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

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: theta(m)5 degrees T8s, theta(m)10 degrees T8s, theta(m)15 degrees T8s, theta(m)15 degrees T12s, and theta(m)15 degrees T16s, where theta(m) 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 (a(roll))(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 a(a) 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 x 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 theta(m)5 degrees T8s, theta(m)10 degrees T8s, and theta(m)15 degrees T8s. However, it presents two peaks under the conditions of theta(m)5 degrees T12s, theta(m)15 degrees T8s, and theta(m)15 degrees T8s. The axial resultant acceleration gives rise to the fluctuation of bubble rising velocity. (C) 2014 Elsevier Ltd. All rights reserved.