In this paper the effect of nanoparticle concentration and temperature on the thermal conductivity of Yttria-Ethylene glycol nanofluid has been investigated. In addition, the effect of aging on the viscosity and the thermal conductivity of these nanofluids also have been studied. The nanofluids were prepared by two-step method, and particle size distributions were characterized using acoustic spectroscopy. It was found that the thermal conductivity of Yttria nanofluids increases beyond the classical Hamilton-Crosser model. Moreover, the enhancement in the thermal conductivity of this nanofluid showed high temperature dependence behavior. For instance at 3.0% by volume particles loading, the thermal conductivity enhancement increased from 16.6% at 26 °C to 27.0% at 59 °C, making these nanofluids attractive and effective for cooling systems that operates at high temperatures. Finally, time dependent viscosity and thermal conductivity measurements showed stable behavior for 16 days of study demonstrating the good stability of these nanofluids.

The clustering phenomenon on the solid wall during dropwise condensation is analyzed with reflection spectrum. From the theoretical prediction of the reflectivity for thin liquid films with different thickness on stainless steel surface, it is ascertained that the reflectivity corresponds to the coacervate characteristics of the steam molecular. Furthermore, the experimental data of the reflection spectrum during dropwise condensation in literature also demonstrated that the reflection feature and so as the coacervate characters lie between liquid and steam after the droplet departing during an actual continuous condensation process. The clustering model is used to analyze the results, indicating that clusters form on the blank surface. And it is found that different microstructures of the solid wall would lead to different deposition rates of the clusters, which prompts an effective way to enhance heat transfer process of condensation by accelerating the deposition rate of clusters with surface modification.

In the present work, the effective thermal conductivity of single walled carbon nanotube dispersions in water was investigated experimentally. Single-walled carbon nanotubes (SWNTs) were synthesized using the alcohol catalytic chemical vapour deposition method. The diameter distribution of the SWNTs was determined using resonance Raman spectroscopy. Sodium deoxycholate (SDC) was used as the surfactant to prepare the nanofluid dispersions. Photoluminescence excitation spectroscopy (PLE) reveals that majority of the nanotubes were highly individualized when SDC was employed as the surfactant. The nanofluid dispersions were further characterized using transmission electron microscopy, atomic force microscopy (AFM) and optical absorption spectroscopy (OAS). Thermal conductivity measurements were carried out using a transient hot wire technique. Nanotube loading of up to 0.3 vol% was used. Thermal conductivity enhancement was found to be dependent on nanotube volume fraction and temperature. At room temperature the thermal conductivity enhancement was found to be non-linear and a maximum enhancement of 13.8% was measured at 0.3 vol% loading. Effective thermal conductivity was increased to 51% at 333 K when the nanotube loading is 0.3 vol%. Classical macroscopic models fail to predict the measured thermal conductivity enhancement precisely. The possible mechanism for the enhancement observed is attributed to the percolation of nanotubes to form a three-dimensional structure. Indirect effects of Brownian motion may assist the formation of percolating networks at higher temperature thereby leading to further enhancements at higher temperature.

