The flow and heat transfer characteristics of oscillatory flow in a smooth tube and two-start spirally corrugated tube were investigated by using a three-dimensional unsteady numerical simulation. The simulation was performed under variable properties, pressure and velocity conditions, with helium (He) as the working medium. The results indicated that longitudinal swirl vortexes were generated with the guidance of a spirally corrugated channel in a two-start spirally corrugated tube in which the fluid flowed spirally forward. The heat absorption (Q) of a two-start spirally corrugated tube exceeded that of a smooth tube (Q(0)). The difference in the average heat absorption was 561 W and the average of Q/Q(0) was 1.36. At the same inlet and wall temperatures of 575 K and 1000 K, the outlet temperature of the smooth and spirally corrugated tube increased by 205 K and 365 K, respectively. Therefore, the spirally corrugated tube presented a superior heat transfer performance when compared to that of the smooth tube. Two types of performance evaluation criterion (PEC) calculation methods in a cycle were used to evaluate the heat transfer enhancement of a spirally corrugated tube. The average value of transient PEC in a cycle was 1.69, and the PEC calculated by average parameters in a cycle was 1.38. When compared with the change of pressure in a MPa level in a heating tube, the pressure drop of hundreds of Pa was negligible, However, the outlet temperature of the heating tube could be subject to an additional temperature increase of hundreds of K with the negligible pressure drop of hundreds of Pa. Thus, the benefits were apparent for the heat transfer enhancement by using spirally corrugated tubes in the heater. (C) 2018 Elsevier Ltd. All rights reserved.