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.     

Experimental study on the separation performance of a novel gas–liquid separator

A novel two-stage dynamic separator called high-gravity cyclone separator (HGCS) has been designed for gas–liquid separation. It is mainly composed of a cyclone chamber and rotary drum. In this study, its performance, including the separation efficiency and pressure drop, is experimentally investigated, and the effects of the operating conditions and drum parameters are evaluated. For droplets with a mean diameter of 7 μm, the results indicate that the optimal gas inlet velocity and high-gravity factor are 12 m/s and 59.4, respectively, and the separation efficiency reaches 98 %. The effect of liquid concentration is sensitive to the high-gravity factor. At a liquid concentration of 57 g/m³, the maximum efficiency will be 98.75 % when increasing the high-gravity factor to 85.6. Furthermore, a smaller radial height is preferable when the gas inlet velocity is greater than 12 m/s, and a better separation efficiency can be obtained by increasing the drum length to 190 mm. However, when the length is 235 mm, the efficiency will be poor because of the Kelvin–Helmholtz and Rayleigh–Taylor instabilities. Compared with the predominant roles of gas inlet velocity, drum length and radial height in pressure drop, the effects of liquid concentration and high-gravity factor are small.     

Parametric analysis and optimization of gas-particle flow through axial cyclone separator: A numerical study

The separation of particles through an axial swirl tube cyclone separator is numerically investigated using Eulerian-Lagrangian approach by solving Reynolds Averaged Navier-Stokes equations with RNG K-epsilon model as turbulence closure and Discrete phase modeling (DPM) of particles. The four significant geometric parameters in an axial swirl tube cyclone separator for improving the performance are identified to be blade angle, blade length, blade-tube distance and number of blades. The impact of these parameters on the output parameters of a cyclone separator, is studied through numerical analysis with the open source CFD solver OpenFOAM. A one factor analysis is performed to understand the individual contributions of the parameters and a multiobjective optimisation is done using the Design of Experiments (DoE) approach. The blade length was found to be the most sensitive parameter whereas the blade tube distance had the least effect. Using statistical methods such as Analysis of Variance (ANOVA) and Multi Objective Genetic algorithm (MOGA), a set of Pareto optimum solutions are generated, with an effective trade off between the pressure drop and filtration efficiency. The configurations obtained after optimisation are validated with CFD simulations and found to be having a better overall performance as compared to the conventional configuration.     

He II heat transfer through random packed spheres: Pressure drop

Heat flow induced pressure drop through superfluid helium (He II) contained in porous media is examined. In this experiment, heat was applied to one side of a He II column containing a random pack of uniform size polyethylene spheres. Measured results include steady state pressure drops across the random packs of spheres (nominally 35 μm, 49 μm, and 98 μm diameter) for different heat inputs. Laminar, turbulent, and transition fluid flow regimes are examined. The laminar permeability and equivalent channel shape factor are compared to our past studies of the temperature drop through He II in the same porous media of packed spheres. Results from the pressure drop experiments are more accurate than temperature drop experiments due to reduced measurement errors achieved with the pressure transducer. Turbulent results are fitted to models with empirically derived friction factors. A turbulent model considering only dynamic pressure losses in the normal fluid yields the most consistent friction factors. The addition of the laminar and turbulent heat flow equations into a unifying prediction fits all regimes to within 10%.     

Inverse design optimisation of a novel range hood based on intelligent algorithms and computational fluid dynamics simulations

Our aim in the present study is to increase grease separation by optimising the discharge performance of cooking oil fumes. A novel range hood with an outer cylinder and guide vanes of exhaust (GVE) is proposed. The geometric configuration of the hood is optimized by a reverse design method developed by coupling back propagation neural networks, mind evolutionary algorithms, and computational fluid mechanics. The primary objective of the range hood is to maximise the exhaust airflow rate with good grease separation. At the optimised conditions, the inlet and outlet blade angles are 80° and 176°, respectively, while the heights of the blade and guide vane are 0.180 and 0.245 m, respectively. The optimal number of blades and guide vanes are 29 and 7, respectively, while the optimal diffuser diameter is 0.340 m. The proposed range hood exhibits excellent performance of grease particle separation compared to multi-blade centrifugal fans with volutes. In addition, the outer cylinder and GVE of the range hood exhibit a large separation efficiency for particles in the size range of 1–4 μm, while impeller blades mainly separate grease particles in the size range of 4–10 μm.     

