Iranian Journal of Chemical Engineering (IJChE)

Abstract Particle size distribution is an important parameter in flotation process, which affects the floatability and therefore the flotation kinetics. This study aims to investigate the effects of particle size distribution on flotation kinetics of bituminous coal. For this purpose, a series of batch flotation experiments were conducted in rougher stage, and concentrates were collected in different time periods. Then particle size distribution for each concentrate was determined. Five flotation kinetic models were applied for the modeling of data obtained from the flotation tests using MATLAB (Matrix Laboratory) software. The relationship between flotation rate constant, maximum combustible recovery and particle size were studied. The results show that the maximum flotation combustible recovery and flotation rate are obtained with an intermediate particle size (-250 +106 μm). Results of flotation tests fitted well to all five kinetic models. It is found that the first - order model with rectangular distribution of floatability, provides the best fit to the experimental data obtained from the flotation processes among the tested models.

Abstract In this study, unmodified graphite and graphite modified with a silane agent were used to ameliorate the thermal conductivity coefficient and dynamical properties of unsaturated polyester resin. The effect of unmodified graphite and modified graphite addition on thermal conductivity coefficient and dynamical properties of unsaturated polyester resin in the graphite amounts of 0.02% and 0.3% by weight were studied using solid thermal conductivity measuring device and DMA test. The results showed that the silane modifier can help to create strong covalent bonds between graphite particles and unsaturated polyester resin network and cause changes in thermal and dynamic properties compared to unmodified graphite particles. Adding 0.3% of the weight of the unmodified graphite to the unsaturated polyester resin resulted in a 7% raise in the storage modulus in the glassy region. However, adding the same amount of graphite modified using the silane agent increased the storage module by 33% in the glassy region. Silane modifier caused better dispersion of graphite particles in the resin structure. Superior dispersion of graphite particles caused more interaction between graphite particles and resin network, which significantly increased the modulus of unsaturated polyester resin. In contrast, better dispersion of graphite particles because of the presence of silane agent increased the thermal resistance at the surface of graphite particles, which reduced the thermal conductivity coefficient compared to unmodified graphite.

Abstract Pearlescent pigments are a variety of pigments that can generate an optical pleasant appearance in the system because of the ability of easy parallel orientation of a large number of platelet-like particles. In the present work, the green pearlescent pigments based on mica (biotite) and mica-titania flakes covered with a thin film of nickel oxide were prepared with novel methods via the homogeneous precipitation of nickel acetate with sodium / potassium hydroxide, and in the presence of mica (biotite), titania, ammonium molybdate or mica-titania flakes. The synthesized pigments were characterized by means of X-ray diffractometery (XRD), Thermal Gravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC) and X-Ray fluorescence (XRF) analyses. By comparing the XRD pattern of synthesized pigments with the mica base pattern, it is clear that the structure of the support does not change due to the layering on these bases. As these layers are hydroxide, oxide and chloride compounds. The XRF analysis shows that the nickel compound is layered well on the mica at 8.823%. The quantity and quality of the produced pigments by methods 1 and 2 were approximately the same. Consequently, due to commercial savings, method 1 was recommended for the preparation of the metallic pearl pigments and mica was known as the best support for the production of the pearlescent pigments by the introduced methods. Furthermore, TGA/DSC curve showed that the introduced pigments were stable up to 200 ˚C. The results showed good chemical resistance and pearl luster effects for the produced pigments.

Abstract The artificial neural network (ANN) approach was applied to develop simple correlations for predicting the thermal conductivity of nitrogen-methane and carbon dioxide-methane mixtures. The genetic algorithm method was used to obtain global optimum parameters (weights and biases) of the ANNs. The methane mole fraction, temperature, pressure, and density as effective parameters on thermal conductivity were network input variables. 171 and 180 data points related to the nitrogen-methane and carbon dioxide-methane gas mixtures, respectively, divided to test and train datasets. Simple correlations were obtained due to the small number of optimal neurons in the ANN structures. The mean relative errors of 0.206% and 0.199% for the testing dataset indicate the high accuracy and validation of the correlations. The work indicates that artificial intelligence approaches are very useful for thermal conductivity modeling in natural gases. A sensitivity analysis was performed on all input variables that indicates that the gas mixture density has the greatest impact on the thermal conductivity.

