## 3 Results and Discussion  
According to the steps shown in the Materials and Methods section, the mechanical work for the micro-Deval was approximated to be \(\sim\)3.4 J per one revolution of the drum. In the Los Angeles machine, it was approximated to be \(\sim\)17.8 J per one revolution of the drum, on average, in the first cycle (13.6 J accounting for impact mechanical work and 4.2 J for rotational mechanical work). In contrast to the micro-Deval apparatus, in the Los Angeles machine, the mechanical work considerably dropped with the mass loss, reaching \(\sim\)14.4 J per rotation on average in the fifth cycle. This calculated mechanical work seems to be lower than the one calculated for the micro-Deval machine by [PERSON] et al. [40]. The difference probably occurred, firstly, because of the higher material content in the mill, and secondly because of the different assumptions made about the charge motions. In the mentioned study, the radius considered for the moment of inertia calculation was higher, and was calculated based on the charge distribution typical for a centrifuging charge motion. This might have led to the overestimation of mechanical work. The energy-related results, along with the main characteristics of both machines, are summarised in Table 1.  
We managed to measure the power difference between the idling power and the net power for the micro-Deval apparatus (Figure 5a). For the Los Angeles, the two curves overlapped (Figure 5b), and it was not possible to measure the power difference. This could be caused by the fact that during the Los Angeles experiments, the drum filling was lower than 1%, and the power draw needed for movements of such a small mass of charge/material was negligible when compared to the mass of the empty steel drum. The measured mechanical work in the micro-Deval was found to be 9.8 Watts (J/s) per drum. When recalculated to mechanical work per one revolution of drum, this equals 5.8 J. The theoretically estimated work represents only about 60% of the measured one for the micro-Deval apparatus. A part of this difference can be attributed to the power losses in bearings and gears, noise and heat generation, etc. [41]. In order to be able to compare the machines, theoretically derived energies (Equations (5)-(13)) were used for later processing and discussion.  
\begin{table}
\begin{tabular}{l l l} \hline  & **Micro-Deval** & **Los Angeles** \\ \hline D (drum) (mm) & 200 & 711 \\ \hline L (drum) (mm) & 154 & 508 \\ \hline \(\omega\) (rpm) & 100 & 32 \\ \hline Mean m\({}_{0}\) (kg) & 0.22 & 1.96 \\ \hline No. of samples & 9 & 3 \\ \hline Filling (\%) & 56.3 & 0.35 \\ \hline P\({}_{0}\) (W) & 5.67 & 9.52 \\ \hline \(\Sigma\)E (kJ) & 315.93 & 23.71 \\ \hline \(\Sigma\)t (min) & 930 & \(\sim\)47 \\ \hline \(\Sigma\)Rev (n) & 93000 & 1500 \\ \hline \end{tabular}
\end{table}
Table 1: Main characteristics of the machines and power estimates. (D—inner diameter of the drum, L—inner length of the drum, \(\omega\)—rotational speed of the drum, Mean m\({}_{0}\)—mean initial mass of the sample, Filling—filled portion of the drum, P\({}_{0}\)—power of the machine in the first cycle, \(\Sigma\)E—cumulative introduced energy, \(\Sigma\)t—cumulative time of abrasion (sum of all cycles’ duration), \(\Sigma\)Rev—cumulative number of revolutions).