Numerical Analysis Of Micro Channel Flow

With the rapid development of the Micro-Electron-Mechanical System (MEMS),microfluidic devices as an important part of which has been got more and more attention by people. The action effect of the various forces in the flow would be changed due to Micro-scale condition, which physical phenomena and macroscopic phenomena are very different in the condition of micro-scale, showing a different flow process from many conventional scale, so that the research of this subject has important practical significance and scientific value and thus becomes a new hot spot in the field of fluid mechanics research.The typical micro channel flows and complex micro channel flows are taked as study objects, the micro-channel flow characteristics are studied based on numerical simulation software. Finite volume method is used and second develop the computational fluid dynamics software with custom functions. The variable property solution model is used for all computing areas. The standard k-εand wall function method is combined to calculate the micro-flow.The effect of velocity slip to the micro-channel gas flow is analysised for laminar flow. First inviscid flow in the tube without consideration of the speed slip is studied, then the pipe flow formula with the velocity slip is derived. According to the numerical simulation by MATLAB, the friction coefficient is smaller as dimensions of the slip length and the radius of micro-channel are equivalent as to the value without consideration of the velocity slip.By numerical simulation the micro-flow characteristics of rectangular channels is studied with different physical parameters, aspect ratios, equivalent diameters, height-width ratios respectively. The numerical results show that: (1) For a determined micro-channel, physical parameters are very important for the laminar and turbulent flow characteristics, the flow resistance coefficient and Poisson number reduces nearly 15% with variable properties compared to which with constant physical properties for laminar flow, which effect the turbulence cases with some as well; (2) In order to eliminate entrance effects, the aspect ratio should be greater than 70 for micro-rectangular channel compared to the normal size channels with aspect ratio should be greater than 50; (3) the flow resistance coefficient and Poisson number are inversely proportional to the equivalent diameter for micro-rectangular channel, in other words the smaller the equivalent diameter, the greater the flow resistance coefficient and Poisson number; (4) The higher height-width ratio for micro-rectangular channel, the smaller the flow resistance coefficient and the better the fluid flow properties.This numerical simulation study is focused on different relative roughnesses, roughness element spacings and flow Reynolds numbers respectively for the micro- rough pipe flow characteristics. The results shows that: (1) In a certain spacing ratio and Reynolds number, there are non-negligible effects for the flow resistance coefficent with relative roughnessε/d≥2% ; (2) With the same Reynolds number, the smaller the spacing ratio,the larger the flow resistance coefficient f and the Poisson number; the difference of Po up to 27% for different spacing ratios; (3) When the inside geometry of flow fixed , the Po increases with the Reynolds number increasing.The study for the impact of the channel flow with different equivalent diameters, Reynolds numbers and the cross sections of the ?-type complex micro-channel respectively shows that: the pressure drop of round-channel flow field increases with the decrease of equivalent diameter, so the equivalent diameter smaller, the change of the velocity flow field more rapid and the temperature lower. The negative pressure zone of round-channel flow field increases with the increase of Reynolds number, and the change of various flow field in corner is significant. In the condition of same equivalent diameter and same Reynolds number, the flow heat transfer effect of square channel is better than the circular channel.