The evolution of electricity markets has led to increasingly complex energy trading dynamics and the integration of renewable energy sources as well as the influence of several external market factors contributed towards price volatility. Therefore, day-ahead electricity price forecasting models, typically using some kind of neural network, play a crucial role in the optimal behavior of market agents. The most prominent models and benchmarks rely on improving the accuracy of predictions and the time for convergence by some sort of a priori processing of the dataset that is used for the training of the neural network, such as hyperparameter tuning and feature selection techniques. What has been overlooked so far is the possible benefit of a posteriori processing, which would consider the effects of parameters that could refine the predictions once they have been made. Such a parameter is the estimation of the residual training error. In this study, we investigate the effect of residual... [more]

The objective of the study was to evaluate the effect of a low-cost solar collector to pre-heat ventilation air in commercial broiler buildings on supplemental heating demand and air quality during the cold season. Six black fabric-based solar collectors of 36 m2 each were installed on the south-facing rooftop of a broiler house. The solar collectors provided fresh warm air into the house during the ON cycle of minimum ventilation and during the OFF cycle of minimum ventilation when the temperature under the collectors met certain criteria. The daily cumulative duration of solar collectors in operation averaged 125 and 133 min during the first two or four weeks of brooding in the fall and winter flocks, respectively. When in operation, the solar collectors were able to raise up to 20 K above the ambient temperature, reducing fuel usage by 7% in the fall and winter flocks. The greatest challenge of solar collector utilization was the collectors providing less than half of ventilation ai... [more]

Safety and reliability of electrical actuators are essential for success of all electric and more electric aircrafts (MEA). Torque limiters improve the reliability of electromechanical actuators (EMA) by restricting the amount of force experienced by the actuator drive train components. If transmitted torque in the shaft exceeds a limit, it gives way in a controlled manner. This protects the actuator from potential failure and jamming. In this paper, different types of existing torque limiters are investigated for their suitability in aerospace EMA application and further integration within the electric motor. They classified based on the torque transmission mechanism and each type is described in detail. Operating principle and basic characteristics are reported. Comparative evaluation of commercially available devices is presented. It is found that those based on friction based and permanent magnet are most suitable due to their good torque density, reliability and high speed capabil... [more]

The gas−liquid slug flow characteristics in a novel honeycomb microchannel reactor were investigated numerically and experimentally. Computational fluid dynamics (CFD) modeling was carried out with Comsol finite element software using the phase-field method, and the simulation results were verified by micro-particle image velocimetry (micro-PIV) analysis. The breakups of liquid slugs at the bifurcations of current honeycomb microchannel followed a complex behavior, leading to non-uniformity in each branch. The pressure distribution inside the microreactor was closely related to the phase distribution. The increasing inlet gas velocity increased the gas phase volume fraction, as well as the gas slug length. Higher gas velocity resulted in stronger turbulence of the liquid phase flow field and a deviation of residence time distribution from normal distribution, but it was favorable to even more residence time during the liquid phase. There also exists a secondary flow in the gas−liquid i... [more]

In the last decade, exploration for unconventional hydrocarbon (shale gas) reservoirs has been carried out in Poland. The drilling of wells in prospective shale gas areas supplies numerous physicochemical measurements from rock and reservoir fluid samples. The objective of this paper is to present the method that has been developed for finding similarities between individual geological structures in terms of their hydrocarbon generation properties and hydrocarbon resources. The measurements and geochemical investigations of six wells located in the Ordovician, Silurian, and Cambrian formations of the Polish part of the East European Platform are used. Cluster analysis is used to compare and classify objects described by multiple attributes. The focus is on the issue of generating clusters that group samples within the gas, condensate, and oil windows. The vitrinite reflectance value (Ro) is adopted as the criterion for classifying individual samples into the respective windows. An addi... [more]

The presence of natural fractures can significantly affect the quality of hydraulic fracturing operations in tightsand and shale or oil/gas formations. This paper describes the procedure used to model natural fractures with continuum damage tensor and the resulting orthotropic permeability tensor. A damage model that uses damage variable in tensor form is presented. In the procedure presented, a nonnegligible angle is assumed to exist between directions of principal stresses in the formation and in the natural-fractures-related damage tensor, and this difference in orientation is modeled by introducing local directions in the model. A damage-dependent permeability tensor in tabular form is then proposed. A second case scenario when the directions of principal stresses and natural fractures align is also analyzed. Numerical results of fracture distribution are presented for both cases, and differences can be seen from the computed contour of the damage variable. The results indicate tha... [more]

