دوماهنامه مهندسی شیمی ایران
پیاپی 132 (فروردین و اردیبهشت 1403)

It is significant to determine the optimal dimensions of the heat exchangers to reduce energy consumption. The helical tube heat exchanger is widely used in industry due to its advantages over other types. Therefore, investigating this type of heat exchanger can be an interesting topic. In this research, conical coil tubes with circular, elliptical, and square cross-sections with 10, 30, and 50° cone angles and 15, 30, and 45 mm pitch were modeled by computational fluid dynamics to evaluate the thermal-hydrodynamic performance. The data relating to the Nusselt number and friction factor for all investigated geometric shapes were compared and analyzed. The results showed that the elliptical cross-section tubes have better heat transfer performance compared to other geometries. The results showed that the elliptical cross-section has a better heat transfer performance compared to the square and circular cross-sections by 34.33% and 0.38%, respectively. Moreover, the lower values of the Nusselt number and the friction factor were obtained for the square cross-section due to the change in the thickness of the boundary layer.

Multiphase fluid flows occur when two or more fluids that could not be able to mix (such as air and water) find an interface. Multiphase flows can be categorized to single component multiphase fluids, e.g., water and vapor, and multi-component multiphase fluids such as oil-water mixture in porous media. These multiphase flow modeling methods that are divided into microscopic, mesoscopic and macroscopic approaches have been the major focus of this review paper by emphasizing on the methods of population balance model, level set, phase field, lattice boltzmann, size exclusion, front-tracking, and volume of fluid. As result of this study, it could be mentioned that the front-tracking and phase field methods could be accounted as methods with high accuracy and that level set and volume of fluid methods are conceptually simple, while the phase field methods are struggling with complex computational analysis. Achieving to the numerical instability like what happens to the lattice Boltzmann method is more probable than phase field and volume of fluid method. Less time is the main advantage of the lattice Boltzmann method while the population balance method is suffering from long time of analysis. Finally, selection of an appropriate methods most be excuted based on concept of problem, time, cost and accuracy of considering systems.

Detergents are one of the most widely used chemicals in the daily life of humans. Their entry into the environment, especially water, can increase the COD of water and cause serious problems for living organisms. There are different methods to reduce COD. The electrocoagulation process as an electrochemical method is a suitable solution to reduce COD. In this study, the effect of electrocoagulation to reduce COD caused by laundry detergent has been surveyed. Process voltage, the number of electrodes, along with coagulation time as key parameters were investigated as influential parameters. The results showed that the 2-electrode mode reduced COD by 70% in 40 minutes at a voltage of 15 volts. This value was the most optimal energy consumption in terms of process time and the amount of reducing the pollution index.

Chlorophyll and carotenoids can be extracted from microalgae using different solvents. In this study, for the first time, the extraction yield of pigments from mixed microalgae was compared in wet and dry conditions. The extraction yield of chlorophyll a, b and carotenoid using acetone solvent (without stirring) from wet algae equal 21.83%, 78.12%, and 66.01% respectively and from dry algae equals 61.34%,57.19%, and 53.27%, respectively. Then, to select the suitable solvent, acetone, ethanol, methanol, dimethyl ether, and tween (20% and 85% ) as non-ionic surfactants were used. Due to the difficult storage conditions of wet algae, dry algae was used in these experiments. The results show that the highest extraction yield of chlorophyll a, b, and carotenoid using tween (85%) without stirring on the tenth day is 91.70%, 87.12%, and 79.9% respectively. Also, the extraction yield with methanol solvent after 10 hours was 82.70%, 65.12%, and 62.90%. To reduce the extraction time using tween (85%), stirring was used. According to the results, the use of stirring increases the extraction rate of pigments, so that the extraction yield reached 98% within 50 min.

