Two-Phase Flows of Droplets in Contractions and Double Bends

Christafakis, A.; Tsangaris, S.

doi:10.1080/19942060.2008.11015230

Cited by 14 publications

(11 citation statements)

References 18 publications

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“…Taylor deformation factor: L : maximum length of the droplet/bubble during the deformation process; B : minimum length of the droplet/bubble during the deformation process. [25] L D L : maximum length of the droplet/bubble during the deformation process;…”

Section: L−b L+bmentioning

confidence: 99%

“…Straight Droplet breakup [30] Tapered/ conical Droplet breakup [27] Sinusoidal/ cosine Oil trapping, droplet breakup [31] Double-bend Provides deformation and rotation [25] Saw-tooth-shaped Directional transportation by periodic half-open capillary channels [32] Hyperbolic channel Capsule dynamics, encapsulate droplet [33] Shark teeth Provides rapid deformation [34] Within constrictions, the number of possible arrangements is high, and Table 3 summarizes the main types of constrictions that are frequently reported in the literature. Table 3.…”

Section: Constriction Geometry Design Purpose Referencesmentioning

confidence: 99%

“…Christafakis and Tsangaris [25] analysed the influence of the Capillary, Reynolds, and Weber numbers and viscosity ratio on the droplet dynamics in a 2D contraction microchannel while using the level-set method (LSM). These authors simulated systems with three or four consecutive droplets, and the droplet shapes, their deformation and migration compare well with literature data.…”

Section: Contractionsmentioning

confidence: 99%

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Review on Microbubbles and Microdroplets Flowing through Microfluidic Geometrical Elements

et al. 2020

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Two-phase flows are found in several industrial systems/applications, including boilers and condensers, which are used in power generation or refrigeration, steam generators, oil/gas extraction wells and refineries, flame stabilizers, safety valves, among many others. The structure of these flows is complex, and it is largely governed by the extent of interphase interactions. In the last two decades, due to a large development of microfabrication technologies, many microstructured devices involving several elements (constrictions, contractions, expansions, obstacles, or T-junctions) have been designed and manufactured. The pursuit for innovation in two-phase flows in these elements require an understanding and control of the behaviour of bubble/droplet flow. The need to systematize the most relevant studies that involve these issues constitutes the motivation for this review. In the present work, literature addressing gas-liquid and liquid-liquid flows, with Newtonian and non-Newtonian fluids, and covering theoretical, experimental, and numerical approaches, is reviewed. Particular focus is given to the deformation, coalescence, and breakup mechanisms when bubbles and droplets pass through the aforementioned microfluidic elements.Micromachines 2020, 11, 201 2 of 22 droplets through a sudden/gradual expansion/contraction, several numerical and experimental works considered the flow through horizontal pipes, but they are mainly focused on pressure drop [6][7][8][9].The heat and mass transfer can be significantly enhanced in a microsystem due to the high surface volume ratio. Currently, bubble/droplet-based microfluidics has been successfully applied in chemical and biological analysis [10,11], the synthesis of advanced materials [12], sample pretreatment [13], and the encapsulation of cells [14]. Droplets are liquid entities that flow in a immiscible liquid continuous phase, and bubbles are gas entities also flowing in a liquid fluid. The use of droplets as microreactors presents a lot of advantages when compared with single-phase microfluidics, such as: confinement of reactants or prevention of longitudinal dispersion, and cross contamination between samples [15]. The reduction of unwanted adhesion/absorption of the material confined in droplets at the microchannel walls, the possibility of varying, in each droplet the physicochemical conditions under which chemical or biological process develop, and the facilitated heat/mass transport due to the fast mixing promoted by droplets are other benefits [15,16]. The use of bubbles might be interesting to produce contrast agents in medical applications [17], as a source of reactants in the gas phase to promote reactions in liquid or solid (i.e., microchannel wall) phases [18], and to study in vitro gas embolisms [19].Microfluidic devices (length scales lower than one millimeter) comprise microfluidic elements, analogous to their macroscale counterparts, to transport and distribute fluids, to promote mixing, reaction, and mass transfer. In the case of multiphase flows, ...

