مهدی بحیرائی

The numerical simulation for micro-mixing of the combined electroosmotic-pressure driven flow inside the microchannels with the triangular obstacles (hurdles) and heterogeneous zeta-potential is carried out. The simulation is conducted by solving the steady state equations of momentum, electric fields and concentration field, while the Nernst-Planck equation is used for identifying the ions distribution inside the channel. It is supposed that a fluid having different concentrations enters the 2D rectangular microchannel. The results show that for the straight homogeneous microchannels, greater adverse pressure gradients cause better mixing. Moreover, the microchannels having the hurdles or heterogeneous zeta-potential produce the superior mixing performance such that the mixing efficiency increases up to 15.4% and 48.1% for the microchannels with the hurdles and heterogeneous zeta-potential, respectively. This improvement reaches 87% for the microchannels with both hurdles and zeta-potential heterogeneity. It is found that the location of the hurdles does not affect the mixing performance while the height of the hurdles has intense effect on the mixing quality. Thereby, changing the height of the hurdles from 0.05H to 0.2H, improves the mixing efficiency about 11.4% and 15.6% for the homogeneous and heterogeneous zeta-potential cases, respectively. The length of the hurdles has different effects based on the zeta-potential situation so that in the case of heterogeneous zeta-potential, length of the hurdles has intense effect on the mixing, while for the homogeneous channels, this effect dramatically decreases. It is also found that increasing the zeta-potential on the hurdles leads to better mixing performance while increment of the zeta-potential on the straight parts of the walls weakens the mixing performance. Investigating the effect of the charge arrangement shows that the NP-PN arrangement makes the mixing quality better.