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Center for Nonlinear Phenomena and Complex Systems

Complexity addresses from a unifying point of view a large body of phenomena occurring in systems composed of interacting subunits. It constitutes a highly interdisciplinary, fast-growing branch of science and provides a privileged interface between mathematical and physical science on the one side and real-world complex systems on the other, as encountered, in particular, in life sciences. The Center is devoted to research on complex systems and the related fields of nonlinear science, statistical physics, thermodynamics, physical chemistry, systems biology, and simulations techniques. It contributes to the promotion of these topics thanks to training and visitor programmes, meeting organization, and the participation to national and international projects. It is composed of researchers of the academic staff of ULB, permanent FRS-FNRS researchers, postdoctoral researchers and graduate students. It is attached to the departments of physics, chemistry and biology of organisms of the Faculty of Sciences, as well as to the department of chemistry and material science of the Faculty of Applied Sciences.

TIPs - Transport phenomena and process engineering

Person in charge of the Unit : Oui

The objective of the research carried out at the Transfers, Interfaces and Processes (TIPs) laboratory of the Université libre de Bruxelles (ULB) is the experimental characterization and the mathematical modeling of transport phenomena within systems containing several phases (gas and/or liquid and/or solid), exchanging matter, heat or momentum, through an interface between these phases, at scales between the micron and the millimeter. The research carried out revolves around mainly fundamental and/or generic questions. They have direct applications in the fields of health, environment, heat transfer technologies and agro-food, chemical, microtechnology, materials and space industries.

Our current research concerns 9 scientific topics: Drying, Enzymatic processes, Evaporation and boiling, Gas-liquid transfers, Microfluidics, Physiological fluids, Soft/Wet microrobotics, Surface rheology and, as a side research area, the characterization of Ancient hydraulic systems.

The TIPs laboratory is composed of 5 professors and approximately 35 researchers. It is divided into two research units : "TIPs - Transport phenomena and process engineering" and "TIPs - Fluid physics".

The TIPs laboratory collaborates with a number of scientific and industrial partners in Belgium, Europe, USA, Israel and Canada, in the frame of several networks funded by the European Commission or by the European Space Agency, and also thanks to support at National level (BELSPO, FNRS, Brussels and Walloon Regions). The team investigates mostly fundamental and/or generic questions, i.e. common to several natural or industrial processes. Studied problems most often involve notions of nonlinear dynamics, physical chemistry (equilibrium and non-equilibrium), statistical mechanics, transport phenomena, applied mathematics, ... The used tools are either theoretical (stability analyses, scaling laws, asymptotic techniques, ...), numerical (commercial or 'home-made' software), or experimental (fluid behavior visualization by interferometry, Schlieren, infrared thermography, ...).

The TIPs laboratory has an experimental facility devoted to the realization, the characterization and the manipulation of systems including several phases (gas and/or liquid and/or solid), exchanging mass, energy or momentum, at a characteristic length scale between the micron and the millimeter. The lab is part of the Micro-milli platform. It is managed by Adam Chafaï, PhD.

TIPs - Fluid Physics

Person in charge of the Unit : Oui

At the TIPs (Transfers, Interfaces and Processes) Department of ULB, the main goal of the ongoing research is to develop new theoretical, numerical and experimental methods allowing to understand and predict the behavior of multiphase systems, and to design or optimize industrial processes dedicated to the transformation of matter (mineral, organic or biological) and energy. There are essentially six main research themes : mixing, gas-liquid mass transfer, dynamics of interfaces and their instabilities, wetting, porous media, heat transfer and phase change (evaporation, crystallization, ...). The Department is made of two complementary research units : the Fluid Physics Unit and the Chemical Engineering Unit. The Fluid Physics Unit collaborates with a number of scientific and industrial partners in Belgium, Europe, USA, Israel and Canada, in the frame of several networks funded by the European Commission or by the European Space Agency, and also thanks to support at National level (BELSPO, FNRS, Brussels and Walloon Regions). The team investigates mostly fundamental and/or generic questions, i.e. common to several natural or industrial processes. Studied problems most often involve notions of nonlinear dynamics, physical chemistry (equilibrium and non-equilibrium), statistical mechanics, transport phenomena, applied mathematics, ... The used tools are either theoretical (stability analyses, scaling laws, asymptotic techniques, ...), numerical (commercial or 'home-made' software), or experimental (fluid behavior visualization by interferometry, Schlieren, infrared thermography, ...).


Multiscale analysis of drying processes

In the field of drying, an important part of our work concentrates on the study of transport processes taking place at the scale of a product, during its drying. We have been interested in various products, from baker's yeast pellets to soils, colloidal suspensions, peppercorns or cocoa beans, in different kind of devices/geometries (laboratory tunnel dryer, fluidized bed, spray dryer, sessile drop, Hele-Shaw cell…). By combining experiments and mathematical modeling, we try to highlight and characterize the key phenomena involved and to develop models, validated experimentally, of the drying kinetics of these products. From the experimental point of view, we have developed various devices, combining continuous measurement of the drying rate and optical characterizations (by the use of microscopes or infrared cameras). From a more fundamental point of view, we are also interested in the quantification and the modeling of the competition that can exist in a porous medium between the evaporation of the liquid and the convective motion induced by capillarity (imbibition).

