Records Added in February 2019
Records added in February 2019
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Showing records 51 to 75 of 179. [First] Page: 1 2 3 4 5 6 7 Last
A Flexible Ramping Capacity Model for Generation Scheduling with High Levels of Wind Energy Penetration
Hungyu Kwon, Jong-Keun Park, Dam Kim, Jihyun Yi, Hyeongon Park
February 27, 2019 (v1)
Keywords: demand curve, flexible ramping capacity, renewable generation, uncertainty, variability
The penetration level of renewable generation has increased significantly in recent years, which has led to operational concerns associated with the system ramping capability. Here, we propose the flexible ramping capacity (FRC) model, which considers the practical ramping capability of generation resources as well as the uncertainty in net load. The FRC model also incorporates the demand curve of the ramping capacity, which represents the hourly economic value of the ramping capacity. The model is formulated mathematically using ramp constraints, which are incorporated into unit commitment (UC) and economic dispatch (ED) processes. Simulations are carried out using a 10-unit system to compare the FRC model with conventional methods. We show that the FRC method can improve reliability and reduce expected operating costs. The simulation results also show that, by using the FRC model, system reliability can be satisfied at high wind power generation levels while achieving economic effici... [more]
A Novel Approach for Microgrid Protection Based upon Combined ANFIS and Hilbert Space-Based Power Setting
Ali Hadi Abdulwahid, Shaorong Wang
February 27, 2019 (v1)
Keywords: adaptive network-based fuzzy inference system (ANFIS), Hilbert space-based power (HSBP), microgrid protection, total harmonic distortion (THD)
Nowadays, the use of distributed generation (DG) has increased because of benefits such as increased reliability, reduced losses, improvement in the line capacity, and less environmental pollution. The protection of microgrids, which consist of generation sources, is one of the most crucial concerns of basic distribution operators. One of the key issues in this field is the protection of microgrids against permanent and temporary failures by improving the safety and reliability of the network. The traditional method has a number of disadvantages. The reliability and stability of a power system in a microgrid depend to a great extent on the efficiency of the protection scheme. The application of Artificial Intelligence approaches was introduced recently in the protection of distribution networks. The fault detection method depends on differential relay based on Hilbert Space-Based Power (HSBP) theory to achieve fastest primary protection. It is backed up by a total harmonic distortion (... [more]
A Parallel Probabilistic Load Flow Method Considering Nodal Correlations
Jun Liu, Xudong Hao, Peifen Cheng, Wanliang Fang, Shuanbao Niu
February 27, 2019 (v1)
Keywords: Correlation Latin hypercube sampling Monte Carlo Simulation (CLMCS), correlation matrix, cumulants, distributed generation (DG), parallel computing, probabilistic load flow (PLF)
With the introduction of more and more random factors in power systems, probabilistic load flow (PLF) has become one of the most important tasks for power system planning and operation. Cumulants-based PLF is an effective algorithm to calculate PLF in an analytical way, however, the correlations among the nodal injections to the system level have rarely been studied. A novel parallel cumulants-based PLF method considering nodal correlations is proposed in this paper, which is able to deal with the correlations among all system nodes, and avoid the Jacobian matrix inversion in the traditional cumulants-based PLF as well. In addition, parallel computing is introduced to improve the efficiency of the numerical calculations. The accuracy of the proposed method is validated by numerical tests on the standard IEEE-14 system, comparing with the results from Correlation Latin hypercube sampling Monte Carlo Simulation (CLMCS) method. And the efficiency and parallel performance is proven by the... [more]
The Impact of Renewable Energy Policies on the Adoption of Anaerobic Digesters with Farm-Fed Wastes in Great Britain
Baboo Lesh Gowreesunker, Savvas A. Tassou
February 27, 2019 (v1)
Subject: Energy Policy
Keywords: anaerobic digesters (AD), animal farms, biogas boilers, combined heat and power (CHP), UK renewable energy incentives
