Next Issue
Previous Issue

E-Mail Alert

Add your e-mail address to receive forthcoming issues of this journal:

Journal Browser

Journal Browser

Table of Contents

Energies, Volume 4, Issue 12 (December 2011), Pages 2132-2310

  • Issues are regarded as officially published after their release is announced to the table of contents alert mailing list.
  • You may sign up for e-mail alerts to receive table of contents of newly released issues.
  • PDF is the official format for papers published in both, html and pdf forms. To view the papers in pdf format, click on the "PDF Full-text" link, and use the free Adobe Readerexternal link to open them.
View options order results:
result details:
Displaying articles 1-12
Export citation of selected articles as:

Research

Jump to: Other

Open AccessArticle Dielectric Barrier Discharge Characteristics of Multineedle-to-Cylinder Configuration
Energies 2011, 4(12), 2133-2150; doi:10.3390/en4122133
Received: 31 August 2011 / Revised: 14 October 2011 / Accepted: 22 November 2011 / Published: 2 December 2011
Cited by 11 | PDF Full-text (2007 KB) | HTML Full-text | XML Full-text
Abstract
A dielectric barrier discharge (DBD) produces a homogenous discharge with low energy consumption, offering broad developmental prospects, and this discharge process is also the mechanism through which charges are transported. Higher reaction efficiency is achieved when more charges are transported. Focusing on the
[...] Read more.
A dielectric barrier discharge (DBD) produces a homogenous discharge with low energy consumption, offering broad developmental prospects, and this discharge process is also the mechanism through which charges are transported. Higher reaction efficiency is achieved when more charges are transported. Focusing on the electrode configuration of the multineedle-to-cylinder (MC) system, i.e., the structure of needles arrayed on the inner coaxial rod, the effect of needle arrangement, including needle length (NL), inter axial needle distance (ID), and inter axial needle rotation angle (INRA), on the transported charge per cycle and discharge power in DBDs is investigated. The finite-element method (FEM) and quasi-static field simulation are adopted to study the active region (AR) where the electric field strength exceeds the breakdown electric field strength between MC electrodes because this region plays a dominant role in DBD. The improvement of its volume ratio in the reactor allows an increase in discharge power. The simulation results are in accordance with the experimental results, which illustrate that quasi-static field simulation is effective and reliable. Simulation results show that mutual effects of nearby needles and between needles and the inner rod exist. As a result, shorter ID (1.5 mm), needles with similar lengths (3.5 mm) are arranged, and an INRA of 0° is proven to be the optimal structure because it produces the highest AR volume ratio. The result is experimentally validated by transported charges per cycle and discharge power obtained through Lissajous figures. Full article
Figures

