1,720,977 research outputs found
Comparative study of two nozzle assemblies for high velocity oxy fuel (HVOF) thermal spray coating process
Full text linkThe aim of this study is to provide the thermal spray coating community with a parametric study and optimized quantifiable variables for two gun nozzle geometries (Oerlikon Metco DJ1050 and DJ2700) used in High Velocity Oxy Fuel thermal spray coating. The study applied a statistical Design of Experiment technique to the results obtained by Computational Fluid Dynamics models performed using the ANSYS FLUENT programme. The study parametrize and optimize the particle velocity and temperature, so as to achieve low to medium particle temperature and the maximum particle velocity, as this is the criterion to gain low porous, more dense coating and higher coating bond strength. The first stage of the research was to study effect of the density variation with the pressure and temperature at the inlet boundary condition. This type of investigation was never conducted before and thus is, to be the best of the author’s knowledge, a novel approach. The computational modelling was then validated against an experimentally measured particle temperature. Equivalence ratio, spray distance, particle size and the air flow rate were found to be the process parameters required to optimize for the required targets. The results of this study also gives description and explanation on the behaviour and interaction between the process variables under investigation via the statistical and mathematical relations developed in the study. Finally, the results of this study were intended to be a guide in the design of the High Velocity Oxy Fuel by referring to the parametric relations and optimized parameters developed in this study by applying a Design of Experiment technique on a reliable set of Computational Fluid Dynamics results, which is considered the novelty of the study. For both the DJ1050 and DJ2700, the equivalence ratio was found to be the most influential parameter followed by the particle size to achieve the criteria of low to medium gas temperature, maximum gas velocity and maximum particle temperature. The less effective parameter was found to be the spray distance. However, a set of optimum operating parameters considered in this study were obtained for each gun, which shows that for the DJ1050 gun a range of the equivalence ratio between 0.87 (fuel − lean) and 1.44 (fuel-rich) can be applied with an average spray distance of 190 mm and an average particle size of 30 μm are the optimum values to be applied to reach the favourable target in HVOF process. While for the DJ2700, the optimized set of the equivalence ratio was biased toward fuel rich mixture (φ > 1) with constant spray distance of 150 mm and particle size of 5 μm to achieve the desired target of HVOF process
An evaluation of a proposed approach for overcoming the environmental and economic challenges of anaerobic digestion process through the production of more bio-products
Full text linkThe transformation to renewable energy has become a requirement nowadays. Thermoplastic starch (TPS) is a type of bio-plastic. Its quality and properties are examined by employing mechanical, physical, and other tests. Despite the proven advantages of using anaerobic digestion (AD) for the conversion of biomass into biogas and the developments on it, there still exist some environmental and economical challenges limiting prosperity and sustainability of AD. Economically, compared to fossil fuel market, biogas, which is the only major product of AD, is not competitive enough compared to the prices of its counterparts.
With the aid of Design Expert software, the present study mainly aims to design and implement an integrated approach so as to potentially overcome these challenges and to make the AD more desirable. The approach incorporates the AD process with the process of producing TPS to form; biogas, bio-slurry and TPS/mango fibre bio-plastic sheet, from the residues of three starchy biomass: potato, mango and avocado. A Hollander Beater was employed as a multi-functional device, to: pre-treat the biomass, isolate the starch and to process mango seed coats. The study found that, the highest energy gain per gram of volatile solids of potato residues was 62.9% at 35 ⁰C, 1.62 g-VS organic concentration and 50% sludge concentration, which yielded a maximum CH4% of 72.4%. While, the highest energy gain by the gram of volatile solids of mango and avocado residues were 65% and 16.5% which yielded a maximum CH4% of 62.4% and 60.9% respectively. The production of a bioplastic sheet with a dimension of 2440*1220*3.2 mm has the same specifications of the optimal bio-plastic sheet produced, resulting in a cost efficiency of up to 65%. To achieve this approximately 353.7 kg potato, 89.9 kg mango and 173.7 kg avocado requires processing.
Therefore the proposed study has achieved its main aim. Economically, this was achieved as a result of an excess amount of the bio-energy been produced (approximately 29%) of the total bio-energy produced. Regarding the environmental challenges which mainly depend on the accumulation of large amounts of the generated digestate, the study has confirmed the biofertiliser potential of the digestate with a suggestion to carry out more tests to confirm its quality and increase the reliability. Countries such as Saudi Arabia which is emerging in this field, can greatly benefit from this study via identifying the obstacles, tackling and avoiding them to improve profitability
Novel enhancement of HVOF thermal sprayed nanostructured WC-12Co / inconel-625 coatings for tribocorrosion applications
Full text linkThe HVOF thermal spray process is gradually becoming one of the leading coating techniques taking over traditional electrolytic chrome plating (EHC) due to EHCs harmful effects on the human body. Despite the high quality coatings produced by the HVOF thermal spray system, its role has yet to be validated in the replacement of other traditional coating techniques where specific surface properties are required in particular service operation. Obstacles associated with high-velocity oxy-fuel (HVOF) thermal spray significantly affect coating performance, especially in erosion and corrosion preventive applications. The coating layer therefore must be enhanced with a view to reducing microstructural defects and thereby prolonging the coating’s service life.
