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2015

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Articles 4081 - 4110 of 7527

Full-Text Articles in Engineering

Numerical Characterization Of Convective Heat Transfer Of Low-Rise Buildings, Ranchi Chen Apr 2015

Numerical Characterization Of Convective Heat Transfer Of Low-Rise Buildings, Ranchi Chen

Open Access Theses

The convective heat transfer coefficient (CHTC) is an important parameter to evaluate the efficiency of building-integrated photovoltaic/Thermal (PV/T) system and the energy exchange within the turbulent atmospheric boundary layer. Reynolds-average Navier-Stokes approach has been frequently used to predict the CHTC at the surface of low rise roof but incapable of predicting transient behavior of separation, reattachment and recirculation both on the windward and leeward surface. However, Large Eddy Simulation approach (LES) could provide accurate flow field and temperature field around the low rise building. ^ The current study uses Large Eddy Simulation with Smagorinsky-Lily model and the Shear Stress Transport …

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Performance Analysis Of Vortex Based Mixers For Confined Flows, Timo Buschhagen Apr 2015

Performance Analysis Of Vortex Based Mixers For Confined Flows, Timo Buschhagen

Open Access Theses

The hybrid rocket is still sparsely employed within major space or defense projects due to their relatively poor combustion efficiency and low fuel grain regression rate. Although hybrid rockets can claim advantages in safety, environmental and performance aspects against established solid and liquid propellant systems, the boundary layer combustion process and the diffusion based mixing within a hybrid rocket grain port leaves the core flow unmixed and limits the system performance. One principle used to enhance the mixing of gaseous flows is to induce streamwise vorticity. The counter-rotating vortex pair (CVP) mixer utilizes this principle and introduces two vortices into …

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High Density Collagen Fibril Constructs With Tunable Mechano-Biology In Acellular And Cellular Configurations, Kevin Blum Apr 2015

High Density Collagen Fibril Constructs With Tunable Mechano-Biology In Acellular And Cellular Configurations, Kevin Blum

Open Access Theses

Collagen has long been used as a material for tissue engineering due to its prevalence in the extracellular matrix of connective tissues. However, traditional collagen materials utilizing atelocollagen and acid solubilized telocollagen have lacked the mechanical integrity and collagen fibril density found in the in vivo state. Here, we utilize collagen oligomers and confined compression to forcibly remove a portion of the fluid phase component. Materials were created with controlled, substantially increased material properties, including order of magnitude increases in collagen fibril density, elastic modulus, compressive modulus,and resistance to proteolytic degradation. The technique was found to be amenable to cell …

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Effect Of Electrode Geometry On High Energy Spark Discharges In Air, Mounia Belmouss Apr 2015

Effect Of Electrode Geometry On High Energy Spark Discharges In Air, Mounia Belmouss

Open Access Theses

The government, aerospace, and transportation industries are deeply invested in developing new technologies to improve the performance and maneuverability of current and future aircraft while reducing aerodynamic noise and environmental impact. One of the key pathways to meet these goals is through aerodynamic flow control, which can involve suppressing or inducing separation, transition and management of turbulence in boundary layers, increasing the lift and reducing the drag of airfoils, and gas mixing to control fluctuating forces and aerodynamic noise [1]. In this dissertation, the complex flow field following a spark discharge is studied for a range of geometries and discharge …

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Characterization Of Vectorization Strategies For Recursive Algorithms, Shruthi Balakrishna Apr 2015

Characterization Of Vectorization Strategies For Recursive Algorithms, Shruthi Balakrishna

Open Access Theses

A successful architectural trend in parallelism is the emphasis on data parallelism with SIMD hardware. Since SIMD extensions on commodity processors tend to require relatively little extra hardware, executing a SIMD instruction is essentially free from a power perspective, making vector computation an attractive target for parallelism. SIMD instructions are designed to accelerate the performance of applications such as motion video, real-time physics and graphics. Such applications perform repetitive operations on large arrays of numbers. While the key idea is to parallelize significant portions of data that get operated by several sequential instructions into a single instruction, not every application …

