An investigation of heat transfer in heat exchange devices with spirally-coiled twisted-ducts using nanofluid

• Published in: Applied thermal engineering 2018-10, Vol.143, p.358-375
• Main Authors: Khoshvaght-Aliabadi, M., Khaligh, S.F., Tavassoli, Z.
• Format: Article
• Language: English
• Subjects: Augmentation; Coil-pitch; Coils; Computational fluid dynamics; Copper; Cu/water nanofluid; Dependence; Ducts; Fluid flow; Friction factor; Heat conductivity; Heat exchange; Heat transfer; Mathematical models; Nanofluids; Nanoparticles; Nusselt number; Performance indices; Pressure drop; Quantum physics; Quantum theory; Spirally-coiled twisted-ducts; Thermodynamics; Twist-pitch; Working fluids
• ISSN: 1359-4311; 1873-5606
• DOI: 10.1016/j.applthermaleng.2018.07.112

[Display omitted] •Thermo-fluidic transport characteristics of spirally-coiled twisted-tube are investigated.•Water and Cu/water are used as working fluid.•Twist-pitch and coil-pitch have considerable effects on performance of studied cases.•Maximum performance indexes of 1.39 and 1.88 are recorded for water and nanofluid. A new design of curved ducts namely spirally-coiled twisted-duct is introduced and analyzed both experimentally and numerically. Water and Cu/water nanofluid at two concentrations of 0.5% and 1% by mass are considered as working fluid. The results show that the dependence of thermo-fluidic transport characteristics on the geometry of spirally-coiled twisted-duct is strongly influenced by twist-pitch (tp) and coil-pitch (cp). The studied ranges are tp = 0.05, 0.1, and 0.15 m and cp = 0.015, 0.025, and 0.035 m. The maximum augmentations of Nusselt number and friction factor are recorded for the spirally-coiled twisted-ducts with the lowest twist-pitch and coil-pitch (i.e. tp = 0.05 and cp = 0.015). One of the key outcomes of this work is that the effect of twist-pitch is more pronounced at higher Graetz numbers, while at lower Graetz numbers the effect of coil-pitch is more noticeable. Likewise, with the deployment of a performance index combining the enhancement in Nusselt number and corresponding augmentation in friction factor, the overall hydrothermal performance of spirally-coiled twisted-ducts is assessed. Among the studied cases, the spirally-coiled twisted-duct at tp = 0.05 m and cp = 0.025 m possesses the highest performance index of 1.39 at the maximum Graetz number. Also, a noticeable heat transfer enhancement due to suspension of copper nanoparticles in water is obtained with a certain augmentation in the pressure drop, and the enhancement is intensified with increasing the concentration of nanoparticles. The performance index enhances up to 1.88 when the 1.0% nanofluid is used in the spirally-coiled twisted-duct at tp = 0.05 m and cp = 0.025 m. Finally, using the obtained results, two correlations are established to model Nusselt number and friction factor inside the spirally-coiled twisted-ducts for the Graetz number range of 14–58.