SECOND LAW OF THERMODYNAMICS ThermodynamicsCarnot’sPrincipleWith the practice of using reversible processes, Sadi Carnot in 1824 advanced the study of thesecond law by disclosing a principle consisting of the following propositions.1. No engine can be more efficient than a reversible engine operating between thesame high temperature and low temperature reservoirs. Here the term heatreservoir is taken to mean either a heat source or a heat sink.2. The efficiencies of all reversible engines operating between the same constanttemperature reservoirs are the same.3. The efficiency of a reversible engine depends only upon the temperatures of theheat source and heat receiver.CarnotCycleThe above principle is best demonstrated with a simple cycle (shown in Figure 21) and anexample of a proposed heat power cycle. The cycle consists of the following reversibleprocesses.1-2: adiabatic compression from TCto THdue to work performed on fluid.2-3: isothermal expansion as fluid expands when heat is added to the fluid attemperature TH.3-4: adiabatic expansion as the fluid performs work during the expansion process andtemperature drops from THto TC.4-1: isothermal compression as the fluid contracts when heat is removed from the fluidat temperature TC.HT-01 Page 72 Rev. 0
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