A Computational Study of Bubble Formation from an Orifice Submerged in Liquid with Constant Gas Flow

TL;DR

This study uses numerical simulations to analyze how various factors influence bubble formation from an orifice submerged in liquid, revealing new insights into bubble size dependence, critical flow rates, and contact angle effects.

Contribution

It introduces a detailed numerical analysis of bubble formation, identifying the linear relationship between bubble volume and gas flow rate and the impact of contact angle variations.

Findings

Detached bubble size increases with gas flow rate and orifice size.

A critical gas flow rate exists for bubble coalescence.

Bubble volume depends linearly on gas flow rate at low flows.

Abstract

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. At low gas flow rates, the volume of detached bubbles in the quasi-static regime is shown to depend linearly on the gas flow rate, 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 increased beyond a critical value resulting in contact line motion on the horizontal outside wall of orifice. The value of such a critical contact angle is found to increase with the orifice size and decrease with the gas flow rate. Such revelations would logically suggest that reducing orifice size for generating smaller bubbles could be more challenging for sub-millimeter orifices with constant gas flow.