Preparation Of Nanofluids Research Articles

Preparation, Sedimentation, and Agglomeration of Nanofluids

AbstractResearch on nanofluids has increased significantly in the last decade due to the distinctive potential in many applications such as enhanced heat transfer processes, drug delivery systems, and membrane manufacturing processes. The study of dispersion behavior of nanoparticles in liquids is a topic of keen interest towards the preparation of stable nanofluids. A comprehensive review on the recent progress in preparation and stability of nanofluids is presented. Settling of nanoparticles is the only predicament towards preparation of stable nanofluids which takes place due to formation of agglomerates. The settling behavior of nanoparticles in nanofluids and techniques to stop agglomeration are described. Nanofluid preparation techniques, assessment method of stability, and methods to reduce agglomeration are discussed.

Hydrogen Sulfide Bubble Absorption Enhancement in Water-Based Nanofluids

Nanoparticles addition is a novel technique for enhancement of mass transfer in absorption process. A bubble column was used for investigation of hydrogen sulfide (H2S) absorption process. Silica and exfoliated graphene oxide (EGO) were used for preparation of nanofluids used as hydrogen sulfide absorbent. The absorption rate of hydrogen sulfide deteriorated by addition of 14 nm silica nanoparticles to water, while EGO–water nanofluid augmented hydrogen sulfide absorption relative to the base fluid. EGO–water nanofluid with 0.02% wt EGO enhanced absorption rate by 40%. For greater mass percentages of EGO in water, the absorption rate was reduced. It is concluded that EGO–water nanofluid is suitable for H2S absorption. Grazing is the main reason for mass transfer enhancement in EGO–water nanofluids. Mathematical modeling was developed for predicting the effective absorption ratio. The maximum deviation of model predictions from the measurements is 13%.

Preparation of carbon-coated iron nanofluid and its application in radiofrequency ablation.

Carbon-coated iron nanoparticles (Fe@C CCINs) were synthesized by carbon arc discharge method and were studied via X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results showed that CCINs have good core-shell structure and are in size of 40-50 nm. Also, carbon-coated iron nanofluid (CCINs-nanofluid) was prepared via two-step method by dispersing as-prepared CCINs and polyvinylpyrrolidone (PVP) into physiological saline. Its dispersion stability and thermal conductivity were detected by gravity sedimentation method and Hotdisk thermal constant analyzer respectively. The results indicated that CCINs-nanofluid possesses good dispersity and stability. Moreover, CCINs-nanofluid showed enhanced thermal conductivity compared with its base fluid physiological saline. The enhancement of thermal conductivity even reaches 41%. Additionally, CCINs-nanofluid injection aided radiofrequency ablation (RFA) was carried out. The relation between tissue temperature and ablation time revealed that by injecting CCINs-nanofluid into pork livers during RFA, target tissue temperatures were less than 100°C. Dissected pork livers showed that there was little or no tissue charring around the ablation probe. Results of ablation area calculation showed that the ablation area of CCINs-nanofluid injection aided RFA was 67% larger than that of saline injection aided RFA, indicating that a larger-volume tumor tissue necrosis at a single session can be achieved by CCINs-nanofluid injection aided RFA.

Preparation, characterization, viscosity, and thermal conductivity of nitrogen-doped graphene aqueous nanofluids

Nanofluids perform a crucial role in the development of newer technologies ideal for industrial purposes. In this study, Nitrogen-doped graphene (NDG) nanofluids, with varying concentrations of nanoparticles (0.01, 0.02, 0.04, and 0.06 wt%) were prepared using the two-step method in a 0.025 wt% Triton X-100 (as a surfactant) aqueous solution as a base. Stability, zeta potential, thermal conductivity, viscosity, specific heat, and electrical conductivity of nanofluids containing NDG particles were studied. The stability of the nanofluids was investigated by UV–vis over a time span of 6 months and concentrations remain relatively constant while the maximum relative concentration reduction was 20 %. The thermal conductivity of nanofluids was increased with the particle concentration and temperature, while the maximum enhancement was about 36.78 % for a nanoparticle loading of 0.06 wt%. These experimental results compared with some theoretical models including Maxwell and Nan’s models and observed a good agreement between Nan’s model and the experimental results. Study of the rheological properties of NDG nanofluids reveals that it followed the Newtonian behaviors, where viscosity decreased linearly with the rise of temperature. It has been observed that the specific heat of NDG nanofluid reduced gradually with the increase of concentration of nanoparticles and temperature. The electrical conductivity of the NDG nanofluids enhanced significantly due to the dispersion of NDG in the base fluid. This novel type of fluids demonstrates an outstanding potential for use as innovative heat transfer fluids in medium-temperature systems such as solar collectors.

