A numerical study of axisymmetric synthetic jet flow was conducted. The synthetic jet cavity was modeled as a rigid chamber with a piston-like moving diaphragm at its bottom. The Shear-Stress-Transportation (SST) k-omega and #61559; turbulence model was employed to simulate turbulence. Based on time-mean analysis, three flow regimes were identified for typical synthetic jet flows. Typical vortex dynamics and flow patterns were analyzed. The effects of changes of working frequency, cavity geometry (aspect ratio), and nozzle geometry were investigated. A control-volume model of synthetic jet cavity was proposed based on the numerical study, which consists of two first-order ODEs. With appropriately selected parameters, the model was able to predict the cavity pressure and average velocity through the nozzle within 10% errors compared with full simulations. The cavity model can be used to generate the boundary conditions for synthetic jet simulations and the agreement to the full simulation results was good. The saving of computational cost is significant. It was found that synthetic jet impingement heat transfer outperforms conventional jet impingement heat transfer with equivalent average jet velocity. Normal jet impingement heat transfer using synthetic jet was investigated numerically too. The effects of changes of design and working parameters on local heat transfer on the impingement plate were investigated. Key flow structures and heat transfer characteristics were identified. At last, a parametric study of an active heat sink employing synthetic jet technology was conducted using Large Eddy Simulation (LES). Optimal design parameters were recommended base on the parametric study.

The ultimate objective of this research is to investigate the effectiveness of cathode gas (air) recirculation for the thermal management of a solid oxide fuel cell (SOFC) stack. SOFCs conventionally operate at high temperatures (>600o C); and recovering heat from stack exhaust is critical to improving the stack and system performance. Prevalent approaches implement bulky and expensive high temperature gas-to-gas heat exchangers. Also, ejectors are being investigated for recirculation of the air; however, an ejector with typically large velocity gradients would incur large viscous losses. An alternative recirculation approach is being developed for distributed entrainment via active flow control. The entrainment would allow recuperative thermal mixing to occur that may be more effective than the preceding two approaches. The ultimate goal of this research thrust is to reduce, or even exclude, the need of an air preheater in a SOFC system. The cathode air preheat contributes to a large portion of the cost of a SOFC system. Verifying and demonstrating the efficacy of the Coand and #259; effect has been the initial focus, and positive results have been demonstrated in a test environment from a fluid mechanics standpoint. This has been based upon three stages of experimental development, inclusive of cross-sectional area and activated blowing degrees-of-freedom. Seed thermal testing of the system has demonstrated legitimate thermal mixing capabilities. EES thermodynamic modeling developments confirm that the approach can reduce or even exclude the air preheat. It is concluded that recuperative thermal mixing with this recirculation approach is indeed feasible and has the potential to greatly reduce the cost and efficiency of the SOFC system.

In this study, the thermal management system of a notebook computer is investigated by using a commercial finite volume Computational Fluid Dynamics (CFD) software. After taking the computer apart, all dimensions are measured and all major components are modeled as accurately as possible. Heat dissipation values and necessary characteristics of the components are obtained from the manufacturer&#039 / s specifications. The different heat dissipation paths that are utilized in the design are investigated. Two active fans and aluminum heat dissipation plates as well as the heat pipe system are modeled according to their specifications. The first and second order discretization schemes as well as two different mesh densities are investigated as modeling choices. Under different operating powers, adequacy of the existing thermal management system is observed. Average and maximum temperatures of the internal components are reported in the form of tables. Thermal resistance networks for five different operating conditions are obtained from the analysis of the CFD simulation results. Temperature distributions on the top surface of the chassis where the keyboard and touchpad are located are investigated considering the user comfort.

The objective of this thesis is to introduce an alternative temperature sensor in CMOS technology with small area, low power consumption, and high resolution that can be easily interfaced. A novel temperature sensor utilizing the interface–trap charge pumping phenomenon and the temperature sensitivity of generation current is proposed. This thesis presents the design and characterization of the proposed temperature sensor fabricated in 0.18µm CMOS technology. The prototype sensor is characterized for the temperature range of 27oC–120oC. It has frequency output and exhibits linear transfer characteristics, high sensitivity, and high resolution. This temperature sensor is proposed for microprocessor thermal management applications.

