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Energies, Volume 10, Issue 1 (January 2017)

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Cover Story (view full-size image) An easy-to-parametrize micro gas turbine (MGT) model which is applicable in the concept phase of [...] Read more.
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Open AccessErratum
Erratum: Shibata, S., et al. Reduced-Capacity Inrush Current Suppressor Using a Matrix Converter in a Wind Power Generation System with Squirrel-Cage Induction Machines. Energies 2016, 9, 223
Energies 2017, 10(1), 146; https://doi.org/10.3390/en10010146
Received: 12 October 2016 / Revised: 24 October 2016 / Accepted: 24 October 2016 / Published: 23 January 2017
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(This article belongs to the Special Issue Selected Papers from 5th Asia-Pacific Forum on Renewable Energy)
Open AccessArticle
Investigation of the Flow Characteristics of Methane Hydrate Slurries with Low Flow Rates
Energies 2017, 10(1), 145; https://doi.org/10.3390/en10010145
Received: 8 September 2016 / Revised: 21 December 2016 / Accepted: 11 January 2017 / Published: 23 January 2017
Cited by 6 | Viewed by 1964 | PDF Full-text (4343 KB) | HTML Full-text | XML Full-text
Abstract
Gas hydrate blockage in pipelines during offshore production becomes a major problem with increasing water depth. In this work, a series of experiments on gas hydrate formation in a flow loop was performed with low flow rates of 0.33, 0.66, and 0.88 m/s; [...] Read more.
Gas hydrate blockage in pipelines during offshore production becomes a major problem with increasing water depth. In this work, a series of experiments on gas hydrate formation in a flow loop was performed with low flow rates of 0.33, 0.66, and 0.88 m/s; the effects of the initial subcooling, flow rate, pressure, and morphology were investigated for methane hydrate formation in the flow loop. The results indicate that the differential pressure drop (ΔP) across two ends of the horizontal straight pipe increases with increasing hydrate concentration at the early stage of gas hydrate formation. When the flow rates of hydrate fluid are low, the higher the subcooling is, the faster the transition of the hydrates macrostructures. Gas hydrates can agglomerate, and sludge hydrates appear at subcoolings of 6.5 and 8.5 °C. The difference between the ΔP values at different flow rates is small, and there is no obvious influence of the flow rates on ΔP. Three hydrate macrostructures were observed: slurry-like, sludge-like, and their transition. When the initial pressure is 8.0 MPa, large methane hydrate blockages appear at the gas hydrate concentration of approximately 7%. Based on the gas–liquid two-phase flow model, a correlation between the gas hydrate concentration and the value of ΔP is also presented. These results can enrich the kinetic data of gas hydrate formation and agglomeration and provide guidance for oil and gas transportation in pipelines. Full article
(This article belongs to the Special Issue Oil and Gas Engineering)
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Open AccessArticle
Bidding Strategy for Aggregators of Electric Vehicles in Day-Ahead Electricity Markets
Energies 2017, 10(1), 144; https://doi.org/10.3390/en10010144
Received: 6 November 2016 / Revised: 8 January 2017 / Accepted: 17 January 2017 / Published: 23 January 2017
Cited by 5 | Viewed by 2216 | PDF Full-text (10660 KB) | HTML Full-text | XML Full-text
Abstract
To make full use of the flexible charging and discharging capabilities of the growing number of electric vehicles (EVs), a bidding strategy for EV aggregators to participate in a day-ahead electricity energy market is proposed in this work. The proposed bidding strategy is [...] Read more.
To make full use of the flexible charging and discharging capabilities of the growing number of electric vehicles (EVs), a bidding strategy for EV aggregators to participate in a day-ahead electricity energy market is proposed in this work. The proposed bidding strategy is able to reduce the operating cost of the EV aggregators and to handle the uncertainties of day-ahead market prices properly at the same time. Agreements between the EV owners and the aggregators are discussed, and a hierarchical market structure is proposed. While assuming the aggregators as economic rational entities, the bidding strategy is established based on the market prices, extra battery charging/discharging costs and the expected profits. The bidding clearing system will display the current/temporal market clearance results of the day-ahead market before the final clearance, and hence the market participants can revise their bids and mitigate the risks, to some extent, of forecasted market price forecast errors. Numerical results with a modified IEEE 30-bus system have demonstrated the feasibility and effectiveness of the proposed strategy. Full article
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Open AccessArticle
A New Method for Simultaneous Determination of the TDC Offset and the Pressure Offset in Fired Cylinders of an Internal Combustion Engine
Energies 2017, 10(1), 143; https://doi.org/10.3390/en10010143
Received: 13 December 2016 / Revised: 16 January 2017 / Accepted: 16 January 2017 / Published: 23 January 2017
Cited by 1 | Viewed by 1303 | PDF Full-text (2217 KB) | HTML Full-text | XML Full-text
Abstract
An innovative computationally efficient method for the simultaneous determination of top dead centre (TDC) offset and pressure offset is presented. It is based on characteristic deviations of the rate of heat release (ROHR) that are specific for both offsets in compression phase and [...] Read more.
An innovative computationally efficient method for the simultaneous determination of top dead centre (TDC) offset and pressure offset is presented. It is based on characteristic deviations of the rate of heat release (ROHR) that are specific for both offsets in compression phase and expansion phase after the end of combustion. These characteristic deviations of the ROHR are derived from first principles and they were also confirmed through manual shifts of the pressure trace. The ROHR is calculated based on the first law of thermodynamics using an in-cylinder pressure trace, engine geometrical parameters and operating point specific parameters. The method can be applied in off-line analyses using an averaged pressure trace or in on-line analyses using a single pressure trace. In both application areas the method simultaneously determines the TDC position and the pressure offset within a single processing of the pressure trace, whereas a second refinement step can be performed for obtaining more accurate results as correction factors are determined more accurately using nearly converged input data. Innovative analytic basis of the method allows for significant reduction of the computational times compared to the existing methods for the simultaneous determination of TDC offset and pressure offset in fired conditions. The method was validated on a heavy-duty and a light-duty diesel engine. Full article
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Open AccessArticle
Study on the Adsorption, Diffusion and Permeation Selectivity of Shale Gas in Organics
Energies 2017, 10(1), 142; https://doi.org/10.3390/en10010142
Received: 26 October 2016 / Revised: 12 January 2017 / Accepted: 16 January 2017 / Published: 23 January 2017
Cited by 10 | Viewed by 1867 | PDF Full-text (2678 KB) | HTML Full-text | XML Full-text
Abstract
As kerogen is the main organic component in shale, the adsorption capacity, diffusion and permeability of the gas in kerogen plays an important role in shale gas production. Based on the molecular model of type II kerogen, an organic nanoporous structure was established. [...] Read more.
