Chalmers Open Digital Repository
Välkommen till Chalmers öppna digitala arkiv!
Här hittar du:
- Studentarbeten utgivna på lärosätet, såväl kandidatarbeten som examensarbeten på grund- och masternivå
- Digitala specialsamlingar, som t ex Chalmers modellkammare
- Utvalda projektrapporter
Forskningspublikationer, rapporter och avhandlingar hittar du i research.chalmers.se
Enheter i Chalmers ODR
Välj en enhet för att se alla samlingar.
Visar 1 - 2 av 2
Senast inlagda
Post
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.
Post
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.
Post
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.
Post
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.
Post
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.