Aqueous Nanofluids Research Articles

Viscosity and rheological behavior of aqueous nanofluids containing TiO2 nanoparticles

Nanofluids containing different concentration of TiO2 nanoparticles were prepared. Their rheological behavior was investigated on LVDV III ultra-programmable Brookfield viscometer at different temperature and particles loading. Results show that rheological behavior of nanofluids is determinated by the concentration of TiO2 in base fluid, nanofluids shows good Newton behavior when nanoparticles loading is low, while shear thinning becomes evident when the volume fraction of particles was continuously increased. Besides, viscosity of nanofluids shows strong nanoparticles loading and temperature dependence, but quite differs from classical viscosity model, as the theory models severely underestimate the value of viscosity, which is attributed to electroviscous effect of nanoparticles in base fluids. The primary electroviscous coefficient is evaluated at different pH values. Modified primary electroviscous coefficient is in good agreement with Booth’s theory.

Application of support vector regression and artificial neural network for prediction of specific heat capacity of aqueous nanofluids of copper oxide

This paper presents the modelling of the specific heat capacity (SHC) of CuO/water nanofluids using a support vector regression (SVR) and artificial neural network models (ANN). The models presented were developed from the experimental data of SCH of CuO nanoparticles, the volume fractions of CuO nanoparticles and fluid temperature. The volume fraction of CuO nanoparticles considered ranges from 0.4 to 2% while the temperature range includes 293–338 K. The results obtained revealed that the SVR model exhibits slightly higher accuracy compared to the ANN model. However, both the SVR and ANN models clearly demonstrate better prediction performance for the SHC of CuO/water nanofluids compared to the existing theoretical models. The results obtained in this study proves that machine learning models provide a more accurate estimation of SHC of CuO/water nanofluids and they are recommended for heat transfer calculations due to their superior accuracy.

Statistical analysis of enriched water heat transfer with various sizes of MgO nanoparticles using artificial neural networks modeling

In the present research, experimental data of the heat transfer coefficient for MgO aqueous nanofluids are modeled by the MLP artificial neural networks (ANN), for 4 types of nanoparticles with diameters of 20, 40, 50 and 60 nm, at 4 solid volume fractions of 0.5%, 1%, 1.5% and 2%, and at 11 Reynolds numbers from 3000 to 25,000. Modeling and predicting of the data like the empirical data, is proved the well capability of the ANN in modeling the data related to nanofluids’ heat transfer coefficient. Another interesting point is that, the heat transfer coefficient increases by decline of the nanoparticles’ diameter, and there is a direct relationship between the rise of solid volume fraction and the heat transfer coefficient. The increment rate of heat transfer coefficient, remained unchanged by increasing the Reynolds number, and increased with the rise of solid volume fraction. Present investigation showed that, ANN is able to save all the rules hidden in these changes with a high accuracy and take the advantage of them to predict the other data. In addition, a correlation in terms of variables affecting the heat transfer coefficient is obtained and presented in the article.

Наножидкости для энергетики: механизм влияния диспергентов на тепловые параметры и кризисные явления при кипении

Abstract: The effect of dispersants organic (CTAB) and inorganic nature (sodium pyrophosphate and sodium silicate) on the critical heat flux (CHF) and heat-transfer coefficient (HTC) of boiling various aqueous nanofluids (NFs) under conditions of free convection is studied. It has been established that the addition of ionic dispersants to aluminosilicate NFs, increasing their aggregative and sedimentation stability, as a rule, worsens their heat-transfer parameters during boiling, causing a sudden pre-crisis heater burnout in a test unit powered by direct current. The mechanism of the phenomenon is revealed. On the contrary, the addition of dispersants and surfactants to carbon-containing NFs with high thermal conductivity, improving their stability, at the same time increases the heat transfer coefficient during boiling of NFs, but also cause pre-crisis heater burnout in the case of direct current heating. The effect of dispersants on crisis phenomena during boiling of water and NFs is analyzed and the causes of sudden pre-crisis heater burnout have been elucidated. Several mechanisms have been proposed for interpreting the observed effects, from which the expediency of using alternating heating current and non-ionic, non-foaming surfactants and dispersants to avoid an early onset of the boiling crisis in order to achieve higher values of the critical heat flux and the heat transfer coefficient during the NFs boiling.

