A Computational Study of Bubble Formation From an Orifice Submerged in Liquid With Constant Gas Flow

Abstract The bubble formation process from an orifice submerged in a liquid with a constant gas flow is studied using numerical simulations with an OpenFOAM volume-of-fluid solver. The computed results show that the detached bubble size tends to increase with the gas flowrate, 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 flowrate above which detached bubbles will combine via coalescence known as bubble pairing. At low gas flow rates, the volume of detached bubbles in the quasi-static regime is shown to depend linearly on the gas flowrate, consistent with a physical mechanistic analysis but not recognized by previous authors. 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 greater than a critical value resulting in contact line motion on the horizontal outside wall of the orifice. The value of such a critical contact angle is found to increase with the orifice size and to decrease with the gas flowrate. Such revelations would logically suggest that reducing orifice size to generate smaller bubbles could be more challenging and practically difficult for submillimeter orifices with a constant gas flow.