Gas-solid separation performance and structure optimization in 3D printed guide vane cyclone separator

Low separation efficiency and large pressure drop are two common problems of cyclones. In this paper, a 3D printed guide vane cyclone separator was designed to study the separation efficiency, turbulent kinetic energy, and particle movement of particle group by experiment and simulation. The results shown that the tangential velocity was the major influence of separating. The bottom of the exhaust pipe was the main region of gas–solid separation and pressure drop. The separation efficiency and pressure drop were positively correlated with the inlet velocity and the particle radius of the fluid. The distribution of turbulent kinetic energy that leaded to the pressure drop loss was concentrated on the inlet of the exhaust pipe. The swirl has external and internal two directions. The optimized cyclone has a longer and narrower blade flow path to obtain higher separation efficiency, especially at low inlet velocity.     

Investigation on separation performance and structural optimization of a two-stage series cyclone using CPFD and RSM

Cyclones are generally operated in series when the efficiency of a single cyclone is not sufficient for the process. This study firstly used computational particle fluid dynamics (CPFD) to simulate the gas-solid two-phase flow characteristics in a two-stage series cyclone separator. The separation efficiency and distribution of energy consumption was interpreted by analyzing particle distribution characteristics. Secondly, the structure of the two-stage cyclone separator was optimized via response surface methodology (RSM) to make up for the disadvantage that the distribution of the separation load was non-uniform. The results showed that the grade efficiency for 3 μm of the first-stage cyclone separator was increased from 45.408% to 59.932% compared to the original model. The pressure drop of the first-stage cyclone separator is about 2.147 kPa while the second-stage cyclone separator is about 2.774 kPa. It can be seen that the overall optimized two-stage cyclone separator has the advantages of high efficiency, low energy consumption and load-balanced separation performance.     

Pressure drop data and prediction method for enhanced external boiling tube bundles with R-134a and R-236fa

The pressure drops of external flow over enhanced tube bundles were experimentally obtained at both adiabatic and diabatic conditions using R-134a and R-236fa as test fluids. The tests were carried out at saturation temperatures of 5 and 15 °C, mass fluxes from 4 to 40 kg m⁻² s⁻¹, heat fluxes from 15 to 70 kW m⁻² and inlet vapour qualities ranging from 10% to 90%. The frictional pressure drop was found to be primarily a function of mass flux and vapour quality. After comparisons were made with prediction methods in literature a new pressure drop prediction method was proposed for adiabatic and diabatic conditions. The proposed method is based on local measurements (4 and 8 tube rows) and flow conditions (evaluated per tube pitch) and the prediction method is well adapted to local incremental implementation for flooded evaporator design.     

Effect of micro-grooves on the two-phase pressure drop of CO2 in a mini-channel tube

The pressure drop characteristics of CO₂ have been experimentally investigated for a mini-channel tube with and without micro rectangular grooves. The multiple mini-channels have an inner diameter of 0.8 mm and the grooves have a rectangular cross section (0.1 × 0.2 mm). The pressure drop was measured for a saturated liquid phase and two-phase. Using the hydraulic diameter, the pressure drop in the grooved mini-channel can be successfully estimated with the correlations used for smooth channels. Because of a smaller hydraulic diameter, the pressure drop of the grooved channel was found to be about 1.3 times and 1.1–1.45 times greater than that of the smooth channel, for liquid and two-phase, respectively. The experimental results were compared with widely used two-phase pressure drop models. Most of the models showed the mean absolute error of 17–35% for the smooth channel and 13–32% for the grooved channel.     

Effect of lubricating oil on cooling heat transfer of supercritical carbon dioxide

In this research, the cooling heat transfer coefficient and pressure drop of supercritical CO₂ with PAG-type lubricating oil entrained were experimentally investigated. The inner diameter of the test tubes ranged from 1 to 6 mm. The experiments were conducted at lubricating oil concentrations from 0 to 5%, pressures from 8 to 10 MPa, mass fluxes from 200 to 1200 kg m⁻² s⁻¹, and heat fluxes from 12 to 24 kW m⁻².In comparison to the oil-free condition, when lubricating oil entrainment occurred, the heat transfer coefficient decreased and the pressure drop increased. The maximum reduction in the heat transfer coefficients—about 75%—occurred in the vicinity of the pseudocritical temperature. The influence of oil was significant for a small tube diameter and a large oil concentration. From visual observation, it was confirmed that this degradation in the heat transfer was due to the formation of an oil-rich layer along the inner wall of the test tube. However, when the oil concentration exceeded 3%, no further degradation in the heat transfer coefficient could be confirmed, which implies that the oil flowing along with CO₂ in the bulk region does not influence the heat transfer coefficient and the pressure drops significantly. For a large tube at a lower mass flux, no significant degradation in the heat transfer coefficient was observed until the oil concentration reached 1%. This is due to the transition of the flow pattern from an annular-dispersed flow to a wavy flow for a large tube, with CO₂ flowing on the upper side and the oil-rich layer on the lower side of the test section.     

