The Schr\"odinger functional running coupling with staggered fermions and its application to many flavor QCD

We discuss the Schr\"odinger functional in lattice QCD with staggered fermions and relate it, in the classical continuum limit, to the Schr\"odinger functional regularized with Wilson fermions. We compute the strong coupling constant defined via the Schr\"odinger functional with staggered fermions at one loop and show that it agrees with the continuum running coupling constant in the Schr\"odinger functional formalism. We compute this running coupling in the ``weak coupling phase'' of many flavor QCD numerically at several values of the bare coupling and for several system sizes from $L/a=4$ to 12. The results indicate that the $\beta$-function for 16 flavors has the opposite sign than for few flavor QCD, in agreement with a recent claim, and with the perturbative prediction.Comment: 3 pages with 2 ps figures; to appear in the proceedings of Lattice '97, Edinburgh, Scotland, July 22--26, 199

Non-perturbative O(a) improvement of the vector current

We discuss non-perturbative improvement of the vector current, using the Schroedinger Functional formalism. By considering a suitable Ward identity, we compute the improvement coefficient which gives the O(a) mixing of the tensor current with the vector one.Comment: 3 pages (LaTeX, 2 ps figures, styles), talk presented at Lattice 9

A First Taste of Dynamical Fermions with an O(a) Improved Action

We present the first results obtained by the UKQCD Collaboration using a non-perturbatively $O(a)$ improved Wilson quark action with two degenerate dynamical flavours.Comment: Talk presented at Lattice '97, Edinburgh (UK), July 1997. LaTeX 3 pages, uses espcrc2, 3 figure

Comparison of continuum models using the kinetic theory of granular flow with discrete particle models and experiments: extent of particle mixing induced by bubbles

The bubble formation and extent of particle mixing induced by a single bubble injected in a mono-disperse uidised bed at incipient \ud uidisation conditions has been studied with a Two-Fluid continuum Model (TFM) using the Kinetic Theory of Granular Flow (KTGF) and com-\ud pared with experiments and simulation results obtained from a Discrete Particle Model (DPM). The eect of dierent gas-particle drag models and frictional viscosity models on the bubble behaviour and extent of particle mixing has been assessed. To describe the extent of particle\ud mixing well, a frictional viscosity model needs to be included, however, the currently available frictional viscosity models need further improvement

Autothermal reactor concept for combined oxidative coupling and methane reforming

A novel autothermal reactor concept has been developed for the simultaneous production of ethylene by oxidative coupling (OCM) and synthesis gas by steam reforming of methane (SRM), supported by a detailed numerical modeling study. The proposed reactor consists of two separate reaction chambers which are thermally coupled. The OCM is carried out in packed bed reverse flow membrane reactor tubes submerged in a fluidized bed where the unconverted methane and by-products, from which the valuable C2 components have been separated, are reformed together with some additional steam producing synthesis gas and consuming the reaction enthalpy emerged from the exothermic OCM

Influence of Bubble-Bubble Interactions on the Macroscale Circulation Patterns in a Bubbling Gas-Solid Fluidized Bed

The macro-scale circulation patterns in the emulsion phase of a gas-solid fluidized bed in the bubbling regime have been studied with a 3D Discrete Bubble Model. It has been shown that bubble-bubble interactions strongly influence the extent of the solids circulation and the bubble size distribution

Novel reactor technology for chemical-looping combustion

No Abstract

Autothermal Reforming of Methane with Integrated CO2 Capture in a Novel Fluidized Bed Membrane Reactor. Part 2 Comparison of Reactor Configurations

The reactor performance of two novel fluidized bed membrane reactor configurations for hydrogen production with integrated CO2 capture by autothermal reforming of methane (experimentally investigated in Part 1) have been compared using a phenomenological reactor model over a wide range of operating conditions (temperature, pressure, H2O/CH4 ratio and membrane area). It was found that the methane combustion configuration (where part of the CH4 is combusted in situ with pure O2) largely outperforms the hydrogen combustion concept (oxidative sweeping combusting part of the permeated H2) at low H2O/CH4 ratios (<2) due to in situ steam production, but gives a slightly lower hydrogen production rate at higher H2O/CH4 ratios due to dilution with combustion products. The CO selectivity was always much lower with the methane combustion configuration. Whether the methane combustion or hydrogen combustion configuration is preferred depends strongly on the economics associated with the H2O/CH4 ratio

Direct Numerical Simulation of Complex Gas-Liquid-Solid Flows using a Combined\ud Immersed Boundary (IB) and Volume Of Fluid (VOF) Approach

In this paper a simulation model is presented for the Direct Numerical Simulation (DNS) of complex multi-fluid flows in which simultaneously (moving) deformable (drops or bubbles) and non-deformable (moving) elements (particles) are present, possibly with the additional presence of free surfaces. Our model combines the VOF model developed by van Sint Annaland et al. (2005) and the Immersed Boundary (IB) model The Volume of Fluid (VOF) part features i) an interface reconstruction technique based on piecewise linear interface representation ii) a three-dimensional version of the CSF model of Brackbill et al. (1992). The Immersed Boundary (IB) part incorporates both particle-fluid and particle-particle interaction via a Direct Forcing Method (DFM) and a hard sphere Discrete Particle (DP) approach. In our model a fixed (Eulerian) grid is utilized to solve the Navier-Stokes equations for the entire computational domain. The no-slip condition at the surface of the moving particles is enforced via a momentum source term which only acts in the vicinity of the particle surface. Specifically Lagrangian force points are used which are distributed evenly over the surface of the particle. Dissipative particle-particle and/or particle-wall collisions are accounted via a hard sphere DP approach using a three-parameter particle-particle interaction model accounting for normal and tangential restitution and tangential friction. The capabilities of the hybrid VOF-IB model are demonstrated with a number of examples in which complex topological changes in the interface are encountered