Abstract: The actual heat transfer coefficients of two commonly-used double H-type finned tubes(ND steel and 316L stainless steel) are obtained through experimental study. A computational model of the overall heat transfer coefficient with the thermal contact resistance being incorporated into the fin efficiency is proposed, and the accuracy of the proposed model is validated through the experiments. The experiments show that the overall heat transfer coefficient of Sample ND is much bigger than that of Sample 316L under the condition of the same manufacturing technology and the same structural dimensions. From the difference between the experimental and the calculated data, the thermal contact resistance of each sample are obtained. By comparing the two samples, it is found that the thermal contact resistance of Sample ND is far less than that of Sample 316L. In addition, for the special double H-type fins, the thermal contact resistance decreases the coefficient of Sample 316L by 7 W/(m²·K) while its impact on Sample ND can be ignored. Meanwhile, the analysis of the computational model shows that when the unit thermal contact resistance is less than 0.001 m²·K·W^-1, its impact on the coefficient is too little to be counted, which proves the results of the experiments. The computational model can be used to predict the thermal contact resistance of finned tubes with special structures so as to determine the influence of the thermal contact resistance on the overall heat transfer coefficient. The study result can provide a reference on the selection of the materials and welding technologies for low-temperature economizer tube bundles in industrial applications.

Key words: low-temperature economizer, double H-type finned tube, overall heat transfer coefficient, thermal contact resistance, experimental study