### Abstract

The coalescence efficiency of two Newtonian droplets submerged in a Newtonian fluid subjected to a simple shear flow was investigated experimentally and theoretically. The experimental investigation was based on observing collisions between two droplets under a microscope. The theoretical investigation considered three drainage models: immobile, partially mobile and mobile interfaces. Both the experimental results and the theoretical analysis showed that a critical approach angle exists below which the colliding droplets separate. Above this critical angle the collision leads to coalescence. Knowledge of the critical angle permits calculation of the coalescence efficiency. The dependence of the coalescence efficiency on various dimensionless groups such as the flow number, the capillary number and the viscosity ratio was studied. The theoretical analysis indicated that the coalescence efficiency decreases as the capillary number and the flow number increase. The experimental results showed that the coalescence efficiency goes through a minimum as the value of the flow number increases. The discrepancy between the experimental and the theoretical results was attributed to some mechanism that enhances coalescence and that is not accounted for in the equation used for the critical thickness for film rupture. Both the experimental and the theoretical results indicated that the coalescence efficiency decreases as the viscosity ratio decreases.

Original language | English |
---|---|

Pages (from-to) | 208-215 |

Number of pages | 8 |

Journal | Progress in Colloid and Polymer Science |

Volume | 118 |

Publication status | Published - 2001 |

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### Keywords

- Coalescence efficiency
- Droplets
- Emulsion
- Simple shear
- Stability

### ASJC Scopus subject areas

- Physical and Theoretical Chemistry
- Polymers and Plastics
- Organic Chemistry
- Colloid and Surface Chemistry
- Materials Chemistry

### Cite this

*Progress in Colloid and Polymer Science*,

*118*, 208-215.

**Theoretical and experimental investigation of the coalescence efficiency of droplets in simple shear flow.** / Mousa, Hasan; Agterof, Wim; Mellema, Jorrit.

Research output: Contribution to journal › Article

*Progress in Colloid and Polymer Science*, vol. 118, pp. 208-215.

}

TY - JOUR

T1 - Theoretical and experimental investigation of the coalescence efficiency of droplets in simple shear flow

AU - Mousa, Hasan

AU - Agterof, Wim

AU - Mellema, Jorrit

PY - 2001

Y1 - 2001

N2 - The coalescence efficiency of two Newtonian droplets submerged in a Newtonian fluid subjected to a simple shear flow was investigated experimentally and theoretically. The experimental investigation was based on observing collisions between two droplets under a microscope. The theoretical investigation considered three drainage models: immobile, partially mobile and mobile interfaces. Both the experimental results and the theoretical analysis showed that a critical approach angle exists below which the colliding droplets separate. Above this critical angle the collision leads to coalescence. Knowledge of the critical angle permits calculation of the coalescence efficiency. The dependence of the coalescence efficiency on various dimensionless groups such as the flow number, the capillary number and the viscosity ratio was studied. The theoretical analysis indicated that the coalescence efficiency decreases as the capillary number and the flow number increase. The experimental results showed that the coalescence efficiency goes through a minimum as the value of the flow number increases. The discrepancy between the experimental and the theoretical results was attributed to some mechanism that enhances coalescence and that is not accounted for in the equation used for the critical thickness for film rupture. Both the experimental and the theoretical results indicated that the coalescence efficiency decreases as the viscosity ratio decreases.

AB - The coalescence efficiency of two Newtonian droplets submerged in a Newtonian fluid subjected to a simple shear flow was investigated experimentally and theoretically. The experimental investigation was based on observing collisions between two droplets under a microscope. The theoretical investigation considered three drainage models: immobile, partially mobile and mobile interfaces. Both the experimental results and the theoretical analysis showed that a critical approach angle exists below which the colliding droplets separate. Above this critical angle the collision leads to coalescence. Knowledge of the critical angle permits calculation of the coalescence efficiency. The dependence of the coalescence efficiency on various dimensionless groups such as the flow number, the capillary number and the viscosity ratio was studied. The theoretical analysis indicated that the coalescence efficiency decreases as the capillary number and the flow number increase. The experimental results showed that the coalescence efficiency goes through a minimum as the value of the flow number increases. The discrepancy between the experimental and the theoretical results was attributed to some mechanism that enhances coalescence and that is not accounted for in the equation used for the critical thickness for film rupture. Both the experimental and the theoretical results indicated that the coalescence efficiency decreases as the viscosity ratio decreases.

KW - Coalescence efficiency

KW - Droplets

KW - Emulsion

KW - Simple shear

KW - Stability

UR - http://www.scopus.com/inward/record.url?scp=0035659367&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0035659367&partnerID=8YFLogxK

M3 - Article

VL - 118

SP - 208

EP - 215

JO - Progress in Colloid and Polymer Science

JF - Progress in Colloid and Polymer Science

SN - 0340-255X

ER -