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  • 1.
    Birgersson, Erik
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet.
    Noponen, M.
    Vynnycky, Michael
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet.
    Analysis of a two-phase non-isothermal model for a PEFC2005Inngår i: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 152, nr 5, s. A1021-A1034Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A non-isothermal, two-phase model for a polymer electrolyte fuel cell (PEFC) is presented, analyzed, and solved numerically under three different thermal, and two hydrodynamic, modeling assumptions; the consequences of these are then discussed in terms of thermal and water management and cell performance. The study is motivated by recent experimental results that suggest the presence of previously unreported, and thus unmodeled, thermal contact resistances between the components of PEFCs and the discrepancy in the value for the capillary pressure that is used by different authors when modeling the two-phase flow in PEFCs. For the three different thermal assumptions (assuming effective heat conductivities, isothermal flow, and interfacial and bulk conductivites), liquid saturations of around 10% are obtained at the cathode active layer for 1000 mA cm(-2) and a cell voltage of 0.6 V. When lowering the capillary pressure (hydrodynamic assumption), liquid saturations of almost 30% and locally up to 100% are observed at the active layer of the cathode. At this current density and voltage, temperature differences across the cell of around 9 degrees C are predicted. In addition, the effect of varying clamping pressure within the framework of the model is touched upon. The benefits of the scaling analysis conducted here, to predict correctly, prior to numerical computations, important characteristic cell performance quantities such as current density and temperature drop are also highlighted.

  • 2.
    Birgersson, Erik
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet.
    Vynnycky, Michael
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet.
    A quantitative study of the effect of flow-distributor geometry in the cathode of a PEM fuel cell2006Inngår i: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 153, nr 1, s. 76-88Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An isothermal three-dimensional model describing mass, momentum and species transfer in the cathode of a proton exchange membrane fuel cell has been used to study four different flow-distributors: interdigitated, coflow and counterflow channels, and a foam. A quantitative comparison of the results shows; that the interdigitated channels can sustain the highest current densities, followed in descending order by the foam, the counterflow and the coflow channels. The foam yields the most uniform current density distribution at higher currents, but care should be taken as to its permeability to avoid unreasonably high-pressure drops.

  • 3.
    Danielsson, Carl-Ola
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet.
    Dahlkild, Anders
    KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet.
    Velin, Anna
    Behm, Mårten
    KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet.
    Nitrate Removal by Continuous Electropermutation Using Ion-Exchange Textile: I. Modeling2006Inngår i: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 153, nr 4, s. D51-D61Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents a steady-state model of the feed compartment of an electropermutation cell, used for nitrate removal, with ion exchange textiles incorporated as a conducting spacer. In the model the ion-exchange textile is treated as a porous medium and volume averaging is applied to obtain a macrohomogeneous two-phase model. The ion-exchange between the two phases is modeled assuming that the rate-determining step is the mass-transfer resistance on the liquid side of the phase interface. Analysis of the model equations reveals appropriate simplifications. The influence of the governing dimensionless numbers is investigated through simulations based on the model.

  • 4.
    Danielsson, Carl-Ola
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik. KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet.
    Velin, Anna
    Behm, Mårten
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik. KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet.
    Dahlkild, Anders
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet.
    Nitrate Removal by Continuous Electropermutation Using Ion-Exchange Textile: II. Experimental Investigation2006Inngår i: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 153, nr 4, s. D62-D67Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Water with nitrate concentrations above 100 ppm has been treated with continuous electropermutation which partially substitutes the nitrate with chloride. The performance of a textile anion exchanger as conducting spacer in the feed compartment of an electropermutation cell was investigated. Experiments with and without textile are compared and the influence of the textile is discussed. The process could, using the textile, successfully treat feed water with 105 ppm nitrate to produce a water with less than 25 ppm nitrate. The importance of establishing a good contact between the membranes and the textile spacer was pointed out. The experimental results were compared to model predictions and a good agreement was found.