Open AccessArticle Optimal Design of Cogeneration Systems in Industrial Plants Combined with District Heating/Cooling and Underground Thermal Energy Storage
Energies 2011, 4(12), 2151-2165; doi:10.3390/en4122151
Received: 2 November 2011 / Revised: 28 November 2011 / Accepted: 2 December 2011 / Published: 6 December 2011
Cited by 7 | PDF Full-text (341 KB) | HTML Full-text | XML Full-text
Abstract
Combined heat and power (CHP) systems in both power stations and large plants are becoming one of the most important tools for reducing energy requirements and consequently the overall carbon footprint of fundamental industrial activities. While power stations employ topping cycles where the
[...] Read more.
Combined heat and power (CHP) systems in both power stations and large plants are becoming one of the most important tools for reducing energy requirements and consequently the overall carbon footprint of fundamental industrial activities. While power stations employ topping cycles where the heat rejected from the cycle is supplied to domestic and industrial consumers, the plants that produce surplus heat can utilise bottoming cycles to generate electrical power. Traditionally the waste heat available at high temperatures was used to generate electrical power, whereas energy at lower temperatures was either released to the environment or used for commercial or domestic heating. However the introduction of new engines, such as the ones using the organic Rankine cycle, capable of employing condensing temperatures very close to the ambient temperature, has made the generation of electrical power at low temperatures also convenient. On the other hand, district heating is becoming more and more significant since it has been extended to include cooling in the warm months and underground storage of thermal energy to cope with variable demand. These developments imply that electric power generation and district heating/cooling may become alternative and not complementary solutions for waste energy of industrial plants. Therefore the overall energy management requires the introduction of an optimisation algorithm to select the best strategy. In this paper we propose an algorithm for the minimisation of a suitable cost function, for any given variable heat demand from commercial and domestic users, with respect to all independent variables, i.e., temperatures and flowrates of warm fluid streams leaving the plants and volume and nature of underground storage. The results of the preliminary process integration analysis based on pinch technology are used in this algorithm to provide bounds on the values of temperatures. Full article
(This article belongs to the Special Issue Energy Policy on Climate Change)
Open AccessArticle A Novel Cogging Torque Simulation Method for Permanent-Magnet Synchronous Machines
Energies 2011, 4(12), 2166-2179; doi:10.3390/en4122166
Received: 16 September 2011 / Revised: 22 November 2011 / Accepted: 30 November 2011 / Published: 6 December 2011
Cited by 8 | PDF Full-text (864 KB) | HTML Full-text | XML Full-text
Abstract
Cogging torque exists between rotor mounted permanent magnets and stator teeth due to magnetic attraction and this is an undesired phenomenon which produces output ripple, vibration and noise in machines. The purpose of this paper is to study the existence and effects of
[...] Read more.
Cogging torque exists between rotor mounted permanent magnets and stator teeth due to magnetic attraction and this is an undesired phenomenon which produces output ripple, vibration and noise in machines. The purpose of this paper is to study the existence and effects of cogging torque, and to present a novel, rapid, half magnet pole pair technique for forecasting and evaluating cogging torque. The technique uses the finite element method as well as Matlab research and development oriented software tools to reduce numerous computing jobs and simulation time. An example of a rotor-skewed structure used to reduce cogging torque of permanent magnet synchronous machines is evaluated and compared with a conventional analysis method for the same motor to verify the effectiveness of the proposed approach. The novel method is proved valuable and suitable for large-capacity machine design. Full article
(This article belongs to the Special Issue Wind Turbines)
Figures

