The results of experimental and theoretical studies of the regularities of two- and three-phase polydisperse flows with particle coalescence, breakup and interphase mass transfer are presented. The systematic experimental study of mass and momentum transfer for the interaction of drops between themselves, with solid particles and with dry or wetted solid surface has been carried out. Generalizing formulae for the parameter of coalescence and breakup, as well as for the initial sizes and velocities of the fragments have been obtained. The critical conditions of drop destruction under the influence of aerodynamic forces have been determined. The methods of constructing mathematical models of multiphase flows with variable fractional composition have been analyzed. A set of models of two- and three-phase flows with strong particle interaction and phase changes have been elaborated. These results have been generalized for a turbulent, two-phase, polydisperse flow. A closed system of equations for the averaged parameters of both phases as well as for their turbulence characteristics have been obtained, accounting for drop collisions and interphase mass transfer. New methods of presentation of the correlation moments for turbulence parameters of both phases have been proposed. Wide numerical investigations of the gas and drop motion in various conditions have been carried out.