Iranian Journal of Chemistry and Chemical Engineering
Volume:29 Issue: 1, Jan-Feb 2010

In this research mass transfer coefficient under jetting regime in different directions (from dispersed to continuous and continuous to dispersed phase) has been studied using an experimental setup. n-Butanol-succinic acid-water with low interfacial tension has been selected as experimental chemical system. The effects of various parameters such as jet velocity, nozzle diameter and the height of the continuous phase above the nozzle, on mass transfer coefficient have been investigated. A correlation has also been derived in order to predict the mass transfer coefficient as a function of physical properties of both phases and aforementioned parameters. Based on the experimental results, mass transfer coefficient increases with an increase in the nozzle diameter and jet velocity, while increasing the height of the continuous phase above the nozzle decreases the mass transfer coefficient. These results may reveal the importance of mass transfer during the jet formation and breakage.

A semi-batch crystallization system is used to determine growth kinetics and morphology of barium carbonate crystals, under a constant pH value and constant temperature in the various relative supersaturations. Results show that crystal growth rate satisfies a first-order kinetic expression at high relative supersaturation, while at relative supersaturation values lower than 3, the kinetic expression is second order. The crystal growth of barium carbonate follows the Burton, Cabera, and Frank mechanism by the kinetic expression G=2 tanh (/). The kinetic parameters obtained from low to high supersaturation ratio by using a numerical methods are =9.5×10-7 ms-1 and β=1.35×10-2. The investigations show that the pH values and relative supersaturation of solutions have an important role on the crystal morphology of barium carbonate and the forms of observed crystals are floc, candy-like, pillar-like, olivary and olivary with end dendrite with respect to operating condition.

The present paper describes the designing of a thermally and economically optimum mechanical draft counter-flow wet cooling tower. The design model allows the use of a variety of packing materials in the cooling tower toward optimizing heat transfer. Once the optimum packing type is chosen, a compact cooling tower with low fan power consumption is modelled within the known design variables. Moreover, a simulation model of the cooling tower is developed for studying the tower’s performance as the main component of a water cooling system. The model also allows the influence of the environmental conditions on the thermal efficiency of the cooling tower to be considered. The thermal performance of the cooling tower is simulated in terms of varying air and water temperatures, and of the ambient conditions. The model is tested against experimental data. The suggested design and simulation algorithms of cooling tower are computed using Visual Studio.Net 2003 (C++).

In the present work an attempt has been made to study the effect of the twisted tapes as bed internals, on the performance of the gas-solid fluidized beds. Experimental investigation has been carried out in cylindrical column with and without twisted tapes. Twelve numbers of twisted tapes of three different widths with four values of the twist ratios for each width were studied at different static bed heights. Twist ratio (y) is the ratio of axial distance for 1800 rotation of the tape (H) and the width (W) of the twisted tape. By using twisted tape the change in pressure drop, fluctuation ratio and expansion ratio have been studied as compared to “without twisted tape”. Incorporation of twisted tapes as baffle decreases the fluctuation ratio and expansion ratio thereby improving the fluidization quality as compared to the “without twisted tape”. However the increase in pressure drop due to presence of twisted tape is only marginal and of the order of, 5.25 to 14.9 percent over that of without twisted tapes. The maximum decrease in luctuation ratio (r) for the tapes of various twist ratio has been found to be 11.6 to 20.5 percent based on the case of “without twisted tape”, thereby indicating a corresponding improvement in the quality of fluidization with reduced degree of bubbling and slugging. Quantitatively the maximum decrease in R for the twisted tapes of various twist ratios has been found to be 17 to 23 percent based on the case of “without twisted tapes”. However, the pressure drop, fluctuation and expansion ratio were in general found to decrease with decrease in twist ratio of a twisted tape. Different correlations have been developed for pressure drop, fluctuation ratio and expansion ratio and compared with their corresponding experimental values.

A method based on Electrical Capacitance Tomography (ECT) and an improved Least Squares Support Vector Machine (LS-SVM) is proposed for void fraction measurement of oil-gas two-phase flow. In the modeling stage, to solve the two problems in LS-SVM, pruning skills are employed to make LS-SVM sparse and robust; then the Real-Coded Genetic Algorithm is introduced to solve the difficult problem of parameters selection in LS-SVM then. In the measurement process, the flow pattern of oil-gas two-phase flow is identified by using fast back-projection image reconstruction and a fuzzy pattern recognition technique and the void fraction is computed using the void fraction model corresponding to the identified flow pattern. Experimental results demonstrate that both the improvement of LS-SVM and the parameter optimization are effective. The results also show that the real-time performance of the proposed void fraction measurement method is good, and the measurement precision can satisfy the application requirement.

