This article reports on the International Nanofluid Property Benchmark Exercise, or INPBE, in which the thermal conductivity of identical samples of colloidally stable dispersions of nanoparticles or “nanofluids,” was measured by over 30 organizations worldwide, using a variety of experimental approaches, including the transient hot wire method, steady-state methods, and optical methods. The nanofluids tested in the exercise were comprised of aqueous and nonaqueous basefluids, metal and metal oxide particles, near-spherical and elongated particles, at low and high particle concentrations. The data analysis reveals that the data from most organizations lie within a relatively narrow band (±10% or less) about the sample average with only few outliers. The thermal conductivity of the nanofluids was found to increase with particle concentration and aspect ratio, as expected from classical theory. There are (small) systematic differences in the absolute values of the nanofluid thermal conductivity among the various experimental approaches; however, such differences tend to disappear when the data are normalized to the measured thermal conductivity of the basefluid. The effective medium theory developed for dispersed particles by Maxwell in 1881 and recently generalized by Nan et al. [J. Appl. Phys. 81, 6692 (1997)], was found to be in good agreement with the experimental data, suggesting that no anomalous enhancement of thermal conductivity was achieved in the nanofluids tested in this exercise.

A Benchmark Study on the Thermal Conductivity of Nanofluids

Researches on the nanofluids have been increased very rapidly over the past decade. In spite of some inconsistency in the reported results and insufficient understanding of the mechanism of the heat transfer in nanofluids, it has been emerged as a promising heat transfer fluid. In the continuation of nanofluids research, the researchers have also tried to use hybrid nanofluid recently, which is engineered by suspending dissimilar nanoparticles either in mixture or composite form. The idea of using hybrid nanofluids is to further improvement of heat transfer and pressure drop characteristics by trade-off between advantages and disadvantages of individual suspension, attributed to good aspect ratio, better thermal network and synergistic effect of nanomaterials. This review summarizes recent researches on synthesis, thermophysical properties, heat transfer and pressure drop characteristics, possible applications and challenges of hybrid nanofluids. Review showed that proper hybridization may make the hybrid nanofluids very promising for heat transfer enhancement, however, lot of research works is still needed in the fields of preparation and stability, characterization and applications to overcome the challenges.

A review on hybrid nanofluids: Recent research, development and applications

Selection of suitable heat transfer fluid for heat dissipation is an important consideration in the design of heat exchanging systems. Nanofluid, a colloidal mixture made of a base fluid and a nanoparticle, is a new generation of heat transfer fluids becoming a high potential fluid in heat transfer applications due to enhanced thermal conductivity. Research studies about nanofluids are on the rise owing to the mounting interest and demand for nanofluids as heat transfer fluids in a wide variety of applications. Recently, nanofluid technology has a new dimension of impregnating two or more nanoparticles in base fluids, namely hybrid or composite nanofluids. This paper reviews the preparation of metal and metal oxides nanofluids and hybrid nanofluids and the various techniques used to study the physical and chemical characteristics of nanofluids. Thermo-physical and heat transfer properties of nanofluids including the improved thermal conductivity, viscosity and specific heat models for nanofluids are presented. Finally, various application areas of nanofluids, such as transportation, electronic cooling, energy storage, mechanical applications etc. are discussed.

A review on preparation, characterization, properties and applications of nanofluids

Continued miniaturization and demand for high-end performance of electronic devices and appliances have led to dramatic increase in their heat flux generation. Consequently, conventional coolants and cooling approaches are increasingly falling short in meeting the ever-increasing cooling needs and challenges of those high heat generating electronic devices. This study provides a critical review of traditional and emerging cooling methods as well as coolants for electronics. In addition to summarizing traditional coolants, heat transfer properties and performances of potential new coolants such as nanofluids are also reviewed and analyzed. With superior thermal properties and numerous benefits nanofluids show great promises in fulfilling the cooling demands of high heat generating electronic devices. It is believed that applications of such novel coolants in emerging techniques like micro-channels and micro-heat pipes can revolutionize cooling technologies for electronics in the future.

A critical review of traditional and emerging techniques and fluids for electronics cooling

Recent advances in modeling and simulation of nanofluid flows—Part II: Applications

The purpose of this review summarizes the important published articles on the enhancement of the convection heat transfer in heat exchangers using nanofluids on two topics. The first section focuses on presenting the theoretical and experimental results for the effective thermal conductivity, viscosity and the Nusselt number reported by several authors. The second section concentrates on application of nanofluids in various types of heat exchangers: plate heat exchangers, shell and tube heat exchangers, compact heat exchangers and double pipe heat exchangers.

Angel Huminic

Papers

Application of nanofluids in heat exchangers: A review

Hybrid nanofluids for heat transfer applications – A state-of-the-art review

Entropy generation of nanofluid and hybrid nanofluid flow in thermal systems: A review

Experimental study of the thermal performance of thermosyphon heat pipe using iron oxide nanoparticles

Heat transfer characteristics in double tube helical heat exchangers using nanofluids