Effect of formation of "long range" secondary dendritic nanostructures in molten salt nanofluids on the values of specific heat capacity. (December 2015)

• Record Type: Journal Article
• Authors: Tiznobaik, Hani; Banerjee, Debjyoti; Shin, Donghyun
• Is Part Of: International journal of heat and mass transfer. Volume 91(2015:Dec.)
• Page Start: 342
• Page End: 346
• Publication Date: 2015-12
• Subjects: Thermal energy storage -- Molten salt -- Concentrated solar power -- Nanoparticle -- Heat capacity; Heat -- Transmission -- Periodicals; Mass transfer -- Periodicals; Chaleur -- Transmission -- Périodiques; Transfert de masse -- Périodiques; Electronic journals; 621.4022
• DOI: 10.1016/j.ijheatmasstransfer.2015.05.072
• Languages: English
• ISSNs: 0017-9310

Abstract

Highlights: Salt nanofluids have the similar heat capacity enhancement regardless of the type of nanoparticles. The nanofluid samples inherently consist of both nanoparticles and long-range nanostructures. Small nanoparticle addition to the eutectic can induce a large amount of long-range nanostructures. Extremely large surface area of nanostructures significantly enhances the effective specific heat. Abstract: Several studies in recent literature have demonstrated the enhancement of specific heat capacity (Cp) of molten-salts on doping with minute concentration of nanoparticles, especially when the synthesis conditions enabled the formation of stable colloidal suspensions (which are also known as "molten-salt nanofluids"). In this study we present additional evidence in support of theory proposed earlier in the literature that stable colloidal suspensions of nanoparticles in a molten-salt medium induces the preferential surface adsorption of the constitutive chemical species in the salt mixture which in turn leads to the nucleation of solid phase of the molten salt (with perhaps a different chemical composition than in the bulk phase) on the nanoparticle surface. The surface adsorbed salt species leads to the nucleation and growth of a semi-solid layer of dendritic shaped phase (dendritic shaped secondary "long range" nanostructures). Incidentally, such nanostructures were not observed in electron microscopy images for samples of pure molten-salt mixtures subjected to control experiments (i.e., without nanoparticles). Hence, this study conclusively demonstrates that the existence of these nanostructures is primarily responsible for the enhancement of specific heat capacity. In this study, three different types of nanoparticles are dispersed in the same molten-salt mixture ("base fluid") and the experimentally measured values of specific heat capacity enhancements obtained in this study are correlated to the formation of dendritic nanostructures that are observed in the images obtained from the electron microscopy of the molten-salt nanomaterial samples.