On the estimation of the size of a droplet emerging from a pore opening into a crossflow field

Salama, Amgad

doi:10.1039/d1sm01204e

Cited by 13 publications

(13 citation statements)

References 54 publications

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“…The idea behind the PFPT is to mitigate fouling by preventing the accumulation of oil droplets at the membrane surface during filtration. The fate of an oil droplet during filtration has been comprehensively studied using computational fluid dynamics (CFD) [29][30][31][32][33][34][35] and direct observation over the membrane surface [36] to understand the physics behind the oil settling and clogging of membrane pores. The results showed that an oil droplet, during the filtration process, undergoes either of the following four fates, namely 1) rejection, 2) permeation, 3) pinning, or 4) breakup.…”

Section: Periodic Feed Pressure Techniquementioning

confidence: 99%

Experimental Investigation of the Novel Periodic Feed Pressure Technique in Minimizing Fouling during the Filtration of Oily Water Systems using Ceramic Membranes

Echakouri¹,

Salama²,

Henni³

2022

Preprint

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Fouling represents a bottleneck problem for promoting the use of membranes in filtration and separation applications. It becomes even more persistent when it comes to the filtration of fluid emulsions. In this case, a gel-like layer that combines droplets, impurities, salts, and other materials form at the membrane's surface, blocking its pores. It is, therefore, a privilege to combat fouling by minimizing the accumulation of these droplets that work as seeds for other incoming droplets to cluster and coalesce with. In this work, we explore the use of the newly developed and novel periodic feed pressure technique (PFPT) in combating the fouling of ceramic membranes upon the filtration of oily water systems. The PFPT is based on alternating the applied transmembrane pressure (TMP) between the operating one and zero. A PFPT cycle is composed of a filtration half-cycle and a cleaning half-cycle. Permeation occurs when the TMP is set at its working value, while the cleaning occurs when it is zero. Three PFPT patterns were examined over two feeds of oily water systems with oil contents of 100 and 200ppm, respectively. The results show that the PFPT is very effective in minimizing the problem of fouling compared to a non-PFPT normal filtration. Furthermore, the overall drops in permeate flux during the cleaning half cycles are compensated by appreciable enhancement due to the significant elimination of fouling development such that the overall production of filtered water is even increased. Inspection of the internal surface of the membrane post rinsing at the end of the experiment proves that all PFPT cycles maintained the ceramic membranes as clean after a 2-hours operation. This can ensure a prolonged lifespan of the ceramic membrane use and a continuous greater permeate volume production. The advantage of the PFPT is that it can be implemented on existing units with minimal modification, ease of operation, and saving energy.

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Section: Periodic Feed Pressure Techniquementioning

confidence: 99%

Experimental Investigation of the Novel Periodic Feed Pressure Technique in Minimizing Fouling during the Filtration of Oily Water Systems using Ceramic Membranes

Echakouri¹,

Salama²,

Henni³

2022

Preprint

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“…Dimensionless numbers are used to provide criteria on the significance of each of the forces and the patterns of the flow. For example, the significance of interfacial tension force in relation to viscous force is measured via the capillary number ( Ca ). − Ca is defined as, Ca = μV/γ , where μ is the dynamic viscosity, V is a characteristic velocity, and γ is the interfacial tension. The Bond number ( Bo ), on the other hand, measures the relative importance of gravitational force compared to interfacial tension force and is used to characterize the shape of bubbles or drops moving in a surrounding fluid.…”

Section: Introductionmentioning

confidence: 99%

“…The Bond number ( Bo ), on the other hand, measures the relative importance of gravitational force compared to interfacial tension force and is used to characterize the shape of bubbles or drops moving in a surrounding fluid. Bo is defined as, Bo = Δ ρgL 2 /γ, where Δρ is the density difference between the continuous and the dispersed phases, g is the gravity, L is some characteristic length scale, and γ is the interfacial tension. , Likewise, Weber number ( We ) measures the ratio between inertial and interfacial tension forces and takes the form We = ρVL/γ . These numbers provide criteria on when capillary forces may be important and when it may be ignored.…”