A numerical framework has been proposed to model the interacting effects of mixture non-ideality and mass transfer on hydrodynamics of a multiphase system using CFD methods. Mass transfer during condensation and vaporization is modeled by chemical potential at the liquid-vapor interface. Species mass transfers are related to the diffusion at the interface which in turn is related to the concentration gradients at the interface. A finite volume scheme is used to solve the equations of motion. Since the thermodynamic non-ideality of the system has been taken into account, the equilibrium calculations were performed using the fugacity coefficient definition for both the liquid and gas phases. The obtained results and their comparison against experimental data show that the proposed framework can simulate the hydrodynamic behavior of multi-component multi-phase systems with thermodynamic non-ideality.

Pore network modeling uses a network of pores connected by throats to model the void space of a porous medium and tries to predict its various characteristics during multiphase flow of various fluids. In most cases, a non-realistic regular lattice of pores is used to model the characteristics of a porous medium. Although some methodologies for extracting geologically realistic irregular networks from pore space images have been presented, these methods require some experimental data which are either unavailable or costly to obtain. 3-dimensional image or 2-dimensional SEM images are among these types of data. In this paper a new irregular lattice algorithm for the construction of these models is proposed. Furthermore, based on some statistical and analytical studies, a fast and reliable procedure is suggested to find the optimum system parameters which may lead to the construction of the smallest cubic irregular pore network model that can be a representative of the target porous medium. The performance of the proposed method has been studied through the construction of an irregular lattice model representing a core plug based on its available experimental data. This study shows that the obtained model can reliably predict the network construction parameters.

Simultaneous capillary dominated displacement of the wetting and non-wetting phases are processes of interest in many disciplines including modeling of the penetration of polluting liquids in hydrology or the secondary migration in petroleum reservoir engineering. Percolation models and in particular invasion percolation is well suited to characterize the slow immiscible displacement of two fluids when both the gravity and viscous effects are negligible. In particular, the characteristic of the percolating cluster and the other important percolation properties at the breakthrough can be inferred. However, with the inclusion of the gravity forces, the behavior may change. For example, as the magnitudes of the gravity forces are comparable to the capillary forces, we have observed a transition in the structure of the interface (i.e. invasion front) depending on the dimensionless Bond number (i.e. ratio of gravity to capillary forces).We have taken a numerical study of the displacement of two immiscible fluids in the presence of the gravity force in a network of random pores. The main contribution is to investigate the effect of heterogeneity by considering various throat size distributions. We consider the injection to take place from one side of the system and displace the displaced fluid from the other side. The condition of the stability or instability of the front (or interface) is observed to be dependent on the dimensionless bond number as well as the heterogeneity of the system.

In order to increase the efficiency of the conveyance of the granular solids, a new experimental set-up is designed. The test rig has longitudinal trapezoidal slots in its conveying pipes. Through experimentation, a correlation for friction factor in terms of solid mass flow rate, fluid flow rate and Froude number is presented. It is shown that the mixture friction factor for pipes with inner trapezoidal slots is 40% smaller than that of pipes with inner rectangular slots. As a result, the arrangement helps to convey materials to longer distances for a given pressure setting.

An improved model of mud dispersion has been introduced in this work. The advantages of this model consist of a new analytical correlation for dispersivity by using resistivity log data and using a new aspect of capacitance dispersion model. Mathematical formulations were expressed, solved by numerical model taking advantage of actual log and formation data. Achieved results yielded reasonable values and trends which can be used to predict the drilling fluid concentration near wellbore region and interpret the well log data. In comparison with the previous models (Civan and Engler, 1994; Donaldson and Chernoglazov, 1987), this model uses more reasonable data and assumptions making it closer to real conditions.

