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Energies, Volume 11, Issue 3 (March 2018)

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Cover Story (view full-size image) Microalgae have long been utilized as food and feed, and, more recently, fuel. When microalgae was [...] Read more.
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Open AccessCorrection Correction: Arshad A.; et al. An Analysis of Photo-Voltaic Hosting Capacity in Finnish Low Voltage Distribution Networks. Energies 2017, 10, 1702
Energies 2018, 11(3), 689; https://doi.org/10.3390/en11030689
Received: 1 February 2018 / Revised: 10 March 2018 / Accepted: 12 March 2018 / Published: 20 March 2018
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Abstract
The authors would like to correct following errors[...] Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle A Fast-Transient Output Capacitor-Less Low-Dropout Regulator Using Active-Feedback and Current-Reuse Feedforward Compensation
Energies 2018, 11(3), 688; https://doi.org/10.3390/en11030688
Received: 20 February 2018 / Revised: 10 March 2018 / Accepted: 15 March 2018 / Published: 19 March 2018
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Abstract
In this paper, output capacitor-less low-dropout (LDO) regulator using active-feedback and current-reuse feedforward compensation (AFCFC) is presented. The open-loop transfer function was obtained using small-signal modeling. The stability of the proposed LDO was analyzed using pole-zero plots, and it was confirmed by simulations
[...] Read more.
In this paper, output capacitor-less low-dropout (LDO) regulator using active-feedback and current-reuse feedforward compensation (AFCFC) is presented. The open-loop transfer function was obtained using small-signal modeling. The stability of the proposed LDO was analyzed using pole-zero plots, and it was confirmed by simulations that the stability was ensured under the load current of 50 mA. The proposed compensation method increases gain-bandwidth product (GBW) and reduces the on-chip compensation capacitor. The proposed AFCFC technique was applied to a three-stage output capacitor-less LDO. The LDO has a GBW of 5.6 MHz with a small on-chip capacitor of 2.6 pF. Fast-transient time of 450 ns with low quiescent current of 65.8 μA was achieved. The LDO was fabricated in 130 nm CMOS process consuming 180 × 140 μm2 of the silicon area. Full article
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Open AccessArticle The Energy Cost Analysis of Hybrid Systems and Diesel Generators in Powering Selected Base Transceiver Station Locations in Nigeria
Energies 2018, 11(3), 687; https://doi.org/10.3390/en11030687
Received: 29 November 2017 / Revised: 31 January 2018 / Accepted: 1 February 2018 / Published: 19 March 2018
Cited by 4 | Viewed by 914 | PDF Full-text (2509 KB) | HTML Full-text | XML Full-text
Abstract
As more locations gain access to telecommunication, there is a growing demand to provide energy in a reliable, efficient and environmentally friendly manner while effectively addressing growing energy needs. Erratic power supply and rising operation costs (OPEX) in Nigeria have increased the need
[...] Read more.
As more locations gain access to telecommunication, there is a growing demand to provide energy in a reliable, efficient and environmentally friendly manner while effectively addressing growing energy needs. Erratic power supply and rising operation costs (OPEX) in Nigeria have increased the need to harness local renewable energy sources. Thus, identifying the right generator schedule with the renewable system to reduce OPEX is a priority for operators and vendors. This study evaluates the energy costs of hybrid systems with different generator schedules in powering base transceiver stations in Nigeria using the Hybrid Optimization Model for Electric Renewable (HOMER). A load range of 4 kW to 8 kW was considered using: (i) an optimised generator schedule; (ii) forced-on generator schedule and (iii) the generator-only schedule. The results showed an optimal LCOE range between averages of USD 0.156/kWh to 0.172/kWh for the 8 kW load. The percent energy contribution by generator ranges from 52.80% to 60.90%, and by the solar PV system, 39.10% to 47.20%. Excess energy ranges from 0.03% to 14.98%. The optimised generator schedule has the highest solar PV penetration of 56.8%. The OPEX savings on fuel ranges from 41.68% to 47% for the different load schedules and carbon emission savings of 4222 kg to 31,428.36 kg. The simulation results shows that powering base stations using the optimised hybrid system schedule would be a better option for the telecom industry. Full article
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Open AccessArticle Research on Economic Comprehensive Control Strategies of Tractor-Planter Combinations in Planting, Including Gear-Shift and Cruise Control
Energies 2018, 11(3), 686; https://doi.org/10.3390/en11030686
Received: 27 January 2018 / Revised: 11 March 2018 / Accepted: 12 March 2018 / Published: 19 March 2018
Cited by 1 | Viewed by 943 | PDF Full-text (3958 KB) | HTML Full-text | XML Full-text
Abstract
An automatic control strategy for forward speed in the planting process is proposed to improve the fuel economy and reduce the labor intensity of drivers. Models of tractors with power-shift transmission (PST) and a precise pneumatic planter with an electric-driven seed metering device
[...] Read more.
An automatic control strategy for forward speed in the planting process is proposed to improve the fuel economy and reduce the labor intensity of drivers. Models of tractors with power-shift transmission (PST) and a precise pneumatic planter with an electric-driven seed metering device are built as research objects and simulated using Matlab with Simulink. The economic comprehensive control strategies for forward speed, including gear-shift schedule and cruise control strategy, are developed. Four levels control mode with different fuel economy performances are implemented to meet different driver or operation condition requirements. In addition, the control strategy is developed for the seed-metering device motor to maintain the required seed spacing in planting. Finally, the fuel economy and effectiveness of the control strategies for forward speed and planting quality are verified by simulations with Matlab/Simulink and Matlab/Stateflow. The simulation results verify the satisfactory performance of the proposed control strategies. The error of seed spacing is less than 3% when planting with speed fluctuation. Under the premise of ensuring planting quality and driver’s demands, the cruise control strategies for forward speed have more significant effects on the fuel economy than previous cruise control strategies. Furthermore, the control mode with higher level has better fuel economy and a larger speed deviation range. Full article
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Open AccessArticle Hydrodynamic Performance of an Array of Wave Energy Converters Integrated with a Pontoon-Type Breakwater
Energies 2018, 11(3), 685; https://doi.org/10.3390/en11030685
Received: 10 February 2018 / Revised: 13 March 2018 / Accepted: 15 March 2018 / Published: 18 March 2018
Cited by 2 | Viewed by 984 | PDF Full-text (7015 KB) | HTML Full-text | XML Full-text
Abstract
The cost of wave energy converters (WECs) can be reduced significantly by integrating WECs into other marine facilities, especially in sea areas with a mild wave climate. To reduce the cost and increase the efficiency, a hybrid WEC system, comprising a linear array
[...] Read more.
