Augmented heat transfer in a triangular duct by using multiple swirling jets

Measurements of derailed heat transfer coefficients on two principal walls of a triangular duct with a swirling flow are undertaken by using a transient liquid crystal technique. The vertex corners of the triangular duct are 45, 45, and 90 deg. The swirl-motioned airflow is induced by an array of tangential jets on the side entries. The effects of flow Reynolds number (8600 less than or equal to Re less than or equal to 21000) and the jet inlet angle (alpha = 75, 45, and 30 deg) ave examined. Flow visualization by using smoke injection is conducted for better understanding the complicated flow phenomena in the swirling-flow channel. Results show that the heat transfer for alpha = 75 deg is enhanced mainly by the wall jets as well as the impinging jets; while the mechanisms of heat heat transfer enhancement for alpha = 45 and 30 deg could be characterized as the swirling-flow cooling. On the bottom wall, jets at a = 75 deg produce the best wall-averaged heat transfer due to the strongest wall-jet effect among the three angles (alpha) investigated On the target wall, however, the heat transfer enhancements by swirling flow (alpha = 45 and 30 deg) are slightly higher than those by impinging jets (alpha = 75 deg). Correlations for wall-averaged Nusselt number Sor the bottom and target walls of the triangular duct are developed in terms of the flow Reynolds number for different jet inlet angles.