As kerogen is the main organic component in shale, the adsorption capacity, diffusion and permeability of the gas in kerogen plays an important role in shale gas production. Based on the molecular model of type II kerogen, an organic nanoporous structure was established. The Grand Canonical Monte Carlo (GCMC) and Molecular Dynamics (MD) methods were used to study the adsorption and diffusion capacity of mixed gas systems with different mole ratios of CO2 and CH4 in the foregoing nanoporous structure, and gas adsorption, isosteric heats of adsorption and self-diffusion coefficient were obtained. The selective permeation of gas components in the organic pores was further studied. The results show that CO2 and CH4 present physical adsorption in the organic nanopores. The adsorption capacity of CO2 is larger than that of CH4 in organic pores, but the self-diffusion coefficient of CH4 in mixed gas is larger than that of CO2. Moreover, the self-diffusion coefficient in the horizontal direction is larger than that in the vertical direction. The mixed gas pressure and mole ratio have limited effects on the isosteric heat and the self-diffusion of CH4 and CO2 adsorption. Regarding the analysis of mixed gas selective permeation, it is concluded that the adsorption selectivity of CO2 is larger than that of CH4 in the organic nanopores. The larger the CO2/CH4 mole ratio, the greater the adsorption and permeation selectivity of mixed gas in shale. The permeation process is mainly controlled by adsorption rather than diffusion. These results are expected to reveal the adsorption and diffusion mechanism of gas in shale organics, which has a great significance for further research. Full article
(This article belongs to the Special Issue Oil and Gas Engineering)
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Open AccessArticle
Particle Swarm Optimization for Outdoor Lighting Design
Energies 2017, 10(1), 141; https://doi.org/10.3390/en10010141
Received: 31 October 2016 / Revised: 11 January 2017 / Accepted: 18 January 2017 / Published: 23 January 2017
Cited by 2 | Viewed by 1592 | PDF Full-text (1304 KB) | HTML Full-text | XML Full-text
Abstract
Outdoor lighting is an essential service for modern life. However, the high influence of this type of facility on energy consumption makes it necessary to take extra care in the design phase. Therefore, this manuscript describes an algorithm to help light designers to [...] Read more.
Outdoor lighting is an essential service for modern life. However, the high influence of this type of facility on energy consumption makes it necessary to take extra care in the design phase. Therefore, this manuscript describes an algorithm to help light designers to get, in an easy way, the best configuration parameters and to improve energy efficiency, while ensuring a minimum level of overall uniformity. To make this possible, we used a particle swarm optimization (PSO) algorithm. These algorithms are well established, and are simple and effective to solve optimization problems. To take into account the most influential parameters on lighting and energy efficiency, 500 simulations were performed using DIALux software (4.10.0.2, DIAL, Ludenscheid, Germany). Next, the relation between these parameters was studied using to data mining software. Subsequently, we conducted two experiments for setting parameters that enabled the best configuration algorithm in order to improve efficiency in the proposed process optimization. Full article
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Open AccessFeature PaperArticle
Stochastic and Deterministic Unit Commitment Considering Uncertainty and Variability Reserves for High Renewable Integration
Energies 2017, 10(1), 140; https://doi.org/10.3390/en10010140
Received: 13 December 2016 / Revised: 12 January 2017 / Accepted: 16 January 2017 / Published: 23 January 2017
Cited by 10 | Viewed by 2456 | PDF Full-text (1590 KB) | HTML Full-text | XML Full-text
Abstract
The uncertain and variable nature of renewable energy sources in modern power systems raises significant challenges in achieving the dual objective of reliable and economically efficient system operation. To address these challenges, advanced scheduling strategies have evolved during the past years, including the [...] Read more.
The uncertain and variable nature of renewable energy sources in modern power systems raises significant challenges in achieving the dual objective of reliable and economically efficient system operation. To address these challenges, advanced scheduling strategies have evolved during the past years, including the co-optimization of energy and reserves under deterministic or stochastic Unit Commitment (UC) modeling frameworks. This paper presents different deterministic and stochastic day-ahead UC formulations, with focus on the determination, allocation and deployment of reserves. An explicit distinction is proposed between the uncertainty and the variability reserve, capturing the twofold nature of renewable generation. The concept of multi-timing scheduling is proposed and applied in all UC policies, which allows for the optimal procurement of such reserves based on intra-hourly (real-time) intervals, when concurrently optimizing energy and commitments over hourly intervals. The day-ahead scheduling results are tested against different real-time dispatch regimes, with none or limited look-ahead capability, or with the use of the variability reserve, utilizing a modified version of the Greek power system. The results demonstrate the enhanced reliability achieved by applying the multi-timing scheduling concept and explicitly considering the variability reserve, and certain features regarding the allocation and deployment of reserves are discussed. Full article
(This article belongs to the Special Issue Advances in Power System Operations and Planning)
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Open AccessArticle
Possibilities and Limitations of CFD Simulation for Flashing Flow Scenarios in Nuclear Applications
Energies 2017, 10(1), 139; https://doi.org/10.3390/en10010139
Received: 19 August 2016 / Revised: 11 January 2017 / Accepted: 12 January 2017 / Published: 23 January 2017
Cited by 5 | Viewed by 1893 | PDF Full-text (4671 KB) | HTML Full-text | XML Full-text
Abstract
The flashing phenomenon is relevant to nuclear safety analysis, for example by a loss of coolant accident and safety release scenarios. It has been studied intensively by means of experiments and simulations with system codes, but computational fluid dynamics (CFD) simulation is still [...] Read more.
