Detailed heat transfer characteristic comparison in straight and 90-deg turned trapezoidal ducts with pin-fin arrays

Comparison of endwall heat transfer and pressure drop characteristics is made between the pin-fin trapezoidal ducts with straight and lateral outlet flows. The effect of pin arrangement for the ducts of different-directional outlet flows is also examined. A transient liquid crystal method is used to measure the detailed heat transfer coefficients on the endwall surfaces. It is found that in the straight trapezoidal duct, the local heat transfer coefficient decreases along the spanwise direction from the long sidewall to the short sidewall. In addition, the staggered pin array produces relatively uniform and higher local heat transfer than the in-line pin array. As the flow turns 90 degrees out of the trapezoidal duct, the pin arrangement affects insignificantly the local and endwall-averaged heat transfer. Results further show that the 90 degrees turned trapezoidal ducts inserted with either staggered or in-line pin array perform the best endwall-averaged heat transfer and, meanwhile, pay the largest pressure-drop penalty. The straight trapezoidal duct with in-line pin array, however, has the lowest endwall-averaged heat transfer coefficients as well as the pressure-drop coefficients. (C) 1999 Elsevier Science Ltd. All rights reserved.