Design and performance evaluation of vacuum cleaners using cyclone technology

A cyclone technology for a vacuum cleaner—axial inlet flow cyclone and the tangential inlet flow cyclone — to collect dusts efficiently and reduce pressure drop has been studied experimentally. The optimal design factors such as dust collection efficiency, pressure drop, and cut-size being the particle size corresponding to the fractional collection efficiency of 50% were investigated. The particle cut-size decreases with reduced inlet area, body diameter, and vortex finder diameter of the cyclone. The tangential inlet twin-flow cyclone has good performance taking into account the low pressure drop of 350 mmAq and the cut-size of 1.5 μm in mass median diameter at the flow rate of 1 m³/min. A vacuum cleaner using tangential inlet twin-flow cyclone shows the potential to be an effective method for collecting dusts generated in the household.     

Effects of separation space diameter on the performance of a novel reverse flow cyclone

ABSTRACT

A numerical study was carried out to investigate the effect of separation space diameter on the performance of a novel reverse flow tangential inlet cyclone design by using the Eulerian-Lagrangian approach. The design of this cyclone is based on the idea of increasing vortex length and decreasing pressure drop compared with traditional cyclones. This novel cyclone differs from the traditional cyclones with separation space and vortex limiter instead of the conical part. A qualitative numerical study was performed to analyze the effect of separation space diameter on the cyclone performance at different flow rates by evaluating velocity profile, pressure drop, fractional and overall efficiencies. The results show that the collection efficiency of smaller particles increases while pressure drop decreases significantly with the increase in separation space diameter for D₁/D < 0.5.     

A Model for the Prediction of the Collection Efficiency Characteristics of a Small,Cylindrical Aerosol Sampling Cyclone

Velocity data from a previous study were nondimensionalized and used in conjunction with a computer program which solves the equations for particle trajectory to predict the collection efficiency for the cyclone. Results for the prediction of cutpoint at the same Reynolds number as that for which the velocities were measured, both for a large cyclone of 88.9 mm diameter and another geometrically similar at one half the scale, are excellent. The model predicts cutpoints of 10 μm and 5.1 μm for the large and small cyclone, respectively, while the actual cutpoints determined from aerosol tests were 9.9 μm and 5.2 μ m. The efficiency curve generated by the model was steeper (geometric standard deviation of 1.1) than the efficiency curve determined through the aerosol testing (geometric standard deviation of 1.4). A simplification of the Dirgo and Leith equation fitting Barth's design curve is suggested which provides a significantly better fit of the aerosol data (geometric standard deviation of 1.3). At 1.5N _{R Q}, where N _{R Q} = (4pg)/(πμD _c), the error in prediction of the cutpoint in the large cyclone is less than 8% while at 04N _{R Q} the error is less than 2%. Although results are good over a limited range of Reynolds numbers, the model is strictly applicable only for flows which are dynamically similar to those studied here.     

A DIRECT APPROACH TO THE DESIGN OF CYCLONES FOR AEROSOL-MONITORING APPLICATIONS

During the past four decades, many investigators have attempted to discover models to describe the performance of cyclone aerosol selectors. These efforts were in general not successful and resulted in “semi-empirical” relationships of narrow application. The introduction of regulatory size-selection curves for air-monitoring applications means that it is no longer adequate to predict only the median cut point (D₅₀) of a size selector. This further complicates the search for a useful cyclone model. Building on previous work, a completely empirical investigation was devised which has resulted in the development of the “Family” approach to cyclone design, and a method for predicting both the D₅₀ cut point and the shape (or slope) of the selection curve. Three cyclone families have been developed and tested, which cover the current range of requirements for size selective particulate sampling. Although this empirical approach does not advance the physical understanding of cyclone separators, it does provide a practical means to design cyclones for specific applications.     

Investigation of load transfer between the fiber and the matrix in pull-out tests with fibers having different diameters

Single-fiber pull-out tests were used for investigation of the interfacial bond strength or toughness and load transfer between polymeric matrices and glass fibers having different diameters. The interfacial bond strength was well characterized by an ultimate interfacial shear strength (τ_ult) whose values were nearly independent of the fiber diameter. The same experiments were also analyzed by fracture mechanics methods to determine the interfacial toughness (G_ic). The critical energy release rate (G_ic) was a good material property for constant fiber diameter, but G_ic for initiation of debonding typically became smaller as the fiber diameter became larger. It was also possible to measure an effective shear-lag parameter, β, characterizing the load transfer efficiency between the fiber and the matrix. β decreased considerably with the fiber radius; this decrease scaled roughly as expected from elasticity theory. The measured results for β were used to calculate the radius of matrix material surrounding the fiber that was significantly affected by the presence of the fiber. The ratio of this radius to the fiber radius (R_m/r _f) was a function of the fiber diameter.     

