Studies of droplets formation regime and actual flow rate of liquid-liquid flows in flow-focusing microfluidic devices

•Droplets formation regime were obtained depending on physical properties of phases and input flow rate.•Smaller and more uniform droplets were generated on dripping regime.•At high input flow rates, the actual flow rate values were lower than nominal one.•Limit value of phase flow rate depend on ph...

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Bibliographic Details
Published in:Experimental thermal and fluid science 2017-07, Vol.85, p.167-175
Main Authors: Costa, Ana Letícia Rodrigues, Gomes, Andresa, Cunha, Rosiane Lopes
Format: Article
Language:English
Subjects:
Cross-junction
Dimensionless numbers
Droplets
Emulsion
Flow rates
Flow velocity
Fluids
Gellan gum
High flow
Hydrodynamics
Low flow
Mathematical analysis
Microchannel
Microchannels
Oils & fats
Phases
Physical properties
Reynolds number
Soybean oil
Soybeans
Surface tension
Viscosity
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Summary:•Droplets formation regime were obtained depending on physical properties of phases and input flow rate.•Smaller and more uniform droplets were generated on dripping regime.•At high input flow rates, the actual flow rate values were lower than nominal one.•Limit value of phase flow rate depend on phases viscosity and microchannel geometry. Studies of droplet formation regime and actual flow rate of liquid-liquid flows were conducted in flow-focusing microfluidic devices using water or gellan solution as aqueous phase and an organic phase composed by soybean oil and polyglycerol polyricinoleate. The influence of flow rate and flow rate ratio (q) on droplets formation regime was evaluated. Squeezing regime was observed at q between 0.5 and 1, while dripping regime occurred at q lower than 0.5. The actual flow rate of the phases was calculated and similar values to the nominal one were found at low flow rates, but the actual values were lower than nominal one at high flow rates. Such differences were associated to the forces balance involved in the droplets formation by flow-focusing mechanism and the reduced dimensions of the channels, implying in an accumulation of the injected fluid. Dimensionless numbers of Reynolds (Rec), Weber (Wed), Capillary (Ca) and Eotvos (Eo) were calculated from the actual velocities. A higher viscosity difference between the phases and lower interfacial tension between water/oil phases led to higher values of Ca and Wed for water than for gellan solution as aqueous phase. Our results showed that the droplets size and formation was influenced by the physical properties of the phases and process conditions (input flow rate), which also defines the droplets formation regime. Therefore, understanding the dynamics of droplets generation in microchannels is essential to ensure that droplets can be created based on specific parameters, such as droplets formation regime and dimensionless numbers, overcoming the limitations of the scale-up (operational conditions and physical properties) of microfluidic systems.
ISSN:0894-1777
1879-2286
DOI:10.1016/j.expthermflusci.2017.03.003