Solution Method for Countercurrent Plug Flow Models of Multicomponent Gas Separation by Permeation

Gas separation using membrane is now an established unit operation in the chemical process industry. The performance of a single stage membrane permeator depends, among other things, on the feed and permeate flow pattern. In this paper, models for five different idealized flow patterns namely cocurrent flow, countercurrent flow, cross flow, perfect mixing and on-side mixing have been presented. A computer program written in Power Basic has also been developed. The models developed can be used for a binary mixture or multi-component gas feed system. A simple bisection method is used instead of the Newton iterative method originally suggested by Shindo et.al.[6] to solve the root finding-problem in order to ensure convergence. In this study countercurrent flow is found to be the most efficient flow pattern, giving the highest degree of separation and requiring the least membrane area.

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A Capillary Electrophoresis Platform With “On-Chip” Electrochemical Detection: Experimental and Computational Flow Studies

10.1115/imece2001/mems-23911 ◽

2001 ◽

Author(s):

Thomas J. Roussel ◽

Robert S. Keynton ◽

Kevin M. Walsh ◽

Mark M. Crain ◽

John F. Naber ◽

...

Keyword(s):

Capillary Electrophoresis ◽

Electrochemical Detection ◽

Power Supply ◽

Electroosmotic Flow ◽

Plug Flow ◽

Finite Element Models ◽

Separation Channel ◽

Flow Models ◽

On Chip ◽

Electrochemical Potentials

Abstract The purpose of this study was to compare experimental electrokinetic plug flow velocities to computational flow models of microfabricated capillaries. Electroosmotic flow studies of dichlorofluorescein and electrophoretic separation of dopamine and catechol in a microfabricated capillary electrophoresis (CE) system were performed both experimentally and computationally. A “balanced cross design” consisting of a bent 2 cm long injection channel and a straight 2 cm long separation channel was used. The geometry of the capillary was 65 μm wide and 20 μm deep. For the fluorescein study, separation voltages ranging between 0.25 kV and 1 kV were applied, while voltages ranging from 100 V to 550 V were used in the separation studies. Laser Induced Fluorescent (LIF) images were obtained for flow visualization and qualitative analysis in the electroosmotic flow studies, while electrochemical potentials were acquired using “on-chip” electrodes interfaced to a custom-designed power supply and electrochemical detection (ECD) circuit. Finite element models of the experimental device were generated and flows were simulated using commercially available software. For the electroosmotic flow studies, the computational results were found to be within ± 11% of the experimentally obtained values. Similarly, the results of the computational separations of catechol and dopamine predicted plug velocities that were within ± 7.6% of the experimentally determined values.

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