bluuebunny/crossref_metadata_2025 huggingface dataset:
Effectiveness Parameters for the Heat and Mass Transfer in a Desiccant Wheel
Authors: Ruivo C.R. , Costa J.J. , Figueiredo A.R.
Published: April 2011

The desiccant wheel is the key component in a solid-desiccant system for air dehumidification. The heat and mass transfer phenomena occurring within the porous channel walls of the wheel and with the airflow are strongly coupled, and some properties of the airflow and of the desiccant medium exhibit important changes during the sorption/desorption processes. The dynamic analysis of such devices integrated in non-conventional HVAC&R systems can be easily done by a project designer using the NTU-effectiveness method, provided that appropriate correlations for two independent effectiveness parameters are available. In this work, the performance of a desiccant wheel was evaluated by numerical modelling the cyclic behaviour of a representative channel of the hygroscopic matrix. The physical model adopted takes into account the gas-side and solid-side resistances, as well as the simultaneous heat and mass transfer coupled with the water adsorption/desorption process in the channel wall domain. Two phases co-exist in equilibrium inside the desiccant porous medium, the equilibrium being characterized by sorption isotherms. The desiccant medium considered is silica gel RD. In the numerical model, the airflow is treated as a bulk flow, and its interaction with the wall channel matrix is represented by appropriate convective heat and mass transfer coefficients. Two independent effectiveness parameters were defined. A set of cases was numerically simulated and the results were analysed to assess the dependence of those effectiveness parameters on the process and regeneration airflow rates and on the channel length. As a conclusion, novel empirical correlations are here purposed.
Dynamic Thermal Diffusivity Measurements – A Tool for Studying Gas-Solid Reactions
Authors: Ahmed Hesham M. , Viswanathan Nurni N. , Seetharaman Seshadri
Published: April 2011

In the present work, the thermal diffusivity measurements of uniaxially cold pressed NiWO4 has been carried out. The measurements were performed isothermally at temperatures between 973 and 1273 K under H2 gas using the laser flash technique. The experimental thermal diffusivity values were found to increase with the reduction progress as well as with increasing temperature. The calculated activation energy was found to be higher than that for chemically controlled reaction. The difference has been attributed to factors like agglomeration of the product as well as sintering of the precursor along with the chemical reaction. In order to sort out the sintering effect on the thermal diffusivity values, complementary experiments have been done on pressed NiWO4 and Ni-W, produced by the reduction of NiWO4 at 1123K, under Argon gas. The porosity change and its effect on thermal diffusivity values have been studied.
Phase Transformation and Thermoelectric Properties of Sn-Filled/Fe-Doped CoSb3 Skutterudites
Authors: Kim Il Ho
Published: April 2011

Sn-filled and Fe-doped CoSb3 skutterudites were synthesized by encapsulated induction melting. A single δ-phase was obtained by subsequent annealing, as confirmed by X-ray diffraction. The as-solidified ingot consisted of mixed phases of -CoSb, -CoSb2, δ-CoSb3 and elemental Sb. The phases could be transformed by annealing, and the phases of the as-solidified ingot annealed at 773 K for 24 h transformed to δ-CoSb3. The temperature dependence of the Seebeck coefficient, electrical resistivity and thermal conductivity were examined from 300 K to 700 K. The positive Seebeck coefficient confirmed p-type conduction. The electrical resistivity increased with increasing temperature, which showed that the SnzCo3FeSb12 skutterudite is highly degenerate. The thermal conductivity was reduced by Sn-filling because the filler atoms acted as phonon scattering centers in the skutterudite lattice. The thermoelectric figure of merit was enhanced by Sn filling and its optimum composition was considered to be Sn0.3Co3FeSb12.
Pulse Electrolysis for the Production of Hard Ni/ZrO2 Composite Coatings
Authors: Dardavila M.M. , Kollia C.
Published: April 2011

Composite electrodeposition technology is one of the methods used to fabricate metal matrix composite coating materials. One of the most challenging issues concerns the addition of homogeneously suspending oxide powders, such as TiO2 and ZrO2 in the electrolyte, in order to result in the uniform dispersion of the oxide powders in the metal matrix [1]. Moreover, the application of a current periodically varied by time during electrodeposition, i.e. pulse current (p.c.) instead of the commonly used direct current (d.c.) has been concluded that leads to the preparation of surfaces with well-defined properties [2]. It is also well known that composite electrodeposits of Ni/metal oxides have remarkable mechanical and anticorrosion properties [3]. In this work nickel matrix composite electrocoatings including ZrO2 micron–sized particles were produced from an additive free Watts type bath under strong agitation conditions applying d.c. and p.c. regime. The synergetic action of the pulse application, the incorporation of the particles into the nickel matrix and the applied hydrodynamic conditions on the crystalline development, the morphological characteristics, the microhardness and the roughness of the composite electrocoatings, were studied.
Finite Element Modeling of Silicon Transport into Germanium Using a Simplified Crystal Growth Technique
Authors: Mechighel Farid , El Ganaoui Mohammed , Pateyron Bernard , Kadja Mahfoud , Dost S.
Published: April 2011

