ME or MEng Master of Engineering Thermodynamics and Heat Transfer 1 — Questions and Answers
Question 1: Which thermodynamic cycle is the theoretical standard for spark-ignition gasoline engines?
- Diesel cycle
- Otto cycle (Correct answer)
- Brayton cycle
- Rankine cycle
Correct answer: Otto cycle
The Otto cycle models the idealized operation of a spark-ignition internal combustion engine with constant-volume heat addition.
Question 2: What does the Clausius inequality state about a thermodynamic cycle?
- The net work output equals heat absorbed
- The cyclic integral of dQ/T is less than or equal to zero (Correct answer)
- Entropy decreases in all real cycles
- Heat always flows from cold to hot reservoirs
Correct answer: The cyclic integral of dQ/T is less than or equal to zero
The Clausius inequality states that the cyclic integral of δQ/T ≤ 0, with equality for reversible processes, forming the basis of the second law.
Question 3: In a heat exchanger, the LMTD method stands for:
- Logarithmic Mean Temperature Difference (Correct answer)
- Linear Mean Thermal Distribution
- Latent Mean Transfer Differential
- Lateral Momentum Transfer Derivative
Correct answer: Logarithmic Mean Temperature Difference
LMTD (Logarithmic Mean Temperature Difference) is used to determine the driving force for heat transfer in a heat exchanger.
Question 4: The thermal efficiency of a Carnot heat engine operating between 600 K (hot) and 300 K (cold) is:
- 25%
- 33%
- 50% (Correct answer)
- 75%
Correct answer: 50%
Carnot efficiency = 1 − T_cold/T_hot = 1 − 300/600 = 0.50 or 50%.
Question 5: Fourier's Law of heat conduction relates heat flux to:
- The cube of the temperature gradient
- The negative of the temperature gradient (Correct answer)
- The square root of the temperature gradient
- The absolute temperature of the material
Correct answer: The negative of the temperature gradient
Fourier's Law states q = −k∇T, meaning heat flux is proportional to the negative temperature gradient.
Question 6: Which dimensionless number is used in convective heat transfer to relate inertial forces to viscous forces in a fluid?
- Nusselt number
- Prandtl number
- Reynolds number (Correct answer)
- Biot number
Correct answer: Reynolds number
The Reynolds number (Re = ρVL/μ) compares inertial to viscous forces and determines laminar vs. turbulent flow regimes.
ME or MEng Master of Engineering Thermodynamics and Heat Transfer 1
Which thermodynamic cycle is the theoretical standard for spark-ignition gasoline engines?