Heat transfer and friction characteristics of spirally corrugated tubes for outer ammonia condensation

Experimental research was conducted to evaluate the heat transfer and friction characteristics of spirally corrugated tubes for the outer condensation of ammonia. The tested tubes were made of stainless steel with 18/20 mm nominal diameters. Experiments were carried out at saturation temperature of 40 °C and wall subcoolings from 1 to 7.5 °C. Heat transfer coefficients on both sides of the tubes and friction factors inside the tubes were experimentally determined. The condensation coefficients turned out to be close to those of a smooth tube. The inner heat transfer enhancement factors ranged from 2.11 to 2.53. The friction factors were 4–5 times higher than those of a smooth tube. The overall heat transfer performance of the corrugated tubes was around 1.27 times higher than the performance provided by smooth tubes.