Numerical investigation and multi-criteria optimization of the thermal–hydraulic characteristics of turbulent flow in conical tubes fitted with twisted tape insert

Abstract

The ever-growing interest in developing compact and more effective heat exchangers necessitates the investigation of combined passive solutions. Despite the diverse related literature, there are no studies on smooth conical tubes (convergent and divergent tubes) fitted with twisted tape inserts. This study analyzes and optimizes the absolute and relative thermal and hydraulic performances of tube heat exchangers, with and without twisted tape inserts, based on Nusselt number and friction factor, by adjusting the tube's diameter ratio and the operational Reynolds number. A consolidated framework of computational fluid dynamics simulations, data-driven multilayered perceptron-based modeling, and gradient-free genetic dual-objective optimization is employed. The results showed that conventional straight tubes are the most favorable in terms of hydraulic performance, with a maximum friction factor of only 0.042. Convergent tubes are the most effective in terms of thermal performance, with Nusselt numbers up to 475.9. Divergent tubes do not show potentials for heat transfer enhancement unless equipped with a tape insert. Twisted tapes effectively improve the thermal performances of all system configurations but also drastically increase the friction factor. Compared to a baseline design of an empty straight tube, the thermal performance can be improved by up to 74.8%. Almost all Pareto frontier solutions belonged to convergent tubes of different configurations. The selected moderate non-dominated solution (assuming equal importance of thermal and hydraulic performances) corresponds to a Nusselt number of 402.9 and a friction factor of 0.130 for a tape-fitted convergent tube with a diameter ratio of 0.445, operating at a Reynolds number of 39,854. In terms of relative performance, the moderate solution corresponds to a Nusselt number ratio of 1.535 and a friction factor ratio of 6.157 using a tape-fitted convergent tube with a diameter ratio of 0.385, operating at a Reynolds number of 31,254. Overall, convergent tubes are recommended as a simple way for boosting the heat transfer rate and the proposed models can be used as flexible tools for selecting the operating conditions based on the designer's preference.

A review of different twisted tape configurations used in heat exchanger and their impact on thermal performance of the system

“…The maximum enhancement of the Nu increased by 35% at a Re of 2400 and a pitch ratio of 11.66. Hassan et al [ 72 ] numerically investigate the η of the HE fitted with TT. The diametric ratio varies from 1.0 to 5.0, and the value of the Re varies from 4000 to 10,000.…”

Numerical Thermal Augmentation of Ternary Nanofluid in a Tube with Stent, Torus-Ring and Surface-Grooved Twisted Tapes Under Non-Uniform Wall Temperature

“…The results revealed that, below Reynolds number 6 000, patterned twisted tape exhibits a greater Nusselt number than conventional twisted tape inserts without any dimples or protrusions. Hassan et al [32] numerically conducted hydrodynamic and heat transfer characteristics investigation of twisted tape inserts in a convergent and divergent conical tube. They claimed that the highest friction factor observed in the straight tubes compared with conical tubes was about 0.042.…”

Optimization of heat transfer performance of CuO/H2O nanofluid in Bessel‐like converging pipe using a two‐phase mixture model

“…Muhammed et al 27 optimized HTP in a conical tube fitted with a twisted tape insert using MOOT. Nonconstraint MOOT was performed on two objective functions ( and ) such that the is maximized while is minimized.…”