A key aspect of the design of specific tariff structures is to identify and characterize homogeneous electricity consumption profiles. Recent research in residential electricity demand has explored load profile segmentation via cluster analysis combined with descriptive data from the dwelling and occupants, which has partly explained electricity load patterns and their underlying drivers but has failed to investigate any consumption heterogeneity among similar households. Thus, the aim of this paper is to reverse this approach and investigate the extent that households with similar characteristics have different electricity consumption patterns. This study combines population-based register data with hourly electricity consumption data for a sample of 67 Danish households. First, a homogenous household group is selected based on several indicators that signal vulnerability. The specific group under investigation is single-person, older, low-income households in detached housing. Second... [more]

Lightning stroke on a transmission tower structure is one of the major reasons that results in high voltages at the tower arms due to the excessive lightning current flowing through the transmission tower to earth. The Surge voltage seen at the tower cross arm on the first tower close to a substation is the worst case. If this voltage is higher than the withstand level of the insulator string, the insulation of substation equipment will be exposed to transient over-voltage called fast front back-flashover (FFBF). The peak of this transient overvoltage is affected by the value of the system’s earthing resistance. This paper studies the effect of reducing the grounding resistance of both the surge arrestor (SA) and the first transmission line tower adjacent to a 66 kV substation on FFBF. Three case studies using PSCAD/EMTDC software are presented to simulate the variation of the potential sire at the substation equipment with different resistance values for the first tower and SA earthin... [more]

Real-scale fire experiments were conducted to understand the fire spread characteristics of the major combustibles handled in traditional markets, a space with high fire risk. The major combustibles were selected through field surveys administered at a number of traditional markets. Through real-scale fire experiments, the horizontal fire spread rate according to the maximum heat release rate of major combustibles was examined. In addition, the separation distance to prevent fire spread to the facing store by radiant heat transfer was examined. As a result of the experiments, it was confirmed that the arrangement method of the combustibles causes a large change in the maximum heat release rate, fire growth rate, and fire spread rate. The horizontal fire spread rate showed a linear proportional relationship with respect to the maximum heat release rate regardless of the type of combustibles, and a correlation to define the relationship was proposed. A correlation equation for predicting... [more]

Aerodynamic drag and bearing friction are the main sources of standby losses in the flywheel rotor part of a flywheel energy storage system (FESS). Although these losses are typically small in a well-designed system, the energy losses can become significant due to the continuous operation of the flywheel over time. For aerodynamic drag, commonly known as windage, there is scarcity of information available for loss estimation since most of the publications do not cover the partial vacuum conditions as required in the design of low loss energy storage flywheels. These conditions cause the flow regime to fall between continuum and molecular flow. Bearings may be of mechanical or magnetic type and in this paper the former is considered, typically hybridized with a passive magnetic thrust bearing. Mechanical bearing loss calculations have been extensively addressed in the open literature, including technical information from manufacturers but this has not previously been presented clearly a... [more]

A 10 kW PEMFC (polymer exchange membrane fuel cell) stack consisting of two 5 kW modules, (A) and (B), connected in series with a multi-function controller unit was constructed and tested. The electrical performance of the V-shaped PEMFC stack was investigated under constant and variable electrical load. It was found that the PEMFC stack was capable of supplying the required 10 kW of electrical power. An optimised purification process via ‘purge’ or humidification, implemented by means of a short-circuit unit (SCU) control strategy, enabled slightly improved performance. Online monitoring of the utilisation of the hydrogen system was developed and tested during the operation of the stack, especially under variable electrical load. The air-cooling subsystem consisting of a common channel connecting two 5 kW PEMFC modules and two cascade axial fans was designed, manufactured using 3D printing technology, and tested with respect to the electrical performance of the device. The dependence... [more]

Hydrate formation from cyclopentane (CP) and carbon dioxide was measured at 281 K by powder X-ray diffraction (PXRD) and macroscopic methods. The effect of initial pressure and CP mass fraction in liquid phase was analyzed. The results showed that hydrate formation was assumed to start with the nucleation of the mixed CP-CO2 hydrate with small fraction of CO2 followed by a large continuous CO2 adsorption. Initial pressure was found to have a positive correlation with the total CO2 consumptions when the initial pressure was below 2.5 MPa. However, the total CO2 consumptions dropped by over a half as the initial pressure was 3.0 MPa. PXRD revealed that all the hydrate samples formed at different initial pressures were structure II. The CO2 consumptions were assumed to be inhibited by the competitive occupation of 51264 cages between CP and CO2 molecules when the initial pressure was above 2.5 MPa. The CO2 consumptions were also found to be reduced as the CP mass fraction was above 0.25.... [more]

