Efficiency enhancement of flat coiled tube using spiral twisted tape insert with various configurations; thermal, hydraulic and exergetic analysis

This study investigates the utilization of twisted tapes within spiral tubes, aiming to fill a significant research gap. Through validated numerical simulations using the SST k-w turbulence model, the intricate aspects of heat transfer and exergy destruction in spirally coiled tubes with twisted tapes are explored. Six distinct conditions are analyzed, including plain spiral tubes (PST) and spiral tubes equipped with twisted tapes of varying configurations (TTM2, TTM3, TTM4, TTM5, and TTM6), focusing on key geometric parameters such as the number of channels, tape diameter, tape thickness, and tape pitch. The impact of these parameters on critical factors including friction factor, Nusselt number, exergy efficiency, and thermal performance coefficient is comprehensively evaluated. Results indicate that varying tape diameter initially affects the Nusselt number negatively before surpassing plain tube performance beyond a specific threshold. Optimal thickness and pitch improve performance, particularly noticeable at a 22 mm diameter. Increasing tape pitch reduces heat transfer, with a significant decline in Nusselt number observed, yet all pitched tapes outperform plain tubes. The thermal performance factor increases with pitch due to a disproportionate decrease in pressure drop versus Nusselt number reduction. Additionally, increasing twisted tape thickness enhances heat transfer, albeit with a sharper increase in exergy destruction due to heightened pressure drop influence. Throughout, the mathematical model utilized is rigorously validated, providing insights into the complex interplay of geometric parameters and their effects on heat transfer and exergy efficiency in spiral tubes with twisted tapes.