# Thermal Behavior of Alveoli with Phase Change Materials in Fruit Packaging
## 2 Materials and Methods  
### Description of Experimental Setup  
The experimental study carried out in this work includes cooling and heating tests in a climatic chamber into which packages containing fruit were introduced. The cooling cycles reproduce the placement of fruit packages in cold rooms. The heating cycles simulate the process of removing fruit packaging from the storage chambers and placing them on displays for sale to the public, subject to the store's ambient temperature. The packaging used was developed as part of the Pack2 Life project [12]. The main characteristics of this packaging are its innovation in terms of thermal attributes, which allow for maintaining a stable temperature inside, together with the modularity characteristics adapted to different conditions of use, for better transport and storage conditions as well as the display of sale to the public. It is made of polypropylene, 600 mm wide, 400 mm deep, and 90 mm high, as shown in Figure 1.  
The phase change materials chosen for this work are commercially available paraffins [20] manufactured by Rubitherm GmbH (Berlin, Germany). They are identified as RT2 HC, RT5 HC, and RT8 HC, and their thermal characteristics are presented in Table 1. These organic PCMs were selected based on their melting and freezing points, which align  
Figure 1: New fruit packaging. with the temperature ranges commonly required for fruit storage (0-6 \({}^{\circ}\)C). This deliberate choice ensures that the results immediately apply to real-world scenarios in cold chain logistics. RT2 HC has a melting range of 1-3 \({}^{\circ}\)C, and it was chosen for its ability to stabilize temperatures quickly due to its low melting point. It is ideal for applications requiring rapid cooling to maintain freshness immediately after harvest. However, while it stands out in terms of cooling speed, its performance in prolonged heating scenarios is less effective due to its lower latent heat capacity. The RT5 HC has a melting range between 5 and 6 \({}^{\circ}\)C. With a moderate melting range and higher latent heat (250 kJ/kg), RT5 HC offers a balance between cooling and heating performance. It is well-suited for maintaining stable temperatures over intermediate periods. The higher latent heat makes it efficient in energy storage, extending thermal stability during transitions between cold storage and ambient conditions. On other hand, RT8 HC has a melting range between 7 and 9 \({}^{\circ}\)C. This PCM was selected for its good performance in heating scenarios, as its melting range aligns with the upper limits of proper fruit storage temperatures. The alveoli chosen for this study, Figure 2, which incorporate phase change materials, are produced in polypropylene, with dimensions to fit fruit packaging and with a shape suitable for both apples and peaches [21; 22]. In this study, fruit simulators were used, consisting of acrylic spheres shown in Figure 3a, with 10 cm diameter, containing a solution of water and agar gel with a volumetric concentration of 2%. Figure 3b shows the internal environment where the fruit simulators were initially tested. These simulators replicated the thermal properties of real fruits, ensuring that the results reflected practical applications. Embedded thermocouples measured temperature changes at various points within the packaging, enabling detailed analysis of thermal behavior across different PCMs and packaging configurations. The temperature sensors made up of T-type thermocouples (See Figure 4a) were inserted in the center of the fruit simulator, as shown in the cross-sectional diagram of Figure 4b, and connected to a temperature datalogger shown in Figure 4c), allowing the temperature measurement with an accuracy of \(\pm\)0.4 \({}^{\circ}\)C that improve the traceability [22].