The flashing phenomenon is relevant to nuclear safety analysis, for example by a loss of coolant accident and safety release scenarios. It has been studied intensively by means of experiments and simulations with system codes, but computational fluid dynamics (CFD) simulation is still at the embryonic stage. Rapid increasing computer speed makes it possible to apply the CFD technology in such complex flow situations. Nevertheless, a thorough evaluation on the limitations and restrictions is still missing, which is however indispensable for reliable application, as well as further development. In the present work, the commonly-used two-fluid model with different mono-disperse assumptions is used to simulate various flashing scenarios. With the help of available experimental data, the results are evaluated, and the limitations are discussed. A poly-disperse method is found necessary for a reliable prediction of mean bubble size and phase distribution. The first attempts to trace the evolution of the bubble size distribution by means of poly-disperse simulations are made. Full article
(This article belongs to the Special Issue Engineering Fluid Dynamics) Printed Edition available
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Open AccessArticle
An Experimental Facility to Validate Ground Source Heat Pump Optimisation Models for the Australian Climate
Energies 2017, 10(1), 138; https://doi.org/10.3390/en10010138
Received: 22 December 2016 / Revised: 12 January 2017 / Accepted: 14 January 2017 / Published: 22 January 2017
Cited by 1 | Viewed by 1607 | PDF Full-text (3922 KB) | HTML Full-text | XML Full-text
Abstract
Ground source heat pumps (GSHPs) are one of the most widespread forms of geothermal energy technology. They utilise the near-constant temperature of the ground below the frost line to achieve energy-efficiencies two or three times that of conventional air-conditioners, consequently allowing a significant [...] Read more.
Ground source heat pumps (GSHPs) are one of the most widespread forms of geothermal energy technology. They utilise the near-constant temperature of the ground below the frost line to achieve energy-efficiencies two or three times that of conventional air-conditioners, consequently allowing a significant offset in electricity demand for space heating and cooling. Relatively mature GSHP markets are established in Europe and North America. GSHP implementation in Australia, however, is limited, due to high capital price, uncertainties regarding optimum designs for the Australian climate, and limited consumer confidence in the technology. Existing GSHP design standards developed in the Northern Hemisphere are likely to lead to suboptimal performance in Australia where demand might be much more cooling-dominated. There is an urgent need to develop Australia’s own GSHP system optimisation principles on top of the industry standards to provide confidence to bring the GSHP market out of its infancy. To assist in this, the Queensland Geothermal Energy Centre of Excellence (QGECE) has commissioned a fully instrumented GSHP experimental facility in Gatton, Australia, as a publically-accessible demonstration of the technology and a platform for systematic studies of GSHPs, including optimisation of design and operations. This paper presents a brief review on current GSHP use in Australia, the technical details of the Gatton GSHP facility, and an analysis on the observed cooling performance of this facility to date. Full article
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Open AccessReview
Estimation of Hourly, Daily and Monthly Global Solar Radiation on Inclined Surfaces: Models Re-Visited
Energies 2017, 10(1), 134; https://doi.org/10.3390/en10010134
Received: 20 September 2016 / Revised: 20 December 2016 / Accepted: 23 December 2016 / Published: 22 January 2017
Cited by 16 | Viewed by 1896 | PDF Full-text (1489 KB) | HTML Full-text | XML Full-text
Abstract
Global solar radiation is generally measured on a horizontal surface, whereas the maximum amount of incident solar radiation is measured on an inclined surface. Over the last decade, a number of models were proposed for predicting solar radiation on inclined surfaces. These models [...] Read more.
Global solar radiation is generally measured on a horizontal surface, whereas the maximum amount of incident solar radiation is measured on an inclined surface. Over the last decade, a number of models were proposed for predicting solar radiation on inclined surfaces. These models have various scopes; applicability to specific surfaces, the requirement for special measuring equipment, or limitations in scope. To find the most suitable model for a given location the hourly outputs predicted by available models are compared with the field measurements of the given location. The main objective of this study is to review on the estimation of the most accurate model or models for estimating solar radiation components for a selected location, by testing various models available in the literature. To increase the amount of incident solar radiation on photovoltaic (PV) panels, the PV panels are mounted on tilted surfaces. This article also provides an up-to-date status of different optimum tilt angles that have been determined in various countries. Full article
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Open AccessArticle
State of Charge and State of Health Estimation of AGM VRLA Batteries by Employing a Dual Extended Kalman Filter and an ARX Model for Online Parameter Estimation
Energies 2017, 10(1), 137; https://doi.org/10.3390/en10010137
Received: 4 November 2016 / Revised: 13 January 2017 / Accepted: 14 January 2017 / Published: 21 January 2017
Cited by 11 | Viewed by 2452 | PDF Full-text (3860 KB) | HTML Full-text | XML Full-text
Abstract
State of charge (SOC) and state of health (SOH) are key issues for the application of batteries, especially the absorbent glass mat valve regulated lead-acid (AGM VRLA) type batteries used in the idle stop start systems (ISSs) that are popularly integrated into conventional [...] Read more.
State of charge (SOC) and state of health (SOH) are key issues for the application of batteries, especially the absorbent glass mat valve regulated lead-acid (AGM VRLA) type batteries used in the idle stop start systems (ISSs) that are popularly integrated into conventional engine-based vehicles. This is due to the fact that SOC and SOH estimation accuracy is crucial for optimizing battery energy utilization, ensuring safety and extending battery life cycles. The dual extended Kalman filter (DEKF), which provides an elegant and powerful solution, is widely applied in SOC and SOH estimation based on a battery parameter model. However, the battery parameters are strongly dependent on operation conditions such as the SOC, current rate and temperature. In addition, battery parameters change significantly over the life cycle of a battery. As a result, many experimental pretests investigating the effects of the internal and external conditions of a battery on its parameters are required, since the accuracy of state estimation depends on the quality of the information regarding battery parameter changes. In this paper, a novel method for SOC and SOH estimation that combines a DEKF algorithm, which considers hysteresis and diffusion effects, and an auto regressive exogenous (ARX) model for online parameters estimation is proposed. The DEKF provides precise information concerning the battery open circuit voltage (OCV) to the ARX model. Meanwhile, the ARX model continues monitoring parameter variations and supplies information on them to the DEKF. In this way, the estimation accuracy can be maintained despite the changing parameters of a battery. Moreover, online parameter estimation from the ARX model can save the time and effort used for parameter pretests. The validation of the proposed algorithm is given by simulation and experimental results. Full article
(This article belongs to the collection Electric and Hybrid Vehicles Collection)
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Open AccessArticle
Energy Management Strategy Based on Multiple Operating States for a Photovoltaic/Fuel Cell/Energy Storage DC Microgrid
Energies 2017, 10(1), 136; https://doi.org/10.3390/en10010136
Received: 10 September 2016 / Revised: 2 January 2017 / Accepted: 13 January 2017 / Published: 21 January 2017
Cited by 22 | Viewed by 2219 | PDF Full-text (5791 KB) | HTML Full-text | XML Full-text
Abstract
It is a great challenge for DC microgrids with stochastic renewable sources and volatility loads to achieve better operation performance. This study proposes an energy management strategy based on multiple operating states for a DC microgrid, which is comprised of a photovoltaic (PV) [...] Read more.
