THE ELECTROHYDRODYNAMICS OF THE CHARGED LIQUID JET ISSUING FROM AN ELECTRIFIED TAYLOR CONE. UNIVERSAL SCALING LAWS

A hybrid experimental–numerical approach to study the dynamics of capillary electrified jets, which uses a quasi-one-dimensional model and the experimentally measured shape of an actual liquid thread (Gañán-Calvo (1997) J. Fluid Mech. 335, 165–188) has been employed in this work to analyze the electrohydrodynamics of the liquid micro-jets issuing from Taylor cones. Different liquids have been used in this study, with electrical permittivities from 6.5 to 38 times the vacuum permittivity, and electrical conductivities ranging from 8.5 to 4.5e-4 S m^-1. Up to 25 different jet shapes corresponding to steady and absolutely stable conditions have been digitized, and the corresponding surface charge distribution, normal external and internal electric fields at the surface, the axial electric field (the slender approach allows to consider the axial electric field constant in the transversal direction), the liquid velocity distribution, the electric current convected by the surface and the one driven through the bulk by Ohmic conduction at each axial point have been calculated. In particular, one of the liquid jets analyzed corresponded to the onset of stability of the steady cone-jet mode, where we supply just the (minimum) liquid flow rate that the electrostatic suction effect at the cone-jet neck is able to withdraw at the minimum needle–electrode potential difference for a given stable cone elongation. This has revealed a surprising result: even in this critical situation, the inner normal electric displacement is at most a mere 15% of the outer one, and this happens only at one point of the whole cone-jet, located close to the point at which the convected electric current equals the current driven by bulk conduction (i.e. a little downstream of the cone-jet neck), being the inner displacement at other points of the jet and the cone hundreds of times smaller than the outer displacement. As one increases the liquid flow rate, the ratio of the maximum inner displacement to the outer displacement becomes proportionally smaller. This result clarifies for the first time the controversy about charge relaxation phenomena in cone-jet electrosprays, since it can be used to show from a physicochemical argument that the charge layer at the whole cone-jet surface is almost relaxed even at the onset of stability, at least for liquid permittivities of the order of the ones used in this study. This result also guarantees a homogeneous bulk conductivity along the hole cone-jet. Secondly, and similarly interesting, the kinetic energy per unit volume acquired by the liquid in the jet results independent of the flow rate for a given liquid and a cone elongation, explained by the fact that the normal electric field (or surface charge distribution) which provokes the main acceleration force (the electrostatic suction effect, at the cone-jet neck and the beginning of the jet) results independent of the flow rate as well. A universal scaling of the electro-hydrodynamic variables, jet size and total emitted electric current is proposed, and the experimental results are collapsed into a universal collection of distributions of non-dimensional variables along the axis. The resulting droplet size, also measured in the same experiments, scales as the jet radius, and the droplet charge results proportional to its surface, a result shown by many investigators but never explained. Other previously used electrohydro-dynamic hypotheses and scaling laws are discussed under these new results.     

Droplet vaporization modeling of rapeseed and sunflower methyl esters

For numerical simulations of the combustion of liquid fuels, a thoroughly validated and verified quantitative model for droplet evaporation is necessary. In this work a simple single droplet infinite conductivity model is simulated for low pressure (0.1 MPa) and various temperatures (550–1050 K) using a chosen property rule (see Eq. (7)) and five convection correlations (C1, C2, C3, C4, and C5, see (Table 1) to obtain the temporal evolution of droplet diameter squared, droplet surface temperature and average evaporation rates of vegetable oil derived biofuels – rapeseed methyl ester (RME) and sunflower methyl ester (SME) – under near-quiescent conditions. The predictions are compared with the experimental and analytical results of Morin et al. [1]. The model uses an effective Reynolds number to conflate the effects of forced and natural convection. It is observed that the predicted temporal history of droplet diameter for RME droplet matches more closely with correlation C1 for T_amb ? 748 K and correlation C2 for T_amb ? 803 K at various ambient temperatures (i.e., from low to high evaporation rate). The correct droplet lifetime is predicted best by C1 for all temperatures. For average evaporation rates for SME, C1 best fits the experimental data. For the average evaporation rate of RME, the present model with C1 gives a better prediction than the theoretical, and corrected theoretical results of Morin et al. [1], and is observed to match closely with their experimental results. The present results using C2 are also found close to the experimental results for RME and SME. It is observed that the oxidation of RME/SME is similar to n-decane – a pure component fuel.     

