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Gaka T.,Polish Institute of Power Engineering | Tabaszewski M.,Poznan University of Technology
Mechanical Systems and Signal Processing | Year: 2011

Analysis of symptom lifetime histories (trends) is widely employed in diagnostics of machines, in particular those designed for long service life. These trends, however, often reveal considerable irregularities, or fluctuations, which cannot be attributed to technical condition evolution. They can render diagnostic reasoning vague and uncertain. This results from the fact that symptom values are influenced not only by object condition parameters, but also by a number of other factors, which sometimes are dominant. More detailed analysis leads to a conclusion that a measure of symptom value fluctuations can itself be used as a diagnostic symptom. This conclusion is supported by the model-based consideration, employing a modification of the Energy Processor (EP) model, developed specifically for this purpose. To illustrate this special feature, several examples are presented and discussed, employing databases obtained for large steam turbines. © 2010 Elsevier Ltd. All rights reserved.


Kupecki J.,Polish Institute of Power Engineering | Badyda K.,Warsaw University of Technology
Archives of Thermodynamics | Year: 2013

Heat exchangers of different types find application in power systems based on solid oxide fuel cells (SOFC). Compact plate fin heat exchangers are typically found to perfectly fit systems with power output under 5 kWel. Micro-combined heat and power (micro-CHP) units with solid oxide fuel cells can exhibit high electrical and overall efficiencies, exceeding 85%, respectively. These values can be achieved only when high thermal integration of a system is assured. Selection and sizing of heat exchangers play a crucial role and should be done with caution. Moreover, performance of heat exchangers under variable operating conditions can strongly influence efficiency of the complete system. For that reason, it becomes important to develop high fidelity mathematical models allowing evaluation of heat exchangers under modified operating conditions, in high temperature regimes. Prediction of pressure and temperatures drops at the exit of cold and hot sides are important for system-level studies. Paper presents dedicated mathematical model used for evaluation of a plate fin heat exchanger, operating as a part of micro-CHP unit with solid oxide fuel cells.


Milewska A.,Polish Institute of Power Engineering | Molga E.,Warsaw University of Technology
Chemical Engineering Research and Design | Year: 2010

Safety aspects in modelling of batch and semibatch stirred tank reactors as well as a model based safety analysis have been considered. Applicability of two basic types of models - i.e. the perfectly mixed reactor model and the CFD model, both formulated for laboratory scale as well as pilot plant scale reactors - has been discussed. A formulation of the appropriate reactor model, which is adequate to the considered case study has been demonstrated and tested experimentally. Particular attention has been devoted to the formulation of robust CFD models employed to simulate a performance of the stirred tank reactors. It has been found that models for perfectly mixed reactors may have quite wide range of application, while the CFD models should be definitely used in case of fast reactions, high viscosity of the reacting mixture as well as of failure leading to stopping of the impeller. The CFD models are able to predict a dynamic behaviour of reactors at any circumstances, so they can play a significant role in safety analysis carried out for industrial scale reactors, for which experimental safety tests are expensive and dangerous. © 2009 The Institution of Chemical Engineers.


Lewtak R.,Polish Institute of Power Engineering | Milewska A.,Polish Institute of Power Engineering
Fuel | Year: 2013

The paper elaborates the influence of the non-equimolar and equimolar counterdiffusion on combustion of single coal char particles in the oxy-fuel combustion conditions. The phenomenon of the non-equimolar counterdiffusion is usually neglected and superseded by the equimolar counterdiffusion. Such a replacement can lead to results, e.g. to char burnout, particle temperature and species concentrations, which do not agree with the real process. The paper presents the numerical results of single coal char particle combustion in the oxy-fuel combustion conditions at which the effect of the equimolar and non-equimolar counterdiffusion has been taken into consideration. It has been assumed that the char carbon heterogeneously reacts with O2, CO2 and H2O forming CO or CO2 and H2 depending on the combustion conditions. The reactions in the gas phase have been neglected to achieve the state of pure diffusion. The combustion of the particle is described by the mass and energy conservation equations commonly used in Euler-Lagrange computations of pulverized coal combustion. Numerical simulations performed for various values of the particle diameter and reagent concentrations clearly show that the use of the equimolar counterdiffusion model always overpredicts the non-equimolar one. Since the molar fluxes of the equimolar counterdiffusion are not coupled each other, the mass transfer towards the particle burning is higher which gives particle temperature and reaction rates too high compared to the non-equimolar counterdiffusion. Occurring discrepancy further develops during combustion also for other quantities describing the process, i.e. char burnout and gas concentrations at the particle surface. A simple correction which is proposed consists in reducing the value of the equimolar mass transfer coefficient that decreases the mass transfer and consequently letting the equimolar counterdiffusion model to be effortlessly used and get results which well follow the non-equimolar model. Such a simplified treatment of complex non-equimolar counterdiffusion can be easily implemented into numerical codes and needs no numerical solution of coupled non-linear equations describing the non-equimolar counterdiffusion. © 2013 Elsevier Ltd. All rights reserved.


