A heat exchanger is a device that transfers unneeded heat from one region to another, and transferred heat may be fully reused, thus improving energy efficiency. To augment this positive process, many studies and investigations on automation technologies have been performed. Inserts are widely used in pipe flow for heat transfer enhancement, since they can break the boundary layer and promote the heat exchange. Segmented twisted tape, which is applicable in 3D printing, is a novel insert and has potential in heat transfer enhancement. To clarify its advantages and disadvantages, this research presents a numerical investigation of vortex flow and heat enhancement in pipes containing one segmented twisted element. Flow state and heat transfer behaviour are obtained by simulation under constant wall temperature with different Reynolds numbers, ranging from 10,000 to 35,000. The effects of geometric parameters, including twist ratio (P/D = 2.0, 3.3 and 4.6) and length ratio (L/P = 0.3, 0.5... [more]

In the recent era, hydrogen has gained immense consideration as a clean-energy carrier. Its storage is, however, still the main hurdle in the implementation of a hydrogen-based clean economy. Liquid organic hydrogen carriers (LOHCs) are a potential option for hydrogen storage in ambient conditions, and can contribute to the clean-fuel concept in the future. In the present work, a parametric and simulation study was carried out for the storage and release of hydrogen for the methylcyclohexane toluene system. In particular, the methylcyclohexane dehydrogenation reaction is investigated over six potential catalysts for the temperature range of 300−450 °C and a pressure range of 1−3 bar to select the best catalyst under optimum operating conditions. Moreover, the effects of hydrogen addition in the feed mixture, and byproduct yield, are also studied as functions of operating conditions. The best catalyst selected for the process is 1 wt. % Pt/γ-Al2O3. The optimum operating conditions selec... [more]

Motivated by a practical problem faced by an energy trading company in Poland, we investigate the profitability of balancing intermittent generation from renewable energy sources (RES). We consider a company that buys electricity generated by a pool of wind farms and pays their owners the day-ahead system price minus a commission, then sells the actually generated volume in the day-ahead and balancing markets. We evaluate the profitability (measured by the Sharpe ratio) and market risk faced by the energy trader as a function of the commission charged and the adopted trading strategy. We show that publicly available, country-wide RES generation forecasts can be significantly improved using a relatively simple regression model and that trading on this information yields significantly higher profits for the company. Moreover, we address the issue of contract design as a key performance driver. We argue that by offering tolerance range contracts, which transfer some of the risk to wind fa... [more]

In this paper, an accurate efficiency evaluation of an innovative three-switch double input DC−DC converter for hybrid vehicle applications was carried out. The converter was used to interface two storages, (e.g., supercapacitor and battery) to the DC link. A refined model was created in MATLAB/Simulink Plecs environment and it was used to compare the traditional four-switch converter (i.e., two DC−DC converters in parallel connection) with the innovative three-switch converter. Loss and efficiency contour maps were obtained for both converters and a comparison between them was performed. A prototype of the three-switch converter was realized and used to validate the simulation thermal model by comparing both efficiency and current waveforms obtained with simulations and experimental tests.

A hybrid electric vehicle (HEV) is a product that can greatly alleviate problems related to the energy crisis and environmental pollution. However, replacing such a battery will increase the cost of usage before the end of the life of a HEV. Thus, research on the multi-objective energy management control problem, which aims to not only minimize the gasoline consumption and consumed electricity but also prolong battery life, is necessary and challenging for HEV. This paper presents an adaptive equivalent consumption minimization strategy based on a recurrent neural network (RNN-A-ECMS) to solve the multi-objective optimal control problem for a plug-in HEV (PHEV). The two objectives of energy consumption and battery loss are balanced in the cost function by a weighting factor that changes in real time with the operating mode and current state of the vehicle. The near-global optimality of the energy management control is guaranteed by the equivalent factor (EF) in the designed A-ECMS. As... [more]

The brake system is a critical component for any passenger vehicle as its task is to convert the kinetic and potential energy of the vehicle into heat, allowing the vehicle to stop. Heat energy generated must be dissipated into the surroundings in order to prevent brake overheating. Traditionally, a lot of experimental testing is performed to ensure correct brake operation under all possible load scenarios. However, with the development of simulation techniques, many vehicle manufacturers today are looking into partially or completely replacing physical experiments by virtual testing. Such a transition has several substantial benefits, but simultaneously a lot of challenges and limitations need to be addressed and understood for reliable and accurate simulation results. This paper summarizes many of such challenges, discusses the effects that can and cannot be captured, and gives a broader picture of the issues faced when conducting numerical brake cooling simulations.