Heat transfer characteristics of miniature two-phase thermosyphons with nanofluids

This paper presents and analyzes experimental data on the total thermal resistances of two-phase miniature thermosyphons with nanofluids; the geometric parameters of the thermosyphons for all experimental samples are identical: total length 700 mm, internal diameter 5 mm. The following nanofluids used as heat carriers are: aqueous nanofluid based on carbon nanotubes, aqueous nanofluid based on synthetic diamond, and aqueous nanofluid based on amorphous carbon. Much attention is also paid to the influence of the filling ratio on the heat transfer characteristics of the thermosyphons. The influence of filling ratio and types of nanofluid on the performance of miniature closed two-phase thermosyphons is demonstrated.

Editorial

Nanofluids are gaining attention in the exchange, conversion, and storage of energy, owing to their enhanced thermophysical characteristics. Since the thermal conductivity of metals are far higher than that of fluids such as water and oil, adding metal nanoparticles into such fluids can result in a new medium with improved heat transfer properties. Apart from pure metals, nanoparticles made of metal-oxides, silicon carbide, composites, bio-based materials, etc. are also used for this purpose. Nanofluids are produced by engineered-dispersion of nanoparticles in a base fluid, which significantly enhances the thermal conductivity of conventional heat transfer fluids (Ganji et al. 2018; Sheikholeslami 2019). However, the thermophysical characteristics of nanofluids depend on the size, shape, and volumetric fraction of the dispersed nanoparticles. An interesting breakthrough in nanofluids is the advent of hybrid nanofluids wherein two or more nanoparticles are immersed in the base fluid, which has shown further enhancement of the thermal and rheological properties (Kumar and Arasu 2018). Nanofluids play important role in energy exchange and conversion applications (Jama et al. 2016;Nagarajan et al. 2014; Said et al. 2014; Reddy et al. 2017; Hussain et al. 2019; Muñoz-Sánchez et al. 2018; Bhalla and Tyagi 2017; Islam et al. 2015). Holkar et al. (2018) listed different nanofluids employed for energy harvesting and their advantages. Apart from these, cupric oxide nanofluid was proposed to improve the heat transfer performance of asphalt solar collectors that harvest solar energy from roads (Hashim 2014). The efficiency of direct absorption solar collectors could be improved by the use of nanofluids as the absorption medium (Nagarajan et al. 2014;Otanicar et al. 2010). A major challenge in the use of nanofluids for energy applications is the contradictory behavior of thermal conductivity and specific heat. While the enhancement of thermal conductivity of base-fluid by the dispersion of nanoparticles is well established, there are no consistent findings on the enhancement of specific heat capacity (SHC) (Lu and Huang 2013), which is a desirable property for energy storage. Several studies reported decline of SHC of aqueous nanofluids, whereas non-aqueous nanofluids showed improvement of SHC (Shin and Banerjee 2010). This issue has been tackled in many studies, and it remains an ongoing challenge. Adding nanoparticles to molten salts that are used as heat transfer fluids in concentrated solar power (CSP) system could enhance the thermophysical properties including SHC and enable the CSP plants operate at higher temperatures (Shin and Banerjee 2010; Lu and Huang 2013). Muñoz-Sánchez et al. (2018) provided a comprehensive review on the use of molten salt-based nanofluids for energy storage and transfer at higher temperatures. Owing to the growing environmental concerns on the conventional synthesis techniques of nanoparticles, the emerging trend is to adopt green synthesis approaches (Genuino et al. 2013; Ghulam 2016). The nanoparticles produced by green synthesis are termed as green nanoparticles, and the nanofluids prepared from them are known as green nanofluids (Narayanan and Rakesh 2019). Several researchers have reported development and characterization of green and eco-friendly nanofluids such as silver and gold nanofluids (Mollick et al. 2014)(John et al. 2015), grapheme-based nanofluids (Mehrali et al. 2016), and coconut fiber-based nanofluids (Adewumi et al. 2018). These green nanofluids would be promising alternatives for their conventional counterparts for various energy conversion applications.

