Experimental investigation of natural convection heat transfer from functionally graded annular fins on an inclined cylinder

Abstract

Annular fins, commonly used in various engineering applications from heat exchangers to electrical equipment, are typically made from highly conductive homogeneous materials. However, these materials, such as aluminum, do not achieve ideal uniform temperature distribution along the fins’ length. Recognizing the potential of Functionally Graded Materials (FGMs) to enhance thermal performance by combining two distinct materials with a gradual transition, this study proposes their use as fin materials to achieve optimal performance. The study encompasses three primary components: (1) finite element analysis to determine the optimal FG annular fin design, (2) fabrication of aluminum and FG fins using powder metallurgy and hot pressing techniques, and (3) experiments to evaluate the thermal performance of FG and aluminum fin arrays by attaching them to a cylinder under natural convection. This study distinguishes itself by elucidating the effects of tilt angle, fin number, and material on natural convection heat transfer. It is also the first experimental study to assess the performance of FG fins on a cylinder with inclinations ranging from 0 to 75 degrees. In these experiments, the thermal performance of fin arrays is evaluated for heat inputs ranging from 25 to 50 W, different fin numbers, and cylinder inclinations. The results clearly indicate that the thermal performance of fin arrays depends on tilt angle, fin material, and spacing. FG fin arrays outperform aluminum fin arrays for all configurations, demonstrating an 18% improvement in heat transfer, and the optimal performance is achieved with fin arrays containing seven fins. Additionally, increasing tilt angle deteriorates natural convective heat transfer, regardless of fin material.