Laboratory experiments on the fragmentation and turbulent exchanges of a metal blob falling in a viscous ambient

JB. Wacheul and M. Le Bars.

In a first step within the framework of Fludyco, we performed heat transfer measurements in a setup using a wide tank in order to quantify more precisly the diffusive exchanges that can occur between the two phases during the fall of the liquid metal. We used a Gallium alloy that is liquid at room temperature. By heating the liquid metal a few tens of degree, we were able to measure its initial and final temperature, thus allowing to compute for the first time the heat transfert integrated along the fall and along the fragmentation process. In addition, high speed video recordings allowed us to measure the speed of the flow, the dilution of the liquid metal, the mean diameter and the breakup distance (https://www.youtube.com/watch?v=v7wbrS9qIxo). These insights in the dynamics of the fall were used to test the theories of equilibration that were put forward in the litterature incording to the different visions on the post impact flow (Wacheul et al. 2017). We found that the the heat transfer is mostly controlled by the smallest scales of the turbulence by setting the length scale of the boundary layer. Further more, the breakup of the liquid metal into a cloud of droplet appears to have a non negligible effect on the diffusive transfert by changing the surface of exchanges. This could lead to more advanced models of planet buillding that would integrate the heat and element exchanged before and after the breakup with the relevant physics.

References

• Experiments on fragmentation and thermo-chemical exchanges during planetary core formation, J.-B. Wacheul and M. Le Bars, Physics of the Earth and Planetary Interiors, 276, pp. 134-144 (2018).
• Fall and fragmentation of liquid metal in a viscous fluid, Wacheul J.−B., Le Bars M., Physical Review Fluids 2 (9), 090507 (2017).