This paper explores the effects of the feed-in tariff (FiT) and renewable heat incentive (RHI) schemes on the adoption of anaerobic digesters (AD), and the potential energy generation from farm-fed wastes in Great Britain. This paper adopts a linear programming model, developed in the International Energy Agency (IEA) TIMES platform, aiming to quantify the degree of adoption of AD and the type of energy generation technologies that can be driven by digester biogas to reduce farm energy costs. The results show that the adoption of AD is cost-beneficial for all farms, but different rates of the FiT and RHI schemes will influence the competitiveness between the implementation of combined heat and power (CHP) systems and the utilisation of biogas to only generate heat. The choice of technology is further dependent on the electricity/heat use ratio of the farms and the energy content of the feedstock. The results show that pig farms will more readily adopt CHP, because of its relatively hig... [more]
Development of Seismic Demand for Chang-Bin Offshore Wind Farm in Taiwan Strait
Yu-Kai Wang, Juin-Fu Chai, Yu-Wen Chang, Ti-Ying Huang, Yu-Shu Kuo
February 27, 2019 (v1)
Subject: Other
Keywords: design earthquake, offshore wind, response spectrum, seismic hazard analysis, supporting structures
Taiwan is located on the Pacific seismic belt, and the soil conditions of Taiwan’s offshore wind farms are softer than those in Europe. To ensure safety and stability of the offshore wind turbine supporting structures, it is important to assess the offshore wind farms seismic forces reasonably. In this paper, the relevant seismic and geological data are obtained for Chang-Bin offshore wind farm in Taiwan Strait, the probabilistic seismic hazard analysis (PSHA) is carried out, and the first uniform hazard response spectrum for Chang-Bin offshore wind farm is achieved. Compared with existing design response spectrum in the local regulation, this site-specific seismic hazard analysis has influence on the seismic force considered in the design of supporting structures and therefore affects the cost of the supporting structures. The results show that a site-specific seismic hazard analysis is required for high seismic area. The paper highlights the importance of seismic hazard analysis to a... [more]
Shear Resistance Properties of Modified Nano-SiO₂/AA/AM Copolymer Oil Displacement Agent
Nanjun Lai, Xin Guo, Ning Zhou, Qian Xu
February 27, 2019 (v1)
Subject: Materials
Keywords: enhanced oil recovery, modification degrees, rheological property, shear resistance, the modified nano-SiO2/AA/AM copolymer
To address the problem regarding poor shear resistance of commonly employed polymers for oil displacement, modified nano-SiO₂/AA/AM copolymer (HPMNS) oil displacement agents were synthesized using acrylic acid (AA), acrylamide (AM), and modified nano-SiO₂ of different modification degrees as raw materials. HPMNS was characterized by means of infrared spectroscopy (IR), nuclear magnetic resonance (¹H-NMR, 13C-NMR), dynamic/static light scattering, and scanning electron microscope. A comparative study of the shear resistance properties for partially hydrolyzed polyacrylamide (HPAM) and HPMNS was conducted. Compared to HPAM, the introduced hyperbranched structure endowed HPMNS with good shear resistance, which was quantified from the viscosity retention ratio of the polymer solutions. From the perspective of rheological property, HPMNS also showed great shear stability after shearing by a Mixing Speed Governor and porous media shear model. Furthermore, with a higher degree of modification... [more]
Design and Output Performance Model of Turbodrill Blade Used in a Slim Borehole
Yu Wang, Bairu Xia, Zhiqiao Wang, Liguang Wang, Qin Zhou
February 27, 2019 (v1)
Keywords: granite section, multistage simulation models, output performances prediction, slim borehole, turbodrill
Small-diameter turbodrills have great potential for use in slim boreholes because of their lower cost and higher efficiency when used in geothermal energy and other underground resource applications. Multistage hydraulic components consisting of stators and rotors are key aspects of turbodrills. This study aimed to develop a suitable blade that can be used under high temperature in granite formations. First, prediction models for single- and multi-stage blades were established based on Bernoulli’s Equation. The design requirement of the blade for high-temperature geothermal drilling in granite was proposed. A Φ89 blade was developed based on the dimensionless parameter method and Bezier curve; the parameters of the blade, including its radial size, symotric parameters, and blade profiles, were input into ANASYS and CFX to establish a calculation model of the single-stage blade. The optimization of the blade structure of the small-diameter turbodrill enabled a multistage turbodrill mode... [more]
