Sharif Digital Repository

Access to potable water with standard quality is an inevitable component of human's lives. Freeze desalination, by consuming lower energy compared to other techniques, relies on the exertion of a cold source which is then accompanied by simultaneous rejection of impurities from water. Regarding this, a numerical study on freeze desalination in a hollow cylinder is carried out to determine the effects of the design variables such as heat flux, hydraulic diameter, initial salt concentration, and freezing time on the ice mass, ice salinity, ice generation speed, and Nusselt number on the cold surface of the inner tube. Results show that increasing the value of heat flux from −250 [Formula... 

Drilling fluid is a complex fluid, including base fluid and other materials, carrying out the vital functions during drilling operation such as cutting transport and controlling formation pressure. In order to optimize performance of a drilling process, a reliable rheological model is required in the computation of fluid flow dynamics. Time-independent Generalized Newtonian formulation are the most common models for describing the rheological behavior of drilling fluids due to its simplicity and ease of use, in spite the fact that they are not able to predict the normal stresses and could not consider effects of active components on the rheological behavior of the drilling fluid and also... 

In this study, the effect of distance-dependent dispersion coefficients on density-driven flow is investigated. The linear asymptotic model, which assumes that dispersivities increase linearly with distance from the source of contamination and reach asymptotic values at a large asymptotic distance, is employed. An in-house numerical model is adapted to handle distance-dependent dispersion. The effect of asymptotic-dispersion on aquifer contamination is analyzed for two tests: (i) a seawater intrusion problem in a coastal aquifer and (ii) a leachate transport problem from a surface deposit site. Global Sensitivity Analysis (GSA) combined with the Polynomial Chaos Expansion (PCE) surrogate... 

In this study, the impacts of salinity, ion type, and aging process were investigated on coalescence and spreading of crude oil interfaces (including an oil droplet and an oil film) under gravity, through drop rest time measurement techniques, aided by an image analysis system. Three different salt solutions of NaCl, Na2SO4, and MgCl2 were studied at different ionic strengths, ranged from 1% to 150% of Persian Gulf seawater ionic strength. According to the results, aging the oil droplet in the brine increased the interfacial rigidity. Addition of a gas phase - by thinning the surface oil film - almost doubled both rest time and spreading time values. In the aged mode, the presence of salt in... 

Water desalination methods on the basis of newly developed graphene-based membrane have been introduced as a more efficient alternative for the conventional water purification technologies such as classical thermal desalination and reverse osmosis (RO). However, the increase of water permeation rate and ion rejection are still the main subjects in this field. In this study, a new method based on using oscillating electric field is proposed to improve the performance of nanoporous graphene. The effects of the amplitude and oscillation frequency of the electric field and the pore size of the membrane on the water permeation and salt rejection are studied by conducting molecular dynamics... 

Implementation of metal organic frameworks (MOFs) in the separation science has attracted many researchers attention. In this study, the role of metal, ligand, the reaction condition and modification on the extraction efficiency of some MOFs was investigated. Among the prevalent reported MOFs, some members of the MIL and MOF–5 families were chosen, and eleven MOF–based sorbents were prepared by changing the metal and ligand type, reaction condition, and/or functionality through post synthetic modification (PSM). MIL–101 and MIL–101–NH2 based structures were initially synthesized based on the chromium and iron salts. Also, three zinc–based structures including MOF–5, [NH2(CH3)2]2... 

Iterative methods have led to better understanding and solving problems such as missing sampling, deconvolution, inverse systems, and impulsive and Salt and Pepper noise removal problems. However, the challenges regarding the speed of convergence and or the accuracy of the answer still remain. In order to improve the existing iterative algorithms, a non-linear method is discussed in this paper. The mentioned method is analyzed from different aspects, including its convergence and its ability to accelerate recursive algorithms. We show that this method is capable of improving Iterative Method (IM) as a non-uniform sampling reconstruction algorithm and some other iterative sparse recovery... 

