---

In recent years, with the advancement of nanoscience, many scientists have used nano materials to solve existing problems in various sectors of oil industry. Nanofluids made with these materials can facilitate the separation of oil and gas in a reservoir and increase oil recovery factor compared to current methods. Therefore, in this work, the effect of clay nanoparticles on oil recovery factor was investigated. For this purpose, two different base fluids, water and ethanol, were used to disperse the nanoparticles. The effect of adding clay nanoparticles on viscosity changes and interfacial surface tension was determined. Also, in order to investigate the effect of nanoparticle concentration in the base fluid on the ultimate oil recovery factor, nanofluids with 3 and 5 wt% were prepared. Results show that oil recovery factor increases significantly in these conditions by adding them into the base fluid, though nanofluids included clay nanoparticles have less stability. Also, the effect of these nanoparticles dispersed in water is greater than in ethanol. For example, at 5 wt%, oil recovery factor for water based nanofluid was 49.7% and for ethanol based nanofluid was 46%.

---

Research Subject: Nowadays, application of biosurfactants in microbial enhanced oil recovery (MEOR) have aroused much attention and several investigations have been conducted on this field. But their performance in comparison to synthetic surfactants in enhanced oil recovery has little been studied. Most of these researches are limited to comparison of one produced biosurfactant with only a chemical surfactant. To fill this gap, in this research, the potential use of a rhamnolipid type biosurfactant  in MEOR was compared to several conventional synthesized surfactants: SDS, SDBS, CTAB and DTAB.
Research Approach: Since the main goal of this research is the comparison between produced biosurfactant and conventional chemical surfactants in oil recovery, several flooding tests were conducted and involved mechanisms were investigated. All of tests were conducted in an oil wet glass micromodel saturated with heavy oil at ambient condition. Injected solutions were prepared at critical micelle concentration of surfactants. During the flooding tests, high quality pictures were taken with a camera connected to the computer to monitor the motion of injected solution in the micromodel.
 Main Results: 40% oil recovery was achieved after biosurfactant flooding while SDBS, SDS, CTAB and DTAB resulted 36%, 34%, 32% and 29% oil recovery, respectively. For mechanistic study, the surface tension (ST) and viscosity measurements were performed and contact angle was determined. The surface tension reduction, wettability alteration towards more water-wet condition and increasing the ratio of injected fluid viscosity to oil viscosity were dominant mechanisms. The rhamnolipid was more effective than other surfactants in reduction of surface tension and altering the wettability towards favorable water-wet conditions. It decreased the surface tension of water from 72 to 28 mN/m, which was the least comparing to other surfactants and increased the capillary number about 19.4 times greater than in water flooding. Additionally, it changed the contact angle from 106 to 6, 94.3%, the widest change among applied surfactants. 

---

  Emulsan compound produced by Acinetobacter calcoaceticus RAG-1 ATCC-31012. At present, this bioemulsifier show potential applications many sectors of food industry (soft cheese and ice creams). The ability of a bacterial to grow and produce emulsan by response surface methodology under shaking incubator conditions at 30°C was studied. Crude oil and ammonium sulfate at different levels use as a carbon and nitrogen source respectively. The medium culture optimum for emulsan production was occurred 4% (v/v) carbon source, 3gr/lit ammonium sulfate and 7% (v/v) inoculum’s size. At optimum levels of these parameters, 2.9 gr/lit biomass at end of fermentation was obtained. Production of emulsan by this bacterial culture resulted in surface tension reduction to 30 mN/m. Coefficients of determination, R², of fitted regression models for biomass production and surface tension are equal to 97.13% and 95.52%, respectively.

