Suspended nanoparticles in conventional fluids, called nanofluids, have been the subject of intensive study worldwide since pioneering researchers recently discovered the anomalous thermal behavior of these fluids. The enhanced thermal conductivity of these fluids with small-particle concentration was surprising and could not be explained by existing theories. Micrometer-sized particle-fluid suspensions exhibit no such dramatic enhancement. This difference has led to studies of other modes of heat transfer and efforts to develop a comprehensive theory. This article presents an exhaustive review of these studies and suggests a direction for future developments. The review and suggestions could be useful because the literature in this area is spread over a wide range of disciplines, including heat transfer, material science, physics, chemical engineering and synthetic chemistry.

https://www.tandfonline.com/doi/pdf/10.1080/01457630600904593

Heat Transfer in Nanofluids—A Review

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

Empirical correlating equations for predicting the effective thermal conductivity and dynamic viscosity of nanofluids

A review of nanofluid stability properties and characterization in stationary conditions

Thermophysical and electrokinetic properties of nanofluids – A critical review

A theoretical model which includes considerations of the effects of an interfacial nanolayer formed by liquid molecule layering on the particle/liquid interface and of micro-convection caused by thermal motion of nanoparticles has been proposed to calculate the effective thermal conductivity of nanofluids. This model accounts for the enhancement in effective thermal conductivity of a nanofluid with respect to the suspended nanoparticle size, volume fraction, temperature and thermal conductivities of the nanoparticle and base fluid. The predicted results are in good agreement with some recently available experimental data.

https://iopscience.iop.org/article/10.1088/0022-3727/38/21/019/pdf

An Cai

Papers

Effective thermal conductivity of nanofluids containing spherical nanoparticles