In doubly fed induction generators (DFIGs), the rotor is excited through slip-ring and brush assemblies. These slip-ring and brush assemblies often require frequent routine maintenance, which affects the reliability of the DFIG. Alternatively, a contact-less energy transfer system, such as a rotary transformer, can be utilized in place of the slip rings. In DFIGs, the rotor frequency is very low, under 5 Hz, and this can lead to a huge rotary transformer since the transformer size is inversely proportional to its operating frequency. However, in a rotor-tied DFIG, whereby the rotor is connected directly to the grid whilst the stator is connected to a back-to-back converter, the rotor frequency becomes the grid frequency and can lead to a reasonably sized rotary transformer. In this paper, the design methodology of a three-phase rotary transformer that can be used in rotor-tied DFIG applications is proposed. The rotary transformer is coupled to the power windings of the rotor-tied DFIG... [more]

With the rapid development of micro-energy power systems, the performance of micro-combustors as key components is in urgent need of further improvement. Aimed at enhancing combustion performance, a hollow hemispherical bluff body was used to analyze the methane combustion process. In this paper, we exploited the detailed reaction mechanism of methane/air with a laminar finite-rate model; the numerical analysis of methane combustion in the micro-combustor was carried out by Ansys Fluent software. The combustion, flow and thermal characteristics of the micro-combustor embedded with a hollow hemisphere bluff body (MCEHB) and the micro combustor embedded with a slotted hollow hemisphere bluff body (MCESHB) are compared, and the effect of slot width ratio on the combustion characteristics and thermal performance is discussed in detail. The results showed that the bluff body slotting treatment is not only beneficial to improving the velocity and temperature distribution behind the bluff bod... [more]

This research article proposes a novel design of solar still; furthermore, it investigates, experimentally, its thermal and productivity performances, as well as its efficiency, under the realistic meteorological conditions of the city of Gafsa, Tunisia (34.4311° N, 8.7757° E), in terms of ambient temperature and solar irradiance. The novel proposed design presents a cylindrical solar still with a rotating transparent plastic (Plexiglass) cover, wiped continuously on the inner surface. A specific technological configuration of the evaporation and condensation compartments is elaborated. A real prototype is manufactured in order to carry out the performance experimental investigation. A performance comparison is carried out between the cylindrical transparent plastic cover rotating and it being fixed, for two experimentation days presenting slightly different meteorological conditions. The experimental water and plastic cover temperatures, the hourly and the cumulative water production,... [more]

Transmission towers are prone to collapse under strong wind load, resulting in significant economic losses. In order to investigate the collapse mechanism and failure modes of the transmission tower under strong wind load and whether the wind vibration factor can greatly reflect the increasing effect of the fluctuating wind, the finite element method (FEM) is utilized to analyze the ultimate bearing capacity of a typical 220 kV transmission tower. The results show that the collapse of the tower under strong wind loads is usually due to the buckling of the leg members. When the reference wind speed is equal to 27 m/s, a small part of the main leg members reaches their yield strength, while the diagonal members are still in the elastic range, and the deformation of the transmission tower is unapparent at this wind speed. When reference wind speed is equal or greater than 30 m/s, the growing variety of main legs is totally into the plastic yield stage, and the overall deformation of this... [more]

This paper proposes a Moiré-inspired metasurface lens system to focus electromagnetic power in the Fresnel near-field region. The proposed metasurface lens (MSL) system is composed of two MSLs and a square patch antenna source. The MSLs are modeled based on the transmit phase distributions of Moiré lens theory, and each unit cell structure (patch shape and Jerusalem cross slot shape) is determined to fit the calculated transmit phase distributions at each location. When changing the unit cell structure, phase and transmittance variations are achieved over 330° and −3 dB. The square patch antenna source is then designed to excite the field to the MSLs. The measured reflection coefficients are below −10 dB at 5.8 GHz while rotating the second MSL. The focal length can be adjusted from a minimum of 38 cm to a maximum of 110 cm according to the rotation angle of the second MSL. The proposed MSL system can be employed for wireless power transmission applications to focus electromagnetic pow... [more]

This paper investigates the impact of the wire selection on the performance of induction motors for automotive applications. The section of wire and the material are evaluated at a high speed of 200 kW in an induction motor designed for premium vehicle applications. The proposed solutions have the same electromagnetic and thermal constraints, as well as the same final encumbrance. The various wire and winding types differ in terms of slot design, phase resistance, end-winding overhanging portion, skin and proximity effects, and equivalent slot thermal conductivity. Their impacts are analyzed in terms of the operating area motor efficiency and they are tested in an automotive drive cycle, highlighting the advantages and disadvantages of each configuration.

