Typical response curves from aerated liquid–liquid systems
are shown in Fig. 3. It shows clearly that the local conductivity
signals are affected by the presence of bubbles and droplets. We
found at relatively low dispersed oil phase holdup (0–20% by
volume) and gas flow rate (QGr7 L/min) ranges the signal noise
is acceptable for determining the mixing time. However, the
signal becomes too noisy to be useful when the dispersed oil
volume fraction and gas flow rate increase. This is why we only
focus on relatively low dispersed oil phase holdups and gas flow
rates. In Fig. 3, initial fluctuations are clearly observed in the time
traces, especially for Probe B, which decays with time and
eventually the tracer concentration reaches an equilibrium value.