Abstract <p>The paper presents results of experimental studies on the mass transfer process between the recirculation zone and the main flow of pseudoliquid fuel in a combustion chamber with sudden expansion. Dependencies of the residence time of aluminum particles in the recirculation zone on the characteristic size, initial velocity, and turbulence intensity of the incoming flow have been obtained. It has been demonstrated that the intensity of the mass transfer process between the recirculation zone and the main flow of an aluminum-air mixture with the particle size <i>d</i>₃₂ = 7.4 µm, as well as for a gas-air mixture, can be estimated using the dimensionless residence time.</p>