Enhanced thermal conductivity of n-octadecane containing carbon-based nanomaterials

In the present study, carbon-based nanomaterials including multiwalled carbon nanotubes (MWCNTs) and vapor-grown carbon nanofibers (CNFs) were dispersed in n-octadecane as a phase change material (PCM) at various mass fractions of 0.5, 1, 2 and 5 wt% by the two-step method. The transient plane source technique was used to measure thermal conductivity of samples at various temperatures in solid (5-25 A degrees C) and liquid (30-55 A degrees C) phases. The experimental results showed that thermal conductivity of the composites increases with increasing the loading of the MWCNTs and CNFs. A maximum thermal conductivity enhancement of 36 % at 5 wt% MWCNTs and 5 A degrees C as well as 50 % at 2 wt% and 55 A degrees C were experimentally obtained for n-octadecane/MWCNTs samples. Dispersing CNFs into n-octadecane raised the thermal conductivity up to 18 % at 5 wt% and 10 A degrees C and 21 % at 5 wt% and 55 A degrees C. However, the average enhancement of 19 and 21 % for solid and liquid phases of MWCNTs composite as well as 33 and 46 % for solid and liquid phase of CNFs promised a better heat transfer characteristics of MWCNTs in n-octadecane. A comparison between results of the present work and available literature revealed a satisfactory enhancement of thermal conductivity. For the investigated n-octadecane/MWCNTs and n-octadecane/CNFs composites, a new correlation was proposed for predicting the thermal conductivity as a function of temperature and nanomaterials loading.