Full article
Transport Phenomena,
Volume 6, Issue 4 , Autumn 2009, Pages 3-14
Abstract
In the present study a mathematical model is developed in order to examine the effects of heat and mass transfers on removal efficiency of particulate matters in venturi type scrubbers. The governing equations including the variations of the particulate concentration, gas temperature, droplet temperature, ...
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In the present study a mathematical model is developed in order to examine the effects of heat and mass transfers on removal efficiency of particulate matters in venturi type scrubbers. The governing equations including the variations of the particulate concentration, gas temperature, droplet temperature, diameter, and velocity are obtained based on the conservation laws and are solved numerically. In order to validate the model, necessary data was measured and collected in a commercial cement plant that uses these types of scrubbers in air pollution control applications. A good agreement between plant data and the model predictions is noticed in general. The results obtained from the model reveal that the existance of temperature difference between the gas and the liquid droplets decreases the overall removal efficiency of particulate matters. This is due to sudden reduction ofrelative velocity between the gas and droplets which is resulted from the existence ofheat and mass transfers between the two fluids, especially in the throat section. In addition, the effects ofvarious operating parameters on the extent ofreduction in the removal efficiency are examined. This study confirms that in most industrial applications ofventuri scrubbers it is necessary to use a direct or an indirect cooling tower in order to decrease the gas temperature before entering the venturi.
Full article
Transport Phenomena,
Volume 6, Issue 4 , Autumn 2009, Pages 15-26
Abstract
This paper reports a study on the effect of the heat flux, cooling water flow rate, fill ratio and extra volume on the overall performance of a partially vacuumed thermosyphon. A rig was made from a 1 m copper tube with an inner and outer diameter of 17.5 and 19 mm. The heights of the evaporator, the ...
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This paper reports a study on the effect of the heat flux, cooling water flow rate, fill ratio and extra volume on the overall performance of a partially vacuumed thermosyphon. A rig was made from a 1 m copper tube with an inner and outer diameter of 17.5 and 19 mm. The heights of the evaporator, the adiabatic section and the condenser are 40, 20 and 40 cm, respectively. The temperatures at different places on the thermosyphon and on the inlet/outlet ofthe cooling water were measured. It was observed that change in heat flux, fill ratio and employing different extra volumes, has a significant effect on its performance. On the other hand, with changes in the cooling water flow rate the performance ofthe thermosyphon was altered regarding the trapped air movement. In order to illustrate the effect ofthe existence ofair in deactivating the thermosyphon, the pipe was cooled down by disconnecting the evaporator power input. It was seen that the thermosyphon loses its performance as the trapped gas occupies the whole condenser. The whole study shows that due to the existence ofthe trapped air, the heat loads can have significant effects on the thermosyphon performance.
Full article
Process Control and Engineering, Process Safety, HSE
Volume 6, Issue 4 , Autumn 2009, Pages 27-33
Abstract
In low-temperature processes, heat rejected from separation columns is removed by refrigeration systems to heat sinks (reboilers & pre-heaters), process streams, other refrigeration streams, or external utilities. The need for efficient utilization and recovery of energy in sub-ambient gas separation ...
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In low-temperature processes, heat rejected from separation columns is removed by refrigeration systems to heat sinks (reboilers & pre-heaters), process streams, other refrigeration streams, or external utilities. The need for efficient utilization and recovery of energy in sub-ambient gas separation processes is still challenging. Performance and reliability of Simulated Annealing (SA) for simultaneous design and optimization of such systems has been investigated previously. In this work, the effect of different refrigerants satisfying a set of process cooling duties at different temperatures is addressed. Cost reduction can be realized by encompassing both effective screening of heat-integrated separation columns and selecting the best refrigerants. A 29.7% cost savings has been shown through a case study. Afterwards, a comprehensive thermodynamic analysis has been carried out on achieved solutions to verify the accuracy of existing shortcut models and robustness of optimized structure. It has been shown that exergy analysis using two different approaches (i.e. stream wise and unit operation wise) are the same, which indicate the accuracy of the used models. Moreover, we have indicated that both utility costs and exergy losses can be considered as an objective function when optimizing the designs.
