04. Boiling and Multi-Phase Flow

The hydrophobically modified alkali-soluble associative polymer (HASE) solution exhibits non-Newtonian shear-thinning viscoelastic properties, and it is well known that the single bubbles rising freely in HASE solutions have uncommon bubble shapes that are distinct from those for general viscoelastic fluids as observed in previous studies. In this study, focusing on large bubbles (D (bubble diameter) > 30 mm), the motion of single bubbles rising in HASE solutions is experimentally examined. When HASE solutions have strong viscoelastic properties, the bubble in HASE solutions becomes an oblate ellipsoidal cap with a very thin and long membrane-like shape at the bottom of the bubble. Also, it is observed that complicated dendritic microstructures at the part of the membrane-like shape are formed. When HASE solutions have weak viscoelastic properties, skirted bubbles with thin filament-like parts are formed. Although skirted bubbles have been observed in the Newtonian liquid, skirted bubbles in HASE solutions are different from those for the Newtonian liquid. Skirted parts of bubbles in the Newtonian liquid stretch almost straight, but skirted parts of the bubble in HASE solutions come around behind bubbles at the downstream regions. Consequently, the HASE solution behind the bubble is enveloped by skirted parts. In addition, it is verified that skirted parts in HASE solutions also have complicated microstructures. The appearance of unique skirted shapes of the bubble depends on the bubble size and the viscoelastic property of the HASE solution.