Latest developments on the viscosity of nanofluids (original) (raw)
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A brief review on viscosity of nanofluids
International Nano Letters, 2014
Since the past decade, rapid development in nanotechnology has produced several aspects for the scientists and technologists to look into. Nanofluid is one of the incredible outcomes of such advancement. Nanofluids (colloidal suspensions of metallic and nonmetallic nanoparticles in conventional base fluids) are best known for their remarkable change to enhanced heat transfer abilities. Earlier research work has already acutely focused on thermal conductivity of nanofluids. However, viscosity is another important property that needs the same attention due to its very crucial impact on heat transfer. Therefore, viscosity of nanofluids should be thoroughly investigated before use for practical heat transfer applications. In this contribution, a brief review on theoretical models is presented precisely. Furthermore, the effects of nanoparticles' shape and size, temperature, volume concentration, pH, etc. are organized together and reviewed.
Empirical and theoretical correlations on viscosity of nanofluids: A review
Renewable and Sustainable Energy Reviews, 2013
In the past decade nanotechnology has developed in many directions. Nanofluid is a mixture of nanosized particles dispersed in fluids. Nanofluids are new generation heat transfer fluids used in heat exchangers for energy conservation. Viscosity is an important property particularly concerning fluids flowing in a tube in heat exchangers. In this regard, an attempt has been made to review the available empirical and theoretical correlations for the estimation of viscosity of nanofluids. The review also extended to preparation of nanofluids, nanoparticle volume concentration, nanofluid temperature, particle size and type of base fluid on viscosity of nanofluids. The available experimental results clearly indicate that with the dispersion of nanoparticles in the base fluid viscosity increases and it further increases with the increase in particle volume concentration. Viscosity of nanofluid decreases with increase of temperature.
The viscosity of nanofluids: a review of the theoretical, empirical and numerical models.
The enhanced thermal characteristics of nanofluids have made it one of the most raplidly growing research areas in the last decade. Numerous researches have shown the merits of nanofluids in heat transfer equipment. However, one of the problems is the increase in viscosity due to the suspension of nanoparticles. This viscosity increase is not desirable in the industry, especially when it involves flow, such as in heat exchanger or microchannel applications where lowering pressure drop and pumping power are of significance. In this regard, a critical review of the theoretical, empirical, and numerical models for effective viscosity of nanofluids is presented. Furthermore, different parameters affecting the viscosity of nanofluids such as nanoparticle volume fraction, size, shape, temperature, pH, and shearing rate are reviewed. Other properties such as nanofluid stability and magnetorheological characteristics of some nanofluids are also reviewed. The important parameters influencing viscosity of nanofluids are temperature, nanoparticle volume fraction, size, shape, pH, and shearing rate. Regarding the composite of nanofluids, which can consist of different fluid bases and different nanoparticles, different accurate correlations for different nanofluids need to be developed. Finally, there is a lack of investigation into the stability of different nanofluids when the viscosity is the target point.
International Communications in Heat and Mass Transfer, 2022
In practice, nanofluids’ thermal conductivity and viscosity are the most important parameters in engineering applications. Viscosity affects pumping performance. Theoretical viscosity correlations are widely used in numerical studies. However, existing correlations show an underestimation of the actual viscosity compared to the measurement results. Although many nanofluid viscosity correlations have been developed, there is no generally accepted correlation. This paper reviews the theoretical, numerical, and experimental viscosity correlations and proposes a new correlation based on an analysis of approximately 1200 experimental and 4000 theoretical data tested for about 50 types of nanofluids in the temperature range 273–333 K and particle diameters 2–300 nm. The studied volume fraction range for the nanofluids was up to 10%. Existing correlations take into account the impact of up to two to three parameters The new viscosity correlation is proposed to predict the effective viscosity of nanofluids based on regression analysis of theoretical and experimental viscosity results, and it considers several factors that significantly affect the effective viscosity of nanofluids, such as nanoparticle diameter, density, temperature, types of nanoparticles, and base fluid.
Viscosity of nanofluids: A review of recent experimental studies
During the past decade, nanotechnology with its rapid development has grabbed the attention of scientists, scholars, and engineers. Nanofluids are one of the surprising outcomes of this technology that could increase the efficiency of thermal systems remarkably. Nanofluids containing solid nanoparticles have a higher viscosity than common working fluids; hence, measuring the viscosity is necessary for designing thermal systems and estimating the required pumping power. In the current review study, an attempt has been made to cover the latest experimental studies performed on the viscosity of nanofluids. An experimental investigation is very vital for the analysis since the theoretical models usually underestimate the nanofluid viscosity. Through experiments, the real effects of volume fraction, temperature, particle size, and shape on the viscosity of nanofluids will be determined.