Preparation of single-helix carbon microcoils by catalytic CVD process

Three-dimensional (3D) single-helix spring-like carbon microcoils (SH-CMCs) were obtained by the catalytic pyrolysis of acetylene at 800-820 °C over the Fe-Ni alloy catalysts; their growth morphologies and microstructure were examined. The diameter of carbon fiber, from which the carbon nanocoils was formed, was about 0.5 μm, the coil diameter was about 1-2 μm, and the coil pitch was about the same with the coil diameter. The SH-CMCs were generally grown by a double-directional growth mode.     

Hydrodynamic instability of a suspension of spherical particles through a branching network of circular tubes

A numerical method is presented for computing the unsteady flow of a monodisperse suspension of spherical particles through a branching network of circular tubes. The particle motion and interparticle spacing in each tube are computed by integrating in time a one-dimensional convection equation using a finite-difference method. The particle fraction entering a descendent tube at a divergent bifurcation is related to the local and instantaneous flow rates through a partitioning law proposed by Klitzman and Johnson involving a dimensionless exponent, q ≥ 1. When q = 1, the particle stream is divided in proportion to the flow rate; as q → ∞, the particles are channeled into the tube with the highest flow rate. The simulations reveal that when the network involves two or more generations, a supercritical Hopf bifurcation occurs at a critical value of q, yielding spontaneous, self-sustained oscillations in the segment flow rates, pressure drop across the network, and particle spacing in each tube. A phase diagram is presented to establish conditions for unsteady flow. As found recently for blood flow in a capillary network, oscillations can be induced for a given network tree order by decreasing the ratio of the tube diameter from one generation to the next or by decreasing the diameter of the terminal segments. The instability is more prominent for rigid than deformable particles, such as drops, bubbles, and cells, due to strong lubrication forces between the tightly fitting particles and tube walls. Variations in the local particle spacing, therefore, have a more significant effect on the effective viscosity of the suspension in each tube and pressure drop required to drive a specified flow rate.     

Research on wet-type swirl dust collection technology and its application in underground excavation tunnels

Wet-type dust collectors are widely used in underground excavation tunnels to control dust pollution. Nozzles and filter screens easily blocked by deposited scale and sticky dust, however, are usually a challenging problem for traditional wet-type dust collectors. This increases the cleaning workload and reduces the service life of the equipment. To address this issue, a wet-type swirl dust collection method without using spray nozzles and filter screens is proposed, and a novel wet-type swirl dust collector is designed. Experiments and field application of the wet-type swirl dust collector were carried out. Experimental results showed that the optimum water intake of the dust collector was 1.0 m³/h at 1480 r/min^?1 impeller speed; the dust suppression efficiency of the dust with particles size less than 75 μm was 93%, and that of dust with particles size of 180–250 μm was 95.2%. The field application in China's Tongqing Mine indicated that the respirable dust at the roadheader driver was reduced to 6.9 mg/m³, with a dust removal rate of 92.0%. The wet-type swirl dust collector effectively improves the dust collection efficiency and makes up for the problem of nozzles and filter screens being easily blocked in underground excavation tunnels by the traditional methods.     

Research on Marangoni Condensation Modes for Water–ethanol Mixture Vapors

In this paper the condensation experiments for water–ethanol vapors were carried out at different vapor pressures over a wide range of ethanol concentration. The condensation modes were observed and quantitatively analyzed in order to clarify the condensation phenomenon and dropwise condensation mechanisms. The cycle time of dropwise condensation, affected by vapor-to-surface temperature difference, ethanol concentration and vapor pressure, was approximate 0.2 s to 2 s. The quantity proportion of drops with the diameter less than 1 mm was more than 70% in all drops for all mixture vapors. The peak values of the maximum departing diameters increased with the ethanol vapor concentration, and were weakly affected by the vapor pressure, and the values were about 1.5 mm to 5 mm. The rivulet condensation mode was usually observed as a transition state appeared when the drop mode changed to film mode. The maximum distance between rivulets was sensitive to the ethanol vapor concentrations and little dependent on the vapor-to-surface temperature difference.     

Performance evaluation of a new micro gas cyclone using simulation and experimental studies to capture indoor fine particles

The aim of this study was evaluating a micro gas cyclone performance with a body diameter of 10?mm to collect indoor fine particles. The design of a cyclone requires minimizing the pressure drop and maximizing the separation efficiency. Overall and grade efficiencies, pressure drops, and cut sizes have been investigated through a theoretical model, simulation, and experimental studies. The experimental part was conducted using an Electrical Low-Pressure Impactor (ELPI) device to measure particle concentration for flow rates of 10–13.3 (l/min). In order to study the pressure drop and velocity behavior for different flow rates, COMSOL software was utilized. The obtained results from experimental work have met the theoretical and simulation outcomes adequately. It has been confirmed by all the obtained results that by increasing the flow rate and subsequently inlet velocity, the particle collection efficiency and pressure drop increase while the cut size decreases.     

