Numerical study of fouling effects in asymmetric flow field-flow fractionation for nanoparticle separation

Asymmetric flow field-flow fractionation (AF4) finds wide applications in nanoparticle separation. However, the selection of operating parameters often relies on experimental trials, and membrane fouling during repeated operation can significantly affect separation performance. In this study, a multiphysics numerical framework was developed to simulate nanoparticle separation in AF4, capturing both the focusing and elution stages under prescribed operating conditions. A fouling model was introduced to relate particle accumulation on the membrane surface to spatial variations in membrane permeability, allowing the coupled evolution of flow redistribution and particle transport to be analyzed. The results show that membrane fouling induces a spatially nonuniform crossflow distribution, which shifts the focusing position and reduces separation resolution. Additional sensitivity analysis further shows that cake-layer-induced reduction of the effective channel height can also deteriorate elution resolution. These findings provide mechanistic insight into fouling-induced separation deterioration and offer guidance for improving parameter selection and the operational robustness of AF4 systems.