Nashrieh Shimi va Mohandesi Shimi Iran
Year:2010 | Volume:29 | Issue:3|Papers Count:15

Zwitterionic (dipolar) intermediates are unstable and very reactive species which are usually generated in situ in many organic reactions and trapped during the reaction by other reactants to afford the products. There are many ways to form different zwitterionic intermediates. One of the most common methods for their generation is addition of non-protic nucleophiles to the activated alkynes. Isocyanides are especially noticeable as nucleophiles in the sense that they formed Huisgen intermediate, as one of the known zwitterionic species. Numerous significant papers have been published over the last two decades with focal theme of trapping Huisgen intermediate formed by the reaction of isocyanides with activated alkynes. In this review, different aspects of these publications based on the role of various trapping agents and then mechanisms of actions are discussed in detail.

Carbon nanotubes with high yield and quality were synthesis by chemical vapor deposition over Co-Mo/ MgO in a fluidized bed reactor. Different parameters such as temperature, ratio of hydrocarbon source to hydrogen, rate of gas, the run duration, the size of catalyst particles, the ramp of temperature and the kind of hydrocarbon source have been examined. The influence of these parameters on the carbon nanotubes yield and quality are reported. In the best operation conditions (900°C, 30 min, rate of gas=1800mL/min, ramp temperature 7°C/min, size of catalyst particle=212 mm, ratio of hydrocarbon source to hydrogen=1/1) single walled carbon nanotubes with 0.9nm average diameter and 300% yield is produced.

In this paper, thermal conductivity of porous media has been modeled based on mathematical analysis in one dimensional space with micro size. First, porous modeling established on three kinds of porosity (Y = 0.52, 0.68 and 0.74) and then to make analysis and calculation easy, reality assumptions were considered. With omitted radiation and convection mechanisms, we can developed one simple model as kP = kgks / (ks - Y (ks - kg)). After developing the model its results for three materials cotton, fiber and sand obtained and then compared to the experimental data and the results of Maxwell model as a valid model. The results obtained for two modes of material into the holes once air and once again water. The results obtained from the model for gas fluid (air) into the holes with great accuracy. Generally, based on the terms of model, in porous media accuracy of the model was increased when the ratio of (ks / kg) was increased. At the other hand, if the bulk has much conductivity or the fluid into the hole has low conductivity, the prediction of model and its adaptation on heat behavior of the body will be better. So the uses of this model were recommended for dense porous materials.

Although there is no long time from the first application of Multi-Stream Heat Exchangers (MSHE), but their benefits have made them attractive to be applied in a various situations. Several methods have been developed for designing of such exchangers due to their wide advantages such as simultaneous heat exchange between more than two streams in a single unit, significant savings in space, energy, structural supports and task flexibility. There is no published design method taking into account the effect of stream pressure drops as a design parameter when designing the heat exchanger. This research describes a new method for designing MSHE’s based on optimum pressure drops, using Simulated Annealing algorithm (SA) and Pinch Technology principles. In optimizing the whole heat exchanger parameters, total annual cost is considered to be the main objective function. The new procedure has been applied to a case study already reported in literature. The results showed 25% reduction in total annual cost and smaller heat exchanger volume by 16.2%. Therefore, the presented design and optimization algorithm in this paper seems to be a good alternative method to conventional design procedures.

The present work examines the influence of solute (acetone) on mean drop size in a mixer settler. For this purpose, two series of experiments were performed in a single stage horizontal mixer-settler with toluene-in-water emulsions. At first, the effects of the impeller speed and hold-up on the mean drop size were examined without acetone. Afterward the same investigation was performed in the presence of acetone. The results show that in the presence of acetone, D32 decreases and the decreasing rate of D32 with impeller speed diminishes. Moreover, the increasing rate of D32 diminishes with the increase in the hold-up. For various acetone concentrations, an empirical model for mean drop size has been proposed. This correlation has a good agreement with experimental data.

