چكيده به لاتين
Diffusion in microfluidic systems is a very useful mechanism for separation due to its smooth flow and small size of micro-scale particles. Therefore, the aim of this research is to simulate the H-shaped microchannel using computational fluid dynamics in order to control the diffusion mechanism with the aim of increasing the separation performance. The H-shaped microchannel has two entrances and two exits, which are separated based on the difference in the diffusion coefficient of the materials. The microchannel design and analysis was done in the Comsol software environment. In order to simulate, two methods of non-dependence on viscosity (ideal state) and dependence on viscosity (non-ideal state) were used with diffusion coefficients of 10-10, 10-11, 10-10 and 10-9 m²/s. The fluid used is water, which is a Newtonian and incompressible fluid. To investigate this geometry, the numerical solution method (finite element method) and the simultaneous solution of two equations of mass transfer and Navier-Stokes were used. Finally, with the desired meshing, the software was placed in stable mode and the desired simulation was performed by the obtained data. Also, the effects of the variables of diffusion coefficient, initial pressure, initial concentration and viscosity correction factor were investigated and by changing the mentioned variables, the effect of each variable on the diffusion and separation process was determined. The results showed that in the viscosity-independent method, concentration changes had no effect on the fluid velocity, and the velocity profile became symmetrical, and in the viscosity-dependent method, an equation was defined for viscosity, which shows the effect of concentration changes on the flow velocity, and made the concentration profile asymmetric. Also, the measured water permeability coefficients increase with the particle concentration gradient, which indicates stronger intermolecular interactions, and at a comparable concentration gradient, the measured water permeability coefficients decreased drastically due to the increase in the viscosity of the medium. Also, it was found that the transfer of particles between two channels is faster at low pressure and high concentration gradient. In the case of no dependence on viscosity, when the diffusion coefficient was considered relatively high, the separation rate was 0.5 mol/m3, but in the case of dependence on viscosity, the separation rate was about 0.4 mol/m3. As a result, in the state of dependence on viscosity compared to the state of non-dependence on viscosity, the amount of separation has decreased by 20%. These results confirm the measured particle diffusion through the H-shaped microchannel.