The cost of wave energy converters (WECs) can be reduced significantly by integrating WECs into other marine facilities, especially in sea areas with a mild wave climate. To reduce the cost and increase the efficiency, a hybrid WEC system, comprising a linear array (medium farm) of oscillating buoy-type WECs attached to the weather side of a fixed-type floating pontoon as the base structure is proposed. The performance of the WEC array is investigated numerically using a boundary element method (BEM) based on the linear potential flow theory. The linear power take-off (PTO) damping model is used to calculate the output power of the WEC array. The performance of the WEC array and each individual WEC device is balanced by using the mean interaction factor and the individual interaction factor. To quantify the effect of the pontoon, the hydrodynamic results of the WEC arrays with and without a pontoon are compared with each other. Detailed investigations on the influence of the structural and PTO parameters are performed in a wide wave frequency range. Results show that the energy conversion efficiency of a WEC array with a properly designed pontoon is much higher than that without a pontoon. This integration scheme can achieve the efficiency improvement and construction-cost reduction of the wave energy converters. Full article
(This article belongs to the Special Issue Wave Energy Potential, Behavior and Extraction)
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Open AccessArticle Assessment of the Induced Electric Fields in a Carbon-Fiber Electrical Vehicle Equipped with a Wireless Power Transfer System
Energies 2018, 11(3), 684; https://doi.org/10.3390/en11030684
Received: 13 February 2018 / Revised: 5 March 2018 / Accepted: 16 March 2018 / Published: 18 March 2018
Cited by 3 | Viewed by 1067 | PDF Full-text (2975 KB) | HTML Full-text | XML Full-text
Abstract
In this study, the electric field induced inside two realistic anatomical models placed near or inside an electric vehicle made of carbon-fiber composite while charging its battery with a wireless power transfer (WPT) system has been investigated. The WPT source consists of two
[...] Read more.
In this study, the electric field induced inside two realistic anatomical models placed near or inside an electric vehicle made of carbon-fiber composite while charging its battery with a wireless power transfer (WPT) system has been investigated. The WPT source consists of two parallel inductive coils operating with a power output of 7.7 kW at two different frequencies of 85 and 150 kHz. Since a misalignment between the primary and the secondary coil creates higher induced fields, a misalignment of 20 cm is also considered as the worst-case exposure condition. The analysis of the obtained results shows that the International Commission on Non-Ionizing Radiation Protection (ICNIRP) basic restrictions are exceeded by 1.3 dB and 4.8 dB for the aligned and misaligned coil positions, respectively. This exceedance is however confined only in a small area of the driver’s foot. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Big Data Analytics for Discovering Electricity Consumption Patterns in Smart Cities
Energies 2018, 11(3), 683; https://doi.org/10.3390/en11030683
Received: 31 January 2018 / Revised: 5 March 2018 / Accepted: 13 March 2018 / Published: 18 March 2018
Cited by 3 | Viewed by 1421 | PDF Full-text (3094 KB) | HTML Full-text | XML Full-text
Abstract
New technologies such as sensor networks have been incorporated into the management of buildings for organizations and cities. Sensor networks have led to an exponential increase in the volume of data available in recent years, which can be used to extract consumption patterns
[...] Read more.
New technologies such as sensor networks have been incorporated into the management of buildings for organizations and cities. Sensor networks have led to an exponential increase in the volume of data available in recent years, which can be used to extract consumption patterns for the purposes of energy and monetary savings. For this reason, new approaches and strategies are needed to analyze information in big data environments. This paper proposes a methodology to extract electric energy consumption patterns in big data time series, so that very valuable conclusions can be made for managers and governments. The methodology is based on the study of four clustering validity indices in their parallelized versions along with the application of a clustering technique. In particular, this work uses a voting system to choose an optimal number of clusters from the results of the indices, as well as the application of the distributed version of the k-means algorithm included in Apache Spark’s Machine Learning Library. The results, using electricity consumption for the years 2011–2017 for eight buildings of a public university, are presented and discussed. In addition, the performance of the proposed methodology is evaluated using synthetic big data, which cab represent thousands of buildings in a smart city. Finally, policies derived from the patterns discovered are proposed to optimize energy usage across the university campus. Full article
(This article belongs to the Special Issue Data Science and Big Data in Energy Forecasting)
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Open AccessArticle Experimental and Numerical Analyses of the Sloshing in a Fuel Tank
Energies 2018, 11(3), 682; https://doi.org/10.3390/en11030682
Received: 31 January 2018 / Revised: 8 March 2018 / Accepted: 15 March 2018 / Published: 17 March 2018
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Abstract
The sloshing of fuel inside the tank is an important issue in aerospace and automotive applications. This phenomenon, in fact, can cause various issues related to vehicle stability and safety, to component fatigue, audible noise, vibrations and to the level measurement of the
[...] Read more.
