Real-time online simulation based on a real-time workshop (RTW) plays a vital role in the study and application of power electronics. However, restricted by the performance of equipment and hardware, the simulators so far available in the market mainly support simulation steps over 50 μs, while large step simulation may result in the action delay of pulse-width modulating (PWM), numerical oscillation and high-level non-characteristic harmonic distortion. In view of these problems, this paper puts forward a modeling method based on integral prediction and interpolation compensation. First of all, prediction is performed one step in advance by the implicit trapezoidal method to find out the accurate time when the triangle carrier wave intersects with the modulation wave. At the same time, a mathematic model is built for the insulated gate bipolar transistor (IGBT) to output equivalent voltage waveform according to the principle of area equivalent. Next, in MATLAB/Simulink, offline simula... [more]

This study provides comprehensive details of evaporative cooling options for building air-conditioning (AC) in Multan (Pakistan). Standalone evaporative cooling and standalone vapor compression AC (VCAC) systems are commonly used in Pakistan. Therefore, seven AC system configurations comprising of direct evaporative cooling (DEC), indirect evaporative cooling (IEC), VCAC, and their possible combinations, are explored for the climatic conditions of Multan. The study aims to explore the optimum AC system configuration for the building AC from the viewpoints of cooling capacity, system performance, energy consumption, and CO2 emissions. A simulation model was designed in DesignBuilder and simulated using EnergyPlus in order to optimize the applicability of the proposed systems. The standalone VCAC and hybrid IEC-VCAC & IEC-DEC-VCAC system configurations could achieve the desired human thermal comfort. The standalone DEC resulted in a maximum COP of 4.5, whereas, it was 2.1 in case of the... [more]

The problem of thermal modeling of modern three-dimensional (3D) integrated circuit (IC) systems in packages (SiPs) is discussed. An effective quasi-3D (Q3D) approach of thermal design is proposed taking into account the specific character of 3D IC stacked multilayer constructions. The fully-3D heat transfer equation for global multilayer construction is reduced to the set of coupled two-dimensional (2D) equations for separate construction layers. As a result, computational difficulties, processor time, and RAM volume are significantly reduced, while accuracy can be provided. A software tool, Overheat-3D-IC, was developed on the base of the generalized Q3D package numerical model. For the first time, the global 3D thermal performances across the modern integrated circuit/through-silicon via/ball grid array (IC-TSV-BGA) and multi-chip (MC)-embedded printed circuit board (PCB) packages were simulated. A ten times decrease of central processing unit (CPU) time was achieved as compared wit... [more]

Torrefied empty fruit bunch (EFB) co-firing is a promising technology to reduce emissions from coal-fired power plants. However, co-firing can influence the combustion and heat transfer characteristics in a coal boiler. In order to study the feasibility of co-firing application of torrefied EFB (T-EFB) in boilers, the combustion characteristics, gas emissions and heat flux distribution were analyzed, respectively. First, the kinetic parameters of T-EFB devolatilization and char oxidation were obtained by experimental analysis. Second, the computational fluid dynamics (CFD) analysis was applied to the actual 500 MWe boiler simulation to further evaluate the differences in the co-firing performance parameters (combustion characteristics and emissions) of the T-EFB and the heat transfer characteristics within the boiler. Numerical results show that T-EFB co-firing can improve the ignition characteristics of pulverized coal, reduce the formation of unburned particles. When the blending rat... [more]

In this work, an effective calculation method of the ion flow field that considers the impact of wind flow and water drops is presented. To be explicit, the nominal electric field is solved by the charge simulation method (CSM) whilst the space charge density is calculated adopting a second order upwind finite volume method. In addition, a method that determines the roughness factor of a conductor surface is used to enhance calculation accuracy. The influence of various properties of the water drops exerting on an ion flow field is analyzed. Eventually, a practical experiment is conducted to verify the calculated result, and the effectiveness and reliability of this method are then proved via comparing calculated and measured results.

