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Articles 1 - 21 of 21
Full-Text Articles in Heat Transfer, Combustion
Effects Of Hydrogen Enrichment And Premixing On Flame Stability In A High-Pressure Axial-Stage Combustor, Alexandre Fernandes C. Santiago Filho
Effects Of Hydrogen Enrichment And Premixing On Flame Stability In A High-Pressure Axial-Stage Combustor, Alexandre Fernandes C. Santiago Filho
Honors Undergraduate Theses
The addition of hydrogen to conventional fuels enhances reactivity and can increase the risk of flashback in premixed gas turbine combustors. This study investigates the effects of premixing length and hydrogen concentration on flame stability in a high-pressure axial-stage combustor. Experiments were conducted at the UCF Propulsion and Energy Research Laboratory using a two-stage configuration, where the primary stage provided a high-temperature vitiated crossflow using a hydrogen-piloted, premixed methane–air mixture, and hydrogen-enriched methane–air mixtures were injected through a concentric fuel-tube injector in the axial stage. Premixing length was varied for pure hydrogen flames, and hydrogen concentration was varied at a …
Two-Phase Transcritical Carbon Dioxide Flow At The Microscale For Thermal Management Applications, Soroush Niazi
Two-Phase Transcritical Carbon Dioxide Flow At The Microscale For Thermal Management Applications, Soroush Niazi
Graduate Studies Theses and Dissertations 2026
High-power electronic and power-conversion devices now generate heat fluxes that exceed what conventional air- and single-phase-liquid cooling can dissipate, motivating the search for more capable coolants and cooling mechanisms. Carbon dioxide is an attractive candidate for this role: it is inexpensive, non-toxic, and environmentally friendly, and near its critical point its thermophysical properties change rapidly, which raises the heat-transfer coefficient. In addition, a large pressure drop produces strong cooling through the Joule–Thomson effect and phase change, so that the throttling element itself becomes a source of cooling. This dissertation studies the throttling, phase change, and choking of high-pressure carbon dioxide …
Performance Analysis Of Labyrinth And Hybrid Seals For Supercritical Co₂ Turbomachinery Applications, Ghanshyam Sarobar Mandal
Performance Analysis Of Labyrinth And Hybrid Seals For Supercritical Co₂ Turbomachinery Applications, Ghanshyam Sarobar Mandal
Graduate Studies Theses and Dissertations 2026
Leaks account for large losses in turbomachinery systems, which has led to research on sealing technologies. The work presented studies the effect of a hybrid seal combining conventional labyrinth geometry and honeycomb structure by simulating supercritical carbon dioxide (sCO₂) flow through this geometry. The CFD solver compares effects such as changes in mass flow rate, formation of vortices, pressure profile, and seal performance as geometry angles of labyrinth teeth and honeycomb walls change at conditions normally found at higher pressures in these seals. Honeycomb walls were placed on the stator, ranging from 125°< θc< 55°. Labyrinth teeth were placed on the rotor at the same degrees. Honeycomb cell diameters were also varied, creating more resistance and turbulence within the flow. It was discovered that the honeycomb angle created stronger effects on vortices and boundary layer formation, while the labyrinth angle mainly affected the throttling of flow and loss generation. Combining all three angles created a relationship dictating the seal leakage. Dimensions of seals were based on gas turbine seals with changes to meet sCO₂ conditions. ANSYS was used to simulate static and rotating conditions until convergence on a specific geometry
Experimental Demonstration Of A Laboratory Scale Packed Bed Reactor For Thermochemical Energy Storage Using Embedded Heating Elements, Zachary Monem
Experimental Demonstration Of A Laboratory Scale Packed Bed Reactor For Thermochemical Energy Storage Using Embedded Heating Elements, Zachary Monem
Graduate Studies Theses and Dissertations 2026
Thermochemical energy storage (TCES) is an emerging technology that is being studied as a carbon-neutral renewable alternative to conventional methods of large-scale power generation, such as the utilization of fossil fuels. TCES makes use of thermochemical materials to store and discharge energy in two-step reversible chemical reactions. Among the most promising TCES materials are metal oxides, which possess significantly higher energy storage densities compared to other TCES materials; consequently, thermochemical reactors are used to store and discharge large amounts of energy during reduction-oxidation cycles using metal oxide materials. The current work focuses on the design and experimental demonstration of a …
Cfd Analysis Of A Full Heat Exchanger Between Ammonia And Supercritical Co2 In Aviation Application, Mairah Ahmed
Cfd Analysis Of A Full Heat Exchanger Between Ammonia And Supercritical Co2 In Aviation Application, Mairah Ahmed
Graduate Studies Theses and Dissertations 2026
