IRANIAN JOURNAL OF SCIENCE AND TECHNOLOGY TRANSACTION B- ENGINEERING
Year:2002 | Volume:26 | Issue:B2|Papers Count:29

This paper presents a simulator and an analytical technique for analysis of a gel treatment process in a stratified oil reservoir. Calculations were performed with multicomponent 1-D simulator in each layer of a reservoir that has the facility to describe the gelation of Na2SiO3 + CaCl2 reagent due to high reservoir temperature (temperature initiation) or/and low pH value in a porous media. Kinetics of these reactions were analyzed in experiments and kinetic constants were obtained. Simplified axial problems of reagent propagation and gelation in near well water saturated zone of a reservoir were considered. Analytical solutions of linear problems in one isolated layer were obtained and analytical technique for simulation of a gel treatment in a stratified reservoir was generated. The proposed technique was tested by a comparison with three case histories of profile improvement in injection wells using a gel treatment.

This paper investigates the implementation of interlacing and irregular rectangular meshes used in conjunction with the DXDR method and a modified dynamic relaxation method, to study the large deflection elastic plates. Numerical computations are conducted to evaluate the accuracy of solutions with different mesh arrangements. Emphasis is placed on the selection of appropriate interlacing meshes and the ability of rectangular meshes to treat non-rectangular boundary conditions. Numerical examples demonstrate in detail the efficiency, accuracy and stability attainable in solving various engineering problems. It is concluded that both interlacing and irregular meshes are more efficient than the usual rectangular ones to study rectangular, circular and elliptical plates. However, the irregular mesh technique is superior in treating non-rectangular boundaries.

The objective of this work is to develop a general and predictive hydrate model for hydrates in equilibrium with brines. The model developed, only needs the ionic radius, the charge on the ions and the concentration of each salt to predict the inhibition effect of the salts in the brines. The model has proven to be consistent with experimental data.

Three-dimesional thermoelasticity solutions are presented for the dynamic analysis of an axisymmetric cross-ply laminated shallow panel subjected to thermal load. The panel is simply supported at four sides and has a finite length. Three-dimensional equations of motion, which are coupled partial differential equations, are reduced to system of differential equations with constant coefficients by means of the trigonometric function expansion in circumferential and axial directions. The resulting ordinary differential equations are then solved by the Galerkin finite element method. Numerical results show that fiber orientation strongly influences the stresses in a single layer panel. When the fibers are aligned circumferentially, the hoop stress becomes large. This is due to the large difference between the radial and circumferential coefficients of thermal expansion when the fibers are oriented circumferentially. Finally, numerical examples are presented for (0), (0/90) and (0/90/0) degrees of laminations stacking and those are compared with the results found in literature.

Morphological studies have been considered very important in fungal fermentation. Morphological parameters and the type of mycelia present (free mycelia without any branches, branched mycelia and branched mycelia with conidiophore) were measured to correlate citric acid production with the morphology of Aspergillus niger. We observed that morphological parameters and the type of mycelia present varied with substrate concentration. They also depended on the type of substrate (molasses and glucose) used. Maximum citric acid (6.8 kg/m3) was produced when branched mycelia with conidiophore were the most available mycelia present in the broth of molasses containing medium. Citric acid was produced in lesser quantity (1.82 kg/m3) when glucose was used. The addition of methanol doubled citric acid production, increased slightly the percentage of branched mycelia with conidiophore and conditioned the surface of the mycelia.

Cloud points of aqueous solutions of poly ethylene glycol (PEG)/inorganic salts are measured using the particle counting method. The average molecular weights of PEG are 3,350 and 10,000. NaH2PO4, Na2HPO4, KH2PO4 and K2HPO4 are the inorganic salts used. Measurements are done for different weight percentage of PEG and salts in water.

The objective of this study was to investigate the theoretical feasibility of using supercritical fluid extraction of Mannitol from plane tree leaf as an alternative technology in the pharmaceutical industry. Simulation of an extraction column using dense liquid and supercritical carbon dioxide was modeled involving partial differential equations, using orthogonal collocation on finite elements. The important solvent extraction parameters such as the partition coefficient, mass transfer coefficient, dispersion coefficient, molecular diffusion and extraction efficiency (the amount of Mannitol extracted versus the amount of solvent used) were investigated as a function of the dimensionless Reynolds and Peclet numbers in order to optimize the extraction column geometry and the carbon dioxide operating conditions. Results demonstrate that the supercritical extraction is a viable technique for Mannitol production and that the process conditions for a large commercial extraction system do not require a high temperature in order to obtain high extraction efficiency. However, at low pressure, the solubility of the Mannitol in carbon dioxide would limit the success of the extraction process and at very high pressures the extraction technique may not be economically feasible. To investigate the authenticity of the mathematical model, the experimental data for the desorption of hexachlorobenzene from soil was compared with the theoretical results of this research. The model is able to predict the experimental data quite well without any adjustable parameters.

