中等过冷度下含不凝性气体蒸汽冷凝传热特性

Analysis of experiments for steam condensation in presence of non-condensable gases with moderate wall subcooling

通过对竖直圆管外表面含不凝性气体蒸汽在中等壁面过冷度条件下的冷凝传热实验研究，分析了混合气体压力0.4～0.6 MPa、空气含量0.07～0.52以及壁面过冷度13～25℃时，蒸汽的冷凝换热特性，给出了冷凝传热过程中的经验关联式，并对氦气的存在及其对换热过程的影响进行了初步分析。结果表明：在混合气体压力及不凝性气体含量不变的条件下，壁面过冷度的降低利于冷凝传热系数的增长；所得到的经验关联式在低过冷度条件下能较好地对换热过程进行预测，且其与实验值的误差在±15%以内；实验条件下未发生氦气分层现象，相同不凝性气体质量分数条件下，氦气的存在会使冷凝传热系数降低约20%。

An experimental investigation was conducted to evaluate the steam heat removal capacity in the presence of non-condensable gases （e.g. air, helium） over a vertical tube external surface under moderate wall subcooling. Under steam/air condition, condensation heat transfer coefficients were obtained under wall subcooling ranging from 13℃ to 25℃, total pressure ranging from 0.4 MPa to 0.6 MPa and air mass fraction ranging from 0.07 to 0.52. The experiments for the influence of wall subcooling on steam condensation heat transfer with a fixed pressure and air mass fraction were made. Under the same pressure with the same non-condensable gases mass fraction, the effect of wall subcooling on condensation heat transfer coefficient with non-condensable gases was negative. An empirical correlation for heat transfer coefficient was developed, covering all data points within 15%. Under steam/air/helium （simulating hydrogen） condition, the effect of helium mole fraction in non-condensable gases on heat transfer coefficient was investigated under wall subcooling ranging from 18℃ to 27℃, total pressure ranging from 0.53 MPa to 0.6 MPa, steam mass fraction ranging from 0.6 to 0.92 and helium mole fraction in non-condensable gases 0.3. The condensation heat transfer coefficients obtained from steam/air/helium condition were lower than those obtained from steam/air case. Helium stratification was not found under the experimental conditions. With the same non-condensable gases mass fraction, presence of helium lowered condensation heat transfer coefficient by around 20%.