The aviation industry’s transition toward lower-carbon propulsion systems has accelerated interest in alternative fuels, including ammonia–hydrogen fuel blends. In this work, a supercritical CO2 Brayton cycle is integrated with the exhaust stream of a turbofan engine to recover waste heat and utilize it for ammonia preheating and cracking. The recovered thermal energy raises the ammonia temperature to the level required for catalytic decomposition, enabling onboard hydrogen production. The proposed architecture combines ammonia cracking with a high-bypass, two-shaft turbofan engine representative of the propulsion system employed on the Boeing 737 MAX 8. This approach addresses the challenges associated with onboard hydrogen …
Pseudo-Boiling Of Supercritical Co2 In A Parallel-Flow Microchannel And A Micro-Jets Impingement Device And Single-Phase And Two-Phase Heat Transfer Of Subcritical Co2 Jets, Pranzal Ahmed
Graduate Studies Theses and Dissertations 2026
Carbon dioxide (CO2) is gaining attention as a low-toxicity, zero-ozone-depletion refrigerant with a global warming potential of 1, making it an attractive alternative to synthetic HFCs/HFOs. Near its critical point, CO2's thermophysical properties change sharply with small shifts in temperature and pressure — a behavior that can be exploited to enhance heat transfer in trans-critical power cycles and electronics cooling. This dissertation experimentally investigates heat transfer during the pseudo-boiling of supercritical CO2 in a parallel-flow microchannel and a micro-jet impingement device, alongside CO2 flow boiling and single-phase water heat transfer in micro-jet impingement. Using microfluidic devices instrumented with embedded resistance …
Analysis Of Variations In Flow-Independent Liquid Jet-In-Crossflow Injections, Michael Scott
Analysis Of Variations In Flow-Independent Liquid Jet-In-Crossflow Injections, Michael Scott
Honors Undergraduate Theses
Liquid fuel injection is a critical mechanism for the deliverance of liquid fuel in contemporary aircraft propulsion combustion systems due to its outsized influence in providing optimal combustion conditions and improving overall aircraft efficiency and performance. Despite this, these liquid jet in crossflow (LJIC) systems are highly variable due to conditions in the jet and the surrounding airflow, leading to variability in performance behavior and inconsistency in fuel mixing and combustion efficiency. This has prompted the introduction of solid pintile obstructions of novel designs to provide a more flow-independent fuel injection scheme and decrease variability of the jet properties against …
Experimental Analysis On Effects Of Inclination And Direction On Supercritical Carbon Dioxide Heat Transfer For Internal Pipe Flow, Emmanuel Gabriel-Ohanu
Experimental Analysis On Effects Of Inclination And Direction On Supercritical Carbon Dioxide Heat Transfer For Internal Pipe Flow, Emmanuel Gabriel-Ohanu
Electronic Theses and Dissertations, 2020-2023
Supercritical carbon dioxide (sCO2) can be utilized as a working or heat transfer fluid in various thermal systems with applications in large-scale power cycles; portable power production units, coolant systems and devices. However, there are no sufficient methods and equations of heat transfer coefficient correlations, and in addition insufficient research studies about the mechanisms controlling heat transfer processes for sCO2. This study is motivated by the need to understand the intricate properties of sCO2 heat transfer and fluid dynamics with an emphasis on flow direction and inclination effects. This paper presents the study on effects of gravity, buoyancy on sCO2 …
Experimental And Computational Heat Transfer Study Of Sco2 Single Jet Impingement, John Richardson
Experimental And Computational Heat Transfer Study Of Sco2 Single Jet Impingement, John Richardson
Electronic Theses and Dissertations, 2020-2023
The present study experimentally investigates the heat transfer capability of supercritical carbon dioxide (sCO2) single-jet impingement. The evaluated jet Reynolds number range is between 80,000 and 1,000,000, with a non-dimensional jet-to-target surface spacing of 2.8. CO2-impinging jet stagnation conditions were maintained at approximately 20 MPa and a temperature of 673 K for most experiments. The goal is to understand how changes in the aforementioned parameters influence heat transfer between the working fluid and the heated surface. Additionally, due to the elevated Reynolds numbers and difference in thermodynamic properties between air and CO2, air-derived impingement correlations may not be appropriate for …
Heat Transfer Characterization Of Carbon Dioxide In Micro Impinging Jet(S) Near Critical Conditions, Stephen Adeoye
Heat Transfer Characterization Of Carbon Dioxide In Micro Impinging Jet(S) Near Critical Conditions, Stephen Adeoye
Electronic Theses and Dissertations, 2020-2023
