Heat Transfer, Combustion Commons^™

Multiphysics Transport In Porous Thermal Protection Systems: Experimental Characterization Of Gas Permeability And Radiative Properties, Yejajul Hakim

Theses and Dissertations--Mechanical and Aerospace Engineering

Porous thermal protection systems (TPS) used in hypersonic vehicles exhibit coupled gas and radiative transport across multiple regimes and length scales. Accurate performance prediction requires reliable characterization of permeability, slip-flow behavior, and radiative transport properties, particularly for low-permeability and charred materials where existing data are limited. This dissertation presents experimental methods for characterizing multiphysics transport in porous TPS materials. A modular flow system was developed to measure permeability and slip behavior in both virgin and charred materials under relevant environments. A transient pressure decay method enables accurate permeability estimation in low-permeability regimes and provides insight into effective pore structure. Results …

Growth Kinetics And Stability Of Metal Halide Perovskite Nanocrystals: Influence Of Stirring Speed And Water Exposure, You-Lin Huang

Theses and Dissertations--Mechanical and Aerospace Engineering

Cesium lead bromide (CsPbBr₃) perovskite nanocrystals (NCs) have garnered significant interest due to their exceptional optoelectronic properties, including high photoluminescence quantum yield, tunable bandgap, and excellent carrier dynamics. These attributes make them promising candidates for applications in light-emitting diodes, photovoltaics, and sensing technologies. However, optimizing their synthesis and improving their environmental stability remain critical challenges. This dissertation explores the growth kinetics of CsPbBr₃ NCs, focusing on the effects of stirring speed and water exposure on their structural and optical properties.

The synthesis of CsPbBr₃ NCs was performed using both mechanochemical (MC) and antisolvent methods, enabling an …

High-Fidelity Coupling For Studies Of Ablative Materials At Hypersonic Conditions, Aleksander Zibitsker

Theses and Dissertations--Mechanical and Aerospace Engineering

The development of accurate models and robust numerical tools for simulating ablative thermal protection materials (TPMs) in hypersonic flows is crucial for advancing atmospheric entry and hypersonic technologies. Traditional methods for simulating ablative materials often rely on heavy assumptions, such as equal heat and mass transfer coefficients and chemical equilibrium in the boundary layer, leading to conservative thermal protection system (TPS) designs and insufficient accuracy for certain in-flight ablation phenomena.

This work presents a high-fidelity and versatile coupled framework between hypersonic flow and material response solvers. The flow domain is modeled with an innovative overset CHAMPS NBS-Cart solver, which features …

Attrition Study Of Copper-Supplemented Iron-Based Oxygen Carrier For Chemical Looping Combustion, Neng Huang

Theses and Dissertations--Mechanical and Aerospace Engineering

Chemical looping combustion (CLC) is a promising technology that can mitigate the carbon emissions for power generation. The cost of oxygen carriers (OCs) impedes the scale up of CLC. Compared to synthetic iron-based OCs, red mud (RM), an abundant iron-based solid waste from industry, is a cost-effective choice due to its intrinsic inclusion of both inert and catalytic phases that are crucial for CLC. It was anticipated that the addition of copper oxide to RM using a mechanical mixing method that can be easily scaled up would enhance both reactivity and oxygen transport capacity (OTC), and the heat of reaction …

A Computational Fluid Dynamic Analysis Of Oxyacetylene Combustion Flow For Use In Material Response Boundary Conditions, Craig Meade

Theses and Dissertations--Mechanical and Aerospace Engineering

Oxyacetylene torches are used in the aerospace industry and research to test thermal protection system materials (TPS) due to their high flame temperatures and high heat flux capabilities. The purpose of this work is to determine a combustion model to accurately simulate the high temperature flow of an oxyacetylene torch. The flow conditions around a sample material can then be used as boundary conditions when modeling TPS material response. Two separate combustion models with equilibrium chemistry were investigated using ANSYS Fluent™; the Eddy-Dissipation Model, and the Partially Premixed model.The results of this study are compared to existing experiments for validation.

