In situ observation of synthesized nanoparticles in ultra-dilute aerosols via X-ray scattering

In-air epitaxy of nanostructures (Aerotaxy) has recently emerged as a viable route for fast, large-scale production. In this study, we use small-angle X-ray scattering to perform direct in-flight characterizations of the first step of this process, i.e., the engineered formation of Au and Pt aerosol nanoparticles by spark generation in a flow of N₂ gas. This represents a particular challenge for characterization because the particle density can be extremely low in controlled production. The particles produced are examined during production at operational pressures close to atmospheric conditions and exhibit a lognormal size distribution ranging from 5–100 nm. The Au and Pt particle production and detection are compared. We observe and characterize the nanoparticles at different stages of synthesis and extract the corresponding dominant physical properties, including the average particle diameter and sphericity, as influenced by particle sintering and the presence of aggregates. We observe highly sorted and sintered spherical Au nanoparticles at ultra-dilute concentrations (< 5 × 10⁵ particles/cm³) corresponding to a volume fraction below 3 × 10^–10, which is orders of magnitude below that of previously measured aerosols. We independently confirm an average particle radius of 25 nm via Guinier and Kratky plot analysis. Our study indicates that with high-intensity synchrotron beams and careful consideration of background removal, size and shape information can be obtained for extremely low particle concentrations with industrially relevant narrow size distributions.

     

Heat transfer and pressure drop in a new type of corrugated channels

An experimental investigation of heat transfer and pressure drop from a new type of corrugated channels is presented. The investigation has been carried out for Reynolds numbers in the range of $\text{800 <}\text{Re}\text{< 5000}$ for one corrugated and one smooth channel. It is found that the heat transfer from the corrugated channel is up to 3.5 times higher than for the smooth one. The pressure drop is however large (5 – 6 times the value of a smooth channel) and it is suggested that the corrugation height and length should be altered in order to balance the increases in heat transfer and pressure drop.     

Testing for the equivalence of factor covariance and mean structures: The issue of partial measurement invariance.

Addresses issues related to partial measurement invariance using a tutorial approach based on the {lisrel} confirmatory factor analytic model. Specifically, we demonstrate procedures for (a) using "sensitivity analyses" to establish stable and substantively well-fitting baseline models, (b) determining partially invariant measurement parameters, and (c) testing for the invariance of factor covariance and mean structures, given partial measurement invariance. We also show, explicitly, the transformation of parameters from an all-X to an all-Y model specification, for purposes of testing mean structures. These procedures are illustrated with multidimensional self-concept data from low (n?=?248) and high (n?=?582) academically tracked high school adolescents. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Phtocrosslinking of polyethylene for production of thin wall insulated wire

A photocrosslinking precess for polyethylene and its industrial irradiation apparatus has recently been developed and used successfully in the manufactre of thin wall crosslinked polyethylene-insulated wires. Polyethylene (PE) resin with the desired amounts of additives, such as photoinitiator, multifunctional crosslinker, and antioxidant is mixe homogeneously. The amixture of PE is granulated, and then extruded on a conductor wire. The coated PE layer in the melt is subsequently irradiated in a specially designed UV irradiation apparatus for 5 to 10 s. The studies show that the photocrosslinked PE-insulation high voltage television wires produced by this new technique possess excellent electrical and mchanical properties and much lower operating cost compared with wires produced by the electron beam crosslinking technique.     

EVALUATION OF A METHOD FOR MEASURING MIXING TIME USING NUMERICAL SIMULATION AND EXPERIMENTAL DATA

A method for measuring mixing performance in large-scale vessels is investigated. The method is evaluated experimentally in a pilotscale reactor and by using a model based on the three-dimensional calculation of the flow field. The method is based on injection of a tracer and measuring the concentration with several detectors at different locations. The mixing performance is measured as the decay rate of the difference between the concentration at the detectors and the final concentration.

The model predicts a strong dependence on injection point. The assumption of a first-order decay rate of the concentration deviation is more appropriate for some injection points.     

