Browsing by Subject "Quenching"

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Defining structurally acceptable properties of high-strength steel bars through material testing
(2015-09-15) Slavin, Chase Meany; Ghannoum, Wassim M.; Engelhardt, Michael D.
Low-cycle fatigue tests were performed on reinforcing bars in order to assess the acceptability of newly developed high-strength reinforcing bars in seismic applications. The steels tested are classified as grade 60 A706, grade 80 A706, grade 80 A615, and grade 100. The high-strength reinforcing bars tested represent the two most common manufacturing processes used today: microalloying and quenching-and-tempering. The results of these tests are presented along with comparisons between the fatigue life of bars based on steel grade and other bar properties. A statistical analysis of the test results is presented in order to assess the impact of many parameters on the low-cycle fatigue performance of grade 60 A706 and higher-strength reinforcing bars.
Development of a fluorescence model for the determination of constants associated with binding, quenching, and FRET efficiency and development of an immobilized FRET-peptide sensor for metal ion detection
(2012-08) Casciato, Shelly Lynn, 1984-; Holcombe, James A.; Liljestrand, Howard M.
This thesis presents a modeling program to obtain equilibrium information for a fluorescent system. Determining accurate dissociation constants for equilibrium processes involving a fluorescent mechanism can prove to be quite challenging. Typically, titration curves and non-linear least squares fitting of the data using computer programs are employed to obtain such constants. However, these approaches only consider the total fluorescence signal and often ignore other energy transfer processes within the system. The current model considers the impact on fluorescence from equilibrium binding (viz., metal-ligand, ligand-substrate, etc.), quenching and resonance energy transfer. This model should provide more accurate binding constants as well as insights into other photonic processes. The equations developed for this model are discussed and are fit to experimental data from titrimetric experiments. Since the experimental data are generally in excess of the number of parameters that are needed to define the system, fitting is operated in an overdetermined mode and employs error minimization (either absolute or relative) to define goodness of fit. Examples of how changes in certain parameters affect the shape of the titrimetric curve are also presented. The detection of metal ions is very important, causing a need for the development of a metal ion sensor that provides selectivity, sensitivity, real-time in situ monitoring, and a flexible design. In order to be able to perform in situ monitoring of trace metal ions, FRET-pair labeled peptides were attached to a Tentagel[trademark] resin surface. After soaking in nonmetal and metal solutions (pH = 7.5), the resin beads gave an enhanced response in the presence of Hg²⁺ and Zn²⁺. Using a t-test, the signals of the beads that were soaked in a solution of each of these metal ions (and that of Cd²⁺) were determined to be significantly different from beads soaked in a solution without metal. However, the standard deviation between a set the beads was too large in order to differentiate a bead that was soaked in nonmetal solution versus one soaked in a metal containing solution.
Electrostatic control and enhancement of film boiling heat transfer
(2018-05) Shahriari, Arjang; Bahadur, Vaibhav; Bogard, David; Ezekoye, Ofodike; Bonnecaze, Roger; Murthy, Jayathi
Boiling heat transfer is severely degraded at high surface temperatures due to the formation of a vapor layer at the surface, commonly known as the Leidenfrost effect. Heat transfer is limited to a critical heat flux (CHF); higher heat fluxes lead to surface dryout and temperature excursions. An externally applied electric field in the vapor layer can significantly enhance boiling heat transfer for electrically conducting or polar liquids. In such liquids, the electric field is concentrated in the vapor layer, and promotes liquid-surface contact, which can significantly enhance boiling heat transfer. This dissertation is a fundamental study of the influence of concentrated interfacial electric fields on film boiling heat transfer for liquids with finite electrical conductivity (like water and organic solvents). This dissertation describes experimental, analytical and numerical studies on various aspects of the physics underlying electrostatic suppression of film boiling. This dissertation also quantifies the heat transfer benefits associated with electrostatic suppression of film boiling. This dissertation is divided into five main studies, which analyze different aspects of electrostatic suppression of the Leidenfrost state. The first part of this dissertation (Chapter 2) describes droplet-based experimental investigations on electrostatic suppression of the Leidenfrost state. It is demonstrated that the Leidenfrost state can be suppressed and surface dryout can be prevented using externally applied electric fields (AC or DC). Elimination of the Leidenfrost state increases heat dissipation capacity by more than one order of magnitude. In preliminary experiments, heat removal capacities exceeding 500 W/cm² are measured for water, which is five times the CHF of water