It is a great challenge for DC microgrids with stochastic renewable sources and volatility loads to achieve better operation performance. This study proposes an energy management strategy based on multiple operating states for a DC microgrid, which is comprised of a photovoltaic (PV) array, a proton exchange membrane fuel cell (PEMFC) system, and a battery bank. This proposed strategy can share the power properly and keep the bus voltage steady under different operating states (the state of charge (SOC) of the battery bank, loading conditions, and PV array output power). In addition, a microgrids test platform is established. In order to verify the effectiveness of the proposed energy management strategy, the strategy is implemented in a hardware system and experimentally tested under different operating states. The experimental results illustrate the good performance of the proposed control strategy for the DC microgrid under different scenarios of power generation and load demand. Full article
(This article belongs to the Special Issue Electric Power Systems Research 2017)
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Open AccessArticle
A High Efficiency Charging Strategy for a Supercapacitor Using a Wireless Power Transfer System Based on Inductor/Capacitor/Capacitor (LCC) Compensation Topology
Energies 2017, 10(1), 135; https://doi.org/10.3390/en10010135
Received: 14 October 2016 / Revised: 22 December 2016 / Accepted: 12 January 2017 / Published: 21 January 2017
Cited by 18 | Viewed by 2885 | PDF Full-text (5233 KB) | HTML Full-text | XML Full-text
Abstract
In the application of rail transit vehicles, when using typical wireless power transfer (WPT) systems with series–series (SS) compensation supply power for supercapacitors, the output current is in an approximately inverse relationship with the duty cycle in a wide range. This renders the [...] Read more.
In the application of rail transit vehicles, when using typical wireless power transfer (WPT) systems with series–series (SS) compensation supply power for supercapacitors, the output current is in an approximately inverse relationship with the duty cycle in a wide range. This renders the typical buck circuit control inappropriate. In order to help resolve the above issues, this paper designs inductor/capacitor/capacitor (LCC) compensation with new compensation parameters, which can achieve an adjustable quasi-constant voltage from the input of the inverter to the output of the rectifier. In addition, the two-port network method is used to analyze the resonant compensation circuit. The analysis shows that LCC compensation is more suitable for the WPT system using the supercapacitor as the energy storage device. In the case of LCC compensation topology combined with the charging characteristics of the supercapacitor, an efficient charging strategy is designed, namely first constant current charging, followed by constant power charging. Based on the analysis of LCC compensation, the system has an optimal load, by which the system works at the maximum efficiency point. Combined with the characteristics of the constant voltage output, the system can maintain high efficiency in the constant power stage by making constant output power the same as the optimal power point. Finally, the above design is verified through experiments. Full article
(This article belongs to the Special Issue Wireless Power Transfer 2016)
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Open AccessArticle
Control of a Three-Phase to Single-Phase Back-to-Back Converter for Electrical Resistance Seam Welding Systems
Energies 2017, 10(1), 133; https://doi.org/10.3390/en10010133
Received: 21 November 2016 / Revised: 4 January 2017 / Accepted: 12 January 2017 / Published: 21 January 2017
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Abstract
DC link back-to-back converters are widely used in industrial applications. This interest comes from their power factor unity capability on the utility grid and to maintain regulated output parameters, thanks to the decoupling between the grid and the load side. In this paper, [...] Read more.
DC link back-to-back converters are widely used in industrial applications. This interest comes from their power factor unity capability on the utility grid and to maintain regulated output parameters, thanks to the decoupling between the grid and the load side. In this paper, a 150 KVA prototype of DC link back-to-back converter for electrical resistance seam welding applications is described. The focus of the paper is on the control strategy developed to absorb constant power from the three-phase utility grid. The key idea is to allow the voltage on the DC bus to vary in order to avoid the propagation at the input side of the pulsed power required by the load. An estimation procedure of the load parameters is presented too. The effectiveness of this control scheme has been proved by simulations and tests. Full article
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Open AccessEditor’s ChoiceArticle
An Improvement in Biodiesel Production from Waste Cooking Oil by Applying Thought Multi-Response Surface Methodology Using Desirability Functions
Energies 2017, 10(1), 130; https://doi.org/10.3390/en10010130
Received: 22 November 2016 / Revised: 11 January 2017 / Accepted: 13 January 2017 / Published: 21 January 2017
Cited by 15 | Viewed by 2030 | PDF Full-text (978 KB) | HTML Full-text | XML Full-text
Abstract
The exhaustion of natural resources has increased petroleum prices and the environmental impact of oil has stimulated the search for an alternative source of energy such as biodiesel. Waste cooking oil is a potential replacement for vegetable oils in the production of biodiesel. [...] Read more.
The exhaustion of natural resources has increased petroleum prices and the environmental impact of oil has stimulated the search for an alternative source of energy such as biodiesel. Waste cooking oil is a potential replacement for vegetable oils in the production of biodiesel. Biodiesel is synthesized by direct transesterification of vegetable oils, which is controlled by several inputs or process variables, including the dosage of catalyst, process temperature, mixing speed, mixing time, humidity and impurities of waste cooking oil that was studied in this case. Yield, turbidity, density, viscosity and higher heating value are considered as outputs. This paper used multi-response surface methodology (MRS) with desirability functions to find the best combination of input variables used in the transesterification reactions to improve the production of biodiesel. In this case, several biodiesel optimization scenarios have been proposed. They are based on a desire to improve the biodiesel yield and the higher heating value, while decreasing the viscosity, density and turbidity. The results demonstrated that, although waste cooking oil was collected from various sources, the dosage of catalyst is one of the most important variables in the yield of biodiesel production, whereas the viscosity obtained was similar in all samples of the biodiesel that was studied. Full article
(This article belongs to the collection Bioenergy and Biofuel)
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Open AccessArticle
Assessment of the Governance System Regarding Adoption of Energy Efficient Appliances by Households in Nigeria
Energies 2017, 10(1), 132; https://doi.org/10.3390/en10010132
Received: 1 December 2016 / Revised: 6 January 2017 / Accepted: 10 January 2017 / Published: 20 January 2017
Cited by 2 | Viewed by 1389 | PDF Full-text (4350 KB) | HTML Full-text | XML Full-text
Abstract
The adoption of energy efficient electrical appliances by households has a great potential to reduce electricity consumption in Nigeria. A well-formulated and implemented policy (mix) to spur adoption is said to be required to drive this process. This article presents an assessment of [...] Read more.
