The discrepancies in the effects of the main parameters found in studies of helical coil heat exchangers are largely the result of not establishing a common basis for comparison. In the present study, fifteen helical coil exchanger configurations with different coil pitch sizes and curvature ratios were examined. All configurations had a fixed length to serve as a common basis for comparison. Water and nanofluids are being investigated as coolants under laminar and turbulent conditions. Thus, the impact of helical geometry and nanofluids on heat exchanger performance is examined under various flow conditions. The findings indicate that the impact of secondary flows leads to a 34% augmentation in the Nusselt number when water flows through the helically coiled heat exchangers in comparison to double-pipe heat exchangers comprising straight tubes. This increase is achieved with a large pitch size and curvature …