## 4 Experimental Results and Analysis
### Comparison of Cascaded Number Layout of PCMs  
Under the experimental conditions, when the air temperature \(T_{\rm in}\) = 338.15 K and the air flow rate \(V\) = 5.0 m\({}^{3}\)/h at the inlet of the dehumidifier, the water output obtained after the experiment for 1h and the air temperature difference \(\Delta T\) between \(T_{\rm in}\) and \(T_{\rm out}\) at the dehumidifier are shown in Figure 11.  
Figure 11: Water output and \(\Delta T\) under different arrangements of PCMs.  
Figure 10: Melting of paraffin on the upper surface of phase change heat storage for CASE4 at different \(V\).  
It can be seen from Figure 11 that CASE4 has the highest water output and the largest air temperature difference at the inlet and outlet of the dehumidifier. It can be seen from Table 2 that the phase change latent heat and phase change temperature of PCM1, PCM 2 and PCM 3 decrease in turn. In CASE4, PCM1, PCM 2 and PCM 3 have the same volumes and are arranged in sequence. Their phase change temperatures decrease step by step, and the decreasing direction of the phase change temperature is consistent with that of the hot air temperature. Therefore, the temperature differences between each PCM and hot air are relatively small. When \(T_{\text{in}}\) = 338.15 K, the temperature ranges of the possible phase transitions of CASE4 and CASE1 are 321.15-338.15 K and 325.15-338.15 K, respectively; that is, the former has a wider temperature range of possible phase transition, more phase transition heat absorption and water output and greater temperature differences between the air inlet and outlet of the dehumidifier. Comparing CASE4 and CASE3, although their possible phase change temperature ranges are both 321.15-338.15 K, in Case4, because the phase change latent heat of PCM1 and PCM2 is greater than that of PCM3, the average phase change latent heat in CASE4 is greater than that of CASE3, the phase change heat absorption and water output are greater and the temperature difference between the air inlet and outlet of the dehumidifier is greater.  
According to Formulas (5) and (6), the GOR and WPC of the experimental device under the above four different arrangement modes can be calculated. If a passive humidification and dehumidification seawater desalination device is installed above the phase change heat storage, the heat in the phase change heat storage is supplied to the passive humidification and dehumidification device by heat pipe for the secondary water output; the secondary water output \(M_{1}\) can be obtained from Formula (7). Figure 12 shows the GOR1 without a secondary water output and the GOR2 with a secondary water output according to Formula (5). Figure 13 shows the WPC1 without a secondary water output and the WPC2 with a secondary water output calculated by Formula (6).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**PCM** & **Phase** & **Phase Change Temperature/K** & **Melting Latent Heat/(kJ/kg)** \\ \hline PCM1 & Solid & 325.15 & 210.3 \\ PCM2 & Solid & 323.15 & 179.0 \\ PCM3 & Solid & 321.15 & 160.0 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Phase change temperature and melting latent heat of the phase change materials.  
Figure 12: GOR1 and GOR2 under different arrangements of PCMs.  
CASE4 has the highest gain output ratio and the lowest water production cost. Compared with CASE1-CASE3, the gain output ratio increased by 9.69%, 3.86% and 2.40%, respectively, and the water production cost of CASE4 decreased by 8.82%, 3.69% and 2.31%, respectively. After the secondary water output by using the heat in phase change heat storage, the water production costs of various arrangements are reduced by 20%, and the gain output ratio is increased by 25%.