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Wyniki wyszukiwania dla: Wireless power transfer
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MAC-layer vulnerabilities of IEEE 802.11 wireless networks
PublikacjaDla sieci bezprzewodowych pracujących według standardu IEEE 802.11 przeprowadzono analizę symulacyjną i badania pomiarowe w specjalnie zestawionej konfiguracji w celu określenia rozdziału pasma transmisyjnego pomiędzy stacje uczciwe i stacje atakujące wybrane mechanizmy protokołu MAC.
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Design of Weather Disruption-Tolerant Wireless Mesh Networks
PublikacjaZ uwagi na wysoki koszt realizacji sieci teleinformatycznych wykorzystujących przewodową transmisję światłowodową, bezprzewodowe sieci kratowe (WMN) oferujące transmisję rzędu 1-10 Gb/s (przy wykorzystaniu pasma millimeter-wave - 71-86 GHz), wydają się być obiecującą alternatywą dla przewodowych sieci MAN. Jednakże z uwagi na właściwości transmisji bezprzewodowej w oparciu o łącza wysokiej częstotliwości, łącza te są bardzo wrażliwe...
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Wireless data transmission for fiber optical sensor system
PublikacjaW artykule opisano możliwość wykorzystania bezprzewodowego systemu transmisji danych do transmisji sygnałów z czujników światłowodowych.
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Selected problems of decision making modelling in power engineering
PublikacjaThe paper presents the selected problems of decision making modelling in power engineering specially investment risk evaluation methods. The proposed model can be used in the range programming the development and investing process in power engineering. Decision making problems in power engineering and the evaluation of investment effectiveness in particular are closely related to modelling which relatively accurately reflects...
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CAES – Energy storage providing stability for national power system
PublikacjaThis paper presents a short characteristics of the power system. It also describes various types of energy storage technologies. The suggested solution of accumulation and generation of electric power is based on the cooperation of gas turbine with Compressed Air Storage Energy systems – CAES. This analysis describes also various types of cooperation of CAES and renewable sources of energy, particularly wind power systems.
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Prediction of flow boiling heat transfer coefficient for carbon dioxide in minichannels and conventional channels
PublikacjaIn the paper presented are the results of calculations using authors own model to predict heat transfer coefficient during flow boiling of carbon dioxide. The experimental data from various resea rches were collected. Calculations were conducted for a full range of quality variation and a wide range of mass velocity. The aim of the study was to test the sensitivity of the in-house model. The results show the importance of taking into...
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Estimation of the Maximum Permissible PV Power to be Connected to the MV Grid
PublikacjaIn recent decades, a significant increase in the share of renewable energy sources in power grids at various voltage levels has been observed. A number of articles have been published highlighting emerging problems in low-voltage grids with a large share of prosumers and in medium- and high-voltage grids to which photovoltaic (PV) plants are connected. The article analyzes the medium-voltage grid in terms of the possibility of...
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Dynamic coloring of graphs
PublikacjaDynamics is an inherent feature of many real life systems so it is natural to define and investigate the properties of models that reflect their dynamic nature. Dynamic graph colorings can be naturally applied in system modeling, e.g. for scheduling threads of parallel programs, time sharing in wireless networks, session scheduling in high-speed LAN's, channel assignment in WDM optical networks as well as traffic scheduling. In...
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Quality Analysis of Audio-Video Transmission in an OFDM-Based Communication System
PublikacjaApplication of a reliable audio-video communication system, brings many advantages. With the spoken word we can exchange ideas, provide descriptive information, as well as aid to another person. With the availability of visual information one can monitor the surrounding, working environment, etc. As the amount of available bandwidth continues to shrink, researchers focus on novel types of transmission. Currently, orthogonal frequency...
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Disaster Resilience of Optical Networks: State of the Art, Challenges, and Opportunities
PublikacjaFor several decades, optical networks, due to their high capacity and long-distance transmission range, have been used as the major communication technology to serve network traffic, especially in the core and metro segments of communication networks. Unfortunately, our society has often experienced how the correct functioning of these critical infrastructures can be substantially hindered by massive failures triggered by natural...
