NCEES Chemical Engineering PE Exam

Question 1

On the NCEES PE Chemical exam, which equation describes the relationship between mole fractions in vapor-liquid equilibrium for an ideal system (Raoult's law)?

Accepted Answer

yi × P = xi × Pi_sat

Answer

Raoult's law states that for ideal mixtures, the partial pressure of component i equals its mole fraction in the liquid (xi) times its pure-component vapor pressure (Pi_sat): yi × P = xi × Pi_sat.

Question 2

In the NCEES PE Chemical exam, what does the 'LMTD' (log mean temperature difference) method calculate in heat exchanger design?

Accepted Answer

The effective driving force for heat transfer when temperature difference varies along the exchanger length

Answer

LMTD is the logarithmic average of the terminal temperature differences in a heat exchanger, providing the correct mean driving force for calculating required heat transfer area: Q = U × A × LMTD.

Question 3

For the NCEES PE Chemical exam, what is the 'residence time distribution (RTD)' concept used for in reactor design?

Accepted Answer

To characterize mixing behavior and deviation from ideal reactor models in real reactors

Answer

RTD analysis (using tracer experiments) characterizes how long different fluid elements spend in a reactor, revealing mixing patterns and deviations from ideal CSTR or PFR behavior.

Question 4

On the NCEES PE Chemical exam, which dimensionless number characterizes the ratio of convective heat transfer to conductive heat transfer in a fluid?

Accepted Answer

Nusselt number

Answer

The Nusselt number (Nu = hL/k) is the dimensionless convective heat transfer coefficient, representing the enhancement of heat transfer by convection relative to conduction through the same fluid layer.

Question 5

In the NCEES PE Chemical exam, what is the 'Fanning friction factor' used to calculate in pipe flow?

Accepted Answer

The pressure drop due to friction in a pipe per unit length

Answer

The Fanning friction factor f (or Darcy-Weisbach friction factor) is used in the Darcy-Weisbach equation to calculate frictional pressure drop in pipe flow: ΔP = f(L/D)(ρV²/2).

NCEES National Council of Examiners for Engineering and Surveying Practice Practice Test

NCEES National Council of Examiners for Engineering and Surveying Practice Practice Test

NCEES Chemical Engineering PE Exam