A numerical simulation study, using finite element method, was carried out to examine the temperature and concentration fields in the dissolution process of silicon into germanium melt. This work utilized a simplified configuration which may be considered to be similar material configuration to that used in the Vertical Bridgman growth methods. The concentration profile for the Si-Ge sample processed using this technique shows increasing transport silicon into the melt with time, moreover, a flat stable interface is observed. The mass and momentum equations for fluid flow, the energy and the solute mass transport were numerically solved. Results showed good agreements with experiments.
Cosmic Censorship!: Thermal Transport in a ‘Naked’ Black Hole
Authors: Corral Bustamante R. Leticia , Rodríguez-Corral Aarón Raúl , Amador-Parra T.J , Vázquez-Tapia E.A.
Published: April 2011

Cosmic censorship!: black hole wrapped up by its entropy and hidden by its event horizon. In this paper, we postulate a metric to solve the Einstein equations of general relativity, which predicts the thermodynamic behavior of a gigantic mass that collapses to a black hole; taking into account the third law of thermodynamics that states that neither physical process can produce a naked singularity. However, under certain conditions, the model allows to evident violation to the cosmic censorship, exposing the hole nakedness. During the collapse of the hole, quantum effects appear: the area decrease and radiation produced has a high entropy, so that increases total entropy and expose the presence of the hole, while the appearance of the event horizon hide the singularity of the exterior gazes. It is verified that in certain circumstances, the model predicts that the hole mass is bigger than its angular momentum; and in all circumstances, this predicts an hole with enormous superficial graveness that satisfy a relationship of the three parameters that describe the hole (mass, charge and angular momentum); factors all indicative that the singularity is not naked. Then, there are no apparent horizons in accord with cosmic censorship conjecture. Even though the surface gravity of the hole prevents destroying its horizon wrapping singularity, there exists evidence of this singularity by the results of the spin-mass relationship and the escape velocity obtained. The lost information and the slow rate of rotation of the semi-major axis of the mass (dragging space and time around itself as it rotates), agree with Einstein's prediction, show the transport of energy through heat and mass transfer, which were measured by entropy of the hole by means of coordinated semi-spherical that include the different types of intrinsic energy to the process of radiation of the hole event horizon.
Solidification of Discontinuous Al2O3 Fiber Reinforced Magnesium (AM60) Matrix Composite
Authors: Zhang Qiang , Hu Henry , Lo Jason
Published: April 2011

Magnesium matrix composites have great potential for aerospace and automotive applications due to its low density and superior specific stiffness. The magnesium composites can often be reinforced by either particles or/and fibers. There were certain studies on solidification behaviors of particle-reinforced magnesium composites in the past. However, development of grain structure during the solidification of fibre-reinforced magnesium is barely investigated. In this work, an Al2O3 fiber reinforced magnesium (AM60) matrix composite (AM60/Al2O3,f) was cast. The solidification behavior of the cast AM60/Al2O3,f composite was investigated by computer-based thermal analysis. Optical and scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) were employed to examine the occurrence of nucleation and grain refinement involved in solidification of the composite. The results show that the addition of Al2O3 fibers leads to the formation of fine grain structure in the matrix of the AM60/Al2O3,f composite. The refinement of grain structure should be primarily attributed to the restriction of grain growth by the limited cellular space formed in the skeleton of the fiber preform structure instead of the nucleation of primary -Mg phase directly on Al2O3 fibers.
The Influence of Acetic Acid on High Temperature Corrosion of Selected Steels Utilized in Automobile Industry
Authors: Grzesik Zbigniew , Migdalska Monika , Mrowec Stanisław
Published: April 2011

The corrosion behavior of X33CrNiMn23-8, X50CrMnNiNbN21-9 and X53CrMnNiN20-8 steels utilized in automobile industry has been studied in oxidizing atmosphere, containing water vapor and acetic acid, usually present in combustion gases of biofuels in car engines. It has been found that the mechanism of corrosion under these conditions is rather complex. After early stages of the reaction, not exceeding 40 hours, the process follows approximately parabolic kinetics, being thus diffusion controlled. It has been shown that the presence of acetic acid highly increases corrosion rate of X33CrNiMn23-8 steel, containing highest chromium content, but has virtually no influence on the corrosion rate of X50CrMnNiNbN21-9 steel with lowest chromium concentration. These differences have been explained in terms of phase and chemical composition of corrosion products.
Effect of Multifilamentary Nb/Cu-Sn Wire Diameter on the Nb3Sn Diffusion Layers Structure
Authors: Popova E.N. , Romanov E.P. , Deryagina I.L. , Sudareva S.V. , Dergunova E.A. , Vorobyova A.E. , Balaev S.M.
Published: April 2011

Bronze-processed Nb3Sn-based multifilamentary composites with external diameter of 0.8 and 0.5 mm and coupled Nb filaments have been studied by transmission (TEM) and scanning (SEM) electron microscopy. After the two-staged annealing, 575°С, 150 h + 650°С, 200 h, commonly used for ITER conductors, a nanocrystalline layer of superconducting Nb3Sn compound is formed in every Nb filament as a result of solid-state reactive diffusion of Sn from the bronze matrix. It is demonstrated that in the wires of smaller external diameter the Nb filaments transformation into the Nb3Sn compound is more pronounced, that is the amount of the residual Nb is smaller. Besides, the nanocrystalline structure of the Nb3Sn diffusion layers is more perfect in 0.5 mm diameter wires, namely, the Nb3Sn grains are finer (their average size being 60 nm compared to 70 nm in 0.8 mm diameter wires) and are more uniform in sizes (the root mean square deviation of grain size distribution is correspondingly 15 and 17 nm).
Physical Properties of Diffusive-Hardening Alloys of Copper with Gallium and Tin
Authors: Shubin A.B. , Shunyaev K. Y. , Bykov V.A. , Noritsin S.I.
Published: April 2011

