Accurate measurement of the thermal conductivity of a heat transfer fluid (HTF) is important for optimizing the performance of a thermal energy storage system. Herein, we develop a system to measure the thermal conductivity of an HTF during temperature variation, and the system was checked to measure several samples comprising water, lauric acid, stearic acid, oleic acid, and coconut oil. The thermal conductivity was measured using a KS-1 sensor of a KD2 Pro analyzer. In the study, a static heat conducting medium was used to control the temperature of the fluid, instead of the commonly used flowing water bath. The measured thermal conductivities of water (298 to 318 K) and lauric acid (323 to 373 K), stearic acid (358 to 372 K), oleic acid (334 to 372 K), and coconut oil (298 to 363 K) were compared to data from previous studies and fitted to available models. The accuracy of the data is further analyzed by relating the number of C and H atoms in the fatty acid, and the fatty acid content in coconut oil.
Freezing of cobalt nitrate hexahydrate (CoNHH) under a static magnetic field was studied at three different magnetic field intensities. The results show that the magnetic field has a significant effect when the sample enters the solid phase and reduces the stochastic behaviour of the nucleation. Thermal properties investigated using thermogravimetric and differential thermal analysis revealed the shift to a lower temperature for the onset of decomposition and melting temperature after the freeze-thaw in a magnetic field. Besides that, we observed a significant change in the FT-IR peaks that might indicate the emergence of cobalt nitrate with a lower hydrate number, a phase separation effect, and the evaporation of NO 3 ions. Refinement of the XRD spectra shows a single phase of CoNHH with a slight lattice parameter change after the freezing-thawing in a magnetic field. The freezing behaviour of CoNHH was compared to that observed previously for water, a salt solution, and an ethylene glycol solution. We investigated the relationship of the freezing behaviour with hydrogen bonding and magnetic properties and its impact on the change in the Gibbs free energy. The results of this study are important to optimise the performance of CoNHH as latent thermal energy storage.
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