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Title: Effect of a slit-shaped trap on depletion kinetics within a microchannel

Abstract

The diffusion-limited trapping reaction kinetics of the growth of the depletion zone within and around a 'slit-shaped' trap in a flat microchannel was studied experimentally and numerically. In the experiment, an ellipse-shaped laser beam acted as a slit trap in a long, flat capillary, and the trapping reaction is photobleaching of fluorescein dye. The parameter studied was the {theta} distance, i.e., the distance from the trap to the point where the reactant concentration has been locally depleted to the specific survival fraction [{theta}] of its initial bulk value. When the trap is perfect, then, due to the geometry of the trap and the reactor, as many as three time regimes can be found, with up to two crossover transitions. The number of crossovers is determined by the relative sizes of the trap and the microreactor. In the case of two crossovers, we show that the first crossover relates to the length of the trap, while the second crossover relates to the width of the reactor. When the slit trap is imperfect and its width cannot be neglected, as is the case in the experiments, a nontrivial early behavior is observed, followed by two regions in time, separated by a singlemore » crossover only.« less

Authors:
; ;  [1];  [1];  [2];  [3]
  1. Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055 (United States)
  2. (Greece)
  3. Department of Physics, Bar-Ilan University, Ramat-Gan 52900 (Israel)
Publication Date:
OSTI Identifier:
20779236
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. E, Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics; Journal Volume: 73; Journal Issue: 4; Other Information: DOI: 10.1103/PhysRevE.73.041104; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ABSORPTION; CAPILLARIES; DIFFUSION; FLUORESCEIN; GEOMETRY; LASERS; PHOTOCHEMISTRY; REACTION KINETICS; SURVIVAL CURVES; TRAPPING; TRAPS; ZONES

