Investigation of natural-convection heat transfer coefficient on a vertical square fin of finned-tube heat exchangers

The finite difference method in conjunction with the least-squares scheme and the experimental temperature data is proposed to predict the average natural-convection heat transfer coefficient and the fin efficiency on a vertical square fin of one-circular tube plate finned-tube heat exchangers. In the present study, the radiation and convection heat transfer coefficients are simultaneously taken into consideration. The heat transfer coefficient on this square fin is very non-uniform. Thus the whole plate fin is divided into several sub-fin regions in order to predict the average heat transfer coefficient image and the fin efficiency on the fin from the knowledge of the fin temperature recordings at several selected measurement locations. The results show that the heat transfer coefficient on the bottom fin region of the tube can be markedly higher than that on the top fin region of the tube. The image value increases with the fin spacing S and approaches an asymptotical value obtained from a single square fin as S → ∞. The fin temperature distributions depart from the ideal isothermal situation and the fin temperature decreases more rapidly away from the circular center with increasing the fin spacing. In order to show the accuracy of the present inverse scheme, a comparison of the average heat transfer coefficient on the fin between the present predicated results and those obtained from the correlation recommended by current textbooks is made.