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Expedited EM-Driven Design of Miniaturized Microwave Hybrid Couplers Using Surrogate-Based Optimization
PublikacjaMiniaturization of microwave hybrid couplers is important for contemporary wireless communication engineering. Using standard computer-aided design methods for development of compact structures is extremely challenging due to a general lack of computationally efficient and accurate simulation models. Poor accuracy of available equivalent circuits results from neglecting parasitic cross-couplings that greatly affect the performance...
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Cost-Efficient Optical Fronthaul Architectures for 5G and Future 6G Networks
PublikacjaFifth-generation and Beyond (5GB) wireless networks have introduced new centralized architectures such as cloud radio access network (CRAN), which necessitate extremely high-capacity low latency Fronthaul (FH). CRAN has many advantageous features in terms of cost reduction, performance enhancement, ease of deployment, and centralization of network management. Nevertheless, designing and deploying a cost-efficient FH is still a...
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Structural Health Monitoring of Overhead Power Transmission Lines
PublikacjaStructural Health Monitoring (SHM) is a novel and continuously developing branch of science and technology that draws attention of scientists all over the world. It creates opportunities to detect, localize and identify structural damage of various types such as: line breakage, permissible sag, bolt loosening, fatigue cracking or insulator contamination. On the other hand the methods used to estimate the remaining operational...
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Uncertainty analysis of measuring system for instantaneous power research
PublikacjaThe paper presents a metrological analysis of the measurement system used for diagnosis of induction motor bearings, based on the analysis of the instantaneous power. This system was implemented as a set of devices with dedicated software installed on a PC. A number of measurements for uncertainty estimation was carried out. The results of the measurements are presented in the paper. The results of the aforementioned analysis helped...
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Influence of metallic porous microlayer on pressure drop and heat transfer of stainless steel plate heat exchanger
PublikacjaThe experimental analysis of passive heat transfer intensification in the case of plate heat exchanger has been carried out. On the heat transfer surface of heat exchanger the metallic porous layer was created. The experiment was accomplished in two stages. In the first stage the commercial stainless steel gasketed plate heat exchanger was investigated, while in the second one – the identical heat exchanger but with the modified...
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Experimental Investigation of Free Convection Heat Transfer from Horizontal Cylinder to Nanofluids
PublikacjaThe results of free convection heat transfer investigation from a horizontal, uniformly heated tube immersed in a nanofluid are presented. Experiments were performed with five base fluids, i.e., ethylene glycol (EG), distilled water (W) and the mixtures of EG and water with the ratios of 60/40, 50/50, 40/60 by volume, so the Rayleigh (Ra) number range was 3 104 Ra 1.3 106 and the Prandtl (Pr) number varied from 4.4 to 176....
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How to choose drive’s rated power in electrified urban transport?
PublikacjaSelection of drive's rated power influences not only vehicle's dynamics, but also its energy efficiency. Mentioned above approach requires a multiphysical model, which covers both mechanical and electrical phenomena. This paper discusses how selection of traction drive's rated power influences vehicle energy consumption on example of a trolleybus. A complex mathematical model was developed in Matlab/Simulink to describe the multiphisical...
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Interdependence between Power Grids and Communication Networks: A Resilience Perspective
PublikacjaPower network resilience is increasingly dependent on communication networks. Besides traditional generation, power networks need to accommodate increasingly high penetration levels of dispersed micro generation, mostly based on renewable sources, and increasing and challenging demand, such as electric vehicles. At the same time the deployment of enabling technologies throughout the power grid makes available new demand resources...
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High-efficiency mini and micro heat exchangers for dispersed power generation
PublikacjaTaking into account the dispersed systems technologies and their development, the ORC systems seem to be promising technology amongst various micro-CHP domestic units (electrical power production below 10 kWe), however practical realization of the ORC cycle in a micro-scale is technically challenging. The system consists in devices such as the vapour generation unit (boiler), expansion device and heat exchangers. Each of them should...
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A new method for determination of flow boiling heat transfer coefficient in conventional diameter channels and minichannels
PublikacjaW pracy przedstawiono rozważania związane z modelowaniem wrzenia w przepływie w kanałach o średnicach konwencjonalnych, małych i minikanałach. Przedstawiono przegląd podejść do modelowania wymiany ciepła i w tym świetle przedstawiono oryginalne podejście autora. W przeciwieństwie do innych podejść metoda autora ma zastosowanie zarówno do kanałów o średnicach konwencjonalnych i minikanałach. Przedstawiono zadowalające porównania...
