This paper suggests a heat recovery concept that is based on preheating/precooling the cold/hot fresh outside air by means of the relatively hot/cold exhaust air in winter/summer weather conditions. To investigate the feasibility of such a concept, an experimental setup is established to simulate conditions similar to an All-Air HVAC system. The prototype consists of a 6.7-m3 air-conditioned chamber by means of a split unit of 5.3-kW capacity. The heat recovery module consists of a duct system that is used to reroute the exhaust air from a conditioned chamber to flow through the fin side of a fin-and-tube heat exchanger of crossflow type. At the same time, outside, fresh air is flowing through the tube side of the fin-and-tube heat exchanger. A parametric study is performed to assess the amount of heat that can be recovered by varying the mass flow rates on both the duct and heat exchanger sides. The results show that up to 200 W of power can be saved for an exhaust flow rate of 0.1 kg... [more]

In this paper, a method of efficient hydrogen production using low-power electrolysis based on pre-magnetic polarization was proposed in order to improve the rate of hydrogen production by water electrolysis, with reduced energy consumption, molecular polarity, and stress−strain characteristics of distilled water under the condition of a pre-magnetic field. By constructing a microphysical model of hydrogen proton energy-level transition and a macroscopic mathematical model corresponding to magnetization vector-polarization hydrogen proton concentration in the pre-magnetic field, the ionic conductivity, electrolyte current density, interelectrode voltage, and hydrogen production efficiency under a varying magnetic field were qualitatively and quantitatively analyzed. In addition, an adjustable pre-magnetic polarization hydrolyzing hydrogen production test platform was set up to verify the effectiveness of the proposed method. The repeated test results, within a magnetic field strength r... [more]

Marine−terrestrial transitional Permian shales occur throughout South China and have suitable geological and geochemical conditions for shale gas accumulation. However, the Permian shales have not made commercial exploitation, which causes uncertainly for future exploration. In this study, high-pressure methane (CH4) adsorption experiments were carried out on the Permian shales in the Lower Yangtze area, and the influences of total organic carbon (TOC) content and temperature on adsorption parameters were investigated. The characteristics and main controlling factors of methane storage capacity (MSC) of the Permian shales are discussed. The results show that the maximum adsorption and the adsorbed phase density of these Permian samples are positively correlated with TOC contents but negatively correlated with temperatures. The pores of organic matter in shale, especially a large number of micropores and mesopores, can provide important sites for methane storage. Due to underdeveloped p... [more]

LNG (Liquefied Natural Gas) vaporizing stations are usually built in the cities and towns, and the BOG (Boiled Off Gas) pressurizing system is a very important element. In the pressurizing system, the severe vibration of the low-temperature reciprocating compressor may lead to a failure of the pipeline system and the equipment. Therefore, this paper analyzes the stress and pressure pulsation of the BOG compressor piping system in the LNG vaporizing station. The beam model was used to establish the pipe model. The static, harmonic and modal analysis were carried out based on the plane-wave theory and the pressure-fluctuation theory, and the influence factors of support spacing, the settlement of the fulcrum foundation, pipe pressure and elbow angle were analyzed. The main conclusions are as follows: (1) the unbalanced excited force caused by pressure pulsation greatly affects the stress of the exhaust pipe and compressor outlet pipe, and has less influence on the stress of the suction p... [more]

Phasor measurement units (PMUs) are a key part of electrical power systems, providing the dynamic monitoring and control of electrical units and impacting overall operation and synchronization of a network if not properly designed. This paper investigates the use of a phase-locked loop (PLL)-based algorithm for PMUs (to accurately find the magnitude, phase, and frequency) in a three-phase system. Various PLLs are reported in the literature, ranging from the very basic to advanced, capable of dealing with normal and abnormal grid behavior and mainly used for the control of grid-connected converters. In this paper, a number of PLLs were utilized to perform PMU functions, and a benchmarking study has been investigated to analyze the developed PLL-driven PMUs under various grid conditions (such as unbalanced faults, harmonics, and frequency variations). The simulation and experimental results were provided to support the performance capabilities and suggested limitations. In addition, the... [more]

This article provides the results of the first attempt to substantiate the rates of energy consumption and energy savings during the well-drilling process. It is proposed to accept the electrical energy consumption rate as a planned indicator of consumption of resources in the production of a unit of work of a specified quality. For a comprehensive assessment of the efficiency of use of energy resources during production of similar or substitute work, we determined specific energy consumption (designed, planned, actual), which includes direct consumption of all energy types in the production of a unit of work for basic and auxiliary production and operational needs, including from the consumption volume of mentioned resources and energy supply. Classification of consumption rates of electrical energy according to its action period and size scale has been proposed. The composition and amount of energy consumption rates during well-drilling have been described. The technological, expedit... [more]

