جستجوی مقالات مرتبط با کلیدواژه « contact angle » در نشریات گروه « مکانیک »

Superhydrophobic surfaces have water repellent properties, and water droplets easily move down on such a tilted surface. Over the years, many researchers have been working on different fabrication methods and applications of these surfaces in diverse fields. The present review focuses mainly on the recent progress in different construction methods and applications of superhydrophobic surfaces in the packaging industry and food supply chain. Hence, this study investigates the essential extracted information from some articles published from 2004- 2021 by Scopus, Springer, Science Direct, Pub Med, Sage journals and the Journal of Packaging Science and Technology databases. Researchers have found various applications of this technology in the development of surfaces with antimicrobial, anti-sticking, anticorrosion, antifouling, anti-icing, antifogging, moisture resistant and migration phenomenon reduction properties, which play key roles along the supply chain (from the time they are manufactured until they reach the end user) especially in the packaging industry, fabricating containers and vehicles. Despite all the researches, more investigations are needed as this technology suffers from limitations such as high cost, poor durability and technical complexity

Studying the dynamic behavior of droplets is very important in electrowetting phenomena. Due to the widespread application of non-Newtonian fluids, especially in bio applications, in the present study, the dynamics of non-Newtonian Carreau droplets under the electrowetting phenomenon has been investigated. The effects of the viscosity, the size and the applied voltage on the oscillations and the change in the height of the droplets have been inspected. The simulations have been conducted using the Finite Element Method (FEM) and in order to validate the method, the results have been compared with the available experimental and numerical results. The results indicate that by increasing the viscosity the amplitude of the oscillations increases but the frequency remains constant. These are similar to those of the Newtonian fluids with this difference that in Newtonian fluids the amplitude is larger but the frequency is smaller. Also, for a Carreau fluids when the power index is smaller than one the results are similar to the Newtonian fluids but when the power index is larger than one the droplet reaches to its final height faster and without any fluctuation. Increasing the height in the non-Newtonian fluid leads to an increase in the amplitude of the oscillations and decreases the amount of frequency in the fluid, which is similar to the Newtonian fluid, with the difference that in the non-Newtonian fluid the amplitude is less but the frequency is higher.

The change of the vapor to liquid phase, which is widely used in industry, is called condensation. Dropwise condensation(DWC) occurs on the hydrophobic and the super hydrophobic surfaces. Research has shown that the creation of micro-nanostructured structures on surfaces is one of the ways . The difference in temperature between the vapor and the liquid can lead to temperature gradient, which causes the convection Marangoni convection. This paper simulates a single drop on surfaces with Cassie and Wenzel structures in four different modes and a smooth surface, and the heat transfer rate for a single drop condensed on these surfaces is calculated in two modes with and without marangoni.The results show that the rate of heat transfer passing through the static drop in the case of the presence of marangoni is higher than the non-Maragoni mode. The rate of heat transfer from the droplet in the without-Marangoni state on the surface with the roughness of the cassie from the smooth surface is 350% ,And the smooth surface is 128% higher than the surface with the roughness of the the Wenzel. In the case of Marangoni, the mode of change of heat transfer rate from these surfaces is affected by the contact angle of the drop on the surface.

Film flotation is a process for separating hydrophobic mineral materials from hydrophilic at the gas-liquid free surface. In this study, for simulation of this process, the impact of spherical hydrophobic particles on an air–water interface was experimented. The aim of this study is to obtain a critical impact velocity in which the hydrophobic particle remains on the liquid surface so that it penetrates completely at higher velocities than the critical velocity. A mathematical model based on energy balance approach was developed to predict the critical impact velocity. The Teflon particles of diameter 3-5mm were used. Distilled water with density of 1000.71 kg/m3 was used as the fluid. The particle impact velocity, cavity profile and velocity of three-phase contact line were obtained for the first time for a number of different particles by using a high speed video camera with the rate of 4500 fps. In the model, the critical impact velocity was obtained by employing the cavity profile and fitted advancing contact angle at critical conditions. It was showed that the mathematical model was in good agreement with experimental observations, including showing a decrease in critical impact velocity with increasing particle diameter.

In this research, water droplet impact process on a solid surface is simulated using a sharp approach for interface modeling. This approach is based on the solving momentum and continuity equations and imposing appropriate jump conditions at the interface. The level set method is used for interface tracking and the ghost fluid method is used to impose jump conditions at the interface accurately. In this way, smearing of quantities across interface is prevented and discontinuities are preserved at interface. The accuracy of numerical procedure is approved via comparison of simulation results with experimental and numerical data. Simulation results show that the used numerical method in comparison with the VOF method, represents more accurate prediction of droplet behavior during impact process. The effect of contact angle between water droplet and surface on the impact process is investigated. For contact angles less than 90°, water droplet spreads on the surface after impact. But, for contact angles greater than 90°, droplet starts to recoil after spreading. In this case, it is possible that droplet rebound from surface after recoiling. Maximum spreading radius of droplet decreases by an increase in contact angle.

