## 4 Conclusions  
In this work, a telecentric endoscopic transmitted light probe was used to measure the droplet size in a DN300 stirred vessel near the impeller region. The DSD was measured at phase fractions between \(\varphi=5\) vol.-% to 50 vol.-% and impeller speeds between \(N=250\) rpm and 400 rpm. The endoscopic probe can be easily installed and the measurement technique including a CNN based analysis is appropriate for the characterization of liquid-liquid systems with industrially relevant phase fractions up to \(\varphi=50\) vol.-%. In addition, large quantities of droplets can be reliably detected resulting in statistically significant and highly resolved DSD with at least 10,000 droplets per distribution. A repetition of the experiments showed minimal deviations for the same experimental parameters within the typical error range of approx. 20 \(\upmu\)m. It could be shown, that telecentric shadowgraphic probes with a modern image analysis based on a CNN can be utilized to accurately characterize particulate liquid-liquid flows at industrial relevant phase fractions. The experimental results show, that the impeller speed as well as the phase fraction mainly affect the Sauter mean diameter in stirred vessels. Especially the latter has a strong influence below a phase fraction of \(\varphi\leq 30\) vol.-%. For higher phase fractions, the influence is marginal and can be neglected. Two models from literature were re-correlated [50,51] and adequately represent the experimental data within relative deviations of 12% [51] and 22% [50]. As expected, the experimental data is better represented by the approach of [PERSON] et al. [51] than by the standard approach [50], which can be explained by the additional substance properties that were taken into account. The enhancement and validation of image analysis techniques in combination with telecentric shadowgraphic probes are part of future work, especially with a focus on industrial phase fractions and apparatus geometries. This new technique discussed here enables the improvement and development of models for the prediction of the behavior of dispersions and other particulate multiphase flows. Possible future applications are manifold, like the detection of cavitation bubbles, the measurement of bubbles in jet-loop-reactors or the use in fixed bed reactors for the characterization of the flow regime to name a few. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app12084069/s1](https://www.mdpi.com/article/10.3390/app12084069/s1)]([https://www.mdpi.com/article/10.3390/app12084069/s1](https://www.mdpi.com/article/10.3390/app12084069/s1)), Figure S1: Coefficients for the fitted models with the theoretical Weber exponent \(C_{9}=-0.6\); Table S2: Relative and absolute deviations for the fitted models  
Figure 8: Parity plot: (**a**) model of [PERSON] et al. [51] within 12% error, (**b**) model of [PERSON] [50] within 22% error (coefficients from Table 2). with the theoretical Weber exponent \(C_{9}=-0.6\); Tables S3-S48: Measured DSD's and Sauter mean diameters of all experiments. Conceptualization, D.W., K.R. and M.H. ; methodology, D.W.; software, D.W.; validation, D.W.; formal analysis, D.W.; investigation, D.W.; resources, E.v.H. and H.-J.B.; data curation, D.W.; writing--original draft preparation, D.W. and A.F. ; writing--review and editing, D.W., A.F., K.R., M.H., E.v.H., H.-J.B.; visualization, D.W.; supervision, A.F., E.v.H., H.-J.B. and R.S. ; project administration, E.v.H., H.-J.B. and R.S. ; funding acquisition, H.-J.B. All authors have read and agreed to the published version of the manuscript. This research was funded by German Research Foundation, grant number 395373747 and the Research Initiative \"Nanokat\" of the Federal State of Rhineland-Palatinate. Not applicable. All data are listed in the Supplementary Material.