MASS-TRANSFER IN SMOOTH AND ROUGH ANNULAR DUCTS UNDER DEVELOPING FLOWCONDITIONS

Rates of solid-liquid mass transfer were measured at the inner surface of an annular duct by the electrochemical technique under developing flow conditions. Variables studied were physical properties of the sol ution, velocity, length of the annulus, inlet port diameter and surfac e roughness. Inlet port diameter was found to have no effect on the ra re of mass transfer. For smooth annuli the laminar flow data fit the e quation: Sh = 1.029Sc(0.33)Re(0.55)(L/d)(-0.472) The turbulent flow da ta fit the equation: Sh = 0.095Sc(0.33)Re(0.85)(L/d)(-0.472) Surface r oughness in the form of V-threads normal to the how was found to have a negligible effect on the rate of mass transfer in the laminar flow r egion while in the turbulent region the data fit the equation: Sh = 0. 167Sc(0.33)Re(L/d)(-0.472)(e/d)(0.33) Under the present conditions, wh ere the dimensionless roughness height e(+) lies between 0.5 and 22, t he rate of mass transfer was found to increase by an amount ranging fr om 10% to 200% depending on e(+).