Numerical Investigation On The Efficient Mixing Of Overbridged Micromixer At Low Reynolds Number

Micromixers have characteristics of small size(equivalent diameter less than 1 mm).The equipment has a very large surface area/volume ratio,and can promote fluid to fully mix quickly,which means it has great application prospect in chemical synthesis,emulsion preparation,high-throughput screening and biochemical field.Based on the method of energy inputted,the micromixer can be categorized into active and passive ones.The former relies on external energy to perturb the fluid for chaotic mixing,but it is difficult to process and has a high cost,while the latter no longer needs other external power to provide except fluid flow energy,therefore has become a research hotspot in micromixers.In this paper,the overbridge structure was introduced into the planner E-shape micromixers to construct a novel bridge-street structure micromixer,in order to enhance the mixing efficiency in the wide range of Reynolds number.We investigated numerically the mixing performance of six overbridged E-shape split-and-recombine micromixers via solving 3D Navier-Stokes equations and adopting species transfer model.It is indicated that at lower Reynolds number the tilted interface in the overbridged channel increases the interfacial area and improves the mass transfer efficiency,while at higher Reynolds number the overbridged channels tend to induce vortices and promote the convective diffusion.The results show that the optimal overbridged micromixer DBEM-3 has excellent mixing efficiency exceeding 94.65% in the range of Re=0.5-100.The optimal structure of overbridged micromixer was studied further with different viscosity ratio fluid and power law fluid.In addition,the pressure drop under various Reynolds number was calculated,and the pressure drop of the power law fluid was represented by Euler number to reflect the magnitude of the momentum loss rate.It is illustrated that DBEM-3 has excellent mixing efficiency in wide Reynolds number for three different fluid systems,which has promising applications in the biochemistry analysis or mixing systems.In addition,this paper explored the influence of nitrogen feed on the mixing efficiency of liquid components,including the study of nitrogen feed methods,nitrogen inlet velocity,and the influence of different viscosity ratio fluid and power-law fluid.The results show that,under the simulated conditions,nitrogen flows are in the form of slug flow in the four nitrogen feeding methods,in which the internal circulation of the warhead induces a larger vortex in the liquid phase,and promotes the direct chaotic mixing of components,and the method of nitrogen side inlet has the most obvious mixing effect.At different inlet velocity,the size and formation time of the slug flow have a great influence on the disturbance degree and disturbance time for the liquid component.The lower the gas velocity is,the smaller disturbance by vortexes,while the higher the gas velocity is,the shorter the time to be subjected to vortexes for the liquid component.Then,the influence of nitrogen in fluid mixing with different viscosity ratios was studied.As the viscosity ratio increased,nitrogen was affected by local viscosity differences,and the velocity gradient of vortex induced by slug flow warhead increased,thus increasing the disturbance of liquid phase fluid and strengthening the rapid mixing of fluid near nitrogen.Finally for the power-law fluid,the smaller the value of the rheological index n is,the more easily it is affected by the elasto-flow disturbance,and the larger eddy current is generated,and the mixing effect is more obvious.