A new heat transfer correlation for natural draft wire-on-tube condensers for a broad geometry span

•Theoretical and experimental study of natural-draft wire-on-tube condensers.•Semi-empirical correlation to predict the air-side heat transfer coefficient.•Tube and wire pitch es play the most important role in the heat transfer rate.•Condenser optmization focused on reducing the material mass. This paper investigates the heat transfer performance of natural draft wire-on-tube condensers considering the geometric range of current designs adopted by the household refrigeration industry. Fifty-four samples with distinct geometries were manufactured and tested inside a standardized climate chamber that sets the air-side conditions, while a purpose-built apparatus was used to circulate hot brine through the coil with a strict control of the inlet temperature and mass flow rate. The results pointed out that the condenser height, and the wire and tube pitches are the key parameters affecting the heat transfer rate. An improved correlation was put forward to calculate the air-side heat transfer coefficient, being able to predict 90% of the experimental data within the ±10% error bounds. Also, it was noticed that the condenser design can be optimized by reducing the wires and tubes mass for a given heat duty.