CFD Study on the Effect of Hydrocyclone Structure on the Separation Efficiency of Fine Particles

Abstract

Effects of geometric structure parameters of 10 mm-diameter hydrocyclones on the particle separation efficiency are studied using computational fluid dynamics (CFD). The fluid velocity profiles and particle trajectories are simulated using RFLOW software with a standard isotropic k-ε turbulent model. The JIS standard CaCO₃-17 particles are adopted as a particulate sample in simulations and experiments. Comparing the simulated results with experimental data, a maximum deviation about 20% in partition curves occurs for 5–10 µm particles. However, fairly good agreements for the cut-size predictions and the fish-hook phenomenon are obtained. The simulated cut-size d ₅₀ is only 2 µm larger than that measured in experiments, while the value of d ₁₀₀ can be accurately predicted. An increase in overflow diameter or a decrease in underflow diameter leads to a lower separation efficiency but a clearer separation sharpness due to lower fluid underflow rate. A short-and-wide rectangular inlet is more efficient for particle separation than a tall-and-narrow one. An inclined inlet conduit plays an inessential role on the efficiency improvement but gains a 2 µm reduction in d ₁₀₀. Comparing the simulated results, the hydrocyclone used in the experiments of this study exhibits a higher separation sharpness than the Rietema type and a higher efficiency than the Bradley type based on the same operation capacity and hydrocyclone size.     

Influence of extrusion,stretching and poling on the structural and piezoelectric properties of poly (vinylidene fluoride‐hexafluoropropylene) copolymer films

Three types of poly (vinylidene fluoride‐hexafluoropropylene) (PVDF–HFP) copolymer films were prepared by extrusion, stretching as well as simultaneously stretching and static electric field poling (SSSEP), respectively, and measured by the differential scanning calorimetric, wide angle X‐ray diffraction, fourier transformation infrared‐attenuated total reflection, and Dynamic mechanical analysis. The experimental results showed that the films prepared by stretching and SSSEP have higher crystallinity and β phase than by extrusion. SSSEP improved the chain orientation enormously both in crystalline and amorphous regions, resulting in the highest storage modulus. Because of the lower β phase content, the extruded films exhibited the lowest piezoelectric coefficient d₃₃. For the stretched and SSSEP films, although the β phase content was similar, the d₃₃ was distinct because of the different potential energy for the rotation of the dipoles. In addition, the SSSEP films gave the maximum d₃₃ (24 pC/N), higher than the other PVDF–HFP copolymer films that have been reported. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 858–862, 2007     

Performance Characteristics of the Aerosol Collectors of the Autonomous Pathogen Detection System (APDS)

This research analyzes the physical performance characteristics of the aerosol collectors of the autonomous pathogen detection system (APDS) that was recently developed by the Lawrence Livermore National Laboratory. The APDS is capable of continuous and fully autonomous monitoring for multiple airborne threat organisms and can be used as part of a monitoring network for urban areas and major public gatherings. The system has already been successfully tested with airborne Bacillus anthracis and Yersinia pestis biowarfare agents. The APDS aerosol collection system consists of a PM-style cap to remove large particles and a low-pressure drop virtual impactor preconcentrator positioned in front of a wetted-wall cyclone. The aerosol collectors operate at flow rates as high as 3750 l/min and collect airborne particles into 4 ml of liquid for subsequent detection. In our tests we determined the overall collection efficiency of the system by measuring the difference between inlet and outlet particle concentrations. The tests were performed with polydisperse oleic acid and monodisperse polystyrene latex (PSL) particles (0.6–3.1 µ m), and for three values of the major air flow rates in the virtual impactor (1760, 2530, and 3300 l/min), two values of the product, or cyclone, flow rates (375 and 450 l/min), and two different volumes of collection liquid (4 and 6 ml). We found that the cutoff size (d₅₀ ) of the entire collection system varied from 1.5 to 2.0 µ m when collecting PSL particles, with 3.1 µ m PSL particles being collected with efficiency of approximately 85%. When collecting oleic acid particles the d₅₀ of the entire system varied from 1.1 to 1.6 µ m. The concentration rates of the aerosol collection system were found to increase with increasing overall collection flow rate and approached one million per minute at the highest tested flowrates. Such high concentrating rates and high air sample volumes make the APDS collection system highly suitable for detecting low concentrations of airborne pathogens.     

