Arezou Jafari

Application of different CFD multiphase models to investigate effects of baffles and nanoparticles on heat transfer enhancement

In this work, the effect of baffles in a pipe on heat transfer enhancement was studied using computational fluid dynamics (CFD) in the presence of Al2O3 nanoparticles which are dispersed into water. Fluid flow through the horizontal tube with uniform heat flux was simulated numerically and three dimensional governing partial differential equations were solved. To find an accurate model for CFD simulations, the results obtained by the single phase were compared with those obtained by three different multiphase models including Eulerian, mixture and volume of fluid (VOF) at Reynolds numbers in range of 600 to 3000, and two different nanoparticle concentrations (1% and 1.6%). It was found that multiphase models could better predict the heat transfer in nanofluids. The effect of baffles on heat transfer of nanofluid flow was also investigated through a baffled geometry. The numerical results show that at Reynolds numbers in the range of 600 to 2100, the heat transfer of nanofluid flowing in the geometry without baffle is greater than that of water flowing through a tube with baffle, whereas the difference between these effects (nanofluid and baffle) decreases with increasing the Reynolds number. At higher Reynolds numbers (2100–3000) the baffle has a greater effect on heat transfer enhancement than the nanofluid.

Application of CFD to evaluate the pore morphology effect on nanofluid flooding for enhanced oil recovery

In this study a computational fluid dynamics (CFD) method has been developed to simulate the effect of pore morphology and its distribution in a 2D micromodel on the enhanced oil recovery factor of nanofluid flooding. Seven types of micromodel with different schematics and pore shapes were considered. SiO2 nanoparticles, dispersed in distilled water, were used for the preparation of the nanofluid and flooding operation. To generate the desirable porous media, the geometries of the micromodels were generated using the commercial grid generation tool, Gambit 2.3. Then, the momentum and mass transport equations were solved based on the finite volume method using the Fluent 6.3 software to investigate the displacement of oil at the pore scale. In order to better understand the nanoparticles’ effects and to confirm the validity of the CFD simulations, numerical results have been compared with the experimental data. The influences of some parameters such as heterogeneity of pores, connectivity of pores with or without throat line, tortuosity and pore shape on the enhanced oil recovery, breakthrough time and fluid trapping in the porous media were investigated. From the results, it has been found that random generation of pore distribution illustrates better results compared to homogeneous pore distribution. In addition, with the presence of nanoparticles in the injected fluid the number of fingers decreases. The fingering effect has the main effect on the oil recovery factor with a lower fingering effect having a higher recovery factor. So, in the homogeneous pattern the nanofluid flow in the porous media is uniform and symmetric. But in the random distribution model, the fluid flow is more realistic and similar to the fluid flow in reservoirs.

Biosynthesis and physicochemical characterization of a bacterial polysaccharide/polyamide blend, applied for microfluidics study in porous media

Screening among some new isolated bacteria from oily samples, which were capable of producing extracellular polymeric substances (EPSs), one was selected and identified as Bacillus sonorensis. An efficient micro-total analysis approach was carried out to assay the produced EPSs by this bacterium. Sucrose and yeast concentrations as carbon and nitrogen sources, respectively, sodium salt concentration and initial pH were selected to be the variables in experimental design. Production of EPS in optimal condition was increased by 5.3 times. Further EPS purification was carried out to identify the biopolymers. The bacteria produced high molecular weight biopolymers with a number average molecular weight (M̅n) of 9.1×106g/mol determined by gel permeation chromatography (GPC). Biopolymer characterization demonstrated the biosynthesis of both polysaccharides and polyamides by the bacteria. For the biopolymer blend, thermal properties and morphological characteristics were studied using simultaneous differential scanning calorimetric and thermal gravimetric analyses (DSC/TGA) and field emission scanning electron microscope (FESEM) analyses. Finally, the biopolymer blend was injected into an oil saturated glass micro model to study the enhancement of oil recovery by biopolymer flooding in contrast with water flooding. It was found that oil recovery increased by 36%, from 23% using water flooding to 59% for biopolymer injection.

Purification of extra cellular poly-γ-glutamic acid as an antibacterial agent using anion exchange chromatography

BLAST analysis of the 16S rRNA gene sequence for the newly isolated bacterium, revealed significant identity (99.5%) with Bacillus sonorensis [Ijadi Bajestani, M., et al., International Journal of Biological Macromolecules, 2017. 96: p. 100-110]. According to the literature review for closely related species of Bacillus sonorensis, the production of poly-γ-glutamic acid (γ-PGA) as an extra cellular biopolymer was investigated for the isolated bacteria which is deposited in IBRC (Iranian Biological Resource Center) as Bacillus sp. Strain M2 (IBRC-M11173). To determine if γ-PGA production by Bacillus sp. Strain M2 is glutamate dependent, it was grown on PGA medium, consisted of sodium glutamate. The results proved that γ-PGA production is highly dependent on glutamate component. In the following, the bioproduct has undergone different purification processes mainly consisting of dialysis, deproteinization and anion exchange chromatography. Based on the high-performance liquid chromatography (HPLC) results for ion chromatography effluents, 59% of the initial PGA in main solution was eluted via NaCl elution. Gel permeation chromatography (GPC) characterization analysis was accomplished to determine the polydispersity and γ-PGA molecular weight. Two major average molecular weights were distinguished; the heavy weight fraction of 7.7×106g/mol with polydispersity index of 1.73 and the other one with an average molecular weight number of 1.7×104g/mol and polydispersity index of 4.4. The antibacterial activity of the extracellular γ-PGA, as an anionic biopolymer, toward Staphylococcus aureus and E. coli, was assayed using the clinical and laboratory standards institute (CLSI) guidelines. For Staphylococcus aureus the minimum inhibitory concentration (MIC) value was about 34g/L while for E. coli this value reaches 53g/L.