Micro-PIV Analysis Of The Microflow In PDMS Microchannel

Microflow technology is the technology of fluid handling process and fabrication of fluidic devices in micro scale. It employed miniaturized fluid handling and detecting system to research the various effects and behavior of the fluid in micro-scale structure. The microflow technology was widely utilized in the area of pharmaceutical industry, biotechnology and biological analysis, medical, chemical analysis, machinery, IT industry or even the national defense and aerospace because of its high-flux of the microchannel and microflow network, efficient fluid handling and detecting mechanisms and the potential low-cost of application. However, micro-flow technology also has the limitation in the method of fabricating microchannel and its network and the research instrument of the microflow handing and detecting system. Therefore, researches of the microflow technology, including the fabrication of microflow devices and microflow detection methods, have become an important direction of researchers and engineers. And it could be seen from the development of the micro-machining technology, microflow experimental and detecting technology and the Micro-PIV technology. In view of this, this paper is mainly research about the Micro-PIV analysis of the low in PDMS microchannel, including the fabrication of PDMS microchannel, the components and algorithm of Micro-PIV system, the wavelet analysis in de-noising the Micro-PIV image and the experimental and theoretical research of microrheology.The traditional technologies such as photolithography and soft lithography were hardly accepted by ordinary laboratories because of the limitation of the harsh conditions, time-consuming, high cost and irregular channel shape of the cross-section. This paper introduced a technique for fabricating microchannel by strain steel microwire. It can obtain 20-100μm in diameter standard circular cross-section microchannels with a variety of topological structure and function such as crossed channel, curving channel and 3D helical channel due to the high strength, high flexibility, good surface properties and good conductivity of the strain steel microwire.Micro-PIV is a non-disturbance measurement technology based on image analysis. We constructed the Micro-PIV experimental system by the microchannel, high-pressure gas-driven devices, microscopes and CCD camera; and constructed the Micro-PIV image processing system by combining the cross correlation algorithm based on FFT, image Denoising, vector amendment and sub-pixel matching. We developed the corresponding program under MATLAB platform to achieve the above functions and verified the algorithm and program by the PIV standard image.Wavelet analysis is a signal analysis method with good characteristics in both time-domain and frequency-domain. Therefore Micro-PIV image could be de-noised by the multi-resolution property of wavelet analysis. And the key problem of the de-noising is the selection of the threshold because of the particularity of the particle image. This paper describes the theory and method of image de-noising through wavelet analysis and applied to the Micro-PIV image de-noising. Flitering the wavelet coefficients after one order decomposition of the particle image can get satisfied results because of its special nature.Analyzing the flow phenomenon by Micro-PIV technology could obtain the velocity vector field, which is the overall and detail information of the flow field. Further, the shear stress distribution in microchannel and the liquid viscosity could be work out by the velocity vector field. In this paper, the flow image of different diameter microchannels were analyzed by Micro-PIV, and calculated the velocity and shear stress distribution of cross-section and the viscosity of the fluid (0.9405×10-4Pa·s) in the channel in diameter 80μm according to the velocity vector field. It is basically in accordance with theory of the laminar flow.In this thesis, we analyzed the particle flow in microchannel and obtained results consistent with the theory of microrheology based on PDMS microchannel and by means of the Micro-PIV technology which combined the wavelet analysis. This indicated the feasibility and reliability of the microchannel fabricating technique and the Micro-PIV analyzing method; and also indicated the possibility and applicability of the integration of these technologies. In the technical details of the experiments and theoretical calculations and analysis, the method introduced in the thesis could provide appropriate improvement and innovation, which rewarded us a more in-depth knowledge and understanding of these interdisciplines.