Sharif Digital Repository

Effect of using Al 2O 3-water nanofluids with different volume fractions and particle diameters on generated entropy, hydrodynamic performance and heat transfer characteristics of a tangential micro-heat sink (TMHS) was numerically investigated in this research. Results indicated that considerable heat transfer enhancement is possible when using Al 2O 3-water nanofluids as coolant and clearly the enhancement improves with increasing particles concentration and decreasing particles size. However, using nanofluid has also induced drastic effects on the pumping power that increases with particles volume fraction and Reynolds number. Finally, it was found that generated total entropy decreases... 

In this research, the problems of adiabatic film-cooling the flat, convex, and concave surfaces are investigated numerically. Two different radii of curvature and one row of vertical injection holes are considered. The Navier-Stokes equations are solved using a fine nonuniform multiblock staggered curvilinear grid and the SIMPLE-based finite volume method. The blowing rates are 0.5 and 1.0 and the mainstream Reynolds number is 10,000. The obtained results indicated that at a low blowing ratio, the cooling effectiveness enhances over the convex surface and reduces over the concave surface compared to the flat surface case. In comparison with the low blowing ratio, the curvature effects at a... 

A high-quality butt joint of aluminum to copper (Al/Cu) can rarely be achieved by conventional fusion and solid-state welding processes. In this research, the appropriateness of friction stir welding (FSW) for making high-quality Al/Cu welds was studied. A sound Al/Cu butt joint was achieved with relatively high strength in uni-axial tensile tests. Mechanical properties and microstructure of the sound friction stir welds were examined. The ultimate tensile strength of the joints reached about 75 percent of the aluminum base metal, with the fracture occurring at aluminum side. The metallurgical study of the welds before and after their failure in tensile tests showed that the heat affected... 

Mathematical formulation and modeling of combustion processes is an important tool in the understanding of this phenomenon. Determination of equilibrium temperature and composition is often the first stage in calculation of combustion characteristics. There are number of different techniques for simulation of combustion process. In this study a basic model has been developed based on the minimization of Gibb's free energy to simulate the combustion processes. A nonlinear mathematical optimization has been developed based on Lagrange multipliers and solved using Quasi-Newton method written in MathCAD environment. The effect of various parameters such as initial temperature, pressure, and... 

Background: Diabetes is associated with many pathological changes and one of the most important consequences of the diabetes is hepatic injury. The present study was performed to investigate the effect of eight weeks endurance training with consumption of cinnamon supplementation on plasma concentrations of liver enzymes,alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in women with type II diabetes. Methods: In this quasi-experimental study,36 female volunteers with type II diabetes (age 52.72±2.64 years and body mass index 29.28±2.94 Kg/m2) were participated. The subjects were homogenized regarding their body mass index and then were divided randomly into four groups... 

Back extrusion technique was employed to characterize phase segregation tendency of mechanically stirred ZA27 alloy at different deformation rates. Variation of segregation intensity with ram diameter was found to follow opposite trends at low and high ram speeds. At sufficiently high ram speeds, small rams are of better performance in minimizing segregation whereas at low ram speeds, large rams result in less pronounced segregation. In addition, increasing ram speed invariably decreases segregation degree. Back extrusion at very high shear rates provided via a Drop Extruder Apparatus capable of displacing ram at speeds in excess of 1m/s results in production of very homogeneous products in... 

Friction Stir Welding (FSW) is a novel solid state welding process for joining materials. In this process a high speed tool is introduced into the weld seam and due to localized frictional heat, plastic deformation and transverse movement along the weld seam, joining is accomplished. In this study aluminum matrix composite A356 + 15%SiCp is chosen for friction stir welding. Fragmentation of SiC particles and silicon needles existing in eutectic phase as well as their homogenous distribution as a result of stirring with high plastic strains, improve mechanical properties such as modulus of elasticity, yield and ultimate strength, elongation and hardness in the weld zone compared to that of... 

Elastomeric bearings are becoming a preferred device for isolating bridges, buildings, and sensitive equipment structures. The technical specifications used to procure these isolators are considered as important factors for the consumers. Lack of communication between structural engineers and rubber technologists, causes structural engineers have slight understanding of rubber properties. In the present study, a number of compounds were initially designed and manufactured, based on a previously studied and manufactured isolator compound. The outcome of the experiments indicated the physical and mechanical properties. Afterwards, the targeted improvement led to modification of the compounds... 

Effort was made to characterise segregation tendency of mechanically stirred ZA27 alloy with back extrusion as a thixoforming process. At sufficiently high ram speeds, at which liquid phase flows forcefully, pooling of the heavy liquid phase owing to gravitational segregation contributes to homogeneity of back extruded products in terms of solid phase distribution, The amount of this contribution depends on the contact time of this liquid with solid skeleton during liquid exertion to the clearance. Hence, at high ram speeds, small rams which demand taller initial slugs are more efficient in minimising the segregation. However, in the case of low speed back extrusion tests, liquid impotency... 

Background: Body weight is regulated by both food intake and energy expenditure. Ghrelin, a hormone produced by the stomach and pancreas, enhances appetite. This study was undertaken to determine the effects of intermittent treadmill running on acylated ghrelin and appetite in individuals with obesity. Methods: Nine inactive male students, with a mean age of 20.56±0.48 yrs, a body mass index of 32.68±0.84 kg/m2 and a maximum oxygen uptake of 34.21±1.48 ml/kg/min, participated in the study in two trials (control and exercise) in a counterbalanced, randomized design. The protocol included intermittent running with a constant intensity at 65% of VO2 max on a treadmill. Blood samples were... 

