热浮力对球床反应堆内燃料球表面对流传热的影响

Effect of thermal buoyancy on the convective heat transfer on the surface of fuel pebbles in a pebble bed reactor

采用大涡模拟(LES)方法研究了低雷诺数(Re=1015)下热浮力对球床面心立方(FCC)单元内的局部流动和传热的影响。为了精确求解燃料球接触面附近的流场,球间接触点表达为面接触,采用结构化网格处理。研究结果表明:热浮力的存在会抑制球床各层平均速度的波动;靠近燃料球表面处的相对时均速度和相对时均温度受热浮力影响变化较大;在中心流场区域,热浮力的存在会减小流场中速度分布的不对称性,使速度最大降低约10%,时均温度至少升高约20%;球表面上尤其在顶部及接触面附近受热浮力影响明显,努塞尔数Nu最大降低约6%。

In this paper,large eddy simulation(LES)method was adopted to study the influence of thermal buoyancy at low Reynolds number(Re=1015)on local flow and heat transfer in a facecentered cubic(FCC)of a pebble bed.The plane-plane contact among the pebbles and structured grid were adopted to accurately solve the flow field near the interface of fuel pebbles.It is found that the existence of thermal buoyancy could restrain the fluctuation of averaged velocity at each layer.The influence of thermal buoyancy on relative time-averaged velocity and relative timeaveraged temperature near the surface of fuel pebbles was great.In the center of flow field,the existence of thermal buoyancy could reduce the asymmetry of velocity distribution.The velocity decreased by 10%at most and the time-averaged temperature increased by 20%at least.On the spherical surface,especially at the top and near the interface,obvious influence of thermal buoyancy was observed.And the Nusselt number Nu number decreased by 6%at most.