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Showing records 133 to 157 of 201. [First] Page: 1 3 4 5 6 7 8 9 Last
Dual-Temperature Evaluation of a High-Temperature Insulation System for Liquid-Immersed Transformer
Xiaojing Zhang, Lu Ren, Haichuan Yu, Yang Xu, Qingquan Lei, Xin Li, Baojia Han
September 21, 2018 (v1)
Subject: Materials
Keywords: dual-temperature, liquid-immersed transformer, natural ester, Nomex T910, thermal aging
A high-temperature oil⁻paper insulation system offers an opportunity to improve the overloading capability of distribution transformers facing seasonal load variation. A high-temperature electrical insulation system (EIS) was chosen due to thermal calculation based on a typical loading curve on the China Southern Power Grid. In order to evaluate candidate high-temperature insulation systems, Nomex® T910 (aramid-enhanced cellulose) immersed in FR3 (natural ester) was investigated by a dual-temperature thermal aging test compared with a conventional insulation system, Kraft paper impregnated with mineral oil. Throughout the thermal aging test, mechanical, chemical, and dielectric parameters of both paper and insulating oil were investigated in each aging cycle. The thermal aging results determined that the thermal class of the FR3-T910 insulation system meets the request of overloading transformer needs.
Electro-Insulating Nanofluids Based on Synthetic Ester and TiO₂ or C60 Nanoparticles in Power Transformer
Zbigniew Nadolny, Grzegorz Dombek
September 20, 2018 (v1)
Subject: Materials
Keywords: dielectrics, fullerene, insulation system, nanofluids, power transformer, synthetic ester, thermal properties, titanium dioxide
The article discusses thermal properties of synthetic ester admixed with nanoparticles. The analyzed thermal properties were: thermal conductivity λ, kinematic viscosity υ, density ρ, specific heat cp, and the thermal expansion factor β- all obtained by means of measurements. On the basis of these, the authors calculated the heat transfer factor α, which determines the ability of the liquid to heat transport. The authors used nanoparticles of fullerene C60 and titanium oxide TiO₂. The analysis of the thermal properties was done for the temperatures of 25, 40, 60 and 80 °C. The authors analyzed the impact of nanoparticles C60 and TiO₂ on thermal properties of synthetic ester. They proved that fullerene C60 in principle had no influence on heat transfer factor α of the ester, while titanium oxide TiO₂ had some positive influence on the factor, the value of which increased about 1⁻3%.
Extremely Pure Mg₂FeH₆ as a Negative Electrode for Lithium Batteries
Sergio Brutti, Luca Farina, Francesco Trequattrini, Oriele Palumbo, Priscilla Reale, Laura Silvestri, Stefania Panero, Annalisa Paolone
September 20, 2018 (v1)
Subject: Materials
Keywords: discharge capacity, high temperature hydrogenation, Mg2FeH6, pressure-composition isotherms, reactive ball milling
Nanocrystalline samples of Mg-Fe-H were synthesized by mixing of MgH₂ and Fe in a 2:1 molar ratio by hand grinding (MIX) or by reactive ball milling (RBM) in a high-pressure vial. Hydrogenation procedures were performed at various temperatures in order to promote the full conversion to Mg₂FeH₆. Pure Mg₂FeH₆ was obtained only for the RBM material cycled at 485 °C. This extremely pure Mg₂FeH₆ sample was investigated as an anode for lithium batteries. The reversible electrochemical lithium incorporation and de-incorporation reactions were analyzed in view of thermodynamic evaluations, potentiodynamic cycling with galvanostatic acceleration (PCGA), and ex situ X-ray Diffraction (XRD) tests. The Mg₂FeH₆ phase underwent a conversion reaction; the Mg metal produced in this reaction was alloyed upon further reduction. The back conversion reaction in a lithium cell was here demonstrated for the first time in a stoichiometric extremely pure Mg₂FeH₆ phase: the reversibility of the overall convers... [more]