Open AccessArticle Comparison of Extremum-Seeking Control Techniques for Maximum Power Point Tracking in Photovoltaic Systems
Energies 2011, 4(12), 2180-2195; doi:10.3390/en4122180
Received: 8 October 2011 / Revised: 22 November 2011 / Accepted: 6 December 2011 / Published: 8 December 2011
Cited by 20 | PDF Full-text (473 KB) | HTML Full-text | XML Full-text
Abstract
Due to Japan’s recent nuclear crisis and petroleum price hikes, the search for renewable energy sources has become an issue of immediate concern. A promising candidate attracting much global attention is solar energy, as it is green and also inexhaustible. A maximum power
[...] Read more.
Due to Japan’s recent nuclear crisis and petroleum price hikes, the search for renewable energy sources has become an issue of immediate concern. A promising candidate attracting much global attention is solar energy, as it is green and also inexhaustible. A maximum power point tracking (MPPT) controller is employed in such a way that the output power provided by a photovoltaic (PV) system is boosted to its maximum level. However, in the context of abrupt changes in irradiance, conventional MPPT controller approaches suffer from insufficient robustness against ambient variation, inferior transient response and a loss of output power as a consequence of the long duration required of tracking procedures. Accordingly, in this work the maximum power point tracking is carried out successfully using a sliding mode extremum-seeking control (SMESC) method, and the tracking performances of three controllers are compared by simulations, that is, an extremum-seeking controller, a sinusoidal extremum-seeking controller and a sliding mode extremum-seeking controller. Being able to track the maximum power point promptly in the case of an abrupt change in irradiance, the SMESC approach is proven by simulations to be superior in terms of system dynamic and steady state responses, and an excellent robustness along with system stability is demonstrated as well. Full article
Open AccessArticle Numerical Analysis of the Magnetic Field of High-Current Busducts and GIL Systems
Energies 2011, 4(12), 2196-2211; doi:10.3390/en4122196
Received: 25 October 2011 / Revised: 29 November 2011 / Accepted: 5 December 2011 / Published: 13 December 2011
Cited by 5 | PDF Full-text (695 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a numerical computation method for determining the magnetic field of high-current busducts of circular cross-section geometry, based on the subdivision of the busduct phase conductors and screens into the conductor filaments and the subsequent application of the mesh-current method, with
[...] Read more.
This paper presents a numerical computation method for determining the magnetic field of high-current busducts of circular cross-section geometry, based on the subdivision of the busduct phase conductors and screens into the conductor filaments and the subsequent application of the mesh-current method, with the aid of the geometric mean distance method. The mathematical model takes into account the skin effect and the proximity effects, as well as the complete electromagnetic coupling between phase conductors and metal enclosures (i.e., screens) of the single-phase isolated busduct system (of circular cross-section geometry). This model could be readily applied to the computation of the magnetic field of the Gas Insulated Transmission Lines (GIL) as well. Full article
Open AccessArticle Biodiesel Production from Acidified Oils via Supercritical Methanol
Energies 2011, 4(12), 2212-2223; doi:10.3390/en4122212
Received: 7 November 2011 / Revised: 30 November 2011 / Accepted: 6 December 2011 / Published: 14 December 2011
Cited by 9 | PDF Full-text (236 KB) | HTML Full-text | XML Full-text
Abstract
In biodiesel production, the vegetable oil used as raw material for transesterification should be free of water and free fatty acids (FFAs), which may consume catalyst and reduce catalyst efficiency. In this work biodiesel was prepared from acidified oils (AO) through a supercritical
[...] Read more.
In biodiesel production, the vegetable oil used as raw material for transesterification should be free of water and free fatty acids (FFAs), which may consume catalyst and reduce catalyst efficiency. In this work biodiesel was prepared from acidified oils (AO) through a supercritical methanol route, in which the esterification of FFAs and transesterification of glyceride with methanol occurred simultaneously. The effects of the mass ratio of methanol to AO, the operation temperature as well as the water content on the FFAs conversion and glycerol yield were investigated. The results indicated that the FFAs conversion for esterification under the condition of 1:1 methanol/oil ratio, 310 °C and 15 min reaction time reached 98.7%, and the glycerol yield for transesterification under 0.25:1 methanol/oil ratio, 290 °C and 20 min reaction time reached 63.5% respectively. Full article
Open AccessArticle Analysis of a Single-Phase Z-Source Inverter for Battery Discharging in Vehicle to Grid Applications
Energies 2011, 4(12), 2224-2235; doi:10.3390/en4122224
