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There is a big wave in China of retrofitting single-purpose coal-fired systems for district heating into heat-oriented combined heat and power (CHP) systems to save energy. Back-pressure steam turbines (BPSTs) and extraction steam turbines (ESTs) are both common in retrofitted systems, but contrastive analyses of their effects on the systems' operation performance are lacking. Moreover, comprehensive evaluation methods of the retrofitted systems remain unknown. In this paper, exergy, exergoeconomic, and exergoenvironmental analyses were conducted to evaluate the thermodynamic, economic, and environmental performances of two real CHP systems: system A using a BPST and system B using an EST. Additionally, a new multi-criteria evaluation method based on rank correlation analysis was proposed for the retrofitted system. The results show that system A is better than system B in thermodynamic and environmental aspects but poorer in the economic aspect. Overall, the multi-criteria evaluation result indicates that system A has a better comprehensive performance than system B. Therefore, the BPST has a better effect than the EST on the retrofitted CHP system for district heating in this study. The findings could provide a reference point for retrofitting work in the future. [ABSTRACT FROM AUTHOR]

A dual output direct AC–AC series resonant converter is presented in this paper, to meet the requirements of modern domestic induction heating. To address the significant limitations of the classic induction heating system, a hybrid control approach comprising pulse frequency modulation and asymmetrical duty-cycle control is developed. A single source is connected to multiple loads with this control technique to achieve minimum switching losses; power controllability of two loads is achieved independently and simultaneously. The power controllability of two loads is achieved independently and simultaneously. This research presents an induction heating system that can heat both ferromagnetic and non-ferromagnetic materials, such as steel and aluminum. A prototype is developed to use switching frequencies of 30 kHz and 150 kHz for steel load and aluminum load, respectively. The experimental setup resulted in an efficiency of 97.5% under wide load resonant condition. The suggested hybrid control approach allows the converter to regulate a wide range of output power while increasing efficiency, making it suitable for practical induction heating. [ABSTRACT FROM AUTHOR]

This paper presents a comparative evaluation of wide-bandgap power semiconductor devices for domestic induction heating application, which is currently a serious alternative to traditional heating techniques. In the induction heating system, the power transferred to the output depends on the equivalent resistance of the load, and the resistance depends on the operating frequency. Due to the switching characteristics of wide-bandgap power semiconductor devices, an induction heating system can be operated at higher operating frequencies. In this study, SiC and Si semiconductor devices are used in the comparison. These devices are compared according to different evaluation issues such as the turn-off energy losses, turn-off times, current fall time, the power losses of the internal diodes, and the conduction voltage drops issues. To perform the proposed evaluation, the series-resonant half-bridge inverter, which is frequently used in state-of-the-art induction heating systems, has been selected. The device suitability in an induction heating system is analyzed with the help of a test circuit. A comparison is made in terms of criteria determined by using the selected switches in the experimental circuit, which is operated in the 200 W to 1800 W power range and 45 kHz to 125 kHz switching frequency range. System efficiency is measured as 97.3% when Si IGBT is used. In the case of using SiC cascode JFET, the efficiency of the system is increased up to 99%. [ABSTRACT FROM AUTHOR]

Heat pump technology can extract low-level heat energy from urban sewage to heat or cool buildings, which can alleviate the two major problems of energy shortage and environmental pollution to a certain extent. This paper introduces the principle of wastewater source heat pump technology and summarizes the current common system forms and their key core technologies. The proposed special heat transfer technology for sewage can effectively solve the problem of blockage and corrosion in the process of sewage heat transfer. Taking the system of an office building in Qingdao as an example, the system design parameter is introduced in detail. The operation monitoring of the heating and air conditioning seasons of this project was completed through a data collection system, and various performance parameters of the system were studied and analyzed. The data was obtained using measured data from one year of system operation. The testing results show that the sewage temperature of the heat pump system in winter is approx. 13.5 °C, the hot water supply temperature is approx. 50 °C, the average COP of the unit is 3.95, and the average COP of the system is 2.96. The calculation results show that the heating energy consumption of the heat pump unit is only 50.81% of that of a traditional heating mode coal-fired boiler and 57.57% of that of an air source heat pump system. In summer, the sewage temperature is approx. 22 °C, the cold-water supply temperature is approx. 5.5 °C, the average COP of the unit is 4.45, and the average COP of the system is 3.25. The cooling energy consumption of the heat pump system is 79.39% of the energy consumption of the traditional chiller and 61.56% of the cooling energy consumption of the air source heat pump system. This shows that the sewage source heat pump system has a remarkable energy-saving effect. [ABSTRACT FROM AUTHOR]

As a renewable energy power generation method, concentrating solar power generation has a broad application prospect. Weather and fluctuation significantly affect the output power of concentrating solar power generation. A heat storage system can stabilize this fluctuation and generate continuous and stable power. Therefore, the research on heat storage systems is of great significance to the development of concentrating solar power generation. This paper mainly studies the operating characteristics of the heat storage system based on solar energy in simultaneous charging, the influence in the change in solar radiation intensity on the charging power and the discharging outlet temperature, and the feasibility of the heat storage tank as an inertial link to stabilize the fluctuation in solar energy and the discharging outlet temperature. In this study, an experimental system for heat storage was established, in which solar energy was used as the heat source, water was used as the heat transfer fluid, and paraffin was used as the phase change heat storage material. When the initial temperature is 50 °C and the charging flow rate is maintained at 0.7 m3/h, at the same time the discharging flow rate is 0.1 m3/h, 0.3 m3/h, and 0.5 m3/h, respectively. The results show that when the solar radiation intensity is lower than 548 W/m2, the curve of heat storage power is almost parallel to the curve of solar radiation intensity; when the solar radiation intensity is lower than 535 W/m2, the moving direction of the thermocline will change; the average discharging outlet temperature in each case is higher than the phase change temperature of the phase change material and this system can continuously supply hot water at more than 69 °C for more than 3 h 32 min; and increasing the discharging flow rate will increase the whole charging and discharging time, thicken the thermocline, and disturb the temperature field in the tank. The experimental analysis will be conducive to profoundly understanding the operation characteristics of the thermocline heat storage tank under the solar heat source and has reference value for the subsequent design of a more efficient heat storage system. [ABSTRACT FROM AUTHOR]

