HEAT TRANSFER PERFORMANCE AT LOW REYNOLDS NUMBERS IN SERPENTINE CHANNELS

A finite volume technique-based in-house code is used for computational fluid dynamics (CFD) simulation and study on two-dimensional flow of fluid and transmission of thermal energy in a periodically fully developed sinusoidal serpentine channel with hydraulic diameter (Dh). This research activity is accomplished for various Reynolds number (Re = 101-2000) on three geometrically different serpentine channels for varying amplitude A ≡ a/D<sub>h</sub> = 0.1, 0.15, and 0.2 at constant wavelength λ* ≡ λ/D<sub>h</sub> = 1.5 of the wavy section. Unsteady flow regimes are characterized through the analysis of time signal plots, and a map is suggested for various flow regimes. The map demarcates steady regimes, both periodic and quasiperiodic regimes of two different types and a regime with chaotic flow at various governing parameters. The normalized ratio of the Nusselt number and that value of the friction coefficient for the serpentine wavy conduit with reference to the plane rectangular conduit are demonstrated to increase sharply in the unsteady regime with respect to the regime of steady flow. As Re increases, the value of goodness factor for the serpentine undulated conduit with respect to the plane rectangular conduit becomes almost constant for A = 0.15 and increases and decreases initially for A = 0.1 and 0.2, respectively, and thereafter remains almost constant. It was also found that the thermal performance factor (TPF) is more than one, suggesting that the gain in the transmission of thermal energy is greater than the pressure drop penalty in those flow regimes, where flow is unsteady for most of the Re. It was further noticed that the TPF increases with an increase in amplitude (A) from 0.1 to 0.15 and therefore remains constant for the increase in A from 0.15 to 0.2 at constant Re.