Negative processes occurring in the natural environment, under dynamic economy development, have become a factor for taking actions limiting destructive human activity. An important area in which initiatives are taken to improve the state of the natural environment is that of companies in the Transport-Shipping-Logistics Sector (TSL sector). The main objective of this article was to analyse the impact of the COVID-19 pandemic on the development of electromobility among companies in the Polish TSL sector, and identify factors that positively influenced or hindered its development during this time. For this purpose, qualitative and quantitative data analyses were carried out based on a literature review, statistical data, and direct research results. Descriptive statistics, chi-square test of concordance, and contingency coefficients were used to process the data. The results showed that the pandemic period did not affect the development of electromobility among TSL companies. Only a few... [more]

The use of phase change material (PCM) as a thermal energy storage system integrated in new buildings, and as retrofits in old buildings, proved its merit as promising renewable energy source. Heating and cooling building applications of PCM have been studied by plenty of scientists, globally, on the basis of numerical and experimental analysis. The performed experiments have mainly focused on one application—active or passive—using permanent prototype design for a certain duration and weather condition. The current study is a new review that focuses on two complementary aspects: (1) Reviewing latest studies in PCM domain and assessing the thermal performance of implemented prototypes within the conducted PCM experimental studies, namely, the effect of the design on the number of acceptable variables and possible PCM applications; and (2) suggesting a new, advanced, flexible, and modular prototype designed to enable several applications of PCM to be adapted and combined within the mode... [more]

This study presents a parameter estimation method that uses an enhanced gray wolf optimizer (EGWO) to optimize the parameters for a two-diode photovoltaic (PV) power generation system. The proposed method consists of three stages. The first stage converts seven parameters for the two-diode model into 17 parameters for different environmental conditions, which provides more precise parameter estimation for the PV model. A PV power generation model is then established to represent the nonlinear relationship between inputs and outputs. The second stage involves a parameter sensitivity analysis and uses the overall effect method to remove the parameters that have smaller effect on the output. The final stage uses an enhanced GWO that is associated with measurement data to optimally estimate the parameters that are selected in the second stage. When the parameters are estimated, the predicted value for the PV power output is calculated for specific values of solar irradiation and module tem... [more]

This review paper examines the key barriers to using green ammonia as an alternative fuel in maritime industry. A literature survey is performed based on research articles and grey literature, with the aim of discussing the technoeconomic problems with and benefits of ammonia and the relevant technologies. The limitations of ammonia as a maritime fuel and its supply chain, the expected percentage demand by 2030 and 2050, its economic performance compared to other shipping fuels such as hydrogen, and the current regulations that may impact ammonia as a maritime fuel are discussed. There are several key barriers to ammonia’s wide adoption: (1) High production costs, due to the high capital costs associated with ammonia’s supply chain; (2) availability, specifically the limited geographical locations available for ammonia bunkering; (3) the challenge of ramping up current ammonia production; and (4) the development of ammonia-specific regulations addressing issues such as toxicity, safety... [more]

There is global concern regarding access to energy, especially in developing countries, as set forth in the Sustainable Development Goals. Although Peru is classified as an emerging economy and would be expected to have achieved full energy coverage, the status of the access to fuels in Peru is unknown. The objective of this study was to comprehensively document the instruments and the progress made on the issue of access to modern fuels and technologies for cooking in Peru to explain the current situation and to highlight the main challenges that the country must face to achieve total access to modern energy sources. A comprehensive literature review was carried out for this work, covering a wide range of publications from 1983 to 2019. A total of 18 political and economic instruments and 95 voluntary instruments were analyzed. It made it possible to build a historical series of the main events leading to access to modern cooking fuels in Peru and to identify eight key challenges. The... [more]

This paper proposes a new structure of the dual-rotor hybrid-excited axial-flux permanent magnet vernier machine (DR-HEAFPMVM) with the modular stator and the consequent-pole PM (CPM) rotor for low-speed, high torque density applications such as in-wheel electric vehicles. The tooth-wound non-overlapping armature windings and direct current (DC) excitation windings are, respectively, arranged in stator main-teeth and split-teeth to obtain the modulated and adjustable air-gap flux densities, resulting in high torque density and outstanding flux-weakening capability. First, the design considerations, operation principles, and air-gap flux density distributions of the proposed machine are elaborated based on the air-gap permeance function. Then, the influence of the pole ratios (PRs) and the DC excitation currents on the main electromagnetic performances of the DR-HEAFPMVM, such as the flux-weakening capability and back-electromotive force (back-EMF), on-load electromagnetic torque, loss... [more]

As a result of the global population growth since World War II, and the major impact of the COVID-19 pandemic on the increase in the number of deaths, carbon emissions resulting from cremations in the funeral industry have increased by more than initially expected. In order to achieve the goal of the Kyoto Protocol and the Paris Agreement, to reach net-zero carbon neutrality by 2050, in this study, we comprehensively examined the literature on the differences in burial methods in terms of carbon emissions, and undertook stepwise analysis of the solution’s sequence from 1990 to 2050 using the recurrence relations in the trend changes using 5-year intervals. By collecting the annual number of global deaths and calculating the average carbon emissions per death to be 245 kg, we analyzed and compared these data with the annual carbon dioxide amount and global population until 2050. In addition, the results for cremation and Cryomation were analyzed and compared to construct a model of comp... [more]

Apart from protecting electrical machines from temperature related failures, thermal management of electrical machines is employed in the design phase of electrical machines to achieve higher efficiencies and higher power densities [...]

