Thermal properties and morphologies of MA–SA eutectics/CNTs as composite PCMs in thermal energy storage

•Myristic-stearic acids eutectics/CNTs as composite PCMs were prepared.•The minimum mass fraction of the CNTs in the composite PCMs was 9%.•Supercooling degrees of the composite PCMs decrease with the increase of the CNTs.•Thermal conductivity of the composite PCMs can be improved by adding CNTs.

Myristic-stearic acids (MA-SA) binary eutectics with appropriate phase change temperature were prepared based on theoretical calculation. The melting temperature of the MA-SA eutectics and the mass fraction of the myristic acid (MA) in the eutectic mixtures are 42.70 °C and 54%, which was measured by Different Scanning Calorimeter (DSC). In order to enhance the thermal conductivity of the MA-SA eutectics, the carbon nanotubes (CNTs) were added into the MA-SA eutectics, and the effects of the CNTs on thermal conductivity of the MA-SA eutectics were investigated experimentally. The minimum mass fraction of the CNTs in the composite PCMs (CPCMs) was determined to be 9% without stratification. The thermal properties and microstructure of the CPCMs were investigated by the DSC and scanning electron microscopy (SEM), respectively. The DSC results showed that the CPCMs exhibited the similar solid-liquid phase change properties as the MA-SA eutectics, and the supercooling degrees of the CPCMs decrease obviously with an increase of the CNTs content in the CPCMs. The thermal conductivity Meter (TCM) was used to measure the thermal conductivities of the CPCMs, and the test results indicated that the thermal conductivities of the CPCMs increase significantly from 0.173 W/(m K) to 0.213 W/(m K), 0.258 W/(m K) and 0.283 W/(m K) as the mass fractions of the CNTs in the CPCMs were 9 wt.%, 12 wt.% and 15 wt.%. The CPCMs with enhanced thermodynamic property will contribute to the energy management and storage in building systems.

Graphical abstractGraphical abstract shows the SEM images of the (a) CNTs, (b) CPCM3, (c) CPCM4 and (d) CPCM5.Figure optionsDownload full-size imageDownload as PowerPoint slide