bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular Dynamics Simulation of Solidification of Ag-x%Au Nanoalloy
Authors: Davoodi J. , Mehri Leila
Published: April 2011

In this investigation, we focus on the glass formation and crystallization process of Ag, Au pure metals as well as Ag-20%Au, Ag-50%Au, and Ag-80%Au (Atoms%) random alloys at the nanoscale. The thermodynamic properties such as solidification temperature and cohesive energy were calculated in the NVT ensemble by the molecular dynamics (MD) simulation technique. The Quantum Sutton-Chen (Q-SC) potential was used to study phase transition and thermal properties of nanoparticles. The temperature dependence of energy was calculated at various concentration of Au. Moreover, the solidification of pure nanoparticles, Ag, Au, and Ag-x%Au nanoalloys were studied at different cooling rates. Our molecular dynamics simulation results show glass structure at fast cooling rates while crystallization at a slow cooling rate. Moreover, the obtained results show that the solidification temperature decreases with decreasing nanoparticle size.
Heat Transfer in Nanocomposites with Monte-Carlo Simulations
Authors: Bui Khoa , Papavassiliou Dimitrios V.
Published: April 2011

Carbon nanotubes (CNTs) have been suggested to be reinforcement fillers in a variety of composite materials due to their exceptional electrical, thermal and mechanical properties. In terms of thermal properties, incorporating CNTs into a polymer matrix should increase the effective thermal conductivity of the resulting composite. However, the presence of resistance to the transfer of heat at the CNT-polymer interface, known as the Kapitza resistance, results in underperformance of CNT nanocomposites, in terms of thermal properties. In this work, we use Monte Carlo simulations to calculate the effective thermal conductivity of CNT nanocomposites taking into account the Kapitza resistance, as well as the effective thermal conductivity for different inclusion geometries (sphere, cylinder and parallelepiped). The effect of the dispersion pattern of the nano-inclusions is also investigated. Finally, comparing the calculated thermal conductivity from the simulations to experiments, the methodology can be used to calculate the Kapitza resistance of such systems.
The Influence of Rubber Blend Aging and Sample Homogeneity on Heat Transport Phenomena
Authors: Koštial Pavel , Jančíková Zora , Ružiak Ivan , Kopal Ivan , Jonšta Petr
Published: April 2011

This paper is devoted to the study of thermal transport phenomena changes caused by natural aging of rubber blends. Thermal conductivity, diffusivity and heat capacity of rubber blends were measured and compared for the same samples before and after half of a year. Samples were stored at room temperature and daily light. In the frame of our investigations there has been observed the decrease of the thermal diffusivity as well as the thermal conductivity in the interval approximately 40-50 %. The changes of specific heat capacity after sample aging were negligible. The explanation of such behaviour we can see in the sample structure degradation caused by the environmental influence.
A Study on the Coupled Thermal and Damage Effects in Deforming Solids
Authors: Vaz M. , Muñoz-Rojas Pablo A. , Lange M.R.
Published: April 2011

Mechanical degradation and ductile failure in metal forming operations can be successfully modelled using fully coupled damage models. In addition, it has been largely reported in the literature that temperature variations affect material behaviour, especially thermal softening. This paper presents a numerical discussion of the coupled effects between ductile damage and temperature evolution based on the simulation of tensile tests of notched specimens.
Numerical Analysis of Solute Segregation in Directional Solidification under Static Magnetic Field
Authors: Nouri Sabrina , Benzeghiba Mouhamed , Benzaoui Ahmed
Published: April 2011

This paper addresses the effect of thermosolutal convection in the formation of defects in directionally solidified alloys. The numerical model is based on a bi-dimensional solution consisting of an implicit time integration scheme to couple thermal and solutal fields, which is supported by a finite volume numerical modeling technique. In this article, the macrosegregation phenomenon under a static magnetic field effect is analyzed numerically by a computer code developed and validated with experimental data. The numerically obtained results have been widely discussed in dependence of the characteristic parameters of the studied problem.
Grain Structure Evolution of Mg Alloy AM60 Influenced by Ca Addition
Authors: Hu Henry , Zhang Qiang , Niu Xiao Ping
Published: April 2011

The demand for weight reduction in automobiles has generated strong interest in research and development of magnesium applications, especially for powertrain components. Ca-alloyed magnesium alloys have excellent creep properties and can be potentially used for powertrain applications. In order to better understand their solidification behavior, the grain structure evolution of Ca-alloyed magnesium alloys AM60 has been investigated in this study. The results of thermal analysis and microstructure evaluation indicate the occurrence of heterogeneous nucleation of primary magnesium during solidification. The crystal structural analysis suggests that the nucleation behavior of Ca-alloyed AM60 may be attributed to a good crystallographic match of // .
Origin of “Inverse Isotope Effect” of Hydrogen Diffusion in Palladium
Authors: Yoshinari Osamu
Published: April 2011

