## 2 Materials and Methods
### Methodology  
The charging and discharging characteristics of the bio-inspired TES tank were evaluated using a custom-built experimental setup, shown in Figure 2. A predetermined mass of the PCM was filled into the bio-inspired TES tank. Tubes of 12.7 mm diameter connected the bio-inspired TES tank to the buffer tank, through which the HTF flowed. The PCM was charged (heated) or discharged (cooled) using HTF, which flowed across the PCM through the branch-structured HTF tubes. For the charging process, hot HTF was  
Figure 1: Bio-inspired TES tank concept. Figure 2: Schematic representation of the custom-built experimental setup. supplied from the buffer tank (200 L capacity), maintained at a temperature higher than that of the phase transition temperature of the PCM using an immersion thermostat (3 kW). For the discharging process, cold HTF was supplied from the buffer tank using a condenser unit (Zanotti uniblock, GCU2020 ED01B, (Valencia, Spain)) that kept the temperature of the HTF in the buffer tank below the PCM melting temperature. The heat transfer fluid was pumped from the buffer tank through copper pipes and flowed through the TES tank at a constant flow rate using a volumetric pump (Pentax, PM45 0.5 HP, (Veronella, Italy)). A flowmeter (Badger Meter ModMAG, M1000, (Barcelona, Spain)) measured the flow rate of the HTF with an uncertainty of 0.3%. One thermocouple (TMQSS-IM050U T-type) placed in the TES tank measured the PCM's temperature with an accuracy of \(\pm\)0.3 \({}^{\circ}\)C and two thermocouples (Pt-100 1/5 DIN class B) placed at the inlet and outlet of the TES tank measured the HTF temperature. The temperature-time data were recorded using a data acquisition system (STEP, DL01-CPU, (Barcelona, Spain)). The heat loss to the surroundings was reduced using polyurethane foam for copper pipes and polystyrene for the TES tank. In the charging cycle, the HTF stored in the buffer tank was utilized to heat the PCM in the bio-inspired TES tank above the melting temperature. The immersion heaters that were integrated inside the buffer tank allowed the HTF to be heated to the objective temperature. The HTF was pumped to the TES tank at a steady flow rate once the buffer tank reached the desired temperature. During the discharging cycle, the heat contained in the bio-inspired TES tank was discharged using the cold HTF stored in the buffer tank. A refrigeration unit was used to cool the HTF stored inside the buffer tank to below the PCM's melting temperature. The HTF was continuously pumped into the TES tank once the buffer tank achieved the required temperature. The impact of varying the HTF operating temperature and flow rate on the thermal performance of the bio-inspired TES tank was investigated. Accordingly, the HTF was delivered to the TES tank at three distinct flow rates of 1.5, 3, and 6 kg/min, and at two distinct operating temperature ranges, between 15 \(\pm\) 1 \({}^{\circ}\)C and 45 \(\pm\) 1 \({}^{\circ}\)C and between 20 \(\pm\) 1 \({}^{\circ}\)C and 35 \(\pm\) 1 \({}^{\circ}\)C.  
To determine the effectiveness of the bio-inspired TES tank, three crucial parameters need to be measured: power transferred, charging time, and discharging time. The time it took for the PCM's temperature to rise from the initial coldest temperature (15 \({}^{\circ}\)C or 20 \({}^{\circ}\)C) to the complete melting temperature (29 \({}^{\circ}\)C) was defined as the charging time. Similarly, the time it took for the PCM's temperature to fall from the initial hottest temperature (45 \({}^{\circ}\)C or 35 \({}^{\circ}\)C) to complete solidification temperature (23.5 \({}^{\circ}\)C) was defined as the discharging time. This particular temperature range was chosen based on the results of differential scanning calorimetry analysis of n-octadecane.