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Influence of metallic porous microlayer on pressure drop and heat transfer of stainless steel plate heat exchanger
PublikacjaThe experimental analysis of passive heat transfer intensification in the case of plate heat exchanger has been carried out. The metallic porous layer was created on the heat transfer surface of analyzed unit. The experiment was accomplished in two stages. In the first stage the commercial stainless steel gasketed plate heat exchanger was investigated, while in the second one – the identical heat exchanger but with the modified...
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An application of multi-agent system for ship’s power systems design
PublikacjaDesign process of transport ship power system consists of structure (topology) and component elements selection. Compliance with the requirements for static components does not guarantee optimal dynamic characteristics of entire power system. Design steps are difficult to formalize and as a consequence to this reason expert and multi-agent systems are used for solving selected design issues. In the paper distributed multi-agent...
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A semi-empirical model for flow boiling heat transfer with account of the reduced pressure effect
PublikacjaIn the present study the attention was focused on the influence of reduced pressure on the predictions of heat transfer during flow boiling at the extensive range of pressures. The results of calculations were to test the sensitivity of the in-house flow boiling model with respect to the selection of the appropriate two-phase flow multiplier, which is one of the distinctive elements of that model. For this purpose a few two-phase...
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Promising Nanoparticle-Based Heat Transfer Fluids—Environmental and Techno-Economic Analysis Compared to Conventional Fluids
PublikacjaProviding optimal operating conditions is one of the major challenges for effective heating or cooling systems. Moreover, proper adjustment of the heat transfer fluid is also important from the viewpoint of the correct operation, maintenance, and cost efficiency of these systems. Therefore, in this paper, a detailed review of recent work on the subject of conventional and novel heat transfer fluid applications is presented. Particular...
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Methods for evaluating rated power of diesel-powered generator set
PublikacjaBasic concepts for evaluating rated power of generator sets powered by combustion engines are presented in this article. A relation between parameters of the engine and the generator are shown. Recommendations contained in the standards and technical literature are systematized. The scheme and methodology for evaluating rated power of the generator set, based on laboratory research, are suggested. Also, the main problems which...
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An experimental investigation on the effect of new continuous core-baffle geometry on the mixed convection heat transfer in shell and coil heat exchanger
PublikacjaIn the article, the authors presented the influence of continuous core-baffle geometry at mixed convection heat transfer in shell and coil heat exchanger. Experiments were carried out for a large power range, i.e. from 100W to 1200W and mass flow rates ranging from 0.01 kg/s to 0.025 kg/s. During the experiments, the mass flow rate of cooling water, the temperature of water at the inlet and outlet as well as the wall temperature...
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Heat transfer intensification by jet impingement – numerical analysis using RANS approach
PublikacjaJet impingement is a method of the heat transfer enhancement applied in the engineering systems. The idea is to generate fast-flow fluid jet which impinge on the heated (or cooled) surface, causing significantly higher heat transfer rate. Although some flat surface jet impingement cases are described in the literature, the validated data is still limited. The reason is coming from the fact, that these flows are hydrodynamically...
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Power electronic transformer based on cascaded H-bridge converter
PublikacjaIn this paper the control strategy of power electronic transformer (PET) is proposed. The analyzed structure of PET uses two seven-level cascaded H-bridge (CHB) rectifiers. The electrical power of PET is transferred between DC-links of CHB converters using dual-active-bridges (DABs) and low voltage high frequency transformers. The roposed solution allows for controlling the active and reactive power with a low level of harmonic...
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Research of Emergency Modes of Wind Power Plants Using Computer Simulation
PublikacjaThe aim of this study is to investigate changes in the wind power plant energy production parameters under the conditions of sudden wind changes and voltage drop. To achieve these goals, a simulation of operation of wind power plants was performed. Twelve wind turbines with variable rotational speed equipped with a Fuhrländer FL 2500/104 asynchronous double-fed induction generator (DFIG) were used, each with an installed capacity...
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Utility analysis and rating of energy storages in trolleybus power supply system
PublikacjaThe article discusses two energy storage applications in power supply system of public electrified transport. The first application aims at reducing the peak power of the traction substation. The second application increases effectiveness of using solar power plant to cover partial power demand of traction supply system. These two applications were discussed and analyzed based on trolleybus supply system in Gdynia, where most measurements...
