Exergy: A Measure of Work Potential

Exergy: A Measure of Work Potential

اسلاید 1: CHAPTER 7Exergy: A Measure of Work Potential

اسلاید 2: Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.7-1FIGURE 7-1 A system that is in equilibrium with its environment is said to be at the dead state.

اسلاید 3: Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.7-2FIGURE 7-3 The immediate surroundings of a hot potato are simply the temperature gradient zone of the air next to the potato.

اسلاید 4: Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.7-3FIGURE 7-8 As a closed system expands, some work needs to be done to push the atmospheric air out of the way (Wsurr).

اسلاید 5: Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.7-4FIGURE 7-10 The difference between reversible work and actual useful work is the irreversibility.

اسلاید 6: Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.7-5FIGURE 7-15 Two heat engines that have the same thermal efficiency, but different maximum thermal efficiencies.

اسلاید 7: Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.7-6FIGURE 7-16 Second-law efficiency is a measure of the performance of a device relative to its performance under reversible conditions.

اسلاید 8: Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.7-7FIGURE 7-20 The exergy of a specified mass at a specified state is the useful work that can be produced as the mass undergoes a reversible process to the state of the environment.

اسلاید 9: Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.7-8FIGURE 7-21 The exergy of a cold medium is also a positive quantity since work can be produced by transferring heat to it.

اسلاید 10: Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.7-9FIGURE 7-22 The exergy of flow energy is the useful work that would be delivered by an imaginary piston in the flow section.

اسلاید 11: Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.7-10FIGURE 7-23 The energy and exergy contents of (a) a fixed mass and (b) a fluid stream.

اسلاید 12: Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.7-11FIGURE 7-26 The Carnot efficiency c = 1 - T0 /T represents the fraction of the energy of a heat source at temperature T that can be converted to work in an environment at temperature T0 .

اسلاید 13: Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.7-12FIGURE 7-27 The transfer and destruction of exergy during a heat transfer process through a finite temperature difference.

اسلاید 14: Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.7-13FIGURE 7-29 Mass contains energy, entropy, and exergy, and thus mass flow into or out of a system is accompanied by energy, entropy, and exergy transfer.

اسلاید 15: Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.7-14FIGURE 7-30 The isolated system considered in the development of the decrease of exergy principle.

اسلاید 16: Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.7-15FIGURE 7-32 Mechanisms of exergy transfer for a general system.

اسلاید 17: Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.7-16FIGURE 7-33 Exergy balance for a closed system when the direction of heat transfer is taken to be to the system and the direction of work from the system.

اسلاید 18: Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.7-17FIGURE 7-34 Exergy destroyed outside system boundaries can be accounted for by writing an exergy balance on the extended system that includes the system and its immediate surroundings.

اسلاید 19: Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.FIGURE 7-42 Exergy is transferred into or out of a control volume by mass as well as heat and work transfer.7-18

اسلاید 20: Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.7-19FIGURE 7-49 The irreversibility associated with a student studying and watching a movie on television, each for two hours.

اسلاید 21: Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.7-20FIGURE 7-50 A poetic expression of exergy and exergy destruction.