MODELOWANIE 3D TERMICZNYCH NAPRĘŻEŃ W PŁASKIM STAŁOTLENKOWYM OGNIWIE PALIWOWYM O NOWATORSKIEJ KONSTRUKCJI

The presented modelling investigation was carried out to analyze thermal stresses and expansion in an anode supported planar Solid Oxide Fuel Cell (pSOFC). The temperature distribution was based on previously developed thermo-electrochemical model predicting fuel cell operation. The design of a single pSOFC consisted of three ceramic layers of membrane electrode assembly: anode, electrolyte, cathode and two cross-flow bipolar plates with 26 ribs. The gases flowed diagonally from one cell corner to the opposite one. The fuel and air flows were cross-wise opposed on each bipolar plate side. The study allowed to indicate the most vulnerable to thermal damage area of the fuel cell in the operating conditions. The results will be useful in further design modification and performance optimization of the SOFC.Przeprowadzone symulacje numeryczne miały na celu analizę termicznych naprężeń i ocenę stopnia wydłużenia płaskiego stałotlenkowego ogniwa paliwowego typu pSOFC (ang. planar Solid Oxide Fuel Cell). Rozkład temperatury w ogniwie wyznaczono w oparciu o wcześniej opracowany model termiczno-elektrochemiczny [11]. Nowatorskie rozwiązanie ogniwa typu pSOFC objęło ceramiczną konstrukcję, w skład której weszły porowate elektrody – anoda i katoda, elektrolit oraz dwie płytki bipolarne z 26-cioma żebrami. Przepływ paliwa i powietrza odbywał się krzyżowo i przeciwprądowo, po przekątnej ogniwa. Wyniki symulacji pozwoliły na określenie obszarów ogniwa narażonych na uszkodzenie w wyniku wysokich wartości naprężeń termicznych. Uzyskane rezultaty FEM umożliwią dalszą modyfikację konstrukcji płaskiego ogniwa  w celu optymalizacji wydajności pSOFC

Effect of the numerical grid density on the modelling of fluid flow in a stirred tank with a PMT impeller

The paper present the results of numerical simulations performed for a stirred tank equipped with a PMT type impeller, filled up with a Newtonian fluid. The effects of the grid density and mesh quality and also of the simulation mode on the modelling of fluid flow in a stirred tank were studied. The results are compared with literature data obtained from LDA measurements. It was found that denser numerical grids give more detailed information about generated flow field near the impeller blades. Additionally, better compatibility of predicting and experimental results was obtained in the case of the transient mode simulation, what also demonstrates a significant effect of the angular position of the impeller against baffles on the generated velocity field

Numerical investigation of a novel burner to combust anode exhaust gases of SOFC stacks

The aim of the present study was a numerical investigation of the efficiency of the combustion process of a novel concept burner under different operating conditions. The design of the burner was a part of the development process of a complete SOFC based system and a challenging combination of technical requirements to be fulfilled. A Computational Fluid Dynamics model of a non-premixed burner was used to simulate combustion of exhaust gases from the anode region of Solid Oxide Fuel Cell stacks. The species concentrations of the exhaust gases were compared with experimental data and a satisfactory agreement of the conversion of hydrocarbons was obtained. This validates the numerical methodology and also proves applicability of the developed approach that quantitatively characterized the interaction between the exhaust gases and burner geometry for proper combustion modelling. Thus, the proposed CFD approach can be safely used for further numerical optimisation of the burner design

3D CFD fluid flow and thermal analyses of a new design of plate heat exchanger

The paper presents a Computational Fluid Dynamics (CFD) numerical study for a new design of a plate heat exchanger with two different flow patterns. The impact of geometric characteristics of the two studied geometries of exchanger plates on the intensification process of heat transfer was considered. The velocity, temperature and pressure distributions along the heat exchanger were examined. The CFD results were validated against experimental data and a good agreement was achieved. The results revealed that geometrical arrangement of the plates strongly influence the fluid flow. An increase in the Reynolds number led to lowering the friction factor value and increasing the pressure drop. The configuration II of the plate heat exchanger resulted in lower outlet hot fluid temperature in comparison with the configuration I, which means improvement of heat transfer

On the Deposition Equilibrium of Carbon Nanotubes or Graphite in the Reforming Processes of Lower Hydrocarbon Fuels

