document: This study proposes a new framework of a numerical modelling of the gas exchange between air and water across their interface, and subsequent chemical reaction in water based on an extended two-compartment model. The major purpose of this study is to provide a fundamental concept for modelling physicochemical processes of the gas exchange, followed by the chemical reaction in water. Demonstrating fundamental data and knowledge on the important environmental transport phenomena, especially the effects of the Schmidt number and the chemical reaction rate on the gas exchange mechanisms across the interface have also been attempted. The gas exchange processes are separated into two physicochemical substeps, the first is the gas–liquid equilibrium between the two phases, and the second is the chemical reaction in the water phase. A first-order, irreversible chemical reaction of the gaseous material after its uptake into the water phase is assumed here to simplify interactions of the chemical reactions and turbulent transport phenomena in water. While a traditional two-compartment model assumes uniform concentration of a material in each compartment, the present two-compartment model uses a computational fluid dynamics (CFD) technique in the water compartment to evaluate temporal development of three-dimensional profiles of the velocity and concentration fields. A direct numerical simulation (DNS) approach is used to evaluate profiles of fluid velocities and concentrations in water, and several important turbulence statistics have been evaluated without using turbulent closures, and subgrid-scale models. We assume that a fluid flow in the water phase is a well-developed turbulent water layer of a low Reynolds number, and the Schmidt number is varied from 1 to 8 to observe the effects of the molecular diffusion of the gas in sub-interface water on the gas exchange rate at the interface. Six degrees of the nondimensional chemical reaction rate are used to find the effect of the chemical reaction rate on the gas exchange mechanisms. Extrapolations of the gas exchange rates and the related transport phenomena toward larger Schmidt number and the faster chemical reaction rate will also be examined to predict the gas exchange processes of the actual gases of Sc∼O(102) based on results from the present numerical experiments.
extractive_keyphrases: predict the gas exchange processes fundamental concept irreversible chemical reaction gas evaluate profiles of fluid velocities and concentrations in water gases molecular diffusion modelling physicochemical processes transport phenomena cfd chemical reaction chemical reactions air numerical experiments gaseous material water phase dns water framework direct numerical simulation gas–liquid equilibrium effects of the schmidt number computational fluid dynamics
abstractive_keyphrases: effect of the chemical reaction rate on the gas exchange mechanisms gas exchange rate at the interface evaluate temporal development of three-dimensional profiles of the velocity and concentration fields gas exchange rates turbulent transport phenomena in water nondimensional chemical reaction rate gas exchange observe the effects of the molecular diffusion chemical reaction rate gas exchange mechanisms concentrations in water chemical reaction in water sc∼o(102) new framework of a numerical modelling fluid flow in the water phase fluid velocities two-compartment model chemical reaction in the water phase liquid gas exchange mechanisms across the interface subgrid-scale models gas exchange processes