The paper presents the sweeping gas membrane distillation realised by using the capillary module (length 1.1 m and area 0.1 m2) without housing (module shell). During the tests, the feed was flowing inside the hydrophobic polypropylene membranes. The studies were performed for two variants of process: with pre-heating (313−330 K) and without heating of the feed (brines). Under low gas flow (0.005 m/s) the evaporation performance varied in the range of 0.15−0.25 L/m2h, depending on the relative humidity (42−63%) and the air temperature (293−300 K). The application of feed pre-heating to 330 K led to an increase in the evaporation performance to 2.4 L/m2h. The permeate flux increased by 60% when the air flow velocities between the capillaries increased to 1.8−2.5 m/s. Increasing the feed flow rate from 0.1 to 0.59 m/s led to increase the permeate flux about 20% for feed temperature 293−310 K, and over 55% for feed temperature higher than 323 K.

High-voltage direct-current (HVDC) transmission systems are considered an outstanding solution due to high electrical losses emerging from long-distance transmission. However, HVDC transmission lines (TLs) are vulnerable to lightning strikes. In this work, the Yunnan-Guizhou 500 kV HVDC transmission system is used as a case study to evaluate the impact of lightning strikes on DC-TL overvoltages, as no research studies have been conducted to assess the lightning transient behavior of DC-TLs. A comprehensive investigation of the 500 kV DC-TL transient performance during lightning strikes is performed, taking into account different technical aspects that have not been studied in detail by previous researchers. Additionally, analysis of the back-flashover phenomenon has not been conducted well in previous work, and results on the effect of changing the lightning strike current peak and tower grounding resistance on shielding-failure flashover are quite limited. The distributed-parameter mo... [more]

Leading-edge inflatable (LEI) kites use a pressurized tubular frame to structurally support a single skin membrane canopy. The presence of the tubes on the pressure side of the wing leads to characteristic flow phenomena for this type of kite. In this paper, we present steady-state Reynolds-Averaged Navier-Stokes (RANS) simulations for a LEI wing for airborne wind energy applications. Expanding on previous work where only the leading-edge tube was considered, eight additional strut tubes that support the wing canopy are now included. The shape of the wing is considered to be constant. The influence of the strut tubes on the aerodynamic performance of the wing and the local flow field is assessed, considering flow configurations with and without side-slip. The simulations show that the aerodynamic performance of the wing decreases with increasing side-slip component of the inflow. On the other hand, the chordwise struts have little influence on the integral lift and drag of the wing, ir... [more]

Selective catalytic reduction (SCR) and denitrification are the best technologies for nitrogen oxides (NOx) control in coal-fired power plants, and their denitration efficiency and ammonia escape rate are closely related to their internal flow characteristics. By adding a deflector to the SCR device, the flow field in the curve can be effectively improved, and the stable and efficient operation of the SCR device can be realized. Based on the numerical simulation method, the SCR system of a coking coal-fired boiler in a steel plant was simulated using k-ε (the turbulence model), and three design schemes of deflectors were proposed and numerically simulated simultaneously. After optimization, the ammonia injection grid’s downstream velocity variance coefficient CV was 6.69, the catalyst upper cross-section velocity variance coefficient was 11.84, the cross-sectional temperature average was 499 K, the maximum temperature deviation was 9 °C, the maximum-to-minimum temperature interval span... [more]

The decarbonisation of building heating in urban areas can be achieved by heat pumps connected to district heating networks. These could be ‘third-generation’ (85/75 °C), ‘fourth-generation’ (50/40 or 50/25 °C) or ‘fifth-generation’ (near ambient) water loops. Networks using thermochemical reactions should require smaller pipe diameters than water systems and be more economic. This work investigates thermochemical transmission systems based on liquid−gas absorption intended for application in urban district heating networks where the main heat source might be a MW scale heat pump. Previous studies of absorption for heat transmission have concentrated on long distance (e.g., 50 km) transmission of heat or cold utilizing waste heat from power stations or similar but these are not directly applicable to our application which has not been investigated before. Absorbent-refrigerant pairs are modelled using water, methanol and acetone as absorbates. Thermodynamic properties are obtained from... [more]

