Sharif Digital Repository

Drop size distribution plays a key role in the liquid extraction systems and related hydrodynamic and mass transfer parameters. In current research work, the size of drops in an extraction spray column has been measured by direct photography method, and the Sauter mean diameter has been obtained accordingly. Then, two types of models are assessed based on using dimensionless analysis and appropriate software. The interfacial tension in used chemical system is 1.8-32 dyne/cm. In first type of models, the correlation is established based on dimensionless parameters similar to approaches defined by other researchers. In second types, dimensional parameters have been used and therefore a new... 

It is well known that the direct synthesis of Di-Methyl Ether (DME) from the Syngas is highly exothermic; therefore, the temperature control for its production and hence a suitable heat transfer pattern is of ought most significance to the success of such process. As such, slurry bubble column reactor is recognized to be a more suitable means for this purpose than other choices including fixed bed reactor which is the usual type of system in which direct DME synthesis takes place. In other words, slurry reactors are desirable due to having suitable heat and mass transfer properties. In this research a mathematical model for direct synthesis of DME from synthesis gas in a slurry reactor for a... 

In this study, test results of four precast concrete beam-column connections and one monolithic concrete connection are presented. The tests constituted the second phase of an experimental program on a 2/5-scale model precast connection. The objective of the test program was to design a simple moment-resisting precast connection for regions of high seismicity. The connection transfers bending moment by a combination of lap-splicing and end anchorage of bars. The end portions of precast beams sit on the column bearing area at the beginning of subassemblage construction. The variables examined were the level of axial load on column, spacing of beam stirrups in the connection length region,... 

The individual and combined effect of shear deformation and rotary inertia on the columns was discussed. It was shown that the shear deformation effect always tends to reduce the buckling load. It was observed that rotary inertia for supported columns has no effect on the buckling load. The critical buckling load of perfect columns subjected to static axial loading was calculated using the Euler-Bernoulli theory  

The purpose of the present paper is to develop light beam method to measurement of interfacial area in a rectangular gas-liquid bubble column. Total interfacial area can be determined in bubble column filled by transparent liquid by light transmission method. According to pervious researches, the fraction of parallel light is function of interfacial area and optical path length that these two parameters imply Transmission Number or N T. The drop diameters were measured in the range of 2.2 to 5 mm, and in this range, the specific area is found to depend only upon the light transmission. Three different systems with various liquid phases have been used in this work. It had been proved that... 

While studying the operation of a rectangular bubble column in laboratory scale, it was observed that under certain circumstances tiny bubbles attach to larger bubbles without causing them to coalesce. In other words, bubbles with large diameters (d > 5 mm) swept tiny bubbles (d < 1 mm) in their way to the top of the column resulting in grapelike clusters of bubbles. This phenomenon was named "bubble bunch" by us and its effect on total gas holdup and interfacial area was discussed. Although it was found to have almost no affect on gas holdup, bubble bunch can increase the interfacial area up to 10% more than what is anticipated in the literature. The process of film thinning was modeled for... 

Red mud (RM) is generated as a by-product during the production of alumina from bauxite ore. In this study, RM packing in a column is used as a catalyst for carbon–carbon double bond formation via Knoevenagel condensation. The reactants are added to the top of the column and then eluted with solvent. The products are collected in high yields and short time. RM packed in a column eliminates a catalyst separation step from the reaction mixture in this work. © 2007 Taylor & Francis Group, LLC  

A new semi-rigid beam-to-column, as well as bracing-to-frame, connection has been developed. In addition to its application in building structures, due to its special features and characteristics, it can best lend itself to offshore jackets, where fracture caused by fatigue has always been a major concern. The adverse effects of welding, material embrittlement, residual stresses, etc., pronounced by cyclic loading on such structures, can be overcome by using this new connection. Moreover, it can be easily used in the structure of various modules used in the topside of platforms and FPSOs. The particular feature of this connection is its geometry, which is so devised that it allows much... 

This paper presents the behavior of high-strength lightweight concrete columns confined with small size diameter hoop reinforcement. The concrete had a strength of up to 87.2 MPa (12,500 psi). The experimental program consisted of axial load tests on eight column specimens. The cross-sectional shape of the column specimens was elliptical, with dimensions of 152 × 229 mm (6 × 9 in.) and height of 762 mm (30 in.). The only longitudinal reinforcements used were four 4.52 mm (0.178 in.) diameter wires that were tack-welded to the lateral reinforcement to maintain the desired configuration of the lateral reinforcement. The influencing parameters included concrete strength and amount and spacing... 

