CFD investigation of body geometry effects on oil droplet-gas cyclone performance

CFD–DEM simulation of the gas–solid flow in a cyclone separator

Numerical study of vortex eccentricity in a gas cyclone

Gas cyclones are widely used in industries to separate solids from gas stream. It is well known that solids loading will significantly affect the performance of gas cyclones. In this work, a numerical study of the gas‐solid flow in a gas cyclone at different solid loadings is carried out by means of Combined Continuum and Discrete Method (CCDM). In the CCDM, the motion of discrete particles is obtained by Discrete Element Method (DEM) which applies Newton’s laws of motion to every particle and the flow of continuum fluid is described by the local averaged Navier‐Stokes equations that can be solved by the traditional Computational Fluid Dynamics (CFD). The model successfully generated the strands flow pattern of solids that is typical in gas cyclones. The simulated pressure drop under different solid loadings agreed with experimental measurement quantitatively. It is predicted that the reaction force of solids on gas phase caused the decrease of the tangential velocity of gas phase and thus the decrease of pressure drop.

This study aims to determine the effect of a square cyclone body shape on the performance of a square cyclone separator. To achieve this goal, four square cyclone separators with square lengths 0, 1, 2, and 3 times the hydraulic diameter of the cyclone body were considered. The simulation of the gas-solid flow was carried out using the Euler-Lagrange approach, while the gas flow was modeled by Navier–Stokes equations and the Reynolds stress turbulent model (RSTM), and the injected solid particle was solved using the Newton equation. The pressure drop, separation efficiency, and flow pattern were investigated to evaluate the performance of square cyclone separators. The results revealed that the pressure drop and separation efficiency decreased as the relative square length increased. In the case with a lower relative square length, the vortex core penetration is less than that in the other cases, which leads to a decrease in the entrainment phenomena and separation efficiency enhancement. At an inlet velocity of 16 m/s, an increase in the relative square length from 0 to 3 reduced the pressure drop by approximately 35%. At an inlet velocity of 24 m/s and a particle diameter of 8 µm, with an increase in the relative square length from 0 to 3, the efficiency decreased from 88.7 to 77.4%.

Effects of different cylinder roof structures on the vortex of cyclone separators

Data plenitude is the bottleneck for data-driven approaches, including neural networks. In particular, Convolutional Neural Networks (CNNs) require an abundant database of training images to achieve a desired high accuracy. Current techniques employed for boosting small datasets are data augmentation and synthetic data generation, which suffer from computational complexity and imprecision compared to original datasets. In this paper, we intercalate prior knowledge based on spatial relation between images in the third dimension by computing the gradient of subsequent images in the dataset to remove extraneous information and highlight subtle variations between images. The approach is coined “Inverted Cone” because the volume of brain images below the level of the eyes is ordered to form an inverted cone geometry. The application explored in this work is deboning, or brain extraction, in brain magnetic resonance imaging (MRI) scans. The difficulty of obtaining ground truth for this application prevents the ability of obtaining a large quantity of training images to train the CNN. We considered a limited dataset of 23 patients with and without malignant glioblastoma. Deboning was performed by employing an optimized CNN architecture with and without the Inverted Cone processing. The classic CNN without prior knowledge achieved a validation accuracy of 77%, while the Inverted Cone CNN model achieved a validation accuracy of 86% in a dataset of 451 brain MRI slices.

The permeability of coal is a critical parameter in estimating the performance of coal reservoirs. Darcy’s law describes the flow pattern that the permeability has a linear relationship with the flow velocity. However, the stress induced deformation and damage can significantly influence the gas flow pattern and permeability of coal. Coals from Songzao coalfield in Chongqing, southwest China were collected for the study. The gas flow velocities under different injection gas pressures and effective stresses in the intact coal and damaged coal were tested using helium, incorporating the role of gas flow pattern on the permeability of coal. The relationships between the flow velocity and square of gas pressure gradient were discussed, which can help us to investigate the transformation conditions of gas linear flow and gas nonlinear flow in the coal. The results showed that the gas flow in the intact coal existed pseudo-initial flow rate under low effective stress. The low-velocity non-Darcy gas flow gradually occurred and the start-up pressure gradient increased in the coal as the effective stress increased. The gas flow rate in the damaged coal increased nonlinearly as the square of pressure gradient increased under low effective stress. The instability of gas flow caused by high ratio of injection gas pressure over effective stress in the damaged coal contributed to the increase of the gas flow rate. As the effective stress increased, the increase of gas flow rate in coal turned to be linear. The mechanisms of the phenomena were explored according to the experimental results. The permeability of coal was corrected based on the relationships between the flow velocity and square of gas pressure gradient, which showed advantages in accurately estimating the performance of coal reservoirs.

