Energies, Volume 13, Issue 1 (January-1 2020) – 286 articles

A horizontal well with hydraulic fractures is key to forming a fracture network in oil shale for the generated hydrocarbon flows. By considering the influence of anisotropic strength, a prediction model is proposed for fracture initiation by studying different fracture initiation modes (FIMs) in oil shale: failure of the intact rock matrix and of the bedding planes. Through a case study on Nong’an oil shale, the influences of wellbore trajectory and bedding planes on the fracture initiation pressure (FIP), location (FIL), and FIM were analyzed and the induced changes in wellbore trajectory design were concluded. The preferred angle between the wellbore axis and the minimum horizontal principal stress was the same of 90° or 270°, when the lowest required FIP corresponded to the failure of the intact rock matrix. However, when the angle corresponded to the failure of the bedding planes, the preferred direction of the wellbore axis was away from the fixed direction and not corresponding to the lowest required FIP due to the fracture morphology. The error between the theoretical and experimental results ranges from 7% to 9%. This research provides a framework for the design of horizontal wellbore trajectories in oil shale, for easier fracture initiation and more complex fracture networks. Full article

Catalytic hydrotreatment is recognized as an efficient method to improve the properties of pyrolysis liquids (PO) to allow co-feeding with fossil fuels in conventional refinery units. The promising catalyst recipes identified so far are catalysts with high nickel contents (38 to 57 wt.%), promoted by Cu, Pd, Mo and/or a combination, and supported by SiO₂, SiO₂-ZrO₂, SiO₂-ZrO₂-La₂O₃ or SiO₂-Al₂O₃. To gain insights into the reactivity of the pyrolytic sugar (PS) and pyrolytic lignin (PL) fraction of PO, hydrotreatment studies (350 °C, 120 bar H₂ pressure (RT) for 4 h) were performed in a batch autoclave. Catalyst performance was evaluated by considering the product properties (H/C ratio, the charring tendency (TGA) and molecular weight distribution (GPC)) and the results were compared with a benchmark Ru/C catalyst. All Ni based catalysts gave products oils with a higher H/C compared to Ru/C. The Mo promoted catalyst performed best, giving a product with the highest H/C ratio (1.54) and the lowest TG residue (0.8 wt.% compared to 12 wt.% for the fresh PS). The results further revealed that the PS fraction is highly reactive and full conversion was achieved at 350 °C. In contrast, the PL fraction was rather inert, and only part of the PL fraction was converted. The fresh and spent catalysts after the hydrotreatment of the PS and PL fractions were characterized by elemental analysis, powder X-Ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM-EDX). The results revealed that the use of PS as the feed leads to higher amounts of coke deposits on the catalysts, and higher levels of Ni agglomeration when compared to experiments with PL and pure PO. This proofs that proper catalyst selection for the PS fraction is of higher importance than for the PL fraction. The Mo promoted Ni catalysts showed the lowest amount of coke and the lowest tendency for Ni nanoparticle agglomeration compared to the monometallic Ni and bimetallic Ni-Cu catalysts. Full article

The quick U-building (QUB) method is used to measure the overall heat loss coefficient of buildings during one to two nights by applying heating power and by measuring the indoor and the outdoor temperatures. In this paper, the numerical model of a real house, previously validated on experimental data, is used to conduct several numerical QUB experiments. The results show that, to some extent, the accuracy of QUB method depends on the boundary conditions (solar radiation), initial conditions (initial power and temperature distribution in the walls) and on the design of QUB experiment (heating power and duration). QUB method shows robustness to variation in the value of the overall heat loss coefficient for which the experiment was designed and in the variation of optimum power for the QUB experiments. The variations in the QUB method results are smaller on cloudy than on sunny days, the error being reduced from about 10% to about 7%. A correction is proposed for the solar radiation absorbed by the wall that contributes to the evolution of air temperature during the heating phase. Full article