Optimal planning of renewable energy generator (REG) units helps to meet future power demand with improved flexibility. Hence, this paper proposes a grid-oriented genetic algorithm (GOGA) based on a hybrid combination of a genetic algorithm (GA) and a solution using analytical power flow equations for optimal sizing and placement of REG units in a power system network. The objective of the GOGA is system loss minimization and flexibility improvement. The objective function expresses the system losses as a function of the power generated by different generators, using the Kron equation. A flexibility index (FI) is proposed to evaluate the improvement in the flexibility, based on the voltage deviations and system losses. A power flow run is performed after placement of REGs at various buses of the test system, and system losses are computed, which are considered as chromosome fitness values. The GOGA searches for the lowest value of the fitness function by changing the location of REG un... [more]

In this study, a novel smart efficiency tracking (SET) algorithm for GaN-based LLC resonant converter for quick battery charging of light electric vehicles is proposed. Conventional frequency modulation (FM) method, single pulse width modulation method (S-PWM) and discontinuous operation mode method (DOM) are used to track the converter efficiency which varies for different loading conditions during the battery charging process. First, the charging modes are explained to define the efficiency variation clearly. Then, the theoretical background of GaN-based LLC resonant converter is presented and the details of design study are given. Third, the principles of three different switching control strategies, the modeling study and the simulation results are put forward. Finally, the details of the implementation of three different switching strategies are presented for the validation of the study. Furthermore, the implementation of the design and its impact on battery charging are discussed... [more]

Power capacitors are widely used in power transmission systems. During their operation, an electric force acting on the electrodes of the power capacitors actuates mechanical vibrations and radiates an audible noise. Considering a power capacitor as a general system, the frequency response with the electric force as the input and mechanical vibration as the output have been measured by engineers in recent years and used to evaluate the acoustic and mechanical features of products. Accidentally, it was found that the frequency of the capacitor vibration was not consistent with its excitation due to electro-mechanical coupling. This electro-mechanical coupling had not been considered in previous vibration models of power capacitors. Therefore, a new vibration model of power capacitors was built up in this paper and a so-called multi-frequency vibration characteristic was revealed. A theoretical analysis showed that the electric force and mechanical vibration of the power capacitors were... [more]

In this paper, an experimental study investigating the effect of the geometrical shape of the circular and rectangular pin fins on the heat transfer performance and the boiling phenomenon is presented. A pool boiling experiment in the HFE-7100 dielectric working fluid under atmospheric pressure was conducted. Boiling curves and boiling heat transfer coefficients of different test cases were plotted to evaluate the heat transfer performance as well as the captured images of the boiling phenomenon on the test samples. Two quantities, flow resistance and wetted perimeter, were calculated to understand the behaviour of the boiling physics due to variation of fin geometrical shape and, hence, their effect on the heat transfer performance. It was found that the cooling performance of the rectangular pin fins was higher than that of the circular pin fins, despite having a slightly higher flow resistance of 4% and 7%, respectively. This is believed to be the result of the longer wetted perimet... [more]

The rapid development of renewable energy sources and electricity storage technologies is further driving the change and evolution of traditional energy systems. The aim is to interconnect the different electricity systems between and within countries to ensure greater reliability and flexibility. However, challenges are faced in reaching it, such as the power grid complexity, the system control, voltage fluctuations due to the reverse power flow, equipment overloads, resonance, incorrect island setting, and the diversity of user needs. The electricity grid digitalization in the market also requires the installation of smart devices to enable real-time information exchange between the generator and the user. Inverter-based distributed generation (DG) may be used to control the grid voltage. Smart PV inverters have the capability to supply both inductive and capacitive reactive power to control the voltage at the point of interconnection with the grid, and only technical parameters of s... [more]

The emission of mercury from coal combustion has caused consequential hazards to the ecosystem. The key challenge to abating the mercury emission is to explore highly efficient adsorbents. Herein, sulfur-functionalized carbon (S-C) was synthesized by using a molten-salt pyrolysis strategy and employed for the removal of elemental mercury from coal-combustion flue gas. An ideal pore structure, which was favorable for the internal diffusion of the Hg0 molecule in carbon, was obtained by using a SiO2 hard template and adjusting the HF etching time. The as-prepared S-C with an HF etching time of 10 h possessed a saturation Hg0 adsorption capacity of 89.90 mg·g−1, far exceeding that of the commercial sulfur-loaded activated carbons (S/C). The S-C can be applied at a wide temperature range of 25−125 °C, far exceeding that of commercial S/C. The influence of flue gas components, such as SO2, NO, and H2O, on the Hg0 adsorption performance of S-C was insignificant, indicating a good applicabili... [more]

