The global warming potential of many working fluids used nowadays for vapor compression refrigeration systems and heat pumps is very high. Many of such fluids, which are used in currently operating refrigerators and heat pumps, will have to be replaced. In order to avoid a redesign of the system, it would be very helpful if efficient and ecological alternative working fluids for a given plant could be found. With modern process simulation tools such a selection procedure seems possible. However, it remains unclear how detailed such a model of a concrete plant design has to be to obtain a reliable working fluid ranking. A vapor compression heat pump test-rig is used as an example and simulated by thermodynamic models with different levels of complexity to investigate this question. Experimental results for numerous working fluids are compared with models of different complexity. Simple cycle calculations, as often used in the literature, lead to incorrect results regarding the efficienc... [more]

Using computational fluid dynamics (CFD), this study explores the effect of a different number of awning windows and their installation locations on the airflow patterns and air contaminant distributions in restrooms in K-12 (for kindergarten to 12th grade) public schools in Taiwan. A representative restroom configuration with dimensions of 10.65 m × 9.2 m × 3.2 m (height) was selected as the investigated object. Based on the façade design feasibility, seven possible awning window configurations were considered. The results indicate that an adequate number of windows and appropriate installation locations are required to ensure the natural ventilation effectiveness of awning windows. The recommended installation configuration is provided.

A novel bistable electromagnetic vibration energy harvester (BEMH) is constructed and optimized in this study, based on a nonlinear system consisting mainly of a flexible membrane and a magnetic spring. A large-amplitude transverse vibration equation of the system is established with the general nonlinear geometry and magnetic force. Firstly, the mathematical model, considering the higher-order nonlinearities given by nonlinear Galerkin method, is applied to a membrane with a co-axial magnet mass and magnetic spring. Secondly, the steady vibration response of the membrane subjected to a harmonic base motion is obtained, and then the output power considering electromagnetic effect is analytically derived. On this basis, a parametric study in a broad frequency domain has been achieved for the BEMH with different radius ratios and membrane thicknesses. It is demonstrated that model predictions are both in close agreement with results from the finite element simulation and experiment data.... [more]

In this study, steady-state analytical modeling of a loop heat pipe (LHP) equipped with a flat evaporator is presented to predict the temperatures and pressures at each important part of the LHP—evaporator, liquid reservoir (compensation chamber), vapor-transport tube, liquid-transport tube, and condenser. Additionally, this study primarily focuses on analysis of the evaporator—the only LHP component comprising a capillary structure. The liquid thin-film theory is considered to determine pressure and temperature values concerning the region adjacent to the liquid-vapor interface within the evaporator. The condensation-interface temperature is subsequently evaluated using the modified kinetic theory of gases. The present study introduces a novel method to estimate the liquid temperature at the condensation interface. Existence of relative freedom is assumed with regard to the condenser configuration, which is characterized by a simplified liquid−vapor interface. The results obtained in... [more]

Part I of this study introduced a mathematical model capable of predicting the steady-state performance of a loop heat pipe (LHP) with enhanced rationality and accuracy. Additionally, investigation of the effect of design parameters on the LHP thermal performance was also reported in Part I. The objective of Part II is to experimentally verify the utility of the steady-state analytical model proposed in Part I. To this end, an experimental device comprising a flat-evaporator LHP (FLHP) was designed and fabricated. Methanol was used as the working fluid, and stainless steel as the wall and tubing-system material. The capillary structure in the evaporator was made of polypropylene wick of porosity 47%. To provide vapor removal passages, axial grooves with inverted trapezoidal cross-section were machined at the inner wall of the flat evaporator. Both the evaporator and condenser components measure 40 × 50 mm (W × L). The inner diameters of the tubes constituting the liquid- and vapor-tran... [more]

The article describes a method to analyze the powertrain operation of electrically driven vehicles in cases of insufficient information (i.e., unknown control algorithms, no torque measurements during vehicle tests). The method implies mathematical modeling with involvement of so-called unknown input observers. A variant of such an observer is proposed. Using that observer, studies of a hybrid vehicle and a pure electric vehicle are performed. The models with torque observers simulated tests of said vehicles conducted on a chassis dynamometer and on roads. For the hybrid vehicle, operating regimes of main powertrain components were identified. For the electric vehicle, the identification revealed a coordinated operation of regenerative braking and mechanical braking. Adequacy of the modeling, including identification of the unmeasured torques, was verified through a comparison with experimental data.