Kupecki J.,Polish Institute of Power Engineering
International Journal of Hydrogen Energy | Year: 2015

This paper presents the results of stationary off-design modelling of a micro-combined heat and power unit with solid oxide fuel cells. Mathematical models of the main components of the system with nominal power output of 1.6 kW were developed and implemented in the commercial modelling software Aspen HYSYS 8.0. The purpose of the study was to perform an analysis of possible operating conditions of the power system, using methodology which makes it possible to track changes in electrical and overall efficiency. Electrical load, fuel and oxidant utilization were varied to observe changes in performance of the micro-CHP unit. Performance maps were created to determine optimal working conditions to achieve either maximum electrical efficiency or power. The currently analysed system exhibits electrical and overall efficiencies exceeding 40% and 80%, respectively. © 2015 The Author. Published by Elsevier Ltd.


Patel A.,University of Cambridge | Hopkins S.C.,University of Cambridge | Glowacki B.A.,University of Cambridge | Glowacki B.A.,Polish Institute of Power Engineering
Superconductor Science and Technology | Year: 2013

The ability of superconductors to sustain persistent currents has been well exploited with (RE)BCO superconducting bulks, which can be magnetized to form a compact source of high magnetic field. However, thin films can also sustain persistent currents, which can be utilized by stacking them in layers to create a type of composite bulk. Such a stack is capable of trapping higher fields than a bulk, as reported in this paper. 12 mm wide, 55 μm thick commercial (RE)BCO tape from Superpower Inc was cut into 12 mm by 12 mm squares, stacked together and magnetized at temperatures between 10 and 77.4 K using a sequence of pulsed magnetic fields. The results are compared to a commercial 14 mm diameter YBCO bulk, showing that the stack of tapes outperformed the bulk at temperatures below approximately 60 K. Particularly high trapped fields were achieved below 50 K, with a maximum of 2.0 T at 10 K measured 0.8 mm from the stack surface. The maximum trapped field possible for a stack of tapes increases significantly with decreasing temperature down to 10 K, rather than saturating at a higher temperature as in the case of a bulk, due to superior thermal stability. The Jc, thermal and mechanical properties of commercial (RE)BCO tapes give them great potential for use as trapped field magnets activated by pulsed magnetic fields. © 2013 IOP Publishing Ltd.


Kedra B.,Polish Institute of Power Engineering
2015 IEEE 15th International Conference on Environment and Electrical Engineering, EEEIC 2015 - Conference Proceedings | Year: 2015

This paper provides a solution for reduction of inverter power rating in active power filter by installing passive power filter. As a result hybrid power filter is obtained. However, possible reduction of inverter power rating strongly depends on hybrid power filter topology. Therefore, three power filter devices are presented, analyzed and compared. These are: active power filter, hybrid power filter based on series connection of shunt passive and active filters and the proposed hybrid filter topology. Analysis of mentioned devices include theoretical considerations, simulations performed in Matlab Simulink software and experiments using laboratory setup prepared and configured for purposes of this study. Main focus of the research is on inverter voltage and current as it determines required semiconductor switches parameters what prejudges the cost of the inverter. As cost is the main barrier of wider active power filer application and universality, reduction of inverter power rating is crucial. The aim of the research isto find a possibly low cost solution for active current harmonics mitigation. © 2015 IEEE.


Kupecki J.,Polish Institute of Power Engineering
Applied Mechanics and Materials | Year: 2014

Paper presents a novel approach to modeling of a micro-combined heat and power (μ-CHP) unit with solid oxide fuel cells (SOFC). The proposed numerical simulator can be applied both to the analysis of a system operation in the design point and in off-design. Main components of the power system have been represented by dedicated sub-models, incorporated in the numerical simulator of a complete μ-CHP unit. The proposed modeling platform offers the possibility of analyzing system with different solid oxide fuel cells, its operation at partial loads and with various fuels. Components of the system can be modified, technical specifications can be adjusted in order to allow simulation of other components. The main equations for electrical and overall efficiency calculations are given and discussed. © (2014) Trans Tech Publications, Switzerland.


Marek E.,Polish Institute of Power Engineering | Swiatkowski B.,Polish Institute of Power Engineering
Applied Thermal Engineering | Year: 2014

In this work, direct observation of char and coal single particle combustion in different gases mixtures has been performed. Investigation focused on the influence of atmosphere composition on combustion process and especially on the comparison between combustion in air-like versus oxy-fuel dry and oxy-fuel wet conditions. For these tests, particles from Pittsburgh coal and South African Coal were prepared manually to cubical shape (approximately 2 mm and 4 mg). To investigate fuel type influence on oxy-fuel combustion, some tests were also conducted for Polish lignite coal from Turów mine. Experiments were carried out in a laboratory setup consisted of an electrically heated horizontal tube operated at 1223 K with observation windows for high speed video recording (1000 frames per second). During the experiments, particle internal temperature was measured to obtain comprehensive temperature-time history profile. Results revealed that particles burned at higher temperatures in high water vapour content mixtures than in dry O2/CO2 mixture. This behaviour was attributed to lower molar specific heat of water than of CO2 and four times higher reaction rate for char-H2O gasification reaction than char-CO2 reaction. Also visible dynamic of combustion process recorded with the high speed camera differs for experiments carried with water vapour addition. © 2014 Elsevier Ltd. All rights reserved.


Chwastek K.,Polish Institute of Power Engineering
Journal of Physics D: Applied Physics | Year: 2010

Consideration of temperature and anisotropy effects in hysteresis modelling allows for tailoring the operation point of magnetic circuits. The recently modified Jiles-Atherton model has been extended to describe the hysteresis loops in MnZn ferrites for two temperatures below the Curie point. Anisotropy is modelled by a proper choice of the value of the quantum number J in the Brillouin function. © 2010 IOP Publishing Ltd.

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