Although curved pipes are commonly used in industrial operations, such as chemical reactors and heat exchangers, few investigations have been performed to develop an understanding of how tightly wound coils impact the heat transfer rate and friction factor in the laminar flow regime. Small coil radius geometries exhibit interesting characteristics that impact both Nusselt number and friction factor. Numerical solutions are presented for rectangular ducts of various coil diameters and aspect ratios which are compared with available experimental and analytical solutions to determine their applicabilty to tightly wound coils. A new non-dimensional parameter called the modified friction factor is presented and correlated to the results presented in this study. Additionally, a correlation for Nusselt number is presented for a variety of coil diameter ratios for curved square channels.

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