Numerical study on heat transfer characteristics of molten salt in a flat tube with circular helical wire

The combination of a new type of irregular-shaped helical wire and flat tube is used to further enhance heat transfer of molten salt for the first time due to the demands of efficient utilization of molten salt. The thermo-hydraulic performance of turbulent flow in a flat tube with irregular-shaped helical wire under constant wall temperature condition is investigated using Fluent software. The effects of helical pitch, wire diameter, gap width between the tube wall and helical wire, different fluids and inlet Reynolds number ranging from 1500 to 8500 are evaluated. It is found that adding irregular-shaped helical wire insert in flat tube can reduce greatly the lengths of flow and thermal entrance regions. The maximum heat transfer performance of flat tube with irregular-shaped helical wire is 400% that of smooth flat tube. The heat transfer performance increases with the wire diameter and decreases with the gap width and helical pitch. The maximum thermal performance factor with a value of 1.72 is observed based on a constant pumping power. Besides, the heat transfer performance of flat tube with irregular-shaped helical wire is 24.0%-40.2% larger than that of circular pipe with helical wire at low Reynolds number.