Relationship between size of oil droplet generated during chemical dispersion of crude oil and energy dissipation rate: Dimensionless,scaling, and experimental analysis

Droplet formation mechanisms during the chemical dispersion of crude oil were investigated using both theoretical and experimental approaches. Dimensionless and force balance analysis identified four distinct regimes of droplet formations. For d>η, d scales either with (ε^?2/5) or (ε^?1/4) or and for d<η, d scales either with (ε^?1/2) or (ε^?1/4) depending on whether the main restoring force against droplet breakage is provided by surface tension or oil viscosity. The symbols d, η, and ε represent the droplet diameter, the Kolmogorov length scale, and energy dissipation rate, respectively. For d>η and <η, the external force, which tries to deform and break the droplet is provided by the pressure difference across the droplet diameter and viscous shear, respectively. Identification of the relationship d～(ε^?1/4) for d<η is a new contribution of this present study. The validity of this relationship was also proven by our experimental observations over a range of physical properties (dynamic viscosity 0.015–8.6 Pa s; oil–water interfacial tension 0.0001–0.015 N/m) and mixing energies (0.00075–0.16 W/kg), similar to those in real environmental settings (e.g., estuary, surface layer of oceans). All these above findings and observations are vital from the stand point of appropriately scaling droplet formation process, during chemical dispersion of crude oil, and in the development of reliable predictive models.     

Investigation of plasma jet gas-dynamic effect on a substrate in conditions of diamond coating synthesis

Experimentally, it was shown that using a gas-dynamic correction in the plasma torch operation mode of jet expansion absence increases the efficiency of DC synthesis more than 10 times. Moreover, the diameter of the homogeneous part of a coating is increased not less than twice in relation to the diameter of the plasma jet.The theoretical explanation of the obtained result is given. It was shown that at subsonic speed of plasma flow spreading along the substrate radius, this effect can only be obtained at Reynolds numbers not exceeding the critical value R_r≤R_r cr=13456.The maximum area of uniform thickness DC is not less than 6 cm².     

Simulation of supercritical water–hydrocarbon mixing in a cylindrical tee at intermediate Reynolds number: Formulation,numerical method and laminar mixing

The objective of this work is to study the flow dynamics and mixing of supercritical water and a model hydrocarbon (n-decane), under fully miscible conditions, in a small scale cylindrical tee mixer (pipe ID = 2.4 mm), at an intermediate inlet Reynolds number of 500 using 3-D CFD simulations. A Peng–Robinson EoS with standard van der Waals mixing rules is employed to model the near-critical thermodynamics with the mixture binary interaction parameter obtained from a Predictive Peng–Robinson EoS using group contribution theory (PPR78). The n-decane stream is introduced at the colder temperature of 700 K to ensure operation above the Upper Critical Solution Temperature (UCST, 632 K) of the water n-decane system while the water stream enters at a higher temperature of 800 K. Under these conditions, the flow in the tee mixer remains laminar and steady-state is reached. Mixing occurs predominantly due to the circulating action of a counter-rotating vortex pair (CVP) in the body of the hydrocarbon jet entering from the top. This CVP is formed due to the reorientation of the streamwise vorticity pre-existing within the hydrocarbon jet as it flows down the vertical pipe of the tee junction. The advective transport is further assisted by a secondary flow of water from the bottom stream, around the hydrocarbon jet, toward the space vacated near the top of the downstream pipe section by the downward motion of the HC jet. The CVP becomes progressively weaker due to vorticity diffusion as it is advected downstream and beyond 10–12 diameter lengths downstream of the mixing joint, transport is mainly controlled by molecular diffusion. It was found that the variations of density and transport properties with temperature do not have a significant impact on the flow and mixing dynamics for a ΔT = 100 K between the two streams. Local cooling of the fluid mixture was also observed in the mixing of water and n-decane streams entering at the same temperature (initially isothermal). This cooling effect is due to the diffusion of species along a gradient in their partial enthalpy in the mixture. Such gradients in species partial enthalpies are non-zero under near-critical conditions even for initially isothermal flows due to the non-ideality of the fluid mixture under these conditions. This local heating/cooling effect at near-critical conditions could give rise to unexpected formation of phases when operating close to critical points.     