The average consumption of raw water in Tarasht power plant is 2800 m3/day, which is considerable, and therefore it is necessary to provide effective solutions in order to improve the consumption pattern and prevent water wastage. After technical investigations, effective solutions such as recirculation of clean drains of boilers, drains of resin filters backwash, purification and recirculation of cooling tower drains, etc. were studied. Considering the volume and quality of the produced effluent of the power plant, the solution of recirculating clean drains was chosen as the most effective method. Among the various implementation methods of clean drain recycling, two methods of fountain pool and heat exchanger were investigated as two more effective technical and economic methods. Economic studies showed that for the provision of equipment and the implementation of 8 m3/h recycling solution of boiler blowdown, it is necessary to spend 1,070,000,000 Tomans for the fountain pool method and 1,425,630,000 Tomans for the heat exchanger method, that the fountain pool method needs about 25% less cost. Also, recirculation of boiler sludge (200 m3/day) to the raw water with the fountain method (functional efficiency 75%) leads to a 5.3% reduction in water consumption and the use of the heat exchanger method (functional efficiency 95%) leads to a reduction of about 6.8% of input raw water. In addition to the economic results, technical studies showed that the fountain pool method has more advantages than other methods of recirculating boilers due to the simplicity of operation, the possibility of removing iron and hydrazine.

In this work, the Monte-Carlo molecular simulation was applied to study the adsorption of H2S and CO2 from natural gas onto silica chabazite zeolite. The isothermal adsorption curves of pure CH4, CO2, and H2S on zeolite were simulated in a pressure range of 0-200 kPa at the temperature of 298, 323 and 348 K. The heat of adsorption analysis indicated that the physical adsorption has occurred. The simulation results showed a good agreement with experimental data and the average relative error of simulated results in 298 K for those gases were reported as 18.31%, 6.6%, and 9.8%, respectively. The isotherm of dual and triple combinations of these gases has been studied in the composition range of 70-90% of CH4. Results indicate that the tendency of chabazite for adsorption of H2S is much more than two other gases, because of its high polarity. In addition, results report that the selectivity of CO2 and H2S on chabazite in dual and triple gas mixtures are almost 2 and 4, respectively.

The purpose of this study was to investigate the effect of different salts on improving the performance of cationic surfactants in terms of the dynamic interfacial strength between the surface of water and oil. Increasing production from oil reservoirs has been a major concern for oil companies. Capillary forces inside the holes cause oil to be trapped between them and it is considered as an unproductive phase. Surfactant flooding is a technique to increase oil recovery in which the phase behavior inside the reservoir can be manipulated by injecting surfactants. The results showed the effect of divalent salts on the improvement of surfactant performance. Also, based on the experiments and previous studies, it can be concluded that the presence of salt in water reduces the interfacial tension force. In addition, divalent salts have a greater effect in reducing interfacial tension compared to monovalent salts.

Kinetics and thermodynamics of biosorption of uranium by microalgae Chlorella vulgaris were studied in a batch system at different temperatures and concentrations. The effect of parameters such as pH, contact time, initial pollutant concentration and temperature on the absorption was studied. By investigating the effect of pH, its optimal value was determined to be 4.5 in the studied temperature and concentration range. The maximum absorption value occurred at a temperature of 15°C and an initial concentration of 500 mg/L. It was observed that the absorption capacity of microalgae Chlorella vulgaris for uranium, decreases with increasing temperature. To study the kinetics of the adsorption process, the saturation type kinetic model was used and the correlation coefficients showed that this model is suitable for uranium biosorption. By modeling the equilibrium sorption of uranium absorption by microalgae with Langmuir and Freundlich models, it was observed that the experimental data is in good agreement with the Langmuir isotherm. Also, by using equilibrium constants at different temperatures, thermodynamic parameters (DS, DH and DG) were determined, which indicates exothermal and spontaneity of the process

In this research, the MPC obtained from the pyrolysis of r-MMIL-88 was applied for preconcentration of two homo and hetero-polycyclic aromatic hydrocarbons. The target analytes were determined by high-performance liquid chromatography with ultra violet detection system (HPLC-UV). Various characterization techniques such as FT-IR spectroscopy, TEM, VSM, and XRD were employed. After that, central composite design (CCD) method was utilized to explore and optimize affecting factors. Applicability of the MPC was explored using dibenzothiophene and 9,10-dimethylanthracene, as the model analytes. Under the optimum condition, LODs and linear ranges were achieved in the domain of 0.05-0.1 µg L-1 and 0.25-500 µg L-1, respectively. Repeatability of the method as RSDs was evaluated which was <7.8% (within-day, n = 5) and <12.5% (between-day, n = 3). Ultimately, the method was applied to analyze well and seawater samples and satisfactory results (RSDs%, 6.7-10.6%; relative recoveries, 94-105%) were obtained. The results of the analysis of real samples showed that this technique can be successfully used to extract and preconcentrate the desired compounds in samples with complex texture.