Numerical and experimental investigation of mixing enhancement in micro-devices

Microreactors and other microstructured devices have a wide range of applications in continuous analytical chemistry, high-throughput production, product formulation, and biological and microbiological analysis systems. They are of particular interest for applications that fit the lab-on-a-chip concept, requiring the handling of small volumes (10-9 to 10-6 l) and a high level of portability [1,2]. Mixing operations in this kind of devices often occur in the laminar regime at quite low Reynolds numbers. Notwithstanding the device’s small dimensions (from mm to µm), molecular diffusion itself may not be relied upon to completely homogenise the feeding streams, especially when fast chemical reactions are involved. The key for efficient mixing in micro-devices relies on the capacity to promote, by advective mechanisms, a fast distribution of the fluids in the cross section of the device’s channel and a fast growth of the intermaterial surface area.

One route leading to efficient mixing is through the generation of flow instabilities that will deform and engulf the fluid streams. This can be caused by inertial effects inherent to the non-linearity of the flow dynamics, or by elastic stresses in flows fluids that present some degree of viscoelasticity. The latter can occur naturally in flows of complex fluids found usually in the polymer, cosmetics and food industries (like flexible long-chain polymer solutions, colloidal gels and concentrated microbial suspensions) and in laboratory analyses (like blood), or can be achieved by adding a small concentration of polymer additives to the flow [3].

A fundamental understanding on the onset conditions of inertial and elastic instabilities can lead to the intensification of mixing in micro-devices and to a better control of product quality, but also to preventing undesirable effects such as the damaging of microorganisms, cells or long molecular chains (like proteins and DNA) due to overstretching. Moreover, flow instabilities can also improve interfacial mass or heat transfer rates, which can be of value to heat exchanger design, heterogeneous reactions or adsorption with monoliths, membrane separations and microfluidic electrochemical systems. A solid theoretical study on the onset of flow instabilities in micro-devices and the ability to control them is, thus, of great relevance for industry and laboratory applications.

This project aims to relate operational conditions, micro-channel geometry and the rheology of the fluids or additives to topological transformations of fluid interfaces induced by flow instabilities, leading to efficient mixing. The student will develop skills in Computational Fluid Dynamics (CFD), and experimental visualisation of flow and mixing patterns with laser techniques (Particle Induced Fluorescence and Planar Laser Induced Fluorescence).

For UK/EU applicants: Applicants should have or expect to achieve at least a 2.1 honours degree in degree in Chemical Engineering, Mechanical Engineering, Physics, Applied Mathematics or another relevant field with strong bases in Fluid Mechanics.

For Overseas applicants: Applicants are expected to be graduates (major in Chemical Engineering, Mechanical Engineering, Physics, Applied Mathematics or another relevant field with strong bases in Fluid Mechanics.) from top national ranked universities (prefer top 100 world ranked universities) with excellent GPA and strong publications at masters level.

The project will be supervised by Dr Claudio Fonte (School of Chemical Engineering and Analytical Science). Informal enquiries with a CV attached can be sent to [Email Address Removed].