Iranian Journal of Chemical Engineering (IJChE)

Abstract Maintaining a constant superficial gas velocity (Usg) is the most common criterion for scaling aerated photobioreactors, yet whether it preserves gas–liquid hydrodynamics is rarely tested directly. Euler–Euler CFD was used to characterize two baffled airlift reactors, a 9.7 L laboratory unit and a 106 L scaled-up unit, over Usg = 0.025–0.10 m·s⁻¹, evaluating gas holdup, gas-phase velocity, and the volumetric mass transfer coefficient (kLa) alongside Reynolds number, Froude number, and power input per unit volume (P/V). Across this range, gas holdup rose 2.4–2.6-fold and kLa rose 1.3–1.6-fold in both reactors, but mean gas velocity increased more in the larger unit (1.4-fold vs. 1.1-fold). Extended-range simulations of the large reactor showed continued but progressively less proportional gains. Froude number was not conserved across scales, and P/V remained consistently higher in the larger reactor. These results show that Usg alone is an insufficient scale-up criterion, gas holdup, kLa, Froude number, and P/V should be evaluated jointly.

Abstract Liquid Composite Molding (LCM), particularly the Resin Infusion (RI) process, has become an attractive manufacturing technique for producing lightweight composite vessel hulls with improved structural performance and reduced production costs. Nevertheless, achieving rapid and uniform resin impregnation while preventing dry spots and premature gelation remains a major challenge. This study presents a numerical investigation of the resin flow behavior in the manufacturing of small composite vessel hulls using a two-phase computational fluid dynamics model based on the Level-Set Method. Five resin injection configurations, including cylindrical, fishbone, radial, parallel, and alternating arrangements, were systematically evaluated in terms of the resin flow pattern, filling time, pressure distribution, and gelation behavior. The numerical model was validated against an analytical gelation-time correlation, resulting in the prediction errors of only 2.60% for the cylindrical configuration and 1.35% for the fishbone configuration. Compared with the conventional cylindrical arrangement, the fishbone configuration reduced the gelation time from 127 min to 96 min, corresponding to an improvement of approximately 24%, while achieving complete mold filling before gelation. Among all investigated strategies, the alternating and radial configurations exhibited the shortest filling times of approximately 30 min and 35 min respectively, whereas the parallel configuration required nearly 120 min. Furthermore, the cylindrical configuration filled only about 90% of the mold before gelation. The results demonstrate that optimized inlet configurations significantly improve the resin distribution uniformity, reduce filling time, and enhance manufacturing efficiency, providing practical guidelines for the design and optimization of resin infusion processes for composite marine structures.

Abstract This study investigates the thermal performance optimization of double-glazed window systems in Tehran climate conditions with the aim of minimizing building energy consumption. Four key design parameters were considered, including glass thickness (2, 4, 6, and 8 mm), glass type (ordinary, reflective, spectrally-selective, and blue-tinted glass), air-gap thickness between glazing layers (3, 6, 8, and 13 mm), and the type of filling gas (air, argon, krypton, and xenon). The modeling and optimization process was carried out using Response Surface Methodology (RSM) in Design-Expert software. The results demonstrated that increasing the air-gap thickness between the glazing layers significantly reduced the building energy consumption. Similarly, increasing the glass thickness improved the thermal insulation performance and decreased energy usage. Among the investigated gases, xenon exhibited the best thermal performance and resulted in the lowest energy consumption. In addition, reflective glass showed superior performance compared with the other glass types in terms of reducing energy demand. The optimization results indicated that the optimum configuration for achieving minimum energy consumption consists of reflective glass, xenon gas filling, an air-gap thickness of 12.75 mm, and a glass thickness of 2.825 mm. Under these optimal conditions, the minimum building energy consumption was obtained as 161.46 kWh/m². The findings of this study provide useful insights for the design and optimization of energy-efficient double-glazed window systems in a high-rise office building located in climates similar to Tehran.

Abstract Objective: C-Phycocyanin (C-PC) is a blue-colored protein antioxidant produced in the microalgae Spirulina platensis (S. platensis) that is used in the food, cosmetic and pharmaceutical industries. The purification methods are often time-consuming and expensive. In this study, Foam fractionation (FF) was used as a simple, rapid, cost-effective, and environmentally friendly method for the purification of C-PC.
Methods: C-PC pigment solution was extracted from dry S. plantensis biomass in phosphate buffer. FF method for the purification of C-PC was optimized using the response surface methodology (RSM). A UV-Vis spectrophotometer was used to determine the identifying absorbance peaks of the C-PC solutions.
Results: The RSM obtained an optimal setting at a pH = 6, aeration rate of 3.5 vvm, and operation time of 21 min for achievement of the highest purification fold (PF), purity index (PI), and C-PC recovery percentage (R) of about 1.56 ± 0.02, 0.59 ± 0.02, and 45.59 ± 0.72%, respectively.
Conclusion: In FF method there are no additional chemicals, also it is fast and has low operating costs, which make it an attractive method.

Abstract Abstract – pH control is crucial in biological and water treatment processes, yet it poses significant challenges due to its nonlinear characteristics. Conventional Proportional-Integral-Derivative (PID) controllers, while operator-friendly, often struggle to maintain satisfactory performance in highly nonlinear systems, especially when subjected to disturbances, measurement delay, and measurement noise. On the other hand, gain scheduling is a technique to cope with the process nonlinearity while maintaining the PID simplicity for the operators. In this paper, a gain-scheduled digital proportional-integral (PI) controller for pH control is presented, where the controller parameters are adapted using fuzzy logic. The control error and its numerical derivative are fed to the fuzzy inference unit with 7 membership functions, fuzzifying the severity of the control deviation. Then, the PI proportional and integral gains are updated in the defuzzification step. A simulation of a benchmark pH process with measurement delay was carried out under various scenarios. The results show that the proposed fuzzy-PI controller significantly outperforms the conventional PI controller. This is especially true in cases of feed disturbance and considerable setpoint changes, where the nonlinear process deviates significantly from the nominal point. In a combined disturbance/setpoint change scenario, the fuzzy-PI controller reduces the integral of absolute error by 54%.

Abstract Modern steam turbines employ extended low-pressure blades, subjecting root connections to severe centrifugal and thermal loads. As a result of these loadings, various and severe dynamic stresses are formed in the structure. Understanding this distribution of stresses and conducting studies on it will greatly help determine the lifespan of items and how to manage them. This study evaluates stress and strain distributions in Ti-6Al-4V turbine roots, specifically comparing BLISK and fir-tree designs under operational conditions. Using nonlinear Finite Element Analysis (FEA) and Local Plastic Stress and Strain Analysis (LPSA), peak von Mises stresses were identified as 890.76 MPa for the BLISK and 390.82 MPa for fir-tree roots. Advanced damage frameworks, including the Modified Mohr-Coulomb and Lemaitre's CDM models, are discussed conceptually to identify critical stress triaxiality states, thereby establishing a reliable baseline for subsequent fracture analyses. The findings establish a reliable baseline for fatigue studies, identifying root-blade transition fillets as critical sites for low- cycle fatigue failure. Understanding material behavior under fatigue loading can help in better determining the scope of application and optimizing the design.