This thesis presents a study on the optimization of friction pads, centered around a custom friction setup designed to enhance the operational efficiency of tube inspection robots. By surface texturing of Polydimethylsiloxane (PDMS) pads, inspired by the remarkable design of lizards' toes, this research pioneers the development of friction pads aimed at significantly elevating the adaptability and effectiveness of robotic systems in the challenging domain of industrial tube inspection. A cornerstone of this study is the novel friction setup, which has been carefully engineered to simulate real-world operational conditions with high precision. This custom-built apparatus, capable of exerting variable normal loads and accommodating diverse surface textures on curved pipe surfaces, has been instrumental in uncovering the intricate behavior of friction pads. Notably, the setup's capacity to measure forces on curved surfaces with a 6-axis load cell, providing critical insights into frictional forces in multiple directions, stands out as a pivotal contribution to the field. Through exhaustive experimentation facilitated by this advanced friction setup, the research has demonstrated that the design and texture of PDMS pads, particularly those featuring triangular grooves at a depth of 1 mm, markedly influence their frictional performance. These pads exhibit superior traction, especially under higher loads and on corroded surfaces, underscoring the importance of angular groove geometries in enhancing mechanical interlocking with surface irregularities. The inverse relationship observed between the coefficient of friction and applied normal force across various textures further highlights the nuanced mechanical behavior of PDMS friction pads under stress, accentuating the critical role of the custom friction setup in enabling these discoveries. This insight necessitates a refined approach to load application, ensuring optimal frictional engagement. This thesis not only advances the understanding of PDMS pad frictional behavior but also introduces a new frictional device testing method through its innovative friction setup. Future explorations will build on this foundation, probing the effects of different PDMS compositions, surface treatments, and environmental conditions on frictional performance, propelled by the capabilities of the custom friction setup.

The microelectronics industry is actively focusing on advanced packaging technologies, notably on three-dimensional stacking of heterogeneous integrated (3D-HI) circuits for enhanced performance. Despite its computational performance benefits, this approach faces challenges in thermal management due to increased power density and heat generation. Conventional cooling methods struggle to address this issue effectively. This study investigates microfluidic intralayer cooling techniques using analytical correlation and computational fluid dynamics (CFD) principles to propose a method capable of managing thermal performance across varying load conditions. The proposed configuration achieved a dissipation of 40 W/cm2 with a volumetric flow rate of 200 mL/min, maintaining chip temperature at 315K. Additionally, extreme hotspot conditions generating 1kW/cm2, along with the presence of thermal resistance from redistribution layers (RDLs), are analyzed. This research aims to establish a model for understanding geometric property variations under different heat flux conditions in 3D heterogeneous integration of semiconductor packaging.

The measurement of the radiation and convection that the human body experiences are important for ensuring safety in extreme heat conditions. The radiation from the surroundings on the human body is most often measured using globe or cylindrical radiometers. The large errors stemming from differences in internal and exterior temperatures and indirect estimation of convection can be resolved by simultaneously using three cylindrical radiometers (1 cm diameter, 9 cm height) with varying surface properties and internal heating. With three surface balances, the three unknowns (heat transfer coefficient, shortwave, and longwave radiation) can be solved for directly. As compared to integral radiation measurement technique, however, the bottom mounting using a wooden-dowel of the three-cylinder radiometers resulted in underestimated the total absorbed radiation. This first part of this thesis focuses on reducing the size of the three-cylinder radiometers and an alternative mounting that resolves the prior issues. In particular, the heat transfer coefficient in laminar wind tunnel with wind speed of 0.25 to 5 m/s is measured for six polished, heated cylinders with diameter of 1 cm and height of 1.5 to 9 cm mounted using a wooden dowel. For cylinders with height of 6 cm and above, the heat transfer coefficients are independent of the height and agree with the Hilpert correlation for infinitely long cylinder. Subsequently, a side-mounting for heated 6 cm tall cylinder with top and bottom metallic caps is developed and tested within the wind tunnel. The heat transfer coefficient is shown to be independent of the flow-side mounting and in agreement with the Hilpert correlation. The second part of this thesis explores feasibility of employing the three-cylinder concept to measuring all air-flow parameters relevant to human convection including mean wind speed, turbulence intensity and length scale. Heated cylinders with same surface properties but varying diameters are fabricated. Uniformity of their exterior temperature, which is fundamental to the three-cylinder anemometer concept, is tested during operation using infrared camera. To provide a lab-based method to measure convection from the cylinders in turbulent flow, several designs of turbulence-generating fractal grids are laser-cut and introduced into the wind tunnel.

