Thermodynamics

Chapter 6THE SECOND LAW OF THERMODYNAMICSTo this point, we have focused our attention on the firstlaw of thermodynamics, which requires that energy beconserved during a process. In this chapter, we introducethe second law of thermodynamics, which asserts thatprocesses occur in a certain direction and that energy hasquality as well as quantity. A process cannot take placeunless it satisfies both the first and second laws of thermodynamics.In this chapter, the thermal energy reservoirs,reversible and irreversible processes, heat engines, refrigerators,and heat pumps are introduced first. Various statementsof the second law are followed by a discussion of perpetualmotionmachines and the thermodynamic temperature scale.The Carnot cycle is introduced next, and the Carnot principlesare discussed. Finally, the idealized Carnot heat engines,refrigerators, and heat pumps are examined.ObjectivesThe objectives of Chapter 6 are to:• Introduce the second law of thermodynamics.• Identify valid processes as those that satisfy both the firstand second laws of thermodynamics.• Discuss thermal energy reservoirs, reversible andirreversible processes, heat engines, refrigerators, andheat pumps.• Describe the Kelvin–Planck and Clausius statements of thesecond law of thermodynamics.• Discuss the concepts of perpetual-motion machines.• Apply the second law of thermodynamics to cycles andcyclic devices.• Apply the second law to develop the absolutethermodynamic temperature scale.• Describe the Carnot cycle.• Examine the Carnot principles, idealized Carnot heatengines, refrigerators, and heat pumps.• Determine the expressions for the thermal efficiencies andcoefficients of performance for reversible heat engines, heatpumps, and refrigerators.| 279