Drop Size Distribution in a Standard Twin‐Impeller Batch Mixer at High Dispersed‐Phase Volume Fraction

The preparation of concentrated aqueous silicone oil emulsions has been investigated with particular attention to the effect of the dispersed‐phase volume fraction ? from 0.01 to 0.5 for a wide range of oil viscosities (50 to 1000 cSt). Oil was added on the top surface of a 6‐L vessel. Drop size distribution and Sauter mean diameter, d₃₂, measurements were carried out over 24 h mixing time. Emulsification was found to be relatively sensitive to the oil phase viscosity, μ_d, for the same ? yielding a narrower drop size distribution for low oil viscosity (50 cSt) and a wider drop size distribution for the highly viscous oil (1000 cSt). For the same ?, increasing μ_d resulted in increasing d₃₂. The equilibrium d₃₂ was found to be well correlated to the viscosity number by for ? = 0.5. For the same oil viscosity, d₃₂ was found to increase with increasing ?. A multiregression of d₃₂ with both ? and V_i for various silicone oil viscosity grades was successfully correlated by with a regression coefficient (R²) of 0.975. This shows a very weak dependence of the equilibrium d₃₂ on ?.     

PREDICTION OF DROP SIZE IN PULSED PERFORATED-PLATE EXTRACTION COLUMNS

A single expression for the prediction of drop size in the mixer-settler, transition and emulsion regimes of operation in pulsed perforated-plate liquid/liquid extraction columns is presented. Analysis of 326 published drop size measurements both with and without mass transfer for 16 liquid/liquid systems from 12 different data sources show that the Sauter mean drop diameter, d ₃₂, in the dispersion is given in terms of column geometry, operating conditions and physical properties of the phases by:

in which ρ_* and σ _* are the density and surface tension of water at 20°C and α and 1 are the fractional plate free area and compartment height respectively. This equation predicts the drop diameter with an average deviation of 11·3% which is much better than the average errors obtained using other available correlations.     

Numerical simulation of the effects of the design feature of a cyclone and the inlet flow velocity on the separation of CO2 particles from a CO2-COF2 mixture

In synthesizing COF₂ from CO, a considerable amount of CO₂ is produced. A method of solidifying CO₂ at low temperature and separating CO₂ particles from the COF₂ gas using a cyclone was designed and the separation efficiency according to the cyclone feature was studied. Optimal sizing and operation conditions of the cyclone were investigated by reviewing the flow velocity profile and the particle trajectory using a numerical analysis with computational fluid dynamics (CFD). The effects of the inlet flow velocity and the ratio of the cyclone diameter to the cone length (D/L) on the recovery efficiency were estimated. Results revealed that the separation efficiency increases with an increase in the ratio of D/L and a decrease in the cyclone size. The recovery efficiency of CO₂ increases with the increase in the inlet flow velocity. Based on these results, we could propose a concept and methodology to design the optimal features and sizing of a cyclone suitable for separating solid CO₂ from gaseous COF₂ at low temperature.     

Wall slip and compressibility like effects in capillary rheometer tests on complex polymer systems

Abstract

Using an appropriate set of capillary dies, the applicability of the Mooney wall slip method has been investigated with several filled compounds. Inconsistent results were obtained, for example, ‘negative’ slip velocity. With respect to data measured in practical capillary rheometry, a model was developed for treating (barrel) pressure data versus die length/diameter ratio at fixed applied apparent shear rate, i.e. the so called Bagley plots. A very simple equation was obtained

P _meas = 2P _ends - 1/β ln [exp (P _ends β) - 4σ_w0 β L/D ]

which yields the wall shear stress at zero pressure σ_w0 , the ends pressure loss P _ends , and a factor β when fitted to experimental data by non-linear regression. Experimental results show that the factor β accounts for both wall slip and compressibility like effects. Negative β values indicate dominating wall slip effects, while positive values demonstrate compressibility like effects. Slip velocity is thus pressure dependent and consequently the combination of wall slip and a pressure dependent viscosity can mask the expected gap dependence in the analysis by Mooney.     

