不均匀加热与节流对平行通道不稳定性的影响

Effect of nonuniform heating and throttling on flow instabilities in parallel channels

摘要:

为研究反应堆内轴向热流不均匀分布、径向不均匀加热和入口节流对密度波不稳定的影响,利用RELAP5/MOD4.0程序对强迫循环平行通道系统进行数值模拟. 由程序中的非平衡非均相模型和半隐式数值格式所得计算结果与实验数据符合较好. 对比轴向热流线性分布及余弦分布工况下的流动不稳定边界,并做出积分热流沿通道长度的变化曲线以分析其机理,还获取了径向不均匀加热与入口节流工况下系统和通道的临界相变数. 结果表明:轴向热流不均匀分布时系统的稳定性取决于沸腾边界的位置以及积分热流沿通道的分布. 与轴向热流均匀分布相比,轴向热流线性增大或减小分别使系统稳定性增强或减弱；入口过冷度较低时,轴向热流余弦分布提高系统稳定性;入口过冷度较高时,系统稳定性可能增强也可能减弱. 与轴向热流余弦分布相比,峰值偏向入口或出口分别会降低或提高系统稳定性. 径向不均匀加热对系统稳定性影响较小. 增大径向入口节流不均匀性时系统稳定性有减小的趋势,增大任一通道入口节流系数均可提高系统的稳定性.

Abstract:

To investigate the effect of nonuniform axial heat flux distribution and uneven radial heating and inlet throttling on density wave oscillations in reactors, RELAP5/MOD4.0 code is applied to conduct numerical simulations of a parallel channel system in forced circulation loops. The results obtained from the combination of non-homogeneous non-equilibrium model and semi-implicit numerical method in the code agree well with experimental data. Flow instability boundaries of linear and cosine axial heat flux distribution are compared and integral of axial heat flux along the channel is plotted to analyze the detailed mechanism. Besides, the critical phase change numbers of system and each channel under different nonuniformity of radial heating and inlet throttling are calculated. The results show that the system stability depends on the location of boiling boundary and the integral of axial heat flux along channel. Increasing or decreasing axial heat flux linearly has stabilizing or destabilizing effect compared with uniform axial heat flux respectively. Cosine heat flux increases system stability at low inlet subcooling. However, system stability could either be strengthened or weakened at high inlet subcooling. Inlet-peaked heat flux decreases system stability while outlet-peaked heat flux increases system stability compared with cosine heat flux. The influence of uneven radial heating on system stability is not significant. System stability decreases with nonuniformity of radial inlet throttling and it increases if the inlet throttling of one channel is increased.