Open AccessArticle
Theoretical and Experimental Investigation of the Voltage Ripple across Flying Capacitors in the Interleaved Buck Converter with Extended Duty Cycle
Energies 2018, 11(4), 1017; doi:10.3390/en11041017 (registering DOI) -
Abstract
The interleaved buck converter with an extended duty cycle is analyzed in terms of unexplored parasitic switching states that diminish the switch utilization and its safety due to high-magnitude charging and discharging currents. The analysis explains the origin of the states and their
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The interleaved buck converter with an extended duty cycle is analyzed in terms of unexplored parasitic switching states that diminish the switch utilization and its safety due to high-magnitude charging and discharging currents. The analysis explains the origin of the states and their effects and demonstrates their correlation with the existing voltage ripple on flying capacitors. The article further demonstrates that the voltage ripple can no longer be arbitrarily chosen as parasitic states emerge whenever the ripple exceeds an identified critical value being equal to the twofold voltage drop on the diode. A simple design criterion for flying capacitance is proposed. For a limited set of battery-powered DC–DC converters, a solution permitting the use of smaller capacitance by adding an extra switch is proposed. The derived findings are verified using experimental and simulation results. Full article
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Open AccessFeature PaperArticle
Comparison of Different Approaches to Predict the Performance of Pumps As Turbines (PATs)
Energies 2018, 11(4), 1016; doi:10.3390/en11041016 (registering DOI) -
Abstract
This paper deals with the comparison of different methods which can be used for the prediction of the performance curves of pumps as turbines (PATs). The considered approaches are four, i.e., one physics-based simulation model (“white box” model), two “gray box” models, which
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This paper deals with the comparison of different methods which can be used for the prediction of the performance curves of pumps as turbines (PATs). The considered approaches are four, i.e., one physics-based simulation model (“white box” model), two “gray box” models, which integrate theory on turbomachines with specific data correlations, and one “black box” model. More in detail, the modeling approaches are: (1) a physics-based simulation model developed by the same authors, which includes the equations for estimating head, power, and efficiency and uses loss coefficients and specific parameters; (2) a model developed by Derakhshan and Nourbakhsh, which first predicts the best efficiency point of a PAT and then reconstructs their complete characteristic curves by means of two ad hoc equations; (3) the prediction model developed by Singh and Nestmann, which predicts the complete turbine characteristics based on pump shape and size; (4) an Evolutionary Polynomial Regression model, which represents a data-driven hybrid scheme which can be used for identifying the explicit mathematical relationship between PAT and pump curves. All approaches are applied to literature data, relying on both pump and PAT performance curves of head, power, and efficiency over the entire range of operation. The experimental data were provided by Derakhshan and Nourbakhsh for four different turbomachines, working in both pump and PAT mode with specific speed values in the range 1.53–5.82. This paper provides a quantitative assessment of the predictions made by means of the considered approaches and also analyzes consistency from a physical point of view. Advantages and drawbacks of each method are also analyzed and discussed. Full article
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Open AccessArticle
Advanced One-Dimensional Entrained-Flow Gasifier Model Considering Melting Phenomenon of Ash
Energies 2018, 11(4), 1015; doi:10.3390/en11041015 (registering DOI) -
Abstract
A one-dimensional model is developed to represent the ash-melting phenomenon, which was not considered in the previous one-dimensional (1-D) entrained-flow gasifier model. We include sensible heat of slag and the fusion heat of ash in the heat balance equation. To consider the melting
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A one-dimensional model is developed to represent the ash-melting phenomenon, which was not considered in the previous one-dimensional (1-D) entrained-flow gasifier model. We include sensible heat of slag and the fusion heat of ash in the heat balance equation. To consider the melting of ash, we propose an algorithm that calculates the energy balance for three scenarios based on temperature. We also use the composition and the thermal properties of anorthite mineral to express ash. gPROMS for differential equations is used to solve this algorithm in a simulation; the results include coal conversion, gas composition, and temperature profile. Based on the Texaco pilot plant gasifier, we validate our model. Our results show good agreement with previous experimental data. We conclude that the sensible heat of slag and the fusion heat of ash must be included in the entrained flow gasifier model. Full article
