In this work, a comprehensive mathematical model was developed in order to evaluate the CO2 capture process in a microporous polypropylene hollow-fiber membrane countercurrent contactor, using monoethanolamine (MEA) as the chemical solvent. In terms of CO2 chemical absorption, the developed model showed excellent agreement with the experimental data published in the literature for a wide range of operating conditions (R2 > 0.96), 1−2.7 L/min gas flow rates and 10−30 L/h liquid flow rates. Based on developed model, the effects of the gas flow rate, aqueous liquid absorbents’ flow rate and also inlet CO2 concentration on the removal efficiency of CO2 were determined. The % removal of CO2 increased while increasing the MEA solution flow rate; 81% of CO2 was removed at the high flow rate. The CO2 removal efficiency decreased while increasing the gas flow rate, and the residence time in the hollow-fiber membrane contactors increased when the gas flow rate was lower, reaching 97% at a gas fl... [more]

Wheat straw is a renewable agricultural by-product that is currently underutilized in the production of bioenergy and bioproducts due to its high ash content, as well as high transport costs due to its low volumetric energy density. The thermogravimetric analysis of this material produces derivative curves with a single broad peak, making it difficult to identify the three conventional pseudo-components (cellulose, hemicellulose, and lignin), which is resolved using the second derivative to determine inflection points. Model-fitting methods and isoconversional methods were applied to determine the degradation kinetics of wheat straw at two different particle sizes, as well as that of a reference feedstock (beech wood), and the obtained values were used to divide the degradation curves to be compared to the experimental data. Seven different pyrolysis reaction networks from the literature were given a similar treatment to determine which provides the best estimation of the actual pyroly... [more]

Conventional construction materials which rely on a fossil-based, nonrenewable extractive economy are typically associated with an entrenched linear economic approach to production. Current research indicates the clear interrelationships between the production and use of construction materials and anthropogenic climate change. This paper investigates the potential for emerging high-performance biobased construction materials, produced sustainably and/or using waste byproducts, to enable a more environmentally sustainable approach to the built environment. Life-cycle assessment (LCA) is employed to compare three wall assemblies using local biobased materials in Montreal (Canada), Nairobi (Kenya), and Accra (Ghana) vs. a traditional construction using gypsum boards and rockwool insulation. Global warming potential, nonrenewable cumulative energy demand, acidification potential, eutrophication potential, and freshwater consumption (FWC) are considered. Scenarios include options for design... [more]

Existing fractured gas reservoir development techniques are mainly based on dual medium numerical-simulation models, which can, to a certain extent, effectively simulate natural fractures with high fracture density; however, these models have some limitations, particularly in terms of simulating the fracture morphology and distribution. Considering carbonate gas reservoirs with complex fractures, in this paper, we establish a numerical-simulation model of embedded discrete-fracture seepage in horizontal wells of carbonate gas reservoirs, in order to compare and study the development effect of carbonate gas reservoirs under different horizontal well fracture parameters. The fracture distribution and structure in carbonate gas reservoirs is obtained using an ant-tracking approach based on 3D seismic bodies, and a numerical-simulation model based on the embedded discrete-fractures model is solved using the open-source program MRST. We considered the following parameters: half fracture len... [more]

High-performance thermal insulators allow a dramatic reduction in the thickness of coatings, thanks to their low thermal conductivity. This study provides an overview about thermal insulation materials, with regards to heat reflective insulators in particular. Then, the numerical investigation method adopted to compute the thermal resistance associated with reflective insulators is introduced. This method has been used in turn to check the accuracy of the declared, measured performance of different, heat-reflective materials on the market. Many manufacturers of reflective insulators were available to provide information and a good agreement between the declared and expected thermal resistance has been found. The choice of a non-experimental approach is meant to check the validity of an already performed test on a reflective insulator using a predictive approach instead of standard, additional testing. Then, the insulation of five typical walls at three different sites in Italy has been... [more]

Hydrogen is an energy carrier in which hopes are placed for an easier achievement of climate neutrality. Together with electrification, energy efficiency development, and RES, hydrogen is expected to enable the ambitious energy goals of the European Green Deal. Hence, the aim of the article is to query the development of the hydrogen economy in the Visegrad Group countries (V4). The study considers six diagnostic features: sources of hydrogen production, hydrogen legislation, financial mechanisms, objectives included in the hydrogen strategy, environmental impact of H2, and costs of green hydrogen investments. The analysis also allowed to indicate the role that hydrogen will play in the energy transition process of the V4 countries. The analysis shows that the V4 countries have similar approaches to the development of the hydrogen market, but the hydrogen strategies published by each of the Visegrad countries are not the same. Each document sets goals based on the hydrogen production t... [more]

