BME Thermodynamics 2

Question 1

Which thermodynamic process occurs at constant entropy?

Accepted Answer

Isentropic

Answer

An isentropic process is reversible and adiabatic, meaning entropy remains constant throughout.

Question 2

The Clausius inequality states that for any cycle, the cyclic integral of δQ/T is:

Accepted Answer

Less than or equal to zero

Answer

The Clausius inequality states ∮(δQ/T) ≤ 0, with equality holding only for reversible cycles.

Question 3

In a Brayton cycle, increasing the compressor pressure ratio (up to the optimal value) generally:

Accepted Answer

Increases thermal efficiency

Answer

Higher pressure ratio increases the thermal efficiency of the Brayton cycle because more compression raises the average temperature of heat addition.

Question 4

For an ideal gas undergoing a polytropic process PVⁿ = C, if n equals the ratio of specific heats γ, the process is:

Accepted Answer

Isentropic

Answer

When n = γ (= Cp/Cv), the polytropic process becomes isentropic (reversible adiabatic).

Question 5

The coefficient of performance (COP) of a heat pump is related to COP of a refrigerator operating between the same temperatures by:

Accepted Answer

COP_HP = COP_R + 1

Answer

COP_HP = COP_R + 1, because the heat pump delivers both the heat removed from the cold reservoir plus the work input.

BME - Bachelor of Mechanical Engineering Practice Test