Review of Experimental Procedure for Determining Liquid Flow in Microchannels

Large scatter in published experimental data has been observed with respect to classical theory. Recent data have confirmed that liquid, fully-developed, laminar flow in smooth microchannels of various cross-section is governed by the Navier-Stokes equations. However, when the dimensions of the channels are comparable with the wall roughness, surface effects become significant, as shown experimentally. To better assess the effect of surface phenomena such as wall roughness, sources of systematic bias must be eliminated. Some of the observed inconsistencies in data could originate from the experimental method. This paper explores and categorizes different approaches found in literature for measuring microflow characteristics and highlights the advantages and disadvantages inherent to these experimental techniques. A discussion of system components, experimental measurement and error analyses is included in the paper, with an emphasis on important issues which may have been overlooked in previous research. This study serves as a summary of experimental procedure and is a useful guideline for research in microfluidics. Moreover, several recommendations are proposed for improvement in areas requiring further study. 1Undergraduate Research Assistant, Microelectronics Heat Transfer Laboratory. 2Post-Doctoral Fellow, Department of Mechanical Engineering. 3Associate Professor, Director, Microelectronics Heat Transfer Laboratory. Member ASME. Nomenclature A = channel area, m Dh = hydraulic diameter, m, ≡ 4A P f = Darcy friction factor g = gravitational acceleration, m/s h = liquid column height, m K = pressure loss coefficient L = channel length, m Nu = Nusselt number p = pressure, Pa P = channel perimeter, m Q = volumetric flow rate, m/s Ra = average roughness, μm Re = Reynolds number, ≡ ρVDh μ V = flow velocity, m/s z = measured value of surface heights, m Greek ∆p = pressure drop, Pa μ = absolute viscosity, N · s/m ρ = liquid density, kg/m ω = absolute uncertainty Subscripts Dh = value measured using hydraulic diameter e = entrance region