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The growth in population increases greenhouse gas (GHG) emissions into the environment. High GHG emissions are attributed to meat production, due to its high energy demand. The largest carbon footprint in the production of poultry meat is generated by combustion. This paper deals with the problem of greenhouse gas emissions (total dust, CO, CO2, NOx, SOx and benzo(a)pyrene) resulting from the generation of energy for heating broiler houses located in different locations in Europe. The study includes continuous measurements of selected microclimate parameters: temperature and relative humidity inside and outside the building, floor temperature, wind speed and direction, and solar radiation intensity. Validation and calibration of the model, emission calculations, and analysis of the obtained results were conducted. Eighteen design variants were assumed, differentiated by the heating fuel used (hard coal, fuel oil, gaseous fuels), material and construction solutions for the floor and the location of the facility. The analysis showed that CO2 emissions for a facility located in northern Europe are 123,153 kg higher compared to the same building located in southern Europe. In addition, increasing the floor's thermal resistance by 3.69 m2·K·W−1 reduced harmful gas emissions by an average of 5.7% for each of the locations analysed. [ABSTRACT FROM AUTHOR]

This article presents an analytical solution for the evaluation of the thermal performance of packed bed sensible heat storage. The numerical model developed was tested for four different solid storage mediums. The thermal energy equation is solved numerically by deploying the finite difference method. The presented analytical solution is based on a novel mathematical approach. The numerical model was validated using the computer simulation package Comsol Multiphysics v5.3. Our numerical model results are in good agreement with the published experimental data, with an overall difference of ~10%. Hence, the numerical model is an efficient way of evaluating the thermal performance of packed bed thermal energy storage systems compared to other numerical strategies or computer simulation techniques. This proves that the novel analytical model has shown to be a reliable and broadly accurate approach to acquire the thermal performance of sensible heat storage. [ABSTRACT FROM AUTHOR]

In this paper, we develop a finite-difference time-domain (FDTD) model in which the time-evolving electrical conductivity of the air ionization plasma in DC voltage needed-plate setup is represented. Maxwell's equations are solved using the FDTD method, and the associated currents and discharge fields are computed over time and in three-dimensional space. The proposed model for the electrical conductivity is dependent on time, the applied DC voltage, and the gap length. The necessary data for developing the proposed model is obtained experimentally using a standard discharge needle, with its spherical tip measuring approximately 40 μ m in diameter. Once high voltage is applied, a steady state is achieved. The electrical conductivity σ (t) and its associated parameters are then calculated using nonlinear equations proposed to reproduce the experimentally obtained plasma behavior in the full-wave FDTD model. Voltage ranges from 4 kV to 9 kV, and gap distances are between 4 mm and 8 mm. [ABSTRACT FROM AUTHOR]

Currently, drilling of directional oil and gas wells under complex technical-technological and mining-geological conditions requires the use of drill pipes made of various materials. In turn, to choose rational modes of strengthening drill pipes and drill string layouts, information on the contact forces and friction forces of the drill string pipes on boreholes is necessary. Drill pipe curved sections friction with boreholes and drill bit resistance moment changes are the main causes of uneven rotation of a drill string during rotary or combined drilling methods and the occurrence of parametric oscillations. To reduce the cost of mechanical energy for well wiring, it is necessary to take into account the "drill string–borehole rocks" force interaction to estimate the magnitude of the frictional forces and their influence on the technological parameters of the drilling process. To solve this problem, mathematical models of "conventionally vertical and inclined drill string sections–borehole" were built. Based on the industrial data, an analysis of the force interaction of a deformed drill string composed of pipes made of different materials (aluminum, titanium, steel) was carried out. Analytical dependences were obtained for determining the contact forces and friction of the pipes on boreholes. A numerical study of the change of these power factors depending on the depth of the well under conditions of intensive vibration loading was carried out. The amplitude values of these forces, the frequency of their change for good sections, as well as the places for the most rational installation of drill pipes in the layout of the drill string were estimated. It was established that the intensity of contact and friction forces for steel drill pipes is greater than for titanium or aluminum ones. It is shown that the greater impact of a solid steel string on contact forces and frictional forces compared to a layout with sections of titanium or aluminum pipes in the range of vibration frequencies of 8–22 Hz corresponds to a bit rotation frequency of 70–80 rpm. The practical application of the obtained research results will contribute to the improvement of technical and economic indicators of the well drilling process. [ABSTRACT FROM AUTHOR]

A numerical model of a flue gas scrubber sump is developed with the aim of enabling optimization of the design of the sump in order to reduce energy consumption. In this model, the multiphase flow of the continuous phase, i.e., water, and the dispersed phase, i.e., air bubbles, is considered. The air that is blown in front of the agitators, as well as the influence of the flow field of the agitators on the distribution of the dispersed phase and the recirculation pumps as outlet, is modeled. The bubble Sauter mean diameter is modeled using the population balance model. The model is used to analyze operating parameters such as the bubble retention time, the average air volume fraction, bubble Sauter mean diameter, the local distribution of the bubble size and the amount of air escaping from the pump outlets at two operating points. The purpose of the model is to simulate the two-phase flow in the sump of the flue gas scrubber using air dispersion technology with a combination of spargers and agitators, which, when optimized, reduces energy consumption by 33%. The results show that the homogeneity of air is lower in the bottom part of the absorber sump and that the amount of air escaping through recirculation pipes equals 1.2% of the total air blown into the absorber sump. The escaping air consists mainly of bubbles smaller than 6 mm. Additional operating point results show that halving the magnitude of the linear momentum source lowers the air retention, as well as the average homogeneity of the dispersed air. [ABSTRACT FROM AUTHOR]

In situ heat injection is a suitable technique for extracting shale oil from reservoirs with high organic matter content but insufficient thermal maturation. To optimize the stimulation process and to avoid unnecessary energy consumption, understanding the thermal process and the effects of thermal parameters is crucial. This research employs a self-developed simulator to build a 2D numerical model of the in situ conversion process of kerogen with electric heaters. A benchmark model is first established to determine the effects of heat injection on crude oil production and kerogen decomposition. Subsequently, this study analyzes the evolution of shale oil within the reservoir, identifying the role of thermal and physical properties in crude oil production and kerogen decomposition during the stimulation treatment. A sensitivity analysis of the thermal properties of the reservoir is also carried out, which allows for defining the role of the thermal conductivity of the rock during the stimulation process. Finally, it is observed that, when using the injection at a constant power, the injection time to achieve a suitable large rate of decomposition is shorter than at a constant temperature—consequently, it has a higher economic advantage. [ABSTRACT FROM AUTHOR]