Superhydrophobic surfaces have extensive applications like as heat transfer improvement, surface corrosion reduction, and fluid drag reduction. In this research, micro-nano structures were grown on the copper using an electrochemical process. The electrolyte is a two-component solution composing of Potassium persulfate and Sodium hydroxide. An octa-decane-thiol coating is used to reduce the surface energy. In the following, effects of different papmrters including the duration of the process and the concentration of electrolyte components on the contact angle increment are examined. To investigate the created micro/nano structures building block scanning electron microscopy pictures in different conditions were taken and inspected. X-ray diffraction analysis of samples’ surfaces showed that micro-nano structures are copper oxide (I). The maximum contact angle of 158.8 degrees was reached after 10 minute of electrochemical process and 24 hour of coating with low surface energy. Also, the durability of the samples exposing to the open air, pure water and seawater are studied. The samples retained their superhydrophobicity property after up to 6 weeks of exposition to the air; in addition, they showed good durability in contact with pure water and sea water

Controlling surface properties, such as wetting, plays an important role in the research and development of various industries. Even though wettability has many applications in diverse technologies, such as painting, filtration, printing, porous media saturation, medicine, climate, soil, plant biology, and oil recovery enhancement, the effect of roughness pattern on contact angle and wetting needs more attention. In this study, application of the Cassie---Baxter equation for calculating the apparent contact angle of drops with different sizes on the rough surfaces is investigated. To do this, the free energy equation is analyzed on a rough and chemically homogeneous surface to study the Cassie-Baxter equation along with line tension and roughness. The contact angle calculated by using the surface fraction approximation of Cassie-Baxter for rough pattern surfaces has been compared with the values obtained from the developed numerical method. Moreover, the concept of length fraction proposed by Jaroslaw and Miller is discussed, and a numerical method is established to compute its value. To do this, spherical drops of different sizes are simulated on an artificial rough surface consisting of an array of cubic roughness. The line and surface fraction occupied by the drop are calculated and compared with the Cassie-Baxter approximation of surface fraction. Furthermore, the difference in advancing contact angle obtained by the numerical method and Cassie-Baxter model are compared. By using a developed numerical method, the length fraction and surface fraction can be computed for a wide range of drop sizes and roughness dimensions. The length fraction and surface fraction obtained in this work show oscillation behavior around the Cassie-Baxter approximation. When the drop radius tends to infinity, both values of surface and length fraction are equal to the Cassie-Baxter approximation. The results of this work help analyze predict the apparent contact angle value for a wide range of drop sizes on rough surfaces for wettability determination.

In this work the effect of carbon nanotube length on the nanofluidic energy absorption system is investigated by using molecular dynamic simulation. For this purpose, four rigid armchair carbon nanotubes (8,8), (10,10), (12,12) and (14,14), and six lengths (5.0 nm, 6.0 nm, 7.0 nm, 8.0 nm, 9.0 nm and 10.0 nm ) for each one are studied. Results of simulations show that the surface of carbon nanotube is frictionless in all length and diameters, causing water molecules defiltrated from carbon nanotubes after applying the loading-unloading cycle on the system. Contact angle which represents hydrophobic intensity of carbon nanotube is decreased averagely 4 and 2 % by increasing length and diameter of carbon nanotube, respectively; therefore, infiltration pressure of water molecules through carbon nanotube is decreased averagely 30 and 15 %, respectively. Moreover, the mass and size of carbon nanotube increase by increasing length and diameter of carbon nanotube, leading to the reduction of energy absorption density and efficiency. Also, density of water molecules in carbon nanotube unlike the bulk of liquid phase is non uniform, decreases in the first and second shells, and increases along the distance between them by increasing length of carbon nanotube.

In present study, impact of single bubble on an inclined wall and its movement are investigated by applying volume of fluid method (VOF) in OpenFOAM open source cfd package using a solver called interFoam. Both phases are incompressible and surface tension between two phases is estimated by CSF method. The effect of some parameters such as contact angle, wall slope and Bond and Morton dimensionless numbers on bubble shapes and velocity are studied. The numerical results show bubble velocity along wall increases with the increase of wall slope angle. The maximum bubble velocity happens at 50 degree. Three bubble regimes are recognized and introduced in this study named as: sliding, bouncing, and zigzagging based on wall slope. The bubble regime changes from sliding to bouncing when wall slope changes from 30 to 40 degrees. In constant Morton number, increment of Bond number increases both velocity and amplitude of fluctuations. In addition, an increment of Morton number in constant Bond number, decreases velocity and amplitude of fluctuations. Moreover, by increment of Morton number, the bubble motion will change from an accelerating motion to a constant velocity condition.

In present work, models that predict contact angle of a droplet with a solid surface, are considered and compared with each other. Two phases were assumed to be Newtonian, incompressible and immiscible fluids. OpenFOAM software is applied to simulate the two phases interface by using Color function VOF (CF-VOF) method. Different models for contact angle of a droplet as Tanner and Yokoi models are implemented in the OpenFOAM. In addition, the dynamics and statics contact angle models were used to compare with recent models in order to choose the best one. The outcome of study shows, even though the static contact angle model is simple to understand, however, it could be the best model to predict the droplet behavior in a wide range of different conditions. The fluid viscosity effect was also considered in different models of the present study. It concluded that the fluid viscosity affects the type of pattern of droplet impact and as viscosity of fluid increases; more energy is needed to uplift the droplet again from the surface. Kelvin-Helmholtz instability (K-H) was also simulated and explained in details which initiates on the interface of two fluids due to velocity differences of droplet and the surrounded air.