Effect of air turbulence on gas transport in soil; comparison of approaches

Geophysical Research Abstracts (GRA) is the conference series publishing the abstracts accepted for the General Assemblies of the European Geosciences Union (EGU). It links the annual conference programmes listing programme groups, included sessions, and their contributions. The abstracts underwent an access review by the session conveners.Xi'an Jiaotong-Liverpool Universit

The Recent High State of the BL Lacertae Object AO 0235 and Cross-Correlations Between Optical and Radio Bands

We present new optical (B, V , R, I) and radio (at 14.5, 8.5, and 4.8 GHz) observations of the γ-ray- loud blazar AO 0235+164 obtained during the high state of 1997 December-1998 January. The data were combined with historical light curves from the literature to study correlated optical and radio variations over a time span of more than 20 years. Flux variability with large and energy-dependent amplitude is observed at both wave bands, with the source varying over all timescales sampled (years-months- days), in agreement with previous reports. We have performed a cross-correlation analysis of optical and radio light curves applying various detailed statistical methods. The principal results of our analysis can be summarized as follows : (1) we find that the optical and radio variations exhibit correlated flux changes at their average level , stressing the conclusion that the same emission mechanism is responsible for the radiation in the two bands (i.e., synchrotron emission from shocked plasma in the jet). However, as previously reported, a few strong flares at optical do not have obvious counterparts at longer wavelengths, possibly indicating that an additional component is present in the optical (e.g., microlensing), or, alternatively, rapid cooling of the synchrotron particles in a radiative shock. (2) Periodic variations are observed at radio frequencies (14.5 and 8.0 GHz) with a pattern repeating every ~5.8 years, as indicated by the Lomb-Scargle periodogram. This is the first report for periodicity at radio wavelengths for this source; future continuous monitoring is needed to confirm this result. (3) Through the analysis of B-V and R-I slopes, we observe large spectral variations, with a bimodal behavior. In the first state, the emission is consistent with a variable power law all across the sampled optical region (from R to V bands); in the second state, the R-I slope is constant while the B-V slope varies, i.e., the continuum has various degrees of curvature at the shorter wavelengths. In general, the power-law slope is not correlated with the f;ux of the source. However, there is an indication that when the source is in the first state, the spectrum becomes softer as the source brightens

Computational modelling of the impact of particle size to the heat transfer coefficient between biomass particles and a fluidised bed

The fluid–particle interaction and the impact of different heat transfer conditions on pyrolysis of biomassinside a 150 g/h fluidised bed reactor are modelled. Two different size biomass particles (350 ?m and 550 ?min diameter) are injected into the fluidised bed. The different biomass particle sizes result in different heattransfer conditions. This is due to the fact that the 350 ?m diameter particle is smaller than the sand particlesof the reactor (440 ?m), while the 550 ?m one is larger. The bed-to-particle heat transfer for both cases iscalculated according to the literature. Conductive heat transfer is assumed for the larger biomass particle(550 ?m) inside the bed, while biomass–sand contacts for the smaller biomass particle (350 ?m) wereconsidered unimportant. The Eulerian approach is used to model the bubbling behaviour of the sand, whichis treated as a continuum. Biomass reaction kinetics is modelled according to the literature using a two-stage,semi-global model which takes into account secondary reactions. The particle motion inside the reactor iscomputed using drag laws, dependent on the local volume fraction of each phase. FLUENT 6.2 has been usedas the modelling framework of the simulations with the whole pyrolysis model incorporated in the form ofUser Defined Function (UDF)

Eulerian Model for the Condensation of Pyrolysis Vapors in a Water Condenser

The paper presents the simulation of the pyrolysis vapors condensation process using an Eulerian approach. The condensable volatiles produced by the fast pyrolysis of biomass in a 100 g/h bubbling fluidized bed reactor are condensed in a water cooled condenser. The vapors enter the condenser at 500 °C, and the water temperature is 15 °C. The properties of the vapor phase are calculated according to the mole fraction of its individual compounds. The saturated vapor pressure is calculated for the vapor mixture using a corresponding states correlation and assuming that the mixture of the condensable compounds behave as a pure fluid. Fluent 6.3 has been used as the simulation platform, while the condensation model has been incorporated to the main code using an external user defined function

Eulerian Model for the Condensation of Pyrolysis Vapors in a Water Condenser

The paper presents the simulation of the pyrolysis vapors condensation process using an Eulerian approach. The condensable volatiles produced by the fast pyrolysis of biomass in a 100 g/h bubbling fluidized bed reactor are condensed in a water cooled condenser. The vapors enter the condenser at 500 °C, and the water temperature is 15 °C. The properties of the vapor phase are calculated according to the mole fraction of its individual compounds. The saturated vapor pressure is calculated for the vapor mixture using a corresponding states correlation and assuming that the mixture of the condensable compounds behave as a pure fluid. Fluent 6.3 has been used as the simulation platform, while the condensation model has been incorporated to the main code using an external user defined function

Three-dimensional multi-relaxation time lattice-Boltzmann model for the drop impact on a dry surface at large density ratio

Extensive application of the multiphase lattice Boltzmann model to realistic fluid flows is often restricted by the numerical instabilities induced at high liquid-to-gas density ratios, and at low viscosities. In this paper, a three-dimensional multi-relaxation time (MRT) lattice Boltzmann model with an improved forcing scheme is reported for simulating multiphase flows at high liquid-to-gas density ratios and relatively high Reynolds numbers. The model is based on a recently presented model in the literature. Firstly, the MRT multiphase model is evaluated by verifying Laplace’s law and achieving thermodynamic consistency for a static droplet. Then, a relationship between the fluid–solid interaction potential parameter and contact angle is investigated. Finally, the improved three-dimensional MRT Lattice Boltzmann model is employed in the simulation of the impingement of a liquid droplet onto a flat surface for a range of Weber and Reynolds numbers. The dynamics of the droplet spreading is reproduced and the predicted maximum spread factor is in good agreement with experimental data published in the literature

CFD modelling of the fast pyrolysis of biomass in fluidised bed reactors, Part A: Eulerian computation of momentum transport in bubbling fluidised beds

The fluid–particle interaction inside a 150 g/h fluidised bed reactor is modelled. The biomass particle is injected into the fluidised bed and the momentum transport from the fluidising gas and fluidised sand is modelled. The Eulerian approach is used to model the bubbling behaviour of the sand, which is treated as a continuum. The particle motion inside the reactor is computed using drag laws, dependent on the local volume fraction of each phase, according to the literature. FLUENT 6.2 has been used as the modelling framework of the simulations with a completely revised drag model, in the form of user defined function (UDF), to calculate the forces exerted on the particle as well as its velocity components. 2-D and 3-D simulations are tested and compared. The study is the first part of a complete pyrolysis model in fluidised bed reactors

A CFD approach on the effect of particle size on char entrainment in bubbling fluidised bed reactors

The fluid – particle interaction inside a 41.7 mg s−1 fluidised bed reactor is modelled. Three char particles of sizes 500 μm, 250 μm, and 100 μm are injected into the fluidised bed and the momentum transport from the fluidising gas and fluidised sand is modelled. Due to the fluidising conditions and reactor design the char particles will either be entrained from the reactor or remain inside the bubbling bed. The particle size is the factor that differentiates the particle motion inside the reactor and their efficient entrainment out of it. A 3-Dimensional simulation has been performed with a completele revised momentum transport model for bubble three-phase flow according to the literature as an extension to the commercial finite volume code FLUENT 6.2