Sharif Digital Repository

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... 

In this study, the properties of super-hydrophobic Ni coating on carbon steel including wetting behavior and corrosion resistance of Nickel coatings deposited on the steel substrate were investigated. For this purpose, Nickel coatings deposited by electrodeposition method in deferent current density (10,20,30,50, 70 mA /cm2) in bath containing 1.5 mol of ethylene de-ammonium de-chloride, 0.5 mol H3BO3, 1 mol Nicl2.6H2o and then immersed in a bath containing 0.01 mol per liter myristic acid and ethanol for 24 hours and then placed in the room temperature for 14 days. Deferent tests were used for characterization, wettability properties, corrosion behavior and morphology of Ni coatings. The... 

This dissertation argues that bi-conductive textured surfaces increase both Critical Heat Flux (CHF) and Heat Transfer Coefficient (HTC) simultaneously. Surface modification is applied to stainless steel specimens by the anodizing method in an electrolyte containing Ammonium Fluoride and DI-Water and Ethylene Glycol as the based solvent. The process of oxidation was under constant DC voltage and constant temperature. The contact angle on self-aligned Nano-porous oxide layer fabricated on the substrate substantially decreases to about 5.7 degree which has a dramatic effect on CHF. Furthermore, the oxide layer augments the boiling efficiency by increasing the number of active sites and... 

The limitation of energy resources and the increasing energy consumption has led researchers to look more closely at industrial processes such as condensation to improve these processes and prevent energy wastage. Increasing the efficiency of the condensation process will improve the performance of energy systems, save energy and protect the environment. In this research, various surfaces are fabricated, each of which in some way makes it possible to improve the condensation process. To perform the condensation test, the condensation surface, which is placed in the condensation test chamber, is cooled with a heat exchanger. Due to the high temperature of water vapor, many of the surfaces... 

Although using solar energies have some limitations, such as low efficiency, require a large space and high starting cost, they are one of the most attractive source of energies. The reasons that cause efficiency of the solar panels decrease are contamination of dust particles on them and formation of water droplet on solar panel surface due to humidity of the air. Also, a solar panel can absorb only 25% of incident light and the others are reflected by the cover glass. Therefore, fabrication of a self-cleaning surface that can inhibit the aggregation of dust particles and also transparent that doesn’t reflect the incident light is crucial.In this work, we aim to obtain a transparent,... 

Growth of the fuel consumption in the world and the greenhouse effect of its pollution get industrial managers and environmental activities attention. Skin drag force has a significant role in energy uses. The drag reduction property of superhydrophobic surfaces shows a new approach for investigators to reduce energy uses. Surface with 150° contact angle called superhydrophobic surface.In this project, a superhydrophobic coating is developed based on acrylic hydroxyl resin by silica nanoparticles. This coating can be sprayed on any surface. Using the Iron oxid particles and silica nanoparticles together produces hierarchical micro-nano structures. This coating has a 160.1° contact angle on... 

Today, with rapid developments and advances in science and technology, different ways have been studied to reduce energy consumption in various industries. Reducing the drag force and thus reducing the friction force is one of these methods which has many applications (e. g, in submarine construction industries). Creating some microgrooves in the microchannels is one of the most effective methods in order to reduce the friction force in microchannels that has recently been studied. In this method the air is trapped within the microgrooves and when the fluid (e. g, water) enters the channel passes over the trapped air within these microgrooves instead of touching the channel walls (solid... 

Ice formation upon various surfaces could lead to many industry problems and result in unpleasant accidents. For instance, the formation of ice on wind turbine blades or airplanes/helicopter wings could cause catastrophic disasters. The methods used to address this problem usually require exogenous energy consumption or anti-ice ingredients. The energy or anti-ice ingredients usage has adverse environmental effects and should be replaced with better approaches. One of these approaches is utilizing modified anti-ice surfaces. In this method, by modifying surface features, such as physical asperities and surface energy, the icing time of the surface could be prolonged. These surfaces are... 

The purpose of this research is producing one phase silica superhydrophobic coating by sol-gel method and drying temperature less than 200 degrees. For preparing micrometer and nanometer scaled hierarchical structure based on silica, TEOS precursor and Fumed Silica nanoparticles were used by density of 43/30 cc/lit and 6/52 gr/lit in order to provide desired roughness in the range of 40 nm. Moreover, HMDS surface modifying agent was used for reducing the surface energy of coating, which is not a danger to the environment in comparison to the same substances. The best Contact Angle is 155 degree and the best Sliding Angle is less than 5 degree. For instance, it was created with the... 

