No abstract

Alkanes and their mixtures (paraffins) have widely been used as phase change materials (PCMs) for low-tomedium temperature thermal energy storage. Among the various alkanes, eicosane, with a nominal melting temperature of 37 °C, has emerged in energy-storage-based passive thermal management technologies, for electronics for example. In an effort to increase the thermal conductivity of eicosane, the effect of adding graphene nanoplatelets (GNPs) as thermally conductive nanofillers was investigated experimentally. The composite PCM samples were prepared by dispersing GNPs in liquid eicosane at various loadings (0, 1, 2, 5, and 10 wt.%) without any surfactants. Thermal conductivity of the composite PCM samples in their solid phase was then measured by means of the transient plane source technique at elevated temperatures from 10 to 35 °C. Latent heat of fusion and melting point of the samples were also characterized using a differential scanning calorimeter. It was shown that for the highest loading examined (10 wt.%), the relative thermal conductivity enhancement is above 400% at 10 °C, indicating that the emerging GNPs have much better performance than the conventional nanofillers attempted in the available literature, such as metal/oxide nanoparticles and carbon nanotubes. Reduced thermal interface resistance, related to the unique two-dimensional planar morphology of GNPs, was interpreted to be responsible for their superior performance. The matrix/filler thermal interface resistance was estimated to range from 6 × 10 −9 to 9 × 10 −9 m 2 K/W. In contrast to the markedly increased thermal conductivity, however, the penalty of decrease in the energy storage capacity, caused by the presence of GNPs, was shown to be less significant.

No abstract

No abstract

An aqueous solution of carbon nanotubes, treated by a concentrated nitric/sulfuric acid mixture to disentangle the nanotubes, was utilized as the working medium in a two-phase closed thermosyphon to investigate its performance. In comparison with the thermosyphon filled with a distilled water medium, the one filled with carbon nanotube suspension has a high evaporation section wall temperature, incipience temperature, and excursion, as well as thermal resistance. The carbon nantotubes’ nanofluid deteriorates the performance of the gravity-assisted heat pipe. Measurements employing the maximum bubble pressure method demonstrate that suspending carbon nanotubes in bulk water gives rise to increased surface tension. In addition, the contact angle of suspension obtained with the sessile drop method on a copper plate is much smaller than that of water. Alterations of solid-liquid-vapor interfacial properties, arising from the addition of carbon nanotubes, change the boiling mechanism and thus deteriorate the boiling heat transfer.