The sloshing of fuel inside the tank is an important issue in aerospace and automotive applications. This phenomenon, in fact, can cause various issues related to vehicle stability and safety, to component fatigue, audible noise, vibrations and to the level measurement of the fuel itself. The sloshing phenomenon can be defined as a highly nonlinear oscillatory movement of the free-surface of liquid inside a container, such as a fuel tank, under the effect of continuous or instantaneous forces. This paper is the result of a research collaboration between the Industrial Engineering Department of the University of Naples “Federico II” and the R&D department of Fiat Chrysler Automobiles (F.C.A.) The activity is focused on the study of the sloshing in the fuel tank of vehicles. The goal is the optimization of the tank geometry in order to allow, for example, the correct fuel suction under all driving conditions and to prevent undesired noise and vibrations. This paper shows results obtained on a reference tank filled by water tinted with a dark blue food colorant. The geometry has been tested on a test bench designed by Moog Inc. on specification from Fiat Chrysler Automobiles with harmonic excitation of a 2D tank slice along one degree of freedom. The test bench consists of a hexapod with six independent actuators connecting the base to the top platform, allowing all six Degrees of Freedom (DOFs). On the top platform there are other two additional actuators to extend pitch and roll envelope, thus the name of “8-DOF bench”. The designed tank has been studied with a three-dimensional Computational Fluid Dynamics (CFD) modeling approach, too. By the end, the numerical and experimental data have been compared with a post-processing analysis by means of Matlab® software. For this reason, the images have been reduced in two dimensions. In particular, the percentage gaps of the free surfaces and the center of gravity have been compared each other. The comparison, for the three different levels of liquid tested, has shown a good agreement with a discrepancy always less than 3%. Full article
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Open AccessArticle Algorithm for Fast and Efficient Detection and Reaction to Angle Instability Conditions Using Phasor Measurement Unit Data
Energies 2018, 11(3), 681; https://doi.org/10.3390/en11030681
Received: 15 February 2018 / Revised: 7 March 2018 / Accepted: 12 March 2018 / Published: 17 March 2018
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Abstract
In wide area monitoring, protection, and control (WAMPAC) systems, angle stability of transmission network is monitored using data from phasor measurement units (PMU) placed on transmission lines. Based on this PMU data stream advanced algorithm for out-of-step condition detection and early warning issuing
[...] Read more.
In wide area monitoring, protection, and control (WAMPAC) systems, angle stability of transmission network is monitored using data from phasor measurement units (PMU) placed on transmission lines. Based on this PMU data stream advanced algorithm for out-of-step condition detection and early warning issuing is developed. The algorithm based on theoretical background described in this paper is backed up by the data and results from corresponding simulations done in Matlab environment. Presented results aim to provide the insights of the potential benefits, such as fast and efficient detection and reaction to angle instability, this algorithm can have on the improvement of the power system protection. Accordingly, suggestion is given how the developed algorithm can be implemented in protection segments of the WAMPAC systems in the transmission system operator control centers. Full article
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Open AccessArticle An Artificially Intelligent Technique to Generate Synthetic Geomechanical Well Logs for the Bakken Formation
Energies 2018, 11(3), 680; https://doi.org/10.3390/en11030680
Received: 4 February 2018 / Revised: 12 March 2018 / Accepted: 14 March 2018 / Published: 17 March 2018
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Abstract
Artificially intelligent and predictive modelling of geomechanical properties is performed by creating supervised machine learning data models utilizing artificial neural networks (ANN) and will predict geomechanical properties from basic and commonly used conventional well logs such as gamma ray, and bulk density. The
[...] Read more.
Artificially intelligent and predictive modelling of geomechanical properties is performed by creating supervised machine learning data models utilizing artificial neural networks (ANN) and will predict geomechanical properties from basic and commonly used conventional well logs such as gamma ray, and bulk density. The predictive models were created by following the approach on a large volume of data acquired from 112 wells containing the Bakken Formation in North Dakota. The studied wells cover a large surface area of the formation containing the five main producing counties in North Dakota: Burke, Mountrail, McKenzie, Dunn, and Williams. Thus, with a large surface area being analyzed in this research, there is confidence with a high degree of certainty that an extensive representation of the Bakken Formation is modelled, by training neural networks to work on varying properties from the different counties containing the Bakken Formation in North Dakota. Shear wave velocity of 112 wells is also analyzed by regression methods and neural networks, and a new correlation is proposed for the Bakken Formation. The final goal of the research is to achieve supervised artificial neural network models that predict geomechanical properties of future wells with an accuracy of at least 90% for the Upper and Middle Bakken Formation. Thus, obtaining these logs by generating it from statistical and artificially intelligent methods shows a potential for significant improvements in performance, efficiency, and profitability for oil and gas operators. Full article
(This article belongs to the Special Issue Unconventional Natural Gas (UNG) Recoveries 2018)
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Open AccessArticle Thermal Performance of Microencapsulated Phase Change Material (mPCM) in Roof Modules during Daily Operation
Energies 2018, 11(3), 679; https://doi.org/10.3390/en11030679
Received: 18 February 2018 / Revised: 13 March 2018 / Accepted: 15 March 2018 / Published: 17 March 2018
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Abstract
This study combines microencapsulated phase change materials (mPCMs) (core material: paraffin; melting points: 37 and 43 °C) and aluminum honeycomb boards (8 mm core cell) to form mPCM roof modules and investigates their heat absorption and release performances, as well as their impact
[...] Read more.
This study combines microencapsulated phase change materials (mPCMs) (core material: paraffin; melting points: 37 and 43 °C) and aluminum honeycomb boards (8 mm core cell) to form mPCM roof modules and investigates their heat absorption and release performances, as well as their impact on indoor heat gain by conducting experiments over a 24-h period, subject to representative weather. The outdoor boundary conditions of the module are hourly sunlight and nighttime natural cooling; on the indoor side of the module, the conditions are daytime air conditioning and nighttime natural cooling. The results indicate that compared to a roof module with a 43 °C melting point mPCM, the roof module with a 37 °C melting point mPCM had improved peak load-shifting capacity, but had a slightly increased indoor heat gain. The mPCMs in both roof modules were successfully cooled during the night, returning to their initial state, to begin a new thermal cycle the next day. Full article
(This article belongs to the Section Energy Storage and Application)
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Open AccessArticle Stochastic Stability Analysis of the Power System with Losses
Energies 2018, 11(3), 678; https://doi.org/10.3390/en11030678
Received: 17 January 2018 / Revised: 13 March 2018 / Accepted: 13 March 2018 / Published: 17 March 2018
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Renewable energy and electric vehicles have become involved in power systems, which has attracted researchers to stochastic continuous disturbances (SDEs). This paper addresses stochastic analysis issues for the stability of a power system with losses under SDEs. Firstly, the quasi-Hamiltonian models of power
[...] Read more.