Section: Introductionmentioning

confidence: 99%

Capillary-Driven Ejection of a Droplet from a Micropore into a Channel: A Theoretical Model and a Computational Fluid Dynamics Verification

et al. 2022

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In this work, the problem of re-ejection of a permeating droplet through a membrane pore back to the feed channel when the transmembrane pressure (TMP) becomes zero is investigated. This problem is important in the context of oily water filtration using membranes. In particular, in the novel periodic feed pressure technique (PFPT), which has been proposed to combat membrane fouling, the TMP alternates between the operating value and zero in a periodic manner. During the period in which TMP is high, filtration occurs, and when it is zero, cleaning commences. We are particularly interested in what happens to a droplet, initially undergoing permeation, when the TMP becomes zero. It is evident that when the TMP is zero the meniscus inside the pore reverses its motion toward the feed channel rather than toward the permeate side by the action of interfacial tension force. A theoretical model is built to determine the rate at which the meniscus inside the pore advances when the TMP is zero. The conservation of momentum equation is used to establish a one-dimensional model that updates the location of the meniscus with time. The derived model considers both quasi-static and dynamic scenarios. In addition, the model accounts for both the viscosity contrast between the two fluids, as well as the gravity. A computational fluid dynamics (CFD) simulation has been built to provide a framework for model verification and validation. The model, based on quasi-static conditions, provides an overall similar trend to that obtained via CFD analysis. Nevertheless, the quasi-static model predicts a more rapid meniscus advancement inside the pore than the CFD simulation. When the dynamic contact angle is incorporated, very good matching is observed.

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“…The displacement of one fluid by another immiscible one is a phenomenon of great importance and finds direct application in many processes. Examples of these processes include petroleum production, filtration/separation operations, pharmaceutical and food industries, and many others. − Between any two immiscible fluids in contact, there exists an interface that separates one fluid from the other. Such an interface represents a surface of discontinuity that is generally curvilinear.…”

Section: Introductionmentioning

confidence: 99%

“…There are other applications in which emerging droplets are forced to terminate earlier by the action of some external forces (e.g., hydrodynamic drag). This finds applications in pharmaceutical industries where the production of nearly uniform-sized emulsions is desirable to achieve uniform release profiles of the drugs . While the breakup phenomenon of an emerging or permeating droplet by a crossflow field has been studied extensively in the context of oily water filtration, the topic is fundamentally so rich to warrant further investigation. − The framework, which has been adapted to define the critical conditions for breakup of permeating/emerging droplets, has been based on constructing a torque balance of the involved forces around a pivotal point …”

Section: Introductionmentioning

confidence: 99%

Investigation of the Different Regimes Associated with the Growth of an Interface at the Exit of a Capillary Tube into a Reservoir: Analytical Solutions and CFD Validation

et al. 2022

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The emergence of a droplet from a capillary tube opening into a reservoir is an important phenomenon in several applications. In this work, we are particularly interested in this phenomenon in an attempt to highlight the physics behind droplet appearance. The emergence of a droplet from a tube opening into a reservoir under quasi-static conditions passes through three stages. The first stage starts when the meniscus in the tube reaches the exit. At this moment, the meniscus intersects the wall of the tube at the equilibrium contact angle. The interface then develops until its radius of curvature becomes equal to the tube radius. During this stage, the capillary pressure increases. In the second stage, the interface continues to evolve with its radius of curvature increasing until the static contact angle with respect to the surface of the reservoir is achieved. This marks the end of the second stage and the start of the third in which the contact line (CL) starts to depart the tube opening along the reservoir surface and the contact angle remains constant. Analytical models for the three stages have been derived based on the law of conservation of linear momentum. The models account for pressure, gravitational, capillary, and viscous forces, while inertia force is ignored. The model can predict the profiles of the mean velocity in the tube, the capillary pressure, and the evolution of the contact angle. In addition, a computational fluid dynamics (CFD) simulation has been conducted to provide a framework for validation and verification of the developed model. The CFD simulation shows qualitative behavior in terms of snapshots of the emerging droplet with time similar to that speculated by the analytical model. In addition, quantitative comparisons with respect to velocity, pressure, and volume profiles of the droplet show very good agreement, which builds confidence in the modeling approach.

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On the estimation of the size of a droplet emerging from a pore opening into a crossflow field

Abstract: The problem of termination of a droplet at the surface of a membrane in crossflow field is an important topic in the context of controlled emulsification of fluids. In this...

Cited by 13 publications

References 54 publications

Experimental Investigation of the Novel Periodic Feed Pressure Technique in Minimizing Fouling during the Filtration of Oily Water Systems using Ceramic Membranes

Experimental Investigation of the Novel Periodic Feed Pressure Technique in Minimizing Fouling during the Filtration of Oily Water Systems using Ceramic Membranes

Capillary-Driven Ejection of a Droplet from a Micropore into a Channel: A Theoretical Model and a Computational Fluid Dynamics Verification

Investigation of the Different Regimes Associated with the Growth of an Interface at the Exit of a Capillary Tube into a Reservoir: Analytical Solutions and CFD Validation

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