The adoption of energy efficient electrical appliances by households has a great potential to reduce electricity consumption in Nigeria. A well-formulated and implemented policy (mix) to spur adoption is said to be required to drive this process. This article presents an assessment of policies that aim to spur adoption among households, and the related governance system. The analytical framework used for this analysis is the Governance Assessment Tool (GAT). Data collection involved semi-structured interviews, a review of policy documents, and secondary quantitative data. The results show that policies in Nigeria had little effect in meeting pre-set goals. The governance system was found to be weakly developed due to a lack of policy, the overlapping work of different governmental organizations, a lack of appropriate resources, and a lack of householders’ involvement in agenda-setting and decision-making processes. Current actions mostly depend on local programmes that run via donor aid. They include the free exchange of CFL bulbs and metering studies of end user energy consumption. The results add further insight in the fields of governance and policy on energy efficiency issues in developing countries. This article also provides suggestions for the design of policies that target the adoption of energy efficient electrical appliances among households in Nigeria. Full article
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Open AccessArticle
A Soft Sensor-Based Fault-Tolerant Control on the Air Fuel Ratio of Spark-Ignition Engines
Energies 2017, 10(1), 131; https://doi.org/10.3390/en10010131
Received: 24 September 2016 / Revised: 10 January 2017 / Accepted: 11 January 2017 / Published: 20 January 2017
Cited by 2 | Viewed by 1617 | PDF Full-text (4421 KB) | HTML Full-text | XML Full-text
Abstract
The air/fuel ratio (AFR) regulation for spark-ignition (SI) engines has been an essential and challenging control problem for engineers in the automotive industry. The feed-forward and feedback scheme has been investigated in both academic research and industrial application. The aging effect can often [...] Read more.
The air/fuel ratio (AFR) regulation for spark-ignition (SI) engines has been an essential and challenging control problem for engineers in the automotive industry. The feed-forward and feedback scheme has been investigated in both academic research and industrial application. The aging effect can often cause an AFR sensor fault in the feedback loop, and the AFR control performance will degrade consequently. In this research, a new control scheme on AFR with fault-tolerance is proposed by using an artificial neural network model based on fault detection and compensation, which can provide the satisfactory AFR regulation performance at the stoichiometric value for the combustion process, given a certain level of misreading of the AFR sensor. Full article
(This article belongs to the Special Issue Combustion and Propulsion)
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Open AccessArticle
Improving Electricity Consumption Estimation for Electric Vehicles Based on Sparse GPS Observations
Energies 2017, 10(1), 129; https://doi.org/10.3390/en10010129
Received: 8 November 2016 / Revised: 7 January 2017 / Accepted: 12 January 2017 / Published: 20 January 2017
Cited by 7 | Viewed by 1227 | PDF Full-text (248 KB) | HTML Full-text | XML Full-text
Abstract
Improving the estimation accuracy for the energy consumption of electric vehicles (EVs) would greatly contribute to alleviating the range anxiety of drivers and serve as a critical basis for the planning, operation, and management of charging infrastructures. To address the challenges in energy [...] Read more.
Improving the estimation accuracy for the energy consumption of electric vehicles (EVs) would greatly contribute to alleviating the range anxiety of drivers and serve as a critical basis for the planning, operation, and management of charging infrastructures. To address the challenges in energy consumption estimation encountered due to sparse Global Positioning System (GPS) observations, an estimation model is proposed that considers both the kinetic characteristics from sparse GPS observations and the unique attributes of EVs: (1) work opposing the rolling resistance; (2) aerodynamic friction losses; (3) energy consumption/generation depending on the grade of the route; (4) auxiliary load consumption; and (5) additional energy losses arising from the unstable power output of the electric motor. Two quantities, the average energy consumption per kilometer and the energy consumption for an entire trip, were focused on and compared for model fitness, parameter, and effectiveness, and the latter showed a higher fitness. Based on sparse GPS observations of 68 EVs in Aichi Prefecture, Japan, the traditional linear regression approach and a multilevel mixed-effects linear regression approach were used for model calibration. The proposed model showed a high accuracy and demonstrated a great potential for application in using sparse GPS observations to predict the energy consumption of EVs. Full article
Open AccessArticle
Wind Profiles and Wave Spectra for Potential Wind Farms in South China Sea. Part II: Wave Spectrum Model
Energies 2017, 10(1), 127; https://doi.org/10.3390/en10010127
Received: 1 October 2016 / Revised: 13 December 2016 / Accepted: 29 December 2016 / Published: 20 January 2017
Cited by 3 | Viewed by 1844 | PDF Full-text (4613 KB) | HTML Full-text | XML Full-text
Abstract
Along with the commercialization of offshore wind energy in China, the South China Sea has been identified as ideal for constructing offshore wind farms, especially for farms consisting of floating wind turbines over deep waters. Since the wind profiles and wave spectra are [...] Read more.
Along with the commercialization of offshore wind energy in China, the South China Sea has been identified as ideal for constructing offshore wind farms, especially for farms consisting of floating wind turbines over deep waters. Since the wind profiles and wave spectra are somewhat primitive for the design of an offshore wind turbine, engineering models describing the wind and wave characteristics in the South China Sea area are necessary for the offshore wind energy exploitation given the meteorological, hydrological, and geographical differences between the South China Sea and the North/Norwegian Sea, where the commonly used wind profile and wave spectrum models were designated. In the present study; a series of numerical simulations were conducted to reveal the wave characteristics in the South China Sea under both typhoon and non-typhoon conditions. By analyzing the simulation results; the applicability of the Joint North Sea Wave Project (JONSWAP) spectrum model; in terms of characterizing the wind-induced wave fields in the South China Sea; was discussed. In detail; the key parameters of the JONSWAP spectrum model; such as the Phillips constant; spectral width parameter; peak-enhancement factor, and high frequency tail decay; were investigated in the context of finding suitable values. Full article
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Open AccessArticle
Wind Profiles and Wave Spectra for Potential Wind Farms in South China Sea. Part I: Wind Speed Profile Model
Energies 2017, 10(1), 125; https://doi.org/10.3390/en10010125
Received: 1 October 2016 / Revised: 17 December 2016 / Accepted: 21 December 2016 / Published: 20 January 2017
Cited by 9 | Viewed by 1772 | PDF Full-text (8015 KB) | HTML Full-text | XML Full-text
Abstract
With the setting of wind energy harvesting moving from coastal waters to deep waters, the South China Sea has been deemed to offer great potential for the construction of floating wind farms thanks to the abundance of wind energy resources. An engineering model [...] Read more.
