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Patel A.,University of Cambridge | Glowacki B.A.,University of Cambridge | Glowacki B.A.,Polish Institute of Power Engineering
Superconductor Science and Technology | Year: 2012

Rapid heat generation is one of the biggest problems faced in carrying out pulsed field magnetization of (RE)BCO superconducting bulks compared to other methods of magnetization. The effects of various thermal conductivities in the ab-plane (k ab) and along the c-axis (k c) of a bulk on its trapped field performance following pulsed field magnetization were modelled. The E-J power law was used, coupled with the heat generation, to simulate the effect of anisotropic thermal conductivity combinations on the peak trapped field and total trapped flux. A thermally isolated bulk is not affected so strongly by thermal conductivity, but on cooling the bulk conductively from its base using a cold head, increasing k c significantly enhances both the trapped field and the flux. Embedding highly thermally conducting copper structures in the bulk material was investigated as a practical way to locally increase k ab and k c. The structures investigated increased the trapped field and flux by a maximum of around 30% without increasing the size of the bulk. Different structures can be used depending on whether an application requires the highest trapped field or highest total flux. © 2012 IOP Publishing Ltd.

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.

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.

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.

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