In two recent papers [1,2], Drs. H. Herwig and O. Hausner dismiss ''almost all'' recent studies that claim special effects for flow and heat transfer through microdevices. They find the approach in those studies misleading and argue that existing observations in microdevices can be explained by merely rescaling the traditional models routinely used for macrodevices. Herwig and Hausner suggest that the same equations, properly non-dimensionalized, should be used for both micro and macrosystems. In Ref. [2], Professor Herwig states emphatically and in capital letters, ''IN A NONDI-MENSIONAL FORM ALL SPECIAL ''MICRO-EF-FECTS'' WILL TURN OUT TO BE SCALING EFFECTS WITHIN A CONTINUUM THEORY EQUALLY VALID FOR MACRO AND MICRO PROBLEMS.''
In this Technical Note, we argue that traditional treatments of transport phenomena may not be appropriate for certain situations involving microdevices. The simplistic dimensional analysis approach advocated in [1,2], though not incorrect, does miss important physics and is therefore misleading. We first start by defining microdevices and what we mean by traditional modeling of mass, momentum and heat transfer in or around conventional devices. We then describe the conditions under which non-traditional modeling of transport phenomena may be needed. Finally, we list the available alternative modeling tools. The focus here will be on fluid transport, but similar arguments can be made for solid transport, for example heat conduction through solid media.
Microelectromechanical systems (MEMS) refer to devices that have characteristic length of less than 1 mm but more than 1 lm, that combine electrical and me-