Iranian Journal of Chemical Engineering (IJChE)

Abstract Struvite crystallization was investigated in the presence of different amino acids at 37°C and pH 8.0 in a continuous crystallization system. Crystal size distributions, filtration rates and morphologies of struvite crystals were determined and discussed as a function of amino acid concentration. The change of morphology depending on the amino acid type and concentration affected the filtration characteristics of struvite crystals. The crystal size distributions of the final products obtained at investigated experimental conditions were evaluated by using modified form of Abegg, Stevens and Larson (ASL) model. Thermogravimetric and differential thermal analysis have been used for thermal characterization of struvite crystals by measuring the changes in their physicochemical properties as a function of increasing temperature with time. The Coats-Redfern integral method was used to evaluate the kinetic parameters in the decomposition sequence observed in the TGA curves. In the presence of all investigated amino acids, the form of precipitate was struvite and newberyite formation was not observed.

Abstract The plane Poiseuille flow with unequal wall temperatures of an incompressible fluid having temperature dependent viscosity in the presence of transverse magnetic field is studied. The coupled differential equations of momentum and energy are solved numerically by RKF45 (Runge-Kutta-Fehlberg fourth-fifth) method. Numerical results for the dimensionless velocity profiles, the temperature profiles and the heat transfer coefficient are presented and discussed graphically for various parameters. The study provides quantitative information of interest; in general, it is observed that the maximum velocity does not occur in the middle of the channel but moves towards the upper wall as the magnetic field increases. The temperature and heat transfer coefficient increases with the increasing value of magnetic field and EPr.

Abstract The gelling of waxy crudes and the deposition of wax on the inner walls of pipelines present a costly problem in the production and transportation of oil. The object of the present study is to investigate the factors that affect the deposition of the paraffin wax on the pipe surface under different conditions using a flow loop system. A series of experiments on wax deposition from a mixture of waxy oil have been performed in a 65cm by 1cm ID flow loop in both laminar and turbulent flow regime. These experiments were done to study the effect of some important factors on the amount of deposited wax on the pipe wall. These factors consist of flow rate, residence time, wax concentration and temperature difference between mixture and pipe wall. It was found that the wax deposition increases with increasing temperature difference and residence time, but the effect of flow rate depends on flow regime. The other goal is mathematical modeling of wax deposition for a multi-component hydrocarbon mixture. The procedure for generating the model is described in detail. Finally, the results obtained from the model were compared with experimental data. It was found that there is an acceptable match between experimental and theoretical data and to some extent, this confirms the validity of the model and also the ability of the developed model to predict the wax deposition on pipelines under different operational condition.

Abstract Flow behavior of gas and agglomerates is numerically investigated in the riser based on a transient two-fluid model. The gas phase is modeled by the LES model, and the solid phase uses a kinetic theory model developed from the molecular model coupling the gas-agglomerates interaction and the agglomerates-agglomerates interaction[1]. We assumed that the ultrafine particles move as natural agglomerates rather than single particles in the riser. The energy transfer and dissipation by the instantaneous collisions between the agglomerates of ultrafine particles and gas phase and between
agglomerates-agglomerates are considered. The diameter of agglomerates is estimated based on the force model by Li and Tong[2].The distributions of velocity, concentration and diameter of agglomerates, are numerically obtained. The influence of flow and agglomerates in the different operating conditions is also analyzed. The results show
that the large agglomerates are rich in the bottom section of the bed. Thus the Fast Fourier Tranform (FFT) is used to get the fluctuated character of the agglomerates in the riser and find the dominant frequency of the agglomerates fluctuation is 0.03-1.26Hz.

Abstract The aim of this contribution is a survey of different nucleation and growth kinetics terms effects on modeling results of KNO 3 Continuous Mixed Suspension Mixed Product Removal (CMSMPR) crystallizer. By studying the four different states in modeling, results show that, although these terms for similar crystallization system and operating conditions are similar, there is very different dynamic behavior in the results such as Particles Size Distribution (PSD), crystals mean size and relative supersaturation. The main difference in modeling results is oscillating behaviors. It is shown that such behavior strongly depends on kinetics terms sensitivity to supersaturation, especially in nucleation models.

Abstract Spray dryer was used to produce potato powder from potato juice. Turning potatoes into powder will increase its substance durability, ease of transportation and the storage. The important factors affecting the powder produced by spray dryer include inlet air temperature, volumetric flow rates of feed and air. Experiments were conducted according to Taguchi’s method by considering 3 levels for each one of the mentioned parameters and 2 levels for atomizer’s nozzle diameter. The objective was to obtain the optimized process conditions for producing potato powder with desirable color. By analyzing the experimental results, the optimized conditions for producing potato powder by spray dryer were determined. It was also revealed that by adding 1 percent maltodextrin (dry mass basis) to the feed, the product’s adhesion will decrease significantly and the amount of product will be increased.

