Bending instability is a significant reason for the success of the electrospinning process for decreasing the fiber’s diameter to nanometer scales and a determining factor in final fiber morphology. Observation of electrospinning of different polymers revealed that electrospun fibers accumulate in a circular area with various diameters in the case of a stationary flat plate target. There is an idea that the diameter of accumulated surface (ASD) is controlled by bending instability, and there is a correlation between electrospun fiber diameter and ASD. In this study, the accumulation behaviors of Polystyrene (PS), Polymethyl methacrylate (PMMA), and coaxially electrospun fibers of PS-PMMA were evaluated concerning their ASD sizes, the rate of ASD’s growth, and the correlation between ADS size and the final diameters. To determine the role of processing parameters on this behavior and the relationship between the ASD and final fiber diameter, some experiments were designed for three factors of voltage, flow rate, and tip to target distance for electrospun fiber diameters and ASD in PMMA electrospinning. Two polynomial equations were found (via regression). Then, the polynomial models statistically were analyzed and discussed. Scanning electron microscopy (SEM) and fluorescent microscopy were applied for morphological studies, and Image J were used for measuring the sizes. The results demonstrated that during the electrospinning, the ASD grew with the natural logarithm of time and so ended to a plateau (specific diameter), and after that, the upcoming electrospun fibers accumulated on the former ones. Moreover, bigger ASDs were accompanied by smaller electrospun fiber diameters.

Bending instability is a significant reason for the success of the electrospinning process for decreasing the fiber’s diameter to nanometer scales and a determining factor in final fiber morphology. Observation of electrospinning of different polymers revealed that electrospun fibers accumulate in a circular area with various diameters in the case of a stationary flat plate target. There is an idea that the diameter of accumulated surface (ASD) is controlled by bending instability, and there is a correlation between electrospun fiber diameter and ASD. In this study, the accumulation behaviors of Polystyrene (PS), Polymethyl methacrylate (PMMA), and coaxially electrospun fibers of PS-PMMA were evaluated concerning their ASD sizes, the rate of ASD’s growth, and the correlation between ADS size and the final diameters. To determine the role of processing parameters on this behavior and the relationship between the ASD and final fiber diameter, some experiments were designed for three factors of voltage, flow rate, and tip to target distance for electrospun fiber diameters and ASD in PMMA electrospinning. Two polynomial equations were found (via regression). Then, the polynomial models statistically were analyzed and discussed. Scanning electron microscopy (SEM) and fluorescent microscopy were applied for morphological studies, and Image J were used for measuring the sizes. The results demonstrated that during the electrospinning, the ASD grew with the natural logarithm of time and so ended to a plateau (specific diameter), and after that, the upcoming electrospun fibers accumulated on the former ones. Moreover, bigger ASDs were accompanied by smaller electrospun fiber diameters.

In this paper, We purpose to analyze the large bending of elastic curved structures that found in the engineering, science and nature. We investigated large bending of an open sector circular cylindrical tube into a complete circular cylindrical tube such that the solid is modeled via an incompressible, homogenous and isotropic hyperelastic material. According to the finite deformation of the structure, in the compressed side of bended beam wrinkles and local buckling may appear. We interpret the onset this instability by using the theory of incremental deformation superimposed on the finite deformation and analytical WKB method for Mooney-Rivilin strain energy function is utilized and boundary loads are defined for bending analysis. Moreover, the instability and numbers of wrinkles is studied in detail. The main results are that the obtained bending conditions are depended on the sector angles before and after deformation, exterior traction and the numbers of wrinkles per surface area. The trend of changes and dependence of these geometric parameters are examined by drawing diagrams

In this paper, the instability of wave motion on the surface of liquid sheet emanating from a swirl injector exposed to inner and outer air streams, before the breakup is considered using the linear instability analysis by a perturbation method. The forces acting on a liquid gas interface in sprays, including surface tension, pressure, inertia force, centrifugal force and viscous force, lead to grow the disturbances originated from inside the injector on the outgoing liquid sheet. Interaction between these forces ultimately breaks up the jet into the ligaments. The linear instability analysis used in the present study is different from prior analysis. A cylindrical liquid sheet has been considered in previous studies but the present study implements the linear instability on a conical annular liquid sheet. Due to the complexity of derived governing equations a semi-analytical and numerical method was utilized in the solution procedure. The present model is capable to solve governing equations for the liquid jet with large range of spray angle. The predicted results compared with the prior studies results and experiments. The results of the current model in comparison with prior models have better accordance with experimental data. Also, the results show that the improved linear theory (the present model) predicts the breakup length better than linear theory.

