Effect of interfacial thermal resistance and nanolayer on estimates of effective thermal conductivity of nanofluids

Ali Khodayari,Matteo Fasano,Masoud Bozorg Bigdeli,Shahin Mohammadnejad,Eliodoro Chiavazzo,Pietro Asinari

doi:10.1016/j.csite.2018.06.005

Abstract

Colloidal suspensions of nanoparticles (nanofluids) are materials of interest for thermal engineering, because their heat transfer properties are typically enhanced as compared to the base fluid one. Effective medium theory provides popular models for estimating the overall thermal conductivity of nanofluids based on their composition. In this article, the accuracy of models based on the Bruggeman approximation is assessed. The sensitivity of these models to nanoscale interfacial phenomena, such as interfacial thermal resistance (Kapitza resistance) and fluid ordering around nanoparticles (nanolayer), is considered for a case study consisting of alumina nanoparticles suspended in water. While no significant differences are noticed for various thermal conductivity profiles in the nanolayer, a good agreement with experiments is observed with Kapitza resistance ≈10−9 m2K/W and sub-nanometer nanolayer thickness. These results confirm the classical nature of thermal conduction in nanofluids and highlight that future studies should rather focus on a better quantification of Kapitza resistance at nanoparticle-fluid interfaces, in order to allow bottom up estimates of their effective thermal conductivity.

Highlights

Since the first report on their peculiar thermal conductivity in 1995, thermophysical properties of colloidal suspensions of nanoparticles have been widely investigated in the biomedical and engineering fields [1].In the biomedical sector, nanofluids show applications in cancer therapy, drug delivery, imaging and sensing [2, 3]
This is due to the fact that, while BR model considers a bulk value of thermal conductivity in the nanolayer, λl is estimated as 8.54, 4.84, 13.42 and 23.21 W/m·K in the BR-LIN, BR-CUB, BR-EXP and BR-LOG models, respectively
Different models based on Bruggeman approximation have been compared with experimental data from the literature, in order to assess the sensitivity of the effective thermal conductivity of nanofluids to Kapitza resistance and liquid layering at the nanoparticle-fluid interface

Summary

Introduction

Since the first report on their peculiar thermal conductivity in 1995, thermophysical properties of colloidal suspensions of nanoparticles (nanofluids) have been widely investigated in the biomedical and engineering fields [1].In the biomedical sector, nanofluids show applications in cancer therapy, drug delivery, imaging and sensing [2, 3]. Since the first report on their peculiar thermal conductivity in 1995, thermophysical properties of colloidal suspensions of nanoparticles (nanofluids) have been widely investigated in the biomedical and engineering fields [1]. Suspending thermally conductive nanoparticles in conventional fluids with the aim of improving their heat transfer properties has been among the most investigated and controversial research areas [18,19,20]. Researchers have studied experimental, semi-empirical and theoretical models for the thermal conductivity of nanofluids, which is typically enhanced respect to the base fluid one [21,22,23,24,25]. Classic Effective Medium Theories (EMTs), such as Maxwell-Garnett (MG) [27] or Bruggeman (BR) [28] approximations, have been progressively amended to include the nanoscale effects at nanoparticle-fluid interface, as well as the nanoparticle size, shape and aggregation [13]

Methods

Results

Conclusion