## 4 Optimal Design of the Heat Dissipation Performance of the Fluid Cold Plate
### Simulation Results and Analysis  
In this study, the fluid inflow and outflow cold plates are set to flow into the upper end and out from the lower end, as shown in Figure 7. As the coolant fluid in electronic components must be non-conductive, a fluorinated liquid with non-toxic, pollution-free, non-conductive, volatile, and other characteristics was selected as the coolant in this study, and the simulation parameters are shown in Table 1. The subject of this article is the X-band GaN PA MMIC phased array radar system. The operating power of this system is 210 W, so we use 210 W for simulation. Based on the simulation results, the temperature and pressure distribution of the fluid inside the cold plate and the temperature distribution of the cold plate were analyzed, and then the basic heat dissipation performances of the designed Type I, II, and III cold plates were discussed. Figure 8 shows the simulation results of the temperature responses of the coolant fluid, cold plate structure, heat source surface and internal pressure of the cold plate in Types I, II and III when the system is in a steady state. The upper part of Figure 8a shows the temperature distribution of the coolant fluid, and the lower part shows the temperature change of the coolant fluid from the inlet (\(-\)298 mm) to the outlet (298 mm) (A-A cross section). The upper part of Figure 8b shows the temperature distribution of the cold plate, and the lower part shows the temperature change of the cold plate from the upper end (\(-\)311 mm) to the lower end (311 mm) (B-B cross section). The upper part of Figure 8c shows the temperature distribution of the heat source surface, and the lower part shows the temperature change from the upper end (\(-\)246.3 mm) to the lower end (255.7 mm) (C-C cross section) of the heat source contact surface. The upper part of Figure 8d shows the internal pressure distribution of the cold plate, and the lower part shows the internal pressure change of the cold plate from the inlet (\(-\)298 mm) to the outlet (298 mm) (D-D cross section). Table 2 shows the difference between  
Figure 6: Fluid meshes. the inlet and the outlet of each state according to the simulation results. From Table 2, we can see that compared to Type II and Type III, the square internal fins (Type I) have the smallest temperature difference in fluid, cold plate or heat source surface, which indicates that Type I has better temperature equalization. Moreover, the highest temperature of Type I is also the lowest among the three cold plates, which proves that Type I has a better heat dissipation performance. It is also known that the fluid pressure difference at the outlet/inlet position of Type I is the largest of these three cold plates. This phenomenon is due to the strong vortex effect when the fluid flows through the square fin, which will slow down the fluid and generate a large pressure difference. Due to the pressure increase of the cooling fluid inside the cold plate, it has a better heat conduction performance. The results show that the fluid vortex effect, as generated by the internal fins, will affect the heat transfer performance of the cold plate. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Fluid Condition**} & \multicolumn{2}{c}{**Heat Transfer Condition**} \\ \hline
**No.** & **Item** & **Parameter/Condition** & **No.** & **Item** & **Parameter/Condition** \\ \hline
1 & Fluid pattern & Turbulent flow & 1 & Material & Aluminum alloy \\ \hline
2 & Fluid material & Fluorinated liquid & 2 & Thermal conductivity & 155 W/mK \\ \hline
3 & Inlet flow velocity & 5 m/s & 3 & Heat source & 210 W \\ \hline
4 & Fluid inlet temperature & 20 \({}^{\circ}\)C & 4 & Boundary condition & Natural convection \\ \hline
5 & Ambient temperature & 25 \({}^{\circ}\)C & 5 & Ambient temperature & 25 \({}^{\circ}\)C \\ \hline
6 & Outlet Pressure & 0 Pa & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Simulation parameters of the heat dissipation of a three-dimensional cold plate.