Magnetic dopant and field effects on the heat discharge of organic PCM based lauric acid

Abstract

In this experimental study, we investigated the heat transfer characteristics during the freezing or heat discharging process of a magnetic-composite phase change material (PCM). Lauric acid (LA) was used as the PCM, Fe3O4and CoFe2O4 were utilised as dopants, and a permanent magnet generated the magnetic field.The time characteristic of freezing data revealed that the magnetic dopant and field increased the heat transfer rate. This improvement resulted in substantial time savings for the solidification process, with a 42% reduction observed for Fe3O4-composite LA and a 33% reduction for CoFe2O4-composite LA. Furthermore, the magnetic field contributed to the reduction in crystal size and crystal growth along the field direction, as observed by digital optical microscopy. The freezing data were correlated with thermal conductivity and viscosity, both strongly depending on the concentration and magnetic field. Their dependence on the magnetic characteristics of the dopant was also evident. The liquid thermal conductivity indicated a critical magnetic field that depends on the dopant type and concentration. For Fe3O4-composite LA and the CoFe2O4-composite LA, the highest liquid thermal conductivity ratios were 121% and 120%, respectively, and these values were achieved at the highest dopant concentration and magnetic field intensity. For small dopant concentrations, the viscosity generally decreased with increasing magnetic field intensity, while for high dopant concentrations, the trend was different. The heat transfer and magneto-viscosity characteristics were closely related to the collaborative effect of magnetic dipolar and magnetic field interactions. The magnetic dopant and field used to control PCM freezing are important factors for optimising the performance of a material as a latent thermal energy storage system.