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

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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