Abstract In this research effect of synthesis method of magnesium aluminate as support of Ni catalysts at the reverse water gas shift (RWGS) reaction was evaluated. The RWGS reaction is applied in Carbon Dioxide Hydrogenation to Form Methanol via a Reverse Water-Gas Shift Reaction (CAMERE) process for the transformation of CO2 into methanol. The MgAl2O4 supports were prepared by sol-gel (M1), surfactant-assisted co-precipitation (M2) and ultrasonic-assisted co-precipitation (M3) techniques. 1.5wt.% Ni/M1 showed highest CO2 conversion (42.1%) and lowest CO selectivity, while 1.5wt.% Ni/M2 showed the lowest CO2 conversion and the highest CO selectivity (>92.5 %). The 1.5wt.% Ni/M3 showed similar catalytic activity as 1.5 wt.%Ni/M2, but with lower CO selectivity. The high CO selectivity of 1.5 wt.% Ni/M2 with a BET surface area of 121.7 m2g-1 was accredited to a higher dispersion of Ni particles resulted by higher total pore volume of this catalyst. High specific surface area along with large total pore volume, is effective in increasing the nickel dispersity. The following pore size distribution and total pore volume order was obtained for catalysts: 1.5wt.% Ni/M2> 1.5wt.% Ni/M3> 1.5wt.% Ni/M1. Among the prepared supports, M1 with BET of 174.5 m2.g-1 showed the highest specific surface area. All prepared supports and catalysts possessed mesoporous structure. Well dispersed NiO species with high interaction with the support were detected by TPR analysis. The SEM images detected particles with less than 80 nm for M2 and 1.5wt.%Ni/M2 samples. The long term stability test performed on 1.5wt.%Ni/M2 showed great catalytic activity after 15h on stream.

Abstract The objective of the investigation was to mathematically correlate the behavior of a supersonic superheated steam flow inside a Laval nozzle, against the decision parameters. The decision parameters are the inlet temperature ranging from 374.3 K to 504.3 K and the inlet pressure from 40050.14 Pa to 133375.7 Pa. Indeed, the outlet temperature, outlet pressure as well as the Mach number are mathematically correlated against the decision parameters. The numerical approach based on the Computational Fluid Dynamics (CFD) is selected to study the behavior of the supersonic superheated steam flow inside the nozzle. By examining the different temperature and pressure conditions of the inlet fluid, it was found that the closest distance from the starting point of condensation to the throat is at the highest pressure and lowest temperature. Conversely, the farthest distance from the starting point of condensation to the throat is at the lowest pressure and highest temperature. In addition, three mathematical correlations were developed. Due to the high accuracy of the mathematical correlations, the efficiency of the predictor models in predicting the outputs was proved.

Abstract In the study, the thermal-hydraulic performance of the zigzag channels with circular cross-section was analyzed by Computational Fluid Dynamics (CFD). The standard K-Ꜫ turbulent scalable wall functions were used for modeling. The wall temperature was assumed constant 353 K and water was used as the working fluid. The zigzag serpentine channels with bend angles of 5 - 45° were studied for turbulent flow from 4000 to 40,000 Reynolds number (Re). The thermal performance of the zigzag 45° channel was better than the other channels and also it had the highest friction factor (f). The bends caused secondary flow, and as the bend angle increased, the secondary flow increased. This Phenomenon had a positive effect on thermal performance and a negative effect on hydraulic performance by increasing the friction factor. The obtained CFD data used to develop correlations for predicting the Nu and f as the functions of Re and bend angles. The correlation constants were optimized by the genetic algorithm method which leads to the mean relative errors of 3.32% and 6.94% for Nu and f estimation, respectively.

Abstract Decreasing pressure losses in microtubes is an important subject, especially when increase in flow capacity is required. In the same pumping power, decreasing the pressure drops is coincides with increasing the fluid flow rate passing through a microtube. The current study aims to examine how the water pressure drop across a microtube can be affected by the addition of small concentrations of different drag-reducing polymeric agents. A kind of laminarization behaviour was found by the addition of the selected polymer to the turbulent flow. The effect of concentration of drag-reducing agent (DRA) on observed viscosity and drag values are reported. Moreover, the effects of different types of drag-reducing agents on friction factor are obtained at the best concentration in the range of examined concentrations. Under this condition amount of drag reduction percentage and increase in capacity of the flow were respectively 33% and 36%. The obtained results show that more drag reduction occurs at a higher flow rate for 20ppm of high molecular weight polyacrylamide.

