The operating regime and mass-transfer mechanisms have been analysed for three geometrically similar spinning cone columns: laboratory scale (inner diameter of the column D-C = 0.148 m), pilot scale (0.346 m), and commercial scale (0.810 m). The method involved transient laminar simulation of the unsteady gas-liquid flow system. The hydrodynamic regime of the flow is found to be unsteady laminar (transitional to turbulent) at all three scales. The intensity of the velocity and the pressure pulsations due to the instability of the flow increases with the column scale in proportion to the Reynolds number. However, the onset of fully developed turbulence does not occur due to the geometrical complexity of the column. The dominant mode of mass transfer changes from the spray mode at the small scale to the film mode at the medium and the large scales. The film-based mass transfer in the large column is less efficient than the spray-based mechanism at the small scale. The computational fluid dynamic (CFD)-predicted values of mass-transfer coefficients agree well with the measurements at both the small and the large scales. The limit of the SCC capacity, in terms of the maximum value of liquid mass velocity attained at the flooding point, increases with scale as L-max similar to D-C(0.4).