In nuclear reactor fuel assemblies, spacer grids are installed among the rod bundles to support the fuel rods and affect the flow field between rods. Mixing vanes, as a swirling device, are set on the upper apex of th...In nuclear reactor fuel assemblies, spacer grids are installed among the rod bundles to support the fuel rods and affect the flow field between rods. Mixing vanes, as a swirling device, are set on the upper apex of the spacer grid. Vortexes produced by mixing vanes move along the axial direction in subchannels and enhance the forced convection heat transfer between the rods and cooling-fluid medium. In this paper, a numerical simulation method was used to investigate vortex motion produced by typical AFA-3G spacer grids in a 5×5-rod bundle by Star-CCM+ software. The shear-stress transport k-ω model was used to simulate turbulence phenomena. A dimensionless parameter, Se, based on the absolute vorticity flux, was reported to specify the intensity of secondary flow. Its physical meaning is the ratio of inertial force to viscous force induced by secondary flow. The results are helpful to take advantage of spacer grids in a much more effective way in pressurized water reactors.展开更多
In this paper, we investigate the positive solutions to the following integral system with a polyharmonic extension operator on R^+_n:{u(x)=c_n,a∫_?R_+~n(x_n^(1-a_v)(y)/|x-y|^(n-a))dy,x∈R_+~n,v(y)=c_n,a∫_R_+~n(x_n^...In this paper, we investigate the positive solutions to the following integral system with a polyharmonic extension operator on R^+_n:{u(x)=c_n,a∫_?R_+~n(x_n^(1-a_v)(y)/|x-y|^(n-a))dy,x∈R_+~n,v(y)=c_n,a∫_R_+~n(x_n^(1-a_uθ)(x)/|x-y|^(n-a))dx,y∈ ?R_+~n,where n 2, 2-n < a < 1, κ, θ > 0. This integral system arises from the Euler-Lagrange equation corresponding to an integral inequality on the upper half space established by Chen(2014). The explicit formulations of positive solutions are obtained by the method of moving spheres for the critical case κ =n-2+a/n-a,θ =n+2-a/ n-2+a. Moreover,we also give the nonexistence of positive solutions in the subcritical case for the above system.展开更多
文摘In nuclear reactor fuel assemblies, spacer grids are installed among the rod bundles to support the fuel rods and affect the flow field between rods. Mixing vanes, as a swirling device, are set on the upper apex of the spacer grid. Vortexes produced by mixing vanes move along the axial direction in subchannels and enhance the forced convection heat transfer between the rods and cooling-fluid medium. In this paper, a numerical simulation method was used to investigate vortex motion produced by typical AFA-3G spacer grids in a 5×5-rod bundle by Star-CCM+ software. The shear-stress transport k-ω model was used to simulate turbulence phenomena. A dimensionless parameter, Se, based on the absolute vorticity flux, was reported to specify the intensity of secondary flow. Its physical meaning is the ratio of inertial force to viscous force induced by secondary flow. The results are helpful to take advantage of spacer grids in a much more effective way in pressurized water reactors.
基金supported by National Natural Science Foundation of China (Grant No. 11571268)Natural Science Basic Research Plan in Shaanxi Province of China (Grant No. 2017JQ1022)the Fundamental Research Funds for the Central Universities (Grant No. GK201802015)
文摘In this paper, we investigate the positive solutions to the following integral system with a polyharmonic extension operator on R^+_n:{u(x)=c_n,a∫_?R_+~n(x_n^(1-a_v)(y)/|x-y|^(n-a))dy,x∈R_+~n,v(y)=c_n,a∫_R_+~n(x_n^(1-a_uθ)(x)/|x-y|^(n-a))dx,y∈ ?R_+~n,where n 2, 2-n < a < 1, κ, θ > 0. This integral system arises from the Euler-Lagrange equation corresponding to an integral inequality on the upper half space established by Chen(2014). The explicit formulations of positive solutions are obtained by the method of moving spheres for the critical case κ =n-2+a/n-a,θ =n+2-a/ n-2+a. Moreover,we also give the nonexistence of positive solutions in the subcritical case for the above system.
