Numerical Investigation of the Thermohydraulic Performance of Flow Inside a Seawater Cooled Double Spirally Coiled Tube Heat Exchangers (DSCTHE)

Deploying HXs on offshore platforms poses significant challenges due to limited space and saline conditions which severely promote fouling. The Double Spirally Coiled Tube Heat Exchanger (DSCTHE) offers thermal advantages, but the performance remains underexplored when using seawater. This study utilized Computational Fluid Dynamics (CFD) to analyse DSCTHE’s heat transfer performance in seawater conditions at 35 g/kg salinity and evaluating the critical impact of seawater induced fouling with respect to water. A simplified method is proposed to represent fouling where thin deposit layers of 0.05 mm and 0.4 mm were modelled by thickening the tube wall and assigning an effective thermal conductivity to represent the combined thermal resistance of the pipe and fouling layer. The simulations showed substantial thermal hydraulic penalties under 0.4 mm fouling thickness which resulted in a significant reduction of the overall heat transfer coefficient (U), dropping by up to 75% relative to clean conditions. Furthermore, this thickness created a significant hydraulic penalty, increasing the pressure drop by approximately 60% compared to the other conditions due to the reduction in hydraulic diameter and subsequent increased friction. Efficiency, measured by the heat transfer rate per unit pumping power (Q/PP), was substantially lowered by 82% under severe fouling conditions at high Reynolds numbers, confirming that the added thermal resistance limits heat transfer gains even with increased flow turbulence. The results provide valuable insights on using seawater in DSCTHE with information that benefit applications such as marine, salination process and offshore devices such as in the oil and gas industries.