APRÈN. Portal de la producció docent del professorat de la UPC

Global warming, caused by the increased concentration of greenhouse gases in the Earth's atmosphere, has necessitated the transition to cleaner energy sources. Hydrogen, a versatile and environmentally friendly energy carrier, represents a promising alternative to traditional fossil fuels. This research project explores methane pyrolysis as a sustainable and economical method of hydrogen production, addressing the challenge of carbon dioxide (CO2) emissions. Using advanced numerical simulations, we aim to model the complex multiphase flows and thermal dynamics involved in methane pyrolysis, providing insights to optimize the process for industrial applications. The main objective of this research is to study methane pyrolysis for hydrogen production through detailed numerical simulations. Calculations will be performed using the Basilisk platform, a high-performance computing tool for simulating multiphase flows developed by Stéphane Popinet at Sorbonne University. Basilisk allows for detailed direct simulation of complex flows with numerous droplets and bubbles, providing a robust framework for our research. Initial simulations have focused on the axisymmetric behavior of a single non-reactive bubble and the formation of bubbles from a single orifice. The results of this research are expected to include a comprehensive understanding of the dynamics of methane pyrolysis in liquid metal, optimization strategies to improve hydrogen production efficiency, and information on the thermal and chemical processes affecting bubble behavior and carbon separation. Studying methane pyrolysis is particularly challenging due to the high temperatures involved and the use of opaque liquid metals. These conditions make it difficult to obtain detailed information on the precise mechanisms underlying the pyrolysis process. This is where numerical simulations become extremely valuable. They provide a means to explore and understand the complex interactions and dynamics within the system, offering insights that are difficult to obtain through experimental observations alone. This research aims to contribute to the development of sustainable hydrogen production methods by exploring methane pyrolysis. Through detailed numerical simulations, we seek to optimize the process and address the challenges associated with carbon emissions, thereby supporting the transition to a cleaner energy future.

Steel production is a very energy-and-emission-intensive process, and with its projected increase in the future, due to steel's vitality in the operation, sustenance, and development of modern economies, there is a huge need for solutions, pathways, and methodologies to increase the sustainability of steel making processes across all production facets, to meet global energy and climate goals. Pebble bed heaters/ Thermal Energy Storage (TES) systems possess great potential to be used as regenerators to recover waste heat across all facets of steel plants. Thus, this thesis focuses on the development of a simulation tool for pebble heaters via numerical modelling of heat transfer and its paraphernalia within packed bed TES systems, as a preliminary instrument for testing use cases and optimizing design decisions for their incorporation in ArcelorMittal's steel production processes, to ultimately enable energy savings and decarbonization. The project was carried out by executing a thorough literature review and survey on heat transfer modelling techniques of packed-bed heat storage devices used in heavy industries and afterwards, developing a more robust model as an improvement to the previously existing one in ArcelorMittal. The finally developed model was a 1D, twoequation model, numerically computed using the finite difference method with an implicit time integration scheme. The model was verified and also validated using experimental data reported from literature sources. A percentage wise sensitivity analysis executed using the model revealed the importance of optimising the specific heat capacity of the solid particles, the height of the pebble heater and the charging time, to maximize energy extraction from the waste heat source. The diameter of the solid particles was also shown to impact the effective thermal conductivity of the TES system (due to its direct proportionality to the radiative contribution of the thermal conductivity), while also influencing the pressure drop across the system. Finally, some proposals were made for further improvement of the model within the model robustness scope, and a few future activities surrounding the thesis timelines were aptly mentioned.

This thesis explores the numerical resolution of mass, momentum, and energy conservation equations, with a focus on their application in absorption and adsorption refrigeration systems. It begins with establishing the fundamentals of computational fluid dynamics, with classic cases examined and validated through custom C++ code. The research then moves to practical case study: falling film heat transfer, a key process in absorption and absorption refrigeration. The simulation of liquid ethylene glycol film flow over a vertical plate is performed using the open foam solver interFoam. The simulation results are validated against both experimental and numerical data, and boundary conditions are optimized for accuracy. Additionally, a new solver, interTempFoam, is introduced to incorporate the temperature transport equation. The heat transfer phenomenon occurring in falling film is analysed and assessed.

