Air Core Diameter Research Articles

Influence mechanism of hydrocyclone main diameter on separation performance

The main diameter of hydrocyclone (HC) has significant effects on separation performance. However, the differences of flow field characteristics within different HCs have not been understood well yet, which makes it impossible to grasp the influence mechanism of the main diameter on the separation performance. Through the study of the migration trajectories of particles, it is found that the greater the diameter and the finer the particles, the more particles escape from the overflow outlet. The relationships between the longest residence time and the HC main diameter for particles with 10 and 15 μm were, respectively, clarified. The high-speed video and particle image velocimetry experiments were performed and found although the main diameter of a large-HC (LHC) is twice that of a mini-HC (MHC), its air-core diameter is much larger than twice that of MHC, which is not beneficial for separations. The axial velocity around the central axis area in LHC is higher than that of the MHC, which helps separate low-density discrete phases from the overflow outlet at a faster speed but not for the separations of high-density discrete phases from the underflow outlet. The angle of the locus of zero vertical velocity in MHC is larger than that of LHC, which is anticipated to enhance the separation efficiency for the high-density discrete phase. This study first reveals the influence mechanism of the HC main diameter on its separation performance from the perspective of the flow field characteristics, which would hopefully provide significant references for the applications of HCs.

Flow dynamics of a liquid–liquid bi-swirl injector

This work presents detailed two-phase flow simulations of liquid–liquid bi-swirl injectors for engineering applications. Liquid oxygen and kerosene are delivered into the injector, which is initially filled with air. A parametric study is conducted on the recess length of the inner tube to investigate its effect on the flow dynamics and spray pattern. The simulations are performed using an improved multiphase flow solver in OpenFOAM, which employs the volume-of-fluid approach for interface tracking and the large-eddy simulation technique for turbulence modeling. Detailed flow dynamics of both fuel and oxidizer, along with their spray patterns, are examined systematically. A comprehensive account is provided on the impact of the recess length on flow evolution, including the film thickness, air core diameter, and spray cone angle. Spectral and dynamic mode decomposition analyses are performed to further examine the flow structures and dynamics. Results from this study can be effectively used to facilitate the design optimization of injectors for liquid-fueled propulsion systems.

Gravitational Vortex Water Turbine (GVWT) Conical Basin Design: the Effects of Cone Angle and Outlet Diameter on Vortex Characteristics

A Gravitational Vortex Water Turbine (GVWT) seems to be a promising technology for low-head hydropower applications. The basin of GVWT plays an important role in the vortex formation as well as its performance. This study aims to analyze the effect of basin design on vortex characteristics in the GVWT. A conical basin is chosen due to the good quality of the vortex. The lab-scale experiment and Computational Fluid Dynamic (CFD) simulation was conducted to gain deeper insight into the effect of cone angle (θ) and basin diameter ratio (d/D) on the vortex characteristic, including air-core diameter, vortex height, and tangential velocity. Both parameters play a major role in regulating the water level and tangential velocity in the basin. The current work shows that the smaller the basin diameter ratio (d/D), the higher the vortex height, leading to a decrease in tangential velocity and vortex strength as the kinetic head is converted to a potential head. Moreover, basin parameters, including the vortex height and tangential velocity, fluctuate due to the variation of cone angle. According to this work, the conical basin with a large cone angle of 20° and a small d/D of 0.2 is suggested, since it produces a vortex with height tangential velocity and vortex height.

