Eddy contact model: CFD simulations of liquid reactions in nearly homogeneous turbulence

An eddy contact model is proposed that describes the mixing rate between two miscible liquids in nearly homogeneous turbulence. The model is patterned after the eddy-break-up concept of Spalding (1971, 13th International Symposium on Combustion, The Combustion Institute (p. 649)) but replaces the eddy dissipation with the Kolmolgoroff time scale and fluid mass with volume fractions. The concept is used to describe the aqueous distribution of several pure fluids engaged in mixing sensitive parallel reactions. Numerical results for a free jet in an axisymmetric tubular reactor are compared with the experimental yield from both ate-coupled and acid-base-ester parallel reactions. It was found by direct comparison with other CFD-based calculations that the eddy contact model is nearly as accurate as Monte-Carlo/PDF methods and is comparable to a Beta function/mixture fraction technique. Moreover, CFD model predictions of selectivity within a scaled down plug flow reactor are shown to be comparable to direct numerical simulations. The eddy contact model is demonstrated to be conceptually simple, easy to implement and computationally efficient. Limitations on the use of the model are also discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.