Non-intrusive probing of fluid mixing with double diffusion layers brings insight into its origin and evolution

The mixing of fluids with considerably different thermal and compositional diffusivities can lead to the phenomenon of a double diffusion layer. This generally appears as a region consisting of a steep compositional gradient that prevents the mixing of two locally circulating flows. One example is in oceans where salinity layers can cause the presence of columns, called “salt fingers,” which can considerably affect the ocean properties around this region. These diffusion layers can also affect geology through magma formation, or the distribution of materials formed from the freezing of fluids, making greater understandings of this phenomenon helpful over a wide range of applications.

Kumar et al. developed an approach to experimentally examine the compositional and flow fields in real-time without disturbing the underlying interactions. This development can further advance the understanding of fluid mixing with double diffusion layers.

Using their technique, the authors examined the composition of the fluid and assessed conditions that lead to the onset and stability of the diffusion layers over time. The results showed plumes of a predominant component of the fluid mixture through the bulk fluid that transported material vertically along gravity. They also revealed how these plumes lead to the formation of a horizontal temperature gradient, which initiated a secondary circulation across the width. They observed a strong dependency on the initial fluid compositions that defined a threshold for which these layers are created, sustained or destroyed.

The results of this work could help to define processing and/or material conditions to promote and hinder gradients between the mixing of multi-component fluids.

Source: “Compositional dependency of double-diffusive layers during binary alloy solidification: Full-field measurements and quantification,” by Virkeshwar Kumar, Atul Srivastava, and Shyamprasad Karagadde, Physics of Fluids (2018). The article can be accessed at https://doi.org/10.1063/1.5049135 .