Calculation of Fin Efficiency for Wet and Dry Fins

Abstract

This paper presents a quantitative evaluation of methods used to calculate fin efficiency for dry and wet fins. The exact solution for circular fins uses Bessel functions, which are tedious to evaluate. The authors provide an empirical modification to the Schmidt equation (Hong and Webb equation), which provides improved accuracy for circular fins. Existing methods to evaluate the fin efficiency of rectangular, plain plate fins are evaluated. The plate-fin methods are compared against the fin efficiency calculated by the sector method using Bessel functions. Use of the sector method with the Hong and Webb equation is recommended. Cases for which the simple “equivalent circular fin” method is a very good approximation are defined. Methods to calculate the fin efficiency of enhanced fin geometries are discussed. The authors show that the wet surface fin efficiency for any fin geometry may be calculated using a simple modification of the dry surface fin efficiency equation. Example calculations are presented, which show that the wet surface fin efficiency can be as much as 35% below the dry surface fin efficiency for high humidity conditions.