Polyimide thin films have been widely used in microelectronic and Micro-Electro-Mechanical System applications due to their many excellent characteristics including low dielectric constant, easy processing, good step coverage ability, high heat resistance and chemical resistance. This paper presents the design, fabrication and complete characterization of an innovative capacitive relative humidity (RH) microsensor. The double polyimide thin films adopted in this study function as a capacitance sensing layer and a protecting layer of top electrodes respectively. To improve the humidity sensitivity and responding speed, interlacing out-of-plane electrodes are designed in the RH microsensor. The higher sensitivity ( 1.25 pF/¢HRH ), optimized sensing linearity ( 99.968¢H ) , very low hysteresis ( 0.24 ¢HRH ), excellent stability ( 1.36 ¢HRH ) , high accuracy ( ¡Ó 1.12 ¢HRH ) and fast response ( within 1 seconds ) characteristics of the RH microsensor have been demonstrated in this thesis.

<p>The role of nitric acid (HNO₃) on the atmospheric corrosion of metals has so far received little or no attention. However, the last decades of decreasing sulphur dioxide (SO₂) levels and unchanged HNO₃ levels in many industrialized countries have resulted in an increased interest in possible HNO₃-induced atmospheric corrosion effects. In this study a new method was developed for studying the corrosion effects of HNO₃ on metals at well-defined laboratory exposure conditions. The method has enabled studies to be performed on the influence of individual exposure parameters, namely HNO₃-concentration, air velocity, temperature and relative humidity, as well as comparisons with newly generated field exposure data.</p><p>The corrosion rate and deposition rate of HNO₃ on copper was shown to follow a linear increase with HNO3 concentration. The deposition velocity (Vd) of HNO₃ increased up to an air velocity of 11.8 cm s^-1. Only at a higher air velocity (35.4 cm s^-1) the Vd on copper was lower than the Vd on an ideal absorbent, implying the Vd of HNO3 at lower air velocities to be mass-transport limited.</p><p>Within the investigated temperature range of 15 to 35 ºC only a minor decrease in the HNO₃-induced copper corrosion rate could be observed. The effect of relative humidity (RH) was more evident. Already at 20 % RH a significant corrosion rate could be measured and at 65 % RH the Vd of HNO₃ on copper, zinc and carbon steel reached maximum and nearly ideal absorption conditions.</p><p>During identical exposure conditions in HNO_3-containing atmosphere, the corrosion rate of carbon steel was nearly three times higher than that of copper and zinc. The HNO₃-induced corrosion effect of copper, zinc and steel turned out to be significantly higher than that induced by SO2 alone or in combination with either NO₂ or O₃. This is mainly attributed to the much higher water solubility and reactivity of HNO3 compared to SO₂, NO₂ and O_3. Relative to SO₂, zinc exhibits the highest sensitivity to HNO₃, followed by copper, and carbon steel with the lowest sensitivity.</p><p>Extrapolation of laboratory data to an assumed average outdoor wind velocity of 3.6 m s-1 enabled a good comparison with field data. Despite the fact that ambient SO₂ levels are still much higher than HNO₃ levels, the results show that HNO₃ plays a significant role for the atmospheric corrosion of copper and zinc, but not for carbon steel. The results generated within this doctoral study emphasize the importance of further research on the influence of HNO₃ on degradation of other materials, e.g. stone and glass, as well as of other metals. </p>

