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Numerical flow calculations were carried out at various axial positions of a gas cyclone separator for industrial applications. Due to the nature of cyclone flows, which exhibit highly curved streamlines and anisotropic turbulence, we used the advanced turbulence model of Large Eddy Simulation (LES). The application of LES reveals better agreement...
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It is very important to improve the cyclone separator separation efficiency for fine particles. On the basis of the Reynolds stress model (RSM), a new two-stage cyclone separation device is modeled and the model is simulated under six kinds of air volumetric flow rate conditions. The two-stage cyclone separator was then tested in the laboratory and...
Citations
... Only the drag force F d , pressure gradient force F p and lift force F l are considered in this study. The virtual mass force, basset force, Magnus force, and the Saffman force [51,52] are neglected in the calculation. The latter two forces are members of the lift force family. ...
Micro-particle manipulation, based solely on the Dean drag force, has begun to be advocated for with the goal of lowering the pumping pressure and simplifying the complexity of the coupling effects of the inertial lift force and the Dean drag force, thus reducing the difficulty of theoretically predicting particle motion. We employed the CFD-DEM two-way coupling method in this work to quantitatively study the lateral (z in axis) motion of particles (7–10 μm), in square or half-circle segment serpentine microchannels, that was only reliant on Dean drag with the blockage ratio dDh= 0.04 (the inertial lift effects show at dDh>0.07). In the square-segment serpentine channel, under the conditions of single-side-wall sheath flow and sedimentation, we discovered that the particles exhibit a twist-type lateral trajectory around each turn, with the larger particles always twisting in the opposite direction of the smaller particles, as a result of the four-grid-pattern distribution of the lateral velocity values at each turn. The large and small particles are separated at the channel’s exit at Re = 56.7, De = 17.8, indicating the likelihood of separation only due to the Dean drag. This separation efficiency decreases as Re and De decreases. The lateral position and velocity values of the particles oscillate, as time passes, due to the twist trajectory, with the oscillation amplitude increasing as Re or De decreases and deflecting toward the inner side of z. In the cases of the two-side-wall-symmetric sheath flow, the particles exhibit only a little lateral deflection, and particle separation is not achieved. The deflection of the oscillation is uncertain and does not change regularly with any physical quantity.
... It offers to map flow structures characterized by high turbulence, vorticity, and anisotropy. At the same time, this turbulence model allows the most accurate estimation of both the efficiency of particle separation and the pressure drop [60][61][62]. In addition, it provides detailed information on flow physics (e.g. ...
... The use of particle-laden turbulent gaseous flows is prevalent in various industrial applications such as coal-fired power plants, circulating fluidised bed reactors, entrained flow gasifiers, cyclone separators, etc. [1][2][3][4]. Recently, there has been a growing interest in incorporating biomass (particularly pulverised) in major power generation systems to minimise fossil fuel usage and encourage carbonneutral low-emission fuel sources [5][6][7][8]. ...
... Small scales are separated from large scales using a filtering technique. Some researchers [45,85,86] consider LES to be more accurate, which is why this technique was used in this study. ...
... The residence time affects the performance of the cyclone as the slower the time the lesser is the efficiency. In fact, roughness of the wall of the chamber, particle density, and inlet velocity are also found to affect the particle residence time [10] . ...
The performance of a cyclone is primarily determined by three key parameters; namely inlet velocity, pressure drop across inlet and outlet, and particle collection efficiency. To achieve optimal design and development cost, it is vital to have an accurate prediction of pressure drop and particle collection efficiency of the cyclone in response to the variation of inlet velocities. The present study focuses on the design of a serial-configured multi-cyclones system that is capable of reducing the particle emission of the flue gas from 4000 mg/Nm 3 to 150 mg/Nm 3 in a palm waste-fueled boiler system. Optimization of inlet velocity on individual cyclones is performed within the serial-configured multi-cyclones system using a combined computational fluid dynamic simulation (CFD) and the Stairmands's high-efficiency cyclone model-based design analysis. To further improve the accuracy of the design analysis and the CFD simulation, the flue gas at the inlet of the serial-configured multi-cyclones system was sampled, and the distribution of particle size was analyzed. It was observed that an inlet velocity of 20 m/s was found to be optimum, which was later used to determine the total number of cyclones in the design of the serial-configured multi-cyclones system. The use of the newly designed outlet ducting of rectangular shape produces the desired pressure gradient with the presence of negative draft along the outlet ducting.