Thermal Fatigue of flip chip component solder joints is widely existing in thermal energy systems, which imposes a great challenge to operational safety. In order to investigate the influential factors, this paper develops a model to analyze thermal fatigue, based on the Darveaux energy method. Under cyclic thermal loading, a theoretical heat transfer and thermal stress model is developed for the flip chip components and the thermal fatigue lives of flip chip component solder joints are analyzed. The model based simulation results show the effects of environmental and power parameters on thermal fatigue life. It is indicated that under cyclic thermal loading, the solder joint with the shortest life in a package of flip chip components is located at the outer corner point of the array. Increment in either power density or ambient temperature or the decrease in either power conversion time or ambient pressure will result in short thermal fatigue lives of the key solder joints in the flip... [more]

At present, when designing a Light Emitting Diode (LED) luminaire, different strategies of development are followed depending on the size of the company. Since on LED datasheets there is only limited information provided, companies designing LED luminaires spend a lot of effort gathering the required input of LED details to be able to design reliable products. Small and medium size enterprises (SMEs) do not have the bandwidth to gather such input and solely rely on empirical approaches leading to approximated luminaire designs, while larger companies use advanced hardware and software tools to characterize parts, design versions, and finally optimize all design steps. In both cases, considerable time and money is spent on prototyping, sampling, and laboratory testing. Digitalization of the complete product development (also known as Industry 4.0 approach) at all integration levels of the solid state lighting (SSL) supply chain would provide the remedy for these pains. The Delphi4LED Eu... [more]

Owing to its outstanding electro-thermal properties, such as the highest thermal conductivity (22 W/(cm∙K) at room temperature), high hole mobility (2000 cm2/(V∙s)), high critical electric field (10 MV/cm) and large band gap (5.5 eV), diamond represents the ultimate semiconductor for high power and high temperature power applications. Diamond Schottky barrier diodes are good candidates for short-term implementation in power converters due to their relative maturity. Nonetheless, diamond as a semiconductor for power devices leads to specificities such as incomplete dopant ionization at room temperature and above, and the limited availability of implantation techniques. This article presents such specificities and their impacts on the optimal design of diamond Schottky barrier diodes. First, the tradeoff between ON-state and OFF-state is discussed based on 1D analytical models. Then, 2D numerical studies show the optimal design of floating metal rings to improve the effective breakdown v... [more]

To balance electricity production and demand, it is required to use different prediction techniques extensively. Renewable energy, due to its intermittency, increases the complexity and uncertainty of forecasting, and the resulting accuracy impacts all the different players acting around the electricity systems around the world like generators, distributors, retailers, or consumers. Wind forecasting can be done under two major approaches, using meteorological numerical prediction models or based on pure time series input. Deep learning is appearing as a new method that can be used for wind energy prediction. This work develops several deep learning architectures and shows their performance when applied to wind time series. The models have been tested with the most extensive wind dataset available, the National Renewable Laboratory Wind Toolkit, a dataset with 126,692 wind points in North America. The architectures designed are based on different approaches, Multi-Layer Perceptron Netwo... [more]

The aim of the article is to present the method for modeling transformer winding inductance, taking into account the complex magnetic permeability and equivalent electric conductivity of the magnetic core. In the first stage of the research, a physical model of a 24-turn coil wound on the distribution transformer core was prepared. The Frequency Response Analysis (FRA) measurements of the coil were taken; then, the inductance of the coil as a function of frequency was calculated from the received frequency response curves. In the second stage, two-dimensional (2D) and three-dimensional (3D) computer models of the coil based on the finite element method (FEM) were established. In order to obtain the equivalent inductance characteristics of the winding modeled in 2D and 3D in a wide frequency range, the equality of the reluctance of the limbs and yokes in both models was assured. In the next stage of the research, utilization of the equivalent properties for the laminated magnetic materi... [more]

The growing complexity and the many challenges related to fast-changing and highly de-carbonised electricity systems require reliable and robust open source energy modelling frameworks. Their reliability may be tested on a series of well-posed benchmarks that can be used and shared by the modelling community. This paper describes and integrates stand-alone, independent modules to compute the costs and benefits of flexible generation options in the open source energy investment modelling framework OSeMOSYS. The modules are applied to a case study that may work as a benchmark. The whole documentation of the modules and the test case study are retrievable, reproducible, reusable, interoperable, and auditable. They create a case to help establish a FAIR-compliant, user-friendly, and low-threshold model and data standards in modelling practices. As is well known, one of the options for balancing high shares of variable renewables is flexible power generation by dispatchable units. The assoc... [more]

Experience shows that under unidirectional wind or certain terrain, the surface of post insulators is non-uniformly polluted between windward and leeward sides, which affects the flashover characteristics. In this paper, a formulation of residual pollution layer resistance was proposed under this non-uniformity and a typical post insulator was taken as an example to analyze and calculate its residual resistance. The theoretical resistance was verified by numerical simulations using COMSOL Multiphysics. The proposed resistance formulation was then implemented in a DC flashover dynamic model to determine the flashover voltage (Ucal), which was validated by artificial flashover tests. Then the factors affecting DC flashover voltage were analyzed. Research results indicate that: the residual resistance formulation agrees well with simulation results, especially when the arc length exceeds 70% of the leakage distance. The good concordance between theoretical and experimental flashover volta... [more]