Extraction of Junction Temperature of SiC MOSFET Module Based on Turn-On dIDS/dt
Delei Huang, Guojun Tan, Chengfei Geng, Jingwei Zhang, Chang Liu
September 20, 2018 (v1)
Subject: Materials
Keywords: junction temperature extraction, silicon carbide, switching transients, thermo-sensitive electrical parameter
In this paper, a method of extracting the junction temperature based on the turn-on current switching rate (dIDS/dt) of silicon carbide (SiC) metal-oxide semiconductor field effect transistors (MOSFETs) is proposed. The temperature dependence of dIDS/dt is analyzed theoretically, and experimentally to show that dIDS/dt increases with the rising junction temperature. In addition, other factors affecting dIDS/dt are also discussed by using the fundamental device physics equations and experiments. The result shows that the increase of the DC-link voltage VDC, the external gate resistance RG-ext, and the decrease of the driving voltage VGG can increase the temperature sensitivity of the dIDS/dt. A PCB (printed circuit board) Rogowski coil measuring circuit based on the fact that the SiC MOSFET chip temperature and dIDS/dt is estimated in a linear way is designed to obtain the junction temperature. The experimental results demonstrate that the proposed junction temperature extracting is eff... [more]
Investigation of Injection Strategy of Branched-Preformed Particle Gel/Polymer/Surfactant for Enhanced Oil Recovery after Polymer Flooding in Heterogeneous Reservoirs
Hong He, Jingyu Fu, Baofeng Hou, Fuqing Yuan, Lanlei Guo, Zongyang Li, Qing You
September 20, 2018 (v1)
Subject: Materials
Keywords: branched-preformed particle gel, enhanced oil recovery, heterogeneous phase combination flooding, heterogeneous reservoirs, injection strategy
The heterogeneous phase combination flooding (HPCF) system which is composed of a branched-preformed particle gel (B-PPG), polymer, and surfactant has been proposed to enhance oil recovery after polymer flooding in heterogeneous reservoirs by mobility control and reducing oil⁻water interfacial tension. However, the high cost of chemicals can make this process economically challenging in an era of low oil prices. Thus, in an era of low oil prices, it is becoming even more essential to optimize the heterogeneous phase combination flooding design. In order to optimize the HPCF process, the injection strategy has been designed such that the incremental oil recovery can be maximized using the corresponding combination of the B-PPG, polymer, and surfactant, thereby ensuring a more economically-viable recovery process. Different HPCF injection strategies including simultaneous injection and alternation injection were investigated by conducting parallel sand pack flooding experiments and large... [more]
ZnS/SiO₂ Passivation Layer for High-Performance of TiO₂/CuInS₂ Quantum Dot Sensitized Solar Cells
Hee-Je Kim, Jin-Ho Bae, Hyunwoong Seo, Masaharu Shiratani, Chandu Venkata Veera Muralee Gopi
September 19, 2018 (v1)
Subject: Materials
Keywords: Charge recombination, Passivation layer, QDSSCs, ZnS/SiO2
Suppressing the charge recombination at the interface of photoanode/electrolyte is the crucial way to improve the quantum dot sensitized solar cells (QDSSCs) performance. In this scenario, ZnS/SiO₂ blocking layer was deposited on TiO₂/CuInS₂ QDs to inhibit the charge recombination at photoanode/electrolyte interface. As a result, the TiO₂/CuInS₂/ZnS/SiO₂ based QDSSCs delivers a power conversion efficiency (η) value of 4.63%, which is much higher than the TiO₂/CuInS₂ (2.15%) and TiO₂/CuInS₂/ZnS (3.23%) based QDSSCs. Impedance spectroscopy and open circuit voltage decay analyses indicate that ZnS/SiO₂ passivation layer on TiO₂/CuInS₂ suppress the charge recombination at the interface of photoanode/electrolyte and enhance the electron lifetime.