When the fluid passes through the microchannel, some energy is lost due to drag force and pressure drop. One of the methods used in the last few decades to optimize energy consumption is creating superhydrophobic surfaces in microchannels. These surfaces, with their features such as increasing the contact angle and reducing the contact angle hysteresis, can reduce energy loss, which is due to the presence of unevenness on the surface, and by trapping air and creating a two-phase flow, they reduce the drag force. On the other hand, the air trapped inside these irregularities will also affect the heat transfer of the passing fluid in the microchannel, which by creating resistance in 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... 

In this project, melamine formaldehyde was chosen as initial substrate for its high porosity. Then for having superhydrophobic surface, surface functional groups were silanized and deactivated as a result. It was assumed that high porosity of prepared sorbent and its nonpolar nature, can increase extraction efficiency. To study extraction efficiency of the prepared sorbent, it was filled inside a needle and used for needle-trap head-space extraction of BTEX (abbreviation for Benzene, Toluene, Ethylbenzene and Xylenes). Needle packed with sorbent was held on headspace of sample containing BTEX and head- space was pumped with a peristaltic pump. Pumping introduces fresh sample to sorbent... 

Ice accretion may cause malfunction or serious performance degradation in outdoor facilities and structures, such as aircraft, ship, locks and dams, offshore platforms, solar panels, wind turbines, power transmission towers and lines, and sports facilities, leading to huge economic loss or even loss of human lives. Icephobic materials, typically applied in the form of coatings, have received growing attention in the last decade. This work focuses on surfaces with a surface tension gradient which has icephobic properties. various surface tension gradients such as linear, exponential, cycloid and parabola have been imposed on a surface in order to achieve the shortest time for a droplet to... 

In this research we developed a superhydrophobic and anti-wear coating on a glass substrate using SiO2 nanoparticles to form a transparent superhydrophobic thin film and SiC nanoparticles to improve the wear resistance of coating.
Silica nanoparticles were produced via a simple sol gel method from Tetraethylorthosilicate (TEOS) as precursor. Hexamethyldisilazane (HMDS) and Tetramethylclourosilane (TMCS) were used as hydrophobic inducing agents and at last SiC nanoparticles were dispersed in the solution in order to provide wear resistance. The final results indicate the contact angle (CA) of water droplet on the surface was about 158° and sliding angle (SA) lower than 9°. Studying the... 

Titanium nano-oxide (TiO2) coatings have been used for self-cleaning, antimicrobial, and dust-proof designs. The degree of wetting of a solid surface with water in humid air depends on how the surface tension of the existing phases relates. The ratio between these tensions estimates the contact angle between a drop of water and the surface on which it is placed. A contact angle above 150 º is essential for surface overflow. In this study, 18 different combinations of titanium oxide and FAS, PDMS and PMS nanoparticles were obtained with a static contact angle of 165 to 150 º and a dynamic contact angle of 7 º.1 to 4.5 º. Following the measurement of water droplet slip speed on a sloping... 

Increasing energy consumption and limited energy resources are instances of the concerns of human societies and environmentalists today. The condensation process, as one of the most important processes in the industry, plays an important role in saving and regeneration the existing energy. Nowdays, surface optimization is one of the modern ways to improve condensation.In this research, two methods have been used to construct surfaces useful for enhancement of droplet condensation, including hybrid surfaces and solid infused surfaces. In the construction of hybrid surfaces, superhydrophobic coating with silica nanoparticles based on hydroxyl acrylic resin was used. The superhydrophilic parts... 

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... 

Superhydrophobic surfaces have attracted much attention in recent years due to their unique properties. Artificial superhydrophobic surfaces can be fabricated by employing chemical modifying a hierarchical structured surface (micro- and nanostructures) with a low surface free energy material. In this report, we used a simple one-step coating process to prepare superhydrophobic sorbents with a large surface area. Surface chemistry and porosity are fundamental parameters for an efficient sorbent capable of extracting low levels of analytes. Considering physical and chemical peroperties of chlorobenzenes, superhydrophobic materials make to be good sorbents. So in this project melamine... 

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... 

Many researches have been made on super hydrophobic and photocatalyst nano coatings in the last decades as a solution to some environmental issues. Among all semiconductors chosen for this property, titanium dioxide is often used because of it's low cost, ease of accessibility and stability in different chemical circumstances to break up organic pollutions. Mixing this property of TiO2 with hydrophobic manner of SiO2 causes a superhydrophobe & photocatalyst nano coating. Doping TiO2 with another semiconductor may also improve photocatalytic behavior of coating by increasing surface area of reaction or decreasing the band-gap.In this research TiO2-SiO2 hybrid nano coating is made via...