(7bn) The Mesoscopic Physics of Discrete Media: Towards the Control of Dynamic Structures

Profile: Process design engineer. Background in corporate R&D, management and consultancy for multinational companies. 7 years of experience in powder technology, heat transfer and water engineering. Doctorate in experimental and numerical spray drying within P&G and research in modelling multiphase flows, fouling and dynamic self-organization at Hexxcell, Imperial College and Univesity College London. Partners in consumer goods and energy sectors.

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Research Interests:

My work looks into complex dynamics in multiphase flow and the self-assembly of granular media. I am intrigued by how under the right balance between attractive forces and disruptive stresses, granular matter can be organised into well-defined spatial patterns that can propagate all the way into mesoscopic dynamic structures from relatively simple individual interactions. Examples of a rich variety of clustered structures of different sizes that are in constant formation and breakage are all around us in nature e.g. the equilibrium between the flow of sand or snow particles, flakes, clusters and static beds in a storm, a river bed, a desert or an avalanche, and industry e.g. the equilibrium of dense and dilute flow ares, cluster formation and breakage in fluidization, spray dryers, burners, combustors or mixers. Despite we can independently describe flow, growth and breakage phenomena, we do not understand well how metastable structures appear from the balance of all three. In the best cases, complex effects due to clustergins in transition regimes are avoided, in the worst, neglected. I want to explore a more organic approach to design a new generation of smart materials and processes, whereas the dynamic features of granular media are not avoided but exploited in benefit of a more efficient, more resilient and self-controlled operation. Examples include the manipulation of wall deposition, consolidation and agglomeration in spray dryers to control particle size and energy consumption, tuning heat and mass transfer rates in a fluidised bed by imposing an structured bubble flow introducing pulsed airflow, the control of reaction rates by changing the density of catalyst bed or the manipulation of the duty of shell-and-tube heat exchangers in the oil industry or the flux and selectivity of separation membranes with the dynamic control of the structure of an ubiquitous fouling layer.

Teaching Interests:

I have hands-on experience in various industries as an engineer where I had the chance to train crews, mentor student and address a diverse set of audiences, from officials to clients, management or scientists. I also have a hybrid profile as experimentalist and modeller, and from this standpoint, I believe I can produce and deliver undergraduate and postgraduate courses within transport phenomena, powder technology and core process chemical engineering, such as separation, design and heat transfer engineering or numerical modelling. I could move into a number of other specialised areas with some preparation and perhaps I will require more work to be involved in chemistry or biotechnology. My previous posts cover manufacture of granular detergents for Procter & Gamble, seawater desalinization for Acciona, and heat transfer engineering for the oil & gas sector, ExxonMobil, consulting for Hexxcell Ltd, spin off Imperial College London. The areas I have worked in include corporate R&D, management and consultancy, and institutions varying from large multinationals to universities and start-ups. I have supervised operators, researchers, technical officials and interns in addition to currently supervising PhD and Master students at UCL. I believe that I can relate my experience in the real-world challenges awaiting a young chemical engineer to my teaching responsibilities. I would be very interested in contributing to developing the student curriculum and mentor undergraduates and I am also sure that I would enjoy making them aware of the landscape and engaging into the specialization they require as function of their individual strengths and the careers they have in mind.

Research Experience:

Beyond the proprietary contributions, my public research has focused on multi-phase flow, powder technology and fluid dynamics. My doctorate dealt with droplet/particle agglomeration during spray drying of granular detergents with a strong component in fluif mechanics and turbulence. It represents a turning point in the industry because it has unravelled major deficiencies in historical practices. Developing new instrumentation methods [1] we discovered that the vortex flow employed in swirl spray dryers breaks down inside full-scale units due to wall effects [2]. This had remained undetected in smooth lab/pilot devices and so it was unnoticed for decades in academic research causing major issues in traditional models. Now we know that distinct recirculation regimes appear in response to varying levels of friction and new scale up rules are designed accordingly [3]. My research into fouling however led to a most fundamental change in the traditional view of particle formation in spray drying. We proved that most of the powder generated in a swirl unit results from the continuous formation and breakage of a clustered structure generated at its walls. It is revolutionary because it contradicts decades of research assuming spray dried granules were formed by airborne agglomeration of droplets and particles. We have refuted this hypothesis and for the first time quantified how much and for how long particles dry and agglomerate in dynamic wall structures [4]. From this new perspective, we redefined how agglomeration is envisaged in swirl spray drying [5], designed new methods to quantify how sprays interact [6] and optimized the operation and design rules of swirl dryers to improve energy efficiency based on controlling wall deposition, consolidation and resuspension [7]. On these grounds, I was relocated in 2015 to Imperial College London as visiting researcher to implement a numerical frame describing the process. In my following postdoctoral positions, I have continued to expand my numerical skills and I have explored other important fouling phenomena in the oil industry and later joining University College London. Here I deal with more fundamental granular physics involved in the control of an structured bubble flow in pulsed gas-solid fluidised beds, and I work with Prof Mark Miodownic on new avenues to develop smart materials for orthopaedics and responsive fabrics.