Density functional theory-based molecular modeling (DFT/MM) validates that KI and I2 undergo exothermic van der Waals (vdW) aggregation in acetonitrile (AN) or in the presence of 4-tert-butylpyridine (TBP), forming potassium triiodide (KI3) and, further mutual vdW aggregation leads to the formation of (KI3)2 and AN, (KI3)2 and (AN)2 and (KI3)2 and TBP in the AN-based Dye sensitized solar cells (DSSC) electrolytes. All KI3 aggregates have a very low energy gap, 0.17 eV, 0.14 eV and 0.05 eV of lowest unoccupied molecular orbital (LUMO) + 1 and LUMO, respectively, verifying efficient electron diffusion in μm-thick DSSC electrolytes. Hydrogen-bonding aggregation of anatase TiO2 model, Ti9O18H and OH, with N3 (proton) dye is also validated by DFT/MM, and the energy structure verifies unidirectional electron flow from highest occupied molecular orbital (HOMO) on thiocyanide (SCN) groups of N3 dye to LUMO on the TiO2 model at the aggregates. Further, DFT/MM for the aggregation of K+I3− with N... [more]

Waterflooding is a common recovery method used to maintain reservoir pressure and improve reservoir oil sweep efficiency. However, injecting cold water into a reservoir alters the state of in-situ formation stress and can result in the formation fracturing. In other words, it can cause the initiation and growth of thermally induced fractures (TIFs), even when the original fracture propagation pressure is not exceeded. TIFs can cause non-uniform distribution of the fluid flow in wellbores, a reduction in sweep efficiency, and early water breakthrough in nearby production wells. Modelling and history matching workflows that consider the dynamic nature of the TIF problem are critical. These workflows improve and validate reservoir and geomechanical models, identify and confirm observed TIF onset and propagation periods, and provide a history-matched sector model with the rock mechanical and thermal properties and stress gradients that can be used with confidence for subsequent studies. Mo... [more]

Pre-cooling of inlet air using evaporative cooling is an effective approach to enhance the performance of air-cooled condensers in air conditioning applications. Ultrasonic mist generators have emerged as a promising alternative to conventional evaporative cooling systems based on cooling pads or spray cooling. This paper presents the developed numerical model of an ultrasonic mist generator for the evaporative pre-cooling of the inlet air of the condenser in air conditioning applications. The model was validated against the experimental data obtained in a wind tunnel experimental facility. A parametric analysis including some physical variables involved in the cooling process was carried out, including the main axial air velocity, the injection air velocity and the water mass flow rate of atomized water. The dimensionless groups water-to-air mass flow and air-to-air mass flow ratios were found to most affect the average evaporative cooling efficiency. A maximum value of 0.654 was foun... [more]

The Trans-European Replacement Reserve Exchange (TERRE) project is the European implementation project for exchanging Balancing Energy (BE) from Replacement Reserves (RR). Its main objective is to operate a common European platform that gathers all RR Balancing Energy Orders (BEOs) from Transmission System Operators’ (TSOs) local BE markets into a Common Merit Order List (CMOL). It provides an optimized allocation of RR, covering all TSOs’ RR BE needs, by executing the Activation Optimization Function (AOF). In this paper, the mathematical formulation of the AOF is presented, which explicitly incorporates all standard products and constraints that are provisioned in the approved implementation framework. The clearing problem is formulated as a Mixed Integer Linear Programming model and solved within an iterative algorithm for the handling of Paradoxically Accepted Orders (PAOs). The modeling framework allows the coordination of two distinct market setups, i.e., the self-dispatch and ce... [more]

Sonochemical reactors can be very effective in many applications, including: degradation of chemical pollutants, inactivation of microorganisms, or production of biofuels. However, due to various factors, the ultrasonic power that is dissipated into sonicated liquid may vary in time. Hence, it is obvious that the ultrasonic power must be known for an optimal design and operation of the sonoreactor. In this paper, we present a method for on-line estimation of the ultrasonic power in continuous flow sonoreactors. In this method, we design an observer that estimates unknown model parameters by using a mathematical model of the sonoreactor and by measuring input and output temperatures in the sonoreactor system. The effectiveness of the method is shown for a simulated and real continuous flow sonoreactors. We also discuss the possibilities of ultrasonic power stabilization by using control algorithms.