  • 5.
    Holm, Richard
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet. KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Söderberg, L. Daniel
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    A theoretical analysis of the flow stability in roll forming of paper2005Inngår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 20, nr 2, s. 212-216Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper deals with the fundamental mechanisms that control partial roll dewatering in papermaking. The flow around the forming cylinder is modelled in a cylindrical coordinate system and the wire is assumed to be impermeable. The governing equations are reduced based on a discussion where the magnitude of the different terms is estimated. Given this reduced set of equations a non-linear equation for the position of the wire is deduced. This clearly shows that one of the most important parameters is the Weber number, We, which is the non-dimensional number that can be obtained by comparing the effect of wire tension in relation to the momentum of the incoming headbox jet. The characteristics of the non-linear equation are discussed and the equation is linearized around the trivial solution to the equations, which gives that the wire is displaced a constant distance from the roll along the whole wrap. The linear equation has a standing wave solution with a specific wavelength that scales with We. This solution is compared to previously measured profiles regarding the wavelength of the waves.

  • 6.
    Holm, Richard
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet. KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Söderberg, L. Daniel
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Norman, Bo
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik, Pappersteknologi.
    Experimental studies on dewatering during roll forming of paper2005Inngår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 20, nr 2, s. 205-211Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Pressure and wire position measurements have been performed in an experimental facility, the KTH-Former, which intends to model the roll-forming zone of a paper machine. The measured pressure distributions in the forming zone are shown to have more complex patterns than the simple model p=T/R, which normally is referred to as the nominal pressure. It is also shown that an increase in wire tension has a similar effect as a decrease in flow-rate on the shape of the pressure distribution. This is a consequence of that the flow to a large extent is governed by the relation between the dynamic pressure and the nominal pressure. For the case of partial dewatering the suction peak that appears at the roll-wire separation point has a strong influence on the pressure distribution upstream. Finally, it is shown that the drainage has a stabilizing effect on the dewatering pressure.

  • 7.
    Ipek, Nulifer
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet. KTH, Tidigare Institutioner                               , Mekanik.
    Cornell, Ann
    KTH, Tidigare Institutioner                               , Kemiteknik.
    Vynnycky, Michael
    KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet. KTH, Tidigare Institutioner                               , Mekanik.
    Single- and two-phase modelling of the electrochemical pickling of steelManuskript (preprint) (Annet vitenskapelig)
  • 8.
    Ipek, Nulifer
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet. KTH, Tidigare Institutioner, Mekanik.
    Lior, Noam
    University of Pennsylvania, Dept. Mech. Eng. and Appl. Mechanics.
    Electrolytic pickling of steel: a critical reviewArtikkel i tidsskrift (Annet vitenskapelig)
  • 9.
    Ipek, Nulifer
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet. KTH, Tidigare Institutioner, Mekanik.
    Lior, Noam
    University of Pennsylvania, Dept. Mech. Eng. and Appl. Mechanics.
    Bark, Fritz H.
    KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet. KTH, Tidigare Institutioner, Mekanik.
    Eklund, A.
    Avesta Sheffield AB.
    Alemany, Antoine
    Université Joseph Fourier, Lab. des Ecoulements Geophysique, Inst. de Mécan. de Grenoble.
    Simple analytical model predicting some features of the electrolytic steel-pickling process2002Inngår i: Russian journal of electrochemistry, ISSN 1023-1935, E-ISSN 1608-3342, Vol. 38, nr 3, s. 238-246Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Electrolytic pickling of steel with neutral solutions, to remove the surface scale, reduces the need for the use of strong acids as needed in conventional pickling. This study is a step towards a more in-depth understanding of the factors affecting the former process. A theoretical model, sufficiently simplified to allow analytical solution, is developed and evaluated to provide a first approximation of the potential and current distributions in the electrolyte and steel band. To gain knowledge and validate the model, a small electrolytic pickling cell is constructed, and experiments, including bubble generation and motion observation, are conducted. The experimental work has shown the remarkable bubble production and adherence to the surfaces, and its effects on reducing pickling efficiency and uniformity. The pickling efficiency is about 30%, confirming other researchers' results. The analytical model shows trends very similar to those observed in the experiments, and provides very valuable guidance. It shows, for example, that the current efficiency decreases as the electrode-band distance increases, and it increases with the band thickness and the band-to-electrolyte conductivity ratio, The energy efficiency decreases by orders of magnitude faster than the current efficiency with all of the above-mentioned parameters, because of the correspondingly strong drop in the band-surface potential. A large amount of current is lost due to interelectrode short circuiting.

