  The process of bubble formation from an orifice submerged in liquid with
constant gas flow is studied by numerical simulations using an OpenFOAM
volume-of-fluid solver named interIsoFoam. The computed results show that the
detached bubble size tends to increase with the gas flow rate, orifice size,
surface tension, liquid contact angle, etc. in qualitative agreement with most
previous authors. For a given orifice size and liquid properties, there exists
a critical gas flow rate above which detached bubbles will combine via
coalescence known as bubble pairing. The detached bubble size seems insensitive
to the contact angle when the liquid adequately wets the orifice wall, but can
increase substantially if the contact angle is increased beyond a critical
value resulting in contact line motion on the horizontal orifice surface. The
value of such a critical contact angle increases with the orifice size as well
as gas flow rate. Such revelations would logically suggest that the usage of
reduced orifice size for generating smaller bubbles could be more challenging
and practically difficult with constant gas flow for sub-millimeter orifices.
