Effective thermal conductivity in granular media with devolatilization: the Lattice Boltzmann modelling

AbstractFlow thermomechanics in reactive porous media is of importance in industry including the thermal processing of fossil fuel (coking understood as a slow pyrolysis) involving devolatilisation. On the way to provide a detailed description of the process, a multi-scale approach was chosen to estimate effective transport coefficients. For this case the Lattice Boltzmann method (LBM) was used due to its advantages to accurately model multi-physics and chemistry in a random geometry of granular media. After account for earlier studies, the paper presents description of the model with improved boundary conditions and a benchmark case. Results from meso-scale LBM calculations are presented and discussed regarding the spatial resolution and the choice of relaxation parameter along its influence on the accuracy compared with empirical formulae. Regarding the estimation of effective thermal conductivity coefficient it is shown that occurrence of devolatilization has a crucial effect by reducing heat transfer. Some quantitative results characterise the propagation of thermal front; also presented is the evolution of effective thermal conductivity. The work is a step forward towards a physically sound simulation of thermal processing of fossil fuel.</jats:p

Effects of Typha x glauca Invasion on Nitrogen Fixation in a Great Lakes Coastal Wetland

1 Broadside. Original created in Microsoft PowerPoint. 48"W x 36"HTypha x glauca is an invasive hybrid which poses a serious threat to Great Lakes region wetlands. Extremely high levels of nitrogen have previously been found in the soils of T. glauca-infested marshes, and this was theorized to be due to elevated rates of N-fixation in T. glauca soils. The purpose of this study was to quantify the rates of N-fixation in the soils of T. glauca-dominated communities and compare them to the N-fixation rates in native plant communities. N-fixation was measured using the acetylene reduction method on soil core samples collected in June, July and August of 2007 in three different plant zones: Typha zone (99% T. glauca present), Transition zone (33% T. glauca present) and Native zone (No T. glauca). N-fixation was found to be higher in the Typha zone than in the Transition and Native zones, and N-fixation was also found to progressively decrease from June to August.Kalamazoo College. Department of Biology. Diebold Symposium, 200

Symulacje przepływu metodą siatkową Boltzmanna w ośrodku porowatym o geometrii zależnej od temperatury

The Lattice Boltzmann method (LBM) has been applied for flow and heat transfer computations. The simulations have been performed with the single-relaxation time model and an advanced formulation of boundary conditions for LBM. For nonsothermal cases, a second distribution function has been used. First, validation tests are reported for heated flow past a single obstacle as well as over a set of regularly and randomly arranged obstacles (grains) that make up a simplified model of a porous medium. The Nusselt number for heat transfer in flow past a single obstacle has been computed. Next, novel simulations of non-isothermal flow in a porous medium of temperature-affected geometry have been undertaken. For the purpose, the thermal dilatation of grains has been accounted for. Results are presented for the pressure head loss and time-varying temperature profiles in the medium. Qualitative computations accomplished to date constitute an encouraging first step to proceed further towards the impact of temperature-affected geometry in such flows, in particular for the coking process.Metoda siatkowa Boltzmanna (LBM) została zastosowana do obliczeń przepływu i wymiany ciepła. Symulacje zostały przeprowadzone dla modelu z pojedynczym czasem relaksacji oraz zaawansowanego schematu warunków brzegowych metody LB. Dla przepływów nieizotermicznych, użyto dwóch funkcji rozkładu. Przedstawiono obliczenia testowe nieizotermicznego opływu pojedynczej przeszkody, jak również opływu regularnie oraz losowo rozmieszczonych przeszkód (ziaren), które tworzą uproszczony model ośrodka porowatego. Wyznaczono liczbę Nusselta dla przepływu ciepła w opływie pojedynczej przeszkody. Podjęto symulacje połączonych zjawisk (przepływ i wymiana ciepła) dla ośrodka porowatego o zmiennej geometrii przeszkód. W tym przypadku uwzględniono rozszerzalność termiczną ziaren. Zaprezentowano wyniki dla straty ciśnienia oraz zmienne w czasie profile temperatury dla przepływu przez ośrodek. Uzyskane dotąd jakościowe wyniki stanowią pierwszy krok do dalszych badań wpływu zależnej od temperatury geometrii ziaren ośrodka na przebieg takich przepływów, a w szczególności na proces koksowania

Transient one-dimensional model of coal carbonization in a stagnant packed bed

Abstract In the present paper, the one-dimensional model for heat and mass transfer in fixed coal bed was proposed to describe the thermal and flow characteristics in a coke oven chamber. For the purpose of the studied problem, the analysis was limited to the calculations of temperature field and pyrolytic gas yield. In order to verify the model, its theoretical predictions for temperature distribution during wet coal charge carbonization were compared with the measurement results found in the literature. In general, the investigation shows good qualitative agreement between numerical and experimental data. However, some discrepancy regarding the temperature characteristics at the stage of evaporation was observed.</jats:p

Transient one-dimensional model of coal carbonization in a stagnant packed bed

In the present paper, the one-dimensional model for heat and mass transfer in fixed coal bed was proposed to describe the thermal and flow characteristics in a coke oven chamber. For the purpose of the studied problem, the analysis was limited to the calculations of temperature field and pyrolytic gas yield. In order to verify the model, its theoretical predictions for temperature distribution during wet coal charge carbonization were compared with the measurement results found in the literature. In general, the investigation shows good qualitative agreement between numerical and experimental data. However, some discrepancy regarding the temperature characteristics at the stage of evaporation was observed