Showing 14 results for Drop
M. H. Rahimian and M. Farshchi,
Volume 21, Issue 1 (7-2002)
Abstract
The internal flow circulation dynamics of a liquid drop moving in a co- or counter-flowing gas stream has been numerically studied. The present work is concerned with the time accurate numerical solution of the two phase flow field at the low Mach number limit with an appropriate volume tracking method to capture motion and deformation of a liquid drop. It is shown that relative velocity between gas and liquid and the parameters controlling the deformation of the drop have the strongest influence on its internal circulation, too. The effects of the liquid Weber number, ranging from 8 to 32, and of gas stream Reynolds number, ranging from 1 to 20 are studied. It was revealed that the largest and the most lasting internal circulation are observed in drops with small deformation in high Reynolds number gas streams. In the case of counter-flowing gas stream, there is a strong internal circulation inside the liquid drop. The locations of the gas separation points on the drop are strongly influenced by the internal circulation of the drop, resulting in a complex wake dynamics.
Keywords: Numerical solution, Two phase flow, Moving droplet, Droplet internal circulation
A. R. Azimian,
Volume 23, Issue 2 (1-2005)
Abstract
In this paper the laminar flow in the rectangular channel bends is simulated using numerical techniques. The turning angle of the channel bend and the area ratio of the channel cross-section are two important parameters to be examined. For flow simulation, the body fitted 3-D continuity and momentum equations are used and a body fitted general purpose code is developed. The existing results of a tied-diriven cavity and the experimental results from a 90 degree square bend were
used for code validation. After the code validation, the effect of the area change in the 90 degree bend is examined.
The numerical results indicated that increasing the area causes changes in the flow pattern, in turn, which has a direct impact on pressure drop. Similar results were obtained for other bend angles including 30, 60, 120, 150 and 180 degree bends. The results showed that increased bend turning angle increases the pressure drop which is in good agreement with existing experimental data.
S. Mortazavi,
Volume 25, Issue 2 (1-2007)
Abstract
The cross-stream migration of a deformable drop in two-dimensional Poiseuille flow at finite Reynolds numbers is studied numerically. In the limit of a small Reynolds number (<1), the motion of the drop depends strongly on the ratio of the viscosity of the drop fluid to the viscosity of the suspending fluid. For a viscosity ratio 0.125, the drop moves toward the centre of the channe while for the ratio 1.0, it moves away from the centre until halted by wall repulsion. The rate of migration increases
with the deformability of the drop. At higher Reynolds numbers (5-50), the drop either moves to an equilibrium lateral position about halfway between the centerline and the wall according to the so-called Segre-Silberberg effect or undergoes oscillatory motions. The steady-state position depends only weakly on the various physical parameters of the flow but the length of the transient oscillations increases as Reynolds number is raised, the density of the drop is increased, or the viscosity of the drop is decreased. Once the Reynolds number is high enough, the oscillations appear to persist forever and no steady state is observed. The numerical results are in good agreement with experimental observations, especially for drops that reach steady-state lateral position.
R. Bagheri and M.a. Golozar,
Volume 25, Issue 2 (1-2007)
Abstract
Using Electrostatic Spray Coating Technique, Polypropylene Powder (EPD 60R) was applied on carbon steel substrates at room temperature. In order to obtain a uniform coating, steel substrates with powder coatings were heated in a vacuum oven at various temperatures up to 250° C for various periods of time up to 45 min and a pressure of 200 mb. The coatings produced had thicknesses of around 470 microns. In order to modify the chemical structure of this polymer, the powder coatings containing various weight percentages of maleic (anhydride (MA) and a peroxide (TBHP or DCP) were also applied onto the steel substrates under the above conditions. Adhesion strength, wear resistance, and ductility of polymer coatings produced were assessed using ASTM standard methods. Results obtained revealed that the polymer coating containing 5 wt%. MA and 0.1 wt% TBHP had the best mechanical properties. Adhesive strength and wear resistance of this coating were 14.3 kgf and 250.3 cm, at 6 kgf, respectively, under the applied load of 6kg. Results obtained from DSC thermographs and IR Spectroscopy also proved the chemical bond formation (grafting) between the polymer and MA. The mechanical properties of coatings on steel substrate stem from such graftings.
