Thermal Conductivity Estimation of Carbon-Nanotube-Dispersed Phase Change Material as Latent Heat Storage Material

This paper reports the results of a comparative evaluation of the measured and theoretical thermal conductivity values of a carbon nanotube-dispersed phase change material (PCM), in which multiwalled carbon nanotubes (MWCNTs) with extremely high thermal conductivity are dispersed in a latent heat storage material. The temperature range to be examined encompasses the temperatures corresponding to the solid-to-liquid phase, including the melting point of the latent heat storage material (PCM). The thermal conductivity of the MWCNT-dispersed PCM was measured using the wire-heating method with mass composition ratio and temperature as the parameters. The ratio of the thermal conductivity of the dispersoid to that of the continuous phase of this test sample was unprecedentedly large-a range that has never been evaluated in other studies. The test MWCNT had a very thin and long shape and was considered to be dispersed in the continuous phase in a deformed and interlaced state. The measured values of the thermal conductivity of the MWCNT-dispersed water were in good agreement with the values estimated using the columnar arrangement (Rayleigh) model formula, in which the heat flow was perpendicular to the axis. However, the measured thermal conductivity of the MWCNT-dispersed latent heat storage material was larger than that estimated by the Rayleigh model. Therefore, calculations were performed using the layer parallel model to determine the thermal conductivity estimation conditions. The estimation conditions enable the thermal conductivity estimation of the MWCNT-dispersion PCM and provide useful information for the design.