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Low Income, Supermarket Accessibility, And The Transportation Network: A Multimodal Analysis Identifying Areas Of Poor Accessibility And Intervention Strategies In Indianapolis, Indiana, Andrea Leigh Bailey Apr 2015

Low Income, Supermarket Accessibility, And The Transportation Network: A Multimodal Analysis Identifying Areas Of Poor Accessibility And Intervention Strategies In Indianapolis, Indiana, Andrea Leigh Bailey

Open Access Theses

The United States Department of Agriculture (USDA) Economic Research Service estimates that 23.5 million people live in food deserts, over half of which are considered low-income residents. Accurately defining a food desert is crucial as the designated areas can benefit from grant opportunities and funding priority. To qualify as an urban food desert, the USDA requires that at least 500 residents or one-third of the population live outside a one-mile buffer from a supermarket as well as have a median income of less than 80% of the area average or a poverty rate of greater than 20%. Approaches in the …

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Asymptotic Modelling Of A Thermopiezoelastic Anisotropic Smart Plate, Yufei Long Apr 2015

Asymptotic Modelling Of A Thermopiezoelastic Anisotropic Smart Plate, Yufei Long

Open Access Theses

Motivated by the requirement of modelling for space flexible reflectors as well as other applications of plate structures in engineering, a general anisotropic laminated thin plate model and a monoclinic Reissner-Mindlin plate model with thermal deformation, two-way coupled piezoelectric effect and pyroelectric effect is constructed using the variational asymptotic method, without any ad hoc assumptions. Total potential energy contains strain energy, electric potential energy and energy caused by temperature change. Three-dimensional strain field is built based on the concept of warping function and decomposition of the rotation tensor. The feature of small thickness and large in-plane dimension of plate structure …

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The Effects Of An Electric Field On The Sintering Of Ceramics, Kara E. Luitjohan Apr 2015

The Effects Of An Electric Field On The Sintering Of Ceramics, Kara E. Luitjohan

Open Access Theses

Sintering is a method used to condense a solid powder material into a single solid mass allowing for the production of metal or ceramic parts. Different sintering techniques involve the manipulation of different processing variables. To fully exploit the processing variables, how they affect the sintering process must be fully understood. One such processing variable is an applied electric field, utilized in spark plasma sintering and flash sintering. Both techniques allow for densification to occur at lower temperatures and in shorter times when compared to other sintering techniques. Though various theories exist in literature for how the electric field affects …

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Quantifying Moisture Transport In Cementitious Materials Using Neutron Radiography, Catherine L. Lucero Apr 2015

Quantifying Moisture Transport In Cementitious Materials Using Neutron Radiography, Catherine L. Lucero

Open Access Theses

A portion of the concrete pavements in the US have recently been observed to have premature joint deterioration. This damage is caused in part by the ingress of fluids, like water, salt water, or deicing salts. The ingress of these fluids can damage concrete when they freeze and expand or can react with the cementitious matrix causing damage. To determine the quality of concrete for assessing potential service life it is often necessary to measure the rate of fluid ingress, or sorptivity. Neutron imaging is a powerful method for quantifying fluid penetration since it can describe where water has penetrated, …

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Individual Analysis Of T2*-Weighted Gradient Echo Imaging In Asymptomatic And Symptomatic Athletes, Xianglun Mao Apr 2015

Individual Analysis Of T2*-Weighted Gradient Echo Imaging In Asymptomatic And Symptomatic Athletes, Xianglun Mao

Open Access Theses

Mild traumatic brain injury (mTBI), is a commonly occurred sports-related injury, especially in contact sports like football and soccer. Hemorrhage will appear as hypointense lesions on T2 *-weighted images, resulting from mTBI. Thus, T 2*-weighted gradient echo pulse sequence can be used to generate magnitude susceptibility-weighted (SW) images, and to further detect negative intensity changes of different regions of interests (ROIs) inside human brains. Our goal was to investigate how the ROI-specific intensity changes in each individual sports athlete over a single competition season and to interrogate whether these changes are correlated with repetitive subconcussive or …

