Multiphysics fields simulation of photothermal catalytic degradation of R134a in a flat plate reactor

Photothermal catalytic degradation is an environment-friendly way to dispose high-global-warming-potential hydrofluorocarbon refrigerants (HFCs). There are challenges in understanding the heat and mass transfer mechanism of this multi-physicochemical process. This study focuses on photothermal catalytic degradation of R134a, one of the hydrofluorocarbon refrigerant, in a flat plate reactor. A numerical model was developed to couple laminar flow, conjugate heat transfer, dilute species transport, surface radiation and chemical reaction. Meanwhile, experiments were conducted to measure the R134a degradation across various temperatures. The parameters of thermal boundary conditions and the kinetics were calibrated by combining the experimental data and the numerical model. The preexponential factor of 0.1146 m/s and activation energy of 21129.1 J/mol were yielded, achieving less than 10 % relative error of the R134a concentration. The average degradation rate was intensified by around one magnitude from 100 °C to 400 °C. Across various temperatures, molecular diffusion always dominated the mass transport process. However, the governing mechanism limiting the photothermal catalytic process was the degradation kinetics, as evidenced by the uniform concentration distribution and the Damköehler number significantly below 1. Several methods were also proposed to enhance the photothermal catalytic degradation rate.