Thermal Performance of Dovetail Fins Under Dehumidifying Operating Conditions: Analytical and Numerical Solutions

Abstract

Abstract Extended surfaces or fins enhance the heat transfer rate between a solid and surrounding fluid. The first scenario is thermal management by dissipating heat from a hot surface. The application sizes range from heat loss through a car radiator to the thermal management of electronic appliances through extended surface heat sinks. The second category is heating, ventilating, and air conditioning (HVAC) applications. The purpose of refrigeration and air conditioning equipment is to cool the atmospheric air by passing it over an extended surface (or fin) at a temperature lower than the passing air. Moreover, if the fin surface temperature is below the dew point temperature of incoming moist air, then the condensation of water vapor occurs on the fin surface. Therefore, heat and mass transfer co-occur over the fin surface. The application is commonly termed a “wet fin.” Enhanced fin geometries (such as wavy, louver, slit, and convex louver) exist. However, simple fin geometries are adopted due to low manufacturing and maintenance costs. The most common fins are longitudinal (or plane) fins, annular (or radial) fins, and spines (or pin fins). A dovetail fin (i.e., variable thickness longitudinal fin) can enhance the performance of a double pipe heat exchanger due to its higher surface area than the rectangular profile fin. Literature shows that the performance of a dovetail fin has been studied for heat loss (or dry operating conditions) only, and no closed-form solution is available for air conditioning (i.e., wet fin) applications. The analysis of a wet fin is more challenging than the dry fin analysis because of the additional consideration of mass transfer due to vapor condensation from the moist air. The thermal performance of an extended surface is commonly described through a dimensionless parameter called fin efficiency. The current work presents a closed-form solution for a dovetail fin’s thermal efficiency and temperature profile that accounts for the combined heat and mass transfer under dehumidification operating conditions. The developed solution is a general case that covers rectangular, tapered, and triangular fins. The solution is validated through available closed-form rectangular and triangular fins solutions. Comparison of results with a two-dimensional finite element numerical solution provided a dovetail fin’s limit of a one-dimensional solution. Preliminary results show that the dovetail fin has higher thermal efficiency than the rectangular and triangular fins.