Full article
Modeling and Simulation
Volume 6, Issue 4 , Autumn 2009, Pages 34-44
Abstract
This paper reports the result of CFD simulation of catalytic oxidation of benzene on monolithic catalyst. The geometries ofthe catalyst and reactor were designed in Gambit software and simulation of catalytic oxidation was carried out in fluent 6.2. Results of simulation showed excellent agreement with ...
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This paper reports the result of CFD simulation of catalytic oxidation of benzene on monolithic catalyst. The geometries ofthe catalyst and reactor were designed in Gambit software and simulation of catalytic oxidation was carried out in fluent 6.2. Results of simulation showed excellent agreement with the experimental data. This study confirmed the accuracy of the used model in this simulation (Mars van Krevelen). Furthermore, CFD made it possible to obtain a more accurate view ofheat transfer and fluid flow. This study confirmed CFD is the best tool for study offluid regime and heat transfer and especially, concentration of species, and surface deposition along the reactor in the chemical process.
Full article
Transport Phenomena,
Volume 6, Issue 4 , Autumn 2009, Pages 44-61
Abstract
A numerical investigation was carried out to solve the flow dimensionless partial differential equations through rectangular microchannels. A purely viscous power law model was used to characterize the flow behavior of non-Newtonian fluids. The flow was assumed to be steady and laminar, and slip conditions ...
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A numerical investigation was carried out to solve the flow dimensionless partial differential equations through rectangular microchannels. A purely viscous power law model was used to characterize the flow behavior of non-Newtonian fluids. The flow was assumed to be steady and laminar, and slip conditions were used as boundary conditions at the walls. The problem was solved for different power law indices as well as for various rectangular aspect ratios. Results showed that the effects ofslip velocity on dilatant fluids are more pronounced than that for pseudoplastic fluids. An increase in the power law index enhances the product of the friction factor and the Reynolds number, as well as the dimensionless incremental pressure drop and the dimensionless maximum velocity, while the hydrodynamic entrance length decreases. Results emphasize the significant effects of channel aspect ratio on the hydrodynamic flow behavior through microchannels.
Full article
Modeling and Simulation
Volume 6, Issue 4 , Autumn 2009, Pages 62-72
Abstract
In this study some properties ofthe methanol-water mixture such as diffusivity, density, viscosity, and hydrogen bonding were calculated at different temperatures and atmospheric pressure using molecular dynamics simulations (MDS). The results were compared with the available experimental data as well ...
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In this study some properties ofthe methanol-water mixture such as diffusivity, density, viscosity, and hydrogen bonding were calculated at different temperatures and atmospheric pressure using molecular dynamics simulations (MDS). The results were compared with the available experimental data as well as some theoretical models; overall indicating a good agreement. This shows the useful and effective application of MDS for determination ofphysical properties.
Research note
Thermodynamics,
Volume 6, Issue 4 , Autumn 2009, Pages 73-86
Abstract
In this research, the effect ofmixed salts together with mixed ionic surfactants on dropinterface coalescence time was studied for the system of water (d) / toluene(c) as a model system. Sodium dodecyl sulfate (SDS) and cetyl trimethyl ammonium bromide (CTAB) as anionic and cationic surfactants were ...
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In this research, the effect ofmixed salts together with mixed ionic surfactants on dropinterface coalescence time was studied for the system of water (d) / toluene(c) as a model system. Sodium dodecyl sulfate (SDS) and cetyl trimethyl ammonium bromide (CTAB) as anionic and cationic surfactants were used. Sodium chloride (NaCl) and magnesium sulfate were used as salts. In the first stage of experiments, the system of water and toluene was influenced separately with SDS+NaCl, SDS+MgSO4, CTAB+NaCl and CTAB+MgSO4. It was observed that drop size increased with SDS+NaCl and also with SDS+MgSO4. Partial coalescence times increased for all systems. Overall, this increase of coalescence time was more obvious when CTAB was applied. Also reduction in drop size was observed. In the case ofmixed surfactants with single salt, it was observed that partial coalescence was suppressed for the system with (SDS+CTAB)+MgSO4. On the other hand, drop size decreased and total coalescence time increased. This may be due to the difference between the anions and cations ofthe two salts. For the case ofmixed surfactants with mixed salts, drop size and coalescence time decreased.