Papers by Keyword: Cavity

Abstract: The aim of this work is the numerical study of natural convection in a square enclosure filled with nanofluids, using (Cu-water) and (TiO₂- water) nanofluids. The finite volume method is used to solve the Navier-Stocks and energy equations. The effects of different relevant parameters, such as types of nanoparticles, volume fraction of nanoparticles (0-30%) and whose Rayleigh number varying from 10³ to 10⁶. It appears from this study that heat transfer increases by increasing the Rayleigh number and the volume fraction of the nanoparticles. The use of nanofluid enhances heat transfer, the highest heat transfer enhancement is observed in Cu-nanofluid. Consequently, the type of nanoparticle is a main factor for the enhancement of heat transfer. A comparison of our results with those of Barakos and Mitsoulis revealed a good agreement.

Abstract: The study aims to determine the load contributes to changes in the tensile strength of steel P22 at high temperatures. The steel sample was loaded under 95 and 125 N at a temperature of 700 °C for 72 hours. The results showed that the strength of P22 decreased with increasing load. At the temperature of 700 °C, the yield strength (YS) value decreased from 200 to 182 MPa and the ultimate tensile strength (UTS) reduced from 353 to 321 MPa as the load increased from 95 to 125 N. The precipitation of carbide in the matrix of P22 was observed in the steel sample loaded under 125 N at 700 °C for 72 hours. Furthermore, the cavity formation located on the boundary and near the carbide was confirmed when the temperature was 700 °C and the load increased from 95 to 125 N. The cavity was proof of a stress increase near the grain boundary, causing a decrease in the steel’s strength after a certain period of working time at high temperatures.

Abstract: The topological phononic crystal is composed of two topologically distinct structures. The topological phononic crystal resonant cavity based are proposed and the acoustic wave propagate characteristics are also presented. The topological cavity with defects will change the resonance frequency and quality factor is also discussed. The advantages of the topological cavity are the better quality factors and the concentrated sound pressure larger than general defect cavity.

Abstract: The third octave sound absorption coefficient testing is conducted to compare the sound absorption properties metal foam and flexible cellular materials, by using sound absorption tester with the method of trasfer function sound absorption tester with the method of trasfer function. The sound absorption mechanisms are discussed by changing the parameters of sound absorption structure, such as the thickness of matrix materials and the thickness of cavity. The results show that pearl wool and glass wool exhibited excellent sound absorption properties. The peak value of sound absorption coefficient for pearl wool reaches to 0.991, and for glass wool, 0.985. The average sound absorption coefficient for pearl wool is 0.729, and for glass wool, 0.679. Among of three metal foams, the foamed aluminum material exhibited optimum sound absorption properties, and is superior to flexible sound absorption materials. The peak value of sound absorption coefficient reaches to 0.993, and the average value reaches to 0.781. This can be attributed to the flow resistance, porosity, thickness, cavity and structure factor, which influence the sound absorption of open cell materials.

Abstract: Ti55 is a type of new near-α titanium alloy featuring good heat resistance and thermal stability at a temperature below 550°C. This paper explores the superplastic behaviors of Ti55 titanium alloy sheets at high temperature. The results showed that at a strain rate between 8.3×10^-4 and 1.32×10^-2s^-1 and a deformation temperature between 885 and 935°C, this material exhibited favorable superplasticity. A 872% tensile elongation was achieved even at a high temperature of 925°C and a high strain rate of 1.32×10^-2s^-1. For a deformation temperature of 925°C and a strain rate range of 8.3×10^-4～1.32×10^-2s^-1, the strain rate sensitivity index (m) was equal to or higher than 0.38, which depends on the specific strain rate and reached its peak at 6.64×10^-3s^-1. The study showed that tiny cavities tended to appear around the rare earth phase particles. As the deformation temperature and the deformation strain rate increased, both size and volume fraction of the cavities decreased significantly. When the plastic deformation further increased, the cavities experienced not only longitudinal aggregation along the tensile strain direction, but also transverse aggregation normal to the tensile strain direction. The typical high-temperature ductile fracture morphology is related to both aggregation and growth of the large number of microscopic cavities and dimples.

