Research

This section highlights my research work and activities from the past to the present.

Thermal property characterisation

Chemical kinetics and sorption

Modelling and simulation

Thermal conductivity of potential thermochemical storage materials are determined under steady and transient conditions within two different devices.

The simultaneous TGA/DSC device helps assessing the material sorption capacity and reaction heat (enthalpy).

Through the above scheme, heat and mass transfer occurring in TES is numerical computed.

Research Projects

Past projects and ongoing ones, if any:

  1. University of Buea (Cameroon), EDU-ABCM (Capacity Building on Student-Centered Energy Education in Cameroon, Ethiopia, Mauritius, and Mozambique), Project Number: 101082957, Call proposals: ERASMUS-EDU-2022-CBHE. From 01/01/2023 to 31/12/2026.

  2. University of Buea (Cameroon), 2020-1-EL01-KA107-078643, ERASMUS+ Programme Mobility for learners and staff –Higher Education Student and Staff Mobility. From 01/09/2020 to 31/12/2023.

  3. INSA-Lyon (France), InPATHES (EU project on developing capacities on thermal energy storage), LCE-20-2014 Project reference: 657466, Call proposals: H2020-LCE-2014-2. From 01/05/2015 to 30/04/2018.

  4. Leuphana University Lueneburg (Germany), Chemical heat storage for catalyst heating measure. 10/2013 - 09/2015 Research Association for Combustion Engines (FVV).

  5. Leuphana University Lueneburg (Germany), Competence Tandem Thermal Battery TM1.1 Innovations Incubator NBank/EFRE 10/2011 - 12/2014 Application number WA3-80124780.


Faculty of Engineering and Technology/ University of Buea - Cameroon (2020 - to now)

At the Faculty of Engineering and Technology, I am dealing with the storage of electricity through hydrogen production and its technico-economic investigation in the Cameroon and Subsaharan context. Electricity storage technologies appear as one of the solutions to most African countries' national electrical grid issues. In this context, hydrogen production from renewable could be used to test their ability for energy storage. It is possible to recover grid losses through hydrogen production and re-inject it into the grid. This research aims at demonstrating numerically and experimentally how much renewable hydrogen can be produced in a Sub-Saharan African context. Another research direction is the investigation of solar PV integration into the grid to evaluate the impact and stability of the power network.

In the meantime, research on sorption, mechanical & thermophysical properties of materials are performed as well as logistic and transport engineering.



ESMER (École Supérieure des Métiers des Énergies Renouvelables) - Bénin (2016 - 2019)

At the Laboratory of Innovative Processes for Sustainable Energy (Labo-PIE), I am dealing with the combination of storage technologies to improve the energy mix in Africa and reduced losses by 10%, if possible. Most of the Africa country national electrical grids are a mix of different energy types (thermal, hydro and renewable energies). However, energy demand is never covered, even the one supposed to match the production. This is due to shortages, outages, losses, and renewables intermittency with the consequence of non-sustainable access to energy. Energy storage technologies appear as one of the solutions. However, energy storage technologies are broad and depend on the nature of energy. It can be electrochemical and thermal. In an African context, local materials and hydrogen production from the grid should be used to testing their ability for energy storage. Grid losses can be recovered and re-injected. This research aims at demonstrating benefits from integrating storage systems into grids; selecting, characterizing and testing potential local materials for thermal storage; technic-economical evaluation of hydrogen/fuel cell or thermal storage (HFC-TES) on the electricity cost, and grid system simulation including storage technology and control (weather, price or demand based forecasting).

Currently, dynamics of two storage technologies is studied with the HEL at the Labo-PIE, as shown on the picture below.

CETHIL-UMR5008, INSA Lyon - France (2015 - 2016)

I was focused on how to optimize the transport of heat and mass in the storage material and its impact on the entire storage system. Manufacturing and thermal analysis of a characterization bench and zeolites composites were the main tasks. It is about identifying thermokinetic barriers and to provide viable solutions. The design and construction of a characterization test bench in closed systems are done in parallel for testing at laboratory scale. The aim is to establish the multi-level relationship (system-materials) that may exist. I had in mind and wanted to study the relationship between thermal storage systems and thermal comfort of the building by implementing equations in TRNSYS or DYMOLA, filling the characteristics of a thermochemical storage system and pair it with a habitat for a dynamic study.

