Investigation of Performance Enhancements for a Liquid-Desiccant Solar Air-Conditioner

Thermally driven liquid-desiccant air-conditioners (LDAC) are a proven but still developing technology. LDACs can use a solar thermal system to reduce the operational cost and environmental impact of the system by reducing the amount of fuel (e.g. natural gas, propane, etc.) used to drive the system. LDACs also have a key benefit of being able to store energy in the form of concentrated desiccant storage. TRNSYS simulations were used to evaluate several different methods of improving the thermal and electrical coefficients of performance (COPt and COPe) and the solar fraction (SF) of a LDAC. The study analyzed a typical June to August cooling season in Toronto, Ontario. Utilizing properly sized, high-efficiency pumps increased the COPe to 3.67, an improvement of 55%. A new design, featuring a heat recovery ventilator on the scavenging-airstream and an energy recovery ventilator on the process-airstream, increased the COPt to 0.58, an improvement of 32%. This also improved the SF slightly to 54%, an increase of 8%. A new TRNSYS TYPE was created to model a stratified desiccant storage tank. Different volumes of desiccant were tested with a range of solar array system sizes. The largest storage tank coupled with the largest solar thermal array showed improvements of 64% in SF, increasing the value to 82%. The COPe was also improved by 17% and the COPt by 9%. When combining the heat recovery systems and the desiccant storage systems, the simulation results showed a 78% increase in COPe and 30% increase in COPt. A 77% improvement in SF and a 17% increase in total cooling rate were also predicted by the simulation. The total thermal energy consumed was 10% lower and the electrical consumption was 34% lower. The amount of non-renewable energy needed from the natural gas boiler was 77% lower. Comparisons were also made between LDACs and vapour-compression (VC) systems. Dependent on set-up, LDACs provided higher latent cooling rates and reduced electrical power consumption. Negatively, a thermal input was required for the LDAC systems but not for the VC systems.

Enhanced Nanoparticle Detection with Liquid Droplet Resonators

Whispering gallery mode particle sensing experiments are commonly performed with solid resonators, whereby the sensing volume is limited to the weak evanescent tail of the mode near the resonator surface. In this work we discuss in detail the sensitivity enhancements achievable in liquid droplet resonators wherein the stronger internal fields and convenient means of particle delivery can be exploited. Asymptotic formulae are derived for the relative resonance shift, line broadening and mode splitting of TE and TM modes in liquid droplet resonators. As a corollary the relative fraction of internal and external mode energy follows, which is shown to govern achievable sensitivity enhancements of solute concentration measurements in droplet sensors. Experimental measurements of nanoparticle concentration based on whispering gallery mode resonance broadening are also presented.

Design of Transparent Conducting Electrodes and Surface Relief Gratings for Plasmonic Polymer Solar Cells

As the concept of renewable energy becomes increasingly important in the modern society, a considerable amount of research has been conducted in the field of organic photovoltaics in recent years. Although organic solar cells generally have had lower efficiencies compared to silicon solar cells, they have the potential to be mass produced via solution processing. A common polymer solar cell architecture relies on the usage of P3HT (electron donor) and PCBM (electron acceptor) bulk heterojunction. One of the main issues with this configuration is that in order to compensate for the high exciton recombination rate, the photoactive layer is often made very thin (on the order of 100 $%). This results in low solar cell photocurrents due to low absorption. This thesis investigates a novel method of light trapping by coupling surface plasmons at the electrode interface via surface relief gratings, leading to EM field enhancements and increased photo absorption. Experimental work was first conducted on developing and optimizing a transparent electrode of the form &'()/+,/&'() to replace the traditional ITO electrode since the azopolymer gratings cannot withstand the high temperature processing of ITO films. It was determined that given the right thickness profiles and deposition conditions, the MAM stack can achieve transmittance and conductivity similar to ITO films. Experimental work was also conducted on the fabrication and characterization of surface relief gratings, as well as verification of the surface plasmon generation. Surface relief gratings were fabricated easily and accurately via laser interference lithography on photosensitive azopolymer films. Laser diffraction studies confirmed the grating pitch, which is dependent on the incident angle and wavelength of the writing beam. AFM experiments were conducted to determine the surface morphology of the gratings, before and after metallic film deposition. It was concluded that metallic film deposition does not significantly alter the grating morphologies.

