Thermal-hydraulic performances in multiple twisted tapes inserted sinusoidal rib tube heat exchangers for exhaust gas heat recovery applications

The article presents a numerical investigation on turbulent thermal and fluid flow characteristics of multiple twisted tapes (MTTs) inserted sinusoidal rib tube (SRT) heat exchangers based on exhaust gas heat recovery background. The effects including geometric parameters of tape number (single, twin, triple and quadruple twisted tapes) and tape arrangements (clockwise and anticlockwise or co-swirl and counter-swirl) in the SRT were comparably studied. A periodic RNG k-epsilon numerical model was employed to depict the heat transfer behaviors and flow structures in the SRTs at a constant wall temperature condition. The results showed that the alone use of the SRT yielded enhanced heat transfer of about 27.4%-39.5% and increased friction loss of around 49.4%-74.7% higher than that in the baseline of spirally corrugated tube (SCT). In addition, it was found that the diverse thermo-hydraulic performances in the SRTs fitted with MTTs were dominated by flow structures of swirl flows and shear flows. By the synergy of longitudinal vortexes from SRT and MTTs, the Nusselt number and friction factor obtained from the SRTs fitted with MTTs were, respectively, larger than that from SCT at about 1.43-1.87 times and 2.66-10.07 times. In contrast to the SCT, the overall thermal performance evaluation criterion (PEC) was enhanced up to 1.59 for the alone use of SRT. Moreover, the PEC could be improved under increased heat transfer and reasonable pressure drop via suitable tape arrangements in the SRTs mounted with MTTs, of which the best PEC was 1.49. At last, the comparisons of present results with previous studies proved that the proposed enhanced devices held some competitive advantages.