O desempenho das Máquinas de Medir a Três Coordenadas (MM3Cs) fica limitado por diversos fatores, que atuam de maneira conjunta gerando os denominados erros volumétricos. Para a temperatura de 20ºC os erros geométricos podem ser considerados constantes, uma vez que variam muito lentamente com o tempo. Porém, se a temperatura é alterada estes erros mudam em grandeza e comportamento, gerando os denominados erros térmicos. Alguns trabalhos têm sido desenvolvidos com o objetivo de estudar e modelar os erros térmicos, porém os resultados alcançados são, ainda, incipientes. Este trabalho apresenta o equacionamento das componentes do erro volumétrico das MM3Cs considerando as influências térmicas. A medelagem foi aplicada a uma MM3C do tipo \"Ponte Móvel\" e combina transformações homogêneas, técnicas de regressão e mínimos quadrados. As grandezas dos erros geométricos e das variações termicamente induzidas destes erros foram coletadas utilizando-se do interferômetro laser, do esquadro mecânico, do nível eletrônico, etc. Os valores das temperaturas foram monitorados através de termopares do tipo T (Cobre-Constantan). Verificou-se que a Máquina não experimenta deformações, além, das provocadas pela livre dilatação dos seus componentes. A partir do modelo proposto foram sintetizadas as componentes do erro volumétrico, os resultados foram discutidos e comparados com aqueles obtidos através da medição de um anel padrão, constatando-se a excelente capacidade do modelo na previsão do erro volumétrico da máquina. No caso, erros da ordem de grandeza de 10 &#956m foram reduzidos em pelo menos 75%, enquanto que para erros maiores que 10 &#956m a eficiência do modelo foi de 90%. / Performance of coordinate measuring machines (CMMs) is limited by numerous factors that operate simultaneously and generate volumetric errors. The most significant portion of the volumetric error is produced by geometric errors. At the temperature of 20ºC, geometric errors can be considered at steady states, once their variation in time is considerably slow. However, if temperature is modified, these errors change in magnitude and behaviour, generating the thermal induced errors. Some work has been developed aiming to study and model the thermal errors, but the achieved results are still incipient. This work presents the derivation of the components of the volumetric error considering its thermal influences. The method was employed and applied to moving bridge CMM and combines homogeneous transformation, regression techniques and least squares methods. The magnitudes of the geometric errors and its thermally induced variations were collected by means of a laser interferometer system, mechanical square, electronic level, etc. Temperature data were monitored by means of T-type thermocouples (copper-constantan). It was verified that the CMM was not susceptible to deformations other than the ones due to the dilatation of its components. From the proposed model, the components of volumetric error were synthesized; the results were discussed and compared to the ones obtained from the measurement of a ring plug, observing the outstanding ability of the model to predict the volumetric error of the machine. Errors of 10 &#956m in magnitude were reduced in at least 75%, whilst errors greater than 10 &#956m, presented a reduction efficiency of 90%. It was verified that the CMM was not susceptible to deformations other than the ones due to the dilatation of its components.

Hong Sin Yi, Grace. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1997. / Includes bibliographical references (leaves 50-51). / Acknowledgments / Abstract / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Metallic Glass and its application --- p.1 / Chapter 1.2 --- Glass Forming Ability (GFA) --- p.2 / Chapter 1.3 --- Equilibrium Phase --- p.3 / Chapter 1.4 --- Nucleation and Growth --- p.6 / Chapter 1.5 --- Spinodal Decomposition --- p.8 / Chapter 1.6 --- Morphology Comparison between Nucleation and Growth and Spinodal --- p.13 / Figures --- p.14 / References --- p.24 / Chapter Chapter 2 --- Experimental Method / Experimental Method --- p.25 / Figure --- p.29 / References --- p.30 / Chapter Chapter 3 --- Metastable liquid miscibility gap in Pd-Si and its glass forming ability / Introduction --- p.32 / Experimental --- p.33 / Results --- p.34 / Discussion --- p.36 / Figures --- p.40 / References --- p.49 / Bibliography --- p.50

The thermal properties of hydrate bearing sediments remain poorly studied, in part due to measurement difficulties inside the hydrate stability envelope. In particular, there is a dearth of experimental data on hydrate-bearing sediments, and most available measurements and models correspond to bulk gas hydrates. However, hydrates in nature largely occur in porous media, e.g. sand, silt and clay. The purpose of this research is to determine the thermal properties of hydrate-bearing sediments under laboratory conditions, for a wide range of soils from coarse-grained sand to fine-grained silica flour and kaolinite. The thermal conductivity is measured before and after hydrate formation, at effective confining stress in the range from 0.03 MPa to 1 MPa. Results show the complex interplay between soil grain size, effective confinement and the amount of the pore space filled with hydrate on the thermal conductivity of hydrate-bearing sediments.

