Removal of oil from biodiesel wastewater by electrocoagulation method

Mohsen Vafaie Sefti,Saeb Ahmadi,Ebrahim Sardari,Hamed Reza Javadian,Reza Katal 한국화학공학회 2013 Korean Journal of Chemical Engineering Vol.30 No.3

An attempt has been made to remove oil and grease (O&G) from biodiesel wastewater as well as O&G and turbidity in the presence of H2O2 and polyaluminum chloride (PAC), as a coagulant-aid by an electrochemical method using iron as sacrificial electrodes. The effects of current density, amount of hydrogen peroxide using as an oxidizing agent and addition of coagulant-aid, on percent removal and energy consumption have been investigated. The removal efficiency of O&G was in the range of 62-86%, whereas O&G removal was 100% in the current density range of 10-12.5 mAcm−2 depending on the concentrations of H2O2 and coagulant aid. It is obtained that electrocoagulation in the absence of coagulant aid and oxidant is not too efficient for the treatment of this type of wastewater.

An Electroosmotically-driven Micromixer Modified for High Miniaturized Microchannels Using Surface Micromachining

Reza Hadjiaghaie Vafaie,Mahnaz Mehdipoor,Adel Pourmand,Elnaz Poorreza,Habib Badri Ghavifekr 한국생물공학회 2013 Biotechnology and Bioprocess Engineering Vol.18 No.3

In order to offer the ability of smaller volumes and high throughput in Lab-On-a-Chip and micro Total Analysis Systems devices, more miniaturized components are needed. Due to a low Reynolds number on the microscale,the mixing process can be particularly troublesome. This problem is compounded by the fact that more miniaturization can be challenging in a microfluidic system. In such a case, electroosmotic (EO) force is an efficient force to perturb low Reynolds number fluid. In this paper,a novel Micro-Electro-Mechanical-Systems (MEMS) based fabrication for microfluidic devices, and a more miniaturized micromixer are presented. The proposed technology process requires the covering of excited electrode patterns by a thin Silicon-Nitride (Si3N4) insulator layer. Fabrication parameters such as Low Pressure Chemical Vapor Deposition (LPCVD)Si3N4 deposition effect, and height of the Phosphor Silicate Glass (PSG) sacrificial layer were investigated for the electroosmotically-driven mixer. Particle tracing for fluid flow was illustrated, the particles were stretched and folded for a long time, which was a proof of chaotic regime. Finite Element Analysis (FEA) revealed that the mixer with covered electrodes provides the high mixing efficiency of above 90% for a 96 μm long microchannel. Using a silicon nitride insulator layer reduces high electric field gradient at sharp corners and edges of the electrodes, leading to the elimination of unwanted electrolyte effects. Thus, the excitation and geometrical parameters were optimized for the micromixer.

Experimental Lnvestigation on Mechanical Characteristics and Environmental Effects on Rubber Concrete

Khorrami, Morteza,Vafai, Abolhassan,Khalilitabas, Ahmad A.,Desai, Chandrakant S.,Ardakani, M. H. Majedi Korea Concrete Institute 2010 International Journal of Concrete Structures and M Vol.4 No.1

The feasibility of the use of scrap tire rubber in concrete was investigated. The tests conducted in two groups: replacing of coarse aggregates with crumb rubber and cement particles with rubber powder. To distinguish the properties of new concrete, the following mechanical and durability tests were designed: compressive, tensile and flexural strength, permeability and water absorption. Rubber addition could affect the concrete properties depend on the type and percentage of the rubber added. Although the rubber addition modifies the mechanical characteristics of concrete in a way, but higher rubber content could not be useful. Concrete durability showed more dependency to the type of rubber instead of percentage of rubber. Moreover, to optimize the mechanical and durability of rubberized concrete, the useful percentage of rubber has been recommended.

Bulk and rheological properties of polyacrylamide hydrogels for water shutoff treatment

Asefe Mousavi Moghadam,Mohsen Vafaie Sefti,Mahsa Baghban Salehi,Hasan Naderi 한국화학공학회 2014 Korean Journal of Chemical Engineering Vol.31 No.3

Presenting an optimal hydrogel for water shutoff, based on the bulk and rheological properties, was themain purpose of this research. To determine gelation time, a bottle test was conducted using central composite designmethod with two factors, AN125VLM and Cr(OAc)3, as copolymer and crosslinker, respectively. To select hydrogelwith high strength network, crosslinking density and consistency modulus were also measured. Hence, a hydrogel with26,340 ppm concentration of copolymer, 0.12 ratio of crosslinker/copolymer, maximum value of crosslinking density(1,950) and consistency modulus (31,900 Pa) was selected as the optimal one. To study the gelation time among differentfactors in porous media, rheological experiments were carried out by Plackett-Burman design to screen the eightfactors (NaCl, CaCl2, KCl and MgCl2 concentrations, temperature, pH, sodium lactate and nanoclay). Accordingly,temperature was the most effective factor controlling the gelation time, while pH and other factors had negligible effecton the gelation time of the optimal hydrogel.

