Study of coating effects on variable profile annular fins when subjected to dehumidifying operating conditions

The coating effects on variable profile annular fins, subjected to dehumidifying operating conditions are studied. The coating has a uniform layer thickness over the entire fin free surface including tip, i.e. non-insulated tip condition is considered. The studies are conducted numerically by a non-dimensional axisymmetric finite element formulation. A piecewise linear relationship is used in the formulation to account for the non-linear psychrometric correlation between temperature and humidity ratio. It is demonstrated that the coating resistance effects are governed by a single dimensionless parameter called coating Biot number. A limiting value of the parameter is identified for which coating resistance effects become negligible. The presented non-dimensional formulation can be used to study other types of fins i.e. spines and longitudinal under partially and fully wet conditions. Similarly, more complicated cases like multiple coating layers and interface resistance at the fin base can also be studied.