Power and heat-work conversion efficiency analyses for the irreversible Carnot engines by entransy and entropy

The concepts of entransy and entropy are applied to the analyses of the irreversible Carnot engines based on the finite time thermodynamics. Taking the maximum output power and the maximum heat-work conversion efficiency (HWCE) as objectives, the applicability of the entransy theory and the entropy generation minimization method to the optimizations is investigated. For the entransy theory, the results show that the maximum entransy loss rate always relates to the maximum output power, while the maximum entransy loss coefficient always leads to the maximum HWCE for all the cases discussed in this paper. For the concept of entropy generation, the maximum entropy generation rate corresponds to the maximum output power when the Carnot engine works between infinite heat reservoirs, while the entropy generation number cannot be defined in this case. When the Carnot engine works between the finite heat reservoirs provided by streams, the minimum entropy generation rate corresponds to the maximum output power with prescribed heat flow capacity rates and inlet temperatures of the streams, while the minimum entropy generation number corresponds to the maximum HWCE. When the heat capacity flow rate of the hot stream is not prescribed, the entropy generation rate increases with increasing output power, while the entropy generation number decreases with increasing HWCE. When the inlet temperature of the hot stream is not prescribed, the entropy generation rate increases with increasing output power, and the entropy generation number also increases with increasing HWCE. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4797494]