Thermal conductivity, molten salt transport properties

There are some density data for solid salts above ambient temperature which are given in the form of thermal expansion coefficients. These have been listed when they seemed reliable. Above the melting point, density data are scarce. Most are available for alkali halides but those available for salts are taken from the critically evaluated compilation Janz, G.J., Thermodynamics and transport properties for molten salts, correlation equations for critically evaluated density, surface tension, electrical conductance, and viscosity data,./. Phys. Chem. Reference Data, 17, Suppl. 2, 1988. 

There are two kinds of polymer material that used in quasi-solid/solid state DSSCs. For quasi-solid electrolytes, polyionic liquids have been proposed as solvent and redox couple as solute. They appear in molten salts and present many promising properties, such as, high chemical and thermal stability and high ionic conductivity Their main drawback is related to its high viscosity, which makes the ions diffusion rather slow. As the transport of ions to the counter electrode in an ionic liquid matrix represents a rate-limiting step in DSSC (Bella, 2015), the performance of quasi-solid electrolytes based solar cell is imsatisfled. 

Melts of these fluorides have satisfactory values of heat capacity, thermal conductivity, and viscosity in the 500-1000°C temperature range and provide an efficient removal of heat when they are used as the coolant over a wide range of compositions. Transport properties of molten salt coolants ensure efficient cooling with natural circulation the salt—waU heat transfer coefficient is close to the same coefficient for water. The thermal diffiisivity of the salt is 300 times smaller than that of sodium. Therefore, all other things being equal, the characteristic solidification time for a volume of the fluoride melt is 300 times longer than that of sodium [2]. 

Another transport property of molten salts for which there is a considerable amormt of data is their thermal conductivity Xth- In earher years the then available measuring techniques led to the conclusion that Xth increases mildly with increasing temperatures. More modem techniques, such as transient hot wire measurements, yield values of that diminish mildly and linearly with increasing temperatures. The scatter of values reported in the literature is large, however, and they have not been critically compiled so far. Gheribi et al. [277] provided an explicit model expression for 2, the required inputs for their model being the ionic radii, and the density, velocity of sound, heat capacity, and melting temperature of the salt. Table 3.21 shows the recommended predicted values in terms of the parameters of the linear temperature dependence ... 

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