The Characteristics Of Drag Reduction Of Liquid Flowing In Micro-channels

With the development of Micro Electro Mechanical System (MEMS) technology, the flow characteristic of Deionized Water in Micro-tubes has recently become a research focus. There are some problems about drag reduction and heat emission, which have a great influence on the developing of MEMS. This paper mainly focus a series of experimental studies aroud the motif of the drag reduction and slip of liquid flowing in Micro-tubes.In this paper the characteristics of drag reduction of surfactant for deionized water flowing in micro-channels was studied by experiments in which Cetyl Trimethyl Ammonium Bromide (CTAB) was used as the adsorption. The experiments show that the flow rate of water in micro-channel without CTAB agrees with the prediction of the conventional Hagen-Poisseuille equation, and, the flow rate in micro-channel increases clearly after CTAB being adsorbed. This indicates that the flow resistence of water reduces about 6.3% after CTAB adsorbed in micro-channel with diameter of 50 micron. The reason is that the adsorption of CTAB changes the wettability of micro-channel from strong hydrophilic to weak hydrophilic, and there is flow slippage at the interface between solid and liquid.The relation between the efficiency of drag reduction and the time of adsorption is also studied, the results suggest that: there is a maximum of drag reduction with the adsorption of CTAB, and there are two adsorption steps: mono-layer adsorption and double-layers adsorption. The wettability of micro-channel changes from hydrophilic to hydrophobic in the course of mono-layer adsorption, and the efficiency of drag reduction will arrive the most value for full mono-layer adsorption.The phenomenon of velocity slippage occurs after the micro-channel modified with CTAB, the slip velocity have a linear relationship with the shear rate but not the slip length. The slip length is about 0.57μm in micro-channel with diameter of 100μm, when diameter is 75μm ,the slip length is about 0.41μm, and the slip length is about 0.32μm when diameter is 50μm.The peaks of glass surface change from about 7nm to 100nm after treatment, and water contact angle increase from 26°to 63°.In the researches of chapter 2 and chapter3, we found the experiment need an original pressure before the water begin to flow in micro-channels.The xperiment of measuring threshold pressure gradient of deoinized water in micro-channel. The experimental results show that the curve of inner diameters of micro-channel and threshold pressure gradient is show as a downtrend, and threshold pressure gradient with CTAB is clearly lower than ones without CTAB in the same micro-channel.Finally, the interface characteristics of two phase flow in Micro-channel was researched, the results indicate that the styles of liquid-gas interface and water-oil interface changes with the different velocity of flow, which changes from concave to even until convex when the velocity increases. The tnterface style changes more difficult in smaller micro channels because of the big surface tension.