Mechanism of the Absent Air Column in Three Products Hydrocyclone Screen (TPHS): Experiment and Simulation

Abstract

Three products hyrdrocyclone screen (TPHS) has been proposed for particle separation based on size. In TPHS, a cylindrical screen was embedded in a conventional hydrocyclone (CH) to combine the centrifugal classification and screening to particle separation based on size. The industrial application of TPHS indicates its better device performance than CH. Although, the earlier studies reveal some common understanding for TPHS, the information of the absent air column remains unknown. Hence, the combination of physical experiment and numerical simulation was considered involving a 75 mm TPHS for this knowledge gap. First, both the computational fluid dynamics (CFD) simulation with Reynolds stress mode and the physical experiment with a high-definition camera illustrate the development process details of a flow field in TPHS. That is, the water was imported along the tangential inlet into TPHS; then under the effects of the feed chamber wall and gravity, the liquid phase spiraled downward until the cylindrical screen passed through the sieve; as the liquid moved to the spigot, it could be discharged in time due to the small underflow port, thus the volume fraction of air rapidly reduced from 1 to 0; subsequently the water filled the TPHS and the absent air column could be observed. Furthermore, the distribution comparisons of air volume fraction and static pressure show that TPHS displayed the absent air core with the negative static pressure in the center region along the z-axis, while CH displayed the opposite features. In addition, despite the different inlet velocity, TPHS consistently presented the vanished air column which could be ascribed to the fact that the present cylindrical screen resulted in positive static pressure distribution inside TPHS.

Computational Modeling of Flow Characteristics in Three Products Hydrocyclone Screen

“…Our earlier work exhibits that TPHS has a higher radial velocity and a lower tangential velocity than CH, which can help fine particles to pass through the screen [14]. The following study revealed that due to the unformed negative pressure zone near outlets, the absent air column in TPHS can be observed to reduce the energy consumption [16]. The prior studies reveal some common comprehensions for TPHS; however, the details of flow characteristics including the pressure distribution and turbulent features remain unknown.…”

“…In addition, the fluid behavior near the wall region was modeled using the stand wall function, shown as follows [16]:…”

“…In view of our previous work [14,16], the combination of PIV test and CFD simulation has been used to comprehensively verify the above-mentioned numerical methods consisting of geometric modeling, numerical models, and solution conditions (see Section 2 for details). Thus, as a series of studies, to simplify the verification process, the water split was adopted to verify the simulation results.…”

“…In addition, the static pressure near each outlet was smallest and negative, which means that the air reflux occurred here. However, the reflux was too weak to form the air column [16].…”

Multiphase Flow Characteristics in the Classification Process of a Novel Wide Neck Thickener: Experiment and Simulation

“…In this study, the size of the WNT assembly in CFD simulation is consistent with that in the experiment (Figure ). The combination of the VOF and the RSM , was used to describe the fluid flow in the WNT. The VOF model serves to characterize the liquid–gas two-phase fluid using water and air in the WNT, as shown in eqs –. 1 ρ normalq [ ∂ ∂t false( α normalq ρ normalq false) + ∇ · false( α normalq ρ normalq u normalq → false) ] = prefix∑ normalp = 1 n ( m pq • − m qp • ) ∑ normalq = 1 n α normalq = 1 ∂ ∂ t ( ρ v⃗ ) + ∇ · ( ρ v⃗ v⃗ ) = prefix− ∇ p + μ ( ∇ v⃗ …”