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Computational Study Of Nano- And Meso-Scale Size Effects On Thermal Transport, Eshaan Mathew Apr 2015

Computational Study Of Nano- And Meso-Scale Size Effects On Thermal Transport, Eshaan Mathew

Open Access Theses

In the era where structures and devices are of the order of a few nanometers, a detailed understanding on the heat carriers in nanostructured devices is required to enable further improvements and advances. ^ In the first portion of this thesis we develop a new methodology using Molecular Dynamics (MD) to determine the thermal conductivity of argon with a modified Leonard Jones potential as a function of the modulation frequency input heat flux. We observe a decrease in the thermal conductivity as the heat transport enters the ballistic regime by an order of magnitude which agrees with some of the …

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Measurement, Characterization, And Effects Of Head Impacts In Women's Soccer, Emily C. Mccuen Apr 2015

Measurement, Characterization, And Effects Of Head Impacts In Women's Soccer, Emily C. Mccuen

Open Access Theses

The potential for long term neurological deficits resulting from repetitive head trauma is a major concern for collision sport athletes. Research conducted on football played has found neurophysiologic changes in the absence of concussion in athletes as early as high school age. Given that female soccer players show the highest rate of concussion for female athletes and a higher rate of concussion than their male counterparts, it is important to characterize the types of impacts female soccer athletes receive and assess female soccer athletes for neurophysiologic changes due to these impacts. This work paired head impact sensors with functional MRI …

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The Effect Of Integrated Science, Engineering, Technology, And Mathematics Lessons On Interest And Engagement Of Secondary Students, Cameron Nunan Apr 2015

The Effect Of Integrated Science, Engineering, Technology, And Mathematics Lessons On Interest And Engagement Of Secondary Students, Cameron Nunan

Open Access Theses

This study set out to answer the research question: Does teaching a single lesson, utilizing the interconnected principles of STEM in STEM courses, increase overall student interest and engagement in STEM classes in secondary schools? The literature review established a need for student interest in STEM to help fill future STEM careers. ^ Integrated STEM lessons were a viable option for increasing interest, but existing research on the matter was limited. Integrated STEM lessons were applied at a test site school using a multiple baseline framework and evaluated responses with a variation of the Intrinsic Motivation Inventory (IMI). According to …

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Flexible Weapons Architecture Design, William C. Pyant Apr 2015

Flexible Weapons Architecture Design, William C. Pyant

Open Access Theses

Present day air-delivered weapons are of a closed architecture, with little to no ability to tailor the weapon for the individual engagement. The closed architectures require weaponeers to make the target fit the weapon instead of fitting the individual weapons to a target. The concept of a flexible weapons aims to modularize weapons design using an open architecture shell into which different modules are inserted to achieve the desired target fractional damage while reducing cost and civilian casualties. This thesis shows that the architecture design factors of damage mechanism, fusing, weapons weight, guidance, and propulsion are significant in enhancing weapon …

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Preparation Of Bismuth Telluride Based Thermoelectric Nanomaterials Via Low-Energy Ball Milling And Their Property Characterizations, Christopher Robinson Apr 2015

Preparation Of Bismuth Telluride Based Thermoelectric Nanomaterials Via Low-Energy Ball Milling And Their Property Characterizations, Christopher Robinson

Open Access Theses

Thermoelectric materials are able to convert energy between heat and electricity with no moving parts, making them very appealing for power generation purposes. This is particularly appealing since many forms of energy generation lose energy to waste heat. The Livermore National Laboratory estimates that up to 55% of the energy created in traditional power plants is lost through heat generation [1]. As greenhouse gas emissions become a more important issue, large sources of waste like this will need to be harnessed. ^ Adoption of these materials has been limited due to the cost and efficiency of current technology. Bismuth telluride …

