Thermal characteristics of packed bed storage system

The thermal behaviour of a packed bed storage system charged with hot air is modelled using two partial differential equations representing the energy conservation in the air and solid phases constituting the bed. These two equations are coupled through the heat exchange process between the two phases. A fully implicit numerical scheme based on forward, upwind and central differencing for the time, first and second space derivatives, respectively, is used to solve the modelling equations. Marching technique is used for the air equation and a tri-diagonal matrix solver is employed to solve the solid equation. The solution yields the thermal structure of the bed, namely the air and solid temperature distribution inside the bed at any particular time, and the variation of total energy stored in the bed with time. The effect of bed length, solid diameter and void fraction on the thermal characteristics of the packed bed is studied. Further, the performance of the bed under variable inlet air temperature and mass flow rate is investigated.     

Inception voltage of corona in bipolar ionized fields-effect oncorona power loss

In this paper, an iterative finite-element-based algorithm is presented as a numerical tool for the solution of the bipolar ionized field around high-voltage DC (HVDC) transmission lines. The effect of including unequal values of the positive and negative corona inception voltages and ion mobilities on the corona power loss is investigated. In addition, the effect of negative ion field enhancement on reducing the positive conductor corona inception voltage is also studied. The present algorithm is applied to different laboratory and full-scale transmission line configurations. Comparison with previously computed V-I characteristics showed that the present computed values were in better agreement with the experiment. Also, it has been found that the effect of unequal corona inception voltages on the corona power loss (or corona current) is noticeable at applied voltages very near to the inception values     

Simulation of energized Franklin rods for lightning protection

In this paper, the onset criterion of the upward streamers from an energized Franklin rod is formulated as a function of the geometry of the rod and the height and current of the downward leader. The electric field in the vicinity of the lightning rod is calculated using the charge simulation technique. The dependency of the radius of protection on the amplitude of the pulse voltage applied to the Franklin rod, the downward leader current, and the tip radius and height of the rod is investigated     

A finite-element analysis of bipolar ionized field

This paper describes a new iterative method for the analysis of the bipolar ionized field in HVDC transmission lines without resorting to Deutsch's assumption. The finite-element technique (FET) is used to solve Poisson's equation where the constancy of the conductors' surface field at the corona inception value is directly implemented in the finite-element formulation. The proposed method has been tested on laboratory and full-scale models. The calculated V-I characteristics agreed well with those calculated and measured previously. The dependence of the corona current as well as its monopolar and bipolar components on the conductor height is discussed. The simplicity in computer programming in addition to the low number of iterations required to achieve convergence characterize the proposed method of analysis     

Performance Characteristics of Alpha-Particle Corona-Streamer Counter

Alpha-particle wire-plate corona counters in air can be operated either in the spark or in the corona-streamer modes. The streamer mode is preferred over the spark mode since it has the advantages of low dead time and the absence of electrode corrosion by sparking. An analysis of the alpha-particle corona-streamer counter is described. The alpha-particle triggered corona pulse characteristics (e.g., pulse shape, amplitude, repetition rate, etc.) are calculated. Not only the pulse characteristics but also the inception voltages of the corona-mode regime are determined. For each wire diameter, a transition gap length between corona and spark modes exists, which is termed ``critical gap length.' The counting rate characteristics have been obtained for wire diameters 0.05-0.1 mm. All the theoretical findings are confirmed by experiment.     

Use of compact-source iodide (CSI) lamps to simulate solar insolation

Simulating, within a laboratory under accurately controlled conditions, the solar insolation which would be received at ground level—in the open air—for a particular location and preselected time of day is difficult. Nevertheless, it is essential if the performance testing of solar-energy collectors is not to be excessively delayed by the vagaries of the weather. This paper examines the problems of achieving a reasonable simulation and concludes that the use of a CSI lamp provides a viable, acceptable compromise. The limitations of employing this system and other commonly available lamps are discussed.     

Photoelastic and theoretical analyses of cracked frames

Photoelastic and theoretical analyses have been carried out to investigate the effect of cracks on the behaviour of two hinged portal frames subjected to two symmetrical vertical concentrated loads. The distribution of internal shear and normal stresses are obtained at different sections at various crack depth ratio. Also, values of stress intensity factor are obtained based on the measured local stress values.Based on the present result, an increase in normal stresses occurred at sections far from the crack location and a decrease in stresses occurred at sections close to the crack location. This is due to the fact that a redistribution in internal forces occurred due to crack presence. It is also noticed that a localized shear stress is created in a pure bending zone due to crack presence, the size of this zone is increased as crack size increased. Good agreement is obtained between experimental and theoretical results.     

On the dielectrophoretic separation of solid particles

An analysis of an idealized high-gradient dielectrophoretic separator that is simply a metal circular filament placed in a uniform electric field between two parallel plates is presented. The analysis is aimed at determining the spatial distribution of the electric field inside the volume of the separator, so that the dielectrophoretic force on a dielectric particle can be evaluated. The conditions necessary for producing dielectrophoretic forces comparable to those in electrostatic separators are determined     

Breakdown voltage and time-to-breakdown as influenced by thesteepness of the applied positive impulse

The volume-time criterion is discussed, and a modification is proposed with the aim of predicting breakdown voltages in SF₆ under positive impulse stresses without introducing an empiricism in the analysis. The electrons initiating the breakdown are those produced by cosmic rays that penetrate to the gas volume. The results obtained, including the breakdown voltage and the time-to-breakdown, as influenced by the steepness of the applied impulse, are discussed and compared with those measured experimentally     

The oxygen,oxygen/sulphur dioxide and oxygen/carbon dioxide electrodes in molten lithium sulphate—potassium sulphate eutectic

Open-ciruit potential, potentiostatic and voltammetric measurements of the O₂, O₂/SO₂ and O₂/CO₂ electrodes have been made in molten Li₂SO₄K₂SO₄ eutectic at 625°C. In the absence of SO₂ the overall reaction of the O₂ electrode is the reduction of O₂ to O^2? through the formation of O^2?₂ ions. In the presence of SO₂ the overall reaction is the reduction of SO₂ and O₂ to SO^2?₄, probably through the formation of SO^2?₃. The overall reaction of the O₂/CO₂ electrode is similar to that of the same electrode in molten carbonates, ie the reduction of CO₂ and O₂ to CO^2?₃. The transfer coefficients and exchange currents have been estimated for these reactions on platinum and gold.