Computational Fluid Dynamics Analysis of Solidification in Baffled Molten Salt-Air-Cooled Heat Exchangers

Abstract

Due to their high freezing point, molten salt heat exchangers face the problem of salt freezing during cyclic operation. As a result, it is critical to detect the onset of salt solidification and anticipate the phase change behavior in high-temperature heat exchange processes, since these parameters influence heat exchanger design and operation. This study presents a three-dimensional transient computational fluid dynamics analysis of a pilot-scale exchanger with molten salt on the tube side and air on the shell side. The investigation focuses on the effects of the baffle arrangement and initial molten salt temperature on the air outlet temperature, pressure drop, and the onset of salt solidification. The pressure–velocity field coupling and turbulence parameters were solved by employing a segregated solver algorithm and a realizable k−ε turbulence model. Verification of the numerical model involved prior findings from a shell-and-tube heat exchanger using pure water as the shell-side fluid. The novel contribution of this work is to predict the time required for the molten salt to begin solidification within the tube bundle when air is used as the working fluid on the shell side of a single-segmented baffled shell-and-tube heat exchanger. The study concludes that, in the absence of a flow diverter, different baffle arrangements have minimal effect on the air outlet temperature or the start of salt solidification. A flow diverter, on the other hand, successfully slows solidification by distributing the flow, even when recirculation zones cause one-third of the heat exchanger length to remain ineffective. These findings provide a standard for future dynamic operation heat transfer assessments of molten salt-air-cooled heat exchangers.