At the beginning of this article, using standard method for analysis of open cooling towers, a computer code (MATPRES) has been compiled which can be used for design and rating of the towers. Then, a new method has been introduced for some types of packed cooling towers. A new computer code (MATDCT) has been presented for problem solving of these kinds of towers. In continuation, with the aim of evaluation of these methods in a packed tower two definitions, mean mass transfer coefficient (hd) and average convection heat transfer coefficient has been introduced. Using these definitions, the possibility of results evaluation of these two methods (DCT,_PRES) has been provided in a packed tower for design and rating situations.

In this paper, in order to investigate the effect of different degree of stenoses and grafting angle on wall shear stress, three dimensional pulsatile blood flow was studied in a coronary-coronary bypass. The blood was considered as Newtonian, homogenous and incompressible fluid. Simulations were carried out in 20, 30 and 40 bypass grafting angle and 50, 75 and 85 stenoses percentages using Fluent software. Results show the stenoses percentage effect on recirculation zone in the upstream of coronary artery. Simulation results also show using 30° bypass angle is a very suitable bypass angle in coronary-coronary bypass grafting.

Determination of the drug’s serum concentration has an important role in pharmacokinetic and toxicity studies. There is a significant relation between serum level and drug effects which can helps to find a therapeutic protocol. The objective of this study is to investigate optimum condition to separate 6 anticonvulsant agents (primidone, phenobarbital, phenytoin, carbamazepine, ethosuximide and diazepam) by chemometrix method in patient’s serum. Also, the impact of physical and chemical disturbances due to serum environment on the calibration curve in simultaneous measurement of six compounds has been evaluated. Chemometrix methods such as experimental design, multivariable analysis and Parto multifactorial decision was used to achieve an optimum analysis time and suitable resolution of neighborhood peaks. pH and organic solvent were selected as the variables. Serum drug’s amount was determined via calibration graph. The analysis method showed the most important factors affecting on retention time of the drugs was methanol percentage in the mobile phase. The involvement of other variables was not significant. The interaction of two factors in retention model exhibited the necessity of carrying out a multifactorial analysis method to separate anticonvusant drugs in RP-HPLC. Our study showed the optimum condition in pH = 26 and V= 60%. There was no effect from serum physical and chemical factors on the determination of drugs in this study in regard to phenobarbital, phenytoin and carbamazepine. Therefore this model can be used for separation of these drugs in mixture but this method should be changed to standard addition in order to measure ethosuximide and diazepam.

Since the pressure of hydrocarbon reservoirs drops due to production, in order to keep the production rate constant or increase enhanced recovery, few methods are used. One of which is gas injection to the reservoir. On the other hand, due to reduction in oil production potential of Aghajari oil field, gas injection is highly required to pressurize and enhance oil recovery. There is a possibility to transfer a part of South Pars Common field produced gas to Aghajari oil district via pipeline to inject it into that reservoir. Produced gases of phases 6, 7 and 8 of South Pars gas reservoir contain impurities such as carbon dioxide (CO2), nitrogen (N2 ), hydrogen sulfide (H2S) and water vapor (H2O). In this research, the effect of injection of the produced sour gas from phases 6, 7 and 8 of South Pars Complex, on minimum miscibility pressure is investigated by compositional simulation method and using CMG software, considering sour gas composition. The yielded results show that minimum miscibility pressure will increase considerably if both acidic gases, H2S and CO2 are stripped from the injected gas.

Quantity of resin that exists in raw oil is an effective parameter in asphaltene precipitation in raw oil. Causes in formation of precipitation in reservoirs are pressure variation, temperature and formation of asphaltene and resin. As till now quantity of resin did not account. For the first time, we consider resin - asphaltene association in raw oil. Association equation of state is one of the most applicable models used for these studies. In association fluid theory, it is assumed that compressibility consists of physical compressibility factor and chemical compressibility factor. For physical part we used Peng - Robinson equation of state that added to chemical part derived in this study. By using the fact that asphaltene and resin do not affect on vapor phase, also considering asphaltene and resin precipitations as being liquid that they are acceptable assumptions, at first vapor - liquid equilibrium calculations then and liquid - liquid equilibrium calculation performed. By calculation of asphaltene precipitation from modeling and compare them with experimental values, precipitation of resin precipitated with asphaltene can be used.