Numerical study of gas–solid flow in a cyclone separator

ABSTRACTA new method for the direct observation of two-dimensional gas flow patterns in a CVD reactor has been developed by combining a laser scanning technique with generating micron-sized TiO2 particles. With this specially developed technology, the size of generated TiO2 particles are quite uniform, and of high density by the use of hydrolysis of Ti-alkoxide in the ceramic honeycomb at the top inlet of the model chamber. In this system, vertical cross sections of the gas flow patterns can be visualized by illuminated TiO2 particles in a He-Ne laser light sheet. Using this technique, detailed gas flow patterns can be clearly identified in the reaction chamber. Changes in the gas flow patterns with the various growth conditions, such as gas flow rate and pressure, have been measured. In this presentation, GaAs thin film growth by the MOCVD method will be reported as an example.This gas flow visualization method could be a useful tool to identify the mechanism of CVD reactions to give better understanding about carrier gas transport and thin film growth for wide band gap semiconductors such as GaN, a-SiC, SiNx, etc.

Performance improvement of cyclone separator by integrated compact bends

In pressure-controlled ventilation (PCV), a decelerating gas flow pattern occurs during inspiration and expiration. In contrast, flow-controlled ventilation (FCV) guarantees a continuous gas flow throughout the entire ventilation cycle where the inspiration and expiration phases are simply performed by a change of gas flow direction. The aim of this trial was to highlight the effects of different flow patterns on respiratory variables and gas exchange. Anesthetized pigs were ventilated with either FCV or PCV for 1 h and thereafter for 30 min each in a crossover comparison. Both ventilation modes were set with a peak pressure of 15 cmH2O, positive end-expiratory pressure of 5 cmH2O, a respiratory rate of 20/min, and a fraction of inspired oxygen at 0.3. All respiratory variables were collected every 15 min. Tidal volume and respiratory minute volume were significantly lower in FCV (n = 5) compared with PCV (n = 5) animals [4.6 vs. 6.6, MD -2.0 (95% CI -2.6 to -1.4) mL/kg; P < 0.001 and 7.3 vs. 9.5, MD -2.2 (95% CI -3.3 to -1.0) L/min; P = 0.006]. Notwithstanding these differences, CO2-removal as well as oxygenation was not inferior in FCV compared with PCV. Mechanical ventilation with identical ventilator settings resulted in lower tidal volumes and consecutive minute volume in FCV compared with PCV. This finding can be explained physically by the continuous gas flow pattern in FCV that necessitates a lower alveolar pressure amplitude. Interestingly, gas exchange was comparable in both groups, which is suggestive of improved ventilation efficiency at a continuous gas flow pattern.NEW & NOTEWORTHY This study examined the effects of a continuous (flow-controlled ventilation, FCV) vs. decelerating (pressure-controlled ventilation, PCV) gas flow pattern during mechanical ventilation. It was shown that FCV necessitates a lower alveolar pressure amplitude leading to reduced applied tidal volumes and consequently minute volume. Notwithstanding these differences, CO2-removal as well as oxygenation was not inferior in FCV compared with PCV, which is suggestive of improved gas exchange efficiency at a continuous gas flow pattern.

Simulation of Gas Flow Pattern and Separation Efficiency in Cyclone with Conventional Single and Spiral Double Inlet Configuration

A study into the influence of the speed of the incoming dust flow and a size of the inlet of a cyclone on its performance. The structure of the flow field has been investigated by calculations made using the Reynolds Stress Turbulence Model (MTNR) for a cyclone separator. The findings show that the maximum tangential velocity in the cyclone decreases when the entry size to the cyclone increases. No acceleration occurs within the cyclone body (maximum tangential velocity is almost constant throughout the cyclone). Increased size of the cyclone inlet reduces the drop of pressure. The cyclone's cutoff diameter increases with the cyclone's inlet size (therefore, the overall efficiency of the cyclone decreases due to a low vortex strength). The effect of altering the entry’s width is more significant than its height, especially for the cut-off diameter. The influence of simulations of velocity fluctuation on prediction of collection efficiency of cyclone separators has been numerically investigated using MTNR and large eddy simulation (MBV). The Euler-Lagrange modeling approach was used by Solidworks Flow Simulation to simulate 3D non-stationary turbulent gas and solid flows in the high-efficiency Starmand cyclone. The simulation results have been compared with available reference data. An analysis of the findings shows that the MTNR and MBV could adequately predict the mean flow field. The study shows that the (MBV) performs well in predicting fluctuating flow field and capture efficiency for each particle size. The results show that prediction of collection efficiency, especially for fine particles, is greatly influenced by simulation of velocity fluctuations in cyclones.

Cyclone separators are widely used in gas-particle separation in the fields of both industrial application and aerosol sampling. For a clear description of the the mechanisms of gas-particle separation and pressure drop, it is essential to evaluate the flow pattern in the cyclone separator. The gas flow patterns in two types of cyclone separators with conventional and symmetrical inlet geometries are analyzed and compared.

Study of the gas-particle radial supersonic jet in the cold spraying