Gallium-based diffusive-hardening solders do not contain lead. These alloys have specific rheological properties. Their synthesis includes, as a rule, mechanical mixing of such initial components as gallium, copper and tin powders [1]. Then the metallic paste undergoes irreversible phase transformations forming a solid alloy with a specific structure. Here, we investigated microstructures of diffusive-hardened Cu-Ga-Sn alloys by SEM and EDX methods. Thermal diffusivity and heat conductivity of alloys mentioned above were studied by the laser flash method. Also differential scanning calorimetry (DSC) experiments were performed to obtain heat properties of the samples.
Synthesis of W- Cu- Ag Nanopowders Produced by a Co-Precipitation Process
Authors: Taghavi Golnaz , Rezaie Hamid Reza , Razavizadeh Hekmat
Published: April 2011

A homogeneous precipitation process was employed to prepare nanosized W-10%wtCu-10%wtAg powders using ammonium meta tungstate, copper nitrate and silver nitrate as precursors. The initial precipitates were obtained by reacting ammonium meta tungstate, copper nitrate and silver nitrate solutions under certain PH and temperature. In order to synthesis W-Cu-Ag composite powders, the initial precipitates washed, dried, and then calcined in air in order to prepare CuWO4-x, Ag2W4O13 and WO3 oxide powders for the next step reduction. The reduction was carried out in a hydrogen atmosphere to form the final W-Cu-Ag nanocomposite powders. The powders were characterized by X-ray diffraction (XRD) technique. The morphologies of the powders were observed by scanning electron microscopy (SEM).
Comparison of Corrosion Performance of Zn and Zn/Al 85/15 Coatings Produced by TWEA
Authors: Güleç Ahmet , Yilmaz Fevzi , Türk Ahmet , Üstel Fatih
Published: April 2011

Zn and Zn/Al 85/15 coatings are produced at optimum conditions by twin wire electric arc (TWEA) spraying technique and are used in various industrial applications to improve corrosion protection. As an alternative for Zn coating, Zn/Al 85/15 alloys coating show very good corrosion resistances and can protect substrate materials against harsh corrosive environments. The weight ratio of 85 Zn and 15 Al is regarded as optimum value. The forms of coating material are wires with different diameters. The aim of this study is comparison of anticorrosion performance of Zn and Zn/Al 85/15 coatings on ductile iron pipe surfaces as protective coatings against corrosion. Test samples were prepared from Zn and Zn/Al 85/15 coated ductile iron pipes. Coatings were investigated by optical microscopy, scanning electron microscopy (SEM) and have been analyzed by energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). They were compared according to protection performance against corrosion in salt spraying test according to ASTM B117. As a result of this study, Zn/Al 85/15 coating showed clear anticorrosion protection capacity against Zn coatings.
Assessment of Thermal Non-Equilibrium Condition on Heat Transfer through a Channel Lined with Porous Media – Constant Wall Temperature
Authors: Abkar M. , Forooghi P. , Abbassi A.
Published: April 2011

In this paper, forced convection in a channel lined with a porous layer is investigated. The main goal is to assess the effect of local thermal non-equilibrium condition on overall heat transfer in the channel. The effects of thermal conductivity of solid and thickness of porous layer are also studied. Flow assumed to be laminar and fully developed. The Brinkman-Forchheimer model for flow as well as the two equation energy model is used. The results showed that when the problem tends to local thermal equilibrium condition, heat transfer is enhanced due to heat conduction through solid phase. Another factor, which can facilitate the heat transfer, is the increase of the thermal conductivity of solid material. This trend is sensitive to the thickness of porous layer and modified Biot number, which is a measure (criterion) of local fluid to solid heat transfer. As thickness and modified Biot number increase, the Nusselt number becomes more sensitive to the thermal conductivity ratio.
Thermo-Mechanical Behaviour of Ultrahigh Molecular Weight Polyethylene-Carbon Nanotubes Composites under Different Cooling Techniques
Authors: Kanagaraj S. , Fonseca A. , Guedes R.M. , Oliveira Monica S.A. , Simões José A.O.
Published: April 2011

Ultrahigh molecular weight polyethylene (UHMWPE) is a unique polymer with outstanding physical and mechanical properties that makes it particularly attractive to fabricate the bearing surface for artificial joints. Despite the requirement of visco-elastic properties of the UHWMPE and its composites, the characterization of them has received relatively little attention. The objective of this work is concerned with the studies on visco-elastic behaviour of UHMWPE and nanocomposites, which were prepared at optimized ball milling time with different cooling techniques. It is observed that stiffness of the materials increases appreciably at 0.2wt.% CNTs with an increase of frequency till 30Hz which confirms the reinforcing effect of CNTs in composites. The loss modulus of the sample is observed to be converged at higher temperature irrespective of frequency. The damping effect of the sample could be kept within the limit of polymer at any frequency range when the temperature is low and it is also possible at any temperatures at higher frequencies except LN2 cooled sample. The relaxation fraction increases with an increase of temperature and decreases with an increase of frequency. It is concluded that air cooled sample could be used wherever modulus is the main criteria irrespective of temperature and frequency, LN2 cooled sample can be used where more damping is required and water cooled samples may be used where more strength and toughness are required.
Experimental Study of Enhanced Pool Boiling Heat Transfer Using Graphite Foam Inserts
Authors: Leong K.C. , Jin L.W. , Pranoto I. , Li H.Y , Chai J.C.
Published: April 2011