A new empirical equation for the estimation of daily dry above ground biomass (D-AGB) for a hybrid of soybean (Glycine max L.) is proposed. This equation requires data for three crop dependent parameters; leaf area index, plant height, and cumulative crop evapotranspiration. Bilinear surface regression analysis was used in order to estimate the factors entering in the empirical model. For the calibration of the proposed model, data yielded from a well-watered soybean crop for the year 2015, in the experimental field (0.1 ha) of the agricultural University of Athens, were used as a reference. Verification of the validity of the model was obtained by using data from a 2014 cultivation period for well-watered soybean cultivation (100% of crop evapotranspiration water treatment), as well as data from three irrigation treatments (75%, 50%, 25% of crop evapotranspiration) for two cultivation periods (2014−2015). The proposed method for the estimation of D-AGB may be proven as a useful tool f... [more]

In the present work, the effects of different operating parameters on the performance of a gravity-assisted heat pipe-based indirect evaporative cooler (GAHP-based IEC) were investigated. The aim of the theoretical study is to evaluate accurately the cooling performance indicators, such as the coefficient of performance (COP), wet bulb effectiveness, and cooling capacity. To predict the effectiveness of the air cooler under a variety of conditions, the comprehensive calculation method was adopted. A mathematical model was developed to simulate numerically the heat and mass transfer processes. The mathematical model was validated adequately using experimental data from the literature. Based on the conducted numerical simulations, the most favorable ranges of operating conditions for the GAHP-based IEC were established. Moreover, the conducted studies could contribute to the further development of novel evaporative cooling systems employing gravity-assisted heat pipes as efficient equipm... [more]

A step up/down AC/DC converter with modified dual loop control is proposed. The step up/down AC/DC converter features the bridgeless characteristic which can reduce bridge-diode conduction losses. Based on the step up/down AC/DC converter, a modified dual loop control scheme is proposed to achieve input current shaping and output voltage regulation. Fewer components are needed compared with the traditional bridge and bridgeless step up/down AC/DC converters. In addition, the intermediate capacitor voltage stress can be reduced. Furthermore, the top and bottom switches still have zero-voltage turn-on function during the negative and positive half-line cycle, respectively. Hence, the thermal stresses can also be reduced and balanced. Simulation and experimental results are provided to verify the validity of the proposed step up/down AC/DC converter and its control scheme.

In the present study, a triplex-tube, employing fin-enhanced phase change materials (PCMs), as a thermal energy storage (TES) system was studied numerically. The main flaw of the PCMs is their low thermal conductivity that restricts their effectiveness for energy storage applications. Metallic (copper) fins are added to the geometry of the system to improve their function by extending the heat transfer area. The effects of the presence, configuration, and dimensions of copper fins were investigated to understand the best design for minimizing the solidification time and achieving the best performance enhancement for the TES system selected for this study. The results revealed that the best performance belonged to fins with a mix configuration, with an attachment angle of 90° and the length and width of 28 mm and 1 mm, respectively. Using this configuration could reduce the required time for complete solidification by around 42% compared to the system without fins. Moreover, it was conc... [more]

Gibbs free energies, based on DFT (Density Functional Theory) calculations, prove that enaminone (2-(anilinemethylidene)cyclohexane-1,3-dione) and ketamine (2-[(phenylimino)-methyl]cyclohexane-1,3-dione) are the most and least stable tautomeric forms of the studied systems, respectively. 1H and 13C NMR spectra prove that 2-(anilinemethylidene)cyclohexane-1,3-diones are the only tautomeric species present in dimethylsulfoxide solution (a very weak signal can be seen only for the p-methoxy derivatives). The zwitterionic character of these enaminones is strengthened by naphthoannulation and by the insertion of the electron-withdrawing substituent into the benzene ring (the latter weakens the intramolecular hydrogen bond in the compound). Substituent and naphtoannulation have no effect on the stability of the studied tautomers. Slight twisting of the benzene ring, with respect to the CArNC plane (seen in the crystalline state), was proven to also take place in vacuum and in solution.