Study of Internal Flow in Open-End and Closed Pressure-Swirl Atomizers with Variation of Geometrical Parameters

This study delves into the examination of internal flow characteristics within closed (with nozzles) and open-end pressure-swirl atomizers (lacking nozzles). The number of inlet channels “n” and the opening parameter “C” were manipulated in this study, as they play a pivotal role in understanding various atomizer attributes, such as uniformity of the air-core diameter, the discharge coefficient, spray angle, and more, all of which hold significance in the design of bipropellant atomizers for liquid rocket engines (LREs). To validate our findings, six distinct hexahedral meshes were generated using Ansys ICEM software 2023. Subsequently, we employed Ansys Fluent, considering the RNG k-ε turbulence model and the VOF (volume-of-fluid) multiphase model to identify the liquid–gas interface, to aid in analyzing the uniformity of the air core, which is directly linked to the even distribution of mass, the mixing ratio of propellants, combustion efficiency, and stability. The results indicate that the uniformity of the air core is not solely contingent on an increase in parameter “n” but is also influenced by an increase in the parameter “C”. It is worth noting that the key dimensions of these six atomizers were determined using a mathematical model based on Abramovich and Kliachko theories.

The Effect of Blade Distances on the Performance of Double-Stage Gravitational Water Vortex Turbine

A gravitational water vortex turbine is a turbine that generates electricity by rotating its runner under vortex flow through basins. The present experimental study investigated the effect of blade distance through a double-stage vortex turbine. The study used rotational speeds, torque, and efficiency to describe the vortex turbine performance under different applied discharges and blade distances. Each blade has a different profile, such as Savonius and a curved blade profile. Each blade independently generates its performance because they constructed under different hollow and solid shafts. The results illustrated that an increased distance between blades produces the best performance with a higher flow rate. A discharge of 9.5×10-3m3/s and a distance of 150 mm has a total mechanical power of 28,51 W with an efficiency of 28.92%. The longest distance between the stage 1 (S1) and stage 2 (S2) turbine causes the smaller air core diameter. It has given an advantage in their performances on rotational speeds, mechanical power, torque, and efficiency generated by the Gravitational Water Vortex Turbine (GWVT).

A note of caution on numerical scheme selection: Evidence from cyclone separator CFD simulations with appropriate near-wall grid sizes

In this paper two things are done. (i) The appropriate numerical scheme set for computational fluid dynamics (CFD) simulations of cyclone separators with various vortex-finder-to-cone-tip diameter ratios (D⁎) has been achieved by comparing the mean flow patterns and performances simulated by two previously proposed numerical scheme sets. The predicted results revealed that the CFD simulations of different cyclone separator designs require the third-order accuracy scheme and proper near-wall grid sizes to preserve flow similarity, especially for cyclone separators with D⁎ < 1. Therefore, the present research alerts caution concerning the lower-order numerical scheme for cyclone separator CFD simulation. (ii) The present CFD work confirms that the near-wall grid size estimation method originally developed for gas cyclones is a possible method for estimating near-wall grid sizes for hydrocyclone with air core diameter (Da) ≤ 0.4Dv. In addition, the capabilities of pressure-strain sub-models for cyclone separator CFD simulations were preliminarily discussed.

CFD study on the influences of size distribution and density of magnetite ore particles on hydrocyclone classification process

Due to the presence of gangue minerals in iron ore, the feed of hydrocyclone in the grinding circuit is a mixture of particles with different densities and sizes. In this study, numerical experiments are performed to investigate the classification characteristics of magnetite ore particles. A significant difference in recovery to underflow of intermediate-sized particles is found due to density effect. By increasing the feed d0.5, the cut size, Ep value, solid concentration and yield of underflow present an increasing trend. Density effect coefficient is proposed and its extreme values are obtained for intermediate-sized particles. Q/M ratio has smaller influences on classification than feed d0.5. The air core diameter, turbulence intensity, equilibrium radius and particle trajectory are analyzed to reveal the migration mechanism of the magnetite and gangue particles under different feed d0.5 and Q/M ratios. This work clarifies the intrinsic classification characteristic of magnetite ore particles.

Light transmission mechanisms in a SMF-capillary fiber-SMF structure and its application to bi-directional liquid level measurement.

