Experimental observations and lattice Boltzmann method study of the electroviscous effect for liquid flow in microchannels

The existing experimental data in the literature on hydrodynamics for liquid flow in microchannels are analyzed and the reasons causing the diversities are discussed and summarized. The present experimental data for deionized water flow in glass microtubes with diameters ranging from 50 to 530 mu m show that the friction factors and transition Reynolds numbers from laminar to turbulent flow are in good agreement with the conventional theoretical predictions. However, the friction factors in stainless steel microtubes with diameters of 119 and 172 mu m are much higher than the conventional theoretical predictions. This discrepancy is attributed to the large surface relative roughness or dense roughness distribution in the stainless steel tubes. Numerical simulations taking into account the electroviscous effect are carried out by using the lattice Boltzmann method. The simulation results show that the electroviscous effect does not play a significant role in the flow characteristics for channel dimensions of the order of microns and hence it can be neglected in engineering applications for moderate electrical conductivity of the liquid and conductivity of the walls. From the literature review and the present test data, it is validated that for liquid flow in smooth microchannels the conventional theoretical prediction for flow characteristics should still be applied.