With the setting of wind energy harvesting moving from coastal waters to deep waters, the South China Sea has been deemed to offer great potential for the construction of floating wind farms thanks to the abundance of wind energy resources. An engineering model describing the wind profiles and wave spectra specific to the South China Sea conditions, which is the precondition for offshore wind farm construction, has, however, not yet been proposed. In the present study, a series of numerical simulations have been conducted using the Weather Forecast and Research model. Through analyzing the wind and wave information extracted from the numerical simulation results, engineering models to calculate vertical profiles of wind speeds and wave spectra have been postulated. While the present paper focuses on the wind profile model, a companion paper articulates the wave spectrum model. For wind profiles under typhoon conditions, the power-law and log-law models have been found applicable under the condition that the Hellmann exponent α or the friction velocity u * are modified to vary with the wind strength. For wind profiles under non-typhoon conditions, the log-law model is revised to take into consideration the influence of the atmospheric stability. Full article
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Open AccessArticle
Thermal Simulation of the Fresh Food Compartment in a Domestic Refrigerator
Energies 2017, 10(1), 128; https://doi.org/10.3390/en10010128
Received: 9 November 2016 / Revised: 5 January 2017 / Accepted: 9 January 2017 / Published: 19 January 2017
Cited by 1 | Viewed by 1651 | PDF Full-text (809 KB) | HTML Full-text | XML Full-text
Abstract
In the field of domestic refrigeration, it is important to look for methods that can be used to simulate, and, thus, improve the thermal behavior of the fresh food compartment. In this sense, this study proposes some methods to model the thermal behavior [...] Read more.
In the field of domestic refrigeration, it is important to look for methods that can be used to simulate, and, thus, improve the thermal behavior of the fresh food compartment. In this sense, this study proposes some methods to model the thermal behavior of this compartment when the shelves’ positions are changed. Temperature measurements at specific locations in this compartment were obtained. Several shelf position combinations were performed to use three 2D interpolation methods in order to simulate the temperature mean and the temperature variance. The methods used were: Lagrange’s interpolation, cubic spline interpolation and bilinear interpolation. Two validation points were chosen to verify the proposed methods. By comparing the experimental results with the computer simulations, it was possible to conclude that the method of Lagrange’s interpolation provided values that were not close to the real measured values. On the other hand, it was observed that the method of bilinear interpolation offered the best results, estimating values which were very close to the actual experimental measurements. These interpolation methods were used to build color thermal graphs that can be used to find some of the most appropriate shelf position combinations in this type of refrigerator. By inspection of these thermal graphs, it can be seen that the lowest average temperature was obtained when one shelf was located at 24.5 cm while the second shelf was located at 29.5 cm measured from the top of the compartment. In the same way, it can be seen that the minimum temperature variance was obtained when only one shelf was inside the compartment and this shelf was located at 29.5 cm. Full article
(This article belongs to the Special Issue Advanced Thermal Simulation of Energy Systems)
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Open AccessArticle
Integrated Traction Control Strategy for Distributed Drive Electric Vehicles with Improvement of Economy and Longitudinal Driving Stability
Energies 2017, 10(1), 126; https://doi.org/10.3390/en10010126
Received: 5 October 2016 / Revised: 6 December 2016 / Accepted: 3 January 2017 / Published: 19 January 2017
Cited by 13 | Viewed by 2728 | PDF Full-text (3588 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents an integrated traction control strategy (ITCS) for distributed drive electric vehicles. The purpose of the proposed strategy is to improve vehicle economy and longitudinal driving stability. On high adhesion roads, economy optimization algorithm is applied to maximize motors efficiency by [...] Read more.
This paper presents an integrated traction control strategy (ITCS) for distributed drive electric vehicles. The purpose of the proposed strategy is to improve vehicle economy and longitudinal driving stability. On high adhesion roads, economy optimization algorithm is applied to maximize motors efficiency by means of the optimized torque distribution. On low adhesion roads, a sliding mode control (SMC) algorithm is implemented to guarantee the wheel slip ratio around the optimal slip ratio point to make full use of road adhesion capacity. In order to avoid the disturbance on slip ratio calculation due to the low vehicle speed, wheel rotational speed is taken as the control variable. Since the optimal slip ratio varies according to different road conditions, Bayesian hypothesis selection is utilized to estimate the road friction coefficient. Additionally, the ITCS is designed for combining the vehicle economy and stability control through three traction allocation cases: economy-based traction allocation, pedal self-correcting traction allocation and inter-axles traction allocation. Finally, simulations are conducted in CarSim and Matlab/Simulink environment. The results show that the proposed strategy effectively reduces vehicle energy consumption, suppresses wheels-skid and enhances the vehicle longitudinal stability and dynamic performance. Full article
(This article belongs to the collection Electric and Hybrid Vehicles Collection)
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Open AccessArticle
Optimal Expansion Co-Planning of Reconfigurable Electricity and Natural Gas Distribution Systems Incorporating Energy Hubs
Energies 2017, 10(1), 124; https://doi.org/10.3390/en10010124
Received: 13 August 2016 / Revised: 28 November 2016 / Accepted: 12 January 2017 / Published: 19 January 2017
Cited by 8 | Viewed by 1915 | PDF Full-text (1586 KB) | HTML Full-text | XML Full-text
Abstract
In a carbon-constrained world, natural gas with low emission intensity plays an important role in the energy consumption area. Energy consumers and distribution networks are linked via energy hubs. Meanwhile, reconfiguration that optimizes operational performance while maintaining a radial network topology is a [...] Read more.