It has been shown that tangential inlet return cyclones are commonly used for inlet air filtration of off-road vehicle engines. The wear of the engine elements, and thus their durability, is determined by the efficiency and accuracy of the inlet air filtration. It has been shown that the possibilities of increasing the separation efficiency or decreasing the pressure drop of a cyclone by changing the main dimensions of the cyclone are limited, because any arbitrary change in one of the dimensions of an already operating cyclone may cause the opposite effect. A literature analysis of the possibility of increasing the filtration efficiency of cyclones by modifying the design of selected cyclone components was conducted. In this paper, three modifications of the cyclone design with a tangential inlet of the inlet air filter of a military tracked vehicle were proposed and performed. The symmetrical inlet of the cyclone was replaced with an asymmetrical inlet. The cylindrical outlet tube wa... [more]

Line start permanent magnet assisted synchronous reluctance motor (LSPMaSynRM) is an important high-efficiency and high-quality motor. Its parameter matching and operating characteristics are complex, with an increase in salient ratio resulting in a valley in the power factor curve. In this study, the formation principle of power factor curve valley was first deduced by the mathematical model of LSPMaSynRM. Then, the parameter matching principle of power factor curve valley was analyzed in detail. On this basis, the characteristics of load rate corresponding to the critical state of the power factor curve valley were obtained, and its influence on whole load efficiency was analyzed. The design principles for optimal efficiency in wide high-efficiency region and specific load point were obtained. Finally, a 5.5 kW LSPMaSynRM was designed and manufactured to verify the validity of the principle.

Regenerative flow machines are known to be simple in construction but complex in flow characteristics. Due to this reason, the design of these machines has been primarily esoteric, and hence its performance heavily relies on the experience and expertise of the designer. Since there are no established rules of thumb for designing them, this paper attempts to provide simple design correlations for systematically designing regenerative flow machines viz. pumps, blowers, and compressors. Three different impeller designs have been considered, namely the (i) single-side vane impeller, (ii) double-side vane impeller, and (iii) peripheral vane impeller, for the three types of machines. More than ten design parameters have been considered for sizing the machines. Experimental and computational data available in open literature have been used to obtain physically meaningful correlations in simple form, and require minimal and practically available inputs. Fluid properties and practical constrain... [more]

In order to research the influence mechanism of bow blades on the flow field of supersonic tandem rotors of compressors, the supersonic rotor rotor37 is taken as the prototype and redesigned as a supersonic tandem rotor. Compared with the prototype rotor37, the efficiency of the design tandem rotor is increased by 0.24% and the stall margin is increased by about 5.6%. Although the negative bow blade deteriorates the flow field in the tip region and the hub region, it significantly increases the efficiency and total pressure ratio of the tandem rotor from 20% span to 85% span. The efficiency of the design point of the tandem rotor with a negative bow angle of 10° is improved by 0.37%, and the stall margin is also increased to 20.71%. Positive bow blades improve the efficiency of the hub region and casing region of tandem rotors, but they significantly reduce the efficiency of the tandem rotor from 10% to 50%. The positive bow blade reduces the pressure ratio and efficiency at the design... [more]

Isolated ultrasonic vibrations were used to treat feed water from a 20 bar steam-producing water tube boiler. Physical treatments such as ultrasounds and reverse osmosis (RO) are recommended as the most eco-friendly for this purpose. A novel bench-scale prototype delivering 6 L/h of treated water was designed and built. The ultrasonic atomization of raw water with 1.7 MHz piezoelectric transducers and subsequent humidification and dehumidification of drag airflow was the innovating sequence of operations used as a treatment technique. To ensure greater humidification capacity to the drag air, the energy available from the thermal inertia of the liquid column (raw water) in the prototype vaporization chamber was used to heat this air flow. After a single pass of raw water through the bench-scale prototype, a 98.0% reduction in conductivity and a 99.0% decrease in the content of total dissolved solids were obtained at a drag air temperature of 70 °C. Compared to RO, two of the main advan... [more]

A design methodology for minimum volume of LCL filters applied to grid connected converters is proposed. It combines the determination of filter parameter values (inductances and capacitances) to hardware design (component technology and inductor construction). Using the proposed strategy, different combinations of L-C-L that meet standard restrictions are determined. The influence of the harmonic content that results from filter design is considered in order to estimate component losses, and filter and bus capacitor lifetimes. Results are presented for filters that lead to the smallest volume, highest capacitor lifetime, or a compromise between both. A case study with three different magnetic material technologies and two types of capacitors is done. The design methodology is experimentally validated for a 1 kW converter. Step-by-step procedures for the determination of filter parameters and inductor hardware design are provided.