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Section: L−b L+bmentioning

confidence: 99%

Section: Constriction Geometry Design Purpose Referencesmentioning

confidence: 99%

Section: Contractionsmentioning

confidence: 99%

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Review on Microbubbles and Microdroplets Flowing through Microfluidic Geometrical Elements

et al. 2020

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“…More recent experimental studies of the flow inside real-size and large-scale model nozzles have revealed the complexity of the two-phase flow structures over different operating conditions (Soteriou et al, 1995;Chaves et al, 1995;Arcoumanis et al, 1999;Payri et al, 2007). The size of the injector nozzle and the high speed of fluid flow make it difficult to carry out experimental observations, so the use of numerical simulations (Bierbrauer and Zhu, 2008;Christafakis and Tsangaris, 2008) is very useful to understand the flow features inside and at the exit of the injector nozzle. Different numerical simulations have been reported focusing on cavitation inside the diesel engine injector.…”

Section: Introductionmentioning

confidence: 99%

Numerical Study of The Effect of Wall Injection on The Cavitation Phenomenon In Diesel Injector

Hassanzadeh

Saadat-Bakhsh

Dadvand

2014

Engineering Applications of Computational Fluid Mechanics

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Cavitation has an important effect on the performance of diesel injectors. It influences the nature of the fuel spray and formation of emissions. In contrast, cavitation increases the hydraulic resistance of the nozzle, creates flow instability, produces noise, and erodes the nozzle wall. In the present study, the effect of wall injection on the boundary layer separation in the cavitating and turbulent flow developing inside a diesel injector has been investigated numerically using two-phase mixture model. Simulations have been performed for different cavitation numbers, injection ratios and injection angles. Furthermore, the effects of various wall injection locations have been investigated and the results have been compared. The results indicated that for a particular injection angle, the highest discharge coefficient and the lowest number of cavitation bubbles were observed at a specific range of cavitation numbers. Also, with the injection from the orifice wall, the critical cavitation number diminishes, and only for a small interval of cavitation numbers, the discharge coefficient becomes a function of pressure difference between the two ends of injector. The idea of the current work could be a starting point for application of wall injection in injectors in order to increase the discharge coefficient, and, at the same time, to decrease the undesired effects of the cavitation phenomenon.

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“…Meacham et al (2005) quantified the formation and ejection of droplets using ultrasound while Amirzadeh and Chandra (2010) detailed the results of using a pneumatic droplet generator. Additional studies have been performed by Gjesing et al (2009) (Christafakis and Tsangaris, 2008). Due to the limited amount of research done on liquid droplet formation from ruptured tubes the aim of the current work is the development of an experimentally validated finite volume model that will simulate liquid droplet formation from a ruptured tube.…”

Section: Introductionmentioning

confidence: 99%

Liquid Droplet Growth from a Punctured Vessel Under Steady Flow Conditions

McGarry

Kohl

Hitt

2011

Engineering Applications of Computational Fluid Mechanics

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ABSTRACT:The liquid droplet growth from a punctured, pressurized vessel immersed in a quiescent medium is studied under steady flow conditions. Local strain rates at the puncture site are also investigated. The droplet growth and local strain rates at the puncture are characterized as functions of various hydrodynamic and geometric conditions. Dimensional analysis shows that the fractional droplet growth rate, Q*, is a function of the Reynolds number, Weber number, hole-to-main tube diameter ratio, D*, and the puncture geometry. A 3-D finite volume computational model is constructed for laminar flow of a Newtonian fluid under steady conditions and validated with supporting experiments. The results show that the fractional growth rate Q* increases with the Weber number and is largest for the lowest Reynolds number of one. In addition, the droplet shape is spherical at low Weber numbers (2.6) and ellipsodial at high Weber numbers (7.8). Additional simulations detail how the growth ratio is lower for small diameter ratios and rectangular punctures. Physiological implications for the hemostatic response (clotting) of a punctured blood vessel can be found by examining the local strain rates in the vicinity of the puncture. The strain rate displays the largest values for the highest Reynolds number (100). In addition, when D* = 0.04 the strain rate is greater at the low (2.6) and high (7.8) Weber numbers, while the strain rate is larger for D* = 0.075 when the Weber number is 5.2. The strain rate is also affected by the puncture shape and displays higher values for the rectangular puncture when Weber < 5.2. Finally, the impact of microgravity on droplet formation was studied. Numerical simulations and quantification of the forces on fluid particles show that there is no effect from gravity on the droplet growth rate or strain rate in medium and large sized veins.

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Two-Phase Flows of Droplets in Contractions and Double Bends

Cited by 14 publications

References 18 publications

Review on Microbubbles and Microdroplets Flowing through Microfluidic Geometrical Elements

Review on Microbubbles and Microdroplets Flowing through Microfluidic Geometrical Elements

Numerical Study of The Effect of Wall Injection on The Cavitation Phenomenon In Diesel Injector

Liquid Droplet Growth from a Punctured Vessel Under Steady Flow Conditions

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