24 research outputs found
Heat Transfer In Multi-layer Energetic Nanofilm On Composites Substrate
The main purpose of this work is to find a physical and numerical description related to the reaction of the multilayer nano energetic material (nEM) in dense film. Energy density of nEM is much higher than the conventional energetic material; therefore, nEM finds more applications in propulsions, thermal batteries, material synthesis, nano igniters, waste disposals, and power generations. The reaction model of a multilayer nEM in a dense film of aluminum and copper oxide deposits on a composite substrate of silica/silicon is studied and solved in different stages. The two main interests in this study are propagation speed and maximum temperature of the reaction. In order to relate speed of reaction and maximum flame temperature a number of other variables such as heat loss, the product porosity, and the reaction length should be estimated. The main aim of this study is to introduce a numerical model which estimates and relates these values in multilayer nEM in a dense film. The following is a summary of the execution steps to achieve this goal. In Part I of this thesis, flame front speed and the reaction heat loss were the main targets. The time-of-flight technique has been developed to measure the speed of flame front with an accuracy of 0.1 m/s. This measurement technique was used to measure the speed of propagation on multilayer nEM over different substrate material up to 65 m/s. A controllable environment (composite silicon\silica) was created for a multilayer standard thin film of aluminum and copper oxide to control the reaction heat loss through the substrate. A number of experimental results show that as the thickness of silica decreases, the reaction is completely quenched. Reaction is not in self-sustaining mode if the silica thickness is less than 200 nm. It is also observed that by ii increasing silica’s thickness in substrate, the quenching effect is progressively diminished. The speed of reaction seems to be constant at slightly more than 40 m/s for a silica layer with thickness greater than 500 nm. This would be the maximum heat penetration depth within the silica substrate, so the flame length was calculated based on the measured speed. In Part II, a numerical analysis of the thermal transport of the reacting film deposited on the substrate was combined with a hybrid approach in which a traditional two-dimensional black box theory was used, in conjunction with the sandwich model, to estimate the maximum flame temperature. The appropriate heat flux of the heat sources is responsible for the heat loss to the surroundings. A procedure to estimate this heat flux using stoichiometric calculations is based on the previous author’s work. This work highlights two important findings. One, there is very little difference in the temperature profiles between a single substrate of silica and a composite substrate of silicon\silica. Secondly, by increasing the substrate thickness, the quenching effect is progressively diminished at given speed. These results also show that the average speed and quenching of flames depend on the thickness of the silica substrate and can be controlled by a careful choice of the substrate. In Part III, a numerical model was developed based on the moving heat source for multilayer thin film of aluminum and copper oxide over composite substrate of silicon\silica. The maximum combustion flame temperature corresponding to the speed of flame front is the main target of this model. Composite substrate was used as a mechanism to control the heat loss during the reaction. Thickness of the substrate, the length of flame front, and the density of the product were utilized for the standard multilayer thin film with 43 m/s flame front speed. The calculated heat penetration depth in this case was compared to the experimental result for the same flame front iii speed. Numerical model was also used to estimate three major variables for a range of 30-60 m/s. In fact, the maximum combustion flame temperature that corresponds to flame speed along with the length of the flame, density of the product behind the flame, and maximum penetration depth in steady reaction, were calculated. These studies will aid in the design of nEM multilayer thin film. As further numerical and experimental results are obtained for different nEM thicknesses, a unified model involving various parameters can be developed
Heat Transfer In Multi-layer Energetic Nanofilm On Composites Substrate