The aim of this study was to carry out the investigation and analysis of two-stage magnetic precession gear dynamics and the determination of the resonance frequencies, which can be a cause of the powertrain system failures. Graphical interpretation of the two-stage precession gear is presented, and two equations of the dynamics of the movable elements of the presented gearbox were determined. On the basis of these equations, the stiffness coefficients and resonance frequencies of the presented gearbox were mathematically derived. The next step was to develop a numerical model of the magnetic precession gear dynamics in the environment of MATLAB Simulink. The elaborated model allowed us to analyze the influence of varying the input speed and the load torque on the operation of the magnetic precession gear. The performed analyses of the dynamics of the magnetic precession gear showed the occurrence of a resonance phenomenon under the influence of load torque ripples with a frequency close to the natural frequency of the studied system. [ABSTRACT FROM AUTHOR]

South Africa's energy network is under severe pressure due to low supply and overwhelming demand. With an increase in renewable energy providers, specifically wind energy, knowing how the supply can satisfy the electricity demand may relieve apprehensions. This research aims to provide insight into the wind energy supply of South Africa and question how well this supply meets the demand of South Africa. The methodology used in this work highlights the importance of access to public datasets to dispel misconceptions in the energy industry. Additionally, the work supports network planning and the arguments for increasing wind energy penetration on the South African grid. Wind profiles and the typical energy production of South African wind farms are compared to electricity demand. The geographical spacing of the operational wind farms is considered. It is observed that wind energy supply assists in the peak electricity hourly demand as well as seasonal peaks. Furthermore, South Africa's coast is analysed to determine the offshore wind power potential, where shallow and deep waters are considered. It is observed that South Africa has a high potential for offshore wind, even after losses are applied. [ABSTRACT FROM AUTHOR]

Thermochemical heat storage is an important solar-heat-storage technology with a high temperature and high energy density, which has attracted increasing attention and research in recent years. The mono-metallic redox pair Co3O4/CoO realizes heat storage and exothermic process through a reversible redox reaction. Its basic principle is to store energy by heat absorption through a reduction reaction during high-irradiation hours (high temperature) and then release heat through an exothermic-oxidation reaction during low-irradiation hours (low temperature). This paper presents the design of a cobalt-oxide honeycomb structure, which is extruded from pure Co3O4, a porous media with a high heat-storage density and a high conversion rate. Based on the experimental data, a three-dimensional axisymmetric multi-physics numerical model was developed to simulate the flow, heat transfer, mass transfer, and chemical reaction in the thermochemical heat-storage reactor. Unlike the previous treatment approach of equating chemical reactions with surface reactions, the model in this paper considers the consumption and generation of solids and the diffusion and transfer of oxygen in the porous medium during the reaction process, which brings the simulation results closer to the real values. Finally, the influence of the physical parameters of the honeycomb-structured body on the storage and exothermic process is explored in a wide range. The simulation results show that the physical-parameter settings and structural design of the cobalt-oxide honeycomb structure used in this paper are reasonable, and are conducive to improving its charging/discharging performance. [ABSTRACT FROM AUTHOR]

The ferrocyanide-based organic redox flow battery (ferrocyanide-based ORFB), based on electrochemistry, has become a potential energy storage technology due to its low price, eco-friendliness, safety, and convenience. However, its low efficiency and poor mass transfer performance hinder the application of the ORFB. The influence of the electrode shape (trapezoid, sector, and rectangle) on the mass transfer and battery performance are studied based on a numerical model, which is verified by the experiments. The results show that battery performance of the trapezoid electrode is better than that of the sector and rectangle electrode. The discharge voltage of the rectangle battery is the lowest, and the discharge voltage of the trapezoid battery is the highest. The discharge voltage of the rectangle battery is 4.47% lower than that of the trapezoid battery. The uniformity factor value of the trapezoid battery is 26.9% higher than that of the rectangle battery. The trapezoid shape is the best design for the electrode, contributing to the application of the ferrocyanide-based ORFBs. [ABSTRACT FROM AUTHOR]

Lithium-ion batteries (LIBs) have circumvented the energy storage landscape for decades. However, safety concerns about liquid–electrolyte-based LIBs have challenged their mobilization. Lithium polymer (LiPo) batteries have gained rising interest due to their high thermal stability. Despite an array of commercially available LiPo batteries, limited studies have ventured into modeling. Numerical simulations allow low-cost optimization of existing battery designs through parameter analysis and material configuration, leading to safer and more energy-efficient batteries. This work examined the electrochemical, thermal, and thermal runaway behavior of a lithium cobalt oxide cathode, graphite anode, and poly(vinylidene fluoride-hexafluoropropylene) electrolyte pouch-type LiPo battery using COMSOL Multiphysics®, and validated results with experimental data. The simulated potential curve exhibited strong agreement with experiment data, while the temperature profile during discharge displayed qualitative discrepancies rationalized by the reversible heat generation. Thermal runaway simulations via oven tests revealed that the highest heat generation is from the cathode–electrolyte reaction, while the solid electrolyte interface decomposition initiates the heat generation process. These results suggest a thorough selection of cathode and electrolyte material to heighten battery safety. Overall, the developed models can be utilized as design tools to investigate various chemistries and designs to estimate the behavior and performance of batteries. [ABSTRACT FROM AUTHOR]

The only strategy for reducing fossil fuel-based energy sources is to increase the use of sustainable ones. Among renewable energy sources, solar energy can significantly contribute to a sustainable energy future, but its discontinuous nature requires a large storage capacity. Due to its ability to be produced from primary energy sources and transformed, without greenhouse gas emissions, into mechanical, thermal, and electrical energy, emitting only water as a by-product, hydrogen is an effective carrier and means of energy storage. Technologies for hydrogen production from methane, methanol, hydrocarbons, and water electrolysis using non-renewable electrical power generate CO2. Conversely, employing photoelectrochemistry to harvest hydrogen is a sustainable technique for sunlight-direct energy storage. Research on photoelectrolysis is addressed to materials, prototypes, and simulation studies. From the latter point of view, models have mainly been implemented for aqueous-electrolyte cells, with only one semiconductor-based electrode and a metal-based counter electrode. In this study, a novel cell architecture was numerically modelled. A numerical model of a tandem cell with anode and cathode based on metal oxide semiconductors and a polymeric membrane as an electrolyte was implemented and investigated. Numerical results of 11% solar to hydrogen conversion demonstrate the feasibility of the proposed novel concept. [ABSTRACT FROM AUTHOR]

This paper reviews the heat transfer model for geothermal reservoirs, the fracture network in reservoirs, and the numerical model of hydraulic fracturing. The first section reviews the heat transfer models, which contain the single-porosity model, the dual-porosity model, and the multi-porosity model; meanwhile the mathematical equations of the porosity model are summarized. Then, this paper introduces the fracture network model in reservoirs and the numerical method of computational heat transfer. In the second section, on the basis of the conventional fracture theory, the PKN (Perkins–Kern–Nordgren) model and KGD (Khristianovic–Geertsma–De Klerk) model are reviewed. Meanwhile, the DFN (discrete fracture network) model, P3D (pseudo-3D) model, and PL3D (planar 3D) model are reviewed. The results show that the stimulated reservoir volume method has advantages in describing the fracture network. However, stimulated reservoir volume methods need more computational resources than conventional fracture methods. The third section reviews the numerical models of hydraulic fracturing, which contains the finite element method (FEM), the discrete element method (DEM), and the boundary element method (BEM). The comparison of these methods shows that the FEM can reduce the computational resources when calculating the fluid flow, heat transfer and fracture propagations in a reservoir. Thus, a mature model for geothermal reservoirs can be developed by coupling the processes of heat transfer, fluid flow and fracture propagation. [ABSTRACT FROM AUTHOR]

