Numerical Study Focusing On Void Distribution Of Subcooled Flow Boiling In Circular Tube Under Motion Condition

In the ocean environment,the nuclear power plant is affected by the winds,waves,and surges,which will induce ship motions.The ship motions mainly contain inclining,rolling and fluctuating motions.The additional transient force field varying with time and space is introduced.The flow and two-phase boiling heat transfer characteristics of the coolant in the nuclear reactor are affected by the ship motions.The ship motions also cause fluctuations in various thermal parameters,which are significantly different from those under static conditions.Therefore,based on the CFD code,the additional force source term under ocean condition is programmed by user-defined function,and the numerical research on the void fraction distribution for subcooled boiling flow in circular tube under ocean condition(including rolling and fluctuating)is carried out in this paper.In this paper,the additional source term caused by the ocean motion is added to the momentum equation by user-defined function.The subcooled boiling numerical calculations in the tube under static condition,rolling condition and fluctuating condition are performed.The phase distribution characteristics in the tube are analyzed and compared with the experimental data respectively.The CFD simulation results agree well with the experimental data,which verifies the applicability and accuracy of the numerical model used in this paper.The rolling motion has an obvious effect on the phase distribution in the circular tube.The local instantaneous void fraction distribution presents a periodic variation with the rolling motion.It is found that the local void fraction distribution of the subcooled boiling in a circular tube is different with different rolling parameters.When the rolling period is greater than 4 s,the local maximum void fraction decreases with the increasing period and its fluctuation period is consistent with the rolling period.When the rolling period is less than 4 s,the local maximum void fraction increases with the increasing period and the period of the local void fraction fluctuation is inconsistent with the rolling motion period.Meanwhile,it is found that the rolling amplitude has a significant effect on the phase distribution.The maximum local void fraction increases with the increasing amplitude since the vapor phase distribution is mainly affected by the acceleration of gravity in the direction perpendicular to the flow direction.In addition,the effects of heat flux,mass flow rate,pressure and tube diameter on the phase distribution of subcooled boiling under rolling condition are consistent with those under static condition.In this paper,the distribution characteristics of local parameters in the tube under rolling condition are studied.The coupling analysis of the influence of phase distribution,velocity distribution and temperature distribution on the local instantaneous heat transfer characteristics at the wall under rolling condition is carried out.The local heat transfer coefficient fluctuates periodically with the rolling motion.The peak value of the local heat transfer coefficient appears at the moment when the motion moves to the negative maximum inclination angle.The minimum of the local heat transfer coefficient appears at the moment when the motion moves to the positive maximum inclination angle.In addition,the fluctuation range of the wall heat transfer coefficient under rolling condition is ± 9% compared with that under static condition.