Heat Transfer Characteristics of a Flow Passage With Long Pin Fins and Improving Heat Transfer Coefficient by Adding Turbulence Promoters on a Endwall

Abstract

Pin fins are normally used for cooling the trailing edge region of a turbine, where their aspect ratio (height H/diameter D) is characteristically low. In small turbine vanes and blades, however, pin fins may also be located in the middle region of the airfoil. In this case, the aspect ratio can be quite large, usually obtaining values greater than 4. Heat transfer tests, which are conducted under atmospheric conditions for the cooling design of turbine vanes and blades, may overestimate the heat transfer coefficient of the pin-finned flow channel for such long pin fins. The fin efficiency of a long pin fin is almost unity in a low heat transfer situation as it would be encountered under atmospheric conditions, but can be considerably lower under high heat transfer conditions and for pin fins made of low thermal conductivity material. A series of tests with corresponding heat transfer models has been conducted in order to clarify the heat transfer characteristics of the long pin-finned flow channel. It is assumed that heat transfer coefficients can be predicted by the linear combination of two heat transfer equations, which were separately developed for the pin fin surface and for tubes in crossflow. To confirm the suggested combined equations, experiments have been carried out, in which the aspect ratio and the thermal conductivity of the pin were the test parameters. To maintain a high heat transfer coefficient for a long pin fin under high-pressure conditions, the heat transfer was augmented by adding a turbulence promoter on the pin-finned endwall surface. A corresponding equation that describes this situation has been developed. The predicted and measured values showed good agreement. In this paper, a comprehensive study on the heat transfer of a long pin-fin array will be presented.

Heat Transfer Characteristics of Pin-Fin Arrays with Ribs to Cool Combustor Liners

“…However, most research groups investigated basic and simple arrangements of pin-fin arrays with no additional devices to enhance heat transfer. Recently, Takeishi et al (9) investigated the overall heat transfer characteristics of pin fins with and without turbulence promoters (TP) on the endwall; they reported that TP enhance pin-fin heat transfer under actual engine conditions where fin efficiency becomes important because of the high heat transfer coefficient and low thermal conductivity of the superalloys used in the pin fins. The present study is an extension of an earlier study by Takeishi et al (9) to measure the local heat transfer coefficients, which are important in the cooling design of combustor liners and trailing edge sections of turbine vanes.…”