To improve the hot-pressing process currently employed in laminated object manufacturing (LOM), an innovative heating-and-pressing separation system is proposed, and heat transfer problems of this system are investigated. A thermal model is first established. It is solved numerically by the finite element method (FEM) software ANSYS, and verified by experiments. Based on the numerical solution under various operating conditions, it is found that the operating temperature of an adhesive can be reached quickly when the heater is maintained at a higher temperature, corresponding to a deeper heat-affected zone. This shortcoming can be effectively reduced if the speed of the heater is increased. Hence, a higher heater temperature together with a higher moving speed is suggested to shorten processing time and promote manufacturing efficiency. Through analysis, the appropriate distance between the roller and the heater, so as to obtain finished parts of high quality, is determined. [ABSTRACT FROM AUTHOR]

This paper provides an overview of plant system studies to establish a common technical view for Sodium-cooled Fast Reactor (SFR) concept (the common SFR concept) between France and Japan based on ASTRID 600 and the new concept with downsized output (ASTRID150). One of important issues on a reactor structure design is to enhance seismic resistance to be tolerable against strong earthquake such that postulated in Japan. A concept of High Frequency Design (HFD) is shared, in which the natural frequency of the reactor structure should be higher than that of peak acceleration of vertical floor seismic response with a horizontal seismic isolation system. The design options related to HFD have been examined and design recommendations are established. ASTRID 600 adopted a gas power conversion system to strictly eliminate the chemical reaction risks due to the proximity of sodium and water in the steam generator units. On the other hand, a steam generator (SG) is thought to be a concept with high technical readiness level and is a reference option in Japan and a backup option in France. Then, design comparison of the SG with single-walled helical coil tubes was mainly conducted in this study from the viewpoint of safety and so on. A common concept of a decay heat removal system is discussed to achieve practical elimination of loss of decay heat removal function. A fuel handling system studies are performed to eliminate and ex-vessel storage of spent fuels in sodium to reduce a construction cost. An adequate confinement system is investigated to achieve practical mitigation of large radiological release to the environment even under the condition of core destructive accident. [ABSTRACT FROM AUTHOR]

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Over the last two decades, the status of MR safety has dramatically changed. In particular, ever since the MR-conditional cardiac device was approved by the Food and Drug Administration (FDA) in 2008 and by the Pharmaceuticals and Medical Devices Agency (PMDA) in 2012, the safety of patients with an implantable medical device (IMD) has been one of the most important issues in terms of MR use. In conjunction with the regulatory approvals for various IMDs, standards, technical specifications, and guidelines have also been rapidly created and developed. Many invaluable papers investigating and reviewing the history and status of MR use in the presence of IMDs already exist. As such, this review paper seeks to bridge the gap between clinical practice and the information that is obtained by standard-based tests and provided by an IMD’s package insert or instructions for use. Interpretation of the gradient of the magnetic flux density intensity of the static magnetic field with respect to the magnetic displacement force is discussed, along with the physical background of RF field. The relationship between specific absorption rate (SAR) and B1+RMS, and their effects on image quality are described. In addition, insofar as providing new directions for future research and practice, the feasibility of safety test methods for RF-induced heating of IMDs using MR thermometry, evaluation of tissue heat damage, and challenges in cardiac IMDs will be discussed. [ABSTRACT FROM AUTHOR]

This article is an editorial published in Frontiers in Environmental Science that focuses on the impact of climate change, land surface processes, and critical zone processes in endorheic basins. Endorheic basins are land-locked drainage systems that do not drain into rivers leading to the ocean. These basins are highly sensitive to climate change and human activities, but our understanding of the processes and fluxes in these areas is limited. The editorial highlights several studies that investigate the hydrological impacts of climate change, the movement of sediments, the unique hydrochemistry of these basins, and the effects of drought and vegetation changes. The authors emphasize the need for precise water resource management and climate adaptation strategies in these regions. [Extracted from the article]

This paper presents a method that has been developed to determine the quantity of accumulated magnetic particles in mice tissues using magnetization measurements. Dispersions of platelet Fe3O4 particles with the size of 30–50 nm and a saturation magnetization of $\sim 80$ Am2/kg were intravenously administered to mice. Primary tissues were dried to measure the magnetization. The amounts of Fe3O4 particles accumulated in the tissues were obtained by dividing the magnetization of tissues by the magnetization of Fe3O4 particles under a magnetic field of 39.8 kA/m. A remarkable accumulation of particles was observed in the liver and the spleen, being supported by the observation of tissues using Prussian blue staining. Total Fe3O4 particles accumulated in primary tissues were $\sim 38$ –40 and 40–44 wt% against the particles in administered dispersions with 3 and 0.4 wt% contents, respectively. The method developed in this paper is considered to be effective for verifying magnetic hyperthermia and thermoablation therapies, in which the quantity of accumulated particles directly reflects the heating power required for those therapies. [ABSTRACT FROM AUTHOR]

