Preparation and investigation of the gas separation properties of polyurethane-TiO2 nanocomposite membranes

Morteza Sadeghi,Hajar Taheri Afarani,Zohreh Tarashi 한국화학공학회 2015 Korean Journal of Chemical Engineering Vol.32 No.1

The effect of TiO2 nanoparticles on the gas separation properties of polyurethane has been investigated. Polyurethane was synthesized using hexamethylene diisocyanate (HDI) and 1,4-butanediol (BDO) as hard segmentand poly(tetramethylene glycol) (PTMG, 2,000 g/mol) as soft segment. The synthesized polymer was in a 1 : 2 : 1 molarratio of polyol : diisocyanate : chain extender through bulk two-step polymerization. PU membranes were prepared bythermal phase inversion method. Scanning electron microscopy (SEM), X-ray diffraction and Fourier Transform Infra-red (FTIR) analyses characterized the prepared membranes. FTIR and SEM results indicate the good interaction be-tween particles and polymer matrix and also the nanoscale dispersion of TiO2 particles in polymer matrix. Gas perme-ation properties of PU-TiO2 nanocomposite membranes with TiO2 contents up to 30 wt% were studied for N2, O2, CH4and CO2 gases at 10 bar and 25 oC. Results suggest a decrease in permeability of studied gases and increase in gas selec-tivities as TiO2 content increases.

Hydroelastic instability of viscoelastic fluids in developing flow through a compliant channel

Morteza Safarifard,Zahra Aghaee,Mohammad Pourjafar,Solmaz Bazargan,Kayvan Sadeghy 한국유변학회 2020 Korea-Australia rheology journal Vol.32 No.2

Linear stability of a viscoelastic fluid obeying the Walters’ B model is analytically and numerically investigated in the entrance region of a plane channel formed between two parallel plates. The plates are compliant and obey the two degree-of-freedom von Karman solid model. Having obtained the base-flow velocity profiles using the boundary-layer theory, their vulnerability to infinitesimally small varicose disturbances is investigated using the temporal, normal-mode, linear stability analysis. The results obtained show that a fluid’s elasticity has a stabilizing effect on the developing velocity profiles. The distance at which the flow becomes unstable shifts further downstream (i.e., towards the fully-developed section) of the channel when the Deborah number is increased. An increase in the flexural rigidity of the plates is shown to have a stabilizing effect on the short waves (i.e., the flutter modes) whereas an increase in its mass can dramatically destabilize such modes. The flow becomes more stable when the stiffness of the soft matter restraining the vertical movement of the plates is increased with the effect being more significant on the long waves (i.e., flow-induced modes). Boosting the dissipating effect of this material is predicted to have a stabilizing effect on the short waves.

Development of optimum modeling approach in prediction of wheelflats effects on railway forces

Javad Sadeghi,Amin Khajehdezfuly,Morteza Esmaeili,Davood Poorveis 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.69 No.5

While the wheel flat is an asymmetrical phenomenon in the railway, majority of researches have used two-dimensional models in the investigation of the effect of wheel flat on the wheel rail forces. This is due to the considerably low computational costs of two dimensional (2D) models although their reliability is questionable. This leaves us with the question of “what is the optimum modeling technique?”. It is addressed in this research. For this purpose, two and three dimensional numerical models of railway vehicle/track interaction were developed. The three dimensional (3D) model was validated by comparisons of its results with those obtained from a comprehensive field tests carried out in this research and then, the results obtained from the 2D and 3D models were compared. The results obtained indicate that there are considerable differences between wheel/rail forces obtained from the 2D and 3D models in the conditions of medium to large wheel-flats. On the other hand, it was shown that the results of the 2D models are reliable for particular ranges of vehicle speed, railway track stiffness and wheel-fats lengths and depths. The results were used to draw a diagram, which presents the optimum modeling technique, compromising between the costs and accuracy of the obtained results.

