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GATE 2024 BT – Question 14

Fundamentals of Biological Engineering · Bioreaction Engineering: Batch, fed-batch and continuous processes, microbial and enzyme reactors, optimization and scale up · 1 mark · Multiple choice

Which one of the following statements is correct about Reynolds Number ($N_{Re}$) in a stirred tank bioreactor?

  1. $N_{Re}$ is independent of the viscosity of the medium
  2. In laminar flow, mixing time increases with an increase in $N_{Re}$
  3. $N_{Re}$ is inversely proportional to the impeller speed
  4. In turbulent flow, mixing time is independent of $N_{Re}$

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Correct answer: (D) In turbulent flow, mixing time is independent of $N_{Re}$

Explanation

$N_{Re} = rac{
ho ND^2}{\mu}$ depends on the viscosity and is proportional to the speed. In laminar flow the mixing time falls as $N_{Re}$ rises. In turbulent flow the dimensionless mixing time is constant, independent of $N_{Re}$.