... Derksen and van den Akker (2000) were among the first to simulate the PVC phenomenon by means of LES simulations. The capabilities of LES to simulate the turbulent flow in a cyclone separator have been reported by Shalaby et al. (2005), Derksen (2003), Derksen et al. (2006) and Shalaby et al. (2008). Early simulations (Derksen & van den Akker, 2000) were limited to small scale cyclones at a moderate inlet Reynolds number. ...
... Shalaby et al. compared an LES with Smagorinksy SGS model with Lagrangian particle tracking to experiment. The normalised tangential and axial velocity profiles provided the correct form to experiment and the difference in pressure drop between the numerical model and experiment was around 2% [86]. This flow field was used to track particle trajectories and estimate a separation efficiency curve, which closely resembled the experimentally derived separation curve, with a small systematic error observed with the LES over predicting the separation efficiency. ...
... Due to the wildly varying geometries (the results in Figure 5.8 are not similar cyclones scaled), swirl numbers and operating Reynolds numbers, the velocity profiles would never be expected to match perfectly. Due to the The results of this study are shown compared to the laser doppler anemometry results from Hoekstra for the Stairmand high efficiency cyclone [22] and the "fine" LES model from Shalaby et al. [86]. The geometry of each cyclone varies greatly, with Reynolds numbers and swirl numbers of Re ≈ 34000, 27000 and 700000 and Sw g ≈ 4.6, 6.0 and 3.1 for the current work, Hoekstra's data and Shalaby's data respectively. ...
Small, high-speed cyclones are used in domestic vacuum cleaners to separate sub-micron sized particulates from an air stream using no moving parts. The complex fluid flow within the cyclone is turbulent and highly-swirling, with small sub-micron particles encountering and responding to fluid structures of a wide spatial and temporal range. The process of particle separation in these cyclonic devices is not well-known and accurate numerical prediction of separation efficiency remains a computationally expensive task. In addition to this, particles are known to exchange charge through collisions, in a process known as tribocharging, which can cause smaller particles to agglomerate into larger structures. This thesis aims to develop a computationally inexpensive particle model able to predict the transport of particle charge which is valid in this highly-swirling flow for small particles. Models of particle tribocharging in the literature have only been validated for particles many orders of magnitude larger than those of interest here. Novel experiments were performed where sub-micron particles were aerodynamically focused to impact a metal plate using an aerosol beam. The results validated the physics of charge transfer at these small scales, with an equilibrium level for the voltage on the plate reached which charged analogous to a capacitor charging circuit. These measurements provided estimates of tune-able constants for a simple capacitor-like tribocharging model from the literature. Capturing collisions between particles in a Lagrangian reference frame is prohibitively expensive computationally, therefore an Eulerian particle model was chosen which can deal with collisions efficiently. The Equilibrium Eulerian method for computing the Eulerian particle velocity field for low Stokes number particles was validated in an analytical Taylor-Green flow. This flow field features fluid gradients and strong streamline curvature, with the length and velocity scales matched with the smallest turbulent scales in a representative cyclone. Strengths and weaknesses of the model were assessed in this challenging flow field, with an Eulerian sub-model for the transport of particle charge implemented. A large eddy simulation of a small, high-speed cyclone was performed with high wall resolution. Flow rates and pressure drop were matched to experimental evidence and partially resolved turbulent structures were observed along the cyclone walls. Lagrangian particle tracking provided a separation efficiency which matched experiment except for the smallest 0.1µm particles. Particles were observed travelling in distinct streaky bands by the walls which matched video evidence obtained experimentally. The Eulerian particle model provided an excellent match to the Lagrangian particle result for separation efficiency, with banding of large 1µm particles by the walls able to be captured, matching both the Lagrangian particles and experiment. The transport of charge and resulting electric field in the cyclone showed significant tribocharging occurring at the cone tip of the cyclone and by the walls which is novel. This work is expected to inform future cyclone design to improve the separation efficiency of small particles.
... The maximum difference between numerical results and available experimental data was 2%. The capability of the LES turbulent model to simulate the flow inside the cyclone was demonstrated [7]. ...
