Browsing by Author "Dr. Stefan Seelecke, Committee Member"

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Analysis of Non-Stochastic Lattice Structure Design for Heat Exchanger Applications
(2009-12-07) Manogharan, Guha Prasanna; Dr. Ola Harrysson , Committee Chair; Dr. Denis Cormier, Committee Co-Chair; Dr. Stefan Seelecke, Committee Member
MANOGHARAN, GUHA PRASANNA. Analysis of Non-Stochastic Lattice Structure Design for Heat Exchanger Applications. (Under the directions of Dr. Ola Harrysson and Dr. Denis Cormier.) Non-stochastic lattice structures are cellular solids with periodically repeating array of cells formed by interconnected struts. Conventional manufacturing limits cellular solid structures to stochastic foams and honeycombs. The recent advancement of Solid Freeform Fabrication (SFF) enables the manufacturing of spatially controlled non-stochastic cellular solids engineered for the requirements of a particular application. Recent developments led to the application of metal cellular solids for air heating applications. This research proposes to optimize the cellular solid structure design for efficient heat transfer with minimum fluidic pressure loss. The novel concept is to design cellular solids with thicker struts in the direction along the fluid flow and thinner struts perpendicular to the flow with appropriate current supply for optimum performance. The model analyzed has a resistive cellular solid at a fixed temperature. The geometries examined include hexagonal lattice and rhombic dodecahedron. The heat transfer can be enhanced by thicker struts in the core of the structures and subsequently, by increasing the current across the cells. With corresponding experimental validation, the analysis indicates that by varying the cell length at the entry and exit along the flow direction, pressure loss can be significantly reduced. The pressure loss can be minimized by thinner struts in the entry and exit of the cellular solid. The study indicates that there is no significant effect of the angle between the edges on the performance of the system in the length scale considered.
Assessment of Cooling Microelectronics using Piezoelectric Bimorphs
(2004-12-15) Halbur, Simon Gilbert; Dr. Paul I. Ro, Committee Chair; Dr. William Roberts, Committee Member; Dr. Stefan Seelecke, Committee Member
As the heat generation of processors for notebook computers continues to increase, so does the need for smaller, more efficient cooling systems. The cooling capabilities of the piezoelectric bimorph were assessed to determine if it could fulfill this need. This was accomplished by first analyzing the current methods used to cool notebook computers using heat transfer theory. Using this data and the known properties of the cooling system, two techniques were applied to try and predict the temperature profile of a processor. By predicting this profile it would be possible to determine the amount of convective cooling required to dissipate the heat for a specific processor. The cooling capabilities of the piezoelectric bimorph were assessed by looking at the theoretical volumetric flow rates and flow velocities it was able to produce through bulk air flow. It was found that the flow rate increases while the flow velocity decreases as the length of the bimorph increases. This was further supported by experimental testing with a heat source that could be regulated to output a specified amount of power. Testing also showed that there exists an optimal bimorph length and optimal gap between the bimorph and heat source, where maximum cooling is obtained. By comparing the cooling requirements of a processor and the cooling capabilities of a piezoelectric bimorph it was found that the bimorph's capabilities are not sufficient for current high power microelectronics. Instead the bimorph was found to be comparable to a heat sink for an older Pentium® processor, which means the bimorph could be viable for low power devices.
Controlled Particle Transport in a Human Airway Replica
(2007-12-07) Rojas, Carlye Rimmele; Dr. William L. Roberts, Committee Chair; Dr. Clement Kleinstreuer, Committee Member; Dr. Stefan Seelecke, Committee Member
The goal of this research is a proof-of-concept for targeted aerosol delivery and validation of computational results. Sodium chloride particles, with a monodisperse particle size of one micrometer are used to represent a drug aerosol in the experimental validation of computational results. A complex oral airway, including a mouth, larynx, pharynx, and trachea was constructed out of laser cured resin, using a three-dimensional printing method. A symmetric three generation (G0 to G3) bifurcating bronchial airway was constructed using the same process. Two-phase flow was conducted through these models to yield particle transport results. The bulk air flow was 2 liters per minute, the highest observed flow rate that will allow the flow to remain laminar throughout the airway model. The flow rate of the particle seeded flow was maintained at 20 milliliters per minute. The velocities of these two flow rates remain within an order of magnitude of each other to inhibit vortices created by shear forces when the two flows were introduced. A series of nozzles (constructed using SL) were used to control the particle injection location. A one millimeter inner diameter seed nozzle is offset, from the center, a given percent of the radius. There were five nozzles, with increasingly offset seed tubes, 0% (centerline of axisymmetric nozzle), 20%, 40%, 60%, and 80%. The airway model was attached to the nozzle so that the nozzle exit is in the same plane as the mouth entrance. The nozzle was rotated so that the seed tube exit can be positioned at various angles within the circular cross-section. By controlling the particle release position, the deposition efficiency can be increased, dramatically, as compared to the uniform injection of the drug. The results show the controlled particle release can determine which branch or branches of the third generation bifurcating bronchial airway the particles will exit. While numerous previous researchers have studied the deposition effects of a uniform injection of aerosol particles in the human airways, the controlled position of particle release is an original idea.
Mechanical Properties of Injection-Molded Nd-Fe-B Type Permanent Magnets
(2002-08-19) Garrell, Monika Gerda; Dr. Ronald O. Scattergood, Committee Member; Dr. Stefan Seelecke, Committee Member; Dr. Albert Shih, Committee Chair
The goal of this research was to investigate the mechanical properties of injection molded Nylon and PPS-based Nd-Fe-B type magnets. The development of new Nd-Fe-B type magnetic materials and the advancement of near-net shape injection molding processes for magnetic component manufacturing have driven the needs to evaluate the mechanical properties of these newly developed materials. PPS (Polyphenylene-Sulfide) and Nylon (Polyamide) are the two most common binders used for these injection molded rare earth magnets. Since magnetic materials are usually used at elevated and cryogenic temperatures in the automotive and computer industry, the temperature dependent properties ranging from -40 to 180°C are critical for the design of devices utilizing permanent magnetic materials. To enlarge the use of bonded magnets, it is essential to establish a data-base of mechanical characteristics over the operational temperature range. This will provide valuable information for material designers to tailor the formulation and process parameters to achieve the desired mechanical properties. This research included a series of mechanical properties testing following appropriate ASTM standards. Tensile and bending strengths were evaluated, since these are considered to be the most fundamental characteristics describing the mechanical behavior of materials. Young's modulus was measured using the dynamic impulse vibration method and compared with that obtained from tensile tests. Scanning Electron Microscopy (SEM) analyses indicated that the debonding on the Nd-Fe-B particle and Nylon interface was the main cause of failure at room and elevated temperatures.