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The solution of an electric circuit problem is only valid if the circuit elements have been validly modelled. The iron-cored coil is a common nonlinear circuit element, especially in power system circuits, where the iron core is laminated grain-oriented silicon-iron sheet. This paper attempts to show that eddy-current loss modelling in such a core is at least as important as hysteresis loss modelling, and demonstrates the accuracy of linear modelling of the eddy-current effect. If the circuit analyst has confidence in this complete model he can then decide which aspects of the model can be ignored with impunity when studying such circuit phenomena as ferroresonance, subharmonics and inrush current.

The requirements of HVdc converter control are achieved by dicrital techniques with minimisation of circuit complexity. Feed-back control is applied to modification of the counting of clock pulses derived from the ac system by a phase-locked frequency multiplier. Symmetry of the derived firinc, oulses can be retained for all modes of operation with smooth transition from full rectification to full inversion.

Abstract A new formulation for the evaporation, flashing, condensation processes taking place in the effects of thermal desalination systems which simulates the operation of both forward and parallel/cross configurations is coupled with an exergo-economic model based on the SPECO method. The thermo-economic model uses accurate properties for the seawater, brine, pure water and vapour and is solved with an equation solver which does not require the development of a specific solution algorithm as in most previous studies. This flexible model is used to analyze the influence of the number of effects N and the temperature difference ΔT e between effects on the technical and economic performance of multi-effect desalination systems with ejector vapour compression. In particular, it is shown that the performance calculated by an earlier black-box approach is not attainable by technically and economically realistic systems. It is also shown that for each feed configuration and a given number of effects there exists an optimum value of ΔT e which minimizes the cost of the produced potable water. This last result forms the basis of a procedure that combines black-box results with the optimum value of ΔT e and can be used to select the appropriate system for any specific application.

Abstract This study develops a novel sustainability assessment methodology for energy systems using life-cycle emission factors and sustainability indicators. Here, the global warming and environmental impact dimensions of the sustainability assessment methodology are examined in detail. A comparative analysis shows that a wind-battery system produces fewer potential global warming, stratospheric ozone depletion, air pollution, and water pollution impacts compared to a gas-fired system. The wind-battery system generates 13% of the life-cycle GHG emissions and 22% of the life-cycle ozone-depleting substance emissions of a gas-fired power plant. Nitrous oxide contributes more than 90% of the stratospheric ozone depletion potential of gas-fired and wind-battery systems.

Abstract Space–time kinetics calculations for CANDU ® 1 reactors are routinely performed using the Improved Quasistatic (IQS) method. The IQS method calculates kinetics parameters such as the effective delayed-neutron fraction and generation time using adjoint weighting. In the current implementation of IQS, the direct flux, as well as the adjoint, is calculated using a two-group cell-homogenized reactor model which is inadequate for capturing the effect of the softer energy spectrum of the delayed neutrons. Additionally, there may also be fine spatial effects that are lost because the intra-cell adjoint shape is ignored. The purpose of this work is to compare the kinetics parameters calculated using the two-group cell-homogenized model with those calculated using lattice-level fine-group heterogeneous adjoint weighting and to assess whether the differences are large enough to justify further work on incorporating lattice-level adjoint weighting into the IQS method. A second goal is to evaluate whether the use of a fine-group cell-homogenized lattice-level adjoint, such as is the current practice for Light Water Reactors (LWRs), is sufficient to capture the lattice effects in question. It is found that, for CANDU lattices, the generation time is almost unaffected by the type of adjoint used to calculate it, but that the effective delayed-neutron fraction is affected by the type of adjoint used. The effective delayed-neutron fraction calculated using the two-group cell-homogenized adjoint is 5.2% higher than the “best” effective delayed-neutron fraction value obtained using the detailed lattice-level fine-group heterogeneous adjoint. The effective delayed-neutron fraction calculated using the fine-group cell-homogenized adjoint is only 1.7% higher than the “best” effective delayed-neutron fraction value but is still not equal to it. This situation is different from that encountered in LWRs where weighting by a fine-group cell-homogenized adjoint is sufficient to calculate the correct effective delayed-neutron fraction. It is concluded that lattice-level weighting with a detailed fine-group heterogeneous adjoint is desirable for the correct calculation of the effective delayed-neutron fraction in CANDU lattices.