Design of Transparent Conducting Electrodes and Surface Relief Gratings for Plasmonic Polymer Solar Cells

As the concept of renewable energy becomes increasingly important in the modern society, a considerable amount of research has been conducted in the field of organic photovoltaics in recent years. Although organic solar cells generally have had lower efficiencies compared to silicon solar cells, they have the potential to be mass produced via solution processing. A common polymer solar cell architecture relies on the usage of P3HT (electron donor) and PCBM (electron acceptor) bulk heterojunction. One of the main issues with this configuration is that in order to compensate for the high exciton recombination rate, the photoactive layer is often made very thin (on the order of 100 $%). This results in low solar cell photocurrents due to low absorption. This thesis investigates a novel method of light trapping by coupling surface plasmons at the electrode interface via surface relief gratings, leading to EM field enhancements and increased photo absorption. Experimental work was first conducted on developing and optimizing a transparent electrode of the form &'()/+,/&'() to replace the traditional ITO electrode since the azopolymer gratings cannot withstand the high temperature processing of ITO films. It was determined that given the right thickness profiles and deposition conditions, the MAM stack can achieve transmittance and conductivity similar to ITO films. Experimental work was also conducted on the fabrication and characterization of surface relief gratings, as well as verification of the surface plasmon generation. Surface relief gratings were fabricated easily and accurately via laser interference lithography on photosensitive azopolymer films. Laser diffraction studies confirmed the grating pitch, which is dependent on the incident angle and wavelength of the writing beam. AFM experiments were conducted to determine the surface morphology of the gratings, before and after metallic film deposition. It was concluded that metallic film deposition does not significantly alter the grating morphologies.

Linear Hyperspectral Unmixing Using L0-norm Approximations and Nonnegative Matrix Factorization

Spectral unmixing (SU) is a technique to characterize mixed pixels of the hyperspectral images measured by remote sensors. Most of the existing spectral unmixing algorithms are developed using the linear mixing models. Since the number of endmembers/materials present at each mixed pixel is normally scanty compared with the number of total endmembers (the dimension of spectral library), the problem becomes sparse. This thesis introduces sparse hyperspectral unmixing methods for the linear mixing model through two different scenarios. In the first scenario, the library of spectral signatures is assumed to be known and the main problem is to find the minimum number of endmembers under a reasonable small approximation error. Mathematically, the corresponding problem is called the $\ell_0$-norm problem which is NP-hard problem. Our main study for the first part of thesis is to find more accurate and reliable approximations of $\ell_0$-norm term and propose sparse unmixing methods via such approximations. The resulting methods are shown considerable improvements to reconstruct the fractional abundances of endmembers in comparison with state-of-the-art methods such as having lower reconstruction errors. In the second part of the thesis, the first scenario (i.e., dictionary-aided semiblind unmixing scheme) will be generalized as the blind unmixing scenario that the library of spectral signatures is also estimated. We apply the nonnegative matrix factorization (NMF) method for proposing new unmixing methods due to its noticeable supports such as considering the nonnegativity constraints of two decomposed matrices. Furthermore, we introduce new cost functions through some statistical and physical features of spectral signatures of materials (SSoM) and hyperspectral pixels such as the collaborative property of hyperspectral pixels and the mathematical representation of the concentrated energy of SSoM for the first few subbands. Finally, we introduce sparse unmixing methods for the blind scenario and evaluate the efficiency of the proposed methods via simulations over synthetic and real hyperspectral data sets. The results illustrate considerable enhancements to estimate the spectral library of materials and their fractional abundances such as smaller values of spectral angle distance (SAD) and abundance angle distance (AAD) as well.