A Study on the Contact Quality Improvement of Fin to Tube Assemblies

The fin-to-tube assembly is a prevalent connection type in heat exchangers, particularly in smaller equipment. During the assembly process, a die expands the tube to close the gap between the tube and the fin collar, enhancing heat transfer. The die expansion reduces the gap and creates slight interference that enables the fin collar to adhere to the tube. However, contact is not uniformly continuous across the width of the mating surfaces, as indicated by recent research. Due to this suboptimal contact quality, the conduction of heat is significantly impaired, and the efficiency of the heat exchanger is thus compromised. This study aims to establish a relationship between the profile shape of the fin hole and the contact quality, offering guidelines to enhance tube-to-fin contact. Tubes of various materials, dies of different sizes, and fins with a collar featuring an hourglass proposed shape are examined. The influence of a fin-hole hourglass shape will be assessed through a series of expansion simulations conducted on diverse finite element models. Subsequently, the micro-gaps formed during the expansion process at the tube-to-fin interface will serve to evaluate the quality of the contact surface, and a thermal transient analysis will be implemented to corroborate the findings.