This research is aimed at examining the effect of using a CO2 laser system as a post-heat treatment and enhancement procedure applied to two coatings types investigated in this research that were deposited by an HVOF thermally sprayed process onto carbon steel 4041 substrates: firstly, 100% tungsten carbide cobalt (nano-structured) WC-12Co (InfralloyTM S7412) and secondly, WC-12Co nanostructured powder mixed with a nickel chromium alloy (Diamalloy 1005- Inconel 625) at an optimised weight percentage composition of 75% and 25% respectively. The work was carried out through the introduction of experimentally based mathematical models developed by applying response surface methodology (RSM) through Box-Behnken design (BBD), based on three levels of each factor selected, namely laser power, scanning speed and focal position/beam size, using Design of Expert software related to the coating’s erosion resistance, melt-pool geometry, mechanical properties and operating cost of the laser treatment. Furthermore, the desirability optimisation approach, based on two criteria (quality and cost), was used for both coatings in conjunction with RSM to determine the optimal combination of the laser parameters to achieve the required laser-treated coating desirability. Different outcomes of surface properties were achieved by varying the laser-processing parameters. The results demonstrate that significant improvement in coating erosion wear (dry and slurry erosion) and mechanical properties (bending strength, surface roughness and microhardness), compared to as-sprayed coating, was achieved after laser treatment in both coating types, especially the singular nanostructured WC-12Co coating. The optimal laser settings found in the quality criteria are 350 W, 37.24 mm and 150.00 mm/min for laser power, focal position and scanning speed, respectively, for the monomial nWC-12Co coating and 350 W, 45 mm and 300 mm/min for the cost criteria. To the same extent, the optimal setting for the mixed coating for the quality criteria are 169 W, 35 mm and 257.4 mm/min and 250 W, 45 mm and 300 mm/min for the cost criterion. The optimal laser setting mentioned in the quality criteria for the erosive wear, for example, saw an approximately five- to seven-fold reduction in mass loss for dry and slurry erosion in comparison to the untreated monomial nWC-12Co coating. The latter setting created an approximately 7-fold reduction in mass losses for the dry erosion and a 27% reduction in mass losses for slurry erosion compared to their untreated counterparts.
This can mainly be ascribed to the elimination of the discrete splat structure, porosity and microcrevice, as well as the enhanced homogeneity of the nano-scale WC hard ceramic distribution across the metal matrix. Less improvement was seen for the mixed coating as a result of high energy fluence (J/mm2); the coating surface became rough and gas pockets started forming within the melted zones, creating a porous coating layer that had a negative impact on coating bending strength and erosion performance. Moreover, the results indicate a strong correlation between irradiance and residence time of the laser processing, along with coating composition, with respect to the melt-pool dimensions. Finally, based on the enhancement achieved in the coating properties under the optimal laser settings for both coatings, compared to the untreated ones, the results prove that laser post processing is a cost-effective procedure (approximately 17% or less of that of HVOF) and therefore will markedly extend the service life of both coatings, saving a lot of money that would be wasted in the case of the untreated ones
Prediction and optimization of residual stresses, weld-bead profile and mechanical properties of laser welded components
Full text linkRecently, laser welding has become a leading industrial joining process. Mainly because it has become highly automated using sophisticated robotic systems. However, to make effective use of automated laser welding it is essential to have a high degree of confidence in predicting the welding outcome. To achieve a desired weld quality, the weldments are normally examined and related to the weld input parameters. This input-output relationship can be in the form of mathematical models that can be programmed and fed to the robotic control system.
This work aims to introduce experimentally based mathematical models developed by applying Response Surface Methodology (RSM) using Design-Expert software V7 to relate the residual stress distribution, weld bead parameters, mechanical properties and operating cost to the laser welding input parameters, namely: laser power, welding speed and focal point position. Also, the desirability approach was used in conjunction with RSM to find out the optimal combination of the welding parameters to achieve the required weld quality. In addition to this, microstructural investigation of the welded joints was carried out to study the effect of varying the welding conditions on the microstructure of the Weld zone (WZ) and Heat affected zone (HAZ). Common materials were investigated in this work (i.e.AISI1016, AISI1045 and AISI304) with different thicknesses and joint configurations using a 1.5 kW CW C02 Rofin laser as a welding source and two focusing lenses with focal lengths
of 127 and 190 mm.
Many models were developed to predict the responses of interest for similar and dissimilar welding. Also, the main effects and the interaction effects of the process parameters on the responses were discussed and presented graphically for all materials and joint configurations. Moreover, by using the developed models the welding process was optimized by determining the optimal combination of the process input parameters at which the desired weld quality can be achieved for each material. Finally, the size and orientation of the solidified structures were related to the welding conditions. It was observed that when the heat input increases the weldbead geometry and the microstructures become bigger and coarser respectively
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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