Sharif Digital Repository

A general investigation of the viscosity of natural gas as a function of temperature, pressure and composition was carried out to develop a generalized correlation. The model obtained was based on 3231 data points of 29 multicomponent mixtures in wide ranges of pressures (0.1-137.8MPa), temperatures (241-473K) and specific gravities (0.573-1.337). Correction terms for non-hydrocarbons of hydrogen sulfide, carbon dioxide and nitrogen were up to 70, 54.4 and 15.8 of mole percent, respectively. The arithmetic average of the model's absolute error was found to be 5.05%, which is acceptable in engineering calculations and has superiority over other methods in its class  

Long-chain branches are incorporated into the molecular backbone of a polypropylene (PP) in a foaming process. The branching of PP occurs by radical reactions of dicumyl peroxide and a tri-functional monomer, trimethylol propane trimethacrylate. Use of peroxide without tri-functional monomer results in scission of PP molecular chains and significant reduction in melt viscosity. The increase in melt viscosity in conjunction with the flow ability of the modified PP indicates that the polymer has a branched structure. Melting temperature of PP remains unchanged with branching reactions implying that reactions occur mainly in amorphous regions of PP. The improvement in melt strength and... 

A resonant interaction analysis is used to study the two-dimensional interaction of a surface wave with two waves on a diffuse interface in a stratified fluid. The fluid system is modeled as a combination of two homogenous finite-depth layer with a free surface, divided by a thin third layer. Two possibilities for the interaction are found: one between the surface wave and two first-mode interfacial waves and a second between the surface wave, a first-mode, and a second-mode interfacial wave. By taking the nondimensional density difference δ as a small perturbation parameter, the evolution equations of the interfacial waves are derived asymptotically. The analysis indicates that growth of... 

Wettability is a key parameter affecting petrophysical properties of reservoir rocks. Mirzaei-Paiaman et al. (Energy Fuels 27:7360–7368, 2013) presented an index (referred to as MPMS) for laboratory characterization of wettability of native- or restored-state reservoir rock samples. To use this index two counter-current spontaneous imbibition (COUCSI) experiments are needed, one on the native- or restored-state core sample and another on the strongly water-wet (SWW) reference system. Slope analysis of recovery data in these two systems gives inputs for determination of MPMS index. The two systems must have the same pore structure, initial water saturation, and viscosity ratio. The case of... 

A novel mathematical-based approach is proposed to develop reliable models for prediction of saturated crude oil viscosity in a wide range of PVT properties. A new soft computing approach, namely least square support vector machine modeling optimized with coupled simulated annealing optimization technique, is proposed. Six models have been developed to predict saturated oil viscosity, which are designed in such a way that could predict saturated oil viscosity with every available PVT parameter. The constructed models are evaluated by carrying out extensive experimental saturated crude oil viscosity data from Iranian oil reservoirs, which were measured using a "Rolling Ball viscometer." To... 

Production and oscillation of sonoluminescence bubbles by laser pulse in the presence of acoustic field in water and different concentrations of sulfuric acid are investigated. In the presence of acoustic field, the laser causes variable speed of sound, surface tension and density; and the host liquid acts as a compressible one and strongly affects the bubble's dynamics equations. The effect of various concentrations of sulfuric acid as a host liquid on the oscillation of bubble radius, bubble wall velocity and bubble interior temperature is studied. Furthermore, the effect of applied frequency on LI-SCBL in the presence of the acoustic field is investigated and an optimum sound wave... 

The results of a flume investigation of surface wave motion over a fluidized bed are presented. It is shown that a resonant wave interaction between a surface wave and two interfacial waves at the interface of the fresh water and the fluidized bed is a strong mechanism for instability of the interface and the subsequent mixing of the layers. The interfacial waves are subharmonic to the surface wave and form a standing wave at the interface. The interaction is investigated theoretically using a fully viscous interaction analysis. It is shown that surface wave height and viscous effects are the determining factors in the instability mechanism. The results indicate that the net effect of... 

In this study an analytical model has been developed to describe air pressure and residual air mass variations in pressure die casting for atmospheric venting. During injection of molten metal into a die cavity, air is evacuated from the cavity through vents. In this study, the influences of air velocity and friction factor due to temperature dependent viscosity and vent roughness change have been investigated. The results of the model show that there is a critical area ratio over which a quasi steady state is reached, therefore, the air pressure in the cavity remains constant. In addition, for each area ratio there is a critical/ minimum time ratio below which outlet Mach number is not... 

In solution of the Euler equations in the steady state external flows, error or residual waves are blamed for decelerating the convergence. These waves may be damped by adding a bulk viscosity term to the momentum equations. We analyse effects of this term on the linearized differential equations, and study its explicit and implicit implementation in one and two space dimensions. Optimum values of the bulk viscosity damping (BVD) are discussed. After generalization to two space dimensions, its performance both alone and in combination with a soft wall boundary condition and residual smoothing in central differencing codes is reviewed. It is shown that BVD is complementary to them, and acts... 

A generalized equation based on modified Eyring's theory for predicting kinematic viscosity of petroleum fractions is proposed in this work. The equation uses two reference fluids including a pair of (C6 and C10), (C10 and C14), or (C14 and C20) for petroleum fractions of molecular weight higher than 70 and lower than 300. Validity and accuracy of this equation have been confirmed by comparing the obtained results of this equation with experimental data. In contrast to other correlations that require so many specific parameters for oil viscosity prediction, this type of equation requires only molecular weight and true boiling point. The results obtained in this work are in agreement with... 