Selected publications:

1. Francia V, Martin L, Bayly AE, Simmons MJH. 2016. Flow Meas. and Instr.50 : 216-228. [Link]

2. Francia V, Martin L, Bayly AE, Simmons MJH. 2015. Exp. Ther. Fluid Sci. 65:52 - 64. [Link]

3. Francia V, Martin L, Bayly AE, Simmons MJH. 2015. Chem. Eng. Sci. 134 : 399-413. [Link]

4. Francia V, Martin L, Bayly AE, Simmons MJH. 2015. AIChE J. 61, 6:1804–1821 [Link]

5. Francia V, Martin L, Bayly AE, Simmons MJH. 2016. Powder Tech. 301 : 1330-1343. [Link]

6. Francia V, Martin L, Bayly AE, Simmons MJH. 2016. Powder Tech. 301 : 1344-1358. [Link]

7. Francia V, Martin L, Bayly AE, Simmons MJH. 2017. Chem. Eng. Sci. 162 : 284-299. [Link]

Research Plans:

I plan to focus a first stage in my career in studying the transitional regime sitting in the interface between continuum fluid and solid mechanics. When a dilute collection of particles consolidates and moves from a so-called inertial to dense and quasi-static regime multi-particle sustained contacts become frequent, and long-range interactions, shape and anisotropy begin to have dominant effects in the system dynamics. These phenomena are extremly difficult to describe in traditional kinetic frames. So far kinetic models remain unequipped to deal with the crosscorrelation of solid velocities, an anysotropic distribution of contacts and local changes in rheology, not to mention describing systems with an intense inter-particle interaction leading to growth or breakage, where process design still heavily relies on experimentation. High-level-of-detail studies e.g. DNS, LB, LES, CFD-DEM, look often into microscale phenomena but they seldom feed new constitutive equations or rate kernels describing mesocopic physics into a macroscopic modelling frame e.g. PBE, CFD, let alone be of use to optimization engines. I want to focus precisely on this gap, connecting physics that naturally occur at a mesoscale such as clustering, breakage and consolidation with kinetic rate models, which are the only suitable alternatives to make a tangible impact in industrial optimization. This is specially crucial for sectors facing challenging granular rheologies, agglomeration and particulate or colloidal fouling.

In my first research programme, I consider developing a cross-disciplinary multi-scale modelling framework to investigate dynamic particle fouling as a combination of deposition, assembly, consolidation and removal of a particulate multi-layer. I expect to do so with the support and collaboration of many of my previous industrial and academic partners. The focus stems from my partnership with Procter & Gamble that has proven dynamic fouling crucial in manufacturing granular detergents but similar particulate and colloidal multilayers are key to many other operations e.g. combustion of biomass, heat exchangers, mixers, membranes and multiple complex fluids and biological systems. My immediate goals will include prediction of dynamic structural properties (e.g. radial distribution functions, fractal scales) and the probability and rate functions for growth, consolidation and breakage under different stimuli e.g. aerodynamic, surface or contact forces, body forces. In other words, I want to lay the experimental and numerical grounds providing transferable outputs to advanced macroscopic models of dynamic multilayer fouling in a stochastic (e.g. collision rates, adsorption or clustering frequency to use in LES/CFD) or a rate-based formulation (e.g. diffusion coefficients, agglomeration/breakage kernels to use in PBE, GPROMS). At a further stage, I will expand my research in several directions. First deepening the expertise in dynamic structures to design new processes and smart powders, then in the applications of our capability into other disciplines modifying the forces at play, the geometrical constrains and the time and spatial scales of the problem. From a theoretical standpoint, the principles and methodologies underpinning the study of self-organization are invariant and much of the expertise acquired along the way may find application in areas such as physics, robotics, data analysis or social sciences. This makes my research to offer a great opportuniy for inter-disciplinary work and a low risk profile not only in the short, but also the long term.