M. Parvinzadeh, S. Moradian, A. Rashidi, M. E. Yazdanshenas,
Volume 31, Issue 2 (12-2012)
Abstract
Polyethylene terephthalate (PET) based nanocomposites containing three differently modified silica particles were prepared by melt compounding. The influence of type and amount of nanosilica on various properties of nanocomposite was studied using atomic force microscope, thermal degradation, thermal-mechanical properties, scanning electron microscope, and reflectance spectra. AFM test was used to study the roughness of composites which indicated that the roughness is related to hydrophilicity degree of silica, increasing with an increase in hydrophilicity of particles. SEM images were studied on the surface, confirming that the surface roughness of nanocomposite depends on the type of nano-silica used. Results of thermal analysis showed that the interaction between nanosilica particle and polyethylene terephthalate chains is effective in thermal stability of composite. UV-vis spectra of polyester nanocomposites indicated that the refraction of hydrophilic silica nanocomposites is more than hydrophobic one, indicating agglomeration of hydrophilic particles at the surface of nanocomposite compared with hydrophobic one.
S. Khorsand, K. Raeissi, F. Ashrafizadeh,
Volume 34, Issue 4 (3-2016)
Abstract
Super-hydrophobic nickel and nickel-cobalt alloy coatings with micro-nano structure were successfully electrodeposited on copper substrates with one and two steps electrodeposition. Surface morphology, wettability and corrosion
resistance were characterized by scanning electron microscopy, water contact angle measurements, electrochemical impedanc spectroscopy (EIS) and potentiodynamic polarization curves. The results showed that the wettability of the micro-nano Ni and Ni-Co films varied from super-hydrophilicity to super-hydrophobicity by exposure of the surface to air at room temperature. The corrosion results revealed the positive effect of hydrophobicity on corrosion resistance of Ni coating (~10 times) and Ni-Co coating (~100 times) in comparison with their fresh coatings. The results showed that super-hydrophobic nickel coating had higher corrosion resistance than super-hydrophobic nickel-cobalt coating.
E. Velayi, R. Norouzbeigi,
Volume 36, Issue 4 (3-2018)
Abstract
A superhydrophobic ZnO surface was prepared on the stainless steel mesh by a one-step chemical bath deposition method without chemical post-treatment. The effect of adding polyethylene glycol 6000 (PEG 6000) as an organic additive and the type of the alkaline agent were investigated on the morphological and wettability properties of ZnO surfaces. The prepared surfaces were characterized by X-ray Diffraction (XRD), stylus profilometer, Scanning Electron Microscope (SEM), Fourier Transform Infrared (FTIR) and Raman Spectrometer. The microstructure studies showed that the addition of PEG led to formation of densely branched and uniform ZnO rods with a length of 1.5 µm and a diameter of about 95 nm on the substrate. The surface wettability studies confirmed that the sample prepared in the presence of hexamethylenetetramine (HMTA) and 0.05 mM PEG with branched tree-like micro/nanostructure exhibited excellent superhydrophobic properties with the water contact angle (WCA) of 158.2°±1.5° and contact angle hysteresis (CAH) of 3.5°. In addition, the superhydrophobic showed good chemical stability in the pH range of 4 to 8.
E. Shirani, A. Razmjou,
Volume 36, Issue 4 (3-2018)
Abstract
The significance of producing superhydrophobic surfaces through modification of surface chemistry and structure is in preventing or delaying biofilm formation. This is done to improve biocompatibility and chemical and biological properties of the surface by creating micro-nano multilevel rough structure; and to decrease surface free energy by Fault Tolerant Control Strategy (FTCS) . Here, we produced a superhydrophobic surface through TiO2 coating and flurosilanization methods. Then, in order to evaluate the physicochemical properties of the modified surfaces, they were characterized by Scanning Electron Microscope (SEM), Fourier Transform Infrared Spectroscopy (FTIR), Contact Angle (CA), cell viability assay (using Hela and MCF-7 cancer cell lines as well as non-cancerous human fibroblast cells) by MTT, Bovine Serum Abumin (BSA) protein adsorption using Bradford and bacterial adhesion assay (Staphylococcus aureus and Staphylococcus epidermidis) using microtiter. Results showed that contact angle and surface energey of superhydrophobic modified surface increased to 150° and decreased to 5.51 mj/m2, respectively due to physicochemical modifications of the surface. In addition, the results showed a substantial reduction in protein adsorption and bacterial cell adhesion in superhydrophobic surface.
