Liquid repellency treatment has many applications in various sectors including oil and gas reservoirs and self-cleaning surfaces. In this study, effect of silica, fluorine-doped silica and ...fluorine-doped silica-coating by fluorosilane nanofluid on ultrahydrophobic and ultraoleophobic surface of carbonate and sandstone rock were investigated. The nanoparticles were synthesized by sol-gel method and characterized using XRD, FTIR, FESEM and DLS and nanofluid was prepared. F-SiO2-F nanoparticle was adsorbed on surface of rocks and confirmed by FESEM and EDXA. Effect of nanofluid on wettability was investigated by measuring contact angles of water, crude oil, condensate, n-decane and ethylene glycol in air and stability of ultrahydrophobic and ultraoleophobic was investigated. Results show that nanofluid (0.05 wt% of nanoparticle) changes contact angle from strongly liquid-wet to strongly gas-wet in all systems. The original contact angle of water, crude oil, condensate, n-decane and ethylene glycol were 37.95°, 0°, 0°, 0° and 0° for carbonate rock and 40.30°, 0°, 0°, 0° and 0° for sandstone rock which altered to 146.47°, 145.59°, 138.24°, 139.06° and 146.52° for carbonate rock and 160.01°, 151.40°, 131.85°, 140.27° and 151.70° for sandstone rock after treatment. The ultraoleophobic and ultrahydrophobic stability were >48 h and 120 min.
We observed the globular cluster NGC 6652 with Chandra for 47.5 ks, detecting six known X-ray sources, as well as five previously undetected X-ray sources. Source A (XB 1832-330) is a well-known ...bright low-mass X-ray binary (LXMB). The second brightest source, B, has a spectrum that fits well to either a power-law model (Gamma ~ 1.3) or an absorbed hot gas emission model (kT ~ 34 keV). Its unabsorbed 0.5-10 keV luminosity (L sub(X) = l.6 super(+0.1) sub(-0.1) x 10 super(34)erg s super(-1)) is suggestive of a neutron star primary; however, Source B exhibits unusual variability for an LMXB, varying by over an order of magnitude on timescales of ~100s. Source C's spectrum contains a strong low-energy component below ~ 1 keV. Its spectrum is well fit to a simplified magnetic cataclysmic variable (CV) model, thus the soft component may be explained by a hot polar cap of a magnetic CV. Source D has an average L sub(X) (0.5-10 keV) ~ 9 x 10 super(32) erg s super(-1) and its spectrum is well fit to a neutron star atmosphere model. This is indicative of a quiescent neutron star LXMB, suggesting Source D may be the third known LMXB in NGC 6652. Source E has L sub(X) (0.5-10 keV) ~ 3 x 10 super(32) erg s super(-1), while Source F has L sub(X) (0.5-10 keV) ~ 1 x 10 super(32) erg s super(-1). Their relatively hard X-ray spectra are well-fit by power-law or plasma emission models. Five newly detected fainter sources have luminosities between 1 and 5 x 10 super(31) erg s super(-1). NGC 6652 has an unusually flat X-ray luminosity function compared to other globular clusters, which may be connected to its extremely high central density.
Fine SiO2 nanosphericals (2-5nm) and new various stable nanofluids including Tween 80, Span 80, Lauric alcohol-3EO, CTAB, SDS and K-Laurate surfactants in water or paraffin based solution were used ...as new SiO2 nanoproducts in oil recovery. These nanofluids can strongly change oil-wet carbonate reservoir rock to complete water-wet wettability and showed an excellent trend of surface tension (S.T) and IFT (interfacial tension) reduction in comparison with pure water and reference solutions. The CaCO3 plates reservoir was then aged for 2, 5 and 8 days into the 1, 3 and 8% of different concentrations of synthesized SiO2 nanofluids (effect of various concentrations via different aging time). Air/water and n-decane/water contact angles on oil-wet and clean carbonate rock aged in designed SiO2 nanofluids were measured and the pH value as a significant factor estimated. The interesting influence of microwave irradiation on surface tension and IFT including various SiO2 nanofluids was investigated after 12 min which some of the especial nanofluid concentrations showed successful reduction. Our findings indicated the important effect of temperature over decreasing of surface tension and IFT between oil and water interface including SiO2 nanofluids after annealing at 70°C. Therefore, this phenomenon can be significantly capable and valuable in applying of new technology in the fabrication of novel nanofluids in EOR processes and saving source of energy regarding to conventional production.
