Review on thermal energy storage with phase change: materials, heat transfer analysis and applications

1. Introduction and overview 2. Film stress and substrate curvature 3. Stress in anisotropic and patterned films 4. Delamination and fracture 5. Film buckling, bulging and peeling 6. Dislocation formation in epitaxial systems 7. Dislocation interactions and strain relaxation 8. Equilibrium and stability of surfaces 9. The role of stress in mass transport.

Thin Film Materials: Stress, Defect Formation and Surface Evolution

The application of mass spectrometric techniques to the realtime measurement and characterization of aerosols represents a significant advance in the field of atmospheric science. This review focuses on the aerosol mass spectrometer (AMS), an instrument designed and developed at Aerodyne Research, Inc. (ARI) that is the most widely used thermal vaporization AMS. The AMS uses aerodynamic lens inlet technology together with thermal vaporization and electron-impact mass spectrometry to measure the real-time non-refractory (NR) chemical speciation and mass loading as a function of particle size of fine aerosol particles with aerodynamic diameters between similar to 50 and 1,000 nm. The original AMS utilizes a quadrupole mass spectrometer (Q) with electron impact (EI) ionization and produces ensemble average data of particle properties. Later versions employ time-of-flight (ToF) mass spectrometers and can produce full mass spectral data for single particles. This manuscript presents a detailed discussion of the strengths and limitations of the AMS measurement approach and reviews how the measurements are used to characterize particle properties. Results from selected laboratory experiments and field measurement campaigns are also presented to highlight the different applications of this instrument. Recent instrumental developments, such as the incorporation of softer ionization techniques (vacuum ultraviolet (VUV) photo-ionization, Li(+) ion, and electron attachment) and high-resolution ToF mass spectrometers, that yield more detailed information about the organic aerosol component are also described. (c) 2007 Wiley Periodicals, Inc.

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Chemical and microphysical characterization of ambient aerosols with the aerodyne aerosol mass spectrometer

Atmospheric-pressure plasmas are used in a variety of materials processes. Traditional sources include transferred arcs, plasma torches, corona discharges, and dielectric barrier discharges. In arcs and torches, the electron and neutral temperatures exceed 3000/spl deg/C and the densities of charge species range from 10/sup 16/-10/sup 19/ cm/sup -3/. Due to the high gas temperature, these plasmas are used primarily in metallurgy. Corona and dielectric barrier discharges produce nonequilibrium plasmas with gas temperatures between 50-400/spl deg/C and densities of charged species typical of weakly ionized gases. However, since these discharges are nonuniform, their use in materials processing is limited. Recently, an atmospheric-pressure plasma jet has been developed, which exhibits many characteristics of a conventional, low-pressure glow discharge. In the jet, the gas temperature ranges from 25-200/spl deg/C, charged-particle densities are 10/sup 11/-10/sup 12/ cm/sup -3/, and reactive species are present in high concentrations, i.e., 10-100 ppm. Since this source may be scaled to treat large areas, it could be used in applications which have been restricted to vacuum. In this paper, the physics and chemistry of the plasma jet and other atmospheric-pressure sources are reviewed.

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The atmospheric-pressure plasma jet: a review and comparison to other plasma sources

Atmospheric pressure plasmas: A review

An accurate determination of electron density, temperature, and velocity distributions is of primary interest for the characterization of steady-state thermal plasma spray jets. Our diagnostic capabilities based on optical emission spectroscopy include measurements of absolute emission coefficients and Stark broadening. In addition, enthalpy probe diagnostics has also been used for temperature and velocity measurements. Observation of large discrepancies between temperatures derived from absolute emission coefficients, Stark broadening, and from enthalpy probe measurements indicate that severe deviations from LTE (local thermal equilibrium) exist in various regimes of plasma spray jets. Nonequilibrum characterization of such turbulent thermal plasma jets suggests that diffusion of high-energy electrons into the fringes of plasma jets and deviations from chemical equilibrium due to high velocities in the core of plasma jets and entrainment of cold gas, are the main reasons for these discrepancies. The establishment of a reliable data base, taking these nonequilibrium effects into account, is a prerequisite for meaningful modeling of real plasma jets.

Diagnostics of a thermal plasma jet by optical emission spectroscopy and enthalpy probe measurements

Material droplet generator systems utilizing single-wire arc spray apparatus and methods are provided. In some embodiments, the apparatus include a single consumable, first wire electrode fed through a gas nozzle and a non-consumable, second electrode outside of and proximate a nozzle exit. In some embodiments, the second electrode may have at least a terminal or end portion having an axis that is oriented substantially perpendicular to an axis of the gas nozzle. The first wire electrode may form an angle of 5 degrees or less with the axis of the gas nozzle. Preferably, the first wire electrode forms an anode while the second electrode forms a cathode. In operation, the apparatus and methods produce a narrow beam thermal spray, which, when deposited upon a substrate surface, results in a high definition spray pattern and coating having distinct boundaries and a controllable thickness.

Single-wire arc spray apparatus and methods of using same

Three-dimensional, transient simulations of the plasma flow inside different plasma spray torches have been performed using a local thermodynamic equilibrium model solved by a multiscale finite-element method. The model describes the dynamics of the arc without any further assumption on the reattachment process except for the use of an artificially high electrical conductivity near the electrodes. Simulations of an F4-MB torch from Sulzer-Metco and two configurations of the SG-100 torch from Praxair are presented. The simulations show that, when straight or swirl injection is used, the arc is dragged by the flow and then jumps to form a new attachment, preferably at the opposite side of the original attachment, as has been observed experimentally. Although the predicted reattachment frequencies are at present higher than the experimental ones, the model is suitable as a design tool.

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Simulation results of arc behavior in different plasma spray torches

This paper is concerned with the application of a two-fluid turbulence model for plasma spray processes at atmospheric pressure, for improving our physical insight into the plasma/particle interactions. In this two-fluid turbulence model, the turbulent stream is treated as a two-phase mixture. The fluid parcels are assumed to be arranged in fragments, and they can exchange mass, momentum, and other properties. A stochastic approach is then used to study particle behavior under the influence of the two-fluid parcels. The Stokes number is introduced as an indicator of particle dispersion behavior. A series of simulations is performed to include the influence of different injection locations, particle sizes, and injection velocities. The results indicate the importance of the existence of large-scale eddies and variable property, Knudsen, and mass-transfer cooling effects on the particle motion and heating history.

Particle behavior in a two-fluid turbulent plasma jet

Boron carbide thin films have been deposited on Si(100) using supersonic plasma jet chemical vapor deposition from boron trichloride and methane. Vickers hardnesses have been measured around 30 GPa and have been found to be dependent on the substrate temperature and the deposition rate. Growth rates as high as 80 μm/h have been achieved and their dependence on substrate temperature is shown. The films are composed solely of pure boron carbide and are not contaminated with chlorine or hydrogen, as found by FTIR and XPS analysis. Micro X-ray diffraction studies indicated that the films were microcrystalline. The influence of a positive bias on the growth rate and composition of boron carbide has also been investigated. We have found that the minimum temperature at which films can be grown could be lowered from 550 to 500°C and that the growth rate was significantly enhanced at any substrate temperature.

Joachim Heberlein

Papers

Diagnostics of a thermal plasma jet by optical emission spectroscopy and enthalpy probe measurements

Single-wire arc spray apparatus and methods of using same

Simulation results of arc behavior in different plasma spray torches

Particle behavior in a two-fluid turbulent plasma jet

Deposition of boron carbide thin film by supersonic plasma jet CVD with secondary discharge