دوماهنامه مهندسی شیمی ایران
پیاپی 104 (امرداد و شهریور 1398)

In this paper the absorption of CO2 by MEA in a falling film reactor is simulated by means of Comsol Multiphysics. The simulated model is considered many aspects of the real process that occurred during the absorption process. The mass transfer process, the heat transfer process and hydrodynamic for liquid and gas phase is considered. Mass and heat transfer coefficient effect is considered by the simulation. The reaction was second order and the velocity profile was considering the effect of shear stress. The simulation results shown that only a small portion of the film thickness(0.002mm) contributed in mass transfer process. The reactor length was 1m(ID: 0.0139m). The simulation shown that by increasing liquid and gas flow rate, absorption rate by MEA increased too.

Thermal conductivity is defined as the ability of a material to heat transfer. In other words, thermal conductivity is the natural tendency of material to energy dispersion when temperature equilibrium disturbed by the imposition of a temperature gradient. Therefore, it plays a significant role in the issues of heat transfer. Due to the various applications of nanoscale materials in heat transfer and the importance of determining the thermal conductivity of nanofluids, this study, investigates eleven models for predicting the thermal conductivity of nanofluids (includes water and TiO2 nanoparticles) and comparing the results of calculations with the experimental results in the articles. Based on this study, it was found that the effective thermal conductivity ratio (thermal conductivity of the mixture of basic fluid and distributed nanoparticle) to the basic fluid conductivity (keff/kf) for variable Volumetric percentages ranging from 0.01 to 0.03 varies between 1.01 and 1.1. In the other words, addition of nanoparticles in the range of 1 to 3 Volume percentage is able to promote the keff/kf to 1.1 (10%). Therefore, thermal conductivity of the mixture of basic fluid and distributed nanoparticle increases up to 10% compared with basic fluid. Also, increasing the diameter of the nanoparticles reduces the thermal conductivity improvement.

In the present study, the problems of salt solution sedimentation on heat exchangers, their modelling procedure, and the heat exchanger fouling removal methods based on the related published investigation are reported. The salt solutions are used in many technological industries, and the sedimentation of stable salts is the main limitation of using them, especially in the high-temperature liquid-vapor system. The methods of these salts removing is online and offline fouling cleaning. Each of these methods has their advantageous and disadvantageous. In the practical application, there are multiple criteria considering different conditions. Although, based on the heat exchanger design condition, the solid salt sedimentation decrement can be improved the system fouling problems.

 A multiphase flow meter is designed to measure the flow rate of two or more phases without phaseseparation.The flow meter must be accurate enough for the desired application. It must be capable to measure the specifications throughout phase fraction of each phase, independent of the flow regime. Various factors are effective on selection of the flowmeter. Moreover, various procedures are present for measurement of multi-phase flows. In this study, a comprehensive review has been implemented on various technologies in multi-phase flowmeasurement in oil industry and the basis of various measurement techniques has been investigated. The advantages, requirements, and constraints of each technology have been reviewed. Finally,the recent advances in this field have been provided for the researchers.

Anaerobic digestion provides a way of treatment and management of organic municipal solid wastes and is a strategy to recover material and energy from waste. This paper aims to review anaerobic digestion from different aspects. First of all, the most important biological reactions included in anaerobic digestion, some strategies to improve the efficiency of the process and suitable reactors are described. Finally, the feasibility of anaerobic digestion in Iran is discussed briefly. According to the studies, the thermal pretreatment with the addition of alkalis, two or multi-steps continuous reactors and changing the operating parameters increase the efficiency of anaerobic digestion process. On the other hand, since much of the waste produced in Iran contains decomposable waste, anaerobic digestion is considered as a suitable process for municipal waste disposal in Iran to produce biogas and fertilizer.

Biofouling is one of the major problems in seawater membrane processes, especially in reverse osmosis (RO) plants. Biofouling occurs as a result of the attachment and growth of microorganisms onto the membrane. Fouling increases the pressure drop across the membrane and consequently increases the energy consumption, decreases the efficiency and shortens the life time of the RO membrane. In particular, biofouling causes a decline in water flux, an increase in salt passage and an increase in biodegradation of the membrane. There is an interest to eliminate or reduce the potential of scaling and biofouling on membranes to minimize cleaning frequency. Monitoring and control of biofouling is the most difficult issue among the other types of fouling, because microorganisms and organic matters that are responsible for biofouling behave differently under different conditions. In this review article, biofilm formation and its effective parameters, conventional and novel methods of monitoring and prevention of biofouling are investigated.