Heat and mass transfer of a circular porous moist object located in a triangular shaped vented cavity

Heat and mass transfer of a circular-shaped porous moist object inside a two-dimensional triangle cavity is investigated by using finite element method.The porous object is considered to be a moist food sample,located in the middle of the cavity with inlet and outlet ports with different configurations of inlet/outlet ports.Convective drying performance is numerically assessed for different values of Reynolds numbers(between 50 and 250),dry air inlet temperature(between 40 and 80℃)and different locations of the port.It is observed that changing the port locations has significant impacts on the flow recirculaitons inside the triangular chamber while convective drying performance is highly affected.The moisture content reduces with longer time and for higher Reynolds number(Re)values.Case P4 where inlet and outlet ports are in the middle of the walls provides the most effective configuration in terms of convective drying performance while the worst case is seen for P1 case where inlet and outlet are closer to the corners of the chamber.There is a 192% difference between the moisture reduction of these two cases at Re=250,T=80℃ and t=120 min.

Effect of Ce addition on microstructures and mechanical properties of A380 aluminum alloy prepared by squeeze-casting

The effect of cerium(Ce)addition on the eutectic Si,β-Al_5Fe Si phase,and the tensile properties of A380 alloy specimens prepared by squeeze-casting were studied by optical microscopy(OM),scanning electron microscopy(SEM),and X-ray diffraction(XRD).The experimental results showed that Ce more effectively modified the eutectic Si and refined theβ-Al_5Fe Si.The refinement effect significantly increased under a specific pressure of 100 MPa with the addition of Ce from 0.1wt%to 0.9wt%.In contrast,the average length and the aspect ratio of the eutectic Si andβ-Al_5Fe Si exhibited their optimal values when the content of the added Ce was greater than 0.5wt%.Needle-like Al_8Cu_4Ce was precipitated with the addition of excessive Ce;hence,the mechanical properties of A380 gradually decreased with increasing Ce content in the range from 0.3wt%to 0.9wt%.

Mechanical and physical characterization of sodium hydroxide treated Borassus fruit fibers

In order to improve the properties by chemical modification and to optimize the alkali concentration, we treated Borassus fruit fine fibers with aqueous sodium hydroxide solutions of different concentra- tions. In each case, the tensile properties of the fibers were determined. The morphology of the untreated and alkali treated fibers was observed using scanning electron microscope. The surface of the fibers became rough on alkali treatment. The tensile properties of the fibers improved on alkali treatment. The fibers attained maximum tensile properties when treated with 15% aqueous sodium hydroxide solution and decreased thereafter. The crystallinity index of the fibers showed a similar trend. The thermal stability of the alkali treated fibers was found to be higher than that of untreated fibers. Further, the char content was maximum for fibers treated with alkali having concentration of 15% and above. The chemical composition indicated that the percentageof a-cellulose was maximum when the fibers were treated with 15% aqueous sodium hydroxide solution and then decreased thereafter thus indicating the beginning of degradation of the fibers at higher concentrations. Thus, the optimum concentration of NaOH was established as 15% for alkali treatment of the Borassus fibers.

Dynamic Mechanical Properties of Tissue after Long-Term Implantation of Collagen and Polypropylene Meshes in Animal Models

Purpose: Pelvic floor reconstructive surgery has grown significantly in recent years. A wide variety of available types of meshes exist but the safety and success has not been adequately proven. We sought to evaluate the effects on dynamic biomechanical properties of tissue after long-term implantation of synthetic and biological grafts. Methods: A total of 96 New Zealand white female rabbits (approximately 3 kg) were used, 72 of which were surgically implanted with acellular, collagen mesh (n = 36) or nonabsorbable monofilament polypropylene mesh (n = 36). There was a no mesh-rupture of fascia group (n = 12) and a second, no-mesh, no-fascia rupture control group (n = 12). In the 59 rabbits, of 72 (13 died) tissue was harvested 3 months (n = 24), 6 months (n = 23) and 9 months (n = 12) later, while in the fascia rupture group, tissue was harvested 6 months later. Tissue samples (2 × 2 cm) underwent dynamic mechanical analysis (DMA) testing during which the dynamic rigidity and tissue damping capacities were measured. The statistical analysis was performed with General Linear Model with Tukeys post hoc testing (sPss v.17.0). Results: With respect to mesh type, the rabbit tissue in which polypropylene mesh was used showed the greatest dynamic rigidity. Those with biological mesh delivered the lowest rigidity results, while the two other groups had almost similar behavior. The meshes exhibited their highest relative dynamic tissue stiffening effect at 9 months. Conclusions: Biological mesh causes lower tissue rigidity, resulting in inferior mechanical response and thus seems to be inferior to polypropylene.