For low permeability coal seam permeability is weak, low degree of gas migration, prone to gas accidents and other issues. In this paper, a numerical model is established to simulate the process of hydraulic fracturing under monotonic loading and cyclic loading, and a method of increasing permeability of coal seam by cyclic loading hydraulic fracturing technology is proposed. Combined with similar experiments, the influence of cyclic load and cyclic load applied parameters on the fracturing effect of coal and rock mass was analyzed by applying a cyclic load with a pulse pump. The effect of cyclic load pressure technology on coal seam drainage was analyzed by application in 20915 gas control roadways of a coal mine in Guizhou. The results show that after fracturing, the fracture extends along the weak plane of the prefabricated fracture, the pore pressure in the fracture is high pressure, and the pore pressure around the fracture decreases step by step. Due to the compression of the crack, the energy is transferred to the two ends of the crack. The pore pressure has an irregular oval distribution, and there is stress concentration. The pressure value reaches 41.48 MPa. After the cyclic load was applied to the model, the pressure reached the maximum value of 27.64 MPa at 3.37 s. Compared with the monotonic load, the pressure value was reduced by 46.27%. Through pressure and ringing analysis, the fatigue damage of specimens can be realized under cyclic loading. In the experiment, the unconstrained initiation pressure was 2.48 MPa, but after the constraint was applied, the initiation pressure increased to 4.58 MPa, and the pressure increase reached about 55%. After multiple loading and unloading, the peak pressure of the specimen can be reduced and the number of cracks can be increased. In the experiment, the gas extraction rate of ordinary drilling was maintained at about 0.019 m3/min, and the gas extraction rate of ordinary fracturing drilling fluctuated at 0.025 m3/min after 21 days of gas extraction. The pumping capacity of 15 Hz and 20 Hz cyclic loading fracturing boreholes tended to be stable after 15 days, which were about 0.041 m3/min and 0.062 m3/min, respectively. Cyclic loading hydraulic fracturing is better than monotonic loading hydraulic fracturing, and the lower the cyclic loading frequency, the better the fracturing effect. [ABSTRACT FROM AUTHOR]

In the course of the documentation works aimed at updating exploitable resources of the groundwater intake, an unexpected change in hydrodynamic field arrangement was observed in a fragment of the area. In relation to the observations made so far, lasting several decades, the groundwater table switched its slope, indicating the flow in the opposite direction than originally. Initially, in the range of the surveyed hydrogeological structure, no object was identified whose draining character could cause such an effect. No significant groundwater extraction or drainage points were documented within a radius of several kilometers. It was only the extended scope of spatial analysis that made it possible to identify the probable cause of a local change in the water table position as a mining pit located in the neighboring hydrogeological structure. The two adjacent hydrogeological structures treated separately so far revealed an experimentally confirmed hydraulic connection. An in-depth analysis of the problem showed the necessity of modifying the existing model of the structure in order to map the observed interactions. An additional simulation module of General-Head Boundary type was applied. The quantity of lateral groundwater exchange between two hydrogeological structures was estimated using mathematical modeling at 3.4 thousand m3/d (reconstructed current state, after model calibration). Further work should aim at treating reservoirs as hydraulically connected after exceeding limiting parameters. [ABSTRACT FROM AUTHOR]

In this study, the development and testing of a hybrid thermal energy storage (TES) including phase change material (PCM) macro-capsules inside a vertical sensible tank is presented. The storage was specifically developed for delivering hot water on board of ships. Accordingly, a commercial PCM was selected and tested. Subsequently, the hybrid TES was designed and tested under mimicked boundary conditions at lab scale, showing the possibility of increasing the volumetric energy storage density up to 30% compared to the sensible configuration. On this basis, two numerical models were developed: a detailed one, implemented in a Fluent environment, aiming at investigating the main parameters affecting the heat transfer efficiency inside the TES and a second one, implemented in an ESP-r environment to simulate the TES as a component to be implemented inside a more complex system, thus helping its accurate design and operation through a reliable modelling phase. Both models were satisfactorily validated against the experimental results, thus being made available for future investigations and design optimization. [ABSTRACT FROM AUTHOR]

Compared to traditional ultrasonic detection methods, the electromagnetic acoustic transducer (EMAT) technique can be applied in many hostile environments such as elevated temperatures, on-line inspections, etc. However, the EMAT technique has a low conversion efficiency. This paper develops a numerical model to study the effects of the coil configurations on the conversion efficiency of shear-wave EMAT on 7050 aluminum alloy. The numerical model is fully validated by the experiment data. The effects of the configuration parameters, including the coil wires' cross-sectional area, coil wires' cross-sectional shape, and distance between coil wires, on the conversion efficiency are then discussed. The results indicate that after using the coil with a square cross-section, the conversion efficiency of EMAT is increased by 22.5%. In addition, the coil wires' cross-sectional area and the distance between coil wires also have a significant effect on the conversion efficiency. [ABSTRACT FROM AUTHOR]

Lhasa is a "solar city" with high altitude, located in a cold zone in China. Due to the lack of mineral energy sources and the fragility of its ecological environment, solar heating technology is the first choice to satisfy the demand of indoor thermal comfort for building heating. In this study, an accurate solar heating system in Lhasa was investigated under the simultaneous charging and discharging operation mode. Based on the solar heating system, a numerical calculation method of the tank temperature distribution under the simultaneous charging and discharging operation mode was proposed and validated by experiments. This numerical method offers a correlation between the output water temperatures of the tank and the input water temperatures of the tank, which can be used to optimize the thermal performance of the solar heating system in future studies. To evaluate the system performance under the simultaneous charging and discharging operation mode, the transient coefficient of performance (COP) of the heating system was calculated based on the experimental measurements. The calculated results showed that the system COP reached an average number of 3.0, which was nearly equal to that of gas-boiler heating system and much higher than that of electrical heating systems. A north-facing room and a south-facing room were both selected to test whether the room temperatures met the heating requirements. The test results showed that the north-facing room had an average temperature over 17 °C while the south-facing room was over 20 °C, which illustrated that a good heating effect was achieved. Although a relatively high system COP was shown with a good heating effect for the solar heating system under the simultaneous charging and discharging operation mode, further recommendations were proposed for the mass flow rates of the solar collecting cycles and control stagey of the fan coil unit (FCU). [ABSTRACT FROM AUTHOR]