Gas-liquid mass transfer in taylor flow through a capillary

The gas-liquid mass transfer in two-phase flow through a capillary has been measured for water-air, ethanol-air and ethylene glycol-air systems. A semi-theoretical model has been developed and compared with experimental results. and a full computer simulations of the flow pattern and mass transfer using a flow simulation program have been made. The measured values are about 30% less than the calculated values.     

Effect of patchwise slip on fluid flow

In this paper, we show that large connected slip patches (hydrophobic patches) are a necessity to induce macroscopic slip effects of water flow in microchannels. For this purpose, the 2D fluid flow between a planar stationary surface with alternating stick and slip patches and a parallel planar surface moving with a constant relative velocity has been studied by computer simulations based on Navier–Stokes equations. A slip patch is defined as the slipping length in a 2D system or a slip area of the surface in a 3D system. The simulations reveal that the ratio (size of each slip patch)/(distance between the two parallel interfaces) has profound effect on the viscous stress on the moving surface when this ratio is around and above one. However, when the ratio is much below one, the effect of the slip patches are minor, even if the area fraction of slip patches are higher than 50 %. Obviously, the stick patches adjacent to the slip patches act as effective barriers, preventing the fluid velocity to increase near the surface with alternating stick and slip patches. The obtained results are scalable and applicable on all length scales, with an exception for narrow channels in the subnano regime, i.e. <1 nm where specific effects as the atomistic composition and the nanostructure of the wall as well as the interactions between the wall and the water molecules have an effect.     

Gas permeation of polymer blends. III. Poly(vinyl chloride) (PVC)/chlorinated polyethylene (CPE)

The permeability P, diffusivity D, and activation energy for diffusion, E_D, of He, O₂, N₂, and CO₂ were determined for blends of PVC/chlorinated polyethylene (CPE), where the chlorine content of the CPE components varied: 36 wt-% for CPE-1, 42 wt-% for CPE-2, and 48 wt-% for CPE-3. The difference in thermal expansion coefficients Δα above and below the glass transition temperature T_g of the polymers and the fractional free volume V_g of the polymers at their T_g were determined. Density and crystallinity measurements for the blends were also carried out as in the earlier work (Shur and Rånby, J. Appl. Polym. Sci., 19 , 1337 (1975)). Dynamic mechanical measurements of the blends were made using a torsion pendulum at about 1 Hz. P and D decreased, but E_D increased with increasing CI content of CPE in the blends. P and D for the blends showed no additivity. The permeability indicated phase inversion for blend compositions at about 10% of CPE-1 and CPD-2 by weight. The experimental and the calculated densities were largely the same for PVC/CPE-1 blends; but for PVC/CPE-2 and PVC/CPE-3 blends, the experimental values were higher than the calculated ones. The Δα and V_g values for PVC and the three CPE samples decreased with increasing CI content in the polymers. Dynamic mechanical measurements indicate that PVC/CPE-1 and PVC/CPE-2 blends form largely incompatible blends, while PVC/CPE-3 blends are compatible to some extent. There is some weak interaction between PVC and CPE-3 giving a low level of compatibility. The solubility of gases obtained from time-lag measurements of diffusion for 50/50 blends decreased for He, O₂, and N₂, but increased for CO₂ with increasing Cl content in CPE. The solubility of He, O₂ and N₂ shows a positive correlation with the Lennard-Jones force constant ?/k. However, a deviation from the linear relation between ?/k and In S was observed for CO₂ and the deviation became larger with increasing Cl content in CPE. The abnormally high solubility of CO₂ is probably due to the high polarizability of this gas. The heat of solution ΔH_s indicates that for He the sorption process may be a molecular slip process (endothermic), but for other gases the sorption may proceed by a dissolution process (exothermic). There is a large difference between the calculated solubility for the blends assuming incompatibility and the experimental values from time-lag measurements. This may partly be due to the uncertainty of sorption values obtained from the time-lag method and/or partly to changes of sorption modes by interaction between PVC and CPE in the blends. The resulting transport behavior of the blends is discussed on the basis of the free volume concept and of phase–phase interaction in the blends.