Abstract Addition of impurities has an important role on the kinetic crystallization. Therefore, influence of impurities on the crystallization kinetics of NaCl, KBr, ADP and Sucrose solutions was investigated in a fluidized bed crystallizer. The growth and dissolution rates were related to the super saturation and impurity concentration. A strong mathematical model is applied to describe crystal growth rates within aqueous solutions as a function of impurity concentration. The model tries to relate the step velocity to the useful parameters such as the surface coverage (θeq), as well as the effectiveness factor of impurity, α. When α>1, the step velocity is stopped at θeq <1 (incomplete coverage of the active sites for adsorption). In the case of α=1, the velocity reaches zero just at θeq=1 (complete coverage) but approaches a limiting value. The value of α is changed by stereo chemical factors and decreases as the supersaturation is increased. The Langmuir adsorption isotherm is used to relate the relative step velocity with the impurity concentration in solution. Experimental results show that increasing the amount of impurity concentration leads to a decrease in the step velocity. Experimental data and model predictions have been compared to show that the agreement between them is very good. The obtained results are suitable for designing and quality control of the crystallization processes in chemical industries.

Abstract In the present paper laminar flow forced convective heat transfer of CuO/water nanofluid in a triangular duct under constant wall temperature condition is investigated numerically. Sometimes, because of pressure drop limitations the need for noncircular ducts arises in many heat transfer applications. We used nanofluid instead of pure fluid because of its potential to increase heat transfer of system. In this paper, the effect of parameters such as nanoparticles diameter, nanoparticles concentration, type of nanoparticles and heat transfer comparison between nanofluid and pure fluid is studied. Comparison of convective heat transfer of nanofluid in isosceles triangular ducts with various apex angles is also presented. In this study, for the presence of nanoparticles, the dispersion model and for solving differential equations, the finite difference method is used. Numerical results indicate an enhancement of heat transfer of fluid with changing to the suspension of nanometer-sized particles in the triangular duct. Results also defined that equilateral triangular duct has a maximum heat transfer in comparison with other types of isosceles triangular duct.

Abstract The boundary layer convective heat transfer equations with low pressure gradient over a flat plate are solved using Homotopy Perturbation Method (HPM), which is one of the semi-exact methods. The nonlinear equations of momentum and energy solved simultaneously via HPM are in good agreement with results obtained from numerical methods. Using this method, a general equation in terms of Pr number and pressure gradient (λ) is derived which can be used to investigate velocity and temperature profiles in the boundary layer.

Abstract Migration of styrene monomer from polystyrene (PS) dishes was conducted during this research at temperatures of 5, 20, and 40 °C. According to the Food and Drug Administration (FDA) regulations, these experiments were performed in contact with 10%ethanol as a food simulant for the oil in water (o/w) emulsions. The dishes were filled in each of the defined temperatures and stored for 35 days. In relatively close intervals (1, 7, 15, 24, and 35 days) the amount of migration which occurred was determined by means of Head Space Gas Chromatography Mass Spectrometry (HS-GC-MS). By increasing storage time and temperature, the amount of migration was increased and in all times and temperatures styrene monomer was detected. In addition, a mathematical model based on the Fick’s second law was validated to predict migration from packaging material into the 10% ethanol. The resulted diffusion coefficients were 3.6×10-18, 4.9×10 -18, and 6×10 -18 (m2/s) in 5 ,20 and 40 °C respectively.

Abstract In this paper, the droplet size distribution of the Tehran refinery crude oil/water emulsions is determined by analyzing the photomicrographs of model emulsions which were taken by microscope. The normal distribution function is fitted to the
experimental data in order to reproduce the droplet size distribution (DSD) of the emulsions by using mean diameter and standard deviation. The effect of different parameters such as surfactant concentration, salinity, and the power of homogenizer on the droplet size distribution and mean droplet diameter of the emulsions are determined. The smaller droplet size was observed in high concentrations of surfactant and in the absence of salt, and also in emulsions which were prepared with lower power of homogenizer.

Abstract Accurate crude oil measurement at the metering station is one of main aims in an oil export terminal. The main objective is to decrease or remove any error at the metering station. It is found that crude oil temperature at metering station has significant effects on measured volume and may cause big uncertainty at the metering point, as crude oil flows through the pipeline pick up the solar radiation and heat up. This causes the crude oil temperature at the metering point to rise and higher uncertainty to be created. The amount of temperature rise depends on the main pipeline flow rate. In Kharg
Island, there is about a 3 km distance between crude oil storage tanks and the metering point. The crude oil flows through the pipeline due to gravity effects as storage tanks are located 60m higher than the metering point. The flow rate could be controlled by the appropriate valves. In this study, based on the climate and geographical conditions of Kharg Island, the temperature at the metering point has been calculated and the effects of main pipe line flow rate have been investigated. Further, the uncertainty in the measurement system due to temperature rise has been studied.

