EIT Thermodynamics 4

Question 1

Which Maxwell relation is derived from the Gibbs free energy G = H - TS?

Accepted Answer

(∂s/∂P)_T = -(∂v/∂T)_P

Answer

From dG = -sdT + vdP, the Maxwell relation (∂s/∂P)_T = -(∂v/∂T)_P follows from equality of mixed partials.

Question 2

An ideal Otto cycle operates with a compression ratio of 8 and k = 1.4. What is the thermal efficiency?

Accepted Answer

56.5%

Answer

η_Otto = 1 - 1/r^(k-1) = 1 - 1/8^0.4 = 1 - 1/2.297 ≈ 0.565 = 56.5%.

Question 3

For a psychrometric process, the dew point temperature is the temperature at which:

Accepted Answer

Moisture begins to condense from air

Answer

The dew point is the temperature at which water vapor in moist air begins to condense when cooled at constant pressure.

Question 4

The Joule-Thomson coefficient μ_JT = (∂T/∂P)_h is zero for:

Accepted Answer

Ideal gases

Answer

For an ideal gas, enthalpy depends only on temperature, so throttling (constant-h) produces no temperature change, giving μ_JT = 0.

Question 5

In an air-standard Brayton cycle, increasing the pressure ratio (while maintaining the same temperature limits) will:

Accepted Answer

Increase thermal efficiency up to a point determined by the temperature limits

Answer

Brayton cycle efficiency increases with pressure ratio, but the optimal pressure ratio for maximum work is determined by the temperature ratio.

(EIT) Engineer In Training Certification Practice Test