reactiondominated

Reactiondominated is a term used in physical chemistry and chemical engineering to denote a regime in which chemical reaction kinetics primarily govern the evolution of species concentrations and conversion, as opposed to mass transport processes such as diffusion or advection. The regime is relevant to reaction–diffusion systems, catalysis, combustion, and environmental transport.

In mathematical models, reaction-diffusion systems are written as ∂C/∂t = D ∇^2 C - R(C). Reactiondominated behavior occurs when the reaction term R(C) overwhelms the diffusion term, so the kinetics set the dominant time scale. Dimensionless analysis uses the Damköhler number Da, defined as the ratio of the characteristic reaction rate to the characteristic transport rate. In typical conventions, Da << 1 indicates kinetics-dominated (reaction-dominated) behavior, while Da >> 1 indicates transport-limited behavior; Da ~ 1 is a mixed regime.

In a reactiondominated regime, concentration gradients arise mainly from kinetics; spatial patterns, local conversions, and reactor performance are controlled by reaction rate constants, catalyst activity, and mixing at the relevant scale. The term is scale-dependent; a system may be reaction-dominated at one length or time scale and transport-dominated at another.

See also: reaction-diffusion, Damköhler number, transport phenomena, kinetic control.