Reduced model for capillary breakup with thermal gradients: Predictions and computational validation

It was recently demonstrated that feeding a silicon-in-silica coaxial fiber into flame—imparting steep silica viscosity gradient—results in the formation of silicon spheres whose size is controlled by feed speed [Gumennik et al., “Silicon-in-silica via axial thermal gradient in-fiber capillary instabilities,” Nat. Commun. 4, 2216 (2013)]. A reduced model to predict droplet from then derived Mowlavi al. [“Particle selection instability locally heated fiber,” Phys. Rev. Fluids 064003 (2019)], but large experimental uncertainties parameter values and temperature profile made quantitative validation impossible. Here, we validate against fully resolved three-dimensional axisymmetric Stokes simulations using exact same physical parameters profile. We obtain excellent agreement for wide range experimentally relevant speeds. Surprisingly, also observe local number at breakup location remains almost constant across all Owing its low computational cost, therefore useful tool designing future experiments.