The Study Of Drag Reduction Experiments Of The Liquid Flow In Microscale

Micro Mechanical System technology has many advantages such as low cost, small volume, light weight and easy to be carried, low energy consumption, high precision and environmental compatibility. It has been widely applied in various fields, such as the national defense, medicine, biological engineering, and aerospace, so it has great potential applications. Many micro mechanical devices are related to liquid flow. Researches about the characteristics and drag reduction effects of microscale have attracted more and more attention. Based on fluid mechanics, this paper mainly studies the characteristics of liquid flow in micro-channels, the drag reduction and the slippage. The works are as follows:First, we introduced the basic theory and current developments of microflow, including researching methods. At the same time, some concepts and models about liquid microflow are emphasized, such as the contact angle, the drag reduction model, and so on.Then, we carried out a series of experiments on the basis of basic principle of microflow. We made a visual micro channel by the laser etching and chemical etching technique. Using the chemical etching solution, we made the micro-channels which were10μm or20μm width, and about10μm depth. The flow situations of deionized water in these micro channels were observed, which will lay a foundation for the drag reduction experiments in the future.Then, some displacement experiments were carried out with deionized water flow in different diameters of microtubes and the different porosity of the circles respectively. The experimental results show that: under a certain temperature, the flow rate of deionized water flow in microtubes and micro circles model increase linearly with the pressure gradient increasing and there exists the thresold pressure gradient.Finally, we studied the drag reduction experiments about liquid flow in microchannel. In this work, we selected the deionized water to do the experiments in the microtubes with inner diameters of50μm,75μm and100μm. The Fluoro-Alkyl Silanes (FAS) was used as the adsorption to change wettability of the microtubes surface. We analyzed the following relations:the drag reduction, the flow rate and the pressure drop, the slip velocity and the shear rate, the slip length and the shear rate, the flow rate of deionized water with or without adsorption of FAS.The results indicate that the flow rate in microtubes adsorbed with FAS is larger than ones without FAS, and the efficiencies of drag reduction are about13%at most. The inner surface wettability of microtubes changes from hydrophilic to hydrophobic by absorbed with FAS, which makes the slippage between deionized water and inner surface of microtubes. The slip velocity is directly proportional to the shear rate in microtubes with different diameters; and slip length is a constant number of0.9μm.