Sharif Digital Repository

In this study, heat transfer and fluid flow inside a rectangular microchannel with partial porous media is simulated numerically. Darcy-Brinkman-Forchheimer equations are used to model the porous media. The effect of height of porous media, permeability (Darcy number), porosity and inlet velocity (Reynolds number) on Hydrodynamic and heat transfer performance are examined. At different values of height of porous media 0.2, 0.4, 0.6, 0.8, and 1 mm the Nusselt number of microchannel are 1.72, 1.78, 1.86, 1.94, and 2.02 compared to the microchannel without porous media. And the porous drop are 1.09, 1.2, 1.49, 1.76, and 2.15 compared to the microchannel without porous media. And FOM are 1.78,... 

One of the most important components of the noise produced by ships is the propeller noise, which reducing it can significantly reduce the overall noise of the ship. The purpose of this research is to reduce the propeller noise by combining the boundary element method, solving noise equations, and inverse method. In the first section of this thesis, a numerical flow solver software is developed that solve the flow around the impeller using the boundary element (panel) method and calculate the pressure distribution, velocity distribution, thrust, and torque of the propeller. Results show that for low skew and rake propellers, the error of numerical results is between 4 to 7 percent, and for... 

Circular cylindrical shells have been widely used in many engineering structures such as spacecraft, submarines, offshores, and storage tanks. Their high stiffness-to-weight ratio and load-carrying capability make them well suited for use in civil and aerospace structures. The consecutive development of material engineering along with the increasing demands for lightweight, heat-resistant, and high strength structures have led to the usage of advanced materials namely functionally graded (FG) materials in designing such structures. In this thesis, the nonlinear static analysis of thin FG cylindrical shells is carried out using the Donnell’s shell theory with first-order approximation and the... 

In this study we solve the porous and semi-porous flow in the entrance region in a channel filled with porous material or partially filled with it. We present a semi-analytical method for solving the momentum equation in porous and semi-porous channel and pipes at the development and fully developed regions in order to acquire the entrance length and velocity profile and its dependence to the interface boundary conditions between the porous and fluid flow. For solving the equations of entrance region we utilize the definition of boundary layer and use integral solution. Subliminally we find the thickness of boundary layer at the walls and interface of regions in the porous layer. For fully... 

In this study, a three dimensional model of water-ethylene glycol based aluminum oxide nanofluid in the laminar flow of an automobile radiator has been numerically studied. The passive heat transfer enhancement method of twisted tape insertion in the flat tubes of radiator is used. The effects of different parameters on heat transfer and pressure drop have been investigated. Simulation results show that utilizing twisted tapes is an effective way of enhancing heat transfer in an automobile radiator. Despite the pressure drop penalty of using twisted tapes, the thermal performance factor which is a proper criteria for evaluating the practical use of the twisted tapes and considers the effect... 

There are numerous ways available to achieve low temperatures that cryocoolers might be among the most important of them. In the meantime, the pulse tube refrigerator has a special place due to its simple geometry and not be using any moving parts. This simple property make the pulse tube refrigerator one of the most popular methods to achieve low temperatures. Nowadays, a pulse tube refrigerator is used for cooling in the range of 4 to 123 Kelvin in two form of one-stage and two-stage and up to an approximate power of 1 KW. Today, due to the temperature and the amount of power required for cooling, as well as the time it takes to reach that temperature, this chiller is used in medical,... 

The integrated development of small-scale electronic and mechanical systems has drawn attention, since they lead to increase in speed and decrease in volume of industry dimensions in the manufacturing sector. That is why microelectromechanical systems are highly considered. MEMS are widely used in Microfluidic systems that can be used in medicine, biology and drug injection. Due to the fact that consistent fluid velocity is necessary in biological applications, electroosmotic flow is more important than ever. To investigate the behavior of biofluids, Newtonian models cannot be used and it is required to use models that predict the behavior of these fluids accurately. In this research... 

The objective of this project is numerical simulation of air flow and heat transfer between two horizontal concentric cylinders with rotation of inner cylinder and inertia of outer cylinder grooves on the inner cylinder. In this study, the air, meanwhile rotational motion by the inner cylinder will enter into the annular space between two cylinders with certain flow rate. It can be mentioned to cooling of power plant generators, Electric motors and rotating machines among usages of air flow between two cylinders. In this article the objective is calculation of pressure drop and Nusselt number, temperature distribution on the inner cylinder under conditions of constant temperature of... 

This paper numerically studies the convection heat transfer enhancement of a developing two dimensional laminar flow in a pipe partially filled with porous materials. One of the most important effects of the systems with porous materials in them, is that they can improve some heat transfer components if they be used in a proper way. This study has been performed under both local thermal equilibrium (LTE) and local thermal non-equilibrium (LTNE) conditions. Two energy equations are used in non-thermal equilibrium condition between fluid and porous material. Darcy-Brinkman-Forchheimer model is used to model the flow inside the porous medium. The effects of different parameters such as, Darcy... 