A windcatcher is a wind-driven natural ventilation system that catches the prevailing wind to bring fresh airflow into the building and remove existing stale air. This technology recently regained attention and is increasingly being employed in buildings for passive ventilation and cooling. The combination of windcatchers and evaporative cooling has the potential to reduce the amount of energy required to ventilate and cool a greenhouse in warm and hot climates. This study examined a greenhouse incorporated with a passive downdraught evaporative cooling windcatcher (PDEC-WC) system using Computational Fluid Dynamics (CFD), validated with experimental data. Different hot ambient conditions of temperature (30−45 °C) and relative humidity (15−45%) were considered. The study explored the influence of different spray heights, layouts, cone angles and mass flow rates on indoor temperature and humidity. The average error between measurements and simulated results was 5.4% for the greenhouse m... [more]

Small Darrieus vertical-axis wind turbines (VAWTs) have recently been proposed as a possible solution for adoption in the built environment as their performance degrades less in complex and highly-turbulent flows. Some recent analyses have even shown an increase of the power coefficient for the large turbulence intensities and length scales typical of such environments. Starting from these insights, this study presents a combined numerical and experimental analysis aimed at assessing the physical phenomena that take place during the operation of a Darrieus VAWT in turbulent flows. Wind tunnel experiments provided a quantification of the performance variation of a two-blade VAWT rotor for different levels of turbulence intensity and length scale. Furthermore, detailed experiments on an individual airfoil provided an estimation of the aerodynamics at high turbulence levels and low Reynolds numbers. Computational fluid dynamics (CFD) simulations were used to extend the experimental result... [more]

Over the past few decades, the aerodynamic improvements of turbocharger turbines contributed significantly to the overall efficiency augmentation and the advancements in downsizing of internal combustion engines. Due to the compact size of automotive turbochargers, the experimental measurement of the complex internal aerodynamics has been insufficiently studied. Hence, turbine designs mostly rely on the results of numerical simulations and the validation of zero-dimensional parameters as efficiency and reduced mass flow. To push the aerodynamic development even further, a precise validation of three-dimensional flow patterns predicted by applied computational fluid dynamics (CFD) methods is in need. This paper presents the design of an up-scaled volute-stator model, which allows optical experimental measurement techniques. In a preliminary step, numerical results indicate that the enlarged geometry will be representative of the flow patterns and characteristic non-dimensional numbers a... [more]

The flow of energy within external gear machines (EGMs) leads to the variation of fluid temperature in the EGMs, which affects their performance. However, the common approaches for the simulation of EGMs assume isothermal conditions. This isothermal assumption negatively impacts their modelling accuracy in terms of the internal flows which are dependent on the fluid temperature (via fluid properties). This paper presents a lumped parameter based thermal model of EGMs where the fluid temperature in the EGM is evaluated considering the effects of compression/expansion, internal flows, and power losses. Further, numerical techniques are developed to model each of these three aspects. The thermal model is validated via the outlet temperature and volumetric efficiency measurements obtained from experiments conducted on six units of an EGM taken as a reference with different internal clearances. The results from the model show that the fluid temperature increases as it is carried from the in... [more]

The volume of magnetic components for space applications, directly related to the launch cost, and their performance are critically influenced by their capability to dissipate the internal electromagnetic power losses. This is the reason why accurate thermal models are required. Furthermore, these models need to be simple and versatile to allow a fast analysis of many different designs. In this study, a specific methodology to analyze inductors and transformers by thermal networks and a simplification based on the Thevenin’s theorem leading to a simple equation are proposed. The specific details to address thermal modelling for space magnetic components are discussed. A generic 50 W Flyback transformer for space applications is analyzed in this study and experimental validation is provided, showing that the proposed method leads to a deviation in the temperature estimation between 1 °C and 5 °C, which is considered quite a good result from the literature review carried out.