The diffusion coefficients of hydrogen (H) and deuterium (D) in Pd were determined in the frame of a quantum mechanical consideration. The three dimensional (3D) wave functions and eigenenergies of H and D at a stable octahedral (o) site and a metastable tetrahedral (t) site were determined by solving the Schrödinger equation with 3D potentials obtained by the first principles calculation. The states of H and D along the diffusion path were also determined by using transient potentials which were obtained with an aid of the nudged elastic band method. The magnitudes of tunneling matrix elements (J) were evaluated from the eigenenergy curves along the diffusion path. In the Pd-H system, thermally activated tunneling transitions are dominant jump processes. On the other hand, in the Pd-D system, it is revealed that a transition via an extended state where the wave function spreads both to o- and t-sites also has a considerable contribution to the diffusion. The calculated diffusion coefficients for H and D quantitatively agreed with experimental values and the so-called inverse isotope effect was reproduced.
The Effect of the Microstructure on Oxidation of Sulfide-Metal Alloys of Copper and Nickel
Authors: Selivanov Evgeny N. , Gulyaeva R.I. , Udoeva L.Y. , Verchinin A.D.
Published: April 2011

The methods of thermal, thermogravimetric, mass spectrometric and high-temperature X-ray analysis have been used to determine the chemism of the processes involving the oxidation of a sulfide-metal copper-nickel alloy during continuous heating to 1190 K in an air flow. It has been found that the fineness of particles, the size of the sulfide phases in these particles, and the phase composition influence the phase transformation temperatures, as well as the kinetics and the sequence of the oxidation processes.
Production of Cu/SiC Nanocomposite Layers by Friction Stir Processing
Authors: Barmouz Mohsen , Givi M.K. Besharati , Asadi Parviz
Published: April 2011

Friction stir processing (FSP) was applied to modify the microstructure of pure copper and Cu/SiC nanocomposite layers. Optical and scanning electron microscopy (SEM) was employed to investigate the microstructure on the modified surface. Also, the wear resistance and friction coefficient behavior of specimens were investigated. FSP homogenizes and refines the copper structure and creates a microstructure with nano-sized SiC particles (30 nm) distributed in the pure copper matrix. Also, it is found that the traversal speed of tool significantly influence the microstructure of developed zone in pure copper. Generally, higher tool traverse speed leads to a more homogeneous microstructure and SiC particles dispersion. This means that higher traverse speeds result in agglomeration of SiC particles which reduces the microhardness values.
The Effect of the Pyrolysis Furnace Type on the Yield of Silicon Carbide Whiskers Produced from Rice Husks
Authors: Farsani Reza Eslami , Akhlaghi Farshad , Sedghi Arman
Published: April 2011

The production of silicon carbide whiskers (SiCw) by using rice husks has attracted a considerable attention due to a lower production cost as compared to the other processing routs. In the present investigation, the effect of pyrolysis furnace type (vertical tube, horizontal tube, and graphite chamber) on the yield of the resultant SiCw was investigated. It was concluded that the maximum yield was achieved by using a horizontal tube furnace whereas the minimum yield was obtained in a vertical tube furnace. These results were rationalized in terms of the different conditions for the evacuation of the produced gases from the different pyrolysis furnaces.
Mathematical Modeling of Heat Transfer in Laser Surface Hardening of AISI 1050 Steel
Authors: Razavi R. Sh. , Gordani G.R. , Tabatabaee S.
Published: April 2011

Laser surface hardening is a method used for surface modification without affecting the bulk properties of materials. Due to rapid cooling and little thermal penetration in the surface layer, a homogenous structure and little distortion are usually obtained. When a high power laser irradiates a material surface, a part of the laser energy is absorbed and conducted into the interior of the material. If the absorbed energy is high enough, the material surface will melt and even vaporizes. Consequently the temperature of the process is of promote importance to incorporate an appropriate structural layer. In this regard, a study has been carried out to implement a mathematical modeling method to control the temperature gradient, which affects on the depth of the hardened layer. The model is based on solving the heat transfer equation and such a condition by assuming that the thermo-physical properties of the material are independent of the temperature. To evaluate the application of the proposed model, laser surface hardening was carried out to AISI 1050 steel, using a 1 kW CO2 laser. It was shown that the experimental results obtained are in good agreement with the proposed model.
Reactive Diffusion at the Cylindrical Dissolving of Copper in the Solder Melt
Authors: Drápala Jaromír , Struhařová Alena , Petlák Daniel , Vodárek Vlastimil , Kubíček Petr
Published: April 2011

Problems of reactive diffusion at the solid phase and melt contact were studied theoretically and experimentally. The main intention was to calculate the time course of the solid phase dissolving in the case of cylindrical dissolving. These calculations were carried out on the assumption for the rate constant of dissolving K = const. In our work we give heed especially to the dominating process, which is the solid metal A dissolved in the melt B. During the dissolving the melt B saturates with the metal A and the process is influenced by convections which are characteristic for the given experimental configuration. A theoretical description of the kinetics of the solid phase dissolving in the melt will be presented for the case of cylindrical dissolving. The aim is to derive a relation for the interface boundary movement c(t) in dependence on time and a time course of growth of the element A concentration in the melt B. There are problems with accurate determination of the interface boundary movement after certain heating times of specimens, when it is observed experimentally, since intermetallic phases create in the original A metal at both the diffusion and cooling and some phases segregate at the solidifying melt cooling. The main intention was an experimental study of the copper dissolving in the tin melt. Experiments aimed to the determination of the Cu wires (diameters from 0.5 to 3.5 mm) dissolution in the solder melt were carried out at various selected temperatures and times. Rapid growth of phases in the metal A and determination of the thickness of layers with these phases pose considerable time demands to X-ray micro-analyses (WDX, EDX) of specimens after their long-time heating.
Self-Diffusion Coefficient of Molecular Fluid in Porous Media
Authors: Andryuschenko Vladimir , Rudyak Valery
Published: April 2011

