I understand that multiphase models should be able to define a primary and secondary phase; however, my secondary phase is a solid cylindrical shape sinking inside a big tank containing primary phase (water). In this case, could I set-up to get the mass transfer coefficient without UDF?

I was asking about the boundary conditions since this cylindrical shape will loss its mass into the bulk in the vessel and the surface area of the cylindrical shape will be decrease with respect to time and agitation speed.