The role of a convective surface in models of the radiative heat transfer in nanofluids

Nanotechnology becomes the core of the 21st century. Nanofluids are important class of fluids which help advancing nanotechnology in various ways. Convection in nanofluids plays a key role in enhancing the rate of heat transfer either for heating or cooling nanodevices. In this paper, we investigate theoretically the role of a convective surface on the heat transfer characteristics of water-based nanofluids over a static or moving wedge in the presence of thermal radiation. Three different types of nanoparticles, namely copper Cu, alumina Al2O3 and titanium dioxide TiO2 are considered in preparation of nanofluids. The governing nonlinear partial differential equations are made dimensionless with the similarity transformations. Numerical simulations are carried out through the very robust computer algebra software MAPLE 13 to investigate the effects of various pertinent parameters on the flow field. The obtained results presented graphically as well as in tabular form and discussed from physical and engineering points of view. The results show that the rate of heat transfer in a nanofluid in the presence of thermal radiation significantly depends on the surface convection parameter. If the hot fluid side surface convection resistance is lower than the cold fluid side surface convection resistance, then increased volume fraction of the nanoparticles to the base fluid may reduces the heat transfer rate rather than increases from the surface of the wedge to the nanofluid. This finding is new and has not been reported in any open literature.

Preparation and application of carbon nanotube nanofluid as a reinforcement of cement slurry

The mechanical properties of carbon nanotubes (CNTs) together with their high aspect ratios have drawn intense interest in their potential for use in composite materials. As common cement slurries are not capable of playing a major role in either preventing the degradation of a cement sheath or improving cement stability in cement-to-formation contacts, the idea of designing CNT-reinforced cements with a high Poisson's ratio, shorter thickening time and less free water and fluid loss came to mind. In this research, the properties of CNT–cement composites, which were synthesised by applying multi-wall CNT–water nanofluids in cement slurry, were thoroughly investigated. The results indicated that the Poisson's ratio of CNT–cement composite with 3 wt% multi-wall CNTs is four times greater than that of the unreinforced cement. Moreover, the free water and fluid loss of the former are 97·5% and 85·0% less than that of the latter.

Influence of nanoparticle concentration on thermo-physical properties of CuO-propylene glycol nanofluids.

Experiments were performed on the preparation and characterization of CuO-propylene glycol nanofluids. The influence of nanoparticle concentration and temperature on nanofluid viscosity reveals existence of a range of nanoparticle concentration and temperature in which the viscosity of nanofluid is lower than that of propylene glycol, possibly due to interactions between nanoparticles and propylene glycol. A temperature-independent, thermal conductivity enhancement of 38% was obtained for nanoparticle concentration of 1.5 vol% over a temperature range of 10-60 degrees C. We believe that particle clustering contributes to the thermal conductivity enhancement in CuO-propylene glycol nanofluids.

A comprehensive review of fundamentals, preparation and applications of nanorefrigerants

Nanofluids attract researchers in many ways for their enhanced heat transfer properties. Nanorefrigerant is one kind of nanofluids. It has better heat transfer performance than traditional refrigerants. Thermal conductivity, viscosity and density are the basic thermophysical properties that must be analyzed before performance analysis. This paper presents a comprehensive review of nucleate pool boiling, flow boiling, condensation and two-phase flow of refrigerant-based nanofluids. The effects of nanolubricants on boiling and two-phase flow phenomena are presented as well. Furthermore, studies of applications and preparation of refrigerant-based nanofluids are presented. For the limited studies done so far, there are some controversies from one study to another. Based on results available in the literatures, it has been found that nanorefrigerants have a much higher and strongly temperature-dependent thermal conductivity at very low particle concentrations than conventional refrigerant. This can be considered as one of the key parameters for enhanced performance for refrigeration and air conditioning systems. Because of its superior thermal performances, latest up to date literatures on this property has been summarized and presented in this paper as well.

