Sudden Decrease of the Dissolved Ozone Concentration in Sprays: A Mass Transfer Phenomenon?

Abstract

Ozone is known to be a powerful oxidant with low persistence and has been shown to possess biocidal activity against a wide number of fungi and bacteria. These properties make ozone a good candidate as a substitute for chemical phytosanitary products in agriculture. However, when water containing dissolved ozone is sprayed, the concentration of ozone decreases dramatically with the spraying distance. This study aims to better understand this ozone loss during spraying and, in particular to identify whether mass transfer occurs. Identification was performed by dioxygen absorption and comparison of its concentration profiles with those for ozone desorption. Droplets were collected at different heights in the spray to measure the dissolved concentrations. Image analysis was used to determine the diameters and velocities of the droplets. Ozone selfdecomposition kinetics were not able to explain the experimental concentration variation obtained in the droplets. The decrease of dissolved ozone in the liquid is then only caused by mass transfer.Most of the mass transfer seems to take place in the liquid sheet that leaves the nozzle. Volumetric * relative to the saturation state

Gas-liquid mass transfer characterization in a thin shrinking film at an atomization nozzle

“…Although significant errors remained associated with the concentration measurement as shown in Fig. 11, the mean values obtained were consistent with the expected theoretical values: a liquid in equilibrium with air at ambient pressure and temperature tends to reach a dissolved concentration of dioxygen of around 8 mg/L, as is the case in the literature, where experimental dioxygen absorption in a spray was performed by liquid collection with a similar nozzle and flowrate (Canado et al, 2020). The global measurements performed by liquid collection exhibited a strong increase in concentration between 0 and 3 cm of the spray.…”

“…is related to the velocity of the fluid. The liquid exits the nozzle with a velocity of around 12.98 m/s as stated in Table .2, and the velocities of the droplets have been measured at around 8.5 m/s in a previous study (Canado et al, 2020) for a similar nozzle and flowrate, indicating a decrease in velocity of the liquid film from the orifice to the formation of droplets. According to the shape of the orifice, the film spreads with a given geometry and angle, and the friction with air causes instabilities to grow in its core and decrease its velocity, so it seems consistent to attribute the decrease of the kL with distance to the decrease of the velocity of the liquid along the film.…”

“…Mass transfer in spray is commonly well understood when considering liquid droplets exchanging solutes with the gas phase, and many correlations have been proposed to predict the extent of the transfer (Hegely et al, 2017;Lépinasse et al, 2012). Several studies have focused on the liquid film behavior and revealed that the atomizing liquid film that produces the droplets seems to enhance the mass transfer due to its hydrodynamic conditions and interfacial area (Canado et al, 2020;Lin et al, 1977;Simpson and Lynn, 1977;Yeh and Rochelle, 2003). Mass transfer enhancement during the formation stage of droplets or bubbles has also been reported, showing the importance of taking the formation region into consideration for mass transfer applications (Wegener et al, 2009;Xu et al, 2008;Yang et al, 2016).…”