Transfer efficiency for airless painting systems

Spray transfer efficiency (TE) is defined as the mass fraction of sprayed paint which is deposited on the intended target, the remainder of the sprayed paint becomes undesirable overspray. The relationship between TE and gun supply pressure (or paint mass flow rate), gun-to-target distance, gun traverse speed, the angle of the spray gun relative to the target (gun-to-target angle), plus spray cone angle is reported herein for a typical fan spray system. Experimental results indicate that spray momentum rate (SMR) and droplet size dictate the TE for the various combinations of parameters considered here. The key finding is that TE correlates with SMR and spray mean drop size (Sauter mean diameter, or D₃₂) via an expression of the form TE=a+b SMR − c (SMR)²+d D₃₂, where a, b, c, and d are coefficients, determined by fitting the experimental data, and SMR is estimated via SMR=m²/ρA, where the paint mass flow rate m, the paint density is ρ, and the gun exit orifice effective tip cross sectional area is A. This expression accounts for physical phenomena that govern sprayed droplet deposition characteristics, such as entrainment, bounce-back, and drop size. Experimental results also show that, for the range of parameters studied, gun traverse speed has no effect on TE, but increasing the angle of the spray gun relative to the target (gun-to-target angle), increasing the spray cone angle, or increasing the gun-to-target distance will decrease TE.     

Conformations and dynamics of adsorbed protein-like chains

Conformations and dynamics of adsorbed protein-like chains are investigated by using Monte Carlo simulation based on the modified orientation-dependent monomer-monomer interaction (ODI) model. The chain size and shape of adsorbed protein-like chains, such as mean-square end-to-end distance 〈R²〉, mean-square radius of gyration 〈S²〉_xy (or 〈S²〉_z), shape factors , and 〈δ^*〉 are discussed here. At the same time, fraction of adsorbed segment f_a and average orientation of bond 〈P₂(cos θ)〉 are also investigated. The adsorbed protein-like chains trend to be more flat when adsorption interaction energy becomes strong. Different kinds of interactions (such as contact interaction, sheet interaction, spin-spin interaction, helical interaction, and adsorbed interaction) are considered in detail. Dynamics of adsorbed protein-like chains are investigated by calculating their diffusion coefficients, and we find that there exist the relationships of Dxy∼N−γxyand Dz∼N−γz, and the values of γ_xy and γ_z are 4-5 times larger than that of general self-avoiding walk (SAW) chains. These investigations may provide some insights into adsorption of proteins.     

Studies on some factors influencing the interfacial tension measurement of polymers

To improve the accuracy of polymer interfacial tension measurement using deformed drop retraction method (DDRM), we examined some factors, such as the shape parameter, the retraction scale D₀, and the distortion criterion γ by means of dissipative particle dynamics (DPD) simulation with 6 different models and analysis with three observation data, and proposing a new shape parameter P. Results show that the shape parameter order of suitable to various retraction scales and larger distortion is P>(a²−b²)>D. This study found that choosing a suitable retraction scale is very important, and that D₀≅0.15 is the most suitable retraction scale in DDRM measurement. In the scale, the three shape parameters cannot make much difference on the measurement deviation from the standard. This study also found that the distortion criterion γ varies with different shape parameters. We also found here when D₀≅0.15 the distortion criterion becomes γ<0.15, and one has a reliable measurement with any shape parameter.     

Abrasive water jet machining and mechanical behavior of banyan tree saw dust powder loaded polypropylene green composites

Banyan tree saw dust powder (BSD) filled Polypropylene (PP) green composites have been fabricated with varying amounts viz., 0%, 20%, and 40% of BSD particulate filler by using a co‐rotating twin screw extruder followed by injection molding. The mechanical properties such as surface hardness, tensile behavior, and impact strength of the fabricated PP/BSD green composites have been studied in order to standardize the composites. Abrasive water jet (AWJ) machining has been reported mainly for ceramics, concrete, and glass but not much literature is available on AWJ machining of polymer composites. This research is aimed at examining the AWJ machining of green polymer composites. The effect of BSD loading on the AWJ machining behavior of the PP/BSD green composites has been investigated. Furthermore, the effect of addition of 4% maleic anhydride grafted PP (coupling agent) and 4% talc (mineral filler) on the machining behavior of PP/BSD composites has also been evaluated. Surface roughness and optical micrographs of the AWJ cut composite specimens were examined to assess the effect of BSD content, AWJ traverse speed and pressure on the machining behavior of the composites. In order to probe the mechanism of AWJ machining behavior of PP/BSD composites, the kerf width and taper have been measured and results are correlated. POLYM. COMPOS., 37:1754–1764, 2016. © 2014 Society of Plastics Engineers     