Influence of Al2O3 and TiO2 nanofluid on hard turning performance

The current paper emphasized on preparation methodology of aqueous Al2O3-water and TiO2-water nanofluids and its application as the coolant in hard turning operations. The nanofluids are prepared through the two-step process, dispersing nanoparticles of Al2O3 (average diameter 44 nm) and TiO2 (average diameter 27 nm) in deionized water at three different % weight concentrations (0.005, 0.01, and 0.05). Air-assisted nanofluid is impinged through spray impingement setup in hard turning of AISI D2 steel (55 HRC) using multilayer (TiN/TiCN/Al2O3)-coated carbide tool. Application of nanofluid through spray impingement technique in hard turning is a novel work which is rarely found in the literature. Also, there is no literature available which presented the comparative hard turning performance under lower weight % concentration of Al2O3 and TiO2 nanofluid although the cost of the nanoparticle is high. Further, flank wear (VBc), cutting temperature (T), average surface roughness (Ra), and chip morphology have been investigated as the cutting responses. Abrasion is the dominant wear mechanism identified for both types of nano cutting fluids. TiO2-water nanofluid attributes enhanced machinability compared with that of Al2O3-water nanofluid due to higher lubricious characteristics of TiO2 which significantly reduces the chip-tool friction thus reduces the cutting heat. The most favorable results are noticed at 0.01% weight concentration of TiO2 and at this condition, compared with the same concentration of Al2O3 nanofluid, 29% reduction in tool-flank wear, 9.7% drop in cutting temperature, and 14.3% reduction in surface roughness are found. Tool life at 0.01 wt% concentrations of TiO2 nanofluids is found to be 154 min taking flank wear criteria of 0.3 mm, which is 2.52 times more than the tool life obtained under dry cutting and 1.47 times higher than the tool life obtained under air-water spray impingement due to excellent wettability, lubrication, and heat dissipation capability of TiO2 nanofluid. However, the employment of deionized water-based TiO2 nanofluid in spray impingement cooling hard machining can be very promising for a practical manufacturing concern.

Long-term colloidal stability of graphene oxide aqueous nanofluids

The use of nanofluids for industrial applications depends on its stability during transport and use. In this work, we demonstrate that graphene oxide (GO)-based aqueous nanofluids can remaining stable for as many as 90 days. The structural and morphological analyses showed that the GO samples have an average thickness of two graphitic layers with interlayer spacing of 1 nm. The long-term colloidal stability of the nanofluids was monitored for 90 days using three different techniques: UV-vis, zeta potential (ζ) and DLS, which confirmed this stability. The observed ζ value (average of −64.8 ± 1.81 mV) at 200 ppm of GO is the highest negative value reported at pH = 4. The particle size distribution after 90 days of storage presented a major population with diameter of (530 ± 40) nm that represented 98% of the scattered light intensity.

Numerical assessment of Ag-water nano-fluid flow in two new microchannel heatsinks: Thermal performance and thermodynamic considerations

The present paper is devoted to the first and second law analysis of a aqueous nano-fluid (NF) containing suspended Ag nanoadditives in two new microchannel heatsinks. The influences of nanoadditives volume fraction (φ) and Reynolds number (Re) on performance indicators based on the first and second law of thermodynamics are taken into account and analyzed. The outcomes reveal that the augmentation of Re and φ causes an intensification in the convective heat exchange coefficient and a decrease in the CPU temperature, thermal irreversibility rate and enhance the CPU temperature uniformity. However, grow of Re intensifies both the pumping power and irreversibility due to flow friction. Additionally, the outcomes depicted the superior performance of NF compared to the base fluid. Moreover, the irreversibility inside the studied heatsinks is mainly due to the heat transfer compared to the flow friction. Finally, the results demonstrate that the heatsink with more path changes is more efficient form the viewpoint of the first and second laws of thermodynamics.

