Can Magnetic Stirrers Become Key Instruments in the Pharmaceutical Industry?
Impeller type, size and speed affect how stirring power is distributed between bulk flow and turbulent fluctuations. Turbine impellers generally favor turbulence, while propeller impellers favor bulk flow. At equal power consumption, a larger, slower impeller of the same type directs more power into bulk flow and macromixing, whereas a smaller, faster impeller favors turbulent fluctuations and micromixing. Stirring methods include manual, magnetic and mechanical stirring. Manual stirring commonly uses a glass rod; magnetic stirring uses magnetic force; mechanical stirring uses a mechanical stirrer。
A mechanical stirrer mainly consists of a motor, stirring shaft and shaft seal. The motor is mounted on a support and its speed is regulated by a controller. The connected shaft rotates when power is applied. The seal connects the shaft to the reactor so reactions can proceed in a closed system. Mixing efficiency depends strongly on shaft and impeller design. Older stirrers used thick glass rods; select a suitable design according to reactor size and shape, neck opening and reaction conditions.
A magnetic stirrer uses attraction between unlike poles and repulsion between like poles to rotate a magnetic bar inside the vessel. It is particularly useful for small reaction volumes or closed systems. Operation is convenient, with heating and temperature control available to maintain experimental conditions and achieve the required mixing. However, highly viscous liquids or reactions involving large amounts of solids may require a mechanical stirrer instead.
Magnetic stirrers are commonly used in food and biopharmaceutical applications. To meet stricter requirements for sterile shaft seals and risk control, industrial bottom-mounted magnetic stirrers emerged in Sweden in the 20th century, in the 80s. They became mainstream and developed toward simpler construction, higher torque, high or very low shear, safe bearing materials, and easier cleaning and sterilization in place. Examples include bioreactor stirrers and high-shear homogenizing stirrers. Demonstrable CIP/SIP capability and safe bearing materials became key selection criteria.
Benchtop magnetic stirrers use repulsion between like poles and changing base polarity to rotate a stir bar. Their drawbacks include low energy-conversion efficiency and suitability mainly for small volumes. Although widely used with stir bars, applications remain largely in research and small-scale work. As domestic research capabilities improve, magnetic stirring applications are expected to expand.
—The above content was sourced from the internet.
