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PhD Thesis Topics
potentially granted by a doctoral contract
from October 2015
Research Group
«Energy and Transfers »
TITLE :
PHD RESEARCH PROPOSAL
(potentially granted by a doctoral contract)
2015
www.lemta.fr
« Semiconductors for thermoelectricity : nanostructuration, interfaces et composition »
SUPERVISORS :
Surname, Name :
Konstantinos TERMENTZIDIS, David LACROIX
Email & phone :
[email protected] (00 33 3 83 68 46 86)
[email protected] (00 33 3 83 68 46 88)
Postal address :
LEMTA - Université de Lorraine - CNRS UMR 7563
Faculté des Sciences et Technologies, BP 70239,
F-54506 VANDOEUVRE CEDEX
CONTENT OF THE WORK :
Atomistic and numerical simulations, Modeling, Theory
ABSTRACT :
The purpose of this PhD research is to improve our knowledge of electronic and heat
transport in nanowires and composite materials with nanoinclusions designed for
thermoelectricity applications.
This implies the modeling of semiconductor materials with atomistic simulation tools
(ab-initio, molecular dynamics, Monte Carlo methods) which are relevant and reliable at
these nanoscales.
COLLABORATIONS :
Institut Jean Lamour (teams 102 and 208) :
Laurent CHAPUT and Nicolas STEIN
Technological Educational Institution, TEI of Sterea Ellada (Greece) :
Xanthippi ZIANNI
RESEARCH GROUP : THERMAL TRANSPORT IN MICRO-NANO SCALE
The group is composed by Engineers and Physicists of Condensed Matter Physics. Their main
interesting is nanostructured semiconductors materials for energy applications. Recent advances
in the field of nano-fabrication technologies allow today the synthesis of nanostructures
(nanowires, nano-objects, superlattices ...) that can be integrated in micro-electronic
devices, thermoelectric, photovoltaic devices. However, the heat transport in these systems
is strongly affected by the interfaces. To increase the reliability, the life-time and to
decrease the cost of these devices, controlling heat flow is a necessity. In our group, we
develop theoeretical models, simulation tools (atomistic and mesoscopic) and experimental
devices dedicated to the exploration of new phenomena observed at very small scales. The
main
numerical
and
experimental
tools
used
are:
• The simulation ab initio (VASP) and molecular dynamics (LAMMPS) for the calculation of
transport
properties
in
nano-scale,
• The simulation of the Boltzmann equation by statistical method (Monte Carlo) for the
description of heat exchange at the meso-scale (between the atomistic and continuum
models),
• The thermal local probe microscopy AFM and the SThM (Scanning Thermal Microscopy).
DETAILED PHD RESEARCH PROPOSAL
State of the art: Thermoelectric effects allow the conversion of a temperature
difference into a voltage (Seebeck effect) and conversely (Peltier effect). Despite these
phenomena which were discovered at the beginning of the XiXth century, the weak
efficiency of thermoelectric materials and their cost have limited the development of this
technology. However, during the past decade the thermoelectricity has been reconsidered
as a potential alternative for energy production with the emergence of new materials
designed at the nanoscale with tailored properties. New nano-fabrication techniques allow
the increase of the Figure of Merit (ZT ∝  ,k)which characterizes the thermoelectric
efficiency. As it can be seen lowering the thermal conductivity (k) and keeping constant the
electric one 
( ) make thermoelectric materials more efficient. Thus, understanding how
electrons and phonons are transported in small scale objects (size below 1µm) is a major
issue for the development of new thermoelectric materials, especially in order to promote
renewable energies. Therefore, the objective on this research is to model accurately the
thermal properties of these materials with atomistic simulation tool.
Research program: In order to improve thermoelectric materials ones has to know
which parameters can be tuned in order to increase their efficiency. In the frame of this
work a “bottom-up” approach will be considered. It starts at the atomic scale with ab-initio
calculations and molecular dynamics simulations and goes to the micron scale with the
resolution of the Boltzmann transport equation with Monte Carlo techniques. Thus, it is a
multi-scale modeling with dedicated numerical simulation tools. In this work, core-shell
nanowires and composite materials made of Bi2Te3 (Bismuth Telluride) will be considered
since they are good candidates for high thermoelectric efficiencies.
In order to study these core-shell objects (Figure 1-left), or the composite materials
(Figure 1-right) several parameters have to be considered:
• First, the interfaces between the two semiconductors (Bi and Te) requires an
accurate modeling of the phonon flow. This could be done with ab-initio tools such
as VASP or with Molecular Dynamics with the LAMMPS code. Kaptiza thermal
resistance, phonon dispersion properties and lifetimes can be addressed with these
simulation tools.