Comparison between Nucleate Pool Boiling Heat Transfer of Graphene Nanoplatelet- and Carbon Nanotube- Based Aqueous Nanofluids.

An increase of nucleate pool boiling with the use of different fluid properties has received much attention. In particular, the presence of nanostructures in fluids to enhance boiling was given special consideration. This study compares the effects of graphene nanoplatelet (GNP), functionalized GNP with polyethylene glycol (PEG), and multiwalled carbon nanotube (CNT) nanofluids on the pool boiling heat transfer coefficient and the critical heat flux (CHF). Our findings showed that at the same concentration, CHF for functionalized GNP with PEG (GNP–PEG)/deionized water (DW) nanofluids was higher in comparison with GNP- and CNT-based nanofluids. The CHF of the GNP/DW nanofluids was also higher than that of CNT/DW nanofluids. The CHF of GNP–PEG was 72% greater than that of DW at the concentration of 0.1 wt %. There is good agreement between measured critical heat fluxes and the Kandlikar correlation. In addition, the current results proved that the GNP–PEG/DW nanofluids are highly stable over 3 months at a concentration of 0.1 wt %.

Performance of Silica Nanoparticles in CO2 Foam for EOR and CCUS at Tough Reservoir Conditions

Summary The use of nanoparticles for CO2-foam mobility is an upcoming technology for carbon capture, utilization, and storage (CCUS) in mature fields. Silane-modified hydrophilic silica nanoparticles enhance the thermodynamic stability of CO2 foam at elevated temperatures and salinities and in the presence of oil. The aqueous nanofluid mixes with CO2 in the porous media to generate CO2 foam for enhanced oil recovery (EOR) by improving sweep efficiency, resulting in reduced carbon footprint from oil production by the geological storage of anthropogenic CO2. Our objective was to investigate the stability of commercially available silica nanoparticles for a range of temperatures and brine salinities to determine if nanoparticles can be used in CO2-foam injections for EOR and underground CO2 storage in high-temperature reservoirs with high brine salinities. The experimental results demonstrated that surface-modified nanoparticles are stable and able to generate CO2 foam at elevated temperatures (60 to 120°C) and extreme brine salinities (20 wt% NaCl). We find that (1) nanofluids remain stable at extreme salinities (up to 25 wt% total dissolved solids) with the presence of both monovalent (NaCl) and divalent (CaCl2) ions; (2) both pressure gradient and incremental oil recovery during tertiary CO2-foam injections were 2 to 4 times higher with nanoparticles compared with no-foaming agent; and (3) CO2 stored during CCUS with nanoparticle-stabilized CO2 foam increased by more than 300% compared with coinjections without nanoparticles.

An experimental investigation on thermal conductivity and stability of aqueous and nonaqueous nanofluids containing Ag–Cu alloy nanoparticles

Advancement in technologies, particularly miniaturized technologies demand coolants having significantly enhanced thermal conductivity. The use of conventional heat transfer fluids in these applications can’t meet that requirement. Nanofluids, in which nanoparticles are dispersed in the conventional heat transfer fluids, have been developed and researched since the last decade in order to explore their promising cooling efficiency that enables development of smaller and smaller devices. Use of smaller particle sizes of highly conductive metals like Ag, Cu, etc in nanofluids can meet that requirement, but the stability of nanofluids particularly, when reactive metals like Cu in very small nano-scale sizes are used in base fluids like water is likely to be hampered. On the other hand, the use of noble metals like Ag in nanofluids are not recommended for their high cost. Keeping these factors in mind, in the present work Ag–Cu alloy nanopartices have been synthesized through wet chemical method at room temperature without using any inert gas protection and then the synthesized alloy nanoparticles are dispersed in water and ethylene glycol to produce nanofluids. The nanoparticles have been characterized by different structural and compositional characterization tools to confirm morphology, composition, elemental distribution within particles, crystal structure, average crystallite size and size distribution of particles. The measurements of thermal conductivity and stability of nanofluids have been carried out for different wt% loading of nanoparticles and have ensured the effectiveness of these nanofluids in targeted heat transfer applications.