Abstract: The subject under study is relevant as the enterprises in different industries are really interested in disperse systems in the form of suspensions. Suspensions are being widely used in many fields. At the same time the problems of improving their quality and increasing the productivity and energy efficiency of machines still exist. In this context, this study aims at getting finely divided suspensions of metals through the erosion of metal plates in the cavitation flow reactor. The construction of the reactor provides for a technically and technologically simple high-capacity process. The leading method of the research is a laboratory experiment and a qualitative and quantitative assessment of the erosion of the metal surface in the region of maximum developed cavitation. The article presents the results of the research into the nature the metal surface damage under cavitation. The sampling materials are copper and fine silver. The experiment shows quite a strong growth of numerous erosions and states that in the beginning in the region of maximum cavitation the net of cavities appears. Then, the cavities fuse and grow in size. Around single caves the areas of plastic deformation with typical metal flows are detected. The minimal sizes of particles, torn away from the surface, are 2-3 mcm. The study is of high practical value for researchers and specialists in nanotechnologies, solid dispersion, sedimentary analysis, flow detection, biomedicine, production of fuel, lubricants, emulsifiers, catalysts, and semiconductors.

Abstract: In order to Figure the common defect in large section special steel forging and find the solution, systematic study was carried out on hundreds of large section special steel forgings in a domestic famous steel mill. The steels included: low-carbon steel Q345D/E, medium-carbon steel 27SiMn, high-carbon steel GCr15SiMn, stainless steel 20Cr13. Both the amount and type of all the defect in the above steel were calculated and analyzed. The results showed that the common defects of the steel were slags, inclusions, loose (cavity) and inner cracks. The evolution of the cavity in the ingot during forging process was simulated by a numerical simulation software Deform-3D. The inner cracks in Q345D/E and 27SiMn initiated after A→F+P transformation The cracks in GCr15SiMn formed after the precipitation of net-like proeutectoid carbides. The cracks in 20Cr13 formed after the precipitation of net-like carbides. The internal cause of the cracks was relevant to composition segregation and internal stress in the forging. The external cause was connected with effect of slow cooling. Based on the above study, a set of new process was proposed and put into industrial application, with the result that the qualified ratio of flaw inspection in the above steel mill was improved from 20% to above 87%.

Abstract: Emerging crises for resources and energy has became one of the major global issues. Unstoppable population and urban growth is demanding shelter. The figure for estimated housing shortage across the world according to the internationally recommended standards is 428,700,000 units. By the year 2030, an additional 3 billion people, about 40 percent of the world’s population, will need access to housing. This translates into a demand for 96,150 new affordable units every day and 4000 every hour.(United Nation –Habitate:2005)(128). All this unstoppable global population growth is resulting in high demand supply gap between resources and thus present trend concentrate to satisfy and minimize this gap. This shooting urbanization problem is leading towards diversion for easy and fast construction methodology.Along with this the problems associated to it are also increasing globally. The problem of Urban Heat Island and Urban Canyon Effect, CO2 emission , Green House Effect , Resource depletion and all such problems are demanding global attention to overcome it and make habitant sustainable for safeguarding future generations to come. The major hurdle for application of sustainable construction is barrier of human mind who concentrates more on initial cost of construction and negligence towards operations energy cost and pay back period calculations.The aim of the paper is to show feasibility of application of waste in construction elements like wall by analysing thermo resistive property of such waste filled cavity wall and equivalence cooling effect calculations for conventional clay brick wall , AC sheets , cavity wall and various waste filled cavity wall by making model and process of simulation using Ansys Fluent .The results of research work shows feasibility of adopting cavity wall and waste fill cavity wall for construction of wall because of its high thermoresistive property so as to mitigate global problems like Urban Heat Islands and operational energy consumption.

Abstract: In this paper, the interference between arbitrary shaped 3D planar crack and cavity existing in the vicinity of the crack front is evaluated. It is assumed that the treated region is unbounded and subjected to uniaxial tension at infinity. The interaction between crack and cavity is treated by body force method. The surface of the crack and cavity is modeled by number of small triangular elements and the density of body force and weight function of the force doublet is assumed at a constant on each triangle. Numerical stress analyses are examined by changing the radius of cavity and the distance between the cavity and crack front systematically. Numerical results are presented for the stresses along the centerline between cavity and crack. To validate the current analysis, numerical results are compared with the results in the literature and found good agreement.

Abstract: Superplastic instability and damage evolution of AZ31B magnesium alloy sheet were investigated in this paper. Maximum elongation of 216% and strain rate sensitivity of 0.36 were obtained at 723k and a strain rate of 1×10^-3s^-1, whose fracture was due to the growth and interlinkage of cavities that nucleated at grain boundary. After superplastic tensile tests and quantitative analysis of cavity volume fraction, A cavity growth model were established, and the damage evolution equation based on the law of the micro-damage evolution and statistical mechanics was derived out, and damage characteristic parameters as well as the critical value of damage variable were identified so as to provide a theoretical ground on which the plastic forming technology of magnesium alloy sheet can be optimized.