The acquisition of information on heat inflow is essential to the control of thermal displays and the rendering of thermal sensations. This paper addresses a method of estimating the amount of heat inflow without using a heat flow sensor and demonstrates sensorless heat inflow control using a Peltier device, which is often employed as a thermal device in thermal displays. Moreover, this paper introduces a method of identifying the thermal contact resistance of the device needed for the proposed observer. The observer estimates heat inflow by using information on electrical currents and temperatures. By using the observer instead of a heat flow sensor, which generally has a larger thermal capacity than a temperature sensor, an improvement in the response of a thermal device is expected. The applicability of the proposal is tested by experiments. [ABSTRACT FROM PUBLISHER]

In many technological processes (e.g., in the chemical, petrochemical, food, and plastics industries), liquids are subjected to high pressures and temperatures. Therefore, knowledge of their thermodynamic properties is essential for understanding, design, and control of the process technology. Direct evaluation of the thermodynamic parameters of liquids under high pressure, using conventional methods, is very difficult. Therefore, the application of these methods in industrial conditions, particularly in on-line control of the technological parameters of liquids, is practically impossible. Ultrasonic methods (e.g., sound speed measurements) are very suitable for this purpose because of their simplicity and accuracy. The sound velocity is closely related to numerous thermodynamic properties of liquids. The objective of this paper is to address the influence of temperature and pressure on the thermodynamic parameters of liquids, using the example of diacylglycerol (DAG) oil, employing ultrasonic methods. In this paper, we present ultrasonic velocity and density measurements (performed by the authors) in DAG oil over a range of pressures and temperatures. On the basis of experimental results (the sound velocity and liquid density versus pressure and temperature) a series of DAG oil thermodynamic parameters such as specific heat ratio, intermolecular free path length, Van der Waals constant b, surface tension, and effective Debye temperature were evaluated as functions of pressure and temperature. [ABSTRACT FROM PUBLISHER]

The conventional wisdom on peak-duty drive design leads to vastly oversized machines, following design strategies that are based on continuous ratings. This paper investigates induction machine time ratings that allow peak electrical capabilities to be fully attained. The machine transient thermal response is used to identify four heating regimes based on the dominant heat-transfer mode: subtransient, transition, transient, and temperature creep. A strong connection between the subtransient mode and i^2 t ratings is presented. The impacts of stator and rotor losses on the end-winding temperature are independently identified. This information is combined into a transient thermal impedance characteristic, which provides time ratings as a function of stator and rotor losses with less than 10% error. This method is also adapted for unbalanced supply conditions and rotor-related excess heating conditions with similar error. An implementation of time rating information on a drive system is shown to exploit machine peak ratings. The presented characterizations inform the short-term peak energy density of induction machines. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of thermal energy control in shopping centers through the application of model predictive control (MPC) strategies. In particular, this paper uses an existing shopping center as pilot case, which is characterized by a large common multifloor space, which, in turn, gives rise to a significant vertical thermal stratification. This paper explores the importance of MPC parameters to energy efficiency and comfort levels. In addition, it addresses some notable extensions, from economic optimization, which paves the way to real-time pricing techniques, to integration with renewables, to robustness enforcement through Kalman filters, to hybrid control with switching signals mixed with continuous signals. [ABSTRACT FROM PUBLISHER]

Over the years, there has been a significant evolution in power semiconductor devices from small low-power devices to very high capacity semiconductor devices. As a result, multimegawatt-range adjustable-speed drive (ASD) systems are gaining acceptance in the global onshore and offshore oil and gas industry. ASDs are used on liquefied natural gas compressor trains, gas pipeline compressors, and other critical rotating machinery. As power levels increase, cooling of a drive system becomes a key application consideration of the overall system safety, reliability, operation, maintainability, and design. This paper highlights, contrasts, and compares drive cooling methods and their operation, materials, fluids, and technologies. Advantages and disadvantages of air and liquid cooling are discussed along with a decision-making flowchart on which cooling method to use at certain power levels and applications. A comparative study of air versus liquid cooling and how misapplication of cooling systems can lead to reduced reliability and high operating and maintenance costs is presented. This paper concludes with general guidelines on specifying and evaluating cooling systems for ASDs. [ABSTRACT FROM AUTHOR]

This paper presents a 3-D coupled electromagnetic-fluid-thermal analysis method for temperature rise prediction in oil-immersed triangular wound core transformer. The temperatures rising inside the transformer are mainly determined by the heat sources and the heat convection effect of the transformer oil. The heat sources which include the electric power losses of transformer core, high-voltage windings, and low-voltage windings can be investigated by electromagnetic analysis using the finite element method in no-load and rated load running situations, respectively. Then, the calculation results of electric power losses are brought into the fluid-thermal field analysis as the heat sources. The temperature distribution inside the transformer and the velocity of transformer oil are analyzed by the finite volume method in the fluid-thermal field. To improve the accuracy of calculation results, the influence of temperature on the electric power losses and the parameters of transformer oil are considered in this paper. Using iterative computations, the power losses of windings are updated in accordance with the thermal field calculation result until the maximum difference of temperature between two adjacent steps is less than 0.01 K. At the end of this paper, the simulation results of coupled analysis used in the 10 kV oil-immersed triangular wound core transformer are compared with analytical formula results proposed by the International Electrotechnical Commission standard, and the good agreement of hot-spot temperature indicates the validity of coupled analysis. [ABSTRACT FROM AUTHOR]

In this paper, a complete design methodology of a triple frequency gyrotron is presented, which can also be further applied to multifrequency operations. Frequencies for operation are selected as 220, 247.5, and 275 GHz for the localized and intense heating of magnetically confined plasmas (i.e., electron cyclotron heating and current drive) for future fusion reactors. A cautious selection procedure of the mode triplet is portrayed in accordance with the all possible physical and technical constraints. Typical cold cavity (beam absent) and single-mode (beam present) calculations are performed and presented with extended interaction structure (including an optimized nonlinear taper section). A triode type configuration is adopted for magnetron injection gun to produce the electron beam with desired characteristics as required for RF behavior. Time-dependent multimode calculations are presented with nonuniform magnetic field and beam parameters optimized by gun simulations. These rigorous calculations affirm proper working of the design with $\approx 1$ -MW continuous wave power for chosen mode triplet and efficiency $\approx 35$ %. [ABSTRACT FROM PUBLISHER]

