Sharif Digital Repository

Special geometrical sections, known as “duct”, which can be installed on merchant vessels stern in order to improve propulsion system and propeller performance, today have evolved considerably. The force which produces by the propeller depends on efficiency of propulsion system. In the way of improving the efficiency of propulsion systems, by using these special geometrical sections, to much research have been done from the mid-twentieth century. The Wake Equalizing Ducts (WEDs) in addition to conduct the more uniform fluid flow to the propeller disk (which causes to improve the propeller operation), affect on flow separation in ship stern zone and will decrease the separated flow zone.... 

In this research, the trends of trade and transportation for the 10 subdivisions of food products and food products as a whole product based upon Standard International Trade Classification, SITC, have been appraised during the time period covering 1965 to 2005 among 125 countries in Asia, Europe and Africa. In this respect, the data of trade for the mentioned goods was gathered and other variables including gross domestic product, population, access to the international waters and area of countries and three transportation networks comprising two multimodal transportation networks and a unimodal network, during the cited period and for 125 countries was gathered. Then, regressions of trade... 

One of the critical challenges in droplet based micro- and nanofluidic devices is handling the droplet breakup such that a controllable droplet size is produced. The experimental and numerical investigations at the microscale indicate that the droplet size can be well controlled by T junction geometries. In the present study we use non-equilibrium molecular dynamics (NEMD) simulations to investigate this phenomenon at the nanoscale. In order to generalize the study the Lennard-Jones type potential between the fluids and the walls have been considered and the strength and the effective range of the potential are changed to consider a wide variety of materials. Our results reveal that the... 

Droplet-based microfluidic logic gates have many applications in diagnostic tests and biosciences due to their automation and cascading ability. Although most biological fluids, such as blood, exhibit non-Newtonian properties, all previous studies in this field have been with Newtonian fluids. Additionally, none of the previous work has studied the functional area of logic gates. In the present work, AND-OR logic gate with power-law fluid is considered. The effect of important parameters such as non-Newtonian fluid properties, droplet length, capillary number, and geometrical properties of the microfluidic system on the operating region of the system has been investigated. The results show... 

In this project, transport and absorption of magnetic particles for the purpose of water purification has been simulated. The used magnetic particles must be collected; otherwise they would cause additional pollution. Therefore, separation and absorption of particles is vital. The particles can be collected with an applied magnetic field. In this study different kinds of magnetic fields are applied and effect of different parameters, such as particle diameter, Reynolds number and magnetic field are considered. By increasing particle diameter and magnetic filed strength, the absorption efficiency increases. But by increasing Reynolds number absorption efficiency decreases. The particle with... 

Droplet formation and breakup processes are one of the important steps in many microfluidic devices with a wide range of biological and chemical applications. The purpose of this study is numerical simulation of non-Newtonian droplet formation under the influence of electric field in a microfluidic system. The innovation aspect of this project is the use of non-Newtonian fluid in this process, which, despite many applications in real issues, has been less studied, and in most of the previous researches, Newtonian fluid assumption has been used to simplify the solving. Also, simultaneously, the effects of an external electric field on this process were also studied. Carboxymethyl cellulose... 

In this paper, we introduced two methods for producing unequal sized droplet from an initial one that don’t have the disadvantages of the available methods. We developed a comprehensive analytical theory for the T-junction with valve method. Also the geometry was simulated using a VOF algorithm and a comparison was performed between numerical and analytical results and very good agreement was observed. The accuracy of numerical results was confirmed by doing the grid independency and time step independency and comparing the results with two analytical benchmarks. We derived accurate analytical relations for calculating the droplet volume ratio, droplet length (L1, L2 and Lwhole) and pressure... 

The stiffness rate of the 300 series austenitic stainless steel has long been known to depend on the stability of the austenite and its susceptibility to martensite formation. In this project, the cold deformation of austenitic stainless steel (304L) and the occurrence of martensite deformation during it are studied. Experimental cold rolling experiments under different strain velocities and initial temperatures in the range of -10° C to 25° C; Performed and microstructure, mechanical properties and percentage of martensite generated in rolled steel are determined and evaluated employing different testing techniques. mathematical modeling of cold rolling operation is also performed using... 

In this research, the effects of natural and artificial aging heat treatments on the mechanical and wear behavior of an aluminum alloy from the 7xxx series have been investigated. The study commenced with annealing of the received samples, which were subsequently divided into four categories. One of these categories was placed in a freezer as annealed samples, while the other two underwent artificial aging heat treatments at temperatures of 180 and 210 degrees Celsius. The final category naturally aged over time. As a result, different structures with varied distributions and morphologies of precipitates were formed, and the mechanical properties, mechanisms, and wear resistance of the... 