Lake Urmia, which was once the second-largest saline lake in the world, has been shrinking dramatically. Moreover, Lake Urmia has become supersaturated with total salinity averaging more than 350 g/l. Salt precipitation and dissolved materials brought by inflowing rivers have formed a layer of sediment with low hydraulic conductivity on the lakebed. Considering the flat bathymetry of Lake Urmia, we conducted a series of numerical simulation scenarios to study the groundwater flow pattern in the vicinity of the hypersaline Lake Urmia using COMSOL Multiphysics®. In the first step, we performed the simulations in steady-state conditions. Secondly, we simulated the lake level fall in 10 years at... 

In this study, a thermal vacuum distillation amine reclaimer unit was industrially and theoretically investigated to remove HSS from a salty amine stream. The presence of ions in the salty amine solution limits application of computer simulation tools to study the process. A thermodynamic equivalent scheme was used for thermal vacuum distillation amine reclaimer, for first time and the simulation results were totally conformed to experimental and industrial data. The effect of critical parameters namely reclaimer vacuum pressure, re-circulation flow rate and HSS amount on performance of thermal amine reclaiming was investigated based on increasing amine solution quality, amine recovery,... 

In this study, water-soluble terpolymers containing highly hydrophilic monomers of acrylamide and maleic anhydride and highly hydrophobic monomers of styrene were synthesized (ASM) through the one-step inverse emulsion polymerization. Proton nuclear magnetic resonance (1H NMR), fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction pattern (XRD) were performed to investigate the chemical structures and structural transformations of ASM. Thermal stability and thermal decomposition steps of ASM were studied by thermogravimetric analysis (TGA). An Ubbelhode capillary viscometer and a rheological mechanical spectrometer (RMS) were employed to obtain the specific, relative, and... 

Clay liners are widely used as porous membrane barriers to control solute transport and to prevent the leakage of leachate both in horizontal and vertical flow scenarios, such as the isolated base and ramps of sanitary landfills. Despite the primary importance of saturated hydraulic conductivity in a reliable simulation of fluid flow through clay barriers, there is no model to predict hydraulic conductivity of clayey soils permeated with saline aqueous solutions because most of the current models were developed for pure water. Therefore, the main motivation behind this study is to derive semi-empirical models for simulating the hydraulic conductivity of clayey soils in the presence of... 

This study aims at analyzing the performance of three units known as low salt rejection reverse osmosis (LSRRO), split-feed counterflow reverse osmosis (SF-CFRO), and split-brine counterflow reverse osmosis (SB-CFRO) and implementing them in a modified multi-stage multi-feed counter-current membrane with cascade recycle for dewatering hypersaline streams to the salinity appropriate for crystallizers' feed. Exergy and primitive pinch analysis showed that dewatering is limited in SF-CFRO as the permeate inlet dictates the maximum salinity difference at the pinch point as well as high frictional pressure loss in the permeate channel. SB-CFRO and LSRRO units can reach high salinities by... 

Understanding of how anthropogenic droughts occur in socio-hydrological systems is critical in studying resilience of these systems. This is especially relevant when a “lock-in” toward watershed desiccation occurs as an emergent outcome of coupling among social dynamics and surface and underground water processes. How the various processes collectively fit together to reinforce such a lock-in and what may be a critical or ignored feedback worsening the state of the socio-hydrological systems remains poorly understood. Here we tackle this gap by focusing on the case of Lake Urmia in Iran, a saline lake that faces the same fate as that of Aral Sea due to over-extraction of water sources that... 

Graphene, due to its unique excellent properties, is proposed as a developing method with high efficiency compared to classical water desalination methods. In this regard, charging the membrane is considered a promising and effective approach to enhance the performance of the graphene membrane. In this research, by using molecular dynamics simulations, the water desalination by charged multilayer graphene is evaluated and the influence of electric charge amount and geometric parameters, including the pore diameter and the interlayer distance, are investigated. According to the results, the multilayer nanoporous graphene with 16.35 Å pore diameter, in which the electric charge is distributed... 