Capillary fiber (CF) has been extensively investigated in a singlemode fiber (SMF)-CF-SMF (SCS) sensing structure since multiple light guiding mechanisms can be easily excited by simply tuning the air core diameter (cladding diameter) and length of the CF. Understanding the light guiding principles in an SCS structure is essential for improved implementation of a CF based fiber sensor. In this work, light guiding principles in a relatively large air core diameter (≥ 20 µm) and long length of CF (> 1 mm) are investigated theoretically and experimentally. It is found that both multimode interference (MMI) and Anti-Resonant Reflecting Optical Waveguide (ARROW) light guiding mechanisms are excited in the SCS structure in the transmission configuration. However, MMI dips are not observed in the spectrum for the air core diameters of CF smaller than 50 µm in the experiment due to large transmission loss in small air core CFs. Further experimental results demonstrate that a CF with a bigger air core diameter shows a higher sensitivity to curvature, and the highest sensitivity of -16.15 nm/m-1 is achieved when an CF-100 was used. In addition, a SMF-CF-20-CF-30-SMF (SCCS) structure is proposed for high sensitivity bi-direction liquid level measurement for the first time, to the best of our knowledge. Two types of ARROW dips (Dip-20 and Dip-30) are simultaneously excited in transmission, hence both liquid level and liquid flow direction can be detected by tracing the dip strength changes of Dip-20 and Dip-30, respectively.

Enhancement on the separation precision of fine particles in a novel hydrocyclone with the vorticose involute-line diversion inlet head

ABSTRACT Inlet head, as the multi-phase flow transport channel, imposes significant effects on the separation performance of a hydrocyclone. Ultra-fine powder is an inevitable product in the mining processing industry and sets extremely high requirements on product quality. Because of favorable water-carrying capability, fine particles can be hardly separated in a conventional feeding body. In order to satisfy the separation requirements of fine particles, this study designed a vorticose involute-line diversion inlet head that can effectively enhance the separation precision of fine particles and improve the product quality. Meanwhile, this study selected four hydrocyclones with different feeding structures for comparative analysis, and explored the isobaric pressure, velocity field, air core, and separation performance of the hydrocyclones through numerical simulation. The numerical analysis results showed that the effective pressure range in the novel hydrocyclone expands and the energy loss drops. The air core diameter is the lowest, the separation space of fine particles is the greatest, and the separation time is the longest, which can achieve a more thorough separation with the highest cutting capability and separation precision of fine particles. Finally, after an optimum design, the separation performance achieves the optimal at a wrap angle of 180°.

High sensitivity liquid level sensor for microfluidic applications using a hollow core fiber structure

Liquid level measurement in microfluidics is challenging, where a sensor with ultra-high sensitivity but miniature in nature is demanded. In this paper, we propose for the first time a microsized fiber sensor structure in both diameter and length for microfluidics applications, which is capable of sub-micrometer scale liquid level measurement. The sensor is simply fabricated by fusion splicing a short section of a hollow core fiber (HCF) between two singlemode fibers (SMFs). HCFs with different air core diameters (10 µm, 20 µm, 30 µm) were investigated and it is found that for a given length of HCF stronger resonant dips were excited in transmission for the HCF with a smaller air core diameter. Thus the HCF structure with an air core diameter of 10 µm (HCF-10) was used for demonstration of high sensitivity liquid level measurement in microfluidics. Simultaneous excitation of both Anti-Resonant Reflecting Optical Waveguide (ARROW) guiding mechanism and Mach-Zehnder interferometer (MZI) in transmission is demonstrated in such an HCF-10 structure when HCF-10 is longer than the critical length. A maximum sensitivity of 0.042 dB/µm (corresponding to a calculated liquid level resolution of ~0.23 µm) was experimentally achieved with an HCF-10 length of ~867 µm, which is three times higher than that of the previous reported to date of the most sensitive fiber optic liquid level sensors based on intensity modulation. In addition, the proposed sensor shows good repeatability of measurement and a very low cross sensitivity to changes in the surrounding refractive index.