  • 10.
    Ipek, Nulifer
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet. KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Lior, Noam
    University of Pennsylvania, Dept. Mech. Eng. and Appl. Mechanics.
    Eklund, A.
    AvestaPolarit AB.
    Improvement of the electrolytic metal pickling process by inter-electrode insulation2005Inngår i: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 32, nr 1, s. 87-96Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The existing industrial electrolytic steel pickling process is only 30% current efficient. Use of approximate modelling of the process and solution of the model predicts that inter-electrode insulation improves the current and energy efficiency, and this paper describes the experimental work that has validated this prediction. Some of the main results are: (a) the current efficiency varied from 20% without insulation to 100% with complete insulation, (b) the use of just partial insulations yielded a significant improvement in the process efficiency and at the same time maintained good electrolyte mixing and homogeneity which can not be attained with complete insulation. The theoretical foundations of this method and its various consequences are discussed. The method is relatively easy to apply to existing industrial electrolytic pickling tanks, and also provides system control flexibility for optimal pickling of different steel grades. The method's application cost is relatively low and saves investment in new equipment if a retrofit of an existing system is desired.

  • 11.
    Ipek, Nulifer
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet. KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Lior, Noam
    University of Pennsylvania, Dept. Mech. Eng. and Appl. Mechanics.
    Vynnycky, Michael
    KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet. KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Bark, Fritz H.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik.
    Numerical and experimental study of the effect of gas evolution in electrolytic pickling2006Inngår i: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 36, nr 12, s. 1367-1379Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    As part of a progressive approach to model the electrolytic pickling process, this paper focuses on the important aspect of hydrogen and oxygen gas evolution on the electrodes and on the steel strip being pickled. The system considered consists of type 316 stainless steel pickled in aqueous sodium sulphate, with lead anodes and stainless steel cathodes. The mathematical model is two-dimensional steady-state, and includes the differential equations describing the effect of migration, giving the potential and current fields, and the Tafel kinetic rate expressions for hydrogen and oxygen gas generation. Experiments were conducted to obtain a better understanding of the process and for model validation. Good agreement between the experimental measurements of the global current efficiency and the model predictions was obtained.

  • 12.
    Lim, Shyang Maw
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx). KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strömningsfysik.
    Dahlkild, Anders
    KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strömningsfysik.
    Mihaescu, Mihai
    KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx). KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strömningsfysik. KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik.
    Influence of upstream geometry on pulsatile turbocharger turbine performance2018Rapport (Annet vitenskapelig)
    Abstract [en]

    This research was primary motivated by limited efforts to understand the effects of secondary flow and flow unsteadiness on the heat transfer and the performance of a turbocharger turbine subjected to pulsatile flow. In this study, we aimed to investigate the influence of exhaust manifold on the flow physics and the performance of its downstream components, including the effects on heat transfer, under engine-like pulsatile flow conditions. Based on the predicted results by Detached Eddy Simulation (DES), qualitative and quantitative flow fields analyses in the scroll and the rotor’s inlet were performed, in addition to the quantification of turbine performance by using the flow exergy methodology. With the specified geometry configuration and exhaust valve strategy, our study showed that 1) The exhaust manifold influences the flow field and the heat transfer in the scroll significantly, and 2) Although the relative inflow angle at the rotor’s inlet is significantly affected by the initial exhaust gas blow down from the exhaust manifold, the consequence on the turbine power is relatively small.

  • 13. Lior, N.
    et al.
    Papadopoulos, Dimitrios
    KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet.
    Gas-cooling of multiple short inline disks in flow along their axis2010Inngår i: Quenching and Cooling, Residual Stress and Distortion Control, 2010, s. 795-819Konferansepaper (Fagfellevurdert)
    Abstract [en]

    To learn about cooling of gas quenched batches, this paper reports on numerical predictions of local and average convective heat transfer coefficients, and overall pressure drops, on batches of five axially aligned, constant temperature, short cylindrical disks (25 cm diameter, 5 cm thickness) with and without a concentric hole, with interdisk spacings of 5-20 cm, in axial turbulent flows of 20 bar nitrogen gas at inlet speeds from 10 m/s to 100 m/s, corresponding to Reynolds numbers (Re) between 3.27×106 and 32.7×106. The heat transfer coefficients along the disk surfaces vary strongly up to a worse case of two orders of magnitude for the upstream disk. This nonuniformity is much lower for the disks downstream, especially after spacing is increased beyond 0.1 m. As expected, the upstream disk exhibited rather different heat transfer coefficients than the ones downstream, the magnitude of the heat transfer coefficient and its uniformity increased with the interdisk spacing, and varied by a factor of about 4-5 along the surfaces. The average heat transfer coefficient (Nusselt number, Nu) on the disks increased approximately with Reynolds number as Re0.85. Re did not have much influence on the nonuniformity of Nu on the disk surfaces. The overall pressure drop along the flow increases with the interdisk spacing, rising by about 60 % as the spacing is increased from 0.05 m to 0.20 m. The presence of a hole increases the heat transfer coefficient in all cases. Some suggestions for reducing the heat transfer coefficient nonuniformity are made.

