## 3 Results and Discussion
### Orthogonal Experiment and Range Analysis  
In Section 3.2, it was proved that a block structure can greatly affect the mass uniformity of the cooling plate, and hence an orthogonal experiment and range analysis were conducted based on Case 5  
Figure 6: A comparison of six models in mass maldistribution and pressure drop. Figure 7: Temperature distributions of Case 2 and Case 5. Here a heat flux of 50 kW/m\({}^{2}\) was applied on the bottom surface of cooling plate. to study the sensibility of structure parameters on flow mass uniformity and pressure drop. Here four parameters were chosen in the optimization: \(w_{1}\), \(h_{1}\), \(h_{2}\), and \(h_{3}\), as shown in Figure 4. Each parameter had three levels and nine simulations were carried out, as shown in Table 3.  
Considering the first evaluation criterion of mass uniformity coefficient, the calculation results are shown in Table 4. It is obvious that the most significant factor affecting mass maldistribution was channel width. The range value of channel width was about three to four times larger than the other three factors. The remaining parameters behaved less effectively to mass uniformity, except for the situation where \(h_{1}\) decreased to a very small value when compared to \(h_{2}\) and \(h_{3}\). This can be seen in Figure 5, where \(h_{1}\) was 2 mm and its mass maldistribution was more severe than Cases 5 and 6, whose \(h_{1}\) was not so small for the contrasting distances. Therefore, it can be confirmed that at constant volumetric flow, the most significant factor affecting mass flow and heat transfer was channel width, which was also validated by [PERSON], [PERSON] et al. [23]. In this simulation, the best structure for a minimum mass maldistribution was with \(w_{1}\) of 6 mm, \(h_{1}\) of 18 mm, \(h_{2}\) of 10 mm, and \(h_{3}\) of 8 mm. Considering the second evaluation criterion of pressure drop in Table 5, it showed the consumption of pump power needed for the coolant flowing through the channel. The channel width still played a key role in pressure drop, but the distance of \(h_{2}\) showed the same importance as channel width, as their range values were almost the same. The long distance of \(h_{2}\) led to a more moderate strike to the block when the coolant flowed into the channel, especially in a high speed. Here, the best structure for a minimum pressure drop was with a \(w_{1}\) of 10 mm, \(h_{1}\) of 14 mm, \(h_{2}\) of 10 mm, and \(h_{3}\) of 8 mm. As such, a small pressure drop required a wide channel and long distance of \(h_{2}\) whereas for mass distribution it required a narrow channel and long distance of \(h_{2}\). Since the distance of \(h_{2}\) showed little effect on mass flow uniformity but much effect on pressure drop, the optimization \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Mass Uniformity Coefficient**} & \multicolumn{2}{c}{**Remarks**} \\ \hline  & A & B & C & D & \\ \hline K1 & 0.343 & 0.460 & 0.463 & 0.446 & \multirow{2}{*}{\(K\) is sum of mass uniformity coefficient: K = \(X_{1}\) + \(X_{2}\) + \(X_{3}\) (X stands for A, B, C, D)} \\ K2 & 0.489 & 0.433 & 0.446 & 0.409 & \\ K3 & 0.487 & 0.426 & 0.410 & 0.464 & \\ k1 & 0.114 & 0.153 & 0.154 & 0.149 & \\ k2 & 0.163 & 0.144 & 0.149 & 0.136 & \\ k3 & 0.162 & 0.142 & 0.137 & 0.155 & \\ R & 0.049 & 0.011 & 0.017 & 0.019 & \\ \hline Key factor & & & A \textgreater{} D \textgreater{} C \textgreater{} B & & \\ \hline Better level & A1 & B3 & C3 & D2 & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Results of range analysis on mass uniformity coefficient.