Spreading of a saturation front of heterogeneous chemical reaction througn an aerosol gloud

A cloud of aerosol particles sediments in air containing reactants. On the basis of a macroscopic chemical and mass transfer model founded on the kinetic theory of heterogeneous reactions we analyzed the spreading of chemical reaction through the cloud of aerosol particlesyesBelgorod State National Research Universit

Effects of transport and phase equilibrium on fast, nearly irreversible reactive extraction

Abstract Integration of reaction and separation can be exploited to drive reversible reactions in the direction of the desired product using multiphase flow contacting. In the case of nearly irreversible, fast reactions, however, the dynamics of the product have little influence on the reactor efficiency in say liquid-liquid reactive extraction. A similar intensification in reaction efficiency to reactive separation can be achieved by exploiting phase equilibrium or asymmetry in mass transfer rates of the reactants. Here, a model for two-layer biphasic flow and homogeneous reaction is proposed for co-current reactive extraction, demonstrating that localization and intensification of reaction occurs in the region between the entrance and crossover. Crossover occurs if the reactant in stoichiometric deficit preferentially populates the reacting phase due to sufficient imbalance in either mass transfer coefficients or phase equilibrium. We develop an infinite Peclet number (convection dominates over bulk diffusion) model that indicates that crossover occurs when for fast, irreversible reactions. u 0 and v 0 are initial charges to the tubular reactor, the 's are mass transfer coefficients for each side of the fluid interface and the h's are Henry's Law coefficients for reactants U and V . The interpretation of this formula is that if v 0 > u 0 , then crossover will occur if the overall mass transfer rate of U is faster than the overall mass transfer rate for V . Downstream of the crossover point, the reactant in stoichiometric excess also dominates the reacting phase due to relative exhaustion of the more-mobile component. A finite Peclet number theory for fast, irreversible reaction shows that the above formula is a conservative limit for crossover-if it holds, crossover will occur regardless of the Peclet number. A formula for the larger parametric region for crossover with finite Peclet number is derived. Verification that crossover is achieved is found by finite-element numerical analysis of the full governing equations. Both theory and numerical analysis predict localization and intensification of the reaction due to crossover. Crossover sets the length scale as approximately two and a half crossover lengths for completed reaction for sufficiently high Peclet number with strong kinetic asymmetry. The theory predicts that taking the ratio of inlet concentrations S = u 0 /v 0 to be the critical value at fixed physical parameters for mass transfer and phase equilibrium maximizes localization and reactor efficiency. Similarly, the kinetic asymmetry should be as large as possible to exploit the benefits of crossover.

A Dual Fluorescence–Spin Label Probe for Visualization and Quantification of Target Molecules in Tissue by Multiplexed FLIM–EPR Spectroscopy

Simultaneous visualization and concentration quantification of molecules in biological tissue is an important though challenging goal. The advantages of fluorescence lifetime imaging microscopy (FLIM) for visualization, and electron paramagnetic resonance (EPR) spectroscopy for quantification are complementary. Their combination in a multiplexed approach promises a successful but ambitious strategy because of spin label-mediated fluorescence quenching. Here, we solved this problem and present the molecular design of a dual label (DL) compound comprising a highly fluorescent dye together with an EPR spin probe, which also renders the fluorescence lifetime to be concentration sensitive. The DL can easily be coupled to the biomolecule of choice, enabling in vivo and in vitro applications. This novel approach paves the way for elegant studies ranging from fundamental biological investigations to preclinical drug research, as shown in proof-of-principle penetration experiments in human skin ex vivo

Spreading of a saturation front of heterogeneous chemical reaction througn an aerosol gloud

yesA cloud of aerosol particles sediments in air containing reactants. On the basis of a macroscopic chemical and mass transfer model founded on the kinetic theory of heterogeneous reactions we analyzed the spreading of chemical reaction through the cloud of aerosol particlesBelgorod State National Research Universit

Behavior of the TTF2 RF Gun with long pulses and high repetition rates *

Abstract This paper presents the behavior of the TTF2 RF gun with long RF pulses (up to 900 µs), high peak power (up to 3 MW) and high repetition rate (up to 10 Hz). The experiments have been realized at the Photo Injector Test Facility of DESY Zeuthen from January to March 2003, where the RF gun has been tested prior to its installation at DESY Hamburg on the TTF2 beamline