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Numerical study of laminar non-premixed biogas-air flames behind backward facing steps

Harish Alagani, Raghavan Vasudevan

Archive of Mechanical Engineering

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2022

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LXIX, nr 2

221–-244

EN

Biogas, a renewable fuel, has low operational stability range in burners due to its inherent carbon-dioxide content. In cross-flow configuration, biogas is injected from a horizontal injector and air is supplied in an orthogonal direction to the fuel flow. To increase the stable operating regime, backward facing steps are used. Systematic numerical simulations of these flames are reported here. The comprehensive numer- ical model incorporates a chemical kinetic mechanism having 25 species and 121 elementary reactions, multicomponent diffusion, variable thermo-physical properties, and optically thin approximation based volumetric radiation model. The model is able to predict different stable flame types formed behind the step under different air and fuel flow rates, comparable to experimental predictions. Predicted flow, species, and temperature fields in the flames within the stable operating regime, revealing their anchoring positions relative to the rear face of the backward facing step, which are difficult to be measured experimentally, have been presented in detail. Resultant flow field behind a backward facing step under chemically reactive condition is compared against the flow fields under isothermal and non-reactive conditions to reveal the sig- nificant change the chemical reaction produces. Effects of step height and step location relative to the fuel injector are also presented.

2

MHD forced convection using ferrofluid over a backward facing step containing a finned cylinder

Toumi Meriem, Bouzit Mohamed, Bouzit Fayçal, Mokhefi Abderrahim

Acta Mechanica et Automatica

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2022

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Vol. 16, no. 1

70--81

EN

In this paper, a numerical study of forced convection on a backward facing step containing a single-finned fixed cylinder has been performed, using a ferrofluid and external magnetic field with different inclinations. The partial differential equations, which determine the conservation equations for mass, momentum and energy, were solved using the finite element scheme based on Galerkin’s method. The analysis of heat transfer characteristics by forced convection was made by taking different values of the Reynolds number (Re between 10 and 100), Hartmann number (Ha between 0 and 100), nanoparticles concentration (φ between 0 and 0.1) and magnetic field inclination (γ between 0° and 90°); also, several fin positions α [0°–180°] were taken in the counter clockwise direction by a step of 5. After analysing the results, we concluded that Hartmann number, nanoparticles concentration, Reynolds number and magnetic field angles have an influence on the heat transfer rate. However, the fin position on the cylinder has a big impact on the Nusselt number and therefore on heat transfer quality. The best position of the fin is at (α = 150°), which gives the best Nusselt number and therefore the best heat trans-fer, but the fin position at (α = 0°) remains an unfavourable case that gives the lowest Nusselt values.

3

Hybrid techology of flue gas denitrification system. Part 1 - preliminary studies of flow turbulence and pressure drop in the elements of rotary air heater baskets

Kwiczala Andrzej, Wejkowski Robert, Jagodzińska Katarzyna

Journal of Power Technologies

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2019

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Vol. 99, nr 2

98--103

EN

The paper presents the results of physical and numerical tests of fluid flow through the filling of a rotary air heater (RAH). A laboratory-scale test bench was used to measure flow resistance across a fragment of a RAH. Seven types of RAH modules were tested-one steel and six ceramic (as catalyst carriers). The relationship between pressure drop and velocity (Renumber) of flow was used to deduce the flow characteristics for each of the RAH modules tested. Measurements carried out on the test bench were used to create a substitute mathematical model, which in the CFD code Ansys Fluent enables accurate mapping of pressure drop and velocity distribution full fit to the real flow conditions. Numerical calculations were used to validate measurements for an alternative model, to create guidelines for the substitute model of the porous zone and to optimize application checking the correctness of created guidelines for simplified calculations. Flow simulations were performed for various turbulence models. Results were compared to the test-bench measurements to determine the best adjustment for this specific type of reverse flow inside the air duct. This research is part of an ongoing research project: “Hybrid Technology of Flue Gas Denitrification System in Steam and Hot Water Boilers”. The aim of the project is to investigate the concept of using rotary air heater fillings as a carrier for catalytic coatings to reduce nitrogen oxides. In the further part of the research project, the replacement porous zone substitute models will make it possible to precisely calculate the entire RAH and will significantly reduce the calculation time as the basis for further project work.