موتورهای شیمیایی غیرقابل برگشت و تجزیه و تحلیل عملکرد بهینه آنها

A new cyclic model of a class of chemical engines is set up, in which not only finite-rate mass transfer and mass leakage but also the internal irreversibility resulting from friction, eddy currents and other irreversible effects inside the cyclic working fluid are taken into account. The influences of these irreversibilities on the performance of the cycle are revealed. The optimal relation between the power output and the efficiency of the cycle is derived. On the basis of the optimal relation, some optimal performances and important performance bounds of the cycle are determined and evaluated. For example, the maximum power-output and the corresponding efficiency, the maximum efficiency and the corresponding power output, the optimal mass-transfer time, the minimum rate of energy loss and so on are calculated and analyzed. The results obtained here cannot only enrich the application of thermodynamic theory but also provide some theoretical guidance for the effective application of energy resources and for the optimal design and development of a class of chemical engines. Moreover, some important conclusions relative to the isothermal endoreversible chemical engines, which have been investigated previously, can be directly deduced from the results in this paper.

It is well known that modern thermodynamics can be used to place not only upper but also lower bounds for some important performance parameters of various energy-conversion devices. Reversible limits are rigorous, but often far from a realistic situation. All energy transformation processes occurring in reality are irreversible and in many cases these irreversibilities must be included in a realistic description of such processes. Analysis of energy converters, operated in finite time, can yield more realistic bounds for interesting practical systems. Since 1975, most of the research related to the influence of thermal resistance and other irreversibilities has been concentrated on thermal engines and other thermal devices [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19] and [20]. Recently, related research has been extended to chemical reactions, chemical engines, chemical converters, chemical pumps and so on [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31] and [32]. The results obtained, show that chemical potential and mass transfer in a chemical engine or chemical pump play roles analogous to temperature and entropy in a thermal engine or heat pump. However, a chemical device is different from a thermal device [32]. Hence, it is necessary and important to study the performance characteristics of a chemical device. De Vos [21] modeled a class of chemical reactors and supposed that all irreversibilities are located in the transport of heat and/or matter from the heat and/or matter source to the engine and from the engine to the heat and/or matter sinks. Gordon et al. [24] derived the upper bounds for the work that can be extracted from an isothermal endo-reversible chemical engine. Chen et al. [25] and [26] studied the effects of the irreversibilities of mass transfer on the performances of an isothermal endo-reversible chemical engine and a combined-cycle isothermal chemical engine. Delgado [28] studied the performance of a chemical engine based on osmosis. Yan et al. [29] and [30] analyzed finite-time thermodynamic performances of a fuel battery. Lin et al. [31] and [32] used optimal control theory to analyze the optimal cyclic configuration and performance of a class of two-reservoir chemical pumps and pointed out the differences between the chemical pump and heat pump. These works are of practical value for many chemical, electrochemical, photochemical, and solid-state devices and have provided us with a good overview of possible developments and applications of chemical-energy conversion devices. An extensive study of endo-reversible chemical engines is to probe the performance characteristics of a class of chemical engines affected synthetically by many irreversibilities. We focus on the search for optimal cyclic performances of the chemical engines. First, a new cyclic model for a class of irreversible chemical engines is put forward. Our consideration is restricted to a class of irreversible isothermal chemical engines which are affected by finite-rate mass transfer, mass leakage and internal irreversibility inside the cyclic working-fluid and whose temperatures are identical. This isothermal model turns out to correspond to many practical electrochemical, solid state and photochemical systems [23]. In addition, we confine our study to simple chemical systems in which a single reactant is converted to a single product [24]. Secondly, based on the methods of the optimal control-theory and the optimal thermodynamics, the fundamental optimal equation between the power output and the efficiency for the irreversible chemical engines is obtained. At the same time, some important performance bounds and the optimal operating regions are determined and evaluated. The influence of mass leakage on these performance bounds is revealed. Thirdly, the optimal performance characteristic of the irreversible chemical engines without mass leakage is also discussed. The effects of the internal irreversibility on the bounds of the power output and efficiency are further analyzed. Finally, the optimal relation between the rate of energy loss and the efficiency is analyzed and evaluated. The conclusions obtained here have an instructive significance and a reference value for the development and optimal design of a class of chemical engines.

The new cyclic model established in this paper is an important and universal model for a class of chemical engines, in which three key sources of irreversibilities are taken into account. This model cannot only be used to analyze the influences of finite-rate mass transfer, mass leakage and the internal irreversibility inside the cyclic working fluid on the performance of the irreversible chemical engines but also cover other simple cyclic models of the chemical engines. Based on the new cyclic model, many important performance bounds and optimal parameters are calculated and analyzed. The effects of irreversibilities on the minimum rate of energy loss are also evaluated. The conclusions obtained here have more realistic significance than the related theories of classical and endoreversible thermodynamics and may provide some new theoretical guidance for the optimal design of a class of chemical engines related to mass-transfer processes.