The present work is expressed to interpret the hydrodynamic parameters of rotation extraction columns in the reactive and non-reactive systems. The solvent extraction technique has been utilized for optimizing the transportation of molybdenum ions to the organic phase in two agitated columns (ORC and Kühni columns). Dispersed phase volume fraction, average droplet diameter, slip velocity, size distribution, and ions permeability of the aqueous phase have been investigated in terms of changing the operational variables including the agitation rate, flow rate of the inlet dispersed and continuous phases, column geometry, and reaction conditions. By considering the reactive and non-reactive... 

In the present work, multistage extraction column performance for reactive separation of molybdenum from the leach aqueous phase by using D2EHPA and TBP in kerosene was investigated by using the axial diffusion model. The variation of volumetric overall mass transfer coefficients based on continuous phases at various operating conditions was obtained. By considering the chemical reaction conditions, the experimental data indicate that the volumetric overall mass transfer coefficients increase with an enhancement in rotor speed and continuous and dispersed phase flow rates. According to the sensitivity analysis, the rotor speed and flow rate of the dispersed phase have more influence on... 

Estimating efficiency of an operating column has to be distinguished from that of a column being designed. This crucial point has been totally overlooked in the literature. All the methods and models available for predicting the Murphree efficiencies of tray columns have been developed for the design case. They generate their own mass and heat transfer rates and empirical parameters rather than produce true transfer rates by using operating column (realistic) data, especially the specifications of outlet streams. In addition, most of these methods are limited in application and insufficient in accuracy, especially if applied outside the range of conditions under which they were formulated.... 

The buckling behaviour of compression members is very important in structural engineering especially those that are made from high strength steel (HSS). This paper presents an investigation into the behaviour of four columns which were designed according to EN 1993-1-1 (2005) so that the buckling capacity of both HSS and mild steel column was equal. A finite element model was created which included imperfections due to residual stresses as well as local and global imperfections. It was found that the buckling capacity of the columns made from 460 MPa steel was lower than that for similar capacity mild steel columns with a yield strength of 275 MPa. Accordingly, a buckling curve for HSS is... 

This paper presents a two-level optimal control for the binary distillation column. From the control point of view, the binary distillation column is a high-order system consisting of several interconnected subsystems (trays) that aim to maximize output purity. Controlling the system in a hierarchical manner not only decreases complexity and solution time but also can improve the control structure's reliability. In this study, the distillation column is decomposed into NT second-order subsystems, each representing one stage (one tray). Accordingly, the cost function is decomposed, and thus, the overall problem is converted into NT lower-order subproblems where each tray has its own... 

In this study, a cryogenic distillation column has been designed and simulated via a computer code based on the theta method of convergence. The required thermodynamic properties are determined from the enhanced predictive Peng-Robinson (E-PPR 78) equation of state which has a good accuracy in predicting the corresponding thermodynamic properties of natural gas components. The combined code of distillation column/equation of state has been verified with that of another study. In the present study, the results are achieved by the constant molar over-flow and inclusion of energy equations assumptions. In order to have more accuracy in the results, the energy equations were considered in the... 

The aim of this paper is to study the influence of the column-to-beam strength ratio on the seismic strengthening of a column with a Fiber-Reinforced Plastic (FRP) wrapping system. FRP wrapped Reinforced Concrete (RC) columns are analyzed to obtain moment-curvature curves using FRP confined concrete characteristics. A pushover analysis of a 2D model was performed on one and three-story moment-resisting frames, with different column-to-beam strength ratios. The results indicate that FRP strengthening is more efficient in frames with a low ratio of column-to-beam strength, due to the type of lateral failure mechanism of the frame. Also, high values of the column-to-beam strength ratio can be... 

Reinforced concrete columns with insufficient transverse steel reinforcement are not capable to dissipate seismic energy due to lack of necessary ductility. In this research, six RC columns with poor transverse reinforcements are tested under cyclic and axial loads as control columns and retrofitted ones. Prestressed and non-pre-stressed CFRP strips used as external transverse reinforcement to evaluate the benefits of active and passive confinement. Results indicate that additional confinement due to the use of CFRP strips enhances the strength, ductility and energy dissipation capacity of columns. The advantages of active confinement versus passive confinement are demonstrated too. © 2006... 

In this survey, the reactive mass transfer data are determined for extraction technique in the modified rotating disc column. Mathematical models are investigated to compute the mass transfer coefficients of the dispersed phase. An increase in the dispersed phase holdup from 0.85 to 0.12 and a decrease in droplet diameter from 2.24 to 0.74 mm are observed with increasing rotation speed from 170 to 410 rpm in the optimized system. The experiments showed that the optimum transport efficiency in rotor speed of 410 rpm in this column is equal to 98.85% and 99.45% for extraction and stripping stages, respectively. The model's achievement is compared with the solvent extraction data and a...