Sharif Digital Repository

In this study, an industrial acetylene hydrogenation unit is simulated utilizing three available kinetic models. The results are compared against six-day experimental data and the best model is selected. Effects of feed temperature and the amount of injected hydrogen on ethylene selectivity are also studied. According to the simulation results, the unit is not working under its optimum conditions. Furthermore, by reduction of the hydrogen flow rate to 52 kg/h, process selectivity is increased. In addition, a new approach is proposed to modify the hydrogenation process and reduce undesired by-products. In the simulation of the modified process, hydrogenation reactors temperature, hydrogen... 

It is important to test the attitude control systems on satellites before they are launched in space. Traditionally this has been done by dropping the satellite, and firing the thrusters before the satellite makes a soft landing in a net. This method only allows a few seconds of testing and does not lend itself to the measurement of pointing accuracy. A better method is to mount the satellite on a spherical air bearing. In this paper behavior of a semi spherical air bearing is studied and analyzed in various conditions. These bearings are used in different applications such as simulation of approximately frictionless condition which is the satellite's situation in space. In this analysis... 

In this study, the local composition based models such as the Wilson, the nonrandom two-liquid (NRTL), and the Wilson-NRF have been applied in correlation and estimation of density, viscosity, and surface tension of biodiesels. The thermodynamic models have been used in correlating the thermophysical properties for 215 experimental data points. These models have the interaction energy between each pair that is considered as adjustable parameters. To decrease the number of these adjustable parameters, it is assumed that the biodiesels are composed of two hypothetical components. The average absolute deviation (AADs) of the correlated density of biodiesels for the Wilson, the NRTL, and the... 

In this article, a new hydration model has been proposed to study the phase behavior of aqueous electrolyte solutions. The proposed model distinguishes between an anion and cation in the electrolyte solution. The model has three adjustable parameters which can be obtained using the experimental data of the mean ionic activity coefficients for 113 electrolyte solutions. The results of the proposed model were compared with those of obtained from the Pitzer, the E-NRTL and the E-Wilson models. The results showed that the proposed model can accurately correlate the mean ionic activity coefficients of the aqueous electrolyte solutions than the other models. Also, the proposed model was used in... 

An approach is proposed to control transient response of fractional order systems with maximum permissible control signal. This goal is achieved using a newly suggested characteristic ratio assignment method. Based on the proposed method, the generalized time constant τ and the characteristic ratios including their pattern, an adjustable parameter β, and the product of two successive characteristic ratios ρ are determined such that predefined level of overshoot and time specification of closed loop step response are obtained while the control signal is confined to a pre assigned maximum magnitude. The raised issue is solved by defining an optimization problem in which the design parameters... 

An analytical model is proposed to study the effect of particle size on melting enthalpy and entropy of metallic nanoparticles (NPs). The Mott's and Regel's equations for melting entropy in the combination of core average coordination number (CAC) and surface average coordination number (SAC) of freestanding NPs are considered. Clusters of icosahedral (IC), body centered cubic (BCC), and body centered tetragonal (BCT) structure without any vacancies and defects are modeled. Using the variable coordination number made this model to be in good agreement with experimental and molecular dynamic (MD) results of different crystal structures. The model predicts melting entropy and enthalpy of... 

The current study was aimed at developing a package of “model + algorithm” for the design of resin in pulp (RIP) and carbon in pulp (CIP) processes of gold, uranium, and base metals. For this purpose, we first formulated a double-resistance model for irreversible adsorption (accompanied by chemical reaction) in CSTRs, and modified the McKay et al. semi-analytical model for reversible uptake in a similar system. We then devised two algorithms for the design and optimization of reversible and irreversible RIP and CIP cascades. The developed algorithms were applied on the extraction of copper, uranium, and gold. The packages are able to specify the optimum number of stages, reactor volume (V),... 

The minimum entropy (ME) control is a chaos control technique which causes chaotic behavior to vanish by stabilizing unstable periodic orbits of the system without using mathematical model of the system. In this technique some controller type, normally delayed feedback controller, with an adjustable parameter such as feedback gain is used. The adjustable parameter is determined such that the entropy of the system is minimized. Proposed in this paper is the PSO-based multi-variable ME control. In this technique two or more control parameters are adjusted concurrently either in a single or in multiple control inputs. Thus it is possible to use two or more feedback terms in the delayed feedback... 

A steady-state equilibrium-stage model based on MESH equations was proposed to simulate saline extractive distillation columns. The interaction parameters between each component of water-CaCl 2 and ethanol-water were obtained from mean ionic activity coefficients and vapor-liquid equilibrium (VLE) experimental data. Additionally, the interaction coefficients for the ethanol-CaCl 2 pair were fitted to experimental VLE data which were reported by Nishi for the ethanol-water-CaCl 2 system. It should be noted that adjustable parameters between each pair were considered to be temperature dependent. The results confirmed that the proposed model could accurately predict the experimental... 

In this study the kinetic modeling of visbreaking reactions for a number of vacuum residue feeds was investigated using available experimental data from the literature. A continuous lumping model was developed for kinetic analysis of visbreaking reactions. The normalized boiling point was used to describe each feed as a continuous mixture and the concentration distribution of the mixture would change under reaction conditions. A continuous model with five adjustable parameters was used to describe visbreaking reactions, and these parameters were optimized for each feed for reaction temperatures in the range of 400-430 C using available experimental data. The model was able to accurately... 

