Iranian journal of chemical engineering
Volume:6 Issue: 4, Autumn 2009

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 of slip 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.

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.

This paper reports the result of CFD simulation of catalytic oxidation of benzene on
monolithic catalyst. The geometries of the 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 of heat transfer and
fluid flow. This study confirmed CFD is the best tool for study of fluid regime and heat
transfer and especially, concentration of species, and surface deposition along the
reactor in the chemical process.

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 of slip 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.

In this study some properties of the 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 of physical properties.

In this research, the effect of mixed 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 5, SDS2,
CTAB 5 and CTAB2. It was observed that drop size increased with
SDS 5 and also with SDS2. 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 of mixed surfactants with
single salt, it was observed that partial coalescence was suppressed for the system with
(SDS0 )2. On the other hand, drop size decreased and total coalescence
time increased. This may be due to the difference between the anions and cations of the
two salts. For the case of mixed surfactants with mixed salts, drop size and coalescence
time decreased.