Heat Pumps and Heat Engines

This chapter overviews the first and second laws of thermodynamics as applied to simple heat pumps and heat engines. The operating principles of heat engines and heat pumps are integral to the study of Engineering Thermodynamics, where Engineering Thermodynamics is generally described as the study of the interactions of heat and work. A practical use of the Carnot cycle is that it determines best theoretical performance of heat engine and heat pump cycles as a function of reservoir temperature. For a heat pump, performance is described by its coefficient of performance (COP), where the maximum efficiency, or Carnot efficiency, is defined differently for heating and cooling modes. Heat engine and heat pump cycles are frequently depicted on temperature-entropy (T-s) diagrams. The chapter discusses more energy that can be extracted when ammonia-water is used as the working fluid. It also explores working fluids in organic or binary Rankine cycles (ORC) heat engines and geothermal heat pumps.