Abstract
Geometric modifications in spiral-wound heat exchangers alter flow passages and heat transfer areas, complicating performance interpretation. A three-dimensional numerical study compares 22 circular tube configurations of a three-layer spiral-wound heat exchanger with shell-side molten salt and tube-side water. The shell and core dimensions, tube counts, and inlet conditions are fixed. Actual tube wall areas and layer-resolved heat flux integrals distinguish area and mean heat flux contributions to heat duty changes, alongside the pressure drop and a relative performance evaluation criterion (PEC). Reducing the nominal axial clearance from 2.0 to 1.5 mm changes the heat duty by +2.32%, −3.78%, and +2.89% in three structural configurations. For G01–G21, the area term is +38.31 kW and the mean heat flux term is −60.76 kW, with the net loss concentrated in the outer layer. At a fixed total radial clearance, uniform allocation gives the highest PEC among the cases examined, while an outward-biased allocation can offset inner-layer losses through increased outer-layer heat transfer. Relative to G02, G01 reduces the pressure drop by 54.37% and increases the PEC by 14.20%; G22 gives the highest heat duty, 655.26 kW. These numerical results show that structural selection requires the simultaneous consideration of the actual area, layer-resolved thermal response, and flow resistance within the specified geometric and modeling constraints.