Three-Dimensional Numerical Investigation of Coupled Flow-Stress-Damage Failure Process in Heterogeneous Poroelastic Rocks
Shikuo Chen, Chenhui Wei, Tianhong Yang, Wancheng Zhu, Honglei Liu, Pathegama Gamage Ranjith
September 19, 2018 (v1)
Subject: Materials
Keywords: coupled flow-stress-damage model, failure progress, heterogeneous, numerical investigation, permeability evolution
The failure mechanism of heterogeneous rocks (geological materials), especially under hydraulic conditions, is important in geological engineering. The coupled mechanism of flow-stress-damage should be determined for the stability of rock mass engineering under triaxial stress states. Based on poroelasticity and damage theory, a three-dimensional coupled model of the flow-stress-damage failure process is studied, focusing mainly on the coupled characteristics of permeability evolution and damage in nonhomogeneous rocks. The influences of numerous mesoscale mechanical and hydraulic properties, including homogeneity, residual strength coefficient, loading rates, and strength criteria, on the macro mechanical response are analyzed. Results reveal that the stress sensitive factor and damage coefficient are key variables for controlling the progress of permeability evolution, and these can reflect the hydraulic properties under pre-peak and post-peak separately. Moreover, several experiment... [more]
Experimental Study on the Reinforcement Mechanism of Segmented Split Grouting in a Soft Filling Medium
Zhipeng Li, Shucai Li, Haojie Liu, Qingsong Zhang, Yanan Liu
August 28, 2018 (v1)
Subject: Materials
Keywords: model experiment, reinforcement mechanism, rock-soil mechanics, segmented grouting, soft filling medium, split grouting
Subsection split grouting technology can effectively improve the grouting efficiency and homogeneity of grouting in a target reinforcement area. It is therefore necessary to clarify the reinforcement mechanism and characteristics of the soft filling medium under the condition of split grouting. A three-dimensional grouting simulation test of segmented split grouting in a soft filling medium was conducted. The distribution characteristics and thicknesses of the grouting veins were obtained under the condition of segmented grouting. The mechanical mechanism of segmented split grouting reinforcement, based on the distribution characteristics of different grouting veins, was revealed. After grouting, a uniaxial compression test and an indoor permeation test were conducted. Based on the method of the region-weighted average, the corresponding permeability coefficient and the elastic modulus of each splitting-compaction region were obtained. The quantitative relationship between the mechanic... [more]
Preparation and Characterization of Polyaluminum Titanium Silicate and its Performance in the Treatment of Low-Turbidity Water
Lina Liao, Peng Zhang
August 28, 2018 (v1)
Subject: Materials
Keywords: coagulant, low turbidity, polyaluminum titanium silicate chloride, zeta potential
Using conventional coagulant, low turbidity water is difficult to achieve standard. This research uses aluminum chloride, titanium tetrachloride, and sodium silicate as raw materials for the preparation of polyaluminum titanium silicate chloride (PATC). PATC is used to treat low turbidity. The synthetic PATC showed the best coagulating effect in treated water under the following experimental conditions: Reaction temperature of 50 °C, and n(Ti)/n(Al), n(-OH)/n(Ti+Al), and n(Si)/n(Ti+Al) were 0.3, 0.2, and 1.0, respectively. The species distribution and the transformation of PATC showed that the interaction between titanium tetrachloride, sodium silicate, and the hydrolysate of Al influenced the morphology distribution of Al. Temperature and -OH greatly affected the distribution of Alb in PATC. The analysis of infrared spectra and X-ray diffraction indicated that both titanium tetrachloride and sodium silicate had complex chemical reactions with aluminum chloride. Si-O-Ti and Si-O-Al pro... [more]
Deformation and Hydraulic Conductivity of Compacted Clay under Waste Differential Settlement
Sifa Xu, Cuifeng Li, Jizhuang Liu, Mengdan Bian, Weiwei Wei, Hao Zhang, Zhe Wang
August 28, 2018 (v1)
Subject: Materials
Keywords: bentonite-sand mixtures, crack, deformation, differential settlement, geogrid, hydraulic conductivity
Landfill is still the most important process to dispose of municipal solid waste in China, while landfill closure aims for pollution control, security control, and better land reuse. However, uneven settlement of landfill cover system is very likely to cause deformation and cracking. The objective of this paper is to examine the effects of geogrid reinforcement on the deformation behaviour and hydraulic conductivity of the bentonite-sand mixtures that are subjected to differential settlement. The laboratory model tests were performed on bentonite-sand mixtures with and without the inclusion of geogrid reinforcement. By maintaining the type and location of the geogrid within the liner systems as constant, the thickness of the bentonite-sand mixtures is varied. The performation of the liner systems with and without the inclusion of geogrid reinforcement was assessed by using jack to control differential settlement. Un-reinforced bentonite-sand mixtures of 100 mm and 200 mm thickness were... [more]
