Simulated Thermal Resistance of Thermogalvanic Cells with Triply Periodic Minimal Surface Structures using ANSYS

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Description
Buildings release an abundance of waste heat that is left unused. Thermogalvaniccells (TGCs) can take advantage of waste heat to generate electricity with a low temperature gradient. In this dissertation, I simulated the thermal transport of TGCs containing different triply periodic minimal…

Buildings release an abundance of waste heat that is left unused. Thermogalvaniccells (TGCs) can take advantage of waste heat to generate electricity with a low temperature gradient. In this dissertation, I simulated the thermal transport of TGCs containing different triply periodic minimal surface (TPMS) structures, compared it to measured values and conducted a mesh convergence study to examine the viability of the computational fluid dynamics (CFD) solutions. Natural convection effects are one of the driving forces in TGCs. Using the Bousinesq approximation, I was able to capture those effects in the CFD simulations as it accounts for the density variations of the fluid. Upon simulating the TGC using the Schwarz P TPMS geometry, the cathode temperature converged as I refined the mesh and approached the measured value. As for the IWP TPMS structure, the solution converged as I refined the mesh, despite having a deviation to the measured values. This was due to the abundance of sharp regions along the walls of the TPMS that ANSYS had difficulty to accurately model. Furthermore, I simulated the TGCs using different boundary condition (BC) approximations to observe the cathode and anode temperatures as well as their overall ∆T across the cell. For the TGC containing the Schwarz P geometry, Case C (constant anode temperature BC with TPMS conduction) was the most accurate while Case D (convection BC at anode with TPMS conduction) deviated from the measured values, had the most accurate ∆T and was well within the uncertainty bounds of the measured values. Larger temperature fluctuations were seen closer to the cathode while the effects steadily decrease as the fluid approaches the anode. Moreover, the TGC containing the IWP structures presented interesting results. The main deviation was from the cathode temperatures because a higher temperature readings meant that more cells in the fluid domain were prone to diverging, thereby resulting in a higher calculated cathode temperature. Simulating the TGC with the Schwarz P geometry produced satisfactory results while the TGC using the IWP geometry deviated due to the software limitations. Finally, the effects of natural convection and TPMS on TGCs were studied and it was found that the absence of natural convection lead to a higher ∆T while the absence of TPMS resulted in a more uniform temperature distribution throughout the domain
Date Created
2021
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Development of High-Temperature Heater for Thermophotovoltaic Energy Conversion System

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Thermophotovoltaic energy conversion is seen as a viable option for efficiently converting heat to electricity. There are three key components to a thermophotovoltaic (TPV) system: a heat source, a heat emitter and a photovoltaic (PV) cell. A heat source heats…

Thermophotovoltaic energy conversion is seen as a viable option for efficiently converting heat to electricity. There are three key components to a thermophotovoltaic (TPV) system: a heat source, a heat emitter and a photovoltaic (PV) cell. A heat source heats up the emitter which causes the emitter to release thermal radiation. The photons are absorbed by a PV cell when they are acting above the bandgap energy. The PV cell then generates electricity from this thermal radiation. In theory, efficiency of a TPV system can be well above 50%. In order for TPV to reach large-scale adaptation, an efficiency at or above 20% is needed. In this project, a high-temperature heater capable of reaching 1000K was developed. The heater involved a copper block machined to hold two cartridge heaters, as well as two thermocouples. It has an accompanying copper lid that can be screwed tight to the main block, with an emitter in between. There is an aperture to allow radiation through the casing towards the PV cell. Preliminary thermal analysis showed that the heater provides uniform temperature distribution across the emitter, which is necessary for proper radiation. A mounting system was also designed to implement the heater into the overall TPV system. Current work is being done to lower the radiation loss from the heater and mounting system, as well as implementation of all auxiliary components to begin testing. The maximum temperature of the heater, radiation heat flux received by the cell, and overall power output and efficiency of the system will be tested.