  • 14.
    Lior, Noam
    KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet.
    The cooling process in gas quenching2004Inngår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 155, s. 1881-1888Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Gas quenching is a relatively new process with several important advantages, such as minimal environmental impact, clean products, and ability to control the cooling locally and temporally for best product properties. To meet the high cooling rates required for quenching, the cooling gas must flow at very high velocities, and such flows are highly turbulent and separated. Consequently, there is a need for good understanding of these flows and their consequences for the process. To that end, we researched the state of the art, and have conducted numerous numerical and experimental studies and developed CFD models on this subject, and show the results for flows inside quench chambers and their components, and for external flows, including multi-jet impingement, on cylindrical and prismatic single and multiple bodies (the quench charge). Velocity distributions and uniformity, pressure drop, and flow effects on heat transfer coefficients and product uniformity, as well as recommendation for improved processes, are shown.

  • 15.
    Macchion, Olivier
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Rizzi, Arthur
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Lior, Noam
    KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet.
    Computational Study of Velocity Distribution for Designing some Gas Quench Chamber and Furnace Ducts2005Inngår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 155, nr Part 2 Sp. Iss. SI, s. 1727-1733Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Gas cooled quenching and many other applications require high-speed uniform-velocity flows, with minimal pressure drop. The flow ducting geometry is often rather complex, with flow splitting, 90-180 degrees bends, and circular-to-rectangular cross-section transition ducts (the latter are used, for example, between the circular blower duct and the rectangular quenching baskets). Similar situations exist in forced convection furnaces. To provide design guidance in the choice of such ducts, and focusing primarily on circular-to-rectangular transition ducts. the flow was modelled and computed, and the results were successfully validated. Sensitivity of the velocity uniformity and pressure drop with respect to the primary geometric parameters, pressure, and Reynolds numbers was examined in the range (1.3) 10(5) # Re # (7.8)10(5), with an ultimate objective to produce optimal designs. For a length-to-diameter ratio AL = L/D < 1.0, flow nonuniformity at the exit plane and pressure drop are increased by 33 and 83%, respectively, as the aspect ratio (rectangular duct width-to-height) AR decreases from 4 to 1. Increasing AR beyond 1.5 leads to linearly increasing nonuniformity and pressure drops. A diverging-contracting duct has proven to lead to lesser nonuniformity, while it did not influence the pressure drop. Increasing the inlet pressure from 1 to 20 bar led to a decrease in flow distortion by 11% at the duct exit planes. At atmospheric pressure, increasing the Reynolds number from (1.3)10(5) to (7.8)10(5) increased distortion by 8%. Some preliminary design recommendations for circular-to-rectangular duct transitions are to try and keep AL > 1 and AR < 1.5.

  • 16.
    Macchion, Olivier
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet. KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Zahrai, Said
    ABB Corporate Research.
    Bouwman, J W
    Ipsen GmbH.
    Heat transfer from typical loads within gas quenching furnace2006Inngår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 172, nr 3, s. 356-362Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Gas quenching in an industrial furnace is considered. The flow and thermal fields in the furnace with two different charges, plates and cylinders, in axial flow are studied numerically. Details of the thermal field characteristics are presented. A variation in heat transfer of maximum 125% is observed in the whole basket, the maximum heat transfer being obtained on the first bodies of the charge. The heat transfer is found to be uniformly distributed in the middle of the charge, with mean values 50% higher than on the sides. Recommendations for improvement of current vacuum quenching furnaces design are proposed.