Performance of under foundation shock mat in reduction of railway-induced vibrations

Javad Sadeghi,Ehsan Haghighi,Morteza Esmaeili 국제구조공학회 2021 Structural Engineering and Mechanics, An Int'l Jou Vol.78 No.4

Under foundation shock mats have been used in the current practice in order to reduce/damp vibrations received by buildings through the surrounding environment. Although some investigations have been made on under foundation shock mats performance, their effectiveness in the reduction of railway induced-vibrations has not been fully studied, particularly with the consideration of underneath soil media. In this regard, this research is aimed at investigating performance of shock mat used beneath building foundation for reduction of railway induced-vibrations, taking into account soil-structure interaction. For this purpose, a 2D finite/infinite element model of a building and its surrounding soil media was developed. It includes an elastic soil media, a railway embankment, a shock mat, and the building. The model results were validated using an analytical solution reported in the literature. The performance of shock mats was examined by an extensive parametric analysis on the soil type, bedding modulus of shock mat and dominant excitation frequency. The results obtained indicated that although the shock mat can substantially reduce the building vibrations, its performance is significantly influenced by its underneath soil media. The softer the soil, the lower the shock mat efficiency. Also, as the train excitation frequency increases, a better performance of shock-mats is observed. A simplified model/method was developed for prediction of shock mat effectiveness in reduction of railway-induced vibrations, making use of the results obtained.

Polyurethane/Poly(vinyl alcohol) Blend Membranes for Gas Separation

Hemmat Shirvani,Morteza Sadeghi,Hajar Taheri Afarani,Rouhollah Bagheri 한국섬유공학회 2018 Fibers and polymers Vol.19 No.5

This Study involves preparation and characterization of polyurethane (PU) and polyurethane/poly(vinyl alcohol) (PU/PVA) blend membranes for gas separation. PU was synthesized by two step polymerization based on isophorone diisocyanate (IPDI), 1,4-butanediamine (BDA), polytetramethylene glycol (PTMG) in the mole ratio of 3:2:1. The prepared blend membranes were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray Diffraction (XRD), and scanning electron microscopy (SEM). The effects of molecular weight of PVA, and blend composition on the gas transport properties of N2, O2, CO2 and CH4 were investigated. Obtained results show that the permeability of gases decreased in blend membranes by poly(vinyl alcohol) (PVA) molecular weights while their gas selectivity enhanced. Comparison of the gas separation performance of the prepared membranes to Robeson upper bound, reveal the enhancement of membrane performance by introducing PVA in PU matrix.

Nonlinear behavior of capacitive micro-beams based on strain gradient theory

Mohammad Fathalilou,Morteza Sadeghi,Ghader Rezazadeh 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.4

This paper studies the size dependent behavior of materials in MEMS structures. This behavior becomes noticeable for a structurewhen the characteristic size such as thickness or diameter is close to its internal length-scale parameter and is insignificant for the highratio of the characteristic size to the length-scale parameter, which is the case of the silicon base micro-beams. However, in some types ofmicro-beams like gold or nickel bases, the size dependent effect cannot be overlooked. In such cases, ignoring this behavior in modelingwill lead to incorrect results. Some previous researchers have applied classic beam theory on their models and imposed a considerablehypothetical value of residual stress to match their theoretical results with the experimental ones. The equilibrium positions or fixedpoints of the gold and nickel micro-beams are obtained and shown that for a given DC voltage, there is a considerable difference betweenthe obtained fixed points using classic beam theory, modified couple stress theory, and modified strain gradient theory. In addition, it isshown that the calculated static and dynamic pull-in voltages using higher order theories are much closer to the experimental results andare higher several times than those obtained by classic beam theory.

Gas Separation Polysulfone Membranes Modified by Cadmium-based Nanoparticles

Elmira Tavasoli,Morteza Sadeghi,Hossein Riazi,Ahmad Arabi Shamsabadi,Masoud Soroush 한국섬유공학회 2018 Fibers and polymers Vol.19 No.10

This paper presents new mixed-matrix membranes (MMMs) synthesized via incorporating hexamethylenetetramine dicyanamide cadmium nanoparticles, a metal organic framework (MOF), into the polysulfone (PSF) matrix. The MMMs are characterized using FTIR and SEM analyses, and their gas permeation properties are evaluated at different MOF loadings and various pressures. The results show that the nanoparticle is compatible with the polymer and distributes homogenously in the matrix. Compared to the pristine PSF membrane, the MMM with 2.5 wt. % of the MOF nanoparticles has lower CO2, CH4, N2 and O2 permeabilities but significantly higher CO2/CH4, CO2/N2 and O2/N2 gas pair selectivities (i.e., 41.66, 20.08 and 5.09, respectively, which are 42.6, 61.6 and 60.02 % higher). As the total pressure increases, the gas permeabilities of the pristine PSF membrane and the MMMs decrease, but their sieving abilities increase. These results suggest that gas selectivities of high free-volume polymers with poor sieving abilities can be improved by incorporating the MOF into the polymer.

