Definition
A fixed-speed agitator is a commonly used equipment in laboratories to agitate, mix, homogenize, or facilitate reactions in liquid or solid-liquid mixtures at a specific constant speed. It rotates the stirring paddle in the medium through a mechanical drive, creating a controlled flow field that ensures that the speed parameters of the experimental process remain consistent and repeatable.
Principle
The core working principle of the constant speed agitator is based on the motor drive and transmission system. Normally, AC or DC motors output constant torque under the action of electronic control circuits, and transmit rotational motion to the mixing shaft through gears or direct transmission mechanisms. The control system monitors the rotational speed through a feedback mechanism (such as a tachymetric sensor) and compares it with a preset value to maintain a stable rotational speed by adjusting the motor input to offset the velocity deviation caused by changes in the viscosity of the medium or fluctuations in load. Its basic relationship can be expressed as:
M = k · ω
where M is the output torque of the motor, ω is the angular velocity, and k is the coefficient related to the characteristics and control of the motor. The stable rotational speed ensures the constant shear force and mixing effect during mixing.
Measurement method
The performance evaluation of a fixed-speed agitator usually focuses on speed accuracy and stability. Speed measurement can be achieved with a non-contact photoelectric sensor or a Hall sensor, which detects the passage frequency of marks or magnets on the stirring shaft and converts them to revolutions per minute (RPM). Standard test methods require that the deviation between the actual rotational speed of the equipment and the set value should be within the allowable range (e.g., ± 1% to ±5%, according to relevant standards) at rated load, and that the fluctuation range during continuous operation should be small. The evaluation of the stirring effect needs to be combined with the specific application, and it is indirectly reflected by measuring parameters such as mixture uniformity, particle dispersion or reaction rate.
Influencing factors
The actual mixing effect of a fixed-speed agitator is affected by a variety of factors. Dielectric viscosity is a major factor, and high viscosity fluids can increase the load, which can cause the actual motor speed to decrease or require higher torque to maintain a constant speed. The shape and size of the agitation paddle directly affects the flow pattern and shear efficiency, such as paddle, turbine or anchor paddles for different mixing needs. Vessel geometry and level height can cause eddy currents or dead zones, affecting mixing uniformity. Changes in ambient temperature can indirectly affect operation by changing the viscosity of the medium or motor performance. In addition, if the verticality and concentricity of the stirring shaft are not good, it may cause vibration, affecting stability and repeatability.
Application:
Constant speed agitators are widely used in many industrial and scientific research fields. In the chemical industry, it is used for solution preparation, polymerization reactions, or catalytic testing, ensuring controllable reaction conditions. In food science, it is used for the simulation and optimization of sauce emulsification, ingredient mixing and other processes. It is commonly used in the field of environmental monitoring for uniform mixing of water samples or soil extracts. The coatings and inks industry relies on it for pigment dispersion and stability testing. In materials science, it can be used for nanomaterial dispersion or battery slurry preparation. These applications rely on equipment to provide stable and repeatable stirring conditions to ensure the consistency of experimental data or processes.
Selection
When choosing a constant speed agitator, it is necessary to comprehensively consider the technical parameters and experimental needs. The speed range should cover the range required for the experiment, and pay attention to whether the equipment can provide sufficient torque at the required speed. Motor type and power need to match the medium viscosity and volume, and high viscosity or high-volume applications often require higher power and robust drive structures. The agitator paddle material (e.g., stainless steel, PTFE) should be chemically compatible to avoid contamination or corrosion. In terms of control, the basic model may only offer simple knob settings, while the advanced model may have a digital display, closed-loop control, or programmable functions. In terms of safety, attention should be paid to insulation level, overheating protection and mechanical stability. In addition, the noise level of the equipment's operation, ease of maintenance and compliance with relevant international standards (e.g. IEC safety requirements for laboratory equipment) are also noteworthy aspects of the selection.