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Number of results: 52
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Abstract

This article presents Jewish mutual aid associations in the Kingdom of Poland in the nineteenth century. Among the discussed matters are: the legal foundations for organising associations of this type, the chronology of their establishment, the socio-professional character of the founders and members, the attitudes of the authorities towards the creation and operation of these associations. The article is based on original, previously rarely used archives. There were 67 associations established in the discussed time period, including 32 in the Piotrków district (gubernia) and 17 in the Warsaw district.
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Abstract

The distinctive feature of money circulation in the area of Cyrenaica during the first decades of the Roman Empire is a considerable demand for small coins. This feature is common for the overwhelming majority of monetized urban areas in the declining years of the Republic and the early days of the Empire, and it was also one of the main reasons for the flourishing practice of cutting coins. A major increase in bronze coin finds cut into halves and quarters resulted from the excavations of the Polish archaeological mission in Ptolemais. At present, the group of cut bronze coins found in Ptolemais consists of 62 specimens, 57 of which come from Polish excavations conducted in the years 2002–2009, whereas fi ve, being surface finds from the site area, are in the collection of the local archaeological museum. This article was enhanced by a set of 21 coins from Cyrenaica, held in private collections.
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Abstract

The aim of this paper was to demonstrate the feasibility of using a Computational Fluid Dynamics tool for the design of a novel Proton Exchange Membrane Fuel Cell and to investigate the performance of serpentine micro-channel flow fields. A three-dimensional steady state model consisting of momentum, heat, species and charge conservation equations in combination with electrochemical equations has been developed. The design of the PEMFC involved electrolyte membrane, anode and cathode catalyst layers, anode and cathode gas diffusion layers, two collectors and serpentine micro-channels of air and fuel. The distributions of mass fraction, temperature, pressure drop and gas flows through the PEMFC were studied. The current density was predicted in a wide scope of voltage. The current density – voltage curve and power characteristic of the analysed PEMFC design were obtained. A validation study showed that the developed model was able to assess the PEMFC performance.
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Abstract

Fast development of computation techniques for electrolyte activities contributed recently to introduction of a few substantial programmes for thermodynamic computing of multiphase systems. The presented study comprises useful information for practical computing using selected thermodynamic models of aqueous electrolyte solutions. Those models enable quantitative description of both phase and ionic equilibria and provide values of activity coefficients. The carried out analysis of individual models involved a comparison of their practical effectiveness features along with problems encountered in evaluation of the coefficients. The authors conclude that for the Solvay soda system the exUNIQUAC model for an in-house code or the MSE model for a commercial one can be used.
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Abstract

The present study deals with modelling and validation of a planar Solid Oxide Fuel Cell (SOFC) design fuelled by gas mixture of partially pre-reformed methane. A 3D model was developed using the ANSYS Fluent Computational Fluid Dynamics (CFD) tool that was supported by an additional Fuel Cell Tools module. The governing equations for momentum, heat, gas species, ion and electron transport were implemented and coupled to kinetics describing the electrochemical and reforming reactions. In the model, the Water Gas Shift reaction in a porous anode layer was included. Electrochemical oxidation of hydrogen and carbon monoxide fuels were both considered. The developed model enabled to predict the distributions of temperature, current density and gas flow in the fuel cell.
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Abstract

The aim of this work was to achieve a deeper understanding of the heat transfer in a microtubular Solid Oxide Fuel Cell (mSOFC) stack based on the results obtained by means of a Computational Fluid Dynamics tool. Stack performance predictions were based on simulations for a 16 anodesupported mSOFCs sub-stack, which was a component of the overall stack containing 64 fuel cells. The emphasis of the paper was put on steady-state modelling, which enabled identification of heat transfer between the fuel cells and air flow cooling the stack and estimation of the influence of stack heat losses. Analysis of processes for different heat losses and the impact of the mSOFC reaction heat flux profile on the temperature distribution in the mSOFC stack were carried out. Both radiative and convective heat transfer were taken into account in the analysis. Two different levels of the inlet air velocity and three different values of the heat losses were considered. Good agreement of the CFD model results with experimental data allowed to predict the operation trends, which will be a reliable tool for optimisation of the working setup and ensure sufficient cooling of the mSOFC stack.
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Abstract

The paper presents an analysis of relations describing entropy generation in a condenser of a steam unit. Connections between entropy generation, condenser ratio, and heat exchanger effectiveness, as well as relations implied by them are shown. Theoretical considerations allowed to determine limits of individual parameters which describe the condenser operation. Various relations for average temperature of the cold fluid were compared. All the proposed relations were verified against data obtained using a simulator and actual measurement data from a 200 MW unit condenser. Based on data from a simulator it was examined how the sum of entropy rates, steam condenser effectiveness, terminal temperature difference and condenser ratio vary with the change in the inlet cooling water temperature, mass flow rate of steam and the cooling water mass flow rate.
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Abstract

