###### Abstract  
For the objective of enhancing the heat transfer ability of spray cooling, a single-nozzle open-loop spray cooling experiment platform was established with a data measuring system. Based on the surface heat transfer coefficient obtained from the experiment, combined with the visualization system to observe the distribution of droplets during the spray cooling process, the influence of heating power, medium flow rate, nozzle height and typical additives on heating surface coverage and heat transfer characteristics were investigated. The criterion non-dimensional criteria equations for Nu, Re, Pr and size coefficients were fitted and analyzed in comparison with experimental data. The main conclusions are as follows: considering the temperature distribution characteristics of the heating surface and the shape of the spray cone, the heat transfer performance can be optimized by increasing the coverage rate under high heat flux when the flow rate changes, appropriately reducing the coverage rate under low heat flux, and appropriately reducing the coverage rate when the height changes, which creates complete coverage in the droplet concentration area to improve the surface heat transfer capacity. Furthermore, the heat transfer coefficients were improved by 29.3%, 21.8% and 23.8% with different additives (CTAB, ethanol and CTAB-ethanol mixtures) in the working fluid. Each solution had an optimal concentration and heat transfer deterioration was observed at high concentrations. When using non-dimensional criteria equations for parameter calculations, the data are more accurate after considering the effect of dimensional coefficients. spray cooling; visualization system; heat transfer performance; surface coverage; additives +
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was expected to reach 190 W/cm\({}^{2}\) by 2020 [6]. What is worse, the microminiaturization of the electronic equipment has greatly shrink the heat dissipation area, which has led to a heat flux of up to 10\({}^{3}\) W/cm\({}^{2}\) in recent years [7]. Spray cooling is based on phase change heat transfer, which has the advantages of strong heat exchange capacity, low coolant flow, good homogeneity, low superheat and high critical heat flux (up to 10\({}^{3}\) W/cm\({}^{2}\)), as one of the most competitive technologies in the field of high heat flux cooling and airborne electronic equipment cooling. Closed-loop spray cooling technology is currently listed by NASA as one of the research priorities for future airborne thermal control systems [8], and the investigation has successfully approached the goal of 10\({}^{3}\) W/cm\({}^{2}\)[9]. Spray cooling is widely used in medical, metallurgy, chip cooling, aerospace and other fields [10], and liquid nitrogen spray cooling can be used in some specific environments to achieve greater cooling capacity instantaneously [11]. The non-uniformity of droplet distribution in spray cooling and its effect on heat transfer performance were investigated by [PERSON] et al. [12] and [PERSON] et al. [13]. Meanwhile, the effects of nozzle arrays [14], splash injection [15], and liquid film flow [16] were studied by some scholars. In each case, references are provided for the enhancement of spray heat transfer. The study of the heat transfer flow mechanisms of spray cooling has been emphasized by researchers in the field of spray cooling in an effort to increase the heat transfer capacity. Using water as a medium for spray cooling trials, [PERSON] et al. [17] concluded that the heat flux on the surface of the simulated heat source increased with increasing heating power. However, an air film between the heating surface and the liquid droplets prevented heat transfer. In a spray cooling experiment, [PERSON] (2018) demonstrated that the critical heat flux increased with an increase in liquid flow rate, but the effect of liquid subcooling on critical heat flux was not significantly altered. [PERSON] et al.