The free-piston engine generator (FPEG) is a novel power generation device with an estimated brake efficiency (energy contained in the fuel that is transformed into useful work) of up to 46%, compared to the 25-35% reported in conventional reciprocating engines. This paper seeks to address a major challenge in the development of new and complex technologies--how do we effectively communicate and understand the influence of key design parameters on its operating performance? In this paper, the FPEG is described using a simple numerical model, a model which is reduced to a forced mass-spring vibration system under external excitation, enabling all the major input parameters to be decoupled. It proved that the engine piston position as a function of time and output power could be predicted directly from the input parameters with acceptable accuracy. The influence of the key FPEG design parameters on the piston oscillation characteristics and electric power output can be characterised with respect to one another and summarised. Key design parameters include piston mass, compression stroke length, piston cross sectional area, and electric load. Compared with previous and more complex numerical models, the presented methods can be used to simply describe the sensitivity of key design parameters on the FPEG performance. It will provide useful general guidance for the FPEG hardware design process. [ABSTRACT FROM AUTHOR]

Brazil has one of the largest electricity markets in South America, which needs to add 6000 MW of capacity every year in order to satisfy growing the demand from an increasing and more prosperous population. Apart from biomass, no other renewable energy sources, besides hydroelectricity, play a relevant role in the energy mix. The potential for wind and wave energy is very large. Brazil's Santa Catarina state government is starting a clean energy program in the state, which is expected to bring more than 1 GW of capacity. Assessment of wave energy resources is needed along the coastline. This work studied the potential wave energy along the north-central coasts of Santa Catarina, in Southern Brazil, by analysis of the hindcast data from the European Centre for Medium-Range Weather Forecasts (ECMWF). The annual offshore wave power was found to be equal to 15.25 kW/m, the bulk of which is provided by southeastern waves. The nearshore energetic patterns were studied by means of a numerical coastal propagation model (Mike21 SW). The mean wave power of 20misobaths is 11.43 kW/m. Supplementary considerations are drawn on realistic perspectives for wave energy converters installations. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to investigate combustion characteristics for rotary engine via numerical studies. A 3D numerical model was developed to study the influence of several operative parameters on combustion characteristics. A novel rotary engine called, "Leaf Spring Rotary Engine", was used to illustrate the structure and principle of the engine. The aims are to (1) improve the understanding of combustion process, and (2) quantify the influence of rotational speed, excess air ratio, initial pressure and temperature on combustion characteristics. The chamber space changed with crankshaft rotation. Due to the complexity of chamber volume, an equivalent modeling method was presented to simulate the chamber space variation. The numerical simulations were performed by solving the incompressible, multiphase Unsteady Reynolds-Averaged Navier-Stokes Equations via the commercial code FLUENT using a transport equation-based combustion model; a realizable κ - ω turbulence model and finite-rate/eddy-dissipation model were used to account for the effect of local factors on the combustion characteristics. [ABSTRACT FROM AUTHOR]

The development of thermal control systems has become an important issue in next-generation electric aircraft design due to the increase in heat exhausted with electrification. In this paper, a wick-type two-phase mechanically pumped fluid loop system for future electric aircraft was proposed through the investigation of current two-phase flow cooling technology. Taking the experimental electric aircraft X-57 as an example, a wick-type two-phase mechanically pumped fluid loop with four evaporators for transporting 12 kW of waste heat within an 80 °C temperature limit was proposed and its feasibility was confirmed. A numerical model was constructed and validated to predict the operating characteristics of a two-phase mechanically pumped fluid loop. The optimal pump outputs under-even and uneven heat load conditions and was investigated for the first time by considering the vapor-liquid separation conditions in each flow path and the power consumption of the pump. Under the optimal pump output condition, the operating characteristics of the wick-type two-phase mechanically pumped fluid loop system were calculated. The calculation results indicate that the proposed wick-type two-phase mechanically pumped fluid loop is suitable as the thermal control system for an X-57 electric aircraft motor, as the calculation results satisfied the operational requirements of the motor. [ABSTRACT FROM AUTHOR]

Plasma parameters of radiofrequency discharge generated at low pressures in an argon-oxygen mixture addressed for biomedical surface sterilization have been optimized. Numerical results illustrate the density distributions of different species and electron temperatures during the electrical discharge process. The current discharge acting in the abnormal range decreases at higher oxygen gas flow rates. The temperature of electrons drops with pressure while it rises by adding oxygen. Nevertheless, electron density displays an adverse trend, exhibited by the electron's temperature. The average particle density of the reactive species is enhanced in Ar/O2 compared to He/O2, which ensures a better efficiency of Ar/O2 in sterilizing bacteria than He/O2. The impact of oxygen addition on the discharge mixture reveals raised oxygen atom density and a reduction in metastable oxygen atoms. A pronounced production of oxygen atoms is achieved at higher frequency domains. This makes our findings promising for biomedical surface sterilization and leads to optimal parameter discharges used for sterilization being at 30% of oxygen gas ratio and 0.3 Torr pressure. [ABSTRACT FROM AUTHOR]

In this paper, we looked at the role of electromechanical storage in railway applications. A mathematical model of a running train was interfaced with real products on the electromechanical storage market supposed to be installed at the substation. Through this simulation, we gathered data on the recoverable energy of the system, its advantages, and its limitations. Various storage powers were run along variations in speed and gradient to paint a clearer picture of this application. Throughout these simulations, the energy savings were between 25% and 38%, saving up to 0.042 kWh/(seat km). [ABSTRACT FROM AUTHOR]

In this work, a design optimization study was conducted to improve the performance of a membraneless microfluidic fuel cell with a double-bridge cross-section of the flow channel. Governing equations including Navier–Stokes, mass-transport, and Butler–Volmer equations were solved numerically to analyze the electrochemical phenomena and evaluate the performance of the fuel cells. Optimization was performed to maximize the peak power density using a genetic algorithm combined with a surrogate model constructed by radial basis neural network. Two sub-channel widths of the flow channel were selected as design variables for the optimization. As a result, a large increase in the inner channel width and a small decrease in the outer channel width effectively increased the peak power density of the MMFC. The optimal design increased the peak power density by 57.6% compared to the reference design. [ABSTRACT FROM AUTHOR]