Experimental and Simulation Studies of Strength and Fracture Behaviors of Wind Turbine Bearing Steel Processed by High Pressure Torsion
Ning Wang, Luis V. Wilches Peña, Ling Wang, B. G. Mellor, Yi Huang
February 27, 2019 (v1)
Subject: Materials
Keywords: high pressure torsion (HPT), mechanical properties, microstructure, white etching area (WEA)
White structure flaking (WSF) has been found to be one of the failure modes in bearing steels under rolling contacts through the formation of cracks associated with a microstructural change called white etching area (WEA). In the present research, the effects of the high-pressure torsion (HPT) process on the microstructure and mechanical properties of an AISI 52100 alloy are studied. An annealed AISI 52100 was subjected to high-pressure torsion at room temperature under a pressure of up to ~6 GPa for up to three turns. Finite-element modeling (FEM) was used to simulate the process under high-pressure torsion and quasi-constrained conditions to reveal the material property changes occurring in HPT. Scanning electron microscopy and microhardness testing after processing were used to investigate the microstructural and mechanical property evolution of the steel. Strain induced microstructural transformations occur and affect the mechanical properties in a similar way to the well-known whi... [more]
Assessment of Renewable Sources for the Energy Consumption in Malta in the Mediterranean Sea
Vincenzo Franzitta, Domenico Curto, Daniele Milone, Davide Rao
February 27, 2019 (v1)
Subject: Energy Policy
Keywords: Malta, Mediterranean Sea, point absorber, Renewable and Sustainable Energy, Wave Energy, Wave Energy Converter (WEC)
The main purpose of this paper is to analyze the energy production in the Maltese islands, focusing on the employment of renewable energies in order to increase their energy independence. The main renewable source here proposed is wave energy: thanks to a strategic position, Malta will be able to produce electrical energy using an innovative type of Wave Energy Converter (WEC) based on the prototype of a linear generator realized by University of Palermo. The use of this new technology will be able to cut down the electrical energy production from traditional power plants and, consequently, the greenhouse gas emissions (GHG). Wave energy source and off-shore photovoltaic (PV) technology are here proposed. Particularly, the installation of 12 wave farms, for a total installed capacity of 86 MW, will generate about 9.5% of Malta’s energy requirement in 2025, while the installation of 9.6 MW of off-shore PV will generate about 0.73%.
Predictive Modeling of a Buoyancy-Operated Cooling Tower under Unsaturated Conditions: Adjoint Sensitivity Model and Optimal Best-Estimate Results with Reduced Predicted Uncertainties
Federico Di Rocco, Dan Gabriel Cacuci
February 27, 2019 (v1)
Keywords: adjoint cooling tower model solution verification, adjoint sensitivity analysis, best-estimate predictions, cooling tower, data assimilation, model calibration, reduced predicted uncertainties
Nuclear and other large-scale energy-producing plants must include systems that guarantee the safe discharge of residual heat from the industrial process into the atmosphere. This function is usually performed by one or several cooling towers. The amount of heat released by a cooling tower into the external environment can be quantified by using a numerical simulation model of the physical processes occurring in the respective tower, augmented by experimentally measured data that accounts for external conditions such as outlet air temperature, outlet water temperature, and outlet air relative humidity. The model’s responses of interest depend on many model parameters including correlations, boundary conditions, and material properties. Changes in these model parameters induce changes in the computed quantities of interest (called “model responses”), which are quantified by the sensitivities (i.e., functional derivatives) of the model responses with respect to the model parameters. Thes... [more]
Effect of Wind Turbine Blade Rotation on Triggering Lightning: An Experimental Study
Xishan Wen, Lu Qu, Yu Wang, Xiaoyue Chen, Lei Lan, Tianjun Si, Jianwei Xu
February 27, 2019 (v1)
Subject: Other
Keywords: blade, rotation, scaled test, up-and-down method, wind turbine