Abstract Emissions and efficiency of a pellet boiler (40 kW) at nominal load were compared with emissions and efficiency at reduced load, while fired with six biomass pellets. The pellets include reed canary grass ( Phalaris arundinacea ), pectin waste from citrus shells ( Citrus reticulata ), sunflower husk ( Helianthus annuus ), peat, wheat straw ( Triticum aestivum ) and wood pellets. The measurements of emissions comprised of carbon monoxide (CO), nitrogen oxides (NO x ), sulphur oxides (SO x ) and flue dust mass concentrations (using DIN plus and isokinetic sampling techniques). Emissions varied as a function of operational loads, for each type of pellets. The CO emissions were insignificant with reed canary grass (RCG), citrus pectin waste (CPW) and straw pellets at nominal load, however, at reduced load same pellets emitted 1.9, 4.0 and 7.4 times higher CO than wood pellets, respectively. Peat pellets emitted maximum CO at nominal load (4221.1 mgNm −3 , 12.6 times higher than wood pellets) however; at reduced load CO emission was insignificant. The highest NO x emissions were reported with CPW, which were 3.4 and 4.6 times higher than wood pellets at nominal load and reduced load, respectively. Dust emissions were highest with sunflower husk and lowest with RCG pellets, at both operational modes. The best performance was reported with wood pellets, followed by RCG and pectin pellets, however, wood pellets combustion emitted 1.7 and 2.0 times higher dust DIN plus than RCG at nominal and reduced loads, respectively. Not only fuel specific combustion optimization but also operational load specific optimization is essential for efficient use of agro-pellets in this type of boilers.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Abstract Catalyst layer structural changes in polymer electrolyte membrane fuel cells have significant impact on the cell performance and durability. In this study, ex-situ experiments are designed to investigate the effect of humidity and/or thermal cycles on the structural changes of catalyst layers. The relative humidity and temperature are controlled by an environmental chamber and the catalyst layer structure is characterized by scanning electron microscopy and optical microscopy. The experimental results indicate that crack growth and development, catalyst agglomerate detachment, and surface bulges are the main structural changes of the catalyst layers. Applying relative humidity and thermal cycling simultaneously causes the most significant crack growth, while applying thermal cycling alone causes no appreciable changes. This indicates that the absolute humidity is the key parameter for the crack growth. Through cyclic voltammetry analysis, it is shown that the electrochemical active surface area decreases from 64.1 m2 g−1 to 49.1 m2 g−1 after 500 combined relative humidity and thermal cycles. Analyses of electrochemical impedance spectroscopy show that the charge transfer resistance and ohmic resistance increase significantly after 500 combined relative humidity and thermal cycles, causing the cell performance degradation.

CFD predictions of laminar mixed convection of Al2O3–water nanofluids by single-phase and three different two-phase models (volume of fluid, mixture, Eulerian) are compared. The elliptical, coupled, steady-state, three-dimensional governing partial differential equations for laminar mixed convection in a horizontal tube with uniform heat flux are solved numerically using the finite volume approach. It is found that single-phase and two-phase models predict almost identical hydrodynamic fields but very different thermal ones. The predictions by the three two-phase models are essentially the same. For the problem under consideration the two-phase models give closer predictions of the convective heat transfer coefficient to the experimental data than the single-phase model; nevertheless, the two-phase models over-predict the enhancement of the convective heat transfer coefficient resulting from the increase of the alumina volume fraction. The results are calculated for two Reynolds numbers (1050 and 1600) and three nanoparticle volume concentrations (<2%). Although single-phase and two-phase models have been used before to analyze mixed convection of nanofluids, this is the first systematic comparison of their predictions for a laminar mixed convection flow which includes the hydrodynamic characteristics and the effect of temperature dependent properties.