Mechanical Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/2263
Browse
6 results
Search Results
Item Metareasoning Approaches to Thermal Management During Image Processing(2022) Dawson, Michael Kenneth; Herrmann, Jeffrey W; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Resource-constrained electronic systems are present in many semi- and fully-autonomous systems and are tasked with computationally heavy tasks such as image processing. Without sufficient cooling, these tasks often increase device temperature up to a predetermined maximum, beyond which the task is slowed by the device firmware to maintain the maximum. This is done to avoid decreased processor lifespan due to thermal fatigue or catastrophic processor failure due to thermal overstress. This thesis describes a study that evaluated how well metareasoning can manage the central processing unit (CPU) temperature during image processing (object detection and classification) on two devices: a Raspberry Pi 4B and an NVIDIA Jetson Nano Developer Kit. Three policies that employ metareasoning were developed; one which maintains a constant image throughput, one which maintains a constant expected detection precision, and a third that trades between throughput and precision losses based on a user-defined parameter. All policies used the EfficientDet series of object detectors. Depending on the policy, these networks were either switched between, delayed, or both. This thesis also considered cases that used the system's built-in throttling policy to control the temperature. A policy was also created via reinforcement learning. The policy was able to adjust the detection precision and program throughput based on a set of states corresponding to the possible temperatures, neural networks, and processing delays. All three designed metareasoning policies were able to stabilize the device temperature without relying on thermal throttling. Additionally, the policy created through reinforcement learning was able to successfully stabilize the device temperature, though less consistently. These results suggest that a metareasoning-based approach to thermal management in image processing is able to provide a platform-agnostic and programmatic way to comply with constant or variable temperature constraints.Item ADVANCED PACKAGING AND THERMAL MANAGEMENT OF DC-DC CONVERTERS AND NOVEL CORRELATIONS FOR MANIFOLD MICROCHANNEL HEATSINKS(2021) Yuruker, Sevket Umut; Ohadi, Michael; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)An advanced packaging configuration of a dual-active-bridge 10 kW DC-DC converter module is introduced in this dissertation. Through utilization of novel heatsinks for the power switches and the transformer assembly, ~20 kW/Lit converter volumetric power density based on numerical and experimental analysis is obtained. Through a unique placement of the high power/high frequency SiC switches on the printed circuit board, many beneficial features such as double-sided cooling, complete elimination of wirebonding, and circumvention of the need for TIM layers between the switches and the heatsinks, and multi functioning heatsinks as electrical busbars is achieved. A Vertically Enhanced Manifold Microchannel System (VEMMS) cooler is developed to address the thermal challenges of a pair of power switches, simultaneously. Both air and liquid cooled versions of VEMMS cooler is presented, thermal resistances of 1.1 K/W and 0.3 K/W for the air and liquid cooled versions, respectively, at reasonable flow rates and pressure drops was obtained. Besides the power switches, thermal management of the transformer assembly is accomplished via Combined Core and Coil (C3) Coolers, where both the magnetic core and coils are liquid cooled simultaneously with electrically insulating but thermally conductive 3D printed Alumina heatsinks, where thermal resistances as low as 0.3 K/W for the magnetic core and 0.09 K/W for the transformer windings is experimentally demonstrated. Furthermore, a system level model was built to investigate the effect of various components in the cooling loop on each other, and what are the limiting factors to prevent a possible thermal runaway failure. Lastly, using a metamodeling approach, closed form pressure drop and heat transfer correlations are developed for thermo-fluidic performance prediction of manifold microchannel heatsinks. Due to complexity and vastness of design variables present in manifold microchannel systems, adequate CFD analysis and optimization require significant computational power. Through utilization of the developed correlations, orders of magnitude reduction in computational time (from days to milliseconds) in prediction of pressure drop and heat transfer coefficient is demonstrated. Extensive mesh independence and residual convergence algorithms are developed to increase accuracy of the created database. Between the correlation and mesh independent CFD results, a mean error of 3.9% and max error of 24% for Nusselt number, and a mean error of 4.6% and max error of 37% for Poiseuille Number predictions are achieved.Item Thermal Isolation of High Power Devices in Heterogeneous Integration(2017) Fish, Michael Christopher; McCluskey, Patrick; Bar-Cohen, Avram; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Heterogeneous integration (HI) technologies present an important development in the pursuit of higher performance and reduced size, weight, power and cost of electronic systems (SWAP-C). HI systems, however, pose additional