The paper formulates a method of active reduction of structure vibrations in the selected resonance zones of the tested object. The method ensures reduction of vibrations of the selected resonance zones by determining the parameters of the active force that meets the desired dynamic properties. The paper presents a method for determining the parameters of the active force by reducing the vibrations of the structure in its resonance zones to a given vibration amplitude. For this purpose, an analytical form was formulated, which will clearly define the dynamic properties of the tested object and the force reducing the vibrations in the form of a mathematical model. The formulated mathematical model is a modified object input function, which in its form takes into account the properties of the active force reducing the vibrations. In such a case, it is possible to use the methods of mechanical synthesis to decompose the modified characteristic function into the parameters of the system and the parameters of the force being sought. In the formulated method, the desired dynamic properties of the system and the vibration reducing force were defined in such a way that the determined parameters of the active force (velocity-dependent function) had an impact on all forms of natural vibrations of the tested system. Based on the formalized method, the force reducing the vibrations of the four-story frame to the desired displacement amplitude was determined. Two cases of determining the active force reducing the vibrations to the desired vibration amplitude of the system by modifying the dynamic characteristics describing the object together with the active force were considered. For both cases, the system's responses to the oscillation generated by harmonic force of frequencies equal to the first two forms of natural vibrations of the tested system were determined. In order to verify the determined force reducing the vibrations of the object and to create a visualization of the analyzed phenomenon, the building structure dynamics were analyzed with the use of PLM Siemens NX 12 software. The determined force parameters were implemented into the numerical model, in which the tested system was modelled, and the response time waveforms were generated with regard to the considered story. The generated waveforms were compared with the waveforms obtained in the formalized mathematical model for determining the active force reducing the vibrations. The vibrations of the tested numerical model were induced by the kinematic excitation with the maximum amplitude equal to 100 mm, which corresponds to the vibration amplitude during the earthquake with a force equal to level 5 on the Richter scale. [ABSTRACT FROM AUTHOR]

We present a novel class of reduced-order regenerator models that is based on Endoreversible Thermodynamics. The models rest upon the idea of an internally reversible (perfect) regenerator, even though they are not limited to the reversible description. In these models, the temperatures of the working gas that alternately streams out on the regenerator's hot and cold sides are defined as functions of the state of the regenerator matrix. The matrix is assumed to feature a linear spatial temperature distribution. Thus, the matrix has only two degrees of freedom that can, for example, be identified with its energy and entropy content. The dynamics of the regenerator is correspondingly expressed in terms of balance equations for energy and entropy. Internal irreversibilities of the regenerator can be accounted for by introducing source terms to the entropy balance equation. Compared to continuum or nodal regenerator models, the number of degrees of freedom and numerical effort are reduced considerably. As will be shown, instead of the obvious choice of variables energy and entropy, if convenient, a different pair of variables can be used to specify the state of the regenerator matrix and formulate the regenerator's dynamics. In total, we will discuss three variants of this endoreversible regenerator model, which we will refer to as ES , EE , and EEn -regenerator models. [ABSTRACT FROM AUTHOR]

A double-bridge shape is proposed as a novel flow channel cross-sectional shape of a membraneless microfluidic fuel cell, and its electrochemical performance was analyzed with a numerical model. A membraneless microfluidic fuel cell (MMFC) is a micro/nano-scale fuel cell with better economic and commercial viability with the elimination of the polymer electrolyte membrane. The numerical model involves the Navier–Stokes, Butler–Volmer, and mass transport equations. The results from the numerical model were validated with the experimental results for a single-bridge channel. The proposed MMFC with double-bridge flow channel shape performed better in comparison to the single-bridge channel shape. A parametric study for the double-bridge channel was performed using three sub-channel widths with the fixed total channel width and the bridge height. The performance of the MMFC varied most significantly with the variation in the width of the inner channel among the sub-channel widths, and the power density increased with this channel width because of the reduced width of the mixing layer in the inner channel. The bridge height significantly affected the performance, and at a bridge height at 90% of the channel height, a higher peak power density of 171%was achieved compared to the reference channel. [ABSTRACT FROM AUTHOR]

With the increasing trend toward the miniaturization of electronic devices, the issue of heat dissipation becomes essential. The use of phase changes in a two-phase closed thermosyphon (TPCT) enables a significant reduction in the heat generated even at high temperatures. In this paper, we propose a modification of the evaporation–condensation model implemented in ANSYS Fluent. The modification was to manipulate the value of the mass transfer time relaxation parameter for evaporation and condensation. The developed model in the form of a UDF script allowed the introduction of additional source equations, and the obtained solution is compared with the results available in the literature. The variable value of the mass transfer time relaxation parameter during condensation r c depending on the density of the liquid and vapour phase was taken into account in the calculations. However, compared to previous numerical studies, more accurate modelling of the phase change phenomenon of the medium in the thermosyphon was possible by adopting a mass transfer time relaxation parameter during evaporation r e = 1. The assumption of ten-fold higher values resulted in overestimated temperature values in all sections of the thermosyphon. Hence, the coefficient r e should be selected individually depending on the case under study. A too large value may cause difficulties in obtaining the convergence of solutions, which, in the case of numerical grids with many elements (especially three-dimensional), significantly increases the computation time. [ABSTRACT FROM AUTHOR]

The current work presents a computationally cost-effective numerical model that successfully simulates a heat pump water heater (HPWH) under typical working conditions of dwellings. The model's main components are a stratified tank and the heat-pump unit. Both systems are coupled, since a good prediction of water temperature is needed to accurately predict the heat-pump performance. Ten thermocouples measured the tank wall temperature. Measurements and simulations were performed under challenging conditions of a heavy stratification. The 190 L tank stratification was successfully modeled employing a 1D model, experimentally adjusted by three tapping cycles, with 6 × 22, 6 × 33, and 3 × 33 L consumptions, covering flowrates of 4 and 6 L/min. Water temperature is obtained with an uncertainty of 2.6 ° C while the heat-pump was ON. A black box model has been used to obtain the heat-pump performance out of the external and condenser temperatures. For the analyzed days, the COP estimation presents an uncertainty of only 5.1%. Finally, an application example is included. It was used to simulate six tapping cycles of the European standard for heat pump water heaters testing (EN 16147). The results show the possibilities for heat-pump manufacturers of applying this calibrated model to predict the performance of HPWHs under different conditions. [ABSTRACT FROM AUTHOR]

In this study, a thermal energy storage tank filled with commercial phase change material flat slabs is investigated. The tank provides heat at around 15 °C to the evaporator of a seasonal thermal energy storage system developed under the EU-funded project SWS-Heating. A 2D numerical model of the phase changed material storage tank based on the finite control volume approach was developed and validated with experimental data. Based on the validated model, an optimization was performed to identify the number, type and configuration of slabs. The final goal of the phase change material tank model is to be implemented into the whole generic heating system model. A trade-off between results' accuracy and computational time of the phase change material model is needed. Therefore, a comparison between a 2D implicit and 2D explicit scheme of the model was performed. The results showed that using an explicit scheme instead of an implicit scheme with a reasonable number of nodes (15 to 25) in the heat transfer fluid direction allowed a considerable decrease in the computational time (7 times for the best case) with only a slight reduction in the accuracy in terms on mean average percentage error (0.44%). [ABSTRACT FROM AUTHOR]