This paper presents the results of an experimental study of heat transfer in a pool boiling evaporator with porous insert. Different types of graphite foams were tested with the phase change coolant FC-72 in a designed thermosyphon. Comparisons between the graphite foams and a solid copper block show that the porous structure enhances pool boiling significantly. The boiling thermal resistance of the tested graphite foams was found to be about 2 times lower than that of the copper block. The bubble formation recorded by a high speed camera indicates that boiling from a graphite foam is more vigorous than from a copper block. The designed thermosyphon with graphite foam insert can remove heat fluxes of up to 112 W/cm2 with the maximum heater temperature maintained below 100°C.
Acoustical Parameters: Aqueous Solution of Borassus Flabellifier Fruit Pulp by Non Destructive Method
Authors: Shrivastava Bhaktdarshan , Mishra A. , Phadke Sushil
Published: April 2011

The change in the wavelength of ultrasonic waves in different medium is due to the elastic properties and the induced particles vibrations in the medium. The study of propagation of ultrasonic wave in liquid systems and solids is now rather well established. Ultrasonic waves are an effective means for examining and analyzing certain physical properties of the materials. It is universally adopted to examine the changes in such physical properties while they occur. In the present study authors are analyzed aqueous solutions of 'Borassus Flabellifier' fruit pulp, which is available in Western part of MP (Dhar-Jhabua Districts) India, at various concentrations have been experimentally determined by using Non Destructive technique (NDT). Some values of acoustical parameters such as intermolecular free length (Lf), Acoustic impedance (Z), and Isentropic compressibility (βs), were computed with the viewpoint importance and applicability in asserting the interactions. These solutions are known for their natural ingredients in pharmaceutical activity as anti-diabetic, pain killing & temperature reducing. In this paper, authors are reported. Ultrasonic wave velocities in a aqueous solution of Borassus Flabellifier fruit pulp at different concentrations using Multi frequency Ultrasonic interferometer Model M-81 S.
Estimation of Effective Moisture Diffusivity in Starchy Materials Following Hydrothermal Treatments
Authors: Bahrani Seyed Amir , Loisel Catherine , Monteau Jean Yves , Rezzoug Sid Ahmed , Maache-Rezzoug Zoulikha
Published: April 2011

Two hydrothermal treatment processes (DV-HMT and DIC treatment) were investigated on standard maize starch for three processing temperatures; 100, 110 and 120°C. The gravimetric change of starch powder during the treatment was analyzed by a simultaneous water diffusion and starch reaction model. The effective diffusivity coefficient (Deff) and reaction rate constant (k) were estimated by minimizing the error between experimental and analytical results. The values of Deff and k clearly increased with temperature. The degree of starch melting was evaluated for the two treatments using the first-order reaction model as a function of processing time. The results suggest that the absorption process is controlled by water–starch reactivity that induces melting phenomenon of starch crystallites, which progresses when temperature increases. The two hydrothermal treatments considerably differ: DIC being more prone to water absorption as demonstrated by the values of Deff and k.
Synthesis of Cobalt Nano Particles on Silica Support Using the Strong Electrostatic Adsorption (SEA) Method
Authors: Chee Kai Ling , Mohd Zabidi Noor Asmawati , Chandra Mohan Sinnathambi
Published: April 2011

Supported cobalt is one of the common catalysts used in Fischer-Tropsch synthesis (FTS). Strong electrostatic adsorption (SEA) was employed to synthesize cobalt nano particles supported on silica. Cobalt nitrate was used as the catalyst precursor and non-porous silica spheres, which were synthesized using the modified Stöber method, were used as a catalyst support. Point of zero charge (PZC) for silica was determined using equilibrium pH at high oxide loading (EpHL) method. The optimum pH was determined by measuring cobalt uptake versus pH. High cobalt uptake at basic pH and low cobalt uptake at acidic pH indicates electrostatic interaction between the cobalt complexes in the precursor solution and the hydroxyl group on the support’s surface. Catalysts prepared at optimum pH were characterized using TPR, XPS and TEM. TPR shows reduction peak at high temperature (587°C) indicating strong interaction between cobalt and silica support. XPS shows presence of Co2+ species on the surface. TEM images of the Co/SiO2 at 5 wt% and 10 wt% cobalt loadings show fairly well-dispersed cobalt oxide nano particles on the spherical silica support with narrow particle size distribution. The findings suggest that SEA was deemed a suitable method to prepare supported cobalt catalysts.
Corrosion Behavior of Laser Nitrided Ti-6Al-4V Alloy: A Review
Authors: Razavi R. Sh. , Gordani G.R. , Man H.C.
Published: April 2011

