Short-circuit Flow Research Articles

Mechanistic study and structural optimization for the improvement of flow field in cyclone annular space with bypass flow

The inefficiency of cyclone separation for fine particulate matter is attributed to the presence of longitudinal circulating flow and short-circuit flow in the annular space. To enhance cyclone performance, a novel cyclone design called enhanced cyclone with split flow (ECSF) has been developed, which effectively suppresses circulating flow, short-circuit flow, and eccentric circulation through bypass flow and underflow. The mechanism of bypass flow on improving the annular space’s flow field is investigated using the Reynolds stress model and discrete phase model, along with an examination of the impact of annular space height. Simulation results demonstrate that bypass flow can directly counteract vertical circulation in the annular space by creating a gas partition near the vortex finder inlet to block short-circuiting. This suppression effect on both vertical circulation and short-circuiting increases with higher bypass flow ratios. Furthermore, while the presence of an annular space limits ECSF performance optimization, its elimination simplifies structure by removing the vortex finder while maximizing separation efficiency. When no annular space exists (height = 0 mm), ECSF achieves highest separation efficiencies for 10 μm and 2.5 μm particles at approximately 96 % and 83 %, respectively; energy consumption is also minimized at only 0.94 kPa. These findings lay a foundation for future application research on ECSF.

Strengthened oil-water separation by swirl vane hydrocyclone based on short-circuit flow regulation

Hydrocyclones make it possible to separate oil/water efficiently. Short-circuit flow (SCF), which is a local secondary vortex in hydrocyclones, significantly restricts efficient separation. This study proposes a novel swirl vane hydrocyclone to regulate the trajectory of the SCF to reduce the SCF rate. The separation process in the hydrocyclone field is calculated using computational fluid dynamics coupled with the population balance modeling. The strengthened separation mechanism by the swirl vane is revealed, and the response of structural parameters, such as the angle, numbers, and width of the swirl vane, to the SCF rate and separation efficiency is investigated using the response surface optimization method. The results show that the swirl vane structure prevents the direct generation of SCF, strengthens the outward migration of the heavy-phase droplets, and reduces the probability of droplet breakage. The optimal structural parameters of the swirl vane are a swirl vane angle of 31°, vane number of 6 pcs, and vane width of 2 mm, which has the lowest SCF rate of 1.62 %. The separation efficiency increases by 21.53 %, and the SCF rate decreases by 85.33 % compared with a conventional hydrocyclone. This study provides theoretical guidance and data support for SCF regulation and the development of oil-water separation hydrocyclone.

Physical and Numerical Study on Right Side and Front Side Gas Blowing at Walls in a Single‐Strand Tundish

The compromise between inclusions removal by small bubbles and proper agitation of fluid flow in tundish by gas blown is challenging. The single‐strand tundish without flow control devices (bare tundish) is used to study the effects of side‐wall gas blowing on the flow field. The water model, particle image velocity measurement and computational fluid dynamics simulation are used to study bubble behavior, fluid flow field, and tracer transport. A large horse shoe vortex and a short circuit flow at the bottom are formed in the bare tundish. Gas blowing at the outlet‐side wall of the tundish creates multiple vortices in the right‐side region, with blowing rate and position greatly influencing the surface flow within the tundish. Gas blowing at the front‐side wall creates a large spiral vortex, agitating the fluid in the tundish and improving the flow field. Increasing the blowing rate strengthens the vortex in the right region, but raising the blowing position affects surface flow and creates a counterclockwise flow toward the shroud. In all schemes, gas blowing at a low position on the front‐side wall with a small gas flowrate is the optimized scheme which shows the smallest dead volume and enhances surface flow.