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Open AccessArticle
Numerical Research of the Effect of Surface Biomimetic Features on the Efficiency of Tidal Turbine Blades
Energies 2018, 11(4), 1014; doi:10.3390/en11041014 (registering DOI) -
Abstract
Horizontal-axis axial flow tidal current turbine is regularly used to exploit the kinematic energy in tidal currents. However, the scaling up of tidal current turbine is very difficult. This is because strong tidal current only exists in the underwater region close to water
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Horizontal-axis axial flow tidal current turbine is regularly used to exploit the kinematic energy in tidal currents. However, the scaling up of tidal current turbine is very difficult. This is because strong tidal current only exists in the underwater region close to water surface, which implies that scaling up by enlarging rotor size is not always applicable to tidal current turbines. Hence, scaling up by improving the energy capture efficiency of the tidal turbine blade becomes a plausible choice. For this reason, apart from the numerous researches based on conventional aerodynamic and hydrodynamic theories, improving efficiency by biomimetic method is attracting increasing interest in recent years. It has been proved that leading-edge tubercles have positive contribution to improving the efficiency of tidal turbine blade. However, leading-edge tubercles can be made on blade only in the manufacturing process, as the post-production of them is quite difficult. Thus, how to improve the energy capture efficiency of the existing blades becomes a challenging issue. To address this issue, numerical research of the effect of surface biomimetic features on blade efficiency is conducted in this paper. For the sake of simplicity, surface bumps are investigated in this preliminary research in order to obtain a basic understanding of the effect of surface biomimetic features. In the research, the influences of surface bumps on blade surface pressure and the ratio of lift to drag forces are investigated in different bump array scenarios and at different tidal current speeds and the angles of attack. The calculation results have shown that surface bumps do improve the ratio of lift to drag forces of the blade in spite of their array arrangement, the angle of attack and tidal current speed. This suggests that the energy capture efficiency of both new and existing blades can be further improved if appropriate biomimetic features are deployed on the blade surfaces. Full article
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Open AccessArticle
Study on Variation of Internal Heat Gain in Office Buildings by Chronology
Energies 2018, 11(4), 1013; doi:10.3390/en11041013 (registering DOI) -
Abstract
The additional process of load calculation during the retrofit of heating, ventilation, and air conditioning (HVAC) equipment has been generally omitted in Korea, in recent years. Instead, a simple replacement of HVAC equipment, based on existing HVAC capacities, has been used, which is
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The additional process of load calculation during the retrofit of heating, ventilation, and air conditioning (HVAC) equipment has been generally omitted in Korea, in recent years. Instead, a simple replacement of HVAC equipment, based on existing HVAC capacities, has been used, which is limited when taking the variation of internal heat gain into consideration, due to changes in the consumption power due to light and office automation (OA) equipment in recent years. Thus, this study aimed to identify a change in internal heat gains over 30 years, from 1985 to 2015, study investigated actual measurement-based academic papers and catalogs about OA equipment, lighting, and the number of occupants per unit area. The heat load produced from OA equipment has increased by approximately 49.6% in 2015 compared to that of 1980, and the heat load from lighting equipment has decreased by 47% compared to that of fluorescent-based lighting, and the heat load from human bodies was approximately 10 W/m2 on average, which showed a minimal change over the past 30 years. The internal heat gain calculated for 30,000 m2 of total floor area has increased constantly for the last 30 years. Note that the internal heat gains were designed excessively, as the values used in literature was approximately 17% to 50% smaller than the value used normally in the case of pre-2000 designs, and the values used after 2000 were approximately 35% to 50% smaller than the design standard value. Full article
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Open AccessArticle
Simulation and Experimental Studies of a Multi-Tubular Floating Sea Wave Damper
Energies 2018, 11(4), 1012; doi:10.3390/en11041012 (registering DOI) -
Abstract
