Jane H. Davidson

Abstract: A numerical model of the negative DC corona plasma along a thin wire in dry air is presented. The electron number density and electric field are determined from solution of the one-dimensional coupled continuity equations of charge carriers and Maxwell's equation. The electron kinetic energy distribution is determined from the spatially homogeneous Boltzmann equation. A parametric study is conducted to examine the effects of linear current density (0.1–100 μA per cm of wire length), wire radius (10–1000 μm), and air temperature (293–800 K) on the distribution of electrons and the Townsend second ionization coefficient. The results are compared to those previously determined for the positive corona discharge. In the negative corona, energetic electrons are present beyond the ionization boundary and the number of electrons is an order of magnitude greater than in the positive corona. The number of electrons increases with increasing gas temperature. The electron energy distribution does not depend on discharge polarity.

Abstract: A thermodynamic analysis of continuous fuel production by redox cycling of ceria in a single solar reactor under isothermal conditions is presented. Ceria is partially reduced in a sweep gas flow of purified nitrogen and reoxidized with either steam or carbon dioxide to produce hydrogen or carbon monoxide, respectively. The sweep gas and oxidizer flows are preheated by the product gases. The influence of selected process parameters, including operating temperature, pressure, and the effectiveness of heat recovery, on the solar-to-fuel conversion efficiency is determined. For a solar concentration ratio of 3000, typical of state-of-the-art solar dish concentrators, and operating temperature of 1773 K, 95.5% of the available gas-phase heat must be recovered to reach conversion efficiencies of 10% and 18% for hydrogen and carbon monoxide production, respectively, assuming the flow rate of inert sweep gas is equivalent to that in a counter-current flow arrangement of gas and ceria. The efficiency depends stro...

Abstract: A numerical model of ozone generation in clean, dry air by positiue DC corona discharges from a thin wire is presented. The model combines the physical processes in the corona discharge with the chemistry of ozone formation and destruction in the air stream. The distributions of ozone and nitrogen oxides are obtained in the neighborhood of the corona discharge wire. The model is ualidated with preuiously published experimental data. About 80% of the ozone produced is attributed to the presence of excited nitrogen and oxygen molecules. A parametric study reueals the effects of linear current density (0.1–100 µAcm of wire), wire radius (10– 1000 µm), temperature (300–800 K) and air uelocity (0.05–2 ms) on the production of ozone. The rate of ozone production increases with increasing current and wire size and decreases with increasing temperature. The air uelocity affects the distribution of ozone, but does not affect the rate of production.

Abstract: Improvements in the effectiveness of solid phase heat recovery and in the thermodynamic properties of metal oxides are the most important paths to achieving unprecedented thermal efficiencies of 10% and higher in non-stoichiometric solar redox reactors. In this paper, the impact of solid and gas phase heat recovery on the efficiency of a non-stoichiometric cerium dioxide-based H2O/CO2 splitting cycle realized in a solar-driven reactor are evaluated in a parametric thermodynamic analysis. Application of solid phase heat recovery to the cycling metal oxide allows for lower reduction zone operating temperatures, simplifying reactor design. An optimum temperature for metal oxide reduction results from two competing phenomena as the reduction temperature is increased: increasing re-radiation losses from the reactor aperture and decreasing heat loss due to imperfect solid phase heat recovery. Additionally, solid phase heat recovery increases the efficiency gains made possible by gas phase heat recovery.

Abstract: Electrons produced in atmospheric pressure corona discharges are used for a uariety of beneficial purposes including the destruction of gaseous contaminants, and surface treatment. In other applications, such as electrostatic precipitators and photocopiers, unintended reactions such as ozone production and deposition of silicon dioxide are detrimental. In both situations, a kinetic description of the electron distribution in the corona plasma is required to quantify the chemical processes. In this paper, the electron density and energy distributions are numerically determined for a positiue dc corona discharge along a wire. The electron density distribution is obtained from the 1-D charge carrier continuity equations and Maxwell’s equation. The non-Maxwellian electron kinetic energy distribution is determined from the Boltzmann equation. The effects of wire size (10-1000 µm) and current density (0.1‐100 µA/cm of wire) on number density and energy distribution of electrons are presented. With increasing current, the electron density increases, but the thickness of the plasma and the electron energy distribution are not affected. Smaller electrodes produce thinner plasmas and fewer, but more energetic electrons, than larger wires. The effect of electrode size on the electron-impact chemical reaction rate is illustrated by the rates of dissociation and ionization of oxygen and nitrogen.

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Abstract: Thermal energy storage in general, and phase change materials (PCMs) in particular, have been a main topic in research for the last 20 years, but although the information is quantitatively enormous, it is also spread widely in the literature, and difficult to find. In this work, a review has been carried out of the history of thermal energy storage with solid–liquid phase change. Three aspects have been the focus of this review: materials, heat transfer and applications. The paper contains listed over 150 materials used in research as PCMs, and about 45 commercially available PCMs. The paper lists over 230 references.

Abstract: Cerium dioxide (CeO2, ceria) is becoming an ubiquitous constituent in catalytic systems for a variety of applications. 2016 sees the 40th anniversary since ceria was first employed by Ford Motor Company as an oxygen storage component in car converters, to become in the years since its inception an irreplaceable component in three-way catalysts (TWCs). Apart from this well-established use, ceria is looming as a catalyst component for a wide range of catalytic applications. For some of these, such as fuel cells, CeO2-based materials have almost reached the market stage, while for some other catalytic reactions, such as reforming processes, photocatalysis, water-gas shift reaction, thermochemical water splitting, and organic reactions, ceria is emerging as a unique material, holding great promise for future market breakthroughs. While much knowledge about the fundamental characteristics of CeO2-based materials has already been acquired, new characterization techniques and powerful theoretical methods are dee...

Abstract: A significant amount of research and development work on the photovoltaic/thermal (PVT) technology has been done since the 1970s. Many innovative systems and products have been put forward and their quality evaluated by academics and professionals. A range of theoretical models has been introduced and their appropriateness validated by experimental data. Important design parameters are identified. Collaborations have been underway amongst institutions or countries, helping to sort out the suitable products and systems with the best marketing potential. This article gives a review of the trend of development of the technology, in particular the advancements in recent years and the future work required.

Abstract: This article reviews the underlying science and describes the technological advances in the field of solar thermochemical production of hydrogen that uses concentrated solar radiation as the energy source of high-temperature process heat.