Influence of the degree of thermal contact in fin and tube heat exchanger: A numerical analysis

Present work aims to investigate the significance of thermal contact area between fins and tubes in a heat exchanger. The heat exchanger type selected for the study is a liquid-gas fin and tube heat exchanger. Four different cases namely I, II, III, and IV, based on a variable degree of thermal contact between fins and tubes are investigated. Case-I with 100% thermal contact area between the fin and tube is set as a reference to cases-II, III, and IV with a thermal contact area of approximately 70%, 50%, and 35%, respectively. Three-dimensional (3D) steady-state numerical models based on finite element method (FEM) are developed for the different cases studied. Conjugate heat transfer mechanism coupled with turbulent flow is simulated to elucidate temperature and velocity profiles. In order to develop a simplified model with desired physical phenomena, only gas-side flow over the fin is simulated in the present study. The performance of the heat exchanger is characterized in terms of overall heat transfer coefficient, Colburn j-factor, flow resistance factor, and efficiency index. Results obtained from numerical modeling are useful to examine the impact of the degree of thermal contact and to compare the performance of heat exchanger design in different cases. Comparative analysis indicates a significant influence of the degree of the thermal contact area between fin and tube on the overall performance. Case-I is found to have higher overall heat transfer coefficient of 47.332 W/(m2 K), higher efficiency index of 9.131 and lower flow resistance factor of 0.123 among the cases investigated and highlights the need for perfect thermal contact between fin and tubes to meet the application based requirements.