reaction massD o w n l o a d e d  b y  [P u r d u e  U n i v e r s i t y  L i b r a r i e s ] a t  00:35 27 J a n u a r y  2014
get away from traditional strategies in chemical engineering. In the following,a comprehensive analysis covering these aspects will be given.2.EFFECT OF MINIATURIZATION ON UNIT OPERATIONS AND REACTIONS 2.1.Enhancement of Heat Transfer and Mass Transfer Processes Diffusion,thermal conductivity,and viscosity are physically similar phenomena that involve the transport of a physical quantity through a gas or liquid. The driv-ing forces for the corresponding transport fluxes of mass,energy,and momentum are the gradients in concentration,temperature,and velocity,respectively,where in all three cases the fluxes are in the same direction as the gradients. For given differences in these properties,a decrease in the characteristic dimensions results in an increase in these gradients and,correspondingly,in higher mass and heat
transfer rates as well as in higher viscous losses. Accordingly,mixing and heat exchange systems with extremely high transfer rates per unit volume can be real-ized by miniaturization; on the other hand,however,the effect of viscous losses has to be taken into account.
Besides the effect of decreasing linear dimensions on the corresponding gradients,the effective surface area for exchange processes has to be considered.With decreasing characteristic dimensions,
the surface-area-to-volume ratio of F IGURE 1Evolutionary development through process intensification.D o w n l o a d e d  b y  [P u r d u e  U n i v e r s i t y  L i b r a r i e s ] a t  00:35 27 J a n u a r y  2014
D o w n l o a d e d  b y  [P u r d u e  U n i v e r s i t y  L i b r a r i e s ] a t  00:35 27 J a n u a r y  2014
F IGURE 2Microreactor for parallel screening of catalysts for partial oxidation of methane.(Source:D. Hönicke, TU Chemnitz.)
Copyright © 2004 by Marcel Dekker, Inc. All Rights Reserved.D o w n l o a d e d  b y  [P u r d u e  U n i v e r s i t y  L i b r a r i e s ] a t  00:35 27 J a n u a r y  2014

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