The two-fluid flow is produced by the combined effects of electroosmotic force in a conducting liquid and pressure gradient force in a non-conducting liquid. The Poisson-Boltzmann and Navier-Stokes equations are solved analytically; and the effects of governing parameters are examined. Poiseuille number increases with increasing the parameters involved. In the absence of pressure gradient, the two fluids demonstrate plug-like velocity profiles. The results reveal that the two-fluid electroosmotic pumping flow rate is feasible for a relatively small interface zeta potential; or large wall zeta potential and electrokinetic radius. For particular values of the governing parameters, the flow rate approaches a specific value as the electrokinetic radius tends to infinity. A back flow (a negative value of the resultant flow rate) occurs for sufficiently small values of the wall zeta potential or sufficiently large values of the interface zeta potential (even in the case of pressure-assisted flow). Zero-value flow rates may also be attained.

The present study aims at modeling the real random rough surface of a microchannel with structured rough channel of known geometric parameters. The surface of the microchannel is created by sinusoidal function using MATLAB code and 2D simulation of the model is carried out with commercial software ANSYS Fluent. The height of the channel is varied from 100 to 250 μ m and length of the channel is 12. 5 mm. The range of Reynolds number selected for analysis is 100 to 500 with water as the fluid medium. The roughness height is selected within the range of actual manufacturing roughness level of microchannels. The results show that channel geometry has significant influence on flow characteristics. A new non-dimensional roughness parameter β , is proposed to represent the dependence of friction factor on geometric parameters in the laminar region. A correlation for flow friction is developed as a function of roughness parameter and Reynolds number.

Solvent extraction is an economically efficient method widely used in the purification of wet phosphoric acid. In this study, a microchannel was applied to promote the mixing and purification of phosphoric acid during continuous production. For this aim, solvent extraction was conducted to purify phosphoric acid via methyl isobutyl ketone/tri-butyl phosphate mixtures. Additionally, the Box-Behnken design method was used to survey the solvent extraction process. The effect of various operational parameters such as solvent concentration (45– 65 %wt. ), temperature (18-28˚ C), and organic/aqueous phase ratio (2: 1– 6: 1) at a constant flow rate of 70 mL/L was examined. Experimental results indicated that the microchannel at the residence time of 6. 85 min could promote the extraction percentage of and sulfate removal of more than 98% and 60%, respectively, compared to the batch extractor.

The passive micromixer is one of the essential devices that can be integrated into the Lab on Chip (LoC) system. Micromixer is needed to increase mixing efficiency. In this paper, two Koch fractal obstacle-based micromixer models of Secondary Snowflakes Fractal Micromixer (SSFM) and Tertiary Snowflakes Fractal Micromixer (TSFM) were designed. The effect of the Koch fractal resistance angles (15o, 30o, 45o, 315o, 330o, 345o) and the influence of the inlet (T and T-vortex) were studied in this paper using COMSOL Multiphysics numerical simulations. The results showed that the TSFM structure with a 30o angle on the T-vortex inlet is optimal. The deflection phenomena generated by the TSFM obstacle enhance the contact area between the two fluids and chaotic convection can be increased at Reynolds Number (Re) 0. 05 and Re 100. This paper examines concentration curves along the channel ranging from 1 mol/L to 5 mol/L. This clearly shows that the fluid flow direction changes within the microchannel. This work provides a new design for the micromixer.

The aim of the present numerical investigation is to analyze the effects of transverse magnetic field on heat transfer and fluid flow characteristics in a rectangular microchannel heat sink (MCHS). The effects of Hartmann number, channel aspect ratio, total channel height and total channel width on heat transfer and fluid flow characteristics are widely investigated. The governing equations for three-dimensional steady, laminar flow and conjugate heat transfer of a microchannel are solved using the finite volume method. The obtained results are discussed with various combinations of pertinent parameters involved in the study. The results reveal that magnetic field can enhance the thermal performance of the MCHS but it is accompanied with a slight increase in pressure drop.

In this study, turbulent compressible gas flow in a rectangular micro-channel is numerically investigated. The gas flow assumed to be in the subsonic regime up to Mach number about 0. 7. Five low and high Reynolds number RANS turbulence models are used for modeling the turbulent flow. Two types of mesh are generated depending on the employed turbulence model. The computations are performed for Reynolds number up to 19000 and two inlet pressures of 1102 kPa and 499 kPa. The longitudinal variations of flow characteristics such as pressure, temperature, Mach number and friction factor are investigated. The experimental data are also used for the sake of comparison and to find which turbulence model has the best performance. The results show that the turbulence models with wall functions have generally better agreement with the experimental data than those one without wall function. The numerical results are different for normal size pipe flow.

The concept of periodic renewal of boundary layers is a promising technique for the enhancement of heat transfer in microchannels. Extending the above concept, microchannel heatsink with modified hexagonal fins has been proposed for disrupting the flow periodically. An experimental study has been carried out to investigate the heat transfer and fluid flow characteristics of a microchannel heat sink with modified hexagonal fins and a conventional type of microchannels with plate fins. The heat transfer and fluid flow characteristics of the modified hexagonal fin microchannels have been compared with the plate fin microchannels. The heat transfer enhancement factor and pressure drop penalty factors are evaluated and compared. The modified hexagonal fin microchannel heat sink has been found to outperform the plate fin microchannel heat sinks in spite of the lesser heat transfer area.