Diffusion in liquid mixtures

Abstract

The understanding of transport and mixing in fluids in the presence and in the absence of external fields and reactions represents a challenging topic of strategic relevance for space exploration. Indeed, mixing and transport of components in a fluid are especially important during long-term space missions where fuels, food and other materials, needed for the sustainability of long space travels, must be processed under microgravity conditions. So far, the processes of transport and mixing have been investigated mainly at the macroscopic and microscopic scale. Their investigation at the mesoscopic scale is becoming increasingly important for the understanding of mass transfer in confined systems, such as porous media, biological systems and microfluidic systems. Microgravity conditions will provide the opportunity to analyze the effect of external fields and reactions on optimizing mixing and transport in the absence of the convective flows induced by buoyancy on Earth. This would be of great practical applicative relevance to handle complex fluids under microgravity conditions for the processing of materials in space.

Testing microbial biomining from asteroidal material onboard the International Space Station

“…One possible hypothesis is that the different fluid dynamics in microgravity (i.e. lack of convection), compared to terrestrial gravity, could have enhanced local saturation of the leached elements around the rock surface 54 , in turn reducing abiotic leaching. However, this would not explain why this was only observed for certain elements.…”

Unraveling dispersion and buoyancy dynamics around radial A + B → C reaction fronts: microgravity experiments and numerical simulations

“…Hence, the corresponding scalings 16 can be applied to predict the product formation for various applications, since such reaction fronts are widely occurring in Nature and technology. Systems where Taylor-Aris dispersion is important but buoyancy effects can be neglected are for example very dilute systems, systems with small h and low solute diffusivity, highly viscous fluids, or space applications where gravity is absent 25 . Our findings provide a basis for further development of dispersion models in the direction of combustion or porous media flows 31 .…”

“…This is due to the fact that a certain range of fluid gap heights and flow rates must be covered to capture different scenarios of front dynamics. Microgravity experiments already were successfully employed in the literature to separate diffusion and advection from gravity-driven convection 24,25 , or for more complex combustion reactions including thermal effects [26][27][28] .…”

Effects of Simulated Microgravity on the Internalization of Cerium Oxide Nanoparticles by Proliferating Human Skeletal Myoblasts

“…Nanoparticle concentration at 24 h was indeed ∼50% higher than at 6 h. Increment of nanoparticle internalization over time under normal gravity can be explained by considering that diluted colloids at a steady state show an inhomogeneous nanoparticle distribution along the gravity direction, corresponding to an exponential concentration distribution. 26 When colloids are administered to cell cultures under normal gravity, there is an increasing availability of nanoparticles in proximity of the cells over time, hence the increasing internalization.…”