Compared with other lightning targets on the ground, the most notable feature of a wind turbine is that the blades are usually in a rotating state when lightning strikes. To study the mechanism of blade rotation influencing wind turbine on triggering lightning, lightning discharge comparison tests based on a typical 2-MW 1:30-scaled wind turbine model with an arching high-voltage electrode were conducted under different modes of stationary and rotating blades. Negative polarity switching impulses of 250/2500 μs were applied to the arching electrode. The up-and-down method was adopted for 50% discharge voltage and the discharge process was observed. The experimental results showed that under the condition of a 4 m gap, the breakdown voltage decreases and the connection point of the leaders approaches the high-voltage electrode with increasing blade speed, indicating that the wind turbine’s blade rotation enhances the triggering of lightning. The analysis showed that the blade rotation c... [more]
A Privacy-Preserving Distributed Optimal Scheduling for Interconnected Microgrids
Nian Liu, Cheng Wang, Minyang Cheng, Jie Wang
February 27, 2019 (v1)
Keywords: cybersecurity, distributed optimization, microgrid, optimal scheduling
With the development of microgrids (MGs), interconnected operation of multiple MGs is becoming a promising strategy for the smart grid. In this paper, a privacy-preserving distributed optimal scheduling method is proposed for the interconnected microgrids (IMG) with a battery energy storage system (BESS) and renewable energy resources (RESs). The optimal scheduling problem is modeled to minimize the coalitional operation cost of the IMG, including the fuel cost of conventional distributed generators and the life loss cost of BESSs. By using the framework of the alternating direction method of multipliers (ADMM), a distributed optimal scheduling model and an iteration solution algorithm for the IMG is introduced; only the expected exchanging power (EEP) of each MG is required during the iterations. Furthermore, a privacy-preserving strategy for the sharing of the EEP among MGs is designed to work with the mechanism of the distributed algorithm. According to the security analysis, the EE... [more]
The Desalination Process Driven by Wave Energy: A Challenge for the Future
Vincenzo Franzitta, Domenico Curto, Daniele Milone, Alessia Viola
February 27, 2019 (v1)
Subject: Energy Policy
Keywords: desalination, Renewable and Sustainable Energy, Water, wave
The correlation between water and energy is currently the focus of several investigations. In particular, desalination is a technological process characterized by high energy consumption; nevertheless, desalination represents the only practicable solution in several areas, where the availability of fresh water is limited but brackish water or seawater are present. These natural resources (energy and water) are essential for each other; energy system conversion needs water, and electrical energy is necessary for water treatment or transport. Several interesting aspects include the study of saline desalination as an answer to freshwater needs and the application of renewable energy (RE) devices to satisfy electrical energy requirement for the desalination process. A merge between renewable energy and desalination is beneficial in that it is a sustainable and challenging option for the future. This work investigates the possibility of using renewable energy sources to supply the desalinat... [more]
One-Dimensional TiO₂ Nanostructured Photoanodes: From Dye-Sensitised Solar Cells to Perovskite Solar Cells
Jung-Ho Yun, Lianzhou Wang, Rose Amal, Yun Hau Ng
February 27, 2019 (v1)
Subject: Materials
Keywords: charge transport, dye-sensitised solar cells (DSCs), light harvesting efficiency, one-dimensional (1D) TiO2 nanostructure, perovskite solar cells (PSCs), photoanode
This review presents one dimensional (1D) TiO₂ nanostructured photoanodes for next generation solar cells such as dye-sensitised solar cells (DSCs) and perovskite solar cells (PSCs). Due to the unique morphological properties, 1D TiO₂ nanostructures can act as express electron channels as well as light scattering layer, leading to improved charge transport properties, such as charge separation, electron injection, and electron lifetime, and light harvesting efficiency. As 1D TiO₂ nanostructures are applied to solar cells, 1D TiO₂ nanostructures should be further modified to overcome some drawbacks. In this review, we have described some solutions by introducing various 1D TiO₂ synthetic methods and device fabrication processes for solar cell applications, where we have described some important surface engineering and hierarchical device design strategies that facilitate charge transport and light utilisation in 1D TiO₂ nanostructured photoanode system.
