The effects of pressure and nanofluid stability on pool boiling CHF using magnetite-water nanofluids

Abstract

Water-based nanofluids are colloidal dispersions of nanoparticles in pure water and have significantly higher critical heat flux (CHF) values compared to pure water at atmospheric pressure. However, when nanofluids are used in the cooling system, it is difficult to keep the nanoparticles dispersed and to clean up the nanoparticles if necessary, especially in nuclear power plant. Furthermore, the required mass of nanoparticles can make the method economically challenging because tons of nanoparticles are needed to provide several thousand tons of nanofluids for nuclear power plant application. In this study, a magnetite-water nanofluid is introduced to overcome the shortcomings of nanofluids and set itself apart from other nanofluids. To assess the potential use of magnetite-water nanofluid as a coolant in nuclear power plants, mainly three experimental works have been done. The first one is the feasibility study of CHF enhancement using magnetite-water nanofluid at lower concentration. The second one is the effect of pressure on CHF enhancement to understand the CHF characteristic. And, the last one is the effect of dispersion stability of nanoparticles in nanofluids on CHF enhancement. First, pool boiling CHF experiments using a Ni-Cr wire were performed to assess the CHF performance using magnetite-water nanofluid according to the nanoparticle concentration. The CHF values between the magnetite-water nanofluid and the other nanofluids with several volume concentrations were compared to evaluate the effect of the magnetite-water nanofluid on the CHF enhancement. The CHF values of the mag-netite-water nanofluid were enhanced from approximately 70% to 140% of pure water as the nanoparticle concentration increased. And, analytical study on the bubble behaviors and surface characteristics were also carried out to understand the mechanism of CHF enhancement. Secondly, pool boiling CHF experiment at higher pressure were also performed to evaluate the effect of pre...