Experimental investigation on the thermal performance and new correlation for thermal conductivity of aqueous copper oxide-doped MCM-41 nanofluids

In the present study, the pure MCM-41- and CuO-doped MCM-41 nanoparticles with various mass fractions of CuO were synthesized and used for the preparation of water-based nanofluids. The obtained nanoparticles were characterized using small-angle X-ray scattering, scanning electron microscopy, transmission electron microscopy and N2 adsorption/desorption analysis. The thermal conductivity of the water-based nanofluids with various mass fractions of nanoparticles including 0.1, 0.5 and 1 mass% was measured by KD2-Pro thermal analyzer. A new correlation is developed for the thermal conductivity of the nanofluid with a reasonably good accuracy (± 5%) when comparing to the experimental data. The thermal performance of these nanofluids together with hydraulic features such as friction factor and heat transfer coefficient was investigated using a mini-channel heat exchanger. The obtained results revealed that the thermal conductivity can be enhanced by 13.1% which belonged to the nanofluid with 1 mass% of CuO-doped MCM-41 nanoparticles. The maximum heat transfer coefficient enhancement was 31% and belonged to the nanofluid containing 50% CuO@MCM-41 nanoparticles at 0.5 mass%. The performance evaluation criterion (PEC) of the various nanofluids was also calculated, and it was identified that the nanoparticles with 50% CuO@MCM-41 dispersed in water have the largest PEC, 16.7% over the base fluid. The friction factor increases by adding the nanoparticles to the pure water. For example, at Re = 1200, the friction factor increases about 36.84% by using the 50%CuO@MCM-41 nanoparticles with 0.5 mass% as compared with the pure water. The friction factor decreases with increasing the Reynolds number. For example, for 50%CuO@MCM-41 and 0.5 mass%, the friction factor decreases up to 34.17% as the Reynolds number increases in the range of 400–1200.

Combustion, performances, and emissions characteristics of diesel engine fuelled with diesel-aqueous zinc oxide nanofluid blends

ABSTRACT Finding the new fuel blend as a green fuel by mixing aqueous zinc oxide nanofluid with diesel to improve diesel engine combustion and performance is the aim of this study. Varying the nanofliud dosing level in diesel from 30 cc to 60 cc, four blends are prepared and their properties are measured. Engine performance tests are conducted with the blends and the best blend is identified as D + 50ZN. The energetic nanoparticles present in the aqueous nanofluid possess large surface area per unit volume, it exhibits high catalytic activity with hydrocarbon causing oxidation of hydrocarbon and also micro explosion phenomena of aqueous nanofluid blend helps to evaporate the blend quickly as soon as the fuel injected from injector with high speed and some millimeters away from the normal spay limit leading to quick preparation of charge during the delay period. Hence, the fuel is completely burnt during the combustion period. Among all blends, The D + 50ZN showed a maximum improvement of about 5.38% in brake thermal efficiency and remarkable reduction in NOX, smoke, HC, and CO is observed as 12.97%, 22.08%, 24.54%, and 10.34%, respectively at maximum rated power output. Abbreviation: ASTM: American Society for Testing and Materials; aTDC: After Top Dead Center; BP: Brake Power; BSFC: Brake Specific Fuel Consumption; bTDC: Before Top Dead Center; BTE: Brake Thermal Efficiency; CO: Carbon Monoxide; DDSA: Dodecenyl Succinic Anhydride; EDS: Energy Dispersive Spectroscopy; HC: Hydrocarbons; JCPDS: Joint Committee on Powder Diffraction Standards; NOX: Oxides of Nitrogen; ppm: Part Per Million; SEM: Scanning Electron Microscope; XRD: X-Ray Diffraction Pattern; ZN: Aqueous Zinc Oxide Nanofluid; ZnO: Zinc Oxide