The chemical reactor omnibook : by Octave Levenspiel,published by Oregon State University Bookstores,Corvallis, OR 97330, U.S.A. 1979; 670 pp., $20.00 + $1.75 p&p.

The deposition of aerosols with gravity in a vertical channel from the inlet to a distance of 50 channel widths was investigated numerically for developing, fully developed, and uniform laminar flows. The relative importance of sedimetation as compared to Brownian diffusion was determined by the parameter σ = v_gh/D where v_g is the settling velocity, h is half the channel width and D the particle diffusivity. A finite difference solution was found for the concentration distribution whereby various values of σ are presented for the penetration over the axial distance.     

Numerical simulation of microparticles penetration and gas dynamics in an axi-symmetric supersonic nozzle for genetic vaccination

This paper describes two phase (solid particles/gas) flow in a supersonic nozzle that is part of a device for micromolecular vaccine/drug delivery. It accelerates micro solid particles to high speeds sufficient to penetrate the viable epidermis layer to achieve the pharmaceutical effect. Helium is used as the driving gas for the solid particles because of its high compressibility factor. A numerical parametric study was performed for gas pressures ranging between 3 and 6 MPa and gold particles of diameters 1.8 μm and 5 μm. The computed results show that uniform particle velocity was achieved at standoff distance of 2 exit diameters (D_e) downstream of the device exit with particles concentrated on the supersonic core jet. Increasing the helium pressure from 3 to 6 MPa caused an increase in the particle velocity of 24% for particles with a diameter of 1.8 μm and 7% for particles of diameter 5 μm at the standoff distance. Furthermore increased gas pressure has adverse effect on particles concentration. As the inlet pressure increases, the particles are concentrated more at the core of the nozzle. Semi-empirical particle penetration calculation confirms the numerical results that the 5 μm particles penetration distance is 45-135 μm and the 1.8 μm diameter penetration is 35-95 μm beneath the skin. Comparison of different geometries has been done in order to understand each section function and to gain optimum performance.     

Evaporation from a nonspherical aerosol particle situated in an absorbing gas

The problem of an aerosol particle evaporating in an infinite expanse of an absorbing gas is considered. The relevant Helmholtz equation (resulting from the steady-state diffusion equation with an absorption term included) with density jump boundary conditions is converted into a boundary integral equation via the use of the Green’s function. The resulting integral equation is valid for particles of arbitrary shape. Explicit numerical results for the local and average evaporation rates are reported for several axisymmetric particles for a range of values of the dimensionless absorption parameter (λ²), where λ is the ratio of the radius of the particle (a) to the diffusion length (l). Here, the diffusion length is defined as l=[D/(vΣ_a)]^1/2, in which v (cm s^-1) is the average thermal speed of the vapor molecules, Σ_a (cm^-1) is the cross-section for absorption of the vapor by the gas, and D (cm² s^-1) is the diffusion coefficient of the vapor in the gas. Our numerical results for the local and average evaporation rates for a sphere exhibit excellent agreement with the corresponding analytical values (maximum deviation <0.40%). We find that the evaporation rate increases with increasing absorption and that this increase depends on the degree of departure of the particle from a spherical shape. The jump distance has a large impact in that it significantly lowers the evaporation rates as it increases in magnitude. It should be remarked that the results of this paper are also directly applicable to the problem of either neutrons or photons undergoing diffusion from a source situated in an absorbing medium.     

