Carbon Nanoparticle Production by Inductively Coupled Thermal Plasmas: Controlling the Thermal History of Particle Nucleation

The process control for reproducibility, uniformity, and achievement of desired structures for carbon black generated in thermal plasma devices is studied in this paper through modeling, and correlated with experimental results. A numerical simulation of the flow and energy fields, stream function lines and the quench rates of the plasma gas in a conical shape reactor at different pressures was made. An argon plasma is used with highly diluted methane (0.6–7%) as the carbon precursor. The quench rates were studied in order to observe the flow development and hence the thermal history of particle nucleation. Three pressure cases of 20.7, 55.2 and 101.3 kPa and two plasma powers cases of 10 and 20 kW were studied. The modeling results enabled carbon nanoflakes production in the experimental tests performed on an inductively coupled thermal plasma system. Results indicate a robust process control enabling very little particle morphology variation over this wide range of reactor pressure values and varying plasma power, and a very high reproducibility of the particle morphologies obtained.     

A noninvasive method for the measurement of flow-induced surface displacement of a compliant surface

A noninvasive optical method is described which allows the measurement of the vertical component of the instantaneous displacement of a surface at one or more points. The method has been used to study the motion of a passive compliant layer responding to the random forcing of a fully developed turbulent boundary layer. However, in principle, the measurement technique described here can be used equally well with any surface capable of scattering light and to which optical access can be gained. The technique relies on the use of electro-optic position-sensitive detectors; this type of transducer produces changes in current which are linearly proportional to the displacement of a spot of light imaged onto the active area of the detector. The system can resolve displacements as small as 2 m for a point 1.8 mm in diameter; the final output signal of the system is found to be linear for displacements up to 200 m, and the overall frequency response is from DC to greater than 1 kHz. As an example of the use of the system, results detailing measurements obtained at both one and two points simultaneously are presented.List of symbols C _t elastic transverse wave speed = (G/)^1/2 - d ⁺ spot diameter normalized by viscous length scale - G frequency average of G() - G() shear storage modulus - G() shear loss modulus - l. viscous length scale = v/u _* - N total number of sampled data values - r separation vector for 2-point measurements = (, ) - rms root-mean-square value - R momentum thickness Reynolds number = U _t8/v - t time - u (y) mean streamwise component of velocity in boundary layer - u _* friction velocity = (t _w/)^1/2 - U free-stream velocity - x, y, z longitudinal, normal and spanwise directions - y _o undisturbed surface position - vertical component of compliant surface displacement - ₉₉ boundary layer thickness for which u(y) = 0.99 U _t8 - _l viscous sublayer thickness 5 l _* - frequency average of G()/ - boundary layer momentum thicknes = - fluid dynamic viscosity - v fluid kinematic viscosity = / - , longitudinal, spanwise components of separation vector r - fluid density - time delay - _w wall shear stress     

Harn

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A continuous review replenishment–disposal policy for an inventory system with autonomous supply and fixed disposal costs

In this study, we analyze an inventory system facing stochastic external demands and an autonomous supply (independent return flow) in the presence of fixed disposal costs and positive lead times under a continuous review replenishment–disposal policy. We derive the analytical expressions of the operating characteristics of the system; and, construct the objective function to minimize the total expected costs of ordering, holding, purchasing and disposal per unit time subject to a fill rate constraint. An extensive numerical analysis is conducted to study the sensitivity of the policy parameters and the benefit of employing a policy which allows for disposal of excess stock in this setting. We model the net demand process as the superposition of normally distributed external demand and inflows, which is expressed as a Brownian motion process. Our findings indicate that the disposal option results in considerable savings even (i) in the presence of non-zero fixed disposal costs, (ii) large actual demand rates with high return ratios (resulting in small net demands) and (iii) for moderate return ratios with high demand variability.     

Laser-induced positive ion and neutral atom/molecule emission from single-crystal CaHPO4·2 H2O: The role of electron-beam-induced defects

We examine laser-induced ion and neutral emissions from single-crystal CaHPO₄·2 H₂O (brushite), a wide-band-gap, hydrated inorganic single crystal, with 248-nm excimer laser radiation. Both laser-induced ion and neutral emissions are several orders of magnitude higher following exposure to 2 keV electrons at current densities of 200 7A/cm² and doses of 1 C/cm². In addition to intense Ca⁺ signals, electron-irradiated surfaces yield substantial CaO⁺, PO⁺, and P⁺ signals. As-grown and as-cleaved brushite show only weak neutral O₂ and Ca emissions, whereas electron-irradiated surfaces yield enhanced O₂, Ca, PO, PO₂, and P emissions. Electron irradiation (i) significantly heats the sample, leading to thermal dehydration (CaHPO₄ formation) and pyrolysis (Ca₂P₂O₇ formation) and (ii) chemically reduces the surface via electron stimulated desorption. The thermal effects are accompanied by morphological changes, including recrystallization. Although complex, these changes lead to high defect densities, which are responsible for the dramatic enhancements in the observed laser desorption.