Numerical calculation on the short-circuit flow rate in a gas cyclone

Short-circuit flow rate is a crucial indicator in assessing the separation performance of cyclone separators. The existing literature lacks a comprehensive exploration of how both structural and operating parameters affect this rate. Previous studies produced inconsistent conclusions, and a calculation formula for short-circuit flow rate is absent. Therefore, this paper proposes a novel method for calculating short-circuit flow rate and analyzes it within cyclone separators under different inlet area coefficients KA, dimensionless vortex finder diameters Der, and inlet velocities Vi using response surface methodology. The findings reveal a significant negative correlation between short-circuit flow rate and KA, while positive correlations with Der and Vi are observed. The calculation formula is derived using response surface methodology. The paper concludes by analyzing the influence mechanisms of KA, Der, and Vi on short-circuit flow rate in the separator, aiming to provide valuable insights for the structural optimization of cyclones in engineering applications.

Numerical simulation investigating the impact of regulated underflow rate on the performance of a cyclone with split flow

A novel cyclone design called enhanced cyclone with split flow (ECSF) incorporates bypass flow and underflow to eliminate or suppress localized secondary flow observed in conventional cyclones. The present study aims to investigate the mechanism of ECSF in suppressing localized secondary flow and explore methods for regulating the bottom flow rate. The turbulent characteristics within the ECSF are obtained using Reynolds stress model, while the trajectory of particles is predicted using discrete phase model to derive the separation performance. The accuracy of the simulation model has been validated through experimental verification. The results demonstrated that the full separation efficiency of ECSF for PM10 and PM2.5 remained above 90 % and 70 %, respectively. Moreover, it exhibited an increasing trend with the rise in the full split ratio, eventually stabilizing at approximately 95 % and 77 %, correspondingly, when the full split ratio reached 20 %. The bypass flow and underflow effectively eliminated or suppressed the upper ash ring and processing vortex core (PVC) phenomenon, respectively. However, the exacerbation of the short-circuit flow phenomenon hindered further improvement in separation efficiency beyond a full diversion ratio of 20 %. When the full split ratio is relatively small, particles may accumulate in the discharge pipe, which can be resolved by introducing auxiliary airflow; however, it is crucial to ensure that the flow rate of auxiliary flow does not exceed 14.29 % of that of feed flow to avoid compromising the separation efficiency. Furthermore, the split flow induces an additional reversed vortex within the ECSF, which extends from the overflow pipe to conical section. Its structural characteristics are influenced by both back pressure of discharge outlet and diameter of underflow pipe. To ensure optimal performance of the ECSF, it is recommended that the underflow pipe diameter should not be smaller than that of the outlet in conical section.

Study of the performance and flow field of a new spiral-roof cyclone separator

This paper addresses deficiencies in the separating efficiency of conventional spiral-roof cyclone separators compared to flat-roof cyclone separators. A novel design is proposed, adding spiral guide vanes into the spiral-roof cyclone separator's annular space. The performance of the new spiral-roof cyclone separator is evaluated through cold-model experiments and numerical simulations and compared with conventional flat-roof and spiral-roof counterparts. The results demonstrate a more than 20% reduction in pressure drop compared to the flat-roof cyclone. The new design exhibits 3%–5% higher efficiency than the conventional spiral-roof cyclone and surpasses the flat-roof cyclone by 2%–3%. The numerical simulations investigate tangential velocity distribution, airflow residence time, short-circuit flow air volume, particles carried away by short-circuit flow, and vortex core stability. The findings confirm the new spiral-roof cyclone as a low-pressure and highly efficient separator with promising practical applications in diverse gas-solid separation operations.

Intensification of low-grade phosphate ore purification using a hydrocyclone with venturi-style inlet

