Microfluid Flow Characteristics And Its Application In Flow Sensors

Flow flux is an important parameter of microfluidics technology. It is necessary to meassure flow flux of microfluid when it is extracted, allotted and mixed because it can ensure the correctness of operation and achieve the goals of saving energy, improving efficiency and reducing cost. Micro flow flux sensors are the main method to realize micro flow flux measurement and researching microfluid technology and designing new micro flow flux sensors are the main task and the one of the important contents of microfluidics technology at present stage.The effect of hydrodynamic entrance on the flow characteristics of microfluid is studied firstly. Based on the continuum assumption, the mathematical model of microfluid flow which takes circular microchannels as the cavities where microfluid flows and takes deionized water as working medium is established and it is numerically simulated. The velocity and pressure profiles of microfluid in the circular microchannels while the velocity of microfluid and the feature sizes of circular microchannels change are obtained.Then, the velocity and pressure profiles of microfluid in the circular microchannels are analyzed.The results show that the velocity of microfluid near the wall decreases to zero gradually while the velocity of microfluid near the center increases with flow length and it leads to that the pressure distribution of microfluid is inhomogeneous in the hydrodynamic entrance region. And then it has an effect on the flow characteristics of microfluid in this region, especially on the flow resistance characteristics of microfluid. Based on the post process of the results, the hydrodynamic entrance length and the additional loss caused by the development of microfluid in the hydrodynamic entrance region of circular microchannels are studied qualitatively and quantitatively. The results show that the hydrodynamic entrance length of the circular microchannel is much larger than the result predicted by classical theory. The additional loss caused by the development of microfluid in the hydrodynamic entrance region increases significantly and the pressure drop between the input and the output of circular microchannels is also larger than the result predicted by classical theory. Then, the formulas of the hydrodynamic entrance length and the additional loss of circular microchannels are provided.Thirdly, based on the achieved hydrodynamic entrance length of the circular microchannel and the additional loss, a new micro flow flux sensor is designed. The body of the new micro flow flux sensor is a circular microchannel and there are two identical piezoelectric microcantilevers in the fully developed region of the circular microchannel. The pressure drop caused by microfluid flowing in the fully developed region of the circular microchannel can be measured by the positive piezoelectric effect of piezoelectric microcantilever. The flow flux of microfluid can be measured based on the relation between the measured pressure drop and the flow flux of microfluid. By the theoretical analysis of input-output relation of the new micro flow flux sensor, the theoretical model which can represent the relation between its output and the flow flux of microfluid is obtained. Then the manufacturing process of the new micro flow flux sensor is designed.Finally, the effect of the structural parameters of piezoelectric microcantilever on the new micro flow flux sensor is analyzed qualitatively by ANSYS. The sensitivity characteristic of the new micro flow flux sensor is also simulated after setting the structural parameters of piezoelectric microcantilever. The sensitivity and the maximum measuring range of this new micro flow flux sensor are provided as a result.