Experimental And Numerical Studies On Mixed Convection In Rectangular Channels

Mixed convection in rectangular channels is frequently encountered in engineering applications, such as nuclear engineering, solar energy collectors and electronic cooling. The effect of heat transfer has a direct impact on the performance of the equipments. Taking the cooling containment of AP1000 as the background, this paper carried out experimental and numerical studies on mixed convection in a rectangular channel.Based on the reviewing of other researchers'achievements, it is found that studies on mixed convection coupled with thermal radiation are relatively scarce. So a vertical rectangular channel with a mixture of convection experimental facility is established to study this problem. The temperature of the channel wall and the velocity field of the cross-section are obtained.With the data processing, the effect of buoyancy and thermal radiation in mixed convection are analyzed qualitatively. The results show that for upward flow in a vertical channel, buoyancy shows a strong effect and leads to a significant decrease (impairment) in heat transfer in the range of small buoyancy number. With increasing buoyancy number the heat transfer coefficient, compared to which under the forced convection conditions, recovers again. Furthermore, it is concluded that thermal radiation plays an important role in the process of heat transfer, especially within the parameter range selected, where heat transfer impairment occurs.Numerical models are evaluated using the experimental data, and the applicable models are selected based on the evaluation. Then the selected model is adopted to study the effect of different radiative emission and tilt angle for mixed convections. The results show that the low Reynolds turbulence models present much more agreement with experimental data than standard k-εturbulence model. However, none model can give correct results over entire range of buoyancy influence. The heat transfer and temperature of heat wall are impaired with larger radiative emission. The ratio of radiation energy is increased with larger radiative emission. The heat transfer ability and the intensity of vortex are strong with the decreasing of the inclined angle of the channel.