硅酸锂球床传热传质特性与吹扫气体流动的DEM-CFD耦合模拟

氦冷固态增殖包层是中国聚变工程实验堆（CFETR）的3种候选包层概念之一，氚增殖球床是包层的核心部件，采用硅酸锂颗粒作为氚增殖材料。球床结构对氚在球床内的输运行为及流动和传热均有重要影响。本文基于离散单元法（DEM）生成了满足氚增殖球床填充率要求的随机堆积结构，通过CFD计算获取了球床结构下氚在吹扫气体内的等效扩散系数及吹扫气体的流动特性，包括速度分布、压力分布及进出口压降；开展了外加热流及有内热源两种工况下球床等效导热系数的模拟。计算结果表明，球床结构下氚在吹扫气体内的等效扩散系数为二元气体扩散系数的40%；受球床结构影响，球床内存在流动迟滞区，壁面出现流动加速；拟合得到Ergun方程的黏性阻力系数C1=87；有内热源工况下的球床等效导热系数低于外加热流工况下的球床等效导热系数。

DEM-CFD Coupled Simulation for Determination of Character of Heat and Mass Transfer and Purge Gas Flow in Li4SiO4 Pebble Bed

The helium cold ceramic blanket is one of the three candidate blanket concepts of China Fusion Engineering Test Reactor (CFETR), and the tritium breeding pebble bed is the core component of the blanket, Li4SiO4 is selected as the tritium breeding material. The structure of the pebble bed plays an important role in the transport behavior, flow and heat transfer of tritium in the pebble bed. In this paper, a randomly packed pebble bed was generated based on the discrete element method (DEM), the equivalent diffusion coefficient of tritium in the pebble bed and the flow parameters of the purge gas were calculated by computational fluid dynamics (CFD) method, including velocity distribution, pressure distribution and inlet/outlet pressure drop. The equivalent thermal conductivity coefficient of pebble bed was simulated under two conditions: external heat flux condition and internal heat source condition. The calculation results show that the equivalent diffusion coefficient of tritium in the purge gas under the pebble bed structure is 40% of the binary gas diffusion coefficient. Flow hysteresis zone in the pebble bed can be observed while the flow of purge gas is accelerated at the near wall region. The viscous drag coefficients of the Ergun equation are obtained, of which C1 equals 87. The equivalent thermal conductivity coefficient of pebble bed under internal heat source condition is lower than that under external heat flux condition.