Costea Monica, Petrescu Stoian, Feidt Michel, Dobre Catalina, Borcila Bogdan
Department of Engineering Thermodynamics, University POLITEHNICA of Bucharest, Splaiul Independentei 313, 060042 Bucharest, Romania.
Laboratory of Energetics, Theoretical and Applied Mechanics (LEMTA), URA CNRS 7563, University of Lorraine, 54518 Vandoeuvre-lès-Nancy, France.
Entropy (Basel). 2021 Apr 22;23(5):504. doi: 10.3390/e23050504.
An irreversible Carnot cycle engine operating as a closed system is modeled using the Direct Method and the First Law of Thermodynamics for processes with Finite Speed. Several models considering the effect on the engine performance of external and internal irreversibilities expressed as a function of the piston speed are presented. External irreversibilities are due to heat transfer at temperature gradient between the cycle and heat reservoirs, while internal ones are represented by pressure losses due to the finite speed of the piston and friction. Moreover, a method for optimizing the temperature of the cycle fluid with respect to the temperature of source and sink and the piston speed is provided. The optimization results predict distinct maximums for the thermal efficiency and power output, as well as different behavior of the entropy generation per cycle and per time. The results obtained in this optimization, which is based on piston speed, and the Curzon-Ahlborn optimization, which is based on time duration, are compared and are found to differ significantly. Correction have been proposed in order to include internal irreversibility in the externally irreversible Carnot cycle from Curzon-Ahlborn optimization, which would be equivalent to a unification attempt of the two optimization analyses.
一个作为封闭系统运行的不可逆卡诺循环发动机，采用直接法和热力学第一定律对有限速度过程进行建模。提出了几个考虑外部和内部不可逆性对发动机性能影响的模型，这些不可逆性表示为活塞速度的函数。外部不可逆性是由于循环与热库之间在温度梯度下的热传递引起的，而内部不可逆性则由活塞有限速度和摩擦导致的压力损失来表示。此外，还提供了一种针对热源和冷源温度以及活塞速度来优化循环流体温度的方法。优化结果预测了热效率和功率输出的不同最大值，以及每个循环和单位时间内熵产生的不同行为。将基于活塞速度的该优化结果与基于持续时间的柯曾 - 艾尔伯恩优化结果进行比较，发现二者存在显著差异。为了将内部不可逆性纳入柯曾 - 艾尔伯恩优化的外部不可逆卡诺循环中，已经提出了修正方法，这相当于对两种优化分析进行统一的尝试。
