Analysis on Thermal Hydraulic Characteristic of Helical Coiled Tube Steam Generator of Liquid Metal Fast Reactor Based on Drift-Flux Model
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摘要: 在液态金属快堆螺旋管蒸汽发生器中,存在一个普遍问题,其一次侧的进、出口温差大幅升高,二次侧出口蒸汽过热度显著增大,这给其设计及运行带来了挑战。基于离散网格法建立了液态金属快堆螺旋管蒸汽发生器热工水力分析模型。模型对整个一、二次侧回路进行网格划分,采用漂移流模型计算二次侧水-水蒸汽的流动与传热,并在一次侧计算中采用液态金属物性与流动传热关联式;采用内节点法对壁面划分网格,考虑两侧流体与管壁间的对流换热以及壁面导热。基于实验数据验证模型可靠性。以铅铋快堆为例,研究不同入口条件下蒸汽发生器的热工水力特性。研究发现一、二次侧之间的壁面热流密度沿程分布极为不均匀,且热流密度峰值极高。算例中壁面热流密度最大值达到1361 kW/m2,最大值与最小值间相差数十倍到数百倍。随着一次侧入口铅铋温度以及铅铋流速的增加,二次侧过冷水区及两相区长度明显缩短,过热蒸汽区长度明显增大;同时,壁面热流密度峰值向螺旋管入口方向移动,二次侧工质压降明显增大。Abstract: In the helical coiled tube steam generator of liquid metal fast reactor, the temperature difference between inlet and outlet of the primary side increases significantly, and the outlet steam superheat degree of the secondary side also increases significantly. This is a common problem and brings new challenges to the safe operation of steam generator. Based on the discrete grid method, a computational model suitable for the thermal-hydraulic characteristics of the helical coiled tube steam generator of the liquid metal fast reactor was established. The model meshed both the primary side circuit and the secondary side circuit. The drift-flux method was adopted to calculate the flux and heat transfer process of two-phase steam-water flow along the helical coiled tube, and the correlations of liquid metal physical properties and liquid metal heat transfer were selected for the primary side calculation. Meanwhile, the inner node method was adopted to divide the tube wall into a series of grids, and the heat conduction equations were built to accurately simulate the convective heat transfer between the fluid on both sides and the tube wall, as well as the wall metal heat conduction process. The present model was then verified based on the experimental data. Finally, taking the lead-bismuth fast reactor as an example, the thermal-hydraulic characteristics of the helical coiled tube steam generator were analyzed under different inlet conditions. It was found that the wall heat flux distribution between the primary and secondary sides is extremely uneven along the helical coiled tube steam generator, and the peak wall heat flux is extremely high. The maximum value of the wall heat flux reaches 1,361 kW/m2, and the difference between the maximum value and the minimum value is tens to hundreds of times in the example of this paper. With the increase of lead-bismuth temperature and velocity at the inlet of primary side, the lengths of the subcooled water zone and the two-phase zone on the secondary side are significantly shortened, and the length of the superheated steam zone is significantly increased. Meanwhile, the peak wall heat flux moves towards the inlet of the helical coiled tube, and the total pressure drop of the working medium on the secondary side also increases significantly.
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表 1 本文模型中流动阻力及传热关联式的选择
Table 1. Flow Resistance and Heat Transfer Correlations Selected in the Present Model
表 2 本文模型计算结果与设计值[26]对比
Table 2. Comparison between the Calculation Results of the Present Model and the Design Parameters
蒸汽发生器运行参数 原始设计值 本文计算值 误差/% 单台功率/MW 125 124.59 0.3 一次侧出口温度/℃ 292 292.23 0.1 一次侧压降/kPa 72 68.60 4.72 二次侧出口温度/℃ 317 319.12 0.67 二次侧压降/kPa 296 284.20 3.99 表 3 本文模型计算结果与设计值[28]对比
Table 3. Comparison between the Calculation Results of the Present Model and the Design Values
蒸汽发生器运行参数 原始设计值 本文计算值 误差/% 一次侧出口钠温度/℃ 308.85 307.92 0.3 二次侧出口蒸汽温度/℃ 456.85 453.75 0.68 表 4 本节算例中螺旋管蒸汽发生器结构、工况参数
Table 4. Structural Parameters and Operation Conditions of Helical Coiled Tube Steam Generator Studied in the Examples of this Section
参数 参数值 结构参数 螺旋管长度/m 20 螺旋直径/mm 500 螺旋上升角 6° 管道内径/mm 9 管道外径/mm 12.2 工况参数 二次侧入口压力/MPa 5.0 二次侧进口质量流速/(kg·m−2·s−1) 1000 二次侧进口温度/℃ 150 一次侧进口铅铋温度/℃ 450 一次侧进口铅铋流速/(m·s−1) 0.7 -
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