Heat Transfer Enhancement with Nanofluids (original) (raw)
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Thermal conductivity, viscosity and heat transfer process in nanofluids: A critical review
Journal of Composites and Compounds, 2020
Heat transfer efficiency has always been at the center of attractions for many researchers and industries, and demand for higher efficiency methods and materials are increased in the last decades. Among the different methods of heat transfer enhancement, using nanofluids has proven to be an effective technique. In the present paper, the properties of nanofluids including viscosity, thermal conductivity as well as convective heat transfer are discussed and useful conclusions about the reported results by different researchers are presented. The effect of volume fraction, temperature, size and shape of particles, base fluid properties, and other factors on viscosity, and thermal conductivity of nanofluids are reviewed. Also, in the present manuscript, the methods of stable nanofluid preparation, and the effective factors on the stability of nanofluids are exhibited in detail. Besides, a summarized number of experimental and mathematical studies on the properties, and stability of nanofluids are listed, compared, and analyzed. The works about the Nusselt number in fluids and nanofluids are presented in detail to determine the future challenges of nanofluids.
The present paper discusses the various effects of parameters like particle volume fraction, particle material, particle size, particle shape, particle material and base fluid, temperature, effect of acidity(PH) on thermal conductivity of nanofluids. And also discusses the different mechanisms of heat transfer enhancement like improvement in the thermal conductivity, effect of Brownian motion, thermophoresis, intensification of turbulence, clustering of nano particles. In order to put the nanofluid heat transfer technologies into reality, fundamental studies are greatly needed to understand the physical mechanisms.
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.
Journal of Chemical & Engineering Data
The aim of this paper is to investigate in depth whether adding nanoparticles or nanotubes to a fluid enhances its heat transfer capabilities. For this reason, the thermal conductivities and viscosities of a selection of nanofluids were thoroughly examined. The systems studied were (a) ethylene glycol with added CuO, TiO 2 , or Al 2 O 3 nanoparticles and (b) water with TiO 2 or Al 2 O 3 nanoparticles or multiwall carbon nanotubes (MWCNTs). All of the measurements were conducted at 298.15 K. In a very recent paper, it was shown that instruments employing the transient hot-wire technique can produce excellent measurements when a finite element method (FEM) is employed to describe the instrument for the geometry of the hot wire. Furthermore, it was shown that an approximate analytic solution can be employed with equal success over the time range from 0.1 to 1 s, provided that four specific criteria are satisfied. Subsequently a transient hot-wire instrument was designed, constructed, and employed for the measurement of the thermal conductivities of nanofluids with an uncertainty of about 2%. A second, validated technique, namely, a hot-disk instrument, was also employed to conduct measurements on some of the systems to provide mutual support for the results of the thermal conductivity measurements. To investigate the effect of any enhancement of the thermal conductivity of the fluids on their application in practical heat transfer, the viscosities of typical concentrations of several of the nanofluids were also measured. A parallel-plate rotational rheometer, able to measure the viscosities of Newtonian and non-Newtonian liquids with an uncertainty of better than 5%, was employed for these measurements because most of the nanofluids considered showed behavior comparable to a Bingham plastic. All of these measurements have allowed an investigation of the change in the heat transfer capability of the base fluid when nanoparticles or MWCNTs are added to it for a typical heat exchanger. It is shown that in general the combined changes in physical properties that accompany suspension of nanoparticles in fluids mean that the heat transfer benefits are all rather modest, even when they are achieved.