Assessment of the Usability and Accuracy of the Simplified One-Diode Models for Photovoltaic Modules
Vincenzo Franzitta, Aldo Orioli, Alessandra Di Gangi
February 27, 2019 (v1)
Keywords: four-parameter model, I-V characteristics, one-diode equivalent circuit, photovoltaic modules, solar energy, three-parameter model
Models for photovoltaic (PV) cells and panels, based on the diode equivalent circuit, have been widely used because they are effective tools for system design. Many authors have presented simplified one-diode models whose three or four parameters are calculated using the data extracted from the datasheets issued by PV panel manufactures and adopting some simplifying hypotheses and numerical solving techniques. Sometimes it may be difficult to make a choice among so many models. To help researchers and designers working in the area of photovoltaic systems in selecting the model that is fit for purpose, a criterion for rating both the usability and accuracy of simplified one-diode models is proposed in this paper. The paper minutely describes the adopted hypotheses, analytical procedures and operative steps to calculate the parameters of the most famous simplified one-diode equivalent circuits. To test the achievable accuracy of the models, a comparison between the characteristics of som... [more]
Gas Hydrate Growth Kinetics: A Parametric Study
Remi-Erempagamo Tariyemienyo Meindinyo, Thor Martin Svartaas
February 27, 2019 (v1)
Keywords: factors that affect gas hydrate growth rate, mass and heat transfer, methane hydrate growth kinetics, reactor scale-up, stirring rate, temperature, water content
Gas hydrate growth kinetics was studied at a pressure of 90 bars to investigate the effect of temperature, initial water content, stirring rate, and reactor size in stirred semi-batch autoclave reactors. The mixing energy during hydrate growth was estimated by logging the power consumed. The theoretical model by Garcia-Ochoa and Gomez for estimation of the mass transfer parameters in stirred tanks has been used to evaluate the dispersion parameters of the system. The mean bubble size, impeller power input per unit volume, and impeller Reynold’s number/tip velocity were used for analyzing observed trends from the gas hydrate growth data. The growth behavior was analyzed based on the gas consumption and the growth rate per unit initial water content. The results showed that the growth rate strongly depended on the flow pattern in the cell, the gas-liquid mass transfer characteristics, and the mixing efficiency from stirring. Scale-up effects indicate that maintaining the growth rate per... [more]
Comparative Study of Shell and Helically-Coiled Tube Heat Exchangers with Various Dimple Arrangements in Condensers for Odor Control in a Pyrolysis System
Sun-Min Kim, Jun-Ho Jo, Ye-Eun Lee, Yeong-Seok Yoo
February 27, 2019 (v1)
Keywords: condenser, dimple, heat exchanger, heat transfer, odor control, pyrolysis, RANS, shell and tube
This study performed evaluations of the shell and helically-coiled tube heat exchangers with various dimple arrangements, that is, flat, inline, staggered, and bulged, at different Dean numbers (De) and inlet temperatures of a hot channel. Conjugated heat transfer was analyzed to evaluate the heat transfer performance of the exchangers through temperature difference between the inlet and outlet, Nusselt number inside the coiled tube, and pressure drop of the coiled tube by using 3-D Reynolds-averaged Navier⁻Stokes (RANS) equations with shear stress transport turbulence closure. A grid dependency test was performed to determine the optimal number of the grid system. The numerical results were validated using the experimental data, and showed good agreement. The inline and staggered arrangements show the highest temperature differences through all De. The staggered arrangement shows the best heat transfer performance, whereas the inline arrangement shows the second highest performance wi... [more]
Energy Optimization and Fuel Economy Investigation of a Series Hybrid Electric Vehicle Integrated with Diesel/RCCI Engines
Ali Solouk, Mahdi Shahbakhti
February 27, 2019 (v1)
Subject: Other
Keywords: Diesel, emissions, fuel economy, hybrid electric vehicle, low temperature combustion (LTC), model predictive control (MPC), optimal energy management, reactively controlled compression ignition (RCCI), time horizon
Among different types of low temperature combustion (LTC) regimes, eactively controlled compression ignition (RCCI) has received a lot of attention as a promising advanced combustion engine technology with high indicated thermal efficiency and low nitrogen oxides ( NO x ) and particulate matter (PM) emissions. In this study, an RCCI engine for the purpose of fuel economy investigation is incorporated in series hybrid electric vehicle (SHEV) architecture, which allows the engine to run completely in the narrow RCCI mode for common driving cycles. Three different types of energy management control (EMC) strategies are designed and implemented to achieve the best fuel economy. The EMC strategies encompass rule-based control (RBC), offline, and online optimal controllers, including dynamic programing (DP) and model predictive control (MPC), respectively. The simulation results show a 13.1% to 14.2% fuel economy saving by using an RCCI engine over a modern spark ignition (SI) engine i... [more]