Oscillating water column (OWC) devices, either fixed or floating, are the most common wave energy converter (WEC) devices. In this work, the fluid dynamic interaction between waves and a U-shaped OWC breakwater embedding a Wells turbine has been investigated through unsteady Computational Fluid Dynamic (CFD) simulations. The full-scale plant installed in the harbor of Civitavecchia (Italy) was numerically modeled. A two-dimensional domain was adopted to simulate the unsteady flow, both outside and inside the U-OWC device, including the air chamber and the oscillating flow inside the conduit hosting the Wells turbine. For the numerical simulation of the damping effect induced by the Wells turbine connected to the air chamber, a porous medium was placed in the computational domain, representing the conduit hosting the turbine. Several simulations were carried out considering periodic waves with different periods and amplitudes, getting a deep insight into the energy conversion process from wave to the turbine power output. For this purpose, the three main steps of the overall energy conversion process have been examined. Firstly, from the wave power to the power of the water oscillating flow inside the U-duct. Secondly, from the power of the oscillating water flow to the air pneumatic power. Finally, from the air pneumatic power to the Wells turbine power output. Results show that the U-OWC can capture up to 66% of the incoming wave power, in the case of a wave period close to the eigenperiod of the plant. However, only two-thirds of the captured energy flux is available to the turbine, being partially dissipated due to the losses in the U-duct and the air chamber. Finally, the overall time-average turbine power output is evaluated showing that it is strongly influenced by a suitable choice of the turbine characteristics (mainly geometry and rotational speed). Full article

Variable structure control with sliding mode can provide good control performance and excellent robustness. Unfortunately, the chattering phenomenon investigated due to discontinuous switching gain restricting their applications. In this paper, a chattering free improved variable structure control (IVSC) for a class of mismatched uncertain interconnected systems with an unknown time-varying delay is proposed. A sliding function is first established to eliminate the reaching phase in traditional variable structure control (TVSC). Next, a new reduced-order sliding mode estimator (ROSME) without time-varying delay is constructed to estimate all unmeasurable state variables of plants. Then, based on the Moore-Penrose inverse approach, a decentralized single-phase robustness sliding mode controller (DSPRSMC) is synthesized, which is independent of time delays. A DSPRSMC solves a complex interconnection problem with an unknown time-varying delay term and drives the system’s trajectories onto a switching surface from the initial time instance. Particularly, by applying the well-known Barbalat’s lemma, the chattering phenomenon in control input is alleviated. Moreover, a sufficient condition is established by using an appropriate Lyapunov theory and linear matrix inequality (LMI) method such that a sliding mode dynamics is asymptotically stable from the beginning time. Finally, a developed method is validated by numerical example with computer simulations. Full article

Strong tectonic movement brings great risk to exploration of shale gas in southern China, especially in Lower Cambrian shale with complex tectonic backgrounds, which has good hydrocarbon-generation matter but low or no gas content. In this paper, the Lower Cambrian shale from the southeast Chongqing region, located in the Upper Yangtze Platform, and the Xiuwu Basin, located in the Lower Yangtze Platform, were selected as the research objects. First, the gas components in shale gas samples were measured, then analysis of nitrogen isotopic was used to reveal the nitrogen sources. Using regional geological backgrounds, core description, and seismic interpretation, combined with the perpendicular and parallel permeability test and focused ion beam–helium ion microscopy (FIB–HIM) observation, the reasons for high content of nitrogen in the Lower Cambrian shale from the Xiuwu Basin and the Southeast Chongqing region were clarified. The results indicate that the main sources of nitrogen in the Lower Cambrian shale gas at the Southeast Chongqing region is the thermal evolution of organic matter and atmosphere. Nitrogen in the atmosphere is filled into the shale reservoir through migration channels formed by detachment layers at the bottom of the Lower Cambrian, shale stratification planes, and widespread thrust faults. Nitrogen was also produced during the thermal evolution of organic matter. Both are responsible for the low content of hydrocarbon and high content of nitrogen of shale gas in the Southeast Chongqing region. Further, the main sources of nitrogen in the Lower Cambrian shale gas at the Xiuwu Basin is the upper mantle, superdeep crust, and atmosphere. Nitrogen in the atmosphere is also filled into the shale reservoir through migration channels formed by detachment layers at the bottom of the Lower Cambrian, shale stratification planes, and widespread thrust faults. Nitrogen was also produced by volcanism during the Jurassic. Both are the causes of the low content of hydrocarbon and high content of nitrogen in shale gas in the Xiuwu Basin. Finally, destruction models for shale gas reservoirs with complex tectonic backgrounds were summarized. This research aimed to provide a theoretical guidance for shale gas exploration and development in areas with complex tectonic backgrounds. Full article