This article explores the issue of shore protection from sea waves and has presented the main methods used for coastal protection. It discusses the construction and operation of the multi-tubular floating sea wave damper that has been developed at the Maritime University of
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This article explores the issue of shore protection from sea waves and has presented the main methods used for coastal protection. It discusses the construction and operation of the multi-tubular floating sea wave damper that has been developed at the Maritime University of Szczecin by Professor Bolesław Kuźniewski. This paper presents the results of the research project aimed at creating and examining a prototype of the device. The research aimed to confirm the two hypotheses: “the largest damping force should occur when the damping units are placed at an optimal distance equal to half the length of the wave to be damped” and “a compensation of the horizontal forces caused by the rippling of water should occur in the damping device”. Simulation studies of the behaviour of the device’s buoyancy elements when floating on waves were performed using the ANSYS AQWAWB and AQWA software. The buoyancy components were modelled as TUBE elements with a diameter of 0.11 m and a length of 1.5 m and as triangular and square surface elements. The results of the experimental research and the computer simulation of the operation of the prototype device have also been presented. The external conditions adopted corresponded to the frequency of a wave equal to 0.807 Hz and to the wave height in front of the device which was equal to 0.1 m. Experimental studies were conducted in an auxiliary model basin with dimensions of 60 m × 7 m × 3.12 m at the Ship Hydromechanics Division, Ship Design and Research Centre (CTO S. A.) in Gdańsk (Poland). The study recorded the distribution of the vertical and horizontal forces acting on the prototype device as well as the wave height both in front of and behind the device. Both hypotheses were proven. Simulation and experimental studies have been summarised. A proposal for future works has also been presented. Full article
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Open AccessArticle
Distributed Coordination Control Based on State-of-Charge for Bidirectional Power Converters in a Hybrid AC/DC Microgrid
Energies 2018, 11(4), 1011; doi:10.3390/en11041011 (registering DOI) -
Abstract
This paper proposes a distributed coordination control for multiple bidirectional power converters (BPCs) in a hybrid AC/DC microgrid with consideration of state-of-charge (SOC) of storages. The researched hybrid AC/DC microgrid is composed of both AC and DC subgrids connected by multiple parallel BPCs.
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This paper proposes a distributed coordination control for multiple bidirectional power converters (BPCs) in a hybrid AC/DC microgrid with consideration of state-of-charge (SOC) of storages. The researched hybrid AC/DC microgrid is composed of both AC and DC subgrids connected by multiple parallel BPCs. In the literature, the storages of a hybrid microgrid are considered to allocate in only the AC subgrid or DC subgrid, which reduces the reliability of the whole system, especially during the islanded mode. Besides, the SOC management has not been considered in BPCs’ operating strategy. This paper considers a hybrid microgrid topology which has energy storages in both AC side and DC side. This ensures the reliability while increasing the complexity of the control strategy at the same time. Further, a distributed coordination control method for multiple BPCs based on SOC was proposed to enhance the reliability of hybrid microgrid. Finally, the performance of the proposed control methods was verified by real-time hardware-in-loop (HIL) tests. Full article
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Open AccessArticle
The Impact of Drive Cycles and Auxiliary Power on Passenger Car Fuel Economy
Energies 2018, 11(4), 1010; doi:10.3390/en11041010 (registering DOI) -
Abstract
In view of the advancement of zero emission transportation and current discussions on the reliability of nominal passenger car fuel economy, this article considers the procedure for assessing the potential for reducing the fuel consumption of passenger cars by using electric power to
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In view of the advancement of zero emission transportation and current discussions on the reliability of nominal passenger car fuel economy, this article considers the procedure for assessing the potential for reducing the fuel consumption of passenger cars by using electric power to operate them. The analysis compares internal combustion engines, hybrid and fully electric concepts utilizing batteries and fuel cells. The starting point for the newly developed, simulation-based fuel consumption analysis is a longitudinal vehicle model. Mechanical power requirements on the drive side incorporate a large variety of standardized drive cycles to simulate typical patterns of car usage. The power requirements of electric heating and air conditioning are also included in the simulation, as these are especially relevant to electric powertrains. Moreover, on-board grid-load profiles are considered in the assessment. Fuel consumption is optimized by applying concept-specific operating strategies. The results show that the combination of low average driving speed and elevated onboard power requirements have severe impacts on the fuel efficiency of all powertrain configurations analyzed. In particular, the operational range of battery-electric vehicles is strongly affected by this due to the limited storage capacity of today’s batteries. The analysis confirms the significance of considering different load patterns of vehicle usage related to driving profiles and onboard electrical and thermal loads. Full article