The overturning and eccentric abrasion of the slipper worsens the lubrication characteristics and increases the friction power loss and kinetic energy consumption of the slipper/swashplate interface to reduce the axial piston pump efficiency. A coupling lubrication numerical model and algorithm and a micro-chamfering structure are developed and proposed to predict more precisely and improve the lubrication characteristics of the slipper/swashplate interface. The simulation results reveal that the slipper without micro-chamfering overturns and contacts with the swashplate, while the one with micro-chamfering forms a certain oil film thickness to prevent this contact effectively. The minimum total power loss of the slipper/swashplate interface has to be effectively ensured under the worst working conditions, such as the high pressure, the low speed, the maximum swashplate inclination angle and the minimum house pressure. The optimal micro-chamfering width and depth are 1.2 mm and 3.5 μm or C1.2-3.5, the simulation average oil film thickness of which is approximately equal to the optimal analytical value. The experimental friction power loss of the slipper/swashplate interface is basically consistent with the simulation one, confirming the correctness and effectiveness of the coupling lubrication numerical model, and the optimization method and providing the further design direction of axial piston pumps. [ABSTRACT FROM AUTHOR]

The most efficient energy management strategies for hybrid vehicles are the "Optimization-Based Strategies". These strategies require a preliminary knowledge of the driving cycle, which is not easy to predict. This paper aims to combine Worldwide Harmonized Light-Duty Vehicles Test Cycle (WLTC) low section short trips with real traffic levels for vehicle energy and fuel consumption prediction. Future research can focus on implementing a new strategy for Hybrid Electric Vehicle (HEV) energy optimization, taking into account WLTC and Google Maps traffic levels. First of all, eight characteristic parameters are extracted from real speed profiles, driven in urban road sections in the city of Messina at different traffic conditions, and WLTC short trips as well. The minimum distance algorithm is used to compare the parameters and assign the three traffic levels (heavy, average, and low traffic level) to the WLTC short trips. In this way, for each route assigned from Google maps, vehicle's energy and fuel consumption are estimated using WLTC short trips remodulated with distances and traffic levels. Moreover, a vehicle numerical model was implemented and used to test the accuracy of fuel consumption and energy prediction for the proposed methodology. The results are promising since the average of the percentage errors' absolute value between the experimental driving cycles and forecast ones is 3.89% for fuel consumption, increasing to 6.80% for energy. [ABSTRACT FROM AUTHOR]

The work aims at investigating the techno-economic performance of a biodiesel micro combined heat and power (CHP) system for residential applications. The CHP unit is based on a direct-injection compression ignition engine providing 6.7 kWel and 11.3 kWth. A 0D model is developed and validated to characterise the behaviour of the biodiesel-fired engine at full and partial load in terms of efficiency, fuel consumption, and emissions. Furthermore, non-dimensional polynomial correlations are proposed to foresee the performance of biodiesel-fuelled engines for micro-CHP applications at partial loads. Afterwards, the CHP system is adopted to satisfy the electric and thermal demand of domestic users in Southern Italy. To this purpose, a parametric analysis is performed considering a different number of apartments and operating strategies (electric-driven and thermal-driven). A bi-variable optimisation based on the primary energy saving (PES) index and payback period (PBT) permits selecting the thermal-driven strategy and five apartments as the most suitable solution. The optimal PBT and PES are equal to 5.3 years and 22.4%, respectively. The corresponding annual thermal self-consumption reaches 81.3% of the domestic request, and the thermal surplus is lower than 8%. Finally, a sensitivity analysis is adopted to define the influence of the costs of energy vectors and a cogeneration unit on the economic feasibility of the biodiesel CHP system. The analysis highlights that the investigated apparatus represents an attractive option to satisfy the energy requests in micro-scale applications, providing valuable energy and economic advantages compared to traditional energy production. [ABSTRACT FROM AUTHOR]

Nowadays the design of large-scale structures can be effectively improved by the adoption of numerical models. Even if experimental tests still play a fundamental role, a methodological approach that combines experimental testing and modelling technique can significantly improve the understanding of the matter. This, in fact, would result in a more reliable optimization process, drastically reducing efforts and uncertainties towards the implementation of the final product. The present work deals with the development of a finite element model for the analysis of a full-scale prototype of an innovative parabolic trough collector. The collector is analysed under several load conditions in order to evaluate its structural behaviour. Each load configuration is also numerically reproduced. Moreover, it is demonstrated that the model is capable of reproducing both the global (stiffness) and local (strain state) behaviour of the structure. Specifically, the comparison between experimental data and numerical results show a good agreement for the global parameter torsional stiffness. Local strain values are also well reproduced in high-stressed zone. Thus, the model can be used as a reliable "virtual tool" for designers to evaluate the suitability of layout modifications, thereby replacing and reducing the amount of commonly needed experimental tests and, consequently, reducing time and costs. Finally, an example of the potentiality of the finite element model adopted for a computer-aided engineering approach is shown to determine the most promising solution for increasing the torsional stiffness of the trough, while simultaneously limiting the required experimental tests. [ABSTRACT FROM AUTHOR]

Large-scale energy storage systems (ESS) are nowadays growing in popularity due to the increase in the energy production by renewable energy sources, which in general have a random intermittent nature. Currently, several redox flow batteries have been presented as an alternative of the classical ESS; the scalability, design flexibility and long life cycle of the vanadium redox flow battery (VRFB) have made it to stand out. In a VRFB cell, which consists of two electrodes and an ion exchange membrane, the electrolyte flows through the electrodes where the electrochemical reactions take place. Computational Fluid Dynamics (CFD) simulations are a very powerful tool to develop feasible numerical models to enhance the performance and lifetime of VRFBs. This review aims to present and discuss the numerical models developed in this field and, particularly, to analyze different types of flow fields and patterns that can be found in the literature. The numerical studies presented in this review are a helpful tool to evaluate several key parameters important to optimize the energy systems based on redox flow technologies. [ABSTRACT FROM AUTHOR]

This paper presents a virtual model of a scroll compressor developed on the one-dimensional analysis software Simcenter Amesim®. The model is semi-empirical: it needs some physical details of the modelled machine (e.g., the cubic capacity), but, on the other hand, it does not require the geometrical features of the spirals, so it needs experimental data to calibrate it. The model also requires rotational speed and the outlet temperature as boundary conditions. The model predicts the power consumption and the mass flow rate and considers leakages and mechanical losses. After the model presentation, this paper describes the test bench and the obtained data used to calibrate and validate the model. At last, the calibration process is described, and the results are discussed. The calculated values fit the experimental data also in extrapolation, despite the model is simple and performs calculations within 7 s. Due to these characteristics, the model is suitable for being used in a larger model as a sub-component. [ABSTRACT FROM AUTHOR]