• Secondly, phonon confinement effects in the nanowires must be considered in order
to appraise thermal conductivity. This can be done with Molecular Dynamics or
Monte Carlo simulations. Several parameters, such as: the roughness of the
interface, the core-shell size ratio, the nanowire length, the doping level or the
material organization (Bi/Te or Te/Bi core-shell) can be modeled with these tools.
• Lastly, the use of Bi2Te3 nanowires, embedded into a polymer matrix, in order to
build a p-n junction is expected. This part of the work will be done in collaboration
with the team 208 of the IJL, where people have recognized experimental skills in
the fields of the nanofabrication and the characterization of thermoelectric devices.
Summary: The PhD candidate will integrate an active team in the field of nanosciences.
Within the PhD thesis, he will study the impact of (i) different stoichiometries of nanowires
composed by Bismuth and Telluride (BixTey) or with alternate layers of the two materials
(superlattice nanowires) and (ii) the nanoinclusion geometry in a host matrix. Their thermal
and electrical properties will be appraised. The team has experience in such systems, (i) for
their thermal properties [D. Lacroix et al. Phys. Rev. B 2005 & Appl Phys Lett. 2006, K.
Termentzidis et al Phys. Rev. B 2009, Nanotechnology 2014 & J. Phys. Cond. Matter 2014]
and (ii) for their thermoelectric properties [K. Termentzidis et al J. Appl. Phys. 2013].
The PhD candidate will use different simulations methods: ab-initio calculations, Molecular
Dynamics and Monte-Carlo computing. He will predict the behavior of thermoelectric
materials at the nano and microscale. The Scientific Operation Group THOMAS of LEMTA
laboratory has the know-how of all the methods mentioned above. One of the challenges of
this thesis would be the integration of electron-phonon interactions to the existing “single
carriers” heat transport theories currently available.
This PhD thesis will give us the opportunity to collaborate with the groups 102 and 208 of
Jean Lamour Institute. The 208 group has recognized competences at international level in
the fabrication, characterization and integration of BiTe alloys for thermoelectric devices,
while the 102 for his experts with DFT calculations. The scientific collaboration with these
two groups as well with Professor Xanthippi Zianni (National Center of Scientific Research,
Greece) will improve our knowledge in this domain, giving us a global vision of all scientific
aspects; namely, from the theoretical point of view (modeling and simulations) to the
experimental one (characterization and integration of such materials into thermoelectric
devices). Establishing this bridge between simulations and experiment will drive us to
materials with tailor thermoelectric properties eg. nanostructuration is the best way to
increase the ZT, while decreasing mainly the thermal conductivity.
Figure 1- (left) Schematic representation of Bi-core, Te-shell nanowire with rough interfaces
(right) Three configurations for core/shell silicon nanowires.
PhD RESEARCH PROPOSAL
TITLE :
(potentially granted by a doctoral contract)
2015
www.lemta.fr
Stability of the two-phase displacement in porous media
studied by MRI techniques
SUPERVISORS :
Director of thesis :
Irina Panfilova
[email protected]
03.83.59.55.96
Co-director :
Sébastien Leclerc
[email protected]
03.83.68.43.59
[email protected]
[email protected]
03.83.59.56.96
03.83.59.56.11
Consultants :
Maude Ferrari
Didier Stemmelen
Postal Address :
LEMTA – Université de Lorraine – CNRS UMR 7563
2 Avenue de la Forêt de Haye, TSA60604,
F-54518 VANDOEUVRE CEDEX
Professional web page of personnel :
http://lemta.univ-lorraine.fr/data/pages_pro/I.Panfilova.pdf
CONTENT OF THE WORK :
Experimental study, numerical modeling
ABSTRACT :
Modeling the stability of a two immiscible liquids flow under the simultaneous effect of
gravity, viscosity and superficial tension is a problem widely discussed in the scientific
community. The complex geometry of the porous space and the viscous and capillary forces
cause the deformation of the displacement front, its fragmentation in form of droplets and a
further deceleration or total immobilisation of these droplets.
The objective of this research is to get the kinetic parameters of these processes by an
experimental study based on the MRI technology and to perform numerical modeling at the
pore scale. The developed model will be applied to simulate the enhanced oil recovery,
where the technology often causes a deformation and dispersion of the displacement front.