This paper presents the current state of knowledge in the field of wireless power transfer. The concept of such a transfer and the basic methods of its implementation are described, together with block diagrams of the necessary devices. The technologies of electrical power transfer over short and long distances are characterized. The most popular electrical power transfer technology based on the phenomenon of electromagnetic induction is discussed in great detail. The analysis of the influences of such factors as the coupling factor, the shape of the coils, the type of ferromagnetic material from which the core of the coils is made, and the mutual position of the transmitting and receiving coils are analyzed on the properties of the wireless power transfer system. The advantages and disadvantages of the used technologies are shown. Furthermore, a wireless power transfer system is presented for charging the batteries of electric vehicles. The standards of wireless power transfer are als... [more]

Offshore wind turbines (OWTs), in comparison to onshore wind turbines, are gaining popularity worldwide since they create a large amount of electrical power and have thus become more financially viable in recent years. However, OWTs are costly as they are vulnerable to damage from extremely high-speed winds and thereby affect operation and maintenance (O&M) operations (e.g., vessel access, repair, and downtime). Therefore, accurate weather forecasting helps to optimise wind farm O&M operations, improve safety, and reduce the risk for wind farm operators. Sequential data-driven models recently found application in solving the wind turbines problem; however, their application to improve offshore operation and maintenance through weather forecasting is still limited and needs further investigation. This paper fills this gap by proposing three sequential data-driven techniques, namely, long short-term memory (LSTM), bidirectional LSTM (BiLSTM) and gated recurrent units (GRU) for long-term... [more]

This paper presents a 2D model of the Ghawar field and investigates the flow behavior in the field during secondary and tertiary recoveries using a simplified well scheme. For the latter, the focus is on chemical Enhanced Oil Recovery (EOR), using polymer solutions. The difference in efficiency between secondary and tertiary recovery and the influence of factors such as degradation are analyzed and presented. Furthermore, the influence of oil viscosity on the recovery factor is investigated as well as the efficiency of the well placement of the model studied. In order to do this, a combined shear-thinning/-thickening model, the Unified Viscosity Model (UVM), is used. COMSOL Multiphysics is used in order to study the model, combining the fluid flow and mass transfer in one study, showing the interdependence of both physics transport phenomena. The results show how the influence of the polymer properties and the rock formation affect the recovery behavior. The particle tracing study allo... [more]

Alkaline direct ethanol fuel cells (DEFCs) represent an efficient energy conversion device for sustainable ethanol fuel. In this study, a design with new structural parameters for the anodic flow field of the alkaline DEFC was modeled with the aid of computational fluid dynamics and was then actually constructed. Single-cell tests were performed to evaluate the impact of the developed design on fuel cell performance. The results show that fuel cell performance significantly increased when using the improved design in the low-temperature range. The higher the temperature in the cell, the lower the influence of the flow field structure on performance. In addition, the influence of external factors, such as the orientation of the cell, the preheating of the fuel, and the direction of the two fuel flows relative to each other (co-current and counter-current), are shown.

Electric and magnetic fields accompany technical personnel in their working environment (work exposure). That is why many countries have the appropriate regulations. The impact of electric and magnetic fields on humans is still not fully recognized. This is the reason why the limit values of its intensity in many countries differs significantly. The article presents changes in the stress limits of the electric and magnetic fields in Poland at the turn of the last dozen years. The last such change was the result of a Directive of the European Union (2013/35/EU). The effects of changes in limit values on the working conditions of technical personnel performing diagnostics of high voltage transformers or working in the immediate vicinity of such transformers are presented. The article shows that recent changes have improved the working conditions of technical personnel in relation to the electric field and worsened the conditions taking into account the magnetic field.

Buildings use up to 40% of the global primary energy and 30% of global greenhouse gas emissions, which may significantly impact climate change. Heating, ventilation, and air-conditioning (HVAC) systems are among the most significant contributors to global primary energy consumption and carbon gas emissions. Furthermore, HVAC energy demand is expected to rise in the future. Therefore, advancements in HVAC systems’ performance and design would be critical for mitigating worldwide energy and environmental concerns. To make such advancements, energy modeling and model predictive control (MPC) play an imperative role in designing and operating HVAC systems effectively. Building energy simulations and analysis techniques effectively implement HVAC control schemes in the building system design and operation phases, and thus provide quantitative insights into the behaviors of the HVAC energy flow for architects and engineers. Extensive research and advanced HVAC modeling/control techniques hav... [more]

