نشریه جداسازی و پدیده های انتقال
سال بیست و یکم شماره 1 (1389)

In this research, a nonequilibrium stage model has been developed based on the film theory for modeling of H2S absorption process. A steady state film model was incorporated into the process model that considers mass transfer between gas and liquid phases in both directions. The method of lines has been used to discretize the set of partial differential equations of the model. The model was validated against the industrial data. The data were obtained from an industrial tray column. The process simulation results are presented in steady and unsteady states. A comparison between the experimental and simulation results showed that the model could reasonably predict the process behavior.

Gas–solid fluidized bed reactors have many industrial applications. Hydrodynamics of these systems requires more investigation due to their complexity of behaviors. In this study, the 2D hydrodynamics of fluidized bed containing 275 μm spherical glass beads was investigated by using CFD analysis. The simulation of fluidized bed, carried out using the two-fluid model combined with kinetic theory of granular flow for description of rheology of solid phase as a pseudo fluid. Whilst the superficial gas velocity were set on the range of 0.1–0.46 m/s. For the system of dense gas-solid fluidized bed, an algebraic granular energy-balance equation is proposed for determining the granular temperature instead of solving the full granular energy balance equation. This simplification does not lead to different results, but significantly reduces the computational effort of the simulation. The CFD simulation results were qualitatively and quantitatively compared with the literature. These comparisons show the good agreement between them. Particles velocity and volume fraction profiles predicted by CFD code were studied to increase insight of the transport phenomena and some physical phenomena such as particles erosion in these systems.

The aim of this research is investigation of the effects that come from presence of the sulfur in the Fe-Mg catalysts. One of the main reasons that reduces catalyst activity is poisoning in the Fischer-Tropsch synthesis. Catalysts with and without sulfur in their texture were studied. It was found out that presence of sulfur in the catalyst texture results in simoultaneous reduction of the selectivity and conversion. Also results show that, dependent on the sulfur content in the catalyst, CO conversion, selectivity to methane and coke formation are simoultaneously reduced. Also effects of sulfur on the catalyst texture and specific surface area of the catalyst were investigated.

Nanofluids are stable suspensions of nano solid particles in a conventional fluid. They have great potential in heat transfer enhancement and can be used in thermal equipment such as thermosyphons as the heat transfer media. A two-phase closed thermosyphon is a device for heat transfer; it consists of an evacuated-closed tube filled with a certain amount of a stable working fluid. In this paper, after preparing two kind nanofluids “Al2O3/Water” and “CuO/Water” in different volume percent (1%~3%) the role of using these nanofluids instead of pure water as the heat transfer media are investigated. Experimental results shows that nanofluid can significant improve efficiency of two-phase closed thermosyphon. For filling ratio of 45%, using the “Al2O3/Water” and “CuO/Water” nanofluid instead of water in the system, resulted in 14.7% and 13.4% gain in the efficiency. For both nanofluids maximum efficiency of two-phase closed thermosyphon tacked place at 35% filling ratio and 3 volume percent.

The generalization performances of the Back Propagation Multi-Layer Perceptron (BPMLP) and the Radial Basis Function (RBF) neural networks were compared together by resorting to several sets of the experimental data collected from a pilot scale packed absorption column. The experimental data were obtained from an 11cm diameter packed tower filled with 1.8 meter ¼ inch ceramic Rashig rings. The column was used for separation of carbon dioxide from air using various concentrations and flow rates of NaOH solution. Two efficient and reliable in-house algorithms were employed for optimal training of both neural networks. A robust procedure was exploited in these articles to predict the optimal widths of isotropic Gaussian basis functions for RBF networks [1]. Another in-house algorithm was also used to train the MLP networks more rapidly and efficiently in comparison with the conventional procedures [2]. The simulation results indicated that the RBF networks can perform more adequately than MLP networks on filtering out the noise and provide more reliable generalization performances because of their more solid theoretical background. Although most of the collected experimental results were just as we expected them, however, some results were out of the traditional trend. The numerous repetitions of these measurements prove that they can not occur due to random measurement errors. For example, absorbed percentage of carbon dioxide in various caustic solutions with different normality followed a peculiar trend which may prove fruitful in some special application.

Isomerization of n-hexane on the Pt/H-Mordenite catalyst was studied at different operating conditions, i.e., temperature, pressure and LHSV. It was found out that temperature increase results in higher conversion and simultaneously reduction of the selectivity to isomerate due to thermodynamic limitation. Increase in pressure, reduces the conversion but increases the selectivity. Decrease in space velocity results in higher conversion and simultaneously reduction of the isoalkane selectivity. Results show that the highest yield for maximum hexane isomerate is obtained at 270°C, 21bar, LHSV = 2h-1 and H2\HC mol ratio = 2.

In this article, the performances of several models proposed by researchers in the field of the prediction of hydrate equilibrium conditions are compared. They include: model used in CSMHYD software (presented by Sloan et al.), model used in HYSYS software, Chen-Guo model and Anderson model. All of the above models except Chen-Guo are developed based on van der Waals-Platteeuw model. To comparing the performances and accuracy of the above models, many sets of published data have been used. Average absolute deviation of pressure (AADP) applied as criterion to show error of each models. Comparison between the results and experimental data shows that Anderson model and model used in the HYSYS software have the minimum and maximum AADP, respectively. In the next step, Anderson model modified for presence of -TSA (-Toluene Sulfuric Acid) as a promoter. The Results of modified Anderson model shows good agreement with the experimental data