Dynamics of single rising bubbles in neutrally buoyant liquid-solid suspensions

Modeling of CSTR flow field for Agaricus bisporus residue fermentation based on CFD numerical simulation

Agaricus bisporus production gets a lot of residues, which could be fermented by a continuous stirred tank reactor (CSTR). This research was conducted to study the characteristics of the multiphase flow field in the reactor and its influence on the efficiency of biogas production in the CSTR fermentation process of Agaricus bisporus residue by using CFD numerical simulation technique. The aim is to reveal the relationship between the reactor operating conditions, flow field characteristics, and biogas production efficiency at the micro-level. We compared the results of different turbulence models by evaluating the power quotients and flow quotients with the experimental results to derive the most suitable flow field model inside the reactor for the Agaricus bisporus residues. The results showed that, under the condition that the number of grids does not affect the simulation results, and considering the model accuracy and efficiency, the numerical method can be chosen as the multiple reference frame (MRF) method of the second-order upwind discrete scheme with the realizable k - ε model. In this way, we can make use of edible mushroom residue as a substrate for resource utilization and provide basic data and theoretical basis for the design and scale-up with anaerobic fermentation to biogas reactor.

Puzzling Bubble Rise Speed Increase in Dense Granular Suspensions

We present an anomalous experimental observation on the rising speed of air bubbles in a Hele-Shaw cell containing a suspension of spherical, neutrally buoyant, non-Brownian particles. Strikingly, bubbles rise faster in suspensions as compared to particle-less liquids of the same effective viscosity. By carefully measuring this bubble speed increase at various particle volume fraction and via velocity field imaging, we demonstrate that this strange bubble dynamics is linked to a reduction in the bulk dissipation rate. A good match between our experimental data and computations based on a Suspension Balance Model (SBM) illustrates that the underlying mechanism for this dissipation-rate deficit is related to a nonuniform particle distribution in the direction perpendicular to the channel walls due to shear-induced particle migration.

Fischer–Tropsch Synthesis in Slurry Bubble Column Reactors: Experimental Investigations and Modeling – A Review

This paper presents an extensive review of the kinetics, hydrodynamics, mass transfer, heat transfer and mathematical as well as computational fluid dynamics (CFD) modeling of Low-Temperature Tropsch Synthesis (LTFT) synthesis in Slurry Bubble Column Reactors (SBCRs), with the aim of identifying potential research and development areas in this particular field. The kinetic expressions developed for F-T synthesis over iron and cobalt catalysts along with the water gas shift (WGS) reactions are summarized and compared. The experimental data and empirical correlations to predict the hydrodynamics (gas holdup, Sauter mean bubble diameter, and bubble rise velocity), mass transfer coefficients and heat transfer coefficients are presented. The effects of various operating variables, including pressure, temperature, gas velocity, catalyst concentration, reactor geometry, and reactor internals on the hydrodynamic and transport parameters as well as the performance of SBCRs are discussed. Additionally, modeling efforts of SBCRs, using axial dispersion models (ADM), multiple cell recirculation models (MCCM) and computational fluid dynamics (CFD), are addressed. This review revealed the following: (1)