The temperature behavior of the toroidal field (TF) main busbar cable-in-conduit conductors for the International Thermonuclear Experimental Reactor in 15 MA plasma current reference scenario is analyzed by Gandalf code in this paper. The current sharing temperature T\text{cs} of MBCN1 sample at SULTAN conditions and TF main busbar at 15 MA scenario is simulated by Gandalf code, and computed from the COMSOL model, and T \text{cs} of MBCN1 sample computed in this paper is close to that tested in SULTAN. The minimum quench energy of TF main busbar with heating pulse input spatial extents of 1, 3, 6, 8, and 10 mm and durations of 40, 60, 80, and 100 $\mu$s is simulated by Gandalf code in this paper. With heating pulse input region length of 1 mm and duration 40 $\mu$s, the normal length of TF main busbar is simulated by Gandalf code. [ABSTRACT FROM PUBLISHER]

Resulting from the curved thermal profile by near-field transducers, the transition curvature in heat-assisted magnetic recording is one of the critical factors significantly limiting the technology from achieving expected high area density capability. In this paper, we present a systematic micromagnetic modeling study to understand the underlying physics and to arrive at a solution that can correct the transition curvature for enhancing recording performance. Analysis show that the straightened transitions of the recording with the solution can yield a linear density increase of 50% at the same high track densities. [ABSTRACT FROM AUTHOR]

In this paper, microchannel heat sink cooling device utilizing supersonic gas flow with isentropic expansion has been designed and analyzed. The objective is to study the feasibility of the supersonic microchannel with bumped section design for electronics cooling. Numerical simulations on the designed microchannel flows and heat transfer analysis have been conducted (in conjunction with a supersonic air flow inside a heated fin array) and compared with experimental results in this paper. The performance of the designed microchannel is also compared with traditional Laval nozzles for the feasibility analysis. Under 350 and 330 K inlet temperature conditions, the calculated Nu number is found higher than pure through channel flows. The supersonic expanding flow is successfully generated with lower heat transfer temperatures and a simpler geometric shape. The design of 100– 300~\mu \textm is found to have highest heat transfer for integrated microchannel width selection. For electronics cooling tests, the newly designed supersonic channel is found sufficient for a cooling capacity around 1.4 MW/ \textm^2 . In addition, the supersonic flow and heat transfer characteristics are also discussed into detail in this paper. [2016-0037] [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses various reports within the issue on topics including an analysis of building heating systems using big data analytics, the security aspects of power systems, and an optimization framework for investments in complex renewable energy systems.

This paper presents a multi-energy microgrid optimal planning method, considering the intra-hour dynamics of the heating system as constraints of the energy dispatch, and consequently of the sizing of the Combined Heat and Power units. The fixed-mass flow rate method and finite difference technique are applied to linearize the dynamic constraints. Moreover, to determine the values of the mass flow rates, a critical scenario representing the slowest heat dynamic process is put forward. Finally, a realistic microgrid case study is presented to illustrate the effect of considering the heat flow dynamics in the overall solution. [ABSTRACT FROM AUTHOR]

In this paper, we developed a 3-dimensional (3D) ray-tracing simulator using MATLAB for establishing the viability of heating, ventilation, and air conditioning (HVAC) ducts as a reliable communication channel for indoor communication at millimeter-wave (mm-wave) frequencies. We present theoretical analysis of image theory ray-tracing and provide the equations for total electric field due to different rays undergoing reflections at the duct walls. We also computed the received signal strength indicator (RSSI) for the dry and moisture-laden air flowing through the HVAC ducts. The ray-tracing results are compared with the experimental and theoretical results we obtained for the HVAC ducts. With transmitter effective isotropic radiated power (EIRP) of 7 dBm, we obtain RSSI which varies between -34 dBm and -53 dBm for dry atmospheric pressure and temperature of 1013.25 hPa and 294.26K, respectively, and duct lengths of up to 8m at 60 GHz. [ABSTRACT FROM AUTHOR]

In thermally modernised buildings, sharing of ventilation heat loss becomes more significant. In the case of the application of ventilation with heat recovery, especially during transitional periods, there arises a question of whether an air system makes it possible to maintain the required indoor air temperature without the necessity of using a basic hydronic heating system. This paper presents the application of a simple thermal network model of a building zone to simulate indoor air temperature in a single room of a multi-storey building with a mechanical ventilation system with heat recovery. Ventilation air was supposed to be the only heat source and its ability to maintain the required indoor air temperature was checked in simulations and then compared with measurements. The 5R1C thermal network model of a building zone was used for simulations. Comparison with measurements showed the Mean Absolute Error (MAE) and Root Mean Square Error (RMSE) of indoor air calculation to be 2.37 °C and 2.45 °C, respectively. When including heat flux from the bottom storey through the floor, MAE = 1.28 °C and RMSE = 1.38 °C were obtained. [ABSTRACT FROM AUTHOR]

