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Experimental evaluation of three different configurations of constructal disc-shaped heat exchangers
No full textThe aim of this work is to experimentally evaluate three different compact branched heat exchangers, measuring, for every single device, the thermal efficiency and the pressure drop. The generality of the analysis of phenomena is enhanced by a comparison of the performance of different refrigerant fluids. In the first configuration, the channels have been designed, varying the inner diameter, to allow for an average constant flow speed throughout the exchanger. In the second one, the flow Reynolds number inside of the channels has been maintained constant. The last configuration is built according to the constructal diameter variation, as indicated in Bejan Constructal Theory. The exchanger manufacturing process is described in detail. The test bench has been assembled using a hot source (Heating Plate with a power of 500 W) and a submersible pump, needed for the fluid recirculation, coupled with flowmeters, to control the mass flow rate within a specific range. The data obtained from several comparative tests have been analyzed, to determine the optimal solution for each refrigerant among the different exchangers
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Computational and Experimental Investigation of Vortex Cooling of a Gas Turbine Blade Using 3-D Stereo-Particle Image Velocimetry and Liquid Crystals
Get PDFThe limiting factor for most gas turbines has been the turbine inlet temperature. Furthermore, higher pressure ratios and turbine inlet temperatures improve the efficiencies on the gas turbine. A big focus has been on new schemes of internal cooling designs of turbine blades, using pressurized air from the engine compressor, and break-through in blade metallurgy, in order to achieve higher turbine inlet temperatures. Significant research has been ongoing for decades to design an internal cooling system for the first stage of the turbine blade consequently higher turbine inlet temperatures can be achieved. The challenging engineering intricacies related to improving the efficiency of a gas turbine engine come with the need to maximize the efficiency of the internal cooling of the turbine blade to withstand the high turbine inlet temperature. Understanding the fluid mechanics and heat transfer of internal blade cooling is therefore of paramount importance. This dissertation presents the impact of swirl flow cooling on the heat transfer of a gas turbine blade cooling passage to understand the mechanics of internal blade cooling. The focus is the continuous cooling flow that must be maintained via nonstop injection of tangential flow, whereby swirl flow is generated. The experimental investigation is presented first with three-dimensional (3-D) Stereo-Particle Image Velocimetry (Stereo-PIV) and second Thermochromic Liquid Crystal (TLC) of a swirl flow that models a gas turbine blade internal cooling configuration. The study is intended to provide an evaluation of the developments of swirl flow cooling methodology utilizing 3-D Stereo-PIV and liquid crystals. The objective of the experimental models is to determine the critical swirl number that has the potential to deliver the maximum axial velocity results with the highest heat transfer at three different Reynolds numbers, 7,000, 14,000, and 21,000. The swirl flow cooling methodology comprises of cooling air channeling through the blade’s internal passages lowering the metal temperature, therefore the experimental cylindrical chamber is made of acrylic allowing detailed measurements and includes seven discrete tangential air inlets designed to create the swirl flow. Additionally, a 3D domain fluent setup employing a steady-state pressure-based solver with a standard k-epsilon turbulence model was applied. The energy equations were activated to handle the temperature effect; the gravitational acceleration is accounted for.
