Influence of gravity on a laminar flow in a microbioanalysis system

Laminar flow which is formed in a microchannel generally provides specific microfluidic characteristics and is applied to a variety of uses such as micro-biochemical analysis, handling of biological objects and micromixing. Influence of gravity on the laminar flow behaviour has not been much investigated because its influence has been considered to be very small due to the largeness of surface effects. In this work, a quantitative investigation into gravity influence on horizontal two-layer laminar flow was carried out using computational fluid dynamics simulation. Results showed the possibility of representing horizontal two-layer laminar flow behaviour by a dimensionless parameter which is a function of density difference, viscosity, microchannel size and velocity, under the condition that the microchannel cross section is square, and interfacial tension and diffusion are negligible. The dimensionless parameter becomes important especially for microfluidics where laminar flow can be formed easily. This simple parameter enables a rough estimation of the horizontal two-layer laminar flow behaviour. The results in this work are useful for microdevice design, biochemical analysis, mixing and chemical reaction.