Effect of Surface Wettability on Droplet Coalescence and Pressure Drop in a Fibrous Filter: Direct Numerical Simulation Coordinated with X-ray Computed Tomography Images

Abstract

In this study, the effect of surface wettability on the coalescence of oil droplets and pressure drop within a fibrous filter were investigated numerically. We simulated the permeation and coalescence of an oil-in-water (O/W) emulsion through a fibrous filter using our direct numerical simulation model based on the phase-field model, the immersed boundary method, and a wetting model that assigns an order parameter to the fiber surface. To appropriate the actual phenomena inside the filter, the microporous structure obtained from X-ray computed tomography (CT) images were employed in the simulation. With a low surface wettability, the arrangement of closely attached fibers at the permeating side of the filter domain promoted droplet coalescence. With a high surface wettability, the arrangement of small interfiber spacing placed at the permeate side significantly enhanced droplet coalescence, owing to the formation of a liquid-bridged structure between the fibers at the permeate side. The pressure drop increased with the high surface wettability. The liquid bridges that formed between the fibers at the permeate side blocked the flow path of the permeating fluid, causing a higher pressure drop. A sparse/dense structure, such as the closely attached fibers and small interfiber spacings at the permeate side, promoted droplet growth. Although the uniform fiber arrangement reduced the number of uncoalesced droplets passing through a filter, the coalescence performance is not very high, and the pressure drop significantly increases because the enlarged droplets block the flow path.

High-Resolution Numerical Simulation of Microfiltration of Oil-in-Water Emulsion Permeating through a Realistic Membrane Microporous Structure Generated by Focused Ion Beam Scanning Electron Microscopy Images

“…S is the random stress tensor, which represents thermal fluctuations at the mesoscopic scale . Details of the calculation of this term are found in refs , . The momentum exchange term f IB is explained in the next section.…”

“…We have shown a simple simulation result of a droplet moving on a surface in our previous paper. 50 It can be seen that the dynamic contact angle is expressed qualitatively. However, whether this model can accurately represent the dynamic contact angle of complex and small scales such as porous media needs to be investigated in the future.…”

“…49 The wall boundary model combined with the immersed boundary method and the wetting model has been validated sufficiently and employed in several applications. [49][50][51]53,54 Hence, the adequacy of the wall boundary model used in this study was proven. It should be noted that recently, several researchers have reported the numerical models for the dynamic contact angle in multiphase flow simulations.…”

Effect of liquid volume fraction and shear rate on rheological properties and microstructure formation in ternary particle/oil/water dispersion systems under shear flow: two-dimensional direct numerical simulation

“…The details of the modelling of interfacial flows are available in our previous papers. [34][35][36][37]…”

Identification of Deposited Oil Structures on Thin Porous Oil Mist Filter Media Applying µ-CT Imaging Technique

“…With a highperformance workstation and a corresponding software using artificial intelligence (AI) segmentation tools, even materials with similar densities or atomic numbers can be easily distinguished by this technique. In the past, glass fibers in glass/epoxy laminate [15], synthetic fibers in concrete [16] or porous PPS (polyphenylene sulfide) filters for the filtration of oil/water emulsions [17,18] have already been investigated using a (µ-)CT but there is still no research done for porous filter material consisting of micro glass fibers and/or PET fibers with diameters down to approximately 1 µm loaded with oil mist.…”