RETRACTED ARTICLE: Dispersion and thermal conductivity of TiO2/water nanofluid

Stability of nanofluids is one of the major challenges for their real-world applications and benefits. Although ultrasonication and addition of surfactant are commonly used to obtain better stability of nanofluids, there is a lack of adequate knowledge on the effects of various parameters and duration of ultrasonication as well as some other influences of surfactant. The effect of ultrasonication on the dispersion of nanoparticles and agitation as well as temperature on the thermal conductivity measurements of aqueous TiO2 nanofluids was experimentally studied. An UV–Vis absorbance analysis was performed to identify the degree of dispersion of nanoparticles (stability) and also to determine the right amplitude as well as the duration of the ultrasonication. In addition, agitation of nanofluids during the measurement of thermal conductivity showed a serious adverse effect as significant fraction of nanoparticles adhered to both the probe and the wall of the sample container. Furthermore, present results showed that the enhanced thermal conductivity of this nanofluid further increases noticeably with increasing temperature.

Thermal efficiency of a flat-plate solar collector filled with Pentaethylene Glycol-Treated Graphene Nanoplatelets: An experimental analysis

The effects of using aqueous nanofluids with the presence of Pentaethylene Glycol-Treated Graphene Nanoplatelets as the working fluids on the thermal performance of flat-plate solar collectors (FPSCs) were investigated experimentally. Water-based nanofluids were prepared with the concentrations of 0.025, 0.05, 0.075, and 0.1 wt%. Then the thermophysical properties were measured. Experimental setup and a MATLAB program were used to study the thermal performance of FPSCs-based nanofluids. The fluid inlet temperatures used in this study were 303, 313, and 323 K, and the flow rates were 0.00833, 0.01667, and 0.025 kg/s. Meanwhile, 500, 750 and 1000 W/m2 were set for the heat flux intensities. As the weight concentration was increased, thermal conductivity, dynamic viscosity, and density also improved, while specific heat decreased. The efficiency of FPSC increased as the flow rate and heat flux intensity were increased. However, the efficiency of FPSC decreased when the temperature of the fluid inlet was increased. Compared to water, the FPSC efficiency recorded an increase of up to 10.7%, 11.1%, and 13.3% for PEG-GNP nanofluids at different mass flow rates. Finally, the regression model was developed through MATLAB to predict the thermal efficiency coefficients of FPSC.

Modelling and optimization of thermophysical properties of aqueous titania nanofluid using response surface methodology

Nanofluid is a colloidal solution of nano-sized particles which enhances the thermal performance, but their viscosity put the limitation for their effective use in many industrial applications as it adversely affects the pumping power. In the present work, response surface methodology (RSM) with three-level factorial design and desirability approach was utilized to optimize thermal conductivity and viscosity of TiO2-water nanofluid simultaneously. In this regard, the impact of temperature of nanofluid (T), the concentration of nanoparticle in base fluid (ϕ) and diameter of nanoparticle (dp) on the viscosity (ν) and thermal conductivity (k) of TiO2-water nanofluid was studied. According to the results, the predicted values were in smart agreement with the experimental data. The maximum percentage error was found to be only 1.67 and 8.23 for viscosity and thermal conductivity of nanofluid, respectively, which demonstrate the preciseness of the applied model. The most dominant factors which affect the viscosity and thermal conductivity of nanofluids were found to be the temperature, concentration and the diameter of nanoparticles. The optimized values of the temperature, concentration of nanoparticles and diameter of nanoparticle obtained according to desirability approach for multi-objective optimization were T = 60 °C, ϕ = 1.41 vol% and dp = 60 nm.

Hydrophobic Silica with Potential for Water-Injection Augmentation of a Low-Permeability Reservoir: Drag Reduction and Self-Cleaning Ability in Relation to Interfacial Interactions.