In this study, the thermal behavior of the coaxial and double U borehole heat exchangers was investigated using numerical simulations in both the long- and short-term. As a reference for borehole heat exchanger specifications, the existing coaxial and double U probes of a geothermal heat pump installed within the Horizon 2020 research project named “Cheap GSHPs” were considered. Nine years of simulations revealed that when borehole heat exchangers are subjected to a balanced thermal load, and intermittent operating modes of the ground source heat pump system are set, the coaxial pipes’ configuration provides better thermal performance due to the higher thermal capacitance of the heat-carrier fluid and the lower borehole thermal resistance. The analysis was conducted considering two different types of ground with different thermal conductivity values. As result, the more conductive ground type highlights the higher yield of the coaxial probe.

An increase of tightly integrated, renewable energy sources with highly varying production leads to a greater need for flexible hydropower plants to “balance” the intermittent production from these sources. From a systems perspective, the intermittency aspect constitutes a disturbance, while the tight integration leads to a multivariable systems, both of which causes increased challenges for good control. This instigates the need for a model based analysis and synthesis tool which can describe dynamic phenomena, supports multiphysics problems, and allows for immediate use in advanced control analysis and design. Previously, an open source Hydro Power Library (OpenHPL) have been developed within the multiphysics Modelica eco-system which satisfies the above requirements: OpenHPL contains a set of model units relevant for hydropower systems, as well as examples of tools for analysis of these models for control purposes. Thus far, OpenHPL has been validated by comparison against other sim... [more]

The energy consumption of urban central heating in northern China is two to four times that in northern Europe and other countries. Beijing has adopted measures, such as ‘coal to gas’ and ‘coal to electricity’, to reduce environmental pollution caused by central heating. Given a peak-to-valley difference in the electricity supply of power plant, which is uneven day and night, this study proposes to store the night-time off-peak electricity in the form of heat energy and drive the ammonia absorption system in the form of steam or hot water during peak or flat electricity. Simulation results of ammonia absorption cooling and heating dual-supply system show that heat source temperature increases, evaporation temperature increases, and cooling water temperature decreases are all beneficial to improve the refrigeration coefficient in the summer cooling condition. In the meantime, heat source temperature increases, evaporation temperature increases, and cooling water temperature decreases ar... [more]

Copper busbar technology is widely used with the aim to achieve electrical connections with power distribution systems because of their flexibility and compactness. The thermal analysis takes into account the heat conduction and convection of a copper busbar system used to supply a test bench with high currents in order to check the electro-thermal behaviour of power circuit breakers during overload and short circuit conditions. This paper proposes a mathematical model for busbars used within a high current power supply. The obtained thermal model can be used to analyse the thermal behaviour of busbars in steady-state conditions at different values of the electric current, cross-section and length of the busbar. Also, the mathematical model allows to calculate the temperature distribution along the busbar at different values of the contact resistances at junction points with other conductors. There is a good correlation between calculated, simulated and experimental results.

Simulating the steam dumping process of a pressurized relief tank is a challenging engineering problem, due to the massive computing resource requirements and its complex physical models. This study gave a comprehensive 3D numerical study for the transient dumping process from the PRT (Pressurizer Relief Tank) to the room containing the tank. The physical model, geometry design and meshing strategy, along with the numerical techniques, have been described in detail. Through parallel simulations based on the open source CFD toolbox OpenFOAM, numerical results for the temperature, pressure, and the velocity distribution are presented. The results show that the maximum velocity throughout the whole domain is 967 m/s over Mach 2 and the maximum pressure on the roof of the room is 2.8 atm. It could provide the guidance information for the safety design of the reactor coolant system. Additionally, comparison cases between OpenFOAM and CFX are tested, and it turns out that OpenFOAM could prod... [more]

Hourly emission factors and marginal costs of energy carriers are determined to enable a simplified assessment of decarbonization measures in energy systems. Since the sectors and energy carriers are increasingly coupled in the context of the energy transition, the complexity of balancing emissions increases. Methods of calculating emission factors and marginal energy carrier costs in a multi-energy carrier model were presented and applied. The model used and the input data from a trend scenario for Germany up to the year 2050 were described for this purpose. A linear optimization model representing electricity, district heating, hydrogen, and methane was used. All relevant constraints and modeling assumptions were documented. In this context, an emissions accounting method has been proposed, which allows for determining time-resolved emission factors for different energy carriers in multi-energy systems (MES) while considering the linkages between energy carriers. The results showed t... [more]

