Analytical And Numerical Investigations Of Laminar Flow And Heat Transfer Characteristics In Rough Microchannels

With the rapid development of microelectromechanical technology(MEMS),microfluidic devices such as microchannel have become a reliable technology for solving the heat dissipation of electronic devices due to their compact structure and high heat exchange efficiency.The effect of wall roughness effect becomes one of the main factors affecting the performance of the microfluidic system.In-depth understanding of the influence of wall roughness on fluid flow and heat transfer characteristics in the microchannel provides a basis for the structural design and performance improvement of microfluidic devices.This thesis mainly conducts a systematic and comprehensive study on the mechanism about the effect of the wall roughness on the microchannel,and analyzes the fluid flow and heat transfer performance of laminar fluid in the microchannel under the effect of the wall surface roughness.The main content and conclusions are as follows:A circular rough microchannel model with sinusoidal rough element structure is constructed.The perturbation method is used to establish the quantitative correlation formula between the Poiseuille number Po of laminar flow fully developed flow,the relative roughness ε,and the wave number λ in the model.The numerical results show that Po grows approximately to the second power with the increase of the relative roughness,and grows approximately linearly with the increase of the wave number.These two parameters are two important factors affecting the flow field.Aiming at the influence of wall roughness on the fluid flow characteristics in the microchannel,the relative roughness ε,the wave number λ and Reynolds number Re on the velocity distribution,pressure drop,and Poiseuille number Po are comprehensively analyzed through numerical simulation.The study found that the flow direction of the fluid near the wall roughness element changes significantly,and the pressure drop of the fluid increases along the flow direction.Within the studied range of the relative roughness and the wave number,the axis velocity increases with the increase of the relative roughness and the wave number.The numerical simulation results of the flow resistance characteristic parameter Poiseuille number Po are consistent with the analytical solution results.The roughness element has a significant influence on the transport characteristics of the microchannel.The larger the relative roughness and the wave number,the more irregular the wall shape,the greater the fluid flow resistance and the larger the Poiseuille number Po.As the Reynolds number Re increases,the Poiseuille number Po also increases,but the effect is very limited.Aiming at the influence of wall roughness on the heat transfer characteristics of the fluid in the microchannel,the influence of the relative roughness ε,the wave number λand Reynolds number Re on temperature distribution and Nusselt number Nu under the two thermal boundary conditions of constant heat flow and constant wall temperature is studied.The presence of the wall roughness of the microchannel can enhance the heat transfer of the fluid,and the increase of the relative roughness and the wave number will increase the disturbance to the fluid in the tube and increase the heat dissipation area,which enhances the heat transfer performance.The comprehensive heat transfer factor PEC is introduced to evaluate the comprehensive heat transfer performance of rough microchannel.It is found that the comprehensive heat transfer performance of the rough microchannel is better than that of the smooth microchannel under the two kinds of thermal boundary conditions.This conclusion has a guiding significance for the optimization design of the artificial rough microchannel radiator.