At the scale of the dryer, we participate in several projects aiming at the development, based on a rational approach, of solar dryers, to be implemented within farmer cooperatives in developing countries (Uganda, Cambodia...). As part of a long-standing collaboration with Polytechnique Montréal, we are also interested in the development of alternative devices for the drying of yeast grains (rotary dryer, conical spouted bed...).

Selected publications :

Van Engeland, C., Spreutels, L., Legros, R., & Haut, B. Convective drying of baker’s yeast containing a carrier. Accepted in Drying Technology. 2018

Sobac, S., Colinet, P., Larbi, Z., & Haut, B. Mathematical modeling of the drying of a spherical colloïdal drop. Submitted to Journal of Colloïd and Interface Science. 2018

Herman, C., Spreutels, L., Turomzsa, N., Konagano, E., & Haut, B. Convective drying of fermented Amazonian cocoa beans (Theobroma cacao var. Forasteiro). Experiments and mathematical modeling. Food and Bioproducts Processing, 108, 81-94. 2018

Talbot, P., Lhote, M., Heilporn, C., Schubert, A., Willaert, F.X., & Haut, B. Ventilated tunnel solar dryers for small-scale farmers organizations: theoretical and practical aspects. Drying Technology, 97, 803-817. 2016

Analysis of ancient hydraulic systems

For several years, we have developed a collaboration with archaeologists in order to analyze ancient hydraulic systems. It is commonly accepted that the Romans possessed a technical mastery of water supply. Nevertheless, few writings on this engineering practice are available. Moreover, due to the scientific knowledge in the field of fluid mechanics during the Roman period, these writings do not contain the usual modern information on the characterization of a hydraulic system. However, thanks to the current knowledge in fluid mechanics, it is now possible to simulate the flow that was taking place in a hydraulic remains presenting a good state of conservation. It is therefore possible to supplement the usual field information with data such as flow rates, velocity and pressure fields, energy losses, yields...

In recent years, we were interested in fountains found in large houses in the southern part of the ancient Roman city of Apamea (Byzantine times). We were able to characterize their functioning using classical fluid mechanics approaches. The analysis of the results obtained clearly shows that these fountains were supplied with water by an aqueduct and that this feed was technically feasible in view of the remains of the Byzantine aqueduct still present in the north of the city.  We were also interested in a peculiar system that can be observed within the ruins of the city of Perge (Turkey). During the Roman Imperial Period, at the middle of the main street of the city, a water channel was operated. This channel has peculiar dimensions and blocks were positioned inside it at a regular interval. By using open surface flow theory, we have been able to characterize the flow in this system and in diversions originating from it.

Selected publications :

Vekemans, O., & Haut, B. Hydraulic analysis of the water supply system of the Roman city of Perge. Journal of Archaeological Science: Reports, 16, 322-329. 2017

Haut, B., Zheng, X.Y., Mays, L., Han, M., Passchier, C., & Angelakis, A.N. Evolution of rainwater harvesting in urban areas through the millennia. A sustainable technology for increasing water availability. In W.J.H. Willems & H.P.J. van Schaik (Eds.), Water and Heritage. The Netherlands: Sidestone Press. 2015

Vannesse, M., Haut, B., Debaste, F., & Viviers, D. Analysis of three private hydraulic systems operated in Apamea during the Byzantine period. Journal of Archaeological Science, 46, 245-254. 2014

Experimental, theoretical and numerical analysis of the exchange phenomena between a bubble and the surrounding liquid

In this research project, we aim to describe the transport phenomena (mass and momentum) taking place inside and around a bubble/drop within a gas-liquid contactor. By combining theoretical (balance equations, stability analysis, asymptotic techniques...), numerical (commercial codes, “home-made” codes) and experimental tools (essentially implementing optical diagnostic techniques: shadowing or interferometry), we can obtain original results, related for example to the dynamics of bubbles in microchannels (paying a special attention to the inertial and capillary migration forces, as well as to the role of surfactants.), the dynamics and morphology of unconfined ellipsoidal bubbles or the coupling between flow, bubble-liquid or gas-droplet mass transfer and chemical reaction.

