Determination of Air Permeability Characteristics of Oil Fume Filter Mesh

Air permeability testing of oil fume filter mesh (grease filter mesh) measures how easily air passes through the multi-layer metallic mesh used in range hoods and kitchen exhaust purification systems, quantifying the critical balance between grease capture efficiency and airflow resistance. This article explains the testing principles, sample types, test items, methods based on standards such as ISO 9237, GB/T 5453, ASTM D737, and ISO 4022, and typical applications in product design and quality control.

Technical Overview

Oil fume filter mesh, commonly known as grease filter mesh, is a porous filtration element—typically manufactured from expanded aluminum foil, woven stainless steel wire, or micro-perforated metal sheets—installed in household range hoods, commercial kitchen exhaust hoods, and oil-fume purification equipment. Because the mesh is positioned directly in the airflow path, its permeability characteristics directly determine system performance: excessive flow resistance reduces exhaust air volume and increases fan energy consumption, while insufficient resistance generally indicates low grease interception efficiency.

Air permeability characteristics are quantified by two complementary parameters. The first is air permeability, defined as the volume of air passing through a unit area of mesh per unit time—expressed in mm/s, L/(m²·s), or m³/(m²·h)—at a specified pressure differential, commonly 100 Pa or 200 Pa. The second is pressure drop, expressed in pascals (Pa), measured at a specified face velocity that simulates real operating conditions. Together, these parameters characterize the flow-resistance behavior of the mesh across its service life. Testing is performed according to recognized methodologies including ISO 9237, GB/T 5453, and ASTM D737 for sheet-type permeable materials, and ISO 4022 for sintered metal and metal-fiber porous media, and may be conducted by manufacturers' laboratories or accredited third-party laboratories.

Testing Samples

Multi-Layer Expanded Aluminum Grease Mesh

This is the most common sample type, consisting of three to eight layers of expanded aluminum foil with staggered pore orientations. The layers are typically bonded, riveted, or framed into a cassette. Samples are cut to the standard test area of the permeability instrument, and layer count, mesh expansion angle, and pore density are recorded because these construction variables strongly influence permeability.

Stainless Steel Woven and Perforated Mesh

Woven wire cloth and micro-perforated stainless steel panels are used in higher-temperature commercial kitchen applications and in baffle-type grease filters. Specimens are prepared free of creases, burrs, and deformation, and the wire diameter, mesh count, or perforation diameter and pitch are documented to enable correlation between structural parameters and measured flow resistance.

Metal Fiber Sintered and Composite Media

Sintered metal fiber felt and metal–nonwoven composite meshes, used as pre-filters or coalescing stages in purification units, are tested as porous media. Because these materials exhibit viscous-dominant laminar flow behavior, their permeability is often characterized using Darcy's law, yielding an intrinsic permeability coefficient in addition to air permeability at a reference pressure differential.

Finished Filter Cartridges and Panels

Complete grease filter cassettes, rectangular panels, and cylindrical filter elements may be tested in a duct or test rig to evaluate the assembled component, including the flow resistance contributed by frames, pleats, and support grids that is not captured by flat-sheet testing alone.

Testing Items

Typical test items for oil fume mesh permeability characterization include:

• Air permeability at a standard pressure differential (e.g., 100 Pa or 200 Pa), reported in mm/s or L/(m²·s)
• Pressure drop at specified face velocities covering the intended operating range of the range hood or exhaust system
• Full flow-resistance curves (pressure drop versus face velocity) for computational fluid dynamics input and fan matching
• Permeability uniformity measured at multiple positions across the mesh surface, expressed as the coefficient of variation
• Permeability retention after grease loading or accelerated aging, quantifying how performance drifts in service
• Batch conformity verification against product specifications or customer-defined acceptance limits

Testing Methods

Fixed-Pressure Differential Method

Following ISO 9237 and GB/T 5453, a circular specimen of defined test area (commonly 20 cm² or 50 cm², or larger areas for coarse mesh) is clamped in the test head of a calibrated digital air permeability tester. A steady airflow is drawn through the specimen until the prescribed pressure differential is stabilized, and the resulting flow rate is measured with calibrated nozzles or orifices. Air permeability is calculated as the volumetric flow rate divided by the test area, with corrections applied for ambient temperature and barometric pressure. A minimum of ten valid measurements at different positions is recommended to characterize material uniformity.