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Open AccessArticle
A Hybrid Seasonal Mechanism with a Chaotic Cuckoo Search Algorithm with a Support Vector Regression Model for Electric Load Forecasting
Energies 2018, 11(4), 1009; doi:10.3390/en11041009 (registering DOI) -
Abstract
Providing accurate electric load forecasting results plays a crucial role in daily energy management of the power supply system. Due to superior forecasting performance, the hybridizing support vector regression (SVR) model with evolutionary algorithms has received attention and deserves to continue being explored
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Providing accurate electric load forecasting results plays a crucial role in daily energy management of the power supply system. Due to superior forecasting performance, the hybridizing support vector regression (SVR) model with evolutionary algorithms has received attention and deserves to continue being explored widely. The cuckoo search (CS) algorithm has the potential to contribute more satisfactory electric load forecasting results. However, the original CS algorithm suffers from its inherent drawbacks, such as parameters that require accurate setting, loss of population diversity, and easy trapping in local optima (i.e., premature convergence). Therefore, proposing some critical improvement mechanisms and employing an improved CS algorithm to determine suitable parameter combinations for an SVR model is essential. This paper proposes the SVR with chaotic cuckoo search (SVRCCS) model based on using a tent chaotic mapping function to enrich the cuckoo search space and diversify the population to avoid trapping in local optima. In addition, to deal with the cyclic nature of electric loads, a seasonal mechanism is combined with the SVRCCS model, namely giving a seasonal SVR with chaotic cuckoo search (SSVRCCS) model, to produce more accurate forecasting performances. The numerical results, tested by using the datasets from the National Electricity Market (NEM, Queensland, Australia) and the New York Independent System Operator (NYISO, NY, USA), show that the proposed SSVRCCS model outperforms other alternative models. Full article
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Open AccessArticle
Load Disaggregation via Pattern Recognition: A Feasibility Study of a Novel Method in Residential Building
Energies 2018, 11(4), 1008; doi:10.3390/en11041008 (registering DOI) -
Abstract
In response to the need to improve energy-saving processes in older buildings, especially residential ones, this paper describes the potential of a novel method of disaggregating loads in light of the load patterns of household appliances determined in residential buildings. Experiments were designed
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In response to the need to improve energy-saving processes in older buildings, especially residential ones, this paper describes the potential of a novel method of disaggregating loads in light of the load patterns of household appliances determined in residential buildings. Experiments were designed to be applicable to general residential buildings and four types of commonly used appliances were selected to verify the method. The method assumes that loads are disaggregated and measured by a single primary meter. Following the metering of household appliances and an analysis of the usage patterns of each type, values of electric current were entered into a Hidden Markov Model (HMM) to formulate predictions. Thereafter, the HMM repeatedly performed to output the predicted data close to the measured data, while errors between predicted and the measured data were evaluated to determine whether they met tolerance. When the method was examined for 4 days, matching rates in accordance with the load disaggregation outcomes of the household appliances (i.e., laptop, refrigerator, TV, and microwave) were 0.994, 0.992, 0.982, and 0.988, respectively. The proposed method can provide insights into how and where within such buildings energy is consumed. As a result, effective and systematic energy saving measures can be derived even in buildings in which monitoring sensors and measurement equipment are not installed. Full article
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Open AccessArticle
Energy Quality Management for a Micro Energy Network Integrated with Renewables in a Tourist Area: A Chinese Case Study
