The Effect Of Rolling On Flow And Heat Transfer Of Natural Circulation In Rod Bundle Channel

The natural circulation has the ability to improve the inherent safety of reactor because of its independence on the external pump.At the same time,the absence of noise is also of great significance for improving the concealment of ship.Therefore,natural circulation has found an increasingly wide utilization in the nuclear power plant on ships.In this paper,using deionized water as working fluid,the effects of inertia force provided by rolling condition on flow and heat transfer characteristics of natural circulation is investigated.The rolling angle is from 10° to 20° and the rolling period is from 15 s to 30 s.The experiment is on two different natural circulation loops.A narrow rectangular channel and a bundle channel are installed on the two loops respectively.The characteristics of flow and heat transfer in the bundle channel are mainly studied,and the related data in the rectangular experimental section are used as reference.The temperature distribution of a tube is obtained.It is found that the fluctuation amplitude of the wall temperature decays the phase delays along the radial direction.The equilibrium value is the same as the calculated result under the steady state.The pressure drop and its compositions of the coolant under rolling condition were analyzed.It is found that the additional pressure drop is the formation of two different waves with two different periods.The driving head caused by the density difference between hot and cold fluid also consists of two different waves with two different periods.The special characteristic of driving pressure drop is the main factor to form the shape of the parameters fluctuation wave under natural circulation.The resistance coefficient fluctuates when the fluctuation of mass velocity happens and is affected by the flow state of the coolant.If the flow under the rolling condition includes laminar flow and transition area,the resistance coefficient will increase greatly when entering the laminar flow area.The resistance coefficient of rod bundle channel varies little in its wide transition area,and the fluctuation of fluid resistance coefficient is very small when the flow is in transition region.Both time averaged characteristics and instantaneous characteristics of resistance coefficient in the rod bundle channel indicate that rolling has a certain effect on the increasing of resistance coefficient.With the increase of Reynolds number,the resistance coefficient reduces slowly in the transition zone.The empirical formula of heat transfer in the bundle channel is verified.It is found that the Markoczy formula can accurately predict the heat transfer in the bundle channel within its applicable range.The influence factors of natural circulation heat transfer under rolling condition are discussed.It is found that besides the circulation flow and additional inertia force,the reverse flow caused by rolling motion and the geometric structure of the channel also have influence on the heat transfer of natural circulation.