tmg chapter one

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CHAPTER

ONEMICROSCALE ENERGY TRANSPORT IN SOLIDS

Arunava Majumdar

Department ofMechanical Engineering,

University ofCalifornia,

Berkeley, CA 94720

1-1 INTRODUCTION

Recent trends in science and technology have indicated an increasing emphasis on minia

turization of engineering systems and study ofmicroscale phenomena. Examples of such

systems include modem microelectronic devices, the development ofmicromechanical

devices and systems, and microsensors. Many such devices and systems utilize con

trolled transport of mass, energy, and/or charge. Therefore, t he s tudy of microscale

transport phenomena has become an integral part of not only understanding the per

formance and operation of miniaturized systems, but also designing new devices. Mi

croscale charge transport has been studied extensively for many years, espcially in the

context ofmodem microelectronic devices. Mass transport and chemical reactions alsohave received attention for understanding processes such as chemical vapor desposition

and biological reactions. In contrast, microscale energy transport has received lim

ited attention in the context of miniaturized engineering systems. The second law of

thermodynamics requires that any irreversible transport of mass or charge must involve

entropy generation and thereby some exchange of energy with the surroundings. Energy

transportcontrols the performance of several miniaturized systems and is an important

ingredient in the processing of mate rial s. I t is clear that microscale energy transport is

both fundamental from a scientific viewpoint and important for engineering applications.

Inthis chapter, we will investigate the differentmechanisms of energy

transport in solids.

There exists two different ways to study energy transport in materials: the macro

scopic approach and the microscopic approach. The macroscopic approach uses phe

nomenological models that require no knowledge of the mechanism of energy transport

or the microstructure of solids. It focuses on the overall large-scale effects and requires

only a constitutjve relation or a simple transport law. Such a relation usually contains

tmg chapter one

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