Energies 2018, 11(4), 1007; doi:10.3390/en11041007 (registering DOI) -
Abstract
For a tourist area (TA), energy utilization is mostly concentrated in certain period of time. Therefore, the peak load is several times more than the average load. A Micro Energy Network Integrated with Renewables (MENR) system is considered as a potential solution to
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For a tourist area (TA), energy utilization is mostly concentrated in certain period of time. Therefore, the peak load is several times more than the average load. A Micro Energy Network Integrated with Renewables (MENR) system is considered as a potential solution to mitigate this problem. To design an appropriate MENR system, a multi-objective energy quality management (EQM) method based on the Genetic Algorithm is proposed. Here, EQM aims at reducing the primary energy consumption and optimizing the energy shares of various renewables in a MENR system. In addition to minimizing life-cycle costs and maximizing the exergy efficiency of a MENR system, the issue of system reliability is addressed. Then, a case study is presented, where the EQM method is applied to a TA located in Dali, China. Three possible reference MENR scenarios are analyzed. After confirming the reference scenarios, advanced MENR scenarios with improved system reliability are discussed. The rest of the work is dedicated to investigating the effects of various energy storage systems (ESSs) parameters and the number of electric vehicles (EVs) on MENR scenarios. The results suggest that there are significant differences between various MENR scenarios depending on the number of EVs and the investment reduction of ESSs. Full article
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Open AccessArticle
Towards Improved Energy and Resource Management in Manufacturing
Energies 2018, 11(4), 1006; doi:10.3390/en11041006 (registering DOI) -
Abstract
Exergy analysis has widely been used to assess resource consumption, and to identify opportunities for improvement within manufacturing. The main advantages of this method are its ability to account for energy quality and consumption. However, its application in industrial practice is limited, which
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Exergy analysis has widely been used to assess resource consumption, and to identify opportunities for improvement within manufacturing. The main advantages of this method are its ability to account for energy quality and consumption. However, its application in industrial practice is limited, which may be due to the lack of its consistent application in practice. Current energy management standard, that facilitate consistent application of procedures do not consider the quality aspects of energy flows. An exergy based energy management standards is proposed in this paper that would take into account energy quality aspects, while facilitating the consistent application of exergy analysis in industrial practice. Building on ISO50001, this paper presents guidelines for implementing energy and resource management in factories, incorporating the concepts of exergy and holistic factory simulation, as illustrated through a manufacturing case study. From the factory level analysis, a chilling process was identified to have significant improvement potential. A dry fan cooler, using ambient air was proposed for the improved efficiency of the chillers. Energy based metrics portrayed a system that operated at high efficiency, however exergy analysis indicated much room for further improvement, therefore impacting decision making for technology selection. The contribution of this paper is in presenting a set of prescriptive guidelines that could possibly be further developed into a new energy management standard that would utilize the advantages of exergy analysis towards improved energy and resource management in manufacturing. Full article
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Open AccessArticle
Performance and Accuracy Investigation of the Two-Step Algorithm for Power System State and Line Temperature Estimation
Energies 2018, 11(4), 1005; doi:10.3390/en11041005 (registering DOI) -
Abstract
Data concerning actual temperatures of line conductors constitutes essential information for the power system operator. The temperature of the power lines can be used to improve the accuracy of the power system model, thereby increasing the accuracy of the state estimation. This article