Important variations of the swirl number are present near the air inlets and decrease with downstream distance as predicted since the second half of the chamber has no more inlets. The axial velocity reaches the maximum downstream in the second half of the chamber. The circumferential velocity decreases downstream distance and reaches the highest towards the center of the chamber. As part of the results relatively low heat transfer rates were observed near the upstream end of the cylindrical chamber, resulting from a low momentum swirl flow as well as crossflow effects. The TLC heat transfer results exemplify how the Nusselt Number (Nu) measured favorably at the midstream of the chamber and values decline downstream. Furthermore, experimental results when compared to the Computational Fluid Dynamics analysis are compatible with each other
Methodology for Fuel Saving Optimization of a Serial Hybrid Electric Vehicle using Gas Turbine as Energy Converter
Get PDFSignificant research efforts have been invested in the automotive industry on hybrid-electrified powertrains in order to reduce the passenger cars’ dependence on oil. Powertrains electrification resulted in a wide range of hybrid vehicle architectures. Fuel consumption of these powertrains strongly relies on the energy converter performance, as well as on the energy management strategy deployed on-board. This paper investigates the potential of fuel consumption savings of a serial hybrid electric vehicle (SHEV) using a gas turbine (GT) as energy converter instead of the conventional internal combustion engine (ICE). An exergotechno explicit analysis is conducted to identify the best GT-system configuration. An intercooled regenerative reheat cycle is prioritized, offering higher efficiency and power density compared to other investigated GT-systems. A SHEV model is developed and powertrain components are sized considering vehicle performance criteria. Energy consumption simulations are performed on WLTP cycle using dynamic programing as global optimal energy management strategy. A sensitivity analysis is also carried out in order to evaluate the effect of the battery size on the fuel consumption. Results show improved fuel consumption with GT as auxiliary power unit (APU) compared to ICE. Moreover, GT offers other intrinsic advantages such as reduced mass, suitable vehicle integration as well as a multi-fuel use capability. Consequently, the studied GT-APU presents a potential for implementation on SHEVs.N/AIncludes bibliographical reference
Experimental analysis of a novel Savonius based spline geometry with flexible blades for VAWT
Get PDFDesign, manufacture and tests in wind tunnel of a Savonius wind rotor with flexible bladesopenEmbargo temporaneo per motivi di priorità nella ricerca previo accordo con terze part
Comphrensive resource balance for ethanol produced from corn and sugarcane
No full textDue to the increase in price of fossil fuels and climate change caused by Greenhouse Gas (GHG) emissions, many countries around the world are trying to produce alternative transportation fuels. Ethanol has emerged as a popular alternative to fossil fuels, especially, in countries such as the U.S. and Brazil. Different feed stocks are being used to produce ethanol, with corn and sugarcane as the major crops currently being converted into ethanol. Ethanol production requires considerable resources. To date energy input has been studied extensively. However, only limited data is available on other resources used, such as water and land, and the environmental degradation due to waste generated and GHG emissions. The primary objective of this study is to estimate the resource balance for ethanol produced from corn and sugarcane in different climatic zones: temperate, dry and tropical for corn, and tropical and dry for sugarcane. The results of the study indicate that ethanol produced from sugarcane uses less or comparable resources compared to ethanol produced from corn. The estimates of Net Energy Value (NEV) for corn ethanol were between -1,656 and 6,305 Btu per gallon, while those of sugarcane ethanol were between 57,606 and 61,319 Btu per gallon for different climatic zones considered in this study. Moreover, the highest estimated water requirements, for dry climate, were 2,650 and 2,050 gallons of water per gallon of ethanol for corn and sugarcane ethanol, respectively. Results for carbon dioxide released to the environment from corn ethanol with respect to fossil fuels show a reduction of 44, 26 and 51 percent for tropical, dry and temperate climate zones, respectively. On the other hand, results show a reduction of 62 and 57 percent for carbon dioxide emissions from ethanol produced from sugarcane in tropical and dry climates, respectively. However, when land use change is accounted for, results indicate a significant increase in carbon dioxide