Determination of the Orthokinetic Coalescence Efficiency of Droplets in Simple Shear Flow Using Mobile, Partially Mobile and Immobile Drainage Models and Trajectory Analysis

Mousa, Hasan; Agterof, W.G.M.; Mellema, J.

doi:10.1205/026387602317446380

Cited by 6 publications

(10 citation statements)

References 41 publications

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“…In linear flows, this critical decreases with increasing droplet diameter [17,18]. These observations are in agreement with the predictions of the drainage models [10,14,15]. Based on these drainage theories, Jaeger et al [13] also predicted that coalescence will only occur when the initial offset in the velocity gradient direction between the centers of mass of the droplets is smaller than a critical offset.…”

Section: Introductionsupporting

confidence: 75%

“…The enhancement of the coalescence efficiency due to confinement may facilitate the formation of very large droplets or strings which were observed by several authors for confined, concentrated emulsions [33]. ) and viscosity ratio used in our experiments (the Hamaker constant used for the calculation of the flow number is taken to be J, which is the same order of magnitude as values used in literature [5,14,15]). The large overestimation of the coalescence efficiency by this PMI model can be attributed to the assumptions that were made concerning the lubricaton force and the shape of the contact area between the droplets.…”

Section: Coalescence Efficiencymentioning

confidence: 63%

“…Based on these drainage models, the coalescence efficiency can be determined by comparing the time needed for drainage with that available during droplet collision [10,13]. A comparison of the coalescence efficiencies determined with the different drainage models and the trajectory analysis can be found in the work of Mousa et al [14]. Finally, by combining the trajectory analysis with droplet deformability, more accurate expressions for the coalescence efficiency of unconfined droplets can be obtained [15].…”

Section: Introductionmentioning

confidence: 99%

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The effect of geometrical confinement on coalescence efficiency of droplet pairs in shear flow

Bruyn

Cardinaels

Moldenaers

2013

Journal of Colloid and Interface Science

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This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. 1The effect of geometrical confinement on coalescence efficiency of droplet pairs in shear flow AbstractDroplet coalescence is determined by the combined effect of the collision frequency and the coalescence efficiency of colliding droplets. In the present work, the effect of geometrical confinement on coalescence efficiency in shear flow is experimentally investigated by means of a counter rotating parallel plate device, equipped with a microscope. The model system consisted of Newtonian droplets in a Newtonian matrix. The ratio of droplet diameter to plate spacing ( ) is varied between 0.06 and 0.42, thus covering bulk as well as confined conditions. Droplet interactions are investigated for the complete range of offsets between the droplet centers in the velocity gradient direction. It is observed that due to confinement coalescence is possible up to higher initial offsets. On the other hand, confinement also induces a lower boundary for the initial offset, below which the droplets reverse during their interaction, thus rendering coalescence impossible.Numerical simulations in 2D show that the latter phenomenon is caused by recirculation flows at the front and rear of confined droplet pairs. The lower boundary is independent of , but increases with increasing confinement ratio and droplet size. The overall coalescence efficiency is significantly larger in confined conditions as compared to bulk conditions.

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Section: Introductionsupporting

confidence: 75%

Section: Coalescence Efficiencymentioning

confidence: 63%

Section: Introductionmentioning

confidence: 99%

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The effect of geometrical confinement on coalescence efficiency of droplet pairs in shear flow

Bruyn

Cardinaels

Moldenaers

2013

Journal of Colloid and Interface Science

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“…III A and III B, it was reported that the critical Ca number and the upper critical initial offset decrease with increasing viscosity ratio. A first reason for this is the lower mobility of the interface at the higher viscosity ratio, which hinders film drainage [Chesters (1991); Mousa et al (2002)]. However, a comparison of Fig.…”

Section: Effects Of Viscosity Ratiomentioning

confidence: 99%

“…The experimental studies of Tretheway et al (1999) showed that the trajectories of interacting droplets in extensional flow depend on the viscosity ratio. Mousa et al (2002) calculated the coalescence efficiencies for different viscosity ratios in shear flow using the partially mobile interface model and found a decrease of the coalescence efficiency with viscosity ratio. Minale et al (1997) experimentally investigated the effect of viscosity ratio on the average droplet size in concentrated sheared blends and found that the accuracy of the fully mobile drainage model increases with decreasing viscosity ratio, whereas the opposite is true for the immobile drainage model.…”

Section: Introductionmentioning

confidence: 99%

The effects of geometrical confinement and viscosity ratio on the coalescence of droplet pairs in shear flow

Bruyn

Chen

Moldenaers

et al. 2014

Journal of Rheology

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SynopsisThe effects of geometrical confinement and viscosity ratio on droplet coalescence in shear flow are experimentally investigated by means of a counter rotating parallel plate device, equipped with a microscope. The ratio of droplet diameter to gap spacing is varied between 0.03 and 0.33 to study both bulk and confined conditions. Three grades of a Newtonian droplet material are combined with a Newtonian matrix, resulting in three different viscosity ratios, namely, 0.1, 1.1, and 2.6. The effects of confinement are qualitatively similar for all three viscosity ratios. For each system, confinement decreases the coalescence angle and renders coalescence possible up to higher capillary numbers and initial offsets. Moreover, for all three viscosity ratios, confinement induces a lower initial offset boundary below which the approaching droplets reverse flow direction without coalescence. However, there are quantitative differences between the systems. With increasing viscosity ratio, the critical capillary number and critical upper and lower offset boundaries decrease. Since the decrease of the upper offset boundary is more predominant, the coalescence efficiency decreases with viscosity ratio. The droplet trajectories of interacting droplets are affected by both the viscosity ratio and geometrical confinement, which clearly has implications on the coalescence behavior. V C 2014 The Society of Rheology.

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Measuring of coalescence in polymer melt blends flowing through converging channels

Miroshnikov

Egorov

Egorova

2011

J of Applied Polymer Sci

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Droplets of polymer blends flowing through convergent channels undergo collisions and coalescence because of the appropriate wineglass-shaped flow paths with essential flow constriction at the entrance zone. Therefore, an attempt has been undertaken to use capillary flow for studying coalescence phenomena in polymer blends. When the initial drop diameters in a barrel (before extrusion), d b , and in the extrudate, d e , are measured, coalescence efficiency can be easily calculated as E c ¼ de , provided that no breakup of elongated domains occurs. Compared with methods employing simple shear flow, it has several advantages. For example, the convergent flow pattern combining both shear and extensional flows is directly related to industrial processing operations like extrusion, injection molding, blowing, etc. The method imposes minor limitations on processing parameters and materials used. Applicability of the technique proposed was verified by systematic studies of coalescence in PMMA/PS binary melts blends during capillary extrusion and by comparing these results to theoretical predictions and experimental data from literature.

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Determination of the Orthokinetic Coalescence Efficiency of Droplets in Simple Shear Flow Using Mobile, Partially Mobile and Immobile Drainage Models and Trajectory Analysis

Cited by 6 publications

References 41 publications

The effect of geometrical confinement on coalescence efficiency of droplet pairs in shear flow

The effect of geometrical confinement on coalescence efficiency of droplet pairs in shear flow

The effects of geometrical confinement and viscosity ratio on the coalescence of droplet pairs in shear flow

Measuring of coalescence in polymer melt blends flowing through converging channels

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