As one of the most important components of power grid, a distribution network is the most vulnerable part in the face of various uncertainties, and influences the stability and economy of a power system. In this paper, the operational information, hardware information and human factors were considered, and a state evaluation model of multi-source information fusion was established. Based on big data fuzzy iteration method and a weighted expert library, a weighted distribution of multi-source information was obtained, and an equipment condition assessment was carried out reasonably. Taking the distribution transformer as an example, the assessment showed that fusion of multi-source information presented in this paper is more comprehensive, and has the ability to reflect the state of equipment. The method proposed in this paper can accurately judge the running state of distribution equipment based on all kinds of information, and provides a reference for the follow-up power marketing for... [more]

Supersonic combustion experiments were performed using three different hydrogen fuel-injection configurations in a cavity-based model scramjet combustor with various global fuel−air equivalence ratios. The configurations tested were angled injection at 15° to the flow direction upstream of the cavity, parallel injection from the front step, and upstream injection from the rear ramp. Planar laser-induced fluorescence of the hydroxyl radical and time-resolved pressure measurements were used to investigate the flow characteristics. Angled injection generated a weak bow shock in front of the injector and recirculation zone to maintain the combustion as the equivalence ratio increased. Parallel and upstream injections both showed similar flame structure over the cavity at low equivalence ratio. Upstream injection enhanced the fuel diffusion and enabled ignition with a shorter delay length than with parallel injection. The presence of a flame near the cavity was determined while varying the... [more]

The paper presents an analysis of the possible location of geological formations suitable for CO2 storage in the Upper Silesia Coal Basin, Poland. The range of the reservoir has been determined on the basis of an analysis of basic geological parameters, which determine the selection criteria for sites suitable for CO2 storage. A dynamic modelling of the CO2 distribution in the aquifer is presented. Based on the constructed model of migration, reactivity, and geochemical transport of CO2 in geological structures, it is possible to identify potential migration routes and escape sites of CO2 on the surface. The analysis of the technical and geological possibilities of CO2 storage was carried out according to the regulations of the complex Polish geological law, specifically in terms of sequestration possibilities in geological formations.

Due to the observed increase of photovoltaic installations capacity in Poland, the research on the performance of different modules became an important issue from the practical and scientific point of view. This paper is intended to help system planners to choose photovoltaic modules and inverters taking into account the actual operating conditions. The study is devoted to the assessment of four different technologies of photovoltaic modules: polycrystalline silicon (pc-Si), amorphous silicon (a-Si), copper indium gallium selenide (CIGS), and cadmium telluride (CdTe). The data was collected at a solar plant located at high latitude location, in the eastern part of Poland, during the fourth year of the plant operation. The influence of irradiance on the temperature and efficiency of modules was studied. The results show that the efficiency of the pc-Si and CIGS modules decreases with rising temperature; however, the efficiency of the a-Si and CdTe modules is more stable. The impact of c... [more]

Personal light electric vehicles (PLEVs) are a phenomenon that can currently be observed in cities, intended to be an ecological form of transport. The authors of the paper make an attempt to determine electricity consumption by PLEVs in the context of managing a large city in accordance with the concept of sustainable development. The article is of a cognitive nature. Research questions posed against the background of the goal formulated are as follows: how strong will the demand for PLEVs be (in the example of e-motor scooters, taking into consideration the number of vehicles) and for the electricity consumed by PLEVs. The method used is a simulation model. The conducted analyses demonstrate that a dynamic growth of PLEVs will result in an increased energy demand, which must be taken into account by the cities, developing according to the sustainable development conception.

In this paper, we propose a side-absorption concentrated module with diffractive grating as a spectral-beam-splitter to divide sunlight into visible and infrared parts. The separate solar energy can be applied to different energy conversion devices or diverse applications, such as hybrid PV/T solar systems and other hybrid-collecting solar systems. Via the optimization of the geometric parameters of the diffractive grating, such as the grating period and height, the visible and the infrared bands can dominate the first and the zeroth diffraction orders, respectively. The designed grating integrated with the lens and the light-guide forms the proposed module, which is able to export visible and infrared light individually. This module is demonstrated in the form of an array consisting of seven units, successfully out-coupling the spectral-split beams by separate planar ports. Considering the whole solar spectrum, the simulated and measured module efficiencies of this module were 45.2% a... [more]

Soot is an important component for heat transfer in combustion processes. However, it is also a harmful pollutant for humans, and strict emissions legislation motivates research on how to control soot formation and release. The formation of soot is known to be triggered by high temperature and high pressure during combustion, and it is also strongly influenced by the local stoichiometry. The current study investigates how the formation of soot is affected by increasing the oxygen concentration in the oxidizer, since this affects both the temperature profile and partial pressures of reactants. The oxygen-to-fuel ratio is kept constant, i.e., the total flow rate of the oxidizer decreases with increasing oxygen concentration. Propane is combusted (80 kWth) while applying oxygen-enriched air, and in-flame measurements of the temperature and gas concentrations are performed and combined with available soot measurements. The results show that increasing the oxygen concentration in the oxidiz... [more]