Technology for the Remediation of Water Pollution: A Review on the Fabrication of Metal Organic Frameworks
Yongning Bian, Nana Xiong, Guocheng Zhu
August 28, 2018 (v1)
Subject: Materials
Keywords: Adsorption, metal organic frameworks, remediation, water pollution
The ineffective control of the release of pollutants into water has led to serious water pollution. Compared with conditions in the past, the polluting components in aquatic environments have become increasingly complex. Some emerging substances have led to a new threat to the safety of water. Therefore, developing cost-effective technologies for the remediation of water pollution is urgently needed. Adsorption has been considered the most effective operational unit in water treatment processes and thus adsorption materials have gained wide attention. Among them, metal organic frameworks (denoted as MOFs) have been rapidly developed in recent years due to their unique physicochemical performance. They are characterized by larger porosity and larger specific surface area, easier pore structure designing, and comfortable structural modification. In many fields such as adsorption, separation, storage, and transportation, MOFs show a better performance than conventional adsorption material... [more]
Effect of Particle Size on Carbon Nanotube Aggregates Behavior in Dilute Phase of a Fluidized Bed
Sung Won Kim
August 28, 2018 (v1)
Subject: Materials
Keywords: aggregates, carbon nanotube, fluidized bed, laser sheet technique, particle size
Fluidized bed reactors have been increasingly applied for mass production of Carbon Nanotube (CNT) using catalytic chemical vapor deposition technology. Effect of particle size (dp = 131 μm and 220 μm) on fluidization characteristics and aggregation behavior of the CNT particles have been determined in a fluidized bed for its design and scale-up. The CNT aggregation properties such as size and shape were measured in the dilute phase of a fluidized bed (0.15 m-ID × 2.6 m high) by the laser sheet technique for the visualization. Two CNT particle beds showed different tendency in variations of the aggregates factors with gas velocity due to differences in factors contributing to the aggregate formation. The CNT particles with a larger mean size presented as relatively larger in the aggregate size than the smaller CNT particles at given gas velocities. The aggregates from the large CNT particles showed a sharp increase in the aspect ratio and rapid decrease in the roundness and the solidit... [more]
Effects of Pulse Interval and Dosing Flux on Cells Varying the Relative Velocity of Micro Droplets and Culture Solution
Zhanwei Wang, Kun Liu, Jiuxin Ning, Shulei Chen, Ming Hao, Dongyang Wang, Qi Mei, Yaoshuai Ba, Dechun Ba
August 28, 2018 (v1)
Subject: Materials
Keywords: cell dosing, convective diffusion, interdiffusion, microdroplet, numerical simulation
Microdroplet dosing to cell on a chip could meet the demand of narrow diffusion distance, controllable pulse dosing and less impact to cells. In this work, we studied the diffusion process of microdroplet cell pulse dosing in the three-layer sandwich structure of PDMS (polydimethylsiloxane)/PCTE (polycarbonate) microporous membrane/PDMS chip. The mathematical model is established to solve the diffusion process and the process of rhodamine transfer to micro-traps is simulated. The rhodamine mass fraction distribution, pressure field and velocity field around the microdroplet and cell surfaces are analyzed for further study of interdiffusion and convective diffusion effect. The cell pulse dosing time and drug delivery efficiency could be controlled by adjusting microdroplet and culture solution velocity without impairing cells at micro-traps. Furthermore, the accuracy and controllability of the cell dosing pulse time and maximum drug mass fraction on cell surfaces are achieved and the dr... [more]
Experimental Study on the Creep Characteristics of Coal Measures Sandstone under Seepage Action
Ziheng Sha, Hai Pu, Ming Li, Lili Cao, Ding Liu, Hongyang Ni, Jingfeng Lu
August 28, 2018 (v1)
Subject: Materials
Keywords: coal measures sandstone, creep characteristics, microscopic morphology, seepage pressure, seepage-creep
