Numerical investigation of influence of non-condensable gas on steam jet condensation

doi:10.11949/0438-1157.20200728

Abstract

Abstract:

The influence of non-condensable gas on the direct contact condensing behavior and heat transfer characteristics of steam jet in subcooled water is investigated by two-dimensional axisymmetric numerical model. Based on Euler-Euler two-fluid model in CFX, the steam condensation is calculated with thermal phase change model. The composition variation of steam-air mixture is realized using species transport equation for the gas phase. The gas mass flow at nozzle outlet is 300 kg/(m²·s), and non-condensable gas is within 15%. The results show that non-condensable gas obstructs the direct contact between steam and subcooled water, forming the thermal resistance and deteriorating the condensation heat transfer. The thermal resistance and the length of jet region increase with the increase of non-condensable gas. While the condensation rate decreases with the increase of non-condensable gas. The presence of non-condensable gas prevents vapor from being condensed completely, and the remaining vapor is independent of the original non-condensable gas.

Key words: direct contact condensation, non-condensable gas, two phase flow, CFD

摘要：

通过二维轴对称数值模型研究了空气等不凝性气体对蒸汽射流与过冷水直接接触冷凝行为和传热特性的影响。采用CFX中的欧拉-欧拉双流体模型，结合热相变模型计算蒸汽的冷凝量、组分传递模型计算混合气体中组分的变化量；喷嘴出口的气体质量流量为300 kg/(m²·s)，不凝气体含量在15%以内。结果表明，不凝气体阻碍了蒸汽与过冷水直接接触，形成热阻，恶化了冷凝传热，且热阻随不凝气体含量增加而增加；冷凝速率随不凝气体含量增加而减小；射流区长度随不凝气体含量增加而增加；不凝气体的存在，使水蒸气不能被完全冷凝，而剩余水蒸气的含量与初始不凝气体含量无关。

关键词: 直接接触冷凝, 不凝气体, 两相流, 计算流体力学

CLC Number:

TK 124

Haibo LI, Maocheng TIAN, Xiaohang QU. Numerical investigation of influence of non-condensable gas on steam jet condensation[J]. CIESC Journal, 2020, 71(S2): 135-141.

李海波, 田茂诚, 屈晓航. 不凝气体对蒸汽射流冷凝影响的数值研究[J]. 化工学报, 2020, 71(S2): 135-141.

Figures/Tables 8

Fig.1 Simulation zone and mesh

Fig.2 Grid independency check

Fig.3 Comparison of radial temperature between CFD and experimental result

Fig.4 Comparison of radial total temperature between CFD and experimental result

Fig.5 Distribution of steam mass fraction

Fig.6 Distribution of gas volume fraction

Fig.7 Distribution of axial gas temperature

Fig.8 Distribution of radial gas temperature

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