For merging bubbles with radii R1 and R2, Li and Liu [44] found the coalescence time for a clean fluid (no surfactants) to be:
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(28) |
where constants reflect conversion to CGS units. The time for two drops or bubbles of radius RB to merge is shorter than the time for a single particle of the same radius to burst at an initially flat surface. For a bubble, with small viscosity ratio κ = µg / µp, the merge time is 0.21 times the bursting time.
This conclusion matches physical intuition, since the shape of the thin film formed by two merging bubbles is more likely to be in the rapid drainage mode with the thinnest spot located in the center.