This thesis is missing page 48, all other copies of this thesis are missing the page as well. -Digitization Centre / Metal injection molding (MIM) employs the advantages of injection molding and powder metallurgy and provides a high productivity means to form intricate, low-cost, high performance metal parts. One of the most unique characteristics of MIM is the binder system and the consequent debinding step, which is considered to be major process improvement barrier in the MIM process. A MIM part with a thick section suffers from a long debinding cycle and it is difficult to avoid defects. Therefore, it is always of interest to find out a method to quickly debind a thick part without defects. PowderFlo® feedstock combines metal powder with an aqueous agar-gel binder system and requires simple air-drying followed by thermal debinding. However, previous studies on this agar-gel binder feedstock mainly focus on sintering, while the debinding step has lacked sufficient attention. A debinding study on agar-gel binder system is conducted in the present project. The metal compacts are formed via compression molding and injection molding, followed with thermal debinding in order to understand the effects of process parameters on debinding with respect to thickness to determine a good debinding schedule. The thickness transition between thick and thin section is particularly important in the debinding to find a protocol to make parts with both thick and thin sections. Thermal debinding experiments show that the initial heating rate is the most significant factor due to it may cause visible defect directly and an increase of initial and secondary heating rates may retard binder removal. The air-drying time has less influence on binder extraction for thicker section. Extending the holding time for water and polymer removal is beneficial to obtain better dimensional control. The overall debinding process parameters have larger effects on thicker parts. For the thickness transition, it is suggested to avoid the combination of too thin and too thick section, increase the joint area, and provide uniform packing during molding. / Thesis / Master of Applied Science (MASc)

The expanding use of renewable and sustainable energy systems is at the forefront of the global effort to reduce CO2 emissions and mitigate climate change. Thermal energy storage has become a critical component of many of these new and innovative systems, and research in this field has expanded to meet their requirements. Water has been traditionally used as a storage medium because of its high heat capacity and low cost, but depending on the application, the storage volume requirements may be excessively large. Phase Change Materials (PCMs) offer an opportunity to reduce the storage volume through latent energy storage. However, energy storage in PCM presents new challenges, and careful design of thermal storage is required to realize the benefits. The design of PCM storage must consider the system operation, operating temperature range, PCM properties, encapsulation, and the heat transfer fluid. In the current state-of-the-art literature, there is no standard method for designing PCM thermal storage based on system requirements. The objective of this thesis is to deliver a methodology to assess the feasibility of using PCM for thermal energy storage in place of water. This is done by identifying which applications benefit from PCM, comparing the analytical and numerical performance of water-only to hybrid water-PCM storage, and developing a method to size PCM containment to achieve theoretical performance when PCM is beneficial. This research study develops analytical solutions for sizing PCM thermal energy storage based on system boundary conditions. These boundary conditions consist of the system itself (e.g. heat pump, absorption chiller), the energy source into the system, and the required load from the system (e.g. a building). The PCM is incorporated into a water tank such that the water acts as both a heat transfer fluid and an energy store. Analytical predictions of the total energy storage capacity in this hybrid water-PCM thermal storage unit are coupled to analytical predictions of the rate of melting and solidification to appropriately determine the required volume and encapsulation thickness of PCM thermal storage based on the system requirements. The results are verified against full-system numerical simulations based on case studies of solar absorption cooling and heat-pump heating. It is shown in this study that the total required volume of storage is a function of the temperature differential of the system, and the total mismatch in time between when energy is available and when it is required. A mathematical formulation is proposed which quantifies the required storage volume based on the temperature differential, the source and load profiles, and the percentage of PCM in the hybrid water-PCM storage unit. Furthermore, the rate of melting and solidification of the thermal storage is coupled to the overall storage size and required time for charging, and a mathematical formulation is proposed which solves for the PCM encapsulation thickness. The method assumes a conservative conduction-dominated domain and demonstrates how complete melting can be ensured before the system reaches its maximum allowable temperature. The map the region of applicability of PCM thermal storage is also presented which is defined in terms of the non-dimensional Biot and Stefan numbers, in which systems utilizing PCM thermal storage will benefit from volume reduction when compared to using water only. This region is characterized with a low Biot number, corresponding to a slender geometry acting as a lumped system, as well as a low Stefan number, corresponding to limited temperature differential and limited sensible energy storage. These characteristics favor the use of PCM thermal storage instead of water only. This thesis presents a novel contribution to the state-of-the-art literature in PCM thermal storage, which is established through the analytical methodology for sizing PCM thermal storage based on system boundary conditions. The details of the contribution are presented in the form of three journal publications that have been integrated into this sandwich Ph.D. thesis on PCM thermal energy storage. / Thesis / Candidate in Philosophy

No description available.