Comprehensive Dense Slurry CFD Model for Performance Evaluation of Industrial Hydrocyclones

In most mineral processing industries, hydrocyclone separators are operated at high feed solids content in the comminution circuits. Computational fluid dynamic (CFD) models developed so far are unable to predict the accurate classification behavior at high feed solid loadings. The dense slurry CFD model adopts algebraic slip mixture (ASM) model corrected with shear lift and hindered settling velocity-based drag forces to account for fluid-particle interactions and granular flow options for particle-particle interactions. The slurry rheology is modeled with a fine fraction-corrected Newtonian viscosity model. This model is utilized for running the multiphase simulations in five hydrocyclones (75-381 mm) at different design and operating conditions for the feed solids content varying between 0 and 65% by weight. Turbulence is modeled using the large Eddy simulation (LES) model. The results are analyzed in terms of air core diameter, water split, solid split, cut size, and sharpness of separation. In 75 and 250 mm hydrocyclones, the modified ASM model can predict accurate performance characteristics, including fine and coarse particle misplacement up to 30 wt % feed solids. Slight deviations are observed in the fine fraction recovery for the 50 wt % and higher feed solids content. Further, the same model is tested to predict the roping phenomena in a 381 mm hydrocyclone.

Effects of Wall Roughness on the Separation Performance of Hydrocyclones under Different Inlet Conditions

Wall roughness is a crucial parameter in the manufacture and operation of hydrocyclones but has been underestimated. This study assesses the effects of wall roughness on the separation performance under different inlet conditions using a two-fluid model and an empirical wall roughness model that modify the logarithmic law of the wall. These models are proven to give good predictions for the in-house experiments on a ⌀150 mm hydrocyclone. The results indicate that small roughness is acceptable in use, whereas large roughness can significantly deteriorate the separation performance. The wall roughness mainly affects the pressure–kinetic energy conversion in the boundary layer by decreasing the tangential velocity and increasing the axial and radial velocities. All these changes further affect the air core diameter, the spatial distribution of particles, and finally, the separation results. The equal pressure condition can provide superior separation results with higher capacity than the equal flow rate condition but still cannot eliminate the adverse effects of wall roughness.

Analytical solution for a strong free-surface water vortex describing flow in a full-scale gravitational vortex hydropower system

Strong free-surface water vortices are found throughout industrial hydraulic systems used for water treatment, flow regulation, and energy generation. Previous models using the volumetric flow rate as a model input have generally been semi-empirical, and have tended to have some limitations in terms of the design of practical hydropower systems. In this study, an analytical model of a strong free-surface water vortex was developed. This model only requires the water head and geometric parameters as its inputs and calculates the maximum volumetric flow rate, air-core diameter, and rotational constant. Detailed experimental depth–discharge data from a full-scale gravitational vortex hydropower system, unavailable in the relevant literature, were obtained, and the simulated results showed excellent agreement with the experimental observations. These data could be used to verify similar models using laboratory-scale physical models in order to investigate the scaling effects. In contrast to previous models, this model does not assume a constant average velocity across the vortex radius and allows precise calculation of the resultant velocity vectors. Therefore, this model presents advantages in turbine design for energy generation systems.

Internal flow dynamics of spill-return pressure-swirl atomizers

The sprays produced by spill-return pressure-swirl atomizers are strongly dependent on the nature of the internal fluid dynamics. Several spill-return atomizers were compared in terms of the spatial and temporal behaviour of the internal air-core, liquid sheet thickness and its perturbations. The only difference amongst the test configurations was the geometrical arrangement of the spill-line (SL) orifice through which the liquid was spilled away. The flow field inside the swirl chamber was examined using high-speed imaging with image post processing using an in-house Matlab code and three orthogonal velocity components acquired using Laser Doppler Anemometry. The dimensions of the production atomizers did not allow direct visualization of their internal flow, so a scaled, modular, transparent plexiglass model was used. Its flow characteristics were equivalent to the original atomizer. The refractive index of the atomizer body was matched to the test liquid using a solution of 1-Bromonaphthalene and kerosene fuel type JET A-1. The test conditions were derived from the original atomizer and were limited to inlet port Reynolds numbers, from 700 to 2000 and spill-to-feed ratios, SFR, from 0 to 0.75. An inviscid analysis, originally derived for Simplex atomizers, was modified and applied to the spill-return version. This approach allows a theoretical prediction of the discharge coefficient and air-core diameter dependent solely on SFR. An axially located SL orifice inhibits any internal air-core forming in the swirl chamber. Off-axial SL orifices generate and stabilize the air-core, which leads to the regular formation of a liquid sheet and a high-quality spray. Nevertheless, some configurations changed the breakup nature of the liquid sheet and consequently the spray quality. Moreover, the turn-down ratio of the liquid supply rate and spray stability depend on the distance of the SL orifices from the swirl chamber centreline. The flow energy losses increase with SFR. The outcomes from this analysis allow the optimization of the SL configuration for specific application and extend the classical inviscid analysis.

