A critical insight on nanofluids for heat transfer enhancement

Abstract

There are numerous reports and publications in reputable scientific and engineering journals that attribute substantial enhancement in heat transfer capabilities for heat exchangers once they employ nanofluids as working fluids. By definition, a nanofluid is a working fluid that has a small volume fraction (5% or less) of a solid particle with dimensions in the nanoscale. The addition of this solid material has a reported significant impact on convective heat transfer in heat exchangers. This work investigates the significance of the reported enhancements in many recent related publications. Observations on these publications' geographical origins, fundamental heat transfer calculations, experimental setups and lack of potential applications are critically made. Heat transfer calculations based on methodologies outlined in random selection of available papers were conducted along with a statistical analysis show paradoxically inconsistent conclusion as well as an apparent lack of complete comprehension of convective heat transfer mechanism. In some of the surveyed literature for example, heat transfer coefficient enhancements were reported to be up to 27% and 48%, whereas the recalculations presented in this work restrain proclaimed enactments to ~ 3.5% and - 4% (no enhancement), respectively. This work aims at allowing a healthy scientific debate on whether nanofluids are the sole answer to enhancing convective heat transfer in heat exchangers. The quantity of literature that confirms the latter statement have an undeniable critical mass, but this volition could be stemming from and heading to the wrong direction. Finally, the challenges imposed by the physical nature of nanoparticles, as well as economic limitations caused by the high price of conventional nanoparticles such as gold (80$/g), diamond (35$/g), and silver (6$/g) that hinder their commercialization, are presented.

Figure 1

Publications on nanofluids by region between 2010 and 2022.

Figure 2

Classification of publications.

Figure 3

Comparison between present work calculations and Bianco for the heat transfer coefficient.

Figure 4

Comparison between present work calculations of the heat transfer coefficient and Farajollahi et al..

Figure 5

Comparison between heat transfer coefficient values recalculated in the present work and those found in Anitha et al..

Figure 6

Comparison between heat transfer coefficient values recalculated in the present work and those found in Kumar and Sonawane.

Figure 7

Summary of microstructure issues in nanofluids.

Figure 8

Steps and measures for nanofluids commercialization.