In this paper the energy performances carried out by an investigation conducted on a Heating, Ventilation and Air Conditioning (HVAC) system, composed by an Air Handling Unit (AHU) for the primary air coupled with a horizontal-pipes Ground-to-Air Heat eXchanger (GAHX) and fan-coil units, for an office building, supposed to be placed in four different cities (Rio de Janeiro, Dubai, Naples, Ottawa) belonging to four different worldwide climatic areas, according to the Köppen climate classification. The investigation is performed by means of a two dimensional numerical model, experimentally validated, of an GAHX solved with finite element method. The results introduced in this paper are carried out by varying the length of the pipes and the air flow velocity; thus, also the number of tubes forming the GAHX is varied since the volumetric flow rate to be provided to the AHU must be kept constant. The energy performances of the above-mentioned HVAC system are analyzed, both in summer and in... [more]

This study addresses the thermal and energy performance assessment of a Building Integrated Photovoltaic Thermal (BIPVT) system installed on the façade of a test room in Solar XXI, a Net Zero Energy Building (NZEB) located in Lisbon, Portugal. A numerical analysis using the dynamic simulation tool EnergyPlus was carried out for assessing the performance of the test room with the BIPVT integrated on its façade through a parametric analysis of 14 scenarios in two conditions: a) receiving direct solar gains on the glazing surface and b) avoiding direct solar gains on the glazing surface. Additionally, a computational fluid dynamics (CFD) analysis of the BIPVT system was performed using ANSYS Fluent. The findings of this work demonstrate that the BIPVT has a good potential to improve the sustainability of the building by reducing the nominal energy needs to achieve thermal comfort, reducing up to 48% the total energy needs for heating and cooling compared to the base case. The operation mo... [more]

Introduced by the Civil Code, the rules of road safety are introducing continuously increasingly strict requirements on motor vehicles. These requirements relate to various aspects of the technical condition of vehicles, both those that determine traffic safety and those that affect the vehicle’s environmental impact. The law requires regular diagnosis of the technical condition of vehicles in service. Diagnostic tests conducted in the form of road tests or the tests performed in workshop conditions allow to determine the symptoms of dysfunctions of the tested vehicle, not always clearly defining the causes and location of damage. The purpose of the work is the design the simulation of a station for of vehicle dynamics tests up to 3.5 t using simulation programs OpenModelica and SciLab. A simulation of the work of the stand for testing the dynamics of vehicles in the form of a chassis dynamometer was achieved. The program enables the simulation of tests: NEDC (New European Drive Cycle)... [more]

The formation of an inlet vortex seriously restricts axial-flow pump device performance and poses a great threat to the safe and stable operation of the entire system. In this study, the change trends of an inlet vortex and its influence on an axial-flow pump are investigated numerically and experimentally in a vertical axial-flow pump device. Four groups of fixed vortex generators (VGs) are installed in front of the impeller to create stable vortices at the impeller inlet. The vortex influence on the performance of pump device is qualitatively and quantitatively analyzed. The vortex patterns at different positions and moments in the pump device are explored to reveal the vortex shape change trend in the impeller and the pressure fluctuation induced by the vortex. The reliability and accuracy of steady and unsteady numerical results are verified by external characteristics and pressure fluctuation experimental results. Results show that it is feasible to install VGs before the impeller... [more]

The research on two-stroke engines has been focused lately on the development of direct injection systems for reducing the emissions of hydrocarbons by minimizing the fuel short-circuiting. Low temperature combustion (LTC) may be the next step to further improve emissions and fuel consumption; however, LTC requires unconventional ignition systems. Jet ignition, i.e., the use of prechambers to accelerate the combustion process, turned out to be an effective way to perform LTC. The present work aims at proving the feasibility of adopting passive prechambers in a high-pressure, direct injection, two-stroke engine through non-reactive computational fluid dynamics analyses. The goal of the analysis is the evaluation of the prechamber performance in terms of both scavenging efficiency of burnt gases and fuel/air mixture formation inside the prechamber volume itself, in order to guarantee the mixture ignitability. Two prechamber geometries, featuring different aspect ratios and orifice number... [more]

