EIT Electrical, Thermodynamics & Fluid Systems 2

Question 1

A 3-phase balanced load draws 30 kW at 0.8 power factor lagging from a 480 V (line-to-line) source. What is the line current?

Accepted Answer

45.1 A

Answer

P = √3 × V_L × I_L × PF → I_L = 30000 / (√3 × 480 × 0.8) ≈ 45.1 A.

Question 2

Which thermodynamic cycle best approximates the operation of a gas turbine engine?

Accepted Answer

Brayton cycle

Answer

Gas turbines operate on the Brayton cycle, which consists of isentropic compression, constant-pressure heat addition, and isentropic expansion.

Question 3

For fully developed laminar flow in a circular pipe, the friction factor f is related to Reynolds number Re by:

Accepted Answer

f = 64/Re

Answer

The Hagen-Poiseuille result gives the Darcy friction factor f = 64/Re for laminar pipe flow.

Question 4

A capacitor is charged to 100 V and then connected in series with a 10 kΩ resistor. After one time constant, the voltage across the capacitor is approximately:

Accepted Answer

36.8 V

Answer

For a discharging RC circuit, V(τ) = V₀ e^(−1) ≈ 0.368 × 100 V = 36.8 V.

Question 5

Steam enters an adiabatic turbine at 3 MPa and 350°C and exits at 100 kPa. If the isentropic efficiency is 85%, the actual work output compared to ideal is:

Accepted Answer

85% of the isentropic work

Answer

Isentropic (turbine) efficiency η_t = w_actual / w_isentropic, so actual work = 0.85 × ideal work.

(EIT) Engineer In Training Certification Practice Test

(EIT) Engineer In Training Certification Practice Test

EIT Electrical, Thermodynamics & Fluid Systems 2