effect of diffusioosmosis and buoyancy-driven convection in a small microfluidic channel. The dead-end channel containing fresh water is fed salty water having a higher density. We simplified and non-denationalized the Navier-Stokes equation, and s derived an expression for the horizontal velocity, U, resulting in a convoluted coupled non-linear convection-diffusion 2D system. Using Taylor-dispersion arguments to support the averaging approach, we derived an expression for concentration deviation, C^' (X,Y,T) and simplified the 2D system into a 1D non-linear system involving only the average concentration, ¯C (X,T) We obtained a numerical solution for the mean concentration, (T) and the time to fill the channel using the finite volume method and MATLAB. We varied the fluid property, (the ratio of density gradient flows to concentration gradient flows) for the effect of gravity with diffusioosmosis and solely diffusioosmosis and compared with results obtained when both factors were involved. The results show that flow proceeds faster with the joint action of gravity and diffusioosmosis in uncharged systems. Furthermore, we observed much faster flows when in charged systems due to the ionic properties of the solute, which further strengthens the electrostatic interactions of the ions with the charged channel walls.