The paper investigates the dynamics of the thermal field of the ACCC (aluminum conductor composite core) line. The system was heated by solar radiation and current flow. Conductor cooling was modeled using the total heat transfer coefficient as the sum of convective and radiative components. The temperature increase generated by the current is described by a system of parabolic differential equations with an appropriate set of boundary, initial and continuity condition. The mentioned boundary-initial problem was solved by a modified Green’s method, adapted to the layered structure of the system. For this purpose, Green’s functions, as the kernels of integral operators inverse to differential ones, were determined. Aluminum resistivity and heat transfer coefficient change significantly with temperature. For this reason, the solution to the problem is presented in the form of a lower and upper estimation of the heating curve and local time constant. A steady-state current rating was also determined. The results are presented graphically and verified by other methods (power balance and finite element). The physical interpretation of the presented solution is also given. Full article

In order to solve issues concerning performance induction and in-cylinder heat accumulation of a certain heavy-duty diesel engine in a plateau environment, working state parameters and performance indexes of diesel engine are calculated and optimized using the method of artificial neural network and genetic algorithm cycle multi-objective optimization. First, with an established diesel engine simulation model and an orthogonal experimental method, the influence rule of five performance indexes affected by five working state parameters are calculated and analyzed. Results indicate the first four of five working state parameters have a more prominent influence on those five performance indexes. Subsequently, further calculation generates correspondences among four working state parameters and five performance indexes with the method of radial basis function neural network. The predicted value of the trained neural network matches well with the original one. The approach can fulfill serialization of discrete working state parameters and performance indexes to facilitate subsequent analysis and optimization. Next, we came up with a new algorithm named RBFNN & GACMOO, which can calculate the optimal working state parameters and the corresponding performance indexes of the diesel engine working at 3700 m altitude. At last, the bench test of the diesel engine in a plateau environment is employed to verify accuracy of the optimized results and the effectiveness of the algorithm. The research first combined the method of artificial neural network and genetic algorithm to specify the optimal working state parameters of the diesel engine at high altitudes by focusing on engine power, torque and heat dissipation, which is of great significance for improving both performance and working reliability of heavy-duty diesel engine working in plateau environment. Full article

Current disquisition is presented to excogitate heat and mass transfer features of second grade fluid flow generated by an inclined cylinder under the appliance of diffusion, radiative heat flux, convective and Joule heating effects. Mathematical modelling containing constitutive expressions by obliging fundamental conservation laws are constructed in the form of partial differential equations. Afterwards, transformations are implemented to convert the attained partial differential system into ordinary differential equations. An implicit finite difference method known as the Keller Box was chosen to extract the solution. The impact of the flow-controlling variables on velocity, temperature and concentration profiles are evaluated through graphical visualizations. Variations in skin friction, heat transfer and mass flux coefficients against primitive variables are manipulated through numerical data. It is inferred from the analysis that velocity of fluid increases for incrementing magnitude of viscoelastic parameter and curvature parameter whereas it reduces for Darcy parameter whereas skin friction coefficient decreases against curvature parameter. Assurance of present work is manifested by constructing comparison with previous published literature. Full article

Electric vehicles (EVs) with wireless power transfer (WPT) systems are convenient, but WPT technology will produce a strong stray electromagnetic field (EMF) in the surrounding space when the system works with high power. Shielding coils can reduce stray EMF efficiently without additional control, and they have advantages of being simple, light, and cheap. In this paper, the series-opposing structure is compared systematically with the inductive structure based on circuit theory and electromagnetic field theory. Simplified circuit models are proposed to give an intuitive and comprehensive analysis of transfer efficiency. Electric field analysis and finite element analysis (FEA) is used to explain the functional principles of shielding coils and to compare the EMF distribution excited by two structures. The simulation results show that both structures decrease the mutual inductance and perform better than the system without shielding coils when they have the same transfer efficiency. Further, the inductive structure system performs best. The most important between two structures is that the shielding effects is independent of turns of shielding coils for inductive structure, while it can be adjusted by changing turns of shielding coils for the series-opposing structure. The experimental results show that the EMF is reduced by 65% for the inductive structure and 40% for the series-opposing structure. The theoretical analysis is confirmed by experimental results. Full article