This study considers airflow simulations to evaluate the impact of different window air-conditioner locations on the thermal comfort in an office room (OR). This thesis compares the air distribution for an office room by using computational fluid dynamics (CFD) modeling to previously studied rooms. The air distribution was modeled on a typical office room window air conditioning unit, air supply from a high pressure on the top and the low pressure exhaust on the bottom considering the existing manufacturing ratios for surface areas. The discharge angle for the supply grill of the AC unit was varied from 20 to 40 degrees. The position of the air conditioner was also varied and studied at 60%, 75% and 90% of the total height of the room. In addition, the location of the occupant within the office room was varied, two locations were studied, one where the occupant is far from the unit and the other to closer to the AC unit at the middle of the room. Predictions of the air movement, room temperature, room relative humidity, comfort level, and distribution of contaminants within the office room are shown. Analysis of these simulations is discussed. Energy estimations are also performed and evaluated. The positions of the air-conditioner unit, the inlet angle and the occupant position in the office room have shown to have an important impact on supply controlling air quality and thermal comfort. Results are in good agreements with the experimental data.The primary function of a HVAC (heating refrigerating and air conditioning) system is the generation and maintenance of comfort for occupants in a conditioned space [1]. This work also provides a detailed analysis of three-dimensional mixed convective flow induced by a window air conditioning system. Using a three dimensional CFD simulation, several characteristics of human comfort are analyzed.

Prestressed concrete piles are commonly used to support over-water highway bridges in marine environments. The reinforcing steel within will ultimately be degraded via corrosion damage due to the penetration of chloride ions from sea water. The service life of these structures is, in part, dictated by the time required to diffuse chloride ions through the concrete cover and subsequently corrode the steel. Therefore, by slowing the rate of diffusion or increasing the chloride threshold of the steel (or both) an increased service life can be expected. This thesis focuses on the latter whereby stainless steel reinforcing alternatives were investigated to elevate the chloride threshold before corrosion begins. The designation "stainless" steel implies corrosion resistance. However, corrosion resistance in itself is not a sufficient condition to make it a suitable alternative for prestressed concrete applications. In this study, the corrosion susceptibility of stainless steel alloys was scrutinized with the understanding that high strength stainless steels are vulnerable to stress corrosion cracking (SCC). This investigation screened three candidate alloys that span the norms of stainless steel compositions: a common austenitic stainless steel with high nickel content (316L), a less common austenitic stainless steel with low nickel but high manganese (XM 29), and a duplex stainless steel with high chromium and an additional constituent, molybdenum (2205). Each alloy was subjected to two stress conditions imposed by varied mechanical fixtures then subjected to various forms of high chloride concentrations. The pH of these conditions was also varied and in one case simulated the high pH common to concrete pore water solutions. Elevated temperatures were used to accelerate the effects of these exposures. Results of Phase 1 showed that for exposure at 135oC (275oF) cracking of alloys 316 L and 2205 occurred after 1 hour while XM29 experience cracking after 24 hours. At 90oC (194oF) alloy 316L cracked after 4 hours; XM29 did not crack after 96 hours while 2205 did crack after 96 hours. The results were interpreted with an Arrhenius relationship between time to cracking and test temperature to extrapolate toward the anticipated service regime. Results of Phase 2 showed that SCC was less likely to initiate in high pH conditions than in low pH conditions at typical marine environment temperatures and chloride concentration. In these limited tests the SCC performance of XM29 was better relative to that of the other two alloys.

Percent Moisture Content (MC %) of wood is defined to be the weight of the moisture in the wood divided by the weight of the dry wood times 100%. Equilibrium Moisture Content (EMC), moisture content at environmental equilibrium is a very important metric affecting the performance of wood in many applications. For best performance in many applications, the goal is to maintain this value between 6% and 8%. EMC value is a function of the temperature and the relative humidity of the surrounding air of wood. It is very important to maintain this value while processing, storing or finishing the wood. This thesis develops a special purpose sensor and processor system to be implemented as a small hand-held device used to sense, calculate and display the value of EMC of wood depending on surrounding environmental conditions. Wood processing industry personnel would use the hand-held EMC calculating and display device to prevent many potential problems that can show significant affect on the performance of wood. The design of the EMC device requires the use of sensors to obtain the required inputs of temperature and relative humidity. In this thesis various market available sensors are compared and appropriate sensor is chosen for the design. The calculation of EMC requires many arithmetic operations with stringent precision requirements. Various arithmetic algorithms and systems are compared in terms of meeting required arithmetic functionality, precision requirements, and silicon implementation area and gate count, and a suitable choice is made. The resulting processor organization and design is coded in VHDL using the Xilinx ISE 6.2.03i tool set. The design is synthesized, validated via VHDL virtual prototype simulation, and implemented to a Xilinx Spartan2E FPGA for experimental hardware prototype testing and evaluation. It is tested over various ranges of temperature and relative humidity. Comparison of experimentally calculated EMC values with the theoretical values of EMC derived for corresponding temperature and relative humidity points resulted in validation of the EMC processor architecture, functional performance and arithmetic precision requirements.