The present study is concerned with measuring and simulating soot and flame structure of a non-premixed gas fired swirl stabilized combustor incorporating a two-step soot model. Soot mass fractions have been measured by gravimetric method. Fluent CFD software has been employed for numerical predictions and the effect of two combustion models on flame structure and soot production are investigated. Both finite rate model with eddydissipation concept and flamelet approaches are employed to model the combustion process and the accuracy of each model is compared with the experimental data. In terms of turbulence modeling, the full Reynolds stress transport model is employed to calculate the turbulent characteristics of highly swirling flow. Measurements and computations are performed for different cases by varying the equivalence ratio, the inlet air temperature and the combustor wall temperature. The numerical predictions and experimental measurements show that soot generation strongly depends on the equivalence ratio and the inlet air temperature, as well as it is also affected by the combustor wall temperature. The numerical results show the significant influence of combustion models on soot formation/oxidation, when investigating the non-premixed natural gas/air flame. The comparison of calculated results against the experimental measurements for rich combustion reveals the superiority of flamelet model over the finite rate model.

In lecithin production unit of Jahan Vegetable Oil Co. (JVOC), Karaj, Iran, studies are made for the lecithin produced by hexane extracted soybean oil, with the standard specification (except for hexane-insoluble (HI) materials), which is above 0.3% in crude lecithin. HI materials in lecithin are detrimental to clarity as it can cause haziness in fluid lecithin and usability in specific application. Analyses of crude oil before and after filtration indicated that filter plates do not effect lyre move of the impurities of residual fines, seed fragments and metal particles. Crude oil has more HI materials during degumming than before degumming. Analyses of oil and lecithin during processing steps showed increase in HI and toluene-insoluble (TI) materials where ever water was added. Degumming water contained about 360-1330 ppm salt (T.S), which contributed to the HI mateials. About 30- 38% of HI are salt and the rest are water-soluble most probably sugar. Salt free water and efficient filtration of oil, as tested in laboratory degumming process, decreased the HI matters in lecithin to below 0.3%.

Coke formed on the internal skin of the reactor tube, limits the on-stream time of cracking furnaces. On the basis of the plant output information and insight in the mechanisms for coke formation in pyrolysis reactors, a mathematical model describing the coke formation has been derived. It consists of four reactions for coke production, assuming that the sources of coke formation are ethylene, propylene, butadiene and aromatics. The coking model was combined with two other models, the kinetic model for the pyrolysis of naphtha and a reactor model. The combination of these models allows accurate prediction of the run length of the reactor with a limitation value of 1100 °C for tube wall temperature. In this model, ethylene, propylene, butadiene and aromatics have been postulated as the coke precursors, 30,10,10 and 50 percent, respectively.

In most previous investigations, journal bearing performance characteristics have been analyzed using different simplified assumptions. The purpose of this study is to eliminate most of those assumptions, using computational fluid dynamics (CFD) techniques to solve the exact governing equations. The bearing has a finite length and operates under incompressible laminar flow and steady conditions. Numerical solutions of the full threedimensional Navier-Stokes equations, coupled with the energy equation in the lubricant field and the heat conduction equations in the bearing and the shaft are obtained. Considering the complexity of the physical geometry, conformal mapping is used to generate an orthogonal grid and the governing equations are transformed for use in the computational domain. Discretized forms of the transformed equations are obtained by control volume method and solved by SIMPLE algorithm. Cavitation effects are also considered by introducing an appropriate three-dimensional cavitation model. In order to study the effect of main parameters on thermohydrodynamic behavior of journal bearings, solutions are obtained for different values of the eccentricity and radial clearance and also for different values of the rotational speed of the shaft. To validate the computational results, comparison with the experimental data of other investigators is made, and reasonable agreement is obtained.

The new model for structure II hydrates in the ternary mixtures methane+water +1,4-dioxane, has been applied to the system methane+water+acetone. Similarly to 1,4- dioxane, acetone also has promoting effects up to a concentration of about 6-mole %. Beyond this concentration, this effect decreases and, gradually, acetone starts to change nature from a gas hydrate-promoting agent into a gas hydrate inhibitor. Based on minimization of the difference between experimental and calculated equilibrium temperatures, the Kihara parameters of acetone have been obtained. The results are in good agreement with the experimental data. The ability and accuracy of this new model are also compared with an existing model.

The solubility of silver nitrate in ethanol was determined at various temperatures. The growth kinetics of silver nitrate in ethanol were then determined using initial derivaties of temperature and desupersaturation in a mixed–batch crystallizer. For more accuracy, high order polynomials were fitted to the solubility, temperature and desupersaturation data. The conventional modes were therefore modified to allow for these high order relashionships.