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Data concerning actual temperatures of line conductors constitutes essential information for the power system operator. The temperature of the power lines can be used to improve the accuracy of the power system model, thereby increasing the accuracy of the state estimation. This article presents a two-step algorithm for the power system state and line temperature estimation. In its second stage, the proposed method searches for a line temperatures vector, which corrects the uncertain power system base model and allows for further minimization of an objective function. As a result, a more accurate estimation is obtained along with a more precise model of the estimated system. The derived model can then be used for more accurate optimization. The presented method enhances standard procedures of power system state estimation, and its advantage is that it does not require direct measurements performed by phasor measurement units or measurements of line conductor temperatures and weather conditions realized by dynamic line rating systems. The results of simulations made on various test models have been examined, confirming the convergence of the procedure to the point at which the average temperature of the line wires together with the voltage values and phase angles are achieved. The algorithm’s performance and improvement method have also been presented. An advantage of the investigated approach is the possibility to calculate the temperature of line wires with the use of primary measurements in the power system. The presented and examined method, however, is sensitive to the measuring device errors. Additionally, an analysis of the method’s errors and ways of reducing them has been performed. Full article
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Open AccessArticle
Wave Power as Solution for Off-Grid Water Desalination Systems: Resource Characterization for Kilifi-Kenya
Energies 2018, 11(4), 1004; doi:10.3390/en11041004 (registering DOI) -
Abstract
Freshwater scarcity is one of humanity’s reoccurring problems that hamper socio-economic development in many regions across the globe. In coastal areas, seawater can be desalinated through reverse osmosis (RO) and transformed into freshwater for human use. Desalination requires large amounts of energy, mostly
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Freshwater scarcity is one of humanity’s reoccurring problems that hamper socio-economic development in many regions across the globe. In coastal areas, seawater can be desalinated through reverse osmosis (RO) and transformed into freshwater for human use. Desalination requires large amounts of energy, mostly in the form of a reliable electricity supply, which in many cases is supplied by diesel generators. The objective of this work is to analyze the wave power resource availability in Kilifi-Kenya and evaluate the possible use of wave power converter (WEC) to power desalination plants. A particular focus is given use of WECs developed by Uppsala University (UU-WEC). The results here presented were achieved using reanalysis—wave data revealed that the local wave climate has an approximate annual mean of 7 kW/m and mode of 5 kW/m. Significant wave height and wave mean period are within 0.8–2 m and 7–8 s respectively, with a predominant wave mean direction from southeast. The seasonal cycle appeared to be the most relevant for energy conversion, having the highest difference of 6 kW/m, in which April is the lowest (3.8 kW/m) and August is the peak (10.5 kW/m). In such mild wave climates, the UU–WEC and similar devices can be suitable for ocean energy harvesting for water desalination systems. Technically, with a capacity factor of 30% and energy consumption of 3 kWh/m3, a coastal community of about five thousand inhabitants can be provided of freshwater by only ten WECs with installed capacity of 20 kW. Full article
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Open AccessArticle
Effect of Wall Boundary Layer Thickness on Power Performance of a Recirculation Microbial Fuel Cell
Energies 2018, 11(4), 1003; doi:10.3390/en11041003 (registering DOI) -
Abstract
Hydrodynamic boundary layer is a significant phenomenon occurring in a flow through a bluff body, and this includes the flow motion and mass transfer. Thus, it could affect the biofilm formation and the mass transfer of substrates in microbial fuel cells (MFCs). Therefore,
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Hydrodynamic boundary layer is a significant phenomenon occurring in a flow through a bluff body, and this includes the flow motion and mass transfer. Thus, it could affect the biofilm formation and the mass transfer of substrates in microbial fuel cells (MFCs). Therefore, understanding the role of hydrodynamic boundary layer thicknesses in MFCs is truly important. In this study, three hydrodynamic boundary layers of thickness 1.6, 4.1, and 5 cm were applied to the recirculation mode membrane-less MFC to investigate the electricity production performance. The results showed that the thin hydrodynamic boundary could enhance the voltage output of MFC due to the strong shear rate effect. Thus, a maximum voltage of 22 mV was obtained in the MFC with a hydrodynamic boundary layer thickness of 1.6 cm, and this voltage output obtained was 11 times higher than that of MFC with 5 cm hydrodynamic boundary layer thickness. Moreover, the charge transfer resistance of anode decreased with decreasing hydrodynamic boundary layer thickness. The charge transfer resistance of MFC with hydrodynamic boundary layer of thickness 1.6 cm was 39 Ω, which was 0.79 times lesser than that of MFC with 5 cm thickness. These observations would be useful for enhancing the performance of recirculation mode MFCs. Full article