Significant variability in cured leaf tobacco-specific nitrosamine (TSNA) content is commonly observed when sampling within dark air-curing barns. This variability may be due to inconsistency in the curing environment within different areas of the barn. A study was initiated in 2012 through support from a CORESTA Study Grant to evaluate if leaf TSNA content is related to microenvironmental conditions in the barn. Seed screened for low conversion of nicotine to nornicotine (sc) and high converter (HC) selections of TR Madole dark tobacco were cured in barns near Princeton and Lexington, Kentucky in 2012 and 2013. Temperature and relative humidity were measured with data loggers placed at 27 locations within each barn for the duration of curing. TSNA content was determined from 20-leaf samples collected from each selection at each of the 27 locations within each barn. There were no significant effects of individual data logger placement in either variety selection on hours above 24°C temperature, hours above 80% relative humidity, or TSNA; therefore, we investigated these data within 3-dimensional aspects of tier, room, and bent within each barn. There were various effects of tier, room, and bent on temperature, relative humidity, and TSNA; but limited significant relationships between temperature, relative humidity, and TSNA.

Interactions of colloidal particles with surfaces occur in natural and engineered systems, and they influence the transport of contaminants through diffusion, aggregation, filtration, and sedimentation. To quantify the transport and fate of colloidal particles and their influence on environmental systems, it is important to understand their interactions with surfaces. These interactions are influenced by physical and chemical surface properties such as hydrophobicity, charge density, and roughness, as well as environmental conditions such as relative humidity (RH). In atmospheric systems, RH induces the capillary force and also influences the contributions of van der Waals and electrostatic forces. To investigate the role of surface properties and RH in the interaction of colloidal particles with surfaces, atomic force microscopy was employed to measure the adhesion and friction forces of colloidal particles including Bacillus thuringiensis spores, silica, and gold at various experimental conditions with several types of surfaces including mica, silica, and radioactive gold. Contributions to the adhesion force by van der Waals, capillary, and electrostatic forces were theoretically calculated and compared to measured forces. Through experimental results and theoretical studies, it was identified how surface properties of interacting surfaces and experimental conditions influence the interfacial interactions of colloidal particles in atmospheric systems. The role of RH in adhesion and friction depends on the hydrophobicity or contact angles of interacting surfaces and surface roughness. Relative humidity also influences the contribution of electrostatic force to the total adhesion force by screening the strength of surface potential or providing a passage for charge leakage. The results of this thesis provide a better understanding of particulate processes that are influenced by the interactions of colloidal particles with surfaces and can be useful in monitoring and control of contamination in atmospheric systems.