The paper deals with the molecular-dynamics simulation of the self-diffusion of fluid molecules in porous media using the hard-sphere potential. A study is made of the velocity autocorrelation functions of the molecules and dependences of the self-diffusion coefficient on the pore sizes, po-rosity, fluid density, and adsorption time.
Sonochemical Synthesis and Characterization of Hydroxyapatite Nanoparticles
Authors: Mohebali M. , Shokuhfar Ali
Published: April 2011

Hydroxyapatite (HA) is a bioactive ceramic, employed mainly in bone tissue engineering since it exhibits superior biocompatibility and osteoconductivity. Attempts have been made to synthesize HA nanoparticles with chemical composition, morphology, crystallinity and Ca/P ratio similar to that of natural bone. While wet chemical methods are becoming more popular for synthesis of HA nanoparticles, ultrasound irradiation has shown to be an effective method to increase the rate of production and also to decrease particle size. However, process variables must be carefully selected. In the present study, HA nanoparticles with desirable characteristics have been synthesized by the aid of ultrasound irradiation and characterized by powder X-ray diffraction (XRD) and electron microscopy techniques.
Numerical Comparison of Two and Three Dimensional Flow Regimes in Porous Media
Authors: Abbasian Arani Ali Akbar , Dehghani Majid
Published: April 2011

The purpose of this work is to study the fluid flow regimes in a porous media with high enough velocities (in the range of laminar flow). In our study, the results obtained from expanding Darcy’s equation to Forchheimer’s equation with volume averaging method have been used for studdying the fluid flow behavior in 2D and 3D models. Results of numerical simulations show that in all cases, there are weak inertial regime, strong inertial regime and transition zone. In all the cases, the domain of weak inertial regime is relatively narrow, and this problem is intensified in the 3D numerical simulations. This could be the reason of missing the weak inertial regime in experimental studies on inertial fluid flow in porous media. The domain of strong inertial regime in 3D models is so wide that after Darcy’s regime, the governed regime is the strong inertial regime. To obtain more accurate and analytical results, more studies should be done on the 2D and the 3D flow regimes.
Free Convection in a Nanofluid Filled Square Cavity with an Horizontal Heated Plate
Authors: Abbasian Arani Ali Akbar , Mahmoodi Mostafa , Amini Meysam
Published: April 2011

The natural convection in a square cavity with a heated horizontal plate containing a nanofluid (water and Ag) is simulated numerically. The heated plate and vertical walls are maintained at a constant temperature, Th and Tc, while the horizontal walls are adiabatic. The nanofluid is assumed to be incompressible and the flow is considered to be laminar. The continuity, momentum and energy equations written in terms of the primitive variables are discretized using a control volume approach and the SIMPLER algorithm. A parametric study is performed and the effect of the Rayleigh number, the location of the heated plate and the volume fraction of the nanoparticles on the fluid flow and the heat transfer inside the cavity are investigated. The results show that the mean Nusselt number of the vertical walls increases with increasing the volume fraction of the nanoparticles. Moreover, for a constant volume fraction of the nanoparticles, the Nusselt number of the vertical walls decreases substantially as the location of the heated plate varies from top to bottom of the cavity.
Effect of SiC Volume Fraction on the Microstructural and Mechanical Properties of Cu/SiC Composite Layer Fabricated by FSP
Authors: Asadi Parviz , Givi M.K. Besharati , Barmouz Mohsen
Published: April 2011

In this study, friction stir processing (FSP) was applied to fabricate a Cu/SiC surface composite layer by incorporation of 5 µm SiC particles. Effects of the traverse speed and SiC volume fraction on the microstructure, hardness and powder distribution pattern of the developed surface layer were investigated. Optical and scanning electron microscopy (SEM) was employed to carry out the microstructural observations. Results show that increasing the volume fraction causes an intense decrease in the grain size and increase in the hardness of the developed surface. To achieve a uniform distribution of particles and uniform microstructure, the traverse speed should decrease as far as possible.
Phase Transformations on ASTM a 744 Gr. CN3MN Superaustenitic Stainless Steel after Heat Treatment
Authors: Ritoni Marcio , Martins M. , Nascimento F. C. , Mei Paulo Roberto
Published: April 2011