The economic and environmental performance of a district heating (DH) system is to a great extent affected by the size and dynamic behavior of the DH load. By implementing energy efficiency measures (EEMs) to increase a building’s thermal performance and by performing cost-optimal energy renovation, the operation of the DH system will be altered. This study presents a systematic approach consisting of building categorization, life cycle cost (LCC) optimization, building energy simulation and energy system optimization procedures, investigating the profitability and environmental performance of cost-optimal energy renovation of a historic building district on the DH system. The results show that the proposed approach can successfully be used to predict the economic and environmental effects of cost-optimal energy renovation of a building district on the local DH system. The results revealed that the financial gains of the district are between 186 MSEK (23%) and 218 MSEK (27%) and the financial losses for the DH system vary between 117–194 MSEK (5–8%). However, the suggested renovation measures decrease the local and global CO₂ emissions by 71–75 metric ton of CO_2eq./year (4%) and 3545–3727 metric ton of CO_2eq./year (41–43%), respectively. Total primary energy use was decreased from 57.2 GWh/year to 52.0–52.2 GWh/year. Full article

The integration of Distributed Energy Resources (DERs) introduces a non-conventional two-way power flow which cannot be captured well by traditional model-based techniques. This brings an unprecedented challenge in terms of the accurate localization of faults and proper actions of the protection system. In this paper, we propose a data-driven fault localization strategy based on multi-level system regionalization and the quantification of fault detection results in all subsystems/subregions. This strategy relies on the tree segmentation criterion to divide the entire system under study into several subregions, and then combines Support Vector Data Description (SVDD) and Kernel Density Estimation (KDE) to find the confidence level of fault detection in each subregion in terms of their corresponding p-values. By comparing the p-values, one can accurately localize the faults. Experiments demonstrate that the proposed data-driven fault localization can greatly improve the accuracy of fault localization for distribution systems with high DER penetration. Full article

The deployment of highly efficient cooling equipment is expected to promote energy savings and greenhouse gas emissions reductions in the tropics. A ground source heat pump (GSHP) has high energy-savings potential for use in Bangkok, Thailand. This study aimed to elucidate the operational conditions of a GSHP when used in Bangkok which was expected to achieve a higher efficiency than an air source heat pump (ASHP) over the long term. An operational experiment on a pilot facility in Bangkok and a simulation over a three-year GSHP operation were conducted. As a result of the operational experiment and simulation, the proposed operational condition was that the 90th percentile value of the hourly heat pump (HP) inlet temperature did not exceed 5 °C above that of the hourly annual ambient temperature during the third year of operation. When a GSHP designed based on this condition was utilized for a small government building, the required number of boreholes were 24, 4, and 3 for air-conditioned areas of 200, 40, and 25 m², respectively, which achieved 40% energy savings. Thus, a small-scale GSHP in Bangkok designed based on the proposed condition can achieve high efficiency within space limitations. Full article

This paper deals with the implementation of a new technique of stochastic search to find the best set of parameters in a mathematical model, applied to the single cage (SC) model of the induction motor (IM). The technique includes a new strategy to generate variable constraints of the domain, seven error functions, weight for the operating zones of the IM, and multi-objective functions. The results are validated with experimental data of the torque and current in an IM, and show better fitting to the experimental curves compared with the results of two different techniques, one deterministic and the other one stochastic. The results obtained allow us to conclude that the best set of parameters for the model depends on the weights assigned to the objective functions and to the operating zones. Full article

This paper presents a highly efficient three-port converter to integrate energy storage (ES) and wireless power transfer (WPT) systems. The proposed converter consists of a bidirectional DC-DC converter and an AC-DC converter with a resonant capacitor. By sharing an inductor and four switches in the bidirectional DC-DC converter, the bidirectional DC-DC converter operates as a DC-DC converter for ES systems and simultaneously as a DC-AC converter for WPT systems. Here, four switches are turned on under the zero voltage switching conditions. The AC-DC converter for WPT system achieves high voltage gain by using a resonance between the resonant capacitor and the leakage inductance of a receiving coil. A 100-W prototype was built and tested to verify the effectiveness of the converter; it had a maximum power-conversion efficiency of 95.9% for the battery load and of 93.8% for the wireless charging load. Full article

