# Experimental Study on Two PCM Macro-Encapsulation Designs in a Thermal Energy Storage Tank
## 2 Materials and Methods
### Experimental Set-Up  
The experiments presented in this paper were carried out at the laboratory of the GREA research group at the University of Lleida in Spain, in a set-up designed to test and characterize latent heat TES systems for mid-low temperature applications (\(-20\)\({}^{\circ}\)C \(<\) T \(<\) 100 \({}^{\circ}\)C). Figure 1 shows a detailed schematic diagram of the experimental set-up composed by a 25 L inertia water tank, whose temperature is controlled by a vapor compression cooling unit ([PERSON] model GCU2030 ED01B [36]) of 5 kW cooling power, two immersion thermostats (OVAN TH100E-2 kW [37], and JP SELECTA-1 kW [38]). The set-up also integrates: two variable speed pumps, used to control the flow and inlet temperature at the TES system; and a flow meter Badger meter type ModMAG M1000 [39] with an accuracy of \(\pm\)0.25 % of the actual value, and the latent heat TES storage. The connections between components were joined using 0.5\" diameter copper pipes insulated with 18 \(\times\) 0.9 mm polyurethane tubes. The data acquisition system used consisted of 3 STEP DL-01 data logger [40] connected to a computer that integrates a system control and data acquisition software (SCADA) developed in InduSoft Web Studio [41]. The data recording interval was set to 10 s.  
Figure 2 shows the PCM storage tank connected to the experimental set-up. The tests were carried out with two different PCM macro-encapsulation designs, namely, ThinICE and FlatICE (Figure 3). The containers were made in HDPE. The external dimensions of  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Properties** & **Value** \\ \hline Melting temperature [\({}^{\circ}\)C] & 15 \\ Latent heat [\(\mid\)/g] & 180 \\ Specific heat capacity [kJ/kg-K] & 1.90 \\ Density [kg/m\({}^{3}\)] & 1700-1800 \\ Thermal conductivity [W/(m\(\cdot\)K)] & 0.43 \\ Maximum operation temperature [\({}^{\circ}\)C] & 60 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Thermophysical properties of PlusICE S15 [35].  
Figure 1: Schematic view of the experimental set-up used to perform the experimentation.  
each design are reported in Figure 3, characterized by presenting similar length and width (A and B), but different thickness, with FlatICE dimensions being double that of ThinICE (C). Furthermore, the (D) dimension reveals that the use of thin macro-encapsulation enabled a larger distance between the slabs, increasing the space that allows circulating the HTF through the TES tank. Considering the aforementioned dimensions shown in Figure 3, the use of ThinICE encapsulation allowed fitting a larger number of slabs inside the tank, but less amount of latent storage material compared with the FlatICE, as shown in Table 2.  
The temperature inside the PCM storage was measured using nine Pt-100 class B, IEC 60751 standard type, with an accuracy of (\(0.3+0.005\cdot\mathrm{T}\)). The sensors were fixed as shown in Figure 4 to the external surface of three different PCM slabs placed at the bottom, middle, and top of the tank, respectively. Moreover, two additional Pt-100 class A IEC 60751 standard type with an accuracy of (\(0.15+0.002\cdot\mathrm{T}\)) sensors were placed at the inlets and outlets of the storage tank.