Study On The Measurement Method Of Liquid Flow Rate In The Microchannel Based On The Construction Of Three-dimensional Flow Field

A new kind of measurement method of liquid flow rate in microchannelbased on the construction of the three-dimensional velocity by the scanningMicro-PIV technique is put forward in this paper. The experimental studies for botha long straight microchannel and three types of T-shaped microchannels were carriedout. The main studies include as follows,Firstly, the preliminary experimental research was carried on in a straightmicrochannel with cross section of300μm×60μm (width×height) using the scanningMicro-PIV technique. The construction of the three-dimensional flow field and themeasurement of flow rate are acquired at eight input standard flow rates. The straightmicrochannel is divided into multi-planes along the direction of the depth of field ofmicroscopic objective. The particle images of every fluid layer are acquired by theregulations of high precision platform of displacement. The algorithm of theensemble cross-correlation is used to evaluate the2D velocities in every fluid layer,so the3D velocities are constructed and the flow rates were calculated by the discreteintegration of velocity on the cross-section of microchannel, the experimental resultsare compared with the standard input flow rate. For the interrogation windows of64×64pixels, the measurement precisions are great within the flow rates between2.481~5.788μl/min, the range of relative errors are0.39%~3.87%; for theinterrogation windows of32×32pixels, the measurement relative errors of flow ratesbetween3.307~8.269μl/min have the high precision, and the range of relative errorsare0.55%~3.69%.Secondly, we measure the water flow rates in three kinds of T-shapemicrochannels based on the measurement of the straight microchannel. The T-shapedmicrochannel of type-1is300μm×200μm×200μm×90μm (inlet×branch1×branch2×height), The type-2is300μm×150μm×150μm×60μm and the type-3is 250μm×150μm×100μm×40μm. Using the same method, shoot at the T node positionof each layer along the direction of the depth of field, and gain the velocity vector ofthe inlet and outlet. Based on the two-dimensional velocities on multiple fluid planesalong the out-of-plane directions of the microchannels, the quasi-three-dimensionvelocities are constructed and the flow rates are calculated velocity distribution usinginterpolation method on the effective cross sections of the microchannels. Comparingthe experimental results with the standard flow rate, we can see that the ranges of theTRE values are0.135%~1.668%for the microchannel of Type-1,0.056%~1.87%forthe Type-2and0.303%~1.928%for the Type-3in the case of the interrogatewindows of64pixels, respectively; the ranges are sequentially0.064%~1.824%,0.036%~1.61%and0.038%~1.191%for the microchannels of Type-1, Type-2andType-3in the case of the interrogate windows of32pixels, respectively. Bycomparing two groups data above, we can see that the calculated flow rates based onthe two types of interrogate windows both reach a high precision, and the TREevaluated by the interrogation windows of32pixels are superior to that of64pixelson the whole. In addition, numerical simulation also been conducted in straightmicrochannel and T-shape microchannels, the simulated results are compared withthe experimental results. The results show that the simulated results of themainstream area hav a good consistency with the experimental results.Finally, according to the above experiments and the calculation method, apreliminary research of the flow rate measurement based on the Particle trackingalgorithm (PTV) proceed. The two dimensional velocity was obtained by rejectingthe bad points and overlying the velocity under the condition of low concentration ofparticles, then the three dimensional velocity and the flow rates are acquired. But themethod needs a further research to improve the measurement precision.