[Relative reaction time]
A dimensionless number defined by the identity
Comment. For flows with homogeneous chemical reactions the value Kτ = 0 corresponds to the case of an equilibrium flow and Kτ → ∞ to the case of a frozen flow. For flows with heterogeneous chemical reactions the surface is said to be ideally catalytic when Kτ = 0 and noncatalytic when Kτ → ∞.