A study of scale formation around air bubble attached on a heat-transfer surface

The purpose of the present study was to investigate the effect of an air bubble on scale formation. Artificial hard water was used, whose hardness was equivalent to 1,000 ppm as CaCO3. Photographs of scaled heat-transfer surfaces showed the distribution of CaCO3 crystals around the bubble and in divergent tail-like areas downstream of the bubble. It was speculated that nucleation seeds were created around the bubble due to the release of CO2 gas at the interface from water to the air bubble. The seeds were carried downstream along streamlines around the bubble. The bubble affected the scale-deposition area approximately forty times larger than the bubble size. In the study, the local temperature effect did not significantly affect the formation of scale deposition.