on common engineering surfaces. A multiphysics analytical model is developed to predict the vapor layer thickness in the Leidenfrost state. The second part of this dissertation (Chapter 3) analyzes the fundamental mechanisms underlying electrostatic suppression of Leidenfrost state. It is shown that the interplay of destabilizing and stabilizing forces determines the minimum (threshold) voltage required to suppress the Leidenfrost state. Detailed linear instability analysis is conducted to investigate the growth of electrostatically-induced perturbations on the liquid-vapor interface in the Leidenfrost state, and predict the threshold voltage required for suppression. The third part of this dissertation (Chapter 4) focuses on suppression of the Leidenfrost state on soft, deformable surfaces, like liquids. It is seen that the nature of electrostatic suppression on a deformable liquid substrate is drastically different from that on a solid substrate. This is due to the existence of an electric field inside the substrate and the deformability of the substrate. A multiphysics analytical model is developed to predict the vapor layer thickness on deformable liquids. The fourth part of this dissertation (Chapter 5) includes experimental studies on suppression of film boiling during high temperature quenching of metals. It is shown that an electric field can fundamentally change the boiling patterns, wherein the stable vapor layer (film boiling) is replaced by intermittent wetting of the surface. This fundamental switch in the heat transfer mode significantly accelerates cooling during quenching. An order of magnitude increase in the cooling rate is observed, with the heat transfer seen approaching saturation at higher voltages. An analytical model is developed to extract voltage dependent heat transfer rates from the measured cooling curve. The fifth part of this dissertation (Chapter 6) develops the concept of using acoustic signature tracking to study electrostatic suppression of film boiling. It is shown that acoustic signature tracking can be the basis for objective measurements of the threshold voltage and frequency required for suppression. Acoustic signature tracking can also detect various boiling patterns associated with electrostatically-assisted quenching. With appropriate calibration, this technique can be used to estimate surface temperatures, heat flux and onset of dryout associated with electrically enhanced boiling. In summary, this dissertation has led to seminal contributions in the field of boiling heat transfer, and essentially opened up a new area of study in the field. This work has shown that electric fields can make the CHF limit irrelevant, and reshape the boiling curve. The present work lays the foundations for electrically tunable boiling heat transfer with conducting liquids. The impact of the proposed work is evident in the area of quenching, where electrically tunable cooling offers a new tool to control the microstructure and mechanical properties of metals.
Magma mingling
(2009-04) Barker, Daniel S.
Silicon nanocrystal functionalization and interactions in dispersion
(2024-05) Stacy, Benjamin Joseph ; Korgel, Brian Allan, 1969-; Delia, Milliron; Truskett, Thomas M; Roberts, Sean
Silicon nanocrystals are semiconductor quantum dots which have size-dependent photoluminescence spanning orange to near-IR wavelengths. Widescale research has been limited due to difficulty in synthesis and a lower quantum yield compared to other common quantum dots. However, the nontoxicity of Si nanocrystals, photoluminescence stability, range of emission, and range of organic functionalization makes them a promising nanomaterial which has a wide array of applications remaining to be explored. Photoluminescent Si nanocrystals were synthesized through thermal annealing of hydrogen silsesquioxane and subsequent etching with hydrofluoric acid to yield hydride terminated Si nanocrystals. The nanocrystals could be terminated with a range of organic ligands through passivation step through hydrosilylation with an organic ligand with a terminal alkene. Hydrosilylation of Si nanocrystals with dodecene at low temperature was conducted. We found that using chloroform for nanocrystal extraction from hydrofluoric acid was an important step for functionalization and primed the Si nanocrystal for functionalization due to free radical generation by the chloroform. This trend was highly size dependent, smaller nanocrystals could undergo low temperature functionalization more readily than large nanocrystals, which still required raised temperature to have a notable passivation yield. Si nanocrystals functionalized with undecenoic acid can be dispersed in water or ethanol. Adding metal ions to the nanocrystal dispersion would for carboxylate-ion complexes with the functional end groups of the ligands attached to the nanocrystal surface. With divalent metal ions, neighboring nanocrystals can be bonded, forming Si nanocrystal gels with high porosity and solvent volume. Addition of certain metal ions to a dilute Si nanocrystal dispersion produces a PL quenching effect. The Si nanocrystals are very sensitive to certain metal ions while having low sensitivity to others. The photoluminescence lifetime of the nanocrystals also increases, showing the potential for Si nanocrystal to act as nontoxic metal ion sensors in water.
Spatter
(2009-03) Barker, Daniel S.