Numerical Study On Heat Transfer Enhancement Of The Steam Generator Tubes In Small Nuclear Reactor

With the advantages of high safety,modularization of design and manufacture,long refueling cycle and wide range of application,small integrated nuclear reactor has aroused extensive attention in the field of advanced nuclear energy.As one of the key components of small integrated nuclear reactor,the flow and heat transfer performance of once through steam generator has an important impact on the safety,reliability and economy of nuclear reactor.However,due to the miniaturization development demand of the nuclear reactor structure,the heat transfer performance of steam generator is limited by the space size.So it is a key issue to optimize the heat transfer performance of steam generator in the development of small integrated nuclear reactor.In this paper,simplified models of the curved heat transfer tubes and the corrugated heat transfer tubes were established based on the design parameters of the IRIS steam generator.Numerical simulations were conducted for the coolant flow and heat transfer characteristics in the heat transfer tubes under the help of RPI boiling model.Then a thorough parametric investigation was conducted for diverse tube structure parameters like pitch,coil diameter,corrugation length and corrugation height by employing the passive enhanced heat transfer technology on the tubes.The main conclusions of this research are listed as follows:(1)The reason for the heat transfer enhancement of curved tubes is that the fluid forms a secondary flow in the tube,which improves the turbulent intensity of the fluid,so that the heat transfer performance of the curved tubes is better than that of the vertical tubes.(2)The reason for the heat transfer enhancement of corrugated tubes is the severely turbulent fluctuation with the boundary-layers redevelopment.The fluid in corrugated tubes can be affected by throttling and ejection effects,and create vortices in the wave peaks,which will destroy the formation of the boundary layer.The flow channel shrinks sharply at the straight sections or wave roughs,thereby enhancing the degree of fluid disturbance and the heat transfer performance.(3)The structure optimization researches of the spiral tubes find that coil diameter dominates over pitch.The pitch has little effect on the flow and heat transfer of the spiral tubes.While the change of coil diameter can get a great influence on the boiling heat transfer coefficient and the vapor mass fraction,especially in the case of high inlet velocity.The larger the coil diameter,the better the heat transfer performance.Therefore,it is better to increase the coil diameter to enhance the heat transfer effect than to change the pitch.(4)The structure optimization researches of the corrugated tubes present the interval optimum principle of heat transfer enhancement for various structure parameters,which is superior for tall and broad corrugation under the corrugated tubes and more suitable for tall and dense corrugation under the sinusoidal corrugated tubes.By changing the proportion of the corrugation length,the heat transfer effect of the corrugated tubes can be enhanced to1.20～1.40 times than that of the smooth straight tube,and 1.05～1.37 times by changing the corrugation height.By changing the distance between the corrugations,the heat transfer enhancement of the sinusoidal corrugated tubes can reach 1.21～2.03 times of that of the smooth straight tube,and the heat transfer enhancement effect of changing the corrugation height can reach 1.06～2.03 times.