Sh. Tavakoli Dehaghi, S. Darvishi, Sh. Nemati, M. Kharaziha,
Volume 37, Issue 3 (12-2018)
Abstract
Abstract: With the advances in the development of biomaterials for tissue replacement, the attention of scientists has been focused on the improvement of clinical implant properties. In this regard, despite the appropriate properties of the stainless steel, the application of stainless steel as implants has been limited due to the weak corrosion resistivity. The purpose of this paper was preparation and characterization of hydrophobic polydimethylsiloxane (PDMS)-SiO2-CuO nanocomposite coating on the 316L stainless steel surface. The 316L stainless steel was coated by SiO2 nanoparticles (20 wt. %), CuO nanoparticles (0.5, 1 and 2 wt. %) and biocompatible PDMS. In this research, x-ray diffraction (XRD) and scanning electron microscopy (SEM) were applied to characterize the coating. Moreover, the roughness and water contact angle of the coatings consisting of various amounts of CuO nanopowder were estimated. Finally, the effects of various amounts of the CuO nanopowder on the corrosion resistivity of nanocomposite coatings were investigated. XRD patterns confirmed the presence of crystalline CuO nanoparticles on the substrate. Due to the non-crystalline nature of silica nanoparticles and the semi-crystalline PDMS polymer, no peak confirming the presence of these phases was detected on the XRD pattern of the nanocomposite coating. SEM images showed the formation of a lotus leaf-like layer on the surface of the nanocomposite coating containing 1 and 2 wt. % CuO. Moreover, water contact angle evolution revealed that while contact angle was 81 degree without CuO nanoparticles, it was enhanced to 146 degree in the presence of 1 wt. % CuO. Moreover, the corrosion study showed the nanocomposite containing 2 wt.% CuO had the best corrosion resistance, the corrosion current density of 2.1E-7 A.cm-2, and the corrosion potential of 0.22 V.
A. Razmjou, F. Noorisafa, N. Emami,
Volume 37, Issue 4 (3-2019)
Abstract
Polyurethane polymer plays an important role in health care, and it is widely used in medical devices and instruments. However, the low biocompatibility and biofilm formation on the surface can be regarded as a challenging issue. Engineering the wetting capability of the surface is an effective way to increase the biodegradability of polymer surfaces with sufficient bulk properties. In this study, the surface modification of polyurethane sheets by a thin layer of polyethylene glycol and trapping of titanium dioxide nanoparticles were carried out by means of physical and chemical changes on the surface to enhance the biocompatibility. The physicochemical properties of the modified surfaces were determined using fourier-transform infrared (FTIR) spectroscopy , scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and contact angle and free surface energy measurement. The biocompatibility of the modified levels was evaluated using the MTT toxicity test on cervical cancer cells (HeLA), bacterial adhesion, biofilm formation, and the protein absorption assay by the Bradford method. A thin, autoclave able and inexpensive thin layer with a solid and stable roughening structure was created covalently on the surface of the polyurethane plates for biological and medical applications. The results, therefore, showed that apart from antibacterial activity, the modified sample also had the ability to reduce the biofilm formation, such that the maximum biofilm attachment inhibition in the first 24 hours was 94% higher than that of the modified sample.
M. Maniei, A. Eshaghi, A. Aghaei,
Volume 38, Issue 2 (9-2019)
Abstract
In this research, MgF2-2%SiO2/MgF2 thin films were applied on a glass substrate. At first, MgF2 thin films with the optical thickness were deposited on the glass slide substrates. Then, MgF2-2%SiO2 thin films were deposited on the glass coated with MgF2 thin films. Finally, the nanocomposite thin films were surface treated by the PFTS solution. Characterization of the thin film was done by X-Ray defractometry (XRD), attenuated total reflectance fourier transform infrared spectroscopy (ATR-FTIR), UV-Vis spectroscopy, and atomic force microscopy (AFM) techniques. Also, the hydrophobic properties of the samples were investigated by measuring the contact angle of the water. The results showed that the deposition of the six layer MgF2 thin films on the two sides of the glass substrate increased the transmission up to 96.4%. For the glass deposited by MgF2-2%SiO2 nanocomposite thin films, transmission was reduced to 94.4%, with its transmission being higher than the pure glass. Also, the water contact angle (WCA) analysis determined that the contact angle of the water droplet on the MgF2-2%SiO2 nanocomposite thin film coated glass was decreased. On the other hand, the contact angle of the water droplet on the MgF2-2%SiO2 nanocomposite thin film coated glass after modification with the PFTS solution was increased up to 119o. So, MgF2-2%SiO2 nanocomposite thin films could be used as an antireflective and self-cleaning coating on the surface of the optical devices.
