Coalescence of viscous particles with solid cores plays an important role in chemical and pharmaceutical industry, in agriculture and in production technology. Coalescence of metal particles, which are partially melted due the laser heating, is an important mechanism responsible for densification of metal powder during selective laser sintering process.

Our model describes coalescence of two or more particles consisting of a solid core and a liquid shell. The flow in the liquid shell is driven by the surface tension. It is assumed that the characteristic Reynolds number is low, so that the creeping flow model can be applied. A two dimensional boundary element model (BEM) is used to solve the governing equations. The numerical model is validated by comparison with available analytical solution for the limiting case of fully viscous particles.

The influence of the liquid properties, the sizes of the particles and the relative sizes of the solid core on the two-phase flow and on the shape evolution of coalescing particles is quantified. In application to the selective laser sintering process densification rate has been defined as an important output parameter. We show that increasing of the solid core radius leads to the decrease of the powder densification rate.

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