In order to calculate heat transfer capacity and air-side pressure drop of an annular radiator (AR), one performance calculation method was proposed combining heat transfer unit (HTU) simulation and plate-and-fin heat exchanger (PFHX) performance calculation formulas. This method can obtain performance data with no need for meshing AR as a whole, which can be convenient and time-saving, as grid number is reduced in this way. It demonstrates the feasibility of this performance calculation method for engineering applications. In addition, based on the performance calculation method, one configuration optimization method for AR using nondominated sorted genetic algorithm-II (NSGA-II) was also proposed. Fin height (FH) and number of fins in circumferential direction (NFCD) were optimized to maximize heat transfer capacity and minimize air-side pressure drop. Three optimal configurations were obtained from the Pareto optimal points. The heat transfer capacity of the optimal configurations increased by 22.65% on average compared with the original configuration, while the air-side pressure drop decreased by 33.99% on average. It indicates that this configuration optimization method is valid and can provide a significant guidance for AR design. Full article

Roof collapse and wall spalling in mines commonly occurred. Grouting in the rock mass of a collapsed zone is one of the most effective technologies for solving this problem. Through grouting, the rock mass of a collapsed zone can be cemented into continuous and stable blocks, and the physical and mechanical parameters of the rock mass can be significantly improved. In order to investigate the mechanical properties and damage of rock samples after the injection of a high-polymer material, we conducted uniaxial compression tests in a laboratory on grouted specimens. A high-polymer material is commonly used to address the gangue stacking that is caused by large roof collapse and wall spalling accidents in the mining face and the cracking of coal walls. Research has shown that a high-polymer material effectively solidifies gangues. The results indicate a micromechanics effect of the grouted specimens under uniaxial compression. The compressive strength, fracture propagation, damage mode, and other specimen behaviors are related to the amount of injected high-polymer materials. A high-polymer material substantially improves the mechanical strength of the prefabricated fractured coal and rock mass via strong material adhesion. The vertically- and horizontally-consolidated coal/rock masses exhibit different properties. The use of a high-polymer material results in distinct properties of the consolidated coal and rock masses. Full article

In this study, the vertically-oriented pulsating heat pipe (PHP) heat exchangers charged with either water or HFE-7000 in a filling ratio of 35% or 50% were fabricated to exchange the thermal energy between two air streams in a parallel-flow arrangement. Both the effectiveness of the heat exchangers and the thermal resistance of PHP with a size of 132 × 44 × 200 mm, at a specific evaporator temperature ranging from 55 to 100 °C and a specific airflow velocity ranging from 0.5 to 2.0 m/s were estimated. The results show that the heat pipe charged with HFE-7000 in either filling ratio is likely to function as an interconnected array of thermosiphon under all tested conditions because of the unfavorable tube inner diameter, whereas the water-charged PHP possibly creates the pulsating movement of the liquid and vapor slugs once the evaporator temperature is high enough, especially in a filling ratio of 50%. The degradation in the thermal performance of the HFE-7000-charged PHP heat exchanger resulted from the non-condensable gas in the tube became diminished as the evaporator temperature was increased. By examining the effectiveness of the present heat exchangers, it is suggested that water is a suitable working fluid while employing the PHP heat exchanger at an evaporator temperature higher than 70 °C. On the other hand, HFE-7000 is applicable to the PHP used at an evaporator temperature lower than 70 °C. Full article

