Experimental results of heat transfer and pressure drop in a corrugated tube, used in chemical and food industry, are presented, for single-phase flow at moderate Reynolds numbers (100<Re<800). The working fluid is ethylene glycol, a highly viscous Newtonian fluid, in steady forced convection. The inside Nusselt numbers in the corrugated tube are improved very sensitively in comparison to the smooth wall, while the friction factor increases a factor of 1.83 - 2.45. The effects of Reynolds and Prandtl numbers on the enhanced heat transfer are presented. Based on the fitting of the experimental data, correlations of Nusselt number and friction factor are proposed for the periodically fully developed region