In many industrial processes, the homogeneous mixing of liquids is crucial for the quality of the final product. Stationary mixers are an effective, economical, and energy-efficient means of achieving this goal. These devices have no moving parts; instead, they utilize the specific design of their internal components to control the liquid flow and thus ensure efficient mixing.
Furthermore, laminar flow, as one of the flow regimes, directly influences the operation and design of stationary mixers. Understanding the relationship between stationary mixers and laminar flow is therefore essential for the design and optimization of mixing processes in industries such as oil and gas, petrochemicals, water treatment, pharmaceuticals, and food processing.
Definition of a stand mixer
A stationary mixer is a cylindrical device containing stationary elements of different shapes. These elements generate controlled turbulence in the liquid flow, thereby separating, mixing, and successively combining the different liquid layers.
Unlike dynamic mixers, which use mechanical energy and electric motors, stationary mixers have no moving parts ; the energy required for mixing comes from the liquid flow. This reduces maintenance costs and energy consumption and extends the service life of the equipment.
Operating principle
The operating principle of a stationary mixer is based on changing the liquid flow rate and increasing the contact area between the phases . As the liquid flows through the internal components, it describes a spiral path and divides into multiple streams. Each component divides the liquid into two or more streams, mixes the different layers, and changes the flow direction.
In laminar flow, mixing occurs primarily through shear and stress in the fluid layer, while in turbulent flow it is mainly caused by natural turbulence and vortices. Therefore, the geometry of the components must be adapted to the flow type.
Concept of laminar flow
Laminar flow is a state of fluid motion in which the particles move along regular, parallel paths and the molecules mix only very slightly. In this type of flow, the movement of each fluid layer is practically independent of neighboring layers.
The Reynolds number is one of the most important parameters for determining the flow pattern and can be calculated using the following formula:
Re=ρ×v×DμRe = \frac{{\rho \times v \times D}}{{\mu}
Where:
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ρ\rho : Density of liquids
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vv : flow velocity
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DD :
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μ Dynamic viscosity of a liquid
A Reynolds number below 2100 indicates laminar flow, between 2100 and 4000 transitional flow , and above 4000 turbulent flow.
In stationary mixers designed for highly viscous liquids, the flow is typically in the laminar range, and the components must be designed to ensure complete mixing even under such calm conditions.
Interior design and structure of the elements
The internal components of a stand mixer are typically made of stainless steel, polypropylene, polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), or titanium . The shapes of the components can vary, but the most common are:
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Helical element:
Two intersecting spirals alternately direct the fluid to the right and left. Suitable for laminar flow. -
Blade elements:
Blades with a specific angle are able to create lateral cuts in the liquid. -
Components of types SMX and SMXL:
developed for highly efficient laminar flows in the chemical and pharmaceutical industries. -
Components with multiple elements:
Combination of several different designs to achieve high efficiency under varying flow conditions.
Each component divides the liquid into two parts, which then mix at different angles. In each step, the number of liquid layers increases significantly until mixing is complete.
For example, in laminar flow, the number of flow layers can increase up to 64-fold after passing through 6 spiral elements.
The relationship between static mixers and laminar flow
In laminar flow, where no natural turbulence occurs, stationary mixers play a crucial role in efficient mixing . A suitable design ensures the uniform mixing of two or more substances, even with high-density liquids and low flow velocities.
Key performance features of this mode include:
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The mixture is obtained by cutting and stretching the layers.
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Increasing the contact area between the liquid components without causing significant disturbances.
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Since the mixing energy is provided by the fluid dynamics, the pressure drop is relatively high.
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Possibility of predicting flow behavior and mixture quality using numerical simulation (CFD).
Design parameters for laminar flow
The following parameters are of particular importance for the optimal design of stationary mixers in laminar flow mode:
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Total length of the mixer (L):
is usually expressed by the pipe diameter (D); the ratio L/ is usually between 10 and 40. -
Differential pressure (ΔP): This must be designed so that the system outlet pressure is kept within the permissible range
while ensuring efficient mixing. -
Number of components:
While each component increases the mixing effect, it also increases the voltage drop; therefore, a balance must be found. -
Component rotation angle:
Typically 90 to 180 degrees to generate optimal shear force in laminar flow. -
Viscosity of the liquid:
The higher the viscosity, the more components are needed and the greater the pressure drop.
