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Plasma-based water purification involves the transport of reactive species across the gas–liquid interface. This process is limited by slow diffusion driven mass transport of reactive species across the interface. Additionally, the plasma gas–liquid contact area is typically limited, contributing to reduced dose delivery. These key factors make it difficult to scale up the treatment process to input flows of industrial interest. In this work, turbulence is explored as a means to introduce a fine grain structure, thus greatly increasing the interfacial surface area, leading to large property gradients and more efficient mass transport. Such a fine scale structure can also enhance the local electric field. The test apparatus explored in this work is the packed bed reactor that places thin water jets into contact with plasma. It is theorized that introducing turbulence, via increasing Reynolds number in such thin jets, may enhance the effective plasma dose at fixed plasma power. In this work, changes in the flow regime, from laminar to turbulent, of water jets in a packed bed water reactor (PBR) configuration are investigated experimentally. Methylene blue dye, a model contaminant, was tested in the PBR to demonstrate enhanced treatment via reduced treatment times. Plasma surface morphology around the jets noticeably changed with the flow regime, and turbulent flow demonstrated a faster hydrogen peroxide uptake, along with slower temperature, electrical conductivity, and a pH change in a batch treatment process, compared to laminar flow. The dye was destroyed significantly faster in the turbulent flow, indicating an increased effective plasma dose.
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Plasma-liquid interactions on acoustically structured Faraday liquid interfaces
Abstract Enhancing mass transport of reactive species and photons at the plasmaliquid interface is an important consideration for the scaling of atmospheric pressure plasmas studied in the laboratory to real-world applications. It is well-known that the introduction of turbulence at any interface will enhance mixing by enhancing species uptake from the gas phase to the liquid phase by surface renewal processes, entrainment, bubbles and surface area modification. The goal of this work is to isolate surface effects associated with turbulence from the multitude of turbulent transport enhanced processes by artificially introducing surface perturbations using Faraday waves. Experiments were also conducted to determine decoloration rate constants of a model contaminant (methylene blue) as a function of both discharge features and hydrodynamics (Faraday surface wavelengths). The local plasma ionization wave at the interfacial structure was modeled and compared to experiments. Interestingly, it was found in experiments that plasma in contact with the water also generated capillary waves thus modifying the surface as well. Plasma ionization waves in combination to acoustic driven Faraday waves adds to the complexity of interpreting the effects of, for example, surface area increases, due to these complex coupled phenomenon. Local plasma ionization wave structure appears to be modified (increased propagation distance) when the liquid is perturbed, leading to increased contact of the liquid water surface with reactive species. Along with interfacial surface area growth, nonlinear convective transport is also increased with perturbations, leading to the general realization that acoustic perturbations can improve transport and thus decoloration of the model contaminant dye.
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- Award ID(s):
- 2206039
- PAR ID:
- 10589281
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- Plasma Sources Science and Technology
- ISSN:
- 0963-0252
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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