## 4 Conclusions  
In this paper, the effects of heating heat flux, coverage of flow rate change, coverage of nozzle height change and additives on heat transfer performance were studied, and the corresponding transient heat transfer coefficients and steady-state heat transfer coefficients were calculated. Combined with the spray visualization morphology inside the cavity under several parameter variations, the change of heat transfer coefficient under several parameter variations was analyzed comprehensively, which provide reference to the question how to effectively strengthen heat transfer. The conclusions of the study are as follows:  
1. Both the transient surface heat transfer coefficient and the steady-state surface heat transfer coefficient of the simulated heating source increase as the heating heat flux increases. During the initial operation of the system under high heat flux conditions, some of the droplets will rapidly produce vapor that blocks heat transfer, resulting in a situation where the transient heat transfer coefficient increases sharply and then decreases slightly and subsequently reaches an equilibrium state. 2. Both transient and steady-state surface heat transfer coefficients increase with increasing flow rate at high heat flux. In the case of large flow rate and small heating heat flux, the transient surface heat transfer coefficient fluctuates and the steady-state heat transfer coefficient decreases, so the heat transfer coefficient increases first and then decreases slightly with the coverage rate. 3. When the spray coverage does not exceed the heating surface, the temperature distribution on the surface of the simulated heat source is not uniform due to the properties of the heating surface and the velocity characteristics of the spray cone. Because of the non-uniformity of the temperature distribution on the surface of the simulated heating source and the different morphology of the spray cone, optimal heat transfer performance can be achieved at lower nozzle height and smaller surface coverage. 4. The addition of cationic surfactants (CTAB), ethanol and CTAB-ethanol mixtures all contributed to the enhancement of surface heat transfer. The addition of the CTAB-water mixture showed the greatest enhancement. The optimum enhanced heat transfer concentrations existed for all three solutions with maximum enhancement of 29.3%, 21.8% and 23.8%, respectively. However, heat transfer deterioration occurs in several solutions if the additive concentration is too high. 5. The higher accuracy and adaptability of the dimensionless criterion correlation formula that integrates Re, Pr and size coefficient. It shows that the dimensional parameters such as spray height and coverage cannot be neglected in the prediction of heat transfer ability. * If it is desired to enhance heat transfer by varying the flow rate, the coverage can be increased at high heat fluxes and reduced appropriately at low and medium heat fluxes. If the heat transfer is enhanced by changing the nozzle height, the nozzle height should be reduced appropriately to reduce the coverage, encouraging the complete coverage surface in the dense area of liquid droplets. If heat transfer is enhanced by additives, the additive concentration needs to be controlled in the optimal range. Conceptualization, Q.N. and Y.W. ; methodology, Y.W. ; validation, Q.N. and N.K. ; formal analysis, N.K. ; investigation, Q.N. ; resources, Y.W. ; data curation, N.K. ; writing--original draft preparation, Q.N. ; writing--review and editing, Y.W. ; visualization, Q.N. ; supervision, Y.W. ; project administration, N.K. ; funding acquisition, Y.W. All authors have read and agreed to the published version of the manuscript. This research was funded by the National Natural Science Foundation of China (Grant No. 51806096).