The coal mine underground reservoir is an effective facility for mine groundwater utilization in water-deficient and ecologically fragile areas. Usually, the artificial reserved coal pillar is used as the dam of underground reservoir, and little research has been done on its tightness performance. Comsol software is used to simulate the leakage of underground reservoirs in Shendong area, in the western part of China, and the long-term tightness of coal pillar dam under different operation conditions is evaluated. The results show that: (1) When the underground reservoir is not connected with the upper water system, the coal pillar dam has good tightness performance. When they are connected, the leakage of reservoir increased due to the raised water level, and the deeper the burial depth, the greater the leakage amount. (2) When reservoir is pumping and storing water, the leakage is only half of that under constant water pressure storage, indicating that this operation mode is beneficia... [more]

To eliminate the harmonics caused by nonlinear loads, repetitive controllers are widely applied as current controllers for active power filters (APF). In practice, a variation in grid frequency leads to the appearance of a fractional-order delay filter. As a result, the resonant frequency of the repetitive controller will deviate from the fundamental frequency and the controller cannot compensate for harmonics accurately. To solve this problem, an improved frequency-adaptive repetitive controller based on virtual variable sampling (IMFA-VVS-RC) for APF is proposed in this paper. To enhance the system stability margin, the proposed RC introduces an infinite impulse response (IIR) low-pass filter. The proposed RC has a high stability margin at high frequencies due to the low gain of the IIR low-pass filter in the region above the cutoff frequency. In this way, the influence of model uncertainty and parameter uncertainty on system stability are reduced at high frequencies. At the same tim... [more]

To study the relationship between sediment concentration and the performance parameters of centrifugal pumps, Jiamakou water supply pumping station with total installed capacity of 30,880 kW was selected to analyze characteristics of the centrifugal pump in this paper. Based on a CFD mixture model, the effects of different sediment concentrations on the movement of solid−liquid two-phase flow and the performance parameters of the centrifugal pump were obtained. Then, fitting equations were established between performance parameters (head, flow rate, shaft power, and efficiency) of the centrifugal pump and sediment concentration at three working conditions (0.8 Q = 2 m3/s, Q = 2.5 m3/s, 1.2 Q = 3 m3/s) by the polynomial least-square method. Calculated values of fitting equations were compared with the measured values in centrifugal pump operation. The results show that, as the sediment concentration increases from 0.1% to 1%, the maximum volume fraction of sediment at blade outlet incre... [more]

The inconsistency of the battery pack will cause the “barrel effect“ when the battery pack is working. The battery with lower power will first reach the discharge cut-off condition, resulting in the battery pack not being fully discharged, reducing the battery utilization rate. This paper uses the state of charge (SOC) as an equilibrium variable and the forgetting factor recursive least square−extended Kalman filter (FFRLS-EKF) method to estimate the SOC. Using a balanced topology based on a bidirectional impact direct current (DC) converter, the energy transfer can occur between any battery and only between batteries that need to be balanced, increasing energy utilization and the effect of equalization. The equalization system is simulated under various conditions, which proves the effectiveness of the equalization control system.

Multi-energy virtual power plants (MEVPPs) effectively realize multi-energy coupling. Low-carbon transformation of coal-fired units at the source side and consideration of demand response resources at the load side are important ways to achieve carbon peak and carbon neutralization. Based on this, this paper proposes a low-carbon economic dispatch model for the MEVPP system considering source-load coordination with comprehensive demand response. Combined with the characteristics of organic Rankine cycle (ORC) waste heat power generation and comprehensive demand response energy to increase the flexibility on both sides of the source and load, the problem of insufficient carbon capture during the peak load period in the process of low-carbon transformation of thermal power units has been improved. First, the ORC waste heat recovery device is introduced into the MEVPP system to decouple the cogeneration unit’s “heat-based electricity” constraint, which improves the flexibility of the unit... [more]

Electrical power transformers are the most exorbitant and tactically prominent components of the South African electrical power grid. In contrast, they are burdened by internal winding faults predominantly on account of insulation system failure. It is essential that these faults must be swiftly and precisely uncovered and suitable measures should be adopted to separate the faulty unit from the entire system. The frequency response analysis (FRA) is a technique for tracking a transformer’s mechanical integrity. Nevertheless, classifying the category of the fault and its gravity by benchmarking measured FRA responses is still backbreaking and for the most part, anchored in personnel proficiency. This work presents a quantum leap to normalize the FRA interpretation procedure by suggesting an interpretation code criteria based on an empirical survey of transformers ranging from 315 kVA to 40 MVA. The study then proposes an analysis of variance (ANOVA) based interpretation tool for diagnos... [more]

