Optimization of needle punched nonwoven filter media for enhanced dust filtration performance

Abstract

Nonwoven fabrics play a critical role in filtration applications due to their unique structural properties, including high porosity, irregular structure, and customizable fiber arrangements. These characteristics make them ideal for various filtration purposes, from industrial air filters to indoor air filters for HVAC and engine air filters for automobiles. To this end, polypropylene fibers were spun at two different finenesses (1.5 and 3 denier) using an industrial-scale melt-spinning machine. The nonwoven filter media were then fabricated based on an I-optimal design response surface methodology (RSM-I-optimal) method using a semi-industrial needle punching line. The process parameters considered include the blending ratio of 1.5 denier fibers (0-100%), needle penetration depth (9-16 mm), needling strokes (110-430 strokes/min), calendering temperature (120-140 °C), and calendering pressure (2-6 bar). The 3D microstructure of the samples was analyzed using X-ray µCT, and the morphology was examined through image analysis. Filtration performance, including efficiency, pressure drop, and quality factor, was characterized according to ISO 11,057. The influence of input variables on filtration performance was evaluated using ANOVA, leading to the development of quadratic models for predicting efficiency, pressure drop, and quality factor. The interaction effects of the process parameters were also studied. Optimal conditions were determined to maximize efficiency and quality factor while maintaining pressure drop below 70 Pa. Under these conditions, the predicted values of efficiency, pressure drop, and quality factor were 94.99%, 61.07 Pa, and 0.0456 1/Pa, respectively. Subsequently, four filter media were manufactured under optimal conditions, and their performance was assessed. The experimental results yielded efficiency, pressure drop, and quality factor of 93.37%, 62.52 Pa, and 0.0434 1/Pa, respectively. Additionally, a numerical dust loading simulation was performed through the realistic 3D structure of the optimized filter medium. The optimized filter exhibited good filtration performance in experiments, modeling, and CFD. This research demonstrates that by carefully optimizing process parameters, the filtration performance of needle punch nonwoven fabrics can be significantly enhanced, making them more effective for industrial filtration applications.

Keywords: Filtration performance; Microstructural properties, numerical simulation; Needled nonwoven fabric; Process parameters; RSM-I-optimal; X-ray micro-computed tomography.

Fig. 1

Melt-spinning machine schematic.

Fig. 2

Schematic of laboratory needle-nonwoven production line.

Fig. 3

A representative 3D reconstruction of a nonwoven filter medium (GeoDict 2024, www.math2market.com).

Fig. 4

The definition of 3D FOD in space.

Fig. 5

Extracted pore network, with distinct colors representing separate pores (GeoDict 2024, www.math2market.com).

Fig. 6

Test rig based on ISO 11,057.

Fig. 7

The images of some of the samples, (a) calendered and (b) non-calendered.

Fig. 8

Process flowchart showing the experimental methodology used for filter media preparation, testing, simulation, and optimization.

Fig. 9

Interaction effects of input variables on filtration efficiency.

Fig. 9

Interaction effects of input variables on filtration efficiency.

Fig. 10

Interaction effects of input variables on filtration pressure drop.

Fig. 11

Interaction effects of input variables on the quality factor.

Fig. 11

Interaction effects of input variables on the quality factor.

Fig. 12

Desirability plot for the optimization.

Fig. 13

Simulation results for the optimized filter structure: (a) pressure distribution in clean filter medium, (b) pressure distribution in loaded filter medium, (c) particle deposits, and (d) loaded filter medium (GeoDict 2024, www.math2market.com).

Fig. 13

Simulation results for the optimized filter structure: (a) pressure distribution in clean filter medium, (b) pressure distribution in loaded filter medium, (c) particle deposits, and (d) loaded filter medium (GeoDict 2024, www.math2market.com).