An algorithm is presented to determine the efficiency of extended surfaces (circular or longitudinal fins with a uniform thickness) when simultaneous heat and mass transfer occur. The temperature distribution over the fin surface is calculated by solving numerically a nonlinear, second-order differential equation.

The overall fin efficiency of a wet surface is evaluated using the temperature and specific humidity differences as the driving forces for heat and mass transfer, respectively. The concept of efficiency of a wet surface fin is similar to the basic definition of a dry surface fin.

The presented algorithm is unique and accurate in determining the condition of the fin surface with regard to being dry or wet. This model could also be used to optimize the cooling and dehumidifying coil design for specific operating conditions.