2. Void fraction

Summary

• Subject Gas volume fraction in two-phase flow

• Main conclusion: \(\langle \alpha_{G} \rangle = \langle j_{G} \rangle / (C_{0} \langle j \rangle + V_{Gj}) \)

Void fraction is a commonly used term for the gas volume fraction in two-phase flows. In chemical engineering, it is usually referred to as gas holdup. Since it gives a direct measure of how much amount of gas we have in the two-phase flow, prediction of the void fraction is important in designing/operating two-phase flow systems. We first define some basic quantities, and then the drift-flux model is introduced.

• 2.1. Averaged quantities
• 2.2. Drift-flux model