Thermohydraulic performance of a semi-alternated twisted tape insert and cylindrical baffles in a tube with ternary nanofluid under sinusoidal wall temperature

Abstract

This study numerically evaluates the thermohydraulic performance of a circular tube consisting of semi-alternated twisted tape mounted with cylindrical baffles and ternary nanofluid (SiO2 + ZnO + CaO) as a working fluid. The circular tube wall was exposed to a sinusoidal temperature that axially varied along the wall. The investigation was performed in the laminar flow regime over the Reynolds number 500–2000 and for nanofluid volume fraction 0.01%-0.05%. The semi-alternated twisted tape has pitch ratio 1.77–5.77, width ratio 0.38–0.68 and thickness ratio 0.019–0.033. The performance was analyzed for Nusselt number, pressure drop, thermal performance factor and pumping power. The results indicate, no significant pressure drop increment with volume fraction of the ternary nanofluid. For a fixed volume fraction of 0.01%, width ratio of 0.48 and thickness ratio of 0.019, there is an improvement in Nusselt number by 35–107%, pressure drop increased from 0.26 Pa to 3.5 Pa, pumping power was found to increase by 40%, and thermal performance factor by 1.35–1.67 times that of the smooth tube, when the pitch ratio decreases from 5.77 to 1.77. For a fixed pitch ratio of 1.77 and width ratio 0.38–0.68, the Nusselt number increased by 50–114%, pressure drop increased from 0.207 Pa to 11.1 Pa and thermal performance factor by 1.18–1.76 times as compared with smooth tube. The Nusselt number increased by 100–115% and thermal performance factor increased from 1.08 to 1.16 times the performance of the smooth tube when the thickness ratio was increased from 0.019 to 0.033.