Potassium chloride, as an osmotic agent and poly methacrylic acid, as a waterswelling additive have been incorporated in polydimethyl siloxane. By using caffeine as a model drug, the results of release experiments from two systems have been compared. Because of osmotic rupturing pseudo-zero-order release kinetics preceded by marked burst effect were observed. Since osmotic pressure of PMAA is higher than that of KCl, drug release rate from PMAA-PDMS matrices is higher than that from KCl-PDMS matrices. Since KCl is release along with the drug, but PMAA is not, therefore water-swelling additives may provide efficient drug release without releasing undesirable substances.

The three-parameter Cubic Simplified Perturbed Hard-Chain (CSPHC) equation of state (EOS) developed by Wang and Guo (1993) is improved by applying the classical critical point constraints, modifying the attractive term, and introducing the volume translation technique. All the pure component parameters in the modified CSPHC EOS have been generalized through correlating with molecular weight, specific gravity/acentric factor. The proposed modified CSPHC (CSPHC-M) EOS has been extensively tested on pure substances. Parallel comparison of the vapor pressure and phase density calculation with the original CSPHC, PR-Mathias, PR-Twu and PR equations of state over a wide range of reduced temperature and pressure have been performed. The comparison indicates that CSPHC-M EOS is a reliable theoretical-based tool for engineering calculations.

Fuzzy systems are used for modelling of explosive cutting process of plates by shaped charges. The aim of such modelling is to show how the depth of penetration varies with the variation of important parameters. It is also demonstrated that singular value decomposition (SVD) can be effectively used to fine tuning of such fuzzy models in a noniterative process. Such application of SVD will highly improve the performance of fuzzy systems to model the very complex process of explosive cutting of plates by shaped charges.

In this paper, internal ballistics of solid rocket motors (SRM), in which the grain is burned from inside (inner burning surface) or from both inside and outside (inner and outer burning surfaces), is numerically simulated. The solution domain includes two passages and a converging-diverging nozzle. It is discretized using a control-volume finite-element method. Governing equations of the quasi one-dimensional Euler flow are integrated over each control volume. The flux-vector components are related to the nodal values using a physical influence scheme. Erosive burning is incorporated in the flowfield calculation using a quasisteady model. In cases with inner and outer burning surfaces, the resulting system of equations deviates from a block tri-diagonal one. Therefore, special care is needed for the efficient solution of this system of equations. To evaluate performance of the present algorithm, transient flow fields of several SRMs with different burning surfaces are simulated, and the results compared with the experimental data and numerical results. The excellent agreement observed in all cases validates the algorithm and approves its accuracy. For SRMs with inner and outer burning surfaces, possibility of their modeling with an equivalent motor is also investigated. In addition, a SRM with area transition along the grain is simulated to demonstrate the general capability of the present code.

In this work, a new procedure for calculating the individual ionic activity coefficients from the emf data is presented. These data are collected by the Ion Selective Electrode (ISE) method. The potentials of the ISE’s against a single junction reference electrode are recorded and used to generate the individual ionic values for electrolyte solutions. The liquid junction potential is calculated using an approximation made by Henderson. The Khoshkbarchi-Vera equation, which is based on the Pitzer’s model, is introduced to predict the individual ionic as well as the mean ionic activity coefficients of electrolytes.

In this paper, the time-optimal control for point-to-point motion of robotic manipulators, with fixed initial and final states, bounded control inputs and jerk constraint for entire path is presented. First, the jerk constraint with respect to state variables is derived. Afterwards the dynamic equations of robotic manipulator in state space form and jerk constraints discretized by forward difference technique. Thus the time-optimal control problem is formulated as a constrained parameter optimization problem. The MATLAB optimization toolbox is used to obtain the solution of the constrained parameter optimization problem. The proposed method can help us to implement the time-optimal control problem with bounded inputs and jerk constraint. Finally, the above-mentioned method is implemented for a 2R planar robotic manipulator. Simulation results show a smooth trajectory for robot motion when the jerk is limited, which can effectively reduce mechanical wear at joints.

The vapor-pressure osmometry (VPO) method was used to measure activities of water for aqueous polymer solutions. The effects of temperature, molecular weight of polymers and their concentrations on the measured activity of water were considered. Using the experimental results, Flory-Huggins interaction parameters for solvent-polymer and polymer-polymer, and the solubility parameters of the used polymers were determined. A simple method was also utilized for determining the Flory-Huggins interaction parameter for solvent in the mixtures of two polymers, polymer(a) and polymer(b). For each case, the mean relative absolute error between calculated and experimental data are reported and it is shown that at studied concentration ranges, the calculated interaction parameter values for calculating thermodynamic properties, are appropriate.