The superaustenitic stainless steel ASTM A 744 Gr. CN3MN (22Cr-25Ni-7Mo-0.2N) has as mainly characteristic high corrosion resistance in severe environment. As the corrosion resistance depends on the microstructure, it was investigated the phase transformations after a solution treatment at 1200°C. Thermocalc calculation for 53Fe-25Ni-22Cr alloy indicates austenitic phase between 1300 and 800°C and austenite + sigma phase below 800°C. The as-cast steel studied presented 2.7 % of precipitates volume fraction and the precipitates were located on the grain boundaries and inside the austenitic grains. X-ray diffraction confirmed the presence of sigma phase in as-cast sample. Scanning electron microscopy showed that the level of Cr and Mo was higher in the precipitates than in the austenitic matrix and the Ni content was higher in matrix compared to precipitates. After heating at 1200°C during 90 minutes, the precipitate volume fraction was reduced to 2.1 % and the grain boundaries precipitates were dissolved. The microstructural analyses made through transmission electron microscopy and X-ray diffraction showed the presence sigma phase and M6C carbide.
Characterization of Microstructure and Properties of Plasma Sprayed Ceramic Coatings on AZ91 Magnesium Alloy
Authors: Moskal Grzegorz , Iwaniak Aleksander , Witala Bartosz
Published: April 2011

The paper presents the microstructure test results of carbide layers with bond coat obtained on the magnesium alloy with WC/Co – NiCr – AZ91D type thermal spraying method. Layers were sprayed with the APS method on the sandblasted surfaces of approx. 5 mm thick elements manufactured with high pressure die casting (HPDC). The standard process parameters were used for the powders sprayed. The scope of the tests included characteristics of the AZ91D alloy top surface after HPDC process and after sandblasting. The stereometric analysis of surface was performed by using the laser profilometer. The top surface geometric parameters were determined and presented in the form of numbers and topographic maps. Both surfaces were subject to SEM analysis by using the Hitachi S3400N microscope and chemical composition analysis in micro areas (EDX analysis by using the Noran System Six software) to determine presence of impurities and other type of artefacts on the alloy surface before plasma spraying. The alloy surfaces were also subject to detailed tests after spraying process (on lateral micro-sections) to determine the influence of the spraying process on the substrate quality and consequently layer adhesion. Phase composition assessment of the NiCr 80/20 type bond coat and carbide layers WC/10Co and WC/8Co was also performed. Further tests referred to top surface morphology of both carbide layers and chemical composition assessment in micro areas.
Synthesis and Characterization of PES/TiO2 Nanofibers Membrane
Authors: Khadem Dariush Jafar , Yaakob Zahira , Shahgaldi Samaneh , Ghasemi Mostafa , Wan Daud Wan Ramli
Published: April 2011

An important recent discovery in the membrane science is the polymeric nanofiber membrane. Membranes have many applications in protein purification, wastewater treatment and fuel cells. One of the versatile technique with the ability of producing cost-effective, highly porous non-woven membranes with large surface area is electrospining. In this study the effect of TiO2 nanoparticles in membrane performance has been investigated. A PES/TiO2 nanofibers membrane has higher flux and permeability than a pristine PES membrane. Also the measurments show that the surface area of the membrane will increase by addition of TiO2 nanoparticles. Moreover, the contact angle was investigated.
Calculation of the Diffusion Coefficient of Uranium in Compacted Clay: Effect of the Temperature
Authors: Korichi S. , Keddam Mourad , Bensmaili A.
Published: April 2011

Diffusion of Uranium in compacted clay was studied through the non-steady state diffusion method for the safety assessment of the radioactive waste in the storage and disposal practices. Since the permeability of the compacted clay is very low, the main mechanism for radionuclide transport is governed by the diffusion phenomenon. The diffusion process of uranium in compacted clay as a porous medium has been modeled by taking into account the effect of sorption. An increase in temperature, caused by the radiation from the canisters, takes place in the repository. Then, the effect of temperature on textural and structural properties of clay and coefficient diffusion has been examined. First, we examined the structure changes of the clay pellets under the influence of the heat in the temperature range 25–100°C. These changes are studied in the region of mesopores and macropores using the method of the mercury porosimetry. Second, the effect of temperature on the diffusion behavior of uranium was simulated. In these simulations, the experimental values of apparent diffusion coefficients of uranium were used to determine the concentration profiles versus time, depth and temperature. As conclusion, it was shown that the temperature plays an important role in the uranium transport through the compacted clay.
Simplified Convective Heat Transfer in Vertical Airflow Regimes with Shading Device
Authors: Haase Matthias , Amato Alex
Published: April 2011

The design of ventilated glass-glass facades in large buildings seems a promising technology to enhance energy efficient building design. In order to describe the optical and thermal heat transfer mechanism in glass-glass configurations with vertical airflow regimes radiation and conduction models have been developed and validated. The convective heat transfer can be calculated depending on air temperatures and air velocity. But obstructions in the vertical airflow regime (i.e. shading device) with reflective and absorptive properties demand the set-up of a new heat transfer balance. Radiative, conductive, and convective heat transfer coefficients for the heat transfer through glass-glass configuration with internal obstructions were developed. The simulation results were validated with measured data of air temperature regimes and different solar radiation in an existing ventilated double-skin façade. The comparison show very good agreement and give confidence in using the model for further energy analysis of this type of façade.
Thermal Properties of Zirconium Oxide-Based Ceramic Targets Modified with Oxides of Rare Earth Elements
Authors: Kostecki Marek , Olszyna Andrzej Roman
Published: April 2011

