Chapter 5 Module 4 Slide 1 The Second Law of Thermodynamics Reversible and Irreversible Processes Instructors Visual Aids Heat, Work and Energy. A First Course in Thermodynamics © 2002, F. A. Kulacki Reversible and irreversible processes...

Chapter 5 Module 4 Slide 2 The Second Law of Thermodynamics Reversible and Irreversible Processes Instructors Visual Aids Heat, Work and Energy. A First Course in Thermodynamics © 2002, F. A. Kulacki Reversible processes A change in state of a system such that if the system is restored to its original state by any means, there is no net effect on the universe. This means that the system and the surroundings are restored to their original states.

Chapter 5 Module 4 Slide 3 The Second Law of Thermodynamics Reversible and Irreversible Processes Instructors Visual Aids Heat, Work and Energy. A First Course in Thermodynamics © 2002, F. A. Kulacki Reversible heating Each incremental increase of temperature, dT, of the heater results in heat transfer,  Q, to the water and a corresponding increase of the water temperature. For slow enough heating, the states of the heater and the water are nearly equilibrium states and the process is said to be an equilibrium process. T1T1 T 1 +dTT 1 +2dTT2T2 T1T1 T 1 +dTT 1 +2dTT2T2 …. Heater

Chapter 5 Module 4 Slide 4 The Second Law of Thermodynamics Reversible and Irreversible Processes Instructors Visual Aids Heat, Work and Energy. A First Course in Thermodynamics © 2002, F. A. Kulacki T water T heater System Boundary Energy in via electricity or gas combustion Neglect vapor loss Assume no heat losses from sides and bottom. Analysis of the slow heating process

Chapter 5 Module 4 Slide 5 The Second Law of Thermodynamics Reversible and Irreversible Processes Instructors Visual Aids Heat, Work and Energy. A First Course in Thermodynamics © 2002, F. A. Kulacki T2T2 T2T2 Final state of equilibrium. T 2 -dT Reversed process of slow cooling, which is reversible for the water. Reversed process…slow cooling: ……..

Chapter 5 Module 4 Slide 6 The Second Law of Thermodynamics Reversible and Irreversible Processes Instructors Visual Aids Heat, Work and Energy. A First Course in Thermodynamics © 2002, F. A. Kulacki Are intermediate states the same as equilibrium states? Generally, no.Generally, no. But for sufficiently slow processes (quasi-equilibrium processes) with infinitesimal temperature differences, dT, they can be regarded as equilibrium processes.But for sufficiently slow processes (quasi-equilibrium processes) with infinitesimal temperature differences, dT, they can be regarded as equilibrium processes. Equilibrium processes are reversible processes.Equilibrium processes are reversible processes.

Chapter 5 Module 4 Slide 7 The Second Law of Thermodynamics Reversible and Irreversible Processes Instructors Visual Aids Heat, Work and Energy. A First Course in Thermodynamics © 2002, F. A. Kulacki The equilibrium heating and cooling process at constant volume. S 1 to S 2 = reversible heating S 2 to S 1 = reversible cooling 2 P V T1

Chapter 5 Module 4 Slide 8 The Second Law of Thermodynamics Reversible and Irreversible Processes Instructors Visual Aids Heat, Work and Energy. A First Course in Thermodynamics © 2002, F. A. Kulacki The irreversible process An irreversible process is said to have taken place when, upon restoring the system to its original state, a net effect is seen for the universe.

Chapter 5 Module 4 Slide 9 The Second Law of Thermodynamics Reversible and Irreversible Processes Instructors Visual Aids Heat, Work and Energy. A First Course in Thermodynamics © 2002, F. A. KulackiIrreversibilities FrictionFriction Unrestrained expansionUnrestrained expansion Mixing of two fluidsMixing of two fluids Heat transfer across a finite temperature differenceHeat transfer across a finite temperature difference Electric resistance heatingElectric resistance heating Inelastic deformation of solidsInelastic deformation of solids Chemical reactionsChemical reactions

Chapter 5 Module 4 Slide 10 The Second Law of Thermodynamics Reversible and Irreversible Processes Instructors Visual Aids Heat, Work and Energy. A First Course in Thermodynamics © 2002, F. A. Kulacki Intermediate states in the system in an internally reversible process are uniform.Intermediate states in the system in an internally reversible process are uniform. No spontaneous processes within the system can occur.No spontaneous processes within the system can occur. Nothing occurs to make the process irreversible.Nothing occurs to make the process irreversible. Internally reversible processes

