Experimental and theoretical analysis of bubble rising velocity in a 3 × 3 rolling rod bundle under stagnant condition

• Axial additional accelerations are studied under rolling condition.
• Factors affecting axial additional accelerations are investigated.
• Axial resultant acceleration in rolling motion is studied.
• Effect of rolling motion on bubble rising velocity is investigated.
• Axial resultant acceleration affects the fluctuation of bubble rising velocity.

As a typical ocean condition, rolling motion has a significant effect on the two-phase flow systems. The influences of rolling motion on the bubble rising velocity were studied theoretically and experimentally. Five following rolling conditions were investigated: θm5°T8s, θm10°T8s, θm15°T8s, θm15°T12s, and θm15°T16s, where θm is the maximum rolling angle and T represents the rolling period. The theoretical results show that the fluctuation amplitude of axial tangential acceleration is much larger than that of axial centrifugal acceleration. Although the amplitude of (aroll)a is much lower than the value of axial gravitational acceleration, it shows evident influence on the phase curve of axial resultant acceleration. The difference between adjacent troughs in the phase curve of aa increases as a result of a decreased rolling period or increased rolling amplitude and parameter y′, where y′ represents the horizontal coordinate that is attached to the frame and is in the plane in which the rolling side-to-side motion takes place. The experiments were conducted in a 3 × 3 rod bundle under stagnant condition. The experimental results show that the fluctuation amplitude of bubble rising velocity increases with the increase in rolling amplitude or the decrease in rolling period. In addition, the effect of rolling amplitude is much more significant than that of rolling period. The fluctuation of bubble rising velocity presents one peak in one rolling period under the conditions of θm5°T8s, θm10°T8s and θm15°T8s. However, it presents two peaks under the conditions of θm15°T12s and θm15°T16s. The axial resultant acceleration gives rise to the fluctuation of bubble rising velocity.