Impact Of Spallation And Internal Radiation On Fibrous Ablative Materials, Raghava Sai Chaitanya Davuluri

Theses and Dissertations--Mechanical and Aerospace Engineering

Space vehicles are equipped with Thermal Protection Systems (TPS) that encounter high heat rates and protect the payload while entering a planetary atmosphere. For most missions that interest NASA, ablative materials are used as TPS. These materials undergo several mass and energy transfer mechanisms to absorb intense heat. The size and construction of the TPS are based on the composition of the planetary atmosphere and the impact of various ablative mechanisms on the flow field and the material. Therefore, it is essential to quantify the rates of different ablative phenomena to model TPS accurately. In this work, the impact of …

Radiative Conductivity Estimation Using Direct Approach For Fibrous Materials, Mohammad Khaleel

Theses and Dissertations--Mechanical and Aerospace Engineering

During planetary entry, space vehicles encounter high loads of thermal energy which requires a thermal protection system. Ablative thermal protection systems are usually made out of fibrous materials that exhibit internal radiation. In order to model the internal radiation response of a thermal protection system one should obtain proper radiative properties as well as thermal properties. The objective of this work is to provide a method that solves for the solid/gas thermal conductivity. Which can be used in coupled detailed radiative analysis.

Keywords: radiative conductivity, fibrous materials, radiative transfer, thermal protection system, P1 approximation, Finite Volume method.

A Decoupled Engineering Methodology For Accurate Prediction Of Ablative Surface Boundary Conditions In Thermal Protection Systems, Justin Cooper

Theses and Dissertations--Mechanical and Aerospace Engineering

The main objective of the present work is to demonstrate a method for prediction of aerothermal environments in the engineering design of hypersonic vehicles as an alternative to the current heritage method. Flat plate and stagnation point boundary layer theory require multiple assumptions to establish the current engineering paradigm. Chief among these assumptions is the similarity between mass and heat transfer. Origins of these assumptions are demonstrated and their relationship to conservative engineering design is analyzed, as well as conditions where they possibly break down. An alternative approach for assessing aerothermal environments from the fluid domain is presented, which permits …

Numerical Investigation On The Effect Of Spectral Radiative Heat Transfer Within An Ablative Material, Raghava S. C. Davuluri, Rui Fu, Kaveh A. Tagavi, Alexandre Martin

Mechanical Engineering Faculty Publications

The spectral radiative heat flux could impact the material response. In order to evaluate it, a coupling scheme between KATS - MR and P1 approximation model of radiation transfer equation (RTE) is constructed and used. A Band model is developed that divides the spectral domain into small bands of unequal widths. Two verification studies are conducted: one by comparing the simulation computed by the Band model with pure conduction results and the other by comparing with similar models of RTE. The comparative results from the verification studies indicate that the Band model is computationally efficient and can be used to …

Fully-Developed Fire Temperature In A Compartment With Varying Wood Fuel Loads, Keisuke Himoto, Masaki Noaki, Ken Matsuyama

Progress in Scale Modeling, an International Journal

Appropriate evaluation of fire behavior during the fully-developed phase is important for assessing the risk of building collapse and fire spread to adjacent buildings. In this study, a series of model experiments was conducted to investigate the fire behavior in compartments with varying wood fuel loads. Under small opening conditions, the increase in the wood fuel load had no notable effect on the heat release rate (HRR), but increased the fire duration and gas temperature. In certain cases, wood surface combustion continued even after flame ejection from the opening had ended, which maintained a high gas temperature for a long …

Fully Coupled Internal Radiative Heat Transfer For The 3d Material Response Of Heat Shield, Raghava S. C. Davuluri, Rui Fu, Kaveh A. Tagavi, Alexandre Martin

Mechanical Engineering Faculty Publications

The radiative transfer equation (RTE) is strongly coupled to the material response code KATS. A P-1 approximation model of RTE is used to account for radiation heat transfer within the material. First, the verification of the RTE model is performed by comparing the numerical and analytical solutions. Next, the coupling scheme is validated by comparing the temperature profiles of pure conduction and conduction coupled with radiative emission. The validation study is conducted on Marschall et al. cases (radiant heating, arc-jet heating, and space shuttle entry), 3D Block, 2D IsoQ sample, and Stardust Return Capsule. The validation results agree well for …

Numerical Reconstruction Of Spalled Particle Trajectories In An Arc-Jet Environment, Raghava S. C. Davuluri, Sean C. C. Bailey, Kaveh A. Tagavi, Alexandre Martin