Fixed-Flow Pressure Drop Method

In this configuration, air is drawn through the specimen or assembled filter at one or more controlled volumetric flow rates corresponding to realistic face velocities—often between 0.5 m/s and 3.0 m/s for grease filter applications—and the resulting static pressure drop is measured with calibrated pressure transducers upstream and downstream of the specimen. This method, aligned with the airflow measurement principles used in equipment performance standards such as GB/T 17713 for range hoods, yields data directly usable for system pressure budget calculations.

Darcy-Based Permeability Determination

For sintered metal fiber and coarse porous mesh media, testing per ISO 4022 is performed by measuring the pressure drop across the specimen at several flow rates. The intrinsic permeability coefficient and inertial coefficient are then derived from the Forchheimer relationship describing laminar and turbulent flow contributions. This approach separates material properties from test geometry and allows extrapolation to other fluids and operating conditions.

Specimen Conditioning and Grease-Loading Assessment

Specimens are conditioned in a standard atmosphere prior to measurement to stabilize temperature and, for hygroscopic composite layers, moisture content. Where service simulation is required, specimens may be pre-loaded with a defined mass of grease substitute or subjected to cyclic cooking-fume exposure, after which permeability is re-measured to determine the allowable pressure-drop increase over the maintenance interval. Testing environments are maintained at approximately 23 °C with humidity recorded, and all instruments are calibrated against traceable reference standards.

Applications

Permeability characterization of oil fume mesh supports a wide range of engineering and commercial activities:

• Product design optimization, including selection of layer count, pore density, mesh orientation, and frame geometry to achieve the target balance between grease interception and airflow resistance
• Fan and motor matching for range hood manufacturers, ensuring rated exhaust air volume and noise targets defined in performance standards such as GB/T 17713 are met
• Incoming quality control for appliance and purification equipment manufacturers, verifying batch-to-batch consistency of mesh supplied by material vendors
• Compliance demonstration and independent verification through accredited third-party laboratories for product certification, tenders, and export documentation
• CFD simulation and ventilation system design for commercial kitchens, using measured pressure drop–velocity data as boundary conditions
• Maintenance planning, establishing pressure-drop thresholds that indicate when mesh cleaning or replacement is required
• Comparative benchmarking of alternative mesh materials, such as aluminum expanded mesh versus stainless steel woven mesh versus metal fiber felt

FAQ

What pressure differential and units are used to report air permeability of oil fume mesh?

The most common reference condition is 200 Pa per ISO 9237 and GB/T 5453, with 100 Pa also widely used. Results are reported in mm/s or L/(m²·s), and can be converted to m³/(m²·h) for engineering use. For assembled filters, pressure drop in Pa at a stated face velocity is the preferred reporting format.

How many specimens should be tested?

For flat-sheet mesh, a minimum of ten measurement positions per sample is recommended per ISO 9237 to capture spatial uniformity. For finished filter panels, at least three identical units are typically evaluated to account for assembly variability.

Does grease accumulation affect permeability results?

Yes. Grease loading progressively blocks the pore structure and increases pressure drop. Testing both clean and grease-loaded specimens provides a practical performance envelope and helps define cleaning intervals for end users.

Which standard should be selected for metal mesh rather than textile mesh?

ISO 9237, GB/T 5453, and ASTM D737 are applicable to rigid and semi-rigid sheet materials within their pressure and flow ranges. For sintered metal fiber media, ISO 4022 provides a more rigorous Darcy-based characterization suitable for porous metallic structures.

Can testing support product certification?

Yes. Test reports issued by accredited third-party laboratories, executed under the relevant ISO, EN, GB, or ASTM methods with calibrated equipment, are widely accepted for certification programs, regulatory submissions, and commercial procurement of range hoods and kitchen purification equipment.