Comparison of purification processes of natural gas obtained from three different regions in the world

Natural gases obtained from different regions in the world as Scholen-Germany, Saudi Arabia and Iran were purified with a package code and the obtained results were compared in this study. For purification process, both natural gases flowing in a vertical pipe and monoethanolamine （MEA） flowing as a film from the internal surface of a pipe were examined together. Both fluids were flown in a vertical and laminar regime. Binary diffusion coefficients, Schmidt numbers （Sc） and dynamical viscosities were calculated individually for three types of natural gases. It is demonstrated that the chemical absorption method by MEA process is the most appropriate method at high DamkOhler （Da） numbers particularly for natural gases containing high concentrations of CO2 and H2S.

Electrical conductivity effect on MHD mixed convection of nanofluid flow over a backward-facing step

In this study,magneto-hydrodynamics (MHD) mixed convection effects of Al2O3-water nanofluid flow over a backward-facing step were investigated numerically for various electrical conductivity models of nanofluids.A uniform external magnetic field was applied to the flow and strength of magnetic field was varied with different values of dimensionless parameter Hartmann number (Ha=0,10,20,30,40).Three different electrical conductivity models were used to see the effects of MHD nanofluid flow.Besides,five different inclination angles between 0°-90° is used for the external magnetic field.The problem geometry is a backward-facing step which is used in many engineering applications where flow separation and reattachment phenomenon occurs.Mixed type convective heat transfer of backward-facing step was examined with various values of Richardson number (Ri=0.01,0.1,1,10) and four different nanoparticle volume fractions (Ф=0.01,0.015,0.020,0.025) considering different electrical conductivity models.Finite element method via commercial code COMSOL was used for computations.Results indicate that the addition of nanoparticles enhanced heat transfer significantly.Also increasing magnetic field strength and inclination angle increased heat transfer rate.Effects of different electrical conductivity models were also investigated and it was observed that they have significant effects on the fluid flow and heat transfer characteristics in the presence of magnetic field.

Optimization study of a PEM fuel cell performance using 3D multi-phase computational fluid dynamics model

An optimization study using a comprehensive 3D, multi-phase, non-isothermal model of a PEM （proton exchange membrane） fuel cell that incorporates significant physical processes and key parameters affecting fuel cell performance is presented and discussed in detail. The model accounts for both gas and liquid phase in the same computational domain, and thus allows for the implementation of phase change inside the gas diffusion layers. The model includes the transport of gaseous species, liquid water, protons, energy, and water dissolved in the ion-conducting polymer. Water is assumed to be exchanged among three phases： liquid, vapottr, and dissolved, with equilibrium among these phases being assumed. This model also takes into account convection and diffusion of different species in the channels as well as in the porous gas diffusion layer, heat transfer in the solids as well as in the gases, and electrochemical reactions. The results showed that the present multi-phase model is capable of identifying important parameters for the wetting behaviour of the gas diffusion layers and can be used to identify conditions that might lead to the onset of pore plugging, which has a detrimental effect on the fuel cell performance. This model is used to study the effects of several operating, design, and material parameters on fuel cell performance. Detailed analyses of the fuel cell performance under various operating conditions have been conducted and examined.

Effect of different heat transfer fluids on discharging performance of phase change material included cylindrical container during forced convection