The Canadian off-grid communities heavily rely on fossil fuels. This unsustainable energetic framework needs to change, and deep geothermal energy can play an important role. However, limited data availability is one of the challenges to face when evaluating such resources in remote areas. Thus, a first-order assessment of the geothermal energy source is, therefore, needed to trigger interest for further development in northern communities. This is the scope of the present work. Shallow subsurface data and outcrop samples treated as subsurface analogs were used to infer the deep geothermal potential beneath the community of Kuujjuaq (Nunavik, Canada). 2D heat conduction models with time-varying upper boundary condition reproducing climate events were used to simulate the subsurface temperature distribution. The available thermal energy was inferred with the volume method. Monte Carlo-based sensitivity analyses were carried out to determine the main geological and technical uncertainties on the deep geothermal potential and risk analysis to forecast future energy production. The results obtained, although speculative, suggest that the old Canadian Shield beneath Kuujjuaq host potential to fulfill the community's annual average heating demand of 37 GWh. Hence, deep geothermal energy can be a promising solution to support the energy transition of remote northern communities. [ABSTRACT FROM AUTHOR]

Non-uniformity of the steam-assisted gravity drainage (SAGD) steam chamber significantly decreases the development of heavy oil reservoirs. In this study, to investigate the steam conformance in SAGD operations, a wellbore model is developed for fluid flow in dual-string horizontal wells. Then, a three-dimensional, three-phase reservoir model is presented. Next, the coupled wellbore and reservoir model is solved with a fully implicit finite difference method. Finally, the effects of the injector wellbore configuration, steam injection ratio and injection time on the steam conformance are investigated. The results indicate that under different injector wellbore configurations, the closer the differences between the pressure drop from the landing position of the short string to the heel of the wellbore and the pressure drop from the landing position of the short string to the toe of the wellbore, the better is the steam conformance. The smaller the difference in the steam injection rate between the long and short injection strings, the higher is the uniformity of the steam chamber. The injector annular pressure profile uniformity is consistent with the steam conformance. Creating a more uniform steam pressure in the annulus of the injector improves the uniformity of the steam chamber. The steam conformance decreases with increasing injection time, so the optimization method of steam chamber uniformity should be adjusted according to different injection times. [ABSTRACT FROM AUTHOR]

This paper is focused on the resort to geothermal energy, through the employment of an Earth-to-Air-Heat Exchanger (EAHX) positioned upstream of the air-handling unit of an air conditioning system, for an office building in Naples (South Italy). The aim is to evaluate the energy performances of this unusual system compared to the common solution of external air directly entering the air-handling unit. The EAHX is extensively designed and two-dimensionally modeled, and the analysis is solved with finite element method. The model is validated with experimental data and this comparison shows good agreement. With the requirement of providing the building with 1300 m3 h−1 of external airflow, different design solutions for the EAHX are studied, by varying the diameter (in the range 0.2–0.5 m) and length (between 20 and 140 m) of the buried pipes. The results indicate that: smaller tube diameters enhance the heat transfer; a tube length between 80 and 100 m is recommended. Using the EAHX, the reduction of the thermal power of the coils in the air-handling unit is greater than 40% in most cases. Finally, the efficiency of the EAHX is assessed as a function of the tube length and diameter, reaching values up to 0.9. [ABSTRACT FROM AUTHOR]

The analytical model (AM) of suspension force in a bearingless flywheel machine has model mismatch problems due to magnetic saturation and rotor eccentricity. A numerical modeling method based on the differential evolution (DE) extreme learning machine (ELM) is proposed in this paper. The representative input and output sample set are obtained by finite-element analysis (FEA) and principal component analysis (PCA), and the numerical model of suspension force is obtained by training ELM. Additionally, the DE algorithm is employed to optimize the ELM parameters to improve the model accuracy. Finally, absolute error (AE) and root mean squared error (RMSE) are introduced as evaluation indexes to conduct comparative analyses with other commonly-used machine learning algorithms, such as k-Nearest Neighbor (KNN), the back propagation (BP) algorithm, and support vector machines (SVMs). The results show that, compared with the above algorithm, the proposed method has smaller fitting and prediction errors; the RMSE value is just 22.88% of KNN, 39.90% of BP, and 58.37% of SVM, which verifies the effectiveness and validity of the proposed numerical modeling method. [ABSTRACT FROM AUTHOR]

The hydrodynamics of electrodialysis and reverse electrodialysis is commonly studied by neglecting membrane deformation caused by transmembrane pressure (TMP). However, large frictional pressure drops and differences in fluid velocity or physical properties in adjacent channels may lead to significant TMP values. In previous works, we conducted one-way coupled structural-CFD simulations at the scale of one periodic unit of a profiled membrane/channel assembly and computed its deformation and frictional characteristics as functions of TMP. In this work, a novel fluid–structure interaction model is presented, which predicts, at the channel pair scale, the changes in flow distribution associated with membrane deformations. The continuity and Darcy equations are solved in two adjacent channels by treating them as porous media and using the previous CFD results to express their hydraulic permeability as a function of the local TMP. Results are presented for square stacks of 0.6-m sides in cross and counter flow at superficial velocities of 1 to 10 cm/s. At low velocities, the corresponding low TMP does not significantly affect the flow distribution. As the velocity increases, the larger membrane deformation causes significant fluid redistribution. In the cross flow, the departure of the local superficial velocity from a mean value of 10 cm/s ranges between −27% and +39%. [ABSTRACT FROM AUTHOR]

During the production of deepwater wells, downhole perforation safety is one of the key technical problems. The perforation fluctuating pressure is an important factor in assessing the wellbore safety threat. Due to difficulty in describing the downhole perforation pressure by using the existing empirical correlations, a prediction model based on data fitting of a large number of numerical simulations has been proposed. Firstly, a numerical model is set up to obtain the dynamic data of downhole perforation, and the exponential attenuation model of perforation pressure in the wellbore is established. Secondly, a large number of numerical simulations have been carried out through orthogonal test design. The results reveal that the downhole perforation pressure is logarithmic to the total charge quantity, increases linearly to the wellbore initial pressure, shows an exponential relationship with downhole effective volume for perforation, and has a power relationship with the thickness of casing and cement as well as formation elastic modulus. Thirdly, the prediction of perforation peak pressure at different positions along the wellbore agrees well with the field measurement within a 10% error. Finally, the results of this study have been applied in the field case, and an optimization scheme for deepwater downhole perforation safety has been put forward. [ABSTRACT FROM AUTHOR]

