Mechatronics Systems Engineering - Theses, Dissertations, and other Required Graduate Degree Essays

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Characterization of degradation, fracture and failure in fuel cell membranes

Author: 
Date created: 
2019-06-21
Abstract: 

Proton exchange membrane (PEM) fuel cells offer a promising clean energy solution for the stringent environmental challenges currently faced by the transportation sector. Ionomer membrane is a key component of this technology that enables critical functions such as protonic conduction, electronic insulation, and reactant separation. During operation, however, various chemical, mechanical and thermal stressors degrade the membrane, which compromises the performance and longevity of a fuel cell. A detailed understanding of these degradation processes and their associated membrane failure modes is, therefore, required to develop more durable and economically viable fuel cell systems. In this work, a comprehensive characterization of fuel cell membrane degradation and failure is performed, with a particular emphasis on membrane fracture, through a series of studies encompassing experimental mechanics, accelerated stress testing, microstructural characterization, and numerical modelling under scenarios relevant to the operational environment. Uniaxial tensile fatigue tests are conducted on double edge notch tension (DENT) specimens to measure fatigue crack growth rates in the ionomer membrane and its electrode-coated composite as a function of temperature, humidity and applied stress. The experimental results are further utilized to develop a Paris law based semi-empirical fracture modelling framework to simulate the crack growth rates while numerically implementing the characteristic time-, temperature- and humidity-dependent elastic-viscoplastic constitutive response of these materials. A laboratory-based X-ray computed tomography (XCT) system is utilized to introduce a novel 3D failure analysis methodology for characterizing post-mortem membrane degradation. This methodology is implemented across a series of accelerated stress tests involving both isolated and conjoint chemical and mechanical membrane degradation, respectively, to explain various membrane failure modes and their mechanisms in relation to the nature of in situ stressors, changes in material properties, and influence of neighbouring components. The non-destructive characteristics of XCT imaging are further leveraged to uniquely investigate the 3D structural evolution of a mechanically degrading membrane through periodic visualization of identical locations inside a custom-developed small-scale fuel cell. Electrode cracks and interfacial delamination are identified as critical defects influencing membrane crack initiation, and direct measurements of in situ crack propagation rates are obtained for the first time.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Erik Kjeang
Nimal Rajapakse
Department: 
Applied Sciences: School of Mechatronic Systems Engineering
Thesis type: 
(Thesis) Ph.D.

Sorbent based enthalpy recovery ventilator (SERV) in northern building applications

Author: 
Date created: 
2019-06-03
Abstract: 

Sorbent-based enthalpy recovery ventilator (SERV) is a potential replacement for conventional heat or enthalpy recovery ventilator (HRV/ERV) that require defrosting mechanisms in cold climates, such as in Canada. Sorbent materials (e.g. silica gel, CaCl2, alumina oxide) are non-toxic, inexpensive materials. However, the bulkiness, high pressure drop and large mass of adsorbent are major disadvantages of SERV in packed bed form. In this study, a novel design of sorbent discs with air channels is investigated which feature high heat and mass transfer performance with low pressure drop. A theoretical model is developed for heat and mass transfer in air channels in sorbent discs. A sensitivity analysis performed on design parameters e.g. channel diameter and spacing to achieve an optimum design. A prototype SERV is built in our laboratory. A custom-made experimental set-up equipped with thermocouples, humidity sensors, and an orifice plate air flow meter is designed based on ASHRAE 84 standards to evaluate the performance of the SERV prototype. The performance of the SERV is evaluated for several air flow rate, cycle time and outdoor air temperatures down to -15°C. It is shown that the proof of concept SERV consisting of 2.5 kg of heat storage materials and 2.1 kg of active sorbent material can recover up to 70% of heat and 80% of moisture from exhaust air (up to 20 CFM). It corresponds to 103 W of heat and 43 g of moisture recovery per hour which is comparable to the packed bed sorbent system reported in the literature, however, the proposed SERV offer a 60% less pressure drop.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Majid Bahrami
Department: 
Applied Sciences: School of Mechatronic Systems Engineering
Thesis type: 
(Thesis) M.A.Sc.