---

Biosurfactants are produced by microorganisms. Surfactin is one of the main lipopeptide biosurfactants produced by different species of Bacillus subtilis. This study aims to analyze the effect of starch-coated Fe⁰and Fe³⁺nanoparticles on the biosurfactant production of Bacillus subtilis. Out of 70 soil samples, 20 Bacillus were isolated and genome sequenced by biochemical methods and 16S rRNA gene. Quantitative and qualitative screening methods were used to isolate and detect biosurfactant production. For the aim of this study, 61 and 63 (Bacillus subtilis subsp. Inaquosorum) were selected. Then, hemolytic activity, surfactant production and reduction of surface tension in Minimal Salt Medium containing Fe⁰ and Fe³⁺ nanoparticles were examined after 48h, 72h and 96h of culture. The binding of the nanoparticles to the surfactant was confirmed by SEM. Strain 61 was the best bacterium and Fe³⁺ was the best nanoparticle and it was cultured. The results were compared with the results of non-nanoparticle bioreactor. Surfactin from strain 61 culture in the Fe³⁺ nanoparticle bioreactor after 72 hours of growth showed higher production than the same strain culture after 72 hours without Fe³⁺, if continuing the research, this strain can be commercialized in the future.
 

---

Condensing flow in nozzle and stationary blades of steam turbine has always been the subject of many studies. Due to the lack of precise relationship between surface tension and small droplet radius, the radial dependence of surface tension has been ignored in calculations and surface tension of flat surface instead of droplet surface tension is used. Gibbs-Tolman-Koenig-Buff equation expressing the radial dependence of surface tension that Kalova provides as a relationship of changes in surface tension versus radius of the surface by fitting response from the exact solution of GTKB equation. The aforementioned relationship is known as Kalova surface tension equation. The present study considers the effect of the Kalova surface tension correction on nucleation and droplet growth in condensing flows in an ultrasonic Laval nozzle. Since Tolman coefficient (δ) is an important parameter in Kalova surface tension equation, by fitting response from Tolman equations a correlation for Tolman coefficient temperature changes suggested for the first time. Kalova Surface tension in addition to the direct impact of the droplets crisis radius, to obtain droplet free energy crisis is also impressive that the impact of both them in the modified classical nucleation equation have been studied for the first time. The results of analytical modeling one-dimensional adiabatic supersonic flow with applying the Kalova surface tension correction and using the proposed equation for Tolman coefficient temperature changes indicate an improvement to the 12% in radius of the droplets and 5% in pressure distribution in the region of condensation shock.

---

In this paper, breakup of liquid jet is simulated using smoothed particle hydrodynamics (SPH) which is a meshless Lagrangian numerical method. For this aim, flow governing equations are discretized based on SPH method. In this paper, SPHysics open source code has been utilized for numerical solutions. Therefore, the mentioned code has been developed by adding the surface tension effects. The proposed method is then validated using dam break with obstacle problem. Finally, simulation of two-dimensional liquid jet flow is carried out and its breakup behavior considering one-phase flow is investigated. Length of liquid breakup in Reyleigh regime is calculated for various flow conditions such as different Reynolds and Weber numbers and the results are validated by an experimental correlation. The whole numerical solutions are accomplished for both Wendland and cubic spline kernel functions and Wendland kernel function gave more accurate results. Effect of fluid viscosity is investigated in the breakup length of the fluid as well. The accomplished modeling presented that smoothed particle hydrodynamics (SPH) is an efficient method for simulation of liquid jet breakup phenomena.

---

In this work the effect of carbon nanotube length on the nanofluidic energy absorption system is investigated by using molecular dynamic simulation. For this purpose, four rigid armchair carbon nanotubes (8,8), (10,10), (12,12) and (14,14), and six lengths (5.0 nm, 6.0 nm, 7.0 nm, 8.0 nm, 9.0 nm and 10.0 nm ) for each one are studied. Results of simulations show that the surface of carbon nanotube is frictionless in all length and diameters, causing water molecules defiltrated from carbon nanotubes after applying the loading-unloading cycle on the system. Contact angle which represents hydrophobic intensity of carbon nanotube is decreased averagely 4 and 2 % by increasing length and diameter of carbon nanotube, respectively; therefore, infiltration pressure of water molecules through carbon nanotube is decreased averagely 30 and 15 %, respectively. Moreover, the mass and size of carbon nanotube increase by increasing length and diameter of carbon nanotube, leading to the reduction of energy absorption density and efficiency. Also, density of water molecules in carbon nanotube unlike the bulk of liquid phase is non uniform, decreases in the first and second shells, and increases along the distance between them by increasing length of carbon nanotube.

---