Mechanical Engineering Faculty Publications

To evaluate the effects of spallation on ablative material, it is necessary to evaluate the mass loss. To do so, a Lagrangian particle trajectory code is used to reconstruct trajectories that match the experimental data for all kinematic parameters. The results from spallation experiments conducted at the NASA HYMETS facility over a wedge sample were used. A data-driven adaptive methodology was used to adapts the ejection parameters until the numerical trajectory matches the experimental data. The preliminary reconstruction results show that the size of the particles seemed to be correlated with the location of the ejection event. The size of …

Kinetics Of Elementary Reactions In Graphene Oxidation And Kinetics Of Oh* In Hydrogen Flames, Siamak Mahmoudi

Theses and Dissertations--Mechanical and Aerospace Engineering

Due to diverse applications of graphene, a kinetic mechanism describing rates of elementary reactions is extremely useful. To achieve that goal the elementary reactions need to be detected and their rates need to be determined. In this work the objectives are to use first-principle tools to find those reactions and analyze their paths in the context of graphene oxidation. Density functional theory (DFT) calculations provide the best approximation to the Schr\"{o}dinger equation, which is not feasible to solve analytically for large molecules like graphene. We have performed these calculations to find stable configurations (geometry optimization) and minimum energy paths between …

The Role Of Live Conifer Fuels In Crown Fires Spread, Adnan Darwish Ahmad

Theses and Dissertations--Mechanical and Aerospace Engineering

Live foliage for some tree and shrub species can support flaming fire spread at much higher moisture content than dead fuel materials. However, the role of live fuels in forest fires has been controversial in the past decades. Although ignition and spread statistical data for live and dead fuels exist in the literature, a clear understanding of the fundamental difference in the burning behavior is missing. To illuminate the role of live fuel on forest fire spreading, a laboratory ignition experiment was designed to examine the burning behavior of live Norway spruce needles. A schlieren-Infrared combined measurement apparatus was developed …

Evaluation Of Radiative Conductivity Inside A Porous Media With The Effect Of Participating Medium Based On Microscale Imaging, Mingping Zheng

Theses and Dissertations--Mechanical and Aerospace Engineering

Space vehicles will experience high loads of heat while entering the planetary atmosphere. At such high temperature, radiation becomes the dominant mode of heat transfer. Since the atmospheric entry environment is nearly impossible to duplicate in a laboratory environment, a numerical model to evaluate thermal performance of the thermal protection system was established. The model simulates the radiative heat transfer process in highly porous media, and the process also takes into account the influence of the participating media. An iterative approach and periodic boundary conditions are used to solve The unbalanced heat flux problem. CT scanned microscale Fiberform and artificial …

Waste Heat Recovery Of Industrial Regenerative Thermal Oxidizer (Rto), A Case Study, James Trimpe Jr.

Theses and Dissertations--Mechanical and Aerospace Engineering

Industrial processes that utilize and release hazardous compounds into the atmosphere are required to break down those compounds before exhausting them from their facilities. An industry-recognized method to break down those hazardous compounds is through thermal oxidation. Thermal oxidation is a process where the compounds are exposed to their auto-ignition temperature in an oxygen-rich environment and combust. The output of thermal oxidation is carbon dioxide, water vapor, and heat. Thermal oxidizers are equipment that performs the thermal oxidation process. The heat output from thermal oxidizers is wasted if directly exhausted into the atmosphere. Regenerative thermal oxidizers (RTOs) use the waste …

Modeling Thin Layers In Material Response Solvers, Christen Setters

Theses and Dissertations--Mechanical and Aerospace Engineering

Thermal Protection Systems (TPS) are a necessary component for atmospheric entry. Most TPS contain thin layers of various materials such as ceramic coatings, pore sealers and bonding agents. When modeling TPS, these thin layers are often neglected due to the difference in scale between the TPS (centimeters) and the thin layers (micrometers). In this study, a volume-averaging flux-conservation method is implemented in the governing equations of a finite volume material response code. The model proposes the addition of a volume and area fraction coefficient which utilizes a weighted-averaging between the amount of thin layer and heat shield material in a …

Development Of Universal Solver For High Enthalpy Flows Through Ablative Materials, Umran Duzel

Theses and Dissertations--Mechanical and Aerospace Engineering

Atmospheric entry occurs at very high speeds which produces high temperature around the vehicle. Entry vehicles are thus equipped with Thermal Protection Systems which are usually made of ablative materials. This dissertation presents a new solver that models the atmospheric entry environment and the thermal protection systems. In this approach, both the external flow and the porous heat shield are solved using the same computational domain. The new solver uses the Volume Averaged Navier-Stokes Equations adapted for hypersonic non-equilibrium flow, and is thus valid for both domains. The code is verified using analytical problems, set of benchmarks and also a …