Utilizing avalanche breakdown for stress measurements on micro-structures

Date created: 
2019-05-15
Abstract: 

This thesis reports on the usage of the breakdown voltage of a p-n junction diode to measure the mechanical stress/strain in micro-resonators. The working principle relies on the dependence of silicon band gap to the mechanical stress which then affects the current-voltage characteristics of the p-n junction. To explore the effects of mechanical stress/strain on breakdown voltage, a flexural-mode micro-resonator is designed by defining a p-n junction at the anchoring region to experience maximum stress during mechanical excitations. An analytical model has been developed for the study and numerical analysis of this phenomenon. The Synopsys Sentaurus TCAD simulations were employed for the investigation of the breakdown voltage dependence to various mechanical stress magnitudes as well as orientations. A micromechanical device with integrated junctions was designed and fabricated for the validation of postulate. Mechanical stress was applied onto the substrate by subjecting it to mechanical vibrations. It is estimated that the breakdown voltage of the device exhibited a high-stress sensitivity of about 240µV/MPa. The mechanical stress can also be measured by monitoring the device current while biased at a constant voltage. In this mode, the steep changes of the junction current in breakdown region led to nearly tenfold higher stress sensitivity compared to a piezoresistive sensor. The high sensitivity, simple measurement, and potential for miniaturization for breakdown voltage sensing make it a promising technique for measurement of stress in micro- and nano-mechanical devices.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Behraad Bahreyni
Department: 
Applied Sciences: School of Mechatronic Systems Engineering
Thesis type: 
(Thesis) M.A.Sc.

Active power decoupling achieving optimum capacitance requirement with minimal compromise in efficiency

Author: 
Date created: 
2019-04-30
Abstract: 

In single-phase AC/DC converters that achieve unity power factor (UPF) at the AC-side, the power waveform contains a large component at the double-line-frequency (DLF), in addition to the average power. This DLF ripple power can have serious undesirable effects on the load in different applications. In order to prevent it from flowing into the load, the DLF ripple power can be mitigated by connecting a capacitor to the DC-link. However, this method, called passive power decoupling, requires large values of capacitance to be used. For 400(VDC)/kW-level applications, it can be only realized using electrolytic capacitors, resulting in low power-density and low reliability. For applications in which power-density and reliability are more critical, an alternative solution is active power decoupling (APD). In active power decoupling, the storage capacitor has a higher utilization factor because the voltage across it is allowed to have larger variations. This situation can be made possible by separating the capacitor from the DC-link by means of a power electronic converter. The DC/DC buck is the simplest converter that can be used for this purpose. The problem with the buck APD is that it cannot use the theoretically minimum required value of capacitance; although many alternatives have been proposed in the literature, they all bring their own sets of disadvantages. In this work, a superior solution is introduced as an improvement to the buck topology which allows utilization of the theoretically minimum required capacitance with minimal compromise in efficiency. The design details and benefits assessment of this solution are elaborated and its operation is verified using both computer simulation and experiment.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Jiacheng (Jason) Wang
Department: 
Applied Sciences: School of Mechatronic Systems Engineering
Thesis type: 
(Thesis) M.A.Sc.

3D designed cellular solids for the case study of soft robotics

Author: 
Date created: 
2019-04-29
Abstract: 

With the advances in technology, robots have tremendously evolved over the past decades, emerging a new paradigm in robotics, called soft robotics, which is largely inspired by the biological systems in nature, and are primarily composed of materials with mechanical moduli similar to that of soft biological materials. The material properties and morphology of the soft bodies can help in achieving the desired performance for the soft robot, by deforming, adapting, and reacting to interaction forces. Most of the soft robots have bodies made out of intrinsically soft and/or flexible materials (for example, silicone rubbers) that can deform and absorb most of the energy arising from a collision. These robotic bodies built with elastomer materials show lack of structural stiffness that limits their use in many practical applications. The objective of this study is to design specific cellular materials and integrate stiffness into soft robotic gripper bodies, by applying both engineering and architectural principles to form a lightweight and stiff body. An architectured cellular robotic body design is demonstrated, with deformable structures for a soft gripper, which is easy to fabricate, lightweight, mechanically durable, and compliant while maintaining its resilience. This cellular body design not only overcomes the stiffness limitation but also other drawbacks of most common pneumatically actuated soft bodies which includes getting easily damaged from high pressure or impact and exhibiting low gripping force due to their soft, deformable bodies. To form a functional system, artificial cellular finger is equipped together with capacitance based pressure sensors on the fingertip in a single-building process with the advantage of multi-material three-dimensional (3D) printing. The integrated architectured grippers, composed of cellular fingers with repeatably reliable bending profile, demonstrated an average gripping force as 16 N on actuation with gripping capability of various objects. It is highly expected that 3D cellular designs open new possibilities for architectured materials that can be used from robotic grippers to many practical applications.

Document type: 
Thesis
File(s): 
etd20269-manpreet-kaur-Movie S1.Intelligent bending.mp4
etd20269-manpreet-kaur-Movie S2.gripper moving.mp4
Senior supervisor: 
Woo Soo Kim
Department: 
Applied Sciences: School of Mechatronic Systems Engineering
Thesis type: 
(Thesis) Ph.D.

