جستجوی مقالات مرتبط با کلیدواژه "porosity" در نشریات گروه "مکانیک"

The purpose of this study is to investigate the effect of geometric properties of porosity, including the pore density ranging 10-40 ppi, percentage of porosity 0.7 and 0.9, and the effect of air preheating in the range of 300-500 K at three different equivalence ratios of 0.7, 1, 1.1 on the temperature distribution and burner stability of a porous medium in ammonia-methane fuel. For this purpose, finite volume method and SIMPLE algorithm were used in Fluent 22 software and a chemical kinetics including 69 species and 389 reactions. According to the relation of pore density and porosity with volumetric heat transfer coefficient, changes in two first parameters lead changes in heat transfer coefficient. The results showed that the temperature difference between the gas and solid phases decreases as pore density increases. At the density of 10 ppi, the highest gas temperature was observed at the outlet, and the maximum temperature difference between the gas and solid phase in this case is about 590 K, and at highest density, the lowest gas temperature was observed, and the temperature difference between the phases Gas and solid in this case is about 243 K. By increasing the porosity from 0.7 to 0.9, heat transfer coefficient decreases and the limits of flammability and burner stability increase. Finally, it was observed that at a fixed equivalence ratio, with an increase in the inlet temperature up to 500 K, the flame front is drawn to the upstream side of the burner. Also, at a fixed inlet temperature, with an increase in the equivalence ratio from 0.7 to 1.1, the stability has increased and flame position is drawn upstream.

Today, the use of biological scaffolds in tissue engineering is being considered in order to repair damaged tissues by creating a suitable substrate for the growth of cells in the body of living organisms. These scaffolds should be able to deliver oxygen and brain materials easily to the cells and also have mechanical properties appropriate to the target tissue. The type of scaffold along with the shape and size of its porosity are among the factors affecting these characteristics. Since square and rectangular scaffolds are not suitable for circular damages, it is necessary to build cylindrical scaffolds with suitable strength and porosity for these applications. In this study, the effect of the type and shape of porosity on the mechanical and biological properties of cylindrical scaffolds has been investigated. According to the results presented in previous researches, scaffolds with concentric sinusoidal and circular porosity shapes and Kagome have better mechanical and biological properties than orthogonal ones. By increasing the percentage of alginic acid and graphene oxide to the tricalcium phosphate scaffold, the porosity and adhesion of cells increases. By adding hydroxyapatite to the PCL scaffold, the modulus and bone formation are improved compared to pure PCL.

It is not possible to fabricate the complex geometry of coherent cooling channels with conventional machining methods, so channels can be created in the mold using additive manufacturing processes such as selective laser melting. Parts created by selective laser melting always have porosity, and the amount of porosity depends on process parameters. On the other hand, the ability to make porous materials with a selective laser melting process has made these materials with features such as lower density and better heat transfer in the aerospace industry, automobile, medical uses and heat exchangers to be the attention of researchers and according to Porosity Percentage, in addition to directly affecting mechanical properties, also affects heat transfer. In this research, the effect of porosity on heat transfer in the mold was investigated. First, the model and mold were designed, in order to investigate the effect of porosity, four simulation models with volume porosity percentage of 0, 10, 20 and 30% were performed and analyzed in the software. The analysis of the results shows that the increase in the percentage of porosity in the mold causes a faster increase in temperature in the mold, also with the increase in the percentage of porosity in the mold, the speed of temperature decrease in the mold increases. And the cooling of the part happens faster. Examining the results of the maximum thermal gradient of the non-porous material compared to the material with 30% porosity shows a 21% increase in the thermal gradient in the porous material

Many parameters,including scanning strategy,speed,power,etc,have an impact on the mechanical and physical properties of the parts made by the selective laser melting process.Correct and optimal selection of these parameters prevents defects such as porosity,incomplete fusion gaps and cracks in the parts of the manufacturing process.Despite all the advantages of the selective laser melting process,the creation of defects directly affects the mechanical properties and fatigue resistance of the parts negatively. In this research,the impact of zero,45,and90degree build orientations,the effect of changing the size of the parts on mechanical properties such as tensile and shear strength,fracture strain,and the number of defects investigated.The built parts were subjected to tensile and shear tests,and the fracture area was examined using SEM and the existing defects identified.The tensile test results showed that larger samples have higher tensile strength than smaller samples.Moreover,higher tensile strength and lower fracture strain were observed in samples made in zerodegree orientation.The results of the shear test also showed that the strength of the shear stress for the small and large samples made in all orientations is almost the same,and the highest shear strain of failure is related to the samples made in the orientation of 45degrees independent of the dimensions.The SEM results also showed that the amount and distribution of spherical holes and fusion gaps in large samples made at90degrees is more than in samples made at 0and45degrees