Using viscous heating to determine the friction factor in microchannels – An experimental validation

• Published in: Experimental thermal and fluid science Vol. 30; no. 8; pp. 725 - 731
• Main Authors: Celata, G.P., Morini, G.L., Marconi, V., McPhail, S.J., Zummo, G.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: New York, NY Elsevier Inc 01-08-2006; Elsevier Science
• Subjects: Applied fluid mechanics; Channels; Deviation; Dissipation; Exact sciences and technology; Fluid dynamics; Fluidics; Friction factor; Fundamental areas of phenomenology (including applications); Heating; Mathematical analysis; Microchannels; Navier-Stokes equations; Physics; Friction factor; Test facilities; Viscous dissipation; Experimental study; Microstructure; Microfluidics
• ISSN: 0894-1777; 1879-2286
• DOI: 10.1016/j.expthermflusci.2006.03.002

Many experimental works on forced convection through microchannels have evidenced deviations from conventional theory in fluid-dynamic and diabatic behaviour. Whereas often these anomalies were ascribed to “new” micro-effects, it can usually be shown that the explanations for different behaviour at microscale are hidden in the conventional theory. There is just the issue of
scaling effects that cause certain phenomena that are negligible at macroscale to become influential when channel geometry is reduced below a certain limit. Such an effect also pertains to viscous dissipation, which becomes important especially in liquid microchannel flows. This paper focuses on the role of viscous heating in such flows, explaining its occurrence in the Navier–Stokes equations and verifying its presence in experimental validation. A criterion will be presented to draw the limit of significance for viscous dissipation effects in microchannel flows. The connection between viscous heating and the friction factor will be demonstrated, which will then provide the basis for comparison in an experimental context. The friction factor obtained through pressure measurements and through evaluation of the viscous heating are confronted. The results show an exceedingly good description of fluid-dynamic behaviour by the viscous heating method for diameters below 100
μm, proving the validity of the principle of scaling effects. This implies that at extremely small diameters temperature measurements suffice to describe head loss, and that in diabatic experiments the viscous heating should be accounted for.