Refinements in Thermal Conductivity Measurements Using Platinum Resistance Wire

Binary and ternary mixtures of molten salt nitrates (LiNO3 -NaNO3 and KNO3) are ideal candidates as large scale phase change thermal energy storage materials and as heat transfer fluids for concentrating solar power systems. They have higher specific heat capacities and wider operating temperature ranges (150-600°C) compared to the silicon based oils which are currently used in parabolic trough type plants. For design considerations related to power plant and equipment, it is critically important to know the thermo-physical properties of molten salt nitrates; as thermal conductivity being one of the most important. In this regard, the measurements of thermal conductivity of molten salt nitrates are of interest in the present study. A modified version of the hot wire device designed by an earlier research has been used as a transient method to measure the thermal conductivity of fluids. The method has been validated with test liquids with known thermal conductivities such as water, 20 weight % sucrose solution and 40 weight % sugar solution at a variety of temperatures. Finally, the thermal conductivity of ternary mixture of 30:21:49 mol % LiNO3 -NaNO3-KNO 3 has been measured at 134°C. This composition is commonly used in the industry since it is close to the eutectic point. The average value and standard deviation of the measured thermal conductivities of the 15 experiments on the ternary mixture are 0.438 W/mK and 8.27E-4 W/mK, respectively. This value of thermal conductivity is inside the range for single and binary components of nitrate salts published in the literature previously. The observed uncertainty in the validation experiments is around 5 % which determines the overall uncertainty of the measurement of thermal conductivity of the ternary mixture in consideration.