Yves Le Guer

Mixing plays an important role in microalgae cultivation as it directly affects nutrient transport, light exposure, and overall reactor performance. However, the extent to which improvements in hydrodynamic mixing enhance biomass productivity remains unclear, particularly under batch conditions where nutrients are limited. This study investigates that question through numerical simulations of a coupled fluid–microalgae model, in which biomass and substrate are transported as scalar fields within an incompressible flow and interact through Monod growth kinetics. Four jet-driven flow configurations are examined alongside a no-flow reference and three complementary limiting regimes: a diffusion-limited case, an intermediate spatially uniform substrate model, and a fully mixed limit. Simulations are initialized from highly segregated conditions to isolate the role of transport processes. The central finding is that, despite marked differences in mixing efficiency across configurations, domain-averaged biomass trajectories converge to within 0.5%, with peak biomass gains confined to a narrow 2–3% range. In the absence of advection, substrate remains inaccessible to biomass, causing net biomass loss driven by endogenous respiration. When flow is introduced, substrate and biomass rapidly come into contact within O(200 s), activating growth. This convergence is explained by a transport–reaction decoupling argument: once advection overcomes the initial segregation and the system enters the reaction-limited regime (Da≪1), integrated yield becomes insensitive to the details of the flow field. Biomass production is then governed primarily by substrate inventory rather than mixing intensity, a result explained by the clear separation between hydrodynamic and biological timescales.

In this paper, we study the problem of waves generated by subaerial landslides; a very complex problem involving granular physics, fluid mechanics and wave processes. Recently, a few studies (Bullard et al., 2019; Rauter et al., 2021) proposed a simplification of the generation stage, considering a water slide (i.e., an inviscid liquid with the same density as the reservoir fluid). In these studies, they concentrate on the prediction of the maximum wave amplitude after generation. In the present paper, we follow the same strategy of simplification, but this time, focus on the energetic transfer processes from the stage of generation, to the end of the main wave transformations.

An active inline mixer suitable for flows at low Reynolds number and high Péclet number is studied. An alternated oscillatory forcing protocol is imposed by three rotating circular arc-walls in a straight channel. In the two-dimensional case, simple phenomenological arguments are used to estimate heuristically the mixing efficiency with two nondimensional control parameters: the Strouhal number based on the bulk flow velocity and the strength of the cross flow relative to the transport flow. The validity and limitations of the proposed mixing conditions are explained by the transport mechanisms in the mixer. The beneficial role of the elliptic flow regions for stretching and folding the passive scalar interfaces is highlighted as well as a correlation between good mixing ability and the chaotic advection of tracers in the mixing zone.

This work shows the formation of a high internal phase ratio oil‐in‐water (O/W) emulsion using a new type of a two‐rod batch mixer. The mixture components have sharply different viscosities [1/3400 for water‐in‐oil (W/O)], similar densities (1/0.974 for W/O), and an O/W ratio of 91% (wt/wt). The simple design of this mixer leads to a low‐energy process (10⁶ < energy density [J m⁻³] < 10⁷), characterized by low rotational speed and laminar flow. The droplet size distribution during the emulsification was investigated according to different physical and formulation parameters such as stirring time (few minutes < t < 1 h), rotational speed (60 < Ω < 120 rpm), surfactant type (Triton X‐405 and X‐100), concentration (from 1 to 15.9 wt % in water), and salt addition (30 g/L). We show that all studied parameters allow a precise control of the droplet size distribution and the rheology. The resulting emulsions are unimodal and the mean droplet diameter is between 30 μm and 8 μm. © 2010 American Institute of Chemical Engineers AIChE J, 2011