Nanofluids in compact heat exchangers for thermal applications: A State-of-the-art review

With the advancement of industries and the trend towards miniaturization, sustainability and higher energy efficiency of devices, compact heat exchangers become an urgent need in the wide range of heat transfer applications. However, the requirements for high heat energy dissipation due to extreme thermal loads may limit their development, mainly because of the inherently poor thermophysical properties of the thermal fluid commonly used. Nanofluids with an optimal design considering their stability, heat transfer enhancement and a lower increase in the pressure drop, are suggested as a promising solution to increase the energy efficiency of thermal energy systems. Here, a thorough and updated review is presented about the heat transfer and fluid flow of these promising nanofluids in compact heat exchangers with mini and micro-passes (channels) for several operation conditions, considering the several factors of nanofluids such as nanoparticles type and shape, base fluid type, preparation method, stability, thermal conductivity and rheology. Moreover, this article presents the experimental and numerical methods employed to investigate nanofluids' thermal performance, analysing the results in terms of heat transfer enhancement and suitability in such heat exchangers. The latter will enable to define the lack of knowledge, the contradictions that may be found between previous studies and the best options for further investigations in this developing field for sustainable thermal energy and better utilization, mainly selecting compact heat exchanger geometry and nanofluids structures (nanoparticle, base fluid and preparation method) and investigation methods (experimental and numerical).

Automated summary

This article provides a comprehensive review of the heat transfer and fluid flow of nanofluids in compact heat exchangers. The study evaluates the impact of factors such as nanoparticles type and shape, base fluid type, preparation method, stability, thermal conductivity, and rheology on the performance of the heat exchanger.