Sweat evaporation is fundamental to human thermoregulation, yet our knowledge of the microscale sweat droplet evaporation dynamics is very limited. To study sweat droplet evaporation, a reliable way to measure sweat evaporation rate from skin and simultaneously image the droplet dynamics through midwave infrared thermography (MWIR) or optical coherence tomography (OCT) is required. Ventilated capsule is a common device employed for measuring sweat evaporation rates in physiological studies. However, existing designs of ventilated capsules with cylindrical flow chambers create unrealistic flow conditions that include flow separation and swirling. To address this problem, this thesis introduces a ventilated capsule with rectangular sweat evaporation area preceded by a diffuser section with geometry based on wind tunnel design guidelines. To allow for OCT or MWIR imaging, a provision to install an acrylic or a sapphire window directly over the exposed skin surface being measured is incorporated in the design. In addition to the capsule, a simplified artificial sweating surface that can supply water in a filmwise, single or multiple droplet form was developed. The performance of the capsule is demonstrated using the artificial sweating surface along with example MWIR imaging.

Human exposure to extreme heat is becoming more prevalent due to increasing urbanization and changing climate. In many extreme heat conditions, thermal radiation (from solar to emitted by the surrounding) is a significant contributor to heating the body, among other modes of heat transfer. Therefore, accurately measuring radiative heat flux on a human body is becoming increasingly important for calculating human thermal comfort and heat safety in extreme conditions. Most often, radiant heat exchange between the human body and surroundings is quantified using mean radiant temperature, T_mrt. This value is commonly measured using globe or cylindrical radiometers. It is based on radiation absorbed by the surface of the radiometer, which can be calculated using a surface energy balance involving both convection and emitted radiation at steady state. This convection must be accounted for and is accomplished using a traditional heat transfer coefficient correlation with measured wind speed. However, the utilized correlations are based on wind tunnel measurements and do not account for any turbulence present in the air. The latter can even double the heat transfer coefficient, so not accounting for it can introduce major errors in T_mrt. This Thesis focuses on the development, and testing of a cost-effective heated cylinder to directly measure the convection heat transfer coefficient in field conditions, which can be used for accounting convection in measuring T_mrt using a cylindrical radiometer. An Aluminum cylinder of similar dimensions as that of a cylindrical radiometer was heated using strip heaters, and the surface temperature readings were recorded to estimate the convection heat transfer coefficient, h. Various tests were conducted to test this concept. It was observed that heated cylinders take significantly less time to reach a steady state and respond to velocity change quicker than existing regular-sized globe thermometers. It was also shown that, for accurate estimation of h, it is required to measure the outer surface temperature than the center temperature. Furthermore, the value calculated matches well in range with classic correlations that include velocity, showing proof of concept.

Gallium based room-temperature liquid metals (LMs) have special properties such as metal-like high thermal conductivity while in the liquid state. They are suitable for many potential applications, including thermal interface materials, soft robotics, stretchable electronics, and biomedicine. However, their high density, high surface tension, high reactivity with other metals, and rapid oxidation restrict their applicability. This dissertation introduces two new types of materials, LM foams, and LM emulsions, that address many of these issues. The formation mechanisms, thermophysical properties, and example applications of the LM foams and emulsions are investigated.LM foams can be prepared by shear mixing the bulk LM in air using an impeller. The surface oxide layer is sheared and internalized into the bulk LM as crumpled oxide flakes during this process. After a critical amount of oxide flakes is internalized, they start to stabilize air bubbles by encapsulating and oxide-bridging. This mechanism enables the fabrication of a LM foam with improved properties and better spreadability. LM emulsions can be prepared by mixing the LM foam with a secondary liquid such as silicone oil (SO). By tuning a few factors such as viscosity of the secondary liquid, composition, and mixing duration, the thermophysical properties of the emulsion can be controlled. These emulsions have a lower density, better spreadability, and unlike the original LM and LM foam, they do not induce corrosion of other metals. LM emulsions can form by two possible mechanisms, first by the secondary liquid replacing air features in the existing foam pores (replacement mechanism) and second by creating additional liquid features within the LM foam (addition mechanism). The latter mechanism requires significant oxide growth and therefore requires presence of oxygen in the environment. The dominant mechanism can therefore be distinguished by mixing LM foam with the SO in air and oxygen-free environments. Additionally, a comprehensive analysis of foam-to-emulsion density change, multiscale imaging and surface wettability confirm that addition mechanism dominates the emulsion formation. These results provide insight into fundamental processes underlying LM foams and emulsions, and they set up a foundation for preparing LM emulsions with a wide range of fluids and controllable properties.

Spray flows are important in a myriad of practical applications including fuel injection, ink-jet printing, agricultural sprays, and industrial processes. Two-phase sprays find particular use for spot cooling applications with high heat fluxes as in casting processes and power electronics. Computability of sprays in a cost-effective manner provides a path to optimize the design of nozzles to tune the spray characteristics for the needs of a particular application. Significant research has so far been devoted to understand and characterize spray flows better, be it from a theoretical, experimental or computational standpoint. The current thesis discusses a methodology for modeling primary atomization using the Quadratic Formula which is derived from an integral formulation of the governing equations. The framework is then applied to different examples of flat-fan hydraulic sprays. For each case, the spray is first resolved as a continuous fluid using the volume of fluid method. Atomization criterion is then applied to the velocity flow-field to determine the sites for primary atomization. At each site, local diameters for particle injection is determined using the quadratic formula. The trajectory of injected particles are then monitored through a particle tracking algorithm. The results from the numerical analysis are compared with experimental data to validate the computational framework.