In the present work,effects of various heat transfer fluids on the discharging performance of a phase change material(PCM) included cylindrical container are numerically assessed during forced convection.The heat transfer fluid air,hydrogen,water and nanofluid with alumina particles are used and the the geometric variation of the PCM embedded region is also considered.The finite element method is used as the solver.Dynamic features of heat exchange with various phases are explored for different heat transfer fluid types,Reynolds number(between 100 and 300) and PCM embedded region geometric variation(h_(x)between 0.01 d_(1) and 0.65 d_(1),hybetween 0.1 h_(1) and 0.4 h_(1)).It is observed that discharging time is significantly influenced by the heat transfer fluid type while full phase transition time for air is obtained as more than 10 times when hydrogen is utilized as heat transfer fluid.The best performance is achieved with nanofluid.When the PCM integrated region size is reduced,discharging time is generally reduced while due to the form of the geometry,vortex formation is established in the PCM region.This results in performance degeneration at the highest radius and height of the inner cylinder.Discharging time increases by about 12% when radius of the inner cylinder is increased from h_(x)=0.35 d_(1) to h_(x)=0.45 d_(1).Dynamic features of PCM temperature and liquid fraction are affected with Reynolds number while discharging time is reduced by about 48% when configurations with the lowest and highest Reynolds number are compared.

Conformal manufacturing of soft deformable sensors on the curved surface

Health monitoring of structures and people requires the integration of sensors and devices on various 3D curvilinear,hierarchically structured,and even dynamically changing surfaces.Therefore,it is highly desirable to explore conformal manufacturing techniques to fabricate and integrate soft deformable devices on complex 3D curvilinear surfaces.Although planar fabrication methods are not directly suitable to manufacture conformal devices on 3D curvilinear surfaces,they can be combined with stretchable structures and the use of transfer printing or assembly methods to enable the device integration on 3D surfaces.Combined with functional nanomaterials,various direct printing and writing methods have also been developed to fabricate conformal electronics on curved surfaces with intimate contact even over a large area.After a brief summary of the recent advancement of the recent conformal manufacturing techniques,we also discuss the challenges and potential opportunities for future development in this burgeoning field of conformal electronics on complex 3D surfaces.

Numerical modeling of condensate droplet on superhydrophobic nanoarrays using the lattice Boltzmann method

In the present study,the process of droplet condensation on superhydrophobic nanoarrays is simulated using a multicomponent multi-phase lattice Boltzmann model.The results indicate that three typical nucleation modes of condensate droplets are produced by changing the geometrical parameters of nanoarrays.Droplets nucleated at the top（top-nucleation mode）,or in the upside interpillar space of nanoarrays（side-nucleation mode）,generate the non-wetting Cassie state,whereas the ones nucleated at the bottom corners between the nanoarrays（bottom-nucleation mode） present the wetting Wenzel state.Time evolutions of droplet pressures at the upside and downside of the liquid phase are analyzed to understand the wetting behaviors of the droplets condensed from different nucleation modes.The phenomena of droplet condensation on nanoarrays patterned with different hydrophilic and hydrophobic regions are simulated,indicating that the nucleation mode of condensate droplets can also be manipulated by modifying the local intrinsic wettability of nanoarray surface.The simulation results are compared well with the experimental observations reported in the literature.

Finite volume element method for analysis of unsteady reaction-diffusion problems

A finite volume element method is developed for analyzing unsteady scalar reaction-diffusion problems in two dimensions. The method combines the concepts that are employed in the finite volume and the finite element method together. The finite volume method is used to discretize the unsteady reaction-diffusion equation, while the finite element method is applied to estimate the gradient quantities at cell faces. Robustness and efficiency of the combined method have been evaluated on uniform rectangular grids by using available numerical solutions of the two-dimensional reaction-diffusion problems. The numerical solutions demonstrate that the combined method is stable and can provide accurate solution without spurious oscillation along the high-gradient boundary layers.

Fabrication of robust aluminum–carbon nanotube composites using ultrasonic assembly and rolling process

This study introduced a novel fabrication of aluminum–carbon nanotube(CNT) composites by employing bulk acoustic waves and accumulative roll bonding(ARB).In this method, CNT particles were aligned using ultrasonic standing wave in an aqueous media, and the arrayed particles were precipitated on the aluminum plate substrate.Then, the plates rolled on each other through the ARB process with four passes.Optical and scanning electron micrographs demonstrated the effective aligning of CNTs on the aluminum substrate with a negligible deviation of arrayed CNTs through the ARB process.The X-ray diffraction pattern of the developed composites showed no peaks for carbon and aluminum carbide.In addition, tensile tests showed that the longitudinal strength of the specimens processed with aligned CNTs was significantly greater than that of the specimens with common randomly dispersed particles.The proposed technique is beneficial for the fabrication of Al–CNT composites with directional mechanical strength.