COLLABORATIONS :
DETAILED PHD RESEARCH PROPOSAL :
This study concerns immiscible two-phase flow in porous media. The complex geometry of
the porous space, the difference in the properties of fluids and capillary force cause a
deformation of the displacement front. The interaction of two immiscible liquids provokes
the trapping of one phase in the other one. We consider the case where the dimensions of
the drops are comparable with the pore size. The movement of drops is either strongly
decelerated or stopped by the capillary force (Fig.1), which presents the main interest in our
study.
Fig.1 Movement and trapping
of droplets in porous media
Fig.2 600 MHz WB spectrometer
We are considering a series of experiments using MRI technique (Fig.2) where we aim to
visualize the propagation and mixing of liquids in porous media. We are especially interested
in the deformation of the displacement front during its progress in the porous sample and in
the formation of the trapped drops.
At the same time, for the modeling at the pore scale, we will use a simulation software
created in our group which models a multi-phase flow in a pore network (capillary network
model of porous medium). This code is well adapted to unstable two-phase displacements.
PROPOSED RESEARCH :
Background
Innovative experimental techniques are used in LEMTA such as Magnetic
Resonance Imaging (MRI), traditionally used in medicine, and Nuclear Magnetic
Resonance (NMR) Spectroscopy. These techniques are exploited, for instance, for
quantitative analysis of flow in opaque materials such as porous media.
The study of liquid flow in porous media is part of the “Observe in the opaque”
action, which started in 2002 with its launch by D. Stemmelen (CR1 CNRS - LEMTA)
with technical assistance of S. Leclerc, Fr. Xu, J.C. Perrin and others specialists of
NMR and MRI.
Topic development
The study of two-phase flow in porous media is of considerable interest in the
petroleum industry (estimation of exploitable reserve, optimization of the recovery
techniques…) but also in the sector of chemical industry (catalytic reactors,
separation, extraction) or in the hydrogeology domain (pollution of aquifers by
NAPL). This explains the importance of the studies aiming to improve the description
of multi-phase flow in porous media. Notably, the simultaneous flow of two
immiscible fluids (water-oil) in porous media is not always well described by the
Darcy's generalized law, which only takes into account water/oil saturation as
additional descriptive variable. This has a substantial impact on the modeling of the
two-phase flow stability under the simultaneous effect of the force of gravity,
viscosity and superficial tension.
Objective of project
The overall purpose of this study is to determine kinetics of the process of phase
trapping during two-phase flow. The phase saturations and the menisci
concentration in the zone of the front deformation will allow us to complete the vector
menisci model proposed in [1]. This model takes into account the vector nature of
capillary forces. This will lead to an improvement of the description of the theory of
oil recovery and hydrogeology.
Preliminary results
The experiments allowing one to visualize the distribution of fluids in 3D real porous
medium (micro-tomography X, acoustical methods, PET-scan...) are not numerous.
Among the known techniques, Magnetic Resonance Imagery (MRI) allows to make
non-invasive measurements (2D, or even 3D mapping) of the concentration of
hydrogen nuclei in the liquid phase in a porous medium. These hydrogen nuclei can
belong to molecules of water or other liquids (oil for example). A preparatory work
done in the laboratory showed that MRI cartography of longitudinal relaxation time
T1 allows, with a prior calibration, to measure the phase saturation in a quite
accurate way.
The measurements by Magnetic Resonance Imaging (MRI) of fluid flow within
granular porous media were presented in the thesis of W.Salameh (LEMTA, 2010).
This study has shown the possibility of visualization of velocity field in porous media
and accurate measurements of interstitial and averaged velocities in packed beds
[2].
3 master thesis (A. Darishev, A. Pakzad, 2011; B. Kabiwa, 2012; G. Carron, E.
Maxant, 2013) were performed in order to validate the analysis of two-phase fluid
flow in porous media by MRI technique. In these experiments the displacement of oil
by water flooding was studied in porous medium formed by the polystyrene beads of
average particle size 0.5 mm. The values of phase velocities and saturations were
measured in longitudinal and transverse sections at different time steps.
Furthermore, fluids distributions in porous samples during the experiments were
mapped.
Research methodology
By using MRI techniques, our aim is to improve the description of two-phase flow in
porous media. We will be using a mix of water and octanol. The porous media model
will be first a stack of mono-dispersed beads (with a diameter in the order of a
hundred microns) before envisaging real porous medium (sandstone). We plan to
realize the experiments of imbibition-drainage in the porous media in conditions of
injection with very weak capillary number (Ca<<1). In these experiments, the front of
displacement (water - octanol) is deformed due to viscous instabilities and capillary
forces. It forms islets of octanol trapped in porous structure by capillarity. This twophase zone (front of dispersion) can be observed by MRI. We will also be able to
analyze the effect of gravity, which plays a stabilizing role for the displacement front.
