A semi-analytical method was described to determine the thermal performance of fin-and-tube heat exchangers with orthotropic fin materials and wet surfaces. The effect of the orthotropic thermal conductivity was investigated over a range of design parameters for both wet and dry fins, and design optimization was carried out using a generalized Newton-Raphson method. The optimized designs were analyzed to gain insight into the relative importance of the different parameters under varying conditions, and a set of curves was determined to provide design optimization guidelines. (C) 2011 Elsevier Ltd. All rights reserved.