Hierarchical modeling of plasma and transport phenomena in a dielectric barrier discharge reactor

Abstract

A novel dual-time hierarchical approach is developed to link the plasma process to macroscopic transport phenomena in the interior of a dielectric barrier discharge (DBD) reactor that has been used for soil remediation (Aggelopoulos et al 2016 Chem. Eng. J. 301 353–61). The generation of active species by plasma reactions is simulated at the microseconds (µs) timescale, whereas convection and thermal conduction are simulated at the macroscopic (minutes) timescale. This hierarchical model is implemented in order to investigate the influence of the plasma DBD process on the transport and reaction mechanisms during remediation of polluted soil. In the microscopic model, the variables of interest include the plasma-induced reactive concentrations, while in the macroscopic approach, the temperature distribution, and the velocity field both inside the discharge gap and within the polluted soil material as well. For the latter model, the Navier–Stokes and Darcy Brinkman equations for the transport phenomena in the porous domain are solved numerically using a FEM software. The effective medium theory is employed to provide estimates of the effective time-evolving and three-phase transport properties in the soil sample. Model predictions considering the temporal evolution of the plasma remediation process are presented and compared with corresponding experimental data.

Modeling of dielectric barrier discharge (DBD) plasma reactor for soil remediation

“…Thus, a 2-D axisymmetric model was introduced to model the plasma discharges. Considering the calculation of the electric power, the 1-D model was not able to provide the same results as the upscaled 2-D axisymmetric, as well the experimental measurements [41].…”

“…A hybrid method is followed in the present study, where the kinetic constants for the gaseous species are given by two-term Boltzmann approximations, whereas the electron, ion, and neutral species behavior is described by reactive transport equations. Based on the method of the fluid approximation opted, initial plasma modeling was performed using the COMSOL Multiphysics CFD software [41]. The plasma formulation is approached solving the transport equation for the electron and the heavy (non-electron) species [54].…”

“…For the case of a NAPL (Non-aqueous phase liquid) pollutant, a model of 50 key reactions is applied [41]. These 50 key reactions are considered as a good approximation, since they are based on species recorded through experiments [31] and on species mentioned in the literature [47], under similar working conditions.…”

“…The momentum transport is solved initially with the assumption of thermal equilibrium and density conservation. The balance equations are presented in Chapter 4 [41].…”

“…The macroscopic effect of thermal transport has been studied in a previous work by the authors [41], where a link was provided between the working frequency of the reactor and the final temperature achieved. In the present study, a different link is proposed regarding the mass species production during cold plasma process and their concentration at the macroscopic scale.…”