Effect of paraffin packaging methods on thermal stratification and thermodynamic performance of a mantled hot water tank

The practical integration of phase change materials (PCMs) into thermal energy storage (TES) systems, such as domestic hot water tanks, is critically dependent on the packaging method, which affects both thermal stratification and heat storage capability. This study experimentally investigates the effect of three different PCM packaging techniques on the performance of a 450-liter vertically mantled hot water tank using 32.5 kg of paraffin (62-66 °C melting point). The methods compared are: (i) cylindrical capsules, (ii) a single central cylindrical rod, and (iii) a bulky cylindrical container. Thus, this study presents an experimental campaign is designed to systematically evaluate how PCMs should be integrated into a hot‑water thermal storage tank. By comparing multiple PCM configurations and operating conditions, the work provides a comprehensive assessment of their thermal performance, charging–discharging behavior, and overall suitability for enhancing sensible heat storage systems. The results for the charging phase show that the single container severely disrupts natural convection, promoting mixing and degrading the thermocline, which is quantified by a significant drop in the normalized Stratification factor. The encapsulated and rod methods, however, preserve stratification at levels comparable to the conventional (PCM-free) tank. During discharging, the encapsulated method suggests superior performance, increasing the usable hot water output by up to 20.6% (from 505 L to 609 L) compared to the conventional tank when charged at 80 °C and discharged at 10 L/min. Most significantly, all PCM configurations are 2-to-3 times more exergy-efficient than the conventional tank. This is because the PCM’s stable latent heat release preserves the thermal quality of the heat, avoiding the rapid temperature decay seen in the conventional tank. The study concludes that a distributed, high-surface-area encapsulated design is the optimal strategy, maximizing both the energy quantity and its thermodynamic quality.