Combined effects of local curvature and elasticity of an isothermal wall for jet impingement cooling under magnetic field effects

The aim of this study is to examine the effects of local curvature and elastic wall effects of an isothermal hot wall for the purpose of jet impingement cooling performance.Finite element method was used with ALE.Different important parametric effects such as Re number(between 100 and 700),Ha number(between 0 and 20),elasticity(between 104 and 109),curvature of the surface(elliptic,radius ratio between 1 and 0.25) and nanoparticle volume fraction(between 0 and 0.05) on the cooling performance were investigated numerically.The results showed that the average Nu number enhances for higher Hartmann number,higher values of elastic modulus of partly flexible wall and higher nanoparticle volume fraction.When the magnetic field is imposed at the highest strength,there is an increase of3.85% in the average Nu for the curved elastic wall whereas it is 89.22% for the hot part above it,which is due to the vortex suppression effects.Nanoparticle inclusion in the base fluid improves the heat transfer rate by about 27.6% in the absence of magnetic field whereas it is 20.5% under the effects of magnetic field at Ha=20.Curvature effects become important for higher Re numbers and at Re=700,there is 14.11% variation in the average Nu between the cases with the lowest and highest radius ratio.The elastic wall effects on the heat transfer are reduced with the increased curvature of the bottom wall.

Influence of austenization temperature on the erosion behavior of austempered ductile irons

The erosion behavior of austempered ductile irons austenized at different temperatures was studied. The results indicate that the erosion rate well correlates with the mechanical properties. At high impact angles, increasing ductility and mechanical energy density results in decreasing erosion rate, whereas increasing hardness reduces the erosion rate at low impact angles. 2008 University of Science and Technology Beijing. All rights reserved.

Severe Plastic Deformation of Steel Induced by Ultrasonic Vibrations

High-intensity ultrasonic vibration was focused on the tip of conical steel specimens to induce severe plastic deformation at room temperature. We found, for the first time, that grain size smaller than 200 nm was obtained. Furthermore, the sharp tip of the conical specimen became umbrella-shaped or disk-shaped. The tip size changed from 0.5 mm diameter to a disk about 5 mm diameter, representing a large amount of plastic deformation in the metal at the tip of the conical specimen.

Energy Savings in Municipal Road Lighting： The Case of the Municipality of Hersonissos

In an era governed by economic crisis, deep recession and lack of funds, the perspective of sustainable development drives local government to a more focused and constant effort to adapt to their daily requirements not only in respect to the central state but also towards the growing needs of the local society. As the need for planning actions in accordance with the principles of sustainable energy remains urgent, municipalities continue to envision and to respond to their role in helping to create a better future for generations to come. Thereupon the vision of the Municipality of Hersonissos, as firstly recorded in its Business Plan for 2011-2014, was, and still is, its＇ development in an Economic, Tourist and Cultural pole by adopting and applying the basic principles of sustainable development. At the same time the Municipality＇s rigid vision, planning, and evaluation, oriented by environmental protection, highlighted the need for networking on European level as although cities are different, their problems are often common. Thus on April 18, 2011, the Municipality of Hersonissos, joined the European Union initiative ＂Covenant of Mayors＂ [1] with the common aim of the fight against climate change. This article presents the significant initiatives taken in this direction in the last decade and their results not only on economical level but also along their social impact. It also aims to point out a municipality＇s vital role in knowledge and technology diffusion within the local society as sustainable energy development can be deployed not only by the private sector but also by the public.

Laser Surface Annealing of Plasma Sprayed Coatings

Laser surface annealing provides a rapid and efficient means for surface alloying and modification of ceramic materials. In this study, Alumina-13% Titania coatings were sprayed with a water-stabilized plasma spray gun. The coated surface was treated by Excimer laser having a wavelength of 248 nm and pulse duration of 24 ns. The surface structure of the treated coating was examined by field emission scanning electron microscope and X-ray diffraction (XRD). A detailed analysis of the effects of various laser parameters including laser energy density (fluence), pulse repetition rate (PRR), and number of pulses on the morphology and the microstructure of the coatings are presented.

