Numerical Study on Corrosion and Heat Transfer Coupling Characteristics of Heat Exchange Tube in LBE Environment
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摘要: 为研究铅铋合金（LBE）换热管内的氧化腐蚀现象及氧化层生长对于换热的影响，本文基于氧化腐蚀模型、传质控制腐蚀模型、氧化层热阻模型，利用FLUENT软件结合用户自定义函数（UDF）对铅铋介质换热管在9500 h内的腐蚀与传热过程进行模拟计算。研究结果表明：基础工况运行9500 h后，磁铁矿层和尖晶石层的平均厚度分别达到23.84 μm和25.02 μm。由于氧化层生长引入额外热阻，壁面平均热阻增加7.8%，换热管壁面温度和出口温度分别升高0.26 K和0.2 K。入口温度越低，氧化层的厚度越小，但厚度随时间逐渐增加，说明相较于去除过程，氧化层生长过程占据主要地位。入口氧浓度越低，氧化层的厚度同样越小，当氧浓度降低到10−7%时，换热管入口磁铁矿层出现局部完全溶解，且溶解范围随时间逐渐扩大。尖晶石层由于较低的去除速率，接触铅铋后依然保持增长，对结构材料起到主要的保护作用。
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关键词:
- 铅铋合金（LBE）换热管 /
- 计算流体动力学（CFD） /
- 氧化腐蚀 /
- 传质控制腐蚀 /
- 氧化层热阻
Abstract: In order to study the phenomenon of oxidation corrosion in LBE heat exchange tube and the effect of oxide layer growth on heat transfer, this study simulates the corrosion and heat transfer process of LBE heat exchange tube in 9500 hours based on the oxidation corrosion model, mass transfer controlled corrosion model and oxide layer thermal resistance model by using the FLUENT in combination with the user-defined function (UDF). The results show that after 9500 hours of operation under baseline conditions, the average thickness of the magnetite and spinel layers reached 23.84 μm and 25.02 μm, respectively. Due to the additional thermal resistance introduced by the oxide layer growth, the average thermal resistance of the wall increased by 7.8%, and the wall temperature and outlet temperature of the heat exchange tube increased by 0.26 K and 0.2 K, respectively. The lower the inlet temperature, the smaller the thickness of the oxide layer is. However, the oxide layer thickness gradually increases with time, indicating that the oxidation layer growth process plays a dominant role compared to the removal process. The lower the inlet oxygen concentration, the smaller the thickness of the oxide layer is. When the oxygen concentration is reduced to 10−7 wt%, the magnetite layer at the inlet of the heat exchange tube appears local dissolution, and the scope of dissolution gradually expands. The spinel layer, on the other hand, continues to grow after exposure to LBE due to low removal rate and provides the main protection for the structural material. -
图 1 磁铁矿层或尖晶石层接触LBE时的化学反应
Figure 1. Chemical Reaction of the Magnetite or Spinel in Contact with LBE
图 2 磁铁矿层厚度与尖晶石层厚度的模拟值与实验值的对比
Figure 2. Comparison of Simulated and Experimental Values of Magnetite and Spinel Thickness
图 4 氧化层厚度、壁面平均热阻、换热管出口和壁面温度随时间的变化
Figure 4. Variation of Oxide Layer Thickness, Average Wall Thermal Resistance, Heat Exchange Tube Outlet Temperature and Wall Temperature with Time
图 5 不同温度下氧化层厚度、壁面平均热阻随时间的变化
Figure 5. Variation of Oxide Layer Thickness and Average Wall Thermal Resistance with Time at Different Temperatures
图 6 不同氧浓度下氧化层厚度及壁面平均热阻随时间的变化
(1)—氧浓度5×10−6%；(2)—氧浓度1×10−6%；(3)—氧浓度1×10−7%。
Figure 6. Variation of Oxide Layer Thickness and Average Wall Thermal Resistance with Time at Different Oxygen Concentrations
图 7 1×10−7%氧浓度磁铁矿层和尖晶石层在不同时间下的轴向厚度分布
Figure 7. Axial Thickness Distribution of Magnetite Layer and Spinel Layer at Different Time under 1×10−7% Oxygen Concentration
表 1 工况一览表
Table 1. List of Operating Conditions
工况序号 氧化层种类 温度/℃ 氧浓度/10−7% 流速/(m·s−1) 1 尖晶石 450 1 2 2 尖晶石 550 1 2 3 尖晶石 450 11 2 4 尖晶石 500 10 1 5 磁铁矿 450 11 2 6 磁铁矿 500 10 1 
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表 2 网格无关性分析
Table 2. Grid Independence Analysis
序号 网格数 出口最高
温度/K磁铁矿层
最大厚度/μm尖晶石层
最大厚度/μm网格1 1273935 806.47 3.07 2.79 网格2 2557035 806.48 3.09 2.82 网格3 4651179 806.49 3.11 2.83 网格4 6406335 806.49 3.12 2.84 网格5 8239335 806.49 3.12 2.84
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