Collective heating systems have multiple end-users with time-varying, often different temperature demands. There are several concepts catering to this, e.g., multi-pipe networks and 2-pipe networks with or without decentralised booster systems. In this study, we focus on 2-pipe networks with a changing supply temperature by smart use of decentralised storage. By grouping high-temperature demands, the average supply temperature can be lowered during large parts of the day, which is beneficial for system efficiency. The actual energy-saving potential, however, can be case-specific and is expected to depend on design choices and implemented control strategies. In this paper, these dependencies are assessed and identified by implementing two optimised rule-based control strategies, providing in such a way a bench-mark for other control strategies. The results show that grouping yields energy savings of up to 36% at similar peak demand as with conventional control strategies. The energy-saving potential is greatest for large storage volumes and small networks, but large networks with large storage and proper control choices can also achieve around 30% energy savings. Moreover, high-temperature time can easily be reduced to less than 40% of the day, which could make space cooling without decentralised booster heat pumps possible, but this requires further research. [ABSTRACT FROM AUTHOR]

Investments in the development of the district heating system require a thorough analysis of the technical, economic, and legal aspects. Regarding the technical and economic context, a mathematical model of the district heating system has been proposed. It optimizes both the technical and economic aspects of the function and development of a district heating system. To deal with non-linearities, the developed linear programming model is divided into three phases: flow, thermal, and pressure. Therein, non-linear dependencies are calculated between the linear optimization phases. This paper presents the main assumptions and equations that were used to calculate the parameters of the heating system, along with the optimal level of heat production, the flow rate of the heating medium in the heat nodes and edges of the network graph, the heat, power, and temperature losses at each edge, and the purchase costs of heat and its transmission. The operation of the model was tested on a real-world district heating system. The case study results confirm that the model is effective and can be used in decision support. The economic results of the model, before the calibration process, were 3.6% different from historical values. After the calibration process, they were very similar to the real data—all percentage deviations were within 1%. [ABSTRACT FROM AUTHOR]

District heating systems are gaining global recognition as an essential tool for reducing greenhouse gas emissions and transitioning to a low-carbon-energy future. In this context, heat pumps are becoming an important technology, providing an effective solution for improving energy efficiency and reducing the reliance on fossil fuels in heating systems. Therefore, this study is focused on the optimal selection of heat pump systems for different types of buildings considering technical, economic, environmental, and social factors. This paper proposes a novel methodology based on mixed-integer nonlinear programming and multi-objective optimization that minimizes total costs and reduces CO2 emissions for heat production and supply systems over a desired period. The methodology is applied to various building types, including renovated and unrenovated apartment buildings, schools, kindergartens, and a supermarket. The study analyzes various types of heat pumps and electric heaters for space heating and domestic hot water production. Optimization results showed that the optimal heating system includes air-to-water heat pumps and electric heaters. Furthermore, for schools and a supermarket, these systems are combined with hybrid heat pumps. The goal of making the heating system neutral in terms of CO2 emissions was achieved for eight out of eleven buildings analyzed. The most profitable investments were in the heating systems of renovated five-story and unrenovated nine-story apartment buildings due to their low energy costs (0.0831 EUR/kWh), short payback periods, and high returns on investment. [ABSTRACT FROM AUTHOR]

The integration of wastewater heat pumps (using purified water) in district heating systems is analyzed in this paper. The simulation procedure is proposed to analyze the impacts of stochasticity of purified water temperature and flow to heat pump integration and operation. The analysis includes calculation of the daily and seasonal coefficient of performance, as well as fossil fuel savings and CO2 emission reduction due to wastewater heat pump use. The proposed procedure is implemented for the case study in the city of Šabac (Serbia) and obtained results are discussed and evaluated. The historical data for two heating seasons was used for simulation. It was shown that the wastewater heat pump could provide 27-28% savings in fuel consumption, and 3.6-4.1% GHG emissions reduction, while the seasonal COP could be 4.2 - 4.3. Simulation based approach shows approximately 40% less savings of fuel consumption, compared to the approach based on the average values of heat pump input parameters. [ABSTRACT FROM AUTHOR]

Thermochemical treatment processes are used to produce a surface layer of the workpiece with improved mechanical properties. One of the important parameters during the gas nitriding processes is the temperature of the surface. In thermochemical treatment processes, there is a problem in precisely determining the surface temperature of heat-treated massive components with complex geometries. This paper presents a simulation of the heating process of a die used to extrude aluminium profiles. The maximum temperature differences calculated in the die volume, on the surface and at the most mechanically stressed edge during the extrusion of the aluminum profiles were analysed. The heating of the die was simulated using commercial transient thermal analysis software. The numerical calculations of the die assumed a boundary condition in the form of the heat transfer coefficient obtained from experimental studies in a thermochemical treatment furnace and the solution of the nonstationary and non-linear inverse problem for the heat conduction equation in the cylinder. The die heating analysis was performed for various heating rates and fan settings. Major differences in the surface temperature and in the volume of the heated die were obtained. Possible ways to improve the productivity and control of thermochemical treatment processes were identified. The paper investigates the heating of a die, which is a massive component with complex geometry. This paper indicates a new way to develop methods for the control of thermochemical processing of massive components with complex geometries. [ABSTRACT FROM AUTHOR]

This paper presents a novel single-phase modified Vienna rectifier (MVR) for the harmonic mitigation and power factor improvement of an induction heating (IH) system. The latter employs a high-frequency resonant inverter that is responsible for the generation of high-frequency harmonics, which, in turn, deteriorates the power quality. This mitigation must be done in accordance with harmonic regulations such as IEEE Std. 519-2014,IEC-555, and EN 61000-3-2, etc. Consequently, an MVR is placed between the power supply and the IH system. The proposed novel MVR topology overcomes the limitations of conventional Vienna rectifiers, such as their unbalanced voltage across output capacitors, high ripple at the output DC bus, and high THD in the supply current, etc. The efficacy of the proposed model has been verified by a series of simulations in PSIM. It is followed by a hardware validation using an Arduino Uno ATmega328 digital controller on a 1.2 kW experimental prototype of the IH system. The simulation and experimental results of the power quality indices comply with the IEEE-519 standards. [ABSTRACT FROM AUTHOR]

