Capillary Based Processes in Microtechnology

Abstract

Capillary Based Processes in Microtechnology

V.S. Stenkamp, W.E. TeGrotenhuis, and S.D. Rassat

Performing thermal and chemical processing in microchannels facilitates extremely rapid heat and mass transfer rates that allows for orders of magnitude reduction in hardware volume and mass. This type of enhanced performance can also occur for multiphase fluids, but the small dimensions involved change the governing physics such that interfacial forces become more pronounced. At Battelle, methods have been found to take advantage of these interfacial forces to induce capillary-based separations in a family of devices that include liquid/gas phase separation, partial condensation with phase separation, distillation, and absorption.

In the case of phase separation, gas residence times on the order of hundreds of seconds and liquid residence times on the order of tens of seconds have been realized. Surface tension and hydrodynamic forces dominate such that separation has been effective in microgravity environments. It has been found that good separation requires not only the use of porous material such as pore throats and wicks, but control of the flow regime as well. The same principles used in phase separation have been modified to allow partial condensation with concomitant phase separation. Heat fluxes up to 55,000 W/m² have been obtained with gas residence times between 10-60 msec.

In the case of separations involving mass transfer, the primary resistance is often encountered in the liquid phase. The use of wicking materials to channel the liquid flow has allowed control of the liquid film thickness and hence the mass transfer rate. In the case of absorption, mass transfer coefficients up to four times higher than conventional packed columns have been achieved thus far.

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