Phase change material emulsions (PCMEs) or phase change slurries have risen interest in scientific community in the last years as potential heat transfer and heat storage fluids [1]. These systems consist on a base fluid, which is a suitable heat transfer fluid, and an emulsified phase change material. The idea is to exploit the latent heat of melting and crystallization of PCM to increase the thermal energy storage capacity of the base fluid and, at once, confer higher thermal conductivity and lower viscosity by the fluid with respect to PCM. Moreover, the large interface between base fluid and PCM favors the heat transfer between the two phases. Main barriers to their application are the difficulty in maintaining emulsion stability and the sub-cooling effect (i.e. the cooling of the paraffin drops below their melting point before recrystallization).[2] Water- and (ethylene glycol+water)-based emulsions with fine droplets of various paraffins were produced by a solvent-assisted emulsification method. Concentrations from 2 to 10 wt% were obtained with paraffins with various melting temperatures between 20 and 70°C. The droplet dimensions were verified and resulted below 100 nm for lower concentrations and slightly higher for 10 wt%.[3] No phase separation or significant growth in PCM drops was observed for the prepared emulsions through storage, after freeze-thaw cycles and under mechanical shear. A subcooling effect was verified and reduced by testing some nucleating agents. The heat of melting was lower than expected, probably due to PCM molecules on the surface of the nanoparticles anchored to the surfactant. Although the emulsions exhibited diminutions in thermal conductivity with respect to the carrier fluids, enhancements in energy storage capacity with respect to base fluid reached up to 40%. In addition, the thermal reliability of the nanoemulsions was corroborated analyzing the changes in latent heat after several thermal cycles.
Phase Change Materials Nano-emulsions for Thermal Energy Transfer and Storage
Barison S;Agresti F;Fedele L;Bobbo S;Rossi S
2019
Abstract
Phase change material emulsions (PCMEs) or phase change slurries have risen interest in scientific community in the last years as potential heat transfer and heat storage fluids [1]. These systems consist on a base fluid, which is a suitable heat transfer fluid, and an emulsified phase change material. The idea is to exploit the latent heat of melting and crystallization of PCM to increase the thermal energy storage capacity of the base fluid and, at once, confer higher thermal conductivity and lower viscosity by the fluid with respect to PCM. Moreover, the large interface between base fluid and PCM favors the heat transfer between the two phases. Main barriers to their application are the difficulty in maintaining emulsion stability and the sub-cooling effect (i.e. the cooling of the paraffin drops below their melting point before recrystallization).[2] Water- and (ethylene glycol+water)-based emulsions with fine droplets of various paraffins were produced by a solvent-assisted emulsification method. Concentrations from 2 to 10 wt% were obtained with paraffins with various melting temperatures between 20 and 70°C. The droplet dimensions were verified and resulted below 100 nm for lower concentrations and slightly higher for 10 wt%.[3] No phase separation or significant growth in PCM drops was observed for the prepared emulsions through storage, after freeze-thaw cycles and under mechanical shear. A subcooling effect was verified and reduced by testing some nucleating agents. The heat of melting was lower than expected, probably due to PCM molecules on the surface of the nanoparticles anchored to the surfactant. Although the emulsions exhibited diminutions in thermal conductivity with respect to the carrier fluids, enhancements in energy storage capacity with respect to base fluid reached up to 40%. In addition, the thermal reliability of the nanoemulsions was corroborated analyzing the changes in latent heat after several thermal cycles.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
