Numerical Simulation Of The Effect Of Spacer Grid Inner Structural Features On Sub-channel Thermal-hydraulic Characteristics

Considering the spacer grid in fuel assembly of PWR(Pressurized Water Reactor),it fixes rod bundle and has significant effect on thermal-hydraulic performance.It is the base of self-reliant design of spacer grid that understanding the effect of spacer grid on flow and heat transfer characteristics in detail.The structure of fuel assembly of PWR is 17×17 rod bundle with many spacer grids,however,5×5 rod bundle with one or two spacer grids is usually used in experiment and numerical investigation.Firstly,numerical simulation model and results was validated by Holloway experiment facility and results.Secondly,the flow and heat transfer characteristics of AFA-3G spacer grid was studied and the effects of it's components(straps,dimples,springs,and mixing vanes)on flowing resistance characteristic was analysed particularly.Thirdly,it was the first time that field synergy method was applied to analyse the heat transfer characteristic in rod bundle with spacer grid instead of mixing factor method.Lastly,the effects of mixing vane on heat transfer characteristics was compared,including 5 shapes and 3 arrangements of mixing vane.Numerical simulation validation indicated that SSG turbulence model is appropriate to simulating flow and heat transfer in rod bundle with spacer grid.As for the simulation results of AFA-3G spacer grid,it's mixing vane plays a crucial role in generating lateral velocity and enhancing heat transfer in rod bundle,and dimple enhance heat transfer in rod bundle by increasing turbulence intensity instead of changing the lateral velocity,meanwhile,the resistance coefficient of springs,mixing vanes,dimples,and straps increase in turn.Evaluation method research indicate:As for the mixing factor method,the flow was divided into three aspects of swirl-flow in sub-channel,cross-flow between adjacent sub-channel and turbulence intensity,and the heat transfer is analysed from the three aspects.Moreover,the applicability of the mixing factor method was greatly affected on lateral flow.As for the field synergy method,the heat transfer characteristic was analysed by synergy angle,and it is better applicable to the analysis of heat transfer in rod bundle with spacer grid,however,the method has little engineering value because of its oneness.For the effects of mixing vane on flow and heat transfer characteristics,mixing vane arrangement has a large effect on lateral flow structure.The pressure drop caused by the mixing vane of series arrangement,circle arrangement and cross arrangement decrease in turn,and the heat transfer indensity of series arrangement,cross arrangement and circle arrangement decrease in turn.The shape of mixing vane has a large effect on lateral flow velocity.For pressure drop and heat transfer indensity,the value of split mixing vane and separate mixing vane is the highest and the lowest,respectively.And,the other three mixing vanes is similar.The numerical simulation method and results have a better reference for the self-reliant design of spacer grid.