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Experimental study of boiling heat transfer in the stagnation point of water microjet
PublikacjaIn the paper presented is a comparison of computational model with experimental data. Numerical model of liquid film with phase change in the stagnation zone due to impingement of the microjet is more widely presented in authors previous work. The radius on which theevaporation process is taking place can be determined from the energy balance on the element of the plate. That radius has also been confirmed experimentally in the...
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Influence of nanoparticle concentration on convective heat transfer of water-Al2O3 nanofluids inside horizontal tubes
PublikacjaNanofluids came to be seen as a new generation of coolants, especially in single-phase systems. Conducted experiments indicate that the increase in thermal conductivity is not the only reason for the intensification of heat transfer when using nanofluids. Preliminary results of the experimental investigation of the forced convection heat transfer of water-Al2O3 nanofluids inside stainless steel tube with 8 mm internal diameter...
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Performance Evaluation of a 650V E-HEMT GaN Power Switch
PublikacjaGaN power switches have better characteristics compared to the state-of-the-art Si power transistors. These devices offer high operating temperature and current densities, fast switching and low on-resistance. However, currently only a few producers offer technology of high voltage GaN transistors. Immaturity of this technology is the reason why experimental evaluation of GaN parameters must be performed to properly exploit their...
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Modelling study of flow boiling heat transfer of perspective fluids for refrigeration technology
PublikacjaThere is a gap of knowledge on flow boiling at high saturation temperatures and higher values of reduced pressure. Thus far, the in-house developed semi-empirical model for flow boiling and flow condensation showed a satisfactory accuracy for calculations for various refrigeration fluids for a wide scope of reduced pressures. This study presents results of calculations of heat transfer coefficient of perspective refrigeration fluids,...
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Possibilities of heat transfer augmentation in heat exchangers with minichannels for marine applications
PublikacjaIn the paper, new trends in development of microchannel heat exchangers are presented. The exchangers developed in this way can be applied in marine applications. Main attention was focused on heat exchangers design with reduced size of passages namely based on microchannels. In our opinion future development of high power heat exchangers will be based on networks micro heat exchangers.
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Comparative Analysis of Reactive Power Compensation Devices in a Real Electric Substation
PublikacjaA constant worldwide growing load stress over a power system compelled the practice of a reactive power injection to ensure an efficient power network. For this purpose, multiple technologies exist in the knowledge market out of which this paper emphasizes the usage of the flexible alternating current transmission system (FACTS) and presents a comparative study of the static var compensator (SVC) with the static synchronous compensator...
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How Chain Transfer Leads to a Uniform Polymer Particle Morphology and Prevents Reactor Fouling
PublikacjaABSTRACT: The effect of adding diethyl zinc as a chain transfer agent during the polymerization of propylene in heptane performed at 80 °C was studied. Although it was expected that the chain transfer would stop after precipitation of the polymer, the polymer molecular weight continued to increase throughout the whole of the polymerization. The presence of diethyl zinc had an additional effect that the polymerizations were devoid...
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THE INFLUENCE OF PHASE SHIFTERS ON THE VOLTAGE STABILITY OF CONNECTED POWER SYSTEMS
PublikacjaThe paper presents the results of simulation tests of connected power systems in which phase shifters were installed on cross-border links. The analysis was carried out in terms of assessing the impact of shifters on node voltage stability. Individual systems were characterized by different balance of active power: deficit or excess. The evaluation of voltage stability was based on the dU/dQ and dU/dP criteria.
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Issues of Estimating the Maximum Distributed Generation at High Wind Power Participation
PublikacjaThis paper presents the methods of estimating the maximum power that can be connected to the power system in distributed generation sources. Wind turbine generator systems (WTGS) were selected as the subject for analysis. Nonetheless, the considerations presented in this paper are only general and also apply to other types of power sources, including the sources that are not considered part of distributed generation.
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Impact of Temperature and Nanoparticle Concentration on Turbulent Forced Convective Heat Transfer of Nanofluids
PublikacjaTheoretical analysis of the influence of nanoparticles and temperature on the average Nusselt (Nu) number and the average heat transfer coefficient (HTC) during the turbulent flow of nanofluid in a horizontal, round tube was carried out. The Nu number is a function of the Reynolds (Re) number and the Prandtl (Pr) number, which in turn are functions of the thermophysical properties of the liquid and the flow conditions. On the other...
