A heat transfer correlation for natural draft wire-and-tube condensers

A dimensionless correlation to estimate the heat transfer coefficient between the external surfaces of natural draft wire-and-tube condensers and the surrounding air is proposed in this study. The experiments were carried out using a purpose-built testing apparatus that reproduces the actual operating conditions of such heat exchangers. A test section to vary the condenser position in relation to the adjacent surfaces was also developed and mounted within a controlled environmental chamber. The correlation was developed based on a total of 72 experimental data points obtained with 24 different condenser samples with tube outer diameter  ranging from 4.8 to 6.2 mm, number of tube rows from 13 to 25, and number of wire pairs from 10 to 90. The tests were performed with an average temperature difference between the condenser surface and the ambient air ranging from 3.6 to 36.1 °C. The proposed correlation predicts 90% of heat transfer data within an error band of ±10%. Comparisons with other correlations available in the open literature are also reported.