The seepage action of underground water accelerates the deformation of roadway surrounding rock in deep mines. Therefore, the study of creep characteristics of surrounding rock under seepage action is the basis for the stability control of roadway surrounding rock in deep water-rich areas. In this paper, a seepage-creep coupling test system for complete rock samples was established. Combined with a scanning electron microscopy (SEM) test system, the seepage-creep law of coal measures sandstone and the damage mechanism were revealed. The study results showed that the maximum creep deformation of sandstone under natural and saturation state decreased gradually with the increase of confining pressure, and the maximum creep deformation under saturation state was greater than the corresponding value under natural state when the confining pressure was same. When the confining pressure was constant, the creep deformation, the constant creep deformation rate and the accelerated creep deformati... [more]
Fabrication of New Liquid Crystal Device Using Layer-by-Layer Thin Film Process
Gitae Moon, Wonjun Jang, Intae Son, Hyun A. Cho, Yong Tae Park, Jun Hyup Lee
August 28, 2018 (v1)
Subject: Materials
Keywords: electrode, layer-by-layer, liquid crystal device, thin film
Indium tin oxide (ITO) transparent electrodes are troubled with high cost and poor mechanical stability. In this study, layer-by-layer (LBL)-processed thin films with single-walled carbon nanotubes (SWNTs) exhibited high transparency and electrical conductivity as a candidate for ITO replacement. The repetitive deposition of polycations and stabilized SWNTs with a negative surfactant exhibits sufficiently linear film growth and high optoelectronic performance to be used as transparent electrodes for vertically aligned (VA) liquid crystal display (LCD) cells. The LC molecules were uniformly aligned on the all of the prepared LBL electrodes. VA LCD cells with SWNT LBL electrodes exhibited voltage-transmittance (V-T) characteristics similar to those with the conventional ITO electrodes. Although the response speeds were slower than the LCD cell with the ITO electrode, as the SWNT layers increased, the display performance was closer to the LCD cells with conventional ITO electrode. This wo... [more]
Effect of Pore Fluid Pressure on the Normal Deformation of a Matched Granite Joint
Qiang Zhang, Xiaochun Li, Bing Bai, Shaobin Hu, Lu Shi
August 28, 2018 (v1)
Subject: Materials
Keywords: constitutive model, effective stress, fracture closure, hydro-mechanical coupling, laboratory experiment, pore pressure
The influence of pore fluid pressure on the normal deformation behaviors of joints is vital for understanding the interaction between hydraulic and mechanical processes of joints. The effect of pore fluid pressure on the normal deformation of a granite matched joint was investigated by laboratory experiments. Experimental results indicate pore fluid pressure significantly affects the normal deformation of jointed sample, and the relative normal deformation of jointed sample during fluid injection consists of the opening of the joint and the dilation of host rock. The action of pore fluid pressure on the joint follows the Terzaghi’s effective stress law. The normal deformation of the joint can be well quantitated by the generalized exponential model. The relative normal deformation of host rock during fluid injection would have a linear relationship with pore fluid pressure, and if affected by gas is more pronounced than water.
Coal Anisotropic Sorption and Permeability: An Experimental Study
Yulong Chen, Xuelong Li, Bo Li
August 28, 2018 (v1)
Subject: Materials
Keywords: adsorption–desorption, anisotropy, bedding plane orientation, Coal, gas
Knowledge of the bedding plane properties of coal seams is essential for the coalbed gas production because of their great influence on the inner flow characteristics and sorption features of gas and water. In this study, an experimental study on the anisotropic gas adsorption⁻desorption and permeability of coal is presented. The results show that during the adsorption⁻desorption process, an increase in the bedding plane angle of the specimen expands the length and area of the contact surface, thereby increasing the speed and quantity of adsorption and desorption. With an increase in the bedding angle, the number of pores and cracks was found to increase together with the volumetric strain. The evolution of permeability of coal heavily depended on stress⁻strain stages. The permeability decreased with the increase of stress at the initial compaction and elastic deformation stages, while it increased with the increase of stress at the stages of strain-hardening, softening and residual st... [more]
Experimental Study on the Damage of Granite by Acoustic Emission after Cyclic Heating and Cooling with Circulating Water
Dong Zhu, Hongwen Jing, Qian Yin, Guansheng Han
August 28, 2018 (v1)
Subject: Materials
Keywords: acoustic emission, cyclic heating and cooling, damage, failure mode, physical and mechanical parameters
