Numerical study and mechanism analysis of heat transfer in a helical tube enhanced by sinusoidal pulsating flow combined with an annular corrugated structure

As an efficient heat transfer enhancement device, a helical tube is widely used in various industrial applications and its composite heat transfer enhancement technique has also elicited widespread attention. This study proposes an innovative technique that combines sinusoidal pulsating flow with annular corrugation and then applies it to a helical tube. Numerical simulation is performed to investigate the effects of pulsation flow parameters on the structure of the flow field and the efficiency of heat transfer. Then, the mechanism of heat transfer improvement is revealed. Results show that the collaborative effects of pulsating flow and annular corrugation can enhance the turbulent intensity of the mainstream fluid. In addition, the structure of the secondary flow field is changed and synergy between the velocity field and the temperature field is enhanced further. Within the studied range, the average Nusselt number (Nu) of sinusoidal pulsating flow in a helical tube with an annular corrugated wall structure is enhanced by 16.05 % and 10.52 % compared with that of steady flow in a smooth helical tube and an annular corrugated helical tube, respectively. With an increase in the dimensionless pulsation frequency (Wo), Nu initially increases and then decreases, while the friction resistance coefficient (fD) gradually increases. As the dimensionless pulsation amplitude (A0) increases, Nu and fD gradually increase. The comprehensive thermal performance evaluation index exhibits a maximum observed value of 1.241 when Dean number = 7709, Wo = 25, and A0 = 0.25 within the studied range.