Renewable energy and electric vehicles have become involved in power systems, which has attracted researchers to stochastic continuous disturbances (SDEs). This paper addresses stochastic analysis issues for the stability of a power system with losses under SDEs. Firstly, the quasi-Hamiltonian models of power systems with losses under SDEs are given. Secondly, a novel analytical method is proposed to analyze the stability of the power system with losses under SDEs based on the stochastic averaging method. Thirdly, comparisons of stability probability under different parameters are performed, from which insights to improve the stability probability of power systems with losses under SDEs can be obtained. Even though it is challenging to assess the stability of a power system with losses under SDEs, the proposed method in this paper could serve well in this regard. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Research on Improved VSG Control Algorithm Based on Capacity-Limited Energy Storage System
Energies 2018, 11(3), 677; https://doi.org/10.3390/en11030677
Received: 15 February 2018 / Revised: 13 March 2018 / Accepted: 14 March 2018 / Published: 16 March 2018
Cited by 2 | Viewed by 707 | PDF Full-text (3425 KB) | HTML Full-text | XML Full-text
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A large scale of renewable energy employing grid connected electronic inverters fail to contribute inertia or damping to power systems, and, therefore, may bring negative effects to the stability of power system. As a solution, an advanced Virtual Synchronous Generator (VSG) control technology
[...] Read more.
A large scale of renewable energy employing grid connected electronic inverters fail to contribute inertia or damping to power systems, and, therefore, may bring negative effects to the stability of power system. As a solution, an advanced Virtual Synchronous Generator (VSG) control technology based on Hamilton approach is introduced in this paper firstly to support the frequency and enhance the suitability and robustness of the system. The charge and discharge process of power storage devices forms the virtual inertia and damping of VSG, and, therefore, limits on storage capacity may change the coefficients of VSG. To provide a method in keeping system output in an acceptable level with the capacity restriction in a transient period, an energy control algorithm is designed for VSG adaptive control. Finally, simulations are conducted in DIgSILENT to demonstrate the correctness of the algorithm. The demonstration shows: (1) the proposed control model aims at better system robustness and stability; and (2) the model performs in the environment closer to practical engineering by fitting the operation state of storage system. Full article
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Open AccessArticle A Hybrid Excited Machine with Flux Barriers and Magnetic Bridges
Energies 2018, 11(3), 676; https://doi.org/10.3390/en11030676
Received: 23 January 2018 / Revised: 11 March 2018 / Accepted: 14 March 2018 / Published: 16 March 2018
Cited by 1 | Viewed by 746 | PDF Full-text (5965 KB) | HTML Full-text | XML Full-text
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In this paper, an U-shape flux barrier rotor concept for a hybrid excited synchronous machine with flux magnetic bridges fixed on the rotor is presented. Using 3D finite element analysis, the influence of axial flux bridges on the field-weakening and -strengthening characteristics, electromagnetic
[...] Read more.
In this paper, an U-shape flux barrier rotor concept for a hybrid excited synchronous machine with flux magnetic bridges fixed on the rotor is presented. Using 3D finite element analysis, the influence of axial flux bridges on the field-weakening and -strengthening characteristics, electromagnetic torque, no-load magnetic flux linkage, rotor iron losses and back electromotive force is shown. Three different rotor designs are analyzed. Furthermore, the field control characteristics depending on additional DC control coil currents are shown. Full article
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Open AccessArticle Life Cycle Performance of Hydrogen Production via Agro-Industrial Residue Gasification—A Small Scale Power Plant Study
Energies 2018, 11(3), 675; https://doi.org/10.3390/en11030675
Received: 28 January 2018 / Revised: 13 March 2018 / Accepted: 13 March 2018 / Published: 16 March 2018
Cited by 2 | Viewed by 959 | PDF Full-text (2100 KB) | HTML Full-text | XML Full-text
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This study evaluates the environmental profile of a real biomass-based hydrogen production small-scale (1 MWth) system composed of catalytic candle indirectly heated steam gasifier coupled with zinc oxide (ZnO) guard bed, water gas shift (WGS) and pressure swing absorber (PSA) reactors.
[...] Read more.
This study evaluates the environmental profile of a real biomass-based hydrogen production small-scale (1 MWth) system composed of catalytic candle indirectly heated steam gasifier coupled with zinc oxide (ZnO) guard bed, water gas shift (WGS) and pressure swing absorber (PSA) reactors. Environmental performance from cradle-to-gate was investigated by life cycle assessment (LCA) methodology. Biomass production shows high influence over all impact categories. In the syngas production process, the main impacts observed are global warming potential (GWP) and acidification potential (AP). Flue gas emission from gasifier burner has the largest proportion of total GWP. The residual off gas use in internal combustion engine (ICE) leads to important environmental savings for all categories. Hydrogen renewability score is computed as 90% due to over 100% decline in non-renewable energy demand. Sensitivity analysis shows that increase in hydrogen production efficiency does not necessarily result in decrease in environmental impacts. In addition, economic allocation of environmental charges increases all impact categories, especially AP and photochemical oxidation (POFP). Full article
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Open AccessArticle Properties of Hydrochar as Function of Feedstock, Reaction Conditions and Post-Treatment
Energies 2018, 11(3), 674; https://doi.org/10.3390/en11030674
Received: 13 February 2018 / Revised: 6 March 2018 / Accepted: 14 March 2018 / Published: 16 March 2018
Cited by 3 | Viewed by 984 | PDF Full-text (3810 KB) | HTML Full-text | XML Full-text
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Hydrothermal carbonization (HTC) is a promising technology to convert wet biomass into carbon-rich materials. Until now, the chemical processes occurring and their influence on the product properties are not well understood. Therefore, a target-oriented production of materials with defined properties is difficult, if
[...] Read more.
