The characterizations of grounding systems subjected to high impulse conditions are known to be dependent on the polarity, current to peak time and discharge time, as well as the electrical properties of the soil, and the grounding electrodes themselves. It is therefore important to investigate the behavior of grounding systems under high impulse conditions under negative impulse polarity, and compare it with positive impulse polarity results. Experimental test results for the same grounding systems installed with various earth electrodes at several sites under positive impulse polarity have previously been presented. In comparison, this paper presents the results of negative impulse polarity injected on the same grounding systems. It is found that a significant difference between positive and negative impulse polarities is observed for the grounding systems installed at high soil resistivity.

In this paper, the amount of SF6 decomposition gases due to the partial discharge (PD) was studied in the SF6 gas-insulated transformer. The long-term PD degradation experiment was performed while controlling the discharge magnitude using the surface discharge, and the gas generation amount was measured by using gas chromatography for SO2F2, SOF2, SO2, CO, and CF4. In addition, to investigate the relationship between the partial discharge energy and the decomposed gas generation amount, partial discharge energy was calculated by a data processing program and converted to the unit of joule per mole. With the finite element method (FEM), the electric field distribution and SF6 gas decomposition mechanism were explained for the partial discharge energy effect on the gas generation. This study helps understand the relationship between the partial discharge energy and the decomposed gas generation ratio with the experimental results and can be used for the diagnosis of PD and maintenance pr... [more]

Alkaloids, typical nitrogen compounds, were found to be abundant in tobacco waste. The recovery of alkaloids from tobacco waste for biological pesticides could reduce the use of traditional chemical pesticides and avoid the pollution of farmland by the leaching of alkaloids from tobacco waste. Considering the fact that alkaloids can easily volatilize, thermal treatment is expected to be a potential technology to achieve the release and recovery of alkaloids from tobacco waste. For better understanding of conversion behavior of nitrogen-containing compounds in tobacco waste during thermal treatment, purge/trap-GC/MS (gas chromatography mass spectrometry), PY-GC/MS (pyrolysis-gas chromatography mass spectrometry), and fixed-bed/ATD-GC/MS (auto-thermal desorption gas chromatography mass spectrometry) were adopted to detect the ingredients and concentration of nitrogen-containing compounds in tobacco waste and/or volatiles. The results of purge/trap-GC/MS showed that nitrogen-containing co... [more]

This work presents a synthesis of hierarchical manganese−iron-layered double hydroxide (MnFe-LDH) nanostructured electrodes using the hydrothermal synthesis route by varying the reaction time for electrochemical energy storage applications. The electrochemical behavior of the MnFe-LDH electrodes synthesized at different reaction times was analyzed in a three-electrode cell configuration using 2 M KOH electrolyte. The uniform and well-organized MnFe-LDH nanosheet electrode (MnFe-12h) showed the maximum areal capacitance of 2013 mFcm−2 at a 5 mVs−1 scan rate, and 1886 mFcm−2 at a 25 mA applied current. Furthermore, the electrochemical behavior of MnFe-12h was examined by assembling an asymmetric cell device using activated carbon (AC) as a negative electrode and MnFe-12h as a positive electrode and it was tested in a wide voltage window range of 0.0 to 1.6 V. This asymmetric cell device achieved an appropriate energy density of 44.9 µW h cm−2 (55.01 W h kg−1), with a power density of 16... [more]

The optimal conditions for the nitric acid dissolution of precipitates of hydroxides and hydrated oxides of rare-earth elements, uranium, and thorium obtained after autoclave alkaline opening of samples of monazite concentrate have been determined. The distribution of radioactive impurities between the solid phase and the solution in the processes of alkaline opening, dephosphorization, and acid dissolution of the pulp was studied. Two options are proposed for the extraction of uranium and thorium in the presence of rare earth elements, followed by separation of the components using tributyl phosphate of various contents in the carbon diluent.