Characteristics of droplets generated by bubble bursting from chromic acid solutions

The effects of electrolyte concentration and gas flow rate on the characteristics of droplets generated from bubbles bursting on the surface of CrO₃ solution were studied with an experimental bubbling system. The experimental conditions included two electrolyte concentrations, 125 and 250 g l^-1 of CrO₃, and three flow rates of sparging air in the range of 4–8 l min^-1. A cascade impactor collected droplet samples for chemical analysis. A laser aerosol spectrophotometer and an aerodynamic particle sizer were employed simultaneously to measure the number concentration and size distribution of the droplets. A layer of foam formed on the liquid surface under all experimental conditions studied except at the gas flow rate of 4 l min^-1 in 125 g l^-1 CrO₃ solution. Foams had a significant effect on the characteristics of droplets generated from bursting bubbles. At identical gas flow rate and electrolyte concentration, the formation of foams led to a reduction in number concentration of droplets larger than 10 μm in aerodynamic diameter and a lower concentration of airborne Cr(VI). In the ranges of gas flow rate and electrolyte concentration tested, the results showed that the airborne Cr(VI) mass concentration increased significantly with gas flow rate and slightly with electrolyte concentration in the presence of foams. The results obtained in the present study should have applications in the emission control of Cr(VI)-containing droplets in chromium electroplating processes.     

Liftoff height behavior in a non-premixed turbulent hydrogen jet with coaxial air

To understand hydrogen lifted flames, the experimental approximation of liftoff height in non-premixed turbulent conditions was studied. The objectives were to analyze liftoff height behavior and to derive the normalized expression for lifted jet with the effective diameter (d_F,eff). Hydrogen flow velocity varied from 100 m/s to 300 m/s. Coaxial air velocity was regulated from 12 m/s to 20 m/s. For the simultaneous measurement of velocity field and reaction zone, particle image velocimetry using hydroxyl radicals (PIV/OH) planar laser-induced fluorescence (PLIF) techniques with neodymium-droped yttrium–aluminum-gamet (Nd:YAG) lasers and charge-coupled device/intensified charge-coupled device (CCD/ICCD) cameras were used. Liftoff height decreased with increased fuel velocity. The flame stabilized in a lower velocity region next to the faster fuel jet due to the mixing effects of the coaxial air flow. The stabilization point was defined as the point where local flow velocity is balanced with turbulent flame propagation velocity. On the basis of the far field concept, we could derive the experimental approximation of the liftoff height divided by the effective diameter.     

PMMA-supported hybrid materials doped with highly near-infrared (NIR) luminescent neutral trikis-β-diketonate Yb3 + complex

Based on self-assembly of a trifluorinated and acylpyrazole-modified β-diketonate ligand HL ((Z)-3-methyl-1-phenyl-4-(2,2,2-trifluoro-1-hydroxyethylidene)-1H-pyrazol-5(4H)-one), LnCl₃⋅ 6H₂O (Ln = La, Yb or Gd) and 2,2′-bpy (2,2′-bipyridine), three trikis-β-diketonate complexes [Ln(L)₃(2,2′-bpy)] (Ln = La, 1; Ln = Yb, 2 or Ln = Gd, 3) were obtained, respectively. Further through physical doping, the series of PMMA-supported hybrid materials PMMA@[Ln(L)₃(2,2′-bpy)] with high thermal stability and good film-forming property are obtained. Especially for PMMA@2, the doping also causes the improved NIR luminescent property (Φ_em = 0.97%) in comparison to the individual Yb^3 +-β-diketonate complex 2 (Φ_em = 0.81%) even up to a concentration of 200:1.     

Catalytic olefin epoxidation with cationic molybdenum(VI) cis-dioxo complexes and ionic liquids

The complexes [MoO₂Cl(HC(bim)₃)]Y (Y = Cl (1), BF₄ (2) and PF₆ (3)) have been prepared by reaction of MoO₂Cl₂(THF)₂ (for 1) or [MoO₂Cl(THF)₃]Y (for 2 and 3) with the tridentate ligand HC(bim)₃ = tris(benzimidazolyl)methane, and characterized by IR and Raman spectroscopy, and ¹H NMR. The turnover frequencies for the epoxidation of cis-cyclooctene at 55 °C with tert-butyl hydroperoxide (TBHP, in decane) as the oxidant and complexes 1–3 as catalysts are in the range of 70–200 mol mol_Mo^?1 h^?1. 1,2-Epoxycyclooctane is always the only reaction product for reaction times up to 24 h. With the aim of facilitating the recyclability of the complexes, the ionic liquids (ILs) [BMIM]Y and [BMPy]Y (BMIM = 1-n-butyl-3-methylimidazolium, BMPy = 1-n-butyl-3-methylpyridinium; Y = BF₄ or PF₆) were applied as ionic solvents. The catalytic performance for cyclooctene epoxidation depends strongly on the catalyst solubility in the IL. Of the 12 catalyst/IL mixtures examined, the systems 1/[BMIM]PF₆ and 1/[BMPy]PF₆ exhibit the most favorable reaction rates allied with good recyclability. The 1/[BMIM]PF₆ system was further applied using different oxidants (aqueous TBHP, aqueous H₂O₂ and urea–hydrogen peroxide adduct) and olefins (norbornene, cyclohexene, styrene, α-pinene).     