The minimum entropy (ME) control is a chaos control technique which causes chaotic behavior to vanish by stabilizing unstable periodic orbits of the system without using mathematical model of the system. In this technique some controller type, normally delayed feedback controller, with an adjustable parameter such as feedback gain is used. The adjustable parameter is determined such that the entropy of the system is minimized. Proposed in this paper is the PSO-based multi-variable ME control. In this technique two or more control parameters are adjusted concurrently either in a single or in multiple control inputs. Thus it is possible to use two or more feedback terms in the delayed feedback... 

In this paper, an industrial ethylbenzene production unit has been simulated and the results are compared against five-day experimental data. According to prevailing unit condition, i.e. recycled ratio of benzene, benzene selectivity, and energy consumption, the unit is not working under its optimum conditions for minimum cost of ethylbenzene production. In the current design, high amount of benzene recycle (6:1) causes to have an additional cost due to fractionation of ethylbenzene from benzene. A new approach is proposed to modify the benzene alkylation process and reduce the unit's energy consumption. In the newly designed scheme, two double-bed alkylation reactors converted into four... 

In this research, thermodynamic modeling and activity coefficient prediction of KCl in the (water + formamide/glucose/proline) mixed solvent systems were reported. Thermodynamic study was performed using the potentiometric data based on extended ion interaction Pitzer-Archer model in various mixed solvent systems containing 0, 10, 20, 30 and 40% mass fractions of formamide and glucose at T = 298.2 K and 0, 2.5, 5.0, 7.5 and 10.0% mass fractions of proline at T = 308.2 K and ambient pressure over ionic strength ranging from 0.0014 to 3.9579 mol·kg- 1. The adjustable parameters were determined and the obtained results were then interpreted based on extended ion interaction Pitzer-Archer model.... 

In this work, PEG 1500, MgSO4 and water were used to create an aqueous two-phase system and the effect of temperature was surveyed by obtaining binodal data and equilibrium data at 35, 40 and 45 C; compositions of mixture were obtained by atomic absorption spectrometer and refractometery method. Results showed that with increasing temperature, the solution tends to attain a two-phase region and the slope and length of tie lines increases. Modified Wilson equation was used to correlate this system, adjustable parameters were evaluated directly from experimental data and good agreement with experimental data was obtained. The overall average relative deviation was found to be less than 6%  

The performance of friction dampers to mitigate the wave-induced vibrations in jacket-type offshore platforms has been investigated in this study. Due to the random nature of ocean waves, a full stochastic analysis method has been used to evaluate the response of the structures equipped with these devices. A stochastic linearization technique has also been used to take the nonlinear behavior of these hysteretic dampers into account. At last, the developed mathematical formulation has been applied to evaluate the response of realistic models, and to find out the optimal values for the adjustable parameters of the friction dampers to dissipate the wave induced vibrations of the platforms. ©... 

Experimental values for surface tension of single and mixed electrolyte solutions were correlated using the models based on the perturbation theory. The Mean Spherical Approximation (MSA) model, coupled with the Ghotbi-Vera (GV) and the Mansoori et al. (BMCSL) equations of state, were used to correlate the experimental values of the surface tension. The results showed that the models can favourably correlate the experimental values for single electrolyte solutions. However, it was observed that the GV-MSA model can more accurately predict the surface tension for single electrolytes, especially at higher concentrations. Two different expressions for concentration dependency of cation hydrated... 

Novel type of two-impinging-jets loop reactor (TIJLR) has been proposed and tested successfully for the solid-liquid catalytic reactions. The TIJLR was tested using the catalytic reaction of isomerization of D-glucose to D-fructose by immobilized glucose isomerase catalyst as a typical model system of solid-liquid catalytic reactions. The TIJLR is characterized by a high intensity reaction chamber, which is separated by a perforated plate from other parts of the reactor. The perforated plate was used as a filter to keep the catalyst particles within the reaction chamber. A compartment model with two adjustable parameters was considered to describe the pattern of flow within the reaction... 

In this investigation, neural networks were used to predict pressure drop of CuO-based nanofluid in a car radiator. For this purpose, the neural network with the multilayer perceptron structure was used to formulate a model for estimating the pressure drop In this way, different concentrations of copper oxide-based nanofluid were prepared. The base fluid was the mixture of ethylene glycol and pure water (60:40 wt%) which usually used as the cooling fluid in automotive industries. The prepared nanofluid samples were used in a car radiator and the pressure drop of nanofluid flows in the system at different Reynolds were measured. The main purpose of this study was developing the optimized... 

A reliable model was used to describe the interfacial tension, composition, and density of the liquid-liquid interfaces of water-hydrocarbons. The parachor model was combined with the equality of the chemical potential of components at the interface and the bulk liquid. The fugacity coefficient was used for computing chemical potentials. To compute the fugacity coefficients of the components, various types of equations of state (The Valderrama Patel-Teja, cubic plus association, and the simplified Perturbed-Chain Statistical Association Fluid Theory) were utilized. These models were applied to the temperature and the pressure range of (285.65–423) K and (1–3000) bar, respectively. The... 

Vapor pressure and liquid density of 20 pure alcohols were correlated using an artificial neural network (ANN) system and statistical associating fluid theory (SAFT) equation of state. The SAFT equation has five adjustable parameters as temperature-independent segment diameter, square-well energy, number of segment per chain, association energy and association volume. These parameters can be obtained by a non-linear regression method using the experimental vapor pressure and liquid density data. In continue, the vapor pressure and liquid densities of pure alcohols were estimated by using an artificial neural network (ANN) system. In the neural network system, it is assumed that thermodynamic...