Laser-induced breakdown spectroscopy (LIBS) with spatial confinement effects and LIBS combined with laser-induced fluorescence (LIBS-LIF) have been investigated to improve the detection sensitivity and element-selectivity of LIBS. An obvious enhancement in the emission intensity of aluminum (Al) atomic lines was observed when a cylindrical wall was placed to spatially confine the plasma plumes. The maximum enhance factor for the emission intensity of Al atomic lines was measured to be around 10. Assuming local thermodynamic equilibrium conditions, the plasma temperatures are estimated to be in a range from 4,000 to 5,800 K. It shows that the plasma temperature increased by around 1,000 K when the cylindrical confinement was applied. Fast images of the laser-induced Al plasmas show that the plasmas were compressed into a smaller volume with a pipe presented. LIBS-LIF has been investigated to overcome the matrix effects of LIBS for the detection of trace uranium (U) in solids. An optical parametric oscillator wavelength-tunable laser was used to resonantly excite the uranium atoms and ions within the plasma plumes generated by a Q-switched Nd:YAG laser. Both atomic and ionic lines can be selected to detect their fluorescence lines. A U concentration of 462 ppm in a glass sample can be detected using this technique at an excitation wavelength of 385.96 nm for resonant excitation of U II and a fluorescence line wavelength of 409.01 nm from U II. The mechanism of spatial confinement effects and the influence of relevant operational parameters of LIBS-LIF are discussed. In this work, detection in open air of trace phosphorus (P) in steels using LIBS-LIF has also been investigated. The optical parametric oscillator laser was used to resonantly excite the P atoms within plasma plumes generated by the Q-switched Nd:YAG laser. A set of steel samples with P concentrations from 3.9 to 720 ppm were analyzed using LIBS-LIF at wavelengths of 253.40 and 253.56 nm for resonant excitation of P atoms and fluorescence lines at wavelengths of 213.55 and 213.62 nm. The calibration curves were measured to determine the limit of detection for P in steels, which is estimated to be around 0.7 ppm.

Progress in synthesis technologies of micro and nanocomposite materials has opened the way to the control of electromagnetic field these media spontaneously emit in their surrounding. If numerous nanostructured materials [1–3] have been designed during the last decade to control both spectrally and directionally the far (propagative) field that they radiate in their surrounding, very few attention has been paid so far to the control of non-radiative field which exponentially decreases from their surface. However, such control is very important to improve the performance of numerous near-field technologies such as the plasmon assisted nanophotolitography [4], the near-field spectroscopy [5] and to develop new energy conversion technologies such as the near-field thermophotovoltai¨c energy conversion [6]. The near field properties of micro and nanostructured materials are closely conditioned by the presence, hybridization and coupling of localized modes within the structure. These modes come from the presence of collective oscillations of free electrons in metallic compounds or from the vibrations of partial charges carried out by atoms in polar materials. In this paper we present an approach we have recently developed [7] to design micro and nanolayered thermal sources with a tailored near-field emission spectrum and we briefly discuss the basic physical mechanisms involved in these modifications of field.

Vertically aligned single-walled carbon nanotubes (VA-SWNTs) is expected to be an extra-ordinal material for various optical, electrical, energy, and thermal devices. The recent progress in growth control and characterization techniques will be discussed. The CVD growth mechanism of VA-SWNTs is discussed based on the in-situ growth monitoring by laser absorption during CVD. The growth curves are characterized by an exponential decay of the growth rate from the initial rate determined by ethanol pressure. The initial growth rate and decay of it are discussed with carbon over-coat on metal catalysts and gas phase thermal decomposition of precursor ethanol. For the precisely patterned growth of SWNTs, we recently propose a surface-energy-difference driven selective deposition of catalyst for localized growth of SWNTs. For a self assembled monolayer (SAM) patterned Si surface, catalyst particles deposit and SWNTs grow only on the hydrophilic regions. The proposed all-liquid-based approach possesses significant advantages in scalability and resolution over state-to-the-art techniques, which we believe can greatly advance the fabrication of nano-devices using high-quality as-grown SWNTs. The optical characterization of the VA-SWNT film using polarized absorption, polarized Raman, and photoluminescence spectroscopy will be discussed. Laser-excitation of a vertically aligned film from top means that each nanotube is excited perpendicular to its axis. Because of this predominant perpendicular excitation, interesting cross-polarized absorption and confusing and practically important Raman features are observed. The extremely high and peculiar thermal conductivity of single-walled carbon nanotubes has been explored by non-equilibrium molecular dynamics simulation approaches. The thermal properties of the vertically aligned film and composite materials are studied by several experimental techniques and Monte Carlo simulations based on molecular dynamics inputs of thermal conductivity and thermal boundary resistance. Current understanding of thermal properties of the film is discussed.