emissions, referred to as carbon debt. Considering the reduction of carbon dioxide emissions resulting from ethanol and the debt amount, the payback time will be very long. Results of this study indicate that if forest is converted into a one cycle cropland, corn ethanol will require a payback period of 300, 672 and 210 years, for tropical, dry and temperate climate zones, respectively. If grassland is converted into cropland, corn ethanol will require a payback period of 112, 242 and 82 years, for tropical, dry and temperate climate zones, respectively. Similarly for sugarcane ethanol, when forests are converted into cropland, the payback period is 102 and 132 years, for tropical and dry climate zones, respectively. If grassland is converted into cropland, the payback period for sugarcane ethanol is 38 and 50 years, for tropical and dry climate zones, respectively. In addition, each gallon of corn ethanol requires about 156, 206 and 135 square feet of land for tropical, dry and temperate climates, respectively. Sugarcane ethanol requires about 75 and 91 square feet for tropical and dry climates, respectively. In addition to carbon dioxide emissions, fertilizers are released to the environment. Results of this study indicate that for corn ethanol, fertilizers released to the environment as surface runoff for nitrogen are estimated as 9,072, 12,247 and 8, 618 milligrams per gallon of ethanol for tropical, dry, and temperate climate zones, respectively. Similarly, for phosphate results were 3,629, 5,897 and 2,268 milligrams per gallon of ethanol for temperate, dry, and tropical climates. As for sugarcane ethanol, results for fertilizers surface runoff are estimated as 908 milligrams per gallon of ethanol for nitrogen, for tropical and dry climate zones, and 4,082 and 4,990 milligrams per gallon of ethanol for phosphate, for tropical and dry climate zones, respectivel
Coupled fluid flow and radiation modeling of a small particle solar receiver
No full textIncludes bibliographical references (p. 74-76)In recent years, concentrating solar thermal power has emerged as the most promising technology for utility scale solar electricity generation. Central receiver systems, which are one method of concentrated solar power, use a field of sun-tracking mirrors called heliostats to focus light on a receiver. Existing receivers used in these systems have temperature and flux limitations, which prevent the use of advanced power cycles and reduces plant efficiencies compared to fossil fuel power plants. The development of air-cooled receivers and small particle receivers in particular are summarized herein. A new type of receiver has been proposed, which makes use of small carbon particles and volumetric absorption in a gas-particle mixture to heat air directly. This thesis builds on previous modeling work done in FORTRAN on the San Diego State University small particle receiver project, expanding the Monte Carlo ray-trace model to include the computation fluid dynamics capabilities of ANSYS FLUENT with the use of several user-defined functions. The input flux is modified to more closely match that provided by a real heliostat field, and the geometry is changed to more accurately approximate a real receiver. The updated model is benchmarked against existing analytical solutions where possible, and compared to the results of the previous model. The new model is run for a variety of gas mass-flow rates, inlet power levels, and power distributions with a baseline target input power of 5 MW. Outlet gas temperatures predicted by the model ranged from 1300 K to 1550 K, and receiver thermal efficiencies ranged from 80% to 91% depending on operating conditions. The highest efficiencies predicted are with the highest mass-flow rate tested of 6 kg/s
The Impact of Inertia Forces on a Morphing Wind Turbine Blade in A Vertical Axis Configuration: A Wind Tunnel Test
No full textIncludes bibliographical references (pages 91-95).There is a growing global demand for "clean" energy due to an increased mandate to reduce greenhouse gases. Wind energy has established itself as an economically competitive source due to major developments made in the efficiency and reliability of conversion systems. Currently, horizontal axis wind turbines (HAWTs) dominate the wind energy conversion market because of their high efficiency. However, recent advances in vertical axis\ud
conversion systems are closing the gap in efficiency. A novel flexible blade concept with the ability to morph and adapt to changing flow conditions was proposed by A. Beyene and T. Ireland, to address part load and performance issues encountered in wind energy conversion\ud
systems. The extension of these benefits to a vertical axis wind turbine (VAWT) would make wind technology a more competitive player in the energy market. A straight bladed vertical axis wind turbine (SB-VAWT) rotor was manufactured, to accommodate flexible and rigid blades. The performance and flexible behavior was studied in the department of\ud
