thermodynamics part ii. remaining topics mechanisms of heat transfer thermodynamic systems and their...
TRANSCRIPT
Thermodynamics
Part II
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
MECHANISMS OF HEAT TRANSFER• Conduction•Convection•Radiation
Conduction
k
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R
TTAH
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dt
dQH
ch
ch
Conduction
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.
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.
Convection
Radiation
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Radiation
Radiation
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.
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
Thermodynamic Process
• Process that changes the state of a thermodynamic system.– Isobaric process– Isothermal Process– Isochoric/Isovolumetric Process– Adiabatic process
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
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
thermodynamicsystem: can exchange heat with its surroundings
state of system:(p, V, T, ...)
thermodynamicprocess:changes state of the system
Heat Q: can leave or enter system
Q > 0: heat added to system
Q < 0: heat removed from system
Work W:
W > 0: system does work on its surroundings
W < 0: surroundings does work on the system