Mixing intensification under turbulent conditions in a high pressure microreactor

Abstract

The turbulent mixing of two miscible fluids is investigated in a high pressure (HP) coflow microreactor operated at 100 bar. Ethanol and CO 2 are selected as model solvents to mimic the final targeted application, i.e.: a supercritical antisolvent process at microscale (µSAS). We first demonstrate experimentally that turbulent mixing can be reached in a microchannel using HP microfluidics. A computational fluid dynamic (CFD) model, performed using direct numerical simulation (DNS) down to the Kolmogorov scale has been applied for the turbulent mixing simulations. The effects of the main operating parameters on the final mixing efficiency has been studied, namely: the temperature, the fluid flowrates, the microchannel dimensions and the capillary inner and outer diameters. According to a predefined intensity of segregation, the characteristic mixing times are determined and used for determining mixing efficiency. The ratio of the total mixing time to the diffusion time depends on the ratio of the kinetic energies (the outer fluid to the inner one). The obtained micromixing times have been related to the turbulent energy dissipation rate ϵ, calculated directly from the velocity fluctuations. The mixing intensification is obtained with much lower characteristic mixing times in the microreactor (one order of magnitude) than previously reported. This fundamental study is an indispensable guidance for several processes, including the µSAS applications.

Process intensification for the synthesis of ultra-small organic nanoparticles with supercritical CO2 in a microfluidic system

“…More recently, we have proven that turbulent conditions can be achieved in high pressure microfluidic devices [16], resulting in ultra-fast mixing times down to 10 -4 -10 -5 s, highly favorable for synthesizing organic nanoparticles.…”

“…The numerical simulation is based on a high performance computing (HPC) massively parallel code, which takes into account all the coupled physical phenomena (i.e. thermodynamics, hydrodynamics, nucleation and growth), for catching all the mixing scale [16]. This coupled experimental/numerical approach allows determining the surface tension with a great confidence for two main reasons.…”

High-Efficient Micro Reacting Pipe with 3D Internal Structure: Design, Flow Simulation, and Metal Additive Manufacturing

“…The simulation data were substituted in Equations (5) and (6) to obtain the mixing index under the corresponding determining size, as shown in Figure 9.…”

“…The simulation data were substituted in Equations (5) and (6) to obtain the mixing index under the corresponding determining size, as shown in Figure 9. Based on the theories and experiment results above, concrete measures were put forward for the design of the micro reacting pipe, including:…”

“…One of the effective methods is adding external instruments to provide energy to produce turbulence directly. For instance, Fan Zhang's team investigated the turbulent mixing of two miscible fluids in a high pressure (HP) coflow micromixer operated at 100 bar [6].…”