This paper proposes and describes a model for evaluating the hydro-mechanical efficiency of external gear machines. The model is built considering and evaluating the main friction losses in the machines, including the viscous friction losses at the tooth tip gap, at the bearing blocks-gears gaps, at the journal bearings, and the meshing loss. To calculate the shear stress at each gap interface, the geometry of the gap has to be known. For this reason, the actual position of the gears inside the pump casing and consequent radial pressure distribution are numerically calculated to evaluate the gap height at the tooth tips. Moreover, the variation of the tilt and reference height of the lateral gaps between the gears and the pump bushings are considered. The shear stresses within the lateral gaps are estimated, for different lateral heights and tilt values. At the journal bearings gaps, the half Sommerfeld solution has been applied. The meshing loss has been calculated according to the suggestion of the International Standards. The hydro-mechanical efficiency results are then discussed with reference to commercial pumps experimentally characterized by the authors in a previous work. The average percentage deviation from experimental data was around 2%, without considering the most critical operating conditions (high delivery pressure, low rotational speed). The limits of this approach are also explained. Finally, the role of each source of loss is discussed, considering different operating conditions and two values of fluid viscosity. Lateral gap losses and meshing loss are much more relevant in determining the hydro-mechanical efficiency variation in the pump's operating range, especially at a low delivery pressure. Moreover, while lateral gap losses increase with the rotational speed, the meshing loss shows the opposite behavior. The tooth tip gap losses are never as relevant, but they increase at high pressure. The journal bearings losses become comparable with the lateral and meshing ones at high delivery pressure values. Considering the pumps analyzed and the operating range of delivery pressure values and rotational speed values, the meshing loss made the mechanical efficiency vary in a percentage range of ±7%, with lateral losses in the range of about the ±15%, when also considering the extreme operating points (low speed, high pressure; high speed, low pressure). The weight of the lateral losses slightly reduced when we analyzed the higher temperature results, while the meshing losses slightly increased. [ABSTRACT FROM AUTHOR]

This article presents a novel methodology to design swash plate type axial piston machines based on computationally based approach. The methodology focuses on the design of the main lubricating interfaces present in a swash plate type unit: the cylinder block/valve plate, the piston/cylinder, and the slipper/swash plate interface. These interfaces determine the behavior of the machine in term of energy efficiency and durability. The proposed method couples for the first time the numerical models developed at the authors' research center for each separated tribological interface in a single optimization framework. The paper details the optimization procedure, the geometry, and material considered for each part. A physical prototype was also built and tested from the optimal results found from the numerical model. Tests were performed at the authors' lab, confirming the validity of the proposed method. [ABSTRACT FROM AUTHOR]

Proton exchange membrane fuel cells (PEMFCs) using porous metallic foam flow-field plates have been demonstrated as an alternative to conventional rib and channel designs, showing high performance at high currents. However, the transport of liquid product water through metal foam flow-field plates in PEMFC conditions is not well understood, especially at the individual pore level. In this work, ex-situ experiments are conducted to visualise liquid water movement within a metal foam flow-field plate, considering hydrophobicity, foam pore size and air flow rate. A two-phase numerical model is then developed to further investigate the fundamental water transport behaviour in porous metal foam flow-field plates. Both the experimental and numerical work demonstrate that unlike conventional PEMFC channels, air flow rate does not have a strong influence on water removal due to the high surface tensions between the water and foam pore ligaments. A hydrophobic foam was seen to transport liquid water away from the initial injection point faster than a hydrophilic foam. In ex-situ tests, liquid water forms and maintains a random preferential pathway until the flow-field edge is reached. These results suggest that controlled foam hydrophobicity and pore size is the best way of managing water distribution in PEMFCs with porous flow-field plates. [ABSTRACT FROM AUTHOR]

In this work, an improved comprehensive model was developed for large coal particles to predict temperature variation and volatile component yields. The kinetics model of volatile component yields, where the volatile matters were assumed to comprise nine species, was combined with heat transfer model. The interaction between volatile yield and heat transfer during pyrolysis of large Maltby coal particles was investigated. An apparent temperature difference has been observed between the surface and core of particles at the initial heating stage. The non-uniform temperature distribution inside coal particles causes non-simultaneous volatile yields release from the surface and core area. The volatile release occurs after the coal temperature rises higher than 350 °C, and its yield steeply increases within the temperature range of 450–520 °C. The peak of volatile release rate corresponds to about 485 °C due to the rapid release of tar and H2O. The tar is almost completely released at around 550 °C. With the increasing particle size, the difference in temperature and volatile yield between the surface and core increases at the end of heating. The results are expected to provide insights into the interaction between heat transfer and volatile yields during pyrolysis of large coal particles. [ABSTRACT FROM AUTHOR]

This paper compares approaches for accurate numerical modeling of transients in the pipe element of district heating systems. The distribution grid itself affects the heat flow dynamics of a district heating network, which subsequently governs the heat delays and entire efficiency of the distribution. For an efficient control of the network, a control system must be able to predict how "temperature waves" move through the network. This prediction must be sufficiently accurate for real-time computations of operational parameters. Future control systems may also benefit from the accumulation capabilities of pipes. In this article, the key physical phenomena affecting the transients in pipes were identified, and an efficient numerical model of aboveground district heating pipe with heat accumulation was developed. The model used analytical methods for the evaluation of source terms. Physics of heat transfer in the pipe shells was captured by one-dimensional finite element method that is based on the steady-state solution. Simple advection scheme was used for discretization of the fluid region. Method of lines and time integration was used for marching. The complexity of simulated physical phenomena was highly flexible and allowed to trade accuracy for computational time. In comparison with the very finely discretized model, highly comparable transients were obtained even for the thick accumulation wall. [ABSTRACT FROM AUTHOR]

In this study, we present a three-dimensional (3-D), multi-scale, multi-physics lithium-ion battery (LIB) model wherein a microscale spherical particle model is applied to an electrode particle domain and a comprehensive 3-D continuum model is applied to a single cell domain consisting of current collectors, porous electrodes, and a separator. Particular emphasis is placed on capturing the phase transition process inside the lithium iron phosphate (LFP) particles that significantly influences the LIB charge and discharge behaviors. The model is first validated against the experimental data measured at various discharge rates. In general, the model predictions compare well with the experimental data and further highlight key electrochemical and transport phenomena occurring in LIBs. Besides elucidating the phase transition evolution inside LFP particles and location-specific heat generation mechanism, multi-dimensional contours of species concentration, temperature, and current density are analyzed under a 3-D cell configuration to provide valuable insight into the charge and discharge characteristics of LIBs. The present multi-scale LIB model can be applied to a realistic LIB geometry to search for the optimal design and operating conditions. [ABSTRACT FROM AUTHOR]

Spiral-coil-type horizontal ground heat exchangers (GHEs) have been increasingly used in ground source heat pump (GSHP) systems due to their higher heat transfer performance. Many attempts have been made to investigate the heat transfer mechanism and establish design methods for the spiral-coil-type ground heat exchangers. Nevertheless, a universal design method for horizontal GHEs has not been reported due to its complexity. In contrast to the spiral-coil-type horizontal GHEs, straight-line-type horizontal GHEs have been widely adopted since they are easy to design for use in industry. In this study, a scale factor model, which could be used to design the coil-type exchanger based on the design length of a straight-line-type heat exchanger, was presented. The ratio of the mean thermal transfer energy between the straight-line-type and spiral-coil-type heat exchangers was numerically investigated by considering weather condition, configuration of GHE, and thermal properties of the ground. Using the numerical results for a total of 108 cases, artificial neural network and linear regression methods were employed for the model development. The proposed model of the scale factor may provide an alternative way to design the spiral-coil-type horizontal GHEs. [ABSTRACT FROM AUTHOR]