Micro-Channels: Reality and Myth

Abstract

Many important problems connected to flows in micro-heat exchangers were not studied in sufficient detail. In particular, the governing physical mechanisms are still not well understood for flows in pipes and channels with hydraulic diameter ranging from 5 to 103 μm, which are often defined as micro-tubes or micro-channels. Experimental and numerical results of pressure driven laminar, continuous, incompressible, flow in different scale and shape channels are analyzed to highlight variations between various studies and these discrepancies are considered. The main objective is to determine whether the classical fluid flow theory based on the Navier- Stokes equations is valid to predict velocity distribution, pressure drop and transition from laminar to turbulent flow in micro-channels. No differences were found between results in micro-channels, unaffected by fluid ionic composition and the nature of the wall, and conventional size channels. The distinctions between different experimental studies must be attributed to different initial conditions, difference between actual conditions of a given experiment and conditions corresponding to the theoretical model, and measurement accuracy.