BE/B Eng Bachelor of Engineering Bachelor of Chemical Engineering 5 — Questions and Answers
Question 1: In a binary liquid-vapor system, what is an azeotrope?
- A mixture where both components are completely immiscible
- A mixture whose vapor composition equals its liquid composition at a given T and P (Correct answer)
- The composition at maximum boiling point for any binary system
- A mixture that cannot be distilled under any conditions
Correct answer: A mixture whose vapor composition equals its liquid composition at a given T and P
An azeotrope is a mixture where the vapor and liquid have identical compositions, making separation by ordinary distillation impossible.
Question 2: Which dimensionless number represents the ratio of momentum diffusivity to thermal diffusivity in a fluid?
- Nusselt number
- Schmidt number
- Prandtl number (Correct answer)
- Biot number
Correct answer: Prandtl number
The Prandtl number (Pr = μcₚ/k = ν/α) is the ratio of kinematic viscosity (momentum diffusivity) to thermal diffusivity.
Question 3: In process design, a 'pinch point' in a heat exchanger network represents:
- The location of maximum pressure drop
- The point where the hot and cold composite curves approach most closely (minimum ΔT) (Correct answer)
- The operating pressure limit of the heat exchanger
- The optimal reflux ratio in a distillation system
Correct answer: The point where the hot and cold composite curves approach most closely (minimum ΔT)
The pinch point is where the hot and cold composite curves on a T-H diagram have the minimum temperature approach, setting the minimum utility requirements.
Question 4: What is the purpose of a 'recycle stream' in a chemical process?
- To cool the reactor by removing heat continuously
- To return unreacted feed material to the reactor to improve overall conversion (Correct answer)
- To purge inert gases that accumulate in the system
- To separate byproducts from the main product stream
Correct answer: To return unreacted feed material to the reactor to improve overall conversion
Recycle streams return unconverted reactants from the separator back to the reactor inlet, increasing the overall conversion per pass through the process.
Question 5: In electrochemical engineering, Faraday's law states that the mass of material deposited or dissolved is proportional to:
- The voltage applied across the electrodes
- The total charge passed through the electrolyte (Correct answer)
- The concentration of ions in solution
- The surface area of the electrode
Correct answer: The total charge passed through the electrolyte
Faraday's law: m = (M·Q)/(n·F), where the deposited mass is directly proportional to the total charge Q passed through the cell.
Question 6: Which type of flow regime in a fluidized bed is characterized by solid particles behaving like a boiling liquid with large bubbles rising through the bed?
- Fixed bed regime
- Bubbling fluidization (Correct answer)
- Pneumatic transport (dilute phase)
- Slugging flow at low velocities
Correct answer: Bubbling fluidization
Bubbling fluidization occurs when gas velocity exceeds the minimum fluidization velocity, causing gas bubbles to form and rise through the particle bed.
Question 7: What is the primary advantage of using a packed column over a plate column in distillation?
- Packed columns handle higher liquid flow rates without flooding
- Packed columns have lower pressure drop, making them suitable for vacuum distillation (Correct answer)
- Packed columns are cheaper to fabricate for large diameters
- Packed columns allow easier side-draw product removal
Correct answer: Packed columns have lower pressure drop, making them suitable for vacuum distillation
Packed columns typically have lower pressure drop per theoretical stage compared to tray columns, making them preferred for vacuum and heat-sensitive distillations.
BE/B Eng Bachelor of Engineering Bachelor of Chemical Engineering 5
In a binary liquid-vapor system, what is an azeotrope?