Preparation and investigation of the physical and chemical properties of clay-based polyacrylamide/Cr (III) hydrogels as a water shut-off agent in oil reservoirs

Farhad Salimi,Mohsen Vafaie Sefti,Khosrow Jarrahian,Majid Rafipoor,Seyyed Saeed Ghorashi 한국화학공학회 2014 Korean Journal of Chemical Engineering Vol.31 No.6

The effects of clay (montmorillonite and kaolinite) in the hydrogels were investigated on various propertiessuch as syneresis and strength of thermal and salinity situations in one of the southern Iranian oil reservoirs. The X-raydiffraction (XRD) patterns exhibited a significant increase in interplanar spacing between the montmorillonite claylayers, varying from the initial value of 12.43 oA to 19.45 oA, which evidences the intercalation formation. It was revealedthat even increasing of the interlayer spacing due to kaolinite modification had no effect on the clay compositions. Formationwater was used to study the strength of the hydrogel in the presence of ions. The results indicated that 15 wt%increase of kaolinite clay (modified and non-modified) leads to 20% decrease of the hydrogels’ syneresis. The diffusionof polymer chains between the clay layers increased the elastic modulus (G') of the prepared hydrogels with modifiedkaolinite and montmorillonite, where the maximum value of G' was observed in 3 wt% of montmorillonite. Finally,the thermogravimetric analysis (TGA) indicated an increase in the thermal stability of the mentioned hydrogels.

Numerical simulation of flattened heat pipe with double heat sources for CPU and GPU cooling application in laptop computers

Wisoot Sanhan,Kambiz Vafai,Niti Kammuang-Lue,Pradit Terdtoon,Phrut Sakulchangsatjatai 한국CDE학회 2021 Journal of computational design and engineering Vol.8 No.2

An investigation of the effect of the thermal performance of the flattened heat pipe on its double heat sources acting as central processing unit and graphics processing unit in laptop computers is presented in this work. A finite element method is used for predicting the flattening effect of the heat pipe. The cylindrical heat pipe with a diameter of 6 mm and the total length of 200 mm is flattened into three final thicknesses of 2, 3, and 4 mm. The heat pipe is placed under a horizontal configuration and heated with heater 1 and heater 2, 40 W in combination. The numerical model shows good agreement compared with the experimental data with the standard deviation of 1.85%. The results also show that flattening the cylindrical heat pipe to 66.7 and 41.7% of its original diameter could reduce its normalized thermal resistance by 5.2%. The optimized final thickness or the best design final thickness for the heat pipe is found to be 2.5 mm.

Congestion effect on maximum dynamic stresses of bridges

Kianoosh Samanipour,Hassan Vafai 국제구조공학회 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.55 No.1

Bridge behavior under passing traffic loads has been studied for the past 50 years. This paper presents how to model congestion on bridges and how the maximum dynamic stress of bridges change during the passing of moving vehicles. Most current research is based on mid-span dynamic effects due to traffic load and most bridge codes define a factor called the dynamic load allowance (DLA), which is applied to the maximum static moment under static loading. This paper presents an algorithm to solve the governing equation of the bridge as well as the equations of motions of two real European trucks with different speeds, simultaneously. It will be shown, considering congestion in eight case studies, the maximum dynamic stress and how far from the mid-span it occurs during the passing of one or two trucks with different speeds. The congestion effect on the maximum dynamic stress of bridges can make a significant difference in the magnitude. By finite difference method, it will be shown that where vehicle speeds are considerably higher, for example in the case of railway bridges which have more than one railway line or in the case of multiple lane highway bridges where congestion is probable, current designing codes may predict dynamic stresses lower than actual stresses; therefore, the consequences of a full length analysis must be used to design safe bridges.

