You wish to reduce the maximum shear rate in your reactor (given by impeller tip speed), without changing the power consumption (agitator power).…
You wish to reduce the maximum shear rate in your reactor (given by impeller tip speed), without changing the power consumption (agitator power). For this, you will:
Select an option to attempt
Correct Answer: Option A
Explanation
Bioreactor impeller scale-up: decrease tip speed, maintain power:Tip speed =where D = impeller diameter, N = rotational speed.Power consumption(for turbulent regime, Power number is constant).To DECREASE tip speed while KEEPING power CONSTANT:Let new diameter(increase D) and new speed(decrease N).From tip speed:. To decrease tip speed:.From power:constant →→.Solution: INCREASE D (larger impeller) and DECREASE N (slower rotation) such that.Result: Tip speed decreases (less shear), power is maintained (same mixing energy), but shear is gentler — important for shear-sensitive cells (mammalian, insect cells).Answer: Increase impeller diameter D and decrease rotation speed N to decrease tip speed while maintaining power constant.