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Senast inlagda

Electrified District Heating Plants using Thermochemical Energy Storage
(2023) Cortés Romea, Javier; Chalmers tekniska högskola / Institutionen för rymd-, geo- och miljövetenskap; Chalmers University of Technology / Department of Space, Earth and Environment; Pallarès, David; Martínez, Guillermo; Toktarova, Alla; Guío-Perez, Diana Carolina
Carbon emissions, particularly from electricity and heat generation, remain a major cause of global warming, accounting for 40 % of global CO2 emissions in 2021. To decarbonize the electricity sector, the use of variable renewable energy (VRE) sources is being encouraged. At the same time, variation management strategies are required to maximize the value of VRE as its share increases and to reduce curtailing. Meanwhile, the heating sector is called to transit into an electrified scheme, which should also reduce the use of biomass, as it is becoming a limited resource. Thermochemical energy storage (TCES) systems, particularly high-temperature solid cycles, such as metal redox-looping, provide a solution for both the electricity and heating sectors. TCES systems have the potential to use non-dispatchable renewable electricity to reduce a metal oxide, which can be stored for long periods of time at ambient conditions and subsequently oxidized to release the stored energy in the form of high-temperature heat (700-1100 °C). This thesis presents an economic assessment of the retrofitting of biomass-firing DH plants by incorporating a TCES scheme based on metal-oxide redox cycles. The viability of the proposed system is analyzed through a case study. Sweden was selected for the study case owing to the existence of a metal extraction and processing infrastructure and the availability of DH plants based on fluidized bed (FB) boilers. The cost of the retrofit was estimated and used as an input in a linear cost optimization model to investigate the impact of the electricity price variability on the cost-optimal size and operation of an electrified DH plant. Today’s typical capacity of biomass-firing DH plants was selected as a reference. The results of the study indicate that as a consequence of including storage the operation of the plant can be adapted to respond to electricity price variations. The proposed process can cover the heat demand at a cost of 55-70 €/MWh. The proposed main scheme proved profitable for the investigated scenarios of electricity price variation, while the economic viability of using solid oxide electrolyzer cells (SOEC) instead of alkaline ones or adding hydrogen storage depends on the potential cost reductions in these technologies in the future.
CFD applied to decanter centrifuges
(2023) Bhat, Anirudh; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Chalmers University of Technology / Department of Mechanics and Maritime Sciences; Sasic, Srdjan; Ghirelli, Federico
Decanter centrifuges have become a crucial part of numerous industrial solid-liquid separation pro cesses. Its use in dewatering of municipal sewage slurries has made it an immensely valuable tool in combating water pollution. The flow and separation of various phases through a decanter centrifuge can be influenced by a host of parameters such as the slurry rheology, the solid phase size distribution, and operational parameters of the the operation such as the mass flow rate of the slurry through the machine, geometrical design features of the centrifuge and many more. The development of a feasible and reliable computational model would facilitate the qualitative testing of the influence of many of these parameters on the performance of the decanter without relying on expensive experimental tests. In this project, computational fluid dynaimcs (CFD) has been used to model the flow of municipal sewage slurry within a decanter centrifuge. A sliding mesh approach was used to model the rotation of the decanter centrifuge and a moving wall boundary condition is applied to the surface of the centrifuge drum to simulate the speed differential. The multiphase flow equations were solved by using the Eulerian mixture multiphase model by modelling the slurry as a two phase mixture of water and the heavier phase to be separated wherein the heavier phase is modelled as a relatively thick and viscous liquid. Direct validation of the developed model against experimental data was not feasible, but a qualitative judgement about the model was made based on the literature survey and the insights provided by the decanter centrifuge manufacturer. Four test cases were run on the developed model to test how it reacts to a change in certain parameters. Three of the cases test the effect of varying the heavier phase’s viscosity and the fourth case tests the model at a higher inlet mass flow rate.