The objective of this dissertation is to study the optical and radiative properties of inhomogeneous metallic structures. In the ongoing search for new materials with tunable optical characteristics, porous metals and nanowires provides an extensive design space to engineer its optical response based on the morphology-dependent phenomena.This dissertation firstly discusses the use of aluminum nanopillar array on a quartz substrate as spectrally selective optical filter with narrowband transmission for thermophotovoltaic systems. The narrow-band transmission enhancement is attributed to the magnetic polariton resonance between neighboring aluminum nanopillars. Tuning of the resonance wavelengths for selective filters was achieved by changing the nanopillar geometry. It concludes by showing improved efficiency of Gallium-Antimonide thermophotovoltaic system by coupling the designed filter with the cell. Next, isotropic nanoporous gold films are investigated for applications in energy conversion and three-dimensional laser printing. The fabricated nanoporous gold samples are characterized by scanning electron microscopy, and the spectral hemispherical reflectance is measured with an integrating sphere. The effective isotropic optical constants of nanoporous gold with varying pore volume fraction are modeled using the Bruggeman effective medium theory. Nanoporous gold are metastable and to understand its temperature dependent optical properties, a lab-scale fiber-based optical spectrometer setup is developed to characterize the in-situ specular reflectance of nanoporous gold thin films at temperatures ranging from 25 to 500 oC. The in-situ and the ex-situ measurements suggest that the ii specular, diffuse, and hemispherical reflectance varies as a function of temperature due to the morphology (ligament diameter) change observed. The dissertation continues with modeling and measurements of the radiative properties of porous powders. The study shows the enhanced absorption by mixing porous copper to copper powder. This is important from the viewpoint of scalability to get end products such as sheets and tubes with the requirement of high absorptance that can be produced through three-dimensional printing. Finally, the dissertation concludes with recommendations on the methods to fabricate the suggested optical filters to improve thermophotovoltaic system efficiencies. The results presented in this dissertation will facilitate not only the manufacturing of materials but also the promising applications in solar thermal energy and optical systems.

Windows are one of the most significant locations of heat transfer through a building envelope. In warm climates, it is important that heat gain through windows is minimized. Heat transfer through a window glazing occurs by all major forms of heat transfer (convection, conduction, and radiation). Convection and conduction effects can be limited by manipulating the thermal properties of a window’s construction. However, radiation heat transfer into a building will always occur if a window glazing is visibly transparent. In an effort to reduce heat gain through the building envelope, a window glazing can be designed with spectrally selective properties. These spectrally selective glazings would possess high reflectivity in the near-infrared (NIR) regime (to prevent solar heat gain) and high emissivity in the atmospheric window, 8-13μm (to take advantage of the radiative sky cooling effect). The objective of this thesis is to provide a comprehensive study of the thermal performance of a visibly transparent, high-emissivity glass window. This research proposes a window constructed by coating soda lime glass in a dual layer consisting of Indium Tin Oxide (ITO) and Polyvinyl Fluoride (PVF) film. The optical properties of this experimental glazing were measured and demonstrated high reflectivity in the NIR regime and high emissivity in the atmospheric window. Outdoor field tests were performed to experimentally evaluate the glazing’s thermal performance. The thermal performance was assessed by utilizing an experimental setup intended to mimic a building with a skylight. The proposed glazing experimentally demonstrated reduced indoor air temperatures compared to bare glass, ITO coated glass, and PVF coated glass. A theoretical heat transfer model was developed to validate the experimental results. The results of the theoretical and experimental models showed good agreement. On average, the theoretical model demonstrated 0.44% percent error during the daytime and 0.52% percent error during the nighttime when compared to the experimentally measured temperature values.

The thermal conductivity of cadmium sulfide (CdS) colloidal nanocrystals (NCs) and magic-sized clusters (MSCs) have been investigated in this work. It is well documented in the literature that the thermal conductivity of colloidal nanocrystal assemblies decreases as diameter decreases. However, the extrapolation of this size dependence does not apply to magic-sized clusters. Magic-sized clusters have an anomalously high thermal conductivity relative to the extrapolated size-dependence trend line for the colloidal nanocrystals. This anomalously high thermal conductivity could probably result from the monodispersity of magic-sized clusters. To support this conjecture, a method of deliberately eliminating the monodispersity of MSCs by mixing them with colloidal nanocrystals was performed. Experiment results showed that mixtures of nanocrystals and MSCs have a lower thermal conductivity that falls approximately on the extrapolated trendline for colloidal nanocrystal thermal conductivity as a function of size.