Flow boiling in helical channel is widely applied in advanced energy equipment such as lead-bismuth reactors. Investigating the bubble motion laws inside helical tubes can reveal the bubble dynamic behaviors under the coupled effects of centrifugal force and Dean vortex secondary flow induced by curved channels. A VOF-Lee phase‑change model incorporating a comprehensive·interphase force framework is established. In this paper, the RNG k-ε turbulence model is employed to capture the turbulent and secondary-flow characteristics of the curved flow channel, and bubble dynamics are numerically investigated at four representative circumferential locations of the helical tube cross-section.The results indicate that bubbles inside the helical tube move along a fixed direction toward the region between the inner and upper sides after lifting off from the wall. The bubble migration direction is influenced by centrifugal force, secondary flow drag force, and buoyancy force. Based on force‑balance analysis, a dimensionless number Zh is introduced, determined by bulk flow velocity, helical radius, and helix angle. The Zh number characterizes the migration angle of bubbles after lifting off inside the helical tube. This study elucidates the regulation mechanism bubble dynamics for nucleate boiling in helical channels under centrifugal force coupling fields, which provides a theoretical basis for the optimal design of helical boiling heat exchangers.

Helical Channel、Bubble migration direction、Force balance models、Centrifugal force