NCEES Thermodynamics 3

Question 1

Steam enters a turbine at 4 MPa, 400°C (h1 = 3214 kJ/kg) and exits at 50 kPa (h2 = 2340 kJ/kg). The turbine is adiabatic. What is the specific work output?

Accepted Answer

874 kJ/kg

Answer

For an adiabatic turbine, w_turbine = h1 − h2 = 3214 − 2340 = 874 kJ/kg.

Question 2

Which statement correctly describes the second law of thermodynamics?

Accepted Answer

The entropy of an isolated system can never decrease

Answer

The second law states that the entropy of an isolated system always increases or remains constant—it never spontaneously decreases.

Question 3

A gas undergoes a polytropic process where PV^n = constant with n = 1.3. If n = γ = 1.4, the process would be:

Accepted Answer

Isentropic

Answer

When n = γ, the polytropic process is isentropic (reversible adiabatic), with no entropy change.

Question 4

For a pure substance on a P-v diagram, the region under the saturation dome represents:

Accepted Answer

A two-phase liquid-vapor mixture

Answer

The two-phase (liquid-vapor) region lies under the saturation dome on a P-v diagram, bounded by the saturated liquid and saturated vapor curves.

Question 5

The exergy (availability) of a closed system is defined relative to:

Accepted Answer

The dead state (environment conditions)

Answer

Exergy is the maximum useful work obtainable as a system reaches equilibrium with the dead state (T0, P0).

NCEES Practice Test

NCEES Practice Test

NCEES Thermodynamics 3