Sharif Digital Repository

The increasing demand of energy and energy consumption, urged researchers of different fields of science to investigate different aspects of energy efficiency methods. One way of optimization of energy consumption is to reduce drag force in moving objects in fluids. Changing the geometry of objects, bubble injection, air suction and blowing on surface, using nano fluid and superhydrophobic surface are just a number of drag reduction methods. Among the mentioned methods, using superhydrophobic surface due to its simplicity, low cost and no need to change in geometry of vehicles attracted attentions of researchers of all over the world. These surfaces with micro/nano roughness combined with... 

Nowdays, one of the most important concerns for scientists is increasing CO2 emmisions and global warming. To overcome this problem, a large number of studies have been carried out to improve energy system performance and reducing the overall energy consumption. One solution to this problem is using the superhydrophobic surfaces with contact angle larger than 150°.In this study, we try to reduce the pressure drop through the galvanized pipes. So, by reducing the pressure drop, power required for pumps can be reduced. To this end, two different coatings by silica nano-particles which were modified with first hydrophobic agent are used. In first coating which is named as PS coating, stearic... 

Through history, increased energy consumption has been encouraged researchers to improve the performance of energy-using devices. Some researchers believe that hydrophobic surfaces can play an important role in this regard.The encounter and the presence of water on different surfaces can have different effects on them. The surface sedimentation of these surfaces, the eating of metal surfaces, the drag force (water friction) due to water collision with the moving object in water and the attachment of algae And other marine organisms to the surfaces, including the limitations and problems faced by professionals and staff associated with this sector.In the present study, the drag reduction of... 

The present study's main aim is to investigate the drag-reduction ability of liquid-infused surfaces inspired by the pitcher plant. The present study can be divided into experimental and numerical sections. In the numerical section, the drag reduction ability of these surfaces was investigated in the internal flows. For this purpose, the effect of different parameters, such as Reynolds number, viscosity and density ratio of working fluid and lubricant, overlayer film thickness, and Ohnesorge number representing the interfacial tension, on the drag reduction was investigated. The results revealed that the variation in density ratio and Ohnesorge number had insignificant impact on drag... 

Water treatment from industrial and domestic pollutants is one of the most important issues in recent decades. In the present research, simulation of water purification using single-layer graphene membrane were studied. The effects of nanopores diameter, applied pressure, concentration of contaminant ions, and functional groups on the amount of filtered water and ion rejection through the membrane were quantified. Contaminant ions including Na+, K+, Mg2+, Ca2+, and Cl- were dissolved in water. Based on the results, by increasing the pore diameter and applied pressure, more water would pass through the membrane. Also it was concluded that pores with functional groups have better performance... 

In the present study, Nano-fluid natural convection on a constant temperature vertical plate is numerically investigated, following the similarity analysis of transport equations. After changing the governing differential equations to the ordinary differential equations, they were numerically solved by the fourth order Runge-Kutta method.. The analysis shows that all three main profiles, velocity, temperature and concentration in their specific boundary layers, and the Prandtle number, depend on three important additional dimensionless parameters, namely a Brownian motion parameter, a thermophoresis parameter, and a buoyancy ratio parameter. Finally, it was found that the Nusselt number in... 

This work numerically simulates pressure drop and heat transfer for flow in a pipe with porous wall. Incompressible two dimensional, ax symmetric laminar or turbulence flow with constant mass flow rate is considered. It is assumed that there is no thermal equilibrium in the porous media region between solid and fluid phase. Effect of porous wall thickness and Darcy number on the rate of heat transfer and pressure drop were investigated. The Darcy number varies from to and porous wall thickness can fill entire pipe. the turbulent model is used to calculate the fluid flow and heat transfer characteristics in turbulent flow. Nusselt number can enhance about ... 

The silencer is used to reduce sound in the vehicle, air conditioning channels, power plants and guns. Functional parameters of the sound amplifier are the amount of noise reduction and pressure drop. There are few studies on the flow and pressure distribution in the silencer, and there is no article about the effect of the size of the internal passages on the pressure drop and acoustical performance of the silencer. Few studies have been done on the effect of the absorbent fiber diameter on the acoustic performance of silencer. In this study, the effect of different shapes of internal channels (extended tubes, baffles and number of chambers) on the pressure drop and acoustic performance of... 

The limitation of fossil fuel sources and environmental damage caused by use of these fuels have made researches on applications of renewable energy, especially solar energy, to be an important issue in recent years. An important issue that arises in the use of photovoltaic panels is the reduction of their efficiency with increasing their temperature. By increase of a degree of Celsius, the efficiency of the photovoltaic panel decreases by 0.45%. The aim of this project is to reduce the temperature of the photovoltaic panel by using porous medium and air. The porous medium used as fins under the panel.Experimental results have shown that by using the medium placed under the photovoltaic... 

Superhydrophobic surfaces have attracted so mucha attenetions in recent years. High contact angle, Low adhesion and low friction drag are the most important features of these surfaces. Two main parameters of these surfaces are hydrophobicity and micro-( or nano) scale roughness. In this Project a 2-D simulation of flow on superhydrophobic surfaces have been considered. Shan-Chen multiphase Lattice Boltzmann Model has been used for the simulation and carnahan-starling equation of state have been used or a higher density ratio. In the first step flow in a channel with smooth walls with different hydrophobicity have been simulated and effects of hydrophobicity on pressure drop have been... 

