Govt. Exams
Entrance Exams
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Topics in Mechanical Engineering
The polytropic process for an ideal gas follows PV^n = constant. When n = 0, the process is:
Correct Answer:
A. Isobaric
EXPLANATION
When n = 0, PV⁰ = P = constant, which is an isobaric process. When n = 1 (isothermal), n = γ (adiabatic), n = ∞ (isochoric).
For a real gas, the compressibility factor Z is defined as:
Correct Answer:
A. Z = PV/nRT
EXPLANATION
Compressibility factor Z = PV/(nRT). For ideal gas, Z = 1. For real gases, Z ≠ 1 due to molecular interactions.
The availability or exergy of a system is zero when the system is in:
Correct Answer:
A. Dead state
EXPLANATION
Exergy is maximum work available from a system. At dead state (T₀, P₀, same as surroundings), exergy is zero as no useful work can be extracted.
In a throttling process (Joule-Thomson expansion), the enthalpy of the fluid:
Correct Answer:
C. Remains constant
EXPLANATION
Throttling is an isenthalpic process where enthalpy remains constant (H_initial = H_final) as the fluid expands through a restriction.
A heat engine operating between two temperature reservoirs has a maximum theoretical efficiency given by:
Correct Answer:
A. Carnot efficiency: η = 1 - (T_C/T_H)
EXPLANATION
The Carnot efficiency is the maximum theoretical efficiency for any heat engine, given by η = 1 - (T_C/T_H), where temperatures are in Kelvin.
