Study Of Mixing Characteristics Of Passive Planar Micromixers And Their Application In Nanoparticle Preparation

With the development of the technology and science, machinery products havealready been minimized. Among these, the miniaturization of fluid control is one ofthe important directions. The characteristic of microfluidic device, i.e., microfluidicchip, is consisted of microchannel network and a variety of functional unitsintegration, which can be achieved the integration of the sample of preparation,reaction, separation and detection, as well as the regulation of these processes.Microfluidic system is mainly applied in the fields of biological, chemical andmedical, with the analysis and measurement of fluid in the aspects of sense, responseand control. Moreover, it also applied in the areas of nanoparticle synthesis, DNAsampling, chemical synthesis, pharmaceutical sampling and analysis, etc. Microfluidictechnology is considered as a key supporting technology, which has been given moreand more attention about it. Unlike microelectronic technology, microfluidictechnology does not emphasis on the size of reduction, but focuses on achievingcomplex manipulated function according to build a microchannel. In microfuildicsystem, it is advantage to improve velocity and efficiency in the chemical analysis andbiological analysis according to effectively control diffusion and mixture.Furthermore, the introduction of micromixer makes a breakthrough in the laminarflow mixing. The characteristic of mass and heat transfer is excellent, which helps themixing fluid more uniform and speedy than other conventional mixing equipment.Therefore, great applications are applied to the preparation of the emulsion, chemicalsynthesis, pharmaceutical preparation, high-throughput screening and biochemical.In this paper, the method of simulation and experiment is used to optimize thepassive micromixer, and analyze the effect of control parameters. Twopolydimethylsiloxane-based (polydimethylsiloxane, PDMS) passive planar passivemicromixers are devised according to the PDMS chip processing system. Furthermore,according to the efficient mixing characteristic in the micromixer, the synthesissystem of micro-mixing/reacting is established and the silver nanoparticle is made byusing one-step method. The thermal performance of nanofluids is evaluated by thequalitative and quantitative analysis, which may offer some data in the design of newworking fluid. The main contents include the following aspects:The mechanisms of enhanced mixing in the Telsa micromixer, the T-shapedmicromixer with non-aligned inputs and the micromixer with vortex-generated unitsare analyzed. The effect of structural and flowing parameters on the performance ofmixer is also simulated using numerical simulation. The results reveal that the effectof different parameters on mixing. To know the method of mixing in the passiveplanar mixer may offer some theoretical basis in design of the new-typed mixer in the further. The results also show that changing the local width of channel and addingobstacle into the mixer can form a chaotic convection so that promoting fluid mixing.Due to the change of structural channel, the interaction of vortices in the differentdimensions is achieved. Hence, it can strengthen the disturbance of the fluid in thechannel to achieve fully mixing.Two kinds of novel passive planar micromixers have been designed which canbe processed easily and achieved fast mixing. The geometry parameters are numericaloptimized according to the optimization method. The mixing performances of passiveasymmetric split-and-recombine micromixer with fan-shaped cavities and micromixerarranged with vortex-generated units are strengthened further. The mixing effect ofasymmetric split-and-recombine micromixer with fan-shaped cavities is significant.The extension vortex in the horizontal plane and the Dean vortex in the vertical planecaused by the sudden enlargement and sudden reduction structure obviously affect theflow pattern changing of mixing fluids in the microchannel. This provides a highreference value to the optimization design of typical planar T-shaped micromixer. Themicromixer arranged vortex-generated units could form extension vortex in thecurved channel, which can increase the disturbance between fluids; form separationvortex behind the baffle; emerge secondary flow and form Dean vortex in the crosssection perpendicular to the direction of fluid flow in the curved channel. The newmicromixers achieve superposition and strengthening of vortices using simple channelstructures. So the contact area of fluids is increased and the mixing effect is improvedsignificantly. This provides reference to the optimization design of typical planarmicromixer with curved channel.The microchip processing technology based on the PDMS and glass is putforward. The whole technological process includes fast making SU-8silicon wafer,replication molding technology and the surface modification bonding and so on.Through researching the influence of various process parameters on the technologicalprocess, the production process has been optimized. To the200μm SU-8glue in theexperiment, the365nm ultraviolet light is adopted and the exposure time is about180s,developing time is about10min; The best quality ratio of PDMS and curing agent is10:1, the curing time of75℃is30min; Finally, the PDMS substrate surface bondswith glass directly after bombarding40~100s by Oxygen plasma, the chip is bondedsuccessfully after thermal insulation4h at100~120℃.The single metallic silver nanofluids are composed which has uniform particlesize and stable dispersion by one step of micro-mixing/reaction method. Throughoptimizing the combination of micromixer and microreactor and the preparationcondition (reactant concentration and the reactant injection pattern), the particle sizedistribution and chemical stability can be controlled effectively. The processing technology of composing single metal nanoparticles is optimized further bycomparative analysis the advantages and disadvantages of nanofluid preparationmethods. At the same time, the thermal physical parameters have been analyzedqualitatively and quantitatively. The influence of particle concentration and synthesismethods on the thermal physical parameters has been analyzed systematically. As thetemperature increasing, the heat conductivity coefficients of silver nanofluids withdifferent concentrations increase. The heat conductivity coefficients of nanofluidswith different partical sizes increase as the particle volume fraction increases.Meanwhile, the particle size of nanoparticle has a great influence on the heatconductivity coefficient. With the decrease of the particle size, the influence of Brownforce on the nanoparticles is more obvious, while the Brownian motion and thethermal diffusion effect of particles in fluid enhance.