High-speed tomographic PIV was used to investigate the coalescence of drops placed on a liquid/liquid interface; the coalescence of a single drop and of a drop in the presence of an adjacent drop (side-by-side drops) was investigated. The viscosity ratio between the drop and surrounding fluids was 0.14, the Ohnesorge number (Oh = μd/(ρdσD) 1/2) was 0.011, and Bond numbers (Bo = (ρ d - ρ s )gD 2/σ) were 3.1-7.5. Evolving volumetric velocity fields of the full coalescence process allowed for quantification of the velocity scales occurring over different time scales. For both single and side-by-side drops, the coalescence initiates with an off-axis film rupture and film retraction speeds an order of magnitude larger than the collapse speed of the drop fluid. This is followed by the formation and propagation of an outward surface wave along the coalescing interface with wavelength of approximately 2D. For side-by-side drops, the collapse of the first drop is asymmetric due to the presence of the second drop and associated interface deformation. Overall, tomographic PIV provides insight into the flow physics and inherent three-dimensionalities in the coalescence process that would not be achievable with flow visualization or planar PIV only.
|Original language||English (US)|
|Number of pages||19|
|Journal||Experiments in Fluids|
|State||Published - Jul 2010|
Bibliographical noteFunding Information:
This work was supported by the American Chemical Society Petroleum Research Fund through Grant 42939-AC9 and the National Science Foundation through Grant CTS-0320327. The authors would like to thank Bernd Wieneke and Steve Anderson of LaVision, Inc for providing the Tomographic PIV software and for assistance with the experiments and processing.