Sand production from a poorly consolidated reservoir could give rise to some severe problems during production. Holding the load bearing solids in place is the main goal of any sand control technique. The only sand control techniques that have found applications in steam assisted gravity drainage (SAGD) are some of the mechanical methods, including wire wrapped screens, slotted liners and more recently, punched screens. Slotted liner is one of the most effective mechanical sand control methods in the unconsolidated reservoir exploitation, which has proven to be the preferred sand control method in the SAGD operations. The main advantage of the slotted liners that makes them suitable for SAGD operations is their superior mechanical integrity for the completion of long horizontal wells. This study is an attempt to increase the existing understanding of the fines migration, sand production, and plugging tendency for slotted liners by using a novel large-scale scaled completion test (SCT) facility. A triaxial cell assembly was used to load sand-packs with specified and controlled grain size distribution, shape and mineralogy, on multi-slot sand control coupons. Different stress levels were applied parallel and perpendicular to different combinations of slot width and density in multi-slot coupons, while brine was injected from the top of the sand-pack towards the coupon. At each stress level, the mass of produced sand was measured, and the pressure drops along the sand-pack and coupon were recorded. Fines migration was also investigated by measuring fines/clay concentration along the sand-pack. The current study employed multi-slot coupons to investigate flow interactions among slots and its effect on the flow performance of liner under typically encountered stresses in SAGD wells. According to the experimental observations, increasing slot width generally reduces the possibility of pore plugging caused by fines migration. However, there is a limit for slot aperture beyond which the plugging is not reduced any further, and only a higher level of sanding occurs. Test measurements also indicated that besides the slot width, the slot density also influences the level of plugging and sand production and must be included in the design criteria. Full article

This manuscript presents an advanced exergo-economic analysis of a waste heat recovery system based on the organic Rankine cycle from the exhaust gases of an internal combustion engine. Different operating conditions were established in order to find the exergy destroyed values in the components and the desegregation of them, as well as the rate of fuel exergy, product exergy, and loss exergy. The component with the highest exergy destroyed values was heat exchanger 1, which is a shell and tube equipment with the highest mean temperature difference in the thermal cycle. However, the values of the fuel cost rate (47.85 USD/GJ) and the product cost rate (197.65 USD/GJ) revealed the organic fluid pump (pump 2) as the device with the main thermo-economic opportunity of improvement, with an exergo-economic factor greater than 91%. In addition, the component with the highest investment costs was the heat exchanger 1 with a value of 2.769 USD/h, which means advanced exergo-economic analysis is a powerful method to identify the correct allocation of the irreversibility and highest cost, and the real potential for improvement is not linked to the interaction between components but to the same component being studied. Full article

Thermal solar systems are interesting solutions to reduce CO ${}_2$ emissions and gradually promote the use of renewable sources. However, sizing such systems and analysing their behavior are still challenging issues, especially for the trade-off between useful solar energy maximization and stagnation risk minimization. The new EPB (Energy Performance of Buildings) standard EN 15316-4-3:2017 offers several methods to evaluate the performance of a forced circulation solar system. One of them is a dynamic hourly method that must be used together with EN 15316-5:2017 for the simulation of the stratified storage tank connected with the solar loop. In this work, such dynamic hourly method is extended to provide more realistic predictions. In particular, modeling of the pump operation due to solar fluid temperature exceeding a set threshold, or due to low temperature differential between solar field and storage tank, is introduced as an on–off control. The implemented code is applied to a case study of solar system for the preparation of domestic hot water and the impact of different design parameters is evaluated. The model predicts a higher risk of overtemperature lock-out or stagnation when the solar field surface is increased, the storage volume is reduced and water consumption is set to zero to simulate summer vacation periods. Finally, a simple modulating control with a time step of a few seconds to a few minutes is introduced, quantitatively showing the resulting benefits in terms of useful solar energy increase, back-up operation savings and reduced auxiliary energy use. Full article

Cellulosic insulation paper is usually used in oil-immersed transformer insulation systems. In this study, the molecular dynamics method based on reaction force field (ReaxFF) was used to simulate the pyrolysis process of a cellobiose molecular model. Through a series of ReaxFF- Molecular Dynamics (MD) simulations, the generation path of ethanol at the atomic level was studied. Because the molecular system has hydrogen bonding, force-bias Monte Carlo (fbMC) is mixed into ReaxFF to reduce the cost of calculation by reducing the sampled data. In order to ensure the reliability of the simulation, a model composed of 20 cellobioses and a model composed of 40 cellobioses were respectively established for repeated simulation in the range of 500–3000 K. The results show that insulating paper produced ethanol at extreme thermal fault, and the intermediate product of vinyl alcohol is the key to the aging process. It is also basically consistent with others’ previous experiment results. So it can provide an effective reference for the use of ethanol as an indicator to evaluate the aging condition of transformers. Full article