The continuous growth and demand of increased operating performances of electronics has brought about an increase in the chip power density posing threat to the thermal management of these devices. Although numerous thermal solutions ranging from passive to active cooling together with a variety of working fluids have been adopted, however, the question whether these available cooling methods could meet up with the ever-growing need for increased operating performances is a concerning one. Jet impingement cooling has been effectively used in many industrial applications due to its high heat transfer capability. The limited study at the micro scale suggests that …
Numerical Study Of Flow Of Supercritical Carbon Dioxide Inside Microchannels With Heat Transfer, Uday Manda
Numerical Study Of Flow Of Supercritical Carbon Dioxide Inside Microchannels With Heat Transfer, Uday Manda
Electronic Theses and Dissertations, 2020-2023
Heat transfer inside microscale geometries is a complex and a challenging phenomenon. As supercritical fluids display large variations in their properties in the vicinity of the critical point, their usage could be more beneficial than traditional coolants. This numerical study, in two parts, primarily focuses on the physics that drives the enhanced heat transfer characteristics of carbon dioxide (CO2) near its critical state and in its supercritical state. In the first part of the study, the flow of supercritical Carbon Dioxide (sCO2) over a heated surface inside a microchannel of hydraulic diameter 0.3 mm was studied using three-dimensional computational fluid …
Hotspot Cooling Performance For Confined Jet Impingement Cooling, Tanvir Ahmed Chowdhury
Hotspot Cooling Performance For Confined Jet Impingement Cooling, Tanvir Ahmed Chowdhury
Electronic Theses and Dissertations, 2020-2023
The current trend in microelectronics is to manufacture devices with increased computational powers and reduced size. These devices with increased power densities are consequently subject to extreme thermal loads. Thermal management of these power loads is extremely challenging. The presence of the hotspots can make this challenge even more difficult. Jet impingement cooling is one of the top candidates for removing such extreme heat fluxes in microelectronics. Jet impingement cooling can achieve heat transfer coefficients (HTCs) due to its normal incident flow-field and ability to thin the local thermal boundary layer in the stagnation region. This dissertation presents the hotspot …
High-Speed Imaging Of Reflected Shockwave-Initiated Combustion, Erik Ninnemann
High-Speed Imaging Of Reflected Shockwave-Initiated Combustion, Erik Ninnemann
Electronic Theses and Dissertations, 2020-2023
Shock tubes are considered ideal reactors and are used extensively to provide valuable chemical kinetic measurements, such as ignition delay times and in-situ species time-histories. However, due to nonideal affects the combustion of fuel inside shock tubes can become nonhomogeneous, particularly at low temperatures, which complicates the acquired data. In this work, the combustion of practical fuels used by society are investigated with high-speed imaging. First, high-speed images were captured through the end wall of the shock tube for two hydrogen-oxygen systems. The combustion process was found to initiate in two modes, one that is homogeneous across the fluid medium …
Rotational And Shower Head Cooling Hole Effects On Leading-Edge Jet Impingement Heat Transfer, Weston Olson
Rotational And Shower Head Cooling Hole Effects On Leading-Edge Jet Impingement Heat Transfer, Weston Olson
Electronic Theses and Dissertations, 2020-2023
Jet Impingement and shower head cooling are critical cooling techniques used to maintain turbine blades at operational temperatures. Jet impingement is extremely effective at removing large amounts of heat flux from the target surface, the inner blade wall, through stagnation point heat transfer. Shower head cooling produces a cooling film around the exterior of the blade, in return reducing external heat flux. The current work consisted of investigating the jet impingement effectiveness with rotational effects for two different cooling schemes. The analysis was conducted numerically using STAR CCM+ with two different turbulence models, the three equation Lag Elliptic Blending K …
A Shock Tube Chemical Kinetic Study Of Ethanol Oxidation At Elevated Pressures, Andrew Laich
A Shock Tube Chemical Kinetic Study Of Ethanol Oxidation At Elevated Pressures, Andrew Laich
Electronic Theses and Dissertations, 2020-2023
Understanding the combustion chemistry of ethanol is critical for continued proliferation and use in future internal combustion engines (ICEs) that will operate in a downsized, turbo-charged, high compression configuration. Detailed chemical kinetic reaction mechanisms already exist for ethanol, which have been validated over a range of operating conditions; however, capturing the conditions that may be seen in future ICEs requires extension of these conditions, namely at elevated pressure. Investigating the kinetics of ethanol existing in a combustion system first involve, for example, understanding a key global metric like ignition delay time (IDT) and measuring major or minor species in a …
Detailed Study Of Flow And Surface Heat Transfer Enhancement Mechanism In The Presence Of Dimples And/Or Protrusions, Gaurav Gupta