Compressive behaviour of thin porous layers with application to PEM fuel cells

Author: 
Date created: 
2019-04-05
Abstract: 

A key factor in Polymer Electrolyte Membrane (PEM) fuel cell performance is the compression due to expansion, swelling, and force exerted by bipolar plates on Membrane Electrode Assembly (MEA) which changes the porous microstructure and transport properties of layers in MEA. During manufacturing and operation of fuel cell, MEA goes through numerous cycles of compression, temperature, and humidity, which introduce hygrothermal stresses and result in change in properties of the layers which leads to adjustment of performance. Transport properties such as thermal conductivity, electrical conductivity, and gas diffusivity are dependent on mechanical properties and microstructure of MEA layers, which necessitate the study of their mechanical properties. The focus of this work is compression of Gas Diffusion Layer (GDL) and Catalyst Layer (CL) which play important role in dictating fuel cell performance. In this thesis, mechanical properties of GDL are measured and modeled analytically. Compression tests are performed on three GDL samples (SGL 34BA, Freudenberg, TGP-H-060). The results suggest a non-linear behaviour for pressure-strain curves which is because of their porous nature. Also, using effective medium theory, a representative geometry is introduced for GDL and the mechanical deformation of the simplified geometry is found analytically and validated by experimental data. Moreover, mechanical deformation of five different CL is measured under cyclic compressive load up to 5 MPa for the first time. Results show that CL behaves elastically below 2 MPa and no plastic deformation is observed; the Young’s modulus is decreased with increase in porosity, which was expected. More than that, cyclic compression tests for higher pressures show a slight change in Young’s modulus at higher pressures (more than 2 MPa) which is because of the change in microstructure at higher pressures. A geometrical platform for CL is developed in this study and a mechanistic compression model is developed based on the simplified geometry. The model is validated by comparing with the experimental results obtained for five different CLs. Using the model, effect of compressive load on porosity and pore size distribution is studied which shows significant change in larger pores and shift in pore size distribution curves.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Majid Bahrami
Ned Djilali
Department: 
Applied Sciences: School of Mechatronic Systems Engineering
Thesis type: 
(Thesis) Ph.D.

Development of capillary-assisted low pressure evaporator for adsorption chillers

Date created: 
2018-06-07
Abstract: 

The sales of air conditioners are poised to intensely increase over the next several years as incomes and global temperatures rise around the world. Conventional air conditioning systems use vapor-compression refrigeration (VCR) technology that has been the dominant technology for close to a century. However, the environmental impact of VCR systems, particularly their high energy consumption, around 36% of energy consumed in the US building sector, is contrary to sustainable development. In addition to the residential sector, VCR systems for vehicle air conditioning (A/C) applications can cause a 20% increase in fuel consumption. Moreover, while the commonly used refrigerants in VCR systems, hydrofluorocarbons (HFCs), are ozone-friendly, they still contribute to global warming. Alternative, natural refrigerants, such as water, have no toxicity and significantly lower global warming potential compared to HFCs. Furthermore, water is an ideal refrigerant for systems driven by low-grade thermal energy. Solar-thermal and waste-heat from industrial facilities and data centers are all abundant sources of low-grade thermal energy, with a temperature less than 100°C. Low-grade thermal energy can be used to run adsorption chillers for air conditioning of vehicle cabins and residential units. When using water as an air conditioning refrigerant, evaporation occurs at pressures below an atmosphere. In such a low pressure (LP) environment, the performance of a flooded evaporator is negatively affected by the hydrostatic pressure. This problem can be resolved by using a capillary-assisted low-pressure evaporator (CALPE) that exploits thin film evaporation. The focus of this doctoral research is to develop an effective CALPE for proof-of-concept demonstration of an adsorption chiller for vehicle A/C applications. In this research, a low pressure evaporator testbed is designed and built for the first time at Laboratory for Alternative Energy Conversion (LAEC) to test CALPE. In addition, a mathematical model is developed to understand detailed phenomena in capillary-assisted evaporation and to provide insight to design an effective and compact CALPE. Several commercial tubes with different fin geometries are tested. The results show that the capillary-assisted tubes provide two times greater heat transfer rate compared to a plain tube. To further enhance the performance, the outside surfaces of CALPE are coated with a thin film of porous copper to increase the capillary action and the surface area available for thin film evaporation. The coating increased the overall heat transfer coefficient by 30%. However, a significant amount of the thermal resistance is from the inside of the evaporator tubes. Therefore, a new µCALPE is designed with microchannels on the inside and rough capillary channels on the outside is 3D printed by using direct metal laser sintering process. The internal microchannels and external capillary channels led to enhanced heat transfer both internally and externally. The µCALPE increased the overall heat transfer coefficient by a factor of 2.5 when compared to the CALPE built with commercial Turbo Chil-40 FPI tubes, which had footprint of four times larger than that of µCALPE. The developed µCALPE is expandable to the entire low-grade thermal energy driven A/C systems in vehicles as well as residential units.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Majid Bahrami
Department: 
Applied Sciences: School of Mechatronic Systems Engineering
Thesis type: 
(Thesis) Ph.D.

