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published_or_final_version / Real Estate and Construction / Master / Master of Science in Real Estate and Construction

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

 Drying process needs lots of energy and usually prone to high equipment and operational cost. Research tasks have focused on improving the drying performance and reducing the energy consumption rate. Among a number of industries, textile manufacturing needs the process intensively. It is surprising that little research has concerned principle enhancement and drying process design. In the support by Fong’s National Engineering Company Limited, a series of research that targeting to the inadequacy of technology development for machinery and process design have been conducted. The redevelopment of machinery design has based upon a heat setting machine –ECO dryer. The machine was used as a working platform to supply all necessary testing information before and after the enhancement. The ductwork and air distribution system design have been revised to improve the unevenness drying problems appeared in the heat setting of fabrics. Two main research scopes have been performed that included the development of a new duct sizing approach –Uniform Jet Velocity (UJV) and redesigning the air chambers. The proposed UJV approach is a new air duct design model developed from fluid dynamics principles. The air jet speed along each nozzle is maintained at a constant rate to provide a uniform jet impingement effect. A duct size algorithm was proposed to adjust the cross sectional area ratio between the main and branch streams for the target of producing a constant impingement velocity across the entire air duct. In the enhancement of the air distribution system design, Computational Fluid Dynamics (CFD) analytical approaches were used to model air flow patterns before and after the redesign of air chambers. The CFD analysis results told that a linear air distribution system with four sub-chamber design could produce the best air distribution pattern on the ECO dryer. The request of an accurate drying cycle time predication is also large in textile industry. It is because the problems of under-and over-drying usually happen in the jet impingement process. The second essential objective in the research is to develop systematical approaches for a good qualifying of a drying cycle. Four analytical models have been studied that included First order kinetics, Diffusion, model based on solutions of diffusion equation and Wet surface. An equation for each of the models was developed to describe the characteristics of a porous type fabric drying process. In the study, the required modeling parameters were empirically determined, and the accuracy among the models has been compared. Findings from the research have proved that the model based on solutions of diffusion equation can be the best strategy in presenting a drying cycle under different machine settings. The investigation has not ceased after the completion of the hot air jet impingement research. The study objectives have moved onto an alternative drying technology using steam as the drying medium. Due to many problems reported in the drying of yarn packages using electro-magnetic waves, moist heat drying technology is urgently needed. At the final part of the research, two CFD simulation models namely constant viscous resistance and increasing viscous resistance were studied. A preliminary result generated from ANSYS CFD analysis results was obtained that has opened up a new study area for further elaboration of a new drying technology, and hopefully can be practically applied to textile industry in the near future. / published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

The designs of three compact dual-band monopole antennas for wireless-local-area-network (WLAN)applications are presented. In these designs, an L-or U-shaped monopole element with microstrip-fed is used to generate a high-frequency band at around 5.5 GHz to cover the high WLAN bands at 5.2/5.8GHz for the IEEE 802.11a standard. An E-shaped element, loop element or meander-microstrip ground stub element with coupled-fed through the monopole element is used to generate a low-frequency band at around 2.4 GHz to cover the low WLAN band for the IEEE 802.11b/g standards. With such arrangements, the three antenna shave very compact radiators of only 11.3×8 mm2,12.6×9 mm2and11.8×9.4 mm2. To investigate the performances for practical uses, these antennas are also designed on a mobile-phone printed-circuit board and studied using computer simulation and measurement. Dual-band antennas with reconfigurable Dual-band antennas with reconfigurable lower band, higher band and dual-band are designed in this thesis. The dual-band antenna consists of two radiating branches generating the frequency bands at around 2.4 GHz and 3.5 GHz for the WiMAX system. Varactors are placed on the corresponding branches for continuously tuning of the operating bands for different WiMAX standards. For frequency tuning of the lower band or higher band, simple and novel DC biasing circuits without requiring any soldering wire are proposed to bias the varactor on a radiating element. While for simultaneous frequency tuning of the two individual bands, simple and novel DC biasing circuits requiring two soldering wires are proposed to bias the varactors on the radiating elements. Both simulation and measurement results show that the DC biasing circuits designed have very little affects on the antennas performances. The design of a monopole ultra-wide band (UWB)antenna with a reconfigurable notch band is presented. The antenna employs a vertical-ellipse radiator to achieve an UWB. A compact defected-ground structure (DGS)is used to create a notch band for the antenna. To frequency tune the notch band, a varactor is placed on the DGS to control the resonance frequency. The tuning performance, in terms of reflection coefficient, radiation pattern, efficiency and gain, of the antennais studied using simulation and measurement. Results show that the notch band can be tuned continuously from 5.2 to 6.32 GHz for the WLAN bands. In the measurement of a monopole antenna with a small ground plane, the feeding cable used to connect the antenna to the measurement equipment Satimo Starlab system causes discrepancies between the simulated and measured radiation patterns, efficiencies and peak gains at lower frequencies. In the designs of antennas in this thesis, the cable effects are studied by modeling the feeding cable using the EM simulation tool CST. Results show that, by using the cable model, the simulated and measured results agree very well. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

Organic solar cells (OSCs) have attracted intense attention in recent years due to their advantages of low cost, easy fabrication, and high flexibility compared to its inorganic counterparts. However, due to the conflicts between the short diffusion length of excitons and long absorption length of incident photons, the thickness of OSCs is typically thin, and thus power conversion efficiency (PCE) is generally lower than traditional silicon solar cells. Therefore, an exquisite design of light trapping schemes is essential to the PCE improvement. Generally, physical guideline of light trapping involves two main approaches: geometric optics methods and wave optics methods. The former aims at elongating optical path inside the photoactive layer and thus enhancing photon absorption. For organic thin film solar cells with typical active layer thickness of 100 nm-200 nm, which is in subwavelength scale, we cannot investigate light harvesting mechanism simply by the geometric optics methods and instead wave optics properties should be considered. In this thesis, two different light trapping enhancement designs are proposed. In order to simulate these structures, we built up programs for absorption power calculation based on scattering matrix method (SMM) by rigorously solving Maxwell’s equations. It is worth to point out that, different from the widely-used calculation method by Absorption = 1-Transmission-Reflection, our algorithm can extract the net optical absorption of the active layer rather than the whole OSCs. This improvement is very important because metal absorption, which does not contribute to exciton generation, can be excluded from the result. In Chapter 3, design of organic solar cell incorporating periodically arranged gradient type active layer is presented. This design can enhance light harvesting with patterned organic materials themselves (i.e. self-enhanced active layer design) to avoid degrading electrical performance in contrast to introducing inorganic concentrators into the active layers such as silicon and metallic nanostructures. Our numerical results show that the OSC with a self-enhanced active layer, compared with the conventional planar active layer configuration, has broadband and wide-angle range absorption enhancement due to better geometric impedance matching and prolonged optical path. In Chapter 4, OSC with interstitial lattice patterned metal nanoparticles (NPs) is proposed, which can improve the light blocking of traditional square lattice patterned NPs structure and achieve broadband absorption enhancement. Compared to square lattice design, the plasmonic mode couplings between individual NPs in the interstitial lattice are more versatile and much stronger. Moreover, plasmonic modes can couple to the guided modes, resulting in large enhancement factor at some wavelengths. These works provide a theoretical foundation and engineering reference for high performance OSC designs. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

abstract / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

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