Energy transfer by heat, work & mass Flashcards
1
Q
Closed system
A
Energy can cross the boundary of a closed system in two forms: heat & work
2
Q
Open system
A
Energy can cross the boundary of a closed system in three forms: heat, work & mass
3
Q
Heat
A
Energy that is transferred between two systems as a result of its temperature difference
4
Q
Adiabatic process
A
A process which does not involve heat transfer
5
Q
Work
A
- Energy transfer associated with a force acting through a distance (e.g. W = Fd)
- An energy interaction between a system and its surroundings
6
Q
What are the three main types of work?
A
- Boundary (PdV)
- Rotating Shaft
- Electrical
7
Q
Sign convention for heat
A
- Heat transfer to system (Qin) +
- Heat transfer from system (Qout) -
8
Q
Sign convention for work
A
- Work done by system (Wout) +
- Work done on system (Win) -
9
Q
Similarities between heat and work (4)
A
- Both are boundary phenomena
- Systems possess energy, not heat/work
- Both are associated with a process (not state)
- Both are path functions
10
Q
State function
A
- Volume change is always deltaV from states 1 to 2, regardless of paths followed
- e.g. v, T, p, u, h
11
Q
Path function
A
- Total work obtained by following a process path, and adding differential amounts of work (delta W) along the path
- e.g W, Q
12
Q
Work interaction between system & surroundings
A
- Must be a force acting on the boundary
- Boundary must move
13
Q
Moving boundary work
A
- System initially at equilibrium
- Quasi-equilibrium process
14
Q
Uniform flow assumption
A
- One-dimensional flow
- All properties are uniform at any cross-section normal to the flow direction
- Properties have the bulk average values over the cross-section
15
Q
Steady flow
A
Sum of mass in - sum of mass out = 0
