Determination of Friction Coefficients as Well as Heat and Mass Transfer Coefficients in Film-Type Countercurrent Apparatuses with Intensifiers

Abstract

AbstractThe problem of mathematical modeling and calculation of heat and mass transfer processes in countercurrent film-type apparatuses with transfer intensifiers is considered and solved. Models of the turbulent boundary layer are used taking into account the damping of turbulent pulsations in accordance with the Deissler function. Expressions for calculating the coefficients of heat and mass transfer are presented, in which the main parameters are the dynamic velocity of friction, dimensionless thickness of the viscous sublayer as well as dimensionless thickness of the boundary layer. To determine the average value of the dynamic velocity on the film surface from the side of the gas flow, a dissipative model is considered, and after integrating the written expression, the average value of the rate of dissipation of kinetic energy in the boundary layer of the gas phase is obtained. From this, the values of the average friction induced shear stress and dynamic velocity at the interface are found, which are connected with the pressure drop of the gas flow in the film-type contact devices. To determine the parameters of the equations of the mathematical model of friction and heat and mass transfer, expressions are presented for calculating the dimensionless characteristics of the boundary layer, taking into account the presence of transfer intensifiers on the surface of the contact devices. The properties of conservatism of the mathematical description of friction and heat transfer of the turbulent boundary layer to various perturbations, which are taken into account parametrically, are used. The results of calculations of the average coefficients of heat and mass transfer in irrigated pipes, random packed beds made of Raschig rings and Berl saddles, structured packed beds made of polyethylene nets, coiled metal packings with notches as well as packings of other types are presented. Satisfactory agreement of the calculation results with the known experimental data of various authors at a gas velocity of 0.5–3.5 m/s is shown. The developed mathematical model of friction and heat and mass transfer makes it possible to calculate film-type contact devices with smooth surfaces, as well as with intensifiers based on the hydraulic resistance known from experiments, which represents the development of the hydrodynamic analogy of the processes of transfer of momentum, mass, and heat.KeywordsHeat and mass transferIntensifiersPackingsEnergy dissipationTurbulent boundary layer