Experimental study of turbulent air natural convection in open-ended vertical parallel plates under asymmetric heating conditions. (October 2020) - Kim, Koung Moon
Highlights: Air natural convection in vertical parallel plates is investigated experimentally for wall temperature conditions up to 500 °C. When both side walls are heated, the reverse flow does not occur at the outlet. Flow behavior is considered by the thermal behaviors based on the measured wall and air temperatures. Flow pattern in the channel would be determined by the geometry rather than thermal boundary condition. Two physical correlations related to the heat transfer and induced flow rate are presented Abstract: In this study, we investigated the turbulent air natural convection phenomena between open-ended vertical parallel plates under asymmetric heating conditions. The rectangular air channel consisted of two insulating walls and two heated walls: one of the vertical walls is heated to maintain uniform wall temperature conditions at various temperatures from 50 to 500 °C, and the other wall is indirectly heated by thermal radiation from the directly heated wall. We measured both wall temperature distributions in the vertical direction and the air temperature profiles with the horizontal direction at certain heights. The results showed that when both walls are heated asymmetrically, reverse flow was absent at the outlet of the channel, as confirmed by a simple visualization method. In addition, we confirmed the practical result of a deviation between the mean air temperature and the measured air temperature at the center of the channel. From the results of the wall temperature distributions and the air temperature profiles, we suggest a reasonable flow behavior, which is the generation of two different recirculation flow patterns that are not affected by changes in the thermal boundary. In addition, we compared the ratio between the convective and radiative heat rates on the directly heated wall. Based on the experimental results, we analyzed the natural convection heat transfer between vertical parallel plates and we proposed two correlations. The heat transfer correlation agreed well with the correlation for turbulent natural convection on a single infinite vertical plate . The correlating equation related to the induced flow rate was presented as a modified Rayleigh number to estimate the flow rate.