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Theoretical Thermodynamics
Technical University Hamburg-Harburg
Abstract-
During the last two decades the problem of momentum, heat and mass transfer in
micro systems has been addressed in many experimental studies. A common
definition of micro systems says that all structures with characteristic
lengths below 1 mm fall within this category. As long as Knudsen Numbers are
below 0.01, which is definitely true for many micro systems the problem can be
treated within a continuum theory.
In almost all studies published so far deviations from what is known in macro systems occur. Often special "micro effects" are proposed to explain these unexpected results. From our point of view, however, this approach is misleading. Instead, all systems - micro and macro - as long as they can be described within a continuum theory should be treated uniquely and in a non-dimensional form. Then it turns out that "micro effects" are scaling effects with respect to models developed for macro systems.
Special attention is given to convective heat transfer problems for which these scaling effects are analyzed in detail, followed by some remarks concerning heat conduction and problems with phase change.
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