Detailed Study Of Flow And Surface Heat Transfer Enhancement Mechanism In The Presence Of Dimples And/Or Protrusions, Gaurav Gupta
Electronic Theses and Dissertations, 2020-2023
Recent advancements in material technology have led to the development of non-porous negative Poisson's ratio (NPR) materials (also called auxetic structures) by making spherical inline dimples on both sides of an elastic sheet. Manufacturing technologies such as 3-D printing and additive manufacturing paved the way to realize the complex shapes needed to achieve NPR behavior. These materials are desirable in many engineering applications, especially in the gas turbines hot-gas-path, due to their unique properties. In the current study, an effort is made to understand the flow physics and surface heat transfer mechanism for channel flow having one wall with spherical …
Tip Clearance Effect On Convective Heat Transfer In Micro Scale Pin Fins, Hanieh Tabkhivayghan
Tip Clearance Effect On Convective Heat Transfer In Micro Scale Pin Fins, Hanieh Tabkhivayghan
Electronic Theses and Dissertations, 2020-2023
Fluid flow and local heat transfer in a microchannel with single and array of pin fins have been studied. For the single pin fin case, a microchannel with a 150-µm diameter pin fin with a tip clearance was experimentally and numerically studied for three Reynolds numbers in laminar regime. Tip clearances of 0, 30, 45 and 100 µm in a 200-µm high microchannel. Experimental and numerical local temperatures and the corresponding Nusselt numbers along the centerline of the pin fin were presented and discussed. Local temperatures were measured on top of the heater surface and downstream the pin fin through …
Fundamental Characteristics Of Supercritical Co2 Combustion, Raghu Veera Manikantachari Kancherla
Fundamental Characteristics Of Supercritical Co2 Combustion, Raghu Veera Manikantachari Kancherla
Electronic Theses and Dissertations
The direct-fired supercritical CO2 (sCO2) cycle is conceptually superior to many of the trending energy production technologies due to their remarkably promising efficiency, environmental friendliness and cost. The accurate simulation of this combustion is very important because the operating conditions are very challenging to its experimentation. Hence, the current work focuses on identifying various thermal, transport, chemical kinetic models, investigating various fundamental characteristics and verifying the validity of important underlying modeling assumptions in focus to supercritical CO2 combustion. In the current work, various thermal and transport property models are identified based on accuracy, computational cost and ease of implementation for …
Ignition Studies Of Oxy-Syngas/Co2 Mixtures Using Shock Tube For Cleaner Combustion Engines, Samuel Barak
Ignition Studies Of Oxy-Syngas/Co2 Mixtures Using Shock Tube For Cleaner Combustion Engines, Samuel Barak
Electronic Theses and Dissertations
In this study, syngas combustion was investigated behind reflected shock waves in order to gain insight into the behavior of ignition delay times and effects of the CO2 dilution. Pressure and light emissions time-histories measurements were taken at a 2 cm axial location away from the end wall. High-speed visualization of the experiments from the end wall was also conducted. Oxy-syngas mixtures that were tested in the shock tube were diluted with CO2 fractions ranging from 60% - 85% by volume. A 10% fuel concentration was consistently used throughout the experiments. This study looked at the effects of changing the …
An Experimental Investigation Of Heat Transfer For Arrays Of Impingement Jets Onto The Featured Surfaces With Cylindrical And Elliptical Raised Surfaces, Marc A. Medina
Honors Undergraduate Theses
This study focuses on multi-jet impingement for gas turbine geometries in which the objective is to understand the influence of the roughness elements on a target surface to the heat transfer. Current work has proven that implementing roughness elements for multi-jet impingement target surfaces has increased heat transfer ranging anywhere from 10-30%. This study has chosen to investigate three different roughness elements, elliptical in cross-section, to compare to smooth surface geometries for multi-jet impingement. An experimental was taken for this study to extend the current knowledge of multi-jet impingement geometries and to further understand the heat transfer performance. A temperature …
A Passive Cooler For A Humid Climate, Steven Gilbert Ring
A Passive Cooler For A Humid Climate, Steven Gilbert Ring
Retrospective Theses and Dissertations
This paper examine a passive cooling system for a humid climate. This system will be divided into two parts, a radiative system and an evaporative system combined into a roof pond system. Performance of the radiative system will be enhanced through the use of a selective cover which will make use of an atmospheric window between 8 and 13um. An attempt will also be made to thermally isolate the radiative system from convective gains with the evaporative system. The evaporative system will consist of a water, solvent and dye layer over the selective cover of the radiative system. The performance …