ABSTRACT
One of the highlights of the last two decades of the twentieth century, in the field of technological advancements, was the relentless effort of the scientific community toward miniaturization. Such concentrated effort manifested in the development of various state-of-the-art micro-or nanoscale devices. Most of these devices utilized the flows of liquids through confinements, having characteristic dimensions of the order of microns or nanometers. Applications of such flows are varied, and encompass the fields of thermal and chemical engineering, material processing, biotechnology, and biomedical engineering. At present, liquid flows through micro-or nanoscale conduits form an integral part of an array of processes and devices, such as complex biophysiological networks, lab-on-a-chip based biomicro/ nanofluidic devices, material/chemical handling processes, certain geophysical processes, and thermal management of microelectronic systems/ devices. In view of these scientific and technological advancements, it is imperative to develop a detailed understanding of transport processes in narrow confinements. Hence, a series of experimental and theoretical studies were initiated in this line of research to delineate the microscale transport
CONTENTS
2.1 Introduction ..................................................................................................35 2.2 Fluid Friction in Narrow Confinements Comprised of Rough
Hydrophobic Substrates .............................................................................. 37 2.2.1 Mesoscale Model Description ........................................................40 2.2.2 Implications of Hydrophobic Interactions on Entrance
Region Hydrodynamics for Microflows .......................................42 2.3 Effects of Heat Transfer on Flow Friction in Narrow Confinements ...44 2.4 Conclusions ...................................................................................................46 References ............................................................................................................... 47
process characteristics more explicitly. By virtue of these investigations, it was observed that the underlying hydrodynamics of liquid flows over such nanoscopic scales deviate appreciably from the well-established paradigm of classical macroscale flows. These deviations were a revelation to the contemporary scientific community, and further encouraged them to devise more sophisticated tools of investigation that aided in better comprehension of mass and thermal transport processes in microsystems, characterized by enhanced surface-to-volume ratio. Studies reported so far in the open literature, pertaining to microscale flow characteristics, were analyzed and meticulously documented in an exhaustive review published very recently by our group (Dey et al., 2012). For microscale flows, the perceived deviations from macroscale flow characteristics are primarily attributed to the dependence of the microflow hydrodynamics on the significant solid-liquid interfacial interactions, due to the commensurate interfacial and system length scales. Moreover, the surface characteristics of the confining flow boundaries have seemingly nontrivial and complex influence on the interfacial interaction mechanisms over such reduced length scales. In essence, the correlation between the bulk flow hydrodynamics and the interfacial inter actions can no longer be trivially precluded for such small scale systems.
