球床模块堆停堆后自然对流传热特性数值研究

Numerical Simulation of Natural Convective Heat Transfer in Pebble Bed Modular Reactor

对冷却流体在球床模块堆内燃料颗粒填充区域中的流动和传热过程进行了研究。数值模拟突然停堆后燃料颗粒区在温差作用下的自然对流过程,分析了瑞利数Ra对燃料填充区域内流场、温度场和局部努塞尔数Nu以及壁面摩擦阻力系数的影响。计算结果表明:当球床模块堆突然停堆时燃料填充区域可形成加热壁面流体上升流动、冷却壁面下降流动的自然循环流动;随着Ra数增大,回流中心向上移动;沿轴向壁面局部Nusselt数和摩擦阻力系数存在极值,并且极值点随Ra数增大而向上移动;与氮气相比,氦气作为冷却介质停堆后具有更均匀的堆芯轴向温度分布。

A numerical simulations of single phase fluid flow and natural convective heat transfer is performed presented in pebble bed modular reactor （PBMR） with the consideration of the inertial and viscous forces. Flow behavior and heat transfer caused by inner heat source in a vertical annulus with saturated fuel particles is numerically investigated at the conditions of shutdown. Distributions of velocity, temperature, local friction coefficient of wall, and Nusselt number are predicted at the different Rayleigh numbers. Simulated results show that the natural circulation of fluid is formed between the heating wall with up-flow and the cooling wall with down-flow. The center of the vortex moves up with the increase of Reyleigh number. The extremum of local Nusselt number and friction factor of wall is existed, and the position moves up along axial direction with the increase of Rayleigh number. Comparing with nitrogen as a cooling medium, Helium fluid will give a more uniform distribution of temperature in the reactor core.