Numerical Simulation On Flow And Heat Transfer Of Liquid In Microchannels

With the miniaturization has been gradually popular in the investigation and application, the microflow involved is also been put on an important position. The flow and heat transfer properties of the liquid flow in microchannels affect the performance of microchannels directly and then the performance of the microdevices. The microdevices are widely used in the biology, medicine, aerospace, mechanical and many other fields, while the reliable theory and experiment are short in the flow and heat transfer of micro devices. This paper is to simulate the liquid flow in the microchannel, in order to make effective predictions about flow and heat transfer characteristics of microchannel, so as to support the design of microchannels and to strengthen and widen the application of micro flow in the field of engineering.Investigations of flow and heat transfer for liquid in microchannels with different geometry have been done based on the continuum methods with the numerical simulation. Effects of equivalent diameters, roughness and lengths of the microchannels on the friction factor and Poiseuille Number are analyzed and compared with the experiment results and the empirical theory of common flow. The Reynolds number range of transition state can be deduced from the curves between Reynolds number and friction factors. Diameters of microchannels have effect on the Reynolds number range of transition state. The friction factor is changed by the roughness of the microchannel in the turbulent flow. There are critical values of equivalent diameter and aspect ratio separately. When the equivalent diameter or the aspect ratio is larger than the critical one, the equivalent diameter or the aspect ratio has little influence on the Poiseuille Number.The effects of channel length, equivalent diameter and the aspect ratio on the heat transfer performances are investigated which include the temperature distributions and heat transfer factors. In the same thermal boundary condition, using the effects of the geometry characters of microchannels such as channel length, equivalent diameter and the aspect ratio on the Nusselt numbers, the expression of geometric parameters, Reynolds number and Nusselt number is fitted which has the physical meaning. Within the Reynolds number investigated, the Nusselt number is proportional to the equivalent diameter and the aspect ratio, but to the length of microchannels it is changed at different Reynolds number.Slip boundary conditions and the temperature-viscosity relation are considered in the simulation to find the effect of such conditions on the microflow and heat transfer. The velocity and temperature distribution, the friction factors and Nusselt number of the microchannel are analyzed with or without the Slip boundary conditions and the viscosity changed with temperature. The effects of boundary slip condition on Nusselt number are different with the Reynolds number changed. The temperature-viscosity relation increases the velocity of liquid significantly at the same pressure differ but decreases the friction factor sharply. But there is little influence on the curves of Nusselt number and Reynolds number.