Effects of reservoir temperature and water salinity on the swelling ratio performance of enhanced preformed particle gels

Amir Farasat,Mohsen Vafaie Sefti,Saeid Sadeghnejad,Hamid Reza Saghafi 한국화학공학회 2017 Korean Journal of Chemical Engineering Vol.34 No.5

Preformed particle gel (PPG) treatment is now one of the most effective remediation techniques for conformance controlling and selective plugging of high-water flow conduits in mature water-flooded oil reservoirs. Recognizing the intrinsic properties of PPGs, e.g., the swelling ratio, in reservoir condition is of prime importance to the optimization of their performance as plugging agents. In this study, the classical and three-level full factorial experimental design methods are joined with laboratory measurements to investigate the swelling ratio dependency of a new class of enhanced PPGs at different brine salinities and reservoir temperatures. To cover severe reservoir conditions, the reservoir temperature from 298 to 418 K and brine salinity from 0 to 225,000 ppm were considered during the laboratory measurements. The results show that the swelling ratio decreases by rising water salinity. Moreover, the swelling ratio rises by increasing reservoir temperature up to 380K and then starts to decrease. The factor screening illustrates that the swelling ratio is more dependent on salinity than the reservoir temperature in low salinity solutions, while is less dependent on salinity in high salinity solutions. In addition, a precise mathematical model was developed to predict the swelling ratio of PPGs in a wide range of salinities and temperatures. The results of this study present a practical insight into the swelling-related behavior of the PPGs at reservoir conditions.

Transient performance of a solar humidification–dehumidification desalination system based on hollow fiber membrane

Zhang Ning,Yin Shao-You,Vafai Kambiz 한국CDE학회 2021 Journal of computational design and engineering Vol.8 No.3

Solar humidification–dehumidification desalination system based on hollow fiber membrane is a promising method to produce drinkable water from brine due to its abilities for low primary energy consumption and pollution prevention for the liquid seawater droplets. As operating conditions change with temporal weather conditions, a dynamic model of this desalination system is developed and experimentally validated in this study. Transient performance is investigated and a regulation strategy is proposed. It is found that the startup time can be reduced substantially by decreasing the mean pore diameter, porosity of the membrane, solar collector area, and volume of the seawater in the storage tank, and increasing the packing fractions of the humidifier. The specific freshwater production (SWP) rate at the equilibrium state grows with longer mean pore diameter, higher porosity of the membrane, more solar collector areas, and less packing fractions of the humidifier. SWP is basically constant with different volumes of the seawater in the storage tank. Variations of solar radiation cause the low freshwater production and high energy consumption especially in the morning and afternoon. Utilizing our model, the hour-by-hour adjustment is also established. The accumulated water production in 1 day can be increased by 13.5% and the energy consumption can decrease by over 23% based on decreasing flow rates of the seawater in the morning and increasing flow rates of the cooling water in the afternoon. The proposed dynamic model will be helpful for the daily regulation of the seawater desalination system and a better performance can be realized.

FE analysis of RC structures using DSC model with yield surfaces for tension and compression

A.H. Akhaveissy,C.S. Desai,D. Mostofinejad,A. Vafai 사단법인 한국계산역학회 2013 Computers and Concrete, An International Journal Vol.11 No.2

The nonlinear finite element method with eight noded isoparametric quadrilateral element for concrete and two noded element for reinforcement is used for the prediction of the behavior of reinforcement concrete structures. The disturbed state concept (DSC) including the hierarchical single surface (HISS) plasticity model with associated flow rule with modifications is used to characterize the constitutive behavior of concrete both in compression and in tension which is named DSC/HISS-CT. The HISS model is applied to shows the plastic behavior of concrete, and DSC for microcracking, fracture and softening simulations of concrete. It should be noted that the DSC expresses the behavior of a material element as a mixture of two interacting components and can include both softening and stiffening, while the classical damage approach assumes that cracks (damage) induced in a material treated acts as a void, with no strength. The DSC/HISS-CT is a unified model with different mechanism, which expresses the observed behavior in terms of interacting behavior of components; thus the mechanism in the DSC is much different than that of the damage model, which is based on physical cracks which has no strength and interaction with the undamaged part. This is the first time the DSC/HISS-CT model, with the capacity to account for both compression and tension yields, is applied for concrete materials. The DSC model allows also for the characterization of non-associative behavior through the use of disturbance. Elastic perfectly plastic behavior is assumed for modeling of steel reinforcement. The DSC model is validated at two levels: (1) specimen and (2) practical boundary value problem. For the specimen level, the predictions are obtained by the integration of the incremental constitutive relations. The FE procedure with DSC/HISS-CT model is used to obtain predictions for practical boundary value problems. Based on the comparisons between DSC/HISS-CT predictions, test data and ANSYS software predictions, it is found that the model provides highly satisfactory predictions. The model allows computation of microcracking during deformation leading to the fracture and failure; in the model, the critical disturbance, Dc, identifies fracture and failure.