Effect of Terminal Design and Bipolar Plate Material on PEM Fuel Cell Performance

Bipolar plates perform as current conductors between cells, provide conduits for reactant gases, facilitate water and thermal management through the cells, and constitute the backbone of a fuel cell stack. Currently, commercial bipolar plates are made of graphite composite because of its relatively low interfacial contact resistance (ICR) and high corrosion resistance. However, graphite composite’s manufacturability, permeability, and durability of shock and vibration are unfavorable in comparison to metals. Therefore, metals have been considered as a replacement material for graphite composite bipolar plates. The main objective of this study is to evaluate the effect of terminal connection design and bipolar plate material on PEM fuel cell overall performance. The study has indicated that single cell performance can be improved by combining terminals into metallic bipolar plates. This terminal design reduces the internal cell resistance and eliminates the need for additional terminal plates. The improved single cell performance by 18% and the increased savings in hydrogen consumption by 15% at the current density of 0.30 A/cm2 was attributed to the robust metal to metal contact between the terminal and the metallic bipolar plates. However, connecting metal terminal directly into graphite bipolar plates did not exhibit similar improvement in the performance of graphite fuel cells because of their brittleness that could have caused damage in the plates and poor contacts.

Statistical Analyses of the Effects of Welding Processes on Load, Extension and Hardness Properties of Welded Mild Steel Plates

Mild steel plates of thicknesses 0.5 mm,0.6 mm,0.7 mm,0.8 mm,0.9 mm and 1.0 mm were prepared as test samples.After welding with the developed welding robot and manual electric arc welding machine these test samples were subjected to Tensile Strength and Hardness tests.All data obtained including hardness,load and extension were analyzed and the data produced from electric arc welding operations,the robot welding operations and un-welded plates(control)were compared with one another.The statistical analyses of hardness,load and extension tests for developed welding robot,manual electric arc welding and un-welded(control)mild steel plates of different thicknesses were carried out.The results revealed that for hardness,the developed robot welding has the highest mean value of 115.30,standard deviation value of 14.32 and variance value of 205.06.The descriptive statistics of the load showed that the developed robot welding samples collectively have the lowest mean value of 2,536.85,standard deviation value of 704.21 and variance value of 495,911.72.The descriptive statistics of the extension in which the developed robot welding samples collectively have the lowest mean value of 1.29,standard deviation value of 0.43 and variance value of 0.18 were also determined.The result for hardness showed homogeneity of variance among hardness tests of the samples,which implies variation in the hardness test among the tests of the samples since p-value is 0.038.While the result for loads shows homogeneity of variance among loads of the samples in which the result reveals that there is no variation in the loads among the tests of the samples since p-value is 0.322.The result for extension shows homogeneity of variance among extensions of the samples in which it revealed that there is variation in the extensions among the tests of the samples since p-value is 0.011.The analysis of variance(ANOVA)test result revealed that there is a significant difference in the hardness of the samples in which developed robot welding operation gave the highest hardness compared with electric arc welding and un-welded(CONTROL)since p-value is 0.028.The ANOVA test result for load revealed that there is no significant difference in the loads of the samples since p-value is 0.51.The ANOVA test result of the extension shows that there is a significant difference in the extension of the samples in which developed robot welding operation gave the lowest extension compared with electric arc welding and un-welded(CONTROL)since p-value is 0.001.The results of hardness also showed the mean difference of 16.48 between developed robot welding and un-welded(CONTROL)samples and 7.26 between developed robot welding and electric arc welding samples.Finally,for extension the mean difference of-5.28 between developed robot welding and un-welded(CONTROL)samples and-1.22 between developed robot welding and electric arc welding samples were established.

纳米流体强制对流过程中充填相变材料的三角形弹性壁通气腔内的相变动力学

本文研究了在层流状态下纳米流体强制对流时三角形弹性壁通气腔内的相变过程动力学。采用有限元方法探讨了雷诺数(Re)、柯西数(Ca)和腔口尺寸对流场和相变动力学的影响。研究发现,Re、Ca和腔口尺寸的变化对进气道下流动再循环和相变动力学有一定的影响。当Re从100增加到200时,相变时间(TF)先缩短后延长。在Re=100时,混合纳米流体相变速度快,相变时间降低约26%。当Ca为最大值时,相变时间减少了12.5%。腔口尺寸对相变有负面影响,而腔口尺寸的增大使相变时间增加了19%。