The urgent need to meet climate goals provides unique opportunities to promote small-scale farm anaerobic digesters that valorize on-site wastes for producing renewable electricity and heat, thereby cushioning agribusinesses against energy perturbations. This study explored the economic viability of mono-digestion of cow manure (CWM) and piglet manure (PM) in small manured-based 99 kWel plants using three treatment schemes (TS): (1) typical agricultural biogas plant, (2) a single-stage expanded granular sludge bed (EGSB) reactor, and (3) a multistage EGSB with a continuous stirred tank reactor. The economic evaluation attempted to take advantage of the financial incentives provided by The Renewable Energy Sources Act in Germany. To evaluate these systems, batch tests on raw and solid substrate fractions were conducted. For the liquid fraction, data of continuous tests obtained in a laboratory was employed. The economical evaluation was based on the dynamic indicators of net present val... [more]

In the north of China, during winter, a large number of activities (such as leisure, work, sightseeing and sports) are engaged in. This paper mainly focuses on human thermal perceptions of outdoor activities in a winter climate, especially the change in thermal perceptions when humans enter a temporary rest space with a shelter effect. A climate chamber was applied in our experiments, and temperature up-steps of 4, 8 and 12 °C were set, respectively. Twenty four college students were invited to engage in activities of different intensities, such as standing, walking (slowly) and biking. Through questionnaire survey and field measurement, the subjects’ thermal sensation, thermal comfort and skin temperature were obtained. Hypothesis testing and non-linear regression methods were introduced to analyze experiment data. Major results were as follows. After temperature up-step changes, thermal sensation and skin temperature reach steady state within 30 min. However, the change in skin tempe... [more]

Based on the COMSOL software, body forces substituted into the Reynolds-averaged Navier−Stokes (RANS) equations as the source terms instead of the actual blade rows were improved to better predict the compressor performance. Improvements in parallel body force modeling were implemented, central to which were the local flow quantities. This ensured accurate and reliable off-design performance prediction. The parallel force magnitude mainly depended on the meridional entropy gradient extracted from three-dimensional (3D) steady single-passage RANS solutions. The COMSOL software could easily and accurately translate the pitchwise-averaged entropy into the grid points of the body force domain. A NASA Rotor 37 was used to quantify the improved body force model to represent the compressor. Compared with the previous model, the improved body force model was more efficient for the numerical calculations, and it agreed well with the experimental data and computational fluid dynamics (CFD) resul... [more]

Promoting the development of green technologies and replacing fossil fuel vehicles with electric ones can abate the environmental anxieties and issues associated with energy supply security. The increasing demand for electric vehicles requires an upgrade and expansion of the available charging infrastructure to accommodate the fast public adoption of this type of transportation. Ethiopia set a pro-electric cars policy and made them excise-free even before the first electric vehicle charging stations were launched by Marathon Motors Engineering in 2021. This paper presents the first ever technical, economic and environmental evaluation of electric vehicle charging stations powered by hybrid intermittent generation systems in three cities in Ethiopia. This paper tests this model using three different battery types: Lead-acid (LA), Flow-Zince-Bromine (ZnBr) and Lithium-ion (LI), used individually. Using these three battery technologies, the proposed hybrid systems are then compared in ter... [more]

This paper presents a newly-designed optimal current algorithm for high-temperature superconductor (HTS)-based multi-input wireless power transfer (WPT) systems. In this way, both high controllability and lower AC losses can be achieved in the proposed systems, and they are especially superior for long-range and long-time operations. Simplified AC loss modeling for HTS windings is developed for the designed transmitter coils. The accordant optimal current vector is derived and analyzed in order to achieve the highest output power and the lowest primary AC losses. With the proper current control of multiple transmitters and the use of a designed HTS coupler, the system controllability can be greatly improved compared with conventional WPT systems. Based on the information on the impedance characteristics on the primary side, the magnetic field generated by different transmitters can be maximized at the target position. Thus, the maximum output power tracking can be realized with a relat... [more]

In the design of inductive power transfer (IPT) systems for multi-load applications, the versatility of the coupling structure and the choice of parameter values are crucial due to the diversity of load appliance types and operating conditions. In this paper, based on the features of various coupling structures, the equivalent circuit models of four topologies, namely single-input single-output (SISO), single-input multiple-output (SIMO), multiple-input single-output (MISO) and multiple-input multiple-output (MIMO), are established, from which general transfer characteristics are obtained and analyzed. Based on the series−series (S/S) compensation topology, a set of design principles for IPT circuits satisfying various output requirements in a multi-load environment is presented. Moreover, a control strategy to address the impedance matching issue and to facilitate communication between the primary and secondary sides is proposed. The proposed control strategy is experimentally validat... [more]