Numerical Simulations Of Premixed Flames Of Multi Component Fuels/Air Mixtures And Their Applications, Essa Kh I J Salem

Theses and Dissertations--Mechanical and Aerospace Engineering

Combustion has been used for a long time as a means of energy extraction. However, in the recent years there has been further increase in air pollution, through pollutants such as nitrogen oxides, acid rain etc. To solve this problem, there is a need to reduce carbon and nitrogen oxides through lean burning, fuel dilution and usage of bi-product fuel gases. A numerical analysis has been carried out to investigate the effectiveness of several reduced mechanisms, in terms of computational time and accuracy. The cases were tested for the combustion of hydrocarbons diluted with hydrogen, syngas, and bi-product fuel in …

3d Numerical Study Of Multiphase Counter-Current Flow Within A Packed Bed For Post Combustion Carbon Dioxide Capture, Li Yang, Fang Liu, Zhengchang Song, Kunlei Liu, Kozo Saito

Mechanical Engineering Faculty Publications

The hydrodynamics within counter-current flow packed beds is of vital importance to provide insight into the design and operational parameters that may impact reactor and reaction efficiencies in processes used for post combustion CO₂ capture. However, the multiphase counter-current flows in random packing used in these processes are complicated to visualize. Hence, this work aimed at developing a computational fluid dynamics (CFD) model to study more precisely the complex details of flow inside a packed bed. The simulation results clearly demonstrated the development of, and changes in, liquid distributions, wetted areas, and film thickness under various gas and liquid …

Laminar And Turbulent Study Of Combustion In Stratified Environments Using Laser Based Measurements, Stephen William Grib

Theses and Dissertations--Mechanical and Aerospace Engineering

Practical gas turbine engine combustors create extremely non-uniform flowfields, which are highly stratified making it imperative that similar environments are well understood. Laser diagnostics were utilized in a variety of stratified environments, which led to temperature or chemical composition gradients, to better understand autoignition, extinction, and flame stability behavior. This work ranged from laminar and steady flames to turbulent flame studies in which time resolved measurements were used.

Edge flames, formed in the presence of species stratification, were studied by first developing a simple measurement technique which is capable of estimating an important quantity for edge flames, the advective heat …

NoX Formation In Light-Hydrocarbon, Premixed Flames, Robert T. Hughes

Theses and Dissertations--Mechanical and Aerospace Engineering

This study explores the reactions and related species of NO_x pollutants in methane flames in order to understand their production and consumption during the combustion process. To do this, several analytical simulations were run to explore the behavior of nitrogen species in the pre-flame, post- flame, and reaction layer regions. The results were then analyzed in order to identify all "steady-state" species in the flame as well as the determine all the unnecessary reactions and species that are not required to meet a defined accuracy. The reductions were then applied and proven to be viable.

Characterization Of Methane-Air Diffusion Flames For Flame Synthesis Application Through Optical Diagnostics, Zhaojin Diao

Theses and Dissertations--Mechanical and Aerospace Engineering

Flame synthesis is a growing field of research aiming at forming new materials and coatings through injection of seed materials into a flame. Accurate prediction of the thermal structure of these flames requires detailed information on the radiative properties and a thorough understanding of the governing combustion processes. The objective of this work is to establish a basic optical diagnostic characterization of different methane-air diffusion flames of different complexity. The basic principles are developed and demonstrated at a rotational symmetric co-flow burner and finally applied to a burner consisting of six clustered microflames which is designed for future flame synthesis …

The Kentucky Re-Entry Universal Payload System (Krups): Sub-Orbital Flights, James Devin Sparks

Theses and Dissertations--Mechanical and Aerospace Engineering

The Kentucky Re-entry Universal Payload System (KRUPS) is an adaptable testbed for atmosphere entry science experiments, with an initial application to thermal protection systems (TPS). Because of the uniqueness of atmospheric entry conditions that ground testing is unable to replicate, scientists principally rely on numerical models for predicting entry conditions. The KRUPS spacecraft, developed at the University of Kentucky, provides an inexpensive means of obtaining validation data to verify and improve these models.