Ensuring the required quality of castings is an important part of the production process. The quality control should be carried out in a fast and accurate way. These requirements can be met by the use of an optical measuring system installed on the arm of an industrial robot. In the article a methodology for assessing the quality of robotic measurement system to control certain feature of the casting, based on the analysis of repeatability and reproducibility is presented. It was shown that industrial robots equipped with optical measuring systems have the accuracy allowing their use in the process of dimensional control of castings manufactured by lost-wax process, permanent-mould casting, and pressure die-casting.
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Abstract

This article presents the results of investigations of the effect of heat treatment temperature on the content of the carbide phase of HS3-1-2 and HS6-5-2 low-alloy high-speed steel. Analysis of the phase composition of carbides is carried out using the diffraction method. It is determined that with increasing austenitising temperature, the intensification of dissolution of M6C carbide increases. As a result, an increase in the grain size of the austenite and the amount of retained austenite causes a significant reduction in the hardness of hardened steel HS3-1-2 to be observed. The results of diffraction investigations showed that M7C3 carbides containing mainly Cr and Fe carbides and M6C carbides containing mainly Mo and W carbides are dissolved during austenitisation. During austenitisation of HS3-1-2 steel, the silicon is transferred from the matrix to carbides, thus replacing carbide-forming elements. An increase in a degree of tempering leads to intensification of carbide separation and this process reduce the grindability of tested steels.
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Abstract

This article discusses the issue of the preparation of the foundry moulds with the use of an industrial robot. The methodology is presented for the determination of the process capacity index for placing inserts with flat and cylindrical faces. On the basis of the relationships developed, the process capability indices were determined at various points in the workspace, which are characterised by different values of the repeatability positioning error. It was shown that the value of the process capacity index can be increased by the selection of a suitable location for the process of placing the inserts in the workspace. It should also be noted that the value of the process's capability index depends on the selection of the place in the robot workspace where the process is carried out. Implementation of the joining process at an analysed point in the robot workspace leads to an increase of the process capability index MCp for inserts with flat faces up to 1.1 (+4.5%) and for inserts with cylindrical faces up to 1.3. This results in an increase of 13% to a level corresponding to the global standard for process reliability (MCp = 1.33).
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Abstract

The introduction of the sustainable development elements in the construction industry leads to finding new ways of using waste minerals that are difficult in storage and recycling. Coal combustion products have been already introduced into building materials as a part of cement or concrete but they have been thought insufficiently compatible with the polymer-cement binders [7]. The paper presents results of the mechanical properties of polymer-cement composites containing two types of mineral additives: waste perlite powder that is generated during the perlite expanding process, and calcium fly ash which is the byproduct of burning coal in conventional furnaces. Mechanical tests of polymer-cement composites modified with wastes were carried out after 28 and 90 days of curing. As a part of preliminary study specific surface area and particle size distribution of mineral wastes were determined.
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Abstract

The work contains a description of a developed experimental and theoretical method of modeling of solid waste combustion in a device equipped with a moving grate and capability to optimize the work of waste incineration plant. Implementation of this issue was based on results of experimental studies made on a laboratory scale boiler. This was possible by defining and testing indicators of quantitative assessment of combustion such as: reaction front rate, ignition rate, the rate of combusted mass loss and the heat release rate. These indicators as measurable "criteria indicators" allow transfer of parameters from a laboratory-scale unit, working in the transient regime into an industrial full scale grate device working continuously in stable determined conditions. This allows for wide optimization possibilities in the operation of a waste incineration plant, in particular the combustion chamber, equipped with a moving grate system.
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Abstract

The paper addresses the issues of quantification and understanding of Solid Oxide Fuel Cells (SOFC) based on numerical modelling carried out under four European, EU, research projects from the 7FP within the Fuel Cell and Hydrogen Joint Undertaking, FCH JU, activities. It is a short review of the main projects’ achievements. The goal was to develop numerical analyses at a single cell and stack level. This information was integrated into a system model that was capable of predicting fuel cell phenomena and their effect on the system behaviour. Numerical results were analysed and favourably compared to experimental results obtained from the project partners. At the single SOFC level, a static model of the SOFC cell was developed to calculate output voltage and current density as functions of fuel utilisation, operational pressure and temperature. At the stack level, by improving fuel cell configuration inside the stack and optimising the operation conditions, thermal stresses were decreased and the lifetime of fuel cell systems increased. At the system level, different layouts have been evaluated at the steady-state and by dynamic simulations. Results showed that increasing the operation temperature and pressure improves the overall performance, while changes of the inlet gas compositions improve fuel cell performance.
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