Selected publications :

Atasi, O., Haut, B., Pedrono, A., Scheid, B., & Legendre, D. Infuence of soluble surfactants and deformation on the dynamics of centered bubbles in cylindrical microchannels. Langmuir (published online). 2018

Rivero-Rodriguez, J., & Scheid, B. Bubble dynamics in microchannels: internial and capillary migration forces. Jounal of Fluid Mechanics, 842, 215-247. 2018

Mikaelian D., Haut B., & Scheid B., Bubbly flow and gas-liquid mass transfer in square and circular microchannels for stress-free and rigid interfaces: dissolution model, Microfluidics & Nanofluidics, 19, 899-911. 2015

Mikaelian, D., Larcy, A., Cockx, A., Wylock, C., & Haut, B. Dynamics and morphology of single ellipsoidal bubbles in liquids. Experimental Thermal and Fluid Science, 64, 1-12. 2015

Transport phenomena in human lungs

Regarding the transport phenomena in the respiratory system, we have two distinct, but coupled, interests. The first objective of our research is to go towards a better understanding of the dynamics of the bronchial mucus, in healthy and unhealthy people. Human bronchi are covered with a thin layer of mucus. This layer acts as a trap for inspired fine particles and microorganisms. However, today, the dynamics of the bronchial mucus is still poorly understood. In addition, it is known that, in the context of certain diseases such as asthma and cystic fibrosis, this dynamics is significantly impaired. In collaboration with the pulmonology department of the Erasme Hospital, our goal is to improve the understanding of the bronchial mucus dynamics by combining in silico (modelling and simulation) and in vitro (laboratory experiments) studies. A specific objective is to analyse the coupling, potentially very important, between the rheology of the mucus and the respiratory conditions (respiration frequency, breathing air temperature and humidity…). Another of our objectives is to understand how the heterogeneity of the lungs (whether natural or induced by pathologies) influences the exchange processes within it (water, heat, oxygen transport). In this context, we are interested in describing the dynamics of the NO, a physiological molecule that can be considered as a marker of different phenomena. In particular, in collaboration with the Karolinska Institute (Sweden), we are studying how this molecule can be used as a tool for monitoring respiratory function on the International Space Station.

Selected publications : 

Karamaoun, C., Sobac, B., Mauroy, B., Van Muylem, A., & Haut, B. New Insights into the Mechanisms Controlling the Bronchia Mucus Balance. PLOS One, published 22 June 2018

Karamaoun, C., Haut, B., & Van Muylem, A. A new role for the exhaled nitric oxide as a functional marker of peripheral airway calibre changes: a theoretical study. Journal of Applied Physiology, 124, 1025-1033. 2018

Karamaoun, C., Van Muylem, A., & Haut, B. Modelling of the nitric oxide transport in the human lungs. Frontiers in Physiology, 7, 255. 2016

In-depth studies of the absorption of CO2 in liquids. Applications to process intensification and recovery system development

At the scale of the interface, our objective is to highlight and characterize the complex coupling that can exist between diffusion, convection and chemical reactions, during the absorption of CO2 in a liquid. We combine an experimental approach, based on interferometry, and theoretical (stability analysis) and numerical approaches.

At the scale of the device, our goal is to integrate the results obtained at the scale of the gas-liquid interface into classical chemical engineering approaches, in order to contribute to the optimization or the design of different kind of processes for the capture of CO2, based on absorption in amine solutions or on the formation of CO2 hydrates.

Selected publications :

Wylock, C., Rednikov, A., Colinet, P., & Haut, B. Experimental and numerical analysis of buoyancy-induced instability during CO2 absorption in NaHCO3-Na2CO3 aqueous solutions. Chemical Engineering Science, 151, 232-246. 2017

Douieb, S., Fradette, L., François, B., & Haut, B. Impact of the fluid flow conditions on the formation rate of carbon dioxide hydrates in a semi-batch stirred tank reactor. AIChE Journal, 61(12), 4387-4401. 2015

Wylock, C., Rednikov, A., Haut, B., & Colinet, P. Nonmonotonic Rayleigh-Taylor instabilities driven by gas-liquid CO2 chemisorption. Journal of Physical Chemistry B, 118(38), 11323-11329

Transport phenomena in the cardiovascular system

Regarding the transport phenomena in the cardiovascular system, our interest lies in the ballistocardiography (BCG) technique. It is a medical technique consisting in measuring, thanks to sensors, the small movements of the body induced by the blood circulation. It is used in particular on the International Space Station, to monitor the time evolution of the heart health of astronauts. Measured signals have been shown to be good indicators of the heart function. Nevertheless, quantitative links between physiological parameters of the heart and the signals measured in BCG have not yet been fully established. In this frame, in collaboration with the cardiology department of the Erasme Hospital (Dr. Pierre-François Migeotte), we develop the fundamental scientific knowledge behind BCG. For this, mathematical models of the body movements induced by the blood flow in the arteries are established, by the combination of fluid mechanics and analytical mechanics approaches. Then, these models are simulated and challenged against BCG signals obtained on Earth, under well-defined conditions, and on patients for whom certain cardiac parameters have been altered in a known manner. 

Identification and characterization, for further industrial applications, of structures of the living world optimally exchanging matter with their environment