Hot dry rock is developed by injecting cold water into high-temperature rock mass. At the same time, cold water is heated in contact with the rock mass. With the continuous influx of cold water, the surrounding rock will undergo a rapid cooling process, which results in several cycles of heating and cooling. However, there is little research on the influence of cycles of heating and cooling with circulating water on the mechanical properties of rock, which is of great importance to the stability of rock mass engineering in the process of energy development. In this paper, the effects of cyclic heating and cooling with circulating water on the damage of granite are studied using uniaxial compressive, Brazilian and acoustic emission (AE) tests. The results show that heat treatment temperature and number of cycles have important effects on the mechanical properties of granite as follows: (1) at the same treatment temperature, an increase in the number of cycles means that the distribution... [more]
Experimental Study of the Microstructural Evolution of Glauberite and Its Weakening Mechanism under the Effect of Thermal-Hydrological-Chemical Coupling
Shuzhao Chen, Donghua Zhang, Tao Shang, Tao Meng
August 28, 2018 (v1)
Subject: Materials
Keywords: brine concentration, gas, glauberite cavern for storing oil &, micro-CT, microstructure, temperature, thermal-hydrological-chemical interactions
The microstructures of rock gradually evolve with changes in the external environment. This study focused on the microstructure evolution of glauberite and its weakening mechanism under different leaching conditions. The porosity were used as a characteristic index to study the effect of brine temperature and concentration on crack initiation and propagation in glauberite. The research subjects were specimens of ϕ3 × 10 mm cylindrical glauberite core, obtained from a bedded salt deposit buried more than 1000 m underground in the Yunying salt formation, China. The results showed that when the specimens were immersed in solution at low temperature, due to hydration impurities, cracks appeared spontaneously at the centre of the disc and the solution then penetrated the specimens via these cracks and dissolved the minerals around the crack lines. However, with an increase of temperature, the dissolution rate increased greatly, and crack nucleation and dissolved regions appeared simultaneou... [more]
A Facile Synthesis of Hexagonal Spinel λ-MnO₂ Ion-Sieves for Highly Selective Li⁺ Adsorption
Fan Yang, Sichong Chen, Chentao Shi, Feng Xue, Xiaoxian Zhang, Shengui Ju, Weihong Xing
July 31, 2018 (v1)
Subject: Materials
Keywords: Adsorption, hydrothermal reaction, ion-sieve, LiMn2O4, λ-MnO2
Ion-sieves are a class of green adsorbent for extraction Li+ from salt lakes. Here, we propose a facile synthesis of hexagonal spinel LiMn₂O₄ (LMO) precursor under mild condition which was first prepared via a modified one-pot reduction hydrothermal method using KMnO₄ and ethanol. Subsequently, the stable spinel structured λ-MnO₂ (HMO) were prepared by acidification of LMO. The as-prepared HMO shows a unique hexagonal shape and can be used for rapid adsorption-desorption process for Li+adsorption. It was found that Li⁺ adsorption capacity of HMO was 24.7 mg·g^−1 in Li+ solution and the HMO also has a stable structure with manganese dissolution loss ratio of 3.9% during desorption process. Moreover, the lithium selectivity (α Li/Mg) reaches to 1.35 × 10³ in brine and the distribution coefficients (Kd) of Li+ is much greater than that of Mg2+. The results implied that HMO can be used in extract lithium from brine or seawater containing high ratio of magnesium and lithium.
Treatment of Oil-Contaminated Water by Modified Polysilicate Aluminum Ferric Sulfate
Zhaoyang You, Li Zhang, Shujuan Zhang, Yongjun Sun, Kinjal J. Shah
July 31, 2018 (v1)
Subject: Materials
Keywords: characterization, coagulant, coagulation, modified PSAFS, oily wastewater
In this experiment, a variety of inorganic materials were simply compounded with Polysilicate Aluminum Ferric Sulfate (PSAFS) to treat emulsified oil-contaminated water. Manganese sulfate (MnSO₄), magnesium sulfate (MgSO₄), and zinc sulfate (ZnSO₄) were selected as the materials to modify PSAFS in order to obtain a coagulant with good flocculation performance. During the preparation of modified PSAFS, metal manganese, magnesium, and zinc were introduced for modification, and four factors were used to optimize the best proportion of modifiers and PSAFS. The results showed that the order of demulsification and oil-removal ability is as follows: Mn-PSAFS (Mn-modified PSAFS) > Zn-PSAFS (Zn-modified PSAFS) > Mg-PSAFS (Mg-modified PSAFS) > PSAFS. Modified PSAFS was characterized by infrared spectroscopy (IR) and a Scanning Electron Microscope (SEM). In the range of 604 cm−1 to 1200 cm−1, due to the complexation reaction between metal ions and polysilicic acid, the absorption peaks of the mod... [more]
Nonlinear Flow Characteristics of a System of Two Intersecting Fractures with Different Apertures
Richeng Liu, Yujing Jiang, Hongwen Jing, Liyuan Yu
July 31, 2018 (v1)
Subject: Materials
Keywords: critical pressure difference, hydraulic aperture, mechanical aperture, Navier-Stokes equations, nonlinear flow
