Study On Flow Of Viscoelastic Fluid In Micro-Channel And Its Application In Mixing Of Fluid

The flow and heat transfer on macro-scale has been studied for many years and acquired great achievement. In recent years, the research in science and engineering has a trend to miniaturization and integration, so the research in microfluidics has attracted many scholars both home and abroad. In microfluidics the characteristic length and velocity of flow are very small, leading to a low Reynolds number (the inertial force is negligible), and the flow is dominated by viscous force..For Newtonian fluid, the flow in microfluidics is in stable laminar regime. So the efficiency of fluid mixing and heat transfer in micro-scale is limited.It was found in recent years that the flow of solutions with small amount of high molecule polymers or surfactant additives (the viscoelastic fluids) was unstable even at a very low Re, which is called elastic instability. In the momentum equations of the viscoelastic fluid flow, there exists an extra elastic term. Therefore even at a very low Re ,this strong elastic term if big enough can still induce instability even turbulence in viscoelastic flow. This unstable flow characteristic has great potential in enhancing the fluid mixing and heat transfer at low Re number. Some experimental researches in this field has been conducted and satisfying results were obtained.In this paper the flow characteristic of viscoelastic fluid in microchannel and its application in enhancing fluid mixing were investigated by numerical simulation. The open source CFD codes were modified to simulate the viscoelastic flow and verified by simulating the drag reducing flow of viscoelastic fluid in straight channel. In this paper, two kinds of microchannel model (one with only one arc, the other with three arcs) were adopted for simulation. From the numerical simulation, the flow characteristic of viscoelasticity fluid in the two microchannel models, the velocity profile of the main flow and in the cross section, the vortex structures and elastic stress profile in the flow fields were obtained and given. Based on the above results, the unstable features and its underlying mechanism of the flow were analyzed. Moreover, the effect of the Weisseberg number and the polymer contribution to the total solution viscosity on the flow was also investigated.Besides, the enhancement of fluid mixing by inducing the elastic unstable flow was also studied numerically in a straight channel. The mixing effect of Newtonian fluid is obtained for comparison. It is indicated that this elastic instability of viscoelastic fluid indeed can enhance significantly the fluid mixing efficiency.