Showing papers by "Huaqing Xie published in 2008"

Thermal properties of heat storage composites containing multiwalled carbon nanotubes

Abstract: Thermal performance enhanced heat storage nanocomposites consisting of palmitic acid (PA) and multiwalled carbon nanotubes (CNTs) were prepared by dispersing chemically treated CNTs into melting PA. The PA/CNT composites remain stable after repeating energy storage and release 80 times. The melting point and latent heat capacity decrease with an increase in the mass fraction of CNTs. PA/CNT composites have enhanced thermal conductivities compared to pure PA, with the enhancement ratios increasing with the mass fraction of CNTs. For PA/CNT composite containing CNTs with a mass fraction of 5.0%, the thermal conductivity enhancement ratios amount up to 36% and 56% in solid and liquid states, respectively.

Surface chemical modification of multiwalled carbon nanotubes by a wet-mechanochemical reaction

Abstract: A wet-mechanochemical reaction for surface modification of multiwalled carbon nanotubes (CNTs) has been developed. In the treatment, CNTs reacted with potassium hydroxide in alcohol solvent at room temperature under mechanical milling. The results from Fourier transmission infrared spectroscopy demonstrate that the nonreactive surfaces of CNTs have been modified successfully by multiple hydroxyl groups. Functionalized carbon nanotubes exhibit higher zeta potential values indicating their high dispersibility in polar solvents. XRD studies corroborate that the surface functionalization does not affect the basic crystal domain size of CNTs. TEM observations reveal that CNTs have been cut into shorter ones by the milling. Shortened CNTs with functionalized surfaces show good dispersion properties.

Effects of Spacer Chain Length and Additives on Solution Properties of Cationic Gemini Surfactant

Abstract: The critical micelle concentration (CMC) has been determined for the gemini surfactant trimethylene-1,3-bis(dodecyldimethyl ammonium bromide)12-s-12,2Br−1 by means of electricity conductivity measurements. For the same number of carbon atoms in the hydrophobic chain per hydrophilic head group, geminis have CMC values well below those of conventional single-chain cationic surfactants. The CMC of 12-3-12 reduces with the addition of n-alcohol except ethanol and with the increase of n-alcohol chain length as well as increase of concentration of n-butanol and sodium chloride. Steady-state fluorescence quenching technology has been employed to study the aggregation number of micelle, which increases with increase in the length of n-alcohol. The Kraft temperature measurements also indicate that the stability of solid surfactant hydrate decreases along with the improvement of concentration of n-butanol and sodium chloride.

Thermal Transport Properties of Nanofluids Containing Carbon Nanotubes

Abstract: Multiwalled carbon nanotubes (CNTs) have been treated by using a mechanochemical reaction method to enhance their dispersibility for producing CNT nanofluids. The thermal conductivity was measured by a short hot wire technique and the viscosity was measured by a rotary viscometer. The thermal conductivity enhancement reaches up to 17.5% at a volume fraction of 0.01 for an ethylene glycol based nanofluid. Temperature variation was shown to have no obvious effects on the thermal conductivity enhancement for the as prepared nanofluids. With an increase in the thermal conductivity of the base fluid, the thermal conductivity enhancement of a nanofluid decreases. At low volume fractions (<0.4 Vol%), nanofluids have lower viscosity than the corresponding base fluid due to lubricative effect of nanoparticles. When the volume fraction is higher than 0.4 Vol%, the viscosity increases with nanoparticle loadings. The prepared nanofluids, with no contamination to medium, good fluidity, stability, and high thermal conductivity, would have potential applications as coolants in advanced thermal systems.© 2008 ASME