Criteria for kinetic and mass transfer control in a microchannel reactor with an isothermal first-order wall reaction

Analytical expressions for distinguishing between different reaction and mass transport regimes in an isothermal microchannel reactor with first-order wall reaction are presented. These expressions are explicit functions of the Damköhler number (Da) and of the Graetz parameter (α Pem/z), as well as of the degree of mass transport control (θ) which is usually set arbitrarily. The power law addition of contributions from fully developed and developing concentration profile conditions allows a correct description for all values of α Pem/z.The scaling analysis suggests that the relative importance of mass transfer effects compared to reaction should be assessed by the rescaled Damköhler number Da*, defined with the correct scales for external and internal diffusion. It is also shown that a Da − α Pem/z parametric map is appropriate for identifying the boundaries between regimes, which can be directly calculated from the dimensionless parameters in a very convenient manner.

► Analytical boundaries for kinetic and mass transfer control in a microreactor.
► Description valid for all values of Graetz parameter, including developing range.
► Definition of rescaled Damköhler number for evaluation of mass transfer effects.
► Regime boundaries can be plotted in a parametric diagram.