Mitigation of the Impact of High Plug-in Electric Vehicle Penetration on Residential Distribution Grid Using Smart Charging Strategies
Chong Cao, Luting Wang, Bo Chen
February 27, 2019 (v1)
Keywords: demand response (DR), GridLAB-D, plug-in electric vehicle (PEV) charging, power distribution system
Vehicle electrification presents a great opportunity to reduce transportation greenhouse gas emissions. The greater use of plug-in electric vehicles (PEVs), however, puts stress on local distribution networks. This paper presents an optimal PEV charging control method integrated with utility demand response (DR) signals to mitigate the impact of PEV charging to several aspects of a grid, including load surge, distribution accumulative voltage deviation, and transformer aging. To build a realistic PEV charging load model, the results of National Household Travel Survey (NHTS) have been analyzed and a stochastic PEV charging model has been defined based on survey results. The residential distribution grid contains 120 houses and is modeled in GridLAB-D. Co-simulation is performed using Matlab and GridLAB-D to enable the optimal control algorithm in Matlab to control PEV charging loads in the residential grid modeled in GridLAB-D. Simulation results demonstrate the effectiveness of the pr... [more]
Inverse Aerodynamic Optimization Considering Impacts of Design Tip Speed Ratio for Variable-Speed Wind Turbines
Zhiqiang Yang, Minghui Yin, Yan Xu, Yun Zou, Zhao Yang Dong, Qian Zhou
February 27, 2019 (v1)
Keywords: aerodynamic optimization, design tip speed ratio (TSR), inverse design, maximum power point tracking (MPPT), variable-speed wind turbine (VSWT)
Because of the slow dynamic behavior of the large-inertia wind turbine rotor, variable-speed wind turbines (VSWTs) are actually unable to keep operating at the design tip speed ratio (TSR) during the maximum power point tracking (MPPT) process. Moreover, it has been pointed out that although a larger design TSR can increase the maximum power coefficient, it also greatly prolongs the MPPT process of VSWTs. Consequently, turbines spend more time operating at the off-design TSRs and the wind energy capture efficiency is decreased. Therefore, in the inverse aerodynamic design of VSWTs, the static aerodynamic performance (i.e., the maximum power coefficient) and the dynamic process of MPPT should be comprehensively modeled for determining an appropriate design TSR. In this paper, based on the inverse design method, an aerodynamic optimization method for VSWTs, fully considering the impacts of the design TSR on the static and dynamic behavior of wind turbines is proposed. In this method, to... [more]
Research on a Household Dual Heat Source Heat Pump Water Heater with Preheater Based on ASPEN PLUS
Xiang Gou, Yang Fu, Imran Ali Shah, Yamei Li, Guoyou Xu, Yue Yang, Enyu Wang, Liansheng Liu, Jinxiang Wu
February 27, 2019 (v1)
Keywords: Aspen Plus, coefficient of performance (COP), dual heat source, heat pump, household water heater, preheater
This article proposes a dual heat source heat pump bathroom unit with preheater which is feasible for a single family. The system effectively integrates the air source heat pump (ASHP) and wastewater source heat pump (WSHP) technologies, and incorporates a preheater to recover shower wastewater heat and thus improve the total coefficient of performance (COP) of the system, and it has no electric auxiliary heating device, which is favorable to improve the security of the system operation. The process simulation software ASPEN PLUS, widely used in the design and optimization of thermodynamic systems, was used to simulate various cases of system use and to analyze the impact of the preheater on the system. The average COP value of a system with preheater is 6.588 and without preheater it is 4.677. Based on the optimization and analysis, under the standard conditions of air at 25 °C, relative humidity of 70%, wastewater at 35 °C, wastewater flow rate of 0.07 kg/s, tap water at 15 °C, and c... [more]
Forecasting the State of Health of Electric Vehicle Batteries to Evaluate the Viability of Car Sharing Practices
Ivana Semanjski, Sidharta Gautama
February 27, 2019 (v1)
Keywords: battery degradation, battery state of health (SoH), car sharing, collaborative economy, driving and charging behavior, electric vehicle (EV), sustainable mobility
Car-sharing practices are introducing electric vehicles (EVs) into their fleet. However, the literature suggests that at this point shared EV systems are failing to reach satisfactory commercial viability. A potential reason for this is the effect of higher vehicle usage, which is characteristic of car sharing, and the implications on the battery’s state of health (SoH). In this paper, we forecast the SoH of two identical EVs being used in different car-sharing practices. For this purpose, we use real life transaction data from charging stations and different EV sensors. The results indicate that insight into users’ driving and charging behavior can provide a valuable point of reference for car-sharing system designers. In particular, the forecasting results show that the moment when an EV battery reaches its theoretical end of life can differ in as much as a quarter of the time when vehicles are shared under different conditions.
