Experimental analysis of the melting and solidification patterns in a PCM encapsulation for domestic hot water production

• A novel effective specific heat capacity is calculated from the properties analysis. • Melting and solidification tests in encapsulated phase change material are conducted. • Phase change material behaviour is assessed using visual and thermal methodologies. • A novel methodology to calculate heat flux based on experimental data is developed. • The Nusselt number evolution is presented to analyse the heat transfer processes. The growing demand for energy storage solutions has increasing interest, particularly in domestic hot water applications. One promising approach involves the use of encapsulated phase change materials (PCM) within hybrid accumulators, which enhance energy storage efficiency. However, understanding the thermal behaviour of these encapsulations remains a challenge. This study aims to analyse the phase changes and the heat transfer processes in encapsulated PCM. The analysis is performed on cylindrical stainless-steel encapsulations containing paraffin. A study of its thermal properties is done and a new coefficient to characterize this kind of materials is obtained. Three configurations are examined to assess the measurement methods and gain a preliminary understanding of the behaviour of the encapsulated PCM: with sensors to measure the PCM temperature, with a transparent cover for direct visualization, or combining both features. Melting and solidification tests in a thermal bath are conducted. A total melting time of 30 min is estimated, while total solidification takes approximately twice because of the low thermal conductivity of the paraffin. An innovative methodology is developed to calculate the heat storage rate and the energy exchanged. This approach is validated against a global energy calculation, achieving a deviation of 2.1 %. The encapsulation with 32 g of PCM stores up to 10 kJ. The rough Nusselt number is calculated, showing values around 1 during solid state and increasing as convection starts to affect the melting process. This research allows the understanding and assessment of the phase change processes of PCM in a cylindrical stainless-steel encapsulation.