Desiccant-enhanced air conditioning equipment has exhibited both the capability to improve humidity control and the potential to save energy costs by lowering the latent energy requirement of the supply air stream. The resulting increasing popularity of desiccant-enhanced air conditioning systems has sparked new interest in the search for a better, more efficient desiccant material. The ultimate goal of this research was to develop a material that, when applied to an existing air-to-air heat exchanger, would achieve the necessary heat and mass transfer in a single process, thus transforming a sensible heat exchanger into a total enthalpy exchanger. This study focuses on the development and determination of appropriate polymeric desiccant materials for use in different heat and mass transfer applications. Various candidate materials were initially studied. It was decided that polyvinyl alcohol best met the pre-determined selection criteria. After the focus material was chosen, numerical models representing two heat and mass transfer applications were created. One-dimensional numerical models were developed for the performance studies of a rotary wheel total enthalpy exchanger. A two-dimensional numerical model was developed for the performance studies of a fixed plate total enthalpy exchanger as well. Material characterization tests were performed to collect material property information required by the numerical models. Sensible, latent, and total efficiencies gathered from both the rotary wheel total enthalpy exchanger and the fixed plate total enthalpy exchanger models indicate potential uses for some candidate polyvinyl alcohol materials. / Master of Science

In this thesis, several possible liquid desiccants (aqueous solutions of LiCl, LiBr, MgCl2 and CaCl2) are investigated to find the most appropriate working fluid to be used in a run-around membrane energy exchanger (RAMEE). The liquid desiccant is one of the main components of the RAMEE and indirectly conditions the outdoor ventilation air by using the energy of the exhaust air, significantly reducing the building energy consumption.<p> Numerical simulations, in this thesis, show that the total effectiveness of the RAMEE changes less than 0.5% when different salt solutions are used. However, the capital and operational costs of the RAMEE are significantly different for different desiccants. MgCl2 is the most inexpensive among the selected salt solutions and is followed by CaCl2, LiBr and LiCl. The price of a LiCl solution in the RAMEE is almost 20 times more than the price of MgCl2 solution. Different thermo-physical properties of the salt solutions result in different pumping energy consumptions for each specific salt solution. For example, the pumping energy consumption for a MgCl2 solution is 3.5 times more than for a LiBr solution in the RAMEE. The change in the volume of the liquid desiccant throughout a year is another characteristic which depends on the thermo-physical properties of the salt solution. Solutions with larger volume expansion require larger storage tanks and will experience longer transient delays. The difference between the volume expansions of different salt solutions is less than 5% of the total solution volume. MgCl2 solution expands more than 17% throughout a yearly operation of the system in Saskatoon.<p> Crystallization of the salt solution is another important parameter in the selection of the liquid desiccant. Simulations show that, for a specific indoor and outdoor operating condition the risk of crystallization is greatest for MgCl2, followed by CaCl2, LiCl and LiBr. The risk increases as the supply or exhaust airstreams become dryer. For a cross flow RAMEE with a total effectiveness of 55% (NTU=10 and Cr*=3) operating in a building with indoor RH of 50%, the critical outdoor humidity below which crystallization will begin to occur is 28% RH for MgCl2, 20% for CaCl2 and 0%RH for LiCl and LiBr. According to the simulations, all four investigated salt solutions can be used in North America (except the states of Nevada, Arizona, New Mexico and parts of Texas) with no risk of crystallization when the indoor humidity is 50% RH. However, with indoor humidity of 30% MgCl2 and CaCl2 solutions will have risk of crystallization for a large number of hours in a year in most of the central western United States. A mixture of 50% LiCl and 50% MgCl2 solution is suggested to be used when the cost-effective MgCl2 solution cannot be used due to crystallization issues. The price of this newly suggested mixture is 30% less than that of a pure LiCl solution and can be used in all North American climates with very small risk of crystallization.