Received: 20 September 2011 / Revised: 23 November 2011 / Accepted: 25 November 2011 / Published: 15 December 2011
Cited by 10 | PDF Full-text (1045 KB) | XML Full-text
Abstract
Vehicle to Grid technology allows the batteries of electric vehicles to operate as energy storage elements for renewable energy power systems. The Z-Source inverter is a new and attractive topology for the power electronics interface. In this paper, the equivalent DC-link voltage ripple
[...] Read more.
Vehicle to Grid technology allows the batteries of electric vehicles to operate as energy storage elements for renewable energy power systems. The Z-Source inverter is a new and attractive topology for the power electronics interface. In this paper, the equivalent DC-link voltage ripple of a single-phase Z-Source inverter for Vehicle to Grid applications is analyzed in this paper before deriving a general design approach for the Z-Source network. These theoretical findings, and design rule for a Z-Source network have been confirmed by computer simulations and a laboratory-implemented prototype. Full article
(This article belongs to the Special Issue Electric and Hybrid Vehicles)
Open AccessArticle Reliability Assessment of Solder Joints in Power Electronic Modules by Crack Damage Model for Wind Turbine Applications
Energies 2011, 4(12), 2236-2248; doi:10.3390/en4122236
Received: 31 August 2011 / Revised: 6 December 2011 / Accepted: 6 December 2011 / Published: 15 December 2011
Cited by 7 | PDF Full-text (1329 KB) | HTML Full-text | XML Full-text
Abstract
Wind turbine reliability is an important issue for wind energy cost minimization, especially by reduction of operation and maintenance costs for critical components and by increasing wind turbine availability. To develop an optimal operation and maintenance plan for critical components, it is necessary
[...] Read more.
Wind turbine reliability is an important issue for wind energy cost minimization, especially by reduction of operation and maintenance costs for critical components and by increasing wind turbine availability. To develop an optimal operation and maintenance plan for critical components, it is necessary to understand the physics of their failure and be able to develop reliability prediction models. Such a model is proposed in this paper for an IGBT power electronic module. IGBTs are critical components in wind turbine converter systems. These are multilayered devices where layers are soldered to each other and they operate at a thermal-power cycling environment. Temperature loadings affect the reliability of soldered joints by developing cracks and fatigue processes that eventually result in failure. Based on Miner’s rule a linear damage model that incorporates a crack development and propagation processes is discussed. A statistical analysis is performed for appropriate model parameter selection. Based on the proposed model, a layout for component life prediction with crack movement is described in details. Full article
Open AccessArticle Study on the Decomposition of Factors Affecting Energy-Related Carbon Emissions in Guangdong Province, China
Energies 2011, 4(12), 2249-2272; doi:10.3390/en4122249
Received: 31 October 2011 / Revised: 18 November 2011 / Accepted: 12 December 2011 / Published: 19 December 2011
Cited by 17 | PDF Full-text (485 KB) | HTML Full-text | XML Full-text
Abstract
Guangdong is China’s largest province in terms of energy consumption. The energy-related carbon emissions in Guangdong province are calculated, and two extended and improved decomposition models for energy-related carbon emissions are established with the Logarithmic Mean Divisia Index method based on the basic
[...] Read more.
Guangdong is China’s largest province in terms of energy consumption. The energy-related carbon emissions in Guangdong province are calculated, and two extended and improved decomposition models for energy-related carbon emissions are established with the Logarithmic Mean Divisia Index method based on the basic principle of Kaya identity. Main results are as follows: (1) the energy-related carbon emissions from the three strata of industry, except the primary industry, and household energy consumption in Guangdong province show increasing trend from 1995 to 2009; (2) the main driving and inhibiting factors which influence energy-related carbon emissions are economic output and energy intensity, respectively, while the contributions of energy mix, industrial structures, population size and living standards are not significant during the period of interest. It is concluded that optimizing the energy mix by exploiting new energy sources and cutting down energy intensity by developing low-carbon technologies are the two most effective approaches to reduce carbon emissions for Guangdong province in the future. The results and proposals in this paper provided reference for relevant administrative departments in the Government of Guangdong province to develop policies for energy conservation and emission reduction as well as to promote development of low-carbon economy. Full article
(This article belongs to the Special Issue Energy Policy on Climate Change)