Electrostatic charge generation in gas-solid fluidized beds is a significant industrial problem. Associated problems include particle agglomeration and particle wall fouling. In the polymerization industry this may result in "sheets" of fused polymer, due to exothermic reaction causing the melting of the polymer, which can fall off and block the distributor plate disrupting fluidizing gas flow. Additionally, blockage of the catalyst feed or the polymer removal system can take place or the product can become non-uniform. All of these problems require shut-down of the reactor which results in lost production time. While this phenomena has been identified for many years, the mechanisms involved are not well understood, especially wall fouling and the distribution of charge within the bed. Isolation of individual parameters such as hydrodynamics, operating conditions, and material involved is necessary to evaluate how each parameter impacts charge generation during fluidization. In this thesis, the fluidization system consisted of a stainless steel column, two online Faraday cups, and a retractable distributor plate. This system allowed for the simultaneous measurement of charge within different regions of the bed: the entrained fine particles, the particles adhered to the column wall, and the bulk of the bed. Additionally, mass and particle size distributions were measured and images of the layer of particles adhered to the column wall were taken for comparison. This allowed for a charge distribution comparison and evaluation of wall fouling. Three different parameters were investigated: duration of fluidization, column wall material, and relative humidity of fluidizing gas. Fluidization time was studied for 15, 30, 60, 120, 180, and 360 min; relative humidity was investigated for 0%, 20%, 40%, 60%, and 80% relative humidity. Both fluidization time and relative humidity were evaluated at four different fluidization gas velocities, two each in the bubbling and slugging flow regimes. Column wall material was evaluated for a stainless steel and carbon steel column at two gas velocities, one each in the bubbling and slugging flow regimes. Fluidization time was found to influence wall fouling in the bubbling flow regime as the particle layer continued to build as fluidization progressed. In the slugging flow regime, the particle layer developed within 15 minutes of the onset of fluidization. The bubbling flow regime was shown to have a greater capacity for charge generation than the slugging flow regime. This was due to the vigorous mixing in the bubbling flow regime resulting in more particle-particle interactions. Column wall material was shown to influence wall fouling in the slugging flow regime due to the differences in surface roughness of the columns. This was due to the particle-wall contacts resulting in frictional charging which is the predominant charging mechanism in this flow regime. Charge was also impacted in the bubbling flow regime in those particles that were adhered to the column wall. Relative humidity was found to influence wall fouling at the lowest gas velocity tested. However, variations in generation of charge occurred at all fluidization gas velocities tested; the charge-to-mass ratios for the particles adhered to the column wall in the slugging flow regime decreased with high relative humidities. This was due to either the formation of a water film layer on the column wall or instantaneous surface water films on the particles throughout fluidization.

Fibre-optic sensing techniques for application in polymer electrolyte fuel cells (PEMFC) are presented in this thesis. Temperature, relative humidity (RH) and air-water two-phase flow sensors are developed and demonstrated based on optical fibre Bragg gratings (FBG). Bragg gratings offer the following characteristics that warrant their development for application in PEMFCs: small size, environmental compatibility and the possibility of multiplexed multi-parameter sensing. Contributions of this work are in novel sensor development and implementation strategies. Important installation design considerations include the sensor proximity to the catalyst layer, sensor strain relief and minimal bending of the fibre. With these considerations, the dynamic and steady-state performance of FBG temperature sensors distributed throughout the flow-field of a single cell PEMFC was validated with a co-located micro-thermocouple. In the development of FBGs for in situ measurement of relative humidity, a polyimide-coated FBG based RH sensor is presented with significantly improved response time and sensitivity over previously reported designs. The RH inside a PEMFC under transient operating conditions is monitored. Step increases in current induce significantly larger increases in RH near the outlet than near the inlet of the cell, and associated transients within the fuel cell are found on a time scale approaching the sensor response time. Finally, to complete the suite of FBG sensors for water management in PEMFCs, an evanescent field based FBG sensor embedded in a microchannel for the measurement of two-phase flow dynamics is presented. Using high speed video for validation, it is established that the novel sensor enables the measurement of droplet average velocity and size in flow regimes representative of an operating fuel cell. / Graduate

The objective of the present project was to develop and evaluate a solution forstorage of textiles in humid indoor environments, in this case churches. The proposed solution is based on creating a microclimate in the storage cabinets separated from the rest of the building. The cabinets were made air tight and insulated. With the use of a simple control system for conservation heating, the relative humidity can be kept below dangerous levels. The project comprises development and evaluation of textile cabinets in three churches on Gotland, Sweden. Measurements over one year show that cabinets with climate control are a simple and reliable method to prevent mould growth. Overall, the control systems have worked according to expectations. The relative humidity and temperature in the cabinets was maintained within a safe interval.