filling of non-trivially shaped microfluidic channels.
The filling behavior of microfluidic channels is the result of a competition between surface tension forces and viscous resistance. The result of this competition can be analytically predicted for simple cases, such as a cylinder with a constant radius. For more complex geometries, a different approach is needed. Computational Fluid Dynamics (CFD) can be used to simulate the filling behavior of these channels and determine the filling time.
In this article two multiphase CFD simulations were performed for non-trivial channel cross sections (a rectangle and a trapezoid) using the Volume of Fluid (VoF) method. Using this approach, we were able to compare the filling times of the different geometries, which is an important design factor.
A multiphase CFD simulation is set up using the Volume of Fluid method. Two phases are defined: a liquid phase (water) and a gas phase (air) with a surface tension between them. The flow is capillary-driven, meaning there is no driving pressure or velocity at the inlet or outlet. Instead, a wetting contact angle between the liquid and the wall is specified, which enables the liquid to slowly creep along the wall. At the start of the simulation the microfluidic channel is empty and the adhesion force causes the channels to slowly fill up, as seen in the figure on the right.
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