Rippled-finned surface type heating or cooling coils primarily increase heat transfer efficiency through:

Rippled-finned surface type heating or cooling coils enhance heat transfer efficiency by creating more turbulence at the fin surfaces. The design of the rippled fins increases the complexity of the flow pattern around the coil, which disrupts the smooth flow of the fluid. This turbulence enhances the mixing of the fluid layer in contact with the fin surface, leading to greater thermal interaction between the fluid and the fin material. As a result, heat exchange occurs more effectively, improving the overall efficiency of the heating or cooling process.

In contrast, other factors such as surface area and airflow resistance also play roles in heat transfer but do not address the mechanism by which rippled fins specifically enhance heat transfer. Simply providing a larger surface area or reducing airflow resistance may contribute to efficiency but is not the primary function of the rippling feature. The increased turbulence directly correlates with improved heat transfer rates, making it the correct reason for the improved efficiency attributed to this specific coil design.