Estimation of heat-transfer characteristics on a vertical annular circular fin of finned-tube heat exchangers in forced convection

The finite difference method in conjunction with the least-squares scheme and experimental measured temperatures is applied to predict the average heat transfer coefficient image and fin efficiency ηf on a vertical annular circular fin of finned-tube heat exchangers for various fin spacings in forced convection. The distribution of the heat transfer coefficient on the fin is assumed to be non-uniform, thus the whole annular circular fin is divided into several sub-fin regions in order to predict the image and ηf values. These two predicted values can be obtained using the present inverse scheme in conjunction with the experimental measured temperatures. The results show that the effect of the fin spacing S on the image value can be negligible when the S value exceeds about 0.018 m. The image value increases with increasing the air speed Vair for 1 m/s ⩽ Vair ⩽ 5 m/s (1550 ⩽ Red ⩽ 7760) and increasing the fin spacing for 0.005 m ⩽ S ⩽ 0.018 m. The present estimated results can be applied to obtain the new correlations of the Nusselt number and fin efficiency based on do, S and Red. The average heat transfer coefficients obtained from this new correlation of the Nusselt number are in good agreement with those given by Hu and Jacobi [X. Hu, A.M. Jacobi, Local heat transfer behavior and its impact on a single-row, annularly finned tube heat exchanger, ASME J. Heat Transfer 115 (1993) 66–74].