How to determine the operating speed of the mixer

The “Mechanical Design Handbook (5th Edition)” contains information on the selection of operating speeds for agitators. Generally, when designing and using mixers, it is necessary to avoid the critical speed in order to prevent resonance. This is because as the speed approaches or reaches the critical value, the vibration of the system increases sharply, leading to damage to the mechanical components as well as problems such as noise and vibration. The N/Nk you mentioned in the question seems to be part of an expression, but the information is incomplete. Generally, N represents the operating speed, while Nk usually refers to the critical speed of the mixer. The specific value to avoid for the critical speed may vary depending on different editions of books or research by experts, but the principle remains the same. Here are some common guidelines: 1. If the operating speed is below the first-order critical speed, it is generally recommended that the operating speed be at least around 80% of the critical speed. 2. If the operating speed is higher than the critical speed, it should be at least about 20% higher than the critical speed to ensure that the system operates in a sufficiently safe range. 3. In the case of multiple critical speeds, it is necessary to ensure that the operating speed is far away from all critical speeds. The specific rotation speed to be chosen also needs to take into account the purpose and the substance being stirred, such as the viscosity of the liquid, its volume, as well as the shape and size of the container; this involves complex calculations related to fluid dynamics and mixing engineering. To avoid adverse effects such as eddies and cavitation during mixing, it is usually necessary to optimize the design through experiments and calculations. In practical operation, adjustments should also be made based on the specific conditions at the site and the actual performance of the equipment. If possible, it is best to consult engineers or technical experts in the relevant field for professional design and adjustment. .