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  • 1.
    Bitaraf Haghighi, Ehsan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Saleemi, Mohsin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Nikkam, Nader
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Ghadamgahi, Mersedeh
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Khodabandeh, Rahmatollah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn E.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Toprak, Muhammet
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Measurement of temperature–dependent viscosity of nanofluids and its effect on pumping power in cooling systems2013Conference paper (Refereed)
    Abstract [en]

    Nanofluids are engineered colloids of nanoparticlesdispersed homogenously in a base fluid, which theirthermophysical properties are changed by adding solidnanoparticles. Among the characteristic parameters,viscosity is one of the most important, as it directly affectsthe pumping power in cooling systems. In this study, theviscosity of water based Al2O3, ZrO2, and TiO2 (with 9wt%for all) nanofluids was measured and its impact on pressuredrop in a simple tubular pipe was estimated for bothlaminar and turbulent flow by classical correlations. Theeffect of temperature on the viscosity of these nanofluidswas also studied in the temperature range of 5˚C - 30˚C. Toassess the applicability of the classical correlations, pressuredrops across an open 30cm long, 0.50mm diameterstainless steel test section was measured for water andnanofluids by a differential pressure transducer. Theaverage viscosity increments compared to water in thetemperature range of 5˚C - 30˚C are 105%, 98% and 31% forAl2O3, ZrO2, and TiO2 nanofluids respectively. Moreover, theresults show that the viscosity of nanofluids decreases withthe increase of temperature; however the relative viscosity,which is defined as the viscosity ratio between a nanofluidand its base fluid is constant in 5˚C - 30˚C temperaturerange.

  • 2.
    Ghadamgahi, Mersedeh
    et al.
    KTH, School of Industrial Engineering and Management (ITM). Ovako Sweden AB, Sweden.
    Olund, Patrik
    Andersson, Nils A. I.
    KTH, School of Industrial Engineering and Management (ITM).
    Jonsson, Pär
    KTH, School of Industrial Engineering and Management (ITM).
    Numerical Study on the Effect of Lambda Value (Oxygen/Fuel Ratio) on Temperature Distribution and Efficiency of a Flameless Oxyfuel Combustion System2017In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 10, no 3, article id 338Article in journal (Refereed)
    Abstract [en]

    The flameless oxyfuel combustion technology has been proven to be a promising new method to reduce the fuel consumption and pollutants in industrial applications. Although this technology is widely used in industrial furnaces, a lack of understanding exists about the effect of the controlling parameters on the final operational conditions is tangible. In this study, a validated computational fluid dynamics (CFD) model is used to simulate six cases of flameless oxyfuel combustion burners with different lambda values (ratio of oxygen/fuel mass flow rates). The CFD model uses the steady laminar flamelet model (SLFM) to solve the probability density function (PDF) for combustion, the discreet ordinates (DO) radiation model with the weighted sum of the gray gases model (WSGGM) to solve radiation, and the realizable k-epsilon to model the turbulence. It is seen that an increased oxygen injection velocity due to an increased lambda value increases the exhaust losses, but produces a larger volumetric flame. This leads to a more uniform temperature distribution. The total temperature difference in a case with a value of 1.02 is reported to be 272 (14.9%), while the amount for a case with a value of 1.2 is 67 (4.7%). This effect is further explained by introducing a new definition value for the furnace efficiency that includes both the thermal and production losses.

  • 3.
    Ghadamgahi, Mersedeh
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Ovako Sweden AB, Sweden.
    Olund, Patrik
    Ekman, Tomas
    Andersson, Nils
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    A Comparative CFD Study on Simulating Flameless Oxy-Fuel Combustion in a Pilot-Scale Furnace2016In: Journal of Combustion, ISSN 2090-1968, E-ISSN 2090-1976, article id 6735971Article in journal (Refereed)
    Abstract [en]

    The current study presents a method to model the flameless oxy-fuel system, with a comparative approach, as well as validation of the predictions. The validation has been done by comparing the predicted results with previously published experimental results from a 200 kW pilot furnace. A suction pyrometer has been used to measure the local temperature and concentrations of CO, CO2, and O-2 at 24 different locations. A three-dimensional CFD model was developed and the validity of using different submodels describing turbulence and chemical reactions was evaluated. The standard k-epsilon model was compared with the realizable k-epsilon model for turbulence, while Probability Density Function (PDF) with either chemical equilibrium or the Steady Laminar Flamelet Model (SLFM) was evaluated for combustion. Radiation was described using a Discrete Ordinates Model (DOM) with weighted-sum-of-grey-gases model (WSGGM). The smallest deviation between predictions and experiments for temperature (1.2%) was found using the realizable k-epsilon model and the SLFM. This improvement affects the prediction of gaseous species as well since the deviation between predictions and experiments for CO2 volume percentages decreased from 6% to 1.5%. This provides a recommendation for model selections in further studies on flameless oxy-fuel combustion.

