Foam formation mechanisms in particle suspensions applied to metal foams

Relating vesicle shapes in pyroclasts to eruption styles

“…3). For Ca 1, the speed at which bubbles relax toward a regular shape is reduced and remnants of coalescence events become more persistent (Koerner 2008). By estimating capillary number from modeling of magma expansion for the different eruptions, and by comparing it to vesicle shapes in pyroclasts from these eruptions with vesicularity φ >≈ 0.6, we show that vesicle shapes in pyroclasts bear a relationship to Ca.…”

“…Consequently, the relationship between , capillary number, P , and fragmentation suggested herein only holds for pyroclastic samples associated with explosive eruptions that have not undergone bubble collapse. For these cases, we therefore suggest that can be related to Ca, through modeling of the expansion velocity, v e (Koerner 2008). Figure 5 shows a representative model result for each eruption as a graph of bubble radius, R, overpressure, P , and capillary number as a function of dimensionless pressure, defined asP = (P m − P frag )/(P initial − P frag ).…”

“…This requires a judicious choice of flow velocity and is typically associated with an externally imposed shear flow (Taylor 1932(Taylor , 1934Rallison 1984;Stone 1994;Rust and Manga 2002a, b;Rust et al 2003). An alternate possibility is the "expansion velocity," v e , of a bubbly fluid (Koerner 2008), defined as the velocity at which the surface of a bubbly fluid or foam is expanding upon bubble growth (Namiki and Manga 2006;Koerner 2008). For an unconfined fluid with bubbles of average size R, at a volume fraction φ, the expansion velocity is…”

“…Koerner (2008) provides an analysis of the evolving structure of expanding bubbly fluids in relation to capillary number. Material rearrangement, which is necessary during expansion of a highly vesicular bubbly fluid, results in bubble coalescence.…”

“…We therefore restrict our analysis to samples with vesicles that are not significantly affected by shear deformation, that is samples where the median elongation is small (≤ 0.35, e.g., Rust and Manga 2002a;Rust et al 2003). We interpret vesicle shapes within the context of recent work on the relationship between the "structure" of expanding bubbly fluids, that is bubble shapes, and capillary number (Koerner 2008). By estimating the capillary number, Ca, (see also Table 1 for notations) through bubble growth modeling, we relate the overpressure of bubbles, which is proportional to the energy needed to initiate and sustain magma fragmentation (Mueller et al 2008), to vesicle shapes in the analyzed pyroclasts.…”