Abstract
Cooling by impinging droplets has been the subject of several studies for decades and still is, and, in the last few years, the potential heat transfer enhancement obtained thanks to nanofluids’ use has received increased interest. Indeed, the use of high thermal conductivity fluids, such as nanofluids’, is considered today as a possible way to strongly enhance this heat transfer process. This enhancement is related to several physical mechanisms. It is linked to the nanofluids’ rheology, their degree of stabilization, and how the presence of the nanoparticles impact the droplet/substrate dynamics. Although there are several articles on droplet impact dynamics and nanofluid heat transfer enhancement, there is a lack of review studies that couple these two topics. As such, this review aims to provide an analysis of the available literature dedicated to the dynamics between a single nanofluid droplet and a hot substrate, and the consequent enhancement or reduction of heat transfer. Finally, we also conduct a review of the available publications on nanofluids spray cooling. Although using nanofluids in spray cooling may seem a promising option, the few works present in the literature are not yet conclusive, and the mechanism of enhancement needs to be clarified.
Highlights
Considerable research has been conducted on the heat transfer of droplets impinging on a hot substrate [1,2,3]
Thanks to their larger thermal conductivity compared to the base liquids [43,44], nanofluids appear to be a very promising way to enhance the heat transfer
The present study aims to review the most recent studies addressing the topics of nanofluid drop impact, heat transfer and sessile droplet evaporation on solid substrates
Summary
Considerable research has been conducted on the heat transfer of droplets impinging on a hot substrate [1,2,3]. The maximum value of the spreading-factor influences the heat transfer rate by limiting the contact area between the droplet and the substrate [16,17,18,19,20]. To quantify the maximum spread factor of a droplet on a substrate, several empirical correlations exist They use as parameters the Weber number [21,22,23,24], the Reynolds number [25] or both [26,27,28]. According to Moon et al [29], the maximum contact area between a droplet and a substrate increases with the Weber number, whereas the time required to reach that condition decreases, improving the cooling efficiency. During the final stage, both the contact angle and droplet radius decrease until the droplet completely disappears
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