فهرست مطالب عسل حسینی منزه

Condensation may occur during various industrial applications, including water collection, desalination, energy generation, and thermal management. This phenomenon affects heat transfer efficiency during energy generation and heat management processes. Film-wise and dropwise condensation were the two types of condensation based on their formation manner. Condenser tubes are one of the energy conversion systems in which the condensation phenomenon dramatically affects the system's efficiency. The high surface energy of the condenser tube results in water film formation on the tube surface, which hinders heat transfer. Therefore, the heat transfer efficiency of the condenser is reduced due to further energy loss. The film-wise condensation should be altered to dropwise ones by reducing the surface energy of the tube to eliminate this issue. Hence, different coatings are applied to increase the condenser tubes' hydrophobicity and heat transfer capacity. In this study, the importance of wettability and heat transfer mechanisms in condenser tubes was determined primarily. Afterward, different coatings used to create dropwise condensation were introduced. Eventually, the applications and attributes of the mentioned coatings based on their cost, strength, durability, and efficiency were introduced.

Porous structures made of titanium have received much more attention due to their appropriate elastic modulus than other biometals, a significant reduction in stress shielding, and proper bonding with bone. Porous implants performance is a function of the type of alloy and the microstructural specimen properties, for instance, the size, the shape, the distribution of the pore, and part density. Therefore, to attain the optimized implant having the elastic modulus matched with the bone and the permeability for bone-cell growth, choosing the appropriate manufacturing method and controlling its parameters is essential. Considering that, in the present article, the mechanical properties of porous titanium implants fabricated by different methods have been gathered and evaluated. Among the different manufacturing methods, additive manufacturing (AM), spark plasma sintering (SPS), and metal injection molding (MIM), with high flexibility, provides porous structures having appropriate mechanical properties. However, the high cost of additive manufacturing methods compared to the other two routes seems challenging for commercializing AM for producing porous titanium implants.

Slurry casting method is a novel process to produce metal forms, which makes it possible to produce a porous structure with open cell. In the present study, the microstructure and compressive behavior of aluminum foams produced by slurry casting method, under different number of immersion times were investigated. For the production of aluminum foams with different cell sizes, polyurethane preforms with characteristics of 45, 55 and 65 ppi were selected, and after immersing in a slurry having a solid mass of 88% and removing the excess semiliquid mixture, the samples were sintered at 630˚C. The size of polyurethane perform cell as well as the number of immersion times control the microstructure and compression performance of porous structures. The results of the study showed that the portability of porous aluminum increases by decreasing the size of preform cell or increasing the number of immersion times, which leads to thicker strut. In addition, the probability of crack existence, exactly at the corner of structures, decrease via enhancing the thickness of strut. Meanwhile, excessive increase in the number of immersion, i.e. third times, was associated with some closed-cells which results in strain localization and stress concentration. Therefore, the maximum plateau stress as well as the superior energy absorption capacity was observed in the sample having the minimum preform pore sizes which was immersed for two times in the aluminum slurry.

Among various manufacturing processes, the use of cold press- sintering has been considered with low cost, high efficiency, and the ability to produce components with the appropriate dimensional accuracy. In this method, at least two components of the alcoholic solution are used in granulation and milling steps. Removing the solutions is accompanied with energy consumption, as well as, an increment in probability of crack initiation, which may limited the widespread utilization of press-sintering process. Therefore, in the present study, the soluble component in the milling step was removed. In following just using PVA as a soluble component in the granulation step, the ceramic / ceramic composite was made. Doing this, samples based on NiO and YSZ were made with different weight percentages of the reinforcement component (25, 30 and 35% wt. zirconia-stabilized yttrium), and then their microstructure, density and micro-hardness were investigated. Microstructural studies indicate that the amount and distribution of porosity, surface quality and depth of cracks in the samples are depended on reinforcement weight. In detailed, at the surface of green tables, no deep crack was observed. In sintered specimens, the best distribution of the gas phase was observed in NiO- 30% wt. YSZ, which results in maximum micro-hardness. Also, the radiography results provided by the above samples indicated that deep crack in the discs is not visible. Therefore, it seems that the starch as a pore former displayed the beset role via porosity distribution and lessening crack nucleation in sample having 30% reinforcement.

The effect of artificial ageing on tensile properties and fracture behavior of 2024 Al alloy in the presence and absence of notch was investigated. The tensile samples having two V notches, as well as, common tensile specimens were prepared according to ASTM E8. T8 heat treatment consisting of solutionizing, cold rolling, and aging was selected to establish precipitation hardening in Al2024 alloy. Considering T8 condition, following solutionizing of Al sheet at 5000C, samples were cold rolled with 30% reduction. Finally artificial aging was applied at 2000C via different times. The results of Brinell test shows that the maximum value of hardness was achieved at 1 hour, which indicated the peak aging condition. Moreover, soaking samples in aging condition at 2000C for 15 minutes and 4 hours were considered as under-aging and over-aging states, respectively. Similar to hardness results, the superior amount of yield strength and ultimate tensile strength of un-notched specimens were observed at peak aging time, while in notched samples, the role of aging time was not prominent due to the presence of V shaped flaws. By applying notches on specimens, the yield and ultimate stress were found to increase with simultaneously decrease in elongation at fracture. It was found that due to localizing plastic deformation around flaws, the presence of notch increases the strength of 2024 Al alloy, while elastic behavior controls deformability far from notches. The energy which was absorbed till fracture, was indicated as toughness and it was found to be absolutely dominated by the elongation at fracture and significantly decreased in notched specimens. The peak-ageing condition of notched tensile specimens had the lowest toughness compare to under-ageing and over-ageing conditions. Although three fracture mechanisms, such as matrix deformation, particle cracking and matrix/particle debonding observed in all samples, the distribution of these mechanisms were more homogeneous in un-notched specimens. In the other words, one may claim that the presence of flaws enhanced the cracked particles, which accompanied with lowering matrix deformability lessened the elongation and toughness.

Two specific characteristics of grey cast iron, i.e. good machinability, as well as, high vibration damping, results in widespread applications in industry. In this research the grey cast iron powder which is fabricated via machining was utilized as raw material for producing foams. The porous structures were manufactured by powder metallurgy method were subjected under two major industrial destructive processes, i.e., corrosion and vibration, in a continuous and parallel manner. To demonstrate the degradation potency and comparison of these two destructive factors, changes in the porosity phase orientation as a result of energy absorption was measured. It was found that the amount of energy absorption, which is associated with the most changes in the porosity phase orientation, is depend on porosity volume, the type of destructive processes and the priority of corrosion and vibration. In the case of two vibration and corrosion processes applied successively, the corrosive atmosphere which induced less microstructural changes is the dominant mechanism. If destructive processes are applied in parallel, a sample with a mean value of 42% porosity can absorb the maximum energy, in which vibration is the dominant mechanism for this mode.