Influence of Porosity on the Flame Speed in Gasless Bimetallic Reactive Systems

FieldValue
dc.contributor.authorAkbarnejad, Hesam
dc.date.accessioned2013-04-29T19:10:44Z
dc.date.available2013-04-29T19:10:44Z
dc.date.created2013
dc.date.issued2013
dc.identifier.urihttp://hdl.handle.net/10393/24081
dc.identifier.urihttp://dx.doi.org/10.20381/ruor-2972
dc.description.abstractSelf-propagating High-temperature Synthesis (SHS) is the synthesis of solid materials by a reaction wave propagating into the initial reactants, typically two metals, which can alloy exothermically. Typically, experiments are performed with the reactants in powder form, with relatively low density. Recent experiments by Bacciochini et al. revealed much larger flame speeds in densified powders near TMD (theoritical maximum density), obtained by the cold spray process. The present thesis investigates why the flame speed increases dramatically with an increase in density of the powders. The investigation rests on the analytical model formulated by Makino by controlling how the variables are affected by changes in density. Flame speed measurements were performed in mixtures of nickel (Ni) and aluminum (Al) at different initial densities. The density was varied by controlling the cold-pressing of the samples inside metallic channels and tubes. Experiments were also performed in ball-milled powders, in order to permit comparison with the experiments performed by Bacciochini in these mixtures at nearly maximum densities. The measurements revealed that the flame speed increases with the initial density, with a discontinuous transition occurring at approximately 60% theoretical maximum density (TMD). This transition also corresponds to the point where the powders deform plastically during the compaction process, suggesting that the intimate contact between the particles is responsible for the flame speed increase. The flame speed dependence on powder density is attributed to the changes in the heat conductivity of the pressed powders. At high densities, where the powders have plastically deformed, the continuous structure yields conductivities close to the idealized solid matrix. At these high densities, the conductivity was modeled using the Effective Medium Theory (EMT). Analytical predictions of the flame speed, using available thermo-chemical data for the Al-Ni system were found in good agreement with the present experiments at high densities. At low densities, since Al-Ni is a mixture of loose powders, the EMT model is no longer applicable. Thus, the thermal conductivity was experimentally measured and then was fitted using the semi-empirical model suggested by Aivazov. Using this data, Makino's model predicts the correct flame speed dependence observed experimentally. The present thesis has thus established that the dependence of flame speed on density is due mainly to the changes in the structure and thermal conductivity of the powders.
dc.language.isoen
dc.publisherUniversité d'Ottawa / University of Ottawa
dc.subjectSHS
dc.subjectbi-metallic mixtures
dc.subjectflame speed
dc.subjectthermal conductivity
dc.subjectporosity effect
dc.titleInfluence of Porosity on the Flame Speed in Gasless Bimetallic Reactive Systems
dc.typeThesis
dc.faculty.departmentGénie mécanique / Mechanical Engineering
dc.contributor.supervisorRadulescu, Matei
dc.embargo.termsimmediate
dc.degree.nameMASc
dc.degree.levelmasters
dc.degree.disciplineGénie / Engineering
thesis.degree.nameMASc
thesis.degree.levelMasters
thesis.degree.disciplineGénie / Engineering
uottawa.departmentGénie mécanique / Mechanical Engineering
CollectionThèses, 2011 - // Theses, 2011 -

Files
Akbarnejad_Hesam_2013_thesis.pdfThesis17.35 MBAdobe PDFOpen