The model porous medium will consist of a glass column filled with randomly packed
spherical polystyrene beads for the drainage process and with borosilicate glass
beads for imbibition. At first, the column is flooded with octanol. It will be
subsequently attached to two reservoirs and placed in the magnet. A three
dimensional image of the porous space will be first acquired; in all experiments the
1H species associated with the water or hydrocarbon are imaged. MRI provides
three dimensional images, able to distinguish the solid, hydrocarbon, and aqueous
phases, as well as velocity maps of the mobile aqueous and octanol phases. Water
will then be injected into the column from the bottom with volumetric flow rate
corresponding to a superficial velocity of low Ca, until the irreducible hydrocarbon
saturation, Sir, is obtained in the form of octanol droplets entrapped in the porous
space by capillary forces. During the experiment, we will acquire a number of
longitudinal and transversal images. Saturation will be defined as the percentage of
the pore volume occupied by octanol. Finally, a 3D image of the distribution of
octanol droplets within the bed will be acquired using a T1-weighting method [3].
We will also use MRI velocimetry techniques in the case of liquid-liquid flow in
porous medium. We expect to measure the velocity of each phase in porous
medium independently of the other phase. It would constitute a considerable
advance in the description of two-phase liquid-liquid flow in porous medium and a
redefinition of the models of relative permeability functions.
To model numerically a two-phase flow on pore scale, we are going to apply a
software simulating multiphase flow in pore networks. This code is well adapted to
the two phase flow with phase structures of meniscus type. The numerical
simulations will be compared with the experimental studies. Another code based on
Comsol Multiphysics and using the diffuse interface method can be applied to model
the flow of drops in porous media. The simulation results based on stochastic
distributions of droplets will allow us obtain the (macroscopic) parameters of the
fragmentation and coalescence kinetics, as well as the position of meniscus and
droplets.
The perspectives of application of this study concern the phenomena strongly
governed by capillary effects, such as the displacement of oil by water or the
capillary fringe in the aquifers.
[1]
Panfilova I. and Panfilov M. Phenomenological meniscus model for two-phase flow through
porous media. Transport in Porous Media, Special Issue on Multiphase Flow and Transport in
Porous Media, v. 58, 1, pp. 87-119 (2005).
[2]
Salameh W., Leclerc S., Stemmelen D., Escanyé J.M. NMR imaging of water flow in packed
beds. Diffusion Fundamentals, 14 (5) 1-5, (2010).
[3]
Johns M. L. and Gladden L.F. Magnetic Resonance Imaging Study of the Dissolution Kinetics
of Octanol in Porous Media, Journal of Colloid and Interface Science 210, 261–270 (1999)
NB : The laboratory has a privileged access to two MRI installations:
-
100 MHz imager with horizontal bore (400 mm of diameter)
- 600 MHz NMR spectrometer with a vertical bore (89 mm) and equipped with a
micro-imaging system.
PHD RESEARCH PROJECT
(potentially granted by a doctoral contract)
2015
www.lemta.fr
TITLE :
NMR and MRI investigation of water transport through multilayer
PEMFC components.
Institution
University of Lorraine / LEMTA Laboratory / CNRS
PhD supervisor
Prof. Olivier Lottin
Co-supervisor
Dr. Jean-Christophe Perrin
Contact
e-mail :
[email protected]
phone :
+33 (0)3.83.59.55.86
activities of the research group : http://lemta.univ-lorraine.fr/pac.html
Mailing address
2 avenue de la Forêt de Haye, TSA60604 54518 Vandoeuvre Cedex, France
International context
The quest for more sustainable energy has become a worldwide priority. During the past decades,
the global demand for energy has exploded, raising the need for highly efficient energy conversion
devices. Today, hydrogen has gained importance as an energy carrier in future transport
applications and fuel cells have reached a state-of-the-art that makes them highly attractive for
car propulsion. Groups of researchers around the world are carrying out the environmental and
economic assessments of the entire hydrogen supply chain and it is generally believed that, when
combined with the right energy sources, fuel cells, and more particularly polymer electrolyte
membrane fuel cells (PEMFCs), have the highest efficiencies and lowest emissions of any vehicular
power source. Fundamental and technological research in the field of PEMFC systems is intense
and, in the past years, more than 35% cost reduction has been achieved in their fabrication.
