Turbulent thermal-hydraulic and thermodynamic characteristics in a traverse corrugated tube fitted with twin and triple wire coils

Thermal-hydraulic behaviors of air turbulent flow in a traverse corrugated tube (TCT) inserted with twin and triple wire coils (WCs) were investigated experimentally. The effects of two different arrangements (twin WCs and triple WCs) and four space ratios (S/D = 0, 3.88, 8.62 and 18.1) on Nusselt number (Nu), friction factor (f), performance evaluation criterion (PEC), Bejan number (Be) and augmented entropy generation number (phi(5)) were investigated at Reynolds number (Re) ranging from 6000 to 18,000. The gained results point out that the compound use of TCT with WCs gives considerably enhanced heat transfer and also increased pressure loss than the plain tube with improved Nu ratios in the range of 1.74-2.61 and augmented f ratios in the range of 4.57-21.34. By analyzing different parameters, it is found that Nu and f in the TCT mounted with WCs increases with WC number increasing and space ratio decreasing. Although the co-use of TCT with WCs exhibits superior Nu than the alone use of the TCT, the former performs higher flow resistance and lower PEC than the latter. The increased heat transfer of about 22.3-84.2% and augmented pressure loss of around 2.91-12.90 times over that of the TCT are obtained for the combined use of TCT with WCs. The largest PEC of about 1.09 is achieved in the TCT with twin WCs at S/D = 18.1 while that is about 1.26 for the TCT alone. In terms of thermodynamic characteristics, both the TCT alone and the co-use of TCT with multiple WCs can reduce the contribution of heat transfer entropy generation to the overall entropy generation, and the Be could be decreased to values of about 0.91 and 0.32 by the former and the latter, respectively. In addition, the obtained results show that the lowest phi(5) of about 0.46 is gained by the TCT with triple WCs at S/D = 0 and Re = 6428 in this study scope. Finally, the Nu and f empirical correlations within respectively +/- 9.0% and +/- 11.0% from experimental data are installed. (C) 2018 Elsevier Ltd. All rights reserved.