mechanical engineering's low speed wind tunnel using a test rig that was built for this study. A mathematical model, validated using a high speed camera and finite element analysis, was developed to predict the magnitude and direction of blade morph. The results show that the\ud
coefficient of performance (CP) greatly depends on the tip speed ratio (TSR), i.e., the rigid blade has CP of 0.11 for a TSR of 1.6, whereas the morphing blade achieved a CP of 0.06 at a TSR of 1.13. Overall, the modified morphing blade has better performance at low RPMs, but the rigid blade performed better at high RPMs. It was observed that the VAWT equipped with flexible blades self-started in the majority of the experiments. The flexible blade's production of power at relatively low TSRs is a rare occurrence in the field. At high RPM, the centrifugal force overwhelmed the lift force, bending the blade out of phase in an\ud
undesired direction increasing drag and therefore reducing the CP. These results suggest that alterations to the current design must be made in order to account for the inertial forces experienced by blades in a vertical axis configuration
EVALUATION OF LIPID EXTRACTION METHODS FROM MICROALGAE CHLORELLA VULGARIS
No full textIncludes bibliographical references (pages 54-57).Algal biofuels have gained increased attention over the past decade due to its potential for substituting fossil fuels and sequestering carbon dioxide in the atmosphere. One of the major obstacles for producing biofuels from microalgae is extracting intracellular lipids, which requires penetration of solvents into the cell wall and membrane. Lipid extraction and the algae concentration processes combined account for the majority of the energy input required to make algal biofuels. Improvements in both of these steps are necessary for making algal biofuels production a net-positive energy process. The goal of this study was to improve the energy efficiency of lipid extraction from microalgae by either decreasing the amount of drying necessary for lipid extraction, or increasing the amount of lipids extracted via pretreatment methods. To achieve the goal, the following objectives were completed: (1) the effects of biomass concentration on solvent extraction yields with chloroform and n-hexane was investigated, (2) the efficiencies of chloroform and n-hexane as an extracting solvent were examined, and (3) the impact of pretreatment of microalgae with ultrasonication, microwaves, and electroporation on extraction yields was investigated. The microalgae Chlorella vulgaris (C. vulgaris) was grown in the laboratory in batch bioreactors. The microalgae was concentrated to different biomass concentrations and the lipids were extracted using two solvent systems: chloroform/methanol/water and n-hexane/ methanol/water. For the chloroform/methanol/water solvent system, the highest total lipid yield of 0.248 g per g of dry C. vulgaris was achieved at algal biomass concentration of about 15% on weight basis. On the other hand, the total lipid yield of 0.139 g per g of dry C. vulgaris was obtained at about 24% algal biomass concentration for the n-hexane/ methanol/water solvent system. Extraction of lipids with n-hexane was 76% of the yield of the extraction with chloroform. Electroporation, ultrasonication, and microwaves were studied for their potential pretreatment methods to increase lipid extraction from C. vulgaris. The yield for lipid extraction increased from 0.246 to 0.311 g per dry g of C. vulgaris when the cells were pretreated with ultrasonication, which is equivalent to a 26.4% increase. Pretreatment with microwaves resulted in a lipid yield of 0.317 g per dry g of C. vulgaris, which is a 28.9% increase. Electroporation resulted in a lipid yield of 0.259 g per dry g of C. vulgaris, which is a low increase of 5.3%, but electroporation was the most efficient in terms of energy requirements. It was also found that pretreatment of the algae does have the potential to replace polar solvents in lipid extraction for cell disruption, however improvements need to be made in the process in order to gain the same yield as a combined chloroform/methanol extraction
Regression analysis of organic working medium for low temperature Rankine Cycle