The titanium alloys-especially Ti-6Al-4V- are attractive materials because of their high specific strength and low density. But these alloys have poor surface properties such as wear and corrosion resistance for many industrial applications. Laser surface nitriding technique, has been the subject of considerable interest as a means of enhancing the surface performance of titanium alloys. In the present paper, the corrosion properties of laser nitrided Ti-6Al-4V alloy that have been reported by several researchers until now is considered. The microstructure changes, phase’s formation and the influence of laser processing parameters on them, in laser nitriding layers of Ti-6Al-4V alloy are investigated in different manners like SEM, TEM, XPS and XRD. At the end of this paper, the effects of laser nitriding on the corrosion behavior of Ti-6Al-4V alloy are reviewed.
Computational Algorithms for Topological Cycle Indices of Tert-Butyl Alcohol by Computational Science
Authors: Ghafooriadl Naser , Asadzadeh Olghi Sohrab , Moghani Ali
Published: April 2011

Recently, the dominant classes and integer-valued characters of un-matured full non-rigid group of tert-butyl alcohol has been found by the third author (see, J. Nano Res. 11, 7-11, 2010). In this paper, the unit subdued cycle index table introduced by S. Fujita for the above molecule is successfully derived for the first time.
Electron Diffusion in ZnO Nanomaterial: An Ac Impedance Investigation
Authors: Rusdi Roshidah , Kamarulzaman Norlida , Nor Sabirin Mohamed , Osman Zurina , Rahman Azilah Abd
Published: April 2011

ZnO is a wide band gap semiconductor with many applications such as in solar cells, varistors, and other electrical components. The ZnO material was synthesized using a sol-gel method. The material was characterized using X-Ray diffraction (XRD) and scanning electron microscopy (SEM). The material is pure and single phase. Electron conduction in ZnO nanomaterials was done using alternating current (ac) impedance. The frequency ranges of the measurements used were 1x 10-3 Hz to 1x 106 Hz and the ac impedance measurements were done within a temperature range of 60oC to 100oC. Nyquist plots were drawn and bulk resistances were obtained. Subsequently, conductivity values were calculated and the diffusion characteristics were obtained. From further analysis of the conductivities with temperature, the diffusion of electrons in the material was studied. It was found that the conductivity increased with the increase of temperature which meant that the rate of diffusion of the electrons through the materials also increased. An Arrhenius relation was concluded for the electron diffusion in the ZnO nanomaterials.
Macrosegregation and Porosity during Directional Solidification of a Ternary Al-9wt%Si-3wt%Cu Alloy
Authors: Gomes L.G. , Jácome P. D. , Ferreira Ileao L. , Moutinho D.J. , Rocha O.L. , Garcia Amauri
Published: April 2011

Macrosegregation and porosity formation have been investigated by both a numerical model and by transient directional solidification experiments. The macrosegregation pattern, the theoretical and apparent densities are presented as a function of the casting length. X-ray fluorescence spectrometry was used to determine the macrosegregation profiles. The measurement of microporosity was performed using pyknometry analysis. The local composition along an Al-9wt%Si-3wt%Cu casting length was used as an input parameter for simulations of microporosity evolution. The results have demonstrated that the presence of Si in the alloy composition has inhibited the inverse copper segregation, which is a typical result of directionally solidified Al-Cu castings. The numerically simulated trend is in good conformity with the experimental scatter.
Diffusion Paths in the Ternarysystem Fe-Co-Ni: An Empirical Approach
Authors: Priimets J. , Ugaste Ü.
Published: April 2011

An empirical approach to the description of diffusion paths in the ternary system Fe-Co-Ni is developed. It is shown that the experimentally determined diffusion path in this system can be described by the universal function, which contains two parameters, extracted from experimental data. The values of these parameters and their possible dependence on initial compositions of diffusion couples are discussed. Using the universal function, typical diffusion paths for the system Fe-Co-Ni have been calculated. It is shown that the calculated diffusion paths are in a qualitatively good agreement with the available experimental data.
Thermal Diffusivity of TBC Layers of RE2Zr2O7 Type
Authors: Moskal Grzegorz
Published: April 2011

The paper presents the results of basic thermal properties of thermal barrier coatings on the base of rare earth zirconate of type Gd2Zr2O7, deposited by the air plasma spraying (APS) method. Measurements of thermal diffusivity with the laser-flash method were performed within the temperature range of 25°C-1100°C with two and ten hours of annealing. The measurements were performed on the single-layer (AMS 5599 alloy), double-layer (AMS 5599 alloy + NiCrAlY interlayer) and three-layer samples (AMS 5599 alloy + NiCrAlY interlayer + ceramic layer of RE2Zr2O7). By using the NETZSCH Proteus software and the results for the single-layer sample, thermal diffusivity of the interlayer itself was determined by means of the double-layer model. A similar method was used to determine the thermal diffusivity of the ceramic layer. The obtained results showed lower thermal diffusivity and thermal conductivity for the new type of coatings in comparison with the standard zirconium concerning TBCs. Those results are slightly different compared with the results obtained for the initial powders, which indicates a crucial role of the ceramic layer microstructure (architecture of cracks and porosity).
Comparison of the Breakthrough Curves Obtained by ASTM D2007-03 Annex 1 and on a Bench Unit for the Selection of Adsorbents for the Removal of Nitrogen and Sulfur Contaminants from Fuels
Authors: Figueiredo M.A.G. , Estrela G.V. , Souza W.C. , Chiaro S.S.X.
Published: April 2011

