Airside thermal-hydraulic and fouling performances of economizers with integrally-molded spiral finned tubes for residual heat recovery

Abstract

Without defects inherent in conventional welded finned tubes, nonwelded integrally-molded spiral finned (IMSF) tubes proposed here have “zero” contact thermal resistance and high joint strength out of trapezoidal cross-section of the fin, and thus greatly improve thermal performances and service life of economizers for residual heat recovery. To guide the applications of this new economizer, a three-dimensional physical-numerical model is established to study airside thermal-hydraulic and fouling performances of the economizer with IMSF-tubes. We investigate the effects of longitudinal and transverse pitches of finned tube bundles on the airside thermal-hydraulic and fouling performances of IMSF-tubes at various Reynolds numbers. The results show that a longitudinal pitch more than 80 mm is suggested for economizer design to avoid working instability of boiler systems due to high pressure drop at small longitudinal pitch, and as compromised, a transverse pitch of an economizer may be more than 100 mm since a small transverse pitch improves thermal-hydraulic performance, but worsens fouling and raises pressure drop. We also put forward new correlations of the Colburn and Fanning friction factors for the IMSF-tube economizer. Compared with other finned tubes, IMSF-tubes improve not only mechanics but also thermal-hydraulic performances of heat exchangers. Our research work may contribute to applications of IMSF-tube economizers for residual heat recovery.