The accumulation of large quantities of low-grade phosphate ore throughout the year occupies land and pollutes the environment. Addressing the challenge of purifying this ore to produce high-grade phosphate is essential for alleviating the shortage of phosphorus resources, making it a pressing research topic. Herein, we propose a hydrocyclone with a venturi-style inlet that combines multiple morphologies to purify low-grade phosphate ore. This innovative design addresses issues with conventional hydrocyclones by reducing short-circuit flow and eliminating circulation flow. Additionally, the new hydrocyclone tackles the overflow entrainment problem of large-density P particles and reduces the possibility of lower-density Si-Mg particles escaping through the underflow pipe, leading to intensified separation performance. The hydrodynamic multiphase flow field characteristics of different hydrocyclone were investigated via CFD simulation to elaborate the reason for the performance intensification. The venturi-style inlet architecture improved the tangential velocity and enhanced the spiral flow field, expanding the length and range of the locus of zero vertical velocity (LZVV) in the primary separation area. This designed hydrocyclone could purify low-grade phosphate ore at lower expenditure and higher performance, with separation efficiency increased from 76% to 92% and precision promoted from 70% to 87% compared to conventional one. This work presented a cheap and efficient technology for purifying low-grade phosphate ore and demonstrated comprehensive potential for the recycling of mineral resources.

Numerical investigation of hydrocyclone inlet configurations for improving separation performance

Optimizing hydrocyclone inlet design is regarded as an effective strategy to mitigate the adverse effect of particle misplacement and improves separation efficiency. This work proposes innovative hydrocyclone designs based on spiral inlet with a specific spiral angle and tangential inlet with a specific curvature radius. The new designs are evaluated and compared with a standard design using a validated two–fluid model. The separation performance, flow characteristics and volume fraction distribution are considered in the evaluation. An optimum spiral inlet design is identified, with an inlet spiral angle of 90° under the current conditions. This inlet design evidently improves the tangential velocity, strengthens the stability of the air core and reduces short-circuit flows. Additionally, the new inlets help improve the volume fraction of coarse particles in the region near the spigot, mitigating the misplacement of coarse and fine particles. This study offers a new perspective for improving hydrocyclone flows and performance.

Study on the effect of a new type of deswirler on the flow field and performance of a cyclone separator

Cyclone separators have a wide range of applications in industry. Recovery of the pressure drop in the vortex finder was achieved by installing a deswirler, which also reduces efficiency to a certain extent. The current work is focused on the optimization of the flow field in the vortex finder, and a new hollow-type deswirler was proposed. The airflow and particle flow were simulated by using the Reynolds Stress Model (RSM) and the Discrete Phase Model (DPM), and performance tests were conducted on different structures. The results show that, the efficiency of the separator is increased and the pressure drop is decreased after the hollow-type deswirler is installed in the vortex finder. Compared with a separator equipped with a traditional deswirler, the efficiency can be increased by 0.94% by adding a hollow-type deswirler. The gas at the center of the hollow-type deswirler backflows, increasing the rotational kinetic energy in the vortex finder. The separation capacity of the main separation zone is maintained while the pressure drop is reduced, and the back-mixing escape of particles is effectively reduced by lowering the vortex core swing and short-circuit flow. The results of this study can provide a reference for the performance enhancement design of cyclone separators.

Investigation on the formation mechanism and flow characteristics of liquid carry-over in gas–liquid cyclone separator

The liquid carry-over (LCO) phenomenon brings about the performance deterioration of gas–liquid cyclone separator and an increase in pressure drop. However, the formation mechanism of the LCO and its manifestation in the separator cylinder and the overflow pipe have not been fully understood. This work investigated the flow process of the LCO by visual observation and quantitative measurement of the overflow liquid flow rate and liquid holdup. The transient gas–liquid flow feature in the overflow pipe and spatiotemporal relationship between the separator inlet and outlet were characterized by time-frequency analysis and wavelet coherence of liquid holdup, respectively. The results showed that the size of air core determines two kinds of sources of the LCO, including the surrounding liquid direct entry into the overflow pipe and the film short-circuit flow beneath the top wall of the separator. When the air core can continuously wrap up the overflow inlet, the film short-circuit flow became the primary source of the LCO, which was embodied in the significant reduction of the overflow liquid flow rate. Three flow patterns, namely, slug flow, churn flow, and annular flow, were classified in the overflow pipe. The inlet intermittent flow of the separator led to the distribution of churn flow expanding toward higher gas velocity, which was interpreted by flow pattern transition theory. The time-averaged overflow liquid holdup was well predicted by drift-flux model. The results are beneficial to the proposal of inhibition methods of the LCO and structure design of the separator.

