Bogdan Firtat, memsOP
BioMEMS are a special area of micro systems, combining fluidic devices with micro nano systems. Modelling such devices, in the development phase, must account for all the phenomena from both worlds. Studying the fluid dynamics within the biosensor is key to improving the functionality and optimising such devices.
CFD tools have been developed for answering questions about how fluids behave in different conditions. Problems from simple fluid flow to mixing, electrophoresis and fluid-structure interactions were solved using such software tools. However, during the miniaturisation to nano scale devices, it was found that the continuous modelling of fluids (as the CFD models) tend to break down and should no longer be taken for granted as the essential assumption for fluid dynamics. Several phenomena that take place at these small scales cannot be accurately solved, or even taken into consideration using the regular CFD models. Fluid flow and heat transfer at the nano scale is very different from the same phenomena at larger scale. This is due to several phenomena that also exist, but it can be easily neglected in the macro world.
Such phenomena include velocity slip, liquid viscosity variation, viscous dissipation, electrokinetic effects. Also, surface roughness (very important in nano channels, sometimes being comparable with the length scale of the channel itself) cannot be neglected, as in the millimetre or micrometre sized channels.