Browsing by Subject "Evaporation"
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Item Artificial Leaf for Biofuel Production and Harvesting: Transport Phenomena and Energy Conversion(2013-08) Murphy, Thomas Eugene; Berberoglu, HalilMicroalgae cultivation has received much research attention in recent decades due to its high photosynthetic productivity and ability to produce biofuel feedstocks as well as high value compounds for the health food, cosmetics, and agriculture markets. Microalgae are conventionally grown in open pond raceways or closed photobioreactors. Due to the high water contents of these cultivation systems, they require large energy inputs for pumping and mixing the dilute culture, as well as concentrating and dewatering the resultant biomass. The energy required to operate these systems is generally greater than the energy contained in the resultant biomass, which precludes their use in sustainable biofuel production. To address this challenge, we designed a novel photobioreactor inspired by higher plants. In this synthetic leaf system, a modified transpiration mechanism is used which delivers water and nutrients to photosynthetic cells that grow as a biofilm on a porous, wicking substrate. Nutrient medium flow through the reactor is driven by evaporation, thereby eliminating the need for a pump. This dissertation outlines the design, construction, operation, and modeling of such a synthetic leaf system for energy positive biofuel production. First, a scaled down synthetic leaf reactor was operated alongside a conventional stirred tank photobioreactor. It was demonstrated that the synthetic leaf system required only 4% the working water volume as the conventional reactor, and showed growth rates as high as four times that of the conventional reactor. However, inefficiencies in the synthetic leaf system were identified and attributed to light and nutrient limitation of growth in the biofilm. To address these issues, a modeling study was performed with the aim of balancing the fluxes of photons and nutrients in the synthetic leaf environment. The vascular nutrient medium transport system was also modeled, enabling calculation of nutrient delivery rates as a function of environmental parameters and material properties of the porous membrane. These models were validated using an experimental setup in which the nutrient delivery rate, growth rate, and photosynthetic yield were measured for single synthetic leaves. The synthetic leaf system was shown to be competitive with existing technologies in terms of biomass productivity, while requiring zero energy for nutrient and gas delivery to the microorganisms. Future studies should focus on utilizing the synthetic leaf system for passive harvesting of secreted products in addition to passive nutrient delivery.Item Passive pumping, evaporation based system for multiscale thermal management(2013-08) Crawford, Robert Vincent; Da Silva, Alexandre K., 1975-Drawing from the lessons of plant transpiration, this dissertation explores a biomimiced system for fluid transport and thermal regulation. This system utilizes evaporation and benefits from the associated passive pumping with an application of a rooftop solar radiation barrier in mind. By directing the incoming energy towards the phase change of water, lower surface temperatures can be maintained thus reducing heat transfer into the structure by conduction. In order to design and construct such a bio-inspired system, several parameters, i.e., the evaporation surface, the delivery path and the working fluid, must be understood as to how they affect and limit operations. Performance factors such as evaporation rate and suction pressure were monitored for the various design constraints of feeding tube length and diameter, membrane area, and working fluid. Additionally, as a heat flux was imposed on the membrane from above and below, the substrate temperature became important. Over the range of parameters tested, hydrodynamic resistances of the delivery path were shown to affect pumping height but not the evaporation rate. Instead, the evaporation rate was controlled by the substrate temperature. Furthermore, the normalized evaporation rate was found to be inversely related to the evaporation surface area. Under contaminated working fluid conditions, particles deposited in the membrane caused decreases in evaporation rates. When applied to a simulated roof situation, the evaporation system was successful at maintaining considerably lower surface temperatures than other conventional and unconventional roof albedos, which, in turn, would reduce heat flux into the interior by conduction. Lastly, in estimating the water consumption, on a typical August day in Austin, TX, the system could use up to 2 gallons/m² while providing enhanced cooling. When the system's resources were compared to being purposed in other ways, they were arguably better utilized in providing evaporative cooling.Item The thermodynamics of evaporation: with emphasis on lake evaporation rates(Texas Tech University, 1967-08) Headrick, James BufordNot available