**3. Results and Discussion**

Three different classifiers were built for each of the working fluids (ethanol and FC-72) using the experimental data. These data comprise 9841 observations for ethanol and 8590 observations for FC-72. The input features considered for all classifiers and both working fluids are the modified versions of Weber, Froude, and Bond numbers, represented by *We*∗ *<sup>l</sup>* , *Fr*<sup>∗</sup> *<sup>l</sup>* , and *Bo*<sup>∗</sup> *<sup>l</sup>* , respectively. These numbers were defined using actual bubble lengths, velocities, and accelerations, estimated via specific image analysis methods. More details regarding the definition of each number and data pre-processing can be found in Pietrasanta et al. [29]. The categorical output data indicate whether a specific observation is classified as slug/plug flow or semi-annular flow, and it was conducted visually. For each working fluid and classifier, the steps described below were carried out.