Gas separation properties of polyvinylchloride (PVC)-silica nanocomposite membrane

Mohammad Mohagheghian,Morteza Sadeghi,Mahdi Pourafshari Chenar,Mahdi Naghsh 한국화학공학회 2014 Korean Journal of Chemical Engineering Vol.31 No.11

Researchers have focused on improving the performance of polymeric membranes through various methods,such as adding inorganic nanoparticles into the matrix of the membranes. In the present study, the separation of oxygen,nitrogen, methane and carbon dioxide gases by PVC/silica nanocomposite membranes was investigated. Silica nano-particles were prepared via sol-gel method. Membranes were prepared by thermal phase inversion method and char-acterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), differential scanningcalorimetry (DSC) and thermal gravimetry (TGA) analyses. The FTIR and SEM analyses demonstrated a nano-scaledispersion and good distribution of silica particles in the polymer matrix. According to TGA results, thermal propertiesof PVC membranes were improved and DSC analysis showed that glass transition temperature of nanocomposite mem-branes increased by adding silica particles. We concluded that the permeability of carbon dioxide and oxygen increasedsignificantly (about two times) in the composite PVC/silica membrane (containing 30 wt% silica particles), while that ofnitrogen and methane increased only 40 to 60 percent. Introducing 30 wt% silica nanoparticles into the PVC matrix,increased the selectivity of CO2/CH4 and CO2/N2 from 15.9 and 21 to 18.2 and 27.3, respectively. The diffusion andsolubility coefficients were determined by the time lag method. Increasing the silica mass fraction in the membraneincreased the diffusion coefficients of gases considered in the current study.

Experimental investigation on the effectiveness of under-foundation isolator against train-induced vibrations considering foundation type

Ehsan Haghighi,Javad Sadeghi,Morteza Esmaeili 국제구조공학회 2024 Structural Engineering and Mechanics, An Int'l Jou Vol.89 No.2

In this paper, the performance of under-foundation isolators against generally annoying train-induced vibrations was examined experimentally. The effect of foundation type on the efficacy of such isolators was investigated for the first time. To this end, laboratory models including a soil container, soil, building with three types of foundation (i.e., single, strip, and mat), and isolator layer were employed. Through various dynamic tests, the effects of foundation type, isolation frequency, and the dominant frequency of train load on the isolator’s performance were studied. The results demonstrated that the vibration level in the unisolated building with the strip and mat foundation was, respectively, 29 and 38% lower than in the building with the single foundation. However, the efficacy of the isolator in the building with the single foundation was, respectively, 21 and 40% higher than in the building with the strip and mat foundation. Furthermore, a lower isolation frequency and a higher excitation frequency resulted in greater isolator efficacy. The best vibration suppression occurred when the excitation frequency was close to the floor’s natural frequency.

Three-dimensional modeling of system of vibrating spherical balls using discrete element method†

Farzin Salehpour-Oskouyi,Morteza Homayoun Sadeghi 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.1

The modeling of particulate systems has been an important focus of research worldwide, as these are fairly common in nature, such asrain drops in air, snowfall, and several industrial processes such as chemistry, agriculture, pharmaceutical, powder metallurgy, soil mechanics,casting, cement manufacturing, civil, and etc. In recent years, one of important aspects of the granular material physics in industriesis controlling way of the granular flow. One of the best ways of controlling the flow is the use of mechanical vibrations to guide theparticles in desirable way. In this paper the effect of horizontal harmonic vibration on the particles flow is theoretically and experimentallyinvestigated. During the base vibration, the spherical particles collide with each other and with the walls as well, causing a globalpattern of particle motion which is interpreted as flow. The motion of spherical particles and the interaction forces due to the vibration isobtained numerically via discrete element method (DEM). Finally, the presented numerical model is compared with the experimental oneand a good agreement between them is noticed.