## 5 Discussion  
In this study, meeting two evaluation criteria was the premise of a qualified air-cooling BTMS design. The evaluation criterion of T\({}_{\rm max}\) (<308.15 K) could be achieved by all designs when the flow rate reached 31.68 \(\times\) 10\({}^{-3}\) m\({}^{3}\)/s. Design 5 delivered the lowest T\({}_{\rm max}\) of 305.49 K, 303.33 K, and 301.90 K at the flow rates of 31.68 \(\times\) 10\({}^{-3}\) m\({}^{3}\)/s, 42.24 \(\times\) 10\({}^{-3}\) m\({}^{3}\)/s, and 52.8 \(\times\) 10\({}^{-3}\) m\({}^{3}\)/s, respectively. The evaluation criterion of \(\Delta\)T (<5 K) could be achieved by Design 2 and 3 at 10.56 \(\times\) 10\({}^{-3}\) m\({}^{3}\)/s, Design 1, 2, 3, 6, and 7 at 21.12 \(\times\) 10\({}^{-3}\) m\({}^{3}\)/s, as well as Design 1, 2, 3, 5, 6, and 7 at 31.68 \(\times\) 10\({}^{-3}\) m\({}^{3}\)/s, 42.24 \(\times\) 10\({}^{-3}\) m\({}^{3}\)/s, and 52.8 \(\times\) 10\({}^{-3}\) m\({}^{3}\)/s, respectively. To make a comprehensive yet balanced comparison, Table 5 lists the performance rankings and status of the two evaluation criteria indicators (T\({}_{\rm max}\) and \(\Delta\)T) of each design at five flow rates. The green cell shading means the design inside met the evaluation criteria (T\({}_{\rm max}\) < 308.15 K or \(\Delta\)T < 5 K). \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Flow Rate**} & & & & & \\ \multicolumn{1}{c}{**(\(\times 10^{-3}\) m\({}^{3}\)/s)**} & & & & & & \\ \hline \multirow{5}{*}{T\({}_{\rm max}\) (\(<\)308.15 K)} & 1  & 2 & 3 & 7 & 4 & 5 & 6 \\  & 21.12 & 1 & 5 & 6 & 7 & 2 & 3 & 4 \\ \cline{1-1}  & 31.68 & 2 [FOOTNOTE:2]Footnote 2: \(\Delta\)T is the difference between the two values  
When the flow rates were 10.56 \(\times\) 10\({}^{-3}\) m\({}^{3}\)/s and 21.12 \(\times\) 10\({}^{-3}\) m\({}^{3}\)/s, none of the designs could meet the requirement of T\({}_{\rm max}\), and only half of the designs could meet the requirement of \(\Delta\)T. At 10.56 \(\times\) 10\({}^{-3}\) m\({}^{3}\)/s, Design 2 is considered as the optimal design due to coming in first place in \(\Delta\)T (4.4 K) and second place in T\({}_{\rm max}\) (316.52 K), though it is unqualified. At 21.12 \(\times\) 10\({}^{-3}\) m\({}^{3}\)/s, Design 1 is the optimal one due to its leading positions in both T\({}_{\rm max}\) (308.78 K) and \(\Delta\)T (3.11 K), though it is also unqualified. Design 3 ranks second in \(\Delta\)T (3.44 K) and Design 5 ranks second in T\({}_{\rm max}\) (309.32 K), but their other indicators (T\({}_{\rm max}\) of Design 3 and \(\Delta\)T of Design 5) are both coincidently ranked sixth. At 31.68 \(\times\) 10\({}^{-3}\) m\({}^{3}\)/s, Design 1 firstly met both evaluation criteria and continued to hold its top position for its first place in \(\Delta\)T (3.14 K) and second in T\({}_{\rm max}\) (305.74 K). Although Design 5 delivers the lowest T\({}_{\rm max}\) (305.49 K), its \(\Delta\)T (4.35 K) is 0.24 K higher than the average \(\Delta\)T of all designs (4.11 K). At 42.24 \(\times\) 10\({}^{-3}\) m\({}^{3}\)/s, T\({}_{\rm max}\) of Design 5 (303.33 K) was 0.47 K lower than Design 1 (303.80 K), but the \(\Delta\)T of Design 5 (3.74 K) was 0.7 K higher than Design 1 (3.04 K). Meanwhile, \(\Delta\)T of Design 7 (2.88 K) was 0.16 K and 0.86 K lower than Design 1 (3.04 K) and Design 5 (3.74 K), respectively. However, T\({}_{\rm max}\) of Design 7 (303.93 K) was 0.13 K and 0.6 K higher than Design 1 (303.8 K) and Design 5 (303.33 K). Therefore, the optimal design at 42.24 \(\times\) 10\({}^{-3}\) m\({}^{3}\)/s becomes a conditional evaluation depending on the aspect in priority: 1. Design 5 is optimal if lower T\({}_{\rm max}\) is the major objective; 2. Design 7 is optimal if \(\Delta\)T is mostly concerned; 3. Design 1 is optimal if a balanced thermal performance is required. At 52.8 \(\times\) 10\({}^{-3}\) m\({}^{3}\)/s, the T\({}_{\rm max}\) of Design 1 (302.4 K), Design 2 (303.33 K), and Design 3 (303.53 K) in CVSG rank fourth, fifth, and sixth, respectively.