Experimental Verification of Expedited Freezing of Nanoparticle-Enhanced Phase Change Materials (NEPCM)

Highly-conductive nano-sized particles are dispersed into phase change materials (PCM) to improve their effective thermal conductivity, thus leading to suspensions that are referred to as nanoparticle-enhanced PCM (NEPCM). In order to assess the extent of expedited phase change due to the enhanced thermal conductivity, the one-dimensional unidirectional freezing process of NEPCM in a finite slab was investigated experimentally. Thermocouple readings were recorded at several equally-spaced locations along the freezing direction in order to monitor the progress of the freezing front. As an example, cyclohexane (C6H12) and copper oxide (CuO) nanoparticles were chosen to develop the NEPCM with three different volume fractions (0.5, 1.0, and 2.0 vol%). It was shown that the freezing rate for the 0.5 vol% NEPCM is considerably raised as compared to pure cyclohexane. However, further increase of the fraction of nanoparticles to 1.0 and 2.0 vol% did not linearly expedite freezing. Significant sedimentation of nanoparticles was observed for the 2.0 vol% NEPCM. Additionally, in this case the undesirable supercooling phenomenon was enhanced, which suppresses the growth rate of the solidified NEPCM.

Volumetric, Viscometric, and Ultrasonic Properties of Liquid Mixtures of Cyclohexane with Alkanols at Different Temperatures

The densities (ρ), viscosities (η), and ultrasonic speeds (u) of pure cyclohexane, 1-butanol, 2- butanol, and those of their binary mixtures, with cyclohexane as common component, covering the whole composition range have been measured at 293.15, 298.15, 303.15, 308.15, 313.15, and 318.15 K. From the experimental data the excess molar volume (VE), deviations in isentropic compressibility (Δks), deviations in viscosity (Δη), deviations in ultrasonic speed (Δu), deviations in acoustic impedance (ΔZ), deviations in internal pressure (ΔPi), excess Gibbs free energy of activation (ΔG*E), entropies (ΔS*), and enthalpies (ΔH*) of activation of viscous flow have been determined. The sign and magnitude of these parameters were found to be sensitive towards interactions prevailing in the studied systems. Partial molar volumes (V0φ,2) and partial molar compressibilities (K0φ,2) of 1-butanol and 2-butanol in cyclohexane have also been evaluated. Moreover, VE values were theoretically predicted by using Flory’s statistical theory. The variations of derived parameters mentioned above with composition offer a convenient method to study the nature and extent of interactions between the component molecules of the liquid mixtures, not easily obtained by other means

Secondary reactions in the γ-radiolysis of hydrocarbons with electron scavengers

Secondary reactions in the liquid phase radiolysis of cyclohexane in the presence of N2O and SF6 have been examined by determining the yields of liquid products. When we added up to 0.3 M N2O, the hydrogen yield was reduced from its initial yield of 5.5 G units to 2.5 G units. The nitrogen yields were about twice the decrease in hydrogen yields. Bicyclohexyl and cyclohexene yields increased from their initial values to 2.27 and 3.50 G units respectively. When we added up to 0.12 M SF6, all the yields were decreased to about one half of their initial value.These results may be interpreted in terms of Dyne's general mechanism for the radiolysis of hydrocarbons if two cyclohexyl radicals are produced for every electron scavenged by N2O, but if none are produced for electrons scavenged by SF6. It is suggested that the total electron yield in pure cyclohexane is about 4.1 G units, of which only 3.0 G units produce hydrogen. The other 2.5 G units of hydrogen from the radiolysis of pure cyclohexane are presumed to arise from direct excitation.