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論文題目「Air Spark Plasma for Frugal Antimicrobial NOx Generation」
(簡易型NOx発生のためのスパーク空気プラズマ)
大野俊聡
The generation of nitrogen oxides and their antimicrobial efficacy using
atmospheric air spark and glow combined plasmas in simple, inexpensive
devices are demonstrated and analyzed. The idea of making a technology
simple, inexpensive and potentially more robust while still meeting important
social and environmental needs has been referred to as “frugal innovation”or
“frugal engineering.” In this research, we have shown that inexpensive,
frugal plasma devices based on spark-like air plasmas can efficiently produce
strongly antimicrobial gas mixtures at rates that make them interesting
for a variety of potential applications. We, also, refer to this application
as frugal plasma, suggesting this is an example of frugal innovation.
Firstly, three types of high-voltage power supplies such as a homemade
flyback transformer, a commercial neon sign transformer and a commercial
high voltage power supply were tested to select suitable power supply for
NOx antimicrobial frugal plasma system. Spark-like discharges in air in
a 1 L confined volume are shown to generate NOx at an initial rate of about
1.7 x 1016 NOx-molecules/J dissipated in the plasma. A homemade flyback
transformer dissipating only about 6.1 W in this confined volume generates
on the order of 2500 ppm NO2 and 200 ppm NO in ten minutes. Power normalized
NO2 and NO concentration by a homemade flyback transformer showed the highest
NOx generating efficiency. Also, the antimicrobial action of the NOx mixture
after several minutes of plasma operation is demonstrated by measuring
rates of E. coli disinfection on surfaces and in water exposed to the NOx
mixture. In both surface and aqueous phase, result showed strong antimicrobial
effect at least 4 to 5 log reduction in 5 minute
Secondly, spark and glow combined discharge was analyzed and also produced
gas chemistry was investigated by changing glow discharge period. Result
showed that a spark discharge is a key of initial NO generation, and NO
concentration dramatically dropped without spark discharges. Ozone, in
addition, was generated in glow discharge phase, and this ozone collision
with NO made NO2. Result also showed discharge balance between spark and
glow discharge is a significant on maximizing NO and NO2 concentration.
As a conclusion, the spark-like discharge systems producing strongly antimicrobial
gas mixtures can operate with inexpensive power supplies, simple automotive
spark plugs, and relatively small sources of electricity.
