Numerical Investigation of Heat Transfer and Flow Resistance of Fluoride Salt on Shell Side of Helically Coiled Heat Exchangers

The Helically Coiled Heat Exchanger (HCHX) is a promising candidate for modular Molten Salt Reactors (MSRs), valued for its high heat transfer efficiency, structural compactness, reduced fouling tendency, and excellent thermal compensation capabilities. The thermal–hydraulic performance of the shell side, crucial for reactor efficiency and safety, requires accurate prediction. This is challenged by the scarcity of reliable correlations for high-Prandtl number fluoride salts under low-Reynolds number conditions. To address this gap, this study explores the heat transfer and flow resistance of FNaBe salt flow in an HCHX using Computational Fluid Dynamics (CFD). The validated CFD model examines the effects of structural parameters (number of layers, tube pitch, and helix angle) and inlet conditions (temperatures and velocities). It is found that the Nusselt number and friction factor increase with more layers but decrease with a higher tube pitch and helix angle. Subsequently, new empirical correlations integrating these geometric parameters are proposed, demonstrating excellent agreement with simulation results (deviations within the range of −10–5% for Nu and −5–10% for f). This study offers vital theoretical support for optimizing compact HCHX designs in MSRs.