Experimental investigation of heat transfer and friction characteristic of fully developed gas flow in single-start and three-start corrugated tubes

18 helically corrugated tubes with different geometrical configurations for exhaust gas heat exchangers are investigated in this study. Experiments are carried out with air flow on the tube side, cooled by a secondary water flow. The dimensionless corrugation pitch p/di varies from 0.27 to 1.53, the dimensionless corrugation height e/di from 0.02 to 0.056, and the corrugation angle φ from 9.2° to 37.0°. To match the typical range of exhaust gas heat exchangers, the examined Reynolds number range is 5000