challenges for thermal management due to the disparate operating conditions of the devices. If the thermal coupling between devices can be reduced through a strategy of thermal isolation, then the SWAP-C of the accompanying thermal solution can also be reduced. This is in contrast to the alternative scenario of cooling the entire package to the maximum reliable temperature of the most sensitive devices. This isolation strategy must be implemented without a significant increase in device interconnect distances. A counter-intuitive approach is to seek packaging materials of low thermal conductivity – e.g. glass – and enhance them with arrays of metallic through-layer vias. This dissertation describes the first ever demonstration of integrating such via-enhanced interposers with microfluidic cooling, a thermal solution key to the high power applications for which HI was developed. Among the interposers tested, the best performing were shown to exhibit lower thermal coupling than bulk silicon in selective regions, validating their ability to provide thermal isolation. In the course of the study, the via-enhanced interposer is modeled as a thermal metamaterial with desirable, highly-anisotropic properties. Missing from the supporting literature is an accurate treatment of these interposers under such novel environments as microfluidic cooling. This dissertation identifies a new phenomenon, thermal microspreading, which governs how heat couples into a conductive via array from its surroundings. Both finite element analysis (FEA) and a new analytic solution of the associated boundary value problem (BVP) are used to develop a model for describing microspreading. This improves the ability to correctly predict the thermal behavior of via-enhanced interposers under diverse conditions.Item THERMOELECTRIC COOLING OF HIGH FLUX ELECTRONICS(2017) Yuruker, Sevket Umut; Yang, Bao; Bar-Cohen, Avram; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)On-chip thermoelectric cooling is a promising solution for thermal management of next generation integrated circuits. This thesis focuses on three thermoelectric cooling applications for high flux electronics. A micro contact enhanced thin film thermoelectric cooler was designed for remediation of a 5kW/cm2 hotspot and its integration with manifold microchannel system is numerically demonstrated. In addition, thermoelectric cooling was utilized for thermal de-coupling of electronic chips with different operating temperatures, eliminating the need to over-cool the entire package. Furthermore, effect of decreasing contact resistances in thin film thermoelectrics was numerically investigated to effectively remove 100W (~280W/cm2) of heat dissipation from quantum cascade lasers. Finally, a system-level optimization methodology is established with comprehensive mathematical modeling, verified with numerical simulations. Master curves are generated to understand the effect of system-level parasitics on performance and optimal design variables. In conclusion, the advantages of thermoelectric cooling for high flux electronics is demonstrated in this thesis.Item Energy Efficient Two-Phase Cooling for Concentrated Photovoltaic Arrays(2013) Reeser, Alexander; Bar-Cohen, Avram; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Concentrated sunlight focused on the aperture of a photovoltaic solar cell, coupled with high efficiency, triple junction cells can produce much greater power densities than traditional 1 sun photovoltaic cells. However, the large concentration ratios will lead to very high cell temperatures if not efficiently cooled by a thermal management system. Two phase, flow boiling is an attractive cooling option for such CPV arrays. In this work, two phase flow boiling in mini/microchannels and micro pin fin arrays will be explored as a possible CPV cooling technique. The most energy efficient microchannel design is chosen based on a least-material, least-energy analysis. Heat transfer and pressure drop obtained in micro pin fins will be compared to data in the recent literature and new correlations for heat transfer coefficient and pressure drop will be presented. The work concludes with an energy efficiency comparison of micro pin fins with geometrically similar microchannel geometry.Item Thermo-Optic Aspects of Large Screen Plasma Display Panels(2007-05-16) Kahn, Jeffry Joseph; Bar-Cohen, Avram; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Plasma Display Panels (PDPs) are a popular technology for large size television displays. Screen inefficiencies, which result in significant localized heat generation, necessitate the use of advanced thermal management materials to reduce the peak temperatures and spatial temperature variations across the screen. In the current study, infrared thermography was used to obtain thermal maps of a typical, 42", high-definition PDP screen for different illumination patterns and for several configurations of externally controlled heaters simulating PDP heat generation. The results were used to validate a three-dimensional numerical thermal model of the PDP designed to predict the beneficial effects of anisotropic graphite heat spreaders on the temperature distribution. In addition, a color analyzer was used to determine the spatial and temporal variations in luminosity across the PDP when operated continuously for 1750 hours. The thermal model and experimental luminosity characteristics were used to evaluate the deleterious effects of temperature on PDP performance.