## 3 Results and Discussion
### Comparison of Average Values of HTC and HF on the Cooled Surface
The lowest HTC values were obtained for the JET system for \(p=0.05\) MPa (Figure 19). Increasing the determination surface to \(A_{2}\) area did  
Figure 21: Comparison of the change in average HTC values from the surface temperature (**A**) and time (**B**) during cooling using three systems of cooling, \(A_{2}\). Figure 22: Comparison of the change in average HF values from the surface temperature (**A**) and time (**B**) during cooling using three systems of cooling, \(A_{2}\). not change these relations (Figure 21). Similar maximum values of HTC on the \(A_{1}\) surface were obtained during cooling with the JET system for water pressure \(p\) = 0.2 MPa, WS system for \(p\) = 0.05 MPa and \(p\) = 0.1 MPa, and AAS system for \(p\) = 0.1 MPa (Figure 20). On the \(A_{2}\) surface, a similar maximum HTC, differing from each other by 56 W/(m\({}^{2}\cdot\)K), was observed for the ASS system for \(p\) = 0.2 MPa and WS system for pressures \(p\) = 0.05 MPa and \(p\) = 0.1 MPa (Figure 21). The mentioned systems allow for achieving similar maximum heat transfer rates with the use of different water flux densities. However, the surface temperature at which the maximum HTC occurs was different for each considered cooling system. The maximum HF value changed in the range from 450 \({}^{\circ}\)C to 530 \({}^{\circ}\)C depending on the cooling system and cooling parameters (Figures 21 and 22). Changing the size of the determination surface did not influence the change of this range. Similar ranges of the maximum heat flux occurrence for the tested cooling systems are reported in the papers [50; 51]. The highest HF on both \(A_{1}\) and \(A_{2}\) surfaces was obtained for the AAS system for water pressure \(p\) = 0.2 MPa. The lowest HFs were observed for the AAS system for \(p\) = 0.05 MPa and the JET system for \(p\) = 0.05 MPa (Figures 20 and 22). The AAS cooling system allows for achieving higher HTC values during transition boiling, which results in a faster reduction in both surface temperature and temperature in the entire sample volume (Figure 16). The ability of the fluid to receive heat from the cooled surface depends on the type of cooling system and the pressure of the fluid. This dependence is very visible in Figure 23, which shows the thermal characteristics of the coolant for all tested cooling systems. The thermal characteristics of the coolant are presented as \(F\) function. Function \(F\) defines normalized HF on the \(A_{2}\) surface for a water flux density of 1 m\({}^{3}\) /(m\({}^{2}\) s). The greatest amount of heat energy removed by water was observed for the AAS cooling system and the lowest for the JET system. The influence of water pressure is ambiguous and depends on the cooling system. For the AAS system, the increase in pressure from 0.1 MPa to 0.2 MPa caused an over 47% increase in the ability of water to dissipate heat. For the WS and JET systems, a decrease in the amount of dissipated energy with increasing the fluid pressure was observed. In the case of the coolant pressure equaling 0.05 MPa, a 29.9% and 67.4% decrease in the ability of the liquid to remove thermal energy from the surface, for the WS and JET systems, respectively, was observed in compared to AAS-cooling. For a coolant pressure of 0.1 MPa, the ability of the coolant to remove heat during WS- and JET-cooling is 39.0% and 69.7% lower than for AAS-cooling. The maximum difference in the possibility of removing the thermal energy, for all considered systems, occurred during cooling, at which the liquid was applied to the cooled surface under a pressure of 0.2 MPa. In this case, the ability of water to dissipate heat during WS- and JET-cooling was reduced by 57.8% and 87.7% in relation to AAS-cooling. Figure 23: Thermal characteristics of the coolant during cooling with the three cooling systems, \(A_{2}\).