The nonlinear flow regimes of a crossed fracture model consisting of two fractures have been investigated, in which the influences of hydraulic gradient, surface roughness, intersecting angle, and scale effect have been taken into account. However, in these attempts, the aperture of the two crossed fractures is the same and effects of aperture ratio have not been considered. This study aims to extend their works, characterizing nonlinear flow through a system of two intersecting fractures with different apertures. First, three experiment models with two fractures having different apertures were established and flow tests were carried out. Then, numerical simulations by solving the Navier-Stokes equations were performed and the results compared with the experiment results. Finally, the effects of fracture aperture on the critical pressure difference and the ratio of hydraulic aperture to mechanical aperture were systematically analyzed. The results show that the numerical simulation res... [more]
A New Pseudo Steady-State Constant for a Vertical Well with Finite-Conductivity Fracture
Yudong Cui, Bin Lu, Mingtao Wu, Wanjing Luo
July 31, 2018 (v1)
Subject: Materials
Keywords: circular closed reservoir, conductivity-influence function, finite-conductivity fracture, normalized conductivity-influence function, Pseudo Steady-State (PPS) constant
The Pseudo Steady-State (PSS) constant bDpss is defined as the difference between the dimensionless wellbore pressure and dimensionless average pressure of a reservoir with a PSS flow regime. As an important parameter, bDpss has been widely used for decline curve analysis with Type Curves. For a well with a finite-conductivity fracture, bDpss is independent of time and is a function of the penetration ratio of facture and fracture conductivity. In this study, we develop a new semi-analytical solution for bDpss calculations using the PSS function of a circular reservoir. Based on the semi-analytical solution, a new conductivity-influence function (CIF) representing the additional pressure drop caused by the effect of fracture conductivity is presented. A normalized conductivity-influence function (NCIF) is also developed to calculate the CIF. Finally, a new approximate solution is proposed to obtain the bDpss value. This approximate solution is a fast, accurate, and time-saving calculat... [more]
Critical Hydraulic Gradient of Internal Erosion at the Soil⁻Structure Interface
Quanyi Xie, Jian Liu, Bo Han, Hongtao Li, Yuying Li, Xuanzheng Li
July 31, 2018 (v1)
Subject: Materials
Keywords: critical hydraulic gradient, internal erosion, orthogonal tests, soil–structure interface
Internal erosion at soil⁻structure interfaces is a dangerous failure pattern in earth-fill water-retaining structures. However, existing studies concentrate on the investigations of internal erosion by assuming homogeneous materials, while ignoring the vulnerable soil⁻structure-interface internal erosion in realistic cases. Therefore, orthogonal and single-factor tests are carried out with a newly designed apparatus to investigate the critical hydraulic gradient of internal erosion on soil⁻structure interfaces. The main conclusions can be draw as follows: (1) the impact order of the three factors is: degree of compaction > roughness > clay content; (2) the critical hydraulic gradient increases as the degree of compaction and clay content increases. This effect is found to be more obvious in the higher range of the degree of soil compaction and clay content. However, there exists an optimum interface roughness making the antiseepage strength at the interface reach a maximum; (3) the evo... [more]
A Parameter Study of the Effect of a Plasma-Induced Ozone Colour-Fading Process on Sulphur-Dyed Cotton Fabric
Dan Zhong, Yao-Hui Liu, Ngan-Ting Cheung, Chi-Wai Kan, Hong Chua
July 31, 2018 (v1)
Subject: Materials
Keywords: colour-fading, cotton fabric, ozone, plasma, sulphur dye
A plasma-induced ozone colour-fading treatment was used for treating a blue sulphur-dyed knitted cotton fabric. Since the process parameters of plasma-induced ozone colour-fading treatment are inter-related with one other, the final colour-fading results are affected. An orthogonal array testing strategy (OATS) method was used for determining the optimum conditions of the plasma-induced ozone colour-fading treatment in this study. Three process parameters used in the plasma-induced ozone colour-fading treatment, i.e., oxygen gas concentration (%), water content in fabric (%), and treatment time (minutes), were used in the optimization process. Experimental results reveal the optimum conditions for fading the colour by plasma-induced ozone colour-fading treatment are: (1) oxygen gas concentration = 70%; (2) water content in fabric = 35%; and (3) treatment time = 30 min. The order of importance of these parameters is: oxygen gas concentration > water content in fabric > treatment time. I... [more]
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