In this research, adsorption of benzene's vapor on natural Iranian zeolite modified by hydrochloric acid at different qualifications was studied. Samples of natural Iranian zeolite (Clinoptilolite) from Semnan were prepared, then their crystal structure was identified using X- Ray Diffraction analysis (XRD). The samples were crushed, sieved in different sizes. Zeolite samples were modified using 1N HCl solution with solid:solution ratio 1:25 . Modified zeolites were used for preparing sampling tubes, and these tubes used in static method to study the effect of different parameters for adsorbing benzene upon zeolite. Breakthrough points in various qualifications (mesh, flow rate, mass, concentration,and temperature) were specified. In general, the obtained results showed that nutural zeolite modified by HCl has acceptable efficiency for sampling benzene, and has adsorption capacity at low concentrations (< 500 ppm) about 1.92 mg benzene/g zeolite and results showed that the optimum qualifications for sampling benzene in the air using natural modified zeolite : mesh: (60/80), mass: (800,200 mg), flow rate: 50 mL/min, and temperature 25°C .

Attentions to use of ultrasound for cleaning of polymeric membranes are less than one decade. In this experiment, the cleaning efficiencies of various frequencies of ultrasound in different membrane modules and the barrier effect of structural design and membrane module during cleaning process using ultrasound were evaluated. Three membranes, hollow fiber without module, flat sheet membrane including stainless steel and acrylic module and spiral wound with polyethylene modules applied during forward flushing cleaning process by ultra pure distilled water for 30 minutes after fouling by skimmed milk 1% using ultrasonic irradiation of 28, 45 and 100 kHz frequencies in constant intensity of 300W. The permeate flux and hydrodynamic resistance of new, fouled and cleaned membranes during sonication using various frequencies of ultrasound were determined separately. In this manner the cleaning efficiency of each treated membranes were calculated. The data statistically analyzed using ANOVA table. The results showed that the most cleaning effects obtained in all tested membranes by various frequencies of ultrasound at first 5 minutes of cleaning process. The highest amounts of cleaning effect achieved in hollow fiber membrane using all tested frequencies especially in 28 kHz. The maximum cleaning efficiency achieved more than 95 percent for the first 5 minutes and may be due to lack of barrier such as holder or membrane support in the design of this membrane module. However, we observed the cleaning efficiency of 92 percent after 30 minutes in flat sheet membrane module using ultrasound in28 kHz and the amounts of cleaning efficiencies in same conditions were lower than hollow fiber module. The other tested frequencies were not significant cleaning effects and stainless steel and acrylic holders in design of membrane module prevented to reach of sonic power to surfaces and pores of flat sheet membrane. The minimum ultrasound cleaning efficiency achieved in spiral wound membrane modules only 21 percent after 30 minutes ultrasonication using 28 kHz during forward flushing and it seems that only outside of membrane surfaces are affected. This is may be due to special design of membrane module and barrier effects of configuration and membrane holders.

Among the degradables plastics that has been fabricated so far, Poly Hydroxy Alkanoates (PHAs) have been attracted because of their complete degradability, low production cost, and also their simple processing compared to other biodegradable polymers. Considering the disposals of plastic waste and excess sludge of wastewater treatment plant problems and production expences reduction, the possibility of producing PHA by treating activated sludge and determining the optimum condition for increasing PHA production were the main issues of this paper. In this research, an anaerobic-aerobic SBR was used to make micro-organism adapted and a batch aerobic reactor was used for its enrichment. Four parameters of sludge retention time, aeration time, volatile fatty acid in municipal wastewater, and optimum carbon source determination for micro-organism enrichment have been studied. First, the rate of acetate and propionate uptake by activated sludge was determined in primary experiments in range of 30-32 and 15-17 mg C. L-1.h-1.g-1 SS in 24 hours were allocated for the production of polymer. In main experiments, Taguchi Method was employed for experiments design. Three levels were assigned for each of these four parameters, nine experimental runs were carried out and the results were analyzed through QUALITEK-4 software. Sludge retention time and aeration time were determined to be 10 days and 3 hours, respectively. Finaly, municipal wastewater containing acetate and propionate as the carbon sources in polymer production reactor were found to be the optimum condition. Results from Taguchi Method revealed that in optimum condition the sludge of municipal wastewater can produce PHA up 12.6% of sludge dry weight.