Chapter 5 Module 4 Slide 11 The Second Law of Thermodynamics Reversible and Irreversible Processes Instructors Visual Aids Heat, Work and Energy. A First Course in Thermodynamics © 2002, F. A. Kulacki Focus on local surroundings.Focus on local surroundings. Definition of the system needs to be carefully considered.Definition of the system needs to be carefully considered. Energetic interactions between system and local surroundings constitute quasi- equilibrium processes.Energetic interactions between system and local surroundings constitute quasi- equilibrium processes. No external irreversibility is present.No external irreversibility is present. Externally reversible processes

FIGURE 5-43 Execution of the Carnot cycle in a closed system. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 5-11

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display FIGURE 5-44 P-V diagram of the Carnot cycle.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. FIGURE 5-45 P-V diagram of the reversed Carnot cycle. 5-13

Instructors Visual Aids Heat, Work and Energy. A First Course in Thermodynamics © 2002, F. A. Kulacki Chapter 5 Module 6 -Slide 15 The Second Laws of Thermodynamics Analysis of the Carnot Cycle The first Carnot Corollary The thermal efficiency of an irreversible power cycle is always less than the thermal efficiency of a reversible power cycle when each operates between the same two thermal reservoirs.The thermal efficiency of an irreversible power cycle is always less than the thermal efficiency of a reversible power cycle when each operates between the same two thermal reservoirs.

Instructors Visual Aids Heat, Work and Energy. A First Course in Thermodynamics © 2002, F. A. Kulacki Chapter 5 Module 6 -Slide 16 The Second Laws of Thermodynamics Analysis of the Carnot Cycle All reversible power cycles operating between the same two thermal reservoirs have the same thermal efficiency. The second Carnot corollary

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display FIGURE 5-46 The Carnot principles.

Instructors Visual Aids Heat, Work and Energy. A First Course in Thermodynamics © 2002, F. A. Kulacki Chapter 5 Module 6 -Slide 18 The Second Laws of Thermodynamics Analysis of the Carnot Cycle The Kelvin temperature scale... A consequence of the Carnot corollaries

Instructors Visual Aids Heat, Work and Energy. A First Course in Thermodynamics © 2002, F. A. Kulacki Chapter 5 Module 6 -Slide 19 The Second Laws of Thermodynamics Analysis of the Carnot Cycle A deduction based on the Carnot corollaries... Thermal efficiency is the same for all reversible cycles operating between two temperature reservoirs.Thermal efficiency is the same for all reversible cycles operating between two temperature reservoirs. Thus, the efficiency of the cycle must depend only on the temperatures of the reservoirs.Thus, the efficiency of the cycle must depend only on the temperatures of the reservoirs. W = Q H - Q C TCTC QHQH QCQC THTH

Instructors Visual Aids Heat, Work and Energy. A First Course in Thermodynamics © 2002, F. A. Kulacki Chapter 5 Module 6 -Slide 20 The Second Laws of Thermodynamics Analysis of the Carnot Cycle From the definition of the thermal efficiency for the cycle, we have The function  depends on the absolute tempera- tures of each of the thermal reservoirs and remains to be determined.

Instructors Visual Aids Heat, Work and Energy. A First Course in Thermodynamics © 2002, F. A. Kulacki Chapter 5 Module 6 -Slide 21 The Second Laws of Thermodynamics Analysis of the Carnot Cycle Thermodynamic temperature For the Carnot cycle, we have only the temperatures of the reservoirs to consider (a direct result of the Carnot corollaries).For the Carnot cycle, we have only the temperatures of the reservoirs to consider (a direct result of the Carnot corollaries). Define the thermal efficiency of the reversible cycle in terms of thermodynamic temperature.Define the thermal efficiency of the reversible cycle in terms of thermodynamic temperature.

Instructors Visual Aids Heat, Work and Energy. A First Course in Thermodynamics © 2002, F. A. Kulacki Chapter 5 Module 6 -Slide 22 The Second Laws of Thermodynamics Analysis of the Carnot Cycle Thermodynamic temperature scale The function  = T H /T C defines the thermodynamic temperature scale.The function  = T H /T C defines the thermodynamic temperature scale. At T H >> T C, thermal efficiency approaches 100%.At T H >> T C, thermal efficiency approaches 100%.

Instructors Visual Aids Heat, Work and Energy. A First Course in Thermodynamics © 2002, F. A. Kulacki Chapter 5 Module 6 -Slide 23 The Second Laws of Thermodynamics Analysis of the Carnot Cycle

Instructors Visual Aids Heat, Work and Energy. A First Course in Thermodynamics © 2002, F. A. Kulacki Chapter 5 Module 6 -Slide 24 The Second Laws of Thermodynamics Analysis of the Carnot Cycle Illustrations adapted from Moran and Shapiro, 3rd Edn., John Wiley, Carnot efficiencies with T C = 298 K. Note that the segment a-b represents efficiencies for most contemporary power producing technologies. Most conventional electric generating systems operate at ~ 40% thermal efficiency with waste heat recovery.