Nowadays, pump-turbine units have to experience multiple start-stops every day to balance the power production and consumption on the grid. During the transient process of turbine start-up, the hydraulic forces applied to the head-cover would change dramatically and induce high-level stresses on the head-cover bolts. As key components of large hydraulic turbine units, the head-cover bolts are subjected to tens of thousands of tonnes of hydraulic excitation force during operation. Special attention should be paid to the design of the head-cover bolts of large hydraulic pump-turbine units because these units have high water heads and high hydraulic excitation forces. Therefore, the safe design of the head-cover bolts is extremely important to maintain the operational safety of the whole unit. This paper investigates the flow-induced stress characteristics of the head-cover bolts during turbine start-up in a large prototype pump-turbine unit. A complete 3D fluid model and a corresponding... [more]

Exergy and energy analyses of two biodiesel production processes that integrate solar energy as the main energy source were developed to determine the process with the higher efficiency from an energy and exergy approach. The biodiesel production processes were simulated in ASPEN PLUS®, and the solar energy supply was studied in TRNSYS®, using EXCEL® simultaneously for the exergetic analysis. The solar thermal energy collection system can supply 81% of the energy required by the alkali process in the Flash separation equipment. For the supercritical process, solar thermal energy can supply 74.5% of the energy in the preheating and separation stages. The energy efficiency of the supercritical process is higher; nevertheless, the exergetic efficiency of the alkaline process is higher than the supercritical one. Solar collection systems contribute from 85% to 93% of the exergy destroyed by the global process for both cases. The alkaline biodiesel production process has the highest advanta... [more]

This study aims to effectively solve the problem of the destruction of the coal roof and floor overlying rock after mining the protective layer, and determines whether the gas in the protected layer can be effectively released. We do this based on the engineering background of the Weng’an Coal Mine; research and analysis of the movement of the roof and floor overlying rocks; the evolution of cracks and the pressure relief characteristics of the protected layer after mining the protective layer; and through theoretical analysis and similar simulation experiments. Through numerical simulation, it was found that the protected layer was depressurized due to the mining of the protective layer, and the decompression rate of the protected layer was 0.2−0.8. In addition, the overall expansion rate of the protected layer was greater than the requirements of the “Detailed Rules for Prevention and Control of Coal and Gas Outbursts” for coal mines, and the investigation of the residual gas pressur... [more]

Thermophotovoltaics is a promising technology for heat recovery and has garnered tremendous attention in the last decades. This work theoretically evaluates the performance of a thermophotovoltaic system equipped with refractory all-ceramic selective thermal emitters made of boron carbide, silicon carbide and beryllium oxide for a high working temperature of 2000 ∘C, which corresponds to the external quantum efficiency of a SiC/Si tandem cell. The influence of thickness and filling ratio on the emissivity of thermal emitters over the wavelength ranging from 0.2 μm to 2.5 μm is studied. The corresponding spectral heat flux and output power are analyzed as well. For a specific configuration, the parameters for the thermophotovoltaic system are obtained, including short circuit current, open circuit voltage, fill factor, total heat flux, output power and conversion efficiency. The proposed all-ceramic thermal emitter ensures the robustness in the high-temperature working condition due to... [more]

Proton Exchange Membrane (PEM) water electrolysis (WE) produces H2 with a high degree of purity, requiring only water and energy. If the energy is provided from renewable energy sources, it releases “Green H2”, a CO2-free H2. PEMWE uses expensive and rare noble metal catalysts, which hinder their use at a large industrial scale. In this work, the electrocatalytic properties of Transition Metal Phosphides (TMP) catalysts supported on Carbon Black (CB) for Hydrogen Evolution Reaction (HER) were investigated as an alternative to Platinum Group Metals. The physico-chemical properties and catalytic performance of the synthesized catalysts were characterized. In the ex situ experiments, the 25% FeP/CB, 50% FeP/CB and 50% CoP/CB with overpotentials of −156.0, −165.9 and −158.5 mV for a current density of 100 mA cm−2 showed the best catalytic properties, thereby progressing to the PEMWE tests. In those tests, the 50% FeP/CB required an overpotential of 252 mV for a current density of 10 mA cm−... [more]

Real-time simulations refer to the simulations of a physical system where model equations for one time-step are solved within the same time period as in reality. An FPGA/CPU-based real-time simulation platform is presented in this paper, with a full-electric vehicle model implemented in a central processing unit (CPU) board and an electric drive model implemented in a field programmable gate arrays (FPGA) board. It has been a challenge to interface two models solved with two different processors. In this paper, one open-loop and three closed-loop interfaces are proposed. Real-time simulation results show that the best method is to transmit electric machine speed from the vehicle model to the electric derive model, with feedback electric machine torque calculated in FPGA. In addition, a virtual vehicle testing tool (CarMaker) is used when building the vehicle model, achieving more accurate modeling of vehicle subsystems. The presented platform can be used to verify advanced vehicle cont... [more]

