## 4 Results and Discussion
### Effect of Different Particle Sizes on the Refractory Properties of Converter Transformers  
The effects and mechanisms of fine water mist with different particle sizes on the fire parameters of the converter transformer are analyzed in this section. Figure 8 shows that as the particle size of the water mist decreases, the rate of water vapor generation in the calculated space increases to 1.1 kg/s, 1.3 kg/s, and 1.5 kg/s, respectively. A higher rate of water vapor generation in a semi-enclosed or enclosed space can effectively reduce the oxygen content, thereby lowering the fire power. Additionally, the heat carried away by evaporation helps reduce the fire temperature. In this case, however, the space was relatively open, and the increase in water vapor had a limited effect on the mass burning rate of the fire. Figure 7: Temperature change trend before and after coating application at different points. During the flame stabilization stage, the mass burning rate for the three particle sizes remained between 0.056 kg/m\({}^{2}\)-s and 0.070 kg/m\({}^{2}\)-s, showing little difference across particle sizes. Only after 450 s did the mass burning rate for the 100 \(\upmu\)m (blue triangle) particle size show a slight decrease. This was due to the higher water evaporation rate, which reduced the oxygen and fuel concentration in the air. In the previous section, it was observed that the temperature of the bottom measurement point where measurement point 05 is located is the highest, so in this section, measurement point 05 (in the middle of the two sprays) and measurement point 08 (directly below the spay) were selected to study the effect of different particle sizes on the surface temperature of the converter transformer, and the specific location is shown in Figure 9. The results show that the cooling effect of the water mist of different particle sizes at measurement point 08 is obvious, and with the increase in the particle size, the cooling effect is improved, and the temperature is reduced by 58%, 63%, and 67%, respectively, with respect to the non-sprinkled without spraying maximum temperature of 289 \({}^{\circ}\)C, the temperature reduction was 58%, 63%, and 67%, respectively, and the temperatures were all kept near the boiling point of 100 \({}^{\circ}\)C.  
Figure 8: Effects of different water mist particle sizes on mass burning rate and water evaporation rate. Figure 9: The influence of water mist with different particle sizes on the temperature of typical measuring points. According to the above, the evaporation rate of smaller particles is higher, which results in more heat being removed. Therefore, the cooling effect should increase as the particle size decreases, which contradicts the calculation results. A reasonable explanation can be found by referring to Figure 10. Figure 10 shows the temperature field distribution: lower temperatures below the spray, higher temperatures in the spray interval, and as the particle size decreases, the high-temperature region expands. This distribution can be explained by the droplet distribution shown in Figure 10. For larger droplets (400 \(\upmu\)m), the spray distribution is more regular, with droplets falling downward. For smaller droplets (200 \(\upmu\)m and 100 \(\upmu\)m), the droplet distribution is more chaotic, with not all droplets falling straight down. This phenomenon is caused by thermal buoyancy. Referring to the mechanism diagram in Figure 10, the droplets fall from the top and attach to the object's surface, where the high-temperature vaporization reduces the surface temperature. However, thermal buoyancy from the flame at the bottom impedes the droplets from falling further, thus reducing the cooling effect on the surface. The effect of buoyancy is more pronounced on smaller droplets, which is why the cooling effect improves as particle size increases. A similar pattern was observed at measurement point 05, where the cooling effect increased as the particle size increased, based on the same principle.