Physically crosslinked nanocomposite hydrogels based on polyvinyl alcohol (PVA) containing Na-montmorillonite were prepared by the cyclic freezing-thawing method. The primarily exfoliated morphology ...of prepared nanocomposite hydrogels was confirmed by X-ray diffractometry (XRD) and transmission electron microscopy (TEM) as complementary techniques. It is shown that some interactions developed between the hydroxyl groups of PVA chains and Na-montmorillonite silicate layers in the nanocomposite hydrogels. Differential scanning calorimetry (DSC) results indicated some shifting in the glass transition temperature of the PVA hydrogel in the presence of the nanoclay. Swelling measurements showed that the swelling ratios of the nanocomposite hydrogels were increased either by decreasing the Na-montmorillonite content or by increasing the swelling medium temperature. Dynamic mechanical-thermal properties results showed higher storage modulus for nanocomposite hydrogels in temperature ranges both below and above 0°C. It was also found that the hardness of the nanocomposite hydrogels increased by increasing the nanoclay loading level.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Polyvinyl alcohol nanoporous nanocomposite hydrogels containing various levels of Na-montmorillonite were prepared by a cyclic freezing-thawing technique. An exfoliated morphology of silicate layers ...was observed for the nanocomposite hydrogels. The uniaxial tensile test indicated that the tensile modulus and tensile strength of the nanocomposite hydrogels increased with increasing Na-montmorillonite content, while their elongation-at-break values decreased. The results showed that by adding 15 wt% of montmorillonite to polyvinyl alcohol hydrogels, the molecular weight of polymer chains between two adjacent cross-links decreased to 56% and the effective cross-linking density increased up to 353%. It is also indicated that all nanocomposite hydrogel samples had nanoscale pore diameters and network mesh sizes less than 30 nm. The nanoporous structure of the nanocomposite hydrogels was confirmed by transmission electron microscopy observations and mercury intrusion porosimetry tests.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
We report observations using the Swift/XRT, NuSTAR, and Chandra X-ray telescopes of the transient X-ray source CXOGC J174540.0-290005 during its 2013 outburst. Due to its location in the field of ...multiple observing campaigns targeting Sgr A*, this is one of the best-studied outbursts of a very faint X-ray binary (VFXB; peak L
X < 1036 erg s−1) yet recorded, with detections in 173 ks of X-ray observations over 50 d. VFXBs are of particular interest, due to their unusually low outburst luminosities and time-averaged mass transfer rates, which are hard to explain within standard accretion physics and binary evolution. The 2013 outburst of CXOGC J174540.0-290005 peaked at L
X(2–10 keV) = 5.0 × 1035 erg s−1, and all data above 1034 erg s−1 were well fitted by an absorbed power law of photon index ∼1.7, extending from 2 keV out to ≳70 keV. We discuss the implications of these observations for the accretion state of CXOGC J174540.0-290005.
The thermophysical properties for a gas condensate mixture taken from a British North Sea reservoir were determined via an initial value method using acoustic information. A distinct functional form ...was considered for the sound velocity in terms of pressure along each isotherm. Detailed results are presented on the computed thermophysical properties, including expansivity, isothermal compressibility, isobaric heat capacity, and the Joule-Thomson coefficient for temperatures between 298.65 and 373.45 K and pressures between 40 and 70 MPa. The acoustically determined condensate gas densities were compared with the experimental densities of
Gozalpour et al. (2001)
for a North Sea condensate gas sample for pressures up to 138 MPa.
The thermophysical properties for a mixture of n-hexane + n-hexadecane were determined via an initial value integration method using acoustic data. A distinct functional form was devised for the ...compressional wave propagation velocity in terms of pressure along each isotherm. Comparison with the experiment confirmed excellent accuracy for the acoustically determined first-order thermodynamic properties within a maximum deviation of 3.64% from the experimental counterparts and up to 400.7 MPa. Given the nature of the integration methodology applied, derived using fundamental thermodynamic relations, exact results should be expected for the thermophysical properties established, within the realm of the thermodynamic principles.
Altering the wettability of the carbonate reservoir rocks from oil-wet to water-wet has figured prominently as one of the enhanced oil recovery methods in recent years. The authors measured the ...effect of different ionic surfactants on the wettability alteration of the rock, saturated with crude oil, and the consequent improvement in oil production was investigated by spontaneous imbibitions of solutions containing cationic, anionic, and cationic-anionic surfactant mixtures. A very low-permeable carbonate rock from one of the Iranian oil reservoirs was selected for this study. The results of imbibition tests were furthermore supported by measuring IFT, taking pictures of producing oil drops from different exterior core plug surfaces and also observing the distribution of the remaining oil in cores at the end of experiments. The results show that cationic surfactants at concentrations higher than CMC can cause a remarkable oil production through alteration of wettability and, moreover, the extent of oil production increases with temperature. In contrast, it is observed that the anionic surfactants are not able to change the wettability of an oil-wet surface and their combination with the cationic type would reduce the oil production potential of cationic surfactants.
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