Industrial applications of stationary mixers in laminar flow
1. Chemical and petrochemical industry
During polymerization, the reaction proceeds slowly and under laminar flow. The use of a stationary mixer ensures a uniform reagent concentration and enables precise temperature control.
2. Food and pharmaceutical industry
When mixing viscous substances such as syrups, sauces, and medical solutions, the flow is typically laminar. A stable and hygienic mixer ensures a uniform, contamination-free mixture.
3. Water and wastewater treatment
When injecting chemicals such as chlorine, electrolytic polymers, and coagulants, laminar flow can lead to insufficient mixing. Installing a stationary mixer immediately after the injection point ensures a uniform distribution of the materials.
4. Oil and gas industry
Stationary mixers are used in transfer lines to homogenize the temperature, concentration, and composition of different phases. They also serve as agglomerators for precise sampling in multi-stage transfer lines.
5. Production of paints and resins
In laminar flow processes, resin and hardener must be thoroughly and uniformly mixed to ensure the desired quality of the final product. Stationary screw mixers are very effective for this application.
Advantages and disadvantages of stationary mixers in laminar flow
To use
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No moving parts → Low maintenance and repair costs
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Suitable for use under high pressure and high temperatures
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Highly efficient mixing of highly viscous liquids
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Easy installation in existing pipelines (direct mounting ) .
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Reduction of investment and operating costs
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Possibility of precisely designing specific laminar flow conditions.
Shortage
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In viscous liquids, a significant pressure drop occurs.
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The mix cannot be controlled immediately (unlike with a dynamic mixing console).
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The healthcare sector needs a thorough overhaul.
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Limits of mixing gases or solids on a large scale
Computational Fluid Dynamics (CFD) analysis in the design of stationary mixers
In recent years, computational fluid dynamics (CFD) has become an effective tool for the design and optimization of stationary mixers. CFD modeling enables the accurate simulation of laminar flows and the control of the following parameters:
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Velocity distribution
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Multi-layer cutting process
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Change of focus
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You can check if your blood pressure has decreased.
Using computational fluid dynamics, we can determine the optimal number of cells, the rotation angle and the aspect ratio to achieve maximum mixing efficiency and minimal pressure loss.
Choose the right food processor
The following factors should be considered when selecting the type and size of a stationary laminator:
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Liquid type ( viscosity , temperature, density, reactivity)
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Volume flow and velocity
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Quantity ratio of ingredients
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Permissible inlet and outlet pressures
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Requirements for hygiene and corrosion resistance
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Installation space and access for maintenance work
For special applications, renowned manufacturers such as Sulzer, Cynix, Commax and Noritak offer special products that have been specifically developed for laminar flows.
Maintenance and cleaning
One of the main advantages of stationary mixers is their ease of maintenance. However, blockages can occur with laminar flow of viscous liquids. Therefore, regular cleaning with a suitable cleaning fluid (CIP/SIP) is recommended.
In the bathroom industry, flawless design and top-quality polish are crucial to prevent dirt build-up.
Future and Innovation
Advances in component design, the use of 3D printing to manufacture complex structures, and the development of new corrosion-resistant materials have revolutionized the future of stationary
mixers. In the field of laminar flow, research focuses on improving energy efficiency, reducing pressure drop, and increasing mixing performance. Furthermore, the integration of stationary mixers with intelligent sensors and digital flow control technologies
enables real-time monitoring of mixing quality.
In conclusion
Stationary mixers are efficient, simple, and cost-effective mixing devices for industrial water lines. In laminar flow environments, precise component design is crucial for mixing performance. Digital modeling and the selection of suitable materials allow for the optimization of these devices’ performance for a wide variety of liquids.
In the chemical, food, pharmaceutical, and oil and gas industries, stationary mixers are a reliable solution for improving quality, reducing energy consumption, and increasing process stability.