Energy-storing electrochemical batteries are the most critical components of high energy density storage systems for stationary and mobile applications. Lithium-ion batteries have received considerable interest for hybrid electric vehicles (HEV) because of their high specific energy, but face inherent thermal management challenges that have not been adequately addressed. In the present investigation, a fully coupled electrochemical and thermal model for lithium-ion batteries is developed to investigate the impact of different thermal management strategies on battery performance. This work represents the first ever study of these coupled electrochemical-thermal phenomena in batteries from the electrochemical heat generation all the way to the dynamic heat removal in actual HEV drive cycles. In contrast to previous modeling efforts focused either exclusively on particle electrochemistry on the one hand or overall vehicle simulations on the other, the present work predicts local electrochemical reaction rates using temperature-dependent data on commercially available batteries designed for high rates (C/LiFePO4) in a computationally efficient manner. Simulation results show that conventional external cooling systems for these batteries, which have a low composite thermal conductivity (~1 W/m-K), cause either large temperature rises or internal temperature gradients. Thus, a novel, passive internal cooling system that uses heat removal through liquid-vapor phase change is developed. Although there have been prior investigations of phase change at the microscales, fluid flow at the conditions expected here is not well understood. A first-principles based cooling system performance model is developed and validated experimentally, and is integrated into the coupled electrochemical-thermal model for assessment of performance improvement relative to conventional thermal management strategies. The proposed cooling system passively removes heat almost isothermally with negligible thermal resistances between the heat source and cooling fluid. Thus, the minimization of peak temperatures and gradients within batteries allow increased power and energy densities unencumbered by thermal limitations.

Nanofluids have been demonstrated to be promising for heat transfer enhancement in forced convection and boiling applications. The addition of carbon, copper, and other high-thermal-conductivity material nanoparticles to water, oil, ethylene glycol, and other fluids has been determined to increase the thermal conductivities of these fluids. The increased effective thermal conductivities of these fluids enhance their abilities to dissipate heat in such applications. The use of nanofluids for spray cooling is an extension of the application of nanofluids for enhancement of heat dissipation. In this investigation, experiments were performed to determine the level of heat transfer enhancement with the addition of alumina nanoparticles to the fluid. Using mass percentages of up to 0.5% alumina nanoparticles suspended in water, heat fluxes and surface temperatures were measured and compare. Compressed nitrogen was used to provide constant spray nozzle pressures to produce full-cone sprays in an open loop spray cooling system. The range of heat fluxes measured were for single-phase and phase-change spray cooling regimes.

Thermophotovoltaic (TPV) devices, also known as (nano-TPVs) are energy-conversion systems which generate electric current from thermal radiation energy by a heat source. Although their conversion efficiency is limited in the far field by the Schockley-Queisser limit, in near field the heat flux transferred to a TPV cell can be significantly enchanced due to the contribution of evanescent waves, in particular supporting a surface mode. Unfortunately, spectral mismatch between the emitter and the TPV cell spectrum limits the TPV conversion efficiency. Photons with energy lower than the TPV cell bandgap may not be able to create electron-hole pairs because mobile carriers start diffusing and drifting between conductance and valence band, and try to exceed the upper limit of the band. This destroys the thermal equilibrium of the semiconductor and results in excess heat. Also, for high energy photons, the difference between the photon's energy and the bandgap energy is lost in Joule heating. Thus, quasimonochromatic, narrow-band and coherent emitters at a frequency near the energy bandgap of the converter is an ideal source to achieve high conversion efficiency. Nano-TPV device consisting of tungsten thermal emitter, maintained at 1200K, and the cell made of GaInAsSb are considered; thermal management system is reviewed assuming a constant heat flux boundary due to heat generation by the cell with a fluid temperature fixed at 293K. Tungsten thermal selective emitters are designed, characterized and optimized based on two-dimensional (2D) tungsten PhC by controlling periodic triangular grooves such that channel plasmon polaritons (CPPs) are coupled efficiently into these grooves to excite a localized groove modes which are well-matched to the GaInAsSb cell external quantum efficiency (EQE). The results show that power output and the 2D TE normal efficiency of the system are predicted to be 0.82x10⁴ W/m² and 43.8%, respectively. This leads to a promising device for many different sectors such as military, space and semiconductor industry. / text

Spray cooling is a technique for achieving large heat fluxes at low surface temperatures by impinging a liquid in droplet form on a heated surface. Heat is removed by droplets spreading across the surface, thus removing heat by evaporation and by an increase in the convective heat transfer coefficient. The addition of nano-sized particles, like aluminum or copper, to water to create a nanofluid could further enhance the spray cooling process. Nanofluids have been shown to have better thermophysical properties when compared to water, like enhanced thermal conductivity. Although droplet size, velocity, impact angle and the roughness of the heated surface are all factors that determine the amount of heat that can be removed, the dominant driving mechanism for heat dissipation by spray cooling is difficult to determine. In the current study, experiments were conducted to compare the enhancement to heat transfer caused by using alumina nanofluids during spray cooling instead of de-ionized water for the same nozzle pressure and distance from the heated surface. The fluids were sprayed on a heated copper surface at a constant distance of 21 mm. Three mass concentrations, 0.1%, 0.5%, and 1.0%, of alumina nanofluids were compared against water at three pressures, 40psi, 45psi, and 50psi. To ensure the suspension of the aluminum oxide nanoparticles during the experiment, the pH level of the nanofluid was altered. The nanofluids showed an enhancement during the single-phase heat transfer and an increase in the critical heat flux (CHF). The spray cooling heat transfer curve shifted to the right for all concentrations investigated, indicating a delay in two-phase heat transfer. The surface roughness of the copper surface was measured before and after spray cooling as a possible cause for the delay.

