Research On Frictional Resistance Of Two-phase Flow In Rectangular Ducts In Rolling Motion

The additional force arising from rolling motions may affect the flow and heat-transfer characteristics of the liquid in the reactor.Compared to round pipes,rectangular ducts present the characteristics of compact layout and high heat-transfer efficient,which can meet the requirements of miniaturization of the heat exchanger in nuclear power plant,but results in the increasing of flow resistance.Carrying out the experiment of thermal-hydraulic properties in the rectangular ducts under rolling conditions can provide data and theoretical references for the design and service of nuclear power plant.In this research,the frictional characteristic of two-phase flow in upwards rectangular ducts was investigated in rolling motion under ambient temperature and pressure,and the frictional resistance of different two-phase flow patterns was studied under vertical,inclined and rolling condition.The range of period and amplitude of rolling motion were chosen to be 8s?16s and 50°?30° for comparing the two-phase frictional resistance under different rolling condition.Different homogeneous and separated flow model were chosen to predict the frictional pressure for three flow patterns.The results showed that all homogeneous models can well predict the frictional pressure drop in narrow ducts,but can be used to calculate the frictional pressure of bubbly flow and annular flow in normal ducts.In separated flow model,only Lee-Lee model showed a good prediction for the frictional pressure.The frictional resistance of bubbly flow in rolling motion is closely related to the void fraction and local parameters in the cross section.A narrow duct is beneficial to restrain the effect of rolling motion on frictional resistance of bubbly flow,and the averaged value together with the amplitude decreased with the increasing of the gas flow rate.Increasing the rolling amplitude would result in the increasing the amplitude of frictional pressure,and it seemed that the rolling amplitude showed stronger influence than rolling period.A new correlation for predicting the transient frictional pressure was given by including the influence of rolling parameters and was validated against the experimental data.Rolling motion effected on the slip of air and water periodicity,which resulted in the changing of frictional characteristic.Rolling motion had little effect on bubbly flow in the cross section.The effect of rolling movement on the resistance characteristic of bubble flow depends on the rolling parameters(rolling period and rolling amplitude),gas flow rate and the size of rectangular ducts.Research on the flow resistance characteristic of slug flow rolling condition was mainly carried out by the establishment of the resistance model.According to the experimental results,the gas and liquid velocity together with the void fraction in Taylor bubbles,liquid slug and the whole slug flow unit was calculated,so the prediction of frictional pressure in rectangular ducts can be given.The predicted result showed good applicability in narrow ducts,and the reasons for less applicable in the wide ducts was given for improvement.Frictional pressure of annular flow under rolling motion was related to the void fraction and the thickness of liquid film.The void fraction and the thickness of liquid film in rectangular duct under vertical and inclined condition were investigated,and the prediction of frictional pressure drop was given considering the heterogeneity of the liquid film and the inconsistent of wall shear stress on both sides,which showed well agreement with the experimental data.A new correlation for predicting the transient frictional pressure of annular flow was given based on homogeneous model by including the influence of rolling parameters and was validated against the experimental data.