Laurent Maquet

Leidenfrost drops on a heated liquid pool

We show that a volatile liquid drop placed at the surface of a non-volatile liquid pool warmer than the boiling point of the drop can experience a Leidenfrost effect even for vanishingly small superheats. Such an observation points to the importance of the substrate roughness, negligible in the case considered here, in determining the threshold Leidenfrost temperature. A theoretical model based on the one proposed by Sobac et al. [Phys. Rev. E 90, 053011 (2014)] is developed in order to rationalize the experimental data. The shapes of the drop and of the substrate are analyzed. The model notably provides scalings for the vapor film thickness. For small drops, these scalings appear to be identical to the case of a Leidenfrost drop on a solid substrate. For large drops, in contrast, they are different and no evidence of chimney formation has been observed either experimentally or theoretically in the range of drop sizes considered in this study. Concerning the evaporation dynamics, the radius is shown to decrease linearly with time whatever the drop size, which differs from the case of a Leidenfrost drop on a solid substrate. For high superheats, the characteristic lifetime of the drops versus the superheat follows a scaling law that is derived from the model but, at low superheats, it deviates from this scaling by rather saturating.

Leidenfrost drops: Effect of gravity

A specific experimental set-up has been installed in a large centrifuge facility in order to study different aspects of Leidenfrost drops under high-gravity conditions (5, 10, 15 and 20 times the Earth gravity). In particular, the drop lifetime and more precisely the variations of drop diameter vs. time have shown to be in good agreement with previous experiments and scaling analysis (Biance A.-L. et al., Phys. Fluids, 15 (2003) 1632). Moreover, so-called chimneys are expectedly observed in the large puddles, the distance between two chimneys depending linearly on the capillary length. Finally, the Leidenfrost point, i.e. the temperature above which the Leidenfrost effect takes place, was unexpectedly found to increase slightly with gravity. A qualitative explanation based on a refined model (Sobac B. et al., Phys. Rev. E, 90 (2014) 053011) recognizing the non-trivial shape of the vapor film under the drop is proposed to explain this observation.

Organization of microbeads in Leidenfrost drops

We investigated the organization of micrometric hydrophilic beads (glass or basalt) immersed in Leidenfrost drops. Starting from a large volume of water compared to the volume of the beads, while the liquid evaporates, we observed that the grains are eventually trapped at the interface of the droplet and accumulate. At a moment, the grains entirely cover the droplet. We measured the surface area at this moment as a function of the total mass of particles inserted in the droplet. We concluded that the grains form a monolayer around the droplet assuming (i) that the packing of the beads at the surface is a random close packing and (ii) that the initial surface of the drop is larger than the maximum surface that the beads can cover. Regarding the evaporation dynamics, the beads are found to reduce the evaporation rate of the drop. The slowdown of the evaporation is interpreted as being the consequence of the dewetting of the particles located at the droplet interface which makes the effective surface of evaporation smaller. As a matter of fact, contact angles of the beads with the water deduced from the evaporation rates are consistent with contact angles of beads directly measured at a flat air-water interface of water in a container.

Leidenfrost droplets of complex fluids: Chapter 24

A droplet may levitate on its own vapor when dropped on a hot surface. This non-wetting situation is a great opportunity to study the evaporation of complex fluids. In this chapter, we present two case studies in order to evidence general statements about the behavior of complex fluids in Leidenfrost droplets. The first case concerns water and a surfactant mixture. While the droplet is evaporating, it is covered by a thin shell of sodium dodecyl sulfate. Eventually, the droplet explodes. The second case concerns microparticles (glass or basalt). During evaporation, the droplet is encapsulated in a monolayer of grains.A droplet may levitate on its own vapor when dropped on a hot surface. This nonwetting situation is a great opportunity to study the evaporation of complex fluids. In this chapter, we present two case studies in order to evidence general statements about the behavior of complex fluids in Leidenfrost droplets. The first case concerns water and a surfactant mixture. While the droplet is evaporating, it is covered by a thin shell of sodium dodecyl sulfate. Eventually, the droplet explodes. The second case concerns microparticles (glass or basalt). During evaporation, the droplet is encapsulated in a monolayer of grains.

Complex fluis droplets in leidenfrost state

A droplet may levitate on its own vapor when dropped on a hot surface. This non-wetting situation is a great opportunity to study the evaporation of complex fluids. In this chapter, we present two case studies in order to evidence general statements about the behavior of complex fluids in Leidenfrost droplets. The first case concerns water and a surfactant mixture. While the droplet is evaporating, it is covered by a thin shell of sodium dodecyl sulfate. Eventually, the droplet explodes. The second case concerns microparticles (glass or basalt). During evaporation, the droplet is encapsulated in a monolayer of grains.A droplet may levitate on its own vapor when dropped on a hot surface. This nonwetting situation is a great opportunity to study the evaporation of complex fluids. In this chapter, we present two case studies in order to evidence general statements about the behavior of complex fluids in Leidenfrost droplets. The first case concerns water and a surfactant mixture. While the droplet is evaporating, it is covered by a thin shell of sodium dodecyl sulfate. Eventually, the droplet explodes. The second case concerns microparticles (glass or basalt). During evaporation, the droplet is encapsulated in a monolayer of grains.

Chapter 24 – Complex Fluids Droplets in Leidenfrost State

A droplet may levitate on its own vapor when dropped on a hot surface. This non-wetting situation is a great opportunity to study the evaporation of complex fluids. In this chapter, we present two case studies in order to evidence general statements about the behavior of complex fluids in Leidenfrost droplets. The first case concerns water and a surfactant mixture. While the droplet is evaporating, it is covered by a thin shell of sodium dodecyl sulfate. Eventually, the droplet explodes. The second case concerns microparticles (glass or basalt). During evaporation, the droplet is encapsulated in a monolayer of grains.A droplet may levitate on its own vapor when dropped on a hot surface. This nonwetting situation is a great opportunity to study the evaporation of complex fluids. In this chapter, we present two case studies in order to evidence general statements about the behavior of complex fluids in Leidenfrost droplets. The first case concerns water and a surfactant mixture. While the droplet is evaporating, it is covered by a thin shell of sodium dodecyl sulfate. Eventually, the droplet explodes. The second case concerns microparticles (glass or basalt). During evaporation, the droplet is encapsulated in a monolayer of grains.