Detached eddy simulation on the turbulent flow in a stirred tank

Low-Cost Eddy-Resolving Simulation in the Near-Field of an Annular Swirling Jet for Spray Drying Applications

Spray drying is one of many industrial applications that use annular swirling jets. For this particular application, the flow characteristics in the near-field of the jet are fundamental to obtaining high-quality dried products. In this article, an annular swirling jet configuration is numerically studied using three low-cost eddy-resolving turbulence methods: detached-eddy simulation (DES), delayed-DES (DDES) and scale-adaptive simulation (SAS). To focus in industrial applicability, very coarse grids are used. The individual performance of these models is assessed through a comparison with laser-Doppler anemometry (LDA) measurements and large-eddy simulation (LES) data from available studies. Results show that all the three turbulence models are suitable for performing industrial cost-effective simulations, capable of reproducing LES results of mean velocities and first-order turbulence statistics at a fraction of the computational cost. Differences in the results of the evaluated models were minor; however, the simulation with DDES still provided a better reproduction of experimental results, especially in the very-near field of the jet, as it enforced RANS behavior near the inlet walls and a better transition from modeled to resolved scales.

A General Review of the Current Development of Mechanically Agitated Vessels

The mixing process in a mechanically agitated vessel is a widespread phenomenon which plays an important role among industrial processes. In that process, one of the crucial parameters, the mixing efficiency, depends on a large number of geometrical factors, as well as process parameters and complex interactions between the phases which are still not well understood. In the last decade, large progress has been made in optimisation, construction and numerical and experimental analysis of mechanically agitated vessels. In this review, the current state in this field has been presented. It shows that advanced computational fluid dynamic techniques for multiphase flow analysis with reactions and modern experimental techniques can be used with success to analyse in detail mixing features in liquid-liquid, gas-liquid, solid-liquid and in more than two-phase flows. The objective is to show the most important research recently carried out.

A Comparative CFD Study on Gas-Liquid Dispersion in A Stirred Tank with Low and High Gas Loadings

The computational fluid dynamics (CFD) combined with a population balance model (PBM) was applied to simulate gas-liquid dispersion in a stirred tank with low and high gas loadings. The model predictions were validated by using the data in the literature. The simulation results show that the flow patterns and gas dispersion characteristics are very different in the stirred tank for low and high gas loadings. A typical two-loop flow pattern forms as that in single-phase stirred tank for low gas loadings, while a triple-loop flow pattern, with two recirculation loops above and one below the impeller is found in the tank for high gas loadings. Shaft power input of impeller agitation plays a major role for gas dispersion with low gas loadings. For high gas loadings, the potential energy due to gas sparging has significant effect on gas dispersion and can not be neglected. Compared to low gas loading, high gas loading causes average gas holdup increased in the stirred tank, while relative local gas holdup in the lower circulation-loop region and near-wall region reduced. The ability of impeller agitation for gas dispersion reduces with high gas loadings, and mean bubble size becomes larger and the volume-averaged bubble size distribution is wider.

CFD Analysis and Design Optimization in a Curved Blade Impeller

Mixing efficiency in stirred tank reactors is an important challenge in the design of many industrial processes. The effect of blade shape on mixing efficiency has been studied in the present work. The computational method has been used to investigate the flow field, power consumption, pumping capacity, hydraulic efficiency, and mixing time in a fully baffled tank stirred by a Rushton turbine and different curved blade impellers. Flow in a stirred tank reactor involves interactions between flow around rotating blades and stationary baffles. The flow field was developed using the sliding mesh (SM) approach in computational fluid dynamics (CFD). The realizable k-ε was used to model the turbulence. A reasonable agreement between the experimental reported data and simulation results indicated the validity of CFD model. It has been revealed that increasing the blade curvature, at approximately the same mixing time would enhance the mixing efficiency up to 61.3 % in comparison with the Rushton turbine. This mixing efficiency would favor the employment of curved blade impellers due to the cost-benefits of stirred tank operations.

Designing and optimizing a stirring system for a cold model of a lithium electrolysis cell based on CFD simulations and optical experiments

A new stirring system to separate lithium metal and chloride gas in lithium electrolysis cells has been designed and applied in cold model experiments.

CFD Simulation of the Discharge Flow from Standard Rushton Impeller

The radial discharge jet from the standard Rushton turbine was investigated by the CFD calculations and compared with results from the Laser Doppler Anemometry (LDA) measurements. The Large Eddy Simulation (LES) approach was employed with Sliding Mesh (SM) model of the impeller motion. The obtained velocity profiles of the mean ensemble-averaged velocity and r.m.s. values of the fluctuating velocity were compared in several distances from the impeller blades. The calculated values of mean ensemble-averaged velocities are rather in good agreement with the measured ones as well as the derived power number from calculations. However, the values of fluctuating velocities are obviously lower from LES calculations than from LDA measurements.