Traditional defrosting methods applied to solve frosting problems of air-source heat pumps operating in cold periods may reduce heat capacity of the system and decrease indoor thermal comfort. In order to improve the performance of air-source heat pump (ASHP) and maintain indoor temperature in defrosting conditions, an air-source heat pump combined with a refrigerant direct-condensation radiant floor heating system with phase change material is proposed and evaluated in this study. Two radiant floor heating terminals with and without composite phase change material modules were compared through experiments. A composite phase change material based on dodecanoic acid-tetradecanol-hexadecanol mixture and expanded graphite was investigated for this application. Experimental results indicate that both heat fluxes of two comparing terminals are higher than 70 W/m2 in heating condition. At the same time, the floor surface temperature, indoor air temperature, and heating capacity of the termin... [more]

Durability of concrete designed for radiation shielding structures is an important issue in nuclear power plant safety. An investigation of the permeability of concrete containing heavyweight aggregates and water-bearing aggregates was performed with respect to gaseous and liquid media. Mix design was developed using Portland and slag cement, crushed magnetite and serpentine aggregate. The use of slag cement in concrete containing magnetite and serpentine aggregates resulted in the substantial improvement of the compressive strength in comparison with Portland cement concrete. The application of slag cement was found to reduce the chloride ingress, regardless of the special aggregate use. The coefficient of chloride migration was within the range 5 ÷ 8 × 10−12 m2/s and 17 ÷ 25 × 10−12 m2/s for slag cement concrete and Portland cement concrete, respectively. At the same time, the carbonation depth was increased twice for slag cement concrete in comparison to Portland cement concrete. Ho... [more]

Sulfolane in contact with water and oxygen forms acidic (by-) products that are major factors in accelerating the corrosion of carbon/stainless steel. In consequence, water-induced corrosion damage can be a serious problem in industrial systems. Hence, the determination of the corrosion resistance of AISI 1010 steel immersed in sulfolane containing 0 to 6 vol.% water was the principal objective of the study. Evaluation of the corrosion resistance of steel electrodes was performed using a potentiodynamic technique and scanning Kelvin probe microscopy. It was observed that the corrosion products layer that formed on the surface of AISI 1010 steel partially protects it against corrosion in sulfolane with a water concentration in the range from 1 vol.% to 4 vol.%. Interestingly, amounts of water above 4 vol.% cause a break-down of the corrosion products layer and deteriorate the corrosion resistance of AISI 1010 steel as well. Moreover, the relationship between the fractal dimension, corro... [more]

Synergistic effect of cellulase and hemicellulase (xylanase) was evaluated because lignocellulosic material is a heterogeneous complex of cellulose and hemicellulose. Various effects of HTec2 addition on enzymatic saccharification and fermentation were evaluated using two different substrates such as corn stover and rice straw. Corn stover and rice straw were pretreated by the LMAA (low-moisture anhydrous ammonia) method at the preselected same conditions (90 °C, 120 h, moisture content = 50%, NH3 loading = 0.1 g NH3/g). It was observed that the enzymatic saccharification yield of pretreated corn stover (76.4% for glucan digestibility) was higher than that of pretreated rice straw (70.9% for glucan) using CTec2 cellulase without HTec2 addition. Glucan digestibility of pretreated corn stover was significantly increased from 76.4% to 91.1% when the HTec2/CTec2 (v/v) increased from 0 to 10. However, it was interesting that the ethanol production was decreased from 89.9% to 76.3% for SSF a... [more]

Various pulse decay methods are proposed to test tight cores. These methods can be divided into three types. This study compares the performance of these methods to test the permeability of unconventional cores in terms of homogeneous cores, dual-medium cores, and gas adsorption, including the pressure equilibrium time, possible errors caused by conventional analysis methods, and reflections on the characteristics of dual-media. Studies shows that the two test methods with an antisymmetric relationship in the boundary conditions have basically identical test performance. When testing homogeneous cores, regardless of whether the gas is adsorptive or not, the pressure equilibrium time of the first type of method is approximately half of that of the second type of method. The dual-medium parameters seriously affect the pressure equilibrium time of different methods, which may cause the difference of order of magnitude. For homogeneous cores, the permeability errors of the first and second... [more]

