Heat transfer characteristics of charging and discharging encapsulated PCMs (SP24, SP26 & SP29) for free cooling: impact of geometry and nanomaterials addition

Herein, free cooling an application of thermal energy storage is investigated through theoretical observations of air being cooled after passing over encapsulated phase change material (PCM). The impact of encapsulation geometry changes from circular to; rectangular, square, and elliptical shapes is studied for the PCM solidification and melting cycles. The study is performed for sp24, sp26, and sp29 PCM types with and without the inclusion of CuO and Al2O3 nanoparticles (NPs). A transient mathematical model for heat transfer behavior of airflow over the encapsulation is constructed and solved using Ansys 20.2 software. It is found that the rectangular-shaped PCM encapsulation with CuO nano-enhanced PCM has the shortest complete melting (similar to 1-2 h) and complete solidification times (similar to 3-9.3 h). Nanoparticle enhancement improves the rate of melting by a maximum of 11.56% with Al2O3 NPs and by 6.12% with CuO NPs at an inlet airflow temperature of 313 K. A maximum outlet air-temperature drop of similar to 3.1 K occurs in the cylindrical geometry with CuO nano-enhancement and the highest Nusselt number is obtained at similar conditions. From this study it is recommended to use either sp24 or sp26 PCMs mixed with nano-alumina and encapsulated within rectangular containers for free cooling applications.

Automated summary

In this study, the application of free cooling using thermal energy storage was investigated by studying the cooling effect of encapsulated phase change material (PCM) on air. The study analyzed the impact of different encapsulation geometries and nanoparticle enhancements on the solidification and melting cycles of PCM. A mathematical model for heat transfer over the encapsulation was developed and solved using Ansys 20.2 software. The results showed that rectangular-shaped PCM encapsulation with CuO nanoparticle enhancement had the shortest solidification and melting times. It was also recommended to use either sp24 or sp26 PCMs mixed with nano-alumina and encapsulated in rectangular containers for free cooling applications.