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Intermittent flows in polymer tubing : thin liquid film dynamic and dewetting

Pascaline Hayoun, Emilie Verneuil, François Lequeux, Etienne Barthel
in collaboration with Alban Letailleur and Jérémie Teisseire from SVI

Intermittent flows are widely observed in the nature and in the industry, for example for oil recovery, gas distillation or fluid transport. Most of the time, those flows can lead to unwanted contamination, especially when polymer tubes are employed, as it is the case in food and pharmaceutical applications (Figure 1). Our study aims at better understanding and eradicates contamination mechanisms during intermittent flow in polymer tubing in order to increase the life time of the materials.

 

Figure 1 : Polymer tubing and example of contamination

 

We are interested by the dewetting process of low viscosity fluids at high flow rate (velocity 1-100 cm/s) in hydrophobic polymer tubing. We have observed that a moving liquid slug can lead to liquid film deposition at the inside wall of the tube, whose dynamic is controlled by the dewetting of the film. We have demonstrated already a succession of more or less complex dynamical processes, which may lead to substrate contamination (Figure 2).

Figure 2 : Thin liquid film destabilization, drops formations (500 frames/sec, flow velocity (0.6 m/s)

 

Also, we are investigating in which extend surface modification can facilitate the dynamic dewetting, in particular by adjusting the characteristic time of dissipation mechanism implied in this process. We observe dramatic behavior changes while tubes become hydrophilic or even more hydrophobic (Figure 3). It is therefore possible to prevent liquid film deposition or stabilized the entrained liquid film in order to avoid tube contamination.

 

Figure 3 : raw silicone is hydrophobic with respect to water (a), surface modification can provide hydrophilic properties to the silicone (b)