The paper is concerned with the thermal properties of cathodic ceramic targets built on the basis of zirconium oxide modified with rare earth metal oxides such as La2O3, Nd2O3, and Gd2O3. The experiments also included the production of the TZ-3Y, TZ-3Y+20mol% coatings (La2O3, Gd2O3) using the EB-PVD method, and characterization of these coatings. Within the temperature range examined (20 to 120oC), the targets that contained rare earth metal oxides appeared to have lower thermal conductivity λ (2.07-1.22 Wm-1K-1) than the TZ-3Y target (3.6-3.05 Wm-1K-1). The present study was a continuation of our earlier experiments devoted to the examinations of zirconium oxide ceramic targets intended for producing refractory, heat-resistant nanocrystalline coatings.
Microstructural Evolution of Synthesized Polyhydroxyalkanoates (PHAs) Corresponding to their Blends
Authors: Kaewkannetra Pakawadee , Promkotra Sarunya
Published: April 2011

Biopolymers of polyhydroxyalkanoates (PHAs) are produced by pure bacterial strain of Alcaligenes eutrophus TISTR 1095 via batch fermentation using sugarcane juice as a carbon source, and yielded up to 21% (w/w) after recovery process. The PHAs are blended with bio-based materials such as tapioca and corn starch including glycerol and methanol to improve their microstructures. The combination of various plasticizers with PHAs is studied in different ratios. The PHAs and starch are mixed for 3% w/v and 30% w/v in hot chloroform, respectively. The varieties of PHAs to starch solution ratios are situated for casting as of films. The PHAs blended films are characterized by polarized light microscopy, differential scanning calorimetry (DSC) and x-ray diffractometry (XRD). The initial PHAs indicate remarkably crystalline structure with cross-polarized light on optical microscope. Macroscopic scales of their films are very brittle and flexible. However, their microscopic scales present small patches of particular components from each starch. Immiscibility of the blends is gradually increased on adding the starch portions. Additional glycerol shows more strongly interfacial adhesion between starch and PHAs, and methanol produces specifically thin films. Melting transition temperatures of blended films are slightly higher than the biosynthesized PHAs as examined by DSC. Corn starch mixture causes highly brittle films than tapioca mixtures, which indicates poor adhesion between corn starch and the PHAs. This result is correspondent to their highly crystallinity from diffractogram. Microstructural evolution of the blended films is increased slightly crystallinity by the solution casting.
Investigation of the Effect of Diffusion Process in the Catalyst Pellet on Overall Reaction Rate of Dehydrogenation of Diethylbenzne to Divinylbenzne
Authors: Zeynali Mohammad Ebrahim
Published: April 2011

The diffusion coefficients of DEB and EVB into a synthesized and a commercial catalyst pellet were determined by numerical integration of the Stewart-Johanson equation at the reaction condition. The continuity equation was solved by the orthogonal collocation method. DVB was prepared by a commercial catalyst. The production rate and effectiveness factor were determined experimentally and compared with the predicted value. It was seen that the diffusion into the catalyst pellet is strongly limiting the process of DVB production.
The Influence of Phase Dispersion of Sulfide Alloys on their Electrochemical Properties
Authors: Selivanov Evgeny N. , Nechvoglod O.V. , Mamyachenkov S.V.
Published: April 2011

It has been found that the dispersion of phases in copper-nickel sulfide-metal alloys influences their electrochemical properties. X-ray diffraction and optical and electron microscopy have been used to study structural characteristics of the samples prepared by crystallization of sulfide melts at different rates of 10÷103 K/s. High-rate cooling of a converter matte leads to the formation of nonequilibrium sulfide phases and a metallic component dissolved in these phases. The electrochemical oxidation of copper-nickel sulfide alloys has been studied by voltammetry with a linear potential sweep. The data point to a reduction of the limiting oxidation currents of the sulfide alloys prepared by high-rate cooling. The compositions of the intermediate phases and solid products of the electrochemical oxidation, which form the passivating layer, have been determined. The electrolysis of dispersed sulfide alloys allows performing the process at low densities of the current and, thus, the diffusion limitations have been removed.
Structural, Mechanical and Magnetic Properties of Mechanically Alloyed Fe40Co60 Powders
Authors: Otmane Fadhela , Bergheul S. , Zergoug M. , Azzaz M.
Published: April 2011

In this work we report on the structural, mechanical and magnetic properties of mechanically alloyed Fe40Co60 powders. Alloying formation, grain size, lattice parameter and internal strain were investigated using X-Ray Diffraction (XRD) measurements. The morphological aspect of the nanostructured powders was analysed by means of the Scanning Electron Microscopy (SEM). Compacted pastilles with circular shape have been under Vickers test of micro Hardness and magnetic measurements of Hysterisis loops. Discussed results according to milling time show that after 60 h milling the grain refinement is about 15.59 nm with internal strain of around 0.5809 %. The micro hardness increases with the decrease of the grain size and the hysterisis loop at 60 h milling is enhanced in term of decreased coercivity.
Modeling of Non-Uniform Thermoelement Devices Subject to Lateral Heat Convection
Authors: Kafafy Raed , Hameed Ammar
Published: April 2011

