Large eddy simulation of turbulent flow and heat transfer in a channel with one wavy wall

The development of a galenical form must take into account the drug's physico-chemical properties as well as the external conditions that govern its performances. In the case of loaded microbeads designed for embolisation, the drug-release kinetics strongly depends on the local hydrodynamic conditions. Currently the apparatuses recommended by the European Pharmacopoeia allow the measurement in vitro of these kinetics; but the measured kinetics are very different from those met in the in vivo embolisation procedures. A new methodology is presented for evaluating the controlled release of a drug from ion exchange resins for embolisation. Experimental and numerical data are reported on the release kinetics of two closely related galenical formulations (DEAE Trisacryl LS and QAE Trisacryl LS).

A new experimental method for the evaluation of the release profiles of drug-loaded microbeads designed for embolisation

The work is devoted to stationary streaming flows resulting from standing capillary waves at interfaces between two immiscible liquids and their effect on the mass transfer rate of a passive scalar. In particular, oscillating liquid droplets immersed in another immiscible liquid are considered. Secondary streaming flows in the Stokes layers near the interface are calculated, as well as the corresponding vortical flows arising in the bulk. It is shown that the vortices can drastically enhance the mass transfer rate of a passive scalar which is to be extracted by one liquid from the other. The corresponding Sherwood number is of the order of [[mid ]uint[mid ]a/[Dscr ]1]1/2, where [mid ]uint[mid ] is the magnitude of the interfacial streaming velocity, a is the droplet radius, and [Dscr ]1 is the diffusion coefficient in liquid 1 (inside the droplet). This means that the effective diffusion coefficient is of the order of [Dscr ]1[[mid ]uint[mid ]a/
 [Dscr ]1]1/2, which is two orders of magnitude higher than [Dscr ]1. The results obtained show that such flows can be of potential interest for novel bioseparator devices.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/52AC6E2570E28A24BBA0E88E6D5B86C7/S0022112001005493a.pdf/div-class-title-stationary-d-c-streaming-due-to-shape-oscillations-of-a-droplet-and-its-effect-on-mass-transfer-in-liquid-liquid-systems-div.pdf

Stationary d.c. streaming due to shape oscillations of a droplet and its effect on mass transfer in liquid liquid systems

The influence of streamwise vortices on turbulent heat transfer in rectangular ducts with various aspect ratios

Enhancement of mass transfer in a two-layer Taylor-Couette apparatus with axial flow

Computer simulations are used to investigate a phenomenon of vorticity enhanced diffusion (VED), a net transport and mixing of a passive scalar across a prescribed vortex flow field driven by a background gradient in the scalar quantity. The central issue under study here is the increase in scalar flux down the gradient and across the vortex field. The numerical scheme uses cylindrical coordinates centered with the vortex flow which allows an exact advective solution and 1D or 2D diffusion using simple numerical methods. In the results, the ratio of transport across a localized vortex region in the presence of the vortex flow over that expected for diffusion alone is evaluated as a measure of VED. This ratio is seen to increase dramatically while the absolute flux across the vortex decreases slowly as the diffusion coefficient is decreased. Similar results are found and compared for varying diffusion coefficient, {ital D}, or vortex rotation time, {tau}{sub v}, for a constant background gradient in the transported scalar vs an interface in the transported quantity, and for vortex flow fields constant in time vs flow which evolves in time from an initial state and with a Schmidt number of order unity. A simple analysismore » shows that for a small diffusion coefficient, the flux ratio measure of VED scales as the vortex radius over the thickness for mass diffusion in a viscous shear layer within the vortex characterized by (D{tau}{sub v}){sup 1/2}. The phenomenon is linear as investigated here and suggests that a significant enhancement of mixing in fluids may be a relatively simple linear process. Discussion touches on how this vorticity enhanced diffusion may be related to mixing in nonlinear turbulent flows. {copyright} {ital 1999 American Institute of Physics.}« less

Erik L. Vold

Papers

Computational simulations of vorticity enhanced diffusion