Hydrothermal carbonization (HTC) is a promising technology to convert wet biomass into carbon-rich materials. Until now, the chemical processes occurring and their influence on the product properties are not well understood. Therefore, a target-oriented production of materials with defined properties is difficult, if not impossible. Here, model compounds such as cellulose and lignin, as well as different definite biomasses such as straw and beech wood are converted by hydrothermal carbonization. Following this, thermogravimetic (TGA) and FTIR measurements are used to get information about chemical structure and thermal properties of the related hydrochars. Some of the isolated materials are thermally post-treated (490 °C and 700 °C) and analyzed. The results show that at “mild” HTC conversion, the cellulose part in a lignocellulose matrix is not completely carbonized and there is still cellulose present. Thermal post-treatment makes the properties of product materials more similar and shows complete carbonization with increase aromatic cross-linking, proven by TGA and FTIR results. Full article
(This article belongs to the Special Issue Thermo Fluid Conversion of Biomass)
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Open AccessArticle A Three-Coil Inductively Power Transfer System with Constant Voltage Output
Energies 2018, 11(3), 673; https://doi.org/10.3390/en11030673
Received: 23 January 2018 / Revised: 13 March 2018 / Accepted: 13 March 2018 / Published: 16 March 2018
Cited by 1 | Viewed by 907 | PDF Full-text (4658 KB) | HTML Full-text | XML Full-text
Abstract
For a traditional 2-coil system outputting constant voltage (CV), the transfer efficiency decreases drastically as transfer distance increases. To solve this problem, this essay proposes a 3-coil system which could achieve CV output and Zero Phase Angle (ZPA) conditions with specific parameter values.
[...] Read more.
For a traditional 2-coil system outputting constant voltage (CV), the transfer efficiency decreases drastically as transfer distance increases. To solve this problem, this essay proposes a 3-coil system which could achieve CV output and Zero Phase Angle (ZPA) conditions with specific parameter values. This 3-coil system could partly relief transfer efficiency fall at a long transfer distance, without any complicated controls. In order to achieve CV and ZPA condition, this essay devises the parameter values based on the decoupling 3-coil model, and a prototype is designed accordingly to verify these characteristics. With 10 cm transfer distance, output voltage deviation is 5.5% as the load varies from 12 Ω to 200 Ω, proving that the output voltage almost keeps constant with load change. Furthermore, with software simulation, a comparison experiment between the proposed 3-coil system and a Series-Inductor-Capacitor-Inductor (S-LCL) compensated 2-coil system is built to verify the efficiency improvement. The transfer distance change leads to the differentiation of voltage gain for both 2-coil and 3-coil systems. So, the input voltage for both systems and the compensated capacitor in receiver loop of the 3-coil system are manipulated for keeping 60 V output voltage on the 12 Ω load. With distance increasing from 10 cm to 20 cm, transfer efficiency varies from 92.61 to 48.9% for the 2-coil system, and from 92.89 to 84.26% for the 3-coil system, effectively proving the efficiency improvement. The experiment and simulation results prove the effectiveness of the proposed method. Full article
(This article belongs to the Special Issue Wireless Power Transfer 2018)
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Open AccessFeature PaperArticle Solar Cell Capacitance Determination Based on an RLC Resonant Circuit
Energies 2018, 11(3), 672; https://doi.org/10.3390/en11030672
Received: 14 February 2018 / Revised: 11 March 2018 / Accepted: 13 March 2018 / Published: 16 March 2018
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Abstract
The capacitance is one of the key dynamic parameters of solar cells, which can provide essential information regarding the quality and health state of the cell. However, the measurement of this parameter is not a trivial task, as it typically requires high accuracy
[...] Read more.
The capacitance is one of the key dynamic parameters of solar cells, which can provide essential information regarding the quality and health state of the cell. However, the measurement of this parameter is not a trivial task, as it typically requires high accuracy instruments using, e.g., electrical impedance spectroscopy (IS). This paper introduces a simple and effective method to determine the electric capacitance of the solar cells. An RLC (Resistor Inductance Capacitor) circuit is formed by using an inductor as a load for the solar cell. The capacitance of the solar cell is found by measuring the frequency of the damped oscillation that occurs at the moment of connecting the inductor to the solar cell. The study is performed through simulation based on National Instruments (NI) Multisim application as SPICE simulation software and through experimental capacitance measurements of a monocrystalline silicon commercial solar cell and a photovoltaic panel using the proposed method. The results were validated using impedance spectroscopy. The differences between the capacitance values obtained by the two methods are of 1% for the solar cells and of 9.6% for the PV panel. The irradiance level effect upon the solar cell capacitance was studied obtaining an increase in the capacitance in function of the irradiance. By connecting different inductors to the solar cell, the frequency effect upon the solar cell capacitance was studied noticing a very small decrease in the capacitance with the frequency. Additionally, the temperature effect over the solar cell capacitance was studied achieving an increase in capacitance with temperature. Full article
(This article belongs to the Special Issue PV System Design and Performance)
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Open AccessArticle Numerical Study on Heat Transfer to an Arc Absorber Designed for a Waste Heat Recovery System around a Cement Kiln
Energies 2018, 11(3), 671; https://doi.org/10.3390/en11030671
Received: 23 January 2018 / Revised: 14 March 2018 / Accepted: 14 March 2018 / Published: 16 March 2018
Cited by 2 | Viewed by 820 | PDF Full-text (5169 KB) | HTML Full-text | XML Full-text
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A numerical study on combined free convection, forced convection, and radiation heat transfers from an industrial isothermal rotating cylinder (cement kiln) is carried out in this work. The investigation is done by the study of two-dimensional (2D) incompressible turbulent flow around the kiln
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A numerical study on combined free convection, forced convection, and radiation heat transfers from an industrial isothermal rotating cylinder (cement kiln) is carried out in this work. The investigation is done by the study of two-dimensional (2D) incompressible turbulent flow around the kiln under steady- and unsteady-state solutions. The results of this study show that the average Reynolds and Rayleigh numbers around the cylindrical kiln are 647,812.1 and 1.75986 × 1011, respectively. A heat absorber is specifically designed around the kiln, according to the available space around the kiln, in a sample cement factory. The study investigates the effect of an added absorber on the heat transfer features, for both constant heat flux and constant temperature, on the kiln. The temperature distribution along the absorber circumference is obtained for designing an efficient thermoelectric waste heat recovery system as a future study. It is observed that the contribution of the radiative heat transfer is significant in the total heat transferred from the kiln to the absorber. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