The main purpose of this work is the physical understanding and the numerical description of the reaction of the dense metastable intermolecular composition (MIC). Energy density of MIC is much higher than conventional energetic material; therefore, MIC finds more applications in the propellant and explosive system. The physical model includes the speed of propagation and rate of reaction, and the relationship between the layer thickness, heat rate, and length of the flame based on physical model. In Part I of this thesis, a one-dimensional model based on Weihs was developed for 20 pairs of a multi-layer of aluminum and copper oxide. This problem was solved using an assumed value of constant atomic diffusion in Arrhenius\u27 equation to obtain the velocity of self- propagation. Using the maximum and minimum measured velocities in a similar configuration, the activation energy was computed and was found to be significantly different. When the velocity was used to obtain a linear temperature profile, the margin of error was significant as well. Therefore, this method was seen to have severe shortcomings. In Part II of this thesis, adiabatic unit cell of one layer of aluminum and copper oxide in an ideal reaction was considered. Temperature profile based on chemical heat generation and phase transformation of reactants has been calculated. This model confirmed the highest possible temperature during reaction of 2920 C ± 5% obtained in the literature, however, the model was unable to provide other important flame characteristics. In Part III, a two-dimensional model was developed introducing the flame at the interface. A black box theory has been used to simplify some of the characteristics of the flame, ignoring diffusion characteristics. Using this model, the length of flame was calculated using the measured value of the speed of propagation of the flame. Measuring some of the characteristics of the flame was the main goal of Part III of this thesis. Controllable environment was created for the multilayer thin film of aluminum and copper oxide to eliminate the number of effective variables that affect the speed of propagation. Transformable heat of reaction was used to control the speed of propagation. In addition, a MIC sample was designed and fabricated to measure the speed of propagation with an accuracy of 0.1 m/s. This measurement technique was used to measure the speed of propagation on variable substrate up to 65 m/s. The flame length was also calculated for different speeds of propagation over different substrates. The temperature distribution on the substrate was calculated numerically. Significant improvements have been made in Part III; however, this model does not provide concentration profiles. For future work, a more complete two-dimensional physical model will be developed for self-propagation reaction of multilayer thin film of aluminum and copper oxide based on thermal transport and atomic diffusion. This two-dimensional model includes the reaction rate, speed of propagation and the temperature profile. Since this model relies on a number of physical variables that are as yet unknown, further work is warranted in this area to carry out a thorough computational study
Facile Regeneration of Carbonyl Compounds from Oximes Under Microwave Irradiations Using N-Bromophthalimide
Um método novo e seletivo para clivagem de oximas envolve a reação das oximas derivadas de aldeídos e cetonas com N-bromoftalimida (NBPI) em acetona sob irradiação de microondas. A new and selective method for the cleavage of oximes has been achieved by a simple reaction of a ketoxime or an aldoxime with N-bromophthalimide (NBPI) in acetone under microwave irradiations
Facile regeneration of carbonyl compounds from oximes under microwave irradiations using N-bromophthalimide
Fabrication of Fibrous Materials Based on Cyclodextrin and Egg Shell Waste as an Affordable Composite for Dental Applications
In this study, the fibrous nanostructures based on cyclodextrin from egg shell waste were fabricated using electrospinning technique under optimal conditions. Scanning electron microscopy (SEM), thermal stability analysis and abrasion testing were used to characterise the final products. The cyclodextrin nanofibrous products were used as new nanostructures in the field of dental coatings due to the obtained properties such as uniform shape, small particle size distribution, high thermal stability and optimal abrasion resistance. The DFT calculations confirmed the chemical stability of the final products. The MTT test results confirmed that the fibrous nanocoatings of the egg shell have no significant side effects on healthy cells. These fibrous nanostructures could be a promising candidate for use as a dental nanocoating material
Novel use of BiOCl as an efficient and selective reagent for cleavage of 2,4-dinitrophenylhydrazones to carbonyl compounds
A novel use of bismuth oxychloride (BiOCl) as an efficient and selective
oxidative catalyst for the clean cleavage of 2,4-dinitrophenyl-hydrazones
under mild conditions is reported. The reactions proceed very smoothly, and
the yields are good to excellent. Over oxidation of aldehydes to carboxylic
acid and the formation of by-products were not observed. The catalyst could
be recovered and reused for at least four reaction cycles without
considerable loss of reactivity
Experimental Flame Speed In Multi-Layered Nano-Energetic Materials
