When and why do gradients of the gas phase composition and pressure affect liquid-gas transfer?

Dynamic modelling of N2O emissions from a full‐scale granular sludge partial nitritation‐anammox reactor

“…For instance, Fiat et al (2019) showed that considering plug flow in the gas phase improved the N 2 O model prediction. A plug‐flow gas phase with concentration gradient was therefore taking into account in this study (Equation 2, Baeten et al, 2020). Still, the liquid phase was assumed completely mixed in this study, whereas in a full‐scale reactor mixing patterns are never ideal.…”

“…The gas–liquid transfer rate (TR i ) of O 2 and NO were modelled with Equation (1), and the one of N 2 O with Equation (2). The choice of the gas–liquid transfer model for each component was governed by the water depth and the solubility of the gas considered, which determine the simplifications which are allowed to be made to the expression of the total liquid–gas transfer made regarding gradients of the gas phase composition and pressure, as well as the gas phase transport regime (Baeten et al, 2020). For the relatively nonsoluble components O 2 and NO, the mass transfer rate can be very well approximated taking considering the mean mole fraction, mean pressure (i.e., pressure at mid‐depth) and a mixed gas phase (Equation 1, see Baeten et al, 2020 for the derivation).…”

“…For the relatively nonsoluble components O 2 and NO, the mass transfer rate can be very well approximated taking considering the mean mole fraction, mean pressure (i.e., pressure at mid-depth) and a mixed gas phase (Equation 1, see Baeten et al, 2020 for the derivation). For the more soluble N 2 O, taking into account the mole fraction gradient for a plug flow gas phase is important for accurate estimation, but may be combined with uniform (top) pressure (Equation 2, see Baeten et al, 2020 for the derivation).…”

Vortex Impeller-Based Aeration of Groundwater

“…Additionally, as recently shown by Baeten et al [21], the height of the tank in a bubble aeration system, i.e., system geometry, can have effects on the aeration efficiency. The authors investigated the effect of the vertical gradient of gas phase composition and the pressure on the total stripping and absorption rate of volatile substances in tall reactors.…”

“…This effect could be explained by a longer residence time of the gas which allowed enhanced gas transport and diffusion. When the K L a doubled, the stripping rate also doubled [21].…”