An aqueous nanofluid containing superhydrophobic silica nanoparticles with a high surface activity and an average size of 7 nm was used to enhance the water injection of a low-permeability well. The mechanism for the aqueous nanofluid to enhance water injection was discussed. Findings indicate that the silica aqueous nanofluid can greatly increase the effective water permeability even after injecting water for 2100 pore volumes. This is because the hydrophobic silica nanoparticles can be well adsorbed onto the surface of the porous channels to cause hydrophilic to hydrophobic transformation. Both the hydrophobic capillary force and adhesion work contribute to increasing water injection; and in particular, there is a critical point in the pressure-permeability curves for the rock cores with different wettabilities. Only above the critical point, the hydrophobic rock core exhibits a higher effective water permeability than that of the hydrophilic one, which is imperative for drag reduction. Moreover, the hydrophobic rock core surface has a remarkable self-cleaning ability and can reduce the expansion ratio of clay and inhibit the formation of scale in association with the increase of effective porosity via decreasing the hydration film amount. This approach, highlighting the important role of wettability alteration in increasing water injection, could potentially promote the application of a silica aqueous nanofluid in enhanced oil recovery.

Formation damage during oil displacement by aqueous SiO2 nanofluids in water-wet/oil-wet glass micromodel porous media

Formation damage during displacement of dead oil by aqueous silica nanofluids was studied in two identical glass micromodels with water-wet and oil-wet surfaces in the presence and absence of connate water saturation. Nanofluids with different contents of the SiO2 nanoparticles were prepared and their particle size distribution was characterized by dynamic light scattering. The effects of the nanoparticles on the dynamic interfacial tension of the nanofluids-dead oil as well as their effects on the dynamic wettability alteration of glass surfaces were studied. The oil recovery factor increases by the concentration of the nanoparticles up to 0.05 wt% and then decreases due to the aggregation of the nanoparticles. When the surface forces are significantly dominant, the oil recovery factor from the water-wet micromodel is 62 and 42% in the absence and presence of the connate water saturation, respectively. This may be attributed to the destabilization of the nanoparticles by the exposure to the connate water, inferred from the narrow capillary fingers in the displacement patterns. The impact of the connate water saturation on the oil recovery from the oil-wet micromodel is negligible. In addition, when either the nanoparticles become destabilized during the displacement or unstable nanofluids are injected, formation damage occurs in the porous media leading to a significant drop in the sweep efficiency. Results indicate that the ultimate recovery factor decreases significantly after the damage taken place. The damage arises from the adsorption of the asphaltenes onto the nanoparticle-aggregates and deposition over the pores and throats, resulting in an increase in residual oil saturation. Field-emission scanning electron microscopy images illustrate that severe irreversible damage is formed over the water-wet surfaces. However, over the oil-wet surfaces, the damage is found almost reversible. Two schematic representations are proposed for the damage as the interconnected interwoven nanoparticles-asphaltenes aggregates deposited over the surface.

WITHDRAWN: Enhancement of Carbon Dioxide Absorption using Nanofluids in Hollow Fiber Membrane Contactor

Abstract In this work, CO 2 gas was absorbed from a gas mixture in a custom made Polyvinylidene fluoride (PVDF) hollow fiber membrane contactors by using a variety of Methyl Diethanolamine (MDEA) aqueous solutions and nanofluids. An ultrasonic dispersion method was used to prepare nanofluids. SiO 2 nanoparticles and carbon nanotubes (CNTs) were dispersed in deionized (DI) water and MDEA without adding any surfactant. The prepared solvents were fed into the tube side of the membrane module, whereas the gas mixture passed through the shell side. CO 2 absorption experiments were carried out using four different liquid flow rates: 10, 20, 30 & 40 ml/min. All experiments were conducted at ambient temperature and atmospheric pressure. CO 2 absorption process carried out by using pure deionized water as a reference. The effects of different parameters on the removal efficiency of CO 2 were investigated and analyzed with a focus on concentrations and types of amines and nanoparticles and liquid flow rates. Carbon nanotubes show substantial enhancement in the absorption of CO 2 from the CO 2 /N 2 gas mixture.