Study of the short-circuit flow and circulation flow’s impact on separation performance of cyclone separator with volute-helical inlet

Short-circuit flow and circulation flow are important secondary flows in a cyclone, which have a negative impact on separation performance. This work proposed new cyclones (VH cyclone), incorporating volute-helical inlets with five tilt angles based on the characteristics of short-circuit flow and circulation flow, in order to enhance separation efficiency without a significant pressure drop compared to a Lapple-type cyclone with a tangential inlet (TI cyclone). The separation performance and Euler number of six cyclones are obtained by experiments and analytical models. The simulation is utilized to explore characteristics of short-circuit flow and circulation flow, with a focus on the impact of these flow patterns on particle motion. The result shows that proportion of short-circuit flow increases initially and then decreases with the increase of the tilt angle, while circulation flow is continually weakened. The cutoff diameter increases first and then decreases while the trend of Euler number is opposite for new cyclones. By considering both separation performance and Euler number, VH4 cyclone (Tilt angle of volute-helical inlet is 6.5°) exhibits optimal performance, with a cutoff diameter 20.41% lower than that of TI cyclone, while their Euler numbers are similar.

Experimental investigation on flow splitting for the elimination of localized secondary flow in cyclones and enhancement of their performance

The limitation of cyclone performance is attributed to the presence of localized secondary flow, including longitudinal circulation, short circuit flow and eccentric circulation. The present study proposes an enhanced cyclone with split flow (ECSF) to effectively suppress the local secondary flow in cyclones. An experimental setup was constructed to evaluate the performance of ECSF under various operating conditions. The results of the experiment demonstrate that the separation efficiency of ECSF surpasses that of Lapple cyclone due to the synergistic effect of split flows in both the by-pass flow and underflow. When the feed velocity is 13 m/s, the ECSF exhibits a reduced separation efficiency of 89.8% for 10 μm silica particles, which surpasses that of the Lapple cyclone by 10.6%. The ECSF achieves its maximum total and reduced separation efficiencies at a feed velocity of 27 m/s, reaching values of 96.3% and 95.7%, respectively. Compared to the Lapple cyclone, the ECSF demonstrates an extended range of operational capabilities with respect to feed velocity. By maintaining a constant total split ratio in ECSF while increasing the proportion of by-pass flow, it is possible to improve its separation efficiency without augmenting overall energy consumption. The findings of this investigation offer valuable insights for enhancing the dust removal efficiency of cyclones.

The Secondary Flows in a Cyclone Separator: A Review

A cyclone separator holds significant importance as the primary gas–solid separation apparatus in the industrial sector. Cyclone separators operate based on a fundamental principle, primarily harnessing the centrifugal force produced by the rotation of air in order to segregate solid particles from the gas stream and then collect them. In addition to the main vortex in the flow field, there are a number of secondary flows, which significantly impact the aggregation of fine particles and contribute to the heightened energy consumption. This paper provides a summary of the three secondary flows in a cyclone separator. These include the recirculation flow in the annular space, which is greatly influenced by the inlet particle concentration. Additionally, the short-circuit flow occurs beneath the vortex finder as a result of the collision between the incoming flow and the rotating flow. Furthermore, the eccentric circumfluence is defined as the deviation of the rotation center caused by the interaction between the upward and downward flows near the discharge. This paper aims to establish a theoretical framework to investigate the flow pattern tracking and the mitigation of secondary flows in order to enhance the operational efficiency of cyclone separators.

