Nanoparticle Dispersions on Ternary Nitrate Salts for Heat Transfer Fluid Applications in Solar Thermal Power

In this study, we report enhancement in heat capacity of SiO2 nanoparticle dispersions in a molten ternary nitrate salt (NaNO3, KNO3, and Ca(NO3)2) to obtain an effective heat transfer fluid (HTF)/thermal energy storage (TES) for concentrated solar power (CSP) application. The enhanced heat capacity of the molten salt mixture is expected to greatly increase thermal storage density of HTF/TES, and thus the cost of electricity produced by CSP plant can be significantly reduced. A custom two-step method was used to synthesize SiO2 nanoparticle/ternary salt mixture. The nanoparticle concentration of the mixture was fixed at 1% by weight for comparison with the previous studies. A modulated differential scanning calorimeter (MDSC) was employed to measure heat capacity of the mixture, and it was found to be enhanced by ∼19% compared to the pure ternary salt.

Heat Capacity of Copper Thin Films Measured by Micro Pulse Calorimeter

Thermal properties of thin films may differ from the bulk value due to the differences in microstructure, such as the grain size, impurities and defects. Heat capacity is one of the thermophysical properties and it is measured by calorimetry. However, traditional calorimeters can’t measure heat capacity of thin films which are quasi-2D and has small heat capacity. Recently, micro calorimeters with suspending membrane structure have been developed to measure the heat capacity of ultra thin films with thickness of sub-micrometer to nanometer scale. Efforts are focused on reducing heat capacitance of the addenda and minimizing the thermal link so as to permit an adiabatic measurement of the heat capacity of thin film. In this paper, a micro pulse calorimeter was developed and heat capacities of the copper thin films were measured by the micro pulse calorimetry. The heating rate of the micro calorimeter is up to 200K/ms with heating power of 4.5mW, and the heat capacity of the calorimeter is about 23.4nJ/K at 300K. Heat capacities of polycrystalline copper thin films with thickness from 20nm to 340nm were measured in the temperature range from 300K to 420K in vacuum of 1mPa. In order to extract the specific heat of the Cu films, mass of the films was calculated with volume and density of the sample film. The specific heat of the Cu films was compared with the literature values of bulk Cu. The specific heat of the 340nm Cu film is close to the literature data of bulk Cu. For the thinner films, enhanced specific heat was observed, and the data shows that the specific heat increases with the decreasing of crystalline size and film thickness.