Laboratoire Matière et Systèmes Complexes

Séminaire MSC/LIED exceptionnel

16h00 en salle 646A le 28/06/2017

Fluid mechanics of 3D printing and why the penguins do not freeze ?

Pirouz Kavehpour UCLA, Mechanical and Aerospage Engineering.

Spreading of liquid drop on cold solid substrates is a complicated problem that involves heat transfer, fluid dynamics, and phase change physics with the combination of complex wetting behavior of contact line. Many researchers are trying to obtain the final shape of the droplet or in other words the contact angle and radius of the drop after the solidification is complete. Understanding the physics behind the non-isothermal spreading of droplet is of utmost importance owing to its broad applications in diverse areas of industry in particular in 3D printing application. This work mainly focuses on obtaining important physical parameters involved in the process of spreading of molten droplets as well as controlling the post-solidification geometry of droplets. A complete set of experimental study is performed that shows the final radius in the case of free fall of droplet under high impact velocity is independent of the initial condition of the impact including the impact velocity and temperature gradients. The analytical modeling of the problem also verifies the accuracy of these results. Interestingly, there is a relationship between the 3D printing process and icephobicity for that one needs to look at nature. Antarctic penguins reside in a harsh environment where air temperature may reach -40C with wind speed of 40 m/s and water temperature remains around -2.2∘C. Penguins are constantly in and out of the water and splashed by waves, yet even in sub-freezing conditions, the formation of macroscopic ice is not observed on their feathers. Bird feathers are naturally hydrophobic ; however, penguins have an additional hydrophobic coating on their feathers to reinforce their non-wetting properties. This coating consists of preen oil which is applied to the feathers from the gland near the base of the tail. The combination of the feather’s hydrophobicity and surface texture is known to increase the contact angle of water drops on penguin feathers to over 140∘ and classify them as superhydrophobic. We here develop an in-depth analysis of ice formation mechanism on superhydrophobic surfaces through careful experimentations and development of a theory to address how ice formation is delayed on these surfaces. Furthermore, we investigate the anti-icing properties of warm and cold weather penguins with and without preen oil to further design a surface minimizing the frost formation which is of practical interest especially in aircraft industry.