The intensive researches in hydrodynamics and mass transfer in the technological apparatuses attract today great attention to the study of separated flows for various values of regime parameters and configurations of streamlined packed bodies. The theoretical description of the effect of flow separation on mass transfer, even for simple shape packings, taking into account the vortex interaction, is a non-trivial problem, and it has not yet been completed. The needs of engineering practice force us to look for ways for developing simplified models that adequately reflect the main patterns of the effect of flow separation on the efficiency of mass transfer and for carrying out the optimal calculation of the corresponding equipment.
In this paper, a new approach for calculating the mass transfer coefficient, taking into account the flow separation and its transformation during multistage interaction of gas and droplets has been proposed. Such processes are specially organized, for example, in absorbers. The novelty of the model lies in the fact that it describes the process of mass transfer taking into account the separation in the boundary zone and the redistribution of the velocity profile of the carrier flow when flowing past packed bodies. The theoretical basis of the model is the Reynolds-averaged Navier-Stokes equations, known as dynamic equations for the functions of stream, vorticity, kinetic energy, and local turbulence scale. In the process of flow past packed bodies, two different zones are formed: a multiply connected flow core, which occupies the main area in the contact zone, and a vortex one, generated by separation. Accordingly, modeling and calculation of the mass transfer coefficient were also carried out by different methods, taking into account the distribution of dynamic functions. To ensure sufficient accuracy, stability and convergence of the numerical solution of dynamic equations in the vortex zone, the modified algorithm with a variable step has been developed.
The analysis of the dependences and plots obtained in two directions: verification of the adequacy of the simulation results in terms of the hydrodynamics of separation and the mass transfer coefficient, has been carried out. It is shown that the numerical results are in good agreement with the known experimental data and the previously studied patterns of separated flows. For reliable practical application, this model requires the identification of control parameters for specific physicochemical systems.