Dr Michael Johns
| Position | Reader |
|---|---|
| College | St Catharine's |
| Qualifications/honours | BSc, Chemical Engineering, University of Natal (South Africa), 1994 PhD, Chemical Engineering, University of Cambridge, 1999 AMIChemE ExxonMobil Teaching Fellow, 2003 |
| mlj21@cam.ac.uk | |
| Research group | Magnetic Resonance |
Research description
Our research interests lie in two distinct areas: structure-processing relationships of materials and contaminant hydrology. In this respect, there is particular focus on the development and use of both magnetic resonance (MR) experimental techniques and Lattice Boltzmann (LB) flow simulation methods. Research is predominately conducted at the Magnetic Resonance Research Centre, which is located on the university's West Cambridge Site. There is significant collaboration with the research group of Lynn Gladden.
Structure-Processing Relationships
Magnetic resonance (MR) imaging, spectroscopy, velocity visualisation and self-diffusion measurements, as well as combinations of these methods, are all been used to investigate the relationship between processing and micro-structure in a range of complex industrial materials, including various emulsions (e.g. suspo-emulsions for agrochemical use), melts/soft solids (e.g. soap and various additives) and particulate products (e.g. detergent granules). Extensive use is made of Rheo-NMR devices that simultaneously combine conventional rheological studies with MR measurements of flow and micro-structure. Such measurements are then extended to in situ laboratory-scale processing equipment (e.g. ram and single screw extruders, drying apparatus). The overall objective is to visualise and quantify the evolving internal micro-structure of these materials during various processing operations, and to then relate this information to performance characteristics and the predictions of appropriate simulation models.
Current/recent projects in this area include:
- In situ ram and single-screw extruders that enable visualisation of the full 3D velocity field. These have demonstrated on various soap formulations. Future work will look at modelling these flow fields, for example by the application of LB simulation techniques.
- We have developed MR techniques, based on the measurement of self-diffusion, which are able to size emulsion droplets non-invasively in <5 seconds in flowing streams without any assumption regards the shape of the droplet size distribution. These are currently being used to study various complex and concentrated emulsions, emulsion inversion and the use of these techniques for on-line control.
- MR techniques have been developed to quantify freezing dynamics and the final micro-structure of droplets produced during Spray-Freezing operations. This has been applied to sucrose/fat solutions, coffee solutions as well as other mixtures. (with Ian Wilson).
- Drying of a variety of industrially relevant materials is being explored.
Contaminant Hydrology
Current Research in this area focuses on the following topics:
- Magnetic resonance methods are being used to study fundamental oil-water interactions in a random porous medium, in particular the dissolution and mobilisation of oil fragments (ganglia) by a flowing aqueous stream. Various Lattice Boltzmann simulation techniques are being developed to comprehensively describe dissolution and liquid interface movements in such complex geometries at the pore-scale. (with Prof. Lynn Gladden)
- MR techniques are being combined with Confocal Microscopy to study the flow and dispersion of complex visco-elastic fluids (intended for oil well treatment purposes) in micro-models that simulate actual rock pore space. Non Newtonian LB simulations are used to model this dispersion based on a pore-scale description.
- MR techniques and LB simulations are being used to assist in the development of biofilm reactors for the removal of radionuclides from contaminated water. (with Prof. Lynn Gladden)
Key publications
Sullivan, S.P., Gladden, L.F. and Johns, M.L. (2006), 3D modelling of shear thinning flow using LB, Jnl. Non-Newtonian Fluid Mech., 133, 91-98.Barnes, E.C., Wilson, D.I. and Johns, M.L. (2006), Velocity Profiling inside a Ram Extruder using Magnetic Resonance (MR) Techniques, Chem. Eng. Sci., 61(5), 1357-1367.
Hollingsworth, K.G. and Johns, M.L., (2005) Spatially resolved emulsion droplet sizing using Inverse Abel Transforms, J. Magn. Reson., 176, 71-78.
Hollingsworth, K.G. and Johns, M.L, (2004) Rheo-NMR of Emulsion Systems, J. Rheol., 48, 787 - 803.
Hindmarsh, J.P., Hollingsworth, K.G., Wilson, D.I. and Johns, M.L., (2004) An NMR study of the Freezing of Emulsion-containing Drops, J. Colloid Interface Sci., 275(1), 165 -171.
Hollingsworth, K.G. and Johns, M.L., (2003) Measurement of emulsion droplet sizes using PFG NMR and regularization methods, J. Colloid Interface Sci., 258 (2), 383-389.