In PEMFCs, hydrogen and oxygen react to form water and, due to the separation of the anodic and
cathodic processes, electrical energy. Protons migrate through the membrane (PEM) and
recombine with oxygen on the surface of the cathodic catalyst where oxygen is reduced and forms
water (Figure 1). The electrolyte of the PEMFC is usually a polymer membrane composed of
poly(tetrafluoroethylene) backbones with sulfonate-terminated side chains, like Nafion®.
To reach the target for transportation fuel cell of $30/kW to compete with the conventional
technology of internal-combustion engines, breakthroughs in material development, acquisition of
fundamental knowledge, and development of experimental methods are still needed.
More specifically, the development of new methods to investigate water management in PEMFC
materials will provide insights into a number of critical phenomena that occurs in running fuel
cells. These methods have the potential to provide critical feedback for validating models of water
transport phenomena for fuel cell research and development.
MEA
bipolar plate
PEM
catalyst
coating
bipolar plate
GFC : Gas Flow Channel
O2
H2
PEM : Proton Exchange Membrane
GDL : Gas Diffusion Layer
H2O
MEA : Membrane Electrode Assembly
MPL : Micro Porous Layer
GFC sealing gasket GDL+MPL
sealing gasket
Figure 1. Proton Exchange Membrane Fuel Cell (PEMFC) components.
Scientific project
This project aims at studying the properties of complex assemblies composed of the
ionomer membrane and one or more elements such as the catalyst layer (electrode) and/or
the gas diffusion layer. The main experimental technique will be MRI (Magnetic Resonance
Imaging) and NMR (Nuclear Magnetic Resonance) spectroscopy. The experimental
methodology will be based on the recent advances made in our group in the imaging of
water profiles through a PEM membrane with both high spatial and temporal resolutions
[Figure 2(a) and (b) and ref(1)].
Figure 2
(a) Experimental setup developed for the
MRI of water distribution in the thickness of
a PEM. The 2D NMR probe is placed under
the cell containing the membrane exposed
to air flows with controlled hygrothermal
conditions.
t<0
RH ~ 0%
RH = 80%
membrane
RH ~ 0%
RH ~ 0%
membrane
y
1L/min 1L/min
t>0
T = 24°C
(b) Water profiles measured by MRI through a 250 µm thick Nafion membrane.
Acquisition time = 70 seconds/profile. Spatial resolution = 6 µm / point.
The study will be focused on the observation of water behavior in the membrane when its
interfaces are exposed to different phenomena:
- inhomogeneities in gas supply due to the electrode;
- mass transfer resistances due to the GDL or the GDE (gas diffusion electrode);
- electrochemical reaction with water formation at the membrane / electrode interface.
The measurements will be systematically compared to the reference case (Nafion
membrane exposed to controlled hygrothermal conditions) and used to develop a coherent
modeling for water transport through the multilayer.
The experimental methodology will be also exploited to characterize PEMs after long runs in
fuel cell conditions, the final objective being the development of a new versatile diagnostic
tool of aged membranes.
References
1) M. Klein, J.-C. Perrin, S. Leclerc, L. Guendouz, J. Dillet, O. Lottin. Spatially and temporally
resolved measurement of water distribution in Nafion using NMR imaging, ECS
Transactions, 58 (1) 283-289 (2013).
Related references:
2) J.-C. Perrin, M. Klein, S. Leclerc, L. Guendouz, J. Dillet, O. Lottin. NMR Investigation of
Water Diffusion in a Nafion membrane Under Traction, ECS Transactions, 58 (1) 781-788
(2013).
3) M. Klein, J.-C. Perrin, S. Leclerc, L. Guendouz, J. Dillet, O. Lottin. Anisotropy of water selfdiffusion in a Nafion membrane under traction, Macromolecules, 46, 23, 9259-9269 (2013).
4) M. Klein, J.-C. Perrin, S. Leclerc, L. Guendouz, J. Dillet, O. Lottin. NMR Study of the
anisotropic transport properties of uniaxially stretched membranes for fuel cells, Diffusion
Fundamentals 18-7 (2013) 1-4.
PhD thesis (Mathieu Klein, 2014) [non-definitive version] :
https://docs.google.com/viewer?a=v&pid=sites&srcid=ZGVmYXVsdGRvbWFpbnxqZWFuY2hyaXN0b3BoZXBlcnJpbnxne
DoxMTYyMTRmYmY0YTZjMDdk
Application procedure
Informal inquiries can be made to Dr Jean-Christophe Perrin ([email protected]) with a copy of your curriculum vitae and cover letter. Applications should be received
and complete by 29 May 2015.
Research Group
«Mechanics of Materials
and Structures »
Research Group
«Fluid, Reactive
and Multiphase Media »