Modelling of macro- and micro-scale mixing in a chemically reactive plume

摘要

Small scale fluctuations and inhomogeneous mixing are known to affect the rate of chemical reactions. This is particularly true for plumes from isolated point sources where high concentration gradients support a high degree of incomplete mixing. We have proposed a mathematical model to calculate the variance and covariance in a chemical reactive plume. For a single reaction containing three species, the system reduces to six equations for the six unknown (co-)variances. Incorporated into a classical dispersion model our fluctuation model has been tested for the NO-NO_2-O_3 system against wind tunnel measurements. It is shown that the essential parameters of the model are the time scales. If the ratio between the time scale for macro-mixing, the time scale for micro-mixing and the time scale of chemical kinetics for each species are kept constant, model results obtained for the scales in the wind tunnel can be transferred to outdoor scales. A brief test of sensitivity is presented.