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Thermodynamics
- The science of energy
- Energy is the ability to cause changes
First law:
Energy can neither be created nor destroyed; rather, it transforms from one form to another
Although all mechanical work can be transformed into heat, not all heat can be transformed into mechanical work
Second law:
Closed systems
consist of a fixed amount of mass, and no mass can cross its boundary.
- Is a properly selected region of space.
- Usually encloses a device that involves mass flow such a compressor, turbine, or nozzle. •Both mass and energy can cross the boundary of a control volume.
Open systems - control volume
If two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other
Zeroth law:
In a system that does not undergo any change, all properties can be measured or calculated, giving certain properties that describe its state
State
State postulate
Two properties are independent if one property can be varied while the other one is held constant.
- Isothermal: constant temperature
- Isobaric: constant pressure.
- Isochoric: constant specific volume
Cycles Initial state = final state
Steady flow process
A process during which a fluid flows through a control volume steadily and has no change with time.
Pressure A normal force exerted by a fluid per unit area.
- Absolute pressure: the actual pressure at a given position.
- Gage pressure: difference between absolute pressure and the local atmospheric pressure.
- Vacuum pressure: pressure below atmospheric pressure.
Kinetic energy
Energy
Motion
Potential energy Elevation of gravitational field
Total energy of a system
Mechanical energy
The form of energy that can be converted to mechanical work completely and directly by an ideal mechanical device.
Heat
Form of energy that is transferred between two systems by virtue of a temperature change.
- Conduction
- Convection
- Radiation
Work
Energy transfer associated with a force acting through a distance.
Electrical work
Electrical power
Shaft work A force acting through a moment arm generates a torque
Spring work
Elastic bars work
Stretching of a liquid