In the present study, imperative parameters including centrifugal force, erosion, streamline, strain rate, and wall shear are evaluated in a cyclone separator. The flaw of the cyclone surface due to erosion is an acute problem in the industry. According to the great importance of the centrifugal force on the separation phenomenon, a comprehensive study is conducted. A computational fluid dynamics (CFD) simulation is realized by applying a Reynolds stress turbulence model (RSM), and particle–air interactions were modeled using a discrete phase model (DPM). The result shows a good agreement between the experimental data and CFD simulation on the tangential velocity and pressure drop. The maximum deviation of the validation process is 6.8%. It is found that the centrifugal force within the cyclone is increased with an enhancement in the inlet velocity. The separation efficiency indicates an increase–decrease treatment in various inlet velocities with inlet velocity up to 16 m⋅s−1 but decreases slightly at a velocity of 20 m⋅s−1. The pressure increases proportionally with inlet velocity. The best performance with the highest separation efficiency (99%) and pressure drop (416 Pa) obtains at the inlet velocity of 16 m⋅s−1 and mass flow rate of 0.01 kg⋅s−1. In addition, the maximum erosion rate was created in the entrance and conical part of the cyclone.
... is the moment of inertia, d is the diameter of the particle, and M is the collision torque between particles and the collision torque between the particle and the wall. Particles in solid-liquid two phase flow are subjected to several different forces, 48,49 such as the drag force, the gravity force, the buoyancy force, the pressure gradient force, the virtual mass force, the basset force, the Magnus force, and the Saffman force. The drag force is written as (in one-dimensional form) ...
The solid–liquid two-phase flow with coarse particles is ubiquitous in natural phenomena and engineering practice, which is characterized by coarse particles, high particle concentration, and large particle size distribution. In this work, the numerical models describing two-phase flows are reviewed, which given that the Eulerian–Lagrangian method is applicable in this work. Then, some modified models are proposed for the situation where the conventional Eulerian–Lagrangian method is not applicable to deal with coarse particles. The continuous phase equations of liquid are solved based on the finite volume method. The pressure implicit with splitting of operators algorithm for solving the Navier–Stokes (N–S) equations of the pseudo-single-phase flow, considering phase fraction and momentum exchange source term, is proposed. The discrete coarse particle is tracked in the Lagrangian method. A virtual mass distribution function is proposed for calculating coarse particle volume fraction. A weighted function method relating to the particle size is given for the interpolation between the Eulerian and Lagrangian fields. The barycentric coordinates are introduced into the particle localization. All the modified models are algorithmically implanted in the open-source field operation and manipulation (OpenFOAM) as a new solver named coarse discrete particle method FOAM (CoarseDPMFoam). Subsequently, the applicability of the numerical simulation method is verified by some typical test cases. The proposed numerical simulation method provides new ideas and methods for the mechanism investigation and engineering application of the two-phase flow with coarse particles.
... Some researchers [e.g. [32][33][34] indicate its greatest conformity with experimental data (in comparison to other turbulence models). It is now often applied in research on cyclone separators [e.g. ...
The study explored areas related to the effect of installing an additional element in the axis of the cyclone separator (in the form of a rod with a circular cross-section) on its performance. 30 geometrical variants (the variable parameters included rod diameter and length) were used for this purpose. The research was carried out using three methods – CFD (based on LES and DPM models), experimental research and stereo-PIV. The use of three research methods made it possible to conduct the process of validating the results. The placement of a rod with a circular cross-section on the axis of the cyclone separator significantly improved its performance (overall separation efficiency, Stk50 and Eu). The most beneficial variant led to an increase in the overall separation efficiency by 8.2% and a reduction in Stk50 by 25.5%. In the case of a pressure drop (expressed as Eu), all variants generated a lower value of Eu than the base variant - the maximum reduction observed was 23.9% (as compared to the base model). Additionally, to comprehensively study the effect of using an additional element on the flow field, the mean and fluctuating velocity and pressure fields were analyzed for individual variants and compared with the standard geometry. Furthermore, it was observed that the use of a rod stabilized the flow in the region confined to the inner vortex, increased the symmetry of the flow, and improved the performance of cyclone separators.