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Open AccessArticle
A Domestic Microgrid with Optimized Home Energy Management System
Energies 2018, 11(4), 1002; doi:10.3390/en11041002 (registering DOI) -
Abstract
Microgrid is a community-based power generation and distribution system that interconnects smart homes with renewable energy sources (RESs). Microgrid efficiently and economically generates power for electricity consumers and operates in both islanded and grid-connected modes. In this study, we proposed optimization schemes for
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Microgrid is a community-based power generation and distribution system that interconnects smart homes with renewable energy sources (RESs). Microgrid efficiently and economically generates power for electricity consumers and operates in both islanded and grid-connected modes. In this study, we proposed optimization schemes for reducing electricity cost and minimizing peak to average ratio (PAR) with maximum user comfort (UC) in a smart home. We considered a grid-connected microgrid for electricity generation which consists of wind turbine and photovoltaic (PV) panel. First, the problem was mathematically formulated through multiple knapsack problem (MKP) then solved by existing heuristic techniques: grey wolf optimization (GWO), binary particle swarm optimization (BPSO), genetic algorithm (GA) and wind-driven optimization (WDO). Furthermore, we also proposed three hybrid schemes for electric cost and PAR reduction: (1) hybrid of GA and WDO named WDGA; (2) hybrid of WDO and GWO named WDGWO; and (3) WBPSO, which is the hybrid of BPSO and WDO. In addition, a battery bank system (BBS) was also integrated to make our proposed schemes more cost-efficient and reliable, and to ensure stable grid operation. Finally, simulations were performed to verify our proposed schemes. Results show that our proposed scheme efficiently minimizes the electricity cost and PAR. Moreover, our proposed techniques, WDGA, WDGWO and WBPSO, outperform the existing heuristic techniques. Full article
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Open AccessArticle
Numerical Study on the Effectiveness of Grouting Reinforcement on the Large Heaving Floor of the Deep Retained Goaf-Side Gateroad: A Case Study in China
Energies 2018, 11(4), 1001; doi:10.3390/en11041001 (registering DOI) -
Abstract
To study the effectiveness of grouting reinforcement on a large heaving floor of the retained goaf-side gateroad (RGSG) at a 900 m depth in the Zhuji coal mine, a numerical model involving strain softening constitutive material was built. First, the simulated deformations of
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To study the effectiveness of grouting reinforcement on a large heaving floor of the retained goaf-side gateroad (RGSG) at a 900 m depth in the Zhuji coal mine, a numerical model involving strain softening constitutive material was built. First, the simulated deformations of the RGSG were compared with field data to verify the reliability of the numerical model. Then, the dynamic distribution of the stress in the RGSG floor was examined to reveal the mechanism of floor heave. Finally, grouting reinforcement was proposed to control the RGSG floor, and the corresponding effectiveness was verified by improving the rock mechanics of the floor strata based on the results of numerical uniaxial compressive tests. The results demonstrated that a fairly good match was achieved between the field and numerical data, and the proposed FLAC3D (Fast Lagrangian Analysis of Continua) numerical model was an effective approach to study the stability of the deep RGSG. A variation of the ratio between horizontal stress to vertical stress in the floor strata was the root cause of floor heave in the deep RGSG. Ideally, the floor heave could be reduced by 41%, 62%, and 79% when the floor strata of 1 m depth were reinforced with grouting schemes I, II, and III, respectively. Full article
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Open AccessArticle
Investigation of Cooling Performances of a Non-Film-Cooled Turbine Vane Coated with a Thermal Barrier Coating Using Conjugate Heat Transfer
Energies 2018, 11(4), 1000; doi:10.3390/en11041000 (registering DOI) -
Abstract
The aim of this paper is to numerically investigate cooling performances of a non-film-cooled turbine vane coated with a thermal barrier coating (TBC) at two turbulence intensities (Tu = 8.3% and 16.6%). Computational fluid dynamics (CFD) with conjugate heat transfer (CHT) analysis
