Concentration fluctuations and chemical conversion associated with mixing in some turbulent flows

Abstract

Microconductivity probes were used for the measurement of point values of mean concentrations and root-mean-square concentration fluctuations for mixing of salt solutions in turbulent shear flows. Mixing studies covered a range of flow conditions, with Reynolds numbers on the order of 104, and included ducted turbulent iets, dispersion in turbulent pipe flow, a plane mixing zone, and several multiple injection systems. The test sections all had characteristic dimensions of about 2 cm. The results for mixing experiments are compared with available previous work. Lack of resolution for root-mean-square concentration fluctuations in some previous work is indicated.Reaction product concentrations for a rapid, second-order, irreversible reaction in multiple injection systems, the plane jet, and the mixing zone were also obtained. The relation between conversion in reaction experiments and fluctuation level and decay in the equivalent mixing experiments is illustrated.

Turbulent motion, mixing, and kinetics in a chemical reactor configuration

“…Noise problems were far more severe in the present application than in previous uses of the probe. Although useful results were obtained, the use of conductivity measuring devices ( Torrest and Ranz, 1969) should be considered for future studies. However, these too have limitations associated with frequency response, range of Schmidt number that can be studied, and size.…”

“…These results were obtained in velocity fields which were approximately isotropic. Torrest and Ranz (1970) measured the concentration decay in a system somewhat similar to the one used here and observed a decay that fell between a (-1) and ( -3 / 2 ) power law dependency. It may be, therefore, that decay of passive scalar fields is rather insensitive to many details of decay of the velocity field and that scalar fields associated with decaying anisotropic velocity fields approximate the -3/2 law.…”

“…Thus, all that remains is to show the equivalence of the mixing to the reaction under stoichiometric conditions. Torrest and Ranz (1970) made similar mixing studies, but their flow geometry was not identical to the reactor system used here. To demonstrate the equivalence from this work, Vassilatos' data, in the form of I,, for very rapid reactions are shown in Figure 9 along with the mixing data without reaction.…”

Modeling Partially Premixed Fast Chemical Reactions in Statistically Homogeneous Turbulent Flow Using One-Dimensional Equations of Change

“…In the area of turbulent chemical reactions, as elsewhere, remarkable insights have been gained using one-dimensional models. In the spirit of G. I. Taylor, Ranz and co-workers (Torrest and Ranz, 1970;Ranz, 1979;Ottino et al, 1979;Ou and Ranz, 1983) and Toor and his co-workers (Toor, 1962(Toor, , 1969Mao and Toor, 1970;Bourne and Toor, 1977) as well as others (e.g., Ashurst et al, 1987;Gibson et al, 1988;Chang et al, 1991;Tryggvason and Dahm, 1991;Kerstein, 1992;Frankel et al, 1993Frankel et al, , 1995Cremer et al, 1994) have attempted to capture the essential physics and chemistry of the turbulent reaction A + B f R while avoiding the full complexity of a chaotic convective diffusion-reaction problem in three dimensions.…”