Experimental Study on Heat Transfer Characteristics of Pure Steam with Incomplete Condensation in Vertical Tube
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摘要: 为研究纯蒸汽在竖直管内非完全冷凝的换热特性，使用内径为25 mm的换热管进行实验，入口压力为0.1~0.3 MPa，蒸汽质量流速为12~70 kg/(m2·s)。研究了入口压力、质量流速和质量含气率对管内平均和局部冷凝换热系数的影响，判别了冷凝过程中液膜流态，分析了液膜湍流度和液滴夹带对竖直管内冷凝换热的影响。结果表明：冷凝换热系数随着质量流速和质量含气率的增大而增大，竖直管的冷凝换热系数随着入口压力的升高而降低。实验中的液膜流型主要在过渡流区间，液滴夹带的发生使局部冷凝换热系数提高。对比4种环状流冷凝换热关系式计算结果发现，Shah的经验关系式基本偏差在±30%以内，平均绝对偏差（MAD）为18.91%。基于实验数据提出的经验关系式，其计算值和实验值基本偏差在±10%以内。Abstract: In order to study the heat transfer characteristics of pure steam with incomplete condensation in a vertical tube, an experiment was carried out using a heat exchange tube with an inner diameter of 25 mm, with an inlet pressure of 0.1~0.3 MPa and a steam mass flux of 12~70 kg/(m2·s). The effects of inlet pressure, mass flux and mass quality on the average and local condensation heat transfer coefficients in the tube were investigated. The liquid film flow pattern in the condensation process was identified, and the effects of liquid film turbulence and droplet entrainment on the condensation heat transfer in the tube were analyzed. It is shown that the condensation heat transfer coefficient increases with the increase of mass flux and mass quality. However, the condensation heat transfer coefficient of vertical tube decreases with the increase of inlet pressure. The liquid film flow pattern in the experiment is mainly in the transition flow region, and the occurrence of droplet entrainment increases the local condensation heat transfer coefficient. Four annular flow condensation heat transfer equations are compared. The results show that the basic deviation of Shah's empirical equation is within ±30%, and the mean absolute deviation (MAD) was 18.91%. An empirical correlation based on the experimental data is developed, and the basic deviation between the calculated value and the experimental value is within ±10%.
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图 3 实验段温度测点布置示意图
Figure 3. Arrangement of Temperature Measuring Points in Experimental Section
图 4 冷却水吸热量和水蒸气放热量结果的比较
Figure 4. Comparison of the Results of Cooling Water Heat Absorption and Steam Heat Release
图 5 平均冷凝换热系数随入口压力和入口蒸汽雷诺数变化曲线
Figure 5. Variation Curve of Average Condensation Heat Transfer Coefficient with Inlet Pressure and Inlet Steam Reg
图 6 平均冷凝换热系数随平均质量含气率变化
Figure 6. Variation of Average Condensation Heat Transfer Coefficient with Average Mass Quality
图 7 管内冷凝流型示意图
Rel—液相雷诺数
Figure 7. Schematic Diagram of Condensation Flow Pattern in Tube
图 8 使用Ciocolini准则判断液膜流动状态
Figure 8. Determination of Liquid Film Flow Pattern Zones by Ciocolini's Criterion
图 9 局部冷凝换热系数随入口压力变化曲线
Figure 9. Variation Curve of Local Condensation Heat Transfer Coefficient with Inlet Pressure
图 10 不同质量流速下局部冷凝换热系数的沿程变化
Figure 10. Variation of Local Condensation Heat Transfer Coefficient along the Tube at Different Mass Fluxes
图 11 局部冷凝换热系数实验值与Nusselt模型计算值比较
Figure 11. Comparison between the Experimental Value of Local Condensation Heat Transfer Coefficient and the Calculated Value of Nusselt Model
图 12 局部冷凝换热系数与韦伯数的关系
Figure 12. Variation of Local Condensation Heat Transfer Coefficient Versus We
图 13 局部冷凝换热系数实验值与经验公式关系式计算值的对比
Figure 13. Comparison of Experimental Results of Local Condensation Heat Transfer Coefficient with the Results Calculated by Empirical Correlation
图 14 本文经验关系式计算值与实验值对比
Figure 14. Comparison between the Calculated Results of the Proposed Empirical Correlation and the Experimental Values
表 1 测量仪表的型号与范围精度
Table 1. Type and Accuracy Range of Measuring Instruments
仪表 型号 测量范围/精度 涡轮流量计 LWGY-15 1~4 m3/h, 0.5% 涡街流量计 EH-Prowirl F 200 2.9~310 m3/h, 0.75% 压力传感器 Keller 0~10×105 Pa, 0.5% K型热电偶 校正后热电偶 0~140℃, ±0.2℃ T型热电偶 校正后热电偶 0~40℃, ±0.2℃ 
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表 2 实验参数不确定度
Table 2. Uncertainties of Experimental Parameters
实验参数 不确定度/% Ts/℃ ±0.2 G/(kg·m−2·s−1) ±0.65 Pin/105 Pa ±1.5 Tc/℃ ±0.5 Mc/(kg·s−1) ±0.5 h/(W·m−2·K−1) 2.02~10.56
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