  • 4.
    Ghadamgahi, Mersedeh
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Ovako AB, Stockholm, Sweden..
    Olund, Patrik
    Ovako AB, Stockholm, Sweden..
    Ekman, Tomas
    AGA AB, Linde Grp, Lidingo, Sweden..
    Andersson, Nils
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Numerical and experimental study on flameless oxy-fuel combustion in a pilot-scale and a real-size industrial furnace2018In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 141, p. 788-797Article in journal (Refereed)
    Abstract [en]

    Previously validated CFD model was used to simulate the flameless oxy-fuel combustion in a pilot-scale furnace and a full-scale soaking pit furnace. The CFD predictions for temperature were compared with experimental data measured by shielded S-type thermocouples for both furnaces. The results indicate the validity of using shielded S-type thermocouples for temperature measurement, although use of the suction pyrometers renders more accurate results. Afterwards, the validation of previously proposed CFD model for simulating the flamaless oxy-fuel combustion is investigated in a full-scale soaking pit furnace in the production route of steel bars. The validation has been done by comparing the predicted temperatures with experimental data obtained by using S-type thermocouples. For both pilot-scale and full-scale furnaces a three dimensional CFD model with realizable k-epsilon, Probability Density Function (PDF) with Steady Laminar Flamelet Model (SLFM) and Discrete Ordinates Model (DOM) with Sum of The Weighted Gray Gases Model (SGGWM) for simulating turbulence, combustion and radiation was performed. The predicted temperature results show a good agreement with measured data from shielded S-type thermocouples for pilot-scale and full-scale furnace. More specifically the maximum deviation was 3.3% and 9.95% respectively. Afterwards, the simulation results on the full-scale furnace have been used to investigate the non-uniformity of temperature distribution inside the chamber. 

  • 5.
    Ghadamgahi, Mersedeh
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration. Ovako Hofors AB, Hofors, Sweden .
    Ölund, P.
    Lugnet, A.
    Saffaripour, Mohsen
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Yang, Weihong
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Design optimization of flameless-oxyfuel soaking pit furnace using CFD technique2014In: Energy Procedia, 2014, Vol. 61, p. 611-614Conference paper (Refereed)
    Abstract [en]

    The effect of the combustion chamber’s configuration on the characteristics of flow and combustion parameters has been numerically investigated for a multi injecting, LPG, Flameless Oxy-fuel burner in a real-size soaking pit furnace, using CFD simulation. The simulation has been performed on two different furnace configurations, namely; small and large chambers of 15 m3 and 27 m3, with a height to width ratios of 1.49 and 2.02 respectively and with corresponding burner capacities of 560 kW and 900 kW. A major experimental trial has been performed in order to validate the results and reasonable consistency has been observed. The predicted results, with particular focus on the temperature distribution and heat transfer rate of two cases have been studied in detail.

  • 6. Gola, A. M.
    et al.
    Ghadamgahi, Mersedeh
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Ovako Sweden AB, Sweden.
    Ooi, S. W.
    Microstructure evolution of carbide-free bainitic steels under abrasive wear conditions2017In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 376-377, p. 975-982Article in journal (Refereed)
    Abstract [en]

    The idea of carbide-free bainitic (CFB) microstructure, a mixture of bainitic ferrite and retained austenite (RA), in high-silicon steels has been recently thoroughly investigated by numerous researchers. In this research, two medium-carbon steel grades were tested in a wear tumbling machine to investigate microstructural changes under wet sliding abrasive wear conditions and to benchmark their performance against conventional tempered martensitic steels. The nature and type of defects responsible for material removal were analysed using scanning electron microscopy. To observe microstructural evolution of heavily deformed top layers of test specimens, special layer-by-layer X-ray diffraction methodology was applied. This technique allows accurate quantification of the volume fraction of RA transformed into untempered martensite at different depths from the worn surface. The results suggest that better performance is achieved in specimens heat treated to carbide-free bainitic microstructure containing higher volume fraction of RA, however with blocks of RA thermally stable at room temperature. The improved wear resistance is due to the increased surface hardness caused by stress-induced transformation of RA into untempered martensite during wear, while maintaining good toughness in the subsurface zones, which prevent brittle cracking.

1 - 6 of 6
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