The flexibility of thermal power plants plays a critical role to accommodate high penetration of fluctuant renewable energy. Heat exchanger is the key device restricting the flexibility and energy efficiency of thermal power plants owing to its large thermal inertia. Therefore, evaluation of the additional entropy generation and transition time for the heat exchanger during transient processes is important, which are quantitative measures of the efficiency and flexibility. Consequently, dynamic models of a heat exchanger are developed. The dynamic behaviors of the heat exchanger are analyzed using numerical simulation and entropy generation analyses. The relationship between additional entropy generation and transition time is determined. Results show that: when flow rate decreases and temperature increases, this relationship is synergetic for hot fluid, metal wall and heat exchanger. The opposite correlation occurs when flow rate increases and temperature decreases. However, the cold fluid has the contrary tendency. The augmentation in heat transfer resistance reduces the additional entropy generation and transition time, whereas the effect of increasing the range of the boundary disturbances, such as temperature and flow rate, is on the contrary. For a heat exchanger, the additional entropy generation versus the transition time can be described by an exponential function.

中文翻译：

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瞬态过程中换热器的熵产生与过渡时间

火力发电厂的灵活性对于适应波动的可再生能源的高渗透率起着至关重要的作用。换热器具有较大的热惯性，是制约火力发电厂灵活性和能效的关键设备。因此，评估换热器在瞬态过程中的额外熵产生和过渡时间很重要，这是效率和灵活性的定量测量。因此，开发了热交换器的动态模型。使用数值模拟和熵生成分析来分析换热器的动态行为。确定附加熵生成和过渡时间之间的关系。结果表明：当流速降低、温度升高时，这种关系对于热流体、金属壁和热交换器是协同作用的。当流速增加和温度降低时，会发生相反的相关性。然而，冷流体具有相反的趋势。传热阻力的增加减少了额外的熵产生和转变时间，而增加边界扰动范围（如温度和流速）的效果则相反。对于换热器，附加熵产生与转变时间的关系可以用指数函数来描述。而增加边界扰动范围（如温度和流速）的效果则相反。对于换热器，附加熵产生与转变时间的关系可以用指数函数来描述。而增加边界扰动范围（如温度和流速）的效果则相反。对于换热器，附加熵产生与转变时间的关系可以用指数函数来描述。