Abstract
From the point of view of finite time thermodynamics, the performance boundaries of thermal machines are considered, taking into account the irreversibility of the heat exchange processes of the working fluid with hot and cold sources. We show how the dynamics of heat exchange affects the shape of the optimal cycle of a heat engine and its performance, in particular, energy conversion efficiency in the maximum power mode. This energy conversion efficiency can depend only on the ratio of the heat transfer coefficients to the sources, or not depend on them at all. A class of dynamic functions corresponding to “natural” requirements is introduced and it is shown that, for any dynamics from this class, the optimal cycle consists of two isotherms and two adiabats, not only for the maximum power problem, but also for the problem of maximum energy conversion efficiency at a given power. Examples are given for calculating the parameters of the optimal cycle for the cases when the heat transfer coefficient to the cold source is arbitrarily large, and for dynamics in the form of a linear phenomenological (Fourier heat transfer) law.
Highlights
Systems converting heat into work have been the main object of thermodynamic research since the time of S
We show how the dynamics of heat exchange affects the shape of the optimal cycle of a heat engine and its performance, in particular, energy conversion efficiency in the maximum power mode
A class of dynamic functions corresponding to “natural” requirements is introduced and it is shown that, for any dynamics from this class, the optimal cycle consists of two isotherms and two adiabats, for the maximum power problem, and for the problem of maximum energy conversion efficiency at a given power
Summary
Systems converting heat into work have been the main object of thermodynamic research since the time of S. The problems of the maximum power of the thermal machine and its maximum energy conversion efficiency at a given power were considered in [4,5,6] and it was shown that for any heat transfer dynamics in the maximum power case, the optimal cycle consists of two isotherms and two adiabats. In the case of maximum energy conversion efficiency at a fixed power, or for the maximum power at a fixed heat consumption, the optimal cycle can consist of no more than three isotherms and three adiabats An example of such a cycle was given in [7] for a somewhat exotic form of dynamic dependencies.
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