Abstract In the current study, numerical simulation of laminar flow and heat transfer of water mixture with carbon nanotubes (CNT) as nanofluids in a 90 degree curved pipe are considered. The incompressible Navier-Stokes and energy equations are solved numerically in a body fitted coordinates system using a control volume technique. An interfacial layer-based model is applied to predict the thermal conductivity of nanofluid. The axial velocity contours, secondary flow patterns and temperature fields for different values of the particles concentrations are examined in detail. Furthermore, the effects of nanoparticles concentration on the heat transfer are studied. The results indicate that due to the secondary flows induced by curvature effects, the heat transfer rate is improved, and enhanced remarkably further using nanofluids. Furthermore, the nanoparticles, especially at higher concentration levels, generate more uniform cross sectional temperature distributions.

Abstract In this investigation, in order to study the effect of hydrodynamic parameters such as impeller speed and hold-up, two series of experiments have been performed with a single stage horizontal mixer-settler equipped with 2 four-blade impellers. In the first series, 15 experiments were carried out with toluene/water system and in the second series, 60 experiments were carried out with toluene/acetone/water system. Results show that in both systems, when the hold-up is constant, the mean drop size decreases with increasing impeller speed and when the impeller speed is constant, the mean drop size increases with increasing hold-up, however, these manners for any system are different quantitatively. It shows that with the addition of solute (acetone) concentration in the system, the mean drop size decreases. The experimental results were compared with the Desnoyer and Quadros models, of which the Quadros model has a little
deviation from Desnoyer model.

Abstract Mass transfer coefficients of rising drops in spray and packed columns with random and structured packing in a liquid-liquid extraction operation were experimentally measured and the results compared. In this work, a high interfacial tension chemical system of toluene-acetic acid-water in a structured packed column is investigated. Results of random and structured packing show that random types are effective only for a drop size less than 9 mm, while the structured ones are shown to have a positive effect on mass transfer coefficient in a wide drop size range. Furthermore, structured packing proved to be slightly more effective than random packing in improving the mass transfer coefficient. The effect of drop size on mass transfer coefficient has also been studied in this work and the results showed that when the drop diameter increases, the mass transfer coefficient increases too. Finally, new correlations for the prediction of the mass transfer coefficient in both a random and structured packed column have been introduced which are in better agreement with the experimental data in comparison with those resulted from Newman, Kronig-Brink and Handlos-Baron models.

Abstract Enhanced design strategies in the industrial cracking furnaces are of practical interest for petrochemical industries. For such engineering purposes the exact simulation of temperature and flow fields in the furnace is mandatory. In this paper, a study was conducted to simulate 3D flue gas flow pattern and temperature field in the radiation section of an industrial cracking furnace in order to improve the design of the steam cracking furnaces, employing the computational fluid dynamics (CFD) technique. The steady-state Reynolds averaged Navier–Stokes (RANS) equations were solved, in a finite volume scheme for a turbulent premixed flow applying the renormalization group (RNG) version of the k
ε− model, together with global combustion kinetics for methane-hydrogen-air. Calculation of the Damkhöler number and optical-thickness was conducted to identify the appropriate methods for the numerical modeling of radiation and turbulence-chemistry interaction phenomena. The predicted results match the literature data quite well. The validated numerical procedure was then employed to investigate alternative design attributed to different burner locations. The alternative design resulted in a more uniform temperature profile on the reactor tubes as well as lower peak flame temperature.

Abstract Drying behavior of sugar beet was investigated in a bench scale fluidized bed dryer with an energy carrier (3 mm glass beads) and a freeze dryer. The effect of the type of dryer (fluidized bed dryer & freeze dryer) on the rate of drying and properties of dried sugar beet were studied. It was found that drying could be useful for the storage of sugar beet for a long time before processing, but the removal of more than 90% of its initial water content is necessary for the dried sugar beet to conserve its sugar content and other properties during storage. The results of experiments in two different dryers
showed that drying time in a fluidized bed dryer with energy carriers is much less than that of a freeze dryer, but the dried matter obtained by the freeze dryer has a better appearance in comparison to fluidized bed dryer. Also, the shrinkage of drying material with a change of moisture content was investigated and it was seen that a linear relation with reasonable error between these two variables was evaluated. The results are useful for mathematical modeling of the
process.

Abstract

Abstract At present, gas engineers use the simple Campbell’s equation to determine the proper length of parallel gas pipelines. The Campbell’s equation was proposed for horizontal pipelines with the assumption that the gas compressibility factor and temperature throughout the pipeline are constant. Therefore, the Campbell’s equation has a notable error for an inclined pipeline. In this paper, the Campbell’s equation was extended in a way that it can be used for inclined pipelines. In order to make a comparison between the extended and original equations, a pipeline with different slopes was used. The results show that in the case of using a pipeline with more than 2 degrees in slope, the resultant error is increased to 11 percent by using the original Campbell’s equation. For validation of the extended Campbell’s equation, the results of this equation are compared to the results of HYSYS software (version 3.1) in which the temperature and gas compressibility factor are not considered constant. The results indicate that the average error of the extended equation is less than 2 percent.