Effect of Dimensionless Numbers on Air Core Diameter of Pressure-Swirl Atomizer

Air core is an important parameter in pressure swirl atomizer since formation of air core determines the thickness of the discharged liquid sheet and the effective flow area of nozzle discharge. This consequently will affect the coefficient of discharge and the spray angle. This study conducted for the investigation of the relation between dimensionless numbers on the air core diameter. Dimensionless numbers are helpful aid for the quantification of independent parameters involving atomizer design and operating conditions simultaneously. Reynolds number, Re and orifice-to-swirl chamber diameter ratio, N are the dimensionless numbers selected for this study. Despite of the availability of study on the effect of dimensionless numbers on air core diameter, more study requires especially for smaller N. An experimental test-rig was constructed to conduct the performance test of the atomizer. Acquired images were analyzed using image-processing software. It was found that N has more significant effect on the change of air core diameter compared to Re. However, it is observed that at Re = 40000, N = 0.07 produces almost similar air core diameter with N = 0.25 at Re &lt; 20000. In contrast, with N = 0.5, air core diameter produces are larger even at Re &lt; 20000. Hence, it can be concluded that both Re and N are important parameters in characterizing the air core diameter in pressure-swirl atomizer.

High sensitivity property of dual-core photonic crystal fiber temperature sensor based on surface plasmon resonance

In this paper, we design and simulate a dual core photonic crystal fiber (DC-PCF) temperature sensor in terms of wavelength sensitivity. The dual core design of the PCF makes it possible to deposit the gold (plasmonic material) layer and analyte (high temperature coefficient liquid) outside the PCF thus makes the fabrication easier. The sensor performance is demonstrated with the help of Matlab environment as well as the finite element method (FEM). Different loss spectra with the variation of temperature has been analyzed. The computational result shows that a wide range of temperature from 0 °C to 60 °C can be detected to investigate the sensor performance. The designed sensor exhibits flat wavelength sensitivity of 2.25 nm/°C with a sensor resolution of 4.44 × 10−2 for y-polarized light. In order to achieve high sensitivity, the structural parameters such as air hole diameter, pitch, gold thickness and core diameter are optimized. In view of wide detection range of temperature and flat sensitivity, this DC-PCF temperature sensor can be a promising candidate for various applications such as for the real time detection of the temperature of manufacturing industry, medical environment, electric vehicle, transformer oil etc.

Effect of Overflow Pipe on the Internal Flow Fields and Separation Performance of W-Shaped Hydrocyclones

The entrainment of fine particles in underflow of a grinding-classification hydrocyclone can cause ore overgrinding, which will lead to reductions in both metal recovery and ball mill throughput. To address this problem, this paper proposed a W-shaped hydrocyclone that can effectively reduce underflow fine particle entrainment. Experimental tests and numerical simulations were employed to deeply investigate overflow pipe diameter influence on the separation performance and internal flow field of W-shaped hydrocyclones. The effects of overflow pipe diameter on air core shape, velocity field, pressure field, and separation performance were studied. The results revealed that as the diameter of the overflow pipe increased, air core gradually stabilized, and air core diameter gradually increased. The diameter of stabilized air core was approximately 45% to 55% of overflow pipe diameter. As overflow pipe diameter increased, hydrocyclone pressure drop decreased, energy consumption was reduced, the tangential velocity decreased, outer vortex axial velocity did not change significantly, and inner vortex axial velocity gradually increased. At the same time, zero-velocity points gradually moved outward, and the inner vortex region expanded. By the increase of overflow pipe diameter, both the underflow yield and split ratio gradually decreased, the coarse particle content in the overflow product increased, and the fine particle content in the underflow product gradually decreased.

