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Flow physics exploration of surface tension driven flows

Javadi, K ; Sharif University of Technology

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  1. Type of Document: Article
  2. DOI: 10.1016/j.colsurfa.2016.12.030
  3. Abstract:
  4. Surface tension driven passive micro-pumping relies mainly on the surface tension properties. To have control over surface tension driven passive micro-pumps (STD-PMPs), it is essential to understand the physical background of the fluid flow in these pumps. Hence, the purpose of this work is to give an exploration of the flow physics of a STD-PMP. In this regard, computer simulation is used to give detailed information about the flow pattern and physical phenomena at different conditions. To this end, a droplet of water, with a specified diameter, is placed onto an entry port connected to another droplet at the exit port via a microchannel. The results indicate that the pumping process, in general, can be divided into three phases: phase of fluid deceleration, phase of fluid acceleration and again a phase of fluid deceleration. The pumping process depends on the physical properties of the operating fluid and geometrical characteristics of the problem such as droplet shape, contact angle, channel height and channel length. Also, temperature gradient and the gravitational field effects are investigated. The results reveal that for a microchannel with a small height (low Reynolds number), the pumping process is a forward process directed from the sample droplet into the reservoir one. However, for the higher height (large enough Reynolds number), the dynamics of the pumping process changes completely. For instance, for Re >18, a pair of counter rotating vortices, flow reversal, counter current flow, droplet oscillations, vortex dynamics, and fluid sloshing appear which are discussed in detail. An equilibrium curve is introduced indicating the path of which the oscillating droplets pass through to reach their final states. © 2016 Elsevier B.V
  5. Keywords:
  6. Droplet ; Passive micropump ; Surface tension driven flows ; Drops ; Flow patterns ; Microchannels ; Microfluidics ; Pumps ; Reservoirs (water) ; Reynolds number ; Surface tension ; Vortex flow ; Counter-current flow ; Counter-rotating vortices ; Droplet oscillations ; Geometrical characteristics ; Gravitational fields ; Low Reynolds number ; Micro pump ; Surface-tension-driven flow ; Flow of fluids ; Acceleration ; Computer simulation ; Contact angle ; Deceleration ; Dynamics ; Flow ; Liquid ; Oscillation ; Physics ; Priority journal ; Pump ; Surface property ; Surface tension ; Surface tension driven passive micro pump
  7. Source: Colloids and Surfaces A: Physicochemical and Engineering Aspects ; Volume 518 , 2017 , Pages 30-45 ; 09277757 (ISSN)
  8. URL: https://www.sciencedirect.com/science/article/pii/S0927775716310731