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<p>Radiative thermal management has become increasingly more relevant within the past few decades due to the avocation for higher efficiency buildings, increases in</p> <p>power densities with decreases in form factors, and cutting-edge technologies for space exploration. This research focuses on engineering coatings with spectrally selective optical properties to achieve ultra-efficient thermal management via passive radiative cooling of both terrestrial and extraterrestrial applications. Terrestrial radiative cooling is a phenomenon of passively cooling exterior surfaces below ambient temperatures by engineering coatings to exhibit low absorptance in the solar spectrum (0.25 μm< λ <2.5 μm), such that a minimal amount of solar irradiation is absorbed, and high emittance in the transmissive portion of the atmosphere (8 μm< λ <13μm), i.e. the sky window, to lose heat to deep-space for a net cooling effect. Deep-space is considered to be an infinite heat sink at 3 K. Extraterrestrial radiative cooling requires the same criteria as terrestrial radiative cooling, however, there is no atmosphere to block a portion of the solar irradiation or the emission from the surface. A key requirement for achieving passive radiative cooling for an ideal emitter during daytime is a total solar reflection >85%, and every 1% above this threshold results in ≈10 W/m2 gain in cooling power. Here, recognizing the broadband nature of solar irradiation, we propose and test a new concept of enhancing solar reflection at a given particle volume concentration by using hierarchical particle sizes, which we hypothesize to scatter each band of the solar spectrum, i.e. VIS, NIR and UV effectively. The hypothesis is tested using a TiO2 nanoparticle-acrylic system. Using the Mie Theory, the scattering and absorption efficiencies and asymmetric parameter</p> <p>of nanoparticles with different sizes and combinations are calculated, then the Monte Carlo Method is used to solve the Radiative Transfer Equation. An overall total solar</p> <p>reflection of ≈91%, which is higher than the ≈78% and ≈88% for 100 nm and 400 nm single particle sizes, respectively was achieved from our hypothesis.</p> <p>With increasingly better RC materials being demonstrated in literature, there is a growing need to understand the real-world utility and benefit of RC with regards</p> <p>to energy savings. A fundamental limit of current radiative cooling systems is that only the top surface facing deep-space can provide the radiative cooling effect, while</p> <p>the bottom surface cannot. Here, we propose and experimentally demonstrate a concept of “concentrated radiative cooling” by nesting a radiative cooling system in a mid-infrared reflective trough, so that the lower surface, which does not contribute to radiative cooling in previous systems, can radiate heat to deep-space via the reflective</p> <p>trough. Field experiments show that the temperature drop of a radiative cooling pipe with the trough is more than double that of the standalone radiative cooling</p> <p>pipe. Furthermore, by integrating the concentrated radiative cooling system as a preconditioner in an air conditioning system, we predict electricity savings of > 75% in Phoenix, AZ, and > 80% in Reno, NV, for a single-story commercial building. We further look into unique applications of radiative cooling for outdoor enclosures</p> <p>of electrical equipment, as demonstrated with a case study of coating pole-type distribution transformers. Utilizing RC paint on the exterior of the case would allow further dissipation of heat to deep-space, as well as, increase the solar reflectance to lessen the heat load on the case. A single 25 kVA pole-type transformer is modeled</p> <p>via CFD with two different exterior case coatings, the standard grey coatings commonly utilized and an RC coating, BaSO4 paint, is analyzed under different operating loads. The RC coating demonstrates great benefits from a thermal management perspective</p> <p>and a gain in the lifetime of the windings. The RC coating cooled a 25 kVA distribution transformer’s core by > 11oC when compared to the standard case and even shows below ambient cooling of the case under minimal heat generations. The lifetime of the distribution transformers was increased by a minimum of 55% when comparing the standard case to the case with a radiative cooling paint based on the Aging Acceleration Factor. A more traditional application of radiative cooling paints is to utilize them on the exterior of buildings to offset the cooling energy demand for air conditioning. This work develops a high-fidelity RC model which accounts for pertinent weather factors including precipitable water, sky clearness, and dynamic convective heat transfer coefficients based on wind speed to further understand the energy savings. We implement our RC model on a single-story residential building to study the impact of RC in every unique ASHRAE climate zone in the United States using the 16 DOE recommended representative cities. Our results show > 7% and > 12% cooling energy savings across the United States for NREL’s building and typical buildings, respectively. Furthermore, warm climates yield the greatest cooling energy savings of up to 22% and 46% for the NREL and the Typical building, respectively. Extraterrestrial radiative thermal management is becoming increasingly pertinent with the development of new space technologies and the need to discover what is beyond</p> <p>our world. Space presents extreme thermal environments for radiative transfer, from a total eclipse case where the body radiates to deep space at 3 K to a full solar load where 1400 W/m2 is radiated onto the surface and a hybrid of both situations. The goal of this work is to engineer micropatterned Lanthanum Strontium Manganite</p> <p>(LSM) Barium Sulfate (BaSO4) coatings as efficient variable emissivity coatings (VECs). The photon transport through the micropatterned system is modeled using</p> <p>geometric optics and Monte Carlo coupled with geometric optics to obtain the coatings reflectivity, transmissivity, and emissivity to predict the ideal reflectivity and</p> <p>emissivity of the micropatterns. Then the micropatterned LSM coatings are experimentally fabricated using screen printing on a BaSO4 paint layer. The coatings are</p> <p>characterized by their temperature-dependent variable emissivity and solar absorptivity from the dual-layer micropatterned coatings. Furthermore, a computational model for a body-mounted cylindrical radiator was developed to investigate the real implications a VEC can have on crewed space vehicles, as well as define some target guidelines for VEC’s to achieve in future technologies.</p>