EXPERIMENTAL INVESTIGATION OF PARAMETERS AFFECTING NANOFLUID EFFECTIVE THERMAL CONDUCTIVITY

The present research reports nanofluid effective thermal conductivity enhancements (ETCE) using an accurate transient short hot wire method system. Preparation of nanofluids was carried out through a two-step method with highly powered pulses similar to that for nanoparticle dispersion in base fluids. Parameters affecting nanofluid heat conductivity such as concentration, sizes, and material of nanoparticleş type of base fluid, temperature, ultrasonic mixing time, and elapsed time after preparation were studied. In the present study, nanoparticles of Al, Al2O3, CuO, SnO2, TiO2, and SiO2 with base fluids of water and ethylene glycol were used. Parameters like concentration, size, temperature, and the type of base fluid showed more noticeable effect on the effective thermal conductivity than the others, and mixing time had the least effect. The results showed that any increase in concentration and temperature, and also any decrease in size of nanoparticles and time elapsed after nanofluid preparation, leads to the ETCE of the nanofluid. However, the effects of nanoparticle material, base fluid, and mixing time on thermal conductivity of the nanofluid showed varying trends. Last, a number of mathematical models for prediction of thermal conductivity of nanofluids were applied.

Characterization of Zinc Oxide Nanoparticles used for Preparation of Nanofluids

Heat transfer equipments needs working fluids with enhanced thermal properties. Nanofluid, which is colloidal solution of solid nanoparticles dispersed in a base fluid, is one of the alternatives to conventional heat transfer fluids. Synthesis of nanoparticles is a first step towards nanofluid preparation by single step method. A study related to nanoparticle synthesis for the development of Zinc oxide-water nanofluid is presented in this paper. Zinc-oxide, being an environment friendly and stable material, is selected as a dispersed phase for nanofluid synthesis. An experimental set up for synthesis of zinc oxide nanoparticles by oxidation route is developed. Oxidation of pure zinc in presence of atmospheric oxygen is carried out at elevated temperature in a tube furnace. A white powder is collected after oxidation and used for further characterization. The average particle size of the powder is determined from X-Ray diffractometer. The shape of the particles is decided from images of scanning electron microscopic. Quantitative analysis has been done by energy dispersive analysis of X-rays. Characterization indicated cylindrical rod shaped particles of average size 32nm.

Nano-Rheology and its Application in Controlled-Release Fragrance Nanocapsules Suspensions

In the present paper, we have introduced the preparation and classification of nanofluids. The factors that influence the viscosity of nanofluids and researches on the fundamental research to specific applications of nanorheology in controlled-release fragrance nanocapsules suspensions are discussed. Finally some problems exist in the research of nanorheology are summarized.

Stable Nanofluids for Convective Heat Transfer Applications

Abstract Nanofluids are stable dispersions of ultrafine or nanoscale metallic, metal oxide, ceramic particles in a given base fluid. It is reported that nanofluids register an extraordinarily high level of thermal conductivity, and thus possess immense potential in improvement of heat transfer and energy efficiency of several industrial applications including vehicular cooling in transportation, nuclear reactors, and microelectronics. The key issues with nanofluids are: (i) a robust, cost-effective and scalable method to produce nanofluids to industrial scale has not yet been developed, (ii) stability in industrial applications is not yet established, and (iii) meaningful data in flow based heat transfer process do not exist. The present work attempts to address all these three issues. We have developed an in-situ technique for preparation of stable nanofluids by wet-milling of the metal oxide powder in the base fluid, and in the presence of a suitable dispersant. The nanofluids thus produced are tested for heat transfer efficiency under flow conditions in double pipe heat exchangers. Alumina nanofluids have been found to show enhancements of around 10–60% for various base fluids flown under different flow conditions. Thermal enhancements have been found to depend on the flow-rate, particle concentration, type of base fluid, and material of the thermal contact surface of the heat exchanger. The nanofluids thus obtained exhibit sustained stability (>30 months) and their stability remains unaltered for several heating-cooling cycles.

