摘要
针对超临界直流锅炉水冷壁系统在跨临界变压运行过程中的特殊流动与传热现象,在压力为19～25MPa、质量流速为300～800kg/(m^2·s)、外壁热流密度为60～250kW/m^2的工况范围内,对垂直上升受热管道内超临界水在跨临界动态过程中的流动与传热特性开展了实验研究。结果表明:在从超临界压力阶跃降低至亚临界压力的动态过程中,受热管内流体极其容易发生壁温飞升现象,该现象由近临界区流体发生的膜态沸腾(又称DNB传热恶化)引起。在近临界压力区,随着压力的升高并逐渐靠近临界压力,发生DNB传热恶化时的起始局部流体焓值会大幅度降低,而且恶化程度逐渐增强,本实验大多数工况甚至在过冷区就开始发生传热恶化现象,严重威胁锅炉水冷壁系统的安全运行。基于本文实验结果和对锅炉水冷壁系统运行的分析认为,当管内的局部流体焓值高于1 600kJ/kg时,水冷壁系统在跨临界动态过程中极有可能出现DNB传热恶化现象。本文实验结果可为超临界锅炉水冷壁系统跨临界变压运行期间的工况设计和调节提供指导。
Aiming at the special flow and heat transfer characteristics in the transcritical variable pressure operating process of the water wall in the supercritical once through boiler, experiments were conducted to investigate the transcritical dynamic flow and heat transfer characteristics in a vertical upward heated pipe under 19 25 MPa of pressure, 300 800 kg/（m^2 · s） of mass velocity and 60 250 kW/m……2 of heat flux on the pipe outerwall. The experimental results showed that a wall temperature rise always occurs in the transcritical dynamic process of the heated pipe, which is caused by the DNB heat transfer deterioration in the near critical pressure region. With the increase of the fluid pressure, the nearer is the fluid pressure close to the critical point, the lower is the fluid enthalpy needed to induce the occurrence of DNB, and the higher the deterioration degree will be. Moreover, DNB heat transfer deterioration even occurs when the working fluid is still in a subcooled state under most of our experimental cases, and this seriously threats the safe running of the water wall system. Based on the parameter range of our experiments and the analysis on the operation of water wall, DNB heat transfer deterioration is likely to occur in the transcritical dynamic process when the local fluid enthalpy in the heated pipe is higher than 1 600 kJ/kg. The experimental results in this research can provide a guidance for the design and adjustment of the operation conditions in the water wall of the supercritical once through boiler.
作者
刘佳伦
李会雄
冯渊
孔祥飞
雷贤良
LIU Jialun;LI Huixiong;FENG Yuan;KONG Xiangfei;LEI Xianliang(State Key Laboratory of Multiphase Flow in Power Engineering,Xi＇an Jiaotong University,Xi＇an 710049,China)
出处
《西安交通大学学报》
EI
CAS
CSCD
北大核心
2018年第11期1-8,126,共9页
Journal of Xi'an Jiaotong University
基金
国家重点基础研究发展计划资助项目(2015CB251502)
关键词
跨临界动态特性
近临界压力区
壁温飞升
DNB传热恶化
临界干度
transcritical dynamic characteristics
near critical pressure region
wall temperaturerise
DNB heat transfer deterioration
critical dryness
