Thermodynamic Definitions with Examples & Extended MCQs
Closed System:
Example: A sealed piston-cylinder with fixed mass but heat transfer allowed.
(Figure: Piston-cylinder with insulated walls except the base.)
Open System:
Example: A turbine where steam enters and exits, transferring both mass and energy.
(Figure: Turbine with inlet and outlet arrows.)
Steady Flow:
Example: Water flowing through a pipe at constant rate and conditions over time.
(Figure: Pipe with constant flow markers.)
Unsteady Flow:
Example: Air filling a balloon where pressure and volume change with time.
(Figure: Balloon inflating over time.)
Uniform Flow:
Example: Same temperature and velocity across the cross-section of a wind tunnel.
(Figure: Arrows evenly distributed across area.)
Boundary:
Example: The wall of a pressure cooker separating inside contents from surroundings.
(Figure: Line surrounding system with arrows.)
Surroundings:
Example: The kitchen and air around a hot coffee mug.
(Figure: System with surroundings cloud.)
Intensive Property:
Example: Temperature of water: 100°C, same for 1g or 1kg.
Extensive Property:
Example: Mass of water: 2 kg in total, changes with quantity.
Internal Energy:
Example: Energy stored in the molecules of compressed air in a tank.
Enthalpy:
Example: Used in steam tables: h = u + Pv, helps in turbine/boiler calculations.
Specific Heat:
Example: Water needs 4.18 kJ/kg°C to heat by 1°C.
Entropy:
Example: Melting ice increases entropy due to more disorder in liquid state.
Boundary Work:
Example: Piston expanding gas: Work = area under P-V curve.
Flow Energy:
Example: Inlet of a pump requires Pv energy per unit mass to push fluid in.
Multiple Choice Questions (MCQs)
1. Which of the following is an intensive property?
A) Volume
B) Mass
C) Temperature
D) Internal Energy
Answer: C
2. In an open system:
A) Only energy crosses the boundary
B) Only mass crosses the boundary
C) Both mass and energy cross the boundary
D) Neither cross the boundary
Answer: C
3. Which of the following represents enthalpy?
A) U + P*V
B) m*c*DeltaT
C) Q - W
D) P*dV
Answer: A
4. For a steady flow process:
A) Properties vary with time
B) Mass flow rate is constant
C) No heat transfer occurs
D) Work is zero
Answer: B
5. Entropy is a measure of:
A) Energy
B) Pressure
C) Disorder
D) Work
Answer: C
6. Specific heat is defined as:
A) Energy per unit volume
B) Energy to raise 1 kg by 1°C
C) Heat per mole
D) Internal energy per unit mass
Answer: B
7. Boundary work is given by:
A) Q - W
B) Integral of PdV
C) m*c*DeltaT
D) U + PV
Answer: B
8. Which property is not state-dependent?
A) Internal Energy
B) Work
C) Pressure
D) Temperature
Answer: B
9. The energy associated with fluid entering a control volume is:
A) Kinetic energy
B) Enthalpy
C) Flow energy
D) Internal energy
Answer: C
10. A closed system allows:
A) Only mass transfer
B) Only energy transfer
C) Both mass and energy transfer
D) No transfer at all
Answer: B
11. Uniform flow implies:
A) Flow properties are same at every point in space and time
B) No change with time
C) Same properties across cross-section at a given instant
D) No flow occurs
Answer: C
12. Which of the following is an extensive property?
A) Pressure
B) Entropy
C) Temperature
D) Density
Answer: B
13. Internal energy depends on:
A) Path taken
B) Final state only
C) Time of process
D) External forces
Answer: B
14. During isothermal expansion of an ideal gas:
A) Internal energy increases
B) Temperature changes
C) Internal energy stays constant
D) Entropy decreases
Answer: C
15. Which term is used in control volume analysis?
A) Internal energy
B) Flow energy
C) Heat transfer
D) Potential energy
Answer: B