| The micromixer is a kind of microdevice that can realize the functions of rapid sample mixing and fast analysis.It is always at the front of the microfluidic functional modules,which is one of the researching focuses.As the fluids in the mixer is at the micro scale,laminar diffusion is the main form of the mixture,so the mixing process is difficult.There are two kinds of the mixture,active mixing and passive mixing,where the passive method does not require additional equipments,the mixing process does not require special control.These features for users of microfluidic chip are enormous improvements over the active mixing.Nonetheless,the structure of the passive mixer is always complex and varied.It is difficult for researchers to choose suitable structures.The design process always depends on experience.This complex design process has become the main bottleneck for the application of passive mixers.Based on the design problem of passive mixer,the paper proposed that the mixed process of the passive micromixer can be divided into on-way mixing and local mixing.They were analyzed by using the numerical method,and the influence factors were considered.Different material micromixers were made to calibrate the on-way mixing coefficient and local mixing coefficient.On the basis of work above,the design method of passive micromixer were proposed,which has the advantages of rapidity and accuracy,and greatly simplifies the design process of micromixerThe main contents are as follows:1)The laminar diffusion equation and navier-stokes coupling equations are constructed to analyze and simulate the mixing process.A straight micro channel is designed for the on-way mixing.The influence of the inlet width ratio and the flow velocity is analyzed.As for the local mixing,the mixers with angled bend,rounded bend,Y-type inlet and cross section of mutations are designed to analyze the influence of geometric parameters and flow velocity.The results show that the influence of the on-way mixing efficiency is proportional to the inlet width ratio and the diffusion coefficient,and is inversely proportional to the flow velocity and channel width,so the formula of the on-way mixing efficiency can be given.For the four kinds of local structure,the local mixing efficiencies are proportional to the flow velocity,and are influenced by their geometric parameters,and the formulas of local mixing efficiency can be proposed for the four local structures.In order to bring the calculation of local mixing efficiency to the on-way mixing,local mixing efficiency can be converted to equivalent on-way mixing length.2)In order to solve the bonding problems of glass chip,a new method of glass-polyurethane chip is proposed.By the experiment,the characteristics of different A/B weight ratio are analysed,and the best proportion of A/B glue weight ratio is found to encapsulate the glass chip.The PMMA material chip is prepared by machining,and a constant pressure mechanism is designed for hot bonding of chip.Using PDMS as the chip material,the substrate with microchannel is fabricated by molding method,and the permanent bonding is realized through the oxidizing surfaces with plasma.3)Using the chips of different types and materials,the mixing efficiency influences of the geometric parameters and flow parameters are verified by experiments,and the on-way mixing coefficient,the local mixing coefficients are calibrated.4)Based on the formulas of the on-way mixing and local mixing,a fast design method of passive micromixer is proposed.For the given mixing target,two types of mixer(one with angled bend and other one with rounded bend)are designed to achieve the same mixing efficiency.For the determination of prothrombin time in clinical treatment,a microfluidic chip is designed and manufactured by using the method of this paper,and a testing platform is built.The experimental results show that the design method is feasible and efficient,which has great significance for the application of passive micromixer. |
PDF Full Text Request