Effect of particle concentration, temperature and surfactant on surface tension of nanofluids

Heat transfer performance with nanofluids depends on the thermo physical properties of the suspension. Surface tension is an important property for heat transfer calculation. In this paper, various parameters that effect on the surface tension of nanofluids such as nanofluid preparation method, effect of volume fraction, temperature, and surfactants on nanofluids have been studied. Additionally, precise assessments on the theoretical correlations related to the surface tension of nanofluids have also been included. Based on the existing experimental results, surface tension augments respectively with volume fraction intensification. Surface tension of nanofluids decreases accordingly with the increase of temperature and surfactant concentration. Nevertheless, there have been some contradictory results on the effect of volume fraction and surfactant on surface tension of nanofluids.

Formation and characterization of thermal and electrical properties of CuO and ZnO nanofluids in xanthan gum

Nanotechnology provides promising possibilities for various oilfield applications in the upstream oil and gas industry. Nanofluids play a vital role in the development of newer technologies suitable for industrial applications and can be explored for use in the upstream petroleum industry. One of the commonly used biopolymers, xanthan gum (XG), is used in the upstream oil and gas industry as a rheological modifier, drilling fluid additive, emulsion stabilizer, and fluid loss controlling agent. Consequently, its use can be studied for the preparation of nanofluids, an application not reported in literature. In this study, zinc oxide (ZnO) and copper oxide (CuO) nanofluids, with varying concentrations of nanoparticles (0.1, 0.3, and 0.5wt.%), were prepared using the two-step method in a 0.4wt.% XG (as a dispersant) aqueous solution as a base. These CuO and ZnO nanofluids were characterized for stability and dispersion using a scanning electron microscope (SEM) and the dynamic light scattering (DLS) method, respectively. It is observed that the CuO nanofluid in XG aqueous solution is more stable than the ZnO nanofluid. XG was observed to form a jelly-like structure around the nanoparticles, keeping them suspended in the solution. This paper investigates and presents the thermal conductivity and electrical conductivity of these nanofluids. The results show that thermal and electrical conductivity are enhanced as the concentration of nanoparticles was increased. The thermal and electrical conductivity was observed to be enhanced by approximately 25 and 50% for ZnO and CuO nanofluid, respectively. This study is expected to form the basis for the development of nanofluid-based technologies with XG as the primary additive in the upstream oil and gas industry.

Rheological studies of semidilute polyacrylamide/carbon nanotube nanofluids

The rheological behavior of aqueous nanofluids formed by polyacrylamide (PAM) and different concentrations of carbon nanotubes (CNT) has been investigated. The overlap concentration, molecular size, and mass of PAM were first obtained from viscometry of dilute samples. Determination of the critical concentration of PAM directed the preparation of nanofluids at distinct semidilute regimes: 3.0 g L−1 and 6.0 g L−1. The slow diffusivities inferred from dynamic light scattering experiments were closely correlated with null stress viscosity extrapolations. The controlled degradation of PAM through sonication was also studied. Thoroughly dispersing MWCNT-COOH in semidilute solutions of PAM led to an improvement in viscosity of approximately 40 %.

Synthesis of TiO<sub>2</sub> – Water Nanofluids for its Viscosity and Dispersion Stability Study

In the present research work, an anatase structure titanium dioxide nanoparticle was synthesized by hydrolysis of titanium isopropoxide in the presence and absence of ultrasonication. The resultant product suspension was peptized for getting narrow size distribution. The synthesized nanoparticles are used for preparation of nanofluids with different volume percent loading of nanoparticles in water ranging from 1% to 5%. The characterization of particles was carried out by TEM, XRD. Our result shows that the use of ultrasonic technique has a significant effect on the homogeneity and then size of TiO2nanoparticles. Viscosity of nanofluids was demonstrated with rheometer (TA instruments). Viscosity results confirmed Newtonian behavior of nanofluids and showing increasing trends with addition of nanoparticles in base fluids. The dispersion of nanoparticles in nanofluids is studied with unique method of UV visible spectrophotometer, which confirm good dispersion stability prepared nanofluid of 50 hrs.

