Hydrodynamic characteristics of harmonically excited thin-film flows : experiments and computations

We present new results from the simultaneous application of Planar Laser-Induced Fluorescence (PLIF) and Particle Tracking Velocimetry (PTV), complemented by Direct Numerical Simula- tions (DNSs), aimed at the detailed hydrodynamic characteriza- tion of harmonically excited liquid-film flows. The experimental campaign spans the Reynolds number range Re = 8 − 320, and three Kapitza numbers Ka = 85, 350 and 1800. PLIF was em- ployed in order to generate spatiotemporally resolved film-height data, and PTV to generate two-dimensional (2D) planar velocity- vector maps of the flow-field underneath the wavy interface. By combining the two optical techniques, instantaneous and highly localised flow-rate data were retrieved, based on which the ef- fect of local film topology on the flow-field is studied in detail. Surprisingly, the instantaneous flow rate is found to vary linearly with the instantaneous film-height, while both experimental and numerical flow-rate data are closely approximated by a simple analytical relationship with only minor deviations. This relation- ship, which is reported here for the first time, includes the wave speed c and mean flow-rate Q, both of which can be obtained by simple and inexpensive methods, thus allowing for spatiotempo- rally resolved flow-rate predictions to be made without requiring any knowledge of flow-field information.Papers presented to the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Costa de Sol, Spain on 11-13 July 2016

Derivation, Implementation, and Validation of Computer Simulation Models for Gas-Solid Fluidized Beds

Applied Science

A coupled solver approach for multiphase flow calculations on collocated grids

Because of increasing computer speed and memory, the numerical solution of the incompressible Navier-Stokes equations by a fully coupled approach is an attractive and emerging trend in computational fluid dynamics (CFD) calculations. The main advantage of this approach is an increased robustness due to the implicit treatment of the pressure velocity coupling (Schneider and Raw, 1987; Deng et al., 2001). Although the equations describing multiphase flows appear similar to single-phase flow equations, their nature is often much more difficult due to the presence of volume fractions, large source terms, and gradients of these as well as density. This makes the requirement for a robust solving approach even more desirable. Almost all multiphase CFD solvers today are based upon standard decoupled approaches (e.g. SIMPLE, SIMPLER, PISO, fractional step, and other pressure projection methods (Ferziger and Peric, 2002)) and most often employ a staggered variable arrangement. In this paper, momentum weighted interpolation is used to determine analytical expressions for the cell face velocities which are employed in the multiphase continu- ity equation in a collocated variable arrangement. A special approach is adopted for the momentum weighted interpolation to handle large source terms, volume fractions, and gradients of these. The resulting linearized equations are solved in a fully coupled manner. The fully coupled method is demonstrated on two practical multiphase cases. Firstly, the method is demonstrated simulating volume of fluid (VOF) computations of a gas-liquid flow case. Secondly, the method is demonstrated on solving the continuous part of an Euler-Lagrange gas-solid flow problem. The difficulties in the first case are large source terms and gradients of density, and in the second case the presence of volume fraction and gradients hereof, as well as source terms. The results are in accordance with results from the staggered segregated approach. Moreover, due to the collocated variable arrangement, complex geometries can be easily handeled. Both robustness and computational efficiency of this fully coupled approach are shown

Heat and mass transfer of drying particles in a fluidised bed

In this study, the heat transfer and drying process of arabica coffee beans in a batch fluidized bed roaster has been studied. Herein, the discrete element method (DEM) has been used and modified to account for resolved 1D temperature and moisture content profiles within each single coffee bean. This approach has the strength to provide much more information on the global (fluidization, mixing) and local (particle data) level compared to existing coffee roaster models. Therefore, the product quality can be evaluated on-line by many more specific criteria beyond the averaged global particle temperature and moisture content. Instead, information of every single particle is available which includes heat and mass transfer coefficients, its local position inside the bed, collision forces, etc. Furthermore, the overall roaster performance is based on e.g. fluidization stability, mixing efficiency or uniformity of quality properties among all particles. More data are presented to account for a broader coffee bean roasting evaluation. Modeling results are in good agreement with experimental data

Platinum catalysed aqueous alcohol oxidation: model-based investigation of reaction conditions and catalyst design

A dynamic transport model is derived to describe the platinum catalyzed aq. alc. oxidn., considering a single spherical catalyst particle surrounded by a stagnant liq. film. The transport model is based on a heterogeneous kinetic model with mass transfer and intra particle diffusion resistances. The developed model uses the kinetic model of Markusse et al. (Catal. Today 66 (2001) 191) and is validated with the exptl. kinetic data of Me a-D-glucopyranoside (MGP) oxidn. obtained by Vleeming et al. (Ind. Eng. Chem. Res.). The model is used to investigate the effect of process conditions, catalyst and particle properties, and transport parameters on the performance of the catalyst for alc. oxidn. It is found that the electron cond. of the catalyst support affects the rate of MGP oxidn. esp. at low bulk liq. oxygen concns., while at high bulk liq. oxygen concns., the catalyst support cond. does not play a role. A major cause of catalyst deactivation is over-oxidn. under oxygen rich conditions. This can be reversed by applying redox-cycle operation, an alternating exposure of the catalyst to oxidative and reductive environments. The advantages of redox-cycle application are demonstrated using the developed model. For reactions of neg. order, such as MGP oxidn., at high bulk oxygen concns. (CO2,L>0.3 mol/m3), concg. the active catalytic material in a layer buried some distance from the surface (core) gives considerable better performance than the conventional \"egg shell\" design of shallow deposition near the surface or uniform distribution. However, at low bulk oxygen concns. (CO2,L?0.3 mol/m3), the performance of the uniform or egg shell distribution catalyst is superior to the core catalyst. [on SciFinder (R)