The reduction of CO2 emissions has become a global concern. In this regard, the EU intends to cut CO2 emissions by 55% by 2030 compared to those of 1990. The utilization of shallow geothermal energy (SGE) in EU countries is considered the most effective measure for decarbonizing heating and cooling. SGE systems utilize heat energy collected from the earth’s crust to provide secure, clean, and ubiquitous energy. This paper provides a literature review on the use of SGE for heating and cooling purposes. The latest advances in materials, new innovative structures, and techno-economic optimization approaches have been discussed in detail. Shallow geothermal energy’s potential is first introduced, and the innovative borehole structures to improve performance and reduce installation cost is outlined. This is followed by an extensive survey of different types of conventional and thermally enhanced collectors and grouts. Attention is mainly given to the techno-economic analysis and optimizatio... [more]

The building sector is one of the largest contributors to the world’s total energy use and greenhouse gas emissions. Advancements in building energy technologies have played a critical role in enhancing the energy sustainability of the built environment. Extensive research and new techniques in energy and environmental systems for buildings have recently emerged to address the global challenges. This study reviews existing articles in the literature, mostly since 2000, to explore technological advancement in building energy and environmental systems that can be applied to smart homes and buildings. This review study focuses on an overview of the design and implementation of energy-related smart building technologies, including energy management systems, renewable energy applications, and current advanced smart technologies for optimal function and energy-efficient performance. To review the advancement in building energy-related technologies, a systematic review process is adopted base... [more]

This paper aims to design an IPT for wireless charging of an e-bike and to control the charge of the e-bike from the primary-side. Optimum IPT design has been made according to the 36 V battery bank requirements. The no-load condition test has been performed before charging started in the IPT system connected to the AC grid. The primary-side DC-link voltage of 4−5 V required for this test is provided by the designed forward converter. The charge control has been also made from the forward converter on the primary-side. For this, the forward converter’s operation in peak current mode (PCM) has been used. Finally, a prototype has been implemented that works at a maximum DC/DC efficiency of 87.52% in full alignment and 83.63% in 3 cm misalignment. The proposed control algorithm has been tested in this prototype at different load stages.

In order to improve the combustion performance of a ramjet under low temperature and pressure, a gliding arc plasma actuator was designed based on a typical evaporation flameholder. The discharge characteristics, as well as the activating effect of single-channel and three-channel gliding arc plasma under different carrier gas flow rates, were studied. Results show that with the increase in the carrier gas flow rate, the average duration of the gliding arc discharge becomes shorter, while the average power increases, and the specific input energy decreases. Compared with single-channel discharge, three-channel discharge has higher discharge power and energy injection rate, which makes a bigger actuated space. Through gliding arc plasma, the kerosene is cracked and H2, CH4, C2H2, C2H4, C3H6 and other small molecule components are produced. For three-channel gliding arc discharge, the effective cracking rate and the production rate of each component are higher than those of the single-ch... [more]

This paper presents a new type of split natural cooling system that maximizes the use of natural cold energy to significantly reduce the power consumption of the air conditioning system in data centers. A split natural cooling system module, which consisted of indoor and outdoor heat exchanger based on micro heat pipe arrays connected by liquid circulation system, was selected for experimental research. The heat transfer process and flow characteristics were analyzed under different outdoor environment temperatures, air and water flow rates, and different ratios of heat transfer components (N) of indoor and outdoor heat exchangers. To improve the utilization of natural cold energy, two kinds of heat dissipation conditions, namely room and heat channel-based, were proposed. The indoor temperature of two conditions at 28 °C and 38 °C were simulated in the laboratory at constant temperature-humidity, respectively. Results indicated that the air flow rate had a greater influence on the hea... [more]

This paper examines different off-grid renewable energy-based electrification schemes for an informal settlement in Windhoek, Namibia. It presents a techno-economic comparison between the deployment of solar home systems to each residence and the supplying power from either a centralized roof-mounted or ground-mounted hybrid microgrid. The objective is to find a feasible energy system that satisfies technical and user constraints at a minimum levelized cost of energy (LCOE) and net present cost (NPC). Sensitivity analyses are performed on the ground-mounted microgrid to evaluate the impact of varying diesel fuel price, load demand, and solar photovoltaic module cost on system costs. HOMER Pro software is used for system sizing and optimization. The results show that a hybrid system comprising a solar photovoltaic, a diesel generator, and batteries offers the lowest NPC and LCOE for both electrification schemes. The LCOE for the smallest residential load of 1.7 kWh/day and the largest m... [more]

The research on the thermal characteristics of railway double-row tapered roller bearing is of great significance for its structural design and operation monitoring. We established the quasi-static mechanical model of the bearing according to the test conditions, and we obtained the load distribution and kinematic parameters of the bearing. We studied the temperature distribution of railway double-row tapered roller bearing under test conditions through finite element analysis, which was consistent with the test results. We built a bearing testbed to study the effects of different rotating speeds on the temperature distribution of the bearing inner ring, outer ring, and roller. The results show that the speed dramatically affects the bearing inner ring. With the rate increase, the temperature difference between the inner and outer rings decreases gradually, and the temperature at the large end of the roller is the highest.