Droplet aspect ratio method

A simple and direct method of contact angle measurement has also been proposed (Yamaki and Katayama, 1975 Carroll, 1976) by observing the shape of the liquid droplet attached to a single fiber, the so-called droplet aspect ratio method . The liquid is assumed to form a symmetrical droplet about the fiber axis as shown schematically in Fig. 2.21. Neglecting the effect of gravity, the droplet shape can be defined by the following expression ... 

The formation of a microemulsion from an array of microtubes has been studied experimentally and computationally by Kobayashi and co-workers [92,93). They used the commercial code CFD-ACE, which uses a piecewise linear interface construction (PLIC) method to determine the interface. They used quarter symmetry, as the channels were eDiptical in shape, but the simulations still required 7-14 days on a 2.5 GHz Pentium IV processor. The simulations captured the main features observed experimentally, including the change of regime from continuous outflow of oil if the channel was below a critical aspect ratio, to a stream of droplets above this threshold. The model was also used to predict the droplet size as a function of oil properties and generally agreed well with the experimental data. 

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