The sustained casing pressure (SCP) phenomenon of shale gas and oil wells occurs frequently after fracturing; therefore, in order to assess the cement sheath’s integrity in the vertical well portion, the cement stones were subjected to a compression test under different temperatures and confining pressures to obtain the mechanical parameters of the cement sheath at different well depths. The integrity of the cement ring between the production casing and the intermediate casing was then investigated using the Moore−Coulomb criterion. We also took into account other elements including pump pressure, production casing wall thickness, and cement ring mechanical properties. The results show that (1) the compressive strength, Poisson’s ratio, and Young’s modulus of cement stone vary obviously under different confining pressures and temperature conditions, and the cement stone shows elastic−brittle failure characteristics at 20 °C. The compressive strength, Poisson’s ratio, and Young’s modulu... [more]

To maximize the potential energy utilization of agricultural and forestry wastes and sludge, experimental studies were conducted on the co-gasification characteristics of two types of sludge (municipal sludge, MS; paper-mill sludge, PS) and a typical biomass straw (ST) under CO2 atmosphere. In this paper, the main two stages of the gasification process, the pyrolysis in the low-temperature region and the CO2-gasification in the high-temperature region, were separately studied and analyzed. The experimental results showed that biomass could effectively promote the pyrolysis of the sludge in the low-temperature region and improve the gasification in the high-temperature region. Due to the complex interactions between components, the characteristic parameters presented obvious nonlinear rules during the co-pyrolysis and co-gasification processes. For the MS-ST mixtures, when increasing the ST content, (i) in the pyrolysis process, the initial reaction temperature gradually decreased, but... [more]

The Pisum sativum (PS), known as the green pea, was used in this investigation to produce a novel green surfactant. The performance of the PS green surfactant was also evaluated using various tests, including contact angle, IFT, emulsion, zeta potential, and oil recovery factor measurement in the presence of formation brine (FB) with a total dissolved solid (TDS) of 150,000 ppm. The characterization study using various tests revealed that the PS green surfactant was nonionic. The critical micelle concentration (CMC) measurement results indicated that the PS green surfactant’s CMC value is 1500 ppm. The IFT and contact angle measurements showed that the green surfactant significantly lowered the IFT and contact angles. The lowest IFT value of 3.71 mN/m and the contact angle of 57.37° were achieved at the FB concentration of 12,500 ppm (optimum salinity). The results of the emulsion tests showed that Winsor type III emulsions were achieved using PS green surfactant and crude oil. The cor... [more]

A new energy material, a high-energy expansion agent (HEEA), was proposed for the harsh engineering environment of a mine. A safety test and field engineering test were carried out. The results showed that the mechanical sensitivity of the HEEA was extremely low, and no combustion and explosion occurred in multiple impact and friction tests. Meanwhile, the HEEA only burns in open spaces without detonation. Through field experiments, the HEEA can achieve a good blasting effect, providing strong support for its promotion in low-disturbance environmental engineering applications.

During the operation of a Pelton turbine, the centerline of the nozzle jet may deviate from the bucket pitch circle due to the low installation and maintenance accuracy, which will reduce the operating efficiency and the stability of the turbine and even cause severe vibrations and damages. Based on the VOF (Volume of Fluid) two-phase flow model and the SST k-ω turbulence model, the flow characteristics of a Pelton turbine were simulated with the nozzle jet deviating from the bucket pitch circle. The pressure pulsation inside the bucket and the force distribution of the runner were obtained, the turbine oscillation and efficiency were measured before and after the jet deviation, and the effects of the radial and axial deviations on the stability and efficiency of the Pelton turbine were analyzed. The results show that both the radial and axial deviations of the jet cause a significant increase in the axial force and the pressure pulsation amplitude of the turbine; the radial and tangen... [more]

The underground roadway of the Buertai Coal Mine adopts the double-roadway layout. Double-roadway layout mode has a roadway that is affected by repeated mining, called reserved roadways. The reserved roadway is strongly affected by mining, and the strata behaviors appear violently. This paper studies the strata behaviors that occur in auxiliary haulage roadway (AHR) during the mining of panel 42106. By analyzing geological conditions, mining influencing factors, and roadway layout, the mechanism of strong rock behavior has been clarified. Then, based on the theoretical analysis, we put forward the treatment method for the manifestation of strong strata behaviors by using hydraulic fracturing technology to break the key stratum. In this way, the high stress of the surrounding rock can be reduced by forcing the hard roof to be broken. After the application of hydraulic fracturing technology, we monitored the deformation of roadways and the periodic weighting law of the working face. The... [more]

