It can be seen from Table 2 and Figure 3b that the spreading diameters on St\({}_{12.6}\) and St\({}_{15.3}\) surfaces are equal to each other (3.8 mm),  
Figure 4: Photo images of water droplet evaporation when the three-phase contact line moves uniformly during the transition from the CCD to the mixed stage on St\({}_{1.0}\) surface. Figure 5: Photo images of water droplet evaporation when the three-phase contact line moves nonuniformly during the transition from the CCD to the mixed stage on St\({}_{46.3}\) surface. as well as on St\({}_{25.8}\) and St\({}_{46.2}\) surfaces (4.0 mm). This is due to the fact that, in each pair of the surfaces under consideration, the possible increase in the contact angle due to the deterioration of the wetting properties is reduced by an increase in roughness. It can be concluded that, during finishing metal surfaces with abrasive materials, in order to achieve the largest contact diameter of water droplet spreading over Cu-ETP copper surfaces, it is necessary to use abrasive materials with the smallest average grain size. In the case of steel surfaces, it is necessary to use abrasive materials with the largest average grain size. From a practical point of view, achieving the largest contact diameter is important for intensifying the phase transition of droplets in the single-phase regime in cooling systems of energy-saturated equipment. Figure 6 presents the dependencies of the specific evaporation rate of water droplets on copper (Figure 6a) and steel (Figure 6b) surfaces at a heating temperature of 80 \({}^{\circ}\)C. A similar nature of the specific evaporation rate of a water droplet on a hydrophobic Teflon surface was recorded in [10]. The experimental results (Figure 6) illustrate the significant dominance of the influence of the droplet spreading diameter, which, in turn, depends on the wetting properties and on the evaporation rate. It can be seen from Figure 6a that the specific evaporation rate of the water droplet on copper surfaces decreases in the sequence Cu\({}_{10}\)-Cu\({}_{12.6}\)-Cu\({}_{15.3}\)-Cu\({}_{21.8}\)-Cu\({}_{25.8}\)-Cu\({}_{46.2}\), i.e., in the sequence of decreasing the initial contact diameter (Figure 2b). With an increase in the contact diameter, the heat exchange area between the surface and the droplet lying on it increases; therefore, the heat transferred to the droplet increases, as well as the evaporation rate. In practice, this leads to a more intensive cooling of energy-saturated equipment in cooling systems. The specific evaporation rate of the droplet on steel surfaces decreases in the sequence St\({}_{46.2}\)-St\({}_{25.8}\)-St\({}_{21.8}\)-St\({}_{15.3}\)-St\({}_{12.6}\)-St\({}_{1.0}\) (Figure 6b). The heat exchange area between the surface and droplet depends not only on the contact diameter, but also on the roughness. In the case of the same diameters on different surfaces (a pair of surfaces St\({}_{12.6}\) and St\({}_{15.3}\), as well as St\({}_{25.8}\) and St\({}_{46.2}\)), the specific evaporation rate of the droplet is higher on the surface, which has a greater roughness, i.e., \(W_{\text{specific}}\) (St\({}_{15.3}\)) \(>W_{\text{specific}}\) (St\({}_{12.6}\)), and \(W_{\text{specific}}\) (St\({}_{46.2}\)) \(>W_{\text{specific}}\) (St\({}_{25.8}\)) (Figure 6b). The greater the roughness, the larger the heat exchange area and, consequently, the higher the evaporation rate. For two pairs of surfaces (St\({}_{12.6}\) and St\({}_{15.3}\), St\({}_{25.8}\) and St\({}_{46.2}\)), the _liquid_ / _ambient_ interfacial surface area will be almost identical, since the initial spreading diameters and contact angles on them are very close to each other.