This paper aims to present the real improvement opportunities of a simple organic Rankine cycle (ORC) as waste heat recovery system (WHRS) from the exhaust gases of a natural gas engine using toluene as the working fluid, based on the exergy and environmental point of view. From the energy and exergy balances, the advanced exergetic analysis was developed to determine the irreversibilities and opportunities for improvement. Since the traditional exergo-environmental analysis, it was found that the component with the greatest potential environmental impact associated with exergy (bF = 0.067 mPts/MJ) and per unit of exergy (ḂD = 8.729 mPts/h) was the condenser, while the exergy-environmental fraction was presented in the turbine (52.51%) and pump-2 (21.12%). The advanced exergo-environmental analysis showed that the environmental impact is more associated with the operational behavior of the components, with 75.33% of the environmental impacts being of endogenous nature, showing that the environmental impacts are generated to a reduced magnitude through the interactions between components. However, it was identified that much of the environmental impacts in ITC 1 could be reduced, with 81.3% of these impacts being avoidable. Finally, the sensitivity analysis results revealed that steel is the material of the components with the least environmental impact. [ABSTRACT FROM AUTHOR]

Based on Green–Lindsay generalized thermoelasticity theory, this paper presents a new refined higher-order time-derivative thermoelasticity model. Thinner one-dimensional skin tissue is considered when its inner surface is free of traction and does not show any temperature increase. The skin tissue's bounding surface has been heated by ramp-type heating. The classical thermoelastic theories are obtained from the present general formula. The governing equations of the present model are obtained. To move the system into a space state, the Laplace transform is used. The inverse of the Laplace transform is also used with Tzuo's method to solve the problem. As a result, the field quantities are obtained numerically, and the results of the current model are graphically represented with a comparison to two different theories of thermoelasticity. The effects of various parameters on thermomechanical waves through the skin tissue are analyzed. The theory notes a vibrational behavior in heat transfer and a different effect on the parameters discussed in this article. [ABSTRACT FROM AUTHOR]

In the framework of the EUROfusion Horizon Europe Programme, ENEA and its linked third parties are in charge of the conceptual design of the steam generators belonging to EU DEMO WCLL Breeding Blanket Primary Heat Transfer Systems (BB PHTSs). In particular, in 2021, design activities and supporting numerical simulations were carried out in order to achieve a feasible and robust preliminary concept design of the Once Through Steam Generators (OTSGs), selected as reference technology for the DEMO Balance of Plant at the end of the Horizon 2020 Programme. The design of these components is very challenging. In fact, the steam generators have to deliver the thermal power removed from the two principal blanket subsystems, i.e., the First Wall (FW) and the Breeding Zone (BZ), to the Power Conversion System (PCS) for its conversion into electricity, operating under plasma pulsed regime and staying in dwell period at a very low power level (decay power). Consequently, the OTSG stability and control represent a key point for these systems' operability and the success of a DEMO BoP configuration with direct coupling between the BB PHTS and the PCS. In this paper, the authors reported and critically discussed the FW and BZ steam generators' thermal-hydraulic and mechanical design, the developed 3D CAD models, as well as the main results of the stability analyses and the control strategy to be adopted. [ABSTRACT FROM AUTHOR]

Placing fresh cement concrete is not permitted during cold weather under normal conditions due to the risk of frost damage. On the other hand, electrically conductive concrete can be used for deicing/snow-melting applications. This paper presents laboratory investigations to develop electrically conductive cold weather concrete (ECCWC) that can be cast and cured below freezing temperatures and has sufficient electrical conductivity for Joule heating. The concrete has additive-based freeze protection (ABFP) systems that consist of optimized amounts of accelerators and corrosion-inhibiting admixtures. Several mixture proportions were made with 0.5%, 0.75%, and 1.0% carbon fibers by volume of concrete to increase the concrete's conductivity. ECCWC specimens were mixed, cast, and cured at −5°C. The measured freezing points of fresh concrete mixtures were below −5°C. The compressive strength development of ECCWC cured at −5°C was slow compared with the strength development of conductive concrete cured at 20°C. However, ECCWC could reach 55 MPa at 28 days of age. The temperature of hardened ECCWC increased by 18.5°C within 20 min when subjected to a potential difference of 30 V (alternating current). ABFP implemented in the ECCWC mixtures reduces the risk of frost damage and provides the opportunity to place fresh conductive cold weather concrete at ambient temperatures of −5°C without the need for taking curing precautions. The developed ECCWC introduces a new method for constructing multifunctional concrete structures to be placed and cured in cold regions. [ABSTRACT FROM AUTHOR]

Ultrasound (US) is acoustic energy that interacts with human tissues, thus, producing bioeffects that may be hazardous, especially in sensitive organs (i.e., brain, eye, heart, lung, and digestive tract) and embryos/fetuses. Two basic mechanisms of US interaction with biological systems have been identified: thermal and non-thermal. As a result, thermal and mechanical indexes have been developed to provide a means of assessing the potential for biological effects from exposure to diagnostic US. The main aims of this paper were to describe the models and assumptions used to estimate the "safety" of acoustic outputs and indices and to summarize the current state of knowledge about US-induced effects on living systems deriving from in vitro models and in vivo experiments on animals. This review work has made it possible to highlight the limits associated with the use of the estimated safety values of thermal and mechanical indices relating above all to the use of new US technologies, such as contrast-enhanced ultrasound (CEUS) and acoustic radiation force impulse (ARFI) shear wave elastography (SWE). US for diagnostic and research purposes has been officially declared safe, and no harmful biological effects in humans have yet been demonstrated with new imaging modalities; however, physicians should be adequately informed on the potential risks of biological effects. US exposure, according to the ALARA (As Low As Reasonably Achievable) principle, should be as low as reasonably possible. [ABSTRACT FROM AUTHOR]

