In this study, the heat transfer coolant utilized in the heat exchanger is a molten salt, which transfers thermal energy to water (steam) for power production by a supercritical Rankine (25MPa) or subcritical Rankine (17MPa) cycle. Molten salts are excellent coolants, with 25% higher volumetric heat capacity than pressurized water, and nearly five times that of liquid sodium. The greater heat capacity of molten salts results in more compact components like pumps and heat exchangers. However, the use of a molten salt provides potential materials compatibility issues. After studying a variety of individual molten salt mixtures, chlorides and fluorides have been given the most serious consideration because of their heat transport and transfer characteristics.
In this study thermal designs of conventional (shell and tube), and compact (printed circuit) heat exchangers are carried out and compared for a given thermal duty. There are a couple of main issues that need to be addressed before this technology could be commercialized. The main issue is with the material compatibility of molten salts (especially fluoride salts) and secondarily, with the pressure difference across the heat exchanger. The heat exchanger’s primary side pressure is nearly atmospheric and the secondary side (power production) is pressurized to about 25MPa for supercritical cycle and 17MPa for subcritical cycle. Further in the analysis, the comparison of both the cycles will be carried out with recommendations.