Polymer electrolyte membrane fuel cells (PEMFCs) are often used for household applications, utilizing hydrogen produced from natural gas from the gas grid. The hydrogen is thereby produced by steam reforming of natural gas followed by a water gas shift (WGS) unit. The H2-rich gas contains besides CO2 small amounts of CO, which deactivates the catalyst used in the PEMFCs. Preferential oxidation has so far been a reliable process to reduce this concentration but valuable H2 is also partly converted. Selective CO methanation considered as an attractive alternative. However, CO2 methanation consuming the valuable H2 has to be minimized. The modelling of selective CO methanation in a household fuel cell system is presented. The simulation was conducted for single and two-stage adiabatic fixed bed reactors (in the latter case with intermediate cooling), and the best operating conditions to achieve the required residual CO content (100 ppm) were calculated. This was done by varying the gas in... [more]

Recently, the concept of “circular economy”, the design for end-of-life, the problem of reduction of waste of electronic and electrical equipment are becoming more and more important. The design of electronic systems for end-of-life considers the possibility of their repair, reuse and recycle, in order to reduce waste. This work proposes a new accurate model of failure probability density, that includes the failure probability of a used component in new equipment. The model has been tested, in conjunction with the International Electrotechnical Commission and Telcordia standard, in real industrial production. Eight years of historical faults have been analyzed and used to derive the fault models of the components. The model and analysis have been used for the analysis of real electronic products. The reuse of components could make an improvement to the reliability of the equipment.

The building sector contributes approximately one third of the total energy consumption worldwide. A large part of this energy is used for the heating and cooling of buildings, which can be drastically reduced by use of energy-efficient glazing. In this study, we performed building energy simulations on a prototypical residential building, and compared commercially available static (low-e, solar IR blocking) to newly developed adaptive thermochromic glazing systems for various climate regions. The modeling results show that static energy-efficient glazing is mainly optimized for either hot climates, where low solar heat gain can reduce cooling demands drastically, or cold climates, where low-e properties have a huge influence on heating demands. For intermediate climates, we demonstrate that adaptive thermochromic glazing in combination with a low-e coating is perfectly suited. The newly developed thermochromic glazing can lead to annual energy consumption improvement of up to 22% in c... [more]

Energy communities are key elements in the energy transition at the local level as they aim to generate and distribute energy based on renewable energy technologies locally. The literature on community energy systems is dominated by the study of electricity systems. Yet, thermal energy applications cover 75% of the total energy consumption in households and small businesses. Community-driven initiatives for local generation and distribution of thermal energy, however, remain largely unaddressed in the literature. Since thermal energy communities are relatively new in the energy transition discussions, it is important to have a better understanding of thermal energy community systems and how these systems function. The starting point of this understanding is to study factors that influence the formation and continuation of thermal energy communities. To work towards this aim, an abstract agent-based model has been developed that explores four seemingly trivial factors, namely: neighborh... [more]

Background: The aim of our study was to identify an optimal heating system for the analyzed church. We also evaluated the energy consumption of the existing system and of those proposed in order to choose the best heating system. Methods: We analyzed the current existing heating system, a mixed system (static heaters and hot air heating) in a Romanian heritage church, build in the 16th century, and we compared it with an underfloor heating system that has been mentioned in the literature as an alternative for church heating. We used a computational fluid dynamics (CFD) analysis of the indoor climate with two turbulence models (k-ε and k-ω). Results: Comparing the two heating systems through boxplot graphs, we could highlight pertinent conclusions regarding the temperatures and velocities of the measured air currents. Thus, of all the heating systems, the underfloor heating had the lowest temperatures, but the highest air velocities, in the churchgoers area, especially under the towers... [more]