Scaling up in pharmaceutical manufacturing, especially with Rapid Mixer Granulators (RMG), requires careful attention to “Motion similarity between lab RMG and production Large RMG “, particularly in maintaining consistent “tip speed”.
Here’s why this is crucial:
Tip speed—the speed at the edge of the rotating impeller directly affects mixing efficiency and granule quality.
When scaling up from lab to production scale, if the RPM is kept constant, the tip speed increases due to the larger impeller size. This can alter mixing dynamics and result in different granule characteristics.
To ensure consistent product quality, it’s essential to adjust the RPM during scale-up to maintain the same tip speed as in the lab scale.
This adjustment ensures that the forces acting on the material remain consistent, leading to uniform mixing and granulation across different scales.
For example, if you’re scaling up from a 20 cm impeller in the lab to a 1-meter impeller in production, reducing the RPM from 300 to 60 can help maintain the same tip speed, ensuring that your production-scale process mirrors the lab-scale results.
Understanding and applying these principles is key to achieving successful scale-up and ensuring consistent product quality.
Tip Speed Calculation
Tip speed = π × d × n
Where,
• π = 3.14
• d = impeller diameter (ft.)
• n = impeller revolutions per minute (rpm)
Let’s use an example of a pump with a 24-inch impeller that was running at 500 rpm. First, convert the 24 inches to ft. by dividing by 12 inches per foot. Then multiply by 3.14 to give you ft. per revolution and then multiply by a speed of 500 revolutions per minute.
Tip speed = [24/12 ×3.14 × 500] = 3140 ft./min.
How to measure the diameter of impeller?
Firstly, measure the radius of impeller and multiply it by 2 to get the diameter.
Measure the outer most tip of the blade to the center of the bore to obtain the radius. Therefore, a propeller or impeller that measures a radius of 3” from the tip of the blade to the center of the bore will have a diameter of 6”.
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