In a carbon-constrained world, natural gas with low emission intensity plays an important role in the energy consumption area. Energy consumers and distribution networks are linked via energy hubs. Meanwhile, reconfiguration that optimizes operational performance while maintaining a radial network topology is a worldwide technique in the electricity distribution system. To improve the overall efficiency of energy infrastructure, the expansion of electricity distribution lines and elements within energy hubs should be co-planned. In this paper, the co-planning process is modeled as a mixed integer quadratic programming problem to handle conflicting objectives simultaneously. We propose a novel model to identify the optimal co-expansion plan in terms of total cost. Operational factors including energy storages and reconfiguration are considered within the systems to serve electricity, cooling and heating loads. Reconfiguration and elements in energy hubs can avoid or defer new elements’ installation to minimize the investment cost, maintenance cost, operation cost, and interruption cost in the planning horizon. The proposed co-planning approach is verified on 3 and 12-node electricity and natural gas distribution systems coupled via energy hubs. Numerical results show the ability of our proposed expansion co-planning approach based on energy hub in meeting energy demand. Full article
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Open AccessArticle
Effect of Thermal-Electric Cross Coupling on Heat Transport in Nanofluids
Energies 2017, 10(1), 123; https://doi.org/10.3390/en10010123
Received: 23 October 2016 / Revised: 4 January 2017 / Accepted: 9 January 2017 / Published: 19 January 2017
Cited by 6 | Viewed by 1547 | PDF Full-text (1543 KB) | HTML Full-text | XML Full-text
Abstract
Nanofluids have an enhanced thermal conductivity compared with their base fluid. Although many mechanisms have been proposed, few of them could give a satisfactory explanation of experimental data. In this study, a mechanism of heat transport enhancement is proposed based on the cross [...] Read more.
Nanofluids have an enhanced thermal conductivity compared with their base fluid. Although many mechanisms have been proposed, few of them could give a satisfactory explanation of experimental data. In this study, a mechanism of heat transport enhancement is proposed based on the cross coupling of thermal and electric transports in nanofluids. Nanoparticles are viewed as large molecules which have thermal motion together with the molecules of the base fluid. As the nanoparticles have surface charges, the motion of nanoparticles in the high-temperature region will generate a relatively strong varying electric field through which the motion will be transported to other nanoparticles, leading to a simultaneous temperature rise of low-temperature nanoparticles. The local base fluid will thus be heated up by these nanoparticles through molecular collision. Every nanoparticle could, therefore, be considered as an internal heat source, thereby enhancing the equivalent thermal conductivity significantly. This mechanism qualitatively agrees with many experimental data and is thus of significance in designing and applying nanofluids. Full article
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Open AccessArticle
Nanostructure and Oxidation Reactivity of Nascent Soot Particles in Ethylene/Pentanol Flames
Energies 2017, 10(1), 122; https://doi.org/10.3390/en10010122
Received: 23 September 2016 / Revised: 10 January 2017 / Accepted: 12 January 2017 / Published: 19 January 2017
Cited by 14 | Viewed by 1503 | PDF Full-text (7828 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
As byproducts of the combustion process of hydrocarbon fuels, soot particles are difficult to remove, and they can greatly harm human health and pollute the environment. Therefore, the formation and growth processes of the soot particles has become a study focus of researchers. [...] Read more.
As byproducts of the combustion process of hydrocarbon fuels, soot particles are difficult to remove, and they can greatly harm human health and pollute the environment. Therefore, the formation and growth processes of the soot particles has become a study focus of researchers. In this paper, the nanostructure and oxidation reactivity of carbonaceous particles collected from ethylene inverse diffusion flames with or without the additions of three pentanol isomers (1-pentanol, 3-methyl-1-butanol, and 2-methyl-1-butanol) were investigated in detail. The nanostructure and oxidation characteristics of nascent soot particles were characterized using high resolution transmission electron microscopy (HRTEM), X-ray diffractometry (XRD) and thermogravimetric analysis (TGA). It was found that the nascent soot cluster of pure ethylene flame had a loose structure, while the additions of pentanol isomers made the soot agglomerates more compact and delayed the growth of graphitic structures. The pentanol isomer additions also contributed to a higher disorder of the crystallite arrangement in the soot nanostructure. According to the TGA experiments, the results showed that the addition of pentanol isomers enhanced the oxidation reactivity of soot particles, which could help to reduce soot particle emissions. Full article
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Open AccessArticle
Numerical Analysis of the Effects of Rotating Wind Turbine Blades on the Aerodynamic Forces Acting on Tower
Energies 2017, 10(1), 121; https://doi.org/10.3390/en10010121
Received: 21 August 2016 / Revised: 9 January 2017 / Accepted: 13 January 2017 / Published: 19 January 2017
Cited by 4 | Viewed by 2899 | PDF Full-text (19017 KB) | HTML Full-text | XML Full-text
Abstract
We have investigated the effects of the rotating blades of an upwind-type three-blade horizontal-axis wind turbine (HAWT) on the basic characteristics of aerodynamic forces acting on its tower by conducting improved delayed detached-eddy simulations (DESs). Three tip-speed ratios were considered for the operating [...] Read more.
We have investigated the effects of the rotating blades of an upwind-type three-blade horizontal-axis wind turbine (HAWT) on the basic characteristics of aerodynamic forces acting on its tower by conducting improved delayed detached-eddy simulations (DESs). Three tip-speed ratios were considered for the operating conditions of the HAWT: λ = 3 (low), λ = 6 (optimum), and λ = 10 (high). The diversion of the flow approaching the tower by the rotating blades and the low-pressure region that formed downwind of the blades significantly affected the aerodynamic forces acting on the tower. For example, the azimuth angle around the tower at which the pressure reached a maximum at each height shifted significantly in the direction of the movement of the blade passing the tower because of the diversion of the flow by the blades. Fluctuations in the lift force of the tower were significantly larger than those in its drag force because of the low-pressure region downwind of the blades. Full article
(This article belongs to the Special Issue Modeling and Simulation for Wind Turbine Loads Analysis)
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Open AccessArticle
Analysis of Dynamic Characteristic for Solar Arrays in Series and Global Maximum Power Point Tracking Based on Optimal Initial Value Incremental Conductance Strategy under Partially Shaded Conditions
Energies 2017, 10(1), 120; https://doi.org/10.3390/en10010120
Received: 21 November 2016 / Revised: 31 December 2016 / Accepted: 12 January 2017 / Published: 19 January 2017
Cited by 4 | Viewed by 1618 | PDF Full-text (8087 KB) | HTML Full-text | XML Full-text
Abstract
Partial shading (PS) is an unavoidable condition which significantly reduces the efficiency and stability of a photovoltaic (PV) system. With PS, the system usually exhibits multiple-peak output power characteristics, but single-peak is also possible under special PS conditions. In fact it is shown [...] Read more.
