UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Thermal and Manufacturing Design of Polymer Composite Heat Exchangers(2014) Cevallos, Juan Gabriel; Bar-Cohen, Avram; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Polymer heat exchangers, using thermally-enhanced composites, constitute a "disruptive" thermal technology that can lead to significant freshwater and energy savings. The widespread use of seawater as a coolant can be made possible by the favorable qualities of thermally-enhanced polymer composites: good corrosion resistance, higher thermal conductivities, higher strengths, low embodied energy and good manufacturability. Polymer composites can bridge the gap between unfilled polymers and corrosion-resistant metals, and can be applied to a variety of heat exchanger applications. However, thermally enhanced polymer composites behave differently from more conventional polymers during the molding process. The desired thin walled large structures are expected to pose challenges during the molding process. This dissertation presents a design methodology that integrates thermo-fluid considerations and manufacturing issues into a single design tool for thermally enhanced polymer heat exchangers. The methodology shows that the choice of optimum designs is restricted by moldability considerations. Additionally, additive manufacturing has the potential to be a transformative manufacturing process, in which complex geometries are built layer-by-layer, which could allow for production and assembly of heat exchangers in a single step. In this dissertation, an air-to-water polymer heat exchanger was made by fused deposition modeling and tested for the first time. This dissertation also introduces a novel heat exchanger geometry that can favorably exploit the intrinsic thermal anisotropy of filled polymers. A laboratory-scale air-to-water polymer composite heat exchanger was made by injection molding. Its performance was verified empirically, and modeled with numerical and analytical tools.Item Characterization, Modeling, and Optimization of Polymer Composite Pin Fins(2005-08-24) Bahadur, Raj; Bar Cohen, Avram; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Increasing electronic product manufacturing volumes and cooling requirements necessitate the use of new materials and innovative techniques to meet the thermal management challenges and to contribute towards sustainable development in the electronic industry. Thermally conductive polymer composites, using high thermal conductivity fillers such as carbon fibers, are becoming commercially available and provide favorable attributes for electronic heat sinks, such as low density and fabrication energy requirements. These polymer composites are inherently anisotropic but can be designed to provide high thermal conductivity values in particular directions to address application-specific thermal requirements. This Thesis presents a systematic approach to the characterization, analysis, design, and optimization of orthotropic polymer composite fins used in electronic heat sinks. Morphological characterization and thermal conductivity measurements of thermally conductive Poly-Phenylene Sulphide composites are used to determine the significant directional thermal conductivity in such composites. An axisymmetric orthotropic thermal conductivity pin fin equation is derived to study the orthotropic thermal conductivity effects on pin fin heat transfer rate and temperature distribution. FEM simulation and water cooled experiments, focusing on the radial temperature variations in single pin fins, are used to validate the analytical model. Theoretical models, CFD modeling, and experiments are used to characterize the thermal performance of heat sinks, fabricated of PPS composite pin fins, in air natural convection and forced convection modes. Simplified solutions, for the orthotropic fin heat transfer rate that are easy to use and can be easily implemented in a heat sink design and optimization scheme, are presented.