Numerical investigation of entropy generation of turbulent flow in a novel outward corrugated tube

The present study numerically investigates the second law analysis of turbulent flow in novel outward helical corrugated tubes by using a Reynolds Stress Model (RSM). A case of a transverse corrugated tube and five cases of helical corrugated tubes with different height-to-diameter ratios and pitch-to-diameter ratios are examined with Reynolds number ranging from 3800 to 43,800 at a constant wall temperature condition. The results indicate that the secondary flow significantly increases the thermal and viscous dissipation irreversibilities. However, the spiral flow inhibits the secondary flow and the production of local entropy. The heat transfer effective zone (Belocal > 0.5) is mainly located at the sub-layer and buffer-layer, and the ineffective zone (Belocal < 0.2) is located at the turbulent severe pulsation zone. A comprehensive consideration of the total entropy generation number (Ns-tot) and average Bejan number (Beave) indicates that the optimal Re is less than 31,000 for all the cases although Re does not exceed 18,800 in the case of Hl/D = 0.15, pl/D = 1.0 and Hl/D = 0.10, pl/D = 0.5. Additionally, the helical corrugated tube exhibits an overall advantage when compared with a transverse corrugated tube with the same geometrical parameters.