Date Created
2021-12
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Fuel Cell Integrated Gas Turbine Hybrid System Under Various Conditions

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A novel concept for integration of flame-assisted fuel cells (FFC) with a gas turbine is analyzed in this paper. Six different fuels (CH4, C3H8, JP-4, JP-5, JP-10(L), and H2) are investigated for the analytical model of the FFC integrated gas…

A novel concept for integration of flame-assisted fuel cells (FFC) with a gas turbine is analyzed in this paper. Six different fuels (CH4, C3H8, JP-4, JP-5, JP-10(L), and H2) are investigated for the analytical model of the FFC integrated gas turbine hybrid system. As equivalence ratio increases, the efficiency of the hybrid system increases initially then decreases because the decreasing flow rate of air begins to outweigh the increasing hydrogen concentration. This occurs at an equivalence ratio of 2 for CH4. The thermodynamic cycle is analyzed using a temperature entropy diagram and a pressure volume diagram. These thermodynamic diagrams show as equivalence ratio increases, the power generated by the turbine in the hybrid setup decreases. Thermodynamic analysis was performed to verify that energy is conserved and the total chemical energy going into the system was equal to the heat rejected by the system plus the power generated by the system. Of the six fuels, the hybrid system performs best with H2 as the fuel. The electrical efficiency with H2 is predicted to be 27%, CH4 is 24%, C3H8 is 22%, JP-4 is 21%, JP-5 is 20%, and JP-10(L) is 20%. When H2 fuel is used, the overall integrated system is predicted to be 24.5% more efficient than the standard gas turbine system. The integrated system is predicted to be 23.0% more efficient with CH4, 21.9% more efficient with C3H8, 22.7% more efficient with JP-4, 21.3% more efficient with JP-5, and 20.8% more efficient with JP-10(L). The sensitivity of the model is investigated using various fuel utilizations. When CH4 fuel is used, the integrated system is predicted to be 22.7% more efficient with a fuel utilization efficiency of 90% compared to that of 30%.

Date Created
2021-05
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Study of Solar Thermophotovoltaic (STPV) Energy Conversion with Selective Metafilm Coatings and GaSb Cell Separated by Glass Microspheres

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Description
Solar energy as a limitless source of energy all around the globe has been difficult to harness. This is due to the low direct solar-electric conversion efficiency which has an upper limit set to the Shockley-Queisser limit. Solar thermophotovoltaics (STPV)…

Solar energy as a limitless source of energy all around the globe has been difficult to harness. This is due to the low direct solar-electric conversion efficiency which has an upper limit set to the Shockley-Queisser limit. Solar thermophotovoltaics (STPV) is a much more efficient solar energy harvesting technology as it has the potential to overcome the Shockley-Queisser limit, by converting the broad-spectrum solar irradiation into narrowband infrared spectrum radiation matched to the PV cell. Despite the potential to surpass the Shockley-Queisser limit, very few experimental results have reported high system-level efficiency.

The objective of the thesis is to study the STPV conversion performance with selective metafilm absorber and emitter paired with a commercial GaSb cell at different solar concentrations. Absorber and Emitter metafilm thickness was optimized and fabricated. The optical properties of fabricated metafilms showed good agreement with the theoretically determined properties. The experimental setup was completed and validated by measuring the heat transfer rate across the test setup and comparing it with theoretical calculations. A novel method for maintaining the gap between the emitter and PV cell was developed using glass microspheres. Theoretical calculations show that the use of the glass of microspheres introduces negligible conduction loss across the gap compared to the radiation heat transfer, which is confirmed by experimental heat transfer measurement. This research work will help enhance the fundamental understanding and the development of the high-efficiency solar thermophotovoltaic system.
Date Created
2020
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Techno-Economic Assessment of CHP in Wastewater Treatment Plants

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Wastewater treatment plant (WWTP) utilization of combined heat and power (CHP) systems allows for the efficient use of on-site biogas production, as well as increased annual savings in utility costs. In this thesis, a literature review of six CHP prime…

Wastewater treatment plant (WWTP) utilization of combined heat and power (CHP) systems allows for the efficient use of on-site biogas production, as well as increased annual savings in utility costs. In this thesis, a literature review of six CHP prime mover technologies is presented. Even though there are different prime mover technologies, the main ones currently being implemented in WWTPs are micro turbines, fuel cells and reciprocating engines. These prime mover technologies offer varying efficiencies, installation costs and maintenance requirements. The prime movers are also all in different stages of development, leading some to be more currently-in-use than others in WWTPs. Currently reciprocating engines and micro turbines occupy the largest shares of the CHP in WWTP sector.
This thesis will also go in detail into equations and calculations created for a techno-economic assessment for installation and maintenance of a CHP system at a WWTP. The equations and calculations created here were then utilized with data from a typical WWTP in the Southwestern United States to create an accurate case study. In this case study, a payback of 5.7 years and a net present value of $709,000 can be achieved when the WWTP generates over 2,000,000 m3 of biogas per year and utilizes over 36,000 GJ of natural gas per year.
Date Created
2020-12
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Thermal Resistance Measurements of Triply Periodic Minimal Surface Structures (TPMS) of the Thermogalvanic Brick