Durability and remaining useful life (RUL) prediction techniques are ones of the key issues for proton exchange membrane fuel cell (FC) commercialization. Herein, the performance degradation of an FC is analyzed based on the whole lifetime experimental data (up to 6500 h). The voltage model with different patterns is developed based on the voltage data, which can be easily measured. The mechanism model is developed based on the evolution of degradation indices reflecting the degradation state. However, the former is sensitive to the local and periodic changes in the voltage curve, leading to a large prediction error, and the latter requires aging data from complex and high-cost characterization, limiting the practical applications. Therefore, a hybrid prediction model combining the voltage and mechanism model is proposed where the respective weight of each model is dynamically determined based on their local prediction errors. The results reveal that the maximum errors in RUL predictio... [more]

The objective of this study is to analyze feeder loss minimization and load balance under given constrains. Effective methods are required for feeder switching/reconfiguration. Feeder switching is a mixed-integer large-scale combinatorial problem for optimization, not easily solvable with classical optimization techniques, especially involving a great number of switches. This paper proposes a fuzzy indexing algorithm for feeder switching, with membership functions defined for switches such as thermometers or indices. The optimal switches can be determined through fuzzy index operations. With membership functions defined, the developed method used numerical operations for indices instead of the “set” operation or the min-max operations of traditional fuzzy algorithms. The optimization problem becomes a simple numeric calculation instead of a large-scale sorting problem and is much faster than most algorithms. It greatly reduces the computation time and enhances efficiency, which is suit... [more]

In tidal two-way contra-rotating units, significant differences in performance often occur when arranging the front and rear impellers, which requires an optimized design of the impellers. To solve this problem, by reducing the blade inlet and outlet angles, the impact of different blade angles on the performance of two-way pump−turbines and the internal flow was explored, and the effects of the blade inlet angle of the impellers on the performance of the counter-rotating pump were obtained. Afterward, the streamline and vorticity of the two-stage impeller at different angles were analyzed. The results show that different blade angles will have a certain impact on the internal flow of the two-way pump−turbine. Different blade outlet angles have a significant impact. The variation in different inlet blade angles is not significant for the vorticity changes in the front impeller and rear impeller. In addition, changes in the outlet blade angle will have an impact on the location of LE im... [more]

This paper presents the mathematical modeling and control design procedure of the compressor motor of an air conditioner using the energy from a photovoltaic system combined with the power grid in a DC microgrid. A comprehensive model considers the interconnection of the photovoltaic cells with their associated DC/DC converter, the DC bus, the three-phase squirrel-cage induction motor with its driver, the bidirectional DC/AC converter, the output filter, and the power grid. The state-of-the-art showed that a complete mathematical model of the proposed system is unavailable. Therefore, the mathematical model of the system is compared and validated in simulation with a block diagram in the Matlab/Simulink environment. In addition, several control approaches are used in the whole system to track the maximum power point of the photovoltaic cells, obtain a soft start on the machine, control the velocity using the variable frequency drive, regulate the DC bus voltage, and manage the power fl... [more]

A low-temperature aerosol cooling and lubrication grinding test bench was built to evaluate the cooling and lubrication performance of the low-temperature aerosol. The mechanism of grinding residual stresses in the inner ring raceway under the coupling effect of grinding force and grinding heat was studied, and the effects of the grinding process parameters and cooling and lubrication conditions on the distribution state of the grinding residual stresses in the surface layer of the inner ring raceway were revealed. The results showed that reducing the initial temperature of the grinding fluid could reduce the residual tensile stresses on the raceway surface. The results also showed that the low-temperature aerosol cooling lubrication method is conducive to the generation of the axial residual compressive stress of −500 MPa and tangential residual compressive stress of −300 MPa in the inner ring raceway surface layer of the bearing. Compared with the convective heat transfer coefficient... [more]

Interval forecasting has become a research hotspot in recent years because it provides richer uncertainty information on wind power output than spot forecasting. However, compared with studies on single wind farms, fewer studies exist for multiple wind farms. To determine the aggregate output of multiple wind farms, this paper proposes an interval forecasting method based on long short-term memory (LSTM) networks and copula theory. The method uses LSTM networks for spot forecasting firstly and then uses the forecasting error data generated by LSTM networks to model the conditional joint probability distribution of the forecasting errors for multiple wind farms through the time-varying regular vine copula (TVRVC) model, so as to obtain the probability interval of aggregate output for multiple wind farms under different confidence levels. The proposed method is applied to three adjacent wind farms in Northwest China and the results show that the forecasting intervals generated by the pro... [more]

Amine solvent has attracted much attention due to its high CO2 capture level and wide application range, but its high energy consumption for recycling restricts its large-scale commercialization. In this work, a multi-objective optimization technology based on the group contribution method was used to select potential amine solvents for CO2 capture. This computer-aided molecular design method considers the thermodynamic and kinetic properties of the candidate solvent and evaluates the influence of relevant parameters on solvent performance. Compared with previous experimental methods used to optimize solvent, this method selects potential solvents from a large number of solvent databases based on group contribution. Firstly, a corresponding classification database was established for various kinds of amine solvents. Then, the traditional experiments were used to verify and screen solvents. At the same time, the method was applied to 31 amine absorbents concerning solubility, molar volu... [more]