Abstract In the present study a mathematical model is developed in order to examine the effects of heat and mass transfers on removal efficiency of particulate matters in venturi type scrubbers. The governing equations including the variations of the particulate concentration, gas temperature, droplet temperature, diameter, and velocity are obtained based on the conservation laws and are solved numerically. In order to validate the model, necessary data was measured and collected in a commercial cement plant that uses these types of scrubbers in air pollution control applications. A good agreement between plant data and the model predictions is noticed in general. The results obtained from the model reveal that the existance of temperature difference between the gas and the liquid droplets decreases the overall removal efficiency of particulate matters. This is due to sudden reduction ofrelative velocity between the gas and droplets which is resulted from the existence ofheat and mass transfers between the two fluids, especially in the throat section. In addition, the effects ofvarious operating parameters on the extent ofreduction in the removal efficiency are examined. This study confirms that in most industrial applications ofventuri scrubbers it is necessary to use a direct or an indirect cooling tower in order to decrease the gas temperature before entering the venturi.

Abstract This paper reports a study on the effect of the heat flux, cooling water flow rate, fill ratio and extra volume on the overall performance of a partially vacuumed thermosyphon. A rig was made from a 1 m copper tube with an inner and outer diameter of 17.5 and 19 mm. The heights of the evaporator, the adiabatic section and the condenser are 40, 20 and 40 cm, respectively. The temperatures at different places on the thermosyphon and on the inlet/outlet ofthe cooling water were measured. It was observed that change in heat flux, fill ratio and employing different extra volumes, has a significant effect on its performance. On the other hand, with changes in the cooling water flow rate the performance ofthe thermosyphon was altered regarding the trapped air movement. In order to illustrate the effect ofthe existence ofair in deactivating the thermosyphon, the pipe was cooled down by disconnecting the evaporator power input. It was seen that the thermosyphon loses its performance as the trapped gas occupies the whole condenser. The whole study shows that due to the existence ofthe trapped air, the heat loads can have significant effects on the thermosyphon performance.

Abstract A numerical investigation was carried out to solve the flow dimensionless partial differential equations through rectangular microchannels. A purely viscous power law model was used to characterize the flow behavior of non-Newtonian fluids. The flow was assumed to be steady and laminar, and slip conditions were used as boundary conditions at the walls. The problem was solved for different power law indices as well as for various rectangular aspect ratios. Results showed that the effects ofslip velocity on dilatant fluids are more pronounced than that for pseudoplastic fluids. An increase in the power law index enhances the product of the friction factor and the Reynolds number, as well as the dimensionless incremental pressure drop and the dimensionless maximum velocity, while the hydrodynamic entrance length decreases. Results emphasize the significant effects of channel aspect ratio on the hydrodynamic flow behavior through microchannels.

Abstract

Abstract "> Waste heat recovery is very important, because it not only reduces the expenditure of heat generation, but also it is of high priority in environmental consideration, such as reduction in greenhouse gases. One of the devices used in waste heat recovery is heat pipe heat exchanger. An experimental and theoretical research is carried out to investigate heat performance of an air to water thermosyphon heat pipe heat exchanger according to ε-NTU method. The experiments were done according to the following procedure: cold water with 0.1kg/s flows through the condensation section and hot air in a closed cycle is blown into the evaporation section. A blower with varying frequency of current turns in the mass flow rate between 0.14-0.6 kg/s and a temperature range of 125-225°C. The results of the experiments show that as the ratio of C Ch c rises, the rate of heat transfer goes up. The efficiency of the heat pipe heat exchanger remains constant as the temperature of the hot stream goes up, but the amount of heat transferred increases.

Abstract ewline"> Dispersion of heavy gases is considered to be more hazardous than the passive ones because it takes place more slowly. When the gas is accidentally released at ground level or where there are many obstacles in the area it is considered to be a heavy gas. In this paper, based on the extensive experimental work of McQuid and Hanna, the model was tested against two types of experiments: A simple experiment “Thorney Island” and a complex experiment “Kit Fox” in order to validate CFD code. In order to accomplish this validation the multiphase approach was employed. Also, the vertical temperature gradient in the atmosphere was investigated. The investigation of wind speed was done taking factors such as time, height and direction into consideration. In order to reduce the number of elements in the computational domain, a combination of 2D and 3D geometry was utilized. The results showed that the wind inlet correction, as well as the temperature gradient, had a significant influence on gas concentration records.