Developing a vector light sensor

Author: 
Date created: 
2019-01-10
Abstract: 

Over the past few decades, numerous sensors have been invented for the measurement of light intensity. In most cases, a setup external to the sensor is required to detect the direction of an incoming beam of light. In this work, the design, fabrication, and characterization of a novel light sensor is described. The three-dimensional structure of the sensor allows it to detect both the intensity as well as the direction of the incident light beam, hence becoming a vector light sensor (VLS). The sensor structure is based on creating photodiodes on sidewalls of miniaturized raised or inverted pyramids etched in silicon. Each photodiode was formed by selective doping of the material on each facet of the pyramid, forming a photodiode with the P-type substrate. A set of signal processing algorithms was developed to estimate the direction and the distance of a light source from the sensors. The light sensing devices with both raised and inverted pyramid structures were then fabricated in a cleanroom based on silicon microfabrication technologies. Throughout the process, the lithography step for the textured surface needed to be optimized. An interface circuit was designed and used to amplify and process the signals from the devices. The device operation was verified experimentally to estimate the direction of a light beam. The small size and low power consumption of the individual sensors make them suitable for applications were simple distance and direction estimation is required. The sensors can be arrayed to provide light-field information in the plane of sensor.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Behraad Bahreyni
Department: 
Applied Sciences: School of Mechatronic Systems Engineering
Thesis type: 
(Thesis) M.A.Sc.

3D architecture electrodes for energy storage applications

Author: 
Date created: 
2018-12-10
Abstract: 

Micro-scale energy storage devices have been developed for the demand of required energy autonomy of the portable and small-scale electronics. One main drawback in realization of micro-scale energy storage devices is limited areal capacitance due to low material loading per unit area on the substrate. 3-D electrodes with high aspect ratio could be promising strategy to overcome this, resulting in higher device performance. Specially, 3D printing technology offers numerous advantages to generate 3D electrodes for energy storage devices, which includes time-saving, cost-effective manufacturing, and realization of tailorable complex electrode designs. In this thesis, novel hierarchical 3D designs were printed by photo-curable 3D printing. Photo-curable resins with conductive fillers were optimized for conductive 3D electrode formation. Finally, energy storage devices with the hierarchical 3D electrodes have been demonstrated for the application of micro-supercapacitors (MSCs). The fabricated 3D hierarchical electrodes demonstrated low electrical resistance to be used as feasible MSCs electrodes. Energy storage from redox reactions was demonstrated in 3D architecture electrodes designed with mechanically durable 3D octet trusses.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Woo Soo Kim
Department: 
Applied Sciences: School of Mechatronic Systems Engineering
Thesis type: 
(Thesis) M.A.Sc.

MagnetoRheological dampers for mass and energy sensitive applications

Date created: 
2018-12-05
Abstract: 

MagnetoRheological (MR) dampers have been used as reliable electronically adjustable shock and motion control devices in the past few years. Although these dampers have proven their performance in practice and the cost has decreased, their usage has been limited to high-end applications. The main drawback of MR dampers is their relatively large weight and energy consumption when compared to their passive counterparts. In this thesis, we investigate factors affecting weight and energy consumption of MR dampers and devise solutions to achieve energy-efficient and light-weight dampers. To this end, an analytic approach is presented to design and build a low-energy consumption and lightweight MR damper. It is shown that the proposed configuration can decrease the mass of MR damper significantly and reduce the energy consumption when AlNiCo alloys are utilized in the magnetic core. A proof-of-concept MR damper for mountain bike applications is designed, fabricated, characterized, and tested in the field, which meets the requirements in mountain bike industry in terms of energy consumption, compression and rebound forces, mass, size, and on-the-fly adjustability of the damping forces, by the user.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Mehrdad Moallem
Department: 
Applied Sciences: School of Mechatronic Systems Engineering
Thesis type: 
(Thesis) Ph.D.