In this work, studies of underground gas storage (UGS) were performed on a partially depleted, naturally fractured gas reservoir through compositional simulation. Reservoir dynamic model was calibrated by history matching of about 20 years of researvoir production. Effects of fracture parameters, i.e. fracture shape factor, fracture permeability and porosity were studied. Results showed that distribution of fracture density affects flow and production of water, but not that of gas, through porous medium. However, due to high mobility of gas, the gas production and reservoir average pressure are insensitive to fracture shape factor. Also, it was found that uniform fracture permeability distribution enhances communication within reservoir and consequently more pressure support is obtained by water bearing of aquifer. Effect of aquifer on the reservoir performance was studied, and it was found that an active aquifer can reduce condensate drop out around the well bore. On the other hand, water invasion is an important issue which may kill the well. Results showed that use of horizontal wells is superior to vertical wells in order to avoid detrimental effects of active aquifer.

The solubility of CO2 in the primary, secondary, tertiary and sterically hindered amine aqueous solutions at various conditions was studied. In the present work, the Modified Kent-Eisenberg (M-KE), the Extended Debye-Hückel (E-DH) and the Pitzer models were employed to study the solubility of CO2 in amine aqueous solutions. Two explicit equations are presented to evaluate the concentration of H+ as well as the equilibrium constants of protonation reactions for the tertiary and sterically hindered amine aqueous solutions. Using the M-KE model, the equilibrium constants of protonation reactions of amines were correlated in terms of temperature, CO2 partial pressure and amine concentration. Also the E-DH and Pitzer models were used to correlate the solubility of CO2 in MDEA aqueous solution. The binary interaction parameters for the models studied in this work as well as the parameters for the equilibrium constants of protonation reactions were obtained using the Davidon-Fletcher-Powell (DFP) minimization method. The results show that the M-KE, E-DH and the Pitzer models can accurately predict the corresponding experimental data. Although the solubility data for CO2 in amine aqueous solutions have been reported in the literature to a large extent, accurate data are required to model the CO2 absorption process. Therefore, two criteria for the tertiary and sterically hindered amines were presented using the M-KE model to screen the experimental data.

In this work, experimental kinetics data of methane hydrate decomposition at temperatures ranging from 272.15 to 276.15 K and at pressures ranging from 10 to 30 bars were modeled by using chemical affinity. This model proposed a macroscopic model which is independent of any intermediate mechanism like heat or mass transfer. The results show there is good agreement with experimental data. Also the two parameters of model were calculated and correlation coefficient of model is higher than 0.9.

Since NOx family, one of the most important causes of air pollution, is the primary source of acid rains, ozone layer depletion, and breathing disorders, mitigation of these pollutants is now a global concern. In the off-gases of internal combustion engines running with oxygen excess, non-thermal plasmas (NTPs) have an oxidative potential, which results in an effective conversion of NO to NO2. This paper aims at studying the methods of mitigating and eliminating NOx in an atmospheric and non-thermal condition by means of plasma reactors. It examines some key parameters such as temperature, space velocity, voltage, and propane/NOx mole ratio. The results showed that, the space velocity in the 11500-2300 h-1 domain did not show any significant results on the NOx conversion. Our findings also revealed that the optimal conditions for conversion of NO into N2, O2, and NO2 are temperature (180 ◦C), voltage (10 kV), and equal mole ratio of propane in NOx. In this condition, the optimal conversion efficiency of 78% and the standard deviation of 12% were obtained. The optimal temperature, voltage, and the mole ratio of propane in NOx conversion to N2 and O2. (efficiency=53%) are 180◦C, 5 kV, and 0.3 respectively. Plasma reactor acts as primery treatment in the direct mitigation of NOx into neutral and non-poisonous molecules of O2 and N2.

Ozone modification method and air-oxidation were used for the surface treatment of polyacrylonitrile(PAN)-based carbon fiber. The surface characteristics of carbon fibers were characterized by X-ray photoelectron spectroscopy (XPS). The interfacial properties of carbon fiber reinforced polyamide 6 (CF/PA6) composites were investigated by means of the single fiber pull-out tests. As a result, it was found that IFSS values of the composites with ozone treated carbon fiber are increased by 60% compared to that without treatment. XPS results show that ozone treatment increases the amount of carboxyl groups on carbon fiber surface, thus the interfacial adhesion between carbon fiber and PA6 matrix is effectively promoted. The effect of surface treatment of carbon fibers on the tribological properties of CF/PA6 composites was comparatively investigated. Experimental results revealed that surface treatment can effectively improve the wear resistance of CF/PA6.