The modeling of carbon deposition from C-H-O reformates has usually employed thermodynamic data for graphite, but has rarely employed such data for impure filamentous carbon. Therefore, electrochemical data for the literature on the chemical potential of two types of purified carbon nanotubes (CNTs) are included in the study. Parameter values determining the thermodynamic equilibrium of the deposition of either graphite or CNTs are computed for dry and wet reformates from natural gas and liquefied petroleum gas. The calculation results are presented as the atomic oxygen-to-carbon ratio (O/C) against temperature (200 to 100 °C) for various pressures (1 to 30 bar). Areas of O/C for either carbon deposition or deposition-free are computed, and indicate the critical O/C values below which the deposition can occur. Only three types of deposited carbon were found in the studied equilibrium conditions: Graphite, multi-walled CNTs, and single-walled CNTs in bundles. The temperature regions of the appearance of the thermodynamically stable forms of solid carbon are numerically determined as being independent of pressure and the analyzed reactants. The modeling indicates a significant increase in the critical O/C for the deposition of CNTs against that for graphite. The highest rise in the critical O/C, of up to 290% at 30 bar, was found for the wet reforming process

3D CFD fluid flow and thermal analyses of a new design of plate heat exchanger

The paper presents a Computational Fluid Dynamics (CFD) numerical study for a new design of a plate heat exchanger with two different flow patterns. The impact of geometric characteristics of the two studied geometries of exchanger plates on the intensification process of heat transfer was considered. The velocity, temperature and pressure distributions along the heat exchanger were examined. The CFD results were validated against experimental data and a good agreement was achieved. The results revealed that geometrical arrangement of the plates strongly influence the fluid flow. An increase in the Reynolds number led to lowering the friction factor value and increasing the pressure drop. The configuration II of the plate heat exchanger resulted in lower outlet hot fluid temperature in comparison with the configuration I, which means improvement of heat transfer

A Comparative Thermodynamic Study of Equilibrium Conditions for Carbon Deposition from Catalytic C–H–O Reformates

The importance of carbon deposition occurring during catalytic fuel reforming is briefly described along with former studies on the process. Thermodynamic fundamentals of modeling the critical conditions of the deposition equilibrium are presented. Computational results of ternary C–H–O diagrams with the threshold lines between the carbon deposition and deposition-free regions are discussed for two new pressure levels of 3 and 30 bar and a temperature range from 200 to 1000 °C. The process pressure does not affect the temperature range typical for the type of deposited carbon allotrope; either graphite, multi-walled carbon nanotubes, or single-walled carbon nanotubes in bundles. However, pressure has a profound influence on the location of the threshold lines for carbon deposition. Three reforming processes of two hydrocarbon fuels are analyzed; catalytic partial oxidation, and wet and dry reforming. Chord lines representing varied compositions of process mixtures are introduced to the ternary diagrams. The intersection points of the chord lines with the threshold lines are used in a novel interpretation of the functions of the oxygen-to-carbon critical ratio against temperature and pressure, which can be used in avoiding carbon deposition in catalytic reforming of natural gas and liquefied petroleum gas

Experimental and numerical investigation of axialand tangential forces in a stirred tank with yield-stress fluids

Complex rheological properties of yield-stress materials may lead to the generation of an intensive mixing zone near a rotating impeller. From the practical point of view, the zone should cover most of the stirred liquid. According to the literature review, several parameters may affect the size of the mixing zone, in particular forces exerted on the liquid. This paper presents both experimental and numerical investigation of axial and tangential forces generated during mechanical mixing of yield-stress fluids in a stirred tank. The tested fluids were aqueous solutions of Carbopol Ultrez 30 of concentration either 0.2 or 0.6 wt% and pH = 5.0. The study was performed for three types of impeller, pitched blade turbine, Prochem Maxflo T and Rushton turbine, in a broad range of their rotational speed, = 60 − 900 rpm. The axial and tangential forces were calculated from the apparent mass of the stirred tank and torque, respectively. The experimental results were compared with CFD predictions, revealing their good agreement. Analysis of the generated forces showed that they are dependent on the rheological characteristic of liquid and the impeller type. It was also found that although axial force was smaller than tangential force, it significantly increased the resultant force

Effect of carbomer microgel pH and concentration on the Herschel–Bulkley parameters

The article presents an experimental investigation of the rheological properties of carbomer microgels.All of the tested fluids were made up from commercial polyacrylic acid, Carbopol Ultrez 30. Intotal, eighteen microgels were prepared, differing in concentration; 0.2, 0.4 and 0.6 wt%, with sixlevels of neutralisation for pH from 4.0 to 9.0. Based on the experimental flow curves it was foundthat all tested microgels are yield stress shear-thinning fluids. Therefore, the Herschel–Bulkley modelwas used and its rheological parameters were determined. It was found that both the concentrationand the pH value significantly affected the yield stress. As the Carbopol concentration increased,the yield point also increased. With the increasing value of pH, the yield stress first increased untila certain maximum level and then decreased. The maximum values of yield stress were obtained forpH=6to 7, depending on polymer concentration. It was also found that flow curves of the testedmicrogels could be described using one universal master curve, thus they have common rheologicalbehaviour