The broader use of cements with a higher content of the main non-clinker components in construction industry is one of the directions leading to the decarbonization in cement production. This contribution analyzes the properties of low-emission cements containing from 44% to 56% of Portland clinker in their composition and indicates the possibilities of wider use in the construction. The obtained results confirmed that following the appropriate technological regimes, low-emission cements can be implemented into the production of concrete exposed to carbonation-induced corrosion (exposure class XC4 according to EN 206), frost-resistant concrete (exposure class XF4 according to EN 206), self-compacting concrete (SCC) and high-performance concrete (HPC). An analysis of the level of CO2 emissions in the production of specific types of concrete using low-emission cements was also made.

There is a significant enhancement of the heat transfer rate with the usage of nanofluid. This article describes a study of the combination of using nanofluid with inserts, which has proved itself in attaining higher benefits in a heat exchanger, such as the radiator in automobiles, industries, etc. Nanofluids are emerging as alternative fluids for heat transfer applications due to enhanced thermal properties. In this paper, the thermal hydraulic performance of ZrO2, awater-based nanofluid with various volume concentrations of 0.1%, 0.25%, and 0.5%, and staggered conical strip inserts with three different twist ratios of 2.5, 3.5, and 4.5 in forward and backward flow patterns were experimentally tested under a fully developed laminar flow regime of 0−50 lphthrough a horizontal test pipe section with a length of 1 m with a constant wall heat flux of 280 W as the input boundary condition. The temperatures at equidistant position and across the test section were measured using K-type ther... [more]

Pressure, temperature, and retention time are the most studied parameters in steam explosion pretreatment. However, this work aimed to fix these parameters and to evaluate the influences of several less investigated steam explosion parameters on the saccharification yield in hydrolysis. In this study, firstly, pinewood samples smaller than 200 µm were treated with steam explosion at 190 °C for 10 min. The variable parameters were biomass loading, N2 pressure, and release time. Steam-exploded samples were hydrolyzed with the Trichoderma reesei enzyme for saccharification for 72 h. The sugar content of the resultant products was analyzed to estimate the yield of sugars (such as glucose, xylose, galactose, mannose, and arabinose). The best glucose yield in the pulp was achieved with 4 g of sample, N2 pressure of 0.44 MPa, and short release time (22 s). These conditions gave a glucose yield of 97.72% in the pulp, and the xylose, mannose, galactose, and arabinose yields in the liquid fracti... [more]

In this paper, the inelastic material models for Type 316H stainless steel, which is one of the principal candidate materials for elevated temperature design of the advanced high temperature reactors (HTRs) pressure retained components, are investigated and the required material parameters are identified to be used for both elasto-plastic models and unified viscoplastic models. In the constitutive equations of the inelastic material models, the kinematic hardening behavior is expressed with the Chaboche model with three backstresses, and the isotropic hardening behavior is expressed by the Voce model. The required number of material parameters is minimized to be ten in total. For the unified viscoplastic model, which can express both the time-independent plastic behavior and the time-dependent viscous behavior, the constitutive equations have the same kinematic and isotropic hardening parameters of the elasto-plastic material model with two additional viscous parameters. To identify th... [more]

Frequency domain spectroscopy is considered to be a promising and novel method for the assessment of the insulation condition of power equipment. This work has practical significance as it explains the microscopic mechanism of this method in a wide temperature range and further establishes its quantitative model. To achieve this, in the present paper, we select oil-impregnated paper—one of the most common insulation materials for power equipment with a complex microstructure—as a test sample, deduce a formula based on the relationship between the real and imaginary parts of the complex permittivity to extract the spectra of independent dielectric processes and measure the frequency domain spectra of oil-impregnated paper under different temperatures, as well as its thermally stimulated depolarization current with a series of bias voltages. The analysis results reveal that oil-impregnated paper’s frequency domain spectra in a wide temperature range are mainly determined by dielectric pr... [more]