The use of adsorbents in the final steps during petroleum fuels refining is still the usual practice in Brazilian refineries. The production of kerosene via the Bender process still demands that the fuel goes through a bed of clay to remove nitrogen contaminants. Thus, several studies are being developed based on adsorption over clays for the removal of nitrogen and sulfur compounds. However, the major problem is the sharp decrease in the adsorbents durability. The procedure currently employed by the refineries is the one recommended by the annex 1 from ASTM D2007 methodology. By this method, the evaluation of the adsorbent capacity is done without any pretreatment for water removal. This study aimed to establish a comparison between the results obtained by ASTM D2007 with the results obtained by a procedure developed on a bench unit which comprises a pretreating stage to remove water from the adsorbents before feeding the column. The results show that the water content strongly influences the adsorption capacity of the clays, and may even spoil high-capacity adsorbents if they are not pretreated for water removal.
High Temperature SO2-Gas Corrosion of Ni-Cr-Co Base Superalloy between 800 and 1000°C
Authors: Bak Sang Hwan , Lee Dong Bok
Published: April 2011

The Ni-base superalloy, INCONEL740, whose major alloying elements are 24.31 wt.%Cr-20 wt.%Co, was corroded in an Ar-0.2%SO2-gas atmosphere between 800 and 1000oC for 50, and 100 hr in an electric furnace. The scales formed after SO2-gas corrosion tests were generally adherent at 800 and 900oC. At 1000oC, massive scale spallation however occurred over the entire surface. The scales consisted of Cr2O3, (Ni,Co)Cr2O4, and TiO2, indicating that not sulfidation but an oxidation reaction prevailed owing to the thermodynamic stability of concerning oxides.
Modeling of Transient Moisture Diffusion in Wood below the Fiber Saturation Point
Authors: Eitelberger Johannes , Hofstetter Karin
Published: April 2011

During the last two decades the macroscopic formulation of moisture transport in wood below the fiber saturation point has motivated many research efforts. From experiments the difference in steady-state and transient transport processes is well known, but could not be explained in a fully physically motivated manner. In the following article, first the microstructure of wood is depicted, followed by a description of the physical background of steady-state and transient transport processes in wood, and thereon based mathematical formulations. For a correct macroscopic description of transient transport processes, three coupled differential equations have to be solved in parallel, which is done using the finite element method. The validation of the whole model by comparison of model predictions with experimentally derived values is currently in progress and will be published in near future.
Fabrication of Multi-Walled Carbon Nanotube/Vinyl Ester Nanocomposites: Dispersion and Stabilization
Authors: Chitsazzadeh M. , Shahverdi H. , Shokrieh Mahmood M.
Published: April 2011

Excellent physical and mechanical properties of carbon nanotubes (CNTs) make them outstanding candidate as fillers to fabricate multi-functional polymer composites. It is assumed that a high level of dispersion in the preparation stage may lead to a more effective nanocomposite. In this research, the dispersion state of multi-walled carbon nanotubes (MWNTs) at various contents in an unsaturated vinyl ester resin is investigated during fabrication by on-line monitoring the viscosity of suspensions as a function of sonication time and energy introduced. The results show that initial viscosities of suspensions increase by adding more MWNTs to the resin. The viscosities gradually increase during the sonication and reach to maximum values, when it is assumed that the dispersion is completed. After this step the viscosity subsequently decreases. The energy density required to achieve a good dispersion of MWNTs in vinyl ester is obtained. The qualities of dispersion in cured composites are characterized by examining the sections using the scanning electron microscope (SEM) to confirm the results of viscosity measurements. The stabilization of MWNTs is achieved by adding a commercial dispersant and stabilizer, BYK-P 104S, by 0.0375 wt% . The results indicate that adding more surfactant to the suspension makes it unstable and leads to flocculation. The stabilization of suspensions is investigated by using viscosity measurement. Also, FT-IR is used to determine the possible mechanism of surfactant to stabilize the MWNTs in vinyl ester.
Numerical Investigation of Impingement Heat Transfer Enhancement on a Flat Plate with an Attached Porous Medium
Authors: Wu Pey Shey , Lo Yi Wen , Cheng Fong Chia
Published: April 2011

The enhancement of impingement heat transfer on a flat plate covered with a thick layer of porous medium with or without a center hole was numerically investigated. The renormalization group turbulence model is selected for the fluid region while Forchheimer extended Darcy’s model is used for porous region. The numerical models were justified by comparisons with available experimental data. Computational results show that an attached porous medium with a center hole can effectively enhance jet impingement heat transfer while an attached thick porous layer without a center hole has detrimental effect. The physics of these results are supported and well explained by the detailed flow patterns. The most influential parameters in this heat transfer process include the jet Reynolds number and the center hole geometry (hole depth and jet-to-hole diameter ratio). A good hole geometry should well trap the jet and direct the coolant along the heated plate.
The Influence of Heat Treatment Parameters on the Thermal Diffusivity of WE54 and Elektron 21 Magnesium Alloys
Authors: Kiełbus Andrzej , Rzychoń Tomasz , Moskal Grzegorz
Published: April 2011

In the present study, the thermal diffusivity and conductivity of WE54 and Elektron 21 alloys were studied. The results showed the thermal diffusivity of WE54 and Elektron 21 alloys were temperature and microstructure dependent. The thermal diffusivity of both alloys was dependent on the content of the solute element in the α-Mg matrix. The solid solution of Y and Gd in Mg has a lower thermal conductivity than alloys where the intermetallic Mg3(Nd,Gd) and Mg14Y2Nd phases are present. The formation of strengthening phases during ageing caused the consumption of the solute element in the α -Mg matrix, and improved the thermal conductivity of the alloys.
In Situ Analysis of Hydrogen Mobility during Hydrogen Permeation through Nb-Based Hydrogen Permeable Membranes
Authors: Yukawa Hiroshi , Nambu Tomonori , Matsumoto Yoshihisa
Published: April 2011