Review on Synthesis, Thermo-Physical Property, and Heat Transfer Mechanism of Nanofluids
Energies, 2016
Nanofluids are suspended nano-sized particles in a base fluid. With increasing demand for more high efficiency thermal systems, nanofluids seem to be a promising option for researchers. As a result, numerous investigations have been undertaken to understand the behaviors of nanofluids. Since their discovery, the thermo-physical properties of nanofluids have been under intense research. Inadequate understanding of the mechanisms involved in the heat transfer of nanofluids has been the major obstacle for the development of sophisticated nanofluids with the desired properties. In this comprehensive review paper, investigations on synthesis, thermo-physical properties, and heat transfer mechanisms of nanofluids have been reviewed and presented. Results show that the thermal conductivity of nanofluids increases with the increase of the operating temperature. This can potentially be used for the efficiency enhancement of thermal systems under higher operating temperatures. In addition, this paper also provides details concerning dependency of the thermo-physical properties as well as synthesis and the heat transfer mechanism of the nanofluids.
Correlations for thermal conductivity and viscosity of water based nanofluids
IOP Conference Series: Materials Science and Engineering, 2012
Abstract: The thermo-physical properties of nanofluids such as thermal conductivity, viscosity, density and specific heat of nanofluids are required for the analysis of convection heat transfer coefficients. The density and specific heat of nanofluids can be estimated with the mixture relations in literature. Information regarding the properties at different volume concentration and temperature is required for the estimation of heat transfer coefficient. The two most fundamental properties which are, experimentally, determined, are viscosity and ...
Preparation, thermo-physical properties and heat transfer enhancement of nanofluids
Research interest in convective heat transfer using suspensions of nano-sized solid particles has been growing rapidly over the past decade, seeking to develop novel methods for enhancing the thermal performance of heat transfer fluids. Due to their superior transport properties and significant enhancement in heat transfer characteristics, nanofluids are believed to be a promising heat transfer fluid for the future. The stability of nanofluids is also a key aspect of their sustainability and efficiency. This review summarizes the recent research findings on stability, thermophysical properties and convective heat transfer of nanosized particles suspended in base fluids. Furthermore, various mechanisms of thermal conductivity enhancement and challenges faced in nanofluid development are also discussed.
A critical synthesis of thermophysical characteristics of nanofluids
International Journal of Heat and Mass Transfer, 2011
A critical synthesis of the variants within the thermophysical properties of nanofluids is presented in this work. The experimental results for the effective thermal conductivity and viscosity reported by several authors are in disagreement. Theoretical and experimental studies are essential to clarify the discrepancies in the results and in proper understanding of heat transfer enhancement characteristics of nanofluids. At room temperature, it is illustrated that the results of the effective thermal conductivity and viscosity of nanofluids can be estimated using the classical equations at low volume fractions. However, the classical models fail to estimate the effective thermal conductivity and viscosity of nanofluids at various temperatures. This study shows that it is not clear which analytical model should be used to describe the thermal conductivity of nanofluids. Additional theoretical and experimental research studies are required to clarify the mechanisms responsible for heat transfer enhancement in nanofluids. Correlations for effective thermal conductivity and viscosity are synthesized and developed in this study in terms of pertinent physical parameters based on the reported experimental data.
A Review of Thermal Conductivity Models for Nanofluids.
Nanofluids, as new heat transfer fluids, are in the centre of attention of researchers while their measured thermal conductivities are more than conventional heat transfer fluids. Unfortunately, conventional theoretical and empirical models cannot explain the enhancement of the thermal conductivity of nanofluids. Therefore, it is important to understand the fundamental mechanisms as well as the important parameters which influence the heat transfer in nanofluids. Nanofluids thermal conductivity enhancement consists of four major mechanisms: Brownian motion of the nanoparticle, nanolayer, clustering, and the nature of heat transport in the nanoparticles. Important factors which affect the thermal conductivity modelling of nanofluids are particle volume fraction, temperature, particles size, pH, and the size and property of nanolayer. In this paper, each mechanism is explained and proposed models are critically reviewed. It is Downloaded by [University of Pretoria] at 04:58 26 November 2014 ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT 2 concluded that there is a lack of reliable hybrid model which includes all mechanisms and influenced parameters for thermal conductivity of nanofluids. Furthermore, more work needs to be conducted on the nature of heat transfer in nanofluids. A reliable database and experimental data are also needed on the properties of nanoparticles.