Theses
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Recent Submissions
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Sustainable Silica Sols from Geothermal Sources and their Potential as Thermal Heat Storage MaterialsGeothermal energy is a renewable energy source but faces challenges such as silica scaling. This scaling leads to corrosion within process equipment and injection wells, ultimately reducing power generation efficiency and increasing maintenance costs. Therefore, extracting silica from geothermal sources is essential. A company, GeO40 TM, has developed a process for extracting silica as colloidal dispersion, which can be also converted into high value dry products such as composite adsorbents. This study aimed to establish an innovative, cost-effective, practical method for converting geothermal colloidal silica sol, into environmentally friendly and sustainable CaCl2/Silica gel composite adsorbents to be used for thermochemical heat storage (TCHS) applications. Solar energy is also a renewable energy and is abundant during summer but insufficient in winter. TCHS systems can be incorporated into solar energy harvesting systems to address the seasonal energy imbalance by storing excess energy and using it later. Composite adsorbents can be utilised in TCHS systems because they can store heat through exothermic adsorption and endothermic desorption reactions. By storing solar energy in TCHS systems, the need for fossil fuels for heating applications can be mitigated. In this study, composite adsorbents by using CaCl2 and geothermally derived colloidal silica were successfully prepared to be used for TCHS applications. The developed method involves precipitating colloidal silica in an alkaline medium with CaCl2 salt. The ions of the salt change the stability of the silica particles and simultaneously combine with the silica particles to produce composite adsorbents. Furthermore, CaCl2 is a very hygroscopic component that raises the final composite adsorbent's water adsorption capacity (WAC), a desirable property of TCHS materials. The thermochemical characteristics of the composite adsorbents were evaluated at 55% RH between 20 and 150°C using simultaneous TG and DSC analysis. Sample 0.50-SD, with the highest salt concentration (48.2 wt.% CaCl2), exhibited the highest heat of desorption (1207.2J/g) and water adsorption capacity (90 wt.%), without any salt leakage. The volumetric heat storage density (Qv) of the samples was calculated to be 172.7 kWh/m3. Using the imbibition technique, the sample's pore volume (Vp) was determined to be 108 cm3. Ten consecutive cycles of adsorption and desorption were conducted on the sample, showing no significant performance loss. Additionally, the sample was characterized by XRD, SEM, and FTIR. An open-type TCHS prototype was designed and built to assess the sample's TCHS performance on a larger scale. Under the conditions of input air at a 10 L/min flow rate, 60 % RH at 20°C for adsorption, and 150°C for desorption, only 38.674 g of 0.50 SD released 53.434 (± 1.215) kJ of heat. Consequently, the adsorption bed's temperature rose by 21°C, while the exhaust air's temperature increased by 16°C, which could be utilized for space heating. Gravimetric heat storage density (QM) of 1382 (± 27) J/g and Qv of 155 (± 4) kWh/m3 were obtained for the sample, exceeding the minimal QV value of TCHS materials (150 kWh/m3) as suggested by Courbon et al. (2017)1. The study suggests that composite adsorbents prepared using geothermally derived colloidal silica could offer an eco-friendly option for TCHS applications.
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Efficient Surrogate Model-Assisted Evolutionary Algorithm for Electromagnetic Design Automation with ApplicationsIn this thesis, the surrogate model-aware evolutionary search (SMAS) framework is extended for efficient interactive optimisation of multiple criteria electromagnetic (EM) designs and/or devices through a novel method called two-stage interactive efficient EM micro-actuator design optimisation (TIEMO). The first robust analytical and behavioural study of the SMAS framework is also carried out in this thesis to serve as a guide for the meticulous selection of multiple differential evolution (DE) mutation strategies to make SMAS fit for use in parallel computing environments. Based on the study of SMAS and the self-adaptive use of the selected multiple DE mutation strategies and reinforcement learning techniques, a novel method, parallel surrogate model-assisted evolutionary algorithm for EM design (PSAED) is proposed. PSAED is tested extensively using mathematical benchmark problems and numerical EM design problems. For all cases, the efficiency improvement of PSAED compared to state-of-the-art evolutionary algorithms (EAs) is demonstrated by the several times up to about 20 times speed improvement observed and the high quality of design solutions. PSAED is then applied to real-world EM design problems as two purposebuilt methods for antenna design and optimisation and high-performance microelectro-mechanical systems (MEMS) design and optimisation in parallel computing environments, parallel surrogate model-assisted hybrid DE for antenna optimisation (PSADEA) and adaptive surrogate model-assisted differential evolution for MEMS optimisation (ASDEMO), respectively. For all the real-world antenna and MEMS design cases, PSAED methods obtain very satisfactory design solutions using an affordable optimisation time and comparisons are made with available alternative methods. Results from the comparisons show that PSAED methods obtain very satisfactory design solutions in all runs using an affordable optimisation time in each, whereas the alternative methods fail and/or seldom succeed to obtain feasible or satisfactory design solutions. PSAED methods also show better robustness and stability. In the future, PSAED methods will be embedded into commercial CAD/CEM tools and will be further extended for use in higher-order parallel clusters.
