A carnot cycle heat pump provies 90mj to a house maintained
These methods derive more realistic upper bounds on performance, often including the path for achieving such upper bounds.
Finite-time thermodynamics (FTT) extends thermodynamic analysis to include finite-time constraints, for example, finite heat transfer rates, heat leaks, and friction while maintaining a finite process/cycle time. The resulting bounds often have limited practical value because reversible operation means either zero rate of operation or infinite system size. IntroductionĬlassical thermodynamics places bounds on thermodynamic measures based on reversible assumptions. The derived formulae could be used for a quick estimation of and the temperatures of the working fluid at the hot and cold sides. The behavior of the considered systems is explained by means of the proposed model. There are four limiting types of operation: open circuit in which both and vanish in the limit of slow operation short circuit in which again and vanish but in the limit of fast operation maximum maximum. Although the dissipation mechanisms are different (e.g., heat leak and Joule heating in the thermoelectric refrigerator, isentropic losses in the reverse Brayton cycle, and limits arising from the equation of state in the reverse Rankine cycle), the characteristic curves have a general loop shape. For comparison purposes, various types of refrigeration/heat pump systems are considered: the thermoelectric refrigerator, the reverse Brayton cycle, and the reverse Rankine cycle. The performance characteristics are cast in terms of cooling rate ( ) versus coefficient of performance The model accounts for finite heat transfer rates, heat leaks, and friction as different sources of dissipation. A finite-time generic model to describe the behavior of real refrigeration systems is discussed.