In this paper, we draw attention to the importance of the lateral convection heat transfer effect on the operation of thermoelements with variable cross-sectional area. The significance of lateral heat convection arises from a new application, in which thermoelements form the walls of a MEMS-based convergent-divergent micronozzle in order to pump heat from the divergent part of the micronozzle to the convergent part to enhance overall performance. To assess the effect of thermoelement, we develop a quasi-one-dimensional model for thermoelements, in which, the physical phenomena of Peltier effect, Joule heating, Seebeck effect, longitudinal heat conduction, and lateral heat convection are considered. The general energy equation of the thermoelement with variable material properties is formulated with heat convection modeled as a lateral heat source. We used the model to study thermoelements with rectangular cross section and uniform thickness, but variable width. The width of the element is maximum at the location forming the micronozzle throat. Several geometries have been investigated; a piece-wise linear, parabolic and piece-wise sine wave. Two parameters which play important role in the thermal performance of thermoelement are identified. These are the thermal resistance ratio; ratio of longitudinal conduction resistance to lateral convection resistance, and heating ratio; ratio of Joule heating to Fourier conducted heat. The effects of varying these two parameters as well as thermoelement geometry have been investigated thoroughly and the results are presented in the form of charts to assist the design and material selection of the thermoelement.
Turbulent Diffusion of Suspended Particles: Analysis of the Turbulent Schmidt Number
Authors: Absi Rafik , Marchandon Stéphane , Lavarde Marc
Published: April 2011

For mass transfer applications, CFD codes need the turbulent Schmidt number . The aim of our study is the analysis of some theoretical closure results and analytical formulations for . We will investigate different formulations of from the basic conservation equations for sediment-water mixtures in turbulent open-channel flows based on a two-fluid description and a kinetic model. The kinetic model for turbulent two-phase flows provides which depends on particle Stokes number. Our study show that the two approaches provide that depends on turbulent kinetic energy (TKE), eddy viscosity and particles settling velocity. For the analysis, accurate analytical formulations for TKE and eddy viscosity calibrated by DNS data are presented.
Determination of the Pore Sizes and their Influence on the Capillary Imbibition into Glass Wool
Authors: Marmoret Laurent , Beji Hassen , Perwuelz Anne
Published: April 2011

A glass wool media is commonly classified as a medium made up of many capillaries. They might, however, be considered analogous to a network of tubes as a bundle of capillaries. The capillary pressure of such a medium would be dependent on the amount of fluid held within the bundles. But, this very simple picture of porous media does not capture all the characteristics of this imbibition. We have determined capillaries radii by using Washburn and Laplace relations. Laplace radius can also be obtained by 3 approaches: using White’s relation and using Jurin’s law with visualized height and with weight. We have observed a single value of capillary radius cannot be used to determine the infiltration height as a function of time. This mechanism of capillary infiltration can be controlled by pores of more than one size and pores are interconnected.
The Influence of Rare Earth, Strontium and Calcium on the Thermal Diffusivity of Mg-Al Alloys
Authors: Rzychoń Tomasz , Kiełbus Andrzej
Published: April 2011

The microstructure and thermal diffusivity of as-cast AM60, AE63, AJ63 and AXJ620 alloys were investigated over the temperature range 20–300°C. The microstructure of as-cast AM60 magnesium alloy consists of dendrites of α-Mg solid solution and divorced eutectic containing “islands” of α-Mg and Mg17Al12 phase. In regions adjacent with divorced eutectic, the supersaturation aluminum solute in the α-Mg matrix is observed. The addition of rare earth, calcium and strontium caused the decrease of the volume fraction of Mg17Al12 compound and aluminum content in α-Mg solid solution. Moreover, the intermetallic compounds such as: Al11RE3, Al4Sr, Al3Mg13Sr, Al2Ca are observed in the interdendritic regions. The thermal diffusivity of AM60 magnesium alloy increases with increasing temperature up to 150°C, above this temperature the increase is less marked. The change in the slope of the temperature variation of the thermal diffusivity is caused by a precipitation of Mg17Al12 phase in the supersaturation of α-Mg areas neighboring the divorced eutectic α-Mg+Mg17Al12. The addition of rare earth, calcium and strontium caused the increase of the thermal diffusivity and thermal conductivity due to the decreasing of aluminum content in α-Mg matrix.
Electromagnetic Radiation Effect on ZnO Nanocrystallites
Authors: Sepet L. , Baydogan Nilgun , Çimenoğlu H. , Kayali E.S. , Tugrul A.B. , Altinsoy N. , Albayrak Gülçin , Sengel H. , Akmaz F. , Parlar A.
Published: April 2011

The changes on energy band gap at induced ZnO nanocrystallite thin film have investigated with the increase of absorbed dose. Irradiated ZnO nanocrystallite thin film exhibiting different absorption edges could adjust the transmittance of energetic electromagnetic radiation. The variations on absorption edge due to energy band gap were controlled by the absorbed dose.
Simulation of Drying Behavior of Cotton Bobbins by a Simultaneous Heat and Mass Transfer Model
Authors: Akyol Ugur , Kahveci Kamil , Cihan Ahmet , Akal Dinçer
Published: April 2011

