BE/B Eng Bachelor of Engineering Bachelor of Chemical Engineering 2 — Questions and Answers
Question 1: In a distillation column, what does the 'reflux ratio' represent?
- Ratio of liquid returned to distillate withdrawn (Correct answer)
- Ratio of vapor to liquid on a tray
- Ratio of feed to bottoms flow rate
- Ratio of reboiler duty to condenser duty
Correct answer: Ratio of liquid returned to distillate withdrawn
The reflux ratio is the ratio of liquid returned to the top of the column to the distillate product withdrawn.
Question 2: Which dimensionless number characterizes the ratio of inertial forces to viscous forces in fluid flow?
- Prandtl number
- Nusselt number
- Reynolds number (Correct answer)
- Grashof number
Correct answer: Reynolds number
The Reynolds number (Re = ρvL/μ) is the ratio of inertial to viscous forces and determines whether flow is laminar or turbulent.
Question 3: What is the primary purpose of a heat exchanger's LMTD (Log Mean Temperature Difference)?
- To calculate the pressure drop across the exchanger
- To determine the average driving force for heat transfer (Correct answer)
- To find the shell-side velocity
- To estimate fouling resistance
Correct answer: To determine the average driving force for heat transfer
LMTD represents the effective average temperature difference driving heat transfer between the two fluid streams.
Question 4: In chemical kinetics, what does a second-order reaction with respect to reactant A mean?
- Two moles of A are produced per reaction
- The rate doubles when temperature doubles
- The rate is proportional to the square of A's concentration (Correct answer)
- A reacts in two separate steps
Correct answer: The rate is proportional to the square of A's concentration
A second-order reaction in A means the rate law is r = k[A]², so doubling [A] quadruples the reaction rate.
Question 5: Which equation describes the pressure drop for incompressible fluid flow through a pipe?
- Clausius-Clapeyron equation
- Darcy-Weisbach equation (Correct answer)
- Hagen-Poiseuille restricted to laminar only
- Bernoulli equation without friction terms
Correct answer: Darcy-Weisbach equation
The Darcy-Weisbach equation (ΔP = f·L/D·ρv²/2) applies to both laminar and turbulent incompressible flow in pipes.
Question 6: What is the function of a catalyst in a chemical reaction?
- Increases the equilibrium conversion of reactants
- Lowers the activation energy without being consumed (Correct answer)
- Raises the reaction temperature for faster kinetics
- Shifts the equilibrium toward products permanently
Correct answer: Lowers the activation energy without being consumed
A catalyst provides an alternative reaction pathway with lower activation energy and is regenerated at the end of the reaction.
Question 7: In absorption operations, which property of the solvent is most critical for effective gas separation?
- High viscosity to retain gas bubbles
- High volatility to recycle easily
- High selectivity and solubility for the target gas (Correct answer)
- Low density to maximize buoyancy
Correct answer: High selectivity and solubility for the target gas
An effective absorption solvent must have high selectivity and solubility for the target component to achieve efficient separation.
BE/B Eng Bachelor of Engineering Bachelor of Chemical Engineering 2
In a distillation column, what does the 'reflux ratio' represent?