Accurate predictions of flow patterns in liquid-liquid flow are critical to the successful design and operation of industrial and geo-energy systems where two liquids are jointly transported. Unfortunately, there is no unified flow pattern map, because all published maps are based on limited ranges of dimensional parameters. Dimensional analysis was performed on oil-water horizontal flows, to obtain some relevant dimensionless parameter groups (DPG) for constructing flow pattern maps (FPM). The following combinations of DPG were used: (i) the ratio of mixture Reynolds number to Eötvös number versus water fraction, (ii) the ratio of Weber number to Eötvös number versus water fraction, (iii) the mixture Froude number versus water fraction, (iv) the water Froude number versus oil Froude number, (v) the ratio of gravity force to viscous force versus water fraction. From twelve published experimental studies, 2696 data points were gathered and analysed covering a variety of flow patterns in... [more]

This paper presents a tightly regulated multi-output isolated converter that employs only an independently regulated synchronous Single-Switched Post-Regulator (SSPR). The proposed converter is a highly accurate single-ended secondary side post-regulator based on a Series Resonant Converter (SRC); furthermore, it has a voltage-doubler characteristic. The proposed post-regulator requires only one auxiliary switch, in contrast with a bulky and expensive non-isolated DC−DC converter. Moreover, the added voltage-doubler can tightly regulate the slave output current. In addition, the voltage-doubler can improve electromagnetic interference characteristics and reduce switching losses arising from the Zero Current Switching (ZCS) operation of all power switches. The validity of the proposed converter is verified using experimental results obtained via a prototype converter applicable to an LED 3D TV power supply.

In this paper, we propose a novel study concerning the future use of a zero-airgap induction motor in applications related to transmission oil pumps. The name of the machine comes from the fact that the rotor touches the stator as it spins. The use of such an eccentric motor provides the possibility to remove the mechanical part that is typically found in the transmission oil pump, increasing its efficiency in this way. We focused on determining the optimum variant of a zero-airgap small power induction motor from the point of view of the electrical and mechanical performance. As such, 18 topologies of induction motors with various numbers of pole pairs and rotor bars were designed and numerically analyzed. For the best variant from each category, different eccentricities were considered to evaluate this effect over the performances of the motors. For the best candidate, various analyses were performed in order to demonstrate the validity of this solution for the proposed application.... [more]

In this paper, a dimmable light-emitting diode (LED) driver, along with the low-frequency current ripple decreased and the bipolar junction transistor (BJT) power dissipation reduced, is developed. This driver is designed based on a single-stage flyback converter. On the one hand, the low-frequency output current ripple reduction is based on the physical behavior of the linear current regulator. On the other hand, when the voltage across the LED string is decreased/increased due to dimming or temperature, the output voltage of the flyback converter will be automatically regulated down/up, thereby making the power dissipation in the BJT linearly proportional to the LED current. By doing so, not only the power loss in the linear current regulator will be decreased as the LED current is decreased or the LED temperature rises, but also the output current ripple can be reduced. Furthermore, the corresponding power factor (PF) is almost not changed, and the total harmonic distortion (THD) is... [more]

The oil-free compressor is a key component in fabricating polyethylene terephthalate (PET) bottles for beverages and water. At present, the main compressor type used for blowing PET bottles is the reciprocating compressor. However, compared to screw compressors, reciprocating compressors have shortcomings of high energy consumption and too many consumable parts. Many manufacturers of PET bottles in Asia are seeking to replace reciprocating compressors with screw compressors, as we know. Screw compressors can be classified as single-screw compressors (SSC) and twin-screw compressors. Since the load in a twin-screw compressor is far larger than that in an SSC, SSCs are more suitable for being developed for high-pressure applications such as PET bottle blowing. This paper presents a performance study on an oil-free single-screw compressor as the first stage of the PET compressor unit. A 5.4 m3·min−1 prototype and its test rig were developed. The thermophysical process of the moist air is... [more]

In grouting support projects, due to the small concealment of micro-fractures, the support effect often fails to meet design requirements. The percolation effect is a common factor that causes grouting failure, and the influence of grouting pressure on the percolation effect is very obvious. In this article, a design of a micro-fracture grouting experimental system is presented that can realize high-pressure grouting and then uses a variety of ultrafine cements to carry out high- and low-pressure grouting tests under different fracture opening conditions, thereby obtaining the grouting pressure and accumulated grouting weight during the grouting process. The results show that a combination of the grouting pressure curve and the cumulative grouting weight curve can determine whether the ultrafine cement will have a percolation effect. Increasing the grouting pressure can reduce the critical fracture opening value and also reduce the occurrence of the percolation effect. The research res... [more]