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Open AccessArticle Comparison of the Net Work Output between Stirling and Ericsson Cycles
Energies 2018, 11(3), 670; https://doi.org/10.3390/en11030670
Received: 22 February 2018 / Revised: 13 March 2018 / Accepted: 14 March 2018 / Published: 16 March 2018
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Abstract
In this paper, we compare Stirling and Ericsson cycles to determine which engine produces greater net work output for various situations. Both cycles are for external heat engines that utilize regenerators, where the difference is the nature of the regeneration process, which is
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In this paper, we compare Stirling and Ericsson cycles to determine which engine produces greater net work output for various situations. Both cycles are for external heat engines that utilize regenerators, where the difference is the nature of the regeneration process, which is constant volume for Stirling and constant pressure for Ericsson. This difference alters the performance characteristics of the two engines drastically, and our comparison reveals which one produces greater net work output based on the thermodynamic parameters. The net work output equations are derived and analysed for three different scenarios: (i) equal mass and temperature limits; (ii) equal mass and pressure or volume; and (iii) equal temperature and pressure or volume limits. The comparison is performed by calculating when both cycles produce equal net work output and then analysing which one produces greater net work output based on how the parameters are varied. In general, the results demonstrate that Stirling engines produce more net work output at higher pressures and lower volumes, and Ericsson engines produce more net work output at lower pressures and higher volumes. For certain scenarios, threshold values are calculated to illustrate precisely when one cycle produces more net work output than the other. This paper can be used to inform the design of the engines and to determine when a Stirling or Ericsson engine should be selected for a particular application. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
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Open AccessFeature PaperArticle Comparative Study of Energy Performance between Chip and Inlet Temperature-Aware Workload Allocation in Air-Cooled Data Center
Energies 2018, 11(3), 669; https://doi.org/10.3390/en11030669
Received: 30 January 2018 / Revised: 10 March 2018 / Accepted: 12 March 2018 / Published: 16 March 2018
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Abstract
Improving the energy efficiency of data center has become a research focus in recent years. Previous works commonly adopted the inlet temperature constraint to optimize the thermal environment in the data center. However, the inlet temperature-aware method cannot prevent the servers from over-cooling.
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Improving the energy efficiency of data center has become a research focus in recent years. Previous works commonly adopted the inlet temperature constraint to optimize the thermal environment in the data center. However, the inlet temperature-aware method cannot prevent the servers from over-cooling. To cope with this issue, we propose a thermal-aware workload allocation strategy with respect to the chip temperature constraint. In this paper, we conducted a comparative evaluation of the performance between the chip and inlet temperature-aware workload allocation strategies. The workload allocation strategies adopt a POD-based heat recirculation model to characterize the thermal environment in data center. The contribution of the temperature-dependent leakage power to server power consumption is also considered. We adopted a sample data center under constant-flow and variable-flow cooling air supply to evaluate the performance of these two different workload allocation strategies. The comparison results show that the chip temperature-aware workload allocation strategy prevents the servers from over-cooling and significantly improves the energy efficiency of data center, especially for the case of variable-flow cooling air supply. Full article
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Open AccessArticle Availability of Ambient RF Energy in d-Dimensional Wireless Networks
Energies 2018, 11(3), 668; https://doi.org/10.3390/en11030668
Received: 23 February 2018 / Revised: 11 March 2018 / Accepted: 13 March 2018 / Published: 15 March 2018
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Abstract
Radio frequency (RF) enabled energy harvesting has garnered increasingly broad applications in energy-constrained wireless networks. In this context, the actual available energy is constrained by the harvesting threshold of RF harvesters. In this paper, we first propose two new metrics, effective energy harvesting
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Radio frequency (RF) enabled energy harvesting has garnered increasingly broad applications in energy-constrained wireless networks. In this context, the actual available energy is constrained by the harvesting threshold of RF harvesters. In this paper, we first propose two new metrics, effective energy harvesting probability (EEHP) and spatial mean harvestable energy (SMHE) to characterize the availability of ambient RF energy. Assuming that the transmitters are spatially distributed according to a d-dimensional homogeneous Poisson point process (HPPP), we derive the distributions of the ambient RF energy for networks, from the perspective of information receivers, with and without interference control (IC). The corresponding EEHP and SMHE are given in integral forms for the case with IC and inverse Laplace transform form for the case without IC, respectively. For a special case where the dimension to path loss ratio equals 0.5, closed-form exact/approximate expressions for EEHP and SMHE are derived. Analytical results are validated by Monte Carlo simulations. Numerical results with distinct network parameters indicate that the harvesting threshold always has a significant effect on the EEHP, while the impact on SMHE can be ignored as the transmitter density increases. The general unified framework considered in this paper expands the applicability of the derived results to arbitrary dimensional networks. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Building Automation and Control Systems and Electrical Distribution Grids: A Study on the Effects of Loads Control Logics on Power Losses and Peaks
Energies 2018, 11(3), 667; https://doi.org/10.3390/en11030667
Received: 12 February 2018 / Revised: 13 March 2018 / Accepted: 13 March 2018 / Published: 15 March 2018
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Abstract
Growing home comfort is causing increasing energy consumption in residential buildings and a consequent stress in urban medium and low voltage distribution networks. Therefore, distribution system operators are obliged to manage problems related to the reliability of the electricity system and, above all,