This paper deals with the reaction of dense Metastable Intermolecular Composite (MIC) materials, which have a higher density than conventional energetic materials. The reaction of a multilayer thin film of aluminum and copper oxide has been studied by varying the substrate material and thicknesses. The in-plane speed of propagation of the reaction was experimentally determined using a time of- flight technique. The experiment shows that the reaction is completely quenched for a silicon substrate having an intervening silica layer of less than 200 nm. The speed of reaction seems to be constant at 40 m/s for silica layers with a thickness greater than 1 μm. Different substrate materials such as glass and photoresist were also used. © 2009 The Combustion Institute
Experimental And Numerical Study Of Dense Layered Nano-Energetic Materials
This paper deals with the reaction of dense Metastable Intermolecular Composite (MIC) materials. The energy density of MIC nanocomposite materials is much higher than that of conventional energetic materials. The reaction of a multilayer thin film of aluminum and copper oxide has been studied by varying the substrate material and thicknesses, to vary the heat loss during the reaction of the MIC material. The in-plane speed of propagation of the reaction was experimentally determined using a time of-flight technique. The experiment shows that the reaction is completely quenched for a silicon substrate having an intervening silica layer of less than 200 nm. The speed of reaction seems to be constant at 40 m/s for silica layers with thickness greater than 1 μm. Different substrate material such as glass was also used. A numerical analysis of the thermal transport from the reacting film shows that the temperature profiles become self similar for substrate thicknesses larger than 1 μm., the maximum temperature stays constant for both silica and composite silica/silicon substrates, showing the effectiveness of the composite substrates to control the heat lost from the reaction, both experimentally and numerically
Modeling of a reacting nanofilm on a composite substrate
This article provides a detailed computational analysis of the reaction of dense nanofilms and the heat transfer characteristics on a composite substrate. Although traditional energetic compounds based on organic materials have similar energy per unit weight, non-organic material in nanofilm configuration offers much higher energy density and higher flame speed. The reaction of a multilayer thin film of aluminum and copper oxide has been studied by varying the substrate material and thicknesses. The numerical analysis of the thermal transport of the reacting film deposited on the substrate combined a hybrid approach in which a traditional two-dimensional black box theory was used in conjunction with the sandwich model to estimate the appropriate heat flux on the substrate accounting for the heat loss to the surroundings. A procedure to estimate this heat flux using stoichiometric calculations is provided. This work highlights two important findings. One is that there is very little difference in the temperature profiles between a single substrate of silica and a composite substrate of silicon silica. Secondly, with increase in substrate thickness, the quenching effect is progressively diminished at a given speed. These findings show that the composite substrate is effective and that the average speed and quenching of flames depend on the thickness of the silica substrate, and can be controlled by a careful choice of the substrate configuration. (C) 2011 Elsevier Ltd. All rights reserved
The Effectiveness of Rule-Governed Democracy Classroom Management Style on Self-Esteem of 3rd-grade High School Male Students
By utilizing classroom management styles, teachers will be able to get rid of possible students’ misconducts and promote a friendly atmosphere which will in effect promote students’ participation in learning activities. Additionally, increased self-esteem, which is an achievement of such utilization, will influence various aspects of students’ future lives. Taking this point into consideration, the present study aimed at determining the efficacy of rule-governed democracy classroom management style on self-esteem of 3rd-grade high-school male students. All 3rd-grade high-school male students of Abdanan city in the academic year 2013 comprised the statistical population to this study. Using convenience sampling, 38 subjects were selected and randomly assigned to experimental and control groups. The research design was pretest-post-test. Cooper Smith's self-esteem questionnaire was used as the research instrument which was administered to the two groups at the outset. The experimental group was given seven 90-minutes sessions of treatment and twice-a-week. The two groups were asked to fill out the same questionnaire for the post-test stage afterwards. Descriptive statistics, including the analysis of covariance was used to analyze the data. The results revealed that the utilization of rule-governed democracy classroom management style in the classroom had significantly increased the self-esteem (public-family-social- and scholastic-professional) of male students in the post-test (p<0/001)