Supersonic separators with neither rotating parts nor chemical process, physically separate particles in a multi-phase flow. In comparison with general separation techniques, which are utilized in industries, specifically this equipment is cheaper, smaller and lighter. Condensation and separation at supersonic velocity is the key to achieve a significant reduction in both capital and operating costs. In this study, a two dimensional de Laval nozzle and few three-dimensional supersonic separator have been modeled. The 3D models modified in shape and dimensions. Impellers were created to form swirl flow. The models were simulated by the use of CFD software ANSYS FLUENT. Diverse inlet pressures... 

Capturing the atmospheric CO2 and turning it into value added products is a topic that has been extensively studied in recent years. One of the methods through which CO2 is valorized is via converting it into carbon nanofiber, CNFs. CNFs can be an important material in future human activities due to its valuable properties such as wide range of electrical conductivity, their superior flexibility and strength, But it is currently obstructed in use due to the high cost of manufacturing and the complexity of the synthesis. Furthermore, in today's world, human life is heavily influenced by greenhouse gases, and avoiding emitting gases like CO2, is almost infeasible. This thesis provides an... 

Osmotically assisted reverse osmosis (OARO) assimilates high efficiency due to non-thermal processes and accessing high salinity. This makes it suitable for high water recovery for the purpose of zero- and minimal liquid discharge desalination. Moreover, forward osmosis (FO) has low fouling efficiency which makes the operating costs of cleaning and replacement lower. This study aims at incorporating OARO and FO in a novel configuration with multiple inlet of the diluted draw solution to the regeneration section. Pinch analysis with simplifying assumptions was carried out for FO and OARO standalone stages. The results showed that pinch point in FO resides either on the beginning or at the end... 

Membrane filtration systems are one of the most widely used and effective methods for desalination of saline water in the seas and oceans and treatment of industrial and domestic effluents in order to provide the fresh water resources needed for human survival on the earth and also meet the needs of various industries. The low efficacy of the traditional technologies necessitates the introduction of novel desalination methods. For this purpose, carbon-based membranes have been proposed as high-performance membranes because of their high mechanical strength, ultrafast permeation, and controllable pore size. In this study, by conducting molecular dynamics simulations, the effects of electric... 

Wettability is the cause of many interactions today and is definitely effective in almost all processes where liquid and solid phases are in contact. Wetting controls by surface engineering can accelerate the process in the industry or improve the quality of daily life. Therefore, the fabrication of complex surfaces with a specific purpose and different wettability has attracted the attention of researchers. In this thesis, silica nanoparticles were synthesized to create roughness and reduce contact between surfaces and liquids at first. Then, using chemical compounds to reduce the surface energy, a transparent (94.20%) superhydrophobic and oleophobic coating was created on the glass. The... 

The internal combustion engine power is determined by the amount of fuel effectively burned inside the engine cylinders. On the other hand, the fuel consumption is proportional to the air mass that enters the cylinders in each cycle. Conventionally, incoming the engine inlet air is at ambient conditions. However, with higher air density, the engine power increases for the same dimensions, so-called turbocharging. Although the engine's structure remains unchanged, it may be necessary to adjust the main systems of the engine simultaneously. This research investigated maximizing the power of a turbocharged diesel engine based on upgrading the degree of turbocharging. For this purpose, the EM355... 

Two-phase flows are widely used in petrochemical industry, chemical processes, boilers, nuclear reactors, cooling systems and air conditioning equipment. Since the problem of earth’s ozone layer and global warming, the analysis of flow characteristics in evaporators are necessary to improve performance of refrigerating systems and saving the environment. Most of the researchers have been studied the evaporation of two phase flow refrigerant through experimental studies and numerical analysis has less attention in the literature. In this Thesis, a mathematical model based on the two-phase separated flow model is developed to simulate the evaporation of pure refrigerant under constant heat... 

The aim of this research is to consider the effect of geometric changes on pumping performance of two phase gas-fluid flow in a vertical pipe. The idea is to inject a light gas to the bottom of a tube full of fluid so we will obtain an upward flow due to density differences. Potential benefits of this device are numerous such as dredging of river estuaries and harbors, sludge extraction in sewage treatment plant, water treatment and many others. There are almost four distinct flow patterns which occurs in the rise pipe, bubbly flow, slug flow, churn flow and annular flow that each of them require special conditions. heat transfer between two phases, phase changes, mass and volume rate... 

In this thesis, gas-liquid two phase flow through channels of spatially varying cross-sections are investigated numerically. These flows have several industrial applications such as nozzles, diffusers, pipeline blowdown, valves and channels with sudden expansions or contractions. Finite volume method in conjunction with a second order Advection Upstream Splitting Method (AUSM+_up) is employed to discretize the governing equations. At low Mach numbers, a pressure-based algorithm with a pressure correction equation is derived. Using the pressure-based algorithm accelerates the convergence rate of the numerical solution of the flows through sudden expansions. The pressure adjacent to the... 

The new generation of electronic devices including 5G internet, wearable electronics, LED optoelectronics or cloud computing devices have higher power density as their computing power increases and their sizes reduce. The increase in power density leads to higher heat generation and consequently higher operating temperature which reduces their lifetime and reliability. In recent years development of novel solutions for electronic cooling has been persued. Thermal interface material that inserted between heat source and heat sink is the main component in electronic cooling. These materials consists of a polymeric base that filled with highly thermally conductive solid particles. By emergence...