https://www.eis.hu.edu.jo/deanshipfiles/pub10311353.pdf

Numerical study of natural convection in partially heated rectangular enclosures filled with nanofluids

Boundary-layer flow of a nanofluid past a stretching sheet

Nanofluids are potential heat transfer fluids with enhanced thermophysical properties and heat transfer performance can be applied in many devices for better performances (i.e. energy, heat transfer and other performances). In this paper, a comprehensive literature on the applications and challenges of nanofluids have been compiled and reviewed. Latest up to date literatures on the applications and challenges in terms of PhD and Master thesis, journal articles, conference proceedings, reports and web materials have been reviewed and reported. Recent researches have indicated that substitution of conventional coolants by nanofluids appears promising. Specific application of nanofluids in engine cooling, solar water heating, cooling of electronics, cooling of transformer oil, improving diesel generator efficiency, cooling of heat exchanging devices, improving heat transfer efficiency of chillers, domestic refrigerator-freezers, cooling in machining, in nuclear reactor and defense and space have been reviewed and presented. Authors also critically analyzed some of the applications and identified research gaps for further research. Moreover, challenges and future directions of applications of nanofluids have been reviewed and presented in this paper. Based on results available in the literatures, it has been found nanofluids have a much higher and strongly temperature-dependent thermal conductivity at very low particle concentrations than conventional fluids. This can be considered as one of the key parameters for enhanced performances for many of the applications of nanofluids. Because of its superior thermal performances, latest up to date literatures on this property have been summarized and presented in this paper as well. However, few barriers and challenges that have been identified in this review must be addressed carefully before it can be fully implemented in the industrial applications.

/pdf/a-review-on-applications-and-challenges-of-nanofluids-ibdekzmmqr.pdf

A review on applications and challenges of nanofluids

This study provides a detailed literature review and an assessment of results of the research and development work forming the current status of nanofluid technology for heat transfer applications. Nanofluid technology is a relatively new field, and as such, the supporting studies are not extensive. Specifically, experimental results were reviewed in this study regarding the enhancement of the thermal conductivity and convective heat transfer of nanofluids relative to conventional heat transfer fluids, and assessments were made as to the state-of-the-art of verified parametric trends and magnitudes. Pertinent parameters of particle volume concentration, particle material, particle size, particle shape, base fluid material, temperature, additive, and acidity were considered individually, and experimental results from multiple research groups were used together when assessing results. To this end, published research results from many studies were recast using a common parameter to facilitate comparisons of data among research groups and to identify thermal property and heat transfer trends. The current state of knowledge is presented as well as areas where the data are presently inconclusive or conflicting. Heat transfer enhancement for available nanofluids is shown to be in the 15-40% range, with a few situations resulting in orders of magnitude enhancement.

Review and Comparison of Nanofluid Thermal Conductivity and Heat Transfer Enhancements

Unsteady heat and mass flow of a nanofluid past a stretching sheet with thermal radiation in the presence of magnetic field is studied. To obtain non-similar equation, continuity, momentum, energy and concentration equations have been non-dimensionalised by usual transformation. The non-similar solutions are presented here which depends on the Magnetic parameter M respectively . The obtained equations have been solved by explicit finite difference method. The temperature and concentration profiles are discussed for the different values of the above parameters with different time steps.

Finite difference solution of mhd radiative boundary layer flow of a nanofluid past a stretching sheet

The thermal conductivities of nanofluid containing a small amount of ultra-dispersed diamond (UDD), silver, and silica nanoparticles were measured using a transient hot-wire method. To explain the enhancement of thermal conductivity of nanofluid, the effective volume of nanoparticles was used instead of the real volume to predict the thermal conductivity of nanofluid. The liquid layering on the surface of nanoparticles may be described as the effective volume of nanoparticles. This liquid layering is one important mechanism of the heat transfer in nanofluids. The effective volume of nanoparticles was estimated from high shear viscosity of nanofluid using the Einstein equation. The Hamilton–Crosser model with an effective volume fraction of nanoparticles resulted in better correlation for the thermal conductivities of nanofluids.