In the present study, the effect of electromagnetic field on the salt and water transport and reduction of carbonate deposit during reverse osmosis desalination was investigated. The electromagnetic field was generated by AC current through a solenoid wound around the membrane separation module. The current intensity and frequency was 25 A and 50 Hz, respectively. Experiments were conducted using CaCO3 solution at the concentration of 5.5 mmol/L. For comparison purposes, desalination by the membrane, in the presence and absence of an electromagnetic field was conducted. While the desalination process temperature was kept constant, the product temperature increased by less than 2 °C when the... 

Retention of lead(II) ions on a polyamide nanofiltration membrane was investigated. Effects of different factors including operating pressure, lead ion concentration, anion nature, pH and composition of feed on the lead ion rejection were studied. The solutions used consisted of Pb(NO3)2, PbCl2 and PbSO4 in the single-salt solution system and Pb(NO3)2, Cu(NO3)2, Zn(NO3)2, Cd(NO3)2, NaNO3 and NH4NO3 in the binary-salt solution system. The influence of divalent and monovalent cations including cadmium, copper, zinc, sodium and ammonium on the rejection of lead ion was examined. The transmembrane pressure and lead ion concentration varied between 10 and 40bar and 20 and 400mg Pb2+/L,... 

In the present work, the hot corrosion behavior of two types of multilayer plasma sprayed TBC were investigated and compared with functionally graded and conventional TBCs. These kinds of multilayer coatings consisted of nano/μ alumina as a top coat on YSZ layer, a metallic bond coat and a functionally graded intermediate layer deposited between YSZ and bond coat layers. All the layers were sprayed on the Ni-base super alloy substrate. The hot corrosion resistance of the plasma sprayed coatings was examined at 1050 °C for 40 h, using a fused mixture of 45 wt% Na2SO4 + 55wt%V2O5. Before and after hot corrosion, the microstructure and phase analysis of the coating were studied using scanning... 

Although the capability of using sulfate anion as a wettability modiffier is well established, no systematic investigation on the effect of sulfate ions and natural surfactants in the crude oil including asphaltene and resin on the interfacial tension (IFT) of acidic crude oil (ACO)/sulfate were performed. In this regards, the fluid/fluid interactions are tested through the IFT measurements for ACO, asphaltene and resin extracted from ACO in the presence of sulfate salts including Na2SO4, MgSO4 and CaSO4 while the concentration of each salt ranges between 0 and 45000 ppm. The obtained results demonstrate that the capability of asphaltene molecules is higher for IFT reduction compared with... 

An equation of state based on the statistical associating fluid theory for potentials of variable range (SAFT-VR) is used to model 7 hydrogen-bonding solvents and 23 electrolyte solutions. Solvent-solvent hydrogen bonding interactions are explicitly taken into account as in other versions of the SAFT approach. In addition, long-range Coulombic interactions between ionic species are accounted for using the non-restricted mean-spherical approximation, while solvent-solvent and solvent-ion dispersion interactions are included and are treated using Yukawa potentials. Previously a similar approach had been proposed in which the dispersion interactions were treated using square-well potentials. In... 

COMSOL Multiphysics is a comprehensive simulation software environment for a wide range of applications. COMSOL has an interactive interface that facilitates the modeling procedure and allows an easy coupling of different physical processes. The Subsurface Flow module extends the COMSOL modeling environment to applications related to fluid flow in saturated and variably saturated porous media. COMSOL is increasingly used in the investigation of geophysical, hydrogeological and environmental phenomena. The main goal of this work is to explore the ability of COMSOL for simulating seawater intrusion (SWI) in fractured coastal aquifers. Numerical modeling of such a problem is of high interest as...