The macro flow behavior is well-developed through many years of research and investigations. May this be the pattern of flow through oil pipe, or the flow past an aircraft wing, or flow through any channel carrying the fluid, are pretty well-developed. With the miniaturization of the flow channels to the micro and nano level, the flow behavior has changed drastically. The fluid and the channel wall interaction became important at the molecular level and as a consequence, molecular level dynamics became prominent over the fluid dynamics. The typical channel scaling for the micro and nano fluids is 1-100 µm and 1-100 nm. The reduced nature of the flow gives rise to the very low value of the Reynolds number (a quantity defined as the ratio of the inertial forces to the viscous forces). With the decrease of the channel size, the inertial forces decrease and flow can be treated as a massless but viscous. Usually, the flow is not pressure driven. It is observed that, the pressure required to drive a flow through a nanochannel is many orders of magnitude higher than the common fluids. Moreover, the surface roughness of the channel wall contributes a lot to the study of the flow.
This reduced size flow has plentiful applications. The branch itself is interdisciplinary and takes into the contribution from other disciplines such as physics, chemistry, biology and engineering. The recent concepts of lab-on-a-chip (LoC), micro fuel cells, biosensors, DNA sequencing, cell extraction, nano-filtration etc. are a boon of this field.
The development of the field comes with the manipulation of the flow. The flow pattern can be manipulated to mimic the behavior of the heart, liver kidney etc. Sperm selection, as used in the IVF (In-Vitro Fertilization) technology, also uses this reduced scale fluidic behavior to separate the motile spermatozoa from the non-motile ones. Another interesting application is the generation of power within a -Nanochannel. The electric power achieved till now is low, of the order of 1 mW. Nevertheless, the field opens up new research scopes for the power generation.
The area has attracted a considerable amount of interest for the computational physicists. Especially the peculiar behavior of the flow under the dominance of the surface effects is acting as an attractive point for them. With the reduction in size, the computation is carried out from the continuum domain to the molecular domain. Typically people use standard Molecular Dynamics, Monte Carlo techniques, Lattice Boltzmann methods, Dissipative Particle Dynamics and Smoothed Particle Hydrodynamics, for the study of such flow behavior. Thus, the modernization of the flow behavior through miniaturization is opening up and yet to open up some more, entirely new, technologies for the society.
- Shaurya Prakash and Junghoon Yeom, Nanofluidics and microfluidics, Elsevier Inc. (2014).
- Reto B. Schoch et al. Transport phenomena in nanofluidics, Reviews of Modern Physics, 80, 839, (2008).
- Drikakis and M. Frank, Advances and challenges in computational research of micro‑ and nanoflows, Microfluid Nanofluid, (2015).
- D. Sherwood et al. Theoretical aspects of electrical power generation from two-phase flow streaming potentials, Microfluid Nanofluid, 15, 347, (2013).