Use of axial dispersion model for determination of Sherwood number and mass transfer coefficients in a perforated rotating disc contactor

The mass transfer process in a perforated rotating disk contactor(PRDC) using a toluene-acetone-water system was investigated.The volumetric overall mass transfer coefficients are calculated in a PRDC column.Both mass transfer directions are considered in experiments.The influences of operating variables containing agitation rate,dispersed and continuous phase flow rates and mass transfer in the extraction column are studied.According to obtained results,mass transfer is significantly dependent on agitation rate,while the dispersed and continuous phase flow rates have a minor effect on mass transfer in the extraction column.Furthermore,a novel empirical correlation is developed for prediction of overall continuous phase Sherwood number based on dispersed phase holdup,Reynolds number and mass transfer direction.There has been great agreement between experimental data and predicted values using a proposed correlation for all operating conditions.

Three-dimensional simulation of interfacial convection in CO_2–ethanol system by hybrid lattice Boltzmann method with experimental validation

By using a hybrid lattice-Boltzmann–finite-difference method(hybrid LBM–FDM method),three-dimensional simulations of solutal interfacial convection were conducted for the process of CO2absorption into ethanol.A self-renewal interface model is adopted as an interfacial perturbation model.The simulation results revealed some three-dimensional features of the induced interfacial convection,such as the development of diverging cellular flow and Rayleigh plume-like convection in liquid phase.The concentration distribution of the simulation result is validated and found to be in well agreement with the Schlieren visualization results qualitatively.Additionally,the mass transfer enhancements by interfacial convection were investigated via both simulation and experiment for the absorption process,and the mass transfer is shown to be enhanced by the interfacial convection by about two-fold comparing with that by diffusion.

Anisotropic diffusion of volatile pollutants at air-water interface

The volatile pollutants that spill into natural waters cause water pollution. Air pollution arises from the water pollution because of volatilization. Mass exchange caused by turbulent fluctuation is stronger in the direction normal to the air-water interface than in other directions due to the large density difference between water and air. In order to explore the characteristics of anisotropic diffusion of the volatile pollutants at the air-water interface, the relationship between velocity gradient and mass transfer rate was established to calculate the turbulent mass diffusivity. A second-order accurate smooth transition differencing scheme （STDS） was proposed to guarantee the boundedness for the flow and mass transfer at the air-water interface. Simulations and experiments were performed to study the trichloroethylene （C2HC13） release. By comparing the anisotropic coupling diffusion model, isotropic coupling diffusion model, and non-coupling diffusion model, the features of the transport of volatile pollutants at the air-water interface were determined. The results show that the anisotropic coupling diffusion model is more accurate than the isotropic coupling diffusion model and non-coupling diffusion model. Mass transfer significantly increases with the increase of the air-water relative velocity at a low relative velocity. However, at a higher relative velocity, an increase in the relative velocity has no effect on mass transfer.

Numerical simulation of Marangoni effect induced by species transfer across iron droplet–molten slag interface

A mathematical model accounting for unsteady mass transfer across interface of a stationary iron droplet immersed into molten slag was established through the volume of fluid coupled with level set method.The Marangoni effect induced by mass transfer was reproduced successfully,and the hydrodynamic instability phenomena at the interface,such as the Marangoni convection flow,the evolution of the interfacial tension during the mass transfer,and the influence of Marangoni effect on the mass transfer rate,were revealed.The results show that the Marangoni convection flow develops quickly and behaves as an ordered structure in the forms of four pairs of the convection cell at the edge of the droplet once the oxygen transfer across the interface starts.The average convection flow velocity along the interface is high,even more than 0.025 m/s,depending on the droplet diameter,which facilitates the mass transfer.The Marangoni convection flow of the large droplet develops more easily than that of the small droplet,and the larger the droplet diameter is,the higher the convection flow velocity and the mass transfer rate are.Moreover,it is shown that the droplet diameter influences the impacting region of the Marangoni convection flow and its duration period.