In this study, the drying process of cotton bobbins for different drying air temperatures has been simulated by a simultaneous heat and mass transfer model. In the model, the mass transfer is assumed to be controlled by diffusion. In order to make the simulation, firstly, drying behavior of cotton bobbins for different drying air temperatures has been determined on an experimental bobbin dryer setup which was designed and manufactured based on hot-air bobbin dryers used in textile industry. In the experimental setup, temperatures of different points in cotton bobbins were measured by thermocouples placed inside the bobbins, and weights of the bobbins during the drying period were determined by means of a load cell. Then, moisture ratio and temperature values of the model have been fitted to the experimental ones. The fit was performed by selecting the values for the diffusion coefficient and the thermal diffusivity in the model in such a way that these values make the sum of the squared differences between the experimental and the model results for moisture ratio and temperature minimum. Results show that there is a good agreement between the model results and the experimental measurements. The results also show that temperature has a significant effect on mass transfer and the temperature dependence of the diffusion coefficient may be expressed by an Arrhenius type relation.
Airborne Pathogens Transport in an Aircraft Cabin
Authors: Acikgoz M.B. , Akay Baris , Miguel Antonio Ferreira , Aydın Murat
Published: April 2011

Airborne pathogens can spread within an aircraft cabin from sneezing, coughing or breathing of a sick passenger. This paper reports a 3D numerical study on the transport of airborne pathogens inside Boeing 767 cabin. After cough or sneeze of an infected passenger, the entire unsteady pathogen dispersion process is simulated. Effects under study include the direction of coughing on the pathogens propagation and the spreading times from infected to hosts passengers.
Electrochemical Hydriding of Mg-Based Alloys
Authors: Vojtěch Dalibor , Knotek Vítězslav , Novák Pavel
Published: April 2011

Mg-based alloys are prospective materials for reversible hydrogen storage in the form of metallic hydrides. Usually, hydrogen saturation is carried out at high temperatures and high hydrogen pressures. This is the reason for the high cost of metallic hydrides in comparison with other hydrogen storage methods. Electrochemical hydriding, on the other hand, can be realized at room temperature. Moreover, this process does not need any hydrogen atmosphere. In the presented work, electrochemical hydriding of several Mg-Ni-Mm-based alloys (Mm = mishmetal) is performed. Hydriding efficiency, mechanism and kinetics are described. It is shown that the additions of Ni, Mm and the formation of eutectic structures support hydriding of alloys.
Suppression of Iron Silicide Formation in the Reaction Layer of Sialon – 7.5% Cr Ferritic Steel Joint
Authors: Hudiyo Firmanto , Hussain Patthi , Mamat Othman
Published: April 2011

Diffusion bonding of sialon and 7.5%-Cr Ferritic Steel (FS) in as-received and nitrided condition was studied. Decomposition of sialon and interdiffusion of elements between the sialon and the steel were observed. The interdiffusion of elements produced reaction layers at the joint. The steel moved into the decomposition part of the sialon and replaced the decomposed sialon in this part. Diffusion of silicon into the steel resulted in the silicon-diffusion layer. FeSi2 was formed in the reaction layer when Si in the decomposition part of the sialon reacted with Fe. The use of nitrided steel in the diffusion bonding had suppressed the formation of the FeSi2 in the layer.
Effect of Temperature on the Growth of Vertically Aligned Carbon Nanotubes from Palm Oil
Authors: Abu Bakar Suriani , Muhamad Salina , Mohamad Saad Puteri Sarah , Md Nor Roslan , Mohd Siran Yosri , Rejab Syahril Anuar M. , Asis Ahmad Jaril , Tahiruddin Shawaluddin , Abdullah Saifollah , Rusop Mohamad Mahmood
Published: April 2011

The effects of synthesis temperature on the quality and quantity of vertically aligned carbon nanotubes (VACNT) were studied using high resolution scanning electron microscopy, and micro-Raman spectroscopy. The VACNT was synthesized by Fe catalytic decomposition of palm oil deposited on silicon substrate by thermal chemical vapour deposition method. The analysis shows that the growth rate increases from 3.8 to 5.5 µm/min as the temperature was increased from 750 to 800°C. The nanotube diameters were observed bigger at low temperature range. Smaller and uniform diameter (~15 nm) was found at 750°C and the increment in diameter size was seen at higher temperature range. Smaller graphite Raman “G” peak width, low ID/IG ratio (~0.52) indicated higher crystallinity of the nanotube and moderate I2D1/ I2D2 ratio for second order Raman peak was also detected at synthesis temperature of 750°C. These results indicated that the optimum synthesis temperature for higher quality VACNT production was at 750°C.
The Effect of Precursor Vaporization Temperature on the Growth of Vertically Aligned Carbon Nanotubes Using Palm Oil
Authors: Abu Bakar Suriani , Muhamad Salina , Mohamad Saad Puteri Sarah , Afif Mohd Zobir Syazwan , Md Nor Roslan , Mohd Siran Yosri , Rejab Syahril Anuar M. , Asis Ahmad Jaril , Tahiruddin Shawaluddin , Abdullah Saifollah , Rusop Mohamad Mahmood
Published: April 2011