Numerical Investigation on the Effect of Cementing Properties on the Thermal and Mechanical Stability of Geothermal Wells
Jongmuk Won, Hyun-Jun Choi, Hyobum Lee, Hangseok Choi
February 27, 2019 (v1)
Subject: Other
Keywords: G-class cement, geothermal well cementing, numerical analysis, thermal conductivity, Young’s modulus
In this paper, a two-dimensional (2-D) Finite Element (FE) analysis of a geothermal well was performed with respect to five different cross-sections corresponding to the design specifications for the geothermal well that is currently constructed in Pohang, South Korea. Among the essential components (such as ground formation, casing, and cementing) of a geothermal well, the thermal and mechanical stability of the cementing component was discussed based on a series of parametric studies with consideration of the thermal conductivity and Young’s modulus of the cementing component. With increasing number of casing layers, the cementing component experiences less stress concentration. In addition, the lower thermal conductivity of the cementing material is advantageous for effectively controlling radial displacement. Consequently, it should be noted in geothermal well cementing construction that long-term strength degradation of the cementing might cause the severe structural instability o... [more]
Experimental Investigation of Crack Extension Patterns in Hydraulic Fracturing with Shale, Sandstone and Granite Cores
Jianming He, Chong Lin, Xiao Li, Xiaole Wan
February 27, 2019 (v1)
Subject: Other
Keywords: anisotropy, crack extension, fracture distribution, heterogeneity, hydraulic fracture
Hydraulic fracturing is an important method of reservoir stimulation in the exploitation of geothermal resources, and conventional and unconventional oil and gas resources. In this article, hydraulic fracturing experiments with shale, sandstone cores (from southern Sichuan Basin), and granite cores (from Inner Mongolia) were conducted to investigate the different hydraulic fracture extension patterns in these three reservoir rocks. The different reactions between reservoir lithology and pump pressure can be reflected by the pump pressure monitoring curves of hydraulic fracture experiments. An X-ray computer tomography (CT) scanner was employed to obtain the spatial distribution of hydraulic fractures in fractured shale, sandstone, and granite cores. From the microscopic and macroscopic observation of hydraulic fractures, different extension patterns of the hydraulic fracture can be analyzed. In fractured sandstone, symmetrical hydraulic fracture morphology could be formed, while some m... [more]
Numerical Study of the Dynamic Response of Heat and Mass Transfer to Operation Mode Switching of a Unitized Regenerative Fuel Cell
Hong Xiao, Hang Guo, Fang Ye, Chongfang Ma
February 27, 2019 (v1)
Keywords: heat transfer, mass transfer, mode switching, transient response, unitized regenerative fuel cells
Knowledge concerning the complicated changes of mass and heat transfer is desired to improve the performance and durability of unitized regenerative fuel cells (URFCs). In this study, a transient, non-isothermal, single-phase, and multi-physics mathematical model for a URFC based on the proton exchange membrane is generated to investigate transient responses in the process of operation mode switching from fuel cell (FC) to electrolysis cell (EC). Various heat generation mechanisms, including Joule heat, reaction heat, and the heat attributed to activation polarizations, have been considered in the transient model coupled with electrochemical reaction and mass transfer in porous electrodes. The polarization curves of the steady-state models are validated by experimental data in the literatures. Numerical results reveal that current density, gas mass fractions, and temperature suddenly change with the sudden change of operating voltage in the mode switching process. The response time of... [more]
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