Author: Vanessa 29Apr. 2025 Category: Understanding filtration
1. What is the pressure drop in the filtration industry?
In the filtration industry, pressure drop refers to the pressure loss generated when a fluid (gas or liquid) passes through the filter medium. It is specifically manifested as the pressure difference between the inlet and outlet of the filter, usually measured in Pascal (Pa) or millimeter water column (mmH₂O).
Pressure drop is an important indicator for measuring the energy consumption and efficiency of the filtration system. Excessive pressure drop will not only increase energy consumption, but may also affect the filtration effect and even damage the filtration equipment.
2. Pressure drop formation mechanism and fluid dynamics analysis
Pressure drop (ΔP) is the core parameter of the filtration system, and its formation follows the classical fluid dynamics principle. According to the Navier-Stokes equation and Darcy’s law, the generation of pressure drop is essentially the process of converting fluid kinetic energy into thermal energy. This conversion is mainly achieved through the following three mechanisms:
(1) Structural resistance of the filter medium
- The porosity (ε) is exponentially related to the pressure drop: ΔP ∝ (1-ε)^2/ε^3;
- A study by the German Mann+Hummel Laboratory showed that when the porosity of the filter material dropped from 85% to 75%, the pressure drop increased by 300%;
- Surface characteristics of the material: For example, DuPont™ Tyvek® material uses a patented spunbond process to control the surface roughness within 0.5μm, effectively reducing boundary layer friction;
(2) Intrinsic characteristics of the fluid
- Viscosity effect: At 30°C, the pressure drop of hydraulic oil (ν=46cSt) is 57 times that of water (ν=0.8cSt);
- Flow rate effect: Following the Fanning equation, ΔP is proportional to the square of the flow rate (ΔP ∝ v^2);
- Density effect: In gas filtration, following the ideal gas law, the pressure drop decreases by about 3% for every 10°C increase in temperature
(3) Dynamic pollution mechanism
- Particle deposition presents a typical “three-stage” characteristic:
- Initial stage (0-2h): surface deposition, linear increase in pressure drop;
- Mid-term (2-8h): deep filtration, logarithmic increase in pressure drop;
- Late stage (>8h): filter cake formation, exponential increase in pressure drop.
The team of Professor Klaus Schröder of RWTH Aachen University in Germany found through high-speed microscopic observation: “In industrial filtration systems, the optimal pressure drop point occurs at the initial stage of filter cake formation, when the filtration efficiency (η) and energy consumption ratio (EER) reach a perfect balance, and this critical value is usually 2.5-3 times the initial pressure drop.”
3. Classification of pressure drop optimization technology principles
(1) Filter material optimization principle
① Gradient density structure design theory
- Fluid dynamics principle: By constructing a gradient distribution of pore size, the fluid velocity field is gradually adjusted to avoid local eddy current loss caused by sudden expansion/contraction;
- Boundary layer control theory: The large pore size structure of the outer layer can reduce the initial flow velocity and turbulence intensity; the small pore size of the inner layer ensures the filtration accuracy;
② Surface hydrophobic modification
- Interface chemistry principle: By reducing the surface free energy (γ<sub>sv</sub>), the solid-liquid contact angle (θ>90°) is increased;
- Capillary effect suppression: The hydrophobic surface destroys the capillary rise phenomenon of the liquid in the micropores and reduces the additional flow resistance;
- Dynamic wetting theory: The composite interface under the Cassie-Baxter state can reduce the actual contact area.
(2) System design optimization principle
① Filter area expansion
- Application of Darcy’s law: Under constant flow, increasing the filter area A can reduce the apparent flow velocity v=Q/A;
- Resistance distribution optimization: By increasing the number of parallel flow channels, the pollutant load per unit area can be reduced;
- Structural mechanics principle: The pleated design achieves area gain through geometric expansion while maintaining structural strength.
② Pulse cleaning technology
- Gas-solid two-phase flow theory: High-pressure pulses form shock waves and generate instantaneous reverse pressure gradients
- Particle peeling mechanism: Combine the balance relationship between inertial force (F=ma) and adhesion force (JKR theory)
- Energy transfer efficiency: Pulse waveform optimization ensures that the pressure wave is effectively transmitted to the deep layer of the filter material
From passive bearing to active utilization, modern filtration technology is reconstructing the value chain of pressure drop. As Dr. Werner, Chairman of the European Filtration Alliance, said: “The future smart filter is not about pursuing the lowest pressure drop, but about achieving the optimal conversion of pressure drop energy.” This material revolution that began in the laboratory is reshaping the energy efficiency map of the entire industrial filtration. Follow Trenntech filtration and learn about the professional knowledge of the filtration industry.