Evaluation of critical heat flux with various silica nanoparticles for the development of multi-functional magnetic nanoparticles

Abstract

As interests in a severe accident have increased after Fukushima nuclear power plant accident in 2011, the concept of multi-functional magnetic nanoparticles (MFMNs) was suggested as one of the mitigation strategies. However, despite numerous advantages of nanoparticles verified by previous research, the use of them in nuclear power plants (NPPs) has some limitations, particularly altering the thermal-hydraulic characteristics of coolant in the system. Therefore, before applying the concept of MFMNs into the system, evaluation of thermal characteristics of nanofluids is highly necessary, especially as to critical heat flux (CHF) for a safety margin. In this study, consequently, we want to find out which shape and size of silica nanoparticles would be suitable for the part of MFMNs through the CHF evaluation. On this basis, pool boiling experiments were conducted with magnetite (25nm) and various size (8nm to 2000nm) and shape (porous and non-porous) of silica nanoparticles, which are components of MFMNs. The flat-type heater was used as the test section of the experimental facility. Furthermore, relatively low concentration conditions ($10^{-5}$ % vol. to $10^{-3}$% vol.) compared with previous studies was applied since the lower concentration of nanoparticles is good for coolant stability and economics. In addition, sonication process was performed for the preparation of well-dispersed stable nanofluids. Consequently, the improvement and deterioration of CHF were observed depending on concentrations and particle size of silica nanoparticles. Furthermore, the surface analysis using scanning electron microscope (SEM) images and contact angle measurement was conducted, and the deposition of nanoparticles on the heater surface and the wettability enhancement were confirmed. Furthermore, the influential parameters on boiling mechanism were additionally investigated. Thus, based on the previous studies and verifications, sufficient discussions on the persuasive mechanisms regarding the experimental results are suggested in this paper.