Multi-dimensional coupling study of the thermal-hydraulic characteristics in a helical coil once-through steam generator under motion conditions

The helical coil once-through steam generator (HCOTSG) has a complex internal structure, and nonlinear oscillatory forces acting on the fluid under motion conditions affect its flow and heat transfer characteristics. Studying the thermal-hydraulic properties under these conditions is crucial for the design, operation, and maintenance of steam generators. This paper develops a three-dimensional flow and heat transfer model for the shell side and a boiling flow model for the tube side, proposing a cross-scale coupled heat transfer calculation strategy. Numerical simulations are conducted for normal operation and motion conditions of a typical HCOTSG. Results show that under normal operating conditions, the average temperatures at the shell-side and tube-side outlets are 558.73K and 572.55K, respectively, with the heat transfer in the two-phase region inside the tube accounting for 69.0 % of the total heat transfer. Under tilted conditions, the maximum pressure shifts in the tilting direction, and the isobar lines form an angle with the horizontal equal to the tilt angle of the steam generator. Under four swinging conditions (case 1–4), the shell-side outlet temperature fluctuation amplitudes are 0.9K, 2.9K, 4.6K, and 3.0K, respectively. Shortening the oscillation period and increasing the maximum swing angle result in more significant thermodynamic imbalances.