Investigation On Flow Resistance In Rod Bundle Under Rolling Condition

Rod bundle type structure is widely used in engineering of thermal power,chemistry and nuclear energy,etc.Due to the particularity of flow channel,the flow resistance characteristic of rod bundle is different from conventional tube.Affected by the additional inertial force in ocean operation conditions,the flow characteristic of rod bundle is different from steady-state.Knowledge of flow resistance in rod bundle under rolling condition can effectively improve the reliability of power equipment used in unsteady-state.In this paper,flow resistance chacteristic of a 3×3 square array rod bundle under steady-state and rolling codition was investigated experimentally.The rod bundle consists of9 stainless steel rods in square array installed in a square plexiglass channel,with the rod diameter of 8mm and the rod pitch of 10mm.In the experiment,air and water under normal temperature and pressure were used as working media,with air flow rate range of 0.06⁵.85m/s and water flow rate range of 0.08⁵.94m/s.Under rolling condition,the rolling amplitude ranged from 5^°to 15^°,and the rolling period ranged from 8s to 16s.Under steady-state condition,the rolling platform was fixed and the test section was in vertical steady-state.In single-phase flow condition,the frictional resistance of single-phase flow in the rod bundle was compared with conventional tube,and relative methods for predicting frictional factor in rod bundle was also compared with the experimental data.Based on the experimental data,a correlation for predicting frictional factor of the rod bundle was derived.In two-phase flow condition,several classical correlations for predicting frictional resistance of two-phase flow were evaluated against the experimental data.The results show that the homogeneous model can predict the experimental data well,but with relatively large deviations at low flow rates.In separated flow model,the Chisholm B and Muller-Steinhagen two-phase frictional resistance model can predict the experimental data very well.Meanwhile,the C factor in the Chisholm C model was also modified to predict the frictional pressure drop of two-phase flow in rod bundle.Under rolling condition,the test section was in sinusoidal rolling motion with the moving of rolling platform.In single-phase flow condition,the effect of rolling motion on transient flow rate and frictional resistance was analyzed,and the time-averaged frictional resistance of single-phase flow was also investigated.The results show that rolling motion has little effect on transient and time-averaged frictional resistance of single-phase flow in rod bundle.In two-phase flow condition,due to the periodical change of air and water distribution,the frictional resistance of two-phase flow changes periodically at low flow rates.The calculation methods of two-phase flow frictional resistance in steady-state can not be used in rolling condition.The effects of flow rates,rolling period and rolling amplitude on transient two-phase flow frictional were discussed.Considering the influence of rolling parameters,a modificatory factor F_roll was derived to show the periodical changes of the two-phase flow frictional resistance.The time-averaged two-phase flow frictional resistance was also investigated,the results show that rolling motion has little influence on the time-averaged two-phase flow frictional resistance,which can be calculated by the methods under steady-state.