Scaling of the bubble formation in a flow-focusing device: Role of the liquid viscosity

• The bubble formation in a flow-focusing device is studied.
• The role of the liquid viscosity on bubble formation is investigated.
• A power-law relation between bubble size and operating parameters is obtained.
• A scaling law is proposed for the prediction of bubble size.

The present work studies the bubble formation in viscous liquids with the viscosity ranging from 5 to 400 mPa s by using a high-speed digital camera. The experiment was carried out in a flow-focusing device with square cross-section of 600×600 μm. Results show that the viscous shear stress strongly influences the dynamics of bubble formation, including the shape and size of bubbles. The bubble size follows power-law relations with the gas flow rate, the flow rate and viscosity of the liquid phase respectively, indicating that bubbles formed in viscous fluids are controlled by a combination of squeezing mechanism and shearing mechanism. Therefore, the bubble size can be predicted by a power-law function depending on the flow rate ratio of gas and liquid phases φ representing the squeezing mechanism and capillary number Ca representing the shearing mechanism. In addition, the dynamics of bubble formation in viscous liquids in a flow-focusing device is also analyzed.

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