Thermal Charging and Discharging Performance Analysis of Microencapsulated Phase Change Material (m-PCM) Slurry in a Double-pipe Heat Exchanger – An experimental investigation

The thermal charging and discharging performance of Microencapsulated phase change material (m-PCM) slurry is experimentally studied using a double-pipe heat exchanger setup. The Microencapsulated PCM particle (Nextek-28D) is used to prepare the m-PCM slurry, with deionised water as the base fluid. The m-PCM particles demonstrate good cyclic thermal stability, and the prepared m-PCM slurry shows excellent flowability with an emulsion characteristic. The flow behaviour of the m-PCM slurry exhibits a consistent 90% increase in pressure loss during the charging cycle. Additionally, there is a 14-16% increase in the friction factor up to a Reynolds number of 11,500 during the discharge cycle. The result is mainly related to the increased viscosity and thermal resistance of the m-PCM slurry at lower temperatures. The convective heat transfer coefficient of the m-PCM slurry increased by a factor of 2.2 compared to plain water. The performance efficiency factor (PEC) of an m-PCM slurry increases by a factor of 1.65 at a Reynolds number of 5,100 during the charging cycle. However, the value decreases at higher Reynolds numbers due to the extended phase-change temperature range of the microcapsules compared to the promoted convective heat transfer. On the other hand, the PEC value increased by a factor of 1.22 during the discharge cycle at a similar Reynolds number. The study findings indicate that the overall performance of m-PCM slurry depends highly on flow parameters but exhibits favourable characteristics as a heat transfer fluid (HTF) for both charging and discharging cycles.