CAI Wenyuan^1，2，WANG Liqiang^1，2，XU Limin³

（1. Jiangsu Key Laboratory of Advanced Food Manufacturing Equipment and Technology， Wu 214122， China；2. School of Mechanical Engineering， Jiangnan University， Wu 214122， China；3. Jiangsu Innovative Packaging Technology Co. ， Ltd. ， Yangzhou，225600， China）

Abstract

Objective The current research on the CFD-DEM coupled method for material screw conveying typically focuses on operational parameters of large particle materials in the screw conveying process. In contrast, there is less research on the geometric friction coefficients in the screw conveying process of ultrafine powders. In order to improve the conveying efficiency of the screw conveyor and reduce the power consumption and wear of the conveyor, the particle flow state, outlet mass flow rate， conveyor power consumption and wear distribution of ultra-fine calcium carbonate in the horizontal variable diameter and variable distance screw conveyor were investigated under different feed rate, screw shaft speed and geometric friction coefficient.

Methods In this study, we adopt the CFD-DEM coupling method， using fluid dynamics software Fluent and discrete element software EDEM， to explore the gas-solid two-phase flow characteristics of ultrafine calcium carbonate powder in the process of horizontal variable-diameter variable-pitch spiral conveying with different operating parameters and geometric parameters, so as to provide theoretical and technical support for the effective conveying of ultrafine powders, and to provide new perspectives and methodological bases for the engineering applications and scientific researches in the related fields. It also provides a new perspective and methodological basis for engineering applications and scientific research in related fields. In the CFD-DEM gas-solid coupling，the gas phase is regarded as a continuous phase and satisfies the continuity equation and momentum conservation equation, and the turbulence model adopts the RNG k-ε model which is more in line with the complex turbulent flow inside the screw conveyor; the particles are regarded as a discrete phase, and their motion behaviors are described by the Newtonian kinetic equations^［15-17］. The simulation model of horizontal variable diameter and pitch screw conveyor constructed in this paper，its simulation model and specific structure are shown in Figures 1 and 2. A tetrahedral unstructured mesh with high adaptability is chosen to be applied for meshing in this study, as shown in Figure 3. The parameter settings of the simulation experiment are detailed in Table 1.

Results Under identical conditions，an increase in the friction coefficient results in a corresponding increase in the initial particle velocity. As the particles advance, the space between them decreases, causing a more significant increase in the axial velocity and mass flow rate of particles with moderate friction coefficients. The conveyor power increases significantly with an increase in feeding speed and friction coefficient. The impact of the friction coefficient on power consumption is more pronounced at high feed speeds and low speeds than at low feed speeds and high speeds. The area of most severe wear is concentrated at the edge of the spiral shaft and spiral blade at the feed opening.

Conclusion Simply increasing or decreasing the friction coefficient will not improve particle axial velocity and mass flow， but there is a local optimum parameter combination. An appropriate increase in speed can reduce particle density and particle residence time， thereby reducing power consumption and geometric wear.

Keywords：ultrafine calcium carbonate；Computational fluid dynamics；Discrete element method；Screw conveyor；Particle flow

DOI：10.13732/j.issn.1008-5548.2024.03.009