A model for predicting the liq. phase mass transfer coeff., kL, for the Sulzer structured packing Mellapak 250.Y and 500.Y was proposed. Exptl. data were considered together with the penetration theory. The value of kL increased with the liq. and gas flow and decreased with the geometric area of the packing. Higher kL values were assocd. with irregular packings of equal geometric area. [on SciFinder (R)]