Carbon nanotubes (CNTs) were fabricated from palm oil using the thermal chemical vapor deposition technique utilizing a two furnace system. The effect of precursor vaporization temperature of the first furnace, in the range of 300-600°C was systematically studied with the synthesis temperature (second furnace) fixed at 750°C for a total time of 30 min. The samples were characterized using field emission scanning electron microscopy and micro-Raman spectroscopy. CNTs of various packing densities and diameters were synthesized with the varying precursor vaporization temperature. Based on micro-Raman measurements nanotube defect level and the presence of SWCNT were dependent on the vaporization temperature. Vertically aligned CNTs (VACNTs) were found to grow within the vaporization temperature range of 400-500°C, with well graphitized and higher yield obtained at 450°C with excellent lateral alignment, uniform nanotubes diameter (~15 nm), orientation and distribution within the CNT bundles. At vaporization temperatures of 300-350°C and 500-600°C, lower growth rate, bigger nanotubes diameter and higher ID/IG ratio were observed which indicated lower nanotubes quality that produced at both temperature ranges.
Speckle-Based Deflection Techniques in Diffusivity Measurements
Authors: Ambrosini Dario , Paoletti Domenica , Di Biase Roberta , Galli Giorgio
Published: April 2011

Optical techniques have a long tradition in flow visualization, allowing both qualitative and quantitative analysis. In particular, speckle photography, introduced in 1968, has been extensively used. The aim of this work is to discuss speckle-based deflection techniques in the investigation of diffusion phenomena in liquids.
Role of Forming Gas Annealing Characteristics on the Selective Surface Oxidation of Fe-Mn-Si-Cr Model Alloy
Authors: Swaminathan Srinivasan , Rohwerder Michael
Published: April 2011

To understand the role of annealing conditions on the segregation and selective oxidation phenomena, Fe 2Mn 2Si 0.8Cr (all in wt.%) model alloy was investigated. The samples were annealed at 820°C in N2-5%H2 forming gas atmospheres over a wide range of dew pints (-80 to 0°C) with dwelling time of 1 to 5 minutes. At all dew points, the strong chemical interaction between Mn and Si causes the formation of manganese silicates. External oxidation of Mn, Si and Cr were decreased at the higher dew points. Increasing the dwelling time shows an extended oxidation front i.e. pronounced external/internal oxidation of Mn, Si and Cr. Basically, the present work addresses the two stages of oxidation front.
Effect of Impinging Jet on Heat Conduction in Workpieces Irradiated by a Moving Heat Source
Authors: Bianco N. , Manca Oronzio , Nardini Sergio , Tamburrino Salvatore
Published: April 2011

A three dimensional conductive field is analyzed and solved by means of the COMSOL Multiphysics code. The investigated work-pieces are made up of a simple brick-type solid. A laser source with combined donut-Gaussian distributions is considered moving with a constant velocity along motion direction. The solid dimension along the motion direction is assumed to be infinite or semi-infinite, while finite width (2ly) and thickness (s) are considered. Thermal properties are considered temperature dependent and the materials are considered isotropic. Surface heat losses toward the ambient are taken into account. Several convective heat flux values on the upper surface, with corresponding Biot numbers, and Peclet numbers are considered with negligible radiative heat losses.Results are presented in terms of profile temperatures to evaluate the effect of impinging jet.
Performance of a Water Ammonia Absorption System Operating at Three Pressure Levels
Authors: Bouaziz Nahla , Ben Iffa R. , Kairouani Lakdar , Chikh Salahs , Bennacer Rachid
Published: April 2011

The present study deals with a compression-absorption machine. The proposed hybrid cooling system uses water-ammonia as a working fluid and operates at three pressure levels. The absorber is at an intermediate pressure (Pint) taken between the evaporator pressure (PEV) and the condenser pressure (PCD), unlike the single stage machine which works between two pressure levels. The proposed new system is studied and compared to the conventional machine. In order to evaluate the performance of the invoked machine, a procedure based on the MAPLE software is set up to compute accurately the thermodynamic properties of the working fluid. The analyses of the numerical results highlight that the performance of the novel proposed configuration is better than that relative to the conventional system. The study reveals the great impact of the intermediate pressure on the performance improvement and on reducing the generator temperature allowing the system to work at low enthalpy. In fact, for an evaporator temperature and a condenser temperature fixed respectively at -10°C and 40°C, the proposed hybrid refrigeration cycle operates at a generator temperature TGE = 75°C and the installation’s COP is about 0.56. While for the same conditions, the single stage machine COP cannot exceed 0.51 with a generator temperature of about 135°C. Consequently, our enhanced novel configuration presents the opportunity to operate at low enthalpy sources.
Numerical Simulation of Transient Temperature Fields in Solids Irradiated by Moving Gaussian and Donut Sources
Authors: Manca Oronzio , Nardini Sergio , Ricci Daniele , Tamburrino Salvatore
Published: April 2011

This work presents a three-dimensional heat transfer model developed for laser material processing with a moving Gaussian and donut heat sources, using Comsol Multhiphysics 3.5 code. The laser beam, having a defined power distribution, strikes the surface of an opaque substrate of semi infinite length but finite width and depth moving with a uniform velocity in the positive axial direction. The solid dimension along the motion direction is assumed to be infinite or semi-infinite, while a finite width and thickness are considered. Thermal properties are considered temperature dependent. Surface heat losses toward the ambient are taken into account. The results are presented in terms of temperature profiles and thermal fields are given for some Biot and material thicknesses at a constant Peclet number.