Citation Formats

Park, Sung Hyun, Peng, Hailin, Kopelman, Raoul, Argyrakis, Panos, Department of Physics, University of Thessaloniki, 54124 Thessaloniki, and Taitelbaum, Haim. Effect of a slit-shaped trap on depletion kinetics within a microchannel. United States: N. p., 2006. Web. doi:10.1103/PHYSREVE.73.0.
Park, Sung Hyun, Peng, Hailin, Kopelman, Raoul, Argyrakis, Panos, Department of Physics, University of Thessaloniki, 54124 Thessaloniki, & Taitelbaum, Haim. Effect of a slit-shaped trap on depletion kinetics within a microchannel. United States. doi:10.1103/PHYSREVE.73.0.
Park, Sung Hyun, Peng, Hailin, Kopelman, Raoul, Argyrakis, Panos, Department of Physics, University of Thessaloniki, 54124 Thessaloniki, and Taitelbaum, Haim. Sat . "Effect of a slit-shaped trap on depletion kinetics within a microchannel". United States. doi:10.1103/PHYSREVE.73.0.
@article{osti_20779236,
title = {Effect of a slit-shaped trap on depletion kinetics within a microchannel},
author = {Park, Sung Hyun and Peng, Hailin and Kopelman, Raoul and Argyrakis, Panos and Department of Physics, University of Thessaloniki, 54124 Thessaloniki and Taitelbaum, Haim},
abstractNote = {The diffusion-limited trapping reaction kinetics of the growth of the depletion zone within and around a 'slit-shaped' trap in a flat microchannel was studied experimentally and numerically. In the experiment, an ellipse-shaped laser beam acted as a slit trap in a long, flat capillary, and the trapping reaction is photobleaching of fluorescein dye. The parameter studied was the {theta} distance, i.e., the distance from the trap to the point where the reactant concentration has been locally depleted to the specific survival fraction [{theta}] of its initial bulk value. When the trap is perfect, then, due to the geometry of the trap and the reactor, as many as three time regimes can be found, with up to two crossover transitions. The number of crossovers is determined by the relative sizes of the trap and the microreactor. In the case of two crossovers, we show that the first crossover relates to the length of the trap, while the second crossover relates to the width of the reactor. When the slit trap is imperfect and its width cannot be neglected, as is the case in the experiments, a nontrivial early behavior is observed, followed by two regions in time, separated by a single crossover only.},
doi = {10.1103/PHYSREVE.73.0},
journal = {Physical Review. E, Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics},
number = 4,
volume = 73,
place = {United States},
year = {Sat Apr 15 00:00:00 EDT 2006},
month = {Sat Apr 15 00:00:00 EDT 2006}
}
  • The diffusion-limited kinetics of the growth of a depletion zone around a static point trap in a thin, long channel geometry was studied using a laser photobleaching experiment of fluorescein dye inside a flat rectangular capillary. The dynamics of the depletion zone was monitored by the {theta} distance, defined as the distance from the trap to the point where the reactant concentration has been locally depleted to the specified survival fraction ({theta}) of its initial bulk value. A dimensional crossover from two dimensions to one dimension, due to the finite width of the reaction zone, was observed. We define amore » 'parallel' and a 'perpendicular' {theta} distance, along the slab long and short dimensions, respectively, and study their time development as a means to study the asymmetrical nature of the slab geometry. For all {theta} values, the crossover occurs concurrently for both {theta} distances when the depletion zone touches the boundary for the first time. We derive theoretical expressions for this geometry and compare them with the experimental data. We also obtain important insight from the ratio of the reactant concentration profiles in the parallel and perpendicular directions. Exact enumeration and Monte Carlo simulations support the anomalous depletion scaling results. Nevertheless, the crossover time ({tau}{sub c}) is still found to scale with the width (W) of the rectangular reaction zone as {tau}{sub c}{approx}W{sup 2}, as expected from the basic Einstein diffusion law.« less
  • Experimental and numerical investigations were carried out to gain a better understanding of the flow characteristics within an annular S-shaped duct, including the effect of the inlet boundary layer (IBL) on the flow. A duct with six struts and the geometry as that used to connect compressor spools on the experimental small two-spool turbofan engine was investigated. A curved downstream annular passage with similar meridional flow path geometry to that of the centrifugal compressor has been fitted at the exit of S-shaped duct. Two types of the IBL (i.e., thin and thick IBL) were used. Results showed that large differencesmore » of flow patterns were observed at the S-shaped duct exit between two types of IBL, though the value of net total pressure loss has not been remarkably changed. According to overall total pressure loss, which includes the IBL loss, the total pressure loss was greatly increased near the hub as compared to that for a thin one. For the thick IBL, a vortex pair related to the hub-side horseshoe vortex and the separated flow found at the strut trailing edge has been clearly captured in the form of the total pressure loss contours and secondary flow vectors, experimentally and numerically. The high-pressure loss regions on either side of the strut wake near the hub may act on a downstream compressor performance. There is a much-distorted three-dimensional flow patterns at the exit of S-shaped duct. This means that the aerodynamic sensitivity of S-shaped duct to the IBL thickness is very high. Therefore, sufficient care is needed to design not only downstream aerodynamic components (for example, centrifugal impeller) but also upstream aerodynamic components (LPC OGV).« less
  • Earlier computations on diffusion in the spherical one-radical one- solute model were extended by taking account of the transient dilution of the solute which occurs during the reaction. Although the drop in concentration of the solute near the center of the reaction zone may be considerable, its effect on the fraction of radicals combining with the solute is only of the order of one percent under the most unfavorable conditions likely to be encountered when the model is applied to gamma -irradiated aqueous solutions. (auth)
  • The relation between field size and tolerance of rabbit's brain to roentgen irradiation via slit-shaped field, 12 mm to 1 mm wide, was studied. Single skin doses between 2,100 r and 27,000 r were given. After 52 weeks the morphology of the lesions was analyzed. The frequency of injuries as well as the lowest focal dose which produced lesions were determined. The effect of irradiation decreased markedly with reduced width of slit. Resulting curves for the occurrence of necrosis and for discrete lesions are both S-shaped. The shape of the curves is discussed, especially the influence of diffusion processes. Publishedmore » data on the area factor make it likely that the tolerance curve for the skin will be S-shaped too.« less