Definition
Pilot mixer, also known as pilot-scale mixing equipment or experimental mixer, is a core equipment for process scale-up research between laboratory and industrial production. It simulates production-scale mixing, dispersion, mass transfer and heat transfer processes to provide key data for process parameter determination, equipment selection and product quality evaluation. Its throughput is usually between a few liters and hundreds of liters.
Principle
The working principle of the pilot mixer is based on fluid mechanics and mixing theory. Its core is to drive the stirring shaft and paddle rotation through a motor, which transfers mechanical energy to the material in the tank, thereby forming a specific flow field in the tank. The stirring process mainly produces shear flow and circulating flow: the shear flow is formed by the velocity gradient between the paddle and the fluid, which is suitable for dispersion, crushing and emulsification; The circulating flow promotes the macroscopic flow of materials in the tank to achieve uniformity of temperature and concentration. The stirring effect is usually characterized by the dimensionless Reynolds number (Re) with the formula Re = ρND²/μ, where ρ is the fluid density, N is the stirring speed, D is the blade diameter, and μ is the hydrodynamic viscosity. This value can be used to determine whether the flow state is laminar, transitional or turbulent.
Measurement and evaluation methods
The evaluation of the pilot mixing process is done by a series of physical and chemical measurements. Mixing time is typically determined by online monitoring of conductivity or pH, i.e., the time it takes from the addition of the tracer to the time the system responds to a specific proportion of a stable value (e.g., 95%). Power consumption is measured directly by a torque sensor or power meter, and its calculation relationship is P = 2πNT, where P is power, N is speed, and T is torque. The stirring power quasi-number Np (Np = P/ρN³D⁵) is the key dimensionless number associated with geometry and power. In addition, the local flow velocity field can be visualized by laser Doppler velocimetry or particle image velocimetry to evaluate the uniformity of agitation.
Main influencing factors
The stirring effect is affected by multiple factors. Geometric factors include the type of stirring paddle (e.g., paddle, turbine, anchor), the ratio of diameter to tank diameter, the height of the paddle from the bottom, and whether there is a baffle in the tank. Operating parameters such as mixing speed directly affect the input power and flow state. In terms of physical parameters, the density and viscosity of the fluid and the rheological properties of non-Newtonian fluids have significant effects on the power demand and mixing efficiency. In addition, the geometric similarity of the tank is a key factor in the process scale-up, often maintaining constant or proportional scaling of key parameters such as power per volume, end-of-blade linear velocity, or mixing time.
Applications
Pilot mixers are widely used in non-medical fields where process scale-up is required. In the chemical industry, it is used for formulation development and process optimization of coatings, inks, and adhesives. In materials science, he is involved in nanomaterial dispersion, battery slurry preparation and composite material synthesis. In the food industry, it is used in the development of processes for sauce emulsification, beverage mixing, and confectionery preparation. In the field of environmental protection, it involves the simulation of water treatment flocculant preparation, sludge conditioning and other processes. Its core value is to provide reliable process data packages for mass production at low cost and risk.
Equipment selection considerations
Selecting a pilot mixer is a systematic project. The first step is to define the process goals, such as mixing, suspension, dispersion or heat transfer. It is necessary to select the appropriate tank and paddle material (such as stainless steel, special alloys) according to the characteristics of the material (such as viscosity, corrosiveness, whether it contains solid particles). The configuration of the motor and reducer should meet the speed and torque range required by the process, and have good speed regulation stability. The control system should be able to accurately set, record and trace key parameters such as rotation speed and temperature. Safety features such as the reliability of mechanical seals, overload protection and explosion-proof design (if handling flammable materials) are essential. The final selection should be based on sufficient process experimental data, and the geometric and operational similarities of the equipment and the future production line should be comprehensively considered.