In particular, with microchannels there has been a great parameter in determining their attachment efficiency. It affects

Downl 1 Copyright © 2006 by ASME emphasis on semiconductor chip cooling. Since large pressure drops are inherent with the use of microchannels it is desired to minimize further increases in pressure drop that can arise due to fouling which can severely limit the efficiency of a microchannel heat exchanger. The smallest hydraulic diameters, Dh, that have been previously used in fouling studies that the authors are aware of were by Yiantsios et al. (1995, 1998, 2003) and Niida et al. (1989). Yiantsios et al. studied fouling in channels with Dh = 952 µm. Their test section consisted of two glass plates separated by Teflon spacer strips to create a channel that was 10 mm by 0.5 mm. Similarity, Niida et al. used an observation cell, made of borosilicate glass with a cross-section of 4 mm by 0.4 mm to provide a Dh of 727 µm. Based on the definitions provided by both Kandlikar & Grande (2002) and Kandlikar & Kuan (2006) these are categorized as minichannels. In the the magnitude of physicochemical interactions between particles and channel wall as well as the hydrodynamic forces that tend to cause particles to detach or prevent them from adhering. Table 1: Diffusion coefficients and Brownian displacements calculated for uncharged spheres in water at 25oC. Diameter Diffusivity at 25oC (m2/s) Average displacement after 1 hour (µm