Drivers to allow widespread adoption of ATES systems: a reflection on 40 years experience in The Netherlands

Drivers to allow widespread adoption of ATES systems: a reflection on 40 years experience in The Netherlands

Vortex finder diameter and depth effects on the separation performance of hydrocyclone

This study performed the numerical simulation of the vortex finder (VF) diameter and depth effects on the separation performance of the hydrocyclone-type devices for multiphase fluid separation, namely the static pressure, pressure drop, split ratio, short-circuit flow, velocity field, and classification accuracy. The static pressure, pressure drop, and split ratio were found to be negatively related to the VF diameter. As the VF diameter increased from 0.26D2 to 0.56D2, the maximum static pressure dropped from 94483.56 to 26067.86 Pa, and the pressure drop was reduced from 93336.50 to 26408.69 Pa. Meanwhile, the steepness index increased with the VF diameter in a particular range. The results strongly indicated that an increased VF diameter led to reduced energy consumption and improved separation accuracy of the hydrocyclone, decreasing the tangential velocity, increasing the short-circuit flow, and disrupting the symmetry of the locus of zero vertical velocity (LZVV). The effects of the VF depth on the separation performance were as follows: with increasing VF depth, short-circuit flow and split ratio decreased, the steepness index increased within a specific range, and the symmetry of the LZVV gradually improved. This implies that increased VF depths can help enhance the separation performance of the hydrocyclone but excessively large VF depths would deteriorate it.

Numerical Simulation of Gas-Solid Two-Phase Heat Transfer in a Kaolin Cyclone Cooling System

The kaolin suspension calcination technology is currently gaining attention as a new process of calcining kaolin. In this paper, the cooling system of the kaolin suspension calcination process designed by CBMI Construction Co., Ltd. is simulated using ANSYS Fluent software to analyze the velocity field and temperature field of the gas–solid two-phase flow using the Eulerian model. A compiled UDF (User-Defined Function) is used to simulate the transfer of mass and heat from the downcomer tube to the different elements. The gas, coming from the gas outlet of the cyclone, enters the next level twin-cylinder cyclone in a spiral state. The results show that the airflow in the cyclone consists of an external spiral flow from the top to the bottom and an internal spiral flow from the bottom to the top. During the downward movement of the airflow, the outer spiral flow is continuously transformed into an inner cyclonic flow. The part of the airflow that rotates close to the inner cylinder is likely to become a ‘short circuit flow’, which largely affects the separation efficiency and cooling effect of the cyclone. There is evident temperature deviation and flow deviation in the twin-cylinder cyclone, which is primarily due to the high cooling air volume and high rotation of air flow coming from the gas outlet of the previous level’s cyclone. The rotation of the air flow is the main cause of the bias temperature and bias flow phenomenon in the twin-cylinder cyclone.

CFD supported scale up of perfusion bioreactors in biopharma

The robust scale up of perfusion systems requires comparable conditions over all scales to ensure equivalent cell culture performance. As cells in continuous processes circulate outside the bioreactor, performance losses may arise if jet flow and stirring cause a direct connection between perfusion feed and return. Computational fluid dynamics can be used to identify such short circuit flows, assess mixing efficiencies, and eventually adapt the perfusion setup. This study investigates the scale up from a 2 L glass bioreactor to 100 L and 500 L disposable pilot scale systems. Highly resolved Lattice Boltzmann Large Eddy simulations were performed in single phase and mixing efficiencies (Emix) furthermore experimentally validated in the 2 L system. This evaluation gives insight into the flow pattern, the mixing behavior and information on cell residence time inside the bioreactors. No geometric adaptations in the pilot scale systems were necessary as Emix was greater than 90% for all conditions tested. Two different setups were evaluated in 2 L scale where the direction of flow was changed, yielding a difference in mixing efficiency of 10%. Nevertheless, since Emix was confirmed to be >90% also for both 2 L setups and the determined mixing times were in a similar range for all scales, the 2 L system was deemed to be a suitable scale down model. The results demonstrate how computational fluid dynamic models can be used for rational process design of intensified production processes in the biopharmaceutical industry.

