Study On Electroosmotic Flow And Micro-Mixing In Heterogeneous Surface Micro-Channel

The microfluidic chip is a technology platform of integrating biological or chemical laboratory basic function units on a chip of several square centimeters, which has great significance for the miniaturization and integration of analytical instruments. Electroosmotic flow(EOF) is widely used in the microfluidic chip as a kind of efficient microflow manipulating technology, such as micro-fluid delivery, DNA sorting, cell separation and so on. This paper studied the complex rough surface effects, the transient characteristics and the micro-mixing of EOF. The main research contents and results are as follows:The finite element method(FEM) was used to simulate the power-law fluids EOF in roughness micro-channels based the Poisson-Nernst-Planck(PNP) mathematical model. The effects of sinusoidal and quasi-fractal surface roughness on the flow characteristics of power-law fluids were analyzed. The results show that the external applied electric potential and the EDL potential distribution are opposite of sinusoidal or quasi-fractal roughness at the raised region and the concave area. The flow of power-law fluids EOF decreases with the increasing of the two kinds of roughness relative height or the iteration number of quasi-fractal roughness. But the flow firstly decreases to a lowest value where the sinusoidal roughness frequency equal to 2.2 and then increasing.The transient characteristics of EOF induced by transverse and longitudinal alternating electric field were studied using the Lattice Boltzmann method. The results show that the EOF transient velocity magnitude is directly proportional to the amplitude of alternating electric field strength and the ionic concentration of solution, but is inversely proportional to the alternating electric field frequency. In the case of EOF induced by transverse alternating electric field, the movement of the fluid in the center of a micro-channel is always lags behind than that in EDL. In the case of EOF induced by longitudinal alternating electric field, the pairs of electrodes, the space between electrodes and the electrodes polarity have great impacts on fluids flow, which can change the direction of EOF transient velocity as well as the vortex's number and size.The flow field and concentration field in three kinds of T-shaped micromixers were investigated contrastively using the FEM, as well as the relationships between mixing efficiency and Re number and Sc number. Results show that the mixing efficiency of two liquids decrease with the increasing of Sc number and Re number, and the decreasing trend becomes slowly. The species mixing efficiency in the passive mixing enhancement model with embedded ribs fluctuates stongly near the ribs. A much gently undulation is found in the active mixing enhancement model with surface heterogeneous Zeta potential, and it can be restrained in the situation of high Re number or low Sc number. In the case of low Re number, mixing efficiency can be improved more efficiently in active mixing enhancement mode with surface heterogeneous Zeta potential. But in the case of high Re number, passive mixing enhancement mode with embedded ribs is more dominant in strengthening mixing.