ch06-lec - Learning Objectives 1 Introduce the second law...

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Learning Objectives 1. Introduce the second law of thermodynamics. 2. Identify valid processes as those that satisfy both the first and second laws of thermodynamics. 3. Discuss thermal energy reservoirs, reversible and irreversible processes, heat engines, refrigerators, and heat pumps. 4. Describe the Kelvin-Planck and Clausius statements of the second law of thermodynamics. 5. Discuss the concepts of perpetual-motion machines.
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Learning Objectives 1. Apply the second law of thermodynamics to cycles and cyclic devices. 2. Apply the second law to determine the absolute thermodynamic temperature scale. 3. Describe the Carnot cycle. 4. Examine the Carnot principles, idealized Carnot heat engines, refrigerators, and heat pumps. 5. Determine the expressions for the thermal efficiencies and coefficients of performance for reversible heat engines, heat pumps, and refrigerators.
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6-1 Introduction to the Second Law of Thermodynamics Overview of the Second Law Satisfying the first law alone does not guarantee that a process will take place The first law does not place any restrictions on the direction of a process From our experiences, we know that processes occur in a certain direction and not in the reverse direction The second law of thermodynamics addresses this issue A process will not occur unless it satisfies both the first and second law of thermodynamics Examples of processes occurring in a certain direction A cup of hot coffee left in a cooler room eventually cools off Water flows down a waterfall Gases expand from a high pressure to a low pressure
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6-1 Introduction to the Second Law of Thermodynamics Overview of the Second Law (cont.) The second law asserts that energy has quality and well as quantity The first law is concerned with the quantity of energy and its transformations, whereas the second law provides the means to determine the quality as well as the degree of degradation of energy during a process The second law is also used to determine the theoretical limits for the performance of engineering systems
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6-2 Thermal Energy Reservoirs Thermal Energy Reservoir (Heat Reservoir) A hypothetical body with a relatively large thermal energy capacity that can supply or absorb finite amounts of heat without undergoing any change in temperature Examples Large bodies of water (oceans, lakes, rivers) The atmosphere A two-phase system Source A reservoir that supplies energy in the form of heat Sink A reservoir that absorbs energy in the form of heat
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6-3 Heat Engines Overview Work can easily be converted to other forms of energy, but converting other forms of energy to work is difficult Work can be converted to heat directly and completely , but converting heat to work requires the use of some special device Heat Engines A device that converts heat to work Characteristics of heat engines They receive heat from a high-temperature source They convert part of this heat to work They reject the remaining waste heat to a low-temperature sink They operate on a cycle
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6-3 Heat Engines Example of a Heat Engine – Steam Power Plant
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