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In this study, a steady-flow approach in finite-time thermo-
dynamics has been used to study on the performance
optimizations of heat engines and heat pumps from the
viewpoints of various ob- jective functions. The topics studied
include: (1) ecological- criterion-function optimizations of
endoreversible Brayton heat engines with isothermal heat
sources, (2) power optimiztions of endoreversible regenerative
Brayton heat engines with isothermal heat sources, (3) power
optimizations of endoreversible inter- cooled Brayton heat
engines with isothermal heat sources, (4) performance-of-
coefficient optimizations of irreversible Carnot heat pumps
with isothermal heat sources, (5) power optimizations of
irreversible Brayton heat engines with isothermal heat sour-
ces,(6) efficiency optimizations of irreversible Brayton heat
en- gines with isothermal heat sources, (7) ecological-
criterion- function optimizations of irreversible Carnot heat
engines with variable-temperature heat sources. The results
obtained are: (1) The better design point of a heat engine is
positioned between the maximum-power point and the maximum-
efficiency point, and with ecological criterion functions as
objective functions, a heat engine has a balance between its
power output, thermal efficiency and entropy gene- ration rate.
(2) The irreversible models consider three types of
irreversibilities: finite thermal conductance between the
working fluid and reservoirs, heat leaks between the resevoirs
and irreversibilities in the processes of expansion and com-
pression, and the power-efficiency relationship obtained by
this model is a closed loop-like curve, similar to the charac-
terisitic curves of real heat engines.
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