  • 17.
    Saleem, Saud
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Metallernas gjutning.
    Vynnycky, Michael
    KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet. KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Metallernas gjutning.
    Fredriksson, Hasse
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Metallernas gjutning.
    The Influence of Peritectic Reaction/Transformation on Crack Susceptibility in the Continuous Casting of Steels2017Inngår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 48, nr 3, s. 1625-1635Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The work presented here examines the surface cracks that can form during the continuous casting of near peritectic steels due to the volume changes during the peritectic reaction/transformation. The investigated samples were collected during plant trials from two different steel grades. The role and mode of the peritectic reaction/transformation are found to depend on the composition of the alloy, resulting in different types of surface cracks. The effect of the local variation in the cooling rate on the formation of the different types of cracks present in each steel grade, which can be due, for example, to the formation of oscillation marks, is demonstrated. The enhanced severity of the surface and internal oxidation, both of which depend on the alloy composition and consequent peritectic reaction, is highlighted. Experimental and theoretical studies show that different types of surface cracks can occur in peritectic steels depending upon the alloy composition and cooling rate, both of which define the fraction of the remaining liquid upon completion of the peritectic reaction/transformation.

  • 18.
    Shugai, Galina
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet. KTH, Tidigare Institutioner                               , Mekanik.
    Holmqvist, Claes
    KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet. KTH, Tidigare Institutioner                               , Mekanik.
    Vynnycky, Michael
    KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet. KTH, Tidigare Institutioner                               , Mekanik.
    Analysis of a model for twin-wire forming2004Inngår i: PROGRESS IN INDUSTRIAL MATHEMATICS AT ECMI 2002    / [ed] Buikis A; Ciegis R; Fitt AD, 2004, Vol. 5, s. 369-373Konferansepaper (Fagfellevurdert)
  • 19.
    Vynnycky, Michael
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet.
    On the modelling of two-phase flow in the cathode gas diffusion layer of a polymer electrolyte fuel cell2007Inngår i: Applied Mathematics and Computation, ISSN 0096-3003, E-ISSN 1873-5649, Vol. 189, nr 2, s. 1560-1575Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A front-tracking approach is derived for the numerical solution of the equations arising in the multi-fluid model for isothermal multiphase multicomponent flow in the gas diffusion layer of the cathode of a polymer electrolyte fuel cell under conditions of local thermodynamic equilibrium. The method is able to find the location of the one-phase/two-phase interface explicitly and without need for the artificial diffusion, smoothing and ad hoe source terms that are required in existing formulations. Also, the analysis indicates the presence of a previously unidentified integrable singularity, which can be removed provided that the dependent variables are chosen correctly. For quantitative comparison, a benchmark example is implemented using both approaches in the commercially available finite-element software Comsol Multiphysics.

  • 20.
    Wiberg, Roland
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet.
    Lior, N.
    Heat transfer from a cylinder in axial turbulent flows2005Inngår i: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 48, nr 8, s. 1505-1517Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Local convective heat transfer coefficients were measured on a two-diameter long cylinder in axial flows of air at conditions unexplored so far, by using thermochromic liquid crystals (TLC) coated on an electrically heated strip-foil consisting bonded to the external surfaces. The Reynolds numbers (Re) based on the cylinder diameter were between 8.9 x 10(4) and 6.17 x 10(5), and the flow in front of the cylinder was modified in some cases by the use of a turbulence generating grid, or by circular disc inserts of two sizes placed upstream of the cylinder. These created a major change in the local convective heat transfer coefficient distribution on the cylinder. Increase of the turbulence intensity from Tu < 0.1% to Tu = 6.7% at the same Re increased the average calculated Nusselt number Nu over the cylinder by 25%, and decreased the Nu non-uniformity over the surface. One of the flow modification inserts also reduced significantly the Nu non-uniformity. The position of flow reattachment was measured using tufts. Our heat transfer data agree well with the small amount if data published of others, when extrapolated to their conditions. Correlations between the Nu and Re in the form Nu = CRee were established and presented for the average Nu on the front, middle and rear cylinder surfaces, and the variation of the local exponent e was shown along the cylinder. Introducing a new technique, a TLC-coated heated flat plate mounted in the flow above the cylinder in the meridional plane was demonstrated to help visualize the flow field above the cylinder. A track of maximum convective coefficients on this plate was found similar in position to the stream line dividing the forward and backward flows in a case measured for the separated flow in a past study.

  • 21.
    Åberg, Jonas
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processteknologi.
    Vynnycky, Michael
    KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet.
    Widell, Björn
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processteknologi.
    Development of a finite element model for study of the developing stress and strain in a solidifying shell2006Rapport (Annet vitenskapelig)
1 - 21 of 21
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