Undesired solid precipitation in coal slag at high temperatures can cause serious blockages, or even the shutdown of coal gasifiers, due to a rapid increase in slag viscosity. In this study, the solid precipitation behaviors of coal slag from different primary phases and under different atmospheres were both experimentally and theoretically investigated. Our results demonstrated that the viscosity of the coal slag in the primary phase of mullite was strongly influenced by the atmosphere at a typical tapping temperature of 1300 °C because of the high content of network formers. The viscosity of the partially crystallized slag was significantly affected by solid precipitation behavior. Iron was converted to magnetite and hematite in air and was reduced to metallic iron under a reducing atmosphere. Increasing CaO content improved both the iron reduction reaction and the slag crystallization behavior. Anorthite precipitation was largely inhibited under a mild reducing atmosphere, leading t... [more]

The exploration of natural substrates for microbial conversion to synthesize industrial platform and fuel chemicals seems to be inevitable within a circular bioeconomy context. Hemicellulose is a natural carbohydrate polymer consisting of a variety of pentose (C5) sugar monomers such as arabinose, mannose, erythrose, and xylose. Among the C5 sugars, L-arabinose (L-Ara) is the second-most-abundant pentose sugar in the lignocellulosic biomass after xylose. L-Ara has been used as an industrial carbon source to produce several value-added chemicals such as putrescine, which is used to synthesize polymers in the textile industry; sugar alcohols that are used as sweeteners in diet foods; and amino acids such as L-lysine, L-glutamate, L-arginine, and L-ornithine, which are used in nutritional supplements, fertilizers, and other products in the food and beverage industries. L-Ara, a natural non-caloric sweetener, is used as a substitute in the food and beverage industry, when the risk of blood... [more]

Alternative sour2ces of energy are on the rise primarily because of environmental concerns, in addition to the depletion of fossil fuel reserves. Currently, there are many alternatives, approaches, and attempts to introduce alternative energy sources in the field of transport. This article centers around the need to explore additional energy sources beyond the current ones in use. It delves into individual energy sources that can be utilized for transportation, including their properties, production methods, and the advantages and disadvantages associated with their use across different types of drives. The article not only examines the situation in the Czech Republic but also in other nations. In addition to addressing future mobility, the thesis also considers how the utilization of new energy sources may impact the environment.

Thermoelectric generator (TEG) has important applications in automotive exhaust waste heat recovery. The Back propagation neural network (BP) can predict the electrical generating performance of TEG efficiently and accurately due to its advantage of being good at handing nonlinear data. However, BP algorithm is easy to fall into local optimum, and its training data usually have deviation since the data are obtained through the simulation software. Both of the problems will reduce the prediction accuracy. In order to further improve the prediction accuracy of BP algorithm, we use the genetic algorithm (GA) to optimize BP neural network by selection, crossover, and mutation operation. Meanwhile, we create a TEG for the heat waste recovery of automotive exhaust and test 84 groups of experimental data set to train the GA−BP prediction model to avoid the deviation caused by the simulation software. The results show that the prediction accuracy of the GA−BP model is better than that of the B... [more]

The exhaustion of fossil energy and the severe pollution induced by using plastics has forced people to embark on the road to sustainable development. The high value of the recycling of plastics has become an important part of energy conservation. Microwave treatment, owning specific interactions between the electric field and the molecules of treated materials, presents potential advantages in the application of plastic pyrolysis. Therefore, the research status of the microwave-assisted pyrolysis (MAP) of plastics to produce high-value-added liquid oil, gas, and solid carbon was reviewed in this paper. The effects of plastic properties, microwave treatment parameters, microwave absorbers, co-pyrolysis, catalysts, and reactor devices on the process and the products were analyzed. It is essential to optimize the experimental design by studying microwave-assisted co-pyrolysis technology and the application of catalysts, understanding the mechanism of co-pyrolysis to improve product selec... [more]

This study examines the literature on improving the low performance of Savonius wind turbines, which are a type of vertical axis wind turbine. The literature studies on improving the performance of Savonius turbines have been summarized into two categories: interior structural design and exterior additional design. Due to the extensive nature of studies focusing on interior design changes, this research primarily focuses on performance studies related to exterior design modifications of Savonius wind turbines, particularly in recent years. This study aimed to provide a comprehensive examination of these performance studies and contribute to the existing literature by presenting a systematic reference on this issue. To achieve this objective, a thorough review of turbine exterior design studies has been conducted. The focus was on determining the percentage increase in power coefficient achieved by turbines with exterior design modifications compared to the classical turbine versions. H... [more]

