Study of two impinging flow microsystems arranged in series. Application to emulsified biofuel production

et al. 2021

Exp Fluids

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Experimental study on drop breakage is carried out in the microchannels utilizing head-on impingement configuration by observing single drop breakup process. In this study, the breakage of oil drops with diameter ranging from 30 to 200 μm is investigated in the vicinity of flows impingement region by using high-speed photography at varied flow rate conditions. The most prominent phenomenon of the single drop breakup in the two streams impinging flow field is that the drop tends to break into multiple fragments. The breakage time and the number of daughter drops in the resulting population are statistically analysed and found to be highly dependent on the mother drop size and energy dissipation rate. Two different micro-system geometries, the 600-600 system and the 600-300 system, are compared to evaluate the advantages and disadvantages of swirl flow developed due to the off-axis layout of inlet channels in the 600-300 system. The results show that swirl flow establishes a low pressure area acting as the dead zone, where drop can be trapped and then drastically stretched to breakup. Compared with the 600-600 system, the detrimental effect of swirl flow inside the 600-300 system on increasing the breakage time can be offset by much greater amount of daughter drops generated. In general, the 600-300 system performs more effectively than the 600-600 system because of the less isotropic flow feature. And this superiority is more distinct when energy dissipation rate is higher. Acronyms Ca Capillary number,-DDSD daughter drop size distribution,-Re Reynolds number,-SSI swirl strength index,-We Weber number,-Wet Weber number in turbulent flow,-We* Weber number defined in this study,

Section: Drop Dynamics In Microfluidic Emulsifiermentioning

confidence: 99%

Experimental investigation on single drop breakage in two-stream impinging microchannels

Bellettre

et al. 2021

Exp Fluids

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“…The emulsion is formed and collected through two 600 µm in width microchannels. Concerning the particular flow pattern and droplet break-up mechanisms occurring in such a system, the reader can refer to several publications (Belkadi et al, 2015, Belkadi et al, 2016, Ji et al, 2020. The specific design of the microsystem enhances a swirl flow in the impinging area, associated with a dead zone.…”

Section: Experimental Device Based On Mht Microsystemmentioning

confidence: 99%

“…Recirculation in MHT has not been presently been investigated. However, a previous work (Belkadi et al, 2016) has shown that using two microsystems implemented in series allows, in some different situations, to reduce the mean droplet size and to refine the droplets distribution.…”

Section: J O U R N a L P R E -P R O O Fmentioning

confidence: 99%

Production of oil in water emulsions in microchannels at high throughput: Evaluation of emulsions in view of cosmetic, nutraceutical or pharmaceutical applications

Nehme

Blel

Chemical Engineering and Processing - Process Intensification

et al. 2021

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This work investigates the quality of emulsions obtained from fast emulsification in a microsystem implemented at high throughput. The aim is to manufacture oil in water (O/W) emulsions in which bioactive ingredients could be encapsulated. These emulsions may be of interest for cosmetic, nutraceutical and/or pharmaceutical applications. A microsystem based on an improved cross-slot configuration is tested for production of emulsions with various formulations in a range of flow rate comprised in 100-600 mL/min. Dispersed lipid phase consists mainly in sunflower oil. The continuous aqueous phase is a Non-Newtonian fluid as it includes xanthan in order to stabilize the emulsions. Several commercial surfactants are also used to stabilize the emulsions. Their stability is examined during a storage period of approximately 30 days. For most tests, the evaluation of emulsions is based on a comparison with emulsions produced from a commercial laboratory rotor stator emulsifier. The results show only a few slight differences between the characteristics of emulsions generated in continuous in the microsystem and those obtained from the batch rotor-stator emulsifier. The results are therefore mostly comparable, which leads to the conclusion that microsystems can offer an interesting alternative to the small-scale production of emulsions.

“…The microfluidic devices designed for highly efficient oil-in-water emulsification utilizing impingement configuration of two streams are shown in Fig. 2; they have been investigated previously by Belkadi et al (2016;2018). Fig.…”

Section: Microfluidic Devicementioning

confidence: 99%

Fast oil-in-water emulsification in microchannel using head-on impinging configuration: Effect of swirl motion

Bellettre

International Journal of Multiphase Flow

et al. 2020

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Liquid-liquid dispersion by head-on impingement in a cross-slot microfluidic device to form oil-in-water emulsion is experimentally investigated at broad range of flow rate conditions. Reynolds number based on the continuous aqueous phase flow is changed from 1000 to 7000 and the oil dispersed volume fraction varies between 3% and 30%. The flow patterns are observed in the vicinity of impinging region to characterize the effect of Reynolds number and oil volume fraction on the water-oil interaction and thus emulsification process. Based on the measured droplet size and size distribution, two geometries are compared, aimed at evaluating the advantages and disadvantages of swirl flow in the collision region for producing high quality emulsion. One configuration, "600-600", corresponds to inlet channels of identical size (600 μm×600 μm), while the other one, "600-300", has a smaller channel for dispersed phase which is off-axis with the water channel. The results show that flow characteristics during dispersing process are significantly different for viscous and turbulent conditions. Dominated by Reynolds number, the flow patterns are classified into three regimes. The more turbulent the flow is, the finer and more monodispersed droplets will be in the o/w emulsion. In the medium Reynolds number regime, characteristics of flow are closer to laminar flow using higher oil volume fraction, compared to small oil volume content. It is particularly evident with 600-300 system because of lowering velocity gradient between two phase streams. Based on results of drop mean diameter and polydispersity index, 600-300 system which generates swirl flow structure only exhibits a superior performance, compared to the conventional equal-size geometry, at relatively higher Reynolds number.