The use of bioenergy has been increasing due to efforts in fossil fuels replacement. Modern bioenergy technologies aim for high efficiency and low pollution levels, which increases the need for methods for the on-line characterization of biofuels. Dielectric methods have been identified as useful for the sensing of solid biofuels because they allow for rapid, nonhazardous, nondestructive, and bulk determination of material properties. The dielectric properties describe the interaction between the material and the electromagnetic waves. Dielectric properties are intrinsic of the materials and can therefore be used for the development of prediction models that can be applied regardless of the measurement technique. The study of the dielectric properties is also important as it improves the understanding of the dielectric behavior of the materials. This thesis focuses on the dielectric properties of solid biofuels and their use in the characterization of these materials. The work presented includes the development of new methods permitting the determination of the dielectric properties of solid biofuels with large particle size (waveguide method), broadband measurement of the dielectric properties (coaxial-line probe), and the use of a previously developed method for the accurate determination of the dielectric properties (free-space method). The results includes the dielectric properties of solid biofuels and their dependence on parameters such as frequency, moisture, density, and temperature. This thesis also presents semi-theoretical models for the determination of moisture content, which obtained a RMSEP of 4% for moisture contents between 34 and 67%, and an empirical model that resulted in a RMSEC of 0.3% for moisture contents between 4 and 13%. Finally, this thesis includes measurements of the influence of salt content on the dielectric properties and a discussion of its use for estimation of the ash content of solid biofuels. 

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To improve the MixAlco process and biomass pretreatment, five studies were conducted. Three studies related to fermentation, whereas the other two investigated the effectiveness of shock tube pretreatment (STP) coupled with oxidative lime pretreatment (OLP). In the first study, the constant-selectivity assumption used in the continuum particle distribution model (CPDM) was determined to be invalid. During a 32-day batch fermentation, selectivity increased from 0.10 to 0.40 g acid/g non-acid volatile solid (NAVS) digested. Future revisions to CPDM should incorporate a non-constant selectivity term. In the second study, a revised procedure was developed to provide a more accurate determination of moisture content. Conventional drying at 105 degrees C allowed product acids to vaporize with water, which introduced errors. Using the revised procedure, calcium hydroxide or sodium hydroxide was added to samples at a concentration of 0.01 g base/g sample, which retained acids in the sample. The mass of additional retained material closely matched that of the additional retained acid. Three related studies involving biomass pretreatment were performed. In the first, recommended parameters for pretreating sugarcane bagasse with OLP and STP were determined. Recommended OLP parameters were 130 degrees C, 6.9-bar O2, and 2-h duration. The effects of solids concentration, liquid fill volume, particle size, type of shotgun shell, number of shocks, and pretreatment order were investigated. Liquid fill volume, particle size, type of shotgun shell, and pretreatment order were significant variables, whereas solids concentration and number of shocks were not. Recommended OLP parameters were used as a basis for an additional experiment. To simulate industrial-scale pile fermentation, fixed-bed batch fermentation of OLP + STP sugarcane bagasse was performed in 1-L PVC fermentors. Rubber mulch was used as a structural support material to prevent filter plugging, which had been reported in previous work. After 42 d, acid concentration reached 8 g/L with yield approximately 0.1 g acid/g NAVS fed. Poor fermentation performance was caused by short solid-liquid contact time and poor pH control. A third biomass pretreatment experiment investigated the potential of pretreated corn stover as a potential ruminant feed. Five samples (raw, OLP, STP, OLP + STP, and STP + OLP) were analyzed for composition and in vitro digestibility. STP followed by OLP increased neutral detergent fiber (NDF) digestibility from 49.3 to 79.0 g NDF digested/100 g NDF fed. On an organic matter basis, STP + OLP corn stover plus water-soluble extractives had a total digestible nutrients (TDN) of 74.9, nearly reaching corn grain at 88.1.

The Plastic Ball Grid Array (PBGA) package and flip-chip technology have been widely used in the microelectronics industry. However, due to the effect of hygroscopic and thermal stresses, the reliability is still of concern during manufacturing and operation, especially for the thermal-mechanical behavior of its corresponding interfaces. Influences of the storage conditions and reflow parameters on the warpage of the PBGA package are investigated in this study first. As the results, the warpage reflected the interaction of the extent of moisture absorption and the change in reflow parameters significantly. Furthermore, a critical relative moisture absorption between 0.25% and 0.30% is found for a considerable warpage response. Next, this study presents an experimental investigation of the adhesion strength of epoxy-based encapsulant material to solder mask coated FR-4 substrate under thermal cycling. Effects of the number of thermal cycles on the interfacial strength are investigated by using button shear test. The relationship between the interfacial strength and thickness of solder mask is also examined. Moreover, to characterize the degradation and fracture behavior, the morphologies of fractured surfaces of the test specimens are analyzed by scanning electron microscopy. The results of this experiment show that the interfacial strength of the epoxy-based encapsulant/solder mask/substrate joint is apparently reduced by thermal fatigue. And, the test specimen with larger solder mask thickness has higher interfacial strength. Finally, the single-lap joint test, nonlinear finite element analysis and Moiré interferometry are employed to obtain strain/stress distributions on the interface of solder mask and substrate. The effects of solder mask thickness and overlap length are then determined, separately. The results of this study can afford important information for characterizing the features of moisture absorption, warpage and interfacial adhesion of PBGA packages. Furthermore, it can be helpful to identify improvements required in reliability of the package design.