In this research the vibration of rotating and non-rotating shells was investigated. In the non-rotating shells field, the vibration of joined cylindrical shells and joined conical shells that each sections of them has independent material, thickness, length and angle were investigated. By analyzing the free vibration of joined conical shells, we can perform the free vibration analysis on every complex thin-walled geometry.In the rotating shells field, first the governing equations of the rotating conical shells are derived and then, the vibration of rotating cylindrical-conical shells and joined conical shells were investigated. The governing equations of rotating conical shells and... 

The growing use of fossil fuels and their impacts on the environmental pollution, mostly originating from internal combustion engines, is one of the important issues in environmentally friendly energy management. One of the key solutions to improve engine performance and reduce exhaust emissions of internal combustion engines is direct injection of bio-fuels. In this regard, in the present study some new biofuels such as Bio-Norouzak, Modified Bio-Ethanol (MBE), and Modified Bio-Diesel (MBF) have been introduced and effects of different parameters on their sprays have been investigated experimentally and analytically. The literature survey shows there is not any comprehensive study on the... 

Numerous applications of Lab on a Chips (LOCs) in chemical/biochemical analyses as well as the emergence of advanced methods for their manufacture attracts many researchers’ attention to these micro instruments. Low sample volume consumption and their high controllability are accounted as the main advantage of LOC systems. Micromixers are among the main components of any LOC in which mixing and/or reaction among two components occur. Micromixers have many potential applications in biological and medical sciences, and so they are repeatedly charged by biofluids. Due to sensibility of biofluids, to avoid disintegration, applying electroosmotic flow instead of pressure-induced flow has priority... 

With the increasing number of applications in internal combustion engines, environmental impact and air pollution caused by emissions has been much attention. Natural gas is a promising fuel for limiting pollution laws in many countries. The use of fuel with a higher ratio of hydrogen gas to carbon pollution reduction motor. In this context and with regard to development policy and also due to the diversity basket NGV fuel, fuel injection, has been modeled analytically and numerically in a direct injection engine. In this study, an analytical model for spray injection fuel delivery and is dissolved. The resolution of the method of separation of variables is taken. The effect of the nozzle... 

Advanced reservoir characterization methods can yield geological models at a very fine resolution, containing 1011-1018 cells while the common reservoir simulators can handle much fewer numbers of cells due to computer hardware limitations. The process of coarsening the fine-scale model to simulation models is known as upscaling. There are three fundamental steps in the procedure of upscaling, i.e. defining the coarse grid geometry, calculating the average properties for the generated coarse grid and simulation of the two-phase flow equations on the generated coarse-scale model. In this thesis, the focus will be on investigating the applicability of optimization in the context of coarse grid... 

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... 

In this thesis, two-phase flow modeling in two-dimensional micro channel with liquid injection from wall is studied. Two models as "separated flow model" and "two-phase mixture flow" is developed. The separated flow model considers gas and liquid flow in separated films of flow with an interface between the phases. The two-phase mixture flow considers equivalent fluid mixture from gas and liquid with local modification in density and viscosity. Governing equations include continuity and momentum solved with control volume method. SIMPLE algorithm's been used to pressure-velocity linked equations. Velocity and pressure profiles plotted for mentioned models at a given situations. By comparing... 

Nonlinear forced vibrations of thin functionally graded circular and elliptical plates under classical boundary conditions are investigated based on the classical plate theory. The von Kármán strain-displacement relations is employed to include geometrical nonlinearity caused by large transverse displacements of the plate thickness order, and modal expansion in polar and elliptical coordinate along with the perturbation method of multiple scale is used to solve the governing equations. The material properties are graded through the plate thickness according to a power-law distribution of the volume fraction of the constituents. Transverse forcing is supposed to be harmonic with angular... 

Direct reduction of iron is a process to reduce iron in solid phase. The output of this procedure is direct reduced iron (DRI) that can be used in electric arc furnacewithout further changes. Midrex technology, which is the most important one among direct reduction of iron processes, provides 60% of DRI.
Required synthesis gas for reduction process is gained from reforming of the natural gas,with the major proportion of methane, with water steam and carbon dioxide in a piece of equipment called “reformer”. As a matter of fact, reformer is a type of plug chemical reactors. Input materials (natural gas, water steam and carbon dioxide) enter from the bottom section to the prepared pipes in... 

Numerical investigation of flow field and determination of velocity components in swirl flow are novel and important subjects in combustion chamber of swirl flow. The exact understanding of vortex phenomena and flow structures in vortex engine results in better design and control in terms of stability, geometry, cooling, and combustion efficiency. Although, numerical approaches are computationally complex, they are worthwhile and efficient. The aim of this work is to study the velocity field in a bidirectional swirl flow within the combustion chamber using numerical approaches. The investigation of flow field has been performed in the cold chamber. Four different models (RSM and LES) have... 

Lab-On-A-Chip is a micro-scale system which utilizes specific tools in order to operate detection tests on samples. One of the most important components of these devices is micromixers which is responsible for appropriate mixing of samples in short period of time. The biggest problem associated to the mixing in micro-scale is the regime that the flow takes during the process. Due to the small dimensions of micromixers the induced flow stream resides in the range of laminar flows and consequently the mixing is conducted solely by diffusion mechanism which is either time-taking or requires long micro-channel that causes the high cost of fabrication. In order to improve the mixing process two...