Transient performance of a PCM-based heat sink with high aspect-ratio carbon nanofillers

• Transient performance of a heat sink incorporated with a TES unit was investigated.
• Organic composite PCMs filled with CNTs and GNPs at various loadings were prepared.
• Effective thermal conductivity and viscosity of the composite PCMs were measured.
• Increased viscosity leading to weakened convection may deteriorate the performance.
• Faster recovery of the TES-based heat sink was verified for all the cases tested.

The effect of using composite phase change materials (PCMs) filled with high aspect-ratio carbon nanofillers on the transient performance of a thermal energy storage (TES)-based heat sink was investigated experimentally under pulsed heat loads of various powers. The composite PCMs were prepared with carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) at various loadings. Several important thermophysical properties of the composite PCMs were characterized as functions of the loading and temperature. It was shown that the presence of the carbon nanofillers is in general undesirable for the heating periods because the enhanced heat conduction was compensated by the weakened natural convection effect. As compared to cases in the presence of CNTs, the GNP-based composite PCMs performed much better due to their greater thermal conductivity enhancement along with much lower viscosity increase. The use of GNP-based composite PCMs was exhibited to be able to improve transient performance of the heat sink at certain conditions. Expedited recovery rates of the TES-based heat sink during the cooling periods, however, were achieved for almost all the cases using composite PCMs.