The hydrogen solubility and the hydrogen permeability have been measured for Nb-based alloys in order to investigate the alloying effects on the hydrogen diffusivity during hydrogen permeation. It is found that the hydrogen solubility decreases by the addition of ruthenium, tungsten or molybdenum into niobium. The mobility for hydrogen diffusion during hydrogen permeation is estimated from the linear relationship between the normalized hydrogen flux, , and the product of the hydrogen concentration and the difference of hydrogen chemical potential, . It is found that the mobility for hydrogen diffusion during hydrogen permeation is larger for Nb-based alloys than pure niobium, especially at low temperature. The activation energy of the mobility for hydrogen diffusion decreases by the addition of ruthenium, tungsten or molybdenum into niobium.
Characterization of Hydrophilic Membranes Based on PVP and Carboxymetylcelulose Staple Fibers Infused with Calcium Alginate
Authors: de Miranda Leila Figueiredo , Terence Mauro Cesar , Ferro Barbosa Isabella Tereza , Martins Rubin Ingrid , Alves Jefferson Fernandes
Published: April 2011

Hydrophilic membranes based on PVP, containing 0.4 and 1% of carboxymethylcellulose staple fibers infused with calcium alginate were obtained and characterized in this study. The main proposal of this study is related to hydrogels based on PVP modified with carboxymethyl cellulose staple fibers infused with calcium alginate. This modified hydrogel is a hydrophilic membrane with better mechanical properties that can incorporate adequate drugs into the fibers for each lesion type. The hydrogels were obtained using ionizing radiation with an electron beam, at a dose of 25 kGy. The membrane’s characterization was performed by tensile and physic-chemical tests (gel fraction and swelling). The results obtained showed that the membranes have higher mechanical strength, a higher swelling degree and a lower gel fraction.
Investigation of a New Sn–Cu–Ga Alloy Solder
Authors: Matsushita M. , Sasaki Y. , Ikuta Y.
Published: April 2011

Soldering processes involving the use of Pb have been known and practiced for more than 5000 years. In 2000, the European Union imposed a ban on the use of Pb because of the fact that Pb is poisonous to humans. Consequently, attempts are being made worldwide to develop a Pb-free solder. Among the various Pb-free solders, the Sn–0.75wt%Cu (Sn-0.75Cu) solder is the suitable one from the viewpoint of cost. Moreover, its acoustic properties are superior to those of the other Pb-free solders. However, the Sn-0.75Cu solder has a few disadvantages: its joining strength is lower than that of the other solders, and its melting temperature is higher than that of the Sn-37wt%Pb (Sn–Pb) solder. Therefore, we have attempted to decrease the melting temperature and improve the joining strength of Sn-0.75Cu to match those of the Sn–Pb solder. It is well known that when Ga is added to a Sn-based alloy, the melting temperature of the alloy decreases. Moreover, Ga has superior wettability. Therefore, we added Ga to the Sn-0.75Cu solder in order to improve the joining strength and decrease the melting temperature of the solder. We observed that the melting temperature of Sn95.3Cu0.7Ga4 reduced to less than that of the Sn–Pb solder. We also investigated the joining strength between the Ga-added solder and a Cu wire. We observed that the joining strength increased with an increase in Ga content, was the highest for Sn97.3Cu0.7Ga2, and then decreased with an increase in Ga content. The peak joining strength of the Ga-added solder was almost 1.5 times that of the Sn-0.75Cu solder. However, the brittleness of the solder increased with an increase in the Ga content. This is a disadvantage of the addition of Ga to Sn.
Kinetics of Low Temperature Nitriding of Precipitation Hardened Stainless Steel
Authors: Kochmański Paweł , Baranowska Jolanta
Published: April 2011

The paper presents results of research on nitrided layers on precipitation hardened stainless steel, known also as 1RK91 (Sandvik NanoflexTM). Samples were subjected to low temperature nitriding. The influence of nitriding parameters on nitriding kinetics was investigated. The nitriding process was carried out in a mixture of NH3 50% and products of its dissociation as well as in 100% ammonia atmosphere at temperature range 425-475°C. To investigate the kinetics of nitrided layer formation, the nitriding time changes between 2 and 8 h. The obtained diffusion layers were examined using the following methods: light and scanning electron microscopy, XRD phase analysis. The distribution profiles of selected chemical elements were acquired using optical spectrometry GDOES.
Numerical Study of Magnetic Field Effects on Buoyancy Driven Convection in a Non-Isothermally Heated Square Enclosure
Authors: Sheikhzadeh Ghanbar Ali , Pirmohammadi Mohsen , Fattahi A. , Mehrabian M.A.
Published: April 2011

