Study On Heat Transfer And Flow Field Of Rod Bundles With Spacer Grids

Numerical calculation method was applied in this paper to study the flow field and convective heat transfer characteristics in fuel rod bundles with grid spacer, in order to get the impact of grid spacer on fluid interchange of the fuel bundle channels.To ensure the rationality of the numerical algorithm,different turbulence models and different quality of grids was selected to check out the grid sensitivity and to determine the suitable numerical analysis method for positioning grid bundle narrow channel flow heat transfer: (1) change the line contact into surface contact between the rigid dimples and the rods and the springs; (2) in the form of hybrid grid, mesh generation of the rod bundle channels was given; (3) SST K-? turbulence model was selected to carry out the numerical calculation.Through the calculation of the two models with and without spacer grid and the comparison of velocity field and temperature field, it is found that the spacer grid can make the speed and temperature distribution on the same cross section more even, also it can effectively reduce heat flux of the rod walls and increase the convective heat-transfer ability.Then, this paper compared the coolant axial velocity distribution in the bundle under the condition of heating and without heating, and then concluded that due to the buoyancy lift effect on the flow field caused by density difference, the buoyancy lift can be neglected in the pressurized water reactor core channel.In order to study the impact of different structures of spacer grids on flow field and temperature field, this paper carried out a comparison on the temperature distribution coefficient, convection heat transfer coefficient of heat flux, turbulence energy, secondary flow and fusion coefficient of the three structures which are respectively with spacer grid channel, without mixed blade channel and only with mixed blade channel. It is found that due to the existence of mixed blade, great mixing effect was generated which made the temperature distribution and quality velocity distribution much more even.