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Mixed, quantum-classical description of electron density transfer in the collision process
PublikacjaIn this work, we investigate an ion-atom model describing the time-dependent evolution of electron density during the collision. For a S3+- H system, numerical simulations are based on classical trajectory calculations, and the electron density behaviour is described with the time-dependent Schrödinger equation. We apply the finite difference method to obtain quantitative insights into the charge transfer dynamics, providing detailed...
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Propagation Characteristics of Partial Discharges in an Oil-Filled Power Transformer
PublikacjaPower transformers are among the most important assets in the power transmission and distribution grid. However, they suffer from degradation and possible faults causing major electrical and financial losses. Partial discharges (PDs) are used to identify the insulation health status and their degradation level. PDs are incipient, low-magnitude faults caused by localized dielectric breakdown. Those activities emit signals in many...
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Interline power flow controller - properties and control strategy in dynamic states
PublikacjaHigh-power electronic converter topologies, in such forms as Unified Power Flow Controllers (UPFC), Static Compensators (STATCOM) and Interline Power Flow Controllers (IPFC), have been used to enhance and optimize the use of transmission facilities, under the concept of a flexible ac transmission system (FACTS). In Europe, the anticipated proliferation of distributed-generation (DG) in the near future, driven by governmental initiatives...
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Impact of the inclination angle of the condenser with refrigerant R410A on heat transfer coefficient – experimental study
PublikacjaIn the paper the authors present results of a laboratory test of the condenser with refrigerant R410A. The effect of the inclination of this condenser on the heat transfer coefficient value has been considered. The test has proved that there is an optimal inclination angle of the condenser which gives maximal value of this coefficient.
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Experimental study on single phase operation of microjet augmented heat exchanger with enhanced heat transfer surface
PublikacjaThe article presents experimental investigations on a prototype heat exchanger. Presented research is focused on combined active and passive enhancement techniques of surface modification and microjet impingement. The results were compared to reference plate heat exchanger without microjet impingement. The Wilson plot method was applied to determine the heat transfer coefficients in the single phase operation. The heat exchanger...
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Low-power device simulator for micro-energy measurement methods testing
PublikacjaThe paper presents low-power device simulator designed for testing of micro-energy measurement methods. Such kind methods can be used for evaluation of power systems based on Energy Harvesting. The device allows to set the current consumption characteristic over the time, thus making possible playing the role of different types of low-power devices e.g. simulating sensor network node.
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A filter bank solution for active power filter control algorithms
PublikacjaThb paper describes the proposed active power fiIter (APF) with a new control circuit based on an algorithm using ufilter bank and a harmonic predictor. The conirol circuit was realized using the digiiaI signor processor ADSP-21065L and FPGA circuiL In the proposed circuit transient performunee of APF is improved The active power fdter circuil has been built and teste6 and some illustrative, experimental results are uIso presented...
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The effect of reduced pressure on carbon dioxide flow boiling heat transfer in minichannels
Publikacja. In the paper presented are the results of the study on the effect of reduced pressure on flow boiling heat transfer data in minichannels as well as conventional ones. That effect renders that most of heat transfer correlations fail to return appropriate results of predictions. Mostly they have been developed for the reduced pressures from the range 0.1-0.3. The special correction has been postulated to the in-house model of flow...
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Dedicated power supply subsystem for ultra-low noise preamplifiers
PublikacjaIn field of electronics there is need for low-noise amplifiers. Noise have the most important influence on analog circuits. Therefore exist necessity to develop new ultra-low noise power supplies, which can cooperate with specified amplifiers and preamplifiers. It is very common that professional power supplies are very expensive and still have disadvantages. This paper proposes simple and inexpensive solution, which fulfill specific...
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The Possibility to use a Nuclear Power Plant as a Source of Electrical Energy and Heat
PublikacjaIn this article issues concernig the possibility of nuclear power plant (NPP) operation also as a source of heat, which means combined heat and power production, have been described. CHP work is possible and profitable only in those areas where high thermal power demand occurs, which means near city agglomerations such as Warsaw or the Tri-City. Two levels of thermal power delivered to the heating system have been considered. Preliminary...