Experimental study of a double tube heat exchanger with 3D-printed twisted tapes

Twisted tape elements contribute to increasing heat transfer rates by promoting turbulence, especially in heat exchangers under laminar regime, characterised by low convection coefficients. In these geometries, additive manufacturing is useful for the exploration of new cross-sectional shapes. The novelty of this work is to experimentally study the hydrodynamic and heat transfer implications of using four common thermoplastic materials in 3D printing twisted tapes, analysing the potential conditions under which materials are appropriate, which has not been previously reported. Tests were performed under laminar flow (Reynolds between 100 and 700), using a 60° brix sugar-water mixture. The 3-m-long heat exchanger contained three twisted tapes (330 mm in length, 90 mm twist pitch, and 3.67 twists each), separated by two spacers of 997.5 mm. Polylactic Acid and Nylon twisted tapes showed overall heat transfer coefficients approximately 20% higher than those of conventional steel ones. All polymeric materials resulted in an increased pressure drop, with Nylon showing the highest values. All polymers achieved higher performance evaluation criteria, particularly for Reynolds > 400, with up to 20% improvement. Although Polylactic Acid initially showed the highest stiffness (2.45 GPa) among the materials tested, its low glass transition temperature (62 °C) was exceeded during operation, leading to a loss of rigidity and visible deformation, limiting its applicability with high temperatures or flow rates. In the Reynolds number range studied, Acrylonitrile Butadiene Styrene and Polyethylene Terephthalate Glycol can be considered the most suitable materials for developing new optimised geometries involving the use of passive elements. • 3D-printed twisted tapes improved heat exchanger performance. • Nylon reported the highest pressure drop, approximately 50% higher. • PLA showed 20% higher heat transfer but deformed at 50 ° C . • All polymers achieved higher PEC with gains up to 20% for Re > 400. • ABS and PETG are suitable for designing new optimised TTE geometries.