With advances in manufacturing technology, flow and transport processes in microchannels or past micro-objects have become relevant for technical applications. Modern manufacturing methods permit the construction of tiny structures of considerably less than one millimeter in different materials such as silicon, glass, metal or plastic. This results in microchannels and microobjects, through which and past which flow and transport processes take place, thus realizing complex functions in tiny spaces. It is found that, depending on the fluid, a continuum-mechanical treatment of flows through and past very small geometries is no longer necessarily possible in many cases. To correctly represent the physics of the flow at such small length scales, corrections to the continuum-mechanical equations or even molecular methods are sometimes necessary.
On the one hand, the term microflow can be defined quite formally as a flow through a microchannel of width d or past a micro-object of dimension d, where 1 < d < 1000μm. On the other hand, depending on the fluid, the flow at such length scales possibly can be described perfectly well by a continuum model. The term microflow is only then justified when the boundaries of the continuum-mechanical treatment are reached, or when certain effects, which play a less important role in macroscopic flows, become important. It is this physically-based concept of a microflow that we will discuss in this chapter.
KeywordsContact Angle Shear Rate Electrical Double Layer Contact Line Knudsen Number
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