Numerical simulation of natural convection heat transfer in the presence of a magnetic field is analyzed in a non-isothermally heated square enclosure. The left wall is heated and cooled with a sinusoidal heat source and the right wall is cooled isothermally. The horizontal walls of the enclosure are adiabatic. The effects of Rayleigh number (Ra = 104, 105 and 106), Hartmann number (Ha = 0, 25, 50 and 100) and amplitude of sinusoidal function (n = 0.25, 0.5 and 1) on temperature and flow fields are analyzed. It is observed that the rate of heat transfer is decreased with increasing the Hartmann number; it is also decreased when decreasing the amplitude of sinusoidal function.
Microstructure and Properties of CBN Diffusion Coating on High-Speed Steel
Authors: Chaus Alexander S. , Čaplovič Lubomír , Porubský Ján
Published: April 2011

CBN diffusion coating on the ball nose end mills made of AISI-M35 high speed steel (HSS) has been produced thermo-chemically. The microstructure and component depth profiles of the CBN diffusion layer have been studied by scanning electron microscopy and energy dispersive X-ray spectrometry. The results on laboratory cutting tests of ball nose end mills made of AISI-M35 HSS with and without complex CBN diffusion coating are also introduced in the paper. The relationship between wear kinetics and tool life has been established. It was shown that under the used cutting conditions the tool life of the mills with the coating was a factor of 1.6 higher than that of the mills without the coating. The higher tribological stability of the coating in cutting process was supported by metallographic observations of the worn surfaces using scanning electron microscopy.
Confined Bubble and Heat Transfer during Flow Boiling in a High Aspect Ratio Mini-Channel
Authors: Wang Yuan , Sefiane Khellil
Published: April 2011

Single vapour bubble growth and heat transfer mechanism during flow boiling in a rectangular horizontal mini-channel were experimentally investigated. The hydraulic diameter of the channel was 1454 μm, with an aspect ratio (Win/din) of 10. Degassed FC-72 was used as the working liquid. In this paper, bubble equivalent radius was found to increase linearly till a critical time, beyond which the growth turned into exponential. Bubble growth rate increases with increasing heat flux. Heat transfer mechanisms of the bubble growth at different heat fluxes and mass fluxes were discussed. In addition, the relation between thermal and flow conditions with bubble temporal geometry was explored.
Partition of Free Fatty Acids in Deacidiﬁcation of Macaúba Pulp Oil by Liquid-Liquid Extraction Using Ethanol/Water as Solvent
Authors: Brito Mariano Renata Gomes , Da Silva Carolina Moura , Couri Sonia , Nogueira Regina Isabel , Freitas Suely Pereira
Published: April 2011

Free fatty acids (FFA) is one of the most frequently determined quality indices in fats and oils industry because it has the economic impacts on production [1]. The FFA in macaúba pulp oil is usually very high (10 to 40%) due to enzymatic activity in the raw material [2]. In this case, alkali neutralization is not economically recommended due to neutral oil loss by occlusion in soapstock. The differential solubility of fatty acids and triacylglycerides (TAG) in various organic solvents has formed the basis of several processes for deacidiﬁcation of crude oils by liquid–liquid extraction [3]. The aim of the present work was to evaluate the influence of raw oil acidity, ethanol/water ratio, water content in ethanol and temperature extraction on partition coefficients of FFA during macaúba oil deacidification. The macaúba crude oil presented high acid index, about 86  1.2 mg KOH/g. The extraction data for the system macaúba oil + free fatty acids + ethanol + water was determined for oil:solvent mass ratios 1:1. Alcoholic solutions containing 2 to 10 % (w/w) of water were used to FFA extraction and the partition coefficients were determined after 24 hours at room temperature (293 K). The phase’s separation was observed for water content in the mixture above 4%. After solvent evaporation, the FFA in oil phase was evaluated by AOCS standard method. Regarding the high acid oil, the single stage liquid-liquid extraction reduced the FFA in macaúba pulp oil in about 23 % while the three batch stages reduced up to 60%. At the selected parameters (ethanol 94oGL, solvent/substrate ratio = 2), the partition coefficients in the firs stage to FFA (KFFA) were 30.45, 12.00 and 1.95, respectively to high acid, acid and low acid macaúba oils and the partition coefficients to TAG (KTAG) were 7.07, 0.04 and 0.02, respectively to high acid, acid and low acid macaúba oils. These results show the potential of ethanol to vegetable oil deacidification. Besides reduced generation of environmental pollutants, this new approach could also lead to reduction in oil losses, especially for low acid oil.
Reducing Hydrogen Permeation through Metals
Authors: Dapor Maurizio , Miotello Antonio
Published: April 2011

Metal–hydrogen systems are of great basic and technological interest in connection to the role of hydrogen as a clean energy carrier. Frequently, metal systems are involved in hydrogen purification, storage, and engines making use of this fuel. The presence of hydrogen in a metallic matrix gives rise to modifications of electrical, optical and mechanical properties. Hydrogen accumulation in metals may cause damage to the material by also producing fracture, thus limiting operating lifetime. Reducing the hydrogen permeation is an important task also for the fusion reactors: it is well known, indeed, that tritium is radioactive so that it is very important to be able to confine tritium during the nuclear fusion process. The theoretical study of permeation is thus of fundamental importance to obtain efficient barriers to permeation. Hydrogen trapping sites have a great influence on the hydrogen permeation through a slab sample. The diffusion of the hydrogen in a crystal is generally described by a parabolic partial differential equation with appropriate boundary conditions. The numerical simulation code PHM (Permeation of Hydrogen through Metals), realized for the study of the permeation of hydrogen in presence of trapping sites, is here described and utilized for the analysis of the influence of reversible and irreversible traps on the diffusion of hydrogen in a metal.