Investigation on Thermal Conductivity, Viscosity and Stability of Nanofluids
2012
In this thesis, two important thermo-physical properties of nanofluids: thermal conductivity and viscosity together with shelf stability of them are investigated. Nanofluids are defined as colloidal suspension of solid particles with the size of lower than 100 nanometer. Thermal conductivity, viscosity and stability of nanofluids were measured by means of TPS method, rotational method and sedimentation balance method, respectively. TPS analyzer and viscometer were calibrated in the early stage and all measured data were in the reasonable range. Effect of some parameters including temperature, concentration, size, shape, alcohol addition and sonication time has been studied on thermal conductivity and viscosity of nanofluids. It has been concluded that increasing temperature, concentration and sonication time can lead to thermal conductivity enhancement while increasing amount of alcohol can decrease thermal conductivity of nanofluids. Generally, tests relating viscosity of nanofluids revealed that increasing concentration increases viscosity; however, increasing other investigated parameters such as temperature, sonication time and amount of alcohol decrease viscosity. In both cases, increasing size of nanofluid results in thermal conductivity and viscosity reduction up to specific size (250 nm) while big particle size (800 nm) increases thermal conductivity and viscosity, drastically. In addition, silver nanofluid with fiber shaped nanoparticles showed higher thermal conductivity and viscosity compared to one with spherical shape nanoparticles. Furthermore, effect of concentration and sonication time have been inspected on stability of nanofluids. Test results indicated that increasing concentration speeds up sedimentation of nanoparticles while bath sonication of nanofluid brings about lower weight for settled particles. Considering relative thermal conductivity to relative viscosity of some nanofluids exposes that ascending or descending behavior of graph can result in some preliminary evaluation regarding applicability of nanofluids as coolant. It can be stated that ascending trend shows better applicability of the sample in higher temperatures while it is opposite for descending trend. Meanwhile, it can be declared that higher value for this factor shows more applicable nanofluid with higher thermal conductivity and less viscosity. Finally, it has been shown that sedimentation causes reduction of thermal conductivity as well as viscosity. For further research activities, it would be suggested to focus more on microscopic investigation regarding behavior of nanofluids besides macroscopic study. IV Acknowledgment There are so many people that we would like to thank due to their support, encouragement, and assistance. Firstly, we should sincerely express our great gratitude to Professor Björn Palm for his enormous patience, sophisticated comments, consistent support, and make the possibility for us to work at ETT laboratory of Energy Department of KTH and acquire very nice experiences. We would also like to thank Dr. Rahmatollah Khodabandeh due to his support and kindness during our thesis work. Very special thanks go to Ehsan Bitaraf Haghighi who played a significant role in our thesis work and opened doors of nanotechnology science for us. He was not only an excellent supervisor with great energy all day long, but also a very gentle friend. Ehsan, without your support and constructive suggestions it was impossible for us to end up with this much work.
A model for temperature and particle volume fraction effect on nanofluid viscosity
Journal of Molecular Liquids, 2010
A theory based model is presented for viscosity of nanofluids and evaluated over the entire range of temperature and volume fraction of nanoparticles. The model is based on Eyring's viscosity model and the nonrandom two liquid (NRTL) model for describing deviations from ideality (Eyring-NRTL model). The equation for viscosity is composed of a contribution due to nonrandom mixing on the local level and another energetic section related to the strength of intercomponent interactions which inhibit components from being removed from their most favorable equilibrium position in the mixture. The experimental data were used to evaluate existing models which do not contain adjustable parameters and Eyring-NRTL model. The Eyring-NRTL model was found to agree well with the experimental data with the restriction that contains adjustable parameters which were interactions in the form of NRTL constants. However, the agreement was even better if temperature dependent interaction parameters were used. Comparisons of predicted and actual viscosity over the entire temperature and volume fraction range illustrate an improvement over the conventional nanofluid viscosity models with 2.91% AAD.
Experimental Investigation on Viscosity of the Nanofluids with Different Parameters
— In this experimental investigation, the effect of concentration, size, and temperature on the viscosity of Al 2 O 3-water nanofluid has been studied. The experiments performed on the various concentration of Al 2 O 3-water nanofluid with particle size 13 nm, 50 nm and 150 nm in the temperature range of 25-80 ℃. The viscosity data were collected using stress-controlled Bohlin Gemini rheometer. The effect of pH value on the viscosity has also been studied. Exponentially decrease in viscosity with an increase in temperature was observed. It has been analyzed and found that the viscosity decreases with temperature and follow the same pattern of decrement for all concentration and size of nanofluid. Al 2 O 3-water nanofluid has been found Newtonian behavior for 50 nm and 150 nm particle size samples at the ambient temperature in the shear rate range 100 s-1 to 250 s-1 .
A new model for calculating the effective viscosity of nanofluids
Journal of Physics D: Applied Physics, 2009
In this paper a new equation for calculating the nanofluid viscosity by considering the Brownian motion of nanoparticles is introduced. The relative velocity between the base fluid and nanoparticles has been taken into account. This equation presents the nanofluid viscosity as a function of the temperature, the mean nanoparticle diameter, the nanoparticle volume fraction, the nanoparticle density and the base fluid physical properties. In developing the model a correction factor is introduced to take into account the simplification that was applied on the boundary condition. It is calculated by using very limited experimental data for nanofluids consisting of 13 nm Al 2 O 3 nanoparticles and water and 28 nm Al 2 O 3 nanoparticles and water. The predicted results are then compared with many other published experimental results for different nanofluids and very good concordance between these results is observed. Compared with the other theoretical models that are available in the literature, the presented model, in general, has a higher accuracy and precision.
Investigations of thermal conductivity and viscosity of nanofluids
International Journal of Thermal Sciences, 2008
A combined experimental and theoretical study on the effective thermal conductivity and viscosity of nanofluids is conducted. The thermal conductivity and viscosity of nanofluids are measured and found to be substantially higher than the values of the base fluids. Both the thermal conductivity and viscosity of nanofluids increase with the nanoparticle volume fraction. The thermal conductivity of nanofluids was also observed to be strongly dependent on temperature. Two static mechanisms-based models are presented to predict the enhanced thermal conductivity of nanofluids having spherical and cylindrical nanoparticles. The proposed models show reasonably good agreement with the experimental results and give better predictions for the effective thermal conductivity of nanofluids compared to existing classical models. Based on the calibration results from the transient hot-wire method, the measurement error was estimated to be within 2%. In addition, the measured values of the effective viscosity of nanofluids are found to be underestimated by classical models.