TED-AJ03-140 Thermodynamics with Finite Speed versus Thermodynamics in Finite Time in the Optimization of Carnot Cycle

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概要

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• Although having thermodynamic optimization as a common objective, the principle methods of cycle analysis; Thermodynamics with Finite Speed (TFS) and Thermodynamics in Finite Time (TFT) are quite different. In TFT, time and the temperature of the working fluid in the cycle are the variables that are optimized. The optimization is based on maximizing the cycle power rather than the cycle efficiency. Analyses that include the internal irreversibilities of the cycle using this method have been neglected until recently and he efforts that have been made have generally not been systematic or applicable to cycles other than the Carnot cycle. An aspect of the past neglect of internal irreversibility issues is that the adiabatic processes of the cycle have received much less attention than the isothermal processes. They have been projected to occur in a short time interval compared to the time allocated to the isothermal processes. This is of no consequence in the optimization of an endo-reversible Carnot cycle, but there can be dramatic consequences when internal irreversibilities are taken into account. As the time frame for the adiabatic processes shortens, the internal irreversibilities increase and may reach values sufficient to dramatically degrade the overall cycle performance. By contrast, in TFS, piston speed and the temperatures of the working fluid in the cycle are the main variables that are optimized. The optimization in TFS that is presented in this paper focuses on both the efficiency and the power output of the engine. The analysis includes the effect of piston speed during both the adiabatic processes and the isothermal processes in determining the internal ireversibilities of the cycle. Two fundamental and powerful tools are used in this optimization. They are (1) the First Law of Thermodynamics for Processes with Finite Speed and (2) the Direct Method. The first tool provides the fundamental equations for the study of irreversible processes with finite speed in any cycle. The second tool is a step-by-step algorithm for study and optimization of any cycle with finite speed by taking into account simultaneously, systematically and directly both the external and internal irreversibilities. This study explores the relative merits of using TFS and TFT in the optimization of a Carnot cycle that includes internal and external irreversibilities. The analysis shows that TFS has well-established fundamentals. It also shows that focusing on speed instead of time assures the direct inclusion of the internal irreversibilities generated by the finite speed. In addition, it includes the effect of the speed on the external irreversibilities of the cycle, especially the heat transfer coefficients that in turn determine the optimum temperatures.

• 一般社団法人日本機械学会の論文

著者

• Harman Charles

  Department Of Mechanical Engineering Duke University

• Petrescu Stoian

  Department of Mechanical Engineering, Bucknell University

• Costea Monica

  Department of Engineering Thermodynamics, Polytechnic University of Bucharest

• Feidt Michel

  L. E. M. T. A., U. R. A. C. N. R. S.

• Feidt Michel

  L. E. M. T. A. U. R. A. C. N. R. S.

• Petrescu Stoian

  Department Of Mechanical Engineering Bucknell University

• Costea Monica

  Department Of Engineering Thermodynamics Polytechnic University Of Bucharest

関連論文

• TED-AJ03-140 Thermodynamics with Finite Speed versus Thermodynamics in Finite Time in the Optimization of Carnot Cycle

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