Non-Supersymmetric AdS Solutions in Type IIB String Theory
(2023) Wikström, Johan; Chalmers tekniska högskola / Institutionen för fysik; Chalmers University of Technology / Department of Physics; E.W. Nilsson, Bengt
The task of finding a satisfactory theory of quantum gravity has turned out to be extremely challenging. In the context of string theory, which is a potential frame work of quantum gravity, this problem is represented by the vast number of possible string compactifications. The swampland program is an effort to sort through these possibilities and define what makes some theories of quantum gravity inconsistent. The result is a number of so-called swampland conjectures. This thesis studies an AdS vacuum in type IIB string theory that is relevant to one of these conjectures. It is explicitly shown that this vacuum, which is an S-fold of the form AdS4 × S 1 × S 5 , satisfies the type IIB equations of motion. The S-fold originates from uplifting a non-compact gauging of the 4-dimensional N = 8 supergravity. A more simple case illustrating non-compact gaugings, related to the gauge group SO(8), is treated here. Also discussed is the topology of the S-fold, which features a non-trivial SL(2, Z) monodromy when the S 1 is encircled, making the background non-geometric. The connection to the swampland program appears when a 2-parameter deformation of the AdS vacuum is used to break supersymmetry. Locally, these deformations only amount to a coordinate redefinition, which protects the vacuum solution from some non-perturbative decay channels. As the non-supersymmetric S-folds are also perturbatively stable, they have been suggested as a potential challenge to the Non SUSY AdS conjecture. However, more evidence of non-perturbative stability is likely needed to make a solid case for non-supersymmetric AdS vacua in quantum gravity.
Data Analysis for Defect Monitoring in Additive Manufacturing – Applying Machine Learning to Predict Porosity in L-PBF
(2023) Sievers, Erik; Chalmers tekniska högskola / Institutionen för data och informationsteknik; Chalmers University of Technology / Department of Computer Science and Engineering; Gulisano, Vincenzo; Papatriantafilou, Marina
Laser powder bed fusion (L-PBF) is an additive manufacturing technique that sees more and more use in industrial settings, but is held back by a lack of cost-effective quality validation of created products. One core attribute of high-quality additive manufactured products is a low porosity, i.e. a high ratio of solid to empty volume inside the object. This thesis provides an overview of the state of the art for in-situ monitoring of L-PBF manufacturing and investigates the use of outlier detection methods as a way of encoding optical tomography data from an L-PBF process. This is done using a commercial L-PBF machine with its accompanying in-situ monitoring camera. The results show that outlier detection methods can be used to detect porosity in created objects (0.94 - 0.99 ROC-AUC, receiver operating characteristics’ area under curve) and that it can generalize between similar object geometries. The thesis also provides a discussion of the limitations of the current research and suggests future work both building upon the methods introduced in the thesis and in the field of in-situ monitoring of L-PBF.
Life-long learning materials enabling the growth of Digital Twin competences
(2023) Ashok Kumar, Alalvanan; Jagadeeswar, Rahul Rao; Chalmers tekniska högskola / Institutionen för industri- och materialvetenskap; Chalmers University of Technology / Department of Industrial and Materials Science; Skoogh, Anders; Skoogh, Anders
In recent times, Digital Twin and Discrete Event Simulations are some of the promis- ing technologies in enabling industry 4.0. Since the developments of these technolo- gies are recent, their definitions and representations vary. Accordingly, there is a need to develop learning materials for these concepts to better help users seeking to develop or improve in these areas academically and professionally. The thesis fo- cuses on the main goal, which is the creation of learning materials with an emphasis on lifelong learning. For this, the learning materials are developed on the guidelines of constructive alignment and Bloom’s taxonomy to better facilitate lifelong learn- ing among the users. The developed learning materials are also developed around real-world problems such that the content is relatable and relevant. In the next phase, the evaluation of these learning materials is done. This is done by procuring feedback from the focus groups stakeholders, industry-level simulation experts, self-analysis and reflection; the pilot study undergoes revision and necessary changes are made. The procured revised learning material hopes to serve as a guide for users seeking to develop learning materials to improve competence in the field of Digital Twin and Discrete Event Simulation.