The system presented in this paper can change the energy storage landscape by having the advantages of a compressed air storage system and pump storage, as well as minimizing the disadvantages of these two systems. One of the advantages of this system compared to similar systems is the lack of combustion of natural gas. Correspondingly, for construction, it does not require specific specifications for the executive site, and control of the energy and heat of the system (due to the use of water as an operational fluid) is easier than similar systems. In addition, this system is very scalable and can be designed in low capacities to high capacities, energy analysis of this research to identify the basic and effective parameters of the system and determine the limitations and relationships between them. The amount of energy saved in the current research system compared to previous research is significant, and 92% efficiency can be achieved. The energy analysis of this research determined the effect of the parameters on each other and their limitations so that the path of its feasibility design was paved. [ABSTRACT FROM AUTHOR]

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This paper studies the effect of gravity orientation on a heat sink, used to passively cool a thick film resistor, by changing the assembly orientation. Using the same geometry and boundary conditions as in the experimental setup, finite element simulations were conducted to evaluate the accuracy of Siemens Flotherm XT 2021.2 simulation software. In order to determine the influence of heat sink orientation, experimental measurements were performed on the resistor and heat sink temperature using thermocouples. Siemens Simcenter Flotherm XT 2021.2 software (Siemens, Munich, Germany) was used to perform finite element simulation. The influence of the heat sink position was evaluated on two setups, one where the resistor is placed directly on the heat sink using screws, and the second one, where a thermal pad was placed between the resistor and the heat sink. Screws were to clamp the parts in both cases. In total, four experiments and simulations were performed with two assemblies with two different gravity orientations for each assembly. In all the cases, the heat sink was placed on a wooden structure to prevent heat transfer through conduction, due to poor thermal conductivity of wood, and to allow unrestricted air flow underneath and around the heat sink. The first simulation was then calibrated for the first scenario, and the rest of the simulations were made using the calibrated one. No other changes in boundary conditions were made. Temperature measurements show an improved cooling when the air speed between the heat sink fins is enhanced due to natural hot air movement generated by the gravity. Gravity has an influence on the cooling regardless of the presence or absence of a thermal interface material. Measured temperatures were reduced up to 8.2 °C due to the rotation of the heatsink. Finite element analysis shows similar temperature values to the measured ones in all the scenarios. [ABSTRACT FROM AUTHOR]

The implementation of renewable energy sources and heat pumps with natural refrigerants in the existing 3rd-generation district heating (DH) systems is a promising technology for the conversion to a 4th-generation DH system. This paper aims to investigate this transition through a case study for the existing DH system in Croatia. The district of Rijeka, which is considered in the case study, has an existing 3rd-generation DH system with a capacity of 9.2 MW, which was originally designed for a temperature regime of 130/70 °C and produces thermal energy from natural gas. In order to use heat pumps efficiently in such a system, the temperature of the distribution system and the energy consumption should be reduced. Trnsys software was used to perform complete dynamic simulations of the DH system. Used baseline models were validated according to the actual energy consumption reported by the heat supplier. The application of heat pumps with natural refrigerants in combination with on-site electricity production (PV system) can almost eliminate system CO2 emissions, reduce primary energy consumption and lower operation costs. Simulations were performed for 18 different scenarios that included 2 different building envelope variants. The results were compared, then discussed and conclusions were drawn. [ABSTRACT FROM AUTHOR]

The article presents an overview of experimental layout design solutions and the general operation scheme of combined heat and power systems with a high-temperature solid oxide fuel cell (SOFC). This system is an environmentally friendly and energy-saving way to produce electricity and heat. The use of high-temperature SOFCs makes it possible to obtain an electrical efficiency of 45–55%. Combining the electrochemical and mechanical system can increase the total efficiency by up to 60–65% in a hybrid power plant. This article discusses the structure and relationship between the components of a hybrid power plant and various modification options for efficient power generation. The technological schemes for existing and tested hybrid power plants with an SOFC and gas turbine are presented and described in detail. When designing a hybrid power plant, the key factors are the choice of design, heat source, and fuel-reforming method; the design of a solid oxide fuel cell and the number of modules in a stack; selecting devices for generating electricity with the development of cogeneration or trigeneration cycles (for possible use in thermal power plants and for the energy supply of social facilities); the direction of material flows within the system; pressure and tightness; and the interconnection of the hybrid power system elements. Researchers have accumulated and described in scientific papers extensive experience in designing, theoretical research, and numerical modeling of hybrid power plants with high-temperature SOFCs. It is shown that experimental hybrid power plants based on SOFCs of the megawatt class are in operation. Hybrid systems with an SOFC are designed only for the kilowatt power class. Trigeneration systems with a steam turbine exist only in the form of theoretical calculations. Trigeneration systems show the highest electrical efficiency, but the highest construction and service costs. Systems based on high-temperature SOFCs can be used for autonomous systems, and in combination with gas and steam turbines only at thermal power plants. Experimental laboratory studies are limited by the high cost of installations and the difficulties of testing the possibility of using combined heat and power systems on an industrial scale. Therefore, a more detailed study of the relationship between the units of a combined heat and power system is recommended in order to achieve the high efficiency indicators obtained from theoretical studies. [ABSTRACT FROM AUTHOR]

