Axial dispersion of gas and solid phases in a gas—solid packed column at trickle flow

Axial dispersion of gas and solid phases in a gas—solid packed column at trickle flow, a promising new countercurrent operation, was evaluated using residence time distribution (RTD) experiments. The column was packed with dumped Pall rings, the gas phase was air at ambient conditions and the solid was a porous catalyst carrier.\ud \ud The RTD experiments for the solid phase were carried out using the “perfect pulse method”, while for the gas phase the “imperfect pulse method” was used. The model parameters were calculated by the methods of moments and various parameter optimization methods.\ud \ud At a given solid flow rate axial dispersion of the gas phase decreases with increasing gas velocity and is strongly dependent upon solid mass flux. Axial dispersion of the solid phase is approximately independent of the gas velocity and it is reduced if the solid mass flux is increased. For conditions of practical importance, 2 – 5 and 5 – 15 Pall ring layers correspond to the height of a mixing unit in the gas and solid phase, respectively

Quantum theory of dispersive electromagnetic modes

A quantum theory of dispersion for an inhomogeneous solid is obtained, from a starting point of multipolar coupled atoms interacting with an electromagnetic field. The dispersion relations obtained are equivalent to the standard classical Sellmeir equations obtained from the Drude-Lorentz model. In the homogeneous (plane-wave) case, we obtain the detailed quantum mode structure of the coupled polariton fields, and show that the mode expansion in all branches of the dispersion relation is completely defined by the refractive index and the group-velocity for the polaritons. We demonstrate a straightforward procedure for exactly diagonalizing the Hamiltonian in one, two or three-dimensional environments, even in the presence of longitudinal phonon-exciton dispersion, and an arbitrary number of resonant transitions with different frequencies. This is essential, since it is necessary to include at least one phonon (I.R.) and one exciton (U.V.) mode, in order to accurately represent dispersion in transparent solid media. Our method of diagonalization does not require an explicit solution of the dispersion relation, but relies instead on the analytic properties of Cauchy contour integrals over all possible mode frequencies. When there is longitudinal phonon dispersion, the relevant group-velocity term is modified so that it only includes the purely electromagnetic part of the group velocity

Effect of dispersion interactions on the properties of LiF in condensed phases

Classical molecular dynamics simulations are performed on LiF in the framework of the polarizable ion model. The overlap-repulsion and polarization terms of the interaction potential are derived on a purely non empirical, first-principles basis. For the dispersion, three cases are considered: a first one in which the dispersion parameters are set to zero and two others in which they are included, with different parameterizations. Various thermodynamic, structural and dynamic properties are calculated for the solid and liquid phases. The melting temperature is also obtained by direct coexistence simulations of the liquid and solid phases. Dispersion interactions appear to have an important effect on the density of both phases and on the melting point, although the liquid properties are not affected when simulations are performed in the NVT ensemble at the experimental density.Comment: 8 pages, 5 figure

The formation of tretinoin-PEG 6000 solid-solid solution to increase the dissolution rate of tretinoin

The formation of solid-solid dispersion of tretinoin which is insoluble in water into water soluble carrier PEG, might accelerate solubility and dissolution rate. The objectives of this study were to obtain dissolution profile and physical properties of Tretinoin-PEG solid dispersion which was prepared by solventfusion method, to obtain the composition of Tretinoin and PEG in which produce solid dispersion with optimum dissolution rate and to obtain the composition of Tretinoin-PEG, which produce an interstitial solid-solid solution. Solvent fusion method at low temperature was choosen to prepare the solid dispersion system. The physical state of formed solid dispersion was determined by X-Ray diffractometer. To unveil the information about the solubility and dissolution rate of tretinoin, a test toward the dissolution rate of tretinoin was performed into the dissolution medium phosphate buffer. The X-Ray diffractogram of tretinoin-PEG solid dispersion in all composition indicated that tretinoin hasformed a molecular dispersion in the PEG crystals in all composition. In solid dispersion was obtained by solvent-fusion method in molecular or in solid-solid solution. Dissolution efficiency (DE) value prooved that molecular dispersion of tretinoin-PEG could increase the dissolution rate of tretinoin. Thus it could concluded that in comparison to the tretinoin and its physical mixture, the solid dispersion of tretinoin-PEG led the higher dissolution rate and the optimum rate was achieved by composition of 1=100 with DE value = 74.Key words : Tretinoin, PEG, Solid Dispersion, Dissolution Rat

Dispersion phenomena in microchannels: Transition from Taylor-Aris to convection-dominated regime

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.This article addresses the qualitative and quantitative properties of solute transport and dispersion in microchannel of finite-length. As the Peclet number increases a transition from the Taylor-Aris to a new regime referred as convection dominated dispersion occurs, which is controlled by the velocity profile near the stagnation points at the solid walls. The properties characterizing dispersion dominated regime can be used for analytical purposes as a chromatographic-based velocimetry and for determining the eventual occurrence of slip at the solid walls of microchannels

Mass transfer in a gas-solid packed column at trickle flow

The height of an overall transfer unit has been evaluated in a gas—solid packed column at trickle flow by measuring column performance during steady state adsorption experiments. Results have been interpreted with an extraction model: mass transfer and axial dispersion in both phases. Using Bodenstein numbers for the gas and solid phases from a previous investigation the height of a true transfer unit has been calculated.\ud \ud The column was filled with dumped Pall rings, the solid phase was a freely flowing catalyst carrier, and the gas phase was air at ambient conditions containing freon-12 as adsorbing component.\ud \ud At low gas velocities column performance is entirely determined by axial dispersion but at higher gas velocities mass transfer limitations become important. For conditions of practical importance the height of a true transfer unit corresponds to 4 – 9 Pall ring layers

Solid state welding of dispersion-strengthened nickel alloys

Two-step solid state welding cycle applied to carefully prepared surfaces of an unrecrystallized alloy prevents loss of parent-metal strength at weld joint of dispersion-strengthened, nickel-chromium alloy