## 1 Introduction  
Nanofluids have attracted considerable attention in heat-transfer fields because of their enhanced thermal properties, such as their thermal conductivity and boiling characteristics. In 1993, [PERSON] et al. measured the thermal conductivity of suspensions in which Al\({}_{2}\)O\({}_{3}\), SiO\({}_{2}\), and TiO\({}_{2}\) were dispersed in water. Authors reported that the thermal conductivity linearly increased with the particle volume concentration [1]. In 1995, [PERSON] and [PERSON] proposed nanofluids as innovative heat-transfer fluids, owing to their enhanced thermal conductivity [2]. In the early 2000s, the dramatic increase of the critical heat flux in pool boiling of nanofluids gave rise to the consideration of nanofluids as an alternative to conventional heat-transfer fluids [3; 4]. After those publications, related studies into the thermal property and boiling characteristic have been actively performed under various experimental conditions. As reviewed by [PERSON] and [PERSON], various measurement techniques for the thermal conductivity of nanofluids, such as the hot-wire method, the steady-state parallel-plate technique, and the temperature oscillation method, have been employed [5]. Various kinds of nanoparticles have been dispersed into base fluids--generally water, oil, and ethylene glycol--to examine the enhancements in the thermal conductivity (summarized in [5; 6]). The significantly enhanced critical heat flux in pool boiling of nanofluids was also evaluated to be outstanding. This has been attributed to the change of the surface wettability due to nanoparticle deposition on heater surfaces. After the observation in these pool-boiling experiments, initially modified heater surfaces were employed to confirm the critical heat flux performance [7; 8]. Significant enhancements in the critical heat flux were acquired from previous studies with the heater surface modified by nanomaterials [9; 10; 11; 12]. While numerous studies on the thermal conductivity of nanofluids have been published, few studies on the specific heat of nanofluids have been performed, and they report that the specific heat of nanofluids decreases with the addition of nanoparticles [13; 14; 15; 16]. Since [PERSON] et al. reported that the specific heat of a polyalphaolefin (PAO) nanofluid was significantly increased by adding a small amount of graphite nanoparticle fibers [17], several research groups reported that the specific heat is increased by adding nanoparticles. In particular, Dr. [PERSON]'s research groups reported that the specific heat of binary molten salt mixtures (or eutectic), which are considered as thermal energy storage media in concentrating solar power plants, can be enhanced via doping with nanoparticles. They used various molten salts (carbonate salts, nitrate salts, and chloride salts) as base fluids, along with both organic and inorganic nanoparticles. A wide range of parametric studies (effects of the nanoparticle concentration, particle shape, size, dispersion quality, etc.) have been performed to identify the mechanism underlying the specific heat increase in the molten salt nanofluids [18; 19; 20; 21; 22]. [PERSON] et al. enhanced the specific heat of a binary nitrate (NaNO\({}_{3}\)-KNO\({}_{3}\)) by dispersing various nanoparticles (Al\({}_{2}\)O\({}_{3}\), SiO\({}_{2}\), TiO\({}_{2}\), and SiO\({}_{2}\)-Al\({}_{2}\)O\({}_{3}\)) [23; 24]. The enhanced specific heat of the molten salt nanofluids was explained in various ways, e.g., electron microscope images and molecular dynamics simulation [25; 26; 27; 28; 29; 30]. Furthermore, a fundamental experimental study into thermal property variations of carbonate salt mixtures was performed using a differential scanning calorimeter (DSC) [31]. Additionally, the viscosity of the molten salt nanofluids was measured at a high temperature of 550 \({}^{\circ}\)C [32]. Most recently, [PERSON] et al. reported the effect of nanoparticles on the corrosivity of nitrate molten salt [33].