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Exploiting Intra-Warp Address Monotonicity For Fast Memory Coalescing In Gpus, Hector Rodriguez-Simmonds Apr 2015

Exploiting Intra-Warp Address Monotonicity For Fast Memory Coalescing In Gpus, Hector Rodriguez-Simmonds

Open Access Theses

Graphics Processing Units (GPUs) are growing increasingly popular as general purpose compute accelerators. GPUs are best suited for applications which have abundant data parallelism wherein the computation expressed as a single thread can be applied over a large set of data items. One key constraint that affects application performance on GPUs is that the underlying hardware is single-instruction, multiple data (SIMD) hardware which requires parallel instructions from the multiple threads to execute in a lock-step manner. The benefits of lock-step execution can be seriously degraded if the threads diverge (because of memory or branches). Specifically in the case of memory, …

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Spectral Broadening Of Frequency Combs Via Pulse Apodization Prior To Nonlinear Propagation, Oscar E. Sandoval Apr 2015

Spectral Broadening Of Frequency Combs Via Pulse Apodization Prior To Nonlinear Propagation, Oscar E. Sandoval

Open Access Theses

This thesis focuses on specific methods for spectrally broadening large repetition rate frequency combs using the idea that tailoring the shape of the seed pulse prior to nonlinear propagation will result in a spectrally flatter comb. A spectrally flat comb is desired for applications in optical communications, arbitrary waveform generation, and microwave photonic filtering. Three experimental setups using Fourier transform pulse shapers, Dispersion Decreasing Fiber (DDF) or Highly Nonlinear Fiber (HNLF) as the nonlinear propagation media were performed. Simulations employing the Split Step Fourier Method to solve the Nonlinear Schrödinger Equation were performed to analyze the experimental results. The first …

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Numerical Simulation And Characterization Of Jet Flows In Indoor Environments, Zhu Shi Apr 2015

Numerical Simulation And Characterization Of Jet Flows In Indoor Environments, Zhu Shi

Open Access Theses

Jet flows are prevalent in indoor environment and other engineering applications. Typical examples in indoor environment include the flow discharged from personal ventilation systems, and the jet exhaled through breathing or coughing. When there is density (or temperature) difference between the jet and surroundings, jet flow becomes stratified jet. Due to its complication, stratified jet flow is difficult to model, especially in the developing or transitional region of the flow. Studying stratified jet flows is of great significance for understanding the mixing dynamics of jet and ambient environment. This is particularly important for optimizing indoor environment design, or obtaining accurate …

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Examining Unawareness Of Construction Law Principles From A Small Contractor's Perspective, Ketaki Shiralkar Apr 2015

Examining Unawareness Of Construction Law Principles From A Small Contractor's Perspective, Ketaki Shiralkar

Open Access Theses

Construction industry encompasses myriads of small trades within itself. If we take a microscope and observe, what looks from outside as one big single unit, is in fact made up of many small cogs of a wheel, important ones though, as without them, the functionality of the industry wouldn't be proper. As much as the existence of these small scale contractor's companies is important, so is their survival. There have been many reasons as to why contractors fail, but this study is limited to focus on one of them, which is, the absence of legal knowledge among employees of a …

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Machining As A Mechanical Property Test Revisited, David L. Smith Apr 2015

Machining As A Mechanical Property Test Revisited, David L. Smith

Open Access Theses

There is much need for data on mechanical behavior of metals at high strains and strain rates. This need is dictated by modeling of processes like forming and machining, wherein the material in the deformation zone is subjected to severe deformation conditions atypical of conventional material property tests such as tension and torsion. Accurate flow stress data is an essential input for robust prediction of process outputs. Similar requirements arise from applications in high speed ballistic penetration and design of materials for armor. Since the deformation zone in cutting of metals is characterized by unique and extreme combinations of strain, …

