The injected fluids in secondary processes supplement the natural energy present in the reservoir to displace oil. The recovery efficiency mainly depends on the mechanism of pressure maintenance. However, the injected fluids in tertiary or enhanced oil recovery (EOR) processes interact with the reservoir rock/oil system. Thus, EOR techniques are receiving substantial attention worldwide as the available oil resources are declining. However, some challenges, such as low sweep efficiency, high costs and potential formation damage, still hinder the further application of these EOR technologies. Current studies on nanoparticles are seen as potential solutions to most of the challenges associated with these traditional EOR techniques. This paper provides an overview of the latest studies about the use of nanoparticles to enhance oil recovery and paves the way for researchers who are interested in the integration of these progresses. The first part of this paper addresses studies about the major EOR mechanisms of nanoparticles used in the forms of nanofluids, nanoemulsions and nanocatalysts, including disjoining pressure, viscosity increase of injection fluids, preventing asphaltene precipitation, wettability alteration and interfacial tension reduction. This part is followed by a review of the most important research regarding various novel nano-assisted EOR methods where nanoparticles are used to target various existing thermal, chemical and gas methods. Finally, this review identifies the challenges and opportunities for future study regarding application of nanoparticles in EOR processes.

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Application of Nanoparticles in Enhanced Oil Recovery: A Critical Review of Recent Progress

A review of recent advances in thermophysical properties at the nanoscale: From solid state to colloids

A comprehensive review of research and development on rheological characteristics of nanofluids for their advanced heat transfer applications is performed and reported in this paper. It identifies the research anomaly and importance on this topic besides analysing rheology of nanofluids. Various classical and recently developed viscosity models for nanofluids are presented and discussed. Nanofluids are classified as metallic and nonmetallic types and research findings on this key property of available nanofluids are analyzed. Effects of several important factors such as concentration of nanoparticles and temperature on viscosity of each type of nanofluids have been explicitly reviewed. Results from various research groups and predictions from viscosity models are also compared and discussed in detail. Role and importance of the viscosity in connection with other thermal properties and parameters for their thermal management applications are highlighted. Furthermore, the research challenges and needs in this important area of nanofluids are also revealed.

A state of the art review on viscosity of nanofluids

Preparation and evaluation of stable nanofluids for heat transfer application: A review

A colloidal mixture of nanometre-sized (<100 nm) metallic and non-metallic particles in conventional fluid is called nanofluid. Nanofluids are considered to be potential heat transfer fluids because of their superior thermal and tribological properties. In recent period, nanofluids have been the focus of attention of the researchers. This paper presents a summary of a number of important research works that have been published on rheological behaviour of nanofluids. This review article not only discusses the influence of particle shape and shear rate range on rheological behaviour of nanofluids but also studies other factors affecting the rheological behaviour. These other factors include nanoparticle type, volumetric concentration in different base fluids, addition of surfactant and externally applied magnetic field. From the literature review, it has been found that particle shape, its concentration, shear rate range, surfactant and magnetic field significantly affect the rheological behaviour of any nanofluid. It has been observed that nanofluids containing spherical nanoparticles are more likely to exhibit Newtonian behaviour and those containing nanotubes show non-Newtonian flow behaviour. Furthermore, nanofluids show Newtonian behaviour at low shear rate values while behave as non-Newtonian fluid at high shear rate values. Authors have also identified the inadequacies in the research works so far which require further investigations.

Rheological behaviour of nanofluids: A review

The preparation of nanofluids is very important to their thermophysical properties. Nanofluids with the same nanoparticles and base fluids can behave differently due to different nanofluid preparation methods. The agglomerate sizes in nanofluids can significantly impact the thermal conductivity and viscosity of nanofluids and lead to a different heat transfer performance. Ultrasonication is a common way to break up agglomerates and promote dispersion of nanoparticles into base fluids. However, research reports of sonication effects on nanofluid properties are limited in the open literature. In this work, sonication effects on thermal conductivity and viscosity of carbon nanotubes (0.5 wt%) in an ethylene glycol-based nanofluid are investigated. The corresponding effects on the agglomerate sizes and the carbon nanotube lengths are observed. It is found that with an increased sonication time/energy, the thermal conductivity of the nanofluids increases nonlinearly, with the maximum enhancement of 23% at sonication time of 1,355 min. However, the viscosity of nanofluids increases to the maximum at sonication time of 40 min, then decreases, finally approaching the viscosity of the pure base fluid at a sonication time of 1,355 min. It is also observed that the sonication process not only reduces the agglomerate sizes but also decreases the length of carbon nanotubes. Over the current experimental range, the reduction in agglomerate size is more significant than the reduction of the carbon nanotube length. Hence, the maximum thermal conductivity enhancement and minimum viscosity increase are obtained using a lengthy sonication, which may have implications on application.

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Ultrasonication effects on thermal and rheological properties of carbon nanotube suspensions

Heat transfer characteristics of multiwall carbon nanotube suspensions (MWCNT nanofluids) in intertube falling-film flow

Effects of a countercurrent gas flow on falling-film mode transitions between horizontal tubes

Horizontal-tube falling-film heat transfer characteristics of aqueous aluminum oxide nanofluids at concentrations of 0 vol %, 0.05 vol %(0.20 wt %), 0.5 vol %(1.96 wt %), 1 vol %(3.86 wt %) (with and without sodium dodecylbenzene sulfonate), and 2 vol %(7.51 wt %) are investigated and compared with predictions developed for conventional fluids. The thermophysical properties of the nanofluids, including thermal conductivity, kinematic viscosity, and surface tension, are reported, as is the mode transition behavior of the nanofluids. The experimental results for heat transfer are in good agreement with predictions for falling-film flow and no unusual Nu enhancement was observed in the present studies. Additionally, a 20% mode transitional Reynolds number increase was recorded for transitions between sheets and jets and jet-droplet mode to droplet mode. Although the findings with water-alumina nanofluids are not encouraging with respect to heat transfer, the results extend nanofluid data to a new type of flow and may help improve our understanding of nanofluid behavior. Moreover, this work provides a basis for further work on falling-film nanofluids.

Investigation on Intertube Falling-Film Heat Transfer and Mode Transitions of Aqueous-Alumina Nanofluids

A liquid falling between horizontal tubes can take the form of droplets, jets, or a continuous sheet mode, depending on the flow rate. The so-called falling-film flow regime is important to heat and mass transfer, and to maintaining wetted-surface conditions in a falling-film tube bundle, and the performance of such tube bundles is important in many air-conditioning systems. In this paper, we review prior work on falling film mode transitions between horizontal tubes and investigate vapour shear effects on the mode transitions. It is shown that vapour shear effects on mode transitions depend on liquid properties. Mode transition hysteresis is reduced by an increasing gas flow velocity. It is also found that the liquid feeding length can have an impact on falling-film mode transitions.

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Binglu Ruan

Papers

Ultrasonication effects on thermal and rheological properties of carbon nanotube suspensions

Heat transfer characteristics of multiwall carbon nanotube suspensions (MWCNT nanofluids) in intertube falling-film flow

Effects of a countercurrent gas flow on falling-film mode transitions between horizontal tubes

Investigation on Intertube Falling-Film Heat Transfer and Mode Transitions of Aqueous-Alumina Nanofluids

Vapor Shear Effects on Falling-Film Mode Transitions Between Horizontal Tubes