In this paper, an innovative hybrid condensing radiant tubes heating system for an industrial building is modelled in three climatic zones of Italy using dynamic simulation software. Radiant tubes are coupled with an air–water heat pump, the latter serving an air heating system with terminals located in the building. The energy performance of the hybrid heating system is optimized by evaluating the best nominal power of the heat pump, the cut-off temperature in a bivalent parallel operation, the bivalent temperature in a bivalent alternative operation, and the peak power of the photovoltaic system on the roof of the building. Energy savings between 40% and 80% are calculated with respect to traditional heating systems, considering the different configurations of the system and the climates. An economic analysis also allows the evaluation of the economic advantages of this hybrid heating system for industrial buildings. [ABSTRACT FROM AUTHOR]

With the continuous development of the Internet of Things (IoT) and new energy utilization technology, the energy management and monitoring mode has undergone fundamental changes. Design and development of remote real-time monitoring and management system for multi-energy heat collection has certain theoretical and practical application value. The existing remote temperature control model fully considers neither the impact of multi-energy collaborative heat collection on remote temperature control strategy, nor the interactions among multiple objective factors, such as climate and location. Therefore, this paper studied the remote temperature control strategy of multi-energy heat collection based on the IoT. First, the paper gave the application architecture of multi-energy heat collection system functions, and developed a multi-energy heat collection system model without simulation performance loss using stochastic modeling ideas. Second, this paper made full use of the error information of the process, thus correcting the predicted value of the remote temperature control output. Finally, the experimental results verified the effectiveness of the model and the control strategy. [ABSTRACT FROM AUTHOR]

Compound casting is a process in which a single component is made from two metallic materials, such as aluminum and steel. Solid-liquid bimetallic compounds can be produced by suitable process control. This technology can reduce the number of joining processes, and the specific properties of the respective metal component can be used for specifically designed product properties, for example, where lightweight and high strength are needed. This paper presents an experimental methodology for producing a purely material-bonded bimetallic joint from cast aluminum and zinc-coated sheet steel in 3D sand casting using an inductive heating system. The process-related temperature characterisation in the compound zone is described using a heating test rig and temperature measurements. It shows that inductive preheating can only produce a material bond between the aluminum casting and the coated steel sheet. Shear tensile tests showed strengths between 15 MPa and 22 MPa. Laser surface pre-treatment using laser ablation cutting on the coated steel sheet was carried out to investigate the benefit of possible microform-locking. The results show a strength-reducing influence on the tensile shear tests. Micrographs showed the formation of Al4.5FeSi and Al7Fe2Si, as well as the formation of other undefined intermetallic phases. The thickness of the compound zone is 10 µm. [ABSTRACT FROM AUTHOR]

Power-to-heat technology represents a promising solution for the decarbonization of the energy sector. The installation of large-scale heat pumps within district heating systems is widely recognized to be a cost-effective and competitive way to provide flexibility to the electric system, enhancing the use of intermittent renewable energy sources. The goal of this paper is to show how the economic and environmental benefits provided by the installation of a large-scale heat pump in existing district heating systems vary according to the installation location in different scenarios. To do that, an integrated methodology is developed. This includes a physical model of the thermo-fluid dynamic of the district heating network and a detailed modeling of the heat pump. To compare the different positions and also the different operating conditions, an approach based on exergy analysis is adopted. Moreover, a specific control strategy of the mass-flow rate is analyzed to further reduce greenhouse gas emissions. The application to a real large-scale district heating network shows that reductions in CO2 emissions of almost 4% can be obtained by installing a single heat pump of about 4 MWe (over a total thermal load of about 305 MWt), while this positive effect can be reduced by up to 63% if placing the heat pump at non-optimal locations. [ABSTRACT FROM AUTHOR]

Phase change materials (PCMs) proved to be valuable and drew the attention of numerous scientists striving to establish novel techniques to minimize energy consumption and expand heat storage; yet a number of challenges hampered their research. This paper provides an overall overview on how to overcome those constraints by adapting nano-enhanced phase change materials, the motivation behind their investigation, their advantages, area of applications, and their impact on thermal management and storage equipment. Recent computational and experimental studies have revealed that nanoparticles are extremely useful in terms of improving the thermo-physical properties of PCMs, allowing nano-PCMs, mainly nano-paraffin, to have a major positive influence on thermal concepts at the economical, ecological, and effectiveness levels. In this context, nano-enhanced PCMs are now able to store and release large amounts of heat in short intervals of time, which is relevant to thermal storage systems and contributes to augmenting and boosting their efficiency. It also improves the thermal performance of cooling and heating systems in buildings and regulates the operating temperature of PV systems, electronic components, and batteries. [ABSTRACT FROM AUTHOR]

The measurement of the two-phase contact area is very important to determine the heat transfer coefficient in the process of direct contact heat transfer, but the direct measurement of the two-phase contact area is a difficult problem. The experiments are carried out utilizing a cylindrical Perspex tube of 100 cm in total height and 15 cm inner diameter. The active column height throughout the experiments is taken to be equal to 50 cm. Liquid Therminol®66 with four different initial temperatures (50 °C, 60 °C, 70 °C and 80 °C) is used as a continuous phase, while liquid R245fa at a constant temperature of 23 °C is used as a dispersed phase. In this paper, the empirical correlations between bubble growth and local convection heat transfer coefficient are obtained through modeling and measurement, and its correctness is verified by experiments. The results show that the bubble diameter is positively correlated with continuous phase temperature, flow rate ratio, and height, but the local convection heat transfer coefficient is negatively correlated with continuous phase temperature, flow rate ratio, and height. At the same time, it is found that the maximum error between the actual bubble diameter and the theoretical bubble diameter is 7%, and the error between the heat flux calculated by the local convection heat transfer coefficient and the actual heat flux is within 10%. This study provides theoretical guidance for an in-depth understanding of the direct contact heat transfer process and the development of high-efficiency waste heat recovery systems. [ABSTRACT FROM AUTHOR]