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The presence of huge amounts of waste heat and the constant demand for electric energy makes this an appreciable research topic, yet at present there is no commercially viable technology to harness the inherent energy resource provided by the temperature…

The presence of huge amounts of waste heat and the constant demand for electric energy makes this an appreciable research topic, yet at present there is no commercially viable technology to harness the inherent energy resource provided by the temperature differential between the inside and outside of buildings. In a newly developed technology, electricity is generated from the temperature gradient between building walls through a Seebeck effect. A 3D-printed triply periodic minimal surface (TPMS) structure is sandwiched in copper electrodes with copper (I) sulphate (Cu2SO4) electrolyte to mimic a thermogalvanic cell. Previous studies mainly concentrated on mechanical properties and the electric power generation ability of these structures; however, the goal of this study is to estimate the thermal resistance of the 3D-printed TPMS experimentally. This investigation elucidates their thermal resistances which in turn helps to appreciate the power output associated in the thermogalvanic structure. Schwarz P, Gyroid, IWP, and Split P geometries were considered for the experiment with electrolyte in the thermogalvanic brick. Among these TPMS structures, Split P was found more thermally resistive than the others with a thermal resistance of 0.012 m2 K W-1. The thermal resistances of Schwarz D and Gyroid structures were also assessed experimentally without electrolyte and the results are compared to numerical predictions in a previous Mater's thesis.
Date Created
2020
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Gasification of Municipal Solid Waste for Power Generation

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The paper analyzes the growing desire to use waste-to-energy strategies on municipal solid waste (MSW) to generate power. The two waste-to-energy technologies that will be explored are incineration and gasification. The background of these two technologies will be explained because…

The paper analyzes the growing desire to use waste-to-energy strategies on municipal solid waste (MSW) to generate power. The two waste-to-energy technologies that will be explored are incineration and gasification. The background of these two technologies will be explained because incineration, which has been the pioneering technology for the past century, has come to be rivaled by gasification with its unique purification feature. Following this section, gasification and incineration power generation are studied to conclude which technology is sounder. This study will be conducted via an analysis to find the thermal and exergetic efficiencies and emissions of each. After analyzing the two technologies, both utilizing a vapor cogeneration power system, their efficiencies were found. For the gasification process, the thermal efficiency was 26% and the exergetic efficiency was 59%. The incineration process had a thermal efficiency of 25% and an exergetic efficiency of 55%. Lastly, the emission from the power generation of each method was explored to see which system had a greater impact on the environment. It was found that the primary emissions of these technologies were carbon dioxide and water.
Date Created
2020-05
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Solar Thermochemical Reactor

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As the need for environmentally friendly and renewable fuel sources rises, many are considering alternative fuel sources, such as solar power. The device explored in this report uses solar power, in theory, to heat a metal oxide, cerium oxide, to…

As the need for environmentally friendly and renewable fuel sources rises, many are considering alternative fuel sources, such as solar power. The device explored in this report uses solar power, in theory, to heat a metal oxide, cerium oxide, to a desired temperature. At specific temperatures and pressures, a reaction between an input gas, carbon dioxide or water vapor, and the metal oxide may produce fuel in the form of hydrogen or carbon monoxide. In order to reach the temperatures required by the reaction, a filament inside a high-temperature radiant heater must be heated to the desired temperature. In addition, the system’s pressure range must be satisfied. A pressure and temperature measurement device, as well as a voltage control, must be connected to an interface with a computer in order to monitor the pressure and temperature of different parts of the system. The cerium oxide element must also be constructed and placed inside the system. The desired shape of the cerium oxide material is a tube, to allow the flow of gas through the tubes and system and to provide mechanical strength. To construct the metal oxide tubes, they need to be extruded, dried, and sintered correctly. All the manufactured elements described serve an essential purpose in the system and are discussed further in this document.
This report focuses on the manufacturing of ceria tubes, the construction of a high-temperature radiant heater filament, and the implementation of a pressure measurement device. The manufacturing of ceria tubes includes the extrusion, the drying, and the sintering of the tubes. In addition, heating element filament construction consists of spot-welding certain metals together to create a device similar to that of a light bulb filament. Different methods were considered in each of these areas, and they are described in this report. All of the explorations in this document move towards the final device, a thermochemical reactor for the production of hydrogen (H2) and carbon monoxide (CO) from water (H2O) and carbon dioxide (CO2).
The results of this report indicate that there are several important manufacturing steps to create the most desirable results, in terms of tube manufacturing and heating element design. For the correct tube construction, they must be dried in a drying rack, and they must be sintered in V-groove plates. In addition, the results of the heating element manufacturing indicate that the ideal heating element filament needs to be simple in design (easily fixed), cost-effective, require little construction time, attach to the ends of the system easily, provide mechanical flexibility, and prevent the coil from touching the walls of the tube it lies in. Each aspect of the ideal elements, whether they are tubes or heating elements, is explored in this report.
Date Created
2020-05
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The Refinement of Electrolyte Material for Solid Oxide Fuel Cell Application