Indirect-mode jet pulse spray system design and monodisperse droplets generation

A novel method called indirect-mode jet pulse spray (JPS) for producing mono-sized droplets was proposed. The jet is stimulated to spray into uniform droplets under the effect of gas pulses, which is generated by employing a distribution mechanism where the periodical switch-on between the gas inlet duct and outlet duct is achieved by rotating. The influence of the processing parameters on the droplet size and its distribution was evaluated using paraffin wax. It was shown that the high jetting pressure and rotational speed favors the uniformity of droplets at a relatively wide range of jetting velocities, suggesting that the indirect JPS system is very stable and robust against the change of working conditions. In the case of P=0.04 MPa and n=350 rpm, most uniform droplets with an average diameter of about 520 μm and a CV of 3.3–4.2% were obtained. A model based on the gas pressure was developed, giving consistent results with the experiments. The optimum experimental results can be well explained by the Weber instability model. The indirect-mode JPS process has excellent size uniformity, materials flexibility and process stability, permitting great potential for broad applications.     

Synthesis,characterization, and photophysics of electroluminescent fluorene/dibenzothiophene- and fluorene/dibenzothiophene-S,S-dioxide-based main-chain copolymers bearing benzimidazole-based iridium complexes as backbones or dopants

A series of electroluminescent copolymers containing fluorene-2,8-disubstituted dibenzothiophene (PFD), fluorene-2,8-disubstituted dibenzothiophene-S,S-dioxide (PFDo) and phosphorescent benzimidazole-based iridium (Ir) complexes in the backbones were synthesized by the Suzuki coupling reaction. The thermal stabilities, HOMO/LUMO levels and triplet energy gap (E_T) values were enhanced with increasing contents of dibenzothiophene (D) or dibenzothiophene-S,S-dioxide (Do) segments in the copolymers. The relative intensities of phosphorescence and fluorescence were affected by the energy transfer and back transfer efficiencies between the polymer backbones and iridium units as evidenced by solid state PL and EL spectra. PLED devices with a configuration of ITO/PEDOT:PSS (50 nm)/metal-free copolymers (P1–P5), Ir-copolymers (P7–P13) and Ir-doped copolymers (P3 doped with Ir-complexes 6 and 8) (60–80 nm)/TPBI (40 nm)/LiF (1 nm)/Al (120 nm) were fabricated, and the electroluminescence (EL) efficiencies depended on the chemical constituents and triplet energies of the copolymers. The space-charge-limited current (SCLC) flow technique was used to measure the charge carrier mobilities of these copolymers, where both hole and electron mobilities were in the following order: the metal-free copolymers (P2, P3 and P5) > Ir-doped copolymers (P3 + 3 or 10 mol% Ir-complex 6) > Ir-copolymers (P7, P8, P12 and P13).     

Construction of three isostructural 3d–4f microporous coordination frameworks based on mixed nicotinate and oxalate ligands

The self-assembly of nicotinic acid and sodium oxalate with mixed 3d–4f metal salts under hydrothermal conditions gave three isostructural 3D 3d–4f coordination polymers, [LnCu(nic)₂(ox)] · xH₂O [Ln = La, x = 1 (1); Ln = Eu, x = 2 (2); Ln = Gd, x = 2 (3)] [ox = oxalate, nic = nicotinate]. All three structures exhibit same unusual 3D microporous heterometallic coordination frameworks that are built up by rare tetranuclear Ln₂Cu₂ clusters and mixed ox and nic linkers. Furthermore, the luminescent property of complex 2 has also been investigated.     

