Pressure drop and heat transfer characteristics of single-phase flow in corrugated tubes for hot-water supply systems.

In this study, the pressure drop and heat transfer characteristics of single-phase flow in a smooth tube, a helical-grooved tube, and 12 corrugated tubes with an outer diameter of 12.7 mm were experimentally investigated, employing water as test fluid. Geometrical parameters considered for the corrugated tubes were corrugation depth (0.3, 0.5, and 0.9 mm) and corrugation pitch (4, 6, 8, 12, 15, 20, and 25 mm). Experiments were conducted by maintaining the inlet water temperature at 20°C and varying the flow rate from 0.005 to 0.18 kg/s. The effects of the difference in corrugation pitch and depth on the pressure drop and heat transfer characteristics of single-phase flow in the corrugated tubes were reported. Furthermore, the measured Nusselt numbers of each tested tube were compared under the same conditions of pumping power and a comprehensive evaluation method for heat transfer tubes was described.