Abstract
In the present study, heat transfer enhancement in circular tubes via internal repeated ring-type ribs is, numerically, investigated and validated with experimental data obtained by Huang et al. (2015). Thermal evaluation is also done for tubes with rectangular, trapezoidal and triangular ribs. Furthermore, entropy and exergy analysis are performed on all the tested tubes. Air is used as the working fluid at (3.6 x 10(3) <= Re <= 1.65 x 10(4)). The rib-depth to tube-inner diameter ratio (e/d) and the rib-pitch to tube-inner diameter ratio (p/d) in the tubes ribs configurations are considered. The performance evaluation criterion (PEC) is employed to estimate the optimum case that gives high thermal hydraulic efficiency (THE). It is found that the best (THE) accompanying with lower entropy and higher exergy are achieved for the tube with ring-type ribs compared to other shapes. The flow phenomena, temperature and pressure contours are illustrated with a consistent evaluation.