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Description
In this study, the viability of doped ceria for SOFC electrolyte application is investigated through calculation of the oxygen anion diffusion through undoped, Zr-doped, Pr-doped, and Gd-doped ceria. DFT calculations are performed to determine the oxygen vacancy formation and activation…

In this study, the viability of doped ceria for SOFC electrolyte application is investigated through calculation of the oxygen anion diffusion through undoped, Zr-doped, Pr-doped, and Gd-doped ceria. DFT calculations are performed to determine the oxygen vacancy formation and activation energy to vacancy migration barriers for each material. All dopants were found to increase the activation energy to vacancy migration and decrease the oxygen vacancy formation energy. These energy barriers are then integrated into a kinetic Monte Carlo simulation that models the oxygen vacancy diffusion over time. From the simulation results, the diffusivity of oxygen anion through each material is calculated as a function of dopant concentration and temperature. It was discovered that diffusivity increased with temperature and decreased with dopant concentration in all dopant cases. Gd-doped ceria exhibited the highest overall oxygen diffusion rates, making it the most effective choice for SOFC electrolyte application, while Zr-doped ceria would be the least effective choice with the lowest diffusion rates.
Date Created
2019-12
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Low temperature soot regime of propane/air in a micro flow reactor with controlled temperature profile

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Description
Micro/meso combustion has several advantages over regular combustion in terms of scale, efficiency, enhanced heat and mass transfer, quick startup and shutdown, fuel utilization and carbon footprint. This study aims to analyze the effect of temperature on critical sooting equivalence…

Micro/meso combustion has several advantages over regular combustion in terms of scale, efficiency, enhanced heat and mass transfer, quick startup and shutdown, fuel utilization and carbon footprint. This study aims to analyze the effect of temperature on critical sooting equivalence ratio and precursor formation in a micro-flow reactor. The effect of temperature on the critical sooting equivalence ratio of propane/air mixture at atmospheric pressure with temperatures ranging from 750-1250°C was investigated using a micro-flow reactor with a controlled temperature profile of diameter 2.3mm, equivalence ratios of 1-13 and inlet flow rates of 10 and 100sccm. The effect of inert gas dilution was studied by adding 90sccm of nitrogen to 10sccm of propane/air to make a total flow rate of 100sccm. The gas species were collected at the end of the reactor using a gas chromatograph for further analysis. Soot was indicated by visually examining the reactor before and after combustion for traces of soot particles on the inside of the reactor. At 1000-1250°C carbon deposition/soot formation was observed inside the reactor at critical sooting equivalence ratios. At 750-950°C, no soot formation was observed despite operating at much higher equivalence ratio, i.e., up to 100. Adding nitrogen resulted in an increase in the critical sooting equivalence ratio.

The wall temperature profiles were obtained with the help of a K-type thermocouple, to get an idea of the difference between the wall temperature provided with the resistive heater and the wall temperature with combustion inside the reactor. The temperature profiles were very similar in the case of 10sccm but markedly different in the other two cases for all the temperatures.

These results indicate a trend that is not well-known or understood for sooting flames, i.e., decreasing temperature decreases soot formation. The reactor capability to examine the effect of temperature on the critical sooting equivalence ratio at different flow rates was successfully demonstrated.
Date Created
2019
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