Mechanical Engineering
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Item THERMAL MANAGEMENT OF INTEGRATED MOTORS FOR ELECTRIC PROPULSION(2022) Yao, Zhaoxi; McCluskey, Francis P; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Electrification of traditional combustion power units has been a major trend. The low emissions, low noise and high efficiency characteristic of electrified power, fit the vision of a low carbon emission future. The development of high power density electric motors is key to facilitating large scale, heavy duty applications. The demand for dense power leads to significant heat flux, causing thermal management to become one of the main obstacles in developing high power density electric motors. Multiple components in the motor generate heat. For example, the motor of interest in this paper is a 1 MW, high power density, surface mounted permanent magnet motor, with a segmented and laminated stator on the outside, and a laminated rotor on the inside. Heat is generated in the stator winding, stator core, magnets, rotor core as well as the motor drive. For high speed motors, windage loss could also be significant in the air gap. Among the heat-generating components, the stator winding is the primary heat source. For this study, a comprehensive thermal management solution was developed. The power density of the motor, based on active mass, exceeded 22 kW/kg and majority of the loss came from the stator windings. Thus, a dedicated direct winding cooling combined with an integrated cooling jacket were deployed. Multiple winding cooling schemes were explored, such as investment-casted cooling channels in potting, hollow conductors, flooded slots and Litz-wire-wrapped cooling tubes. The flooded slots with scaffolding-shaped spacer were chosen in the end, which demonstrate good thermal performance, low pumping power, pressure requirements and low risk of partial discharge as the dielectric coolant also served as liquid insulation. A cooling jacket with integrated power module cooling was designed to cool the stator core and power modules. The cooling jacket included a compression sleeve, which served as the mechanical support to hold the stator segments as well as the cooling surface for the stator cores, and nine cold plates, hosting 18 power modules on top, placed around the curved outer surface of the motor. The cooling concepts were designed, simulated and validated by testing. A functioning prototype was constructed and in the process of testing.Item Phase Change Materials for Vehicle and Electronic Transient Thermal Systems(2020) Jankowski, Nicholas Robert; McCluskey, F. Patrick; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Most vehicle operating environments are transient in nature, yet traditional subsystem thermal management addresses peak load conditions with steady-state designs. The large, overdesigned systems that result are increasingly unable to meet target system size, weight and power demands. Phase change thermal energy storage is a promising technique for buffering thermal transients while providing a functional thermal energy reservoir. Despite significant research over the half century, few phase change material (PCM) based solutions have transitioned out of the research laboratory. This work explores the state of phase change materials research for vehicle and electronics applications and develops design tool compatible modeling approaches for applying these materials to electronics packaging. This thesis begins with a comprehensive PCM review, including over 700 candidate materials across more than a dozen material classes, and follows with a thorough analysis of transient vehicle thermal systems. After identifying promising materials for each system with potential for improvement in emissions reduction, energy efficiency, or thermal protection, future material research recommendations are made including improved data collection, alternative metrics, and increased focus on metallic and solid-state PCMs for high-speed applications. Following the material and application review, the transient electronics heat transfer problem is specifically addressed. Electronics packages are shown using finite element based thermal circuits to exhibit both worsened response and extreme convective insensitivity under pulsed conditions. Both characteristics are quantified using analytical and numerical transfer function models, including both clarification of apparently nonphysical thermal capacitance and demonstration that the convective insensitivity can be quantified using a package thermal Elmore delay metric. Finally, in order to develop design level PCM models, an energy conservative polynomial smoothing function is developed for Enthalpy and Apparent Capacity Method phase change models. Two case studies using this approach examine the incorporation of PCMs into electronics packages: substrate integrated Thermal Buffer Heat Sinks using standard finite element modeling, and direct on-die PCM integration using a new phase change thermal circuit model. Both show effectiveness in buffering thermal transients, but the metallic phase change materials exhibit better performance with significant sub-millisecond temperature suppression, something improved cooling or package integration alone were unable to address.Item Microfabrication and Analysis of Manifold Microchannel Coolers for Power Electronics(2011) Boteler, Lauren Marie; McCluskey, Patrick; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This research presents the analysis and realization of a single phase high performance manifold microchannel cooler for improving the thermal and hydrodynamic performance of multi-chip power electronic modules. This heat exchanger, microfabricated directly into the substrate, enables higher power density electronic products by more efficiently removing the high levels of heat generated. The improved thermal performance and efficiency of the heat exchanger is demonstrated using both numerical and experimental techniques. The improved heat removal is due to the reduction in the number of packaging layers between the device and the heat exchanger and by improvement in convective heat transfer. In addition, the efficiency of the device is enhanced by minimizing fluid pressure drop through the use of large manifold channels to transport fluid to the cooling area and smaller crossover microchannels in the active cooling area. This combination of channels also improves the uniformity of the temperature distribution across the device. The manifold microchannel coolers were fabricated and tested both with and without electrical isolation between the chip and the coolant. Experimentally, the coolers without electrical isolation demonstrated thermal resistivity values as low as 0.06 K/(W/cm2), which is up to a 50X improvement over a standard power package with significant size and weight reduction. The coolers with an incorporated aluminum nitride electrical isolation layer experimentally demonstrated up to a 15X improvement. In addition to experimental results, the interaction between the manifold channels and multiple microchannels was numerically modeled and compared to simpler, one-dimensional approximations based on the Hagen-Poiseuille equation. The comparison shows that the one-dimensional model, while under-predicting total pressure drops, can provide insight into the effect of varying dimensions on system performance. The numerical models were used to identify the impact of varying dimensions across the entire length of the cooler, and a sensitivity analysis was performed with respect to system pressure drop, thermal resistance and uniformity. Additionally, large microchannel velocity gradients, some larger than 10X, were observed along the length of the device which impacts the chip non-uniformity. The simulations showed that when comparing the manifolded design to a comparable straight microchannel cooler, there is a 38X reduction in system pressure drop for similar thermal performance.Item Modeling of a Single-Phase Liquid Cooling System for Power Electronics Applications(2010) DeVoto, Douglas; McCluskey, F. Patrick; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This work investigates the reliability of a single-phase, liquid cooling system used for the thermal management of a medium power level converter system. The system utilizes a plastic insert cold plate design to provide even cooling over the backside of a power electronics device by directing coolant through parallel serpentine channels. Material selection and compression set testing evaluated suitable elastomers for seals and polymers for the plastic insert. Computational fluid dynamics software was used to evaluate the thermal performance of the cooling system under ideal conditions as well as various wear out conditions (e.g. channel blockage, erosion of channel walls). Properties of used 50/50 ethylene glycol water coolant were evaluated to discover additional causes of reduced thermal performance. After completing the cooling system evaluation under initial and degraded conditions, the impact on a power module's operating temperature was correlated to an estimation of the device's reliability.