Thermo-mechanical failure of components in planar-type solid oxide fuel cells (SOFCs) is a major obstacle on the path to bringing this technology to commercial viability. The probability of material degradation and failure in SOFCs depends strongly on the local temperature gradients at the interfaces of different materials. Therefore, it is of paramount importance to accurately predict and manage the temperature fields within the stack, especially near the interfaces. In this work we consider three effects in detail. First, we analyze radiative heat transfer effects within the semi-transparent solid electrolyte and compared them to thermal conduction. We also, present the modeling approach for calculation of surface-to-surface exchange within the flow channels and from the stack to the environment. The simplifying assumptions are identified and their carefully justified range of applicability to the problem at hand is established. This allows thermal radiation effects to be properly included in overall thermal modeling efforts with the minimum computational expense requirement. Second, we developed a series of reduced-order models for the transient heating and cooling of a cell, leading to a framework for optimization of these processes. The optimal design is one that minimizes heating time while maintaining thermal gradients below an allowable threshold. To this end, we formulated reduced order models (validated by rigorous CFD simulations) that yield simple algebraic design rules for predicting maximum thermal gradients and heating time requirements. Several governing dimensionless parameters and time scales were identified that shed light on the essential physics of the process. Finally, an analysis was performed to assess the degree of local thermal non-equilibrium (LTNE) within porous SOFC electrodes, and through a simple scaling analysis we discovered the parameter that gives an estimate of the magnitude of LTNE effects. We conclude that because of efficient heat transfer between the solid and gas in the microscale pores of the electrodes, the temperature difference between gas and solid is often negligible. However, if local variations in current density are significant, the LTNE effects may become significant and should be considered.

LOW TEMPERATURE SYNTHESIS AND CHARACTERIZATION OF SOME LOW POSITIVE AND NEGATIVE THERMAL EXPANSION MATERIALS Kathleen Madara White 151 pages Directed by Dr. Angus P. Wilkinson Low temperature non-hydrolytic sol-gel synthesis was used to explore the possibility of lowering the crystallization temperatures of some known AIVMV2O7 compounds. Crystallization temperatures for ZrP2O7 and ZrP2O7 were unaffected by the use of non-hydrolytic sol-gel methods; however, successful synthesis of these compounds broadens the range of materials that can be produced using this method and suggests the possibility of synthesizing solid solutions (or composites) including ZrP2O7 or ZrV2O7. This research presents for the first time the direct synthesis of ZrP2O7 from separate zirconium and phosphorus starting materials using mild autoclave methods. Characterization of some AIVMV2O7 compounds, using lab and high resolution synchrotron powder XRD, led to the assignment of a new symmetry for CeP2O7 and to the suggestion that the reported structure for PbP2O7 was inadequate. Studies using in situ high temperature lab and synchrotron powder XRD for PbP2O7 and CeP2O7 provided the opportunity to report their thermal properties for the first time, and to compare their behavior to that of some other AIVMV2O7. High pressure diffraction measurements on CeP2O7 provided data for the estimation of bulk moduli and suggested two possible pressure-induced phase transitions. A broad range of MIIIMVP4O14 compounds were prepared using low temperature hydrolytic sol-gel synthesis. Thermal studies revealed nearly linear trends in CTEs and lattice constants with respect to the sizes of MIIIMV cations. Some lower ionic radii compounds had CTEs comparable to that of ZrP2O7 at low temperature, suggesting a similar superstructure. Three compounds were found to exhibit temperature-induced phase transitions.

The development of wide band gap semiconductors for power and RF electronics as well as high power silicon microelectronics has pushed the need for advanced thermal management techniques to ensure device reliability. While many techniques to remove large heat fluxes from devices have been developed, fewer advancements have been made in the development of new materials which can be integrated into the packaging architecture. This is especially true in the development of thermal interface materials. Conventional solders are currently being used for interface materials in the most demanding applications, but have issues of high cost, long term reliability and inducing negative thermomechanical effects in active die. Carbon nanotubes have been suggested as a possible thermal interface material which can challenge solders because of their good thermal properties and 1-D structure which can enhance mechanical compliance between surfaces. In this work, we have developed a novel growth and transfer printing method to manufacture vertically aligned CNTs for thermal interface applications. This method follows the nanomaterial transfer printing methods pioneered at Georgia Tech over the past several years. This process is attractive as it separates the high growth synthesis temperatures from the lower temperatures needed during device integration. For this thesis, CNTs were grown on oxidized Si substrates which allowed us to produce high quality vertically aligned CNTs with specific lengths. Through the development of a water vapor assisted etch process, which takes place immediately after CNT synthesis, control over the adhesion of the nanotubes to the growth surface was achieved. By controlling the adhesion we demonstrated the capability to transfer arrays of vertically aligned CNTs to polyimide tape. The CNTs were then printed onto substrates like Si and Cu using a unique gold bonding process. The thermal resistances of the CNTs and the bonded interfaces were measured using the photoacoustic method, and the strength of the CNT interface was measured through tensile tests. Finally, the heat dissipation capabilities of the vertically aligned CNTs were demonstrated through incorporation with high brightness LEDs. A comparison of LED junction temperatures for devices using a CNT and lead free solder thermal interface was made.

