Mechanism of liquid—solid mass transfer and shear stress in three-phase fluidized beds

Abstract

Abstract Local solid—liquid mass transfer and shear stress in gas—liquid—solid fluidized beds are studied experimentally to clarify the influence of gas flow. The electrochemical method of local mass transfer coefficient measurements was used. The effect of gas velocity on mass transfer is essentially due to a change in the velocity gradient close to the particle surface. In this case, each sphere is surrounded by a gas—liquid mixture, which has a lower homogeneous density, thus increasing the particle terminal velocity, which in turn affects positively the mass transfer coefficients. The turbulence affects the mass transfer in two different conflicting ways. At mean relative velocity, turbulence increases mass transfer, especially at high Re. In the subcritical domain, turbulence increases the drag coefficient and therefore decreases the particle terminal velocity. This latter effect could have a negative influence on mass transfer.