Resolving the spatial scales of mass and heat transfer in direct plasma sources for activating liquids

Abstract

When plasma is in direct contact with liquid, an exchange of mass and heat between the two media occurs, manifested in multiple physical processes such as vaporization and multiphase heat transfer. These phenomena significantly influence the conditions at the plasma–liquid interface and interfere with other processes such as the multiphase transport of reactive species across the interface. In this work, an experimentally validated computational model was developed and used to quantify mass and energy exchange processes at a plasma–liquid interface. On the liquid side of the interface, it was shown that a thin film of liquid exists where the temperature is approximately three times higher than the bulk temperature, extending to a depth of 10 μm. As the depth increased, a strongly nonlinear decrease in the temperature was encountered. On the plasma side of the interface, plasma heating caused background gas rarefaction, resulting in a 15% reduction in gas density compared to ambient conditions. The combined effect of gas rarefaction and liquid heating promoted vaporization, which increased liquid vapor density in the plasma phase. When water is the treated liquid, it is shown that water vapor constitutes up to 30% of the total gas composition in the region up to 0.1 mm from the interface, with this percentage approaching 70–80% of the total gas composition when the water’s temperature reaches its boiling point.

Harnessing plasma-generated reactive species for the synthesis of different phases of molybdenum oxide to study adsorption and photocatalytic activity

“…16,49 Silsby et al reported that upon plasma-liquid interaction, a high-temperature thin liquid film is formed in the plasma-liquid interface region. 50 The electric field and the localized heat generated due to the transfer of highly energetic reactive species increase the temperature of the overall system. 51 In this high-temperature liquid region, the Mo species undergoes a chemical reaction with plasma-generated reactive oxygen species (Step: 9).…”

Liquid-to-gas transfer of sodium in a liquid cathode glow discharge

“…As described above, the sodium loss mechanism is likely due to oxygen recombination, which is favored at low gas temperatures. Therefore, a likely explanation is that as the gas flow rate increases, the temperature in the discharge decreases [2,20] resulting in an increase in the recombination rate of sodium. Furthermore, fluid flow simulations [20] have shown that the gas temperature gradient near the liquid surface reduces by a factor of 2 when the helium flow rate is doubled.…”

“…As mentioned in the introduction, a few mechanisms like Taylor cone formation (electrospray) [8], evaporation/ion bombardment [2,9] and Chemical Vapor Generation [13] have been hypothesized as potential mechanisms for the solute transfer from the liquid to the gas phase.…”

“…One of the key aspects of plasma-liquid interactions enabling its various applications is the transport of species across the plasma-liquid interface [1]. This transfer of species has been observed to be of bi-directional nature: transfer from the gasphase to the liquid phase [1] and the transfer of species from the liquid phase to the gas phase [2]. Transfer from the gas to * Author to whom any correspondence should be addressed.…”