This paper describes the design of a Series-Connected Device based on a fixed–frequency LLC resonant converter (SCDLLC). Isolation of the dc-dc converter like the LLC resonant converter is used for the stability of the high voltage system such as a solid-state-transformer (SST). The series-connected devices driving method is one of the methods applicable to a high voltage system. When driving series-connected devices, an auxiliary circuit for voltage balancing between series-connected devices is required, which can be simply implemented using a passive element. In this paper, LLC converter design with balancing circuits configured in parallel with a device is provided, and both the simulations and experiments were performed. Full article

Microbial fuel cell (MFC) has the potential to become a promising sustainable technology of wastewater treatment. Usually, the investigations on MFCs are aimed at maximized power production in the system. In this article, we focused on the optimization of wood industry wastewater treatment in MFC, in combination with municipal wastewater as a source of microorganisms. We investigated the influence of different external resistance (2000 Ω, 1000 Ω, 500 Ω, and 100 Ω) on power density and wastewater treatment efficiency (chemical oxygen demand (COD) removal) in 1-month MFC operation time. We found that the highest COD removal was for MFCs under R = 1000 Ω after 22 days of MFC operation, while the highest current density was obtained for the lowest applied resistance. The results imply that wastewater treatment parameters such as resistance and time of MFC operation should be a subject of optimization for each specific type of wastewater used, in order to maximize either wastewater treatment efficiency or power production in MFC. Thus, optimization of power production and COD removal efficiency in MFCs need to be run separately as different resistances are required for maximizing these two parameters. When COD removal efficiency is a subject of optimization, there is no universal value of external resistance, but it should be set to the specific wastewater characteristics. Full article

Agriculture affects both the quantity and the quality of water available for other purposes, which becomes problematic, especially during increasingly frequent severe droughts. This requires tapping into the resources that are typically neglected. One such resource is a by-product of anaerobic digestion, in which moisture content typically exceeds 90%. Application of hydrothermal carbonization process (HTC) to this residue could partially remove organic and inorganic material, improve dewatering, decrease the overall solid mass, sanitize the digestate, change its properties, and eliminate problems related with emissions of odors from the installation. However, a significant gap still exists in terms of the dewatering of the hydrochars and the composition of the effluents. This work presents results of experimental investigation focused on the removal of organic compounds from the HTC effluent. Results of qualitative and quantitative analysis of liquid by-products of HTC of the agricultural digestate showed that acetic acid, 3-pyridinol, 1-hydroxyacetone, and 1,3-propanediol were the main liquid organic products of the process. Application of ultrafiltration process with the use of 10 kDa membrane for liquid HTC by-product treatment allows for the reduction of chemical oxygen demand up to 30%, biological oxygen demand up to 10%, and dissolved organic carbon up to 21%. Full article

Different scenarios at different scales must be studied to help define long term policies to decarbonate our societies. In this work, we analyse the Belgian energy system in 2035 for different carbon emission targets, and accounting for electricity, heat, and mobility. To achieve this objective, we applied the EnergyScope Typical Days open source model, which optimises both the investment and the operation strategy of a complete energy system for a target year. The model includes 96 technologies and 24 resources that have to supply, hourly, the heat, electricity, mobility, and non-energy demands. In line with other research, we identify and quantify, with a merit order, different technological steps of the energy transition. The lack of endogenous resources in Belgium is highlighted and estimated at 275.6 TWh/y. It becomes obvious that additional potentials shall be obtained by importing renewable fuels and/or electricity, deploying geothermal energy, etc. Aside from a reduction of the energy demand, a mix of solutions is shown to be, by far, the most cost effective to reach low carbon emissions. Full article

Finite set-model predictive control (FS-MPC) is used for power converters and drives having unique advantages as compared to the conventional control strategies. However, the computational burden of the FS-MPC is a primary concern for real-time implementation. Field programmable gate array (FPGA) is an alternative and exciting solution for real-time implementation because of the parallel processing capability, as well as, discrete nature of the hardware platform. Nevertheless, FPGA is capable of handling the computational requirements for the FS-MPC implementation, however, the system development involves multiple steps that lead to the time-consuming debugging process. Moreover, specific hardware coding skill makes it more complex corresponding to an increase in system complexity that leads to a tedious task for system development. This paper presents an FPGA-based experimental implementation of FS-MPC using the system modeling approach. Furthermore, a comparative analysis of FS-MPC in stationary αβ and rotating dq frame is considered for simulation as well as experimental result. The FS-MPC for a three-phase voltage source inverter (VSI) system is developed in a realistic digital simulator integrated with MATLAB-Simulink. The simulated controller model is further used for experimental system implementation and validation using Xilinx FPGA: Zedboard Zynq Evaluation and Development Kit. The digital simulator termed as Xilinx system generator (XSG) provided by Xilinx is used for modeling-based FPGA design. Full article

