Electrochemical measurements of mass transfer at surfaces with discrete reactive areas

Juhasz, Nikola M.; Deen, William M.

doi:10.1002/aic.690391014

Cited by 13 publications

(6 citation statements)

References 20 publications

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“…Then, the Sherwood number is again close in value to its periodic counterpart. This observation is supported by the results of Juhasz & Deen (1993), who measured the limiting current generated at a rotating electrode patterned with reactive sites. It was found that the limiting current in a laminar flow (at Pe 1) depends subtly on the electrode distribution for small pattern coverages.…”

Section: Random Distribution Of Disks In a Periodic Systemsupporting

confidence: 78%

“…The flow field was assumed to be unidirectional and to have a general algebraic form, as the primary goal was to show that the local Péclet number affects the Sherwood number. They also performed experiments to this effect (Juhasz & Deen 1993). This exposed the shortcomings of the existing contemporary analysis of a series of problems related to mass transport to reactive spots in a non-adsorbing solid surface, where the Sherwood number was calculated using the stagnant-film approximation around the reactive region, i.e.…”

Section: General Problem Statementmentioning

confidence: 97%

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Heat/mass transport in shear flow over a heterogeneous surface with first-order surface-reactive domains

Shah

Shaqfeh

2015

J. Fluid Mech.

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Surfaces that include heterogeneous mass transfer at the microscale are ubiquitous in nature and engineering. Many such media are modelled via an effective surface reaction rate or mass transfer coefficient employing the conventional ansatz of kinetically limited transport at the microscale. However, this assumption is not always valid, particularly when there is strong flow. We are interested in modelling reactive and/or porous surfaces that occur in systems where the effective Damköhler number at the microscale can be O(1) and the local Péclet number may be large. In order to expand the range of the effective mass transfer surface coefficient, we study transport from a uniform bath of species in an unbounded shear flow over a flat surface. This surface has a heterogeneous distribution of first-order surface-reactive circular patches (or pores). To understand the physics at the length scale of the patch size, we first analyse the flux to a single reactive patch. We use both analytic and boundary element simulations for this purpose. The shear flow induces a 3-D concentration wake structure downstream of the patch. When two patches are aligned in the shear direction, the wakes interact to reduce the per patch flux compared with the single-patch case. Having determined the length scale of the interaction between two patches, we study the transport to a periodic and disordered distribution of patches again using analytic and boundary integral techniques. We obtain, up to non-dilute patch area fraction, an effective boundary condition for the transport to the patches that depends on the local mass transfer coefficient (or reaction rate) and shear rate. We demonstrate that this boundary condition replaces the details of the heterogeneous surfaces at a wall-normal effective slip distance also determined for non-dilute patch area fractions. The slip distance again depends on the shear rate, and weakly on the reaction rate, and scales with the patch size. These effective boundary conditions can be used directly in large-scale physics simulations as long as the local shear rate, reaction rate and patch area fraction are known.

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Section: Random Distribution Of Disks In a Periodic Systemsupporting

confidence: 78%

Section: General Problem Statementmentioning

confidence: 97%

Heat/mass transport in shear flow over a heterogeneous surface with first-order surface-reactive domains

Shah

Shaqfeh

2015

J. Fluid Mech.

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“…The problem of trapping of diffusing particles by heterogeneous boundaries, with absorbing regions on the otherwise reflecting surfaces, arises in the analysis of various processes in physics, chemistry, and biology. Examples include electric current through arrays of microelectrodes, [1][2][3] porous membrane transport, [4][5][6] reactions on supported catalysts, 7 water exchange in plants, 8 ligand binding to cell surface receptors, [9][10][11][12][13][14][15][16][17][18] ligand accumulation in cell culture assays, 19,20 to mention just a few. This is an extremely complicated problem, because it involves non-uniform boundary conditions on the surface.…”

Section: Introductionmentioning

confidence: 99%

Trapping of diffusing particles by striped cylindrical surfaces. Boundary homogenization approach

Dagdug

Berezhkovskii

Skvortsov

2015

The Journal of Chemical Physics

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We study trapping of diffusing particles by a cylindrical surface formed by rolling a flat surface, containing alternating absorbing and reflecting stripes, into a tube. For an arbitrary stripe orientation with respect to the tube axis, this problem is intractable analytically because it requires dealing with non-uniform boundary conditions. To bypass this difficulty, we use a boundary homogenization approach which replaces non-uniform boundary conditions on the tube wall by an effective uniform partially absorbing boundary condition with properly chosen effective trapping rate. We demonstrate that the exact solution for the effective trapping rate, known for a flat, striped surface, works very well when this surface is rolled into a cylindrical tube. This is shown for both internal and external problems, where the particles diffuse inside and outside the striped tube, at three orientations of the stripe direction with respect to the tube axis: (a) perpendicular to the axis, (b) parallel to the axis, and

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“…To address this problem, Yang and Lewandowski (1995) developed a microtechnique to evaluate the local mass transfer coefficient in biofilms by measuring the limiting current drawn from a mobile microelectrode. The limiting current technique, based on the reduction of dissolved electroactive species at a cathodically polarized electrode, is often used to determine mass transfer rates to surfaces (Dawson and Trass, 1972;Hanratty, 1991;Juhasz and Deen, 1993). The concept of local mass transport coefficient introduced by Yang and Lewandowski (1995) results directly from the limiting current technique with the exception of using a mobile electrode, instead of a stationary one, to measure the limiting current.…”

Section: Introductionmentioning

confidence: 99%

Microelectrode measurements of local mass transport rates in heterogeneous biofilms

Rasmussen

Lewandowski

1998

Biotechnol. Bioeng.

114

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Microelectrodes were used to measure oxygen profiles and local mass transfer coefficient profiles in biofilm clusters and interstitial voids. Both profiles were measured at the same location in the biofilm. From the oxygen profile, the effective diffusive boundary layer thickness (DBL) was determined. The local mass transfer coefficient profiles provided information about the nature of mass transport near and within the biofilm. All profiles were measured at three different average flow velocities, 0.62, 1.53, and 2.60 cm sec−1, to determine the influence of flow velocity on mass transport. Convective mass transport was active near the biofilm/liquid interface and in the upper layers of the biofilm, independent of biofilm thickness and flow velocity. The DBL varied strongly between locations for the same flow velocities. Oxygen and local mass transfer coefficient profiles collected through a 70 μm thick cluster revealed that a cluster of that thickness did not present any significant mass transport resistance. In a 350 μm thick biofilm cluster, however, the local mass transfer coefficient decreased gradually to very low values near the substratum. This was hypothetically attributed to the decreasing effective diffusivity in deeper layers of biofilms. Interstitial voids between clusters did not seem to influence the local mass transfer coefficients significantly for flow velocities of 1.53 and 2.60 cm sec−1. At a flow velocity of 0.62 cm sec−1, interstitial voids visibly decreased the local mass transfer coefficient near the bottom. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 59:302–309, 1998.

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Electrochemical measurements of mass transfer at surfaces with discrete reactive areas

Cited by 13 publications

References 20 publications

Heat/mass transport in shear flow over a heterogeneous surface with first-order surface-reactive domains

Heat/mass transport in shear flow over a heterogeneous surface with first-order surface-reactive domains

Trapping of diffusing particles by striped cylindrical surfaces. Boundary homogenization approach

Microelectrode measurements of local mass transport rates in heterogeneous biofilms

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