Abstract¡G The main aim of this paper is to utilizing the Shadow Moirè method to study the moisture effect on the warpage of PBGA IC package under the IR-reflow process. An environmental controlled box is designed and built. Three combinations of different moisture and temperature status are chosen for the purpose of study. The result shows that the moisture and temperature change do yielding the change of the warpage of the IC package.

The main objective of this paper is to utilizing the Shadow Moiré method to study the effect of IR-reflow Condition Variations on the warpage of PBGA Packages. Two combinations of different moisture and temperature status are also chosen for the purpose of the study. The result shows that the first peak temperature is the most effective variable on the warpage of PBGA packages under the IR-reflow process.

Moisture damage in asphalt mixes can be defined as loss of strength and durability due to the presence of moisture at the binder-aggregate interface (adhesive failure) or within the binder (cohesive failure). This research focuses on the evaluation of the susceptibility of aggregates and asphalts to moisture damage through understanding the micro-mechanisms that influence the adhesive bond between aggregates and asphalt and the cohesive strength and durability of the binder. Moisture damage susceptibility is assessed using surface energy measurements and dynamic mechanical analysis (DMA). Surface energy is defined as the energy needed to create a new unit surface area of material in vacuum condition. Surface energy measurements are used to compute the adhesive bond strength between the aggregates and asphalt and cohesive bond strength in the binder. DMA testing is used to evaluate the rate of damage accumulation in asphalt binders and mastics. The DMA applies a cyclic, torsional strain controlled loading to cylindrical asphalt mastics until failure. The DMA results are analyzed using continuum damage mechanics that focuses on separating the energy expended in damaging the material from that associated with viscoelastic deformation. A new approach is developed to analyze the DMA results and calculate the rate of damage. The developed approach is used to evaluate six asphalt mixtures which have performed either well or poorly in the field. The resistance of the field mixes to moisture damage is shown to be related to the calculations of bind energies and the accumulated damage in the DMA.

Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references (leaves 471-490). Also available in electronic version. Access restricted to campus users.

Thesis (M. Phil.)--University of Hong Kong, 1984.

The use of soil cement as a growth medium was examined in this study. During the monitoring, green soil cement revealed diverse ecological values. The survival rates of plants in each soil conditions were higher than 80%,which was very promising. Furthermore, the survival rates dropped when the soil density reached95%, which means soil density might influence the survival rate of plant. Plant growth rates in sandy soil were higher than that in soil cement. In particular, low soil density facilitated plant growth in sandy soil, whereas density effect was not clear to plant growth performance in soil cement. Experiments were undertaken to study the soil-water characteristics of sandy soil and soil cement in field and laboratory condition. The influence of vegetation and material density on the development of negative pore water pressure (PWP) and degree of saturation (Sr) in the studied materials was investigated. The field planting experiments proved a promising survival rate of Schefflera heptaphylla in both types of materials while sandy soil promoted better growth of the seedlings than the soil cement. From the field study, PWP and Sr of sandy soil responded noticeably and promptly to natural drying and wetting cycles. However, the responses in soil cement were relatively mild. When subjected to the same drying-wetting cycles, PWP responded more slowly and to a smaller magnitude compared with that of soil cement. In addition, Sr changed little in soil cement. An increase in the density of the sandy soil promoted rapid development of negative PWP, while an opposite trend was observed for soil cement. Attempts have been made to explain the observations from the perspectives of material permeability and change in water content during a drying period in both soil types. Furthermore, in sandy soil, the development of PWP (with a measurement limit of -90 kPa) was minimally affected by the presence of vegetation, while vegetation noticeably helped the development of negative PWP in the soil cement. Bounds of the soil-water characteristic curve of the studied materials were presented based on estimates from the drying and wetting scanning curves derived from the field monitoring. A complementary laboratory study was carried out in an environmental chamber with controllable temperature and humidity. Monitoring results from the laboratory agreed well with that obtained from the field. / published_or_final_version / Civil Engineering / Master / Master of Philosophy