起伏强度和周期对自然循环流动特性的影响

摘要

为了研究起伏运动对自然循环流动特性的影响，针对以5 MW低温核供热堆（ NHR）为基础建立的自然循环试验回路，自行开发计算程序研究起伏强度和周期对自然循环流动波动、加热段出口过冷度以及换热器二次侧出口过冷度的影响。建立数学模型，坐标系固定于试验本体上，采用流体相对速度，将起伏条件下自然循环问题转化为非惯性参考系问题，考虑起伏运动引入附加力对自然循环的影响，在重力g的前面乘一个随时间变化的系数（1－k· sin（ωdt ））。计算结果表明：起伏强度k越大，流量和温度波动越大；起伏周期T越大，流量波动越大且呈现出明显的非线性波动，大周期的起伏运动可能造成加热段出口出现饱和甚至沸腾的情况。对起伏运动影响自然循环机理的分析表明：起伏引入的附加作用力和重力一起构成一个交变力场，在有密度差的情况下形成自然循环驱动力，从而引起自然循环流动。%In order to investigate the effect of heaving motion on the flow characteristics of natural circulation, a cal-culation program was developed to study the influence of heaving strength and heaving cycle on the flow fluctuation of natural circulation, undercooling in the outlet of heating section and undercooling in the outlet of the secondary side of heat exchanger based on a natural circulation loop of 5MW experimental low temperature nuclear heating reactor ( NHR) .A mathematical model was established and the coordinate system was mounted on the experimental appara-tus. The issue of natural circulation under heaving condition could be treated as a problem in non-inertial reference frame.Considering the effect of an additional force resulting from heaving motion on natural circulation, a time-de-pendent coefficient (1-ksin(ωd t) ) was multiplied with gravity acceleration g.Calculation results indicated:higher level of heaving strength would lead to more serious fluctuation of flow and temperature;flow fluctuation exhibited an obvious nonlinear property and long-periodic heaving motion would result in saturation or even boiling.The analysis of the influence mechanism of heaving motion on natural circulation showed an alternating field composed of the addi-tional force and gravity, forming the driving force of natural circulation in case of flow density contrast.