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The aim of this paper is to numerically investigate cooling performances of a non-film-cooled turbine vane coated with a thermal barrier coating (TBC) at two turbulence intensities (Tu = 8.3% and 16.6%). Computational fluid dynamics (CFD) with conjugate heat transfer (CHT) analysis is used to predict the surface heat transfer coefficient, overall and TBC effectiveness, as well as internal and average temperatures under a condition of a NASA report provided by Hylton et al. [NASA CR-168015]. The following interesting phenomena are observed: (1) At each Tu, the TBC slightly dampens the heat transfer coefficient in general, and results in the quantitative increment of overall cooling effectiveness about 16–20%, but about 8% at the trailing edge (TE). (2) The protective ability of the TBC increases with Tu in many regions, that is, the leading edge (LE) and its neighborhoods on the suction side (SS), as well as the region from the LE to the front of the TE on the pressure side (PS), because the TBC causes the lower enhancement of the heat transfer coefficient in general at the higher Tu. (3) Considering the internal and average temperatures of the vane coated with two different TBCs, although the vane with the lower thermal conductivity protects more effectively, its role in the TE region reduces more significantly. (4) For both TBCs, the increment of Tu has a relatively small effect on the reduction of the average temperature of the vane. Full article
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Open AccessArticle
Flexible, Heat-Resistant, and Flame-Retardant Glass Fiber Nonwoven/Glass Platelet Composite Separator for Lithium-Ion Batteries
Energies 2018, 11(4), 999; doi:10.3390/en11040999 (registering DOI) -
Abstract
A new type of high-temperature stable and self-supporting composite separator for lithium-ion batteries was developed consisting of custom-made ultrathin micrometer-sized glass platelets embedded in a glass fiber nonwoven together with a water-based sodium alginate binder. The physical and electrochemical properties were investigated and
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A new type of high-temperature stable and self-supporting composite separator for lithium-ion batteries was developed consisting of custom-made ultrathin micrometer-sized glass platelets embedded in a glass fiber nonwoven together with a water-based sodium alginate binder. The physical and electrochemical properties were investigated and compared to commercial polymer-based separators. Full-cell configuration cycling tests at different current rates were performed using graphite and lithium iron phosphate as electrode materials. The glass separator was high-temperature tested and showed a stability up to at least 600 °C without significant shrinking. Furthermore, it showed an exceptional wettability for non-aqueous electrolytes. The electrochemical performance was excellent compared to commercially available polymer-based separators. The results clearly show that glass platelets integrated into a glass fiber nonwoven performs remarkably well as a separator material in lithium-ion batteries and show high-temperature stability. Full article
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Open AccessArticle
Classification Method to Define Synchronization Capability Limits of Line-Start Permanent-Magnet Motor Using Mesh-Based Magnetic Equivalent Circuit Computation Results
Energies 2018, 11(4), 998; doi:10.3390/en11040998 (registering DOI) -
Abstract
Line start permanent magnet synchronous motors (LS-PMSM) are energy-efficient synchronous motors that can start asynchronously due to a squirrel cage in the rotor. The drawback, however, with this motor type is the chance of failure to synchronize after start-up. To identify the problem,
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Line start permanent magnet synchronous motors (LS-PMSM) are energy-efficient synchronous motors that can start asynchronously due to a squirrel cage in the rotor. The drawback, however, with this motor type is the chance of failure to synchronize after start-up. To identify the problem, and the stable operation limits, the synchronization at various parameter combinations is investigated. For accurate knowledge of the operation limits to assure synchronization with the utility grid, an accurate classification of parameter combinations is needed. As for this, many simulations have to be executed, a rapid evaluation method is indispensable. To simulate the dynamic behavior in the time domain, several modeling methods exist. In this paper, a discussion is held with respect to different modeling methods. In order to include spatial factors and magnetic nonlinearities, on the one hand, and to restrict the computation time on the other hand, a magnetic equivalent circuit (MEC) modeling method is developed. In order to accelerate numerical convergence, a mesh-based analysis method is applied. The novelty in this paper is the implementation of support vector machine (SVM) to classify the results of simulations at various parameter combinations into successful or unsuccessful synchronization, in order to define the synchronization capability limits. It is explained how these techniques can benefit the simulation time and the evaluation process. The results of the MEC modeling correspond to those obtained with finite element analysis (FEA), despite the reduced computation time. In addition, simulation results obtained with MEC modeling are experimentally validated. Full article
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