N. Bahremandi Tolou, H. R. Salimi Jazi, M. Kharaziha, N. Lisi, G. Faggio, A. Tamburrano,
Volume 39, Issue 1 (5-2020)
Abstract
In recent years, graphene has been considered in various tissue engineering applications such as nerve guide conduits because of its unique properties such as high electrical and mechanical properties, porous structure for exchange of nutritious and waste materials, biocompatible, capability of drug and growth factor delivery. In the current study, nerve guide conduits based on a 3D graphene were synthesized by induction heating chemical vapor deposition (ICVD). Graphene was synthesized on Ni foam template at 1080 ͦC. Fabricated samples were characterized by Raman analysis and Scanning Electron Microscopy. Raman analysis showed that the synthesized graphene is in the form of a turbostratic multilayered graphene with little defects. Cyclododecane (CD) as a temporary protective layer was used to remove nickel. After removing nickel, the free-standing 3D-graphene structure was coated with a polymer (PCL) by drop and dip coating methods to obtain the composite conduit. A comparison of the electromechanical results of the 3D-graphene/PCL conduit and PCL conduit indicated that firstly, grapheme increased the electrical conductivity of the composite conduit which will help promote nerve regeneration and axon growth. Secondly, tensile strength and flexibility of the 3D-graphene/PCL conduit was improved compared to the PCL conduit.
A. Zolriasatein, S. Navazani, M. Rezaei Abdadchi, N. Riahi Noori ,
Volume 39, Issue 3 (12-2020)
Abstract
In this paper, the effect of adding aluminum trihydrate (ATH) on electrical (including dielectric constant, dielectric loss and strength, volume and surface resistivity) and hydrophobic properties of two-part room temperature volcanized (RTV) silicone rubber resin coatings were investigated. For this purpose, the RTV-ATH nanocomposite was made by physical mixing and its electrical and hydrophobic properties were compared with those of pure RTV. The results showed an increase in the dielectric constant (from 3.11 to 4.13), the dielectric loss (by ~ 0.06) and the dielectric strength (by ~ 4 KV/mm) of the RTV-ATH composite compared to the pure RTV. Moreover, ATH increased volume resistivity and reduced the surface resistivity of composite coatings. On the other hand, by spraying of coatings, no improvement in the hydrophobicity class of composite coating compared to pure RTV was observed and both samples were standardized in the HC2 standard class. Structural analysis of samples was performed by X-ray diffraction, optical microscopy and scanning electron microscopy and the presence of the main phases in them was confirmed.
S. Borhani Esfahani, H. R. Salimi Jazi, M. H. Fathi, A. Ershad Langroudi, M. Khoshnam,
Volume 40, Issue 1 (5-2021)
Abstract
In this research, a kind of environmentally-friendly inorganic-organic hybrid nanocomposite coating based on silica containing titania/silica core/shell nanoparticles was synthesized and characterized for conservation of facade tiles in historical buildings. The matrix of the composite was prepared by sol-gel process via two methods of ultrasonic and reflux stirring. Tetraethyl orthosilicate (TEOS) and poly-dimethyl siloxane hydroxy-terminated (PDMS-OH) were used for the formation of silica network and creation of flexibility and hydrophobicity, respectively. Titania nanoparticles were used in the form of titania/silica core/shell as ultraviolet absorber. The synthesized nanocomposite was applied on the microscope slides and tiles by dip coating technique. The properties of nanoparticles and coatings were characterized by Fourier-transform infrared spectroscopy (FTIR), Transmission electron microscopy (TEM) and water contact angle measurement. The results revealed that formation of titania/silica core/shell structure was successful. The investigation of PDMS content effect on transparency, cohesion and hydrophobicity of the coating confirmed that the optimum content of this siloxane was around 20 wt.%. In general, the results showed that the silica-based hybrid nanocomposite reinforced with TiO2/SiO2 core/shell nanoparticles could produce a transparent and hydrophobic coating for tile and glass protection.
