Effects Of Surface Characteristics Of Silicon Substrate On The Interfacial Slip In Micro-channel

As one of important branch of micro electromechanical system, micro-fluidic system is playing a vital role in the field of biology, medicine, and chemical engineering. The research of drag reduction in micro channel becomes focus point with the development of micro-fluidic system. Surface wettability can influence the fluidic flow in many cases, especially in the micro channels. Superhydrophobic surfaces can reduce the adsorption between liquid and solid in micro channel by decreasing surface free energy, and then bring about the slip velocity, so the drag reduction can be realized. In this paper, the influence of surface wettability on microfluidic flows is studied in detail by experimental analysis and numerical simulation, the content of the research is as follow:The flow field of micro channel which grouped by four kind walls with different wettability, was tested by micro particle image velocity (Micro-PIV) system, the relationship between slip velocity and wall wettability was studied. The results show that, on the whole, the slip velocity increases by the enhancing of wall wettability, and in the micro channel with different hydrophobic walls, the maximum velocity located close to the wall with more hydrophobicity.In the conditions of different inlet pressure, the moving process of bubble in the micro channels with different hydrophobic walls was recorded by high speed camera. The influence of wall wettability and inlet pressure on bubble dynamic contact angle (DCA) was discussed. The results show that bubble’s DCA increases by the enhancing of wall wettability. The wettability of one wall can affect the influence of the other wall on DCA. In addition, when the inlet pressure is less than 40 kPa, comparing with inlet pressure, the wall wettability dominate the bubble’s DCA.However, when the inlet pressure is bigger than 40 kPa, the inlet pressure acts important factor.The flow field and bubble shape was simulated by computational fluid dynamics. The relationship between DCA, slip velocity and wall wettability was mainly analyzed, and the results of simulation verified the experimental research. The results indicate that the shape of bubble head is depend on flow velocity distribution. The relationship between DCA and slip velocity is definite, therefore, the DCA can be used to represent the slip velocity effectively.