Estimation of Thermal Conductivity of Nanofluid Using Experimental Effective Particle Volume

This study focused on the synthesis of stable nanofluids and their direct application to the CO2 absorption process. A sol-gel process was used as the synthesis method of nanoparticles in nanofluid. The particle size and stability were determined by SEM image and zeta potential of the nanofluid. Three types of nanofluids containing approximately 30 nm, 70 nm, and 120 nm particles were synthesized and all nanofluids had a stable zeta potential of approximately − 45 mV. Addition of nanoparticles increased the average absorption rate of 76% during the first 1 minute and total absorption amount of 24% in water. The capacity coefficient of CO2 absorption in the nanofluid is 4 times higher than water without nanoparticles, because the small bubble sizes in the nanofluid have large mass transfer areas and high solubility.

Synthesis of Silica Nanofluid and Application to CO2 Absorption

This study was performed to investigate the convective heat transfer coefficient of nanofluids made of several alumina nanoparticles and transformer oil which flow through a double pipe heat exchanger system in the laminar flow regime. The nanofluids exhibited a considerable increase of heat transfer coefficients. Although the thermal conductivity of alumina is not high, it is much higher than that of the base fluids. The nanofluids tested displayed good thermal properties. One of the possible reasons for the enhancement on heat transfer of nanofluids can be explained by the high concentration of nanoparticles in the thermal boundary layer at the wall side through the migration of nanoparticles. To understand the enhancement of heat transfer of nanofluid, an experimental correlation was proposed for an alumina-transformer oil nanofluid system.

/pdf/effect-of-alumina-nanoparticles-in-the-fluid-on-heat-3jx5ub3erk.pdf

Effect of alumina nanoparticles in the fluid on heat transfer in double-pipe heat exchanger system

Hydrophilic coating solutions were synthesized by adding glycidoxypropyltrimethoxysilane (GPS) to the colloidal silica suspensions adjusted to different pH. The coating solutions were coated on polyethyleneterephthalate (PET) film substrates. The pH of the colloidal silica suspensions adjusted before adding the GPS had a profound effect on chemical structure of the coating solutions and hydrophilic property of the coating films. 29Si NMR spectroscopic studies showed that the solution prepared under an acidic condition (pH 4) consisted of hydrolyzed GPS monomers without siloxane bond and dimer with one siloxane bond, whereas that under a basic condition (pH 9.6) was made up larger oligomers with two or three siloxane bonds. Contact angles for water in the coating films prepared under acidic conditions exhibited smaller than those under basic conditions, indicating more hydrophilic in acidic conditions. In especial, in the case of coating films preparedunder highly acidic conditions (pH 1 and 2), the contact angles were less than 5°, which is superhydrophilic.

Synthesis of Hydrophilic Coating Solution for Polymer Substrate Using Glycidoxypropyltrimethoxysilane

A nanofluid is a mixture of solid nanoparticles and a common base fluid. Nanofluids have shown great potential in improving the heat transfer properties of liquids. However, previous studies on the characteristics of nanofluids did not adequately explain the enhancement of heat transfer. This study examined the distribution of particles in a fluid and compared the mechanism for the enhancement of heat transfer in a nanofluid with that in a general microparticle suspension. A theoretical model was formulated with shear-induced particle migration, viscosity-induced particle migration, particle migration by Brownian motion, as well as the inertial migration of particles. The results of the simulation showed that there was no significant particle migration, with no change in particle concentration in the radial direction. A uniform particle concentration is very important in the heat transfer of a nanofluid. As the particle concentration and effective thermal conductivity at the wall region is lower than that of the bulk fluid, due to particle migration to the center of a microfluid, the addition of microparticles in a fluid does not affect the heat transfer properties of that fluid. However, in a nanofluid, particle migration to the center occurs quite slowly, and the particle migration flux is very small. Therefore, the effective thermal conductivity at the wall region increases with increasing addition of nanoparticles. This may be one reason why a nanofluid shows a good convective heat transfer performance.

/pdf/effect-of-particle-migration-on-the-heat-transfer-of-2yuis9ebcg.pdf

Hyun Uk Kang

Papers

Estimation of Thermal Conductivity of Nanofluid Using Experimental Effective Particle Volume

Synthesis of Silica Nanofluid and Application to CO2 Absorption

Effect of alumina nanoparticles in the fluid on heat transfer in double-pipe heat exchanger system

Synthesis of Hydrophilic Coating Solution for Polymer Substrate Using Glycidoxypropyltrimethoxysilane

Effect of particle migration on the heat transfer of nanofluid