Experimental Study on Boiling Two-Phase Flow Instability in a Single Helically Coiled Tube
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摘要: 加热通道内发生沸腾相变时会出现流动不稳定，研究螺旋管内沸腾两相流动不稳定过程对螺旋管式直流蒸汽发生器的设计和运行具有重要意义。本文通过在热工实验平台中开展单根螺旋管内的沸腾两相流动实验，研究螺旋管内发生沸腾两相流动时的流动不稳定现象，通过实验分析加热功率上升过程中螺旋管内流量压降等参数在不同时刻的变化规律以及频谱特征，并将发生的沸腾两相流动不稳定性进行分类。结果表明在实验参数范围：压力为0.1~3 MPa、流量为300~1200 kg/h、入口过冷度为20~100℃、实验段加热功率为0~200 kW时，螺旋管加热通道内随着功率的增加会先出现流量漂移不稳定性，当流量漂移至另一流量值后，在低出口含汽率情况下会出现高频低振幅的密度波振荡，在高含汽率下会出现低频高振幅的密度波振荡。通过实验研究还发现入口过冷度、入口流量以及系统压力的增加均会提高系统的稳定性。Abstract: The boiling phase change happened in the heating channel will induce flow instability. Thus, studying the two-phase flow instability in helically coiled tubes is of great significance in the design and operation of helical-coil one-through steam generators. In this paper, the boiling two-phase flow experiment in a single helically coiled tube is carried out on the thermal experimental platform, and the flow instability phenomenon when boiling two-phase flow occurs in the helically coiled tube is studied. In the experiment, the boiling two-phase flow instability is classified by analyzing the variation and spectral characteristics of parameters such as flow rate and pressure drop in the helically coiled tube at different times during the rise of heating power. The results show that when the experimental parameters are in the range of 0.1~3 MPa for pressure, 300~1200 kg/h for flow rate, 20~100℃ for inlet subcooling and 0~200 kW for heating power in the experimental section, the helically coiled tube heating channel exhibits flow drift instability as the power increases. Once the flow drifts to another flow value, low-amplitude high-frequency density wave oscillations occur under low steam quality conditions, while high-amplitude low-frequency density wave oscillations occur under high steam quality conditions. In addition, the increase of inlet subcooling, inlet flow rate and system pressure will improve the stability of the system.
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Key words:
- Helically coiled tube /
- Flow boiling /
- Flow instability /
- Density wave oscillations
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图 1 螺旋管内流动不稳定性实验回路流程图
1—水箱；2—过滤器；3—屏蔽电动泵；4—文丘里流量计；5—预热段；6—实验段；7—稳压器；8—混凝器；9—冷却回路主泵；10—换热器
Figure 1. Flow Chart of Experimental Loop of Flow Instability in Helically Coiled Tube
图 2 螺旋管本体及温度测点示意图
Figure 2. Diagram of Helically Coiled Tube and Temperature Measuring Point
图 3 单次流动不稳定实验工况下功率增加过程及16层盘管壁面温度变化
Figure 3. Power Increase Process and 16-layer Coil Wall Temperature Change under Single Flow Instability Test Condition
图 5 流量漂移结束后加功率过程中压差不稳定性波动特征
Figure 5. Characteristics of Unstable Fluctuation of Pressure Difference during Power Increase after Flow Drift
图 6 不同时间段内流量和压差瞬态变化特性
Figure 6. Transient Variation Characteristics of Flow and Pressure Difference in Different Time Periods
图 7 高频振荡向低频振荡过渡时流量和压差的瞬态变化特性
Figure 7. Transient Variation Characteristics of Flow and Pressure Difference during the Transition from High Frequency Oscillation to Low Frequency Oscillation
图 8 不同入口过冷度下流动不稳定性发生时的热流密度
Figure 8. Heating Flux for Flow Instability at Different Inlet Subcoolings
图 9 不同流量下流动不稳定性发生时的热流密度
Figure 9. Heating Flux for Flow Instability at Different Flow Rates
图 10 不同系统压力下发生流动不稳定时的热流密度
Figure 10. Heating Flux for Flow Instability at Different System Pressures
表 1 实验参数的不确定度
Table 1. Uncertainty of Experimental Parameters
参数 不确定度/% 参数 不确定度/% 长度 0.31 温度 0.167 面积 0.62 质量流速 1.0 压力 0.06 热损失 5.7 压差 0.06 入口过冷度 1.671 
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表 2 实验工况参数范围
Table 2. Parameters Range of Experimental Conditions
参数 参数范围 系统压力/MPa 0.1~3 初始入口流量/(kg·h−1) 300~1200 入口过冷度/℃ 20~100 实验段加热功率/kW 0~250
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