For more complex geometries than smooth circular pipes, other friction factor equations were located in the literature applied to liquid salt systems. In a scaled experimental analysis of the liquid salt, pebble bed core design of the PB-AHTR [88], the pressure loss equation used is Darcy’s formula (3), with a theoretical friction factor based on the available correlations in packed beds (i.e. Ergun’s equation). Ergun’s equation is further identified in other sources related to molten salts, in applied simulation experiments (in packed bed geometries) [89], and in the parameter design analysis of the LSPBR (Liquid Salt Pebble Bed Reactor; variant of the AHTR) [24]. From