A method for joining metals in the semisolid state is presented. A model alloy Sn-15%Pb was used to demonstrate the concept. By presented process, dendritic microstructure of the weld zone can be avoided. Moreover, near-weld zone of the cold worked substrates which is affected by heat would have a globular structure due to a thermomechanical treatment. The two substrates were heated up locally in the joint line to the semisolid temperature range. At this point a stirrer was introduced into the weld seam in order to mix the two sides into a single uniform joint. Localized mechanical properties of different zones were examined using Shear Punch Test (SPT), showing a good strength in the weld... 

The influence of different parameters such as welding pressure, rotational speed, and traverse speed on the weld properties has been evaluated earlier but there are some important parameters yet to be thoroughly investigated. In this study, an effort has been made to determine the influence of different ratios of rotational speed/traverse speed on mechanical properties of different zones of friction stir welded AZ31 magnesium alloy. Mechanical properties of different zones were determined by a shear punch test. It was found out that increasing the aforementioned ratio leads to a slight decrease in yield and ultimate strength of the stir zone and the transitional zone. It was also observed... 

Accurate description of wall-bounded turbulent flows requires a fine grid near walls to fully resolve the boundary layers. We consider a locally simplified transport model using an assumed near-wall viscosity profile to project the wall boundary conditions using the boundary transfer method. Related coefficients are obtained numerically. By choosing a near-wall viscosity profile, we derive an analytic wall function, which significantly reduces the CPU costs. The performance of this wall function is compared to other near-wall treatments proposed in the literature for two frequently used benchmark cases: near-equilibrium channel flow and flow over a backward-facing step with separation and... 

Three-dimensional, transient turbulent particulate flow in an FCC riser is modeled using an Eulerian/Granular approach. The turbulence in the gas phase is described by a modified realizable (kg-g) closure model and the kinetic theory of granular flow (KTGF) is employed for the particulate phase. Separate simulations are conducted for a rectangular and a cylindrical riser with similar dimensions. The model predictions are validated against experimental data of Sommerfeld et al (2002) and also compared with the previously reported LES-KTGF simulations of Hansen et al (2003) for the rectangular riser. The (kg-g)-KTGF model does not perform as well as the LES-KTGF model for the riser with a... 

Body weight is influenced by both food intake and energy expenditure. Acylated ghrelin enhances appetite, and its circulating level is suppressed by Growth Hormone. Data on the acylated ghrelin responses to exercise of different intensities in obese individuals are currently not available. This study examined the effects of an intermittent exercise protocol on acylated ghrelin levels and hunger ratings in obese people. Nine inactive male ran on the treadmill at 0900 with progressive intensities of 50, 60, 70, and 80% of VO2max for 10, 10, 5, and 2 min respectively. Blood samples were collected before the exercise at 0845 (-15 min as the resting values), after each workload (10, 23, 31, and... 

An imprinted interpenetrating polymer network (IPN) was synthesized and used as a medium for isolation of carbamazepine from urine samples. The polymer network consisted of a homogeneous polystyrene–sol gel hybrid constructed by in–situ radical polymerization method. In this process, within the sol–gel reaction duration, styrene monomer could penetrate into the reaction mixture and after the polymerization initiation, a monolithic IPN structure was prepared. The scanning electron microscopy (SEM) image and energy dispersive spectroscopy (EDX) are indications of the polystyrene dispersion at nano- to micro-meter level in the sol gel matrix. Eventually, the synthesized IPN was used as a... 

Aluminum alloys and high density polyethylene are utilized in a wide variety of industrial applications. In the present work the feasibility of friction stir butt welding between AA5059 alloy and high density polyethylene sheets is examined. The bonding mechanism, joint strength, and microhardness are considered in this study. Various welding parameters and tool alignment were investigated until sound joints were achieved by positioning approximately 85% of the rotating tool in the aluminum material on the advancing side (1.4 mm offset) at constant spindle speed and traverse speed of 710 rpm and 63 mm/min, respectively. The results indicate that AA5059 aluminum and high density polyethylene... 

In this paper, the ball valve performance is numerically simulated using an unstructured CFD (Computational Fluid Dynamics) code based on the finite volume method. Navier-Stokes equations in addition to a transport equation for the vapor volume fraction were coupled in the RANS solver. Separation is modeled very well with a modification of turbulent viscosity. The results of CFD calculations of flow through a ball valve, based on the concept of experimental data, are described and analyzed. Comparison of the flow pattern at several opening angles is investigated. Pressure drop behind the ball valve and formation of the vortex flow downstream the valve section are also discussed. As the... 

Most part of Iran is dominated by arid and semi-arid areas due to low annual rainfall. The need for production of fresh water from brackish water is considerably high, especially in dry regions. In this study 1 month daily-based experimental data from a solar still site has been reported. The technical and operational problems of this site which finally contributed to the total cease of the site are described. Then a detailed analysis is investigated on progress of a prototype which constructed in order to solve the site's problems. The results of 1 month of experimental data of the final design showed that the last prototype could be used to solve the current problems of the site. The...