Effect of thermal radiation on convection heat transfer in cooling channel of photovoltaic thermal system

The effect of thermal radiation on convection heat transfer in flat-box type cooling channel of photovoltaic thermal system with tilt angle of 30 degree was studied by 3D numerical simulation under constant heat flux boundary condition. The temperature contours and velocity fields of fluid near the outlet were obtained. The variations of wall temperature and convection Nusselt number along flow direction for all the separate walls composing the cooling channel were compared and analyzed. The results show that due to thermal radiation, the deflection of the maximum velocity region to heated top wall, together with the asymmetry of temperature field is weakened. For natural convection, radiation promotes the formation of multi-vortices. For mixed convection, heat transfer on all the cooling channel walls is enhanced under the condition of lower heat flux while heat transfer on heated top wall is deteriorated when the heat flux is relative high. Also, pressure re-rising is promoted by thermal radiation.