Development of a Sharp-Cut Cyclone for Ambient Aerosol Monitoring Applications

Aerosol samplers for ambient PM2.5 are required to possess a steep aerodynamic particle size selection curve, i.e., a 'sharp cut' at 2.5 mu m aerodynamic diameter. For long-term and continuous PM monitors the selector system also requires low maintenance and the ability to operate at high loadings. While a sharp cut is easier to achieve with an impactor-based selector, the other require ments are more easily met with a cyclone. Four alternative PM2.5 selectors were tested against these criteria: two were pre-existing commercial designs and two were novel cyclone prototypes. The main aim of the work was to assess the characteristics of the selectors when clean and under various loading conditions. The aerodynamic size-selection characteristics of the PM2.5 selectors were tested before and after loading with dust, under both laboratory and field conditions. Aerosol penetration measurements were made using an Aerodynamic Particle Sizer. Many repeat tests were performed on two specimens of the Well Impactor Ninety-Six (WINS), two specimens of a novel Sharp-Cut Cyclone (SCC), one member of the GK cyclone family (GK4.39), and one University Research Glass ware (URG) cyclone. Four loadings of the WINS and SCC were made in the laboratory using a narrow-fraction alumina dust. The penetration curves were measured after each loading. Five cumulative outdoor loadings were made by setting up four PM2.5 samplers, two with the WINS and two with the SCC, in a suburban garden during the summer months. The penetration curves were mea sured at weekly intervals after sampling times ranging from 96 to 132 h. Three further cumulative loadings were tested in a similar experiment in a city-center underground car park. When clean, all three PM2.5 size selectors were shown to have 50%penetration (D₅₀) values close to 2.5 mu m, although the penetration curve shape differs for the three selector designs. Under loading the D₅₀ value for both the WINS and SCC fell, with the decrease being largest for the WINS. With high loadings the SCC D₅₀ fell to 2.35 mu m and the WINS D₅₀ fell to 2.15 mu m. The WINS deviation was large enough to potentially lead to under sampling of PM2.5. The SCC cyclone was seen to provide a sharp cut for ambient air sampling applications that is less affected than the WINS by loading. Additionally, the SCC is a dry system whereas the WINS uses an oiled substrate. While the WINS cut point is unlikely to shift to an unacceptable degree during 24 or 96 h sampling periods, it would perform less well than the SCC over extended sampling periods.     

On the solubility parameter of polar polymers

The binary cluster integral, β, was computed from intrinsic viscosity data. Subtracting from β the polar contribution, β_e, calculated from YRCR theory,⁹ the nonpolar interaction parameter, β_n, was found. The calculations were performed for poly(vinylacetate) and poly(methyl methacrylate), each in 16 solvents. The correlation between β_n and the solvent solubility parameter, δ₁, was found to be similar to that reported^8,17 for solutions of natural rubber, cis-polybutadiene and for poly(vinyl chloride). This correlation can be crudely approximated by the formula where E and F are functions of the ill-defined symmetry of the solvent molecule and δ_m is the δ₁ value for the local maximum of the function. At δ₁ = constant, the more spherical is the molecule, the higher is the β_n value. It was shown that for most cases separation of the solvent into two classes (linear and nonlinear) is sufficient. This β_n behavior finds support in the Funk and Prausnitz⁶ report on aromatic–saturated hydrocarbon mixtures and in the theoretical calculations of Huggins.^21,22     

Analysis of particle trajectories in a quick-contact cyclone reactor using a discrete phase model

The Eulerian–Lagrangian approach with a discrete phase model (DPM) is used to investigate the motion trajectories of the particles at the range of 1–50 μm in the quick-contact cyclone reactor, in which the cracking reactions and the separations of catalysts and products can occur respectively and simultaneously. The results show that the typical motion trajectories of the particles in the quick-contact cyclone reactor can be described as three types: trapping, escaping and dust ring. The first typical motion of particles corresponds to the particles successfully separated from the gas flow, while the other two types can lead to more coking and erosion in the reactor. Moreover, a pre-vortex flow is observed in the mixing-reaction chamber. Additionally, the grade separation efficiency of each particle size is also obtained by counting the numbers of escaping and capturing particles. The particles with diameter larger than 10 μm are separated completely from the gas. The reactor also has a strong capability to trap the particles of small diameters (5 μm <d_p<10 μm). Both results indicate that the separation efficiency of the reactor has met the requirement as a primary separator. Compared with the experimental results, the separation efficiency in the simulated method is higher than 98% with errors of no more than 1.31%. It is illustrated that separation efficiency of the reactor can be predicted by CFD simulation.     

