EFFECTS OF REVERSE FLOW ON THREE-DIMENSIONAL MIXED CONVECTION IN A HORIZONTAL SQUARE DUCT - THE CASE OF THREE HEATED OR COOLED WALLS OF THE DUCT

摘要

Effects of the reverse flow on mixed convection heat transfer and flows in a horizontal square duct with three heated or cooled walls were examined numerically and experimentally for various inlet fluid temperatures. The working fluid was water. This analysis was performed in two cases. In the first case, the wall temperature (T_W = 60℃ was higher than the inlet temperature (T_0 = 10-50℃). In the second case, the wall temperature (T_W = 5℃) was lower than the inlet temperature (T_0 = 10-40℃). In the numerical analysis, the SIMPLE procedure and QUICK scheme were used to solve the governing equations through a control volume method. The temperature dependences of the kinematic viscosity and thermal conductivity of water were considered. In the experiment, the flow was visualized by a dye-injection method. The results show that a reverse flow appears on the upper wall in the first case, whereas it does on the bottom wall in the second case. The size of the flow reversal increases linearly with the product of the Richardson number Ri (= Gr/Re~2) and Prandtl number Pr (= v/a). The heat transfer behavior was also discussed corresponding to the flow.