Studies on Transport Properties of Powder Ejector based on Double Venturi Effect

The venturi ejector can form vacuum fields to transport particles due to venturi effect. The transportation performance of powder ejectors based on single- and double-venturi effect and the influence of nozzle position on the transportation performance were respectively investigated by the experimental method and the numerical simulation based on the CFD-DEM coupling method. The present results show the wind speed of the particle inlet increases due to the double-venturi effect, which is beneficial for particles into the injector; the driving force exerting on particles by fluid increases, meaning that particles can be transported to a long distance; the closer the nozzle is to the export, the greater the wind speed of the particle inlet is and the greater the suction force exerting on particles is; the closer the nozzle is to the export, the less the deposition number of particles in the injector is; however, particles can be hindered into the venturi tube if the nozzle is very close to the export. Additionally, in order to reduce the particle deposition, the optimal solution is presented here, namely, the nozzle position away from the export, y∗ = 30 mm.

Introduction

Pneumatic conveying technology has many merits, such as flexible layout, no dust pollution, low operation cost and simple maintenance. Thus, pneumatic conveying technology is widely used to petroleum, chemical, metallurgical, pharmaceutical, food and mineral processing industries. Venturi powder ejector is the gas-solid one based on the venturi effect. Some experimental and numerical studies on the venturi injector were carried out in the past decade in order to understand the transport properties of it.

Researcher conducted experimental and numerical studies of the jet tube based on venturi and analyzed the relationship between the different parameters with experimental and numerical methods. Researcher carried out a series of experimental investigations for both single-phase gas and gas-coal mixture flows through the venturi, and showed that the sharp decreases in static pressure and volumetric loading ratio were observed inside the venturi. Researcher carried out a computational study on the flow behavior for a gas-solid injector by the Eulerian approach, showing that the time average axial particle velocity increases first and then decreases. Researcher investigated behaviors of a two-phase gas-solid venturi with the experimental and numerical methods. Researcher used the discrete element method (DEM) to study the gas-solid injector, and they found that the solid particles distinctly accumulate near the bottom of the left-hand region of the injector due to the solid particles gravity and the gas circumfluence.

The above studies only focused on the ejector with one venturi structure, namely, the single-venturi effect was mentioned in the ejector. In the field of gas flow measurement, the device based on double-effect is widely used to increase the pressure difference and to improve the measuring precision. However, the ejector with the double-venturi effect is not often applied to transport particles. The research object here is the venturi powder ejector based on double-venturi effect. The ejector consists of a nozzle and a whole venturi tube. Both of the nozzle and the venturi tube can generate the venturi effect, and it means that double-venturi effect exists in the ejector. The airflow with a high speed jets from the nozzle of the venturi ejector, which forms the vacuum field due to the venturi effect and forces particles enter into the suction chamber under the influence of gravity and entrainment. Then, particles moves with the airflow.

The Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) coupling method has been successfully employed in complex gas-solid flow systems. Researcher adopted the CFD-DEM method to model the gas-particle two-phase flow, the gas phase was treated as a continuum and modeled with computational fluid dynamics (CFD), particle motion and collisions were simulated with the DEM code. Researcher adopted the CFD-DEM approach to simulate the dense gas-solid flow, DEM was employed to model the granular particle phase and the classical CFD is used to simulate the fluid flow. Researcher presented CFD-DEM simulations of a gas-solid fluidized bed and proposed a new drag model. Researcher developed a new method for validation of the simulation of a gas-solid fluidized bed via CFD-DEM. Researcher applied the CFD-DEM coupled method to simulate the gas-solid flow characteristic within the fibrous media to study the influence of the fiber structure and particle properties on particle deposition and agglomeration in the filtration process.

In this paper, the transport properties of powder ejectors based on single- and double-venturi effect and the influence of nozzle position on the transportation performance were respectively investigated by the experimental method and the numerical simulation based on the CFD-DEM coupling method.

Conclusions

The transportation performance of ejectors based on single- and double-venturi effect were respectively investigated by the experimental method and the numerical simulation based on CFD-DEM coupling method. The present results show the wind speed of particle inlet increases due to double-venturi effect, which is beneficial for particles into the injector. The driving force for particles by the fluid increased, which is beneficial for particles to be transferred to a long distance.