Additive Manufacturing (AM) processes which include Selective Laser Sintering (SLS) have experienced tremendous growth and development since their introduction over 20 years ago. It becomes highly important at this stage to evaluate the sustainability of the process and refine it to reduce energy and material consumption. In this study, a sustainability analysis was performed on the SLS process with Nylon-12 using the Environmental and Resource Management Data (ERMD) known as Eco-Indicators. The energy perspective alone was considered and a Total Energy Indicator (TEI) value was calculated using various parameters to quantify process sustainability: process productivity, energy consumption rate, etc. Precise thermal control of selective laser sintering (SLS) is desirable for improving geometric accuracy, mechanical properties, and surface finish of parts produced. An experimental setup to monitor the temperature distribution was designed using Resistance Temperature Detectors (RTD) as a part of this study. Discrepancies in temperature profiles were investigated and recommendations were made to improve thermal characteristics of the SLS process. / text

This dissertation presents a series of studies related to the study and control of slurry flow, process temperature, and aggressive diamonds in Chemical Mechanical Planarization (CMP). The purpose of these studies is to better understand the fundamentals of CMP and to explore solutions to some of CMP’s greatest challenges. Within-wafer removal rate non-uniformity (WIWRRNU) is a critical parameter to determine film thickness planarity on a wafer-scale level and it grossly impacts yield. Resolving this issue continues to be an area of intense focus in the industry. The first study in this dissertation shows the feasibility of adopting a new method to improve WIWRRNU during copper CMP that is solely based on intentional local temperature manipulation of the pad. A pad surface thermal management system is developed to locally change pad surface temperature. This system consists of one or more thermal transfer modules contacting the pad surface. In this study, the system is employed to adjust the "center-fast" copper removal rate profile to illustrate its effect during the process. Results shows that, when two thermal transfer modules are employed, local removal rates in the wafer center region decrease significantly while maintaining the removal rates near the wafer edge thereby significantly improving WIWRRNU. Another contribution of this dissertation is the investigation of the effect of pad groove design on slurry injection scheme during interlayer dielectric CMP. A novel slurry injector with multiple slurry outlets is designed, which provides optional slurry injection schemes (i.e. one injection point scheme and multi-injection point scheme). These schemes are compared with the standard slurry application method on a concentrically grooved pad and an xy-groove pad, respectively. On the concentrically grooved pad, the one injection point scheme generates significantly higher oxide removal rates (ranging from 22 to 35 percent) compared to the standard slurry application method at different slurry flow rates. On the xy-groove pad, the one injection point scheme still results in higher removal rates (ranging from 3 to 9 percent), however, its removal rate enhancement is not as high as that of the concentrically grooved pad. In order to further improve slurry availability on the xy-groove pad, the multi-injection point scheme is tested. Results show that the multi-injection point scheme results in significantly higher removal rates (ranging from 17 to 20 percent) compared to the standard slurry application method. This work underscores the importance of optimum slurry injection schemes for accommodating particular groove designs. The last contribution of this dissertation involves a study regarding aggressive diamond characterization and wear analysis during CMP. A 3M A3700 diamond disk is used to condition a Cabot Microelectronics Corporation (CMC) D100 pad for 30 hours. The top 20 aggressive diamonds for two perpendicular disk orientations are identified before the polishing, as well as after 15- and 30-hour polishing. The furrow surface area generated by these top 20 aggressive diamonds and their evolution are analyzed and compared. Results show that the original top 20 aggressive diamonds identified before polishing are subjected to wear after the first 15-hour polishing as the furrow surface area that they generate decreases dramatically (by 47%). As these original aggressive diamonds are worn, seven new aggressive diamonds are "born" and join the new top 20 list for both disk orientations. After the second 15-hour wafer polishing, the furrow surface area of these new top 20 aggressive diamonds do not change significantly. The furrow surface area created by all the active diamonds exhibits the same trend as the top 20 aggressive diamonds, confirming that most pad conditioning work is performed by these aggressive diamonds and that the disk loses its aggressiveness in the first 15 hours of polishing and then maintains its aggressiveness during the second 15 hours, albeit to a lesser extent.