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Growing home comfort is causing increasing energy consumption in residential buildings and a consequent stress in urban medium and low voltage distribution networks. Therefore, distribution system operators are obliged to manage problems related to the reliability of the electricity system and, above all, they must consider investments for enhancing the electrical infrastructure. The purpose of this paper is to assess how the reduction of building electricity consumption and the modification of the building load profile, due to load automation, combined with suitable load control programs, can improve network reliability and distribution efficiency. This paper proposes an extensive study on this issue, considering various operating scenarios with four load control programs with different purposes, the presence/absence of local generation connected to the buildings and different external thermal conditions. The study also highlights how different climatic conditions can influence the effects of the load control logics. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Research on Optimal Wind Power Penetration Ratio and the Effects of a Wind-Thermal-Bundled System under the Constraint of Rotor Angle Transient Stability
Energies 2018, 11(3), 666; https://doi.org/10.3390/en11030666
Received: 12 February 2018 / Revised: 8 March 2018 / Accepted: 11 March 2018 / Published: 15 March 2018
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Abstract
Large-scale wind-thermal-bundled power that is transmitted by mixed ultra-high voltage direct current (UHVDC)/ultra-high voltage alternating current (UHVAC) systems has become crucial for large-scale wind farms in China. Equations describing the electromagnetic power characteristics under short circuits for UHVAC lines and UHVDC blocks are
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Large-scale wind-thermal-bundled power that is transmitted by mixed ultra-high voltage direct current (UHVDC)/ultra-high voltage alternating current (UHVAC) systems has become crucial for large-scale wind farms in China. Equations describing the electromagnetic power characteristics under short circuits for UHVAC lines and UHVDC blocks are derived based on an analysis of the external characteristics of a doubly fed wind farm and UHVDC systems. The effect of wind power penetration ratio on rotor angle transient stability is analysed, and the optimal wind power penetration ratio under the constraint of rotor angle transient stability is determined. The effects of system parameters, such as the UHVDC transmission capacity and the reactance of UHVAC lines on the optimal wind power penetration ratio are discussed. The trend of rotor angle stability varies from a monotonic deterioration to concave, and the optimal wind power penetration ratio increases from 0 to 30% under an UHVDC block when the reactance of UHVAC lines increases from 0.005 to 0.02. The optimal wind power penetration ratio under a short circuit increases from 40% to 60% when the reactance of UHVAC lines decreases from 0.02 to 0.006 and decreases from 40% to 30% when the capacity of UHVDC decreases from 3200 MW to 1600 MW. The analysis is verified by simulating an actual system in China’s Northwest Power Grid. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle A New Analytical Wake Model for Yawed Wind Turbines
Energies 2018, 11(3), 665; https://doi.org/10.3390/en11030665
Received: 26 January 2018 / Revised: 28 February 2018 / Accepted: 13 March 2018 / Published: 15 March 2018
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Abstract
A new analytical wake model for wind turbines, considering ambient turbulence intensity, thrust coefficient and yaw angle effects, is proposed from numerical and analytical studies. First, eight simulations by the Reynolds Stress Model are conducted for different thrust coefficients, yaw angles and ambient
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A new analytical wake model for wind turbines, considering ambient turbulence intensity, thrust coefficient and yaw angle effects, is proposed from numerical and analytical studies. First, eight simulations by the Reynolds Stress Model are conducted for different thrust coefficients, yaw angles and ambient turbulence intensities. The wake deflection, mean velocity and turbulence intensity in the wakes are systematically investigated. A new wake deflection model is then proposed to analytically predict the wake center trajectory in the yawed condition. Finally, the effects of yaw angle are incorporated in the Gaussian-based wake model. The wake deflection, velocity deficit and added turbulence intensity in the wake predicted by the proposed model show good agreement with the numerical results. The model parameters are determined as the function of ambient turbulence intensity and thrust coefficient, which enables the model to have good applicability under various conditions. Full article
(This article belongs to the collection Wind Turbines)
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Open AccessReview Algal Biomass from Wastewater and Flue Gases as a Source of Bioenergy
Energies 2018, 11(3), 664; https://doi.org/10.3390/en11030664
Received: 17 November 2017 / Revised: 12 March 2018 / Accepted: 14 March 2018 / Published: 15 March 2018
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Abstract
Algae are without doubt the most productive photosynthetic organisms on Earth; they are highly efficient in converting CO2 and nutrients into biomass. These abilities can be exploited by culturing microalgae from wastewater and flue gases for effective wastewater reclamation. Algae are known
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Algae are without doubt the most productive photosynthetic organisms on Earth; they are highly efficient in converting CO2 and nutrients into biomass. These abilities can be exploited by culturing microalgae from wastewater and flue gases for effective wastewater reclamation. Algae are known to remove nitrogen and phosphorus as well as several organic contaminants including pharmaceuticals from wastewater. Biomass production can even be enhanced by the addition of CO2 originating from flue gases. The algal biomass can then be used as a raw material to produce bioenergy; depending on its composition, various types of biofuels such as biodiesel, biogas, bioethanol, biobutanol or biohydrogen can be obtained. However, algal biomass generated in wastewater and flue gases also contains contaminants which, if not degraded, will end up in the ashes. In this review, the current knowledge on algal biomass production in wastewater and flue gases is summarized; special focus is given to the algal capacity to remove contaminants from wastewater and flue gases, and the consequences when converting this biomass into different types of biofuels. Full article
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Open AccessArticle A New Exact Mathematical Approach for Studying Bifurcation in DCM Operated dc-dc Switching Converters
Energies 2018, 11(3), 663; https://doi.org/10.3390/en11030663
Received: 31 January 2018 / Revised: 27 February 2018 / Accepted: 13 March 2018 / Published: 15 March 2018
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Abstract
A bifurcation study for dc-dc converters operated in DCM is performed using an accurate method. When applying classical techniques significant difficulties are encountered in the calculations. For example, using the averaging method the validity of the result is limited to half the switching
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A bifurcation study for dc-dc converters operated in DCM is performed using an accurate method. When applying classical techniques significant difficulties are encountered in the calculations. For example, using the averaging method the validity of the result is limited to half the switching frequency and higher order effects are neglected Another approach is to perform a Taylor expansion of the state transition matrices. However, this is somehow also an averaging but the fact that the Taylor series is truncated leads to unacceptable inaccuracy. A new mathematical technique for discontinuous conduction mode (DCM) analysis of dc-dc switching converters is proposed in order to predict bifurcation and chaos. The proposed technique is based on exact calculation of the state transition matrices and of the Jacobian thus providing higher accuracy of the results compared to other previously reported approaches. Beside the fact the new technique allows for exact diagnosis of instability, it is also highly general, in the sense that it can be applied to any dc-dc DCM operated converter employing any type of control. The good agreement between theoretical, simulation and experimental results, with an error lower than 0.94%, confirms the validity of the proposed method. Full article
