We design microchannel devices for making chemical separations in gas-liquid and liquid-liquid systems. Micromachined contactor plates with a matrix of uniform holes separate the microchannels. For example, the micromachined contactor plate might be 25 micron thick Kapton substrate with machined holes that are about 25 microns in diameter. The mass transfer resistance of the contactor plate is a function of several parameters, including the thickness of the contactor plate, porosity, tortuosity, and the solute diffusion coefficient in the wetting liquid that fills the holes.
Achieving high contact area per unit system volume, thin-film con-tacting, and establishing uniform flow distribution result in substantially higher throughput per total system volume over con-ventional technologies. These devices achieve much higher mass transfer rates than are found in macroscale technologies. For instance, when applied to solvent extraction, there is intimate contact of two immis-cible fluids as they flow through very thin channels. These channels are smaller than the normal mass transfer boundary layer. This reduces the mass transfer resistances in each phase and thereby increases the overall mass transfer rates.
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