Simulation Study on the Dynamic Behaviors of Water-in-Oil Emulsified Droplets on Coalescing Fibers

Abstract

Although increasing superwetting membranes have been developed for separating oil−water emulsions based on the "size-sieving" mechanism, their pores are easily blocked and fouled by the intercepted emulsified droplets, which would result in a severe membrane fouling issue and a sharp decline in flux. Instead of droplet interception, a fiber-based coalescer separates oil/water emulsions by inducing the emulsified droplets to coalesce and transform into layered oil/water mixtures, exhibiting an ability to work continuously for a long time with high throughput, which makes it a promising technology for emulsion treatment. However, the underlying mechanism of the separation process is not well understood, which makes it difficult to further improve the separation performance. Hence, in this work, the dynamic behaviors of water-in-oil emulsified droplets on the surface of the coalescing fiber were numerically investigated based on the phase-field model. The attachment, transport, and detachment behaviors of droplets on fibers were directly observed, and the effects of fiber wettability, orientation, arrangement, and fluid speed were studied in detail. First, it was observed that the droplets will move downstream along the fiber surface under the effect of fluid shear, and the large droplets tend to coalesce with their downstream small droplets on the same fiber surface because they move faster compared to the small droplets. Second, it was found that the emulsified droplet will spontaneously transport to the intersection of two angled fibers under the drive of asymmetric Laplace pressure, which demonstrated that the emulsified droplets tend to gather at the intersection of fibers when permeating through a coalescing medium. Third, it was found that the detachment behaviors of droplets from the fiber surface are strongly affected by their size, fiber wettability, and fluid velocity. In addition, the results of our simulation show that the backside of two closely attached fibers can further inhibit the detachment of droplets. We truly believe that our research results are of significance to optimize the parameters of a fiber-based coalescer for separating oil− water emulsions and to develop novel oil/water separators.

Fabrication and Characterization of Prochloraz Nanoemulsion against Penicillium citrinum for the Postharvest Storage of Navel Oranges

“…A droplet with low Laplacian pressure exhibits a relatively large trend from small to large droplets. 50 The TSI values of the prochloraz nanoemulsions prepared at different surfactant concentrations is shown in Figure 2C. The highest TSI value of nanoemulsion was observed when the surfactant concentration was 4 wt % (>1.5), followed by the TSI value of the nanoemulsion with surfactant concentrations of 5, 8, and 7 wt % (1.0−1.5).…”

“…Second, the Laplace pressure inside a small drop is greater than the Laplace pressure inside a large drop. A droplet with low Laplacian pressure exhibits a relatively large trend from small to large droplets …”

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

“…Although several dynamic contact angle models have been developed to date, − it is still difficult to judge whether the models can be applied to this situation. In this study, as in recent numerical studies that investigated the dynamic wetting on porous media, ,, the above contact angle models developed by previous researchers have not been employed.…”

“…Another important approach for the design and analysis of cross-flow microfiltration is based on computational fluid dynamics (CFD), which has a large amount of popularity because it has good potential to investigate membrane separation phenomena, as CFD models are more feasible and less expensive for parametric studies and can potentially reveal details of fluid motion inside a membrane. − The volume-of-fluid (VOF) method was used in the previous studies , to analyze the oil droplet behavior at a pore entrance in the cross-flow microfiltration of oil–water dispersions. Asadi et al constructed a 2-dimensional (2D) CFD model and employed molecular and shear-induced diffusion coefficients to predict the back-diffusion of oil droplets from the membrane wall toward the bulk flow.…”

ZnO Nanoneedle-Modified PEEK Fiber Felt for Improving Anti-fouling Performance of Oil/Water Separation

“…The decontamination of oily wastewater attracts continuous attention since it is closely related to human health and environment security. − Compared with skimming, centrifugation, adsorption, chemical coagulation, and other approaches, the membrane separation technology is considered to be the most effective method with merits of inexpensiveness, low energy cost, convenient manipulating, and high selectivity. − The critical point of the membrane separation technology is confrontation with the declination of separation properties caused by membrane fouling . For oil-removing membrane, the fouling resistance could be achieved by promoting water locking capability and preventing oil affinity .…”