## 2 Experimental Setup and Procedures  
The current work is performed on an experimental test rig presented by [PERSON] et al. [16]. The representation of the setup with its details is demonstrated in Figure 1. As shown, it comprises a refrigeration cycle (vapor-compression cycle, R-22) and the cycle of ice storage. The refrigeration cycle is created to cool the ethylene glycol solution and heat transfer fluid (HTF) to the mandatory operating temperature during charging. The TCHC (test section), which houses measurement equipment, makes up most of the ice storage cycle. Samples of experimental results for ice formation during charging and discharging operations are shown in Figure 1. A heat transfer fluid is an aqueous ethylene glycol solution with a freezing point of \(-19\)\({}^{\circ}\)C and a concentration of 35% by weight (HTF). The experimental setup specifications are presented in Table 2. The cylindrical acrylic ice storage tank is fabricated to be filled with distilled water (PCM). The PCM fills the tank to half a pitch above the top turn of the TCHC. The details of the coil's geometrical parameters are presented in Table 3. Two typical insulated reservoirs for charging and discharging each are filled with 45 L of HTF. Data acquisition with 16 channels is used to instantaneously record the HTF temperature distribution in 15 different locations with calibrated (T-type) thermocouples. Figure 2 represents the positions of the nine thermocouples in the middle turns of TCHC. The remaining six thermocouples are on three vertical axes on upper, lower, and middle turns. Some thermocouples are employed to determine the inlet and outlet HTF temperatures. Figure 1: Experimental setup. (**a**) Schematic illustration. (**b**) Experimental test rig photo [16]. (**c**) Sample of charging experimental results. (**d**) Sample of discharging experimental results at certain time slots. Furthermore, a rotameter is employed to evaluate the volume flow rate of HTF, which is constant in this study at 10 L/min. The charging and discharging HTF temperatures are maintained at \(-12\)\({}^{\circ}\)C and \(10\)\({}^{\circ}\)C, respectively, for all experiments in the current work. A digital temperature controller (DTC) with a set point differential of \(\pm 1\)\({}^{\circ}\)C is used to keep the charging and discharging temperatures inside the charging or discharging reservoirs \begin{table}
\begin{tabular}{l l} \hline \hline
**Item** & **Description** \\ \hline \multirow{4}{*}{Ice storage tank} & Acrylic “Insulated” \\  & Inner diameter = 250.8 mm \\  & Height = 350 mm \\  & Thickness = 6 mm \\ \hline \hline Twin-Centric Helical Coils (TCHC) & Geometrical parameters are described in Table 3 \\ \hline Charging reservoir & 45 L capacity \\ \hline Discharging reservoir & 45 L capacity \\ \hline Charging temperature, \({}^{\circ}\)C & \(-12\) \\ \hline Discharging temperature, \({}^{\circ}\)C & 10 \\ \hline HTF volume flow rate, L/min & 10 \\ \hline \hline Digital Temperature Controller (DTC) & Temperature control, with a set point differential of \(\pm 1\)\({}^{\circ}\)C \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Experimental setup specifications. \begin{table}
\begin{tabular}{l l l l l l} \hline \hline
**Description** & **Inner Coil** & **Outer Coil** & **Outer Coil** \\ \hline Outer tube & & & & & \\ diameter (\(d_{l,o}\)), & & & 9.52, 12.70, 15.88 & & \\ mm & & & & & \\ \hline Centerline & & & & & \\ radius (\(R_{coil,c}\)), & 29.76 & & & 92.46 & \\ mm & & & & & \\ \hline Pitch (p), mm & 30 & 40 & 50 & 30 & 40 & 50 \\ \hline No. of turns (N) & 6.67 & 5 & 4 & 6.67 & 5 & 4 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Geometrical parameters of the twin-centric helical coils. Figure 2: Positions of thermocouples on the horizontal plane at the mid-turn of TCHC [16]. during the experiments. An air-conditioned laboratory unit uses a 22 \(\pm\) 1 \({}^{\circ}\)C dry bulb temperature and 50 \(\pm\) 5% relative humidity. The experimental procedures start with positioning the valves for charging or discharging.