This research investigates the application of heat recovery technologies to capture waste heat and improve the energy efficiency of industrial processes, with a particular case in a local foundry industry in Spain. Waste heat should be reused within the industrial plant rather than emitting it into the atmosphere. The flow rates and temperatures were measured and analyzed from the waste energy streams to determine profitable heat recovery applications and processes for waste heat recovery and reuse. Amongst them, the most profound possible points for heat recovery were the waste heat from the slag of the molten process, the cooling process of the hot metal pieces inside the moulders, waste sand containing thermal energy, hot water used after cooling the induction oven, the hot wall of the maintenance ovens, the hot gases from the oven and the de-moulding process. Considering these, the main objective was thus to take advantage of the electrical energy introduced in the melting process by recovering and pre-heating the metal pieces before melting. Various technologies have proved viable - heat exchangers, Thermoelectric generators and Organic Rankine Cycle, amongst others for electricity generation from low-temperature streams and thermal energy generation. An important aspect to note is the intermittency of heat generation and, as such, the need to implement suitable storage devices to store the excess generated heat in thermal storage or electricity to the grid. Furthermore, other materials like molten salts for thermal energy storage and implementing renewable energy sources were reviewed

The goal of this internship was to develop a numerical sizing tool for the aqueous organic redox flow battery systems, as KEMIWATT enters its commercialization phase. The “Process Generator” tool was developed using Visual Basic .NET, and it optimizes the architecture of the battery for any use-case targeted by KEMIWATT. For this optimization, the tool considers several economic and technical constraints. The optimal battery configurations that are proposed are not only the cheapest options, but also most efficient in their utility of the hydraulic and electrical components of the battery. The tool can scan databases of equipment (tanks, pumps, etc.) from different suppliers, and choose particular equipment models most suited to the project needs. In addition, another aspect of this internship was to calculate the effective heating/cooling requirements for the battery systems, so that the processes can always be maintained at the most efficient temperature for the electrolytes. This requirement is calculated for two of the electrolyte tank configurations that KEMIWATT utilizes (rectangular and cylindrical). Based on this requirement, heat exchangers are designed, which use water to provide the necessary heating or cooling as is needed, to maintain optimal temperature

This work is denominated Numerical resolution of heat and mass transfer phenomena. Application to the analysis of heat loss by convection in a flat solar collector. It is divided into eight chapters and four annexes. Chapter 1 presents the objectives, scope, and exclusions of the work. Chapter 2 is dedicated to the analysis of heat conduction in solids, while Chapter 3 covers the various methodologies of resolution of the Convection-Diffusion Equation. An introduction to the numerical resolution of the Navier Stokes equations is presented in Chapter 5. The experimental work on the flat solar collector and its results are presented in Chapter 6. The final conclusions are presented in Chapter 7 and the bibliography that was used for the development of this paper is presented in Chapter 8. In addition, three annexes are presented, Annexes A, B, and C which present the computational codes developed. Annex D presents the daily reports of the experimental part for the selected days.

In this project, self-build CFD code in C++ is employed to simulate several classical fluid dynamic, heat and mass transfer problems such as Driven Cavity, Deferential Heat Cavity, Square Cylinder problem. Besides, this work also includes a code of absorption chiller in condition of falling film, and the result of the code will be compared with previous work of other researchers. The inform consists of 6 chapters. Chapter 1 is introduction where the objective and scope is explained. In chapter 2, the govern equation of both mass, momentum and energy equation will be deduced at different conditions using different hypothesis and simplification. In chapter 3, the discretization of the govern equation and the mesh of the domain will be carried out. In chapter 4, the algorithm of fractional method step will be explained and, also the algorithm for the falling film. In chapter 5, the result of each corresponding code will be compared with high resolution benchmark result. In the final chapter 6, an experiment of component of absorption chiller with falling film of aqueous LiBr driven by gravity is carried out. The experiment should be operated in vacuum condition at absolute pressure around 1000 Pa, but no experiment data is acquired due to the lack of time. The information of experiment apparatus will be demonstrated in the annex.

Aquest projecte té com a objectiu entendre la fenomenologia de la transferència de calor i mecànica de fluids que hi ha darrera les equacions de conservació de la massa, moment i energia mitjançant la resolució numèrica amb la creació de codis propis CFD&HT per flux laminar. Aquest codi serà validat amb diferents problemes de referència (benchmark). Els coneixements i resultats obtinguts seran enfocats a problemes d'energia solar de baixa i mitja temperatura.