In this thesis, several possible liquid desiccants (aqueous solutions of LiCl, LiBr, MgCl2 and CaCl2) are investigated to find the most appropriate working fluid to be used in a run-around membrane energy exchanger (RAMEE). The liquid desiccant is one of the main components of the RAMEE and indirectly conditions the outdoor ventilation air by using the energy of the exhaust air, significantly reducing the building energy consumption.<p> Numerical simulations, in this thesis, show that the total effectiveness of the RAMEE changes less than 0.5% when different salt solutions are used. However, the capital and operational costs of the RAMEE are significantly different for different desiccants. MgCl2 is the most inexpensive among the selected salt solutions and is followed by CaCl2, LiBr and LiCl. The price of a LiCl solution in the RAMEE is almost 20 times more than the price of MgCl2 solution. Different thermo-physical properties of the salt solutions result in different pumping energy consumptions for each specific salt solution. For example, the pumping energy consumption for a MgCl2 solution is 3.5 times more than for a LiBr solution in the RAMEE. The change in the volume of the liquid desiccant throughout a year is another characteristic which depends on the thermo-physical properties of the salt solution. Solutions with larger volume expansion require larger storage tanks and will experience longer transient delays. The difference between the volume expansions of different salt solutions is less than 5% of the total solution volume. MgCl2 solution expands more than 17% throughout a yearly operation of the system in Saskatoon.<p> Crystallization of the salt solution is another important parameter in the selection of the liquid desiccant. Simulations show that, for a specific indoor and outdoor operating condition the risk of crystallization is greatest for MgCl2, followed by CaCl2, LiCl and LiBr. The risk increases as the supply or exhaust airstreams become dryer. For a cross flow RAMEE with a total effectiveness of 55% (NTU=10 and Cr*=3) operating in a building with indoor RH of 50%, the critical outdoor humidity below which crystallization will begin to occur is 28% RH for MgCl2, 20% for CaCl2 and 0%RH for LiCl and LiBr. According to the simulations, all four investigated salt solutions can be used in North America (except the states of Nevada, Arizona, New Mexico and parts of Texas) with no risk of crystallization when the indoor humidity is 50% RH. However, with indoor humidity of 30% MgCl2 and CaCl2 solutions will have risk of crystallization for a large number of hours in a year in most of the central western United States. A mixture of 50% LiCl and 50% MgCl2 solution is suggested to be used when the cost-effective MgCl2 solution cannot be used due to crystallization issues. The price of this newly suggested mixture is 30% less than that of a pure LiCl solution and can be used in all North American climates with very small risk of crystallization.

abstract: Limited access to clean water due to natural or municipal disasters, drought, or contaminated wells is driving demand for point-of-use and humanitarian drinking water technologies. Atmospheric water capture (AWC) can provide water off the centralized grid by capturing water vapor in ambient air and condensing it to a liquid. The overarching goal of this dissertation was to define geographic and thermodynamic design boundary conditions for AWC and develop nanotechnology-enabled AWC technologies to produce clean drinking water. Widespread application of AWC is currently limited because water production, energy requirement, best technology, and water quality are not parameterized. I developed a geospatial climatic model for classical passive solar desiccant-driven AWC, where water vapor is adsorbed onto a desiccant bed at night, desorbed by solar heat during the day, and condensed. I concluded passive systems can capture 0.25–8 L/m2/day as a function of material properties and climate, and are limited because they only operate one adsorption-desorption-condensation cycle per day. I developed a thermodynamic model for large-scale AWC systems and concluded that the thermodynamic limit for energy to saturate and condense water vapor can vary up to 2-fold as a function of climate and mode of saturation. Thermodynamic and geospatial models indicate opportunity space to develop AWC technologies for arid regions where solar radiation is abundant. I synthesized photothermal desiccants by optimizing surface loading of carbon black nanoparticles on micron-sized silica gel desiccants (CB-SiO2). Surface temperature of CB-SiO2 increased to 60oC under solar radiation and water vapor desorption rate was 4-fold faster than bare silica. CB-SiO2 could operate >10 AWC cycles per day to produce 2.5 L/m2/day at 40% relative humidity, 3-fold more water than a conventional passive system. Models and bench-scale experiments were paired with pilot-scale experiments operating electrical desiccant and compressor dehumidifiers outdoors in a semi-arid climate to benchmark temporal water production, water quality and energy efficiency. Water quality varied temporally, e.g, dissolved organic carbon concentration was 3 – 12 mg/L in the summer and <1 mg/L in the winter. Collected water from desiccant systems met all Environmental Protection Agency standards, while compressor systems may require further purification for metals and turbidity. / Dissertation/Thesis / Doctoral Dissertation Civil, Environmental and Sustainable Engineering 2020

This diploma thesis focuses on polar pesticides and their analysis in agricultural commodities. One of the aims was establishing of the method for quantitative determination of diquat and paraquat using liquid chromatography with tandem mass spectrometry. Optimization parameters based on the European reference laboratories recommendations, availability of laboratory equipment and method suitability for routine analyses were taken into account. Extraction of analytes was based on shaking with acidified methanol with formic or hydrochloric acid. Considering the matrix complexity, purification with sorbents and/or acetonitrile precipitation were applied. Method validation was carried out on several levels for selected representative agricultural commodities. Part of the thesis is a field experiment where potatoes plants were sprayed with the diquat active substance. Samples of treated plants and tubers were analyzed for diquat residues. The validated method was also used for screening of diquat and paraquat residues in feed samples collected within official controls of the Central Institute for Supervising and Testing in Agriculture in 2020. The final method enables to analyze diquat and paraquat with sensitivity suitable for the maximal residue limit controls.