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GATE 2025 BT – Question 44

Fundamentals of Biological Engineering · Bioreaction Engineering: Batch, fed-batch and continuous processes, microbial and enzyme reactors, optimization and scale up · 2 marks · Multiple choice

For a specific bioreactor configuration, the power requirement for a Rushton-turbine impeller agitating an unaerated Newtonian fluid in the turbulent regime will be

  1. proportional to the stirring speed of the impeller
  2. proportional to the square of the stirring speed of the impeller
  3. proportional to the cube of the stirring speed of the impeller
  4. inversely proportional of the stirring speed of the impeller

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Correct answer: (C) proportional to the cube of the stirring speed of the impeller

Explanation

In the turbulent regime the power number $N_P = \frac{P}{\rho N^3D^5}$ is constant, so $P \propto N^3$.