No full textIncludes bibliographical references (p. 65-67).The United State's Industrial Sector uses about thirty percent of the total U.S. energy use, and is responsible for about thirty percent of carbon dioxide emission. Many of the industrial processes require a large quantity of thermal energy of which a large portion is eventually exhausted to the environment. Recovering this waste heat offers the largest opportunity to reduce the U.S. manufacturing sector's energy use. The objective of this study is to establish an evaluation method that combines environmental impact of existing working fluids and their thermodynamic properties as they apply to ultra-low grade heat Organic Rankine Cycle (ORC). Global warming and ozone depleting potentials are used to evaluate the environmental impact of the most common working fluids as well as their toxicity and flammability. Physical properties are used to evaluate these fluids for ultra-low grade heat ORC application. With regard to the environmental impact, the preferable working fluids are Hydrofluorocarbons (HFCs) - which do not contain chlorine and do not damage the ozone layerand Hydrocarbons (HCs) - which naturally exists in nature. Considering both environmental and performance characteristics, based on this study, the preferable working fluids are 1,1,1,3,3- Pentafluoropropane (HFC-245fa), followed by 1,1,1,2-Tetrafluoroethane (HFC-134a), 1,1,1,2,3,3,3-Heptafluoropropane (HFC-227ea), 1,1,1,2,3,3-Hexafluoropropane (HFC- 236ea), 1,1,1,3,3,3-Hexafluoropropane (HFC-236fa), Butane (HC-600), Isobutane (HC- 600a), Pentane (HC-601), and Isopentane (HC-601a). To develop a classifier that can predict the probability of any working fluid being a desirable candidate for ultra-low grade heat ORC, logistic regression analysis was used. The phase out year, ozone depleting potential, global warming potential, type of fluid, and critical temperature of the screened working fluids and above results were used to develop this classifier. With the help of this classifier any working fluid can be classified as a desirable or undesirable candidate for ultra-low grade heat ORC. This study makes it clear that none of the current working fluids have all the criteria for an ideal refrigerant. The Ozone depletion and climate change are global issues. However, the choice of alternative refrigerants is a domestic issue. Policy makers in each government should decide which characteristics of ideal working fluid should be neglected in order to maximize the efficiency of the recovered waste energy and reduce environmental impacts of emissions
Modeling and analysis of latent heat high temperature thermal energy storage for concentrating solar power plants
No full textIncludes bibliographical references (pages 86-89).Power tower concentrated solar power (CSP) plants are capable of producing extremely high temperatures, as they have the ability to oversize their solar field and achieve a greater concentration ratio. This theoretically allows power towers to use more efficient, higher temperature cycles including air Brayton and supercritical Rankine cycles, as well as experimental cycles such as the supercritical CO2 cycle. As part of this thesis, the heat demand of each cycle, as well as the cycle diagram is examined for its suitability for use with CSP plants with thermal energy storage (TES). This will help develop criteria to determine if these cycles could be coupled with a higher temperature storage system. After the general cycle overview, this thesis describes the development, validation, and results of a TES system targeted for use with an air Brayton power cycle. This research analyzes the use of metal alloys as phase change storage materials and makes a case for their use with CSP plants. The numerical model developed here is intended to analyze the performance of high temperature systems suitable for thermodynamic cycles that do not have a commercially available storage system. The storage system essentially combines a heat exchanger and storage system to help realize potential savings over molten salt two-tank storage systems currently employed by industry. FLUENT computational fluid dynamics software is used to model the storage tank. After initial modeling of a hypereutectic binary alloy system it was discovered that FLUENT does not properly account for an individual material phase diagram. So, the thermal properties were altered in FLUENT in order to accurately reflect the thermal performance of the primary storage material chosen for study, AlSi. The model was also analyzed with pure metals and eutectic binary alloys in an effort to achieve stable air temperatures that could support an air Brayton turbine. These included both cascaded and non-cascaded geometries as well as reversed and non-reversed flow. The results of the cascaded models show that the heat exchanger/thermal storage concept is able to buffer the air entering the turbine, and produces relatively stable outlet air temperatures. It was found that using a single, pure metal as the storage material produced the highest, most stable air temperatures of the systems studied. With further optimization and research, this system could become a viable storage option for CSP plants in support of higher temperature cycles
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