tailieunhanh - Lecture Companion site to accompany thermodynamics: An engineering approach (7/e): Chapter 8 - Yunus Çengel, Michael A. Boles

Chapter 8 - Exergy: A measure of work potential. After studying this chapter you will be able to: Examine the performance of engineering devices in light of the second law of thermodynamics; define exergy (also called availability), which is the maximum useful work that could be obtained from the system at a given state in a specified environment; define reversible work, which is the maximum useful work that can be obtained as a system undergoes a process between two specified states;. | Chapter 8 Exergy: A Measure of Work Potential Study Guide in PowerPoint to accompany Thermodynamics: An Engineering Approach, 7th edition by Yunus A. Çengel and Michael A. Boles The energy content of the universe is constant, just as its mass content is. Yet at times of crisis we are bombarded with speeches and articles on how to “conserve” energy. As engineers, we know that energy is already conserved. What is not conserved is exergy, which is the useful work potential of the energy. Once the exergy is wasted, it can never be recovered. When we use energy (to heat our homes, for example), we are not destroying any energy; we are merely converting it to a less useful form, a form of less exergy. Exergy and the Dead State The useful work potential of a system is the amount of energy we extract as useful work. The useful work potential of a system at the specified state is called exergy. Exergy is a property and is associated with the state of the system and the . | Chapter 8 Exergy: A Measure of Work Potential Study Guide in PowerPoint to accompany Thermodynamics: An Engineering Approach, 7th edition by Yunus A. Çengel and Michael A. Boles The energy content of the universe is constant, just as its mass content is. Yet at times of crisis we are bombarded with speeches and articles on how to “conserve” energy. As engineers, we know that energy is already conserved. What is not conserved is exergy, which is the useful work potential of the energy. Once the exergy is wasted, it can never be recovered. When we use energy (to heat our homes, for example), we are not destroying any energy; we are merely converting it to a less useful form, a form of less exergy. Exergy and the Dead State The useful work potential of a system is the amount of energy we extract as useful work. The useful work potential of a system at the specified state is called exergy. Exergy is a property and is associated with the state of the system and the environment. A system that is in equilibrium with its surroundings has zero exergy and is said to be at the dead state. The exergy of the thermal energy of thermal reservoirs is equivalent to the work output of a Carnot heat engine operating between the reservoir and the environment. For more information and animations illustrating this topic visit the Animation Library developed by Professor S. Bhattacharjee, San Diego State University, at this link. Exergy Forms Now let’s determine the exergy of various forms of energy. Exergy of kinetic energy Kinetic energy is a form of mechanical energy and can be converted directly into work. Kinetic energy itself is the work potential or exergy of kinetic energy independent of the temperature and pressure of the environment. Exergy of kinetic energy: Exergy of potential energy Potential energy is a form of mechanical energy and can be converted directly into work. Potential energy itself is the .

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