Accurate value determination of natural gas viscosity plays a key role in its management as it is one of the most important parameters in natural gas engineering calculations. In this study, a comprehensive model is suggested for prediction of natural gas viscosity in a wide range of pressures, temperatures, densities and compositions. The new model can be applicable for gases containing heptane plus and non-hydrocarbon components. It is validated by the 2011 viscosity data from 18 different gas mixtures. Compared to existing similar models and correlations, its results are quite satisfactory  

A simple method for estimating the apparent viscosity of semi-solid alloys was investigated. A drop weight of 50Kg and backward extrusion equipments were used to test the deformation. Backward extrusion was employed in a closed die system due to the very little separation of liquid from solid phases compared with other methods at very high deformation rate. The half of the calculated impact velocity, 700mm/s was considered as an average velocity for deformation during the test, since the slop of the velocity changes against time is constant in the middle stage of the deformation. The initial height of the sample and the thickness of the residual compressed solid at the bottom of the cup were... 

The uniaxial viscosity and sintering stress of WC-10Co-0⊙ 9VC (wt-%) were obtained by a loading dilatometer as functions of fractional density (0⊙ 64< ρ< 0⊙ 93) and temperature (1084< T< 1297° C) according to a Newtonian constitutive law commonly used to simulate sintering. The viscosity is suggested to follow In η= a+ Q/RT+ bρ with the values of a= 52⊙ 3±4⊙ 5 and b= 16⊙ 8±0⊙ 2. Q reflects the temperature dependence of η and estimated to be 502±52 kJ mol-1. The sintering stress exhibited almost a constant value in the range of 0·05–0·4 MPa. It is shown that Rahaman's model best fits the experimental results. This paper describes experiments performed on nanostructured WC–Co feedstock to... 

A viscosity model, based on Eyring's absolute rate theory combined with a cubic PR equation of state and Wong-Sandler mixing rule, has been proposed in order to correlate viscosities of aqueous solutions of alkanolamine mixtures at atmospheric pressure and different temperatures. In the proposed method, the energy and size parameters in studied Equation of State (EoS) have been obtained using the Wong - Sandler (WS) mixing rule combined with the NRTL and Wilson Gibbs equations. The NRTL and Wilson parameters for aqueous solutions of alkanolamine mixtures have been correlated using measured viscosity data at atmospheric pressure and different temperatures. The overall average deviation... 

Mixing of solid nanoparticles in viscous fluids is a key stage in synthesis of nanocomposites and can affect their final properties. A multi-step preparatory mixing is developed to synthesize the nanocomposites of layered silicate in thermosetting polymers. This study aims to investigate the influences of mixing conditions and steps taken to process the thermosetting nanocomposites on the viscoelastic properties of suspensions. We also examine subsequent influences of mixing on the microstructure and dispersion state of cured hybrids of organically modified clays in a polyester resin. The nanocomposites were prepared in a sequential mixing process developed for the model nanocomposites of... 

This paper focuses on developing a new method that represents user-accessible correlation for the estimation of water-based nanofluids viscosity. For this, an evolutionary algorithm, namely Gene Expression Programming (GEP), was adapted based on a wide selection of literature published databanks including 819 water-based nanofluids viscosity points. The developed model utilized the base fluid viscosity as well as volume fraction and size of the nanoparticles as the inputs of the model. Several statistical parameters integrated with graphical plots were employed in order to assess the accuracy of the proposed GEP-based model. Results of the evaluation demonstrate fairly enough accuracy of the... 

The variation of the applied field results in a subsequent change of magnetization with time. There is a relationship between the coercivity (Hc), as the equilibrium characteristic of the system, and its magnetic stability (1/S), as a parameter characterizing the time dependence. 1/S as a function of Hc has been measured and studied for different Fe1-xCox samples. We synthesized several samples with different values of x by applying various magnetic fields during the grains' growth, and observed a linear relationship between 1/S and Hc. © 2007 Elsevier B.V. All rights reserved  

In this study, the nodal discontinuous Galerkin method is formulated in three-dimensions and applied to simulate three-dimensional non-cavitating/cavitating flows. For this aim, the three-dimensional preconditioned Navier-Stokes equations based on the artificial compressibility approach considering appropriate source terms to model cavitating phenomena are used. The spatial derivative terms in the resulting equations are discretized by utilizing the nodal discontinuous Galerkin method on tetrahedral elements and the derivative of the solution vector with respect to the artificial time is discretized by applying an explicit time integration method. An artificial viscosity method is formulated... 

The presence of asphaltene means additional difficulties related to transport and processing due to the increased crude oil viscosity caused by the asphaltene. For a better knowledge of the flow properties of asphaltene containing crude oils, it is necessary to understand how asphaltene affects the rheological properties. The aim of this article is to provide information on such rheological properties of oil-asphaltene slurry systems. The results of rheological experiments show that the non-Newtonian flow curves can be approximated by the Bingham plastic model to determine the apparent viscosity and the yield stress as a function of asphaltene concentration and temperature. An explanation is... 

High molecular weight homopolymers of acrylamide (PAM) and (2-methacryloyloxyethyl) trimethyl ammonium chloride (PDMC) and copolymer of DMC with acrylamide (P(AM-co-DMC)) were synthesized using solution polymerization technique. The synthesized polymers were characterized by Fourier transform infrared (FTIR), 1HNMR, 13CNMR spectroscopy and differential scanning calorimetry (DSC) and viscometery. 1HNMR and 13CNMR studies confirmed the structure of the synthesized polymers. The behavior of the synthesized polymers was investigated in water-acetone and water-methanol mixtures. The plot of intrinsic viscosity of either PAM or P(AM-co-DMC) with respect to acetone (methanol)/water ratio in...