Stokes flow through a periodically constricted tube and the resistance due to a contraction

Summary The Stokes flow through a tube which is periodically constricted is studied by using eigenfunction expansions and matching. Both streamlines and pressure drops are computed. It is found that if straight sections of a tube are long enough, the total pressure drop is a sum of Poiseuille pressure drops and the excess pressure drops due to the diameter changes.     

Experimental study of turbulent single-phase flow and heat transfer inside a micro-finned tube

Single-phase heat transfer and pressure drop characteristics of a commercially available internally micro-finned tube with a nominal outside diameter of 7.94 mm were studied. Experiments were conducted in a double pipe heat exchanger with water as the cooling as well as the heating fluid for six sets of runs. The pressure drop data were collected under isothermal conditions. Data were taken for turbulent flow with 3300 ≤ Re ≤ 22,500 and 2.9 ≤ Pr ≤ 4.7. The heat transfer data were correlated by a Dittus–Boelter type correlation, while the pressure drop data were correlated by a Blasius type correlation. The correlation predicted values for both the Nusselt number and the friction factors were compared with other studies. It was found that the Nusselt numbers obtained from the present correlation fall in the middle region between the Copetti et al. and the Gnielinski smooth tube correlation predicted Nusselt number values. For pressure drop results, the present correlation predicted friction factors values were nearly double that of the Blasius smooth tube correlation predicted friction factors. It was also found that the rough tube Gnielinski and Haaland correlations can be used as a good approximation to predict the finned tube Nusselt number and ffriction factor, respectively, in the tested Reynolds number range.     

Characteristics of an artificial graphite anode material for rapid charging: manufactured with different coke particle sizes

An artificial graphite anode material (10–15 μm) is produced using coke at two sizes (10–15 μm, 2–5 μm) and the electrochemical properties are compared and discussed. We produce and measure an artificial graphite anode material using coke with a particle size of 10–15 μm, limited lithium ion insertion–desorption pathways, increased migration pathways, and low-speed charge–discharge characteristics. When a block is manufactured using coke at a particle size of 2–5 μm and an anode material is created with a particle size of 10–15 μm, voids capable of storing lithium ions between the coke particles form inside the anode material. These spaces are utilized and the capacity was measured. In addition, the lithium ion insertion-deintercalation path and lithium ion diffusion distance are controlled and the high-speed discharge properties were measured (78.3%) at low temperatures (5C/0.1C, ? 10 °C). At the same time, the high specific surface area due to the small size of the coke was controlled by the binder pitch used in the block, leading to excellent initial efficiency performance.

     

The best screw shape for fine zinc oxide particles feeding

One of the most important requirements of particles feeding is a very homogeneous mass flow of fine particles. Screw feeders are among equipment used to feed particles in many industries. In this study, the performance of four single screw feeders with different pitch and blade shape screws has been studied experimentally for steady and stable feeding of fine zinc oxide particles at flow rates corresponding to laboratory scale range (under 10 g/min). The following results were obtained from this investigation: (I) the sticking problem of fine particles in angular pitch screw was solved by changing the pitch shape to circular; (II) the distribution of the fluctuations and their intensity in mass flow rates also lessen by using the circular pitch and a thin blade screw in place of the circular pitch and a thick blade screw. Also for both feeders, the feeding was often interrupted in low flow rates, but it will be disappeared by increasing the flow rate. Furthermore, the results of experiments show that the performance of the circular pitch and a thin blade screw feeder was better than other screw feeders and able to both swirl and mix the particles with different characteristics and reduce the mean aggregate size of the particle size distribution (PSD) when transmitting the zinc oxide particles.     

Toward a carbon nanotube anode gas-filled radiation detector

A prototype gas-filled proportional counter (PC) based on micro-scale tungsten wire and carbon fiber, and nano-scale carbon nanotube (CNT) anodes was built and tested with a ⁹⁰Sr source. Tungsten anodes of 500 μm down to 4 μm diameter were used to observe the gradual decrease in operating voltage for the proportional region with a decreasing anode diameter. The 40 nm diameter CNTs anodes ranged in length from 35 to 105 μm. The absolute detection efficiency was measured at ∼10⁻⁶%. An electrostatic computer model was used to predict the resulting electric field associated with a single CNT in the coaxial configuration. For a single anode coaxial design the model predicted that the electric field was insufficient for secondary ionizations which contributed to a low amplitude signal and that the small volume of the ionization region resulted in the low absolute detection efficiency. To overcome the problems of low absolute detection efficiency and operational issues with the single anode, CNT arrays were investigated. Electrostatic modeling of 100 nm×40 μm long CNTs in an array with a 50 μm pitch conducted for a parallel plate configuration indicated that each anode functioned independently.