Experimental failure analysis of two‐serial‐bolted composite plates

In this study, a failure analysis of two‐serial‐bolted glass‐fiber‐reinforced epoxy composite plates was performed. To determine the influences of the joint geometry and stacking sequences on the bearing strength and failure mode, parametric studies were carried out experimentally. Three different geometrical parameters—the ratio of the edge distance to the hole diameter (E/D), the ratio of the plate width to the hole diameter (W/D), and the ratio of the distance between two holes to the hole diameter (K/D)—were considered. For this reason, the E/D, W/D, and K/D ratios were designed to range from 1 to 5, from 2 to 5, and from 3 to 5, respectively. Furthermore, the tests were performed with various preload moments (2, 3, 4, and 5 Nm) and without any preload moments (0 Nm). Because of the observed effect of the material parameters on the failure behavior, composite laminated plates were stacked in two different stacking sequences: [0°/0°/30°/30°]_s and [0°/0°/45°/45°]_s. The experimental results indicated that the failure response of the two‐serial‐bolted joints were strictly affected by the material parameters, geometrical parameters, and values of the applied preload moments. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

磨料水射流技术在钢结构表面清洗中的应用

介绍了磨料水射流清洗技术的装备、原理以及常见的磨料的性质,通过与干喷砂清洗技术的对比,体现了磨料水射流技术在环境保护、安全施工、经济方面的优势.     

Formation of self-assembled platinum particles on diamond and their embedding in diamond by microwave plasma chemical vapor depositions

Single-crystalline and polycrystalline diamond films containing platinum particles with sizes of ≤ ≈ 100 nm have been formed through a self-assembling process. Pt thin films pre-deposited on diamond were found to completely change in shape to grains during a subsequent diamond overgrowth process using a microwave-plasma chemical-vapor-deposition (MPCVD) technique. The self-assembled Pt grains on flat diamond surfaces had approximately spherical particles with rather uniform sizes when the pre-deposited Pt films were sufficiently thin or less than ≈ 1 μm in thickness. The average diameter of such Pt particles, D, was well controlled simply by changing the thickness of the pre-deposited Pt film, t_pt, since D was proportional to t_pt. Such spherical Pt particles were completely embedded after sufficient diamond overgrowth. Transmission electron microscope observations revealed that most of the spherical Pt particles were well crystallized and that the interfacial structures between the diamond overlayer and the buried Pt particles were sufficiently sharp without any appreciable mixing regions.     

Macroscopic diesel fuel spray shadowgraphy using high speed digital imaging in a high pressure cell

Spray formation from diesel fuel injection through a realistic heavy-duty multi-hole common rail injector is studied in a newly developed high pressure, high temperature cell, using digital high speed shadowgraphy at 4500 frames per second. Care is taken to establish accurate synchronisation between camera and injection system and because of the relatively large exposure time, an effective camera image time is calculated for every frame. Further emphasis is given to determining the actual start of fuel mass injection by comparing (for each injection) a predetermined, rail pressure dependent needle relaxation distance to the actual needle lift signal. The spatiotemporal evolution of the spray is found to reproduce well in general, but often sprays suffer from short-lived, small, laterally moving anomalies, which influence axial motion and the spray cone angle. High speed shadowgraphy allows this to be observed and taken into account. After an overview of methods found in the literature, an algorithm for geometrical analysis is presented, which is based on an extension of a combination of those methods. In this algorithm, a local spray angle ϑ_i(x) is determined from lateral cross-sections at 80% of the shadow level in order to encompass most of the spray without being too sensitive to background noise. The macroscopic cone angle ϑ_cone is derived from the approximate constancy of ϑ_i(x) over a relatively long axial distance. Spray penetration is obtained by lateral integration of the spray shadow. A procedure for accurate correlation of spray growth with time shows that the growth is proportional to t^b with b = 0.57 ± 0.02 for a common rail pressure of 150 MPa and a gas density 33 kg/m³ (N₂ at room temperature). The exact value of b is very sensitive to uncertainties in synchronisation and the start of injection determination. The spray cone angle ϑ_cone is not constant, but varies with time during an injection, mainly as a result of spray shape changes.     

