| Microfluidic technology is an emerging technology developed at the end of the20 th century.It has been widely studied in the fields of chemical and biological detection.Microfluidic chip is an important part of microfluidic technology and microfluidic chip is the carrier of microfluidic technology.The driving of fluid on the chip is a key technology.At present,the common driving methods of microfluidic chips are mechanical driving and non-mechanical driving.The main difference is whether the driving system itself has mobile mechanical components.At present,the most widely used fluid drive control method is electroosmotic drive in non-mechanical drive,which has the advantages of directly driving fluid,simplicity of operation and no need to move parts.The core of electroosmotic control is electroosmotic flow.The generation of electroosmotic flow is due to the surface effect of the microchannel wall,and the charge is accumulated at the wall to form an electric double layer.The electroosmotic flow is generated by the external electric field generated by the electrode in the microchannel.Therefore,the reasonable design of electrodes layout is the key to realize the effective control of electroosmotic flow.In the past design of electroosmotic electrodes layout,most of them used the trial method,based on the designer’s experience and the original electroosmotic flow model,it is difficult to maximize the required performance under the premise of ensuring the structural function.Aiming at this problem,this paper will use the topology optimization method to design the electrodes of the electroosmotic flow model.Compared with size optimization and shape optimization in structural optimization,the main feature of topology optimization is that reliable design schemes can be proposed in the absence of designer’s design experience.The essence of topology optimization is to discretize the design region based on the design objectives and constraints of the optimization problem,and to obtain the optimal distribution of materials in the design region.In this paper,the topology optimization model of electroosmotic flow electrode is established based on the RAMP materials interpolation format of variable density method,and the characteristic size of electrodes structure is controlled by filtering equation and threshold projection.The adjoint sensitivity of the model is obtained by continuous adjoint analysis method.Based on the obtained adjoint sensitivity,the moving asymptotes method is used to evolve the structural design variables of the electrode layout,and finally the topology optimization of electroosmotic flow electrodes is realized.The materials interpolation is achieved by applying a mixed boundary condition of electrical insulation and electric potential on the microchannel wall.Based on the above model and its solution method,this paper completes the electrodes design of electroosmotic micropump and electroosmotic micromixer.The main research contents are as follows:(1)Topology optimization model of electroosmotic flow: The multi-field coupling equation of electroosmotic flow is analyzed.The Helmholtz-Smoluchowski is used to approximate the electric double layer near the microchannel wall as the electroosmotic slip wall.Under the constraints of Navier-Stokes equation and convection-diffusion equation,the electroosmotic flow model is transformed into a variational problem,and then the adjoint method based on Lagrange multiplier and the iterative method based on gradient information are analyzed and solved.(2)The model of electroosmotic micropump is established with the maximum net flow of electroosmotic micropump as the design goal.Numerical iteration of the established numerical model.The influencing factors of the flow rate of the micropump are studied and analyzed.The results show that the flow rate of the fluid in the microchannel is affected by the voltage and the characteristic size of the electrodes design area.In this paper,when the applied voltage of the electroosmotic micropump model is 160 V,the Reynolds number in the microchannel can reach 2.5,which realizes the effective pumping of the fluid in the microchannel,and then verifies the feasibility of using the topology optimization method to design the electroosmotic micropump electrodes.(3)The topology optimization model of electroosmotic micromixer is established with the design goal of effective mixing of two different concentration solutions in electroosmotic micromixer.The established mathematical model is numerically solved.The effects of different parameters on the mixing performance of electroosmotic micromixer were studied.The results show that the mixing effect can be effectively improved by changing the voltage,Reynolds number,Peclet number,characteristic size of mixing area and mixer series scheme.Under the reasonable design scheme,the mixing evaluation index of micromixer can reach below 5%,and the design goal of complete mixing of different concentration solutions can be realized. |
