gasentrained

Gas entrained refers to the presence of gas within a liquid flow, resulting in a gas–liquid mixture or foam. It occurs when gas is captured and carried by the moving fluid, either from a free surface during turbulence or from local pressure changes that generate bubbles. Entrainment can involve ambient air or dissolved gases released into the liquid.

In natural systems, gas entrainment is common in fast-flowing rivers, rapids, and waterfalls where turbulence pulls air into the water. In engineered settings, it can be intentional, as in aeration tanks and some fermentation or water treatment processes, or unintentional, such as in pumps, pipelines, spillways, and mixing vessels. Entrained gas affects flow behavior by increasing void fraction, altering density and viscosity locally, and changing pressure losses and mixing patterns.

Key implications of gas entrainment include enhanced mass transfer of gases to or from the liquid, which can improve or hinder chemical and biological processes. It can also cause foaming, wear, corrosion, and flow instabilities, as bubbles coalesce, break up, or form pockets that modify the effective flow area. In piping and equipment design, excessive entrainment can lead to inefficiencies, gas-lock, cavitation risk, and pump performance issues.

Measurement and control centers on quantifying gas hold-up or void fraction and the bubble size distribution. Techniques include optical probes, electrical impedance tomography, acoustic sensors, high-speed imaging, and tomography. Understanding gas entrainment is essential for optimizing aeration, reactor performance, and the stability of multiphase flows in both natural and industrial contexts.