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Failure Analysis Of High Performance Ballistic Fibers, Jennifer S. Spatola Apr 2015

Failure Analysis Of High Performance Ballistic Fibers, Jennifer S. Spatola

Open Access Theses

High performance fibers have a high tensile strength and modulus, good wear resistance, and a low density, making them ideal for applications in ballistic impact resistance, such as body armor. However, the observed ballistic performance of these fibers is much lower than the predicted values. Since the predictions assume only tensile stress failure, it is safe to assume that the stress state is affecting fiber performance. The purpose of this research was to determine if there are failure mode changes in the fiber fracture when transversely loaded by indenters of different shapes. An experimental design mimicking transverse impact was used …

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Dynamics Of Transitions Between Capillary Stable States Under Weightlessness, Praveen Srikanth Apr 2015

Dynamics Of Transitions Between Capillary Stable States Under Weightlessness, Praveen Srikanth

Open Access Theses

The study of two phase systems with one of the phases obstructing the other is of importance in a lot of fields. Liquid droplets in airways and air bubbles in the blood stream both fall under this category of problems. Helium bubbles in hydrazine fuel lines of satellites also have been found to cause frequent thruster shutdown and also seriously affect spacecraft control. Studies have been carried out until now to look at static equilibrium topologies and stability of such two phase systems in straight, bent and laterally compressed capillaries. In this investigation we look at the dynamics of the …

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Design And Heat Transfer Analysis Of Accelerating Distributed Combustion System, Yashovardhan U. Wagh Apr 2015

Design And Heat Transfer Analysis Of Accelerating Distributed Combustion System, Yashovardhan U. Wagh

Open Access Theses

Over the past few decades, there has been a significant increase in greenhouse gases such as CO2, N2O, and CH4 produced from gas turbine engines. Keeping this in mind, current research work is being carried out for reducing NOx produced from combustors. The objective of this research is to determine the feasibility of Distributed Combustion Systems (DCS) for increasing efficiency and reducing NOx emissions. ^ A DCS has a main combustion zone (MCZ) where 90% of the fuel is burned and is followed by a secondary combustion zone (SCZ) in which jets carrying fuel are …

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Ads-B Used In Improvement Of Air Traffic Control, Hao Wang Apr 2015

Ads-B Used In Improvement Of Air Traffic Control, Hao Wang

Open Access Theses

Automatic dependent surveillance – broadcast (ADS-B) is a central component of the NextGen air traffic control program. This surveillance technology can replace current secondary surveillance radars (SSR) and improve cockpit situational awareness. The service can improve traffic surveillance capabilities by sharing accurate aircraft position information between pilots and air traffic controllers. In addition, ADS-B provides pilots with weather as well as air traffic information for nearby area. In order to receive these traffic and weather services, a pilot must have appropriate onboard equipment including GPS receiver, Universal Access Transceiver, antenna and multi-function cockpit display which is capable of receiving and …

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An Experimental Investigation Of A Premixed Laminar Flame Using Tunable Diode Laser And Quantitative Imaging Of Radiation Intensity, Weichao Wang Apr 2015

An Experimental Investigation Of A Premixed Laminar Flame Using Tunable Diode Laser And Quantitative Imaging Of Radiation Intensity, Weichao Wang

Open Access Theses

Simultaneous CO concentration and temperature measurements using Tunable Diode Laser Absorption Spectroscopy (TDLAS) are reported in this study. Ro-vibrational transitions of CO, R(27) and R(6) are used for probing absorbance profiles. Premixed ethylene-air flat flame on a McKenna burner is used for creating combustion gaseous products at equivalence ratio 0.83 to 1.82. Nitrogen shroud flow is used for preventing air mixing. Both Direction Absorption (DA) and Wavelength Modulation Spectroscopy (WMS) experiments are conducted. Experimental results are compared with literature and simulation using CHEMKIN and chemical equilibrium. Reasonable agreements are achieved between experiment and simulation. The CO detection limit is determined …