Abstract A continuous process was designed and optimized at a conceptual stage for the biodiesel production from waste vegetable oils. Unlike previous studies, the process was optimized taking into account the technical and economic considerations, simultaneously, to find the optimum operating conditions fort he commercial scale productions. The effect of major variables on the yield of the process was studied by modeling esterification and transesterification reactors. The mole fraction of free fatty acids (FFAs) in the feedstock, production rate, conversion and molar ratio of the reactants in both reactors were chosen as major variables. By considering the economic potential as the objective function of the process optimization, the optimum mole fraction of FFA was obtained as about 0.50 (24 wt %). Also, the optimum values of the conversion and molar ratio of the reactants in the esterification and transesterification reactors were found as        82-89 % (depending on the different production rates), 11:1 and 96 %, 8:1 respectively. It was found that the economic potential increases linearly as the production rate increases. Therefore, the production rate should be set at its maximum possible practical value. The break-even point at the optimum values of these variables, as mentioned above, occurs at the production rate of 157 ton/yr.

Abstract Micro-reformers used for producing hydrogen with a high surface-to-volume ratio in small-scale fuel cells were investigated. To this end, scrutinizing and exploiting all areas of micro reformers is very important. Parallel micro-channels have shown good performance in eliminating dead volumes. Inlet/outlet configuration has great effect on the velocity distribution through micro-channels. In this study, four configurations (1 inlet/1 outlet on the same and opposite sides; 1 inlet/2 outlets on the same and opposite sides) were studied through simulation and 1 inlet/2 outlets on opposite sides were found to have the lowest velocity difference, hence having the best configuration. Simulations were carried out at 600 °C, 1 atm, with S/C=3 and feed flow rate of 100 mL/min. Three channel patterns (i.e., parallel, splitting-jointing and pin-hole) were compared in terms of Figure of Merit (FoM) and specific conversion. Parallel channel design revealed a high value of specific conversion to be about 5.36   , while splitting-jointing and pin-hole were 5.33  and 4.91 , respectively. Based on FoM, pin-hole design had a high value of 1.34   , while the values of splitting-jointing and parallel designs were 0.037  and 1.28 , respectively.

Abstract Wind energy is used to rotate a magnetic turbine in order to remove heat from the surface of a photovoltaic (PV) panel. A three-bladed turbine, which rotates with wind energy, has rotational motion underneath the studied PV panel in order to move Magnetic Nano-Particles (MNPs). In addition, effects of the magnetic field strength (B=450-830 mT), rotational velocity of the magnetic turbine (ω), and the concentration of MNPs (ϕ) on the heat removal from the PV panel area were investigated. Results showed that heat removal from PV panel was intensified by motion of pinned MNPs in the ferrofluid via the exerted external force of magnetic field. Concurrent application of available magnetic field along with ferrofluid led to 7.6-24 % temperature reduction for a PV panel. Furthermore, the produced electrical energy of the PV panel was augmented between 2.55-3.13 W depending on ϕ, ω, and B. Moreover, the impact of ω on cooling performance was also investigated, and a significant enhancement to generated power was observed. Eventually, the maximum amount of the produced power (3.13 W), maximum power enhancement percentage (32.63 %), and thermal efficiency (24 %) were achieved for B=830 mT, ω=50 cycles/min, and ϕ=0.05 (w/v).

Abstract The gas antisolvent (GAS) process has been employed for pharmaceutical micronization. Ampicillin was dissolved in organic solvent and carbon dioxide as an antisolvent was injected into this solution, consequently, volume expansion and sharp reduction in liquid solvent power were shown. The particles in GAS process are not seen in any operating conditions. Thermodynamic modeling of GAS can evaluate the operating conditions. In this project, the‌ effect of solvent on optimal thermodynamic conditions of the binary system (CO2, solvent) and ternary system (CO2, solvent, ampicillin) were investigated. The relative change in molar volume in different solvent (ethanol, 1-propanol, 1-butanol, and 1-pentanol) was studied for determination of the optimum operating conditions. The combination of Peng-Robinson EOS and Vidal and Michelsen mixing rule (LCVM) was selected to determine the optimum operating condition of the GAS process. The effect of solvent on minimum pressure was investigated. The calculated Pmin was 70, 70.86, 72.2 and 73.4 bar for ethanol, 1-propanol, 1-butanol, and 1-pantanol at, 308.15 K respectively. According to modeling results, when the molecular weight of the solvent was increased, the value of Pmin was increased.