Depending on the application of bismuth telluride thermoelectric materials in cooling, waste heat recovery, or wearable electronics, their material properties, and geometrical dimensions should be designed to optimize their performance. Recently, thermoelectric materials have gained a lot of interest in wearable electronic devices for body heat harvesting and cooling purposes. For efficient wearable electronic devices, thermoelectric materials with optimum properties, i.e., low thermal conductivity, high Seebeck coefficient, and high thermoelectric figure-of-merit (zT) at room temperature, are demanded. In this paper, we investigate the effect of glass inclusion, microwave processing, and annealing on the synthesis of high-performance p-type (BixSb1−x)2Te3 nanocomposites, optimized specially for body heat harvesting and body cooling applications. Our results show that glass inclusion could enhance the room temperature Seebeck coefficient by more than 10% while maintaining zT the same.... [more]

This work addresses for the first time the study of olive stone (OS) biomass pretreatment by reactive extrusion technology using NaOH as the chemical agent. It is considered as a first step in the biological conversion process of the carbohydrates contained in the material into bio-based products. OS is a sub-product of the olive oil extraction process that could be used in a context of a multi-feedstock and multi-product biorefinery encompassing all residues generated around the olive oil production sector. OS biomass is pretreated in a twin-screw extruder at varying temperatures—100, 125 and 150 °C and NaOH/biomass ratios of 5% and 15% (dry weight basis), in order to estimate the effectiveness of the process to favour the release of sugars by enzymatic hydrolysis. The results show that alkaline extrusion is effective in increasing the sugar release from OS biomass compared to the raw material, being necessary to apply conditions of 15% NaOH/biomass ratio and 125 °C to attain the best... [more]

This paper presents the design and a short cycle repeatability test of a silica gel-based thermal energy storage system using low grade heat for the desorption phase. The system was designed to test the degradation in the energy storage density of the adsorbent material for a 2 h working period in a short number of cycles (5 cycles). Low grade heat of 70 °C is used for regeneration during the desorption phase in each cycle. It was found that a reduction of 1.6 W/kg per each cycle of energy storage was observed, up to 5 cycles. The maximal heat storage density was 292 kJ/kg at the first cycle and reduced to 225 kJ/kg at the fifth cycle. Furthermore, the total amount of water vapor adsorbed in the silica gel was observed as well. The test of energy storage was performed under a short time period (maximal approx. 165 min).

Knowing correct values of the rock mechanical properties is crucial for many engineering applications in subsurface. Rocks may show two failure modes during cutting: ductile and brittle. In the ductile mode, rock deforms plastically, and the debris is powdered ahead of the cutting face. On the other hand, chips are the major cutting characteristics for the brittle failure during rock cutting. The critical depth of cut represents the transition point between these two models, so knowing this value helps better predict the failure mechanism of rock. In this paper, a new method is introduced based on measuring the roughness of the groove for determining the transition point of failure modes for every rock sample after the scratch test. The graph depicting the average change in the surface roughness (Rt) versus the scratched surface roughness (ΔR) can be used to identify the rock failure mode and determine the transition point for the cutting process. The value of this slope increases unti... [more]

Oil-based drilling fluid has many advantages, such as stable performance, strong anti-pollution ability, and strong inhibition, and it has been widely used in the world. However, at present, there is no unified evaluation standard for the effect of flushing fluid under this condition, and most of them are based on the flushing effect evaluation of water-based drilling fluid. However, there are few studies on wetting reversal phenomenon, reasonable dosage, and flushing time between oil-based drilling fluid and flushing fluid on the two-phase interface. Therefore, it is necessary to establish a comprehensive evaluation method for the effect of flushing fluid under oil-based drilling fluid, and explore the relationship between the amount of flushing fluid and flushing efficiency, so as to determine the reasonable range of flushing fluid consumption. In this paper, using the existing experimental instruments, a type A oil-based flushing fluid commonly used in oil fields was selected for th... [more]

