Influence of structural and operational parameters on heat transfer and reaction in helical tube pyrolysis reactors

Helical tubes are known for their ability to enhance heat and mass transfer due to secondary flow effects. However, their application in pyrolysis reactors remains underexplored. This study presents a three-dimensional numerical model coupling fluid flow, heat transfer, and pyrolysis reaction kinetics in a helical reactor. The model is implemented in ANSYS Fluent with validated turbulence and species transport equations. Parametric studies were conducted to evaluate the effects of inlet velocity, helical pitch (100-500 mm), coil diameter (400-800 mm), and tube inner diameter (19-59 mm) on thermal and reaction performance. Results show that increasing velocity improves heat transfer (Nu increases, f decreases) but reduces conversion due to shorter residence time. Pitch variation has a negligible impact. Increasing coil diameter reduces Nu by ~8% but raises conversion from 63% to 96% due to longer tube length. For inner diameter, the optimal value is 39 mm, maintaining > 95% conversion while balancing pressure drop and heat transfer. These findings provide practical design guidance for helical pyrolysis reactors.