## 4 Discussion  
The experimental results showed that the pads evaluated produced cooling efficiencies above 42% and temperature drops up to 5.0 \({}^{\circ}\)C, as can be seen in Figures 5 and 7, even with environmental conditions that are not suitable for evaporative cooling (low dry-bulb temperature and high relative humidity of inlet air). The major drawback is the increase in relative humidity that in this case was up to 35%. The alternative pads presented similar results to those of the cellulose pads. However, the environmental conditions were not kept constant due to experimental limitations, making it difficult to established an unbiased comparison between the pads from the experimental test results. For this reason, the model proposed by [PERSON] et al. [32] was used to simulate each one of the pads in equal environmental and operative conditions. The results presented in Table 8 and Figure 2 show that the model used adequately describes the behaviour of each pad. With this, it was indeed possible to obtain the correlation (3) to compute the convective heat and mass transfer coefficients of each pad, which is useful for performing different thermo-fluid analysis as in Computer Fluid Dynamics simulations. There are few research studies about cooling pads that report those coefficients, ref. [13] being the first one to report the coefficients of the coconut coin fibre and non-woven fabric perforated materials. This study allowed us to confirm that the cellulose pad coefficients were similar to those found by [PERSON] et al. [5], [PERSON] and [PERSON] [21], [PERSON] et al. [30], [PERSON] et al. [56], [PERSON] et al. [57]. The cellulose pad studied in this work serves as reference to validate the model proposed by [PERSON] et al. [32]. Several research studies are in concordance with the inverse correlation of the cooling efficiency and the relative humidity with the air inlet velocity found here [1; 24; 29]. Although the behaviour of the coconut shield with small particles (\(CS_{1}\)) was unexpected, some other research studies had documented similar behaviours [12; 13; 58] with pads based on natural fibres. This behaviour could be attributed to the resistance to the air flow across the pad. For some pads, especially with smaller particle sizes, such as the \(CS_{1}\) pad, the particles are arranged in such a way that the high resistance to air flow limits the free transit of the air across the pad, decreasing the surface area in contact with the water. When the inlet air increases, the pressure drop forces the air to flow through small orifices that could be full of water, raising the turbulence of the flow, incrementing the water-air contact and resulting in a drastic decrease in the dry-bulb temperature of outlet air. For the other material that had a lower particle size, the effect is less noticeable. According to the results shown in Figures 3 and 4, the magnitude of the convective heat and mass transfer coefficients are inversely proportional to the specific surface area found for the alternative pads. That is, those coefficients compensate in some way for the low magnitude of the total wetted surface. On the other hand, alternative pads that had a similar specific surface area to the cellulose one (coconut shells and burnt clay brick) presented the highest cooling efficiency, with a high relative humidity at the outlet, which is also an indicator of high water consumption, while the cellulose pad kept it lower due to its lower convective mass transfer coefficient. The accuracy of the model results was not affected by not considering the water flow in accordance with [27; 28; 29; 44] or the porosity of the materials as was established by [PERSON] et al. [16]. It was considered that the water flow was enough to maintain the pads wetted. Water flow beyond the maximum evaporation rate has no beneficial effects [31], and it only affects the pressure drop across the pad, as was shown in Figure 11. So, it is desirable to maintain an equilibrium between the water flow and the evaporative water rate.