## 2 Materials and Methods  
The temperature-controlled container with a cold energy storage system developed by South China Agricultural University (Guangzhou, China) is shown in Figure 1, and the specific dimensions of the container are shown in Table 1. The container is mainly composed of a cold storage area, fresh-keeping area, circulating duct, and fan. The construction material of the container is mainly glass fiber reinforced plastic (GFRP). The insulation layer consists of vacuum insulation board (VIP) and polyurethane (PU), and the properties of the materials are shown in Table 2. The airflow in the container is driven by the fans (0.13 m \(\times\) 0.13 m, DC, 24 V, 0.7 A), and for the adjustment of the control system, the airflow speed when the fan is activated is standardized to 4.4 m/s. Due to the airflow circuit between the cold storage area and the freshness preservation area, the cold energy released from the PCM is continuously transported to the fresh-keeping area in order to maintain a low-temperature environment of 2-8 \({}^{\circ}\)C.  
Figure 1: Schematic structure of a temperature-controlled container with a cold energy storage system: 1—fresh-keeping area; 2—fan; 3—insulation surface; 4—circulating duct; 5—cold storage area; 6—control area; 7—circulating duct; 8—cold storage plate. A prototype based on the temperature-controlled container with a cold energy storage system was built and is shown in Figure 2 with a basket of fresh products, a paperless recorder, and 14 PT100 sensors. The temperatures of the air inlet and outlet, the center and the surface of the cold storage plate, the fresh-keeping area, the external environment, and the fresh products were collected using PT100 sensors (adhesive-type Class A, accuracy \(\pm\) 0.15, temperature range \(-\)60\(\sim\)180 \({}^{\circ}\)C), which were connected to a paperless recorder (SIN-R9600, accuracy 2%, Hangzhou Lianmei Automation Technology Co., Ltd., Hangzhou, China). The air inlet velocity was measured at five different points using an anemometer (model Testo410i, range 0.4\(\sim\)30 m/s, accuracy \(\pm\) (0.2 m/s + 2% of the measured value)), and the average value was taken. The cold storage plates were made of 2 mm thick aluminum alloy (outer dimensions: 1 m \(\times\) 0.04 m \(\times\) 0.2 m) and are shown in Figure 3 with a 3 cm filling port on the top, which is used for the water injection (5 kg of water per plate), and a PT100 sensor was placed in the center of the cold storage plates to measure the PCM temperature. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Functional Zone** & **Lengths/mm** & **Widths/mm** & **Heights/mm** \\ \hline Outer dimensions of the container & 2000 & 1800 & 1720 \\ Cold storage area & 1535 & 305 & 1480 \\ Fresh-keeping area & 1800 & 1200 & 1460 \\ Dimensions within the control area & 300 & 200 & 1480 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Specific dimensions of the container. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Materials** & **Heat Conduction** & **Thermal Resistance** & **Densities** \\  & **/W (m\({}^{\circ}\)C)\({}^{-1}\)** & **/W\({}^{-1}\) (m\({}^{2,\circ}\)C)** & **/(kg\(\cdot\)m\({}^{-3}\))** \\ \hline GFRP & 0.4651 & 0.0086 & 2800 \\ VIP & 0.0244 & - & 45 \\ PU & 0.0048 & - & 280 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Physical properties of materials. Figure 2: Temperature-controlled container with a cold energy storage system: 1—circulating duct; 2—cold storage area; 3—cold storage plate; 4—paperless recorder; 5—fresh-keeping area; 6—fan (outlet); 7—fan (inlet); 8—PT100; 9—ravel oranges. To effectively utilize the results, the temperature at a representative point is often adopted to represent the overall temperature of the cold storage area. Therefore, only the temperatures of two pieces of the cold storage plates shown using the red points in Figure 2 were selected and averaged, and this value was used as the temperature representative point for the real-time status of all the cold storage plates.