Heat transfer and flow characteristics in horizontal spiral coils with flat tubes and rectangular ribs: CFD and optimization

The present work focuses on the analysis of heat transfer and flow characteristics in a horizontal spiral coil with rectangular ribbed flat tubes. The influence of Reynolds numbers (Re) ranging from 3000 to 12000, relative rib height (H n ) from 0.04 to 0.08, and relative rib pitch (P n ) values from 0.3 to 0.5 were investigated using numerical simulations. Furthermore, the Taguchi method was applied to determine the configuration that yielded the highest Witte–Shamsundar efficiency (FSE). The results indicated that adding ribs increased heat transfer and FSE compared to the baseline case. Increasing the Reynolds number and rib height, and decreasing the rib pitch, resulted in increased heat transfer, pressure loss, and entropy generation. Adding ribs increased heat transfer by 1.73–26.58%, but pressure loss also increased by 3.6–36.34% compared to the baseline configuration. With ribs added, the thermohydraulic performance reached 1.004–1.141, and the FSE increased by 0.52–8.11% compared to the baseline case. The optimization results showed that the configuration with H n = 0.08, P n = 0.3, and Re = 3000 yielded the highest FSE. In this optimal configuration, thermohydraulic performance reached 1.109, heat transfer increased by 22.35%, and the FSE increased by 7.29% compared to the baseline case. The Reynolds number had the most significant influence on FSE (75.19%), while the relative rib pitch had the least influence (7.04%). The configuration with rectangular ribbed flat tubes offers benefits in terms of heat transfer, thermohydraulic performance, and Witte–Shamsundar efficiency, and, therefore, can be considered for tube processing and practical applications.