Free vibration of orthotropic and cross–ply laminated hemispherical shells using elasticity approach is studied. The Navier type equations are transformed into partial differential equations with constant coefficients in radial direction, assuming that the ratio of the thickness to mean radius of each lamina of the shell is small and hence can be neglected with respect to unity. The partial differential equations are reduced to ordinary differential equations, by applying Galerkin method, using Legendre polynomials along the meridian direction. The resulting ordinery differential equations are solved exactly for each layer. Connecting all of the exact solutions by means of appropriate continuity conditions and by using a method of successive approximation the solution of the problem is achieved. Convergence tests have been carried out to demonstrate the veracity of the approach. Numerical results are presented and compared with the latest results found in the literature.

In this article, a full temporal and spatial description of discharge for pure nitrogen gas in a nearly uniform electric field is reported. Results of simulation given provide a full understanding of the discharge at different stages of the ionization process. Effects of the primary energetic electrons and the secondary electrons are clearly shown at each stage of the ionization growth being followed in the discharge gap. Presented are the local electric field distribution and temporal behavior of the streamers at each point of the discharge medium along with the secondary processes affecting ionization growth.

The 2D hypersonic real gas flow has been analyzed on an adaptive unstructured grid using Roes Flux Difference Splitting and AUSM schemes. In high temperature and hypersonic regime, the flow is extremely compressible and ideal gas assumption is not valid. In fact in these flows, due to changes in the flow properties, composition of fluid elements will also change. To solve steady and unsteady 2D Euler equations for real gases, assumption of a general equation of state for real gases in equilibrium is considered. We use an unstructured Delaunay triangulation and adapt it in high gradient areas. Results are compared with known numerical and exact solutions. The scheme is convergent, and provides accurate results with fairly small number of cells due to adaptation and application of the algorithm to one dimensional shock tube and blunt body problem shows its quality and robustness.

Mixture ratio (oxidant/ fuel) in combustion chamber has influence on combustion and thermodynamic properties as thrust and impulse; therefore, calculation of this parameter in the injector plate of liquid propellant rockets is very important. We have proposed an experimental method in which water and oil (simulating oxidant and fuel) passed from injection plate enter in elemental vessels. A computer code based on existent theoretical methods is developed and its results are compared with experimental results.

The use of adaptive feed-forward controllers has proven to be a very successful strategy for controlling noise and vibration in a variety of applications. One reason is that the feed-forward controller is an open loop controller, which can be designed to cancel the undesired noise in a position with any accuracy. However, the feed-forward controller requires an input signal, called a reference signal, correlated to the noise source. Consequently, a single reference controller can only reduce noise radiated from a single noise source. In many applications, there is a need to attenuate noise produced by several noise sources. In this paper, three different structures, single, modulating and individual controller, for multiple input feed-forward controllers have been studied and some design aspects are investigated.

In this paper, Euler equations are solved to simulate compressible flow on unstructured moving grids. Solution domain is discretized using control-volume finiteelement method. This method is benefited from the power of finite element in discretizing solution domain, and the capability of finite volume in conserving physical quantities. For the evaluation of flux vector components at the control-volume surfaces, we employed the fluxdifference scheme of Roe, modified for moving grids. Geometric conservation laws are implemented carefully to prevent solution errors produced by grid movement. To demonstrate the accuracy of the algorithm in solving fluid flow problems on moving grids, a number of test problems have been carried out.

Near field circular jet is studied experimentally at discharge Reynolds number range of 21000 to 100000. The effect of Reynolds number on the initial boundary layer mean velocity profile is negligible, but is significant on the exit turbulent velocity profile, extend of the partial self-reservation zone, spread of the shear layer and the viscous shear stress. With decrease Reynolds number the entrainment rate decreased.

A mathematical model has been developed and simulated to describe contaminated soil bioremediation. The model equations consist of a system of three nonlinear partial differential equations. Dimensional analysis of the model equations has been performed, and solution of these equations has been conducted by an implicit finite difference method. A computer program is runed for solving the model equations and by using this program, the influence of the principal parameters (porosity, soil aggregate radius, and partition coefficient of the substrate) on the fate of chemicals has been studied. The rates of substrate, oxygen diffusion and biodegradation rate have been found to be the controlling mechanisms for remediation in the aggregates.

Terrace wall arrangement is one of the most common arrangements for methanesteam reforming reactor furnaces. In this work, a mathematical model of heat transfer in terrace wall furnaces has been developed. The model has been coupled with a reliable chemical reaction model to predict the behavior of an industrial steam-reforming reactor. The heat transfer model is similar to the zone method models, which considers heat conduction of the furnace walls in addition to the convective and radiative heat transfer. Among different operating variables, the effect of thermal conductivity of the furnace wall and the height of the burners on the performance of the reactor have been also studied.