Leuphana Universität Lüneburg - Germany (2011 - 2015)

During my stay in Germany, research was to develop heat storage system based on reversible thermochemical reactions, such as dehydration and hydration of inorganic salts, which exhibits very high energy density (up to 628 kWh·m-3 of storage material). The chosen inorganic salt (SrBr2·6H2O) reacting with pure water vapour operates within a closed system. The objective was to design a system that thermodynamically matches the combination with micro-CHP waste heat. Therefore, investigations were performed from the material at micro-scale to the system at lab-scale. Models were developed on the basis of heat and mass transfer with chemical reaction and were done in order to numerically analyse the system. Experiments were additionally performed to consolidate the numerical tools for future studies. Characterization experiments were designed and tested. Thermo-physical properties (thermal conductivity, specific heat capacity, permeability, chemical kinetics) of the reactive salt were then determined to be used as parameters into the so developed models.

The numerical simulations lead to the time-space evolution of heating fluid, reactive bed temperatures and reactor pressure. The originality of the numerical work was to model the coupled heat and mass transfer with chemical reaction on a 3D geometry to be close to the reality. Results help to numerically and experimentally analyse the thermochemical heat storage performances. The bed energy density was experimentally found to be 531 kWh·m-3 of salt hydrate. Based on the condensation temperature during the experimentation, a reactor energy density of 140 kWh·m-3 and a storage capacity of 65 kWh with a thermal efficiency of 0.78 are obtained. This system proves the recovery capacity of more than 2/3 of the input thermal energy. Various aspects of design and recommendations for optimisation aspect that could help during prototype development were taken into account and addressed. Comparison simulation-experiment was then performed and discussed, showing encouraging results, even if limited at lab-scale.

Materials Science Lab, University of Yaoundé 1 - Cameroon (2008 - 2009)

Challenges in the semiconductor industry include reducing device size and lowering production costs, while improving performances and functionalities. Furthermore, the rapid development of the electronic industry, which occurred in recent years, calls for new growth methods and changes in semiconductor material’s properties. The inclusion of nanostructures, mainly silicon, in semiconductor materials during the formation process has been considered long time ago. Understanding the growth mechanism of nanocavities created by such an inclusion is crucial to the development of new manufacturing materials at low cost.

After implantation (or inclusion), the materials are generally highly degraded: impurities randomly embedded, not all at substitutional positions, and most are electrically inactive, which impairs the usefulness of the material. It is, often necessary, therefore, to subject the embedded matter to thermal annealing during microelectronic applications.

This fulfils two major roles:

– reconstitution of the material’s crystal structure by patching up the defects

– activation of embedded impurities.

It must be noted that, after the annealing, the distribution of impurities in the material is more spread out. If the material is amorphous, the ion trajectories are random, because no direction is favoured. Where the embedded ion is a gas, bubbles are therefore formed; where the ions are metal, cavities appear in the material. Still, the experiments provide important information on the growth of nanocavities and their environment. However, the spatial-temporal resolution of the experimental devices does not allow for the observation of the kinetics, even less the understanding, of the processes at microscopic level.

Control of materials’ structure at the nano-scale allows us not only to consider the realisation of many new applications, but also to vary the properties of certain materials. A significant proportion of current projects concerns electrical energy generation: solar cells or thin gel titanium oxide nanoparticles, battery lithium electrodes, hydrogen fuel cells, etc. The medical sector is likewise very involved. For example, nanoparticles encapsulated in small hollow spheres of polymers injected into the body can improve certain technical observations.

The subject dealt with here allows us to understand and control the production process of these materials at the microscopic scale (thin layers), followed by the purification of these layers by gettering, which is a procedure designed to optimise the operation of devices based on semiconductors, ridding the active area of unwanted impurities by nanocavities. These impurities are then combined in a buried layer damaged and stable below an upper layer of excellent crystal quality. The high-energy ion implantation is suitable for this application, since most of the crystallographic residual damages are localised in depth.

Precursors usually give birth to nanocavities, which will grow under the influence of temperature during annealing and lead to a growth governed by two mechanisms, namely Oswald Ripening and Coalescence Migration, of which we have studied only the first. The curves obtained for the OR mechanism show that the nanocavities grow much faster at high temperatures. These curves also show us the conservation of their physical nature before and after annealing, and that the temporal evolution of these nanocavities complies with the implementation laws of various electronic components. The comparison with the results of J. H. Evans is an important validation test of the developed model. In addition, the reproduction of the experimental results will determine the appropriate parameters. Non-smooth digital curves are due to the fact that we do not consider the distribution of nano- cavities on the surface, but rather a constant number of voids as well as a constant total volume of cavities. A continuation would be constituted of simulations taking into account the loss of nano-surface cavities and variations in the number of voids of all growth mechanisms.