Penetration Cutoff Velocities of Shaped Charge Jets

The maximum depth of penetration, P_max, of a shaped charge jet can theoretically be calculated from 5 quantities for the purely continuous, or for the initially continuous and then particulated, or for the fully particulated penetrating jet. These quantities are the distance Z₀ of the target plate from the virtual origin, the value of γ (i.e. the square root of the ratio of target to jet density), the jet tip velocity v_j,0 the efficient residual velocity v_j,min, and the particulation time t_p. Instead of calculating the individual values of v_j,min for the individual depths of penetration P_exp at various standoff distances, this quantity can quite simply be read from the standoff diagram by means of the penetration cutoff lines- a so-called Standoff/Cutoff-diagram -, using the experimentally determined depth of penetration P_exp. The penetration cutoff lines are lines which start at the virtual origin and which represent the ideal increment in depth of penetration per jet velocity interval in the standoff diagram, the abscissas of this line corresponding to the jet tip velocities. The methods are demonstrated and explained, using the results of three firings with one type of shaped charge as an example. The shots were made at 6, 12, and 24 calibers standoff distance, and the cratering history was also determined in these trials.     

Experimental analysis of increases in wall pressure due to slight impacts on the wall of a vessel

When one causes slight impacts on the wall of a storage vessel, the particulate solid is packed more densely. Consequently, the pressures on the bottom, front and side walls of the vessel increase notably. The elucidation of the phenomenon of the wall pressure increases is of importance for the design of storage vessels for particulate solids. In the present study the wall pressure increases due to slight impacts on the front wall of the vessel for two kinds of glass beads (median diameter D_p50 = 134 μm and 1055 μm) and a PVC powder (D_p50 = 161 μm) were measured. The results indicate that the wall pressure increases with increasing packing ratio and, after the packing ratio reaches a maximum, the wall pressure does not increase even if a large number of slight impacts are given. Hence, the pressure increase ratio is closely related to the change of the packing ratio. The dense packing of the particulate solid due to impacts elastically deforms the walls of the vessel. Since the elastic deformation of the wall pushes the particulate solid back, the directions of the frictional forces at the walls are partially reversed. The side wall pressure increase becomes larger with increasing distance from the top of vessel and the wall pressure is almost unchanged near the top free surface.     

Comparison of the effects of anionic and cationic surfactant concentration on mean drop size in a mixer-settler extractor

In this study, the effect of Aniline and SDS (Sodium Dodecyl Sulfate) surfactant on mean drop size, D₃₂, was investigated in a horizontal mixer-settler. For this purpose, three series of experiments were conducted in a single stage mixer-settler on the liquid–liquid dispersion of a toluene–water system. At first, the effects of impeller speed and hold-up on the mean drop size were examined without any surfactant. Afterwards the same investigation was performed in the presence of SDS (Seri 1) and then in the presence of Aniline (Seri 2). The results revealed that D₃₂ in Aniline system is larger than D₃₂ in SDS system. In addition, the results show that D₃₂ in the presence of Aniline depends on the impeller speed with a power low function, having an exponent of −1.11 which has a good agreement with Hinze–Kolmogorov's theory.     

Elastic behavior of adsorbed single compact chains

Elastic behaviors of short single two-dimensional compact chains adsorbed on the attractive surface are investigated in this paper by using the enumeration calculation method. In our model a single compact chain is fixed with one of its end at a position above the impenetrable surface, and then it is pulled away from the attractive surface slowly through elastic force acting. We investigate the chain size and shape of adsorbed compact chains, such as mean-square end-to-end distance per bond 〈R²〉/N mean-square radii of gyration per bond 〈S²〉_x/N and 〈S²〉_y/N, shape factors 〈δ〉, and fraction of adsorbed monomers f_a in order to illuminate how the size and shape of adsorbed compact chains change during the process of tensile elongation. Especially for strong attraction interaction there are some special behaviors in the chain size and shape during this process. If there exits adsorption interaction, single compact chain is first almost pulled down to the adsorption surface and then moves in the direction of force until to leave the adsorption surface. These changes become more obvious with strong adsorption interaction. Our calculation can show this elastic process of adsorbed compact chains visually and simply. On the other hand, some thermodynamics properties are also studied here. We use average energy per bond, average Helmholtz free energy per bond, elastic force f and energy contribution to elastic force f_u to study the elastic behavior of adsorbed single compact chains in the process of tensile elongation. Elastic force f has a long plateau during the tensile elongation for strong adsorption interaction, which agrees well with experimental and theoretical ones. These investigations can provide some insights into the elastic behaviors of adsorbed protein chains.     

