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Thermodynamics
Part II
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Remaining Topics
• Mechanisms of Heat Transfer• Thermodynamic Systems and Their
Surrounding• Thermal Processes• Laws of Thermodynamics• Heat Engines and Heat Pumps• Carnot Engine• Internal Combustion Engine• Refrigerator and Airconditioner
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MECHANISMS OF HEAT TRANSFER• Conduction•Convection•Radiation
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Conduction
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Conduction
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Convection1. The heat current due to convection
is directly proportional to the surface area.
2. The viscosity of fluid slow natural convection near a stationary surface, giving a surface film that on a vertical surface typically has about the same insulating value as 1.3 cm of plywood. Forced convection decreases the thickness of the film.
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Convection
3. The heat current due to convection is found to be approximately proportional to the 5/4 power of the temperature difference between the surface and the main body of fluid.
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Convection
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Radiation
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Radiation
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Radiation
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Thermodynamic System
• In general, a thermodynamic system is any collection of objects that is convenient to regard as a unit, and that may have the potential to exchange energy with its surroundings.
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Thermodynamic State
• A set of values of properties of a thermodynamic system that must be specified to reproduce the system
• The individual parameters are known as state variables, state parameters or thermodynamic variables.– ex. Temperature, pressure and volume
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Thermodynamic Process
• Process that changes the state of a thermodynamic system.– Isobaric process– Isothermal Process– Isochoric/Isovolumetric Process– Adiabatic process
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In summary…
• Thermodynamic system:able to exchange heat with its surroundings
• State variables: p, V, T, ...describe the thermodynamic system
• Thermodynamic process:changes the state ( p, V, T, ...) of the system
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Thermodynamic Process
Heat Q: can leave or enter system
Work W:• system can do work on its surroundings• surroundings can do work on the system
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thermodynamicsystem: can exchange heat with its surroundings
state of system:(p, V, T, ...)
thermodynamicprocess:changes state of the system
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Heat Q: can leave or enter system
Q > 0: heat added to system
Q < 0: heat removed from system
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Work W:
W > 0: system does work on its surroundings
W < 0: surroundings does work on the system