Abstract
An analysis of the Stirling and Ericsson cycles from the point of view of the finite time thermodynamics is made by assuming the existence of internal irreversibilities in an engine modeled by these cycles, and the ideal gas as working substance is considered. Expressions of efficiency in both regimes maximum power output and maximum ecological function are also shown. Appropriate variables are introduced so that the objective functions, namely power output, ecological function and efficiency can be functions of the reservoirs temperatures ratio and certain “measurable” parameters as a thermal conductance, the general constant of gases and the compression ratio of the cycle. Several results from the finite time thermodynamics literature are used, so that the developed methodology leads directly to appropriate expressions of the objective functions in order to simplify the optimization process.
Highlights
As it is known, thermal engines can be assumed as endothermic or exothermic devices
It is important to point out that Stirling and Ericsson cycles have an efficiency which goes towards the Carnot efficiency as it is shown in some textbooks
Since the end of the previous century, and on recent times, Stirling and Ericsson engines characteristics have resulted in renewed interest in the study and design of such engines, and in the analysis of its theoretical idealized cycle, as it is shown in many papers [3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]
Summary
Thermal engines can be assumed as endothermic or exothermic devices. Among the first, Otto and Diesel engines are the best known; and among the second two devices, Stirling and Ericsson engines are very interesting and similar to the theoretical Carnot engine [1,2]. The Carnot cycle was modified so that the working substance has THW and TCW temperatures different than its reservoirs temperatures, fulfilling TH > THW > TCW > TC The efficiency for this cycle is known as Curzon-Ahlborn-Novikov-Chambadal efficiency, and it is written by the definition TC TH as [29,30], CAN 1. This paper has two purposes; the first one is to show a methodology for writing objective functions including compression ratio as an important parameter; the second one is to show how in the context of finite time thermodynamics the Stirling and Ericsson cycles have an efficiency that in their limit cases is always reduced to the Curzon and Ahlborn cycle efficiency, as in classical equilibrium thermodynamics these cycles have an efficiency like the Carnot cycle efficiency
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