Supercooling elimination of cryogenic-temperature microencapsulated phase change materials (MPCMs) and the rheological behaviors of their suspension

Phase change materials (PCMs) when amalgamated in a shell material to form microencapsulated-PCMs (MPCMs) usually exhibit high levels of supercooling due to the limited crystallization process. In the present study, various efforts were made to reduce this phenomenon, including increasing the MPCM size, employing nucleating agents, and embedding copper nanoparticles into the MPCM shells. It was observed that with an in-crease in the microcapsule size from 43 mm to 76 mm, the supercooling was reduced by a value of 10.2 degrees C from melting/freeing point peak temperature differences of 37.6 to 27.4 for the 1200 rpm and 800 rpm samples respectively. Comparatively, the implementation of octadecanol nucleating agent 30 wt % resulted in a reduction of supercooling by 22.9 degrees C. The introduction of Cu nanoparticles with a decane core can also reduce the supercooling degree by 4.6 degrees C, while the thermal conductivity the MPCM samples with a hexadecane core increased from 0.173 to 0.182 W m-1 K-1 before and after the addiction of the Cu nanoparticles. Furthermore, di(propylene glycol) methyl ether was used as a carrier fluid for the MPCMs to study the slurry rheological behaviors with various MPCM compositions. It was observed that the MPCM suspension with 10-20% MPCM mass concentration did not exhibit shear thinning, while the 30% sample conveyed shear thinning properties. Furthermore, near the crystallization temperature of the PCM, the slurry viscosity sharply rose, attributed to the volume changes and non-cooperative motion of MPCM microcapsules.(c) 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Automated summary

This study aimed to reduce the supercooling phenomenon in microencapsulated phase change materials (MPCMs) through methods such as increasing microcapsule size, employing nucleating agents, and embedding copper nanoparticles. It was found that these methods were effective in reducing supercooling. Additionally, the rheological behavior of MPCMs was influenced by the MPCM composition.