Transport properties of nano manganese ferrite–propylene glycol dispersion (nanofluids): new observations and discussion

Experiments were conducted on the preparation of manganese ferrite nanoparticles and their surface modification for dispersion in propylene glycol. The appropriate concentrations of ferrous sulphate and manganese sulphate (precursors) for synthesis of uniform Mn0.43Fe2.57O4 nanoparticles (size range ~20–25 nm) were found to be 0.05 and 0.025 M, respectively. These nanoparticles were coated with citric acid and dispersed in propylene glycol for the preparation of nanofluids. The effects of temperature and nanoparticle concentration on nanofluid viscosity and thermal conductivity have been studied. Our study on the influence of nanoparticle concentration on viscosity reveals the existence of a viscosity minimum for 0.25 vol% of citric acid-modified Mn0.43Fe2.57O4–propylene glycol nanofluid. A thermal conductivity enhancement of 68 % was observed for 2 vol% nanofluid. Correlating viscosity and thermal conductivity measurements, particle clustering seems to be the major factor responsible for thermal conductivity enhancement.

Preparation and thermal properties of oil-based nanofluid from multi-walled carbon nanotubes and engine oil as nano-lubricant

Nowadays, different materials with various nanostructures are used as additives for improving properties of lubricants. In this research, the effect of multi-walled carbon nanotubes (MWCNTs) in different concentrations on some of the properties of engine oils was studied. Viscosity, pour point, flash point and thermal conductivity as four quality parameters, which are effective in functionality of engine oil, were also studied. Among the different methods, which have been applied for dispersing nanotubes inside the base oil, the functionalization method for carbon nanotubes and using planetary ball mill have been determined as the best methods for stabilization of nanotubes inside the SAE 20W50 engine oil. According to the obtained results, thermal conductivity and flash point of nano-lubricants with 0.1wt% improved by 13.2% and 6.7%, respectively, with respect to the base oil.

Stability of Nanofluids

It has long been established that a suspension of nanosized solid particles in liquids provide useful advantages in industrial heat transfer fluid systems. Numerous investigations on nanofluids show a significant enhancement in thermal conductivity over the base fluid in which these nanoparticles are dispersed. However, the stability of the suspension is critical in the development and application of these new kind of heat transfer fluids. Rather, high discrepancy in the published data for the same nanoparticles on the physical and thermal characteristics of nanofluids is primarily due to different methods adopted by different researchers to obtain stable nanofluids. Sedimentation and agglomeration of nanoparticles in nanofluids and their dispersion stability has not been well addressed in the literature. Hence, there is a need to establish a standard method of preparation of these nanofluids so as to obtain a unified data which can eventually be utilized for the application of nanofluids. This chapter focuses on the stability of nanofluids prepared via two step process. Different parameters that affect the stability of nanofluids have been discussed. Different techniques that have been used for the evaluation of the stability characteristics of nanofluids have been elucidated.

Preparation and Thermal Stability of Oil-based Au Nanofluids

Two cationic surfactants,N-cetyl-N-(hydroxyethyl)-N,N-dimethyl ammonium bromide(CHDAB) and 1,4-bis(cetyldimethylammonium) propane dibromide(G16-4-16),were used as surface-modified reagents for preparation of hydrophobic gold nanoparticles from reduction of HAuCl4 with KBH4 in mixture of petroleum ether/n-butanol/H2O.The results show that gemini surfactant G16-4-16 is better for coating and dispersing,and the gold nanoparticles coated by the gemini surfactant G16-4-16 have a narrow size distribution with an average diameter of 5.2 nm.Stable nanofluids containing gold nanoparticles with hydrocarbon(toluene) as base liquids were prepared.The thermal stability of the nanofluids as a function of time was monitored using UV-Vis absorption method.It is shown that the gold nanofluid has good thermal stability,which has a stable time of 20 h at 130 ℃.The thermal conductivity of the gold nanofluids was performed by point heat source method.The enhancements of thermal conductivity of the gold nanofluids containing 1.5%(mass fraction) gold nanoparticles can reach 17%.