Pressure drop in a stationary mixer

introduction

Static mixers are widely used in the chemical, food, pharmaceutical, and water treatment industries and mix fluids without moving parts. Pressure drop is a key consideration in the design and operation of static mixers. Excessive pressure drop can lead to higher operating costs, reduced efficiency, and even system damage. In this article, we discuss the factors that influence pressure drop in static mixers and how to reduce it.

1. What is the pressure drop in a stationary mixer?

Pressure drop refers to the energy lost by the fluid as it flows through the mixer and is typically measured in Pascal (Pa) or bar . The higher the pressure drop, the more energy is required to pump the fluid, which in turn increases operating costs.

2. Parameters that influence the pressure drop in a stationary mixer

The magnitude of the pressure drop in a stationary mixer is influenced by several factors. The most important of these are:

2.1. Design and development of the mixer

Number of mixing elements: The more elements, the greater the pressure drop.
Faucet length: Longer faucets create a greater pressure difference.
Shape of the elements:
- Scroll elements have a lower pressure drop than more complex elements.
- Elements with sharp corners create greater flow resistance.

2.2 Properties of liquids

Viscosity: Fluids with higher viscosity (such as oils) produce a greater pressure drop.
Density: Heavier liquids (such as some chemical solutions) lose more pressure.
Flow velocity: The faster the fluid moves, the greater the pressure drop (quadratic dependence on the flow velocity).

2.3 Operating conditions

Flow velocity: An increasing flow velocity leads to an increasing pressure drop.
Fluid temperature: For fluids such as polymers, increasing temperature can decrease viscosity and thus lower pressure.
Inlet pressure: A higher initial pressure can partially compensate for a lower pressure.

2.4 Mixer material and surface roughness

Smooth surface: reduces friction and pressure drop.
Rough surface: increases flow resistance and pressure drop.

2.5 Type of mixture required

Complete mixing: requires more components and a higher pressure drop.
Partial mixing: low pressure.

3. Calculation of the pressure drop in a stationary mixer

Empirical fluid dynamics relationships and equations are used to calculate pressure drop. A common equation is the Darcy-Weisbach pressure drop equation:

$ΔP = f\cdot ()^{\cdot} (ρ\cdotv22)$

Variables:

ΔP: Differential pressure (Pa)
f: coefficient of friction (depends on material and surface roughness)
L: Length of the mixer (m)
Dₕ: Hydraulic diameter (m)
ρ: density of the liquid (kg/m³)
v: fluid velocity (m/s)

4. Solutions to reduce pressure drop in static mixers

To improve the stability of the mixer and reduce the pressure drop , the following solutions are recommended:

4.1 Optimization of the mixer design

Reduce the amount of ingredients (if possible without compromising the quality of the mixture).
Use of aerodynamically designed elements (reduction of flow resistance).
Reduce the length of the mixer (while maintaining efficiency).

4.2. Setting operating conditions

Flow control (use of flow control valves).
Select the appropriate inlet pressure .
Adjust the temperature of liquids (for temperature-sensitive liquids).

4.3 Selection of suitable materials

Use low-friction coatings (e.g. PTFE).
Polish the inside surface of the faucet to reduce roughness.

4.4 Use of simulation software

Computational Fluid Dynamics (CFD) modeling to predict pressure drop prior to construction.

5. Conclusion

The pressure drop in a stationary mixer depends on several factors, including mixer design, fluid properties, operating conditions, and surface material. Understanding these parameters and applying optimization strategies can reduce pressure drop and improve system efficiency. When designing a stationary mixer, it is important to strike a balance between mixing quality and pressure drop to achieve optimal performance and reduce energy costs.