Temperature and concentration dependence of diffusion coefficient in dilute solutions

Temperature and molecular weight dependence of k_D in D(C) = D(O) [1 + Ck_D], where D(C) is the diffusion coefficient for the density fluctuations in a dilute polymer solution, is investigated by first expressing D(C) as a function of the static structure factor S(q,C) within the framework of the Kirkwood-Riseman theory. The continuous transition of k_D from negative values under theta conditions to positive values in good solvents is calculated using various models for the intermolecular interaction potential and the results are presented graphically as function of a reduced variables $\text{S}\text{?}\text{R}{}_{\mathrm{H}}$ that combines both molecular weight and temperature effects. It is shown that the negative value of k_D at the theta temperature can be explained at least partially, in terms of an increase in the chain dimensions of two overlapping molecules. The concentration dependence of the self-diffusion coefficient is also discussed.     

Electron–hole drops in synthetic diamond

In this paper we give the first report of a high-density phase of condensed electron–hole drops in diamond. Synthetic crystals grown by the high pressure–high temperature technique were optically highly excited by laser pulses with photon energies above the band-gap of diamond. At temperatures below ≈170 K we observe novel broad luminescence bands, in addition to the well-known free exciton spectra, with characteristic features identifying them as originating from electron–hole drops. Fits to the photoluminescence spectra yield an electron–hole density within the drops of n₀=9.6×10¹⁹ cm⁻³, a reduced band-gap of E_g′=5.224 eV (instead of E_g=5.49 eV) due to the attractive interaction of the particles in the condensed phase, and a work function of φ=52 meV with respect to the free exciton threshold E_gx.     

Separation of surface and bulk phase diffusivities: A kinetic theory analysis

A kinetic model for the effective (e.g. surface plus bulk) diffusivity in a porous bed composed of rectangular channels is presented. The merit of this approach is that no distinction is made between the bulk and adsorbed phase and the effective axial flux can therefore be compared directly with experimental measurements. We utilize the elements of the BGK kinetic equation and express D_eff as an explicit function of the surface potential and collision frequency. Details concerning gas-gas collision dynamics and gas-solid interactions are contained in the relaxation time, τ, and the external force, F_s, respectively. For definiteness, the analysis is limited to hard sphere gas-gas collisions, although no special significance is implied by this choice. The assumption of a discontinuous gas-solid interaction potential results in a separation of the form D_eff = D_g + K_eqD_s, with interactive modification of both D_g and D_s. Preliminary calculations indicate that only when K_eq, is large will surface diffusion become a significant mode of transport.     

Photopolymerization of acrylate suspensions with visible dyes

Polymerization behavior of silica loaded diacrylate suspensions in the presence of color changing dyes was studied via cure depth measurements and photorheology. The dyes have their maximum absorption peak in the visible range; however, spectrophotometry revealed significant absorption also in the UV range where the photoinitiators are active. Thus, the dyes behave as other inert dyes and they affect the curing behavior. The effect of the dye concentration on the sensitivity D_p, critical energy dose E_c and time parameters determined via photorheology was studied and the data was fit to theoretical models. The measured values of 1/D_p, E_c and the photorheology time parameters linearly increase with increasing dye concentration c_D as predicted by the models.     

Gas-liquid-liquid extraction in a novel rotating microchannel extractor

In this work, a novel rotating microchannel extractor (RME) is designed and further used for the extraction of chromium (III) from water. Unexpectedly, the micro-extraction had the same effect as carrying out 2.9-stage cross-flow extractions. Various factors, including the gas intake methods, gas intake quantity (Q_g), distance between inner rotor and outer wall (D), rotational inner rotor speed (R) and volumetric flow rate (Q_a, Q_o), were selected to investigate their effect on the extraction efficiency (η) thoroughly. The relation map of η with We_a and We_o−g for RME provides a comprehension for the gas–liquid–liquid extraction process in this RME system.