# Fluid Dynamics in a Continuous Pump-Mixer
## 3 Results
### Experimental Results
#### 3.1.4 Effects of the Process Parameters on the DSD  
Several parameters affect the DSD and the Sauter mean diameter, namely the feed phase ratio, the flow rate, and the impeller speed. The largest and most pronounced influence was found for the feed phase ratio, \(\varphi_{F}\). The DSDs for \(N=375\) and \(425\) rpm are exemplarily depicted in Figure 8 for different feed phase ratios, \(\varphi_{F}\). Figure 8a shows that the \(q_{3}\) distribution shifted towards larger drops with increasing feed phase ratio, \(\varphi_{F}\), if the impeller speed and flow rate were kept constant. This could be seen with all investigated impeller speeds and flow rates only if the feed phase ratio was varied. This is consistent with observations in literature for batch vessels [23, 24]. In general, higher phase fractions lead to more collisions between droplets and therefore increase  
Figure 8: (**a**) Measured DSDs at an impeller speed of \(N=375\) rpm, a total flow rate of \(\dot{V}_{tot}\approx 1.2\) L/min at different feed phase ratios measured at position \(MP_{1}\). (**b**) Measured DSD’s at an impeller speed of \(N=425\) rpm, a total flow rate of \(\dot{V}_{tot}\approx 1.3\) L/min at different feed phase ratios measured at position \(MP_{1}\). Figure 7: (**a**) Measured local holdup at the position \(MP_{H}\) at different impeller speeds and a feed phase ratio \(\varphi_{F}=20\) vol.-%; (**b**) measured local holdup at the position \(MP_{H}\) at a constant impeller speed \(N=425\) rpm and different feed phase ratios. coalescence. Nevertheless, the degree of the influence of the feed phase ratio, \(\varphi_{F}\), on the DSD depends on the impeller speed, too. The effect of \(\varphi_{F}\) = 10-20 vol.-% was rather small for \(N\) = 375 rpm (see Figure 8a) and larger for \(\varphi_{F}\) > 20 vol.-%. At higher impeller speeds, this effect becomes equally pronounced, which can be seen in the \(q_{3}\) distributions depicted for \(N\) = 425 rpm in Figure 8b, where the effect of \(\varphi_{F}\) on the DSD was almost equal for all feed phase fractions. This effect was also visible in the Sauter mean diameters, which are exemplarily depicted for \(N\) = 425 rpm in Figure 9a. All measured DSD data are listed in the supplementary material in Tables S3-S292. In Figure 9a the Sauter mean diameter for \(N\) = 425 rpm shows a linear relationship with respect to the total flow rate \(\dot{V}_{tot}\) at a constant feed phase ratio \(\varphi_{F}\). The slope is almost equal for different feed phase ratios and a constant impeller speed when increasing the Sauter mean diameter by increasing the flow rate. The vertical distance, so to say the difference in the Sauter mean diameters, between the different feed phase ratios (dashed lines) varied and was the highest around the feed phase ratio \(\varphi_{F}\) = 20 vol.-%. This can be seen as a transition point, where assumingly more coalescence is present, and the droplet diameter rises faster. This transition could also be observed for the other impeller speeds and was then even more pronounced. For \(N\) = 375 rpm the transition was found at \(\varphi_{F}\) = 20 to 25 vol.-%, while the effect on \(\varphi_{F}\) in other regions was rather negligible. For \(N\) = 400 rpm, the transition was more consistent across all values of \(\varphi_{F}\) = 10 to 30 vol.-%. Likewise, Figure 9a, other impeller speeds are shown in the supplementary material in Figures S2 and S3 and all measured Sauter mean diameters are listed in Table S2. Figure 9b shows the Sauter mean diameter as a function of the total flow rate of all experiments without considering the impeller speed. We can conclude that increasing the feed phase ratio increases the Sauter mean diameter and increasing the flow rate has the same effect but has less impact than the feed phase ratio. The slope of the dashed lines in Figure 9b show that the influence of the flow rate seemed to vary at around \(\varphi_{F}\) = 20 and 25 vol.-%.