Open AccessArticle Effects of Viscous Dissipation on the Slip MHD Flow and Heat Transfer past a Permeable Surface with Convective Boundary Conditions
Energies 2011, 4(12), 2273-2294; doi:10.3390/en4122273
Received: 28 October 2011 / Revised: 23 November 2011 / Accepted: 14 December 2011 / Published: 20 December 2011
Cited by 6 | PDF Full-text (430 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents an analysis of the energy exchange resulting from a 2D steady magnetohydrodynamics (MHD) flow past a permeable surface with partial slip in the presence of the viscous dissipation effect under convective heating boundary conditions. A magnetic field can effectively control
[...] Read more.
This paper presents an analysis of the energy exchange resulting from a 2D steady magnetohydrodynamics (MHD) flow past a permeable surface with partial slip in the presence of the viscous dissipation effect under convective heating boundary conditions. A magnetic field can effectively control the motion of an electrically conducting fluid in micro scale systems, which can be applied for fluid transportation. Local similarity solutions for the transformed governing equations are obtained, and the reduced ordinary differential equations solved numerically via an explicit Runge-Kutta (4, 5) formula, the Dormand-Prince pair and shooting method, which is valid for fixed positions along the surface. The effects of various physical parameters, such as the magnetic parameter, the slip coefficient, the suction/injection parameter, the Biot number, the Prandtl number and the Eckert number, on the flow and heat transfer characteristics are presented graphically and discussed. The results indicate that the heat transfer rate increases with the increase in Biot number, slip coefficient, suction and magnetic parameter, whereas it decreases with the increase in Eckert number and injection. Full article
Open AccessArticle Alternative Scenarios for the Development of a Low-Carbon City: A Case Study of Beijing, China
Energies 2011, 4(12), 2295-2310; doi:10.3390/en4122295
Received: 31 October 2011 / Revised: 30 November 2011 / Accepted: 9 December 2011 / Published: 20 December 2011
Cited by 28 | PDF Full-text (247 KB) | HTML Full-text | XML Full-text
Abstract
The establishment of low-carbon cities has been suggested all over the World, since cities are key drivers of energy usage and the associated carbon emissions. This paper presents a scenario analysis of future energy consumption and carbon emissions for the city of Beijing.
[...] Read more.
The establishment of low-carbon cities has been suggested all over the World, since cities are key drivers of energy usage and the associated carbon emissions. This paper presents a scenario analysis of future energy consumption and carbon emissions for the city of Beijing. The Long-range Energy Alternatives Planning (LEAP) model is used to simulate a range of pathways and to analyze how these would change energy consumption and carbon emissions from 2007 to 2030. Three scenarios have been designed to describe future energy strategies in relation to the development of Beijing city, namely a reference scenario (RS), control scenario (CS), and integrated scenario (IS). The results show that under the IS the total energy demand in Beijing is expected to reach 88.61 million tonnes coal equivalent (Mtce) by 2030 (59.32 Mtce in 2007), 55.82% and 32.72% lower than the values under the RS and the CS, respectively. The total carbon emissions in 2030 under the IS, although higher than the 2007 level, will be 62.22% and 40.27% lower than under the RS and the CS, respectively, with emissions peaking in 2026 and declining afterwards. In terms of the potential for reduction of energy consumption and carbon emissions, the industrial sector will continue to act as the largest contributor under the IS and CS compared with the RS, while the building and transport sectors are identified as promising fields for achieving effective control of energy consumption and carbon emissions over the next two decades. The calculation results show that an integrated package of measures is the most effective in terms of energy savings and carbon emissions mitigation, although it also faces the largest challenge to achieve the related targets. Full article
(This article belongs to the Special Issue Low Carbon Transitions Worldwide)

Other

Jump to: Research

Open AccessCorrection Correction: Hu, X.; Sun, F. and Zou, Y. Estimation of State of Charge of a Lithium-Ion Battery Pack for Electric Vehicles Using an Adaptive Luenberger Observer. Energies 2010, 3, 1586–1603
Energies 2011, 4(12), 2132; doi:10.3390/en4122132
Received: 6 November 2011 / Published: 30 November 2011
PDF Full-text (147 KB) | HTML Full-text | XML Full-text
Abstract The authors would like to make the following corrections to their published paper in Energies [1]. [...] Full article
(This article belongs to the Special Issue Hybrid Vehicles)

Journal Contact

MDPI AG
Energies Editorial Office
St. Alban-Anlage 66, 4052 Basel, Switzerland
energies@mdpi.com
Tel. +41 61 683 77 34
Fax: +41 61 302 89 18
Editorial Board
Contact Details Submit to Energies
Back to Top