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Motion of a space tether system in the atmosphereThe space tether system under consideration consists of two rigid bodies with significantly different ballistic coefficients. Because of this difference one of the bodies acts as a stabilizer for the main body – a spacecraft – during the motion of the tether system in the atmosphere. The investigations are focused on the stability of motion of the tether system in the atmosphere. During its motion in the atmosphere the tether system makes use of torques from aerodynamic forces to maintain a desired orientation. This aerodynamic method of stabilization is passive and does not require energy expenses. Such a tether system can be used to stabilize the motion before landing onto the surface of Earth or other planets with atmospheres. The aerodynamic tether system is helpful for returning payloads from outer space, especially using small landing modules. It is also possible to utilize in the removal of space debris by reducing the altitude of their orbits. By achieving the spacecraft motion stability during descent the tether system enables a reduction in the target landing area at the final stage of the descent. The modelling of motion of the tether system includes two parts – (i) the deployment of the tether system, and (ii) the descent of deployed tether system through the dense layers of the atmosphere. The motion of the deployed tether system is investigated with regard to the terms of its stability. The tether system can be in stable motion even if either or both bodies are statically unstable. The stability of the system is assessed relative to the parameters – the mass, the geometrical dimensions of the bodies and the length of the tether. It is found that increasing the length of the tether, as a controlled part of the deployment process during descent, can provide an additional stabilizing factor for the tether system. The model of the deployment process, based on the model of an elastic tether, represents the tether as a set of nodes with mass and with elastic connections. The control of the deployment is based on the length and the rate of change of the length of the tether. The aerodynamic resistance of the tether and its mass characteristics are both taken into consideration during modelling of the deployment. The described and numerically realized mathematical models allows the parameters for the space tether system motion in the atmosphere to be determined.
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Investigation of size, concentration and particle shapes in hydraulic systems using an in-line CMOS image matrix sensorThe theoretical and experimental investigation of the novel in-line CMOS image sensor was performed. This sensor is aimed to investigate particle size distribution, particle concentration and shape in hydraulic liquid in order to implement the proactive maintenance of hydraulic equipment. The existing instruments such as automatic particle counters and techniques are not sufficiently enough to address this task because of their restricted sensitivity, limit of concentration to be measured and they cannot determine particle shape. Other instruments cannot be used as inline sensors because they are not resistant to the arduous conditions such as high pressure and vibration. The novel mathematical model was proposed as it is not possible to use previously developed techniques based on using optical system and complicated algorithms. This model gives the output signal of the image sensor depending on the particle size, its distance from the light source (LED) and image sensor. Additionally, the model takes into account the limited exposure time and particle track simulation. The results of simulation based on the model are also performed in thesis. On the basis of the mathematical model the image processing algorithms were suggested in order to determine particle size even when this size is lower than pixel size. There are different approaches depending on the relation between the size of the particle and the pixel size. The approach to the volume of liquid sample estimation was suggested in order to address the problem of low accuracy of concentration measurement by the conventional automatic particle counters based on the single photodiode. Proposed technique makes corrections on the basis of particle velocity estimation. Approach to the accuracy estimation of the sensor was proposed and simulation results are shown. Generally, the accuracy of particle size and concentration measurement was considered. Ultimately, the experimental setup was used in order to test suggested techniques. The mathematical model was tested and the results showed sufficient correlation with the experiment. The zinc dust was used as a reference object as there are the particles within the range from 1 to 25 microns which is appropriate to check the sensitivity. The results of experiments using reference instrument showed the improved sensitivity and accuracy of volume measured compared to the reference one.