Combustion characteristics were studied experimentally for single droplets of fuel slurries based on wet coal processing waste with municipal solid waste components (cardboard, plastic, rubber, and wood) and used turbine oil. We established the ignition delay time for three various groups of fuel compositions in motionless air at 600–1000 °C. The minimum values are 3 s, and the maximum ones are 25 s. The maximum temperatures in the droplet vicinity reach 1300 °C during fuel combustion for compositions with 10% of used oil. The combustion temperatures of fuel compositions without oil are 200–300 °C lower. The concentrations of anthropogenic emissions in flue gases do not exceed those from dry coal combustion. Adding used oils to composite fuels reduces the concentrations of dioxins and furans in flue gases when municipal solid waste in the fuel burns out due to high combustion temperatures. Based on the experimental research findings, we have elaborated a strategy of combined industrial and municipal waste recovery by burning it as part of composite fuels, as illustrated by three neighboring regions of the Russian Federation with different industrial structures and levels of social development. This strategy suggests switching three typical coal-fired thermal power plants (one in each of the regions) to composite liquid fuel. It will reduce the hazard of waste to the environment and decrease the consumption of high-quality coals for power generation. Implementing the developed strategy for 25 years will save 145 Mt of coal and recover 190–260 Mt of waste. The positive economic effect, considering the modernization of fuel handling systems at thermal power plants and the construction of a fuel preparation plant, will make up 5.7 to 6.9 billion dollars, or 65–78%, respectively, of the main costs of three thermal power plants operating on coal within the identical period. Full article

Reynolds-stress closure modeling is critical to Reynolds-averaged Navier-Stokes (RANS) analysis, and it remains a challenging issue in reducing both structural and parametric inaccuracies. This study first proposes a novel algebraic stress model named as tensorial quadratic eddy-viscosity model (TQEVM), in which nonlinear terms improve previous model-form failure due to neglection of nonlocal effects. Then a data-driven regression model based on a fully-connected deep neural network is designed to determine the TQEVM coefficients. The well-trained data-driven model using high-fidelity direct numerical simulation (DNS) data successfully learned the underlying input-output relationships, further obtaining spatial-dependent optimal values of these coefficients. Finally, detailed validations are made in wall-bounded flows where nonlocal effects are expected to be significant. Comparative results indicate that TQEVM provides improvements both for the stress-strain misalignment and stress anisotropy, which are clear advantages over linear and quadratic eddy-viscosity models. TQEVM extends to the scope of resolution to the wall distance $y^{+}\approx 9$ as well as provides a realizable solution. RANS simulations with TQEVM are also carried out and the obtained mean-flow quantities of interest agree well with DNS. This work, therefore, results in a high-fidelity representation of Reynolds stresses and contributes to further understanding of machine-learning-assisted turbulence modeling and regression analysis. Full article

This work presents a fault ride-through control scheme for a non-isolated power topology used in a hybrid energy storage system designed for DC microgrids. The hybrid system is formed by a lithium-ion battery bank and a supercapacitor module, both coordinated to achieve a high-energy and high-power combined storage system. This hybrid system is connected to a DC bus that manages the power flow of the microgrid. The power topology under consideration is based on the buck-boost bidirectional converter, and it is controlled through a bespoke modulation scheme to obtain low losses at nominal operation. The operation of the proposed control scheme during a DC bus short-circuit failure is shown, as well as a modification to the standard control to achieve fault ride-through capability once the fault is over. The proposed control provides a protection to the energy storage systems and the converter itself during the DC bus short-circuit fault. The operation of the converter is developed theoretically, and it has been verified through both simulations and experimental validation on a built prototype. Full article