Heat (Mass) Transfer Distribution in a Two-Pass Trapezoidal Channel With a $180deg$ Turn

The heat transfer characteristics of airflows in serpentine cooling channels in stator vanes of gas turbines were studied. The cooling channels were modeled as a two-pass trapezoidal channel with a $180deg$ turn. Naphthalene sublimation experiments were conducted and the heat and mass transfer analogy was applied to study the local heat (mass) transfer distributions on one of the two primary walls of the channel. Results were obtained for turbulent airflow through the channel with smooth walls, and with transverse ribs on one wall and on two opposite walls, over a range of Reynolds numbers between about 10,000 and 60,000. The results showed that there was a very large variation of the local heat (mass) transfer distribution in the turn and downstream of the turn. In all of the cases studied, the regional average heat (mass) transfer was higher on the downstream half of the turn than on the upstream half of the turn and was higher in the turn with the flow entering the channel through the smaller straight section than when the flow was reversed. The shape of the local heat (mass) transfer distribution at the turn was not significantly affected by varying the air mass flow rate. In the smooth wall case, the local heat (mass) transfer was high near the end wall and the downstream outer wall in the turn and was relatively low in two regions near the upstream outer wall and the downstream edge at the tip of the divider wall in the turn. With ribs on two opposite walls, the variation of the local heat (mass) transfer was larger, especially in the turn and downstream of the turn, than in the smooth wall case. The pressure drop across the turn was higher in the case of the flow entering the channel through the larger straight section than when the flow was reversed. As expected, the ribs increased the pressure drop across the turn.