The performance of redox flow batteries is notably influenced by the electrolyte, especially in slurry-based flow batteries, as it serves as both an ionic conductive electrolyte and a flowing electrode. In this study, carbon additives were introduced to achieve a rechargeable zinc slurry flow battery by minimizing the zinc plating on the bipolar plate that occurs during charging. When no carbon additive was present in the zinc slurry, the discharge current density was 24 mA∙cm−2 at 0.6 V, while the use of carbon additives increased it to up to 38 mA∙cm−2. The maximum power density was also increased from 16 mW∙cm−2 to 23 mW∙cm−2. Moreover, the amount of zinc plated on the bipolar plate during charging decreased with increasing carbon content in the slurry. Rheological investigation revealed that the elastic modulus and yield stress are directly proportional to the carbon content in the slurry, which is beneficial for redox flow battery applications, but comes at the expense of an incre... [more]

In this paper, the feasibility study to develop strain-based seismic design criteria applicable for the components of nuclear power plants are carried out as an alternative rule to the current stress-based criteria. To do this, two acceptance criteria are investigated through the detailed example of an application for the surge line nozzles in a nuclear steam supply system, which are known as one of the seismic fragile components in nuclear power plants. These strain-based seismic design criteria are primarily to prevent two types of failure modes, such as a ductile fracture and a cyclic fatigue-induced damage due to continuous large amplitude cyclic loads during seismic event. Through the example problem, the required procedures are described step-by-step with calculations of an accumulated plastic strain, triaxiality factor by the elasto-plastic seismic analysis using the finite element method. For a precise inelastic seismic analysis, the Chaboche kinematic and Voce isotropic harden... [more]

This paper presents the effect of the impact of moisture in paper insulation used as insulation of transformer windings on its thermal conductivity. Various types of paper (cellulose and aramid) and impregnated (mineral oil, synthetic ester, and natural ester) were tested. The impact of paper and impregnated types on the changes in thermal conductivity of paper insulation caused by an increase in moisture were analyzed. A linear equation, describing the changes in thermal conductivity due to moisture, for various types of paper and impregnated, was developed. The results of measuring the thermal conductivity of paper insulation depending on the temperature are presented. The aim of the study is to develop an experimental database to better understand the heat transport inside transformers to assess aging and optimize their performance.

In this study, enhanced oil recovery (EOR) techniques—namely low salinity and nanofluid EOR—are probed at the nanometer-scale using an atomic force microscope (AFM). Mica substrates were used as model clay-rich rocks while AFM tips were coated to present alkyl (-CH3), aromatic (-C6H5) and carboxylic acid (-COOH) functional groups, to simulate oil media. We prepared brine formulations to test brine dilution and cation bridging effects while selected concentrations (0 to 1 wt%) of hydrophilic SiO2 nanoparticles dispersed in 1 wt% NaCl were used as nanofluids. Samples were immersed in fluid cells and chemical force mapping was used to measure the adhesion force between polar/non-polar moieties to substrates. Adhesion work was evaluated based on force-displacement curves and compared with theories. Results from AFM studies indicate that low salinity waters and nanoparticle dispersions promote nanoscale wettability alteration by significantly reducing three-phase adhesion force and the reve... [more]

Greenhouse gases such as carbon dioxide and methane cause global warming and consequently climate change. Great efforts are being made to reduce greenhouse gas emissions with the objective of addressing this problem, hence the popularity of technologies conductive to reducing greenhouse gas emissions. CO2 emissions can be reduced by improving the thermal efficiency of combustion engines, for example, by using cogeneration systems. Coal mine methane (CMM) emerges due to mining activities as methane released from the coal and surrounding rock strata. The amount of methane produced is primarily influenced by the productivity of the coal mine and the gassiness of the coal seam. The gassiness of the formation around the coal seam and geological conditions are also important. Methane can be extracted to the surface using methane drainage installations and along with ventilation air. The large amounts of methane captured by methane drainage installations can be used for energy production. Thi... [more]