The CO2 emissions from road vehicles must be reduced in order to avoid a 1.5 ◦C global warming. To reduce tailpipe emissions, a strong trend is to electrify powertrains to shift away from the use of fossil fuel. Among alternatives, the fuel cellhybrid electric vehicle (FCHEV) is seen as a promising configuration. With the high energy density of hydrogen propulsion systems, it is regarded viable for heavy-dutylong cycle hauling. The aim of this thesis is thus to explore optimal control of energy and thermal management systems of FCHEVs. With the intention of increasing knowledge of how to control FCHEVs for a driving mission, this thesis models an FCHEV powertrain for optimal control purposes. The developed model is used in conjunction with dynamic programming to find the hydrogen optimal control strategies of the energy and thermal management systems. Finally, a sensitivity analysis is performed, investigating how the fuel cell characteristics influence the control strategies. The results propose a feasible complete powertrain model for optimal control purposes and provides insight on how to optimally control the powertrain for various scenarios, minimizing hydrogen consumption. It is concluded that for demanding missions, the fuel cell should consistently provide the main power output and together with the battery handle power transients. For less demanding missions, the fuel cell should be controlled with an on/off strategy, switching between being atidle and working in its most efficient region. It is also concluded that integrated energy and thermal strategies for the fuel cell during a driving mission can increase fuel efficiency, with the optimal thermal strategy being dependent on the fuel cell’s characteristics.

To improve the performance of the three-way catalytic (TWC) converter, advanced control strategies and on-board diagnostics (OBD) systems are needed. Both rely on a relatively accurate but computationally efficient TWC converter model. This thesis aims to develop a control-oriented model that can be employed to develop the control strategies and OBD systems of the TWC converter. The thesis consists of two parts, i.e., the high-fidelity model development and the model reduction. Firstly, a high-fidelity model is built using the energy and mass conservation principles. In this model, a constant inlet simulation is used to validate the warming-up characteristics, and a driving cycle simulation is used to calibrate the reaction rate parameters. The results of the simulation show that the high-fidelity model has adequate accuracy. Secondly, a reduced-order model is developed based on phase and reaction simplifications of the high-fidelity model. The aim of the development of the reduced-order model is to propose a computationally efficient model for further development of control strategies and state estimators for OBD systems. The accuracy of the reduced-order model is then validated by means of simulations. / Thesis / Master of Applied Science (MASc)

Yes / The ever-increasing demand for high-processing electronic systems has unequivocally called for improved microprocessor performance. However, increasing microprocessor performance requires increasing power and on-chip power density, both of which are associated with increased heat dissipation. Electronic cooling using fins have been identified as a reliable cooling approach. However, an investigation into the thermal behaviour of fin would help in the design of miniaturized, effective heatsinks for reliable microprocessor cooling. The aim of this paper is to investigates the simultaneous effects of surface roughness, porosity and magnetic field on the performance of a porous micro-fin under a convective-radiative heat transfer mechanism. The developed thermal model considers variable thermal properties according to linear, exponential and power laws, and are solved using Chebychev spectral collocation method. Parametric studies are carried using the numerical solutions to establish the influences of porosity, surface roughness, and magnetic field on the microfin thermal behaviour. Following the results of the simulation, it is established that the thermal efficiency of the micro-fin is significantly affected by the porosity, magnetic field, geometric ratio, nonlinear thermal conductivity parameter, thermogeometric parameter and the surface roughness of the micro-fin. However, the performance of the micro-fin decreases when it operates only in a convective environment. In addition, we establish that the fin efficiency ratio which is the ratio of the efficiency of the rough fin to the efficiency of the smooth fin is found to be greater than unity when the rough and smooth fins of equal geometrical, physical, thermal and material properties are subjected to the same operating condition. The investigation establishes that improved thermal management of electronic systems would be achieved using rough surface fins with porosity under the influences of the magnetic field. / Supported in part by the Tertiary Education Trust Fund of Federal Government of Nigeria, and the European Union’s Horizon 2020 research and innovation programme under grant agreement H2020-MSCA-ITN- 2016SECRET-722424.

