جستجوی مقالات مرتبط با کلیدواژه « ریزمخلوط گر » در نشریات گروه « مکانیک »

In the present paper, the mixing in electroosmotic flow is studied numerically and simulated in the presence of a magnetic field with three different locations. The flow geometry was included a two-dimensional duct between two parallel plates, and the flow was assumed to be incompressible, steady and laminar. The governing equations of the problem, including modified momentum equations (Navier-Stokes) for the fluid flow field, the equations of external and internal electric potential fields, the equations of distribution of the positive and negative ions (Nernst-Planck), the magnetic field equation, and the concentration equation for species have been solved using the finite volume numerical method. The obtained numerical results were validated against the analytical solutions of an EOF with uniform microchannel walls zeta potentials. The numerical results show that in the presence of a magnetic field, so the final mixing efficiency reaches to 93.3 %. However, this is while the magnetic field has been applied before the electric double layer.

In this paper, the mixing efficiency in electroosmotic flow inside a micromixer is simulated numerically for different states of non-uniform wall Zeta potential. The geometry of flow is a two-dimensional channel between two parallel plates and the flow is assumed to be incompressible, steady and laminar. The governing equations, including a Laplace equation for the distribution of external electric potential, a Poisson equation for the distribution of electric double layer potential, the Nernst-Planck equation for the distribution of ions concentration, the species convection-diffusion equation, the modified Navier-Stokes equations for the fluid flow field, have been solved using the finite volume numerical method. In order to validate the numerical results, the analytical results of an ideal electroosmotic flow in where throughout the walls are charged is compared with the obtained numerical results. The numerical results show that, by linear-ascending, linear-descending and parabolic changes of the wall Zeta potential at the middle length of the microchannel, the mixing efficiency increases compared to a constant Zeta potential. For the cases of linear changing of Zeta potential, the mixing efficiency increases to 86% and for parabolic change of Zeta potential the mixing efficiency increases to 75%, while the Zeta potential is constant at middle length the maximum of mixing efficiency increases to 64%. In the case that only the upper wall at middle length is charged, the results show that a vortex region is created in the flow. This vortex region causes a maximum (100%) mixing efficiency.

Mixing within electrokinetic micromixers is studied numerically in this article. The micromixer studied here is simply a heterogeneous parallel plate microchannel which is imposed to the electroosmotic flow field. For the thorough modeling of such flows, the coupled equations of Navier-Stokes, Nernst-Planck, Poisson-Boltzmann and concentration equations are solved for the flow motion, electric charges transport, electric field and species concentrations, respectively. Numerical solution of these set of equations for the heterogeneous microchannels is complicated and difficult. Therefore, a simple and approximate model such as Helmholtz-Smoluchowski has been proposed which is appropriate for the case of microchannels with the homogenous properties on the walls. Validation of Helmholtz-Smoluchowski model has been well-used for the prediction of two dimensional flow fields, yet its application is rarely validated for the prediction of concentration field and mixing performance. In this article mixing due to electroosmotic flow field is investigated using Nernst-Planck equations as well as Helmholtz-Smoluchowski models and the accuracy of the Helmholtz-Smoluchowski model is evaluated. Comparison of the results indicates that in the proper condition the approximate model can predict the mixing performance accurately along the micromixer length.

Numerical investigation of 3D electrokinetic mixing through micromixer has performed both qualitatively and quantitatively. In order to reduce numerical expenses of 3D flows، we implement the Helmholtz-Smoluchowski method for the numerical modeling of electroosmotic flows. According to the previous study of electrokinetic mixing inside the heterogeneous microchannels، existence of the vortexes within the flow field always increase the mixing performance for 2D flows. However، investigations of 3D micromixers show that this increase does not happen for all the situations and in some cases، existence of the vortexes does not enhance the mixing performance. Findings of this research indicate that the asymmetry degree of the flow field pattern is the key parameter for the mixing performance. Within the 3D flow field، there are more opportunities to increase the asymmetries. Consequently، mixing performances of the 3D flows are much larger compared to those of 2D flows. Studies of various 3D cases for electroosmotic micromixer show that mixing performance can be improved or deteriorated depending on the arrangement of the heterogeneities over the microchannel walls. These results confirmed that 2D simulation of mixing could not explain the complete benefits of passive micromixers. These results can apply to the simulation of micromixers used in Lab-on-a-chip devises.