In high-pressure hydrogen systems, the check valve is one of the most easy-to-damage components. Generally, the high-pressure hydrogen flow can generate a strong impact on the check valve, which can cause damage and failure. Therefore, it is useful to study the transient flow characteristics of the high-pressure hydrogen flow in check valves. Using dynamic mesh generation and the National Institute of Standards and Technology (NIST) real hydrogen gas model, a transient-flow model of the high-pressure hydrogen for the check valve is established. First, the flow properties of high-pressure hydrogen during the opening process is investigated, and velocity changes and pressure distribution of hydrogen gas flow are studied. In addition, the fluid force, acceleration, and velocity of the valve spool are analyzed quantitatively. Subsequently, the effect of the hydrogen inlet-pressure on the movement characteristic of the valve spool is investigated. The results of this study can improve both... [more]

A model hydrochar was synthesized from glucose at 180 °C and its Cu(II) sorption capacity was studied experimentally and computationally as an example of molecular-level adsorbent design. The sorption capacity of the glucose hydrochar was less than detection limits (3 mg g−1) and increased significantly with simple alkali treatments with hydroxide and carbonate salts of K and Na. Sorption capacity depended on the salt used for alkali treatment, with hydroxides leading to greater improvement than carbonates and K+ more than Na+. Subsequent zeta potential and infrared spectroscopy analysis implicated the importance of electrostatic interactions in Cu(II) sorption to the hydrochar surface. Computational modeling using Density Functional Theory (DFT) rationalized the binding as electrostatic interactions with carboxylate groups; similarly, DFT calculations were consistent with the finding that K+ was more effective than Na+ at activating the hydrochar. Based on this finding, custom-synthes... [more]

A transverse jet in the supersonic crossflow is one of the most promising injection schemes in scramjet, where the control or enhancement of jet mixing is a critical issue. In this paper, the effect of the backward facing step on the characteristics of jet mixing was investigated by three-dimensional large eddy simulation (LES). The simulation in the flat plate configuration (step height of 0) was performed as the baseline case to verify the computation framework. The distribution of the velocity and pressure obtained by the LES agreed well with the experiment, which shows the reliability of the LES code. Then, two steps with a height of 1.0D and 1.58D (D is the injector diameter) were numerically compared to the non-step baseline case. The comparison of the three cases illustrates the effect of the large-scale recirculation region on the variable distribution, and shock and vortex structures in the flow field. In the windward region, the shear layers become thicker, and the convection... [more]

This paper proposes a coil design method for the magnetically coupled resonant wireless power transfer (MCR-WPT) system. Based on the Biot−Savart law, the magnetic flux density at the observation point was derived, and the magnetic flux of the observation plane generated by the exciting coil was deduced to build the calculation model of power transfer efficiency (PTE) and power delivered to the load (PDL). The PTE and PDL curves via coil parameters could be fitted in minutes using numerical calculation. The coil was designed according to transmission objectives and dimension constraints. In addition, the calculated PTE and PDL were compared with those from finite element analysis to verify the credibility of the method. Finally, the actual curves of PTE and PDL were achieved, which showed a strong positive correlation with the corresponding curves from the calculation model. The relative average deviations of PDL curves were less than 6.11%. Meanwhile, coils designed with the numerical... [more]

The feasibility and cost-effectiveness of hydrogen-based microgrids in facilities, such as public buildings and small- and medium-sized enterprises, provided by photovoltaic (PV) plants and characterized by low electric demand during weekends, were investigated in this paper. Starting from the experience of the microgrid being built at the Renewable Energy Facility of Sardegna Ricerche (Italy), which, among various energy production and storage systems, includes a hydrogen storage system, a modeling of the hydrogen-based microgrid was developed. The model was used to analyze the expected performance of the microgrid considering different load profiles and equipment sizes. Finally, the microgrid cost-effectiveness was evaluated using a preliminary economic analysis. The results demonstrate that an effective design can be achieved with a PV system sized for an annual energy production 20% higher than the annual energy requested by the user and a hydrogen generator size 60% of the PV nomi... [more]

In the contactless unregulated power converter application with high output current, optimizing coil structures and using synchronous rectification are important for achieving high efficiency. This paper proposes a separated planar structure of coils to achieve the design goals and gives its equivalent circuit model. On the power transmitting pad, double coils are used to enhance the ability of the output power levels. In order to implement full-wave synchronous rectification (FWSR), the power receiving pad also adopts double coils. The power coils on both sides have similar structures to obtain a balance-induced voltage in each half of the switching period, and the principles of the optimal turn ratio in coils are discussed. Meanwhile, four typical self-driven coil structures are compared and analyzed. The effect of the coupling coefficient and load currents on the loss of the duty cycle is discussed. To satisfy the requirements of output voltage, the rules for selecting the minimum f... [more]

