## 3 Results
### Pressure Drop across the Pad
Average pressure drop across the cellulose pad varied from 1.2 Pa when \(u\) = 0.5 m s\({}^{-1}\) and \(Q\) = 2 L min\({}^{-1}\) m\({}^{-1}\) to 32.3 Pa when \(u\) = 3.5 m s\({}^{-1}\) and \(Q\) = 10 L min\({}^{-1}\) m\({}^{-1}\). While the pad with \(PS_{2}\) material was above 10 Pa and the other ones were above 20 Pa for the minimum speed tested. This shows a big difference between \(\Delta P\) of the cellulose and the alternative materials. Figure 9 shows the \(\Delta P\) for an inlet air velocity of 1.0 m s\({}^{-1}\) and a water flow of 6.2 L min\({}^{-1}\) m\({}^{-1}\). The \(CS_{1}\) presents the highest \(\Delta P\) due to the used of the smallest particle size, while the \(PS\) pads present the lowest \(\Delta P\), between the alternative pads. The \(PS_{2}\) had the lowest value due to the highest particle size. The differences in the \(\Delta P\) values were more noticeable for high \(u\) and \(Q\) values (data not show). Figure 10 shows the normalized average pressure drop across the different pads tested as a function of the inlet air velocity with a constant water flow of 6.2 L min\({}^{-1}\) m\({}^{-1}\). As was expected for a porous medium, \(\Delta P\) increased with \(u\). When \(\Delta P\) was normalized with respect to the maximum \(\Delta P\) of each pad material, no visual differences in the behaviour of \(\Delta P\) as \(u\) changed were seen. From low to high \(u\), \(\Delta P\) was affected in the same way for all the pads. The relation between \(\Delta P\) and \(u\) can be described with the same exponential function, fitted to their respectively \(\Delta P\) values for each pad material. \begin{table}
\begin{tabular}{l l c c c c} \hline \hline
**Pad** & **Test** & \(\overline{\Delta P}\) & \(\widetilde{\Delta P}\) & \(\sigma\) & \(\sigma^{2}\) \\ \hline \multirow{4}{*}{\(CL\)} & \(Q_{1}\) & 1.9450 & 1.9400 & 0.0414 & 0.0017 \\  & \(Q_{2}\) & 6.1400 & 6.1200 & 0.0573 & 0.0033 \\  & \(Q_{3}\) & 10.0170 & 10.0400 & 0.0440 & 0.0019 \\ \hline \multirow{4}{*}{\(CS_{1}\)} & \(Q_{1}\) & 1.9827 & 1.9400 & 0.0852 & 0.0073 \\  & \(Q_{2}\) & 6.1321 & 6.1200 & 0.1640 & 0.0269 \\  & \(Q_{3}\) & 8.1764 & 8.1300 & 0.4248 & 0.1805 \\ \hline \multirow{4}{*}{\(CS_{2}\)} & \(Q_{1}\) & 1.9896 & 1.9800 & 0.1389 & 0.0193 \\  & \(Q_{2}\) & 5.9684 & 6.0400 & 0.2677 & 0.0716 \\  & \(Q_{3}\) & 9.7014 & 9.7600 & 0.5464 & 0.2986 \\ \hline \multirow{4}{*}{\(BC\)} & \(Q_{1}\) & 2.0832 & 2.0500 & 0.2869 & 0.0823 \\  & \(Q_{2}\) & 6.0147 & 5.9800 & 0.2579 & 0.0665 \\  & \(Q_{3}\) & 9.7360 & 9.7900 & 0.4150 & 0.1723 \\ \hline \multirow{4}{*}{\(PS_{1}\)} & \(Q_{1}\) & 2.3979 & 2.4400 & 0.2310 & 0.0534 \\  & \(Q_{2}\) & 6.0732 & 6.0800 & 0.7191 & 0.5171 \\  & \(Q_{3}\) & 8.6864 & 8.6600 & 0.6682 & 0.4465 \\ \hline \multirow{4}{*}{\(PS_{2}\)} & \(Q_{1}\) & 2.1481 & 2.1600 & 0.2472 & 0.0611 \\  & \(Q_{2}\) & 6.3353 & 6.2200 & 0.6723 & 0.4520 \\ \cline{1-1}  & \(Q_{3}\) & 8.6104 & 8.4800 & 0.6734 & 0.4535 \\ \hline \hline \end{tabular}
\end{table} 
Table 10: _Cont._Figure 11 shows the normalized average pressure drop across the different pads tested as a function of the water flows for a constant inlet air velocity of 1 m s\({}^{-1}\). For all the pads, except for the cellulose one, the pressure drop is highly influenced by the water flow through the pad, being the \(CS_{1}\) pad the most affected and the \(PS\) pad the least affected. The \(\Delta P\) of the cellulose pad changes about 9% due to increasing the water flow, meanwhile the \(CS_{1}\) pad changes 80%. In the cellulose material, the water forms a thinner layer in comparison with the alternative pads where it considerably increases the resistance to air flow.