Transition from laminar to turbulent flow in liquid filled microtubes

The transition to turbulent flow is studied for liquids of different polarities in glass microtubes having diameters between 50 and 247 mum. The onset of transition occurs at Reynolds numbers of similar to1,800-2,000, as indicated by greater-than-laminar pressure drop and micro-PIV measurements of mean velocity and rms velocity fluctuations at the centerline. Transition at anomalously low values of Reynolds number was never observed. Additionally, the results of more than 1,500 measurements of pressure drop versus flow rate confirm the macroscopic Poiseuille flow result for laminar flow resistance to within -1% systematic and +/-2.5% rms random error for Reynolds numbers less than 1,800.