CHEE2325 – Lecture 2
General balance equation:
- For an arbitrary property, X, in an arbitrary system:
Accumulation = Input - Output + Generation - Consumption
∆ X=X ¿ − X out + X generated −X consumed
1st law of thermodynamics:
- ‘Energy can be converted from one form to another but cannot be created or
destroyed.’
- Like mass, energy is a conserved quantity.
- Energy in and out of a system can occur in 3 forms; work (W), heat (Q) and
energy flow that is part of a mass flow.
∆ E=E¿ −E out +Q+W
Shaft work:
- Shaft work is the work done without any change in the system boundary. For
example, a turbine transfers work out of the turbine via a shaft, but the turbine
does not change volume.
Boundary work:
- Boundary work is mechanical work, commonly related to compression and
expansion of a gas in a piston-cylinder device. This work is caused by a
change in the volume of the system and moving the boundary of the system.
V2
W B=∫ P dV
V1
- For a constant pressure process:
W B=P ∆ V
Flow work:
- Flow work is work done on a control volume (open) system to push the flow in
and out of the system.
W flow =W flow ,∈ ¿−W =P ×V −P ×V ¿
flow , out ¿ ¿ out out
General balance equation:
- For an arbitrary property, X, in an arbitrary system:
Accumulation = Input - Output + Generation - Consumption
∆ X=X ¿ − X out + X generated −X consumed
1st law of thermodynamics:
- ‘Energy can be converted from one form to another but cannot be created or
destroyed.’
- Like mass, energy is a conserved quantity.
- Energy in and out of a system can occur in 3 forms; work (W), heat (Q) and
energy flow that is part of a mass flow.
∆ E=E¿ −E out +Q+W
Shaft work:
- Shaft work is the work done without any change in the system boundary. For
example, a turbine transfers work out of the turbine via a shaft, but the turbine
does not change volume.
Boundary work:
- Boundary work is mechanical work, commonly related to compression and
expansion of a gas in a piston-cylinder device. This work is caused by a
change in the volume of the system and moving the boundary of the system.
V2
W B=∫ P dV
V1
- For a constant pressure process:
W B=P ∆ V
Flow work:
- Flow work is work done on a control volume (open) system to push the flow in
and out of the system.
W flow =W flow ,∈ ¿−W =P ×V −P ×V ¿
flow , out ¿ ¿ out out