Photovoltaic technology has become a huge industry, based on the enormous applications for solar cells. In the 19th century, when photoelectric experiences started to be conducted, it would be unexpected that these optoelectronic devices would act as an essential energy source, fighting the ecological footprint brought by non-renewable sources, since the industrial revolution. Renewable energy, where photovoltaic technology has an important role, is present in 3 out of 17 United Nations 2030 goals. However, this path cannot be taken without industry and research innovation. This article aims to review and summarise all the meaningful milestones from photovoltaics history. Additionally, an extended review of the advantages and disadvantages among different technologies is done. Photovoltaics fundamentals are also presented from the photoelectric effect on a p-n junction to the electrical performance characterisation and modelling. Cells’ performance under unusual conditions are summaris... [more]

The road to decarbonization has led to the exploration of sustainable energy sources for domestic and industrial use [...]

Gas hydrates are widespread all over the world. They feature high energy density and are a clean energy source of great potential. The paper considers experimental and theoretical studies on gas hydrates in the following key areas: formation and dissociation, extraction and transportation technologies of natural methane hydrates, and ignition, and combustion. We identified a lack of research in more areas and defined prospects of further development of gas hydrates as a promising strategic resource. One of the immediate problems is that there are no research findings for the effect of sediments and their matrices on hydrate saturation, as well as on gas hydrate formation and dissociation rates. No mathematical models describe the dissociation of gas hydrates under various conditions. There is a lack of research into the renewal and improvement of existing technologies for the easier and cheaper production of gas hydrates and the extraction of natural gas from them. There are no models... [more]

Solar-pumped lasers (SPLs) allow direct solar-to-laser power conversion, and hence, provide an opportunity to harness a renewable energy source. Herein, we report significant improvements in end-side-pumped solar laser collection efficiency and beam brightness using a novel 1.5-m-diameter compound solar concentrator combining a Fresnel lens and modified parabolic mirror. A key component of this scheme is the off-axis-focused parabolic mirror. An original dual-parabolic pump cavity is another feature. To determine the dependence of the SPL performance on the distance between the focus and central axis of the modified parabolic mirror, several systems with different distances were optimized using TracePro and ASLD software. It was numerically calculated that end-side pumping a 5-mm-diameter, 22-mm-long Nd:YAG crystal rod would generate 74.6 W of continuous-wave solar laser power at a collection efficiency of 42.2 W/m2, i.e., 1.1 times greater than the previous record value. Considering t... [more]

One of the main trends in the development of modern engine building is the use of biodiesel fuel, which can lead to a decrease in the reliability of engines that are not adapted to it. However, at present there is no general method for determining the reliability of fuel systems of internal combustion engines. In this paper, a reliability model of engine fuel systems when operating on biofuel has been developed. Comprehensive indicators for assessing the reliability of diesel engine fuel systems are the coefficient of readiness and technical use. The availability factor of the fuel system when operating on biodiesel fuel without the replacement of structural materials was 0.66, while with the replacement it was 0.71, and the coefficient of technical utilization without replacement of materials was 0.36, and with the replacement of 0.4. Recommendations are given to improve the reliability of the engine fuel system components. The resulting model allows for complex comparisons of the eff... [more]

The Paris Agreement requires countries to propose their National Determined Contributions (NDCs) and encourages companies to engage in climate action. This two-stage study explores the mutual influence of national and corporate carbon reduction targets and their effect on the adoption of renewable energy using Hierarchical Linear Modeling (HLM). The subjects are companies nested in the G20, engaging in the Science-Based Target initiative (SBTi) or the RE100 initiative. These empirical results show corporate targets are positively correlated to adoption of renewable energy, and development of renewable energy varies by country groups, however; national targets are insignificantly correlated. Our key findings: (1) companies which set SBTs are more willing to use renewable energy to achieve their targets but prefer power purchase agreements (PPAs) and renewable energy certificates (RECs) to investment in renewables. (2) The effect of a national-level target on corporate renewable energy u... [more]

(1) The German energy system transformation towards an entirely renewable supply is expected to incorporate the extensive use of green hydrogen. This carbon-free fuel allows the decarbonization of end-use sectors such as industrial high-temperature processes or heavy-duty transport that remain challenging to be covered by green electricity only. However, it remains unclear whether the current legislative framework supports green hydrogen production or is an obstacle to its rollout. (2) This work analyzes the relevant laws and ordinances regarding their implications on potential hydrogen production plant operators. (3) Due to unbundling-related constraints, potential operators from the group of electricity transport system and distribution system operators face lacking permission to operate production plants. Moreover, ownership remains forbidden for them. The same applies to natural gas transport system operators. The case is less clear for natural gas distribution system operators, wh... [more]