To increase the technology readiness level (TRL) of the spacecraft, two sub-orbital missions were developed. The first mission, KUDOS, launched August 13th, 2017 on a Terrier-Improved Malamute …

Multiphase Interaction In Low Density Volumetric Charring Ablators, Ali D. Omidy

Theses and Dissertations--Mechanical and Aerospace Engineering

The present thesis provides a description of historical and current modeling methods with recent discoveries within the ablation community. Several historical assumptions are challenged, namely the presence of water in Thermal Protection System (TPS) materials, presence of coking in TPS materials, non-uniform elemental production during pyrolysis reactions, and boundary layer gases, more specifically oxygen, interactions with the charred carbon interface.

The first topic assess the potential effect that water has when present within the ablator by examining the temperature prole histories of the recent flight case Mars Science Laboratory. The next topic uses experimental data to consider the instantaneous gas …

Solvent Degradation And Emissions From A 0.7mwe Pilot Co2 Capture System With Two-Stage Stripping, Jesse Thompson, Heather Nikolic, Megan Combs, Saloni Bhatnagar, Jonathan Pelgen, Keemia Abad, Kunlei Liu

Center for Applied Energy Research Faculty and Staff Publications

The UKy-CAER team successfully tested an advanced 0.7 MWe post-combustion CO₂ capture system on a coal-fired power plant using a heat integration process combined with two-stage stripping to enhance the CO₂ absorber performance. One of the unique feature of the UKy-CAER integrated process is a two-stage stripping unit for solvent regeneration. The secondary stripper is empowered by the heat rejection from a conventional steam-heated (primary) stripper. The secondary stripper outlet stream at the commercial scale can be used as boiler secondary combustion air, consequently enriching the flue gas with CO₂, resulting in less energy penalty required …

A Physics-Based Approach To Modeling Wildland Fire Spread Through Porous Fuel Beds, Tingting Tang

Theses and Dissertations--Mechanical and Aerospace Engineering

Wildfires are becoming increasingly erratic nowadays at least in part because of climate change. CFD (computational fluid dynamics)-based models with the potential of simulating extreme behaviors are gaining increasing attention as a means to predict such behavior in order to aid firefighting efforts. This dissertation describes a wildfire model based on the current understanding of wildfire physics. The model includes physics of turbulence, inhomogeneous porous fuel beds, heat release, ignition, and firebrands. A discrete dynamical system for flow in porous media is derived and incorporated into the subgrid-scale model for synthetic-velocity large-eddy simulation (LES), and a general porosity-permeability model is …

Notes On Contributions To The Science Of Rare Earth Element Enrichment In Coal And Coal Combustion Byproducts, James C. Hower, Evan J. Granite, David B. Mayfield, Ari S. Lewis, Robert B. Finkelman

Center for Applied Energy Research Faculty and Staff Publications

Coal and coal combustion byproducts can have significant concentrations of lanthanides (rare earth elements). Rare earths are vital in the production of modern electronics and optics, among other uses. Enrichment in coals may have been a function of a number of processes, with contributions from volcanic ash falls being among the most significant mechanisms. In this paper, we discuss some of the important coal-based deposits in China and the US and critique classification systems used to evaluate the relative value of the rare earth concentrations and the distribution of the elements within the coals and coal combustion byproducts.

Effect Of Spalled Particles Thermal Degradation On A Hypersonic Flow Field Environment, Raghava S. C. Davuluri, Huaibao Zhang, Alexandre Martin

Mechanical Engineering Faculty Publications

Two-way coupling is performed between a spallation code and a hypersonic aerothermodynamics CFD solver to evaluate the effect of spalled particles on the flow field. Time accurate solutions are computed in argon and air flow fields. A single particle simulations and multiple particles simulations are performed and studied. The results show that the carbon vapor released by spalled particles tend to change the composition of the flow field, particularly the upstream region of the shock.

Energy Resources Use Metrics, Rahul Y. Nehete

Theses and Dissertations--Mechanical and Aerospace Engineering

Energy resources use has been considered as a key component of sustainable development. Data related to global, regional, state, sector, industry and process demonstrate that a significant reduction of energy resources for a given production rate in manufacturing processes requires an introduction of transformational technologies at the process level, propagating the impact to higher scales, leading not just to a gradual improvement of traditional technologies but to more sustainable development.

The study offers two approaches to the formulation of the limits of energy use in the context of sustainable development. The first is to construct a map of key selected …