Partial shading (PS) is an unavoidable condition which significantly reduces the efficiency and stability of a photovoltaic (PV) system. With PS, the system usually exhibits multiple-peak output power characteristics, but single-peak is also possible under special PS conditions. In fact it is shown that the partial shading condition (PSC) is the necessary but not sufficient condition for multiple-peak. Based on circuit analysis, this paper shows that the number of peak points can be determined by short-circuit currents and maximum-power point currents of all the arrays in series. Then the principle is established based on which the number of the peak points is to be determined. Furthermore, based on the dynamic characteristic of solar array, this paper establishes the rule for determination of the relative position of the global maximum power point (GMPP). In order to track the GMPP within an appropriate period, a reliable technique and the corresponding computer algorithm are developed for GMPP tracking (GMPPT) control. It exploits a definable nonlinear relation has been found between variable environmental parameters and the output current of solar arrays at every maximum power point, obtained based on the dynamic performance corresponding to PSC. Finally, the proposed method is validated with MATLAB®/Simulink® simulations and actual experiments. It is shown that the GMPPT of a PV generation system is indeed realized efficiently in a realistic environment with partial shading conditions. Full article
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Open AccessArticle
Characterization and Analysis of Energy Demand Patterns in Airports
Energies 2017, 10(1), 119; https://doi.org/10.3390/en10010119
Received: 26 September 2016 / Revised: 10 January 2017 / Accepted: 11 January 2017 / Published: 19 January 2017
Cited by 4 | Viewed by 1918 | PDF Full-text (8139 KB) | HTML Full-text | XML Full-text
Abstract
Airports in general have high-energy consumption. Influenced by many factors, the characteristics of airport energy consumption are stochastic, nonlinear and dynamic. In recent years, airport managers have made huge efforts to harmonize airport operation with environmental sustainability by minimizing the environmental impact, with [...] Read more.
Airports in general have high-energy consumption. Influenced by many factors, the characteristics of airport energy consumption are stochastic, nonlinear and dynamic. In recent years, airport managers have made huge efforts to harmonize airport operation with environmental sustainability by minimizing the environmental impact, with energy conservation and energy efficiency as one of their pillars. A key factor in order to reduce energy consumption at airports is to understand the energy use and consumption behavior, due to the multiple parameters and singularities that are involved. In this article, a 3-step methodology based on monitoring methods is proposed to characterize and analyze energy demand patterns in airports through their electric load profiles, and is applied to the Seve Ballesteros-Santander Airport (Santander, Spain). This methodology can be also used in airports in order to determine the way energy is used, to establish the classification of the electrical charges based on their operation way as well as to determine the main energy consumers and main external influencers. Results show that airport present a daily energy demand pattern since electric load profiles follow a similar curve shape for every day of the year, having a great dependence of the terminal building behavior, the main energy consumer of the airport, and with heating, ventilation and air conditioning (HVAC) and lighting being the most energy-intensive facilities, and outside temperature and daylighting the main external influencers. Full article
(This article belongs to the Special Issue Energy Conservation in Infrastructures 2016)
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Open AccessArticle
Mixed Lubrication Effects in the Lateral Lubricating Interfaces of External Gear Machines: Modelling and Experimental Validation
Energies 2017, 10(1), 111; https://doi.org/10.3390/en10010111
Received: 20 October 2016 / Revised: 21 November 2016 / Accepted: 9 January 2017 / Published: 19 January 2017
Cited by 10 | Viewed by 2088 | PDF Full-text (10063 KB) | HTML Full-text | XML Full-text
Abstract
This article presents a novel mixed-thermoelastohydrodynamic (TEHD) model for the lateral lubricating interfaces which exist between floating lateral bushings and gears in external gear machines (EGMs). The proposed model integrates the influence of surface asperities along with the fluid structure and thermal interaction [...] Read more.
This article presents a novel mixed-thermoelastohydrodynamic (TEHD) model for the lateral lubricating interfaces which exist between floating lateral bushings and gears in external gear machines (EGMs). The proposed model integrates the influence of surface asperities along with the fluid structure and thermal interaction in the interface, especially in the regions of very low film thicknesses by following a stochastic approach in modelling the mixed lubrication regime. Furthermore, the current work includes validation of the predictions of the mixed-TEHD model against experimentally measured leakages from the lateral gap and compares the performance of this model with a previously developed full film TEHD model for the lateral gaps in EGMs. Full article
(This article belongs to the Special Issue Energy Efficiency and Controllability of Fluid Power Systems)
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Open AccessArticle
Decision Support System for a Low Voltage Renewable Energy System
Energies 2017, 10(1), 118; https://doi.org/10.3390/en10010118
Received: 6 November 2016 / Revised: 4 January 2017 / Accepted: 9 January 2017 / Published: 18 January 2017
Cited by 9 | Viewed by 1624 | PDF Full-text (5691 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents the development of a decision support system (DSS) for a low-voltage grid with renewable energy sources (photovoltaic panels and wind turbine) which aims at achieving energy balance in a pilot microgrid with less energy consumed from the network. The DSS [...] Read more.
This paper presents the development of a decision support system (DSS) for a low-voltage grid with renewable energy sources (photovoltaic panels and wind turbine) which aims at achieving energy balance in a pilot microgrid with less energy consumed from the network. The DSS is based on a procedural decision algorithm that is applied on a pilot microgrid, with energy produced from renewable energy sources, but it can be easily generalized for any microgrid. To underline the benefits of the developed DSS two case scenarios (a household and an office building with different energy consumptions) were analyzed. The results and throw added value of the paper is the description of an implemented microgrid, the development and testing of the decision support system on real measured data. Experimental results have demonstrated the validity of the approach in rule-based decision switching. Full article
(This article belongs to the Special Issue Smart Microgrids: Developing the Intelligent Power Grid of Tomorrow)
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