A study of laminar flow of polar liquids through circular microtubes

Recently, the validity of using classical flow theory to describe the laminar flow of polar liquids and electrolytic solutions through microtubes has been questioned for tube diameters as large as 500 mum [Brutin and Tadrist, Phys. Fluids 15, 653 (2003)]. This potential increase in flow resistance, which has been attributed to electrokinetic effects and enhanced surface roughness effects, is critical to the understanding of certain biofluid systems. We seek to characterize this phenomenon for a variety of capillary/liquid systems. Using a numerical solution to the Poisson-Boltzmann equation, we have calculated the electroviscous effect for the systems under consideration. We have also measured the pressure drop as a function of flow rate across well-characterized stainless steel and polyimide microtubes ranging in diameter from 120 mum to 440 mum. Deionized water, tap water, a saline solution, and a variety of glycerol/water mixtures were used. The calculations and measurements suggest that any deviation from Poiseuille flow for tubes larger than 50 microns in diameter is more likely caused by the enhanced importance of surface roughness in microtubes than by electrokinetic effects. (C) 2004 American Institute of Physics.