Steady natural convection cooling of a localized heat source at the bottom wall of an enclosure filled with Cu-water nanofluid for a variety of thermal boundary conditions at the sidewalls has been studied in the present paper. Finite difference method was employed to solve the dimensionless governing equations of the problem. The effects of governing parameters, namely, solid volume fraction, the different values of the heat source length and the different locations of the heat source on the streamlines and isotherms contours as well as maximum temperature, Nusselt number and average Nusselt number along the heat source were considered. The present results are validated by favorable comparisons with previously published results. The results of the problem are presented in graphical and tabular forms and discussed.

In this paper, a numerical solution of flow and heat transfer in micropolar fluid outside a stretching permeable cylinder with thermal stratification and suction/injection effects. The governing system of partial differential equations is converted to ordinary differential equations by using similarity transformations, which are then solved using numerical technique. The cases of strong concentration of microelement and weak concentration of microelement were considered. Our purpose from this study is to investigate the effects of the governing parameters, namely the suction/injection parameter, thermal stratification parameter, Prandtl number, vortex viscosity parameter and Reynolds number on the velocity profiles, pressure distributions, angular velocity profiles and temperature profiles as well as the skin friction coefficient, dimensionless wall couple stress and the Nusselt number. The numerical results are validated by favorable comparisons with previously published results. The results are shown graphically. The values of the skin friction coefficient, dimensionless wall couple stress and the Nusselt number are presented in tables. Copyright  2011 John Wiley & Sons, Ltd.

This paper presents a numerical investigation of laminar mixed convection cooling of heat source embedded on the bottom wall of an enclosure filled with nanofluids. The transport equations for a Newtonian fluid are solved numerically with a finite volume approach using the SIMPLE algorithm. The influences of governing parameters, namely, Rayleigh number location and geometry of the heat source, the type of nanofluid and solid volume fraction of nanoparticles on the cooling performance is studied. The present results are validated by favourable comparisons with previously published results. The results of the problem are presented in graphical and tabular forms and discussed.

Via Gaussian 98, calculations have been carried out as B3LYP/6-31G** basis sets and the predominant tautomers of benzalbarbituric acid (BenzalBA) have been defined taking in consideration the energy of the density functional theory. The electronic transition energies have been calculated for the possible tautomers by the configuration interaction between the ground configuration Eigenfunction and the excited configuration Eigenfunctions explaining the absence of the relative intensity change in the UV spectrum by the heat effect as a result of the coincidence of the transition energies of the possible tautomers. The electronic spectra (UV–visible) were scanned for BenzalBA in different solvents of different polarities to determine the Einstein transition probabilities, dipole strengths, oscillator strengths, lifetime of the excited states and extinction coefficients. The hydrogen bonding and the orientation energy of the polar solvent molecules toward BenzalBA molecule were determined from the spectral studies in mixtures of polar and non-polar solvents. Some complexes were prepared from BenzalBA with some divalent metal ions, i.e. Fe++, Zn++ or Cu++. Their structures have been confirmed by elemental analysis, mass spectra, 1H NMR spectra, atomic absorption spectra and UV–visible spectra. It has been concluded that the structures of the complexes have the C2h point group symmetry in which two BenzalBA moieties are chelated to any one of the metal ions Fe++, Zn++ and Cu++.

A method has been developed to synthesize metal and metal oxide nanostructures in high yields on the surface of SiO2/Si substrate. In this method, starting materials in a covered alumina crucible are thermally evaporated under a high vacuum or a low pressure of ambient air. Spherical gold nanoparticles with a size of 15nmand nanowires with a diameter of 70nmwere synthesized. SnO2 rough microwires, smooth nanowires, and nanoknives were synthesized by using Sn granules, SnO powder, and SnO2 powder as source materials, respectively. The microwires showed a quadrangular cross section and a length of several microns, while the nanowires showed a circular cross section and approximately the same length. The effects of source temperature and deposition time on nanostructure growth were studied. X-ray diffraction patterns suggested that the as-synthesized products consisted of crystalline nanostructure. Nanocomposite gas sensors on the base of noble metal and metal oxide were fabricated. These SnO2 nanowire gas sensors showed a reversible response to dilute NO2 gas at operating temperatures ranging between room temperature and 300 ◦C even at high concentrations. The results demonstrated that gold doping improved the sensor response.

Electrodes with micro-gaps are fabricated by using dc-sputtering and FIB techniques. SnO2 nanowires are deposited on the micro-gap (1–30 m) by suspension dropping method to fabricate a micro-gas sensor. The sensing ability of various SnO2 micro-gap sensors is measured. A comparison between sensors reveals that the short-gap electrode has numerous advantages in terms of reliability, high sensitivity and detection of low concentrations of NO2, while the large-gap electrode is relatively sensitive for high concentrations. Conductance measurements are carried out at different surface temperatures and NO2 concentrations in order to investigate the effects that the gap size has on the overall sensor conductance. The results suggest that the interface between the electrode and sensitive layer has a very important role for the sensing mechanism of tin dioxide gas sensors.

SnO2 microwires, nanowires and rice-shaped nanoparticles were synthesized by a thermal evaporation method. The diameters of microwire and nanowire were 2mand 50–100 nm, respectively, with approximately the same length (∼20m). The size of nanoparticles was about 100 nm. It was confirmed that the as-synthesized products have SnO2 crystalline rutile structure. The sensing ability of SnO2 particle and wire-like structure configured as gas sensors was measured. A comparison between the particle and wire-like structure sensors revealed that the latter have numerous advantages in terms of reliability and high sensitivity. Although its high surface-to-volume ratio, the nanoparticle sensor exhibited the lowest sensitivity. The high surface-to-volume ratio and low density of grain boundaries is the best way to improve the sensitivity of SnO2 gas sensors, as in case of nanowire sensor which exhibited a dramatic improvement in sensitivity to NO2 gas.