Study on Plumbing Cleaning by Fine Bubbles

In recent years, the cleaning effects of FBs (Fine Bubbles) have been attracting attention. However, quantitative evaluation and clarification of the cleaning mechanism have not yet been achieved in the plumbing cleaning technology using FBs. Moreover, the effectiveness of UFBs (Ultrafine Bubbles) has not been clarified yet for plumbing cleaning either. Therefore, in this study, we used an artificially created object to be cleaned and experimentally investigated the cleaning rate, cleaning mechanism, and differences in diameter distribution of bubbles with respect to the plumbing cleaning using FBs. The results showed that not only the cleaning rates of water with MBs (Microbubbles) and water with MBs and UFBs were higher than those of tap water, but also the generation of MBs for water with UFBs may further enhance the cleaning effect compared to water with only MBs. However, under conditions where high cleaning rates could be achieved with tap water alone, the enhancement of cleaning rates with water with MBs or water with MBs and UFBs were marginal. In both cases where the test plates were made of PVC and SUS304, the cleaning rate was improved by FBs. The cleaning mechanism is thought to involve the coalescence of multiple MBs, resulting in the formation of larger diameter bubbles that adsorb or push the object to be cleaned toward downstream side due to hydrophobic interaction or electrical interaction. The results of the bubble diameter measurement showed that the number of bubbles increased and the distribution of bubble diameters changed in water with MBs and UFBs compared to water with MBs. We concluded that these changes allow bubbles to penetrate the gaps between the object to be cleaned and the test plate, facilitating cleaning.