Based on the locus of ink on the well-rotating disc, a model for the mean residence time of liquid in a rotating packed bed, t = phi'epsilon(ctg(alpha(2)/2)- ctg(alpha(1)/2))\omega u), is proposed. Model predictions agreed with the reported data with relative error within +/-15%. A modified surface renewal model based on Danckwerts', k(L) = ((1 + S)/t) root D/S[(St + 0.5) root erf(St) + e(-St) root St/pi] is used. For evaluation of the mass transfer coefficient, prediction of surface renewal frequency S is assumed as S = phi omega (phi is a model parameter), and effective contact time t is determined by the residence time model. Model predictions for k(L) agreed well with the experimental data with relative error within +/-14%.