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.在海上平台部署热交换器（Heat Exchangers, HXs）面临诸多严峻挑战，一方面平台空间有限，另一方面高盐环境会大幅加剧结垢现象。双螺旋盘管换热器（Double Spirally Coiled Tube Heat Exchanger, DSCTHE）具备优异的换热性能，但采用海水作为介质时的运行表现仍未得到充分探索。本研究采用计算流体动力学（Computational Fluid Dynamics, CFD）方法，分析了盐度为35g/kg的海水环境下双螺旋盘管换热器的换热性能，并评估了相较于清水工况，海水诱导结垢对其运行的关键影响。本研究提出一种简化的结垢模拟方法：通过增厚管壁并赋予等效导热系数，以表征管壁与垢层的总热阻，进而模拟厚度分别为0.05mm和0.4mm的垢层。仿真结果显示，当垢层厚度达到0.4mm时，换热器的热力水力性能损失显著，总传热系数（overall heat transfer coefficient, U）相较清洁工况最高下降75%。此外，该垢层厚度还会造成显著的水力性能损耗：由于水力直径减小、摩擦阻力增大，其压降相较其他工况提升约60%。以单位泵送功率下的传热量（Q/PP）衡量的换热效率，在高雷诺数（Reynolds number）下的重度结垢工况中降低了82%，这证实即便流动湍流度提升，新增的热阻仍会限制换热收益。本研究结果为双螺旋盘管换热器在海水环境中的应用提供了宝贵参考，相关结论可应用于海洋工程、海水淡化工艺以及油气工业等领域的海上设备。