Understanding and Evaluating Extended Surfaces

Abstract

Extended surfaces are widely used in heat transfer equipment in power and process plants. While various types of extended surfaces are used in the industry, this paper will limit the discussions to the widely used configurations in heat recovery equipment and boilers, namely curcumferential solid and serrated fins used in the outside of the tubes. Such surfaces are suitable for clean gas applications such as Gas Turbine Heat Recovery systems and have the advantages of reducing the overall size of the equipment and also minimizine the gas pressure drop. However, several consultants, users of extended surface equipment and even designers are not so familiar with a few important aspects of extended surface heat transfer and unfortunately select or buy equipment using a spread sheet approach. Solely because it has more surface area compared to another design. With a few examples this paper will try to bring out the fact that through proper use of fin configuration one can transfer the same or even more energy with a lower surface area, less gas pressure drop and lower tube wall and fin tip temperature.