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Micromachines 2022, 13, 1456 8 of 10 differed due to the high-energy ball milling process conferred by the DSC results. With the increasing mass fraction of the steatite powder, the PCMSB composites exhibited higher thermal conductivity. The composites composed of PCMSB had an average thermal conductivity of 0.2226 W/mK. In comparison with paraffin, the thermal conductivity value of the PCMSB composite was 7.7% higher. The enthalpy value of PCMSB seemed to increase when compared to the PCMS, and for the ball-milled composites, the value also seemed to marginally increase the latent heat capacity. The solid PCM/steatite composite received heat initially, leading to an increase in temperature over time. In the following step, a melting process began and continued until the solid PCM composite transformed into the liquid state. As the PCM composite moved into the melting zone, its temperature increased slightly. Due to the continuous heat supply during melting, the PCM composites had a higher latent heat value. In order to begin the solidification process, the liquid PCM must cool down. During the solidification of the PCM, the temperature was nearly constant because high heat transfers through convection. The solidification of the PCM composites followed the removal of heat from the liquid PCM. Due to the heat being released, the latent heat of freezing was lower [26]. As a result, the addition of the steatite powder to the paraffin wax resulted in significant changes in the thermal properties of the PCMS and PCMSB composites. 3.5. Performance during Charging and Discharging During the charging and discharging processes, the data logging system was used to determine the average temperature of the PCMS and PCMSB composite. Heat is transferred more efficiently through longitudinal fins. Temperatures were recorded based on three different trials, and the average readings were calculated. Figure 6 shows the average experimental values measured on the LHTES system. Pure paraffin PCM (Figure 6a) took 180 min for the complete charging operation, whereas the PCMS (Figure 6b) and PCMSB (Figure 6c) exhibited 180 and 210 min to attain a steady state. The increase in the thermophysical properties of the composites and the influence of the mechanical milling increased the charging time indicating the greater amount of thermal energy being stored. The graphs show that the discharging time of the PCMSB was greater than the steatite encapsulated PCM. The PCMSB took 270 min to attain the steady state against the 240 min recorded for PCMS, thereby indicating the increase in thermal stability and operational sustainability during the discharging process. The use of ball-milled steatite additives that were highly thermally conductive in PCM composites enhanced the thermal conductivity and increased the heat transfer efficiency. During the transition from liquid to solid, the material experienced supercooling. Since the crystallization process was delayed, the material remained liquid even at cold temperatures. Consequently, the composite with ball-milled steatite fabricated composite exhibited better discharge characteristics [27]. Figure 6a–c, which denote the experimentation data using the PCM, PCMS, and PCMSB systems, show a significant increase in the available latent heat discharging time. The addition of steatite had only a marginal increase in the latent heat capability in the case of both PCMS and PCMSB. The enhancement in the discharge time was correlated with the better stability attained due to a reduction in particle size. The increase in melting and solidification time was due to the smaller particle and increased thermal conductivity of the ball-milled steatite. The thermal conductivity of the composites depended on the bonding between the atoms. The higher the bonding, the greater the melting temperature, and the thermal conductivity will also be higher, as the heat flow will be higher in these substances. This remains the reason behind the increase in melting time with respect to the increase in the thermal conductivity. Moreover, conduction was the major heat transfer mode occurring across the system during the discharging process. On average, the melting time increased by 17% with the PCMSB composite, compared with the pure paraffin and PCMS. The increase in the liquefaction period denoted the enhanced capability to utilize the available sensible heat. The discharging cycle results showed an increase in the solidification time by incorporating ball-milled steatite with paraffin PCM. This enhancement denoted thePDF Image | Heat Charging–Discharging Periods of Paraffin Wax
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