Modification and laboratory evaluation of a TSI ultrafine condensation particle counter (Model 3776) for airborne measurements

A butanol-type ultrafine condensation particle counter (UCPC, Model 3776, TSI, Inc., Shoreview, MN, USA), which can achieve a 50% detection efficiency diameter (d₅₀) of 2.5 nm using a capillary-sheath structure, was modified and tested in the laboratory for airborne measurements. The aerosol flow rate through the capillary is a key factor affecting the quantification of aerosol particle number concentrations. A pressure-dependent correction factor for the aerosol flow rate was determined using a newly added mass flow meter for the sheath flow and the external calibration system. The effect of particle coincidence in the optical sensing volume was evaluated using an aerosol electrometer (AE, Model 3068B, TSI, Inc.) as a reference. An additional correction factor for the coincidence effect was derived to improve the quantification accuracy at higher concentrations. The particle detection efficiency relative to the AE was measured for mobility diameters of 3.1–50 nm and inlet absolute pressures of 101–40 kPa. The pressure dependence of the d₅₀ value, asymptotic detection efficiency, and shape of the particle detection efficiency curve is discussed, along with simple theoretical calculations for the diffusion loss of particles and the butanol saturation ratio in the condenser.

© 2017 American Association for Aerosol Science     

Coalescence of drops in a liquid-liquid dispersion by passage through a fibrous bed

A model which describes the operation of a fibrous bed coalescer is presented. From this model, a theoretical equation can be derived for the filter coefficient, λ, at small velocities where the effect of turbulence is negligible. This expression which considers the void fraction of the bed, ?, the drop diameter, d_p, the average saturation, S_m, the fiber diameter, d_P, and the effective fiber diameter d_fe, is:where β is the fraction of collisions which lead to coalescence. At larger velocities, a suitable empirical equation is obtained by multiplying the above expression by the square root of the velocity at which the filter coefficient begins to decrease divided by the superficial velocity. These equations describe the data of various workers. A method of obtaining the average saturation in a fibrous bed is presented. A possible correlating equation is found to be:where U is the superficial velocity.     

A simple method for identifying bubbling/jetting regimes transition from large submerged orifices using electrical capacitance tomography (ECT)

The bubbling–jetting transition regimes from large orifice submerged in water were investigated for various orifice diameters. A simple and fast way for identifying the regime transition was successfully developed using electrical capacitance tomography (ECT). In all the experiments deionised water was liquid phase and air was gas phase. Orifice gas velocity (V_N) and orifice diameter (d_o) were varied from 0.8 to 186 m/s and 4–21 mm, respectively. It was found that the V_N,trans. strongly depends on the orifice diameter. In the small orifice diameter (d_o < 10 mm), V_N,trans. greatly decreases with the increase of orifice diameter. However, in the large orifice diameter (d_o > 10 mm), the effect of orifice diameter on the transition velocity is insignificant. Finally, the data obtained by ECT compares with other works and the dimensionless orifice Reynolds number (Re_o ～11,000) is preferred to identify the bubbling–jetting transition regimes.     

Scaling of continuous twin screw wet granulation

Scaling rules were developed and tested for a continuous twin screw wet granulation process using three scales (11, 16, and 24 mm barrel diameter) of twin screw granulators (TSG). The distributive feed screw configuration used produced high porosity granules (50–60%) with broad bimodal size distributions, especially in the 16 and 24 mm TSGs. Three dimensionless numbers, Froude number (Fr), liquid‐to‐solid ratio (LSR), and powder feed number (PFN), were identified and their effect on granule size distribution (GSD), porosity and liquid distribution tested. Granule size increased with increasing LSR as expected. However, Fr and PFN had no significant effect on d₁₀ or d₅₀ and only a small effect on d₉₀. In contrast, granulator scale had a strong effect on GSD, with d₉₀ increasing almost linearly with barrel diameter. This is consistent with breakage of large granules being a dominant mechanism and directly controlled by the geometry of the screw. © 2016 American Institute of Chemical Engineers AIChE J, 63: 921–932, 2017