Abstract In this study, hydrodynamic characteristics such as gas holdup (ε), liquid phase velocity, and mass transfer coefficient (kLa) for air-diesel system were modeled for bubble column (BCR), airlift (ALR), and airlift with the net draft tube (ALR-NDT) reactors at different superficial gas velocities ranging from 0.008 to 0.085 m s-1. A 3D two-fluid Eulerian-Eulerian model was developed using computational fluid dynamic (CFD) technique to model the three configurations of column reactors and predict the hydrodynamic parameters. The results of 3D-CFD modeling showed a good agreement with the experimental data where average error was less than 14 and 9% for ε and kLa, respectively. Although the vortex occurred in BCR and ALR at high gas velocities, however optimum liquid and gas circulation and distribution observed in ALR-NDT. Furthermore, the formation of dead zone (kLa = 0) in the reactors was studied, and the results revealed that ALR-NDT has a lower volume of dead zones (about 8%) in comparison with BCR and ALR. In order to reduce the dead zone in BCR and ALR systems, the location of gas diffuser and draft tube were investigated. The dead zone was decreased by 12% with shifting of gas diffuser to the bottom of the BCR. Also, by increasing the distance of gas diffuser from draft tube, the dead zone was decreased by 40% specifically near the walls of ALR. Meanwhile, the simultaneous shifting of gas diffuser and draft tube to lower position in ALR had no effect on dead zone formation and its distribution.

Abstract In this study, a comprehensive model was proposed in order to predict the tensile strength of nanocomposites considering the effects of the random orientation of nanoparticles, interphase properties and also the inevitable aggregation/agglomeration phenomenon. The model was structured based on the nanoparticle shape (e. g. platelet, cylindrical and spherical) so it could perfectly demonstrate the random orientation. It was revealed that neglecting the aggregation/agglomeration of the nanoparticles ( ) drastically rises the prediction error to about 12% while considering decreased the error to about 7-9% for samples with low content of nanoparticles (< 0.5 Vol.). Moreover, the model was completely capable of characterizing the polymer/particle interphase regardless of the polymer type and the nanoparticles shape. Model verification was accomplished by comparing its predictions with the tensile test results of the prepared nanocomposite samples of different compositions (Polystyrene/Silica, Polystyrene/Graphene Oxide and Polystyrene/Carbon nano-tubes). Also, the samples were subjected to TEM in order to qualitatively evaluate the behavior of the different shaped nanoparticles in the polystyrene matrix.

Abstract Stimuli-responsive amphiphilic core-shell polymer nanoparticles are an important category of smart materials which have been studied due to their advantages of changing of physical or chemical properties in response of stimuli. In this study, poly[2(dimethylamino)ethyl methacrylate] (PDMAEMA) as hydrophilic core with hydrophobic layer polystyrene (PS) as shell were synthesized by seeded emulsion polymerization to achieve dual-sensitive core-shell nanoparticle (CSNP). Temperature- and CO2- responsive CSNPs were investigated as two important smart behaviors. The CSNPs were characterized by dynamic light scattering (DLS) and scanning electron microscopy (SEM). In addition, two essential parameters including the polymerization conversion and stability of polymer latexes were investigated. Obtained results showed that hydrophilicity-hydrophobicity balance of the latex nanoparticles could be changed by variation of temperature and induction of CO2 gas flow, as a result of temperature- and CO2-responsivities of the PDMAEMA core. The particle size of CSNP was increased when the temperature rised above the lower critical solution temperature (LCST) of the PDMAEMA. It is due to the formation of hydrogen bonds between water molecules and tertiary amine group which lead to swell in PDMAEMA below LCST, and deswelling from water above LCST of the PDMAEMA. Furthermore, the size of the latex nanoparticles was increased from 696 nm to 853 nm after CO2-bubbling which led to increase hydrophilicity or water swelling of PDMAEMA in latex nanoparticles.

Abstract Water and solid effective diffusivities and shrinkage were correlated for finite hollow cylinder-shaped apple samples during the candying operation in the osmotic solution. Experiments were conducted in the sucrose solution as an osmotic agent at different temperatures (i.e., 40, 50, and 60 °C) and at a constant concentration of 55 °Brix. The effective diffusivities of water and solid were calculated by fitting the water loss and solid uptake experimental data to Fick’s second law and fractional calculus method, considering the shrinkage of the samples during the candying process. The obtained results exhibited that the volume of the apples reduced linearly by increasing the water loss. For above conditions of the candying process, water effective diffusivities with Fick second law were determined in the range of 3.7×10−10 m2/s–8.73×10−10 m2/s, and those with fractional calculus method were in the range of 2.75×10−10 m2/s–6.98×10−10 m2/s. The results indicated that the coefficient of determination for the fractional calculus method was more than the coefficient of determination for the Fick model. The value of the empirical parameter α for the Non-Fickian diffusion model was always higher than unity, meaning that the dehydration process had a super-diffusive mechanism.