Using MM3 force-field simulations in combination with optical measurements, we investigate the morphology and dispersion of a variety of single-walled carbon nanotubes (SWNTs) non-covalently functionalized by carbazole polymers. Our results elucidate that isomer types of poly-carbazoles together with their length govern the morphology of carbazole-SWNT hybrids and, hence, their dispersion and bundling properties. The p-p stacking between the carbazole and the SWNT results in a stable carbazole-SWNT hybrid complex with the SWNT-carbazole interaction increasing with a decrease in the polymer length. All oligocarbazoles preferentially bind to larger diameter SWNTs with the strongest interactions observed for the hybrids with 2,7-isomers. While short oligocarbazoles cover only one side of the tube, long 2,7-isomers tend to gradually coil around the entire tube. In contrast, 3,6and 2,7-3,6-oligocarbazoles irregularly bunch together on a small area of the tube. The small size of carbazole oligomers and their localization on one side of the nanotube prevents tube unbundling, and leads to photoluminescence quenching in SWNTs functionalized by 2,7-3,6-oligocarbazoles.

PEG-derivatized corannulene compound has been found to be very effective in solubilizing single-walled carbon nanotubes in tetrahydrofuran. Solubilizing efficiency is close to the commonly used anionic surfactant, sodium dodecyl sulfate (SDS). Corannulene derivative has also been found to have a tendency to disperse metallic nanotubes more effectively than the SDS counterpart. Theoretical calculations predict higher dispersion interactions of corannulene backbone with the convex surface of nanotubes in comparison to those calculated with other commonly used polyaromatic hydrocarbon derivatives.

Adverse effects of synthetic refrigerants on the environment have led to replacing them with natural refrigerants. The common candidates are ammonia, carbon dioxide, and several hydrocarbon compounds and their mixtures. Ammonia has been used mainly in large-scale cooling purposes such as large-scale supermarkets and climatic rooms. However, in such systems, leakage of ammonia may arise severe results on human health and may damage products in the cooled space. Recently, in last decade, a well-known refrigerant, CO2, has gained more attention to be applied in refrigeration systems due to having prominent thermo-physical properties. The performance analysis of a CO2/NH3 cascade (CAS) system has been theoretically examined in the current study. The detailed performance analysis of the system and optimization of the operating parameters have been studied extensively. In addition, the second-law analysis of the system with both cycles has been performed. Optimum operating conditions of the system are also determined and correlations are developed. Finally, the coefficient of performance (COP) correlations developed by several researchers in literature and those of current study are compared against available experimental COP results. The comparisons showed that the proposed correlations can be utilized for the accurate prediction of the COP of a cascade CO2/NH3 system within the studied range of operating conditions.

No abstract

No abstract

Lean Premixed Combustion (LPC) is recently proposed in gas turbine combustors which have been operated traditionally in the non-premixed mode. In this method, fuel and air are mixed before entering the combustor. With LPC, the flame temperature is reduced due to the operating with excess air conditions. Thus, thermal NO x can be reduced to negligible levels at these lean conditions. On the other hand, the local and global flame extinction risks and therefore flame instabilities may arise because of operating at fuel-lean conditions near the lean flammability limit. In order to control such flames, both their chemical kinetics and flame propagation properties should be investigated in detail, mainly for various equivalence ratios.In this study, the numerical simulations based on experimental data obtained from the combustion chamber setup of the ICARE are performed. The experimental results concern turbulent premixed methane-air flames stabilized on a Bunsen type burner; they are obtained by LDA for the cold and hot flow velocity statistics and by laser induced Mie and Rayleigh scattering techniques for flame front statistics. The operating conditions in experiments are chosen to be close to the gas turbine combustor operating conditions. Numerical simulations are performed by using the Fluent ® software. Both the analysis of the flow and turbulence properties of the chamber by using the k-ε turbulence model and its variants and the premixed flame properties of the methane/air mixtures are investigated. The influence of the equivalence ratio on the flame properties is examined as well. It is observed that increase in equivalence ratio results in decrease in the flame length and the flame brush thickness. Similar tendencies are observed in the experiments. Flame front properties are examined with the combustion model provided by the Fluent ® software, namely Zimont premixed model, and y the well-known CFM turbulent premixed combustion model. Satisfactory results are obtained.

No abstract

No abstract