New Insights into Mass Transfer when Using the Rotating Disk Apparatus for Newtonian and Non-Newtonian Fluids

The rotating disk apparatus (RDA) is used to study reaction kinetics. However, the current equations used to interpret the results from the RDA make oversimplifying assumptions. Some of these assumptions are not met in practice, yet no work has been done to study their impact on the mass transfer of the proton (H+) to the disk. The objectives of the current work are threefold: study flow regimes under the rotating disk in the RDA for Newtonian and non-Newtonian fluids, investigate the impact of the reactor boundaries on the mass transfer of H+ to the disk in Newtonian fluids, and identify the dimensions of the reactor that minimize this impact. The mass transfer of the H+ was compared between different dimension reactors. Contrary to information reported in the literature, both the diameter of the reactor and the axial distance between the base of the disk and the bottom of the reactor have an impact on the rate of mass transfer of H+ to the disk. Moreover, the velocity profiles in the reactor showed three flow regimes: fully axisymmetric, fully asymmetric flow, and intermediate flow. These different regimes varied depending on the axial distance between the base of the disk and the bottom of the reactor, the diameter of the reactor, the rotational speed of the disk, and the kinematic viscosity of the reacting fluid.