## 2 Materials and Methods
### Experimental Materials and Equipment  
As shown in Figure 2, the PTFE, PVDF, and PP flat sheet hydrophobic porous membranes were used in the experiments. Figure 3 shows the DCMD system. Figure 4 shows images captured via SEM (scanning electron microscopy) of membrane samples. Tables 1 and 2 show the equipment and the physical property parameters of selected hydrophobic porous membranes, respectively.  
Figure 4: Images captured via SEM (scanning electron microscopy) of membrane samples’ inside surfaces (**a**) PTFE [50], (**b**) PVDF [50], (**c**) PP [51].  
Figure 3: Direct contact membrane distillation equipment.  
Figure 2: The three different hydrophobic porous membranes used in the experiments.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Equipment** & **Equipment Model** & **Manufacturers** \\ \hline Membrane & MFPT-2213 & Hangzhou Cobalt Filter Material Co., Hangzhou China. \\ Membrane Components & & Xiamen Guochu Co., Xiamen China. \\ Pump & YZ-1515X & Lange Constant Flow Pump Co., Baoding China. \\ Constant Temperature Tank & DC-1010 & Xiamen Guochu Co., Xiamen China. \\ Temperature and conductivity sensors & EC-4110 & Suntex Instruments Co., Taiwan China. \\ Electronic scale & XH3180-K & Xinhen Instruments Co., Shanghai China. \\ \hline \end{tabular}
\end{table}
Table 1: DCMD system components.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Thickness (\(\mu\)m)** & **Pore Size (\(\mu\)m)** & \begin{tabular}{c} **Thermal Conductivity** \\ **(W\(\cdot\)m\({}^{-1}\)\(\cdot\)K\({}^{-1}\))** \\ \end{tabular} & \
\begin{tabular}{c} **Porosity** \\ **\%** \\ \end{tabular} &
\begin{tabular}{c} **Contact Angle (\({}^{\circ}\))** \\ **[5,17,52]** \\ \end{tabular} \\ \hline PTFE & 205 & 0.22 & 0.2651 & 53.75 & 140 \(\pm\) 3 \\  & 185 & 0.45 & 0.2651 & 46.77 & 140 \(\pm\) 3 \\  & 168 & 1 & 0.2651 & 53.12 & 140 \(\pm\) 3 \\ \hline PP & 177 & 0.22 & 0.13 & 55.22 & 148.1 \\  & 193 & 0.45 & 0.13 & 37.73 & 148.1 \\  & 228 & 1 & 0.13 & 55.89 & 148.1 \\ \hline PVDF & 150 & 0.22 & 0.22 & 85 & 120 \(\pm\) 10 \\  & 125 & 0.45 & 0.22 & 90 & 120 \(\pm\) 10 \\  & 100 & 1 & 0.22 & 90 & 120 \(\pm\) 10 \\ \hline \end{tabular}
\end{table}
Table 2: Physical property parameters of the selected hydrophobic porous membranes.  
The temperature and conductivity sensors were used to detect the temperature and conductivity of the hot and cold sides in actual time. The temperature detection range of the hot side is from 0 to 100 \({}^{\circ}\)C and the conductivity detection range is from 0 to 199 ms/cm, with an accuracy of 0.01 ms/cm. The temperature detection range of the cold side is from 0 to 100 \({}^{\circ}\)C and the conductivity detection range is from 0 to 2000 \(\upmu\)s/cm, with an accuracy of 0.01 \(\upmu\)s/cm.  
The experimental steps were as follows:  
Firstly, each group of test lasted for 3 h, and after the system was stabilized, the data were recorded every 15 min, and a total of 12 groups of data were recorded in each test;  
Then, the stable data of each group of tests were arithmetically averaged to find the average permeate flux and error calculations were performed.  
The aim of this article is to determine the optimal time for membrane performance without considering pollution. In subsequent studies, the situation of membrane fouling will be studied separately.