## 3 Results and Discussion
### Effect of Coverage on Heat Transfer Performance by Changing Flow Rate  
The visualization images of the interior of the chamber with the flow rate of 25 L/h, 30 L/h, 35 L/h and 40 L/h with 100 W/cm\({}^{2}\) heating heat flux are shown in Figure 7. As can be seen from the nozzle product manual and computer measurements, in this experimental system, when the Ge Qiang 1/8 1 mm nozzle flow rate is 25 L/h, the spray cone angle is 25\({}^{\circ}\), as illustrated in Figure 7a. The droplet jet cannot overcome gravity's acceleration when the flow rate is too low, so a complete spray cone cannot be formed and a corresponding coverage cannot be calculated. The spray cone angle is 30\({}^{\circ}\) when the flow rate is 30 L/h, 40 degrees when the flow rate is 35 L/h, and 45 degrees when the flow rate is 40 L/h. By setting nozzle coverage to 100% at a flow rate of 40 L/h, it is possible to determine a nozzle height of 2.89 cm. With this height fixed, reducing the flow rate to 35 L/h and 30 L/h, the corresponding coverage rates can be calculated as 77% and 42%, respectively.  
Figures 8-11 show the effect of coverage on transient surface heat transfer coefficient by changing flow rate at different heating heat fluxes (50-200 W/cm\({}^{2}\)). From Figures 8-11, it can be seen that the transient surface heat transfer coefficient increases with the increase in coverage at different heating heat fluxes when the medium flow rate is increased, and the phenomenon is more obvious especially at high heat fluxes. When the heating heat flux is low, the heat exchange on the surface of the heat source is not completely in the boiling zone, the greater the flow rate, the greater the droplet velocity, and the greater the number of instantaneous droplets. As a result, at this time, some droplets that are not ready to  
Figure 7: Visualization images of the influence of flow rate change on spray coverage at a heating heat flux of 100 W/cm\({}^{2}\): (**a**) flow rate 25 L/h; (**b**) flow rate 30 L/h, coverage 42%; (**c**) flow rate 35 L/h, coverage 77%; (**d**) flow rate 45 L/h, coverage 100%.  
Figure 12 shows the effect of coverage on steady-state surface heat transfer coefficient by changing flow rate effect of varying coverage by flow rate. It can be seen from the figure that the steady-state surface heat transfer coefficient increases with increasing coverage at higher heat fluxes. This coverage increases as the flow rate increases, so the greater the coverage, the greater the number of droplets on the heat transfer surface, the stronger the heat transfer effect in the boiling zone at high heat fluxes, and therefore the heat transfer coefficient increases. At the heat flux of 100 W/cm\({}^{2}\) and below, the surface heat transfer coefficient first increases and then slightly decreases with the increase in coverage. As can be seen from Figures 8-11, the transient surface heat transfer coefficient fluctuates for large  
Figure 11: The influence of coverage rate of changing flow rate at 200 W/cm\({}^{2}\) on transient surface heat transfer coefficient.  
Figure 10: The influence of coverage rate of changing flow rate at 150 W/cm\({}^{2}\) on transient surface heat transfer coefficient.  
flow rates and small heating heat fluxes. Therefore, the steady-state heat transfer coefficient also decreases. Figure 12 also further verifies the above conclusion.