This dissertation studies the problem of increasing battery life-time and reducing CPU heat dissipation without degrading system performance in commodity-OS-based general-purpose (GP) mobile computers using the dynamic voltage scaling (DVS) function of modern CPUs. The dissertation especially focuses on the impact of task scheduling on the effectiveness of DVS in achieving this goal. The task scheduling mechanism used in most contemporary general-purpose operating systems (GPOS) prioritizes tasks based only on their CPU occupancies irrespective of their deadlines. In currently available autonomous DVS schemes for GP mobile systems, the impact of this GPOS task scheduling is ignored and a DVS scheme merely predicts and enforces the lowest CPU speed that can meet tasks' deadlines without meddling with task scheduling. This research, however, shows that it is impossible to take full advantage of DVS in balancing energy/power and performance in the current DVS paradigm due to the mismatch between the urgency (i.e., having a nearer deadline) and priority of tasks under the GPOS task scheduling. This research also shows that, consequently, a new DVS paradigm is necessary, where a "DVS-friendly" task scheduling assigns higher priorities to more urgent tasks. The dissertation begins by showing how the mismatch between the urgency and priority of tasks limits the effectiveness of DVS and why conventional real-time (RT) task scheduling, which is intrinsically DVS-friendly cannot be used in GP systems. Then, the dissertation describes the requirements for "DVS-friendly GP" task scheduling as follows. Unlike the existing GPOS task scheduling, it should prioritize tasks by their deadline. But, at the same time, it must be able to do so without a priori knowledge of the deadlines and be able to handle the various tasks running in today's GP systems, unlike conventional RT task scheduling. The various tasks include sporadic tasks such as user-interactive tasks and tasks having dependencies on each other such as a family of threads and user-interface server/clients tasks. Therefore, the first major result of this research is to propose a new DVS paradigm for commodity-OS-based GP mobile systems in which DVS is performed under a DVS-friendly GP task scheduling that meets these requirements. The dissertation then proposes GPSched, a DVS-friendly GP task scheduling mechanism for commodity-Linux-based GP mobile systems, as the second major result. GPSched autonomously prioritizes tasks by their deadlines using the type of services that each task is involved with as the indicator of the deadline. At the same time, GPSched properly handles a family of threads and user-interface server/clients tasks by distinguishing and scheduling them as a group, and user-interactive tasks by incorporating a feature of current GPOS task scheduling — raising the priority of a task that is idle most of the time — which is desirable to quickly respond to user input events in its prioritization mechanism. The final major result is GPScheDVS, the integration of GPSched and a task-based DVS scheme customized for GPSched called GPSDVS. GPScheDVS provides two alternative modes: (1) the system-energy-centric (SE) mode aiming at a longer battery life-time by reducing system energy consumption and (2) the CPU-power-centric (CP) mode focusing on limiting CPU heat dissipation by reducing CPU power consumption. Experiments conducted under a set of real-life usage scenarios on a laptop show that the best, worst, and average reductions of system energy consumption by the SE mode GPScheDVS were 24%, -1%, and 17%, respectively, over the no-DVS case and 11%, -1%, and 5%, respectively, over the state-of-the-art task-based DVS scheme in the current DVS paradigm. The experiments also show that the best, worst, and average reductions of CPU energy consumption by the SE mode GPScheDVS were 69%, 0%, and 43% over the no-DVS case and 26%, -1%, and 13% over the state-of-the-art task-based DVS scheme in the current DVS paradigm. Considering that no power management was performed on non-CPU components for the experiments, these results imply that the system energy savings achievable by GPScheDVS will be increased if the non-CPU components' power is properly managed. On the other hand, the best, worst, and average reductions of average CPU power by the CP mode GPScheDVS were 69%, 49%, and 60% over the no-DVS case and 63%, 0%, and 30% over the existing task-based DVS scheme. Furthermore, oscilloscope measurements show that the best, worst, and average reduction of peak system power by the CP mode GPScheDVS were 29%, 10%, and 23% over the no-DVS case and 28%, 6%, and 22% over the existing task-based DVS scheme signifying that GPScheDVS is effective also in restraining the peak CPU power. On the top of these advantages in energy and power, the experimental results show that GPScheDVS even improves system performance in either mode due to its deadline-based task scheduling property. For example, the deadline meet ratio on continuous videos by GPScheDVS was at least 91.2%, whereas the ratios by the no-DVS case and the existing task-based DVS scheme were down to 71.3% and 71.0%, respectively. / Ph. D.