Abstract
In recent years, it has become clear that 1 μm or less sized fine air bubbles have different properties from those of mm or cm sized air bubbles. This study examined the effect of fine bubbles on the removal of salt fixed in the gap of aluminum plate as a verification of cleaning action by fine bubbles. As a result, it was confirmed that the removal effect of fixed salt is higher in fine bubble water than in control water, and that the degree of effect depends on the concentration of fine bubbles. It was also confirmed that less than 1 μm sized ultrafine bubble water has a higher removal effect than the control water. As a mechanism of removing fixed salt, it is conceivable that peeling effect, like lifting up part of fixed salt, in which fine bubbles are dissolved by pressure change around the fixed salt to become supersaturated, causing further bubbling around there, and/or physical collision effect of microbubbles. In addition, it was confirmed that the removal effect of a system in which fine bubbles were regularly introduced was much higher than the one that does not introduce fine bubbles regularly. In addition, even when the gap between fixed salt and aluminum plate was narrowed, the superiority of fine bubble cleaning was confirmed.
Highlights
The International Organization for Standardization (ISO) defined fine bubbles as air bubbles of 100 μm or less
In the system with only ultrafine bubbles (Sample D), the removal rate eventually became the same as that of the control water, the removal behavior was observed to improve in the early stage
While uniform dissolution behavior of fixed salt was observed in control water, peeling behavior of fixed salt was observed in the system with only ultrafine bubbles
Summary
The International Organization for Standardization (ISO) defined fine bubbles as air bubbles of 100 μm or less. The total surface area of multiple fine bubbles with the same volume as a single cm-sized bubble is extremely large, thereby dramatically improving the chemical reaction, physical adsorption, and mass transport at the gas-liquid interface. Fine bubbles improve the dissolution efficiency of contained gas due to their huge total surface area. Fine bubbles have varied applications in agriculture and fisheries industry, environmental improvement, industrials, medical care, and food. High environmental affinity and safety can be obtained by constructing these fine bubbles from air and water (Sivakumar and Pandit, 2002; Oshita, 2010; Terasaka, 2014a; Detlef, 2018). Fine bubbles have been introduced for cleaning in most toilets in expressway service areas in Japan and cleaning (removal) of sea salt particles flying in coastal structures. In this research, the effect of fine bubbles on the removal of salt fixed to a gap of aluminum plate was examined to verify the cleaning action of fine bubbles
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