The use of superhydrophobic surfaces is one the most promising methods for reducing the friction and increasing the flow rate in fluid transfer systems. Since in such systems the surface structure plays a key role, in the first part of this study, the performance of the hierarchical nanostructures is explored. These nanostructures are inspired by the superhydrophobic surface of the lotus leaf. The flow is considered between two walls with hierarchical nanostructures and simulate the system via the molecular dynamics (MD) method. The size of the nanostructures and the distance between them have been studied to find whether a design with maximum flow rate exists. The nanostructures have two... 

The solar-driven humidification-dehumidification desalination system with a geothermal dehumidifier (SD-HDH-GD) has been given special attention, for producing drinking water and subsurface irrigation applications. This contribution scrutinizes the performance of the geothermal dehumidifier of the SD-HDH-GD system. To this aim, a comprehensive three-dimensional transient computational fluid dynamics model of the geothermal dehumidifier and the surrounding soil is developed. An experimental setup is established to verify the developed numerical model. At first, the performance of the system in a short-term period of 12 hours is investigated, and the effect of several operation parameters is... 

In this work, mathematical models are employed to predict transient temperature field, fluid flow within the melt zone and distribution of thermal and residual stresses during and after GTAW process. At the first step, fluid flow in the weld pool and transient temperature field within the metal being welded are determined by simultaneously solving the equations of conservation of mass, energy and momentum. To do so, a commercial finite volume base-program, FLUENT, is utilized. In the next step, temperature distribution during cooling as well as resulting thermal and residual stresses are predicted by means of a commercial finite element base program, ABAQUS. The employed models are capable... 

Lamniar flow through porous media has been investigated using finite volume staggered grid. In order to study turbulent flow modelling turbulent flow using RANS models with the aid of Fluent software has been done. And the microscopic and macroscopic results are compared with LES results. None of the RANS models used (k-e, RNG, k-wv2f, v2f and RSM) were able to model the flow through porous media properly, although k-e and RSM gave the best microscopic and macroscopic results  

In this study, the numerical simulation of turbulent flow using Open Source software OpenFOAM, The impact of air flow around the high-rise buildings and classification based on the height and arrangement of the buildings has been against the flow. Numerical method used, the finite volume method uses a piso algorithm, Navier-Stokes equations are solved and the speed and pressure can be obtained. Large Eddy Simulation model is a simulation model used in this software. In general tall buildings against wind loads has three types of move, move along the wind, prependicular along the wind and the twisting motion that occurs at the same time, they are, but, due to the variable nature and... 

In terms of thermodynamics and heat transfer, heat pipes such as closed two-phase thermosyphon are of great importance in saving energy. In this study, a computational fluid dynamics model for simulation of a thermosyphon heat pipe with two-phase flow including phase change heat transfer was developed. The study has mainly focused on the effects of volume concentrations of Nanoparticles and the operating temperature on the heat transfer performance of the thermosyphon. The analysis was performed to compare heat transfer performance between a solid copper tube and a thermosyphon heat pipe which contained deionized water and graphene oxide(GO)/water Nanofluid as its working fluids. Based on a... 

Providing fresh water for domestic and agricultural purposes has become one of the most pressing issues of the present century. Due to the dependency of conventional desalination on fossil fuels, these methods are associated with carbon dioxide and other greenhouse gas emissions. Therefore, renewable energy-based desalination systems have come to the fore. This study scrutinizes the performance of the solar Humidification-Dehumidification (HDH) desalination systems with subsurface condensers. In this system, solar energy evaporates water, and subsurface condensers condense water vapor into fresh water. Therefore, this system uses two renewable solar and geothermal energy. Due to the lack of... 

Nowadays, the cooling of electronic equipment has become a challenge for designers and scientists due to their progress. One of the most effective solutions for cooling these devices is using microchannel heat sinks. Researchers conducted so many studies experimentally, numerically, or a combination of them to increase the efficiency of microchannel heat sinks. Several methods have been proposed in previous studies to improve the cooling performance, such as using fins, nanoparticles, porous material, etc. Although increasing the heat exchange surface by using fins is caused to increase heat transfer, it also causes an increase in pressure drop. For this reason, researchers are looking for... 

Nowadays, Thermomechanical processes are used to change the microstructure and create desirable mechanical properties in metals. In this research, with the aim of improving the mechanical properties and formability of 7000 series aluminum alloys, the Cyclic Quench-Rolling (CQR) process was designed and investigated as a new thermomechanical process with solid solution strengthening mechanism. First, for solution heat treatment, the 7075-T6 aluminum sheet was placed in the oven at 460 °C for 5 hours and quenched in water. After making the solid solution, in each cycle of CQR, a rolling step was performed, then intermediate solutioning heat treatment and then quenching was performed. To study...