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Recursive Tree Traversal Dependence Analysis, Yusheng Weijiang Apr 2015

Recursive Tree Traversal Dependence Analysis, Yusheng Weijiang

Open Access Theses

While there has been much work done on analyzing and transforming regular programs that operate over linear arrays and dense matrices, comparatively little has been done to try to carry these optimizations over to programs that operate over heap-based data structures using pointers. Previous work has shown that point blocking, a technique similar to loop tiling in regular programs, can help increase the temporal locality of repeated tree traversals. Point blocking, however, has only been shown to work on tree traversals where each traversal is fully independent and would allow parallelization, greatly limiting the types of applications that this transformation …

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Investigation Of Industry Perceptions Of Building Information Modeling (Bim)-Based Estimating Practices In The U.S. And China, Zhihang Yi Apr 2015

Investigation Of Industry Perceptions Of Building Information Modeling (Bim)-Based Estimating Practices In The U.S. And China, Zhihang Yi

Open Access Theses

While the Building Information Modeling (BIM) technology has been seen as next revolutionary technology for the Architectural, Engineering, Construction and Facility Management (AEC/FM) fields, the AEC/FM industry does not implement BIM technology on the cost estimating practices as widely as expected. The efficiency improvement on cost estimating with BIM could be accomplished through automating quantity take-offs, closely collaborating design with the estimating professionals and so on. This research explores the advantages and barriers of imbedding BIM technology into the estimating practices which enables the industry deepen their understandings on BIM-based cost estimation method. This study also compares the industry perceptions …

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Linear Matrix Inequality-Based Nonlinear Adaptive Robust Control With Application To Unmanned Aircraft Systems, David William Kun Apr 2015

Linear Matrix Inequality-Based Nonlinear Adaptive Robust Control With Application To Unmanned Aircraft Systems, David William Kun

Open Access Theses

Unmanned aircraft systems (UASs) are gaining popularity in civil and commercial applications as their lightweight on-board computers become more powerful and affordable, their power storage devices improve, and the Federal Aviation Administration addresses the legal and safety concerns of integrating UASs in the national airspace. Consequently, many researchers are pursuing novel methods to control UASs in order to improve their capabilities, dependability, and safety assurance. The nonlinear control approach is a common choice as it offers several benefits for these highly nonlinear aerospace systems (e.g., the quadrotor). First, the controller design is physically intuitive and is derived from well known …

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Loss Of Accuracy Using Smeared Properties In Composite Beam Modeling, Ning Liu Apr 2015

Loss Of Accuracy Using Smeared Properties In Composite Beam Modeling, Ning Liu

Open Access Theses

Advanced composite materials have broad, proven applications in many engineering systems ranging from sports equipment sectors to components on the space shuttle because of their lightweight characteristics and significantly high stiffness. Together with this merit of composite materials is the challenge of improving computational simulation process for composites analysis. Composite structures, particularly composite laminates, usually consist of many layers with different lay-up angles. The anisotropic and heterogeneous features render 3D finite element analysis (FEA) computationally expensive in terms of the computational time and the computing power. ^ At the constituent level, composite materials are heterogeneous. But quite often one homogenizes …

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Using Mixtures Of Fatty Acid Methyl Esters As Phase Change Materials For Concrete, Leah Christine Liston Apr 2015

Using Mixtures Of Fatty Acid Methyl Esters As Phase Change Materials For Concrete, Leah Christine Liston

Open Access Theses

Phase change materials (PCMs) are an effective way of storing/releasing thermal energy via phase transformations. Incorporating PCMs into concrete pavements at airports has been suggested as a means to reduce the accumulation of snow and ice on runways. This thesis reports on the development of two phase change materials composed of binary mixtures of fatty acid methyl esters (FAME) which provide a solid-liquid transition slightly above 0°C with a high enthalpy of fusion. Current findings of this study indicate that these mixtures have the necessary properties to be a high performance PCM with the potential to reduce the levels of …

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