Synthesis,luminescence, and structural characterization of Zn and Cd coordination polymers of flexible bis(imidazolyl) derivatives

Coordination polymers [Zn(imc)(L¹)] · H₂O, (1, imc = iminodiacetate, L¹ = bis(N-imidazolyl)methane) [Zn(hba)₂(L²)]₂ · EtOH · 3H₂O, (2, hba = p-hydroxybenzoate, L² = bis(N-benzimidazolyl)methane), [Cd(mal)(H₂O)(L³)](3, L³ = 1,4-bis(N-imidazolyl)butane, mal = maleate) have been prepared and structurally characterized. Complex 1 consists of hexa-coordinated central Zn ions and exhibits 2D network structure. The Zn atoms in 2 have tetrahedral coordination geometry, and are linked by bis(imidazolyl) ligands into 1D chain structure. The cadmium ions in 3 are hepta-coordinated with pentagonal bipyramidal geometry. Complex 3 displays 2D grid structure. The TGA showed that the coordination polymers are stable up to 200 °C. All the three complexes are emissive at room temperature in their solid state.     

Quality of diamond wafers grown by microwave plasma CVD: effects of gas flow rate

We found a strong impact of gas flow rate on diamond growth process in a 5 kW microwave plasma chemical vapour deposition reactor operated on CH₄-H₂ gas mixtures. Diamond films of 0.1–1.2 mm thickness and 2.25 in. in diameter were produced at H₂ flow rates varied systematically from 60 sccm to 1000 sccm at 2.5% CH₄. The highest growth rate, 5 μm h⁻¹, was observed at intermediate F values (≈300 sccm). Carbon conversion coefficient (the number of C atoms going from gas to diamond) increases monotonically up to 57% with flow rate decrease, however, this is accompanied with a degradation of diamond quality revealed from Raman spectra, thermal properties and surface morphology. High flow rates were necessary to produce uniform films with thermal conductivity >18 W cm⁻¹ K⁻¹. Diamond disks with very low optical absorption (loss tangent tgδ<10⁻⁵) in millimetre wave range (170 GHz) have been grown at optimized deposition conditions for use as windows for high-power gyrotrons.     

Impactor designed to increase mass output rate of nanoparticles from a pneumatic nebulizer

A modular impactor was designed to remove large droplets from aerosols generated by a pneumatic nebulizer, the Six-Jet Atomizer from TSI Inc. (Shoreview, MN), with the aim of generating dry nanoparticles. Three interchangeable nozzle heads were designed to provide droplet cutoff diameters of 0.5, 1, and 2 μm at an air flow rate of 8.3×10^?4 m³ s^?1 (50 L min^?1), which corresponds to all six jets of the nebulizer operated at 25 °C and an air pressure of 241 kPa (35 psi). The collection and output characteristics of the 0.5 μm impactor were evaluated from dry particle size distributions produced by nebulizing an aqueous solution with a NaCl mass fraction of 1% both with and without the impactor present. The impactor characteristic cutoff curve was sharp (impactor geometric standard deviation, GSD_imp=1.15–1.19) with a 50% cutoff diameter d₅₀ that ranged from 0.48 μm at 3.0×10^?4 m³ s^?1 to 0.74 μm at 11.7×10^?4 m³ s^?1. The rate of dry NaCl particle generation ranged from 0.5 to 5 g s^?1 (0.04 to 0.4 g day^?1) with mass median diameters MMD_p=80–123 nm and geometric standard deviations GSD_p=1.6–1.8 (depending on flow rate). Anomalous negative impactor efficiencies were observed at flow rates >8.3×10^?4 m³ s^?1 for 100 to 400 nm droplets and at all flow rates for droplets smaller than 100 nm. This phenomenon will be investigated further as a way to increase the generation rate of nanoparticles. A step-by-step procedure is presented for the selection of an appropriate impactor design and operating flow rate for a desired maximum aerosol particle size.     

NIR luminescence comparison of Zn-Nd Schiff-base complex doped or single-nodal grafted into PMMA

Through doping or grafting of a new ZnNd Schiff-base complex monomer [Zn(L)(4-vinyl-Py)Nd(NO₃)₃] (2; H₂L = N,N′-bis(3-methoxy-salicylidene)phenylene-1,2-diamine; 4-vinyl-Py = 4-vinyl-pyridine) into PMMA (poly(methyl methacrylate)), two kinds of hybrid materials 2@PMMA and Poly(2-co-MMA) with significantly improved physical properties including good Nd^3 +-centered near-infrared (NIR) luminescence were obtained. Especially the single-nodal ZnNd-grafted Poly(2-co-MMA) soluble in organic solvents exhibits the high sensitization efficiency (η_sens = Φ_Nd^L/Φ_Nd^Nd = 81%) even at a high feed molar ratio up to 1:50.     