Toward a better understanding of a Tri-Flo separator using prototyping, central composite design (CCD) and CFD simulation

ABSTRACT Recently, a two-stage dynamic dense medium separator, called Tri-Flo, has become more applicable for treating difficult-to-wash coals. In this study, a 70-mm diameter transparent Tri-Flo separator was manufactured using prototyping and the effects of geometrical and operating parameters were investigated. Central composite design (CCD) was used in the experimental phase. The effects of internal tubes diameter, the installation slope, and the internal flow rate on the Tri-Flo performance were analyzed. CFD simulation was also used for better understanding of the flow pattern and interpretation of the experimental results. The results indicated that the air core diameter in both stages of the separator increases with all three variables. It was also found that medium recovery to float product in rougher and cleaner stages increases with unit inclination and internal tubes diameter, while it decreases with medium flow rate. The decrease in the air core size with increasing the feed tube diameter was an outstanding finding in both experiments and simulations. On average, a 16% decrease in the air core diameter was obtained when the feed tube diameter was increased from 23 mm to 26 mm. The results of the CFD simulation showed that there is a meaningful compatibility between the experimental observations and mathematical simulations.

Bragg labeled wavelength calibrates interferometric sensors in hollow core fiber.

A Bragg labeled wavelength (BLW) employed to the sensitivity calibration in an interference pattern has been proposed and experimentally demonstrated. According to the critical condition of Fabry-Perot (FP) interference and the antiresonant (AR) effect, the length of hollow core fiber (HCF) is artificially controlled to form a FP microcavity by collapsed fusion splicing. Dual-spectral features of the BLW and inline multimode interference (IMMI) dominate the transmission spectrum of the collapsed Bragg HCF (BHCF). The location of the BLW remains unchanged once the air-core diameter is selected. Sensing performance is investigated to validate the calibration function of the proposed BHCF. In particular, the temperature sensitivity of the BLW and multimode interference are 12.8pm/°C and 87.1pm/°C, respectively, corresponding to the reference sensitivity induced by the Bragg structure and the measurement sensitivity of the IMMI. All these findings highlight the calibration of HCF-based interferometric sensors in practical applications.

Response of inner flow and spray characteristics of a pressure swirl injector to pressure oscillation in supply system

The present work focused on the response of the two phase flow of a pressure swirl injector to pressure oscillation in supply system. A mechanical pulsator was used to generate pressure oscillation in supply system. The inner flow of the injector and spray were captured by backlit shadowgraph technique and the droplet size was recorded by laser diffraction technique. In addition, image processing and proper orthogonal decomposition were used to analyze the data. The results indicate that the inner flow, spray and droplet size oscillate along with pressure oscillation mainly at the driving frequency. The oscillation of air core was used to characterize the inner flow. The dynamics of air core center and air core diameter was analyzed and the modes of the inner flow were obtained. Then, the way the oscillation propagated inside the nozzle was identified as a long wave manner. When the liquid was emanated from the nozzle, thick film resulted from pressure peak was faster when compared with thin film resulted from the trough of pressure oscillation. This characteristic was found to be responsible for the sudden shrink of the spray, and changed the spray pattern from a hollow cone to a pagoda. Finally, the thick and fast film produced a dense spray and large droplets. The whole paper discussed the response of inner flow and spray characteristics of a pressure swirl injector to pressure oscillation, and revealed the way the pressure oscillation propagated from supply system to spray field.