Effect of lithium nitrate and calcium nitrate composition on the thermal properties of quaternary molten salts mixture for heat transfer application

Abstract

Abstract.Mixed molten salt is considered as a promising medium for both heat transfer and energy storage in thermal power because of its many advantages such as low the melting point, large heat capacity, good thermal stability and low cost. In order to determine the thermal properties of the molten salt, the nitrate quaternary mixture of the molten salt are prepared based on the different composition of the lithium nitrate and calcium nitrate. The other salts in the mixture are potassium nitrate and sodium nitrate. Mixture of molten salts were heated in furnace at 150 for 4 hours and increased the temperature to 400 for 8 hours for homogenize the salt mixture. Then, decreased the temperature to 115 for an hour. The melting point and thermal stability of the mixture was determined by using thermogravimetric analysis [TGA] while the heat capacity was determined by using differential scanning calorimetry [DSC]. The lowest melting point using different composition of lithium nitrate, 10wt%NaNO3, 4Owt%KNO3, 20wt%Ca[NO3]2, 30wt%LiNO3 which is 97.1 while the heat capacity is 6.33 J/g . For the experiment using various composition of calcium nitrate, the lowest melting point is from 14wt% NaNO3 + 48wt% KNO3 + 13wt% LiNO3 + 25wt% Ca[NO3]2 which is 111.7 and the heat capacity is 2.06 J/g . From the result, the addition of lithium nitrate in the quaternary molten salts give more effect to the reduction of melting point value but higher heat capacity. IntroductionMolten salt is a means of storing heat at a high temperature. Molten salt is constituting of potassium nitrate, calcium nitrate, sodium nitrate, lithium nitrate. It has the property to absorb heat and to store the heat energy that is released to the water to transfer energy when needed. Molten salt that have high thermal energy storage capacity will increase the efficiency and enhance the performance for thermal energy storage. Thermal energy storage capacity of a salt mixture is dependent on melting point, density and specific heat capacity. Lower the melting point, more efficiency the molten salt. Then for thermal stability of the salt mixtures plays an important role in determining its utility as a potential thermal energy storage media. Nitrate mixtures and mixtures of nitrate and nitrite are being used in the applications because of low melting point, low unit cost, high heat capacity and moderate density which imply excellent energy storage capability. Binary mixtures of alkali molten nitrates or nitrites present phase diagrams with a