Definition
A mixer is a type of laboratory equipment that achieves uniform mixing of two or more materials through mechanical action. It is widely used in chemistry, biology, pharmaceuticals, food and materials science, and other fields to facilitate dissolution, emulsification, homogenization, or accelerate reaction processes. According to the differences in working methods and structures, mixers can usually be divided into magnetic mixers, mechanical mixers, scroll mixers and other types.
Principle
The basic principles of mixers are based on fluid mechanics and mass transfer theory. By using rotating stirring components (such as paddles, magnetic rotors, or scroll discs) to apply shear force and circulation flow to the material in the vessel, the concentration gradient and phase interface are broken, and the spatial distribution of components is uniform. For Newtonian fluids, the relationship between stirring power and rotational speed can be roughly described as:P = KρN3D5, among themPfor power,ρis the fluid density,Nis the rotational speed,Dis the diameter of the stirring paddle,Kis the power constant. The mixing behavior of non-Newtonian fluids needs to be further analyzed in combination with rheological parameters.
Measurement method
The evaluation of agitation often relies on the quantitative determination of mixing uniformity. Common methods include conductivity (determining ion distribution by monitoring the conductivity of a solution over time), tracer (sampling to analyze concentration variance after adding staining or fluorescent markers), temperature distribution mapping (for exothermic or endothermic reaction systems), and visual observation (tomography for opaque systems). Mixing timeθDefined as the time it takes from the start of mixing to the system reaching a predetermined uniformity threshold, it is a key parameter to measure mixing efficiency.
Influencing factors
The mixing effect is affected by multiple factors. The equipment parameters include the shape, diameter and installation position of the stirring paddle, the speed range and the power output characteristics. The material properties involved viscosity, density, particle size, multiphase interfacial tension and rheological properties. Operating conditions such as vessel geometry, liquid volume, temperature and pressure environment can also significantly change the flow field structure and hybrid dynamics. In addition, for biologically sensitive samples, cell damage or protein denaturation due to shear forces needs to be taken into account in the parameter settings.
Application
In chemical synthesis, mixers are used to ensure adequate contact with reactants and heat transfer; During biological culture, it maintains cell suspension and nutrient uniformity. The pharmaceutical industry relies on it to achieve drug homogenization and crystallization control; It is commonly used in the field of food testing for emulsification and dispersion of sample preparation; In environmental analysis, it is used for mixing processes in water quality simulation experiments. Different applications have differentiated requirements for stirring strength, accuracy, and sample compatibility.
Selection
The selection should be based on the experimental requirements and systematic considerations. First, the properties of the sample (such as corrosiveness, viscosity, volatility) are clarified to determine the material compatibility and sealing requirements. According to the mixing target (dissolution, suspension, gas-liquid dispersion, etc.), the appropriate mixing type and paddle configuration are selected; The speed range and control accuracy should match the process dynamics requirements. Additional features such as heating, cooling, programmed control, or aseptic design can be selected based on experimental conditions. Relevant industry standards (e.g., ISO, ASTM, GB for specific mixing processes) are also required to ensure method compliance. It is recommended to verify the feasibility of the parameters through small-scale tests before determining the equipment specifications.