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 over(h, ̄) and fin efficiency η_f 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 over(h, ̄) and η_f 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 over(h, ̄) value can be negligible when the S value exceeds about 0.018 m. The over(h, ̄) value increases with increasing the air speed V_air for 1 m/s ≤ V_air ≤ 5 m/s (1550 ≤ Re_d ≤ 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 d_o, S and Re_d. 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].