Accurate forecasts of corporate failure in the Chinese energy sector are drivers for both operational excellence in the national energy systems and sustainable investment of the energy sector. This paper proposes a novel integrated model (NIM) for corporate failure forecasting in the Chinese energy sector by considering textual data and numerical data simultaneously. Given the feature of textual data and numerical data, convolutional neural network oriented deep learning (CNN-DL) and support vector machine (SVM) are employed as the base classifiers to forecast using textual data and numerical data, respectively. Subsequently, soft set (SS) theory is applied to integrate outputs of CNN-DL and SVM. Hence, NIM inherits advantages and avoids disadvantages of CNN-DL, SVM, and SS. It is able to improve the forecasting performance by taking full use of textual data and numerical data. For verification, NIM is applied to the real data of Chinese listed energy firms. Empirical results indicate... [more]

Exact models are a necessary prerequisite for optimal hardware configuration and the design of high-performance controllers. The photovoltaic system is considered a dynamic nonlinear multimodal system, where an optimization method must be used to resolve non-linearity and to identify the parameters describing the models of such systems. This has incited several researchers to work on and to develop several optimization methods. Recently, a number of methods have been proposed, including deterministic approaches, as well as probabilistic and stochastic numerical approaches, that aimed at obtaining a more accurate model for the PV cell and module array. This paper demonstrates the application of a performance optimization method based on discrete symbiotic organism search (DSOS), that mimics the behaviors of an organism in an ecosystem to survive. The high performance of such a method is attributable to the simplicity of the algorithm used; this algorithm is different from other heuristi... [more]

Sports halls must meet strict requirements for energy and indoor air quality (IAQ); therefore, there is a great challenge in the design of the heating, ventilation, and air conditioning (HVAC) systems of such buildings. IAQ in sports halls may be affected by thermal stratification, pollutants from different sources, the maintenance of building, and the HVAC system of the building, as well as by the activities performed inside the building. The aim of this study is to investigate thermal stratification conditions in accordance with the performance of the HVAC systems in the basketball training hall of Žalgirio Arena, Kaunas in Lithuania. Field measurements including temperature, relative humidity, and CO2 concentration were implemented between January and February in 2017. The temperature and relative humidity were measured at different heights (0.1, 1.7, 2.5, 3.9, 5.4, and 6.9 m) and at five different locations in the arena. Experimental results show that mixing the ventilation applica... [more]

The Climate Change scenario projected by the IPCC for the year 2050 predicts noticeable increases in temperature. In severe summer climates, such as the Mediterranean area, this would have very negative effects on thermal comfort in the existing housing stock, given the current high percentage of dwellings which are obsolete in energy terms and house a population at serious risk of energy poverty. The main aim of this paper is to generate a predictive model in order to assess the impact of this future climate scenario on thermal comfort conditions in an entire building category. To do so, calibrated models representing linear-type social multi-family buildings, dating from the post-war period and located in southern Spain, will be simulated extensively using transient energy analyses performed by EnergyPlus. In addition, a sensitivity analysis will be performed to identify the most influential parameters on thermal discomfort. The main results predict a generalized deterioration in ind... [more]

Aiming at the melt splashing behavior in the smelting process of an oxygen-enriched side-blowing furnace, the volume of fluid model and the realizable k−ε turbulence model are coupled and simulated. The effects of different operating parameters (injection velocity, immersion depth, liquid level) on splash height are explored, and the simulation results are verified by water model experiments. The results show that the bubbles with residual kinetic energy escape to the slag surface and cause slag splashing. The slag splashing height gradually increases with the increase in injection velocity, and the time-averaged splashing height reaches 1.01 m when the injection speed is 160 m/s. Increasing the immersion depth of the lance, and the slag splashing height gradually decreases. When the immersion depth is 0.12 m, the time-averaged splashing height is 0.85 m. Increasing the liquid level is beneficial to reduce the splash height, when the liquid level is 2.7 m, the splash height reduces to... [more]

In the last decade, growing awareness about CO2 emissions is supporting the authorities in a more sustainable society. The proposed solutions embrace different topics, such as renewable energy implementation, lower waste production, and carbon capture and storage technologies (CCS). The latter is based upon the best available knowledge about the thermophysical properties of CO2, which are not always satisfactory for its complete characterization. In this work, it is investigated the interaction of the CO2 in solid phase (dry-ice) with sandy soil, a phenomenon that can potentially occur following pipeline ruptures. An experimental setup and a numerical model have been developed to measure and validate the temperature profiles beneath the dry-ice bank at steady-state conditions. The model has been validated with the experimental data by defining a suitable range of the thermal conductivity at the solid phase (0.25−0.30 W m−1 K−1) that led to the best match (deviation of 7.81%). Finally,... [more]