Ashrafizadeh Seyed Ali
Department of Chemical Engineering, Dezful Branch, Islamic Azad University, Dezful 6461645169, Iran.
Entropy (Basel). 2019 Jun 19;21(6):606. doi: 10.3390/e21060606.
In recent decades, the second law of thermodynamics has been commonly applied in analyzing heat exchangers. Many researchers believe that the minimization of entropy generation or exergy losses can be considered as an objective function in designing heat exchangers. Some other researchers, however, not only reject the entropy generation minimization (EGM) philosophy, but also believe that entropy generation maximization is a real objective function in designing heat exchangers. Using driving forces and irreversibility relations, this study sought to get these two views closer to each other. Exergy loss relations were developed by sink-source modeling along the heat exchangers. In this case, two types of heat exchangers are introduced, known as "process" and "utility" heat exchangers. In order to propose an appropriate procedure, exergy losses were examined based on variables and degrees of freedom, and they were different in each category. The results showed that "EGM" philosophy could be applied only to utility heat exchangers. A mathematical model was also developed to calculate exergy losses and investigate the effects of various parameters. Moreover, the validity of the model was evaluated by some experimental data using a double-pipe heat exchanger. Both the process and utility heat exchangers were simulated during the experiments. After verifying the model, some case studies were conducted. The final results indicated that there was not a real minimum point for exergy losses (or entropy generation) with respect to the operational variables. However, a logic minimum point could be found for utility heat exchangers with regard to the constraints.
近几十年来，热力学第二定律已被广泛应用于热交换器分析。许多研究人员认为，在热交换器设计中，可将熵产生或㶲损失最小化视为目标函数。然而，其他一些研究人员不仅反对熵产生最小化（EGM）理念，还认为熵产生最大化才是热交换器设计中的实际目标函数。本研究利用驱动力和不可逆性关系，试图使这两种观点更趋一致。通过沿热交换器进行冷热源建模，建立了㶲损失关系。在这种情况下，引入了两种类型的热交换器，即“工艺”热交换器和“公用工程”热交换器。为了提出一种合适的方法，基于变量和自由度对㶲损失进行了研究，且每类中的㶲损失各不相同。结果表明，“EGM”理念仅适用于公用工程热交换器。还建立了一个数学模型来计算㶲损失并研究各种参数的影响。此外，利用双管热交换器的一些实验数据对模型的有效性进行了评估。在实验过程中对工艺热交换器和公用工程热交换器都进行了模拟。在验证模型后，进行了一些案例研究。最终结果表明，相对于运行变量，㶲损失（或熵产生）不存在真正的最小值点。然而，对于公用工程热交换器，在考虑约束条件时可以找到一个合理的最小值点。