The concept of geological engineering-integrated fracturing is widely applied in the conventional and unconventional reservoirs, aiming to achieve efficient and economic development. There is no doubt that fine reservoir evaluation is the basis and core of geological engineering-integrated fracturing. Therefore, in this paper, we performed a series of investigations on the basis of formation fine evaluation by using RoqScan technology. Firstly, the physical parameters of the target well located in Daniudi Gas Field were evaluated by a laboratory test and logging interpretation. Next, the composition and function of the RoqSCAN tool were introduce in detail. Furthermore, the elements, minerals, and rock mechanical parameters of the target well were evaluated by the RoqSCAN tool. Finally, the fine reservoir model was established on the basis of fine formation evaluation. Moreover, we conducted a series of research on porosity and principal stress of the target formation to compare the di... [more]

The use of Horizontal wells is a common method of underground natural gas storage (UGS), but there is still a need to discuss whether they are more suitable for slotted liner or perforation completions. To address this issue, a numerical model is developed to predict the gas injection rate of horizontal wells while considering the skin factor. Here, a novel uncoupled iteration method is employed to determine the skin factor deriving from turbulence in each time step when the bottom hole pressure is fixed. The uncoupled method begins with an estimate of the initial gas injection rate, which is then used to calculate a turbulent skin factor. This turbulent skin factor is then used to update the gas injection rate, iterating continuously until convergence is achieved. The effects of slotted liner and perforation design parameters, formation damage, and injection pressure on the skin factor are analyzed. The main findings suggest that the error in the gas injection rate calculated by the n... [more]

A fault is a common geological structure in coal mining. Large deformation or even instability and collapse often occur in roadways in fault areas, which restricts the safe and efficient production of mines. With the track roadway of the 5206 working face of Xin’an Coal Mine as the engineering background, this study aims to explore the failure mechanism of surrounding rock under the influence of fault structures. Field investigation and numerical simulation were used comprehensively to analyze the failure characteristics of the surrounding rock under the influence of a unidirectional fault structure. Based on the principle of thick-layer transboundary anchorage, the hierarchical continuous support technology of transboundary anchoring in the fault structure area was proposed. The results show that the stress near the fault area is relatively concentrated, and the rock mass strength is low, which may easily cause the deformation and failure of the surrounding rock under the dynamic stre... [more]

Petroleum-derived gasoline is still the most widely used liquid automotive fuel for ground vehicles equipped with spark-ignition engines. One of the most important properties of gasoline fuels is their antiknock performance, which is experimentally evaluated via the octane number (ON). It is widely accepted that the standard methods for ON measuring (RON: research octane number and MON: motor octane number) are very expensive due to the costs of the experimental facilities and are generally not suitable for field monitoring or online analysis. To overcome these intrinsic problems, it is convenient that the ON of gasoline fuels is estimated via faster methods than the experimental tests and allows for acceptable results with acceptable reproducibility. Various ON prediction methods have been proposed in the literature. These methods differ in the type of fuels for which they are developed, the input features, and the analytical method used to underlie the link between input features and... [more]

The integration of industrial batteries with photovoltaic applications is a common practice to charge the batteries using solar energy. Long-duration flow batteries are useful in dealing with the intermittency of renewable energy sources and offer a great opportunity for total fossil fuel replacement. In this study, the effects of different battery operation time and load profiles on the temperature dynamics of a containerised vanadium flow battery system are modelled and simulated for a range of locations and seasons to identify active cooling or heating requirements that might be needed to maintain safe operating temperatures. This paper explores and analyses the stack, tank, and container temperature dynamics of 6 h and 8 h containerised vanadium flow batteries (VFBs) during periods of higher charge and discharge current using computer simulations that apply insulation with passive or active hybrid cooling thermal management where needed to keep the battery temperature within a safe... [more]

One of the problems with the doubly-fed induction generator (DFIG) is its high vulnerability to network perturbations, notably voltage dips, because of its stator windings being coupled directly to the network. As the DFIG’s stator and rotor are electromagnetically mated, the stator current peak occurs during a voltage dip causing an inrush current to the critical converter back-to-back and an overload of the DC-link capacitor. For this purpose, a series of researchers have achieved a linear and non-linear controller with a crowbar-based protection scheme. With this type of protection, the Rotor Side Converter (RSC) is disconnected momentarily, and consequently, its control of both the active and reactive output power of the stator is totally lost, leading to incorrect power quality at the point of common coupling (PCC). In this document, a robust nonlinear controller by Advanced Backstepping with Integral Action Control (ABIAC) is initially employed to monitor the rotor and the networ... [more]