In this paper a comprehensive review of flow visualization techniques used for the analysis of spray characteristics is presented and an experimental demonstration of different lighting techniques has been made. Still photographs of sprays from an airblast atomizer and a swirl atomizer are taken under backlighting, slit lighting, incident lighting (front flash) and a new method of capturing scattered light image at 1200 to the incident light is introduced in the present work. Photographs taken by these methods are shown to be useful for deriving useful observations such as jet breakup phenomenon, the internal details and the external appearance of the spray. It is demonstrated that the information obtainable from each technique is different and that a combination of different techniques may be necessary for proper diagnosis. The article also includes a discussion on the jet breakup phenomenon as observed in the photographs and in addition a new concept of shear formation of smaller droplets from the surface of a liquid jet by the co-flowing air stream in an airblast atomizer has been proposed.

A linear instability analysis of an inviscid annular liquid sheet emanating from an atomizer subjected to inner and outer swirling air streams and a non-swirl round liquid jet has been carried out. The dimensionless dispersion equation that governs the instability was derived and was solved by Numerical method to investigate the effects of the liquid-gas swirl orientation on the maximum growth rate and its corresponding unstable wave number that produces the finest droplets. To understand the effect of air swirl orientation with respect to liquid swirl direction, four possible combinations with both swirling air streams with respect to the liquid swirl direction have been considered. Results show that at low liquid swirl Weber number a combination of co-inner air stream and counter-outer air stream has the largest most unstable wave number and shortest breakup length. The combination of inner and the outer air stream co-rotating with the liquid has the highest growth rate. Also, the results for round liquid jet and planar liquid sheet show that the linear theory accurately predicts the variation in breakup length with jet velocity.

in this research, their effects on the flight of airplanes were investigated. The study area is the country of Iran, and the flight routes of Kermanshah, Ahvaz and BandarAbbas to Tehran. The research data includes maps of the Vertical Transect (profile) of the jet stream, the daily average of the Zonal wind (U-Wind) and meridional wind (V-Wind) components for the winter period of 2018 through NOAA/NCEP environmental databases. Also, flight route information was received from FlightRadar24 and Flightaware systems. First, by using Vertical Transect maps, the days containing strong U-Wind were extracted, and the average position of the core of the Jet Streams in the Zonal and meridional wind components, the Tropospheric level of 200 HP was detected. The list of flights was prepared, and the Zonal Wind maps were produced. Finally, the height of the flights was compared with the level of the currents of the Jet Streams, and the influence or lack of influence of the Jet Streams on the flights was studied. According to the results of the research, all the Jet Streams caused turbulence for all flights, and they caused a decrease in the speed of flights between Ahvaz and BandarAbbas to Tehran and an increase in the speed of flights between Kermanshah and Tehran according to the direction and type of Jet Streams. It was also found that all the Jet Streams had a speed of more than 90 knots, so the capacity to create tension and turbulence such as CAT was seen in them

In this study a mechanism was modeled to control the jet path of Nano fibers produced by electros pinning through inducing a magnetic field over the jet path. Firstly, a model was developed for the jet path in which the fibers composed of a series of viscoelastic segments. Considering the mass and momentum conservation and maxwellian model of stretching viscoelastic segments using three equations governing the jet dynamics of the jet model in electros pinning, a program was developed in MATLAB with Runge–Kutta method. After ensuring the accuracy of the model, its behavior was evaluated in the presence of a magnetic field. The field induced a uniform force distribution over the jet. As the intensity of the magnetic field increased; the instability and bending radius of the jet reduced. The results of the research showed that utilizing a suitable mechanism for applying magnetic field can provide help in controlling the jet path and alignment of the Nano fibers.

This paper investigates the influence of a weak-jet on the development of a turbulent axisymmetric strong jet. A parametric study is carried out to evaluate simultaneously the effect to the jets-spacing (S/D=3 and S/D=7. 5) and their velocity ratios in range 0≤ λ ≤ 1. The mixing phenomenon is studied numerically by the finite volume method using the 3D-RANS second-order model, which gives a good agreement with the available data. Three distinct regions of this type of jets interaction are evidenced. This study confirms that the jets spacing affects strongly the converging region and has a minor effect on the combining region. It is found that the weak jet attracts the strong jet and the combining region extends from 30D to 40D where the self-similarity of a single jet is obtained. The jet width decreases when velocity ratio and jets spacing augment. In the combining region, in comparison with the free jet, it is found that the addition of a weak-jet increases the decay rate of the centerline velocity.