Effect of interparticle force on gas dynamics in a bubbling gas–solid fluidized bed: A CFD-DEM study

CFD simulation of gas–solid fluidized bed hydrodynamics; prediction accuracy study

The present study aims at increasing the prediction accuracy of simulating gas–solid fluidized bed hydrodynamics. Two simulation packages, Fluent and MFIX, were used to predict the pressure drop, voidage, and solid-phase velocities by solving mass, momentum, and energy balance equations. A 2D multi-fluid Eulerian model with the kinetic theory of granular flow (KTGF) was applied to simulate the process by considering two different drag models. The same comparative criterion of average absolute relative deviation (AARD%) was considered to compare the present simulation with the previous works. Compared to the prior works, the minimum decrease in error (AARD% of 5.91%) was 3.17% related to the estimation of the time-averaged voidage by applying the Gidaspow model, while the maximum reduction in error (ARRD% of 5.88%) was 17.35% attributed to the prediction of pressure drop by employing the Syamlal-O’Brien model, both in Fluent software. However, MFIX software was the best CFD tool in predicting time-averaged voidage by AARD% values less than 9% under all conditions. Furthermore, similar patterns in contours were observed for solid-phase volume fraction and gas/solid phase velocities in both simulation tools, which are compatible with results from the literature without any significant difference.

CFD-DEM Simulation of the Transport of Manganese Nodules in a Vertical Pipe

The present study aims to describe the characteristics of the hydraulic transport of manganese nodules in a vertical pipe. The solid–liquid two-phase flows were simulated using a numerical technique that combines the computational fluid dynamics (CFD) method and the discrete element method (DEM). Manganese nodules with diameters of 5.0 mm, 15.0 mm, and 30.0 mm were selected. The effects of the initial solid volume fraction and the initial mixture velocity were investigated. The results show that with increasing initial solid volume fraction, the liquid and solid velocities decrease but the total pressure drop over the pipe increases. Small particles are responsible for high particle collision frequency, which causes decreases in both the liquid velocity and the total pressure drop. Energy loss is aggravated by increasing the initial mixture velocity, manifesting in the increase of the total pressure drop. The retention ratio of manganese nodules varies inversely with the initial mixture velocity. A formula is proposed to describe the pressure drop due to the presence of solid particles and collisions.

A novel micro-spiral pneumatic selection system for the separation of fresh tea leaves

There are no standard machines or systems used for grading the new tea leaves in the market, a micro-spiral pneumatic selection system was designed to separate fresh tea leaves, solving the difficulties in tea leaf selecting and separation. The system can flexibly separate the tea leaves continuously in high quality. And the simulation model was established based on the experiments results to optimize the design parameters. The maximum constant air flow rate separation tests showed that the symmetrical distribution effect of six tubular fans provided better balance than four tubular fans, and three grades of fresh tea can be differentially sorted. Additionally, solid particle simulation tests showed that separation begins at heights between 0.27 and 0.37 m. When the air flow rates range from 4.4 to 6.6 m/s, fresh tea leaves containing only one leaf per stem are well separated from multi-leaf containing stems. Furthermore, solid particle simulation tests indicated that different sizes of fresh tea leaves can be distributed in corresponding annular regions of specific widths; therefore, the flow field simulation tests showed that an optimized system could separate tea leaves according to the number of leaves on the stem. To sum, this study reported a novel micro-spiral pneumatic selection system with high efficiency for the separation of fresh tea leaves.