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Continuous stirring refers to sustained agitation of a liquid mixture in a processing vessel to maintain homogeneity, temperature control, and reaction conditions over time. In chemical engineering, this is typically achieved with a mechanically driven impeller mounted on a shaft, sometimes aided by baffles. The approach contrasts with batch stirring, where mixing occurs in discrete intervals. Continuous stirring is commonly realized in a continuous stirred tank reactor (CSTR) or similar mixer system with steady feed and product withdrawal.

Key design parameters include impeller type and location, rotation speed, power input per volume (P/V), Reynolds number, and vessel geometry. The mixing regime—laminar or turbulent—affects mixing time, heat transfer, and mass transfer. Baffles, fill level, and aspect ratios influence flow patterns and dead zones. Temperature and concentration gradients are reduced by adequate mixing, while heat exchange is provided by jackets or coils. Scale-up aims to preserve comparable hydrodynamics and P/V.

Applications span chemical synthesis, polymerization, fermentation, crystallization control, and wastewater treatment. Continuous stirring enables steady-state operation, consistent product quality, and integration with other continuous units. Advantages include reduced batch variation, improved heat and mass transfer, and higher productivity. Disadvantages can include higher equipment costs, sensitivity to viscosity and shear, fouling, and maintenance requirements.

Related concepts include batch stirring and plug-flow mixing. As a general technique, continuous stirring underpins many industrial processes requiring long, steady operation with controlled mixing and thermal conditions.