We report on two studies that involve molecular dynamics (MD) simulations of grain boundary motion in nanocrystalline (nc) nickel. The first study is conducted to examine the effects of an applied tensile stress on the grain boundary motion in 5 nm3 nc-Ni specimens, half of which contain free surfaces, while the other half have periodic boundary conditions. Grain boundary sliding (GBS) and grain rotation are the deformation mechanisms exhibited by the nc-Ni specimens, in contrast to dislocation-mediated deformation mechanisms found in bulk samples. Specimens that contain free surfaces display a lower yield stress and a lower average grain boundary velocity compared to their periodic counterparts. These phenomena are attributed to the higher degree of grain boundary sliding present within the free surface specimens. The second study examines thermal effects of various annealing temperatures on grain boundary motion in 5 nm3 periodic nc-Ni specimens. It is found that grain growth exhibits a linear relationship with time, as opposed to parabolic grain growth observed in bulk metals. During the annealing process, it is also observed that the average grain boundary energy decreases with t-1/2, as grains oriented themselves in a lower-energy configuration with their neighbors via grain rotation. An Arrhenius plot of average grain boundary velocity and energy per atom within a grain boundary displays identical slopes, and thus, identical activation energies of ~ 53 kJ for both characteristics. This can be attributed to the fact that grain boundary velocity and energy per atom are governed by the same entity, which is grain boundary diffusion. The annealed samples display a grain rotation-coalescence growth mechanism, where adjacent grains rotate concurrently, to decrease the misorientation energy of the grain boundary between them. It is observed that some grains have achieved the same orientation at the end of the growth process, indicating that the grain boundary has been annihilated, and the two grains have coalesced into a single larger grain. / Master of Science

Thermal Management of Electric Motors / Permanent Magnet Synchronous Motors (PMSMs) have garnered widespread adoption in electric vehicles owing to their exceptional characteristics, including high power density, robust torque capability, and superior efficiency compared to conventional electric motors. Implementing permanent magnets facilitates the absence of a heat source on the rotor side, contributing significantly to their exceptional performance. However, despite these advantages, the heightened vulnerability of permanent magnets necessitates rigorous thermal management and analysis for PMSMs, particularly during short-duration peak performances and steady-state continuous operations. Operating under such conditions can potentially adversely affect the permanent magnets, winding insulation, and overall motor performance. Therefore, addressing thermal concerns associated with PMSMs emerges as a critical endeavor. This research tackles these thermal challenges by employing a combined approach of Lumped Parameter Thermal Network (LPTN) and Computational Fluid Dynamics (CFD) for accurate and cost-effective thermal modeling. A CFD analysis is performed to analyze the effect of water jacket and oil splash cooling and to calculate the heat transfer coefficients resulting from these two methodologies. A conjugate heat transfer CFD model is used to analyze the water jacket with the aid of a multi-phase CFD model to simulate the effect of the oil splash on end-windings. CFD heat transfer coefficients are then integrated into an LPTN model to calculate the temperature distribution of the motor. Furthermore, a comparative analysis is used to show the difference between integrating CFD-derived heat transfer coefficients and the analytical heat transfer coefficients in the LPTN model. VI In summary, this research underscores the importance of effective thermal management in maximizing the performance and longevity of PMSMs in electric vehicles. By leveraging advanced modeling methodologies, it seeks to address the intricate thermal concerns associated with PMSMs, paving the way for significant advancements in electric vehicle technology and inspiring sustainable transportation solutions. / Thesis / Master of Applied Science (MASc) / Electric vehicles are crucial for the future of sustainable transportation, offering a cleaner alternative to conventional combustion-engine cars and helping reduce greenhouse gas emissions. Permanent Magnet Synchronous Motors (PMSMs) are key to their performance, providing high efficiency and power density. However, their effectiveness can be hindered by thermal issues, particularly during peak performance or continuous operation. This research addresses these thermal challenges by combining Lumped Parameter Thermal Network (LPTN) models with Computational Fluid Dynamics (CFD) simulations. By analyzing water jacket and oil splash cooling systems, the study calculates heat transfer coefficients and integrates these into the LPTN model to assess motor temperature distribution. The research highlights the critical role of effective thermal management in enhancing PMSM performance and longevity, aiming to advance electric vehicle technology and support sustainable transportation solutions.

