*3.5. Effect of Droplet Size on the Evaporation Performance*

Figure 16 shows the turbulence kinetic energy under different droplet sizes. By increasing the droplet size from 5 to 60 μm, the turbulence kinetic energy in the mixing zone of the flue gas and the droplets changes slightly, which indicates the slight difference in the mixing intensity between flue gas and droplet. By further increasing the droplet size from 60 to 150 μm, the turbulence kinetic energy in the mixing zone of the flue gas and the droplets becomes significantly stronger, and this is because the larger droplet size has a more substantial rigidity and turbulence. Figure 17 displays temperature under different droplet sizes, and smaller droplet size corresponds with the higher temperature in the mixing zone of the flue gas and the droplets because the smaller size droplet has a larger specific surface area and is sufficiently heated to evaporate.

**Figure 15.** Effect of initial wastewater temperature on evaporation performance.

**Figure 16.** Turbulence kinetic energy under different droplet sizes (m2/s2).

**Figure 17.** Temperature under different droplet sizes (K).

Figure 18 shows the effect of wastewater flow rate on the evaporation performance of the droplet in the spray drying tower. As the droplet size increases, it can be seen that the trajectory of the droplets will diffuse toward the tail of the drying tower, the complete evaporation distance is extended, and the atomization evaporation effect is reduced. When the droplet sizes are 5 and 60 μm, the difference in the evaporation performance is slight. Considering the atomization cost and other factors, it is more economical and practical to choose a droplet size of 60 μm.