Although tight sandstone gas formations are abundant in China, their single-well productivities and exploitation efficiencies are restricted by water blocking from drilling and completion. At present, shut-in, chemical additive application, and hydraulic fracturing are the common approaches applied to handle this problem. However, these approaches are also characterized by low efficiencies or even cause secondary damage. In this study, the impact of high temperatures (of up to 800 °C) on the microstructure of a tight sandstone, including water blocking and gas permeability, are investigated through the electric heating of a simulated wellbore. The results show that the threshold temperature for fracturing of the tight sandstone is approximately 450 to 600 °C. Many secondary microcracks emerged near the wellbore beyond this temperature, improving the gas permeability, with some microcracks visible even after cooling. The gas permeability of the formation after heating to 800 °C increase... [more]

Post-mining deformations that occur on the surface pose a significant threat to natural environments and urbanized areas. Preventing the effects of deformation is a significant challenge for specialists in geotechnical and civil engineering. Geomaterials, such as geosynthetics or geopolymers, could minimize the damage that occurs. The first section of the article explores the securing of an area, strengthening the rock mass with geosynthetic materials. We provide descriptions of the properties of these materials and the method surrounding their introduction into the soil. The second section presents the research problem, i.e., we describe the damage caused by underground mining. In the last section, we propose a solution for securing the ground with the use of geogrids and geopolymer injections into the rock mass. The analyses led us to conclude that an area subjected to mining influences may be strengthened by the use of geosynthetic materials. The use of geosynthetics in a mining are... [more]

Acceleration of energy transition will become the crucial social, political and technical challenge of the 21st century and will be largely associated with the growing use of renewable energy sources, including solar power. This study provides some experimental results of using solar hot water systems (HWS) embedded in apartment buildings located in the energy-efficient district called Zhatay in Yakutsk city, in the Republic of Sakha (Yakutia). The low annual solar fraction of HWS was found for 2019. It is equal to 0.2869 and caused by thermal energy loss from the hydraulic circuit during the nighttime. The study suggests increasing solar fraction in HWS and implementing a software and hardware system. The experimental evaluation of these studies was performed by testing a solar water heating pilot plant in Kaftanchikovo village in Tomsk Region (Western Siberia). As a result of HWS testing, it was found that the annual solar fraction can be significantly increased by preventing the hea... [more]

The scrapping of old waterflooding wells and the increase in new waterflooding wells results in mixed flooding of high−low pressure wells in various oil layers in waterflooding systems. In order to meet production operation requirements, the whole system is in a state of high pressure, which leads to an increase in energy consumption and complicates the operation of waterflooding networks. According to the pressure distribution of wells, proceeding with regional accurate waterflooding can reduce operation costs and improve development efficiency. Considering the technical constraints of waterflooding networks, a method was proposed, which can quantitatively optimize classification and zoning for waterflooding of high−low pressure wells according to the pressure of networks and wells. At the same time, the ant colony algorithm and genetic algorithm were fused to form a new adaptive ant colony genetic hybrid algorithm, which can effectively determine the best pumping scheme of the waterf... [more]

To investigate the parameters of sucrose dust explosion, the minimum ignition energy (MIE) and minimum ignition temperature (MIT) were evaluated. The experiments tested the MIE of sucrose dust under different conditions of dust quantity, ignition delay time (IDT), and powder injection pressure (PIP). The experiments tested the MIT of different particle sizes. The results demonstrate that the MIE of sucrose powder under three conditions was an open-up quadratic polynomial. When the dust quantity, the IDT, and PIP were 0.5 g (417 g/m3), 90 ms, and 150 kPa, respectively, the MIE was 58.9 mJ, 62.6 mJ, and 52.4 mJ. The MIT was positively correlated with the particle size of sucrose dust, and the MIT was 340 °C. At the molecular level, the “O−H” bonds of the sucrose molecule hydroxyl groups were broken by the discharge of electrodes or high temperature to generate H2. The combustion of H2 caused the explosion to spread to the surrounding sucrose dust and made the deposited dust rise, forming... [more]

The importance of power in society is indisputable. Virtually all economic activities depend on electricity. The electric power systems are complex, and move studies in different areas are motivated to make them more efficient and solve their operational problems. The smart grids emerged from this approach and aimed to improve the current systems and integrate electric power using alternative and renewable sources. Restoration techniques of these networks are being developed to reduce the impacts caused by the usual power supply interruptions due to failures in the distribution networks. This paper presents the development and evaluation of the performance of a multi-objective version of the Bacterial Foraging Optimization Algorithm for finding the minor handling switches that maximize the number of buses served, keeping the configuration radial system and within the limits of current in the conductors and bus voltage. An electrical system model was created, and routines were implement... [more]