Shrinking volume, coupled with higher performance, microprocessors and integrated circuits have led to serious heat dissipation issues. In an effort to mitigate the excessive amounts of waste heat and ensure electronic survivability, heat sinks and spreaders are incorporated into heat generating device structures. This inevitability creates a thermal pathway through an interface. Thermal interfaces can possess serious thermal resistances for heat conduction. The introduction of a thermal interface material (TIM) can drastically increase the thermal performance of the component. Exceptional thermal properties of multiwall carbon nanotubes (MWCNTs) have spurred interest in their use as TIMs. MWCNTs inherently grow in vertically-oriented, high aspect ratio arrays, which is ideal in thermal interface applications because CNTs posses their superior thermal performance along their axis. In this paper, laser flash thermal characterization of sandwich‐bonded and cap‐screw‐bonded aluminum discs for both adhesive-infiltrated and “dry”, 100% MWCNT arrays, respectively. Thermal contact resistances as low as 18.1 mm2K/W were observed for adhesive‐infiltrated arrays and, even lower values, down to 10.583 mm2K/W were measured for “dry” MWCNT arrays. The improved thermal performance of the arrays compared to thermal adhesives and greases currently used in the electronics and aerospace industries, characterize MWCNT arrays as a novel, lighter‐weight, non‐corrosive replacement.

High performance/small package electronics create difficult thermal issues for integrated circuits. Challenges exist at material interfaces due to interfacial contact resistances. Multiwall carbon nanotube (MWCNT) arrays are considered to be excellent candidates for use as thermal interface materials (TIMs) due to outstanding thermal/mechanical properties. In this work, MWCNT array TIMs are analyzed in aluminum and carbon fiber composites via flash diffusivity analysis. The effect of TIM thickness, areal/bulk density, surface cleanliness, and volumetric packing fraction; along with the effect of substrate finish and interfacial contact pressure on thermal performance are analyzed. Trends show the best TIMs possess low thickness, high bulk density and packing fraction, and clean surfaces. Pressure dramatically increases thermal performance after establishing contact, with diminishing returns from additional pressure. Diffusivities approaching 40 mm2/s and 0.65 mm2/s are recorded for aluminum and composite systems. Oxygen plasma etching and high temperature annealing (“Graphitizing”) are investigated as methods to remove amorphous carbon from array surfaces. Graphitized TIMs report diffusivity improvements up to 53.8%. Three methods of incorporating MWCNTs into composites are attempted for thermal/mechanical property enhancement. Conductance calculations show increasing diffusivity without increasing thickness enhances thermal performance in composites. MWCNTs for mechanical property enhancement produce no change, or detrimental effects.

Thesis (Ph.D.)--Mechanical Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Graham, Samuel; Committee Co-Chair: Nair, Sankar; Committee Member: Grover - Gallivan, Martha; Committee Member: McDowell, David; Committee Member: Schelling, Patrick; Committee Member: Zhang, Zhuomin

Capacitance manometer with sensors maintained at temperatures above the temperature of the vacuum vessel may read a higher gas pressure than the true value. This arises due to a transport process of molecules induced by molecule-surface collisions called thermal transpiration effect. Thermal transpiration effect depends on the pressure, the temperature gradient, gas, geometry and surface properties of the interconnecting pipe between the capacitance manometer and the vacuum vessel. To determine the height of the thermal transpiration effect for the biomolecular gas tetrahydrofuran, an experimental setup has been built. Its suitability to measure the thermal transpiration effect has been tested. Measurements of thermal transpiration effects for nitrogen and tetrahydrofuran have been analyzed with the semi-empirical Takaishi-Sensui equation. The coefficients of the Takaishi-Sensui equation can be used to determine the magnitude of the thermal transpiration effect for different temperature gradients, diameters of the interconnecting pipe and pressures.