Numerical modeling of grade mixing and inclusion entrapment in eight strand billet tundish

This study aims to investigate the effect of tundish level control on the change in element content and inclusion amount in molten steel during the low tundish-level steel grade transition. Based on multiphase flow, mass transfer, and discrete phase, a three-dimensional transient numerical simulation of the tundish was established in Ansys Fluent. The model uses moving mesh refinement technology to obtain clear steel and slag interface with a small number of meshes. The numerical simulation results were verified through industrial experiments and physical simulations. The results indicate that when the tundish is at a low level, strand 3 becomes a short-circuit flow, and the number of inclusions in strand 3 is approximately four times that in strand 1. If the old grade density is higher than that of the new grade, the unqualified length of the element content in the transition billet is 10.2 m shorter than that in the opposite order. When the filling speed of the tundish is three times the normal flow rate, the length of the transition billet with an unqualified number of inclusions is 7.1 m less than that when the filling speed is 2 times the normal flow rate. In addition, at the initial stage of the low tundish level steel grade transition, the minimum amount of inclusions in the transition billet can be reduced to 40% of the average amount of inclusions in the old grade; however, the maximum number of inclusions in the transition billet increase by a factor of 2.5 times the average number of inclusions in the new grade at the end stage of the low tundish-level steel grade transition. It can be observed that the inclusions in the initial stage of the low tundish-level steel grade transition have less effect on the quality of the old grades; however, they have a greater effect on the new grades in the final stage of the low tundish-level steel grade transition.

Effects of helical fins on the performance of a cyclone separator: A numerical study

This study aimed to investigate the separation performance of a cyclone separator after reshaping its cylindrical body by installing the helical triangular fins. A numerical simulation based on Fluent was adopted to perform an orthogonal test to optimise the structure of the cyclone separator with helical triangular fins. Three structural parameters of the helical triangular fins were selected as optimisation variables: base width, fin size, and fin pitch, and their influences on the evaluation indices of the cut-off diameter were investigated. The optimal combination scheme was determined by range analysis, and the cyclone separator performances before and after optimisation were compared and analysed. The significant influence of the structural parameters on the cut-off diameter was in descending order as the fin pitch, fin size, and base width. For particles with diameter of 0.1, 0.5, 1, 2, and 3 μm, the separation efficiency of the cyclone separator with optimized helical triangular fins increased by 7.4 %, 15.9 %, 20.1 %, 10.9 % and 14.8 % respectively. Moreover, the cut-off diameter of the finned cyclone separator is reduced by 30.7 %, while the pressure drop is only increased by 6.6 %. The short circuit flow and back-mixing were alleviated, thereby considerably enhancing the stability of the flow field. Therefore, the finned cyclone separator was found to play a critical role in increasing the separation of fine particulate matter.

Numerical simulation and experimental validation for investigating the novel hydraulicbarrier-hydrocyclone in industrial beneficiation process

In the face of the dwindling reserves of high-quality phosphate rock resources in the world, beneficiation and purification of low-grade phosphate ore is a possible solution to alleviate the growing scarcity for strategic phosphorus resources. Hydrocyclone is one of the common equipment for solid–solid separation in liquid medium, which is suitable for mineral beneficiation processing. The study investigated the industrial beneficiation of low-grade phosphate ore by novel hydraulicbarrier-hydrocyclone. The results from computational fluid dynamics (CFD) simulation revealed that Semi-through hydraulicbarrier (S-Hb) hydrocyclone had the optimal performance, making short-circuit flow reduced to 7.17% and eliminating fish hook effect, so that the classification efficiency increased by 5% and separation sharpness reached 0.9516. The reasons leading to performance intensification were elaborated in accordance with the optimization and integration of hydrodynamics multiphase flow field by hydraulicbarrier, including the pressure, velocity, turbulent kinetic energy distribution and air core development, as well as streamline analysis, etc. The results from practical industrial experiment indicated that the P2O5 grade was increased to 23.6wt.% from an initial grade of 17.5wt.%, meeting the medium-grade phosphate ore specifications, and the SiO2 content was decreased from 29.0wt.% to 4.2wt.%, meanwhile, the proportional error was 0.74% about cutting size compared to simulation results, indicating excellent consistency. The investigation offered an economically viable route to beneficiate the low-grade phosphate ore, cogently supporting sustainable development of phosphorus resources in chemical engineering.