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Open AccessFeature PaperArticle On-Line Detection of Coil Inter-Turn Short Circuit Faults in Dual-Redundancy Permanent Magnet Synchronous Motors
Energies 2018, 11(3), 662; https://doi.org/10.3390/en11030662
Received: 8 February 2018 / Revised: 11 March 2018 / Accepted: 12 March 2018 / Published: 15 March 2018
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Abstract
In the aerospace and military fields, with high reliability requirements, the dual-redundancy permanent magnet synchronous motor (DRPMSM) with weak thermal coupling and no electromagnetic coupling is needed. A common fault in the DRPMSM is the inter-turn short circuit fault (ISCF). However, research on
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In the aerospace and military fields, with high reliability requirements, the dual-redundancy permanent magnet synchronous motor (DRPMSM) with weak thermal coupling and no electromagnetic coupling is needed. A common fault in the DRPMSM is the inter-turn short circuit fault (ISCF). However, research on how to diagnose ISCF and the set of faulty windings in the DRPMSM is lacking. In this paper, the structure of the DRPMSM is analyzed and mathematical models of the motor under normal and faulty conditions are established. Then an on-line ISCF detection scheme, which depends on the running modes of the DRPMSM and the average values for the difference of the d-axis voltages between two sets of windings in the latest 20 sampling periods, is proposed. The main contributions of this paper are to analyze the calculation for the inductance of each part of the stator windings and propose the on-line diagnosis method of the ISCF under various operating conditions. The simulation and experimental results show that the proposed method can quickly and effectively diagnose ISCF and determine the set of faulty windings of the DRPMSM. Full article
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Open AccessArticle Visual Investigation of the Occurrence Characteristics of Multi-Type Formation Water in a Fracture–Cavity Carbonate Gas Reservoir
Energies 2018, 11(3), 661; https://doi.org/10.3390/en11030661
Received: 23 February 2018 / Revised: 12 March 2018 / Accepted: 14 March 2018 / Published: 15 March 2018
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Abstract
It is difficult to investigate the formation process and occurrence states of water in multi-type reservoirs, due to the strong heterogeneity and complex microstructure of the fracture–cavity carbonate gas reservoirs. To date, there is no systematic study on the occurrence characteristics of multi-type
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It is difficult to investigate the formation process and occurrence states of water in multi-type reservoirs, due to the strong heterogeneity and complex microstructure of the fracture–cavity carbonate gas reservoirs. To date, there is no systematic study on the occurrence characteristics of multi-type formation water, especially through visual observation experiments. In this paper, a new creation method for visual micromodels based on CT scan images and microelectronic photolithography techniques was described. Subsequently, a gas–drive–water visual experiment was conducted to intuitively study the formation mechanism and the occurrence states of formation water. Then, the ImageJ gray analysis method was utilized to quantitatively investigate the gas-water saturation and the proportion of residual water film. Finally, the occurrence characteristics of formation water and its effects on gas seepage flow were comprehensively analyzed. Visual experimental results showed that: the migration processes of natural gas in different types of reservoirs are different; the water in multiple media consists of native movable water and residual water, and residual water is composed of secondary movable water and irreducible water; the residual water mainly occurs in different locations of different reservoirs with the forms of “water film”, “water mass”, “water column” and “water droplets”; the main influencing factors are capillary force, surface tension, displacement pressure and channel connectivity. Quantitative results reflect that the saturation of movable water and residual water are the parameters related directly to reservoir physical properties, pore structure and displacement pressure—the smaller the size of flow channel, the larger the space occupied by water film; the thickness proportion of water film is increasing exponentially with the channel size; the thickness proportion of water film decreases as the increase of displacement pressure; the thickness proportion of water film is essentially constant when the displacement pressure increases to a certain extent. The conducted visual investigation not only improves our intuitive understanding of the occurrence characteristics of formation water, but also provides a theoretical basis for the efficient development of fracture-cavity gas reservoirs. Full article
(This article belongs to the Section Energy Sources)
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Open AccessArticle Multi-Model Prediction for Demand Forecast in Water Distribution Networks
Energies 2018, 11(3), 660; https://doi.org/10.3390/en11030660
Received: 24 February 2018 / Revised: 11 March 2018 / Accepted: 13 March 2018 / Published: 15 March 2018
Cited by 1 | Viewed by 863 | PDF Full-text (1953 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
This paper presents a multi-model predictor called Qualitative Multi-Model Predictor Plus (QMMP+) for demand forecast in water distribution networks. QMMP+ is based on the decomposition of the quantitative and qualitative information of the time-series. The quantitative component (i.e., the daily consumption prediction) is
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This paper presents a multi-model predictor called Qualitative Multi-Model Predictor Plus (QMMP+) for demand forecast in water distribution networks. QMMP+ is based on the decomposition of the quantitative and qualitative information of the time-series. The quantitative component (i.e., the daily consumption prediction) is forecasted and the pattern mode estimated using a Nearest Neighbor (NN) classifier and a Calendar. The patterns are updated via a simple Moving Average scheme. The NN classifier and the Calendar are executed simultaneously every period and the most suited model for prediction is selected using a probabilistic approach. The proposed solution for water demand forecast is compared against Radial Basis Function Artificial Neural Networks (RBF-ANN), the statistical Autoregressive Integrated Moving Average (ARIMA), and Double Seasonal Holt-Winters (DSHW) approaches, providing the best results when applied to real demand of the Barcelona Water Distribution Network. QMMP+ has demonstrated that the special modelling treatment of water consumption patterns improves the forecasting accuracy. Full article
(This article belongs to the Special Issue Smart Water Networks in Urban Environments)
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