Numerical study of the cold finned-tube bundle heat exchanger under natural convection for a novel passive displacement cooling system

In a passive displacement cooling (PDC) system, conventional finned-tube heat exchangers are being employed and their performance is not optimal under natural convection. In this study, an experimental set-up has been established to validate the numerical model for finned-tube heat exchanger optimization under natural convection. The numerical difference between the predicted and measured data is less than 3.4%, showing that the numerical model could predict the heat transfer and flow rate accurately under natural convection. Subsequently, the effects of fin spacing, coil configuration, tube row number, and fin depth on the coil performance under natural convection have been investigated. The results show that the one-row coil performs better than the two-row coil for a PDC system with 8-10 fins per inch (FPI), despite the smaller heat transfer area. Compared with the conventional two-row circular-tube coil with 10FPI, the one-row circular-tube coil improves the mass flow rate and heat transfer rate by around 29.1% and 20.0% respectively. The findings enable a more responsive and energy-efficient PDC system for green buildings.