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Published byHoratio Barrett Modified over 9 years ago
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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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Convection 1.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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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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thermodynamic system: can exchange heat with its surroundings state of system: (p, V, T,...) thermodynamic process: 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
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