The porous and low-permeability characteristics of a shale gas reservoir determine its high gas storage efficiency, which is manifested in the extremely high breakthrough pressure of shale. Therefore, the accurate calculation of breakthrough pressure is of great significance to the study of shale gas preservation conditions. Based on a systematic analysis of a low-field NMR experiment on marine shales of the Longmaxi Formation in the Sichuan Basin, a shale gas breakthrough pressure determination technique different from conventional methods is proposed. The conventional methods have low calculation accuracy and are a tedious and time-consuming process, while low-field NMR technique is less time-consuming and of high accuracy. Firstly, the NMR T2 spectrum of shale core sample in different states is measured through low-field NMR experiment. The NMR T2 spectra of sample in water-saturated state and dry state are combined to model the mathematical relationship between shale gas breakthrou... [more]

In cases where a dye-sensitized solar cell (DSSC) is exposed to light, thermal energy accumulates inside the device, reducing the maximum power output. Utilizing this energy via the Seebeck effect can convert thermal energy into electrical current. Similar systems have been designed and built by other researchers, but associated tests were undertaken in laboratory environments using simulated sunlight and not outdoor conditions with methods that belong to conventional data analysis and simulation methods. In this study four machine learning techniques were analyzed: decision tree regression (DTR), random forest regression (RFR), K-nearest neighbors regression (K-NNR), and artificial neural network (ANN). DTR algorithm has the least errors and the most R2, indicating it as the most accurate method. The DSSC-TEG hybrid system was extrapolated based on the results of the DTR and taking the worst-case scenario (node-6). The main question is how many thermoelectric generators (TEGs) are nee... [more]

In thermal conversion utilization, nitrogen-rich biomass such as waste wood-based panels will release a large amount of NO into the atmosphere, causing serious harm to the surroundings. By means of co-pyrolysis, N in waste wood-based panels can be fixed in chars instead of discharging into the atmosphere in the form of volatile matter, which can reduce NO emission and lay a foundation for the preparation of nitrogen-rich carbon materials with high added value. As the most commonly used adhesive in the production of wood-based panels, urea-formaldehyde resin adhesive (UF) is the main nitrogen source in waste wood-based panels. Therefore, the purpose of this paper is to explore the effects of glucose, ethyl maltol and 2,5-dimethyl-4-hydroxy-3(2H)-furanone (DMHF) on nitrogen migration and conversion during UF pyrolysis by adjusting the different proportions of model compounds and UF. Thermogravimetric analysis showed that ethyl maltol and DMHF had lower thermal stability and the pyrolysis... [more]

After the massive integration of distributed energy resources, energy storage systems and the charging stations of electric vehicles, it has become very difficult to implement an efficient grid energy management system regarding the unmanageable behavior of the power flow within the grid, which can cause many critical problems in different grid stages, typically in the substations, such as failures, blackouts, and power transformer explosions. However, the current digital transition toward Energy 4.0 in Smart Grids allows the integration of smart solutions to substations by integrating smart sensors and implementing new control and monitoring techniques. This paper is proposing a hybrid artificial intelligence multilayer for power transformers, integrating different diagnostic algorithms, Health Index, and life-loss estimation approaches. After gathering different datasets, this paper presents an exhaustive algorithm comparative study to select the best fit models. This developed archi... [more]

In view of the problems of low matrix permeability and low oil recovery in shale reservoirs, CO2 huff and puff technology is considered as an effective method to develop shale oil reservoirs. However, the production behaviors of actual shale reservoirs cannot be reproduced and the EOR potentials cannot be evaluated directly by scaled models in the laboratory. Conventional CO2 huff and puff has problems such as early gas breakthrough and gas channeling leading to inefficient development. In this article, with the help of a three-dimensional experimental simulation apparatus, a new method of CO2 huff and puff with a horizontal well assisted by pumping production and water injection disturbance is developed. The dynamic characteristic, pressure field distribution of soaking and the enhanced oil recovery effect are comprehensively evaluated. The results show that the soaking stage of CO2 huff and puff can be divided into three stages: differential pressure driving, diffusion driving and di... [more]

As a new type of power device, the X-type rotary engine (XRE) is regarded as a major revolution of the internal combustion engine with its special structure and high-efficiency hybrid cycle (HEHC). A 3D CFD model of an XRE with hydrogen−gasoline fuel is firstly built in this paper. The gasoline is premixed with air in the intake of the XRE. The hydrogen is directly injected (DI) into the cylinder with four different injection positions. The effects of the hydrogen injection position on the combustion process, engine thermodynamic performance, and unburned carbon emissions and NOx emissions are investigated. The results show that, due to the interaction between the in-cylinder main flow field and the injected hydrogen gas flow, different hydrogen concentration zones are formed at different injection positions. Furthermore, a larger hydrogen distribution area and being closer to the ignition position led to a faster in-cylinder combustion rate and a higher in-cylinder temperature and pre... [more]

With the development of energy storage and conversion or advanced propulsion systems, heat transfer enhancement methods have become widely applied [...]