## 3 Results and Discussion
### Optimization of Serpentine Channel  
In order to enhance heat dissipation power, there must be some sacrifices in mass uniformity and pressure loss. The referred serpentine channel was the one to increase its channel width as large as possible and here in the present dimension its width was 45 mm as shown on the left of Figure 4. For the optimization, some flow splitter plates were set along with the serpentine channel. The width of each splitter plate was 2 mm. Then a splitter plate was used to branch the coolant into two flows and three plates were used for four flows, which can be seen in the right of Figure 4. The dimensions of the different optimized strategies are shown in Table 2.  
Figure 4: Middle section of computational domain for serpentine optimization. The left one is a referred serpentine channel of Case 1 with the largest channel width. The right one is a schematic of a flowing channel with splitter plates. Figure 3: The flowing distribution of six models. The flow detail and mass uniformity can be clearly observed in Figures 5 and 6. Without any splitter plate, as seen in Figure 5a, coolant flowed mostly like the cavity plate type, as the channel width was as large as possible to increase the heat transfer surface. However, due to dead flow zones (the areas colored by white), its pressure drop was larger than those of Cases 2 and 3. Figure 5b shows the flow process of Case 2 with one splitter plate. Compared with Case 1, its pressure drop decreased because most of coolant flow was restrained in the two channels so that the areas of dead flow zones and flow resistance were reduced. Furthermore, Case 2 showed better mass flow uniformity than Case 3, which was divided into four channels by three splitter plates. In Case 3, most coolant flowed into the two middle channels due to flow interference, as they directly connected to the inlet orifice without any flow turn, so that mass maldistribution was enlarged in this case. Conversely, however, its pressure dropped continuously because of the continuous decrease of the dead flow zone. In order to improve mass maldistribution phenomena, a block was set in the inlet location. The block actively divided the coolant flowing into the different channels and mostly reduced the effect of flow interference. However, the structure of the block significantly influenced flow characteristics and heat transfer performance. Once the block was unsuitable, its effect could be against the improvement of mass uniformity and heat transfer capacity. Like Case 4, mass maldistribution \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Case** & \(\mathbf{w_{1}}\) & \(\mathbf{w_{2}}\) & \(\mathbf{h_{1}}\) & \(\mathbf{h_{2}}\) & \(\mathbf{h_{3}}\) & **Re** & **Remark** \\ \hline
1 & 45 & - & - & - & - & 7.28 & without splitter plate \\
2 & 22.5 & - & - & 6 & - & 12.65 & one splitter plate \\
3 & 6 & 29.5 & - & 6 & - & 27.57 & three splitter plates \\
4 & 6 & 29.5 & 2 & 6 & 6 & 27.57 & three splitter plates \\
5 & 6 & 29.5 & 10 & 6 & 6 & 27.57 & three splitter plates \\
6 & 6 & 29.5 & 15 & 6 & 6 & 27.57 & three splitter plates \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Value of the design variables in the six cases. Figure 5: Flow characteristics of cooling plates of six models. did not improve but its pressure loss was greatly enlarged by local loss induced by the wall effect of the block. The large pressure loss also happened in Cases 5 and 6. However, due to the promotion of block structure, mass maldistribution was greatly improved. All the pressure drops and mass percentages in each channel of the different cases are shown in Figure 6.  
Among the six cases, Cases 2 and 5 showed better comprehensive performance when taking mass uniformity and pressure drop into consideration. However, when the attention was paid to heat transfer as shown in Figure 7, the temperature in the bottom surface of the cooling plate with channel configuration of Case 5 was lower than that of Case 2.