Direct optical access to the combustion chamber of a gasoline direct injection (GDI) engine provides extremely valuable information about the combustion process. Experimental measurements of the geometric characteristics of the turbulent flame—such as the flame radius, flame center, flame edges and flame brush thickness—are of fundamental interest in support of the development and validation of any combustion model. To determine the macroscopic properties of sprays and flames, visualization and digital image processing techniques are typically used in controlled experimental setups like single-cylinder optical engines or closed vessels, while optical measurements on mass-production engines are more uncommon. In this paper the optical experimental setup (consisting of a high-speed camera, a laser light source and a data acquisition system) used to characterize the planar turbulent flame propagation in the cylinder of a 3.5 L GDI V6 mass-production engine, is described. The image acquisi... [more]

We propose an innovative framework termed phasor-based control (PBC) to facilitate the integration of heterogeneous and intermittent distributed energy resources (DER) on the electric grid. PBC presents a unified approach that is agnostic to optimization criteria and to the particular characteristics of participating resources. It is enabled by synchronized, high-precision voltage phasor measurements that allow stating control objectives in grid-specific, rather than resource-specific, terms. We present qualitative justification and examine the general feasibility of this control approach, including the behavior of candidate control algorithms in simulation. Initial results suggest that PBC has significant potential to support stable and resilient grid operations in the presence of arbitrarily high penetrations of DER.

A fast terminal sliding mode control is proposed in this paper for improving the dynamic performance and robustness of a permanent magnet in-wheel motor system driven by a voltage source inverter. Firstly, a fast terminal sliding mode approaching law was designed to accelerate the approaching rate of the control system. Then, a torque load observer was designed to compensate for disturbances and uncertainties. Finally, fuzzy rules were designed to suppress the chattering phenomenon. Simulation and experimental results demonstrated that the fast terminal sliding mode control strategy presented better response speed than the conventional sliding mode control strategy. It had better dynamic performance and anti-interference and effectively reduced the chattering phenomenon in the control process.

The massive integration of distributed energy resources in power distribution systems in combination with the active network management that is implemented thanks to innovative information and communication technologies has created the smart distribution systems of the new era. This new environment introduces challenges for the optimal operation of the smart distribution network. Local energy markets at power distribution level are highly investigated in recent years. The aim of local energy markets is to optimize the objectives of market participants, e.g., to minimize the network operation cost for the distribution network operator, to maximize the profit of the private distributed energy resources, and to minimize the electricity cost for the consumers. Several models and methods have been suggested for the design and optimal operation of local energy markets. This paper introduces an overview of the state-of-the-art computational intelligence methods applied to the optimal operatio... [more]

The paper deals with the problem of modelling and analyzing the dynamic properties of a Junction Field Effect Transistor (JFET) made of silicon carbide. An examination of the usefulness of the built-in JFET Simulation Program with Integrated Circuit Emphasis (SPICE) model was performed. A modified model of silicon carbide JFET was proposed to increase modelling accuracy. An evaluation of the accuracy of the modified model was performed by comparison of the measured and calculated capacitance−voltage characteristics as well as the switching characteristics of JFETs.

With the gradual increase in the installed capacity of wind turbines, more and more attention has been paid to the economy of wind power. Economic model-predictive control (EMPC) has been developed as an effective advanced control strategy, which can improve the dynamic economy performance of the system. However, the variable-speed wind turbine (VSWT) system widely used is generally nonlinear and highly coupled nonaffine systems, containing multiple economic terms. Therefore, a nonlinear EMPC strategy considering power maximization and mechanical load minimization is proposed based on the comprehensive VSWT model, including the dynamics of the tower and the gearbox in this paper. Three groups of simulations verify the effectiveness and reliability/practicability of the proposed nonlinear EMPC strategy.

Offshore wind energy is regarded as a key alternative to fossil fuels in many parts of the world. Its exploitation is based on the sound evaluation of wind resources. This study used data from a meteorological mast, a floating light detection and ranging (LiDAR) device, and the Modern-Era Retrospective Analysis for Research and Applications, a reanalysis data set established by the NASA Center for Climate Simulation, to evaluate wind resources of the Changhua-South Offshore Wind Farm. The average wind speeds evaluated at a height of 105 m in the studied wind farm were 7.97 and 8.02 m/s according to the data obtained from the floating LiDAR device and a mast, respectively. The full-load hours were 3320.5 and 3296.5 h per year when data from the LiDAR device and mast were used, respectively. The estimated annual energy production (AEP) with a probability of 50% (P50) reached 314 GWh/y, whereas the AEPs with a probability of 75% (P75) and with a probability of 90% (P90) were 283 GWh/y and... [more]