Compute clusters are consuming more power at higher densities than ever before. This results in increased thermal dissipation, the need for powerful cooling systems, and ultimately a reduction in system reliability as temperatures increase. Over the past several years, the research community has reacted to this problem by producing software tools such as HotSpot and Mercury to estimate system thermal characteristics and validate thermal-management techniques. While these tools are flexible and useful, they suffer several limitations: for the average user such simulation tools can be cumbersome to use, these tools may take significant time and expertise to port to different systems. Further, such tools produce significant detail and accuracy at the expense of execution time enough to prohibit iterative testing. We propose a fast, easy to use, accurate, portable, software framework called Tempest (for temperature estimator) that leverages emergent thermal sensors to enable user profiling, evaluating, and reducing the thermal characteristics of systems and applications. In this thesis, we illustrate the use of Tempest to analyze the thermal effects of various parallel benchmarks in clusters. We also show how users can analyze the effects of thermal optimizations on cluster applications. Dynamic Voltage and Frequency Scaling (DVFS) reduces the power consumption of high-performance clusters by reducing processor voltage during periods of low utilization. We designed Tempest to measure the runtime effects of processor frequency on thermals. Our experiments indicate HPC workload characteristics greatly impact the effects of DVFS on temperature. We propose a thermal-aware DVFS scheduling approach that proactively controls processor voltage across a cluster by evaluating and predicting trends in processor temperature. We identify approaches that can maintain temperature thresholds and reduce temperature with minimal impact on performance. Our results indicate that proactive, temperature-aware scheduling of DVFS can reduce cluster-wide processor thermals by more than 10 degrees Celsius, the threshold for improving electronic reliability by 50%. / Master of Science

No description available.

Thermal sensitivity has been of scientific interest for almost a century. Despite this, several research questions within this field remain unanswered, particularly regarding the specific distribution of thermal sensitivity to cold across the human body. Additionally, while exercise is known to cause a cold stimulus to be perceived as less unpleasant according to the principle of thermal alliesthesia, less has been reported on the effects of exercise on thermal sensitivity to cold. With applications mainly related to clothing insulation and design in mind, the present research project aimed to investigate thermal sensitivity to cold at whole body segments, as well as within body segments, at rest and during exercise. Additionally, a comparison of thermal sensitivity to cold between genders and between ethnic groups was also performed.

This thesis describes the influence of thermal mass on the space conditioning energy consumption and indoor comfort conditions of multi-storey buildings with concrete, steel and timber structural systems. The buildings studied were medium sized educational and commercial buildings. When calculating a building’s life-cycle energy consumption, the construction materials have a direct effect on not only the building’s embodied energy but also on the space conditioning energy. The latter depends, amongst other things, on the thermal characteristics of the building’s materials; thermal mass can also be an influence on comfort conditions in the building. A modelling comparison has been undertaken between three very similar medium-sized buildings, each designed using structural systems made primarily of timber, concrete and steel. The post-tensioned timber version of the building is a modelled representation of a real three-storey educational building that has been constructed recently in Nelson, New Zealand. The concrete- and steel-structured versions have been designed on paper to conform to the required structural codes and meet, as closely as possible, the same performance, internal space layout and external façade features as the real timber-structured building. Each of these three structurally-different buildings has been modelled with two different thermal envelopes (code-compliant and New Zealand best-practice) using a heating, ventilating and air conditioning (HVAC) system with heating only (educational scheme) and heating and cooling (commercial scheme). The commercial system (with cooling) was applied only to the buildings with the best-practice thermal envelope. The analysis of each of these nine different construction and usage categories includes the modelling of operational energy use with an emphasis on HVAC energy consumption, and the assessment of indoor comfort conditions using predicted mean vote (PMV). From an operational energy use perspective, the modelling comparison between the different cases has shown that, within each category (code-compliant, low-energy and low-energy-commercial), the principal structural material has only a small effect on overall performance. The most significant differences are in the building with the best-practice thermal envelope with the commercial HVAC system, were the concrete building has slightly lower HVAC energy consumption, being 3 and 4% lower than in the steel and timber buildings respectively The assessment of indoor comfort conditions during occupied periods through using PMV for each of the three categories shows that the timber structure consistently exhibited longer periods in the over-warm comfort zone, but this was much less pronounced in south-facing spaces. To examine the reasons for the less acceptable PMV in the timber-structure versions, an analysis of indoor timber and concrete surface temperatures was carried out in both buildings. It was found that, particularly in north-facing spaces, there were large diurnal swings in the temperatures of timber surfaces exposed to solar radiation. These swings were much less in the case of concrete surfaces so the environment was perceived to be more comfortable under such conditions because of the reduced influence of higher mean radiant temperatures. To moderate this potential downside of solar-exposed internal timber surfaces, better results are achieved if, when timber is used for thermal mass, the timber is not exposed to direct solar radiation, for example locating it in the ceilings or on the south side of the building. Two other approaches to combating the potential overheating problem in the timber-structured buildings were analysed in an illustrative mode; addition of external louvres to reduce direct solar gains at critical times of day and year; and use of phase change material (PCM) linings to act as light-mass energy buffers. Although external louvres increase comfort conditions significantly by reducing the periods of an overly warm environment, they produce an increase in heating energy consumption through reducing beneficial solar gains. The use of PCM linings shows little benefit to overall indoor comfort conditions for the building of this case-study.

No description available.