REVIEW OF THE INFLUENCE OF NANOFLUIDS ON THE NUCLEATE POOL BOILING

Leonardo Lachi Manetti¹; Elaine Maria Cardoso¹

¹ UNESP - Universidade Estadual Paulista

doi:10.20906/CPS/COB-2015-0728

Resumo

In the last years, nanofluids have been extensively investigated because of their significant effect on the critical heat flux and pool boiling characteristics, due to nanoscale structures deposited on the heating surface. The favorable perspective of using nanofluids in thermal systems to improve the critical heat flux during the boiling process has attracted the attention of many researchers. The main motivation has been the industrial trend toward producing compact and miniaturized equipment, in particular in the area of microelectronics and microcooling. Researchers generally agree with the idea of a critical heat flux (CHF) enhancement, despite existing differences among the experimental results. The same cannot be said for the heat transfer coefficient (HTC), because the mechanism for HTC enhancement or degradation is not fully understood. Therefore, the main question nowadays regarding nanofluid pool boiling heat transfer mechanisms is whether they increase or decrease the HTC in comparison with base fluid boiling alone. Both the HTC and the CHF may be attributed, mainly, to changes in the surface wettability caused by nanoparticle deposition. In this case, the nanolayer formed on the heating surface increases the wettability, which makes the rewetting process much easier and explains, in part, the high CHF values. A decrease in the contact angle can also partially explain a reduction in the HTC, since the frequency of active sites and bubble departure tends to decrease. This paper mainly focuses on the experimental studies reported in the literature, in the last five years, on the pool boiling phenomena using nanofluids as working fluid. An analysis on contradictory data provided by researchers for the HTC behavior is carried out. Also, the heat transfer mechanisms pointed in the literature as responsible for the heat transfer behaviors are contrasted.

Palavras-chave: Nanofluids; nucleate pool boiling; heat transfer coefficient; critical heat flux; heat transfer mechanism