Experimental and computational fluid dynamic study of reacting gas jet in liquid: Flow pattern and heat transfer

The flow behavior of a jet reactor (consisting of a gaseous jet submerged in a molten-metal bath) is very complex. These are operated at high temperatures (1500–3000 K) and need to be contained within a heavy metal enclosure. The design of such reactors requires a prior knowledge of the jet dimensions, flow pattern and heat transfer characteristics. However, the fuel opaqueness and the high temperature of the jet create difficulties in observing the reaction mass visually and therefore the literature contains a very brief account of the experimental measurements of the flow pattern. Hence, a systematic study has been undertaken with a reaction pair (HCl gas jet submerged in aqueous NH₃), which has the potential for simulating the real systems. The present work is concerned with the CFD simulations by employing k–ε turbulence model and large eddy simulations (LES). The measurements and simulations have been carried out over a wide range of gas velocities (53–323 m/s) and these have been compared with the CFD simulations. A comprehensive comparison has also been made between the k–ε and the LES for the mean flow, temperature and the turbulent kinetic energy. An attempt has been made to understand the relative performance of these models. Further, complete energy balance has been established between the energy supply rate through the jet and the energy dissipation rate within the reactor. The plume characteristics obtained from CFD simulations have been compared qualitatively with the photographic images.     

Experimental determination of bulk modulus of 14 Å tobermorite using high pressure synchrotron X-ray diffraction

Using a diamond anvil cell, 14 Å tobermorite, a structural analogue of calcium silicate hydrates (C–S–H), was examined by high-pressure synchrotron X-ray diffraction up to 4.8 GPa under hydrostatic conditions. The bulk modulus of 14 Å tobermorite was calculated, K_o = 47 GPa. Comparison of the current results with previous high pressure studies on C–S–H(I) indicates that: (1) the compression behavior of the lattice parameters a and b of 14 Å tobermorite and C–S–H(I) are very similar, implying that both materials may have very similar Ca–O layers, and also implying that an introduction of structural defects into the Ca–O layers may not substantially change in-plane incompressibility of the ab plane of 14 Å tobermorite; and (2) the bulk modulus values of 14 Å tobermorite and C–S–H(I) are dominated by the incompressibility of the lattice parameter c, which is directly related to the interlayer spacing composed of dreierketten silicate chains, interlayer Ca, and water molecules.     

Hydrothermal synthesis,crystal structure and properties of a thermally stable dysprosium porphyrin with a three-dimensional porous open framework

A thermally stable dysprosium porphyrin with a three-dimensional (3D) porous open framework, [Dy(H₂TPPS)]_n∙ nH₃O∙2nH₂O (1) (H₂TPPS = tetra(4-sulfonatophenyl)porphyrin), has been synthesized via hydrothermal reactions and structurally analyzed by an X-ray single-crystal diffraction method. The 24-membered macrocyclic ring of H₂TPPS is exactly coplanar and the center is free from metal. The dysprosium ion is coordinated by eight O_sulfonic atoms from eight H₂TPPS moieties, forming a distorted square anti-prism geometry. Complex 1 shows a void space of 210 Å³, occupying 9.06% of the unit-cell volume. The 3D porous open framework of 1 is thermally stable up to 380 °C. Complex 1 exhibits a red fluorescence emission with a quantum yield and lifetime of 2.7% and 136 μs, respectively. CV result reveals one reductive peak at − 0.33 V and one quasi-reversible wave with E_1/2 = − 0.81 V.     

NUMERICAL PREDICTION OF THE PERFORMANCE OF A MANIFOLD SAMPLER WITH A CIRCULAR SLIT INLET IN TURBULENT FLOW

The performance of a bioaerosol manifold sampler with a circular slit inlet in a turbulent flow field was modeled using a 3-D numerical approach. The standard κ–ε turbulence model was used for simulating the mean turbulent flow, and the Lagrangian approach was used for predicting the particle trajectories. The ratios of wind velocities to sampler inlet velocities were from 0.5 to 3.5. Calculations were conducted for particle sizes of 2, 8, 15,and26 μm. The agreement between numerical and empirical sampling efficiencies was good. It was found that lower sampling efficiencies at high R values were associated with increased positive pitch of the velocity vectors generated at the inlet slit. Unbalanced sampling velocities between the upstream and downstream arcs were found only at high R values. At an inlet velocity of 0.8 m/s, sampling efficiencies for 15 μm particles decreased about 24% as R was increased from 0.5 to 3.5. A similar effect was observed at an inlet velocity of 0.4 m/s. Turbulence decreased sampling efficiency and was related to the sum of the magnitudes of the wind and sampling velocity vectors.