The growing interest in the use of unconventional energy sources is a stimulus for the development of dedicated devices and technologies. Drain water heat recovery (DWHR) units can be an example of such devices. They allow the recovery of part of the heat energy deposited in grey water. This paper describes the results of research on the assessment of the financial profitability of the use of two horizontal heat exchanger solutions, taking into account the actual distribution of cold water temperature during the operating year in the plumbing and two operating regimes of the premises as the residential and service facilities. The analysis showed that the use of a horizontal heat exchanger with increased efficiency in a dwelling in a 15-year life cycle allowed for achieving more than twice as much savings (reaching up to EUR 1427) compared to a classic horizontal heat exchanger. At the same time, it was shown that the installation of this type of equipment was more profitable the greate... [more]

The paper deals with the Bayesian state estimation of nonlinear stochastic dynamic systems. The stress is laid on the point-mass filter, solving the Bayesian recursive relations for the state estimate conditional density computation using the deterministic grid-based numerical integration method. In particular, the grid design is discussed and the novel density difference grid is proposed. The proposed grid design covers such regions of the state-space where the conditional density is significantly spatially varying, by the dense grid. In other regions, a sparse grid is used to keep the computational complexity low. The proposed grid design is thoroughly discussed, analyzed, and illustrated in a numerical study.

The design and implementation of an energy-management system (EMS) applied to a residential direct current microgrid (DC-µG) is presented in this work. The proposed residential DC-µG is designed to provide a maximum power of one kilowatt by using two photovoltaic arrays (PAs) of 500 W, a battery bank (BB) of 120 V−115 Ah, a supercapacitor module of 0.230 F and a bidirectional DC−AC converter linked to the AC main grid (MG). The EMS works as a centralized manager and it defines the working operation mode for each section of the DC-µG. The operation modes are based on: (1) the DC-link bus voltage, (2) the generated or demanded power to each section of the DC-µG and (3) the BB’s state of charge. The proposed EMS—during the several working operation modes and at the same time—can obtain the maximum energy from the PAs, reduce the energy consumption from the main grid and keep the DC-link bus voltage inside a range of 190 V ± 5%. The EMS and local controllers are implemented by using LabVIE... [more]

Light-emitting diode (LED) grow lights are increasingly used in large-scale indoor farming to provide controlled light intensity and spectrum to maximize photosynthesis at various growth stages of plants. As well as converting electricity into light, the LED chips generate heat, so the boards must be properly cooled to maintain the high efficiency and reliability of the LED chips. Currently, LED grow lights are cooled by forced convection air cooling, the fans of which are often the points of failure and also consumers of a significant amount of power. Natural convection cooling is promising as it does not require any moving parts, but one major design challenge is to improve its relatively low heat transfer rate. This paper presents a novel heat sink design for natural convection cooling of LED grow lights. The new design consists of a large rectangular fin array with openings in the base transverse to the fins to increase air flow, and hence the heat transfer. Numerical simulations a... [more]

This paper focuses on autonomous navigation for an electric freight vehicle designed to collect freight autonomously using pallet handling robots installed in the vehicle. Apart from autonomous vehicle navigation, the primary hurdle for vehicle autonomy is the autonomous collection of freight irrespective of freight orientation/location. This research focuses on generating parking pose for the vehicle irrespective of the orientation of freight for its autonomous collection. Freight orientation is calculated by capturing the freight through onboard sensors. Afterward, this information creates a parking pose using mathematical equations and knowledge of the vehicle and freight collection limitations. Separate parking spots are generated for separate loading bays of the vehicle depending on the availability of the loading bay. Finally, results are captured and verified for different orientations of freight to conclude the research.

Magnetic refrigeration is a fascinating superior choice technology as compared with traditional refrigeration that relies on a unique property of particular materials, known as the magnetocaloric effect (MCE). This paper provides a thorough understanding of different magnetic refrigeration technologies using a variety of models to evaluate the coefficient of performance (COP) and specific cooling capacity outputs. Accordingly, magnetic refrigeration models are divided into four categories: rotating, reciprocating, C-shaped magnetic refrigeration, and active magnetic regenerator. The working principles of these models were described, and their outputs were extracted and compared. Furthermore, the influence of the magnetocaloric effect, the magnetization area, and the thermodynamic processes and cycles on the efficiency of magnetic refrigeration was investigated and discussed to achieve a maximum cooling capacity. The classes of magnetocaloric magnetic materials were summarized from prev... [more]

Utility-sponsored residential energy reduction programs have seen rapid advancement in the Unites States (US) over the past decade. These programs have particularly emphasized investments in energy efficient appliances and enveloped improvements. They have generally required co-investment by residents and, as a result, have mostly reached medium to high-income residents, with low income residences, in effect, supporting the utility investments through higher energy costs. Additionally, utility initiatives directed toward behavior-based energy reduction have reached residences with more advanced technologies, such as smart meters and smart Wi-Fi thermostats linked to phone apps, technologies generally not present in low-income residences. This research seeks to inform development of behavior-based energy reduction programs aimed specifically at low-income residences, premised on peer-to-peer energy education and support. It focuses on the design and implementation of a pilot program for... [more]