Thermohydraulic performance intensification of lobed heat exchangers using tube axis corrugation: Numerical assessment on geometrical configurations

Geometrical parameters effect on turbulent flow field and heat transfer characteristics in a heat exchanger tube with tri-lobed cross section is numerically investigated. Three types of the tubes including twisted tube (TT), corrugated tube (CT) and corrugated twisted tube (CTT) are studied and compared in terms of thermohydraulic parameters. To capture the turbulent fluctuations over the range of Reynolds number from 4000 to 20,000, shear stress transport (SST) k-ω model is implemented into the code. In this study, the geometrical design variables consist of twist ratio, amplitude ratio, and wavelength ratio. According to the results, for the TT, the more the twist ratio, the greater the Nusselt number and friction factor. Due to the vortices generated by the centrifugal force in the CT, the mean Nusselt number